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author	Benoît Thébaudeau <benoit.thebaudeau@advansee.com>	2013-05-03 10:32:25 +0000
committer	Stefano Babic <sbabic@denx.de>	2013-05-05 17:55:04 +0200
commit	f49d92a35bce06d7844efecbd53896dc12b4ebdf (patch)
tree	3a0e5ae3bd4bc818ca0d21f88a09a67633585c5b /board/genesi
parent	e2003c16c02a1ed186f93b8aafb76919a9bf9e1c (diff)
download	u-boot-f49d92a35bce06d7844efecbd53896dc12b4ebdf.zip u-boot-f49d92a35bce06d7844efecbd53896dc12b4ebdf.tar.gz u-boot-f49d92a35bce06d7844efecbd53896dc12b4ebdf.tar.bz2

imx: iomux-mx51: Fix MX51_PAD_EIM_CS2__GPIO2_27

In ALT1 mode, EIM_CS2 is GPIO2[27], not ESDHC1.CD. Hence, rename MX51_PAD_EIM_CS2__SD1_CD to MX51_PAD_EIM_CS2__GPIO2_27. Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>

Diffstat (limited to 'board/genesi')

-rw-r--r--

board/genesi/mx51_efikamx/efikamx.c

1 files changed, 1 insertions, 1 deletions

\input texinfo @c -*-texinfo-*- @c Copyright (C) 1988--2020 Free Software Foundation, Inc. @c @c %**start of header @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use @c of @set vars. However, you can override filename with makeinfo -o. @setfilename gdb.info @c @c man begin INCLUDE @include gdb-cfg.texi @c man end @c @settitle Debugging with @value{GDBN} @setchapternewpage odd @c %**end of header @iftex @c @smallbook @c @cropmarks @end iftex @finalout @c To avoid file-name clashes between index.html and Index.html, when @c the manual is produced on a Posix host and then moved to a @c case-insensitive filesystem (e.g., MS-Windows), we separate the @c indices into two: Concept Index and all the rest. @syncodeindex ky fn @syncodeindex tp fn @c readline appendices use @vindex, @findex and @ftable, @c annotate.texi and gdbmi use @findex. @syncodeindex vr fn @c !!set GDB manual's edition---not the same as GDB version! @c This is updated by GNU Press. @set EDITION Tenth @c !!set GDB edit command default editor @set EDITOR /bin/ex @c THIS MANUAL REQUIRES TEXINFO 4.0 OR LATER. @c This is a dir.info fragment to support semi-automated addition of @c manuals to an info tree. @dircategory Software development @direntry * Gdb: (gdb). The GNU debugger. * gdbserver: (gdb) Server. The GNU debugging server. @end direntry @copying @c man begin COPYRIGHT Copyright @copyright{} 1988-2020 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being ``Free Software'' and ``Free Software Needs Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,'' and with the Back-Cover Texts as in (a) below. (a) The FSF's Back-Cover Text is: ``You are free to copy and modify this GNU Manual. Buying copies from GNU Press supports the FSF in developing GNU and promoting software freedom.'' @c man end @end copying @ifnottex This file documents the @sc{gnu} debugger @value{GDBN}. This is the @value{EDITION} Edition, of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger} for @value{GDBN} @ifset VERSION_PACKAGE @value{VERSION_PACKAGE} @end ifset Version @value{GDBVN}. @insertcopying @end ifnottex @titlepage @title Debugging with @value{GDBN} @subtitle The @sc{gnu} Source-Level Debugger @sp 1 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN} @ifset VERSION_PACKAGE @sp 1 @subtitle @value{VERSION_PACKAGE} @end ifset @author Richard Stallman, Roland Pesch, Stan Shebs, et al. @page @tex {\parskip=0pt \hfill (Send bugs and comments on @value{GDBN} to @value{BUGURL}.)\par \hfill {\it Debugging with @value{GDBN}}\par \hfill \TeX{}info \texinfoversion\par } @end tex @vskip 0pt plus 1filll Published by the Free Software Foundation @* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA@* ISBN 978-0-9831592-3-0 @* @insertcopying @end titlepage @page @ifnottex @node Top, Summary, (dir), (dir) @top Debugging with @value{GDBN} This file describes @value{GDBN}, the @sc{gnu} symbolic debugger. This is the @value{EDITION} Edition, for @value{GDBN} @ifset VERSION_PACKAGE @value{VERSION_PACKAGE} @end ifset Version @value{GDBVN}. Copyright (C) 1988-2020 Free Software Foundation, Inc. This edition of the GDB manual is dedicated to the memory of Fred Fish. Fred was a long-standing contributor to GDB and to Free software in general. We will miss him. @menu * Summary:: Summary of @value{GDBN} * Sample Session:: A sample @value{GDBN} session * Invocation:: Getting in and out of @value{GDBN} * Commands:: @value{GDBN} commands * Running:: Running programs under @value{GDBN} * Stopping:: Stopping and continuing * Reverse Execution:: Running programs backward * Process Record and Replay:: Recording inferior's execution and replaying it * Stack:: Examining the stack * Source:: Examining source files * Data:: Examining data * Optimized Code:: Debugging optimized code * Macros:: Preprocessor Macros * Tracepoints:: Debugging remote targets non-intrusively * Overlays:: Debugging programs that use overlays * Languages:: Using @value{GDBN} with different languages * Symbols:: Examining the symbol table * Altering:: Altering execution * GDB Files:: @value{GDBN} files * Targets:: Specifying a debugging target * Remote Debugging:: Debugging remote programs * Configurations:: Configuration-specific information * Controlling GDB:: Controlling @value{GDBN} * Extending GDB:: Extending @value{GDBN} * Interpreters:: Command Interpreters * TUI:: @value{GDBN} Text User Interface * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs * GDB/MI:: @value{GDBN}'s Machine Interface. * Annotations:: @value{GDBN}'s annotation interface. * JIT Interface:: Using the JIT debugging interface. * In-Process Agent:: In-Process Agent * GDB Bugs:: Reporting bugs in @value{GDBN} @ifset SYSTEM_READLINE * Command Line Editing: (rluserman). Command Line Editing * Using History Interactively: (history). Using History Interactively @end ifset @ifclear SYSTEM_READLINE * Command Line Editing:: Command Line Editing * Using History Interactively:: Using History Interactively @end ifclear * In Memoriam:: In Memoriam * Formatting Documentation:: How to format and print @value{GDBN} documentation * Installing GDB:: Installing GDB * Maintenance Commands:: Maintenance Commands * Remote Protocol:: GDB Remote Serial Protocol * Agent Expressions:: The GDB Agent Expression Mechanism * Target Descriptions:: How targets can describe themselves to @value{GDBN} * Operating System Information:: Getting additional information from the operating system * Trace File Format:: GDB trace file format * Index Section Format:: .gdb_index section format * Man Pages:: Manual pages * Copying:: GNU General Public License says how you can copy and share GDB * GNU Free Documentation License:: The license for this documentation * Concept Index:: Index of @value{GDBN} concepts * Command and Variable Index:: Index of @value{GDBN} commands, variables, functions, and Python data types @end menu @end ifnottex @contents @node Summary @unnumbered Summary of @value{GDBN} The purpose of a debugger such as @value{GDBN} is to allow you to see what is going on ``inside'' another program while it executes---or what another program was doing at the moment it crashed. @value{GDBN} can do four main kinds of things (plus other things in support of these) to help you catch bugs in the act: @itemize @bullet @item Start your program, specifying anything that might affect its behavior. @item Make your program stop on specified conditions. @item Examine what has happened, when your program has stopped. @item Change things in your program, so you can experiment with correcting the effects of one bug and go on to learn about another. @end itemize You can use @value{GDBN} to debug programs written in C and C@t{++}. For more information, see @ref{Supported Languages,,Supported Languages}. For more information, see @ref{C,,C and C++}. Support for D is partial. For information on D, see @ref{D,,D}. @cindex Modula-2 Support for Modula-2 is partial. For information on Modula-2, see @ref{Modula-2,,Modula-2}. Support for OpenCL C is partial. For information on OpenCL C, see @ref{OpenCL C,,OpenCL C}. @cindex Pascal Debugging Pascal programs which use sets, subranges, file variables, or nested functions does not currently work. @value{GDBN} does not support entering expressions, printing values, or similar features using Pascal syntax. @cindex Fortran @value{GDBN} can be used to debug programs written in Fortran, although it may be necessary to refer to some variables with a trailing underscore. @value{GDBN} can be used to debug programs written in Objective-C, using either the Apple/NeXT or the GNU Objective-C runtime. @menu * Free Software:: Freely redistributable software * Free Documentation:: Free Software Needs Free Documentation * Contributors:: Contributors to GDB @end menu @node Free Software @unnumberedsec Free Software @value{GDBN} is @dfn{free software}, protected by the @sc{gnu} General Public License (GPL). The GPL gives you the freedom to copy or adapt a licensed program---but every person getting a copy also gets with it the freedom to modify that copy (which means that they must get access to the source code), and the freedom to distribute further copies. Typical software companies use copyrights to limit your freedoms; the Free Software Foundation uses the GPL to preserve these freedoms. Fundamentally, the General Public License is a license which says that you have these freedoms and that you cannot take these freedoms away from anyone else. @node Free Documentation @unnumberedsec Free Software Needs Free Documentation The biggest deficiency in the free software community today is not in the software---it is the lack of good free documentation that we can include with the free software. Many of our most important programs do not come with free reference manuals and free introductory texts. Documentation is an essential part of any software package; when an important free software package does not come with a free manual and a free tutorial, that is a major gap. We have many such gaps today. Consider Perl, for instance. The tutorial manuals that people normally use are non-free. How did this come about? Because the authors of those manuals published them with restrictive terms---no copying, no modification, source files not available---which exclude them from the free software world. That wasn't the first time this sort of thing happened, and it was far from the last. Many times we have heard a GNU user eagerly describe a manual that he is writing, his intended contribution to the community, only to learn that he had ruined everything by signing a publication contract to make it non-free. Free documentation, like free software, is a matter of freedom, not price. The problem with the non-free manual is not that publishers charge a price for printed copies---that in itself is fine. (The Free Software Foundation sells printed copies of manuals, too.) The problem is the restrictions on the use of the manual. Free manuals are available in source code form, and give you permission to copy and modify. Non-free manuals do not allow this. The criteria of freedom for a free manual are roughly the same as for free software. Redistribution (including the normal kinds of commercial redistribution) must be permitted, so that the manual can accompany every copy of the program, both on-line and on paper. Permission for modification of the technical content is crucial too. When people modify the software, adding or changing features, if they are conscientious they will change the manual too---so they can provide accurate and clear documentation for the modified program. A manual that leaves you no choice but to write a new manual to document a changed version of the program is not really available to our community. Some kinds of limits on the way modification is handled are acceptable. For example, requirements to preserve the original author's copyright notice, the distribution terms, or the list of authors, are ok. It is also no problem to require modified versions to include notice that they were modified. Even entire sections that may not be deleted or changed are acceptable, as long as they deal with nontechnical topics (like this one). These kinds of restrictions are acceptable because they don't obstruct the community's normal use of the manual. However, it must be possible to modify all the @emph{technical} content of the manual, and then distribute the result in all the usual media, through all the usual channels. Otherwise, the restrictions obstruct the use of the manual, it is not free, and we need another manual to replace it. Please spread the word about this issue. Our community continues to lose manuals to proprietary publishing. If we spread the word that free software needs free reference manuals and free tutorials, perhaps the next person who wants to contribute by writing documentation will realize, before it is too late, that only free manuals contribute to the free software community. If you are writing documentation, please insist on publishing it under the GNU Free Documentation License or another free documentation license. Remember that this decision requires your approval---you don't have to let the publisher decide. Some commercial publishers will use a free license if you insist, but they will not propose the option; it is up to you to raise the issue and say firmly that this is what you want. If the publisher you are dealing with refuses, please try other publishers. If you're not sure whether a proposed license is free, write to @email{licensing@@gnu.org}. You can encourage commercial publishers to sell more free, copylefted manuals and tutorials by buying them, and particularly by buying copies from the publishers that paid for their writing or for major improvements. Meanwhile, try to avoid buying non-free documentation at all. Check the distribution terms of a manual before you buy it, and insist that whoever seeks your business must respect your freedom. Check the history of the book, and try to reward the publishers that have paid or pay the authors to work on it. The Free Software Foundation maintains a list of free documentation published by other publishers, at @url{http://www.fsf.org/doc/other-free-books.html}. @node Contributors @unnumberedsec Contributors to @value{GDBN} Richard Stallman was the original author of @value{GDBN}, and of many other @sc{gnu} programs. Many others have contributed to its development. This section attempts to credit major contributors. One of the virtues of free software is that everyone is free to contribute to it; with regret, we cannot actually acknowledge everyone here. The file @file{ChangeLog} in the @value{GDBN} distribution approximates a blow-by-blow account. Changes much prior to version 2.0 are lost in the mists of time. @quotation @emph{Plea:} Additions to this section are particularly welcome. If you or your friends (or enemies, to be evenhanded) have been unfairly omitted from this list, we would like to add your names! @end quotation So that they may not regard their many labors as thankless, we particularly thank those who shepherded @value{GDBN} through major releases: Andrew Cagney (releases 6.3, 6.2, 6.1, 6.0, 5.3, 5.2, 5.1 and 5.0); Jim Blandy (release 4.18); Jason Molenda (release 4.17); Stan Shebs (release 4.14); Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9); Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4); John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9); Jim Kingdon (releases 3.5, 3.4, and 3.3); and Randy Smith (releases 3.2, 3.1, and 3.0). Richard Stallman, assisted at various times by Peter TerMaat, Chris Hanson, and Richard Mlynarik, handled releases through 2.8. Michael Tiemann is the author of most of the @sc{gnu} C@t{++} support in @value{GDBN}, with significant additional contributions from Per Bothner and Daniel Berlin. James Clark wrote the @sc{gnu} C@t{++} demangler. Early work on C@t{++} was by Peter TerMaat (who also did much general update work leading to release 3.0). @value{GDBN} uses the BFD subroutine library to examine multiple object-file formats; BFD was a joint project of David V. Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore. David Johnson wrote the original COFF support; Pace Willison did the original support for encapsulated COFF. Brent Benson of Harris Computer Systems contributed DWARF 2 support. Adam de Boor and Bradley Davis contributed the ISI Optimum V support. Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS support. Jean-Daniel Fekete contributed Sun 386i support. Chris Hanson improved the HP9000 support. Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support. David Johnson contributed Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support. Jeff Law contributed HP PA and SOM support. Keith Packard contributed NS32K support. Doug Rabson contributed Acorn Risc Machine support. Bob Rusk contributed Harris Nighthawk CX-UX support. Chris Smith contributed Convex support (and Fortran debugging). Jonathan Stone contributed Pyramid support. Michael Tiemann contributed SPARC support. Tim Tucker contributed support for the Gould NP1 and Gould Powernode. Pace Willison contributed Intel 386 support. Jay Vosburgh contributed Symmetry support. Marko Mlinar contributed OpenRISC 1000 support. Andreas Schwab contributed M68K @sc{gnu}/Linux support. Rich Schaefer and Peter Schauer helped with support of SunOS shared libraries. Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree about several machine instruction sets. Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM contributed remote debugging modules for the i960, VxWorks, A29K UDI, and RDI targets, respectively. Brian Fox is the author of the readline libraries providing command-line editing and command history. Andrew Beers of SUNY Buffalo wrote the language-switching code, the Modula-2 support, and contributed the Languages chapter of this manual. Fred Fish wrote most of the support for Unix System Vr4. He also enhanced the command-completion support to cover C@t{++} overloaded symbols. Hitachi America (now Renesas America), Ltd. sponsored the support for H8/300, H8/500, and Super-H processors. NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors. Mitsubishi (now Renesas) sponsored the support for D10V, D30V, and M32R/D processors. Toshiba sponsored the support for the TX39 Mips processor. Matsushita sponsored the support for the MN10200 and MN10300 processors. Fujitsu sponsored the support for SPARClite and FR30 processors. Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware watchpoints. Michael Snyder added support for tracepoints. Stu Grossman wrote gdbserver. Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made nearly innumerable bug fixes and cleanups throughout @value{GDBN}. The following people at the Hewlett-Packard Company contributed support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++} compiler, and the Text User Interface (nee Terminal User Interface): Ben Krepp, Richard Title, John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific information in this manual. DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project. Robert Hoehne made significant contributions to the DJGPP port. Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its development since 1991. Cygnus engineers who have worked on @value{GDBN} fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler, Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton, JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner, Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David Zuhn have made contributions both large and small. Andrew Cagney, Fernando Nasser, and Elena Zannoni, while working for Cygnus Solutions, implemented the original @sc{gdb/mi} interface. Jim Blandy added support for preprocessor macros, while working for Red Hat. Andrew Cagney designed @value{GDBN}'s architecture vector. Many people including Andrew Cagney, Stephane Carrez, Randolph Chung, Nick Duffek, Richard Henderson, Mark Kettenis, Grace Sainsbury, Kei Sakamoto, Yoshinori Sato, Michael Snyder, Andreas Schwab, Jason Thorpe, Corinna Vinschen, Ulrich Weigand, and Elena Zannoni, helped with the migration of old architectures to this new framework. Andrew Cagney completely re-designed and re-implemented @value{GDBN}'s unwinder framework, this consisting of a fresh new design featuring frame IDs, independent frame sniffers, and the sentinel frame. Mark Kettenis implemented the @sc{dwarf 2} unwinder, Jeff Johnston the libunwind unwinder, and Andrew Cagney the dummy, sentinel, tramp, and trad unwinders. The architecture-specific changes, each involving a complete rewrite of the architecture's frame code, were carried out by Jim Blandy, Joel Brobecker, Kevin Buettner, Andrew Cagney, Stephane Carrez, Randolph Chung, Orjan Friberg, Richard Henderson, Daniel Jacobowitz, Jeff Johnston, Mark Kettenis, Theodore A. Roth, Kei Sakamoto, Yoshinori Sato, Michael Snyder, Corinna Vinschen, and Ulrich Weigand. Christian Zankel, Ross Morley, Bob Wilson, and Maxim Grigoriev from Tensilica, Inc.@: contributed support for Xtensa processors. Others who have worked on the Xtensa port of @value{GDBN} in the past include Steve Tjiang, John Newlin, and Scott Foehner. Michael Eager and staff of Xilinx, Inc., contributed support for the Xilinx MicroBlaze architecture. Initial support for the FreeBSD/mips target and native configuration was developed by SRI International and the University of Cambridge Computer Laboratory under DARPA/AFRL contract FA8750-10-C-0237 ("CTSRD"), as part of the DARPA CRASH research programme. Initial support for the FreeBSD/riscv target and native configuration was developed by SRI International and the University of Cambridge Computer Laboratory (Department of Computer Science and Technology) under DARPA contract HR0011-18-C-0016 ("ECATS"), as part of the DARPA SSITH research programme. The original port to the OpenRISC 1000 is believed to be due to Alessandro Forin and Per Bothner. More recent ports have been the work of Jeremy Bennett, Franck Jullien, Stefan Wallentowitz and Stafford Horne. @node Sample Session @chapter A Sample @value{GDBN} Session You can use this manual at your leisure to read all about @value{GDBN}. However, a handful of commands are enough to get started using the debugger. This chapter illustrates those commands. @iftex In this sample session, we emphasize user input like this: @b{input}, to make it easier to pick out from the surrounding output. @end iftex @c FIXME: this example may not be appropriate for some configs, where @c FIXME...primary interest is in remote use. One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro processor) exhibits the following bug: sometimes, when we change its quote strings from the default, the commands used to capture one macro definition within another stop working. In the following short @code{m4} session, we define a macro @code{foo} which expands to @code{0000}; we then use the @code{m4} built-in @code{defn} to define @code{bar} as the same thing. However, when we change the open quote string to @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same procedure fails to define a new synonym @code{baz}: @smallexample $ @b{cd gnu/m4} $ @b{./m4} @b{define(foo,0000)} @b{foo} 0000 @b{define(bar,defn(`foo'))} @b{bar} 0000 @b{changequote(<QUOTE>,<UNQUOTE>)} @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))} @b{baz} @b{Ctrl-d} m4: End of input: 0: fatal error: EOF in string @end smallexample @noindent Let us use @value{GDBN} to try to see what is going on. @smallexample $ @b{@value{GDBP} m4} @c FIXME: this falsifies the exact text played out, to permit smallbook @c FIXME... format to come out better. @value{GDBN} is free software and you are welcome to distribute copies of it under certain conditions; type "show copying" to see the conditions. There is absolutely no warranty for @value{GDBN}; type "show warranty" for details. @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc... (@value{GDBP}) @end smallexample @noindent @value{GDBN} reads only enough symbol data to know where to find the rest when needed; as a result, the first prompt comes up very quickly. We now tell @value{GDBN} to use a narrower display width than usual, so that examples fit in this manual. @smallexample (@value{GDBP}) @b{set width 70} @end smallexample @noindent We need to see how the @code{m4} built-in @code{changequote} works. Having looked at the source, we know the relevant subroutine is @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN} @code{break} command. @smallexample (@value{GDBP}) @b{break m4_changequote} Breakpoint 1 at 0x62f4: file builtin.c, line 879. @end smallexample @noindent Using the @code{run} command, we start @code{m4} running under @value{GDBN} control; as long as control does not reach the @code{m4_changequote} subroutine, the program runs as usual: @smallexample (@value{GDBP}) @b{run} Starting program: /work/Editorial/gdb/gnu/m4/m4 @b{define(foo,0000)} @b{foo} 0000 @end smallexample @noindent To trigger the breakpoint, we call @code{changequote}. @value{GDBN} suspends execution of @code{m4}, displaying information about the context where it stops. @smallexample @b{changequote(<QUOTE>,<UNQUOTE>)} Breakpoint 1, m4_changequote (argc=3, argv=0x33c70) at builtin.c:879 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3)) @end smallexample @noindent Now we use the command @code{n} (@code{next}) to advance execution to the next line of the current function. @smallexample (@value{GDBP}) @b{n} 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\ : nil, @end smallexample @noindent @code{set_quotes} looks like a promising subroutine. We can go into it by using the command @code{s} (@code{step}) instead of @code{next}. @code{step} goes to the next line to be executed in @emph{any} subroutine, so it steps into @code{set_quotes}. @smallexample (@value{GDBP}) @b{s} set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>") at input.c:530 530 if (lquote != def_lquote) @end smallexample @noindent The display that shows the subroutine where @code{m4} is now suspended (and its arguments) is called a stack frame display. It shows a summary of the stack. We can use the @code{backtrace} command (which can also be spelled @code{bt}), to see where we are in the stack as a whole: the @code{backtrace} command displays a stack frame for each active subroutine. @smallexample (@value{GDBP}) @b{bt} #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>") at input.c:530 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70) at builtin.c:882 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30) at macro.c:71 #4 0x79dc in expand_input () at macro.c:40 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195 @end smallexample @noindent We step through a few more lines to see what happens. The first two times, we can use @samp{s}; the next two times we use @code{n} to avoid falling into the @code{xstrdup} subroutine. @smallexample (@value{GDBP}) @b{s} 0x3b5c 532 if (rquote != def_rquote) (@value{GDBP}) @b{s} 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \ def_lquote : xstrdup(lq); (@value{GDBP}) @b{n} 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\ : xstrdup(rq); (@value{GDBP}) @b{n} 538 len_lquote = strlen(rquote); @end smallexample @noindent The last line displayed looks a little odd; we can examine the variables @code{lquote} and @code{rquote} to see if they are in fact the new left and right quotes we specified. We use the command @code{p} (@code{print}) to see their values. @smallexample (@value{GDBP}) @b{p lquote} $1 = 0x35d40 "<QUOTE>" (@value{GDBP}) @b{p rquote} $2 = 0x35d50 "<UNQUOTE>" @end smallexample @noindent @code{lquote} and @code{rquote} are indeed the new left and right quotes. To look at some context, we can display ten lines of source surrounding the current line with the @code{l} (@code{list}) command. @smallexample (@value{GDBP}) @b{l} 533 xfree(rquote); 534 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\ : xstrdup (lq); 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\ : xstrdup (rq); 537 538 len_lquote = strlen(rquote); 539 len_rquote = strlen(lquote); 540 @} 541 542 void @end smallexample @noindent Let us step past the two lines that set @code{len_lquote} and @code{len_rquote}, and then examine the values of those variables. @smallexample (@value{GDBP}) @b{n} 539 len_rquote = strlen(lquote); (@value{GDBP}) @b{n} 540 @} (@value{GDBP}) @b{p len_lquote} $3 = 9 (@value{GDBP}) @b{p len_rquote} $4 = 7 @end smallexample @noindent That certainly looks wrong, assuming @code{len_lquote} and @code{len_rquote} are meant to be the lengths of @code{lquote} and @code{rquote} respectively. We can set them to better values using the @code{p} command, since it can print the value of any expression---and that expression can include subroutine calls and assignments. @smallexample (@value{GDBP}) @b{p len_lquote=strlen(lquote)} $5 = 7 (@value{GDBP}) @b{p len_rquote=strlen(rquote)} $6 = 9 @end smallexample @noindent Is that enough to fix the problem of using the new quotes with the @code{m4} built-in @code{defn}? We can allow @code{m4} to continue executing with the @code{c} (@code{continue}) command, and then try the example that caused trouble initially: @smallexample (@value{GDBP}) @b{c} Continuing. @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))} baz 0000 @end smallexample @noindent Success! The new quotes now work just as well as the default ones. The problem seems to have been just the two typos defining the wrong lengths. We allow @code{m4} exit by giving it an EOF as input: @smallexample @b{Ctrl-d} Program exited normally. @end smallexample @noindent The message @samp{Program exited normally.} is from @value{GDBN}; it indicates @code{m4} has finished executing. We can end our @value{GDBN} session with the @value{GDBN} @code{quit} command. @smallexample (@value{GDBP}) @b{quit} @end smallexample @node Invocation @chapter Getting In and Out of @value{GDBN} This chapter discusses how to start @value{GDBN}, and how to get out of it. The essentials are: @itemize @bullet @item type @samp{@value{GDBP}} to start @value{GDBN}. @item type @kbd{quit} or @kbd{Ctrl-d} to exit. @end itemize @menu * Invoking GDB:: How to start @value{GDBN} * Quitting GDB:: How to quit @value{GDBN} * Shell Commands:: How to use shell commands inside @value{GDBN} * Logging Output:: How to log @value{GDBN}'s output to a file @end menu @node Invoking GDB @section Invoking @value{GDBN} Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started, @value{GDBN} reads commands from the terminal until you tell it to exit. You can also run @code{@value{GDBP}} with a variety of arguments and options, to specify more of your debugging environment at the outset. The command-line options described here are designed to cover a variety of situations; in some environments, some of these options may effectively be unavailable. The most usual way to start @value{GDBN} is with one argument, specifying an executable program: @smallexample @value{GDBP} @var{program} @end smallexample @noindent You can also start with both an executable program and a core file specified: @smallexample @value{GDBP} @var{program} @var{core} @end smallexample You can, instead, specify a process ID as a second argument or use option @code{-p}, if you want to debug a running process: @smallexample @value{GDBP} @var{program} 1234 @value{GDBP} -p 1234 @end smallexample @noindent would attach @value{GDBN} to process @code{1234}. With option @option{-p} you can omit the @var{program} filename. Taking advantage of the second command-line argument requires a fairly complete operating system; when you use @value{GDBN} as a remote debugger attached to a bare board, there may not be any notion of ``process'', and there is often no way to get a core dump. @value{GDBN} will warn you if it is unable to attach or to read core dumps. You can optionally have @code{@value{GDBP}} pass any arguments after the executable file to the inferior using @code{--args}. This option stops option processing. @smallexample @value{GDBP} --args gcc -O2 -c foo.c @end smallexample This will cause @code{@value{GDBP}} to debug @code{gcc}, and to set @code{gcc}'s command-line arguments (@pxref{Arguments}) to @samp{-O2 -c foo.c}. You can run @code{@value{GDBP}} without printing the front material, which describes @value{GDBN}'s non-warranty, by specifying @code{--silent} (or @code{-q}/@code{--quiet}): @smallexample @value{GDBP} --silent @end smallexample @noindent You can further control how @value{GDBN} starts up by using command-line options. @value{GDBN} itself can remind you of the options available. @noindent Type @smallexample @value{GDBP} -help @end smallexample @noindent to display all available options and briefly describe their use (@samp{@value{GDBP} -h} is a shorter equivalent). All options and command line arguments you give are processed in sequential order. The order makes a difference when the @samp{-x} option is used. @menu * File Options:: Choosing files * Mode Options:: Choosing modes * Startup:: What @value{GDBN} does during startup @end menu @node File Options @subsection Choosing Files When @value{GDBN} starts, it reads any arguments other than options as specifying an executable file and core file (or process ID). This is the same as if the arguments were specified by the @samp{-se} and @samp{-c} (or @samp{-p}) options respectively. (@value{GDBN} reads the first argument that does not have an associated option flag as equivalent to the @samp{-se} option followed by that argument; and the second argument that does not have an associated option flag, if any, as equivalent to the @samp{-c}/@samp{-p} option followed by that argument.) If the second argument begins with a decimal digit, @value{GDBN} will first attempt to attach to it as a process, and if that fails, attempt to open it as a corefile. If you have a corefile whose name begins with a digit, you can prevent @value{GDBN} from treating it as a pid by prefixing it with @file{./}, e.g.@: @file{./12345}. If @value{GDBN} has not been configured to included core file support, such as for most embedded targets, then it will complain about a second argument and ignore it. Many options have both long and short forms; both are shown in the following list. @value{GDBN} also recognizes the long forms if you truncate them, so long as enough of the option is present to be unambiguous. (If you prefer, you can flag option arguments with @samp{--} rather than @samp{-}, though we illustrate the more usual convention.) @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This @c way, both those who look for -foo and --foo in the index, will find @c it. @table @code @item -symbols @var{file} @itemx -s @var{file} @cindex @code{--symbols} @cindex @code{-s} Read symbol table from file @var{file}. @item -exec @var{file} @itemx -e @var{file} @cindex @code{--exec} @cindex @code{-e} Use file @var{file} as the executable file to execute when appropriate, and for examining pure data in conjunction with a core dump. @item -se @var{file} @cindex @code{--se} Read symbol table from file @var{file} and use it as the executable file. @item -core @var{file} @itemx -c @var{file} @cindex @code{--core} @cindex @code{-c} Use file @var{file} as a core dump to examine. @item -pid @var{number} @itemx -p @var{number} @cindex @code{--pid} @cindex @code{-p} Connect to process ID @var{number}, as with the @code{attach} command. @item -command @var{file} @itemx -x @var{file} @cindex @code{--command} @cindex @code{-x} Execute commands from file @var{file}. The contents of this file is evaluated exactly as the @code{source} command would. @xref{Command Files,, Command files}. @item -eval-command @var{command} @itemx -ex @var{command} @cindex @code{--eval-command} @cindex @code{-ex} Execute a single @value{GDBN} command. This option may be used multiple times to call multiple commands. It may also be interleaved with @samp{-command} as required. @smallexample @value{GDBP} -ex 'target sim' -ex 'load' \ -x setbreakpoints -ex 'run' a.out @end smallexample @item -init-command @var{file} @itemx -ix @var{file} @cindex @code{--init-command} @cindex @code{-ix} Execute commands from file @var{file} before loading the inferior (but after loading gdbinit files). @xref{Startup}. @item -init-eval-command @var{command} @itemx -iex @var{command} @cindex @code{--init-eval-command} @cindex @code{-iex} Execute a single @value{GDBN} command before loading the inferior (but after loading gdbinit files). @xref{Startup}. @item -directory @var{directory} @itemx -d @var{directory} @cindex @code{--directory} @cindex @code{-d} Add @var{directory} to the path to search for source and script files. @item -r @itemx -readnow @cindex @code{--readnow} @cindex @code{-r} Read each symbol file's entire symbol table immediately, rather than the default, which is to read it incrementally as it is needed. This makes startup slower, but makes future operations faster. @item --readnever @anchor{--readnever} @cindex @code{--readnever}, command-line option Do not read each symbol file's symbolic debug information. This makes startup faster but at the expense of not being able to perform symbolic debugging. DWARF unwind information is also not read, meaning backtraces may become incomplete or inaccurate. One use of this is when a user simply wants to do the following sequence: attach, dump core, detach. Loading the debugging information in this case is an unnecessary cause of delay. @end table @node Mode Options @subsection Choosing Modes You can run @value{GDBN} in various alternative modes---for example, in batch mode or quiet mode. @table @code @anchor{-nx} @item -nx @itemx -n @cindex @code{--nx} @cindex @code{-n} Do not execute commands found in any initialization file. There are three init files, loaded in the following order: @table @code @item @file{system.gdbinit} This is the system-wide init file. Its location is specified with the @code{--with-system-gdbinit} configure option (@pxref{System-wide configuration}). It is loaded first when @value{GDBN} starts, before command line options have been processed. @item @file{system.gdbinit.d} This is the system-wide init directory. Its location is specified with the @code{--with-system-gdbinit-dir} configure option (@pxref{System-wide configuration}). Files in this directory are loaded in alphabetical order immediately after system.gdbinit (if enabled) when @value{GDBN} starts, before command line options have been processed. Files need to have a recognized scripting language extension (@file{.py}/@file{.scm}) or be named with a @file{.gdb} extension to be interpreted as regular @value{GDBN} commands. @value{GDBN} will not recurse into any subdirectories of this directory. @item @file{~/.gdbinit} This is the init file in your home directory. It is loaded next, after @file{system.gdbinit}, and before command options have been processed. @item @file{./.gdbinit} This is the init file in the current directory. It is loaded last, after command line options other than @code{-x} and @code{-ex} have been processed. Command line options @code{-x} and @code{-ex} are processed last, after @file{./.gdbinit} has been loaded. @end table For further documentation on startup processing, @xref{Startup}. For documentation on how to write command files, @xref{Command Files,,Command Files}. @anchor{-nh} @item -nh @cindex @code{--nh} Do not execute commands found in @file{~/.gdbinit}, the init file in your home directory. @xref{Startup}. @item -quiet @itemx -silent @itemx -q @cindex @code{--quiet} @cindex @code{--silent} @cindex @code{-q} ``Quiet''. Do not print the introductory and copyright messages. These messages are also suppressed in batch mode. @item -batch @cindex @code{--batch} Run in batch mode. Exit with status @code{0} after processing all the command files specified with @samp{-x} (and all commands from initialization files, if not inhibited with @samp{-n}). Exit with nonzero status if an error occurs in executing the @value{GDBN} commands in the command files. Batch mode also disables pagination, sets unlimited terminal width and height @pxref{Screen Size}, and acts as if @kbd{set confirm off} were in effect (@pxref{Messages/Warnings}). Batch mode may be useful for running @value{GDBN} as a filter, for example to download and run a program on another computer; in order to make this more useful, the message @smallexample Program exited normally. @end smallexample @noindent (which is ordinarily issued whenever a program running under @value{GDBN} control terminates) is not issued when running in batch mode. @item -batch-silent @cindex @code{--batch-silent} Run in batch mode exactly like @samp{-batch}, but totally silently. All @value{GDBN} output to @code{stdout} is prevented (@code{stderr} is unaffected). This is much quieter than @samp{-silent} and would be useless for an interactive session. This is particularly useful when using targets that give @samp{Loading section} messages, for example. Note that targets that give their output via @value{GDBN}, as opposed to writing directly to @code{stdout}, will also be made silent. @item -return-child-result @cindex @code{--return-child-result} The return code from @value{GDBN} will be the return code from the child process (the process being debugged), with the following exceptions: @itemize @bullet @item @value{GDBN} exits abnormally. E.g., due to an incorrect argument or an internal error. In this case the exit code is the same as it would have been without @samp{-return-child-result}. @item The user quits with an explicit value. E.g., @samp{quit 1}. @item The child process never runs, or is not allowed to terminate, in which case the exit code will be -1. @end itemize This option is useful in conjunction with @samp{-batch} or @samp{-batch-silent}, when @value{GDBN} is being used as a remote program loader or simulator interface. @item -nowindows @itemx -nw @cindex @code{--nowindows} @cindex @code{-nw} ``No windows''. If @value{GDBN} comes with a graphical user interface (GUI) built in, then this option tells @value{GDBN} to only use the command-line interface. If no GUI is available, this option has no effect. @item -windows @itemx -w @cindex @code{--windows} @cindex @code{-w} If @value{GDBN} includes a GUI, then this option requires it to be used if possible. @item -cd @var{directory} @cindex @code{--cd} Run @value{GDBN} using @var{directory} as its working directory, instead of the current directory. @item -data-directory @var{directory} @itemx -D @var{directory} @cindex @code{--data-directory} @cindex @code{-D} Run @value{GDBN} using @var{directory} as its data directory. The data directory is where @value{GDBN} searches for its auxiliary files. @xref{Data Files}. @item -fullname @itemx -f @cindex @code{--fullname} @cindex @code{-f} @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a subprocess. It tells @value{GDBN} to output the full file name and line number in a standard, recognizable fashion each time a stack frame is displayed (which includes each time your program stops). This recognizable format looks like two @samp{\032} characters, followed by the file name, line number and character position separated by colons, and a newline. The Emacs-to-@value{GDBN} interface program uses the two @samp{\032} characters as a signal to display the source code for the frame. @item -annotate @var{level} @cindex @code{--annotate} This option sets the @dfn{annotation level} inside @value{GDBN}. Its effect is identical to using @samp{set annotate @var{level}} (@pxref{Annotations}). The annotation @var{level} controls how much information @value{GDBN} prints together with its prompt, values of expressions, source lines, and other types of output. Level 0 is the normal, level 1 is for use when @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 3 is the maximum annotation suitable for programs that control @value{GDBN}, and level 2 has been deprecated. The annotation mechanism has largely been superseded by @sc{gdb/mi} (@pxref{GDB/MI}). @item --args @cindex @code{--args} Change interpretation of command line so that arguments following the executable file are passed as command line arguments to the inferior. This option stops option processing. @item -baud @var{bps} @itemx -b @var{bps} @cindex @code{--baud} @cindex @code{-b} Set the line speed (baud rate or bits per second) of any serial interface used by @value{GDBN} for remote debugging. @item -l @var{timeout} @cindex @code{-l} Set the timeout (in seconds) of any communication used by @value{GDBN} for remote debugging. @item -tty @var{device} @itemx -t @var{device} @cindex @code{--tty} @cindex @code{-t} Run using @var{device} for your program's standard input and output. @c FIXME: kingdon thinks there is more to -tty. Investigate. @c resolve the situation of these eventually @item -tui @cindex @code{--tui} Activate the @dfn{Text User Interface} when starting. The Text User Interface manages several text windows on the terminal, showing source, assembly, registers and @value{GDBN} command outputs (@pxref{TUI, ,@value{GDBN} Text User Interface}). Do not use this option if you run @value{GDBN} from Emacs (@pxref{Emacs, , Using @value{GDBN} under @sc{gnu} Emacs}). @item -interpreter @var{interp} @cindex @code{--interpreter} Use the interpreter @var{interp} for interface with the controlling program or device. This option is meant to be set by programs which communicate with @value{GDBN} using it as a back end. @xref{Interpreters, , Command Interpreters}. @samp{--interpreter=mi} (or @samp{--interpreter=mi3}) causes @value{GDBN} to use the @dfn{@sc{gdb/mi} interface} version 3 (@pxref{GDB/MI, , The @sc{gdb/mi} Interface}) included since @value{GDBN} version 9.1. @sc{gdb/mi} version 2 (@code{mi2}), included in @value{GDBN} 6.0 and version 1 (@code{mi1}), included in @value{GDBN} 5.3, are also available. Earlier @sc{gdb/mi} interfaces are no longer supported. @item -write @cindex @code{--write} Open the executable and core files for both reading and writing. This is equivalent to the @samp{set write on} command inside @value{GDBN} (@pxref{Patching}). @item -statistics @cindex @code{--statistics} This option causes @value{GDBN} to print statistics about time and memory usage after it completes each command and returns to the prompt. @item -version @cindex @code{--version} This option causes @value{GDBN} to print its version number and no-warranty blurb, and exit. @item -configuration @cindex @code{--configuration} This option causes @value{GDBN} to print details about its build-time configuration parameters, and then exit. These details can be important when reporting @value{GDBN} bugs (@pxref{GDB Bugs}). @end table @node Startup @subsection What @value{GDBN} Does During Startup @cindex @value{GDBN} startup Here's the description of what @value{GDBN} does during session startup: @enumerate @item Sets up the command interpreter as specified by the command line (@pxref{Mode Options, interpreter}). @item @cindex init file Reads the system-wide @dfn{init file} (if @option{--with-system-gdbinit} was used when building @value{GDBN}; @pxref{System-wide configuration, ,System-wide configuration and settings}) and the files in the system-wide gdbinit directory (if @option{--with-system-gdbinit-dir} was used) and executes all the commands in those files. The files need to be named with a @file{.gdb} extension to be interpreted as @value{GDBN} commands, or they can be written in a supported scripting language with an appropriate file extension. @anchor{Home Directory Init File} @item Reads the init file (if any) in your home directory@footnote{On DOS/Windows systems, the home directory is the one pointed to by the @code{HOME} environment variable.} and executes all the commands in that file. @anchor{Option -init-eval-command} @item Executes commands and command files specified by the @samp{-iex} and @samp{-ix} options in their specified order. Usually you should use the @samp{-ex} and @samp{-x} options instead, but this way you can apply settings before @value{GDBN} init files get executed and before inferior gets loaded. @item Processes command line options and operands. @anchor{Init File in the Current Directory during Startup} @item Reads and executes the commands from init file (if any) in the current working directory as long as @samp{set auto-load local-gdbinit} is set to @samp{on} (@pxref{Init File in the Current Directory}). This is only done if the current directory is different from your home directory. Thus, you can have more than one init file, one generic in your home directory, and another, specific to the program you are debugging, in the directory where you invoke @value{GDBN}. @item If the command line specified a program to debug, or a process to attach to, or a core file, @value{GDBN} loads any auto-loaded scripts provided for the program or for its loaded shared libraries. @xref{Auto-loading}. If you wish to disable the auto-loading during startup, you must do something like the following: @smallexample $ gdb -iex "set auto-load python-scripts off" myprogram @end smallexample Option @samp{-ex} does not work because the auto-loading is then turned off too late. @item Executes commands and command files specified by the @samp{-ex} and @samp{-x} options in their specified order. @xref{Command Files}, for more details about @value{GDBN} command files. @item Reads the command history recorded in the @dfn{history file}. @xref{Command History}, for more details about the command history and the files where @value{GDBN} records it. @end enumerate Init files use the same syntax as @dfn{command files} (@pxref{Command Files}) and are processed by @value{GDBN} in the same way. The init file in your home directory can set options (such as @samp{set complaints}) that affect subsequent processing of command line options and operands. Init files are not executed if you use the @samp{-nx} option (@pxref{Mode Options, ,Choosing Modes}). To display the list of init files loaded by gdb at startup, you can use @kbd{gdb --help}. @cindex init file name @cindex @file{.gdbinit} @cindex @file{gdb.ini} The @value{GDBN} init files are normally called @file{.gdbinit}. The DJGPP port of @value{GDBN} uses the name @file{gdb.ini}, due to the limitations of file names imposed by DOS filesystems. The Windows port of @value{GDBN} uses the standard name, but if it finds a @file{gdb.ini} file in your home directory, it warns you about that and suggests to rename the file to the standard name. @node Quitting GDB @section Quitting @value{GDBN} @cindex exiting @value{GDBN} @cindex leaving @value{GDBN} @table @code @kindex quit @r{[}@var{expression}@r{]} @kindex q @r{(@code{quit})} @item quit @r{[}@var{expression}@r{]} @itemx q To exit @value{GDBN}, use the @code{quit} command (abbreviated @code{q}), or type an end-of-file character (usually @kbd{Ctrl-d}). If you do not supply @var{expression}, @value{GDBN} will terminate normally; otherwise it will terminate using the result of @var{expression} as the error code. @end table @cindex interrupt An interrupt (often @kbd{Ctrl-c}) does not exit from @value{GDBN}, but rather terminates the action of any @value{GDBN} command that is in progress and returns to @value{GDBN} command level. It is safe to type the interrupt character at any time because @value{GDBN} does not allow it to take effect until a time when it is safe. If you have been using @value{GDBN} to control an attached process or device, you can release it with the @code{detach} command (@pxref{Attach, ,Debugging an Already-running Process}). @node Shell Commands @section Shell Commands If you need to execute occasional shell commands during your debugging session, there is no need to leave or suspend @value{GDBN}; you can just use the @code{shell} command. @table @code @kindex shell @kindex ! @cindex shell escape @item shell @var{command-string} @itemx !@var{command-string} Invoke a standard shell to execute @var{command-string}. Note that no space is needed between @code{!} and @var{command-string}. If it exists, the environment variable @code{SHELL} determines which shell to run. Otherwise @value{GDBN} uses the default shell (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.). @end table The utility @code{make} is often needed in development environments. You do not have to use the @code{shell} command for this purpose in @value{GDBN}: @table @code @kindex make @cindex calling make @item make @var{make-args} Execute the @code{make} program with the specified arguments. This is equivalent to @samp{shell make @var{make-args}}. @end table @table @code @kindex pipe @kindex | @cindex send the output of a gdb command to a shell command @anchor{pipe} @item pipe [@var{command}] | @var{shell_command} @itemx | [@var{command}] | @var{shell_command} @itemx pipe -d @var{delim} @var{command} @var{delim} @var{shell_command} @itemx | -d @var{delim} @var{command} @var{delim} @var{shell_command} Executes @var{command} and sends its output to @var{shell_command}. Note that no space is needed around @code{|}. If no @var{command} is provided, the last command executed is repeated. In case the @var{command} contains a @code{|}, the option @code{-d @var{delim}} can be used to specify an alternate delimiter string @var{delim} that separates the @var{command} from the @var{shell_command}. Example: @smallexample @group (gdb) p var $1 = @{ black = 144, red = 233, green = 377, blue = 610, white = 987 @} @end group @group (gdb) pipe p var|wc 7 19 80 (gdb) |p var|wc -l 7 @end group @group (gdb) p /x var $4 = @{ black = 0x90, red = 0xe9, green = 0x179, blue = 0x262, white = 0x3db @} (gdb) ||grep red red => 0xe9, @end group @group (gdb) | -d ! echo this contains a | char\n ! sed -e 's/|/PIPE/' this contains a PIPE char (gdb) | -d xxx echo this contains a | char!\n xxx sed -e 's/|/PIPE/' this contains a PIPE char! (gdb) @end group @end smallexample @end table The convenience variables @code{$_shell_exitcode} and @code{$_shell_exitsignal} can be used to examine the exit status of the last shell command launched by @code{shell}, @code{make}, @code{pipe} and @code{|}. @xref{Convenience Vars,, Convenience Variables}. @node Logging Output @section Logging Output @cindex logging @value{GDBN} output @cindex save @value{GDBN} output to a file You may want to save the output of @value{GDBN} commands to a file. There are several commands to control @value{GDBN}'s logging. @table @code @kindex set logging @item set logging on Enable logging. @item set logging off Disable logging. @cindex logging file name @item set logging file @var{file} Change the name of the current logfile. The default logfile is @file{gdb.txt}. @item set logging overwrite [on|off] By default, @value{GDBN} will append to the logfile. Set @code{overwrite} if you want @code{set logging on} to overwrite the logfile instead. @item set logging redirect [on|off] By default, @value{GDBN} output will go to both the terminal and the logfile. Set @code{redirect} if you want output to go only to the log file. @item set logging debugredirect [on|off] By default, @value{GDBN} debug output will go to both the terminal and the logfile. Set @code{debugredirect} if you want debug output to go only to the log file. @kindex show logging @item show logging Show the current values of the logging settings. @end table You can also redirect the output of a @value{GDBN} command to a shell command. @xref{pipe}. @node Commands @chapter @value{GDBN} Commands You can abbreviate a @value{GDBN} command to the first few letters of the command name, if that abbreviation is unambiguous; and you can repeat certain @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB} key to get @value{GDBN} to fill out the rest of a word in a command (or to show you the alternatives available, if there is more than one possibility). @menu * Command Syntax:: How to give commands to @value{GDBN} * Command Settings:: How to change default behavior of commands * Completion:: Command completion * Command Options:: Command options * Help:: How to ask @value{GDBN} for help @end menu @node Command Syntax @section Command Syntax A @value{GDBN} command is a single line of input. There is no limit on how long it can be. It starts with a command name, which is followed by arguments whose meaning depends on the command name. For example, the command @code{step} accepts an argument which is the number of times to step, as in @samp{step 5}. You can also use the @code{step} command with no arguments. Some commands do not allow any arguments. @cindex abbreviation @value{GDBN} command names may always be truncated if that abbreviation is unambiguous. Other possible command abbreviations are listed in the documentation for individual commands. In some cases, even ambiguous abbreviations are allowed; for example, @code{s} is specially defined as equivalent to @code{step} even though there are other commands whose names start with @code{s}. You can test abbreviations by using them as arguments to the @code{help} command. @cindex repeating commands @kindex RET @r{(repeat last command)} A blank line as input to @value{GDBN} (typing just @key{RET}) means to repeat the previous command. Certain commands (for example, @code{run}) will not repeat this way; these are commands whose unintentional repetition might cause trouble and which you are unlikely to want to repeat. User-defined commands can disable this feature; see @ref{Define, dont-repeat}. The @code{list} and @code{x} commands, when you repeat them with @key{RET}, construct new arguments rather than repeating exactly as typed. This permits easy scanning of source or memory. @value{GDBN} can also use @key{RET} in another way: to partition lengthy output, in a way similar to the common utility @code{more} (@pxref{Screen Size,,Screen Size}). Since it is easy to press one @key{RET} too many in this situation, @value{GDBN} disables command repetition after any command that generates this sort of display. @kindex # @r{(a comment)} @cindex comment Any text from a @kbd{#} to the end of the line is a comment; it does nothing. This is useful mainly in command files (@pxref{Command Files,,Command Files}). @cindex repeating command sequences @kindex Ctrl-o @r{(operate-and-get-next)} The @kbd{Ctrl-o} binding is useful for repeating a complex sequence of commands. This command accepts the current line, like @key{RET}, and then fetches the next line relative to the current line from the history for editing. @node Command Settings @section Command Settings @cindex default behavior of commands, changing @cindex default settings, changing Many commands change their behavior according to command-specific variables or settings. These settings can be changed with the @code{set} subcommands. For example, the @code{print} command (@pxref{Data, ,Examining Data}) prints arrays differently depending on settings changeable with the commands @code{set print elements NUMBER-OF-ELEMENTS} and @code{set print array-indexes}, among others. You can change these settings to your preference in the gdbinit files loaded at @value{GDBN} startup. @xref{Startup}. The settings can also be changed interactively during the debugging session. For example, to change the limit of array elements to print, you can do the following: @smallexample (@value{GDBN}) set print elements 10 (@value{GDBN}) print some_array $1 = @{0, 10, 20, 30, 40, 50, 60, 70, 80, 90...@} @end smallexample The above @code{set print elements 10} command changes the number of elements to print from the default of 200 to 10. If you only intend this limit of 10 to be used for printing @code{some_array}, then you must restore the limit back to 200, with @code{set print elements 200}. Some commands allow overriding settings with command options. For example, the @code{print} command supports a number of options that allow overriding relevant global print settings as set by @code{set print} subcommands. @xref{print options}. The example above could be rewritten as: @smallexample (@value{GDBN}) print -elements 10 -- some_array $1 = @{0, 10, 20, 30, 40, 50, 60, 70, 80, 90...@} @end smallexample Alternatively, you can use the @code{with} command to change a setting temporarily, for the duration of a command invocation. @table @code @kindex with command @kindex w @r{(@code{with})} @cindex settings @cindex temporarily change settings @item with @var{setting} [@var{value}] [-- @var{command}] @itemx w @var{setting} [@var{value}] [-- @var{command}] Temporarily set @var{setting} to @var{value} for the duration of @var{command}. @var{setting} is any setting you can change with the @code{set} subcommands. @var{value} is the value to assign to @code{setting} while running @code{command}. If no @var{command} is provided, the last command executed is repeated. If a @var{command} is provided, it must be preceded by a double dash (@code{--}) separator. This is required because some settings accept free-form arguments, such as expressions or filenames. For example, the command @smallexample (@value{GDBN}) with print array on -- print some_array @end smallexample @noindent is equivalent to the following 3 commands: @smallexample (@value{GDBN}) set print array on (@value{GDBN}) print some_array (@value{GDBN}) set print array off @end smallexample The @code{with} command is particularly useful when you want to override a setting while running user-defined commands, or commands defined in Python or Guile. @xref{Extending GDB,, Extending GDB}. @smallexample (@value{GDBN}) with print pretty on -- my_complex_command @end smallexample To change several settings for the same command, you can nest @code{with} commands. For example, @code{with language ada -- with print elements 10} temporarily changes the language to Ada and sets a limit of 10 elements to print for arrays and strings. @end table @node Completion @section Command Completion @cindex completion @cindex word completion @value{GDBN} can fill in the rest of a word in a command for you, if there is only one possibility; it can also show you what the valid possibilities are for the next word in a command, at any time. This works for @value{GDBN} commands, @value{GDBN} subcommands, command options, and the names of symbols in your program. Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest of a word. If there is only one possibility, @value{GDBN} fills in the word, and waits for you to finish the command (or press @key{RET} to enter it). For example, if you type @c FIXME "@key" does not distinguish its argument sufficiently to permit @c complete accuracy in these examples; space introduced for clarity. @c If texinfo enhancements make it unnecessary, it would be nice to @c replace " @key" by "@key" in the following... @smallexample (@value{GDBP}) info bre @key{TAB} @end smallexample @noindent @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is the only @code{info} subcommand beginning with @samp{bre}: @smallexample (@value{GDBP}) info breakpoints @end smallexample @noindent You can either press @key{RET} at this point, to run the @code{info breakpoints} command, or backspace and enter something else, if @samp{breakpoints} does not look like the command you expected. (If you were sure you wanted @code{info breakpoints} in the first place, you might as well just type @key{RET} immediately after @samp{info bre}, to exploit command abbreviations rather than command completion). If there is more than one possibility for the next word when you press @key{TAB}, @value{GDBN} sounds a bell. You can either supply more characters and try again, or just press @key{TAB} a second time; @value{GDBN} displays all the possible completions for that word. For example, you might want to set a breakpoint on a subroutine whose name begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN} just sounds the bell. Typing @key{TAB} again displays all the function names in your program that begin with those characters, for example: @smallexample (@value{GDBP}) b make_ @key{TAB} @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see: make_a_section_from_file make_environ make_abs_section make_function_type make_blockvector make_pointer_type make_cleanup make_reference_type make_command make_symbol_completion_list (@value{GDBP}) b make_ @end smallexample @noindent After displaying the available possibilities, @value{GDBN} copies your partial input (@samp{b make_} in the example) so you can finish the command. If you just want to see the list of alternatives in the first place, you can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?} means @kbd{@key{META} ?}. You can type this either by holding down a key designated as the @key{META} shift on your keyboard (if there is one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}. If the number of possible completions is large, @value{GDBN} will print as much of the list as it has collected, as well as a message indicating that the list may be truncated. @smallexample (@value{GDBP}) b m@key{TAB}@key{TAB} main <... the rest of the possible completions ...> *** List may be truncated, max-completions reached. *** (@value{GDBP}) b m @end smallexample @noindent This behavior can be controlled with the following commands: @table @code @kindex set max-completions @item set max-completions @var{limit} @itemx set max-completions unlimited Set the maximum number of completion candidates. @value{GDBN} will stop looking for more completions once it collects this many candidates. This is useful when completing on things like function names as collecting all the possible candidates can be time consuming. The default value is 200. A value of zero disables tab-completion. Note that setting either no limit or a very large limit can make completion slow. @kindex show max-completions @item show max-completions Show the maximum number of candidates that @value{GDBN} will collect and show during completion. @end table @cindex quotes in commands @cindex completion of quoted strings Sometimes the string you need, while logically a ``word'', may contain parentheses or other characters that @value{GDBN} normally excludes from its notion of a word. To permit word completion to work in this situation, you may enclose words in @code{'} (single quote marks) in @value{GDBN} commands. A likely situation where you might need this is in typing an expression that involves a C@t{++} symbol name with template parameters. This is because when completing expressions, GDB treats the @samp{<} character as word delimiter, assuming that it's the less-than comparison operator (@pxref{C Operators, , C and C@t{++} Operators}). For example, when you want to call a C@t{++} template function interactively using the @code{print} or @code{call} commands, you may need to distinguish whether you mean the version of @code{name} that was specialized for @code{int}, @code{name<int>()}, or the version that was specialized for @code{float}, @code{name<float>()}. To use the word-completion facilities in this situation, type a single quote @code{'} at the beginning of the function name. This alerts @value{GDBN} that it may need to consider more information than usual when you press @key{TAB} or @kbd{M-?} to request word completion: @smallexample (@value{GDBP}) p 'func< @kbd{M-?} func<int>() func<float>() (@value{GDBP}) p 'func< @end smallexample When setting breakpoints however (@pxref{Specify Location}), you don't usually need to type a quote before the function name, because @value{GDBN} understands that you want to set a breakpoint on a function: @smallexample (@value{GDBP}) b func< @kbd{M-?} func<int>() func<float>() (@value{GDBP}) b func< @end smallexample This is true even in the case of typing the name of C@t{++} overloaded functions (multiple definitions of the same function, distinguished by argument type). For example, when you want to set a breakpoint you don't need to distinguish whether you mean the version of @code{name} that takes an @code{int} parameter, @code{name(int)}, or the version that takes a @code{float} parameter, @code{name(float)}. @smallexample (@value{GDBP}) b bubble( @kbd{M-?} bubble(int) bubble(double) (@value{GDBP}) b bubble(dou @kbd{M-?} bubble(double) @end smallexample See @ref{quoting names} for a description of other scenarios that require quoting. For more information about overloaded functions, see @ref{C Plus Plus Expressions, ,C@t{++} Expressions}. You can use the command @code{set overload-resolution off} to disable overload resolution; see @ref{Debugging C Plus Plus, ,@value{GDBN} Features for C@t{++}}. @cindex completion of structure field names @cindex structure field name completion @cindex completion of union field names @cindex union field name completion When completing in an expression which looks up a field in a structure, @value{GDBN} also tries@footnote{The completer can be confused by certain kinds of invalid expressions. Also, it only examines the static type of the expression, not the dynamic type.} to limit completions to the field names available in the type of the left-hand-side: @smallexample (@value{GDBP}) p gdb_stdout.@kbd{M-?} magic to_fputs to_rewind to_data to_isatty to_write to_delete to_put to_write_async_safe to_flush to_read @end smallexample @noindent This is because the @code{gdb_stdout} is a variable of the type @code{struct ui_file} that is defined in @value{GDBN} sources as follows: @smallexample struct ui_file @{ int *magic; ui_file_flush_ftype *to_flush; ui_file_write_ftype *to_write; ui_file_write_async_safe_ftype *to_write_async_safe; ui_file_fputs_ftype *to_fputs; ui_file_read_ftype *to_read; ui_file_delete_ftype *to_delete; ui_file_isatty_ftype *to_isatty; ui_file_rewind_ftype *to_rewind; ui_file_put_ftype *to_put; void *to_data; @} @end smallexample @node Command Options @section Command options @cindex command options Some commands accept options starting with a leading dash. For example, @code{print -pretty}. Similarly to command names, you can abbreviate a @value{GDBN} option to the first few letters of the option name, if that abbreviation is unambiguous, and you can also use the @key{TAB} key to get @value{GDBN} to fill out the rest of a word in an option (or to show you the alternatives available, if there is more than one possibility). @cindex command options, raw input Some commands take raw input as argument. For example, the print command processes arbitrary expressions in any of the languages supported by @value{GDBN}. With such commands, because raw input may start with a leading dash that would be confused with an option or any of its abbreviations, e.g.@: @code{print -p} (short for @code{print -pretty} or printing negative @code{p}?), if you specify any command option, then you must use a double-dash (@code{--}) delimiter to indicate the end of options. @cindex command options, boolean Some options are described as accepting an argument which can be either @code{on} or @code{off}. These are known as @dfn{boolean options}. Similarly to boolean settings commands---@code{on} and @code{off} are the typical values, but any of @code{1}, @code{yes} and @code{enable} can also be used as ``true'' value, and any of @code{0}, @code{no} and @code{disable} can also be used as ``false'' value. You can also omit a ``true'' value, as it is implied by default. For example, these are equivalent: @smallexample (@value{GDBP}) print -object on -pretty off -element unlimited -- *myptr (@value{GDBP}) p -o -p 0 -e u -- *myptr @end smallexample You can discover the set of options some command accepts by completing on @code{-} after the command name. For example: @smallexample (@value{GDBP}) print -@key{TAB}@key{TAB} -address -max-depth -raw-values -union -array -null-stop -repeats -vtbl -array-indexes -object -static-members -elements -pretty -symbol @end smallexample Completion will in some cases guide you with a suggestion of what kind of argument an option expects. For example: @smallexample (@value{GDBP}) print -elements @key{TAB}@key{TAB} NUMBER unlimited @end smallexample Here, the option expects a number (e.g., @code{100}), not literal @code{NUMBER}. Such metasyntactical arguments are always presented in uppercase. (For more on using the @code{print} command, see @ref{Data, ,Examining Data}.) @node Help @section Getting Help @cindex online documentation @kindex help You can always ask @value{GDBN} itself for information on its commands, using the command @code{help}. @table @code @kindex h @r{(@code{help})} @item help @itemx h You can use @code{help} (abbreviated @code{h}) with no arguments to display a short list of named classes of commands: @smallexample (@value{GDBP}) help List of classes of commands: aliases -- Aliases of other commands breakpoints -- Making program stop at certain points data -- Examining data files -- Specifying and examining files internals -- Maintenance commands obscure -- Obscure features running -- Running the program stack -- Examining the stack status -- Status inquiries support -- Support facilities tracepoints -- Tracing of program execution without stopping the program user-defined -- User-defined commands Type "help" followed by a class name for a list of commands in that class. Type "help" followed by command name for full documentation. Command name abbreviations are allowed if unambiguous. (@value{GDBP}) @end smallexample @c the above line break eliminates huge line overfull... @item help @var{class} Using one of the general help classes as an argument, you can get a list of the individual commands in that class. For example, here is the help display for the class @code{status}: @smallexample (@value{GDBP}) help status Status inquiries. List of commands: @c Line break in "show" line falsifies real output, but needed @c to fit in smallbook page size. info -- Generic command for showing things about the program being debugged show -- Generic command for showing things about the debugger Type "help" followed by command name for full documentation. Command name abbreviations are allowed if unambiguous. (@value{GDBP}) @end smallexample @item help @var{command} With a command name as @code{help} argument, @value{GDBN} displays a short paragraph on how to use that command. @kindex apropos @item apropos [-v] @var{regexp} The @code{apropos} command searches through all of the @value{GDBN} commands, and their documentation, for the regular expression specified in @var{args}. It prints out all matches found. The optional flag @samp{-v}, which stands for @samp{verbose}, indicates to output the full documentation of the matching commands and highlight the parts of the documentation matching @var{regexp}. For example: @smallexample apropos alias @end smallexample @noindent results in: @smallexample @group alias -- Define a new command that is an alias of an existing command aliases -- Aliases of other commands d -- Delete some breakpoints or auto-display expressions del -- Delete some breakpoints or auto-display expressions delete -- Delete some breakpoints or auto-display expressions @end group @end smallexample @noindent while @smallexample apropos -v cut.*thread apply @end smallexample @noindent results in the below output, where @samp{cut for 'thread apply} is highlighted if styling is enabled. @smallexample @group taas -- Apply a command to all threads (ignoring errors and empty output). Usage: taas COMMAND shortcut for 'thread apply all -s COMMAND' tfaas -- Apply a command to all frames of all threads (ignoring errors and empty output). Usage: tfaas COMMAND shortcut for 'thread apply all -s frame apply all -s COMMAND' @end group @end smallexample @kindex complete @item complete @var{args} The @code{complete @var{args}} command lists all the possible completions for the beginning of a command. Use @var{args} to specify the beginning of the command you want completed. For example: @smallexample complete i @end smallexample @noindent results in: @smallexample @group if ignore info inspect @end group @end smallexample @noindent This is intended for use by @sc{gnu} Emacs. @end table In addition to @code{help}, you can use the @value{GDBN} commands @code{info} and @code{show} to inquire about the state of your program, or the state of @value{GDBN} itself. Each command supports many topics of inquiry; this manual introduces each of them in the appropriate context. The listings under @code{info} and under @code{show} in the Command, Variable, and Function Index point to all the sub-commands. @xref{Command and Variable Index}. @c @group @table @code @kindex info @kindex i @r{(@code{info})} @item info This command (abbreviated @code{i}) is for describing the state of your program. For example, you can show the arguments passed to a function with @code{info args}, list the registers currently in use with @code{info registers}, or list the breakpoints you have set with @code{info breakpoints}. You can get a complete list of the @code{info} sub-commands with @w{@code{help info}}. @kindex set @item set You can assign the result of an expression to an environment variable with @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with @code{set prompt $}. @kindex show @item show In contrast to @code{info}, @code{show} is for describing the state of @value{GDBN} itself. You can change most of the things you can @code{show}, by using the related command @code{set}; for example, you can control what number system is used for displays with @code{set radix}, or simply inquire which is currently in use with @code{show radix}. @kindex info set To display all the settable parameters and their current values, you can use @code{show} with no arguments; you may also use @code{info set}. Both commands produce the same display. @c FIXME: "info set" violates the rule that "info" is for state of @c FIXME...program. Ck w/ GNU: "info set" to be called something else, @c FIXME...or change desc of rule---eg "state of prog and debugging session"? @end table @c @end group Here are several miscellaneous @code{show} subcommands, all of which are exceptional in lacking corresponding @code{set} commands: @table @code @kindex show version @cindex @value{GDBN} version number @item show version Show what version of @value{GDBN} is running. You should include this information in @value{GDBN} bug-reports. If multiple versions of @value{GDBN} are in use at your site, you may need to determine which version of @value{GDBN} you are running; as @value{GDBN} evolves, new commands are introduced, and old ones may wither away. Also, many system vendors ship variant versions of @value{GDBN}, and there are variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well. The version number is the same as the one announced when you start @value{GDBN}. @kindex show copying @kindex info copying @cindex display @value{GDBN} copyright @item show copying @itemx info copying Display information about permission for copying @value{GDBN}. @kindex show warranty @kindex info warranty @item show warranty @itemx info warranty Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty, if your version of @value{GDBN} comes with one. @kindex show configuration @item show configuration Display detailed information about the way @value{GDBN} was configured when it was built. This displays the optional arguments passed to the @file{configure} script and also configuration parameters detected automatically by @command{configure}. When reporting a @value{GDBN} bug (@pxref{GDB Bugs}), it is important to include this information in your report. @end table @node Running @chapter Running Programs Under @value{GDBN} When you run a program under @value{GDBN}, you must first generate debugging information when you compile it. You may start @value{GDBN} with its arguments, if any, in an environment of your choice. If you are doing native debugging, you may redirect your program's input and output, debug an already running process, or kill a child process. @menu * Compilation:: Compiling for debugging * Starting:: Starting your program * Arguments:: Your program's arguments * Environment:: Your program's environment * Working Directory:: Your program's working directory * Input/Output:: Your program's input and output * Attach:: Debugging an already-running process * Kill Process:: Killing the child process * Inferiors Connections and Programs:: Debugging multiple inferiors connections and programs * Threads:: Debugging programs with multiple threads * Forks:: Debugging forks * Checkpoint/Restart:: Setting a @emph{bookmark} to return to later @end menu @node Compilation @section Compiling for Debugging In order to debug a program effectively, you need to generate debugging information when you compile it. This debugging information is stored in the object file; it describes the data type of each variable or function and the correspondence between source line numbers and addresses in the executable code. To request debugging information, specify the @samp{-g} option when you run the compiler. Programs that are to be shipped to your customers are compiled with optimizations, using the @samp{-O} compiler option. However, some compilers are unable to handle the @samp{-g} and @samp{-O} options together. Using those compilers, you cannot generate optimized executables containing debugging information. @value{NGCC}, the @sc{gnu} C/C@t{++} compiler, supports @samp{-g} with or without @samp{-O}, making it possible to debug optimized code. We recommend that you @emph{always} use @samp{-g} whenever you compile a program. You may think your program is correct, but there is no sense in pushing your luck. For more information, see @ref{Optimized Code}. Older versions of the @sc{gnu} C compiler permitted a variant option @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this format; if your @sc{gnu} C compiler has this option, do not use it. @value{GDBN} knows about preprocessor macros and can show you their expansion (@pxref{Macros}). Most compilers do not include information about preprocessor macros in the debugging information if you specify the @option{-g} flag alone. Version 3.1 and later of @value{NGCC}, the @sc{gnu} C compiler, provides macro information if you are using the DWARF debugging format, and specify the option @option{-g3}. @xref{Debugging Options,,Options for Debugging Your Program or GCC, gcc, Using the @sc{gnu} Compiler Collection (GCC)}, for more information on @value{NGCC} options affecting debug information. You will have the best debugging experience if you use the latest version of the DWARF debugging format that your compiler supports. DWARF is currently the most expressive and best supported debugging format in @value{GDBN}. @need 2000 @node Starting @section Starting your Program @cindex starting @cindex running @table @code @kindex run @kindex r @r{(@code{run})} @item run @itemx r Use the @code{run} command to start your program under @value{GDBN}. You must first specify the program name with an argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of @value{GDBN}}), or by using the @code{file} or @code{exec-file} command (@pxref{Files, ,Commands to Specify Files}). @end table If you are running your program in an execution environment that supports processes, @code{run} creates an inferior process and makes that process run your program. In some environments without processes, @code{run} jumps to the start of your program. Other targets, like @samp{remote}, are always running. If you get an error message like this one: @smallexample The "remote" target does not support "run". Try "help target" or "continue". @end smallexample @noindent then use @code{continue} to run your program. You may need @code{load} first (@pxref{load}). The execution of a program is affected by certain information it receives from its superior. @value{GDBN} provides ways to specify this information, which you must do @emph{before} starting your program. (You can change it after starting your program, but such changes only affect your program the next time you start it.) This information may be divided into four categories: @table @asis @item The @emph{arguments.} Specify the arguments to give your program as the arguments of the @code{run} command. If a shell is available on your target, the shell is used to pass the arguments, so that you may use normal conventions (such as wildcard expansion or variable substitution) in describing the arguments. In Unix systems, you can control which shell is used with the @code{SHELL} environment variable. If you do not define @code{SHELL}, @value{GDBN} uses the default shell (@file{/bin/sh}). You can disable use of any shell with the @code{set startup-with-shell} command (see below for details). @item The @emph{environment.} Your program normally inherits its environment from @value{GDBN}, but you can use the @value{GDBN} commands @code{set environment} and @code{unset environment} to change parts of the environment that affect your program. @xref{Environment, ,Your Program's Environment}. @item The @emph{working directory.} You can set your program's working directory with the command @kbd{set cwd}. If you do not set any working directory with this command, your program will inherit @value{GDBN}'s working directory if native debugging, or the remote server's working directory if remote debugging. @xref{Working Directory, ,Your Program's Working Directory}. @item The @emph{standard input and output.} Your program normally uses the same device for standard input and standard output as @value{GDBN} is using. You can redirect input and output in the @code{run} command line, or you can use the @code{tty} command to set a different device for your program. @xref{Input/Output, ,Your Program's Input and Output}. @cindex pipes @emph{Warning:} While input and output redirection work, you cannot use pipes to pass the output of the program you are debugging to another program; if you attempt this, @value{GDBN} is likely to wind up debugging the wrong program. @end table When you issue the @code{run} command, your program begins to execute immediately. @xref{Stopping, ,Stopping and Continuing}, for discussion of how to arrange for your program to stop. Once your program has stopped, you may call functions in your program, using the @code{print} or @code{call} commands. @xref{Data, ,Examining Data}. If the modification time of your symbol file has changed since the last time @value{GDBN} read its symbols, @value{GDBN} discards its symbol table, and reads it again. When it does this, @value{GDBN} tries to retain your current breakpoints. @table @code @kindex start @item start @cindex run to main procedure The name of the main procedure can vary from language to language. With C or C@t{++}, the main procedure name is always @code{main}, but other languages such as Ada do not require a specific name for their main procedure. The debugger provides a convenient way to start the execution of the program and to stop at the beginning of the main procedure, depending on the language used. The @samp{start} command does the equivalent of setting a temporary breakpoint at the beginning of the main procedure and then invoking the @samp{run} command. @cindex elaboration phase Some programs contain an @dfn{elaboration} phase where some startup code is executed before the main procedure is called. This depends on the languages used to write your program. In C@t{++}, for instance, constructors for static and global objects are executed before @code{main} is called. It is therefore possible that the debugger stops before reaching the main procedure. However, the temporary breakpoint will remain to halt execution. Specify the arguments to give to your program as arguments to the @samp{start} command. These arguments will be given verbatim to the underlying @samp{run} command. Note that the same arguments will be reused if no argument is provided during subsequent calls to @samp{start} or @samp{run}. It is sometimes necessary to debug the program during elaboration. In these cases, using the @code{start} command would stop the execution of your program too late, as the program would have already completed the elaboration phase. Under these circumstances, either insert breakpoints in your elaboration code before running your program or use the @code{starti} command. @kindex starti @item starti @cindex run to first instruction The @samp{starti} command does the equivalent of setting a temporary breakpoint at the first instruction of a program's execution and then invoking the @samp{run} command. For programs containing an elaboration phase, the @code{starti} command will stop execution at the start of the elaboration phase. @anchor{set exec-wrapper} @kindex set exec-wrapper @item set exec-wrapper @var{wrapper} @itemx show exec-wrapper @itemx unset exec-wrapper When @samp{exec-wrapper} is set, the specified wrapper is used to launch programs for debugging. @value{GDBN} starts your program with a shell command of the form @kbd{exec @var{wrapper} @var{program}}. Quoting is added to @var{program} and its arguments, but not to @var{wrapper}, so you should add quotes if appropriate for your shell. The wrapper runs until it executes your program, and then @value{GDBN} takes control. You can use any program that eventually calls @code{execve} with its arguments as a wrapper. Several standard Unix utilities do this, e.g.@: @code{env} and @code{nohup}. Any Unix shell script ending with @code{exec "$@@"} will also work. For example, you can use @code{env} to pass an environment variable to the debugged program, without setting the variable in your shell's environment: @smallexample (@value{GDBP}) set exec-wrapper env 'LD_PRELOAD=libtest.so' (@value{GDBP}) run @end smallexample This command is available when debugging locally on most targets, excluding @sc{djgpp}, Cygwin, MS Windows, and QNX Neutrino. @kindex set startup-with-shell @anchor{set startup-with-shell} @item set startup-with-shell @itemx set startup-with-shell on @itemx set startup-with-shell off @itemx show startup-with-shell On Unix systems, by default, if a shell is available on your target, @value{GDBN}) uses it to start your program. Arguments of the @code{run} command are passed to the shell, which does variable substitution, expands wildcard characters and performs redirection of I/O. In some circumstances, it may be useful to disable such use of a shell, for example, when debugging the shell itself or diagnosing startup failures such as: @smallexample (@value{GDBP}) run Starting program: ./a.out During startup program terminated with signal SIGSEGV, Segmentation fault. @end smallexample @noindent which indicates the shell or the wrapper specified with @samp{exec-wrapper} crashed, not your program. Most often, this is caused by something odd in your shell's non-interactive mode initialization file---such as @file{.cshrc} for C-shell, $@file{.zshenv} for the Z shell, or the file specified in the @samp{BASH_ENV} environment variable for BASH. @anchor{set auto-connect-native-target} @kindex set auto-connect-native-target @item set auto-connect-native-target @itemx set auto-connect-native-target on @itemx set auto-connect-native-target off @itemx show auto-connect-native-target By default, if the current inferior is not connected to any target yet (e.g., with @code{target remote}), the @code{run} command starts your program as a native process under @value{GDBN}, on your local machine. If you're sure you don't want to debug programs on your local machine, you can tell @value{GDBN} to not connect to the native target automatically with the @code{set auto-connect-native-target off} command. If @code{on}, which is the default, and if the current inferior is not connected to a target already, the @code{run} command automaticaly connects to the native target, if one is available. If @code{off}, and if the current inferior is not connected to a target already, the @code{run} command fails with an error: @smallexample (@value{GDBP}) run Don't know how to run. Try "help target". @end smallexample If the current inferior is already connected to a target, @value{GDBN} always uses it with the @code{run} command. In any case, you can explicitly connect to the native target with the @code{target native} command. For example, @smallexample (@value{GDBP}) set auto-connect-native-target off (@value{GDBP}) run Don't know how to run. Try "help target". (@value{GDBP}) target native (@value{GDBP}) run Starting program: ./a.out [Inferior 1 (process 10421) exited normally] @end smallexample In case you connected explicitly to the @code{native} target, @value{GDBN} remains connected even if all inferiors exit, ready for the next @code{run} command. Use the @code{disconnect} command to disconnect. Examples of other commands that likewise respect the @code{auto-connect-native-target} setting: @code{attach}, @code{info proc}, @code{info os}. @kindex set disable-randomization @item set disable-randomization @itemx set disable-randomization on This option (enabled by default in @value{GDBN}) will turn off the native randomization of the virtual address space of the started program. This option is useful for multiple debugging sessions to make the execution better reproducible and memory addresses reusable across debugging sessions. This feature is implemented only on certain targets, including @sc{gnu}/Linux. On @sc{gnu}/Linux you can get the same behavior using @smallexample (@value{GDBP}) set exec-wrapper setarch `uname -m` -R @end smallexample @item set disable-randomization off Leave the behavior of the started executable unchanged. Some bugs rear their ugly heads only when the program is loaded at certain addresses. If your bug disappears when you run the program under @value{GDBN}, that might be because @value{GDBN} by default disables the address randomization on platforms, such as @sc{gnu}/Linux, which do that for stand-alone programs. Use @kbd{set disable-randomization off} to try to reproduce such elusive bugs. On targets where it is available, virtual address space randomization protects the programs against certain kinds of security attacks. In these cases the attacker needs to know the exact location of a concrete executable code. Randomizing its location makes it impossible to inject jumps misusing a code at its expected addresses. Prelinking shared libraries provides a startup performance advantage but it makes addresses in these libraries predictable for privileged processes by having just unprivileged access at the target system. Reading the shared library binary gives enough information for assembling the malicious code misusing it. Still even a prelinked shared library can get loaded at a new random address just requiring the regular relocation process during the startup. Shared libraries not already prelinked are always loaded at a randomly chosen address. Position independent executables (PIE) contain position independent code similar to the shared libraries and therefore such executables get loaded at a randomly chosen address upon startup. PIE executables always load even already prelinked shared libraries at a random address. You can build such executable using @command{gcc -fPIE -pie}. Heap (malloc storage), stack and custom mmap areas are always placed randomly (as long as the randomization is enabled). @item show disable-randomization Show the current setting of the explicit disable of the native randomization of the virtual address space of the started program. @end table @node Arguments @section Your Program's Arguments @cindex arguments (to your program) The arguments to your program can be specified by the arguments of the @code{run} command. They are passed to a shell, which expands wildcard characters and performs redirection of I/O, and thence to your program. Your @code{SHELL} environment variable (if it exists) specifies what shell @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses the default shell (@file{/bin/sh} on Unix). On non-Unix systems, the program is usually invoked directly by @value{GDBN}, which emulates I/O redirection via the appropriate system calls, and the wildcard characters are expanded by the startup code of the program, not by the shell. @code{run} with no arguments uses the same arguments used by the previous @code{run}, or those set by the @code{set args} command. @table @code @kindex set args @item set args Specify the arguments to be used the next time your program is run. If @code{set args} has no arguments, @code{run} executes your program with no arguments. Once you have run your program with arguments, using @code{set args} before the next @code{run} is the only way to run it again without arguments. @kindex show args @item show args Show the arguments to give your program when it is started. @end table @node Environment @section Your Program's Environment @cindex environment (of your program) The @dfn{environment} consists of a set of environment variables and their values. Environment variables conventionally record such things as your user name, your home directory, your terminal type, and your search path for programs to run. Usually you set up environment variables with the shell and they are inherited by all the other programs you run. When debugging, it can be useful to try running your program with a modified environment without having to start @value{GDBN} over again. @table @code @kindex path @item path @var{directory} Add @var{directory} to the front of the @code{PATH} environment variable (the search path for executables) that will be passed to your program. The value of @code{PATH} used by @value{GDBN} does not change. You may specify several directory names, separated by whitespace or by a system-dependent separator character (@samp{:} on Unix, @samp{;} on MS-DOS and MS-Windows). If @var{directory} is already in the path, it is moved to the front, so it is searched sooner. You can use the string @samp{$cwd} to refer to whatever is the current working directory at the time @value{GDBN} searches the path. If you use @samp{.} instead, it refers to the directory where you executed the @code{path} command. @value{GDBN} replaces @samp{.} in the @var{directory} argument (with the current path) before adding @var{directory} to the search path. @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to @c document that, since repeating it would be a no-op. @kindex show paths @item show paths Display the list of search paths for executables (the @code{PATH} environment variable). @kindex show environment @item show environment @r{[}@var{varname}@r{]} Print the value of environment variable @var{varname} to be given to your program when it starts. If you do not supply @var{varname}, print the names and values of all environment variables to be given to your program. You can abbreviate @code{environment} as @code{env}. @kindex set environment @anchor{set environment} @item set environment @var{varname} @r{[}=@var{value}@r{]} Set environment variable @var{varname} to @var{value}. The value changes for your program (and the shell @value{GDBN} uses to launch it), not for @value{GDBN} itself. The @var{value} may be any string; the values of environment variables are just strings, and any interpretation is supplied by your program itself. The @var{value} parameter is optional; if it is eliminated, the variable is set to a null value. @c "any string" here does not include leading, trailing @c blanks. Gnu asks: does anyone care? For example, this command: @smallexample set env USER = foo @end smallexample @noindent tells the debugged program, when subsequently run, that its user is named @samp{foo}. (The spaces around @samp{=} are used for clarity here; they are not actually required.) Note that on Unix systems, @value{GDBN} runs your program via a shell, which also inherits the environment set with @code{set environment}. If necessary, you can avoid that by using the @samp{env} program as a wrapper instead of using @code{set environment}. @xref{set exec-wrapper}, for an example doing just that. Environment variables that are set by the user are also transmitted to @command{gdbserver} to be used when starting the remote inferior. @pxref{QEnvironmentHexEncoded}. @kindex unset environment @anchor{unset environment} @item unset environment @var{varname} Remove variable @var{varname} from the environment to be passed to your program. This is different from @samp{set env @var{varname} =}; @code{unset environment} removes the variable from the environment, rather than assigning it an empty value. Environment variables that are unset by the user are also unset on @command{gdbserver} when starting the remote inferior. @pxref{QEnvironmentUnset}. @end table @emph{Warning:} On Unix systems, @value{GDBN} runs your program using the shell indicated by your @code{SHELL} environment variable if it exists (or @code{/bin/sh} if not). If your @code{SHELL} variable names a shell that runs an initialization file when started non-interactively---such as @file{.cshrc} for C-shell, $@file{.zshenv} for the Z shell, or the file specified in the @samp{BASH_ENV} environment variable for BASH---any variables you set in that file affect your program. You may wish to move setting of environment variables to files that are only run when you sign on, such as @file{.login} or @file{.profile}. @node Working Directory @section Your Program's Working Directory @cindex working directory (of your program) Each time you start your program with @code{run}, the inferior will be initialized with the current working directory specified by the @kbd{set cwd} command. If no directory has been specified by this command, then the inferior will inherit @value{GDBN}'s current working directory as its working directory if native debugging, or it will inherit the remote server's current working directory if remote debugging. @table @code @kindex set cwd @cindex change inferior's working directory @anchor{set cwd command} @item set cwd @r{[}@var{directory}@r{]} Set the inferior's working directory to @var{directory}, which will be @code{glob}-expanded in order to resolve tildes (@file{~}). If no argument has been specified, the command clears the setting and resets it to an empty state. This setting has no effect on @value{GDBN}'s working directory, and it only takes effect the next time you start the inferior. The @file{~} in @var{directory} is a short for the @dfn{home directory}, usually pointed to by the @env{HOME} environment variable. On MS-Windows, if @env{HOME} is not defined, @value{GDBN} uses the concatenation of @env{HOMEDRIVE} and @env{HOMEPATH} as fallback. You can also change @value{GDBN}'s current working directory by using the @code{cd} command. @xref{cd command}. @kindex show cwd @cindex show inferior's working directory @item show cwd Show the inferior's working directory. If no directory has been specified by @kbd{set cwd}, then the default inferior's working directory is the same as @value{GDBN}'s working directory. @kindex cd @cindex change @value{GDBN}'s working directory @anchor{cd command} @item cd @r{[}@var{directory}@r{]} Set the @value{GDBN} working directory to @var{directory}. If not given, @var{directory} uses @file{'~'}. The @value{GDBN} working directory serves as a default for the commands that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to Specify Files}. @xref{set cwd command}. @kindex pwd @item pwd Print the @value{GDBN} working directory. @end table It is generally impossible to find the current working directory of the process being debugged (since a program can change its directory during its run). If you work on a system where @value{GDBN} supports the @code{info proc} command (@pxref{Process Information}), you can use the @code{info proc} command to find out the current working directory of the debuggee. @node Input/Output @section Your Program's Input and Output @cindex redirection @cindex i/o @cindex terminal By default, the program you run under @value{GDBN} does input and output to the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal to its own terminal modes to interact with you, but it records the terminal modes your program was using and switches back to them when you continue running your program. @table @code @kindex info terminal @item info terminal Displays information recorded by @value{GDBN} about the terminal modes your program is using. @end table You can redirect your program's input and/or output using shell redirection with the @code{run} command. For example, @smallexample run > outfile @end smallexample @noindent starts your program, diverting its output to the file @file{outfile}. @kindex tty @cindex controlling terminal Another way to specify where your program should do input and output is with the @code{tty} command. This command accepts a file name as argument, and causes this file to be the default for future @code{run} commands. It also resets the controlling terminal for the child process, for future @code{run} commands. For example, @smallexample tty /dev/ttyb @end smallexample @noindent directs that processes started with subsequent @code{run} commands default to do input and output on the terminal @file{/dev/ttyb} and have that as their controlling terminal. An explicit redirection in @code{run} overrides the @code{tty} command's effect on the input/output device, but not its effect on the controlling terminal. When you use the @code{tty} command or redirect input in the @code{run} command, only the input @emph{for your program} is affected. The input for @value{GDBN} still comes from your terminal. @code{tty} is an alias for @code{set inferior-tty}. @cindex inferior tty @cindex set inferior controlling terminal You can use the @code{show inferior-tty} command to tell @value{GDBN} to display the name of the terminal that will be used for future runs of your program. @table @code @item set inferior-tty [ @var{tty} ] @kindex set inferior-tty Set the tty for the program being debugged to @var{tty}. Omitting @var{tty} restores the default behavior, which is to use the same terminal as @value{GDBN}. @item show inferior-tty @kindex show inferior-tty Show the current tty for the program being debugged. @end table @node Attach @section Debugging an Already-running Process @kindex attach @cindex attach @table @code @item attach @var{process-id} This command attaches to a running process---one that was started outside @value{GDBN}. (@code{info files} shows your active targets.) The command takes as argument a process ID. The usual way to find out the @var{process-id} of a Unix process is with the @code{ps} utility, or with the @samp{jobs -l} shell command. @code{attach} does not repeat if you press @key{RET} a second time after executing the command. @end table To use @code{attach}, your program must be running in an environment which supports processes; for example, @code{attach} does not work for programs on bare-board targets that lack an operating system. You must also have permission to send the process a signal. When you use @code{attach}, the debugger finds the program running in the process first by looking in the current working directory, then (if the program is not found) by using the source file search path (@pxref{Source Path, ,Specifying Source Directories}). You can also use the @code{file} command to load the program. @xref{Files, ,Commands to Specify Files}. @anchor{set exec-file-mismatch} If the debugger can determine the name of the executable file running in the process it is attaching to, and this file name does not match the name of the current exec-file loaded by @value{GDBN}, the option @code{exec-file-mismatch} specifies how to handle the mismatch. @table @code @kindex exec-file-mismatch @cindex set exec-file-mismatch @item set exec-file-mismatch @samp{ask|warn|off} Whether to detect mismatch between the name of the current executable file loaded by @value{GDBN} and the name of the executable file used to start the process. If @samp{ask}, the default, display a warning and ask the user whether to load the process executable file; if @samp{warn}, just display a warning; if @samp{off}, don't attempt to detect a mismatch. @cindex show exec-file-mismatch @item show exec-file-mismatch Show the current value of @code{exec-file-mismatch}. @end table The first thing @value{GDBN} does after arranging to debug the specified process is to stop it. You can examine and modify an attached process with all the @value{GDBN} commands that are ordinarily available when you start processes with @code{run}. You can insert breakpoints; you can step and continue; you can modify storage. If you would rather the process continue running, you may use the @code{continue} command after attaching @value{GDBN} to the process. @table @code @kindex detach @item detach When you have finished debugging the attached process, you can use the @code{detach} command to release it from @value{GDBN} control. Detaching the process continues its execution. After the @code{detach} command, that process and @value{GDBN} become completely independent once more, and you are ready to @code{attach} another process or start one with @code{run}. @code{detach} does not repeat if you press @key{RET} again after executing the command. @end table If you exit @value{GDBN} while you have an attached process, you detach that process. If you use the @code{run} command, you kill that process. By default, @value{GDBN} asks for confirmation if you try to do either of these things; you can control whether or not you need to confirm by using the @code{set confirm} command (@pxref{Messages/Warnings, ,Optional Warnings and Messages}). @node Kill Process @section Killing the Child Process @table @code @kindex kill @item kill Kill the child process in which your program is running under @value{GDBN}. @end table This command is useful if you wish to debug a core dump instead of a running process. @value{GDBN} ignores any core dump file while your program is running. On some operating systems, a program cannot be executed outside @value{GDBN} while you have breakpoints set on it inside @value{GDBN}. You can use the @code{kill} command in this situation to permit running your program outside the debugger. The @code{kill} command is also useful if you wish to recompile and relink your program, since on many systems it is impossible to modify an executable file while it is running in a process. In this case, when you next type @code{run}, @value{GDBN} notices that the file has changed, and reads the symbol table again (while trying to preserve your current breakpoint settings). @node Inferiors Connections and Programs @section Debugging Multiple Inferiors Connections and Programs @value{GDBN} lets you run and debug multiple programs in a single session. In addition, @value{GDBN} on some systems may let you run several programs simultaneously (otherwise you have to exit from one before starting another). On some systems @value{GDBN} may even let you debug several programs simultaneously on different remote systems. In the most general case, you can have multiple threads of execution in each of multiple processes, launched from multiple executables, running on different machines. @cindex inferior @value{GDBN} represents the state of each program execution with an object called an @dfn{inferior}. An inferior typically corresponds to a process, but is more general and applies also to targets that do not have processes. Inferiors may be created before a process runs, and may be retained after a process exits. Inferiors have unique identifiers that are different from process ids. Usually each inferior will also have its own distinct address space, although some embedded targets may have several inferiors running in different parts of a single address space. Each inferior may in turn have multiple threads running in it. To find out what inferiors exist at any moment, use @w{@code{info inferiors}}: @table @code @kindex info inferiors [ @var{id}@dots{} ] @item info inferiors Print a list of all inferiors currently being managed by @value{GDBN}. By default all inferiors are printed, but the argument @var{id}@dots{} -- a space separated list of inferior numbers -- can be used to limit the display to just the requested inferiors. @value{GDBN} displays for each inferior (in this order): @enumerate @item the inferior number assigned by @value{GDBN} @item the target system's inferior identifier @item the target connection the inferior is bound to, including the unique connection number assigned by @value{GDBN}, and the protocol used by the connection. @item the name of the executable the inferior is running. @end enumerate @noindent An asterisk @samp{*} preceding the @value{GDBN} inferior number indicates the current inferior. For example, @end table @c end table here to get a little more width for example @smallexample (@value{GDBP}) info inferiors Num Description Connection Executable * 1 process 3401 1 (native) goodbye 2 process 2307 2 (extended-remote host:10000) hello @end smallexample To find out what open target connections exist at any moment, use @w{@code{info connections}}: @table @code @kindex info connections [ @var{id}@dots{} ] @item info connections Print a list of all open target connections currently being managed by @value{GDBN}. By default all connections are printed, but the argument @var{id}@dots{} -- a space separated list of connections numbers -- can be used to limit the display to just the requested connections. @value{GDBN} displays for each connection (in this order): @enumerate @item the connection number assigned by @value{GDBN}. @item the protocol used by the connection. @item a textual description of the protocol used by the connection. @end enumerate @noindent An asterisk @samp{*} preceding the connection number indicates the connection of the current inferior. For example, @end table @c end table here to get a little more width for example @smallexample (@value{GDBP}) info connections Num What Description * 1 extended-remote host:10000 Extended remote serial target in gdb-specific protocol 2 native Native process 3 core Local core dump file @end smallexample To switch focus between inferiors, use the @code{inferior} command: @table @code @kindex inferior @var{infno} @item inferior @var{infno} Make inferior number @var{infno} the current inferior. The argument @var{infno} is the inferior number assigned by @value{GDBN}, as shown in the first field of the @samp{info inferiors} display. @end table @vindex $_inferior@r{, convenience variable} The debugger convenience variable @samp{$_inferior} contains the number of the current inferior. You may find this useful in writing breakpoint conditional expressions, command scripts, and so forth. @xref{Convenience Vars,, Convenience Variables}, for general information on convenience variables. You can get multiple executables into a debugging session via the @code{add-inferior} and @w{@code{clone-inferior}} commands. On some systems @value{GDBN} can add inferiors to the debug session automatically by following calls to @code{fork} and @code{exec}. To remove inferiors from the debugging session use the @w{@code{remove-inferiors}} command. @table @code @kindex add-inferior @item add-inferior [ -copies @var{n} ] [ -exec @var{executable} ] [-no-connection ] Adds @var{n} inferiors to be run using @var{executable} as the executable; @var{n} defaults to 1. If no executable is specified, the inferiors begins empty, with no program. You can still assign or change the program assigned to the inferior at any time by using the @code{file} command with the executable name as its argument. By default, the new inferior begins connected to the same target connection as the current inferior. For example, if the current inferior was connected to @code{gdbserver} with @code{target remote}, then the new inferior will be connected to the same @code{gdbserver} instance. The @samp{-no-connection} option starts the new inferior with no connection yet. You can then for example use the @code{target remote} command to connect to some other @code{gdbserver} instance, use @code{run} to spawn a local program, etc. @kindex clone-inferior @item clone-inferior [ -copies @var{n} ] [ @var{infno} ] Adds @var{n} inferiors ready to execute the same program as inferior @var{infno}; @var{n} defaults to 1, and @var{infno} defaults to the number of the current inferior. This is a convenient command when you want to run another instance of the inferior you are debugging. @smallexample (@value{GDBP}) info inferiors Num Description Connection Executable * 1 process 29964 1 (native) helloworld (@value{GDBP}) clone-inferior Added inferior 2. 1 inferiors added. (@value{GDBP}) info inferiors Num Description Connection Executable * 1 process 29964 1 (native) helloworld 2 <null> 1 (native) helloworld @end smallexample You can now simply switch focus to inferior 2 and run it. @kindex remove-inferiors @item remove-inferiors @var{infno}@dots{} Removes the inferior or inferiors @var{infno}@dots{}. It is not possible to remove an inferior that is running with this command. For those, use the @code{kill} or @code{detach} command first. @end table To quit debugging one of the running inferiors that is not the current inferior, you can either detach from it by using the @w{@code{detach inferior}} command (allowing it to run independently), or kill it using the @w{@code{kill inferiors}} command: @table @code @kindex detach inferiors @var{infno}@dots{} @item detach inferior @var{infno}@dots{} Detach from the inferior or inferiors identified by @value{GDBN} inferior number(s) @var{infno}@dots{}. Note that the inferior's entry still stays on the list of inferiors shown by @code{info inferiors}, but its Description will show @samp{<null>}. @kindex kill inferiors @var{infno}@dots{} @item kill inferiors @var{infno}@dots{} Kill the inferior or inferiors identified by @value{GDBN} inferior number(s) @var{infno}@dots{}. Note that the inferior's entry still stays on the list of inferiors shown by @code{info inferiors}, but its Description will show @samp{<null>}. @end table After the successful completion of a command such as @code{detach}, @code{detach inferiors}, @code{kill} or @code{kill inferiors}, or after a normal process exit, the inferior is still valid and listed with @code{info inferiors}, ready to be restarted. To be notified when inferiors are started or exit under @value{GDBN}'s control use @w{@code{set print inferior-events}}: @table @code @kindex set print inferior-events @cindex print messages on inferior start and exit @item set print inferior-events @itemx set print inferior-events on @itemx set print inferior-events off The @code{set print inferior-events} command allows you to enable or disable printing of messages when @value{GDBN} notices that new inferiors have started or that inferiors have exited or have been detached. By default, these messages will not be printed. @kindex show print inferior-events @item show print inferior-events Show whether messages will be printed when @value{GDBN} detects that inferiors have started, exited or have been detached. @end table Many commands will work the same with multiple programs as with a single program: e.g., @code{print myglobal} will simply display the value of @code{myglobal} in the current inferior. Occasionally, when debugging @value{GDBN} itself, it may be useful to get more info about the relationship of inferiors, programs, address spaces in a debug session. You can do that with the @w{@code{maint info program-spaces}} command. @table @code @kindex maint info program-spaces @item maint info program-spaces Print a list of all program spaces currently being managed by @value{GDBN}. @value{GDBN} displays for each program space (in this order): @enumerate @item the program space number assigned by @value{GDBN} @item the name of the executable loaded into the program space, with e.g., the @code{file} command. @end enumerate @noindent An asterisk @samp{*} preceding the @value{GDBN} program space number indicates the current program space. In addition, below each program space line, @value{GDBN} prints extra information that isn't suitable to display in tabular form. For example, the list of inferiors bound to the program space. @smallexample (@value{GDBP}) maint info program-spaces Id Executable * 1 hello 2 goodbye Bound inferiors: ID 1 (process 21561) @end smallexample Here we can see that no inferior is running the program @code{hello}, while @code{process 21561} is running the program @code{goodbye}. On some targets, it is possible that multiple inferiors are bound to the same program space. The most common example is that of debugging both the parent and child processes of a @code{vfork} call. For example, @smallexample (@value{GDBP}) maint info program-spaces Id Executable * 1 vfork-test Bound inferiors: ID 2 (process 18050), ID 1 (process 18045) @end smallexample Here, both inferior 2 and inferior 1 are running in the same program space as a result of inferior 1 having executed a @code{vfork} call. @end table @node Threads @section Debugging Programs with Multiple Threads @cindex threads of execution @cindex multiple threads @cindex switching threads In some operating systems, such as GNU/Linux and Solaris, a single program may have more than one @dfn{thread} of execution. The precise semantics of threads differ from one operating system to another, but in general the threads of a single program are akin to multiple processes---except that they share one address space (that is, they can all examine and modify the same variables). On the other hand, each thread has its own registers and execution stack, and perhaps private memory. @value{GDBN} provides these facilities for debugging multi-thread programs: @itemize @bullet @item automatic notification of new threads @item @samp{thread @var{thread-id}}, a command to switch among threads @item @samp{info threads}, a command to inquire about existing threads @item @samp{thread apply [@var{thread-id-list} | all] @var{args}}, a command to apply a command to a list of threads @item thread-specific breakpoints @item @samp{set print thread-events}, which controls printing of messages on thread start and exit. @item @samp{set libthread-db-search-path @var{path}}, which lets the user specify which @code{libthread_db} to use if the default choice isn't compatible with the program. @end itemize @cindex focus of debugging @cindex current thread The @value{GDBN} thread debugging facility allows you to observe all threads while your program runs---but whenever @value{GDBN} takes control, one thread in particular is always the focus of debugging. This thread is called the @dfn{current thread}. Debugging commands show program information from the perspective of the current thread. @cindex @code{New} @var{systag} message @cindex thread identifier (system) @c FIXME-implementors!! It would be more helpful if the [New...] message @c included GDB's numeric thread handle, so you could just go to that @c thread without first checking `info threads'. Whenever @value{GDBN} detects a new thread in your program, it displays the target system's identification for the thread with a message in the form @samp{[New @var{systag}]}, where @var{systag} is a thread identifier whose form varies depending on the particular system. For example, on @sc{gnu}/Linux, you might see @smallexample [New Thread 0x41e02940 (LWP 25582)] @end smallexample @noindent when @value{GDBN} notices a new thread. In contrast, on other systems, the @var{systag} is simply something like @samp{process 368}, with no further qualifier. @c FIXME!! (1) Does the [New...] message appear even for the very first @c thread of a program, or does it only appear for the @c second---i.e.@: when it becomes obvious we have a multithread @c program? @c (2) *Is* there necessarily a first thread always? Or do some @c multithread systems permit starting a program with multiple @c threads ab initio? @anchor{thread numbers} @cindex thread number, per inferior @cindex thread identifier (GDB) For debugging purposes, @value{GDBN} associates its own thread number ---always a single integer---with each thread of an inferior. This number is unique between all threads of an inferior, but not unique between threads of different inferiors. @cindex qualified thread ID You can refer to a given thread in an inferior using the qualified @var{inferior-num}.@var{thread-num} syntax, also known as @dfn{qualified thread ID}, with @var{inferior-num} being the inferior number and @var{thread-num} being the thread number of the given inferior. For example, thread @code{2.3} refers to thread number 3 of inferior 2. If you omit @var{inferior-num} (e.g., @code{thread 3}), then @value{GDBN} infers you're referring to a thread of the current inferior. Until you create a second inferior, @value{GDBN} does not show the @var{inferior-num} part of thread IDs, even though you can always use the full @var{inferior-num}.@var{thread-num} form to refer to threads of inferior 1, the initial inferior. @anchor{thread ID lists} @cindex thread ID lists Some commands accept a space-separated @dfn{thread ID list} as argument. A list element can be: @enumerate @item A thread ID as shown in the first field of the @samp{info threads} display, with or without an inferior qualifier. E.g., @samp{2.1} or @samp{1}. @item A range of thread numbers, again with or without an inferior qualifier, as in @var{inf}.@var{thr1}-@var{thr2} or @var{thr1}-@var{thr2}. E.g., @samp{1.2-4} or @samp{2-4}. @item All threads of an inferior, specified with a star wildcard, with or without an inferior qualifier, as in @var{inf}.@code{*} (e.g., @samp{1.*}) or @code{*}. The former refers to all threads of the given inferior, and the latter form without an inferior qualifier refers to all threads of the current inferior. @end enumerate For example, if the current inferior is 1, and inferior 7 has one thread with ID 7.1, the thread list @samp{1 2-3 4.5 6.7-9 7.*} includes threads 1 to 3 of inferior 1, thread 5 of inferior 4, threads 7 to 9 of inferior 6 and all threads of inferior 7. That is, in expanded qualified form, the same as @samp{1.1 1.2 1.3 4.5 6.7 6.8 6.9 7.1}. @anchor{global thread numbers} @cindex global thread number @cindex global thread identifier (GDB) In addition to a @emph{per-inferior} number, each thread is also assigned a unique @emph{global} number, also known as @dfn{global thread ID}, a single integer. Unlike the thread number component of the thread ID, no two threads have the same global ID, even when you're debugging multiple inferiors. From @value{GDBN}'s perspective, a process always has at least one thread. In other words, @value{GDBN} assigns a thread number to the program's ``main thread'' even if the program is not multi-threaded. @vindex $_thread@r{, convenience variable} @vindex $_gthread@r{, convenience variable} The debugger convenience variables @samp{$_thread} and @samp{$_gthread} contain, respectively, the per-inferior thread number and the global thread number of the current thread. You may find this useful in writing breakpoint conditional expressions, command scripts, and so forth. @xref{Convenience Vars,, Convenience Variables}, for general information on convenience variables. If @value{GDBN} detects the program is multi-threaded, it augments the usual message about stopping at a breakpoint with the ID and name of the thread that hit the breakpoint. @smallexample Thread 2 "client" hit Breakpoint 1, send_message () at client.c:68 @end smallexample Likewise when the program receives a signal: @smallexample Thread 1 "main" received signal SIGINT, Interrupt. @end smallexample @table @code @kindex info threads @item info threads @r{[}@var{thread-id-list}@r{]} Display information about one or more threads. With no arguments displays information about all threads. You can specify the list of threads that you want to display using the thread ID list syntax (@pxref{thread ID lists}). @value{GDBN} displays for each thread (in this order): @enumerate @item the per-inferior thread number assigned by @value{GDBN} @item the global thread number assigned by @value{GDBN}, if the @samp{-gid} option was specified @item the target system's thread identifier (@var{systag}) @item the thread's name, if one is known. A thread can either be named by the user (see @code{thread name}, below), or, in some cases, by the program itself. @item the current stack frame summary for that thread @end enumerate @noindent An asterisk @samp{*} to the left of the @value{GDBN} thread number indicates the current thread. For example, @end table @c end table here to get a little more width for example @smallexample (@value{GDBP}) info threads Id Target Id Frame * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8) 2 process 35 thread 23 0x34e5 in sigpause () 3 process 35 thread 27 0x34e5 in sigpause () at threadtest.c:68 @end smallexample If you're debugging multiple inferiors, @value{GDBN} displays thread IDs using the qualified @var{inferior-num}.@var{thread-num} format. Otherwise, only @var{thread-num} is shown. If you specify the @samp{-gid} option, @value{GDBN} displays a column indicating each thread's global thread ID: @smallexample (@value{GDBP}) info threads Id GId Target Id Frame 1.1 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8) 1.2 3 process 35 thread 23 0x34e5 in sigpause () 1.3 4 process 35 thread 27 0x34e5 in sigpause () * 2.1 2 process 65 thread 1 main (argc=1, argv=0x7ffffff8) @end smallexample On Solaris, you can display more information about user threads with a Solaris-specific command: @table @code @item maint info sol-threads @kindex maint info sol-threads @cindex thread info (Solaris) Display info on Solaris user threads. @end table @table @code @kindex thread @var{thread-id} @item thread @var{thread-id} Make thread ID @var{thread-id} the current thread. The command argument @var{thread-id} is the @value{GDBN} thread ID, as shown in the first field of the @samp{info threads} display, with or without an inferior qualifier (e.g., @samp{2.1} or @samp{1}). @value{GDBN} responds by displaying the system identifier of the thread you selected, and its current stack frame summary: @smallexample (@value{GDBP}) thread 2 [Switching to thread 2 (Thread 0xb7fdab70 (LWP 12747))] #0 some_function (ignore=0x0) at example.c:8 8 printf ("hello\n"); @end smallexample @noindent As with the @samp{[New @dots{}]} message, the form of the text after @samp{Switching to} depends on your system's conventions for identifying threads. @anchor{thread apply all} @kindex thread apply @cindex apply command to several threads @item thread apply [@var{thread-id-list} | all [-ascending]] [@var{flag}]@dots{} @var{command} The @code{thread apply} command allows you to apply the named @var{command} to one or more threads. Specify the threads that you want affected using the thread ID list syntax (@pxref{thread ID lists}), or specify @code{all} to apply to all threads. To apply a command to all threads in descending order, type @kbd{thread apply all @var{command}}. To apply a command to all threads in ascending order, type @kbd{thread apply all -ascending @var{command}}. The @var{flag} arguments control what output to produce and how to handle errors raised when applying @var{command} to a thread. @var{flag} must start with a @code{-} directly followed by one letter in @code{qcs}. If several flags are provided, they must be given individually, such as @code{-c -q}. By default, @value{GDBN} displays some thread information before the output produced by @var{command}, and an error raised during the execution of a @var{command} will abort @code{thread apply}. The following flags can be used to fine-tune this behavior: @table @code @item -c The flag @code{-c}, which stands for @samp{continue}, causes any errors in @var{command} to be displayed, and the execution of @code{thread apply} then continues. @item -s The flag @code{-s}, which stands for @samp{silent}, causes any errors or empty output produced by a @var{command} to be silently ignored. That is, the execution continues, but the thread information and errors are not printed. @item -q The flag @code{-q} (@samp{quiet}) disables printing the thread information. @end table Flags @code{-c} and @code{-s} cannot be used together. @kindex taas @cindex apply command to all threads (ignoring errors and empty output) @item taas [@var{option}]@dots{} @var{command} Shortcut for @code{thread apply all -s [@var{option}]@dots{} @var{command}}. Applies @var{command} on all threads, ignoring errors and empty output. The @code{taas} command accepts the same options as the @code{thread apply all} command. @xref{thread apply all}. @kindex tfaas @cindex apply a command to all frames of all threads (ignoring errors and empty output) @item tfaas [@var{option}]@dots{} @var{command} Shortcut for @code{thread apply all -s -- frame apply all -s [@var{option}]@dots{} @var{command}}. Applies @var{command} on all frames of all threads, ignoring errors and empty output. Note that the flag @code{-s} is specified twice: The first @code{-s} ensures that @code{thread apply} only shows the thread information of the threads for which @code{frame apply} produces some output. The second @code{-s} is needed to ensure that @code{frame apply} shows the frame information of a frame only if the @var{command} successfully produced some output. It can for example be used to print a local variable or a function argument without knowing the thread or frame where this variable or argument is, using: @smallexample (@value{GDBP}) tfaas p some_local_var_i_do_not_remember_where_it_is @end smallexample The @code{tfaas} command accepts the same options as the @code{frame apply} command. @xref{frame apply}. @kindex thread name @cindex name a thread @item thread name [@var{name}] This command assigns a name to the current thread. If no argument is given, any existing user-specified name is removed. The thread name appears in the @samp{info threads} display. On some systems, such as @sc{gnu}/Linux, @value{GDBN} is able to determine the name of the thread as given by the OS. On these systems, a name specified with @samp{thread name} will override the system-give name, and removing the user-specified name will cause @value{GDBN} to once again display the system-specified name. @kindex thread find @cindex search for a thread @item thread find [@var{regexp}] Search for and display thread ids whose name or @var{systag} matches the supplied regular expression. As well as being the complement to the @samp{thread name} command, this command also allows you to identify a thread by its target @var{systag}. For instance, on @sc{gnu}/Linux, the target @var{systag} is the LWP id. @smallexample (@value{GDBN}) thread find 26688 Thread 4 has target id 'Thread 0x41e02940 (LWP 26688)' (@value{GDBN}) info thread 4 Id Target Id Frame 4 Thread 0x41e02940 (LWP 26688) 0x00000031ca6cd372 in select () @end smallexample @kindex set print thread-events @cindex print messages on thread start and exit @item set print thread-events @itemx set print thread-events on @itemx set print thread-events off The @code{set print thread-events} command allows you to enable or disable printing of messages when @value{GDBN} notices that new threads have started or that threads have exited. By default, these messages will be printed if detection of these events is supported by the target. Note that these messages cannot be disabled on all targets. @kindex show print thread-events @item show print thread-events Show whether messages will be printed when @value{GDBN} detects that threads have started and exited. @end table @xref{Thread Stops,,Stopping and Starting Multi-thread Programs}, for more information about how @value{GDBN} behaves when you stop and start programs with multiple threads. @xref{Set Watchpoints,,Setting Watchpoints}, for information about watchpoints in programs with multiple threads. @anchor{set libthread-db-search-path} @table @code @kindex set libthread-db-search-path @cindex search path for @code{libthread_db} @item set libthread-db-search-path @r{[}@var{path}@r{]} If this variable is set, @var{path} is a colon-separated list of directories @value{GDBN} will use to search for @code{libthread_db}. If you omit @var{path}, @samp{libthread-db-search-path} will be reset to its default value (@code{$sdir:$pdir} on @sc{gnu}/Linux and Solaris systems). Internally, the default value comes from the @code{LIBTHREAD_DB_SEARCH_PATH} macro. On @sc{gnu}/Linux and Solaris systems, @value{GDBN} uses a ``helper'' @code{libthread_db} library to obtain information about threads in the inferior process. @value{GDBN} will use @samp{libthread-db-search-path} to find @code{libthread_db}. @value{GDBN} also consults first if inferior specific thread debugging library loading is enabled by @samp{set auto-load libthread-db} (@pxref{libthread_db.so.1 file}). A special entry @samp{$sdir} for @samp{libthread-db-search-path} refers to the default system directories that are normally searched for loading shared libraries. The @samp{$sdir} entry is the only kind not needing to be enabled by @samp{set auto-load libthread-db} (@pxref{libthread_db.so.1 file}). A special entry @samp{$pdir} for @samp{libthread-db-search-path} refers to the directory from which @code{libpthread} was loaded in the inferior process. For any @code{libthread_db} library @value{GDBN} finds in above directories, @value{GDBN} attempts to initialize it with the current inferior process. If this initialization fails (which could happen because of a version mismatch between @code{libthread_db} and @code{libpthread}), @value{GDBN} will unload @code{libthread_db}, and continue with the next directory. If none of @code{libthread_db} libraries initialize successfully, @value{GDBN} will issue a warning and thread debugging will be disabled. Setting @code{libthread-db-search-path} is currently implemented only on some platforms. @kindex show libthread-db-search-path @item show libthread-db-search-path Display current libthread_db search path. @kindex set debug libthread-db @kindex show debug libthread-db @cindex debugging @code{libthread_db} @item set debug libthread-db @itemx show debug libthread-db Turns on or off display of @code{libthread_db}-related events. Use @code{1} to enable, @code{0} to disable. @end table @node Forks @section Debugging Forks @cindex fork, debugging programs which call @cindex multiple processes @cindex processes, multiple On most systems, @value{GDBN} has no special support for debugging programs which create additional processes using the @code{fork} function. When a program forks, @value{GDBN} will continue to debug the parent process and the child process will run unimpeded. If you have set a breakpoint in any code which the child then executes, the child will get a @code{SIGTRAP} signal which (unless it catches the signal) will cause it to terminate. However, if you want to debug the child process there is a workaround which isn't too painful. Put a call to @code{sleep} in the code which the child process executes after the fork. It may be useful to sleep only if a certain environment variable is set, or a certain file exists, so that the delay need not occur when you don't want to run @value{GDBN} on the child. While the child is sleeping, use the @code{ps} program to get its process ID. Then tell @value{GDBN} (a new invocation of @value{GDBN} if you are also debugging the parent process) to attach to the child process (@pxref{Attach}). From that point on you can debug the child process just like any other process which you attached to. On some systems, @value{GDBN} provides support for debugging programs that create additional processes using the @code{fork} or @code{vfork} functions. On @sc{gnu}/Linux platforms, this feature is supported with kernel version 2.5.46 and later. The fork debugging commands are supported in native mode and when connected to @code{gdbserver} in either @code{target remote} mode or @code{target extended-remote} mode. By default, when a program forks, @value{GDBN} will continue to debug the parent process and the child process will run unimpeded. If you want to follow the child process instead of the parent process, use the command @w{@code{set follow-fork-mode}}. @table @code @kindex set follow-fork-mode @item set follow-fork-mode @var{mode} Set the debugger response to a program call of @code{fork} or @code{vfork}. A call to @code{fork} or @code{vfork} creates a new process. The @var{mode} argument can be: @table @code @item parent The original process is debugged after a fork. The child process runs unimpeded. This is the default. @item child The new process is debugged after a fork. The parent process runs unimpeded. @end table @kindex show follow-fork-mode @item show follow-fork-mode Display the current debugger response to a @code{fork} or @code{vfork} call. @end table @cindex debugging multiple processes On Linux, if you want to debug both the parent and child processes, use the command @w{@code{set detach-on-fork}}. @table @code @kindex set detach-on-fork @item set detach-on-fork @var{mode} Tells gdb whether to detach one of the processes after a fork, or retain debugger control over them both. @table @code @item on The child process (or parent process, depending on the value of @code{follow-fork-mode}) will be detached and allowed to run independently. This is the default. @item off Both processes will be held under the control of @value{GDBN}. One process (child or parent, depending on the value of @code{follow-fork-mode}) is debugged as usual, while the other is held suspended. @end table @kindex show detach-on-fork @item show detach-on-fork Show whether detach-on-fork mode is on/off. @end table If you choose to set @samp{detach-on-fork} mode off, then @value{GDBN} will retain control of all forked processes (including nested forks). You can list the forked processes under the control of @value{GDBN} by using the @w{@code{info inferiors}} command, and switch from one fork to another by using the @code{inferior} command (@pxref{Inferiors Connections and Programs, ,Debugging Multiple Inferiors Connections and Programs}). To quit debugging one of the forked processes, you can either detach from it by using the @w{@code{detach inferiors}} command (allowing it to run independently), or kill it using the @w{@code{kill inferiors}} command. @xref{Inferiors Connections and Programs, ,Debugging Multiple Inferiors Connections and Programs}. If you ask to debug a child process and a @code{vfork} is followed by an @code{exec}, @value{GDBN} executes the new target up to the first breakpoint in the new target. If you have a breakpoint set on @code{main} in your original program, the breakpoint will also be set on the child process's @code{main}. On some systems, when a child process is spawned by @code{vfork}, you cannot debug the child or parent until an @code{exec} call completes. If you issue a @code{run} command to @value{GDBN} after an @code{exec} call executes, the new target restarts. To restart the parent process, use the @code{file} command with the parent executable name as its argument. By default, after an @code{exec} call executes, @value{GDBN} discards the symbols of the previous executable image. You can change this behaviour with the @w{@code{set follow-exec-mode}} command. @table @code @kindex set follow-exec-mode @item set follow-exec-mode @var{mode} Set debugger response to a program call of @code{exec}. An @code{exec} call replaces the program image of a process. @code{follow-exec-mode} can be: @table @code @item new @value{GDBN} creates a new inferior and rebinds the process to this new inferior. The program the process was running before the @code{exec} call can be restarted afterwards by restarting the original inferior. For example: @smallexample (@value{GDBP}) info inferiors (gdb) info inferior Id Description Executable * 1 <null> prog1 (@value{GDBP}) run process 12020 is executing new program: prog2 Program exited normally. (@value{GDBP}) info inferiors Id Description Executable 1 <null> prog1 * 2 <null> prog2 @end smallexample @item same @value{GDBN} keeps the process bound to the same inferior. The new executable image replaces the previous executable loaded in the inferior. Restarting the inferior after the @code{exec} call, with e.g., the @code{run} command, restarts the executable the process was running after the @code{exec} call. This is the default mode. For example: @smallexample (@value{GDBP}) info inferiors Id Description Executable * 1 <null> prog1 (@value{GDBP}) run process 12020 is executing new program: prog2 Program exited normally. (@value{GDBP}) info inferiors Id Description Executable * 1 <null> prog2 @end smallexample @end table @end table @code{follow-exec-mode} is supported in native mode and @code{target extended-remote} mode. You can use the @code{catch} command to make @value{GDBN} stop whenever a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set Catchpoints, ,Setting Catchpoints}. @node Checkpoint/Restart @section Setting a @emph{Bookmark} to Return to Later @cindex checkpoint @cindex restart @cindex bookmark @cindex snapshot of a process @cindex rewind program state On certain operating systems@footnote{Currently, only @sc{gnu}/Linux.}, @value{GDBN} is able to save a @dfn{snapshot} of a program's state, called a @dfn{checkpoint}, and come back to it later. Returning to a checkpoint effectively undoes everything that has happened in the program since the @code{checkpoint} was saved. This includes changes in memory, registers, and even (within some limits) system state. Effectively, it is like going back in time to the moment when the checkpoint was saved. Thus, if you're stepping thru a program and you think you're getting close to the point where things go wrong, you can save a checkpoint. Then, if you accidentally go too far and miss the critical statement, instead of having to restart your program from the beginning, you can just go back to the checkpoint and start again from there. This can be especially useful if it takes a lot of time or steps to reach the point where you think the bug occurs. To use the @code{checkpoint}/@code{restart} method of debugging: @table @code @kindex checkpoint @item checkpoint Save a snapshot of the debugged program's current execution state. The @code{checkpoint} command takes no arguments, but each checkpoint is assigned a small integer id, similar to a breakpoint id. @kindex info checkpoints @item info checkpoints List the checkpoints that have been saved in the current debugging session. For each checkpoint, the following information will be listed: @table @code @item Checkpoint ID @item Process ID @item Code Address @item Source line, or label @end table @kindex restart @var{checkpoint-id} @item restart @var{checkpoint-id} Restore the program state that was saved as checkpoint number @var{checkpoint-id}. All program variables, registers, stack frames etc.@: will be returned to the values that they had when the checkpoint was saved. In essence, gdb will ``wind back the clock'' to the point in time when the checkpoint was saved. Note that breakpoints, @value{GDBN} variables, command history etc. are not affected by restoring a checkpoint. In general, a checkpoint only restores things that reside in the program being debugged, not in the debugger. @kindex delete checkpoint @var{checkpoint-id} @item delete checkpoint @var{checkpoint-id} Delete the previously-saved checkpoint identified by @var{checkpoint-id}. @end table Returning to a previously saved checkpoint will restore the user state of the program being debugged, plus a significant subset of the system (OS) state, including file pointers. It won't ``un-write'' data from a file, but it will rewind the file pointer to the previous location, so that the previously written data can be overwritten. For files opened in read mode, the pointer will also be restored so that the previously read data can be read again. Of course, characters that have been sent to a printer (or other external device) cannot be ``snatched back'', and characters received from eg.@: a serial device can be removed from internal program buffers, but they cannot be ``pushed back'' into the serial pipeline, ready to be received again. Similarly, the actual contents of files that have been changed cannot be restored (at this time). However, within those constraints, you actually can ``rewind'' your program to a previously saved point in time, and begin debugging it again --- and you can change the course of events so as to debug a different execution path this time. @cindex checkpoints and process id Finally, there is one bit of internal program state that will be different when you return to a checkpoint --- the program's process id. Each checkpoint will have a unique process id (or @var{pid}), and each will be different from the program's original @var{pid}. If your program has saved a local copy of its process id, this could potentially pose a problem. @subsection A Non-obvious Benefit of Using Checkpoints On some systems such as @sc{gnu}/Linux, address space randomization is performed on new processes for security reasons. This makes it difficult or impossible to set a breakpoint, or watchpoint, on an absolute address if you have to restart the program, since the absolute location of a symbol will change from one execution to the next. A checkpoint, however, is an @emph{identical} copy of a process. Therefore if you create a checkpoint at (eg.@:) the start of main, and simply return to that checkpoint instead of restarting the process, you can avoid the effects of address randomization and your symbols will all stay in the same place. @node Stopping @chapter Stopping and Continuing The principal purposes of using a debugger are so that you can stop your program before it terminates; or so that, if your program runs into trouble, you can investigate and find out why. Inside @value{GDBN}, your program may stop for any of several reasons, such as a signal, a breakpoint, or reaching a new line after a @value{GDBN} command such as @code{step}. You may then examine and change variables, set new breakpoints or remove old ones, and then continue execution. Usually, the messages shown by @value{GDBN} provide ample explanation of the status of your program---but you can also explicitly request this information at any time. @table @code @kindex info program @item info program Display information about the status of your program: whether it is running or not, what process it is, and why it stopped. @end table @menu * Breakpoints:: Breakpoints, watchpoints, and catchpoints * Continuing and Stepping:: Resuming execution * Skipping Over Functions and Files:: Skipping over functions and files * Signals:: Signals * Thread Stops:: Stopping and starting multi-thread programs @end menu @node Breakpoints @section Breakpoints, Watchpoints, and Catchpoints @cindex breakpoints A @dfn{breakpoint} makes your program stop whenever a certain point in the program is reached. For each breakpoint, you can add conditions to control in finer detail whether your program stops. You can set breakpoints with the @code{break} command and its variants (@pxref{Set Breaks, ,Setting Breakpoints}), to specify the place where your program should stop by line number, function name or exact address in the program. On some systems, you can set breakpoints in shared libraries before the executable is run. @cindex watchpoints @cindex data breakpoints @cindex memory tracing @cindex breakpoint on memory address @cindex breakpoint on variable modification A @dfn{watchpoint} is a special breakpoint that stops your program when the value of an expression changes. The expression may be a value of a variable, or it could involve values of one or more variables combined by operators, such as @samp{a + b}. This is sometimes called @dfn{data breakpoints}. You must use a different command to set watchpoints (@pxref{Set Watchpoints, ,Setting Watchpoints}), but aside from that, you can manage a watchpoint like any other breakpoint: you enable, disable, and delete both breakpoints and watchpoints using the same commands. You can arrange to have values from your program displayed automatically whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,, Automatic Display}. @cindex catchpoints @cindex breakpoint on events A @dfn{catchpoint} is another special breakpoint that stops your program when a certain kind of event occurs, such as the throwing of a C@t{++} exception or the loading of a library. As with watchpoints, you use a different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting Catchpoints}), but aside from that, you can manage a catchpoint like any other breakpoint. (To stop when your program receives a signal, use the @code{handle} command; see @ref{Signals, ,Signals}.) @cindex breakpoint numbers @cindex numbers for breakpoints @value{GDBN} assigns a number to each breakpoint, watchpoint, or catchpoint when you create it; these numbers are successive integers starting with one. In many of the commands for controlling various features of breakpoints you use the breakpoint number to say which breakpoint you want to change. Each breakpoint may be @dfn{enabled} or @dfn{disabled}; if disabled, it has no effect on your program until you enable it again. @cindex breakpoint ranges @cindex breakpoint lists @cindex ranges of breakpoints @cindex lists of breakpoints Some @value{GDBN} commands accept a space-separated list of breakpoints on which to operate. A list element can be either a single breakpoint number, like @samp{5}, or a range of such numbers, like @samp{5-7}. When a breakpoint list is given to a command, all breakpoints in that list are operated on. @menu * Set Breaks:: Setting breakpoints * Set Watchpoints:: Setting watchpoints * Set Catchpoints:: Setting catchpoints * Delete Breaks:: Deleting breakpoints * Disabling:: Disabling breakpoints * Conditions:: Break conditions * Break Commands:: Breakpoint command lists * Dynamic Printf:: Dynamic printf * Save Breakpoints:: How to save breakpoints in a file * Static Probe Points:: Listing static probe points * Error in Breakpoints:: ``Cannot insert breakpoints'' * Breakpoint-related Warnings:: ``Breakpoint address adjusted...'' @end menu @node Set Breaks @subsection Setting Breakpoints @c FIXME LMB what does GDB do if no code on line of breakpt? @c consider in particular declaration with/without initialization. @c @c FIXME 2 is there stuff on this already? break at fun start, already init? @kindex break @kindex b @r{(@code{break})} @vindex $bpnum@r{, convenience variable} @cindex latest breakpoint Breakpoints are set with the @code{break} command (abbreviated @code{b}). The debugger convenience variable @samp{$bpnum} records the number of the breakpoint you've set most recently; see @ref{Convenience Vars,, Convenience Variables}, for a discussion of what you can do with convenience variables. @table @code @item break @var{location} Set a breakpoint at the given @var{location}, which can specify a function name, a line number, or an address of an instruction. (@xref{Specify Location}, for a list of all the possible ways to specify a @var{location}.) The breakpoint will stop your program just before it executes any of the code in the specified @var{location}. When using source languages that permit overloading of symbols, such as C@t{++}, a function name may refer to more than one possible place to break. @xref{Ambiguous Expressions,,Ambiguous Expressions}, for a discussion of that situation. It is also possible to insert a breakpoint that will stop the program only if a specific thread (@pxref{Thread-Specific Breakpoints}) or a specific task (@pxref{Ada Tasks}) hits that breakpoint. @item break When called without any arguments, @code{break} sets a breakpoint at the next instruction to be executed in the selected stack frame (@pxref{Stack, ,Examining the Stack}). In any selected frame but the innermost, this makes your program stop as soon as control returns to that frame. This is similar to the effect of a @code{finish} command in the frame inside the selected frame---except that @code{finish} does not leave an active breakpoint. If you use @code{break} without an argument in the innermost frame, @value{GDBN} stops the next time it reaches the current location; this may be useful inside loops. @value{GDBN} normally ignores breakpoints when it resumes execution, until at least one instruction has been executed. If it did not do this, you would be unable to proceed past a breakpoint without first disabling the breakpoint. This rule applies whether or not the breakpoint already existed when your program stopped. @item break @dots{} if @var{cond} Set a breakpoint with condition @var{cond}; evaluate the expression @var{cond} each time the breakpoint is reached, and stop only if the value is nonzero---that is, if @var{cond} evaluates as true. @samp{@dots{}} stands for one of the possible arguments described above (or no argument) specifying where to break. @xref{Conditions, ,Break Conditions}, for more information on breakpoint conditions. @kindex tbreak @item tbreak @var{args} Set a breakpoint enabled only for one stop. The @var{args} are the same as for the @code{break} command, and the breakpoint is set in the same way, but the breakpoint is automatically deleted after the first time your program stops there. @xref{Disabling, ,Disabling Breakpoints}. @kindex hbreak @cindex hardware breakpoints @item hbreak @var{args} Set a hardware-assisted breakpoint. The @var{args} are the same as for the @code{break} command and the breakpoint is set in the same way, but the breakpoint requires hardware support and some target hardware may not have this support. The main purpose of this is EPROM/ROM code debugging, so you can set a breakpoint at an instruction without changing the instruction. This can be used with the new trap-generation provided by SPARClite DSU and most x86-based targets. These targets will generate traps when a program accesses some data or instruction address that is assigned to the debug registers. However the hardware breakpoint registers can take a limited number of breakpoints. For example, on the DSU, only two data breakpoints can be set at a time, and @value{GDBN} will reject this command if more than two are used. Delete or disable unused hardware breakpoints before setting new ones (@pxref{Disabling, ,Disabling Breakpoints}). @xref{Conditions, ,Break Conditions}. For remote targets, you can restrict the number of hardware breakpoints @value{GDBN} will use, see @ref{set remote hardware-breakpoint-limit}. @kindex thbreak @item thbreak @var{args} Set a hardware-assisted breakpoint enabled only for one stop. The @var{args} are the same as for the @code{hbreak} command and the breakpoint is set in the same way. However, like the @code{tbreak} command, the breakpoint is automatically deleted after the first time your program stops there. Also, like the @code{hbreak} command, the breakpoint requires hardware support and some target hardware may not have this support. @xref{Disabling, ,Disabling Breakpoints}. See also @ref{Conditions, ,Break Conditions}. @kindex rbreak @cindex regular expression @cindex breakpoints at functions matching a regexp @cindex set breakpoints in many functions @item rbreak @var{regex} Set breakpoints on all functions matching the regular expression @var{regex}. This command sets an unconditional breakpoint on all matches, printing a list of all breakpoints it set. Once these breakpoints are set, they are treated just like the breakpoints set with the @code{break} command. You can delete them, disable them, or make them conditional the same way as any other breakpoint. In programs using different languages, @value{GDBN} chooses the syntax to print the list of all breakpoints it sets according to the @samp{set language} value: using @samp{set language auto} (see @ref{Automatically, ,Set Language Automatically}) means to use the language of the breakpoint's function, other values mean to use the manually specified language (see @ref{Manually, ,Set Language Manually}). The syntax of the regular expression is the standard one used with tools like @file{grep}. Note that this is different from the syntax used by shells, so for instance @code{foo*} matches all functions that include an @code{fo} followed by zero or more @code{o}s. There is an implicit @code{.*} leading and trailing the regular expression you supply, so to match only functions that begin with @code{foo}, use @code{^foo}. @cindex non-member C@t{++} functions, set breakpoint in When debugging C@t{++} programs, @code{rbreak} is useful for setting breakpoints on overloaded functions that are not members of any special classes. @cindex set breakpoints on all functions The @code{rbreak} command can be used to set breakpoints in @strong{all} the functions in a program, like this: @smallexample (@value{GDBP}) rbreak . @end smallexample @item rbreak @var{file}:@var{regex} If @code{rbreak} is called with a filename qualification, it limits the search for functions matching the given regular expression to the specified @var{file}. This can be used, for example, to set breakpoints on every function in a given file: @smallexample (@value{GDBP}) rbreak file.c:. @end smallexample The colon separating the filename qualifier from the regex may optionally be surrounded by spaces. @kindex info breakpoints @cindex @code{$_} and @code{info breakpoints} @item info breakpoints @r{[}@var{list}@dots{}@r{]} @itemx info break @r{[}@var{list}@dots{}@r{]} Print a table of all breakpoints, watchpoints, and catchpoints set and not deleted. Optional argument @var{n} means print information only about the specified breakpoint(s) (or watchpoint(s) or catchpoint(s)). For each breakpoint, following columns are printed: @table @emph @item Breakpoint Numbers @item Type Breakpoint, watchpoint, or catchpoint. @item Disposition Whether the breakpoint is marked to be disabled or deleted when hit. @item Enabled or Disabled Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints that are not enabled. @item Address Where the breakpoint is in your program, as a memory address. For a pending breakpoint whose address is not yet known, this field will contain @samp{<PENDING>}. Such breakpoint won't fire until a shared library that has the symbol or line referred by breakpoint is loaded. See below for details. A breakpoint with several locations will have @samp{<MULTIPLE>} in this field---see below for details. @item What Where the breakpoint is in the source for your program, as a file and line number. For a pending breakpoint, the original string passed to the breakpoint command will be listed as it cannot be resolved until the appropriate shared library is loaded in the future. @end table @noindent If a breakpoint is conditional, there are two evaluation modes: ``host'' and ``target''. If mode is ``host'', breakpoint condition evaluation is done by @value{GDBN} on the host's side. If it is ``target'', then the condition is evaluated by the target. The @code{info break} command shows the condition on the line following the affected breakpoint, together with its condition evaluation mode in between parentheses. Breakpoint commands, if any, are listed after that. A pending breakpoint is allowed to have a condition specified for it. The condition is not parsed for validity until a shared library is loaded that allows the pending breakpoint to resolve to a valid location. @noindent @code{info break} with a breakpoint number @var{n} as argument lists only that breakpoint. The convenience variable @code{$_} and the default examining-address for the @code{x} command are set to the address of the last breakpoint listed (@pxref{Memory, ,Examining Memory}). @noindent @code{info break} displays a count of the number of times the breakpoint has been hit. This is especially useful in conjunction with the @code{ignore} command. You can ignore a large number of breakpoint hits, look at the breakpoint info to see how many times the breakpoint was hit, and then run again, ignoring one less than that number. This will get you quickly to the last hit of that breakpoint. @noindent For a breakpoints with an enable count (xref) greater than 1, @code{info break} also displays that count. @end table @value{GDBN} allows you to set any number of breakpoints at the same place in your program. There is nothing silly or meaningless about this. When the breakpoints are conditional, this is even useful (@pxref{Conditions, ,Break Conditions}). @cindex multiple locations, breakpoints @cindex breakpoints, multiple locations It is possible that a breakpoint corresponds to several locations in your program. Examples of this situation are: @itemize @bullet @item Multiple functions in the program may have the same name. @item For a C@t{++} constructor, the @value{NGCC} compiler generates several instances of the function body, used in different cases. @item For a C@t{++} template function, a given line in the function can correspond to any number of instantiations. @item For an inlined function, a given source line can correspond to several places where that function is inlined. @end itemize In all those cases, @value{GDBN} will insert a breakpoint at all the relevant locations. A breakpoint with multiple locations is displayed in the breakpoint table using several rows---one header row, followed by one row for each breakpoint location. The header row has @samp{<MULTIPLE>} in the address column. The rows for individual locations contain the actual addresses for locations, and show the functions to which those locations belong. The number column for a location is of the form @var{breakpoint-number}.@var{location-number}. For example: @smallexample Num Type Disp Enb Address What 1 breakpoint keep y <MULTIPLE> stop only if i==1 breakpoint already hit 1 time 1.1 y 0x080486a2 in void foo<int>() at t.cc:8 1.2 y 0x080486ca in void foo<double>() at t.cc:8 @end smallexample You cannot delete the individual locations from a breakpoint. However, each location can be individually enabled or disabled by passing @var{breakpoint-number}.@var{location-number} as argument to the @code{enable} and @code{disable} commands. It's also possible to @code{enable} and @code{disable} a range of @var{location-number} locations using a @var{breakpoint-number} and two @var{location-number}s, in increasing order, separated by a hyphen, like @kbd{@var{breakpoint-number}.@var{location-number1}-@var{location-number2}}, in which case @value{GDBN} acts on all the locations in the range (inclusive). Disabling or enabling the parent breakpoint (@pxref{Disabling}) affects all of the locations that belong to that breakpoint. @cindex pending breakpoints It's quite common to have a breakpoint inside a shared library. Shared libraries can be loaded and unloaded explicitly, and possibly repeatedly, as the program is executed. To support this use case, @value{GDBN} updates breakpoint locations whenever any shared library is loaded or unloaded. Typically, you would set a breakpoint in a shared library at the beginning of your debugging session, when the library is not loaded, and when the symbols from the library are not available. When you try to set breakpoint, @value{GDBN} will ask you if you want to set a so called @dfn{pending breakpoint}---breakpoint whose address is not yet resolved. After the program is run, whenever a new shared library is loaded, @value{GDBN} reevaluates all the breakpoints. When a newly loaded shared library contains the symbol or line referred to by some pending breakpoint, that breakpoint is resolved and becomes an ordinary breakpoint. When a library is unloaded, all breakpoints that refer to its symbols or source lines become pending again. This logic works for breakpoints with multiple locations, too. For example, if you have a breakpoint in a C@t{++} template function, and a newly loaded shared library has an instantiation of that template, a new location is added to the list of locations for the breakpoint. Except for having unresolved address, pending breakpoints do not differ from regular breakpoints. You can set conditions or commands, enable and disable them and perform other breakpoint operations. @value{GDBN} provides some additional commands for controlling what happens when the @samp{break} command cannot resolve breakpoint address specification to an address: @kindex set breakpoint pending @kindex show breakpoint pending @table @code @item set breakpoint pending auto This is the default behavior. When @value{GDBN} cannot find the breakpoint location, it queries you whether a pending breakpoint should be created. @item set breakpoint pending on This indicates that an unrecognized breakpoint location should automatically result in a pending breakpoint being created. @item set breakpoint pending off This indicates that pending breakpoints are not to be created. Any unrecognized breakpoint location results in an error. This setting does not affect any pending breakpoints previously created. @item show breakpoint pending Show the current behavior setting for creating pending breakpoints. @end table The settings above only affect the @code{break} command and its variants. Once breakpoint is set, it will be automatically updated as shared libraries are loaded and unloaded. @cindex automatic hardware breakpoints For some targets, @value{GDBN} can automatically decide if hardware or software breakpoints should be used, depending on whether the breakpoint address is read-only or read-write. This applies to breakpoints set with the @code{break} command as well as to internal breakpoints set by commands like @code{next} and @code{finish}. For breakpoints set with @code{hbreak}, @value{GDBN} will always use hardware breakpoints. You can control this automatic behaviour with the following commands: @kindex set breakpoint auto-hw @kindex show breakpoint auto-hw @table @code @item set breakpoint auto-hw on This is the default behavior. When @value{GDBN} sets a breakpoint, it will try to use the target memory map to decide if software or hardware breakpoint must be used. @item set breakpoint auto-hw off This indicates @value{GDBN} should not automatically select breakpoint type. If the target provides a memory map, @value{GDBN} will warn when trying to set software breakpoint at a read-only address. @end table @value{GDBN} normally implements breakpoints by replacing the program code at the breakpoint address with a special instruction, which, when executed, given control to the debugger. By default, the program code is so modified only when the program is resumed. As soon as the program stops, @value{GDBN} restores the original instructions. This behaviour guards against leaving breakpoints inserted in the target should gdb abrubptly disconnect. However, with slow remote targets, inserting and removing breakpoint can reduce the performance. This behavior can be controlled with the following commands:: @kindex set breakpoint always-inserted @kindex show breakpoint always-inserted @table @code @item set breakpoint always-inserted off All breakpoints, including newly added by the user, are inserted in the target only when the target is resumed. All breakpoints are removed from the target when it stops. This is the default mode. @item set breakpoint always-inserted on Causes all breakpoints to be inserted in the target at all times. If the user adds a new breakpoint, or changes an existing breakpoint, the breakpoints in the target are updated immediately. A breakpoint is removed from the target only when breakpoint itself is deleted. @end table @value{GDBN} handles conditional breakpoints by evaluating these conditions when a breakpoint breaks. If the condition is true, then the process being debugged stops, otherwise the process is resumed. If the target supports evaluating conditions on its end, @value{GDBN} may download the breakpoint, together with its conditions, to it. This feature can be controlled via the following commands: @kindex set breakpoint condition-evaluation @kindex show breakpoint condition-evaluation @table @code @item set breakpoint condition-evaluation host This option commands @value{GDBN} to evaluate the breakpoint conditions on the host's side. Unconditional breakpoints are sent to the target which in turn receives the triggers and reports them back to GDB for condition evaluation. This is the standard evaluation mode. @item set breakpoint condition-evaluation target This option commands @value{GDBN} to download breakpoint conditions to the target at the moment of their insertion. The target is responsible for evaluating the conditional expression and reporting breakpoint stop events back to @value{GDBN} whenever the condition is true. Due to limitations of target-side evaluation, some conditions cannot be evaluated there, e.g., conditions that depend on local data that is only known to the host. Examples include conditional expressions involving convenience variables, complex types that cannot be handled by the agent expression parser and expressions that are too long to be sent over to the target, specially when the target is a remote system. In these cases, the conditions will be evaluated by @value{GDBN}. @item set breakpoint condition-evaluation auto This is the default mode. If the target supports evaluating breakpoint conditions on its end, @value{GDBN} will download breakpoint conditions to the target (limitations mentioned previously apply). If the target does not support breakpoint condition evaluation, then @value{GDBN} will fallback to evaluating all these conditions on the host's side. @end table @cindex negative breakpoint numbers @cindex internal @value{GDBN} breakpoints @value{GDBN} itself sometimes sets breakpoints in your program for special purposes, such as proper handling of @code{longjmp} (in C programs). These internal breakpoints are assigned negative numbers, starting with @code{-1}; @samp{info breakpoints} does not display them. You can see these breakpoints with the @value{GDBN} maintenance command @samp{maint info breakpoints} (@pxref{maint info breakpoints}). @node Set Watchpoints @subsection Setting Watchpoints @cindex setting watchpoints You can use a watchpoint to stop execution whenever the value of an expression changes, without having to predict a particular place where this may happen. (This is sometimes called a @dfn{data breakpoint}.) The expression may be as simple as the value of a single variable, or as complex as many variables combined by operators. Examples include: @itemize @bullet @item A reference to the value of a single variable. @item An address cast to an appropriate data type. For example, @samp{*(int *)0x12345678} will watch a 4-byte region at the specified address (assuming an @code{int} occupies 4 bytes). @item An arbitrarily complex expression, such as @samp{a*b + c/d}. The expression can use any operators valid in the program's native language (@pxref{Languages}). @end itemize You can set a watchpoint on an expression even if the expression can not be evaluated yet. For instance, you can set a watchpoint on @samp{*global_ptr} before @samp{global_ptr} is initialized. @value{GDBN} will stop when your program sets @samp{global_ptr} and the expression produces a valid value. If the expression becomes valid in some other way than changing a variable (e.g.@: if the memory pointed to by @samp{*global_ptr} becomes readable as the result of a @code{malloc} call), @value{GDBN} may not stop until the next time the expression changes. @cindex software watchpoints @cindex hardware watchpoints Depending on your system, watchpoints may be implemented in software or hardware. @value{GDBN} does software watchpointing by single-stepping your program and testing the variable's value each time, which is hundreds of times slower than normal execution. (But this may still be worth it, to catch errors where you have no clue what part of your program is the culprit.) On some systems, such as most PowerPC or x86-based targets, @value{GDBN} includes support for hardware watchpoints, which do not slow down the running of your program. @table @code @kindex watch @item watch @r{[}-l@r{|}-location@r{]} @var{expr} @r{[}thread @var{thread-id}@r{]} @r{[}mask @var{maskvalue}@r{]} Set a watchpoint for an expression. @value{GDBN} will break when the expression @var{expr} is written into by the program and its value changes. The simplest (and the most popular) use of this command is to watch the value of a single variable: @smallexample (@value{GDBP}) watch foo @end smallexample If the command includes a @code{@r{[}thread @var{thread-id}@r{]}} argument, @value{GDBN} breaks only when the thread identified by @var{thread-id} changes the value of @var{expr}. If any other threads change the value of @var{expr}, @value{GDBN} will not break. Note that watchpoints restricted to a single thread in this way only work with Hardware Watchpoints. Ordinarily a watchpoint respects the scope of variables in @var{expr} (see below). The @code{-location} argument tells @value{GDBN} to instead watch the memory referred to by @var{expr}. In this case, @value{GDBN} will evaluate @var{expr}, take the address of the result, and watch the memory at that address. The type of the result is used to determine the size of the watched memory. If the expression's result does not have an address, then @value{GDBN} will print an error. The @code{@r{[}mask @var{maskvalue}@r{]}} argument allows creation of masked watchpoints, if the current architecture supports this feature (e.g., PowerPC Embedded architecture, see @ref{PowerPC Embedded}.) A @dfn{masked watchpoint} specifies a mask in addition to an address to watch. The mask specifies that some bits of an address (the bits which are reset in the mask) should be ignored when matching the address accessed by the inferior against the watchpoint address. Thus, a masked watchpoint watches many addresses simultaneously---those addresses whose unmasked bits are identical to the unmasked bits in the watchpoint address. The @code{mask} argument implies @code{-location}. Examples: @smallexample (@value{GDBP}) watch foo mask 0xffff00ff (@value{GDBP}) watch *0xdeadbeef mask 0xffffff00 @end smallexample @kindex rwatch @item rwatch @r{[}-l@r{|}-location@r{]} @var{expr} @r{[}thread @var{thread-id}@r{]} @r{[}mask @var{maskvalue}@r{]} Set a watchpoint that will break when the value of @var{expr} is read by the program. @kindex awatch @item awatch @r{[}-l@r{|}-location@r{]} @var{expr} @r{[}thread @var{thread-id}@r{]} @r{[}mask @var{maskvalue}@r{]} Set a watchpoint that will break when @var{expr} is either read from or written into by the program. @kindex info watchpoints @r{[}@var{list}@dots{}@r{]} @item info watchpoints @r{[}@var{list}@dots{}@r{]} This command prints a list of watchpoints, using the same format as @code{info break} (@pxref{Set Breaks}). @end table If you watch for a change in a numerically entered address you need to dereference it, as the address itself is just a constant number which will never change. @value{GDBN} refuses to create a watchpoint that watches a never-changing value: @smallexample (@value{GDBP}) watch 0x600850 Cannot watch constant value 0x600850. (@value{GDBP}) watch *(int *) 0x600850 Watchpoint 1: *(int *) 6293584 @end smallexample @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware watchpoints execute very quickly, and the debugger reports a change in value at the exact instruction where the change occurs. If @value{GDBN} cannot set a hardware watchpoint, it sets a software watchpoint, which executes more slowly and reports the change in value at the next @emph{statement}, not the instruction, after the change occurs. @cindex use only software watchpoints You can force @value{GDBN} to use only software watchpoints with the @kbd{set can-use-hw-watchpoints 0} command. With this variable set to zero, @value{GDBN} will never try to use hardware watchpoints, even if the underlying system supports them. (Note that hardware-assisted watchpoints that were set @emph{before} setting @code{can-use-hw-watchpoints} to zero will still use the hardware mechanism of watching expression values.) @table @code @item set can-use-hw-watchpoints @kindex set can-use-hw-watchpoints Set whether or not to use hardware watchpoints. @item show can-use-hw-watchpoints @kindex show can-use-hw-watchpoints Show the current mode of using hardware watchpoints. @end table For remote targets, you can restrict the number of hardware watchpoints @value{GDBN} will use, see @ref{set remote hardware-breakpoint-limit}. When you issue the @code{watch} command, @value{GDBN} reports @smallexample Hardware watchpoint @var{num}: @var{expr} @end smallexample @noindent if it was able to set a hardware watchpoint. Currently, the @code{awatch} and @code{rwatch} commands can only set hardware watchpoints, because accesses to data that don't change the value of the watched expression cannot be detected without examining every instruction as it is being executed, and @value{GDBN} does not do that currently. If @value{GDBN} finds that it is unable to set a hardware breakpoint with the @code{awatch} or @code{rwatch} command, it will print a message like this: @smallexample Expression cannot be implemented with read/access watchpoint. @end smallexample Sometimes, @value{GDBN} cannot set a hardware watchpoint because the data type of the watched expression is wider than what a hardware watchpoint on the target machine can handle. For example, some systems can only watch regions that are up to 4 bytes wide; on such systems you cannot set hardware watchpoints for an expression that yields a double-precision floating-point number (which is typically 8 bytes wide). As a work-around, it might be possible to break the large region into a series of smaller ones and watch them with separate watchpoints. If you set too many hardware watchpoints, @value{GDBN} might be unable to insert all of them when you resume the execution of your program. Since the precise number of active watchpoints is unknown until such time as the program is about to be resumed, @value{GDBN} might not be able to warn you about this when you set the watchpoints, and the warning will be printed only when the program is resumed: @smallexample Hardware watchpoint @var{num}: Could not insert watchpoint @end smallexample @noindent If this happens, delete or disable some of the watchpoints. Watching complex expressions that reference many variables can also exhaust the resources available for hardware-assisted watchpoints. That's because @value{GDBN} needs to watch every variable in the expression with separately allocated resources. If you call a function interactively using @code{print} or @code{call}, any watchpoints you have set will be inactive until @value{GDBN} reaches another kind of breakpoint or the call completes. @value{GDBN} automatically deletes watchpoints that watch local (automatic) variables, or expressions that involve such variables, when they go out of scope, that is, when the execution leaves the block in which these variables were defined. In particular, when the program being debugged terminates, @emph{all} local variables go out of scope, and so only watchpoints that watch global variables remain set. If you rerun the program, you will need to set all such watchpoints again. One way of doing that would be to set a code breakpoint at the entry to the @code{main} function and when it breaks, set all the watchpoints. @cindex watchpoints and threads @cindex threads and watchpoints In multi-threaded programs, watchpoints will detect changes to the watched expression from every thread. @quotation @emph{Warning:} In multi-threaded programs, software watchpoints have only limited usefulness. If @value{GDBN} creates a software watchpoint, it can only watch the value of an expression @emph{in a single thread}. If you are confident that the expression can only change due to the current thread's activity (and if you are also confident that no other thread can become current), then you can use software watchpoints as usual. However, @value{GDBN} may not notice when a non-current thread's activity changes the expression. (Hardware watchpoints, in contrast, watch an expression in all threads.) @end quotation @xref{set remote hardware-watchpoint-limit}. @node Set Catchpoints @subsection Setting Catchpoints @cindex catchpoints, setting @cindex exception handlers @cindex event handling You can use @dfn{catchpoints} to cause the debugger to stop for certain kinds of program events, such as C@t{++} exceptions or the loading of a shared library. Use the @code{catch} command to set a catchpoint. @table @code @kindex catch @item catch @var{event} Stop when @var{event} occurs. The @var{event} can be any of the following: @table @code @item throw @r{[}@var{regexp}@r{]} @itemx rethrow @r{[}@var{regexp}@r{]} @itemx catch @r{[}@var{regexp}@r{]} @kindex catch throw @kindex catch rethrow @kindex catch catch @cindex stop on C@t{++} exceptions The throwing, re-throwing, or catching of a C@t{++} exception. If @var{regexp} is given, then only exceptions whose type matches the regular expression will be caught. @vindex $_exception@r{, convenience variable} The convenience variable @code{$_exception} is available at an exception-related catchpoint, on some systems. This holds the exception being thrown. There are currently some limitations to C@t{++} exception handling in @value{GDBN}: @itemize @bullet @item The support for these commands is system-dependent. Currently, only systems using the @samp{gnu-v3} C@t{++} ABI (@pxref{ABI}) are supported. @item The regular expression feature and the @code{$_exception} convenience variable rely on the presence of some SDT probes in @code{libstdc++}. If these probes are not present, then these features cannot be used. These probes were first available in the GCC 4.8 release, but whether or not they are available in your GCC also depends on how it was built. @item The @code{$_exception} convenience variable is only valid at the instruction at which an exception-related catchpoint is set. @item When an exception-related catchpoint is hit, @value{GDBN} stops at a location in the system library which implements runtime exception support for C@t{++}, usually @code{libstdc++}. You can use @code{up} (@pxref{Selection}) to get to your code. @item If you call a function interactively, @value{GDBN} normally returns control to you when the function has finished executing. If the call raises an exception, however, the call may bypass the mechanism that returns control to you and cause your program either to abort or to simply continue running until it hits a breakpoint, catches a signal that @value{GDBN} is listening for, or exits. This is the case even if you set a catchpoint for the exception; catchpoints on exceptions are disabled within interactive calls. @xref{Calling}, for information on controlling this with @code{set unwind-on-terminating-exception}. @item You cannot raise an exception interactively. @item You cannot install an exception handler interactively. @end itemize @item exception @r{[}@var{name}@r{]} @kindex catch exception @cindex Ada exception catching @cindex catch Ada exceptions An Ada exception being raised. If an exception name is specified at the end of the command (eg @code{catch exception Program_Error}), the debugger will stop only when this specific exception is raised. Otherwise, the debugger stops execution when any Ada exception is raised. When inserting an exception catchpoint on a user-defined exception whose name is identical to one of the exceptions defined by the language, the fully qualified name must be used as the exception name. Otherwise, @value{GDBN} will assume that it should stop on the pre-defined exception rather than the user-defined one. For instance, assuming an exception called @code{Constraint_Error} is defined in package @code{Pck}, then the command to use to catch such exceptions is @kbd{catch exception Pck.Constraint_Error}. @vindex $_ada_exception@r{, convenience variable} The convenience variable @code{$_ada_exception} holds the address of the exception being thrown. This can be useful when setting a condition for such a catchpoint. @item exception unhandled @kindex catch exception unhandled An exception that was raised but is not handled by the program. The convenience variable @code{$_ada_exception} is set as for @code{catch exception}. @item handlers @r{[}@var{name}@r{]} @kindex catch handlers @cindex Ada exception handlers catching @cindex catch Ada exceptions when handled An Ada exception being handled. If an exception name is specified at the end of the command (eg @kbd{catch handlers Program_Error}), the debugger will stop only when this specific exception is handled. Otherwise, the debugger stops execution when any Ada exception is handled. When inserting a handlers catchpoint on a user-defined exception whose name is identical to one of the exceptions defined by the language, the fully qualified name must be used as the exception name. Otherwise, @value{GDBN} will assume that it should stop on the pre-defined exception rather than the user-defined one. For instance, assuming an exception called @code{Constraint_Error} is defined in package @code{Pck}, then the command to use to catch such exceptions handling is @kbd{catch handlers Pck.Constraint_Error}. The convenience variable @code{$_ada_exception} is set as for @code{catch exception}. @item assert @kindex catch assert A failed Ada assertion. Note that the convenience variable @code{$_ada_exception} is @emph{not} set by this catchpoint. @item exec @kindex catch exec @cindex break on fork/exec A call to @code{exec}. @anchor{catch syscall} @item syscall @itemx syscall @r{[}@var{name} @r{|} @var{number} @r{|} @r{group:}@var{groupname} @r{|} @r{g:}@var{groupname}@r{]} @dots{} @kindex catch syscall @cindex break on a system call. A call to or return from a system call, a.k.a.@: @dfn{syscall}. A syscall is a mechanism for application programs to request a service from the operating system (OS) or one of the OS system services. @value{GDBN} can catch some or all of the syscalls issued by the debuggee, and show the related information for each syscall. If no argument is specified, calls to and returns from all system calls will be caught. @var{name} can be any system call name that is valid for the underlying OS. Just what syscalls are valid depends on the OS. On GNU and Unix systems, you can find the full list of valid syscall names on @file{/usr/include/asm/unistd.h}. @c For MS-Windows, the syscall names and the corresponding numbers @c can be found, e.g., on this URL: @c http://www.metasploit.com/users/opcode/syscalls.html @c but we don't support Windows syscalls yet. Normally, @value{GDBN} knows in advance which syscalls are valid for each OS, so you can use the @value{GDBN} command-line completion facilities (@pxref{Completion,, command completion}) to list the available choices. You may also specify the system call numerically. A syscall's number is the value passed to the OS's syscall dispatcher to identify the requested service. When you specify the syscall by its name, @value{GDBN} uses its database of syscalls to convert the name into the corresponding numeric code, but using the number directly may be useful if @value{GDBN}'s database does not have the complete list of syscalls on your system (e.g., because @value{GDBN} lags behind the OS upgrades). You may specify a group of related syscalls to be caught at once using the @code{group:} syntax (@code{g:} is a shorter equivalent). For instance, on some platforms @value{GDBN} allows you to catch all network related syscalls, by passing the argument @code{group:network} to @code{catch syscall}. Note that not all syscall groups are available in every system. You can use the command completion facilities (@pxref{Completion,, command completion}) to list the syscall groups available on your environment. The example below illustrates how this command works if you don't provide arguments to it: @smallexample (@value{GDBP}) catch syscall Catchpoint 1 (syscall) (@value{GDBP}) r Starting program: /tmp/catch-syscall Catchpoint 1 (call to syscall 'close'), \ 0xffffe424 in __kernel_vsyscall () (@value{GDBP}) c Continuing. Catchpoint 1 (returned from syscall 'close'), \ 0xffffe424 in __kernel_vsyscall () (@value{GDBP}) @end smallexample Here is an example of catching a system call by name: @smallexample (@value{GDBP}) catch syscall chroot Catchpoint 1 (syscall 'chroot' [61]) (@value{GDBP}) r Starting program: /tmp/catch-syscall Catchpoint 1 (call to syscall 'chroot'), \ 0xffffe424 in __kernel_vsyscall () (@value{GDBP}) c Continuing. Catchpoint 1 (returned from syscall 'chroot'), \ 0xffffe424 in __kernel_vsyscall () (@value{GDBP}) @end smallexample An example of specifying a system call numerically. In the case below, the syscall number has a corresponding entry in the XML file, so @value{GDBN} finds its name and prints it: @smallexample (@value{GDBP}) catch syscall 252 Catchpoint 1 (syscall(s) 'exit_group') (@value{GDBP}) r Starting program: /tmp/catch-syscall Catchpoint 1 (call to syscall 'exit_group'), \ 0xffffe424 in __kernel_vsyscall () (@value{GDBP}) c Continuing. Program exited normally. (@value{GDBP}) @end smallexample Here is an example of catching a syscall group: @smallexample (@value{GDBP}) catch syscall group:process Catchpoint 1 (syscalls 'exit' [1] 'fork' [2] 'waitpid' [7] 'execve' [11] 'wait4' [114] 'clone' [120] 'vfork' [190] 'exit_group' [252] 'waitid' [284] 'unshare' [310]) (@value{GDBP}) r Starting program: /tmp/catch-syscall Catchpoint 1 (call to syscall fork), 0x00007ffff7df4e27 in open64 () from /lib64/ld-linux-x86-64.so.2 (@value{GDBP}) c Continuing. @end smallexample However, there can be situations when there is no corresponding name in XML file for that syscall number. In this case, @value{GDBN} prints a warning message saying that it was not able to find the syscall name, but the catchpoint will be set anyway. See the example below: @smallexample (@value{GDBP}) catch syscall 764 warning: The number '764' does not represent a known syscall. Catchpoint 2 (syscall 764) (@value{GDBP}) @end smallexample If you configure @value{GDBN} using the @samp{--without-expat} option, it will not be able to display syscall names. Also, if your architecture does not have an XML file describing its system calls, you will not be able to see the syscall names. It is important to notice that these two features are used for accessing the syscall name database. In either case, you will see a warning like this: @smallexample (@value{GDBP}) catch syscall warning: Could not open "syscalls/i386-linux.xml" warning: Could not load the syscall XML file 'syscalls/i386-linux.xml'. GDB will not be able to display syscall names. Catchpoint 1 (syscall) (@value{GDBP}) @end smallexample Of course, the file name will change depending on your architecture and system. Still using the example above, you can also try to catch a syscall by its number. In this case, you would see something like: @smallexample (@value{GDBP}) catch syscall 252 Catchpoint 1 (syscall(s) 252) @end smallexample Again, in this case @value{GDBN} would not be able to display syscall's names. @item fork @kindex catch fork A call to @code{fork}. @item vfork @kindex catch vfork A call to @code{vfork}. @item load @r{[}@var{regexp}@r{]} @itemx unload @r{[}@var{regexp}@r{]} @kindex catch load @kindex catch unload The loading or unloading of a shared library. If @var{regexp} is given, then the catchpoint will stop only if the regular expression matches one of the affected libraries. @item signal @r{[}@var{signal}@dots{} @r{|} @samp{all}@r{]} @kindex catch signal The delivery of a signal. With no arguments, this catchpoint will catch any signal that is not used internally by @value{GDBN}, specifically, all signals except @samp{SIGTRAP} and @samp{SIGINT}. With the argument @samp{all}, all signals, including those used by @value{GDBN}, will be caught. This argument cannot be used with other signal names. Otherwise, the arguments are a list of signal names as given to @code{handle} (@pxref{Signals}). Only signals specified in this list will be caught. One reason that @code{catch signal} can be more useful than @code{handle} is that you can attach commands and conditions to the catchpoint. When a signal is caught by a catchpoint, the signal's @code{stop} and @code{print} settings, as specified by @code{handle}, are ignored. However, whether the signal is still delivered to the inferior depends on the @code{pass} setting; this can be changed in the catchpoint's commands. @end table @item tcatch @var{event} @kindex tcatch Set a catchpoint that is enabled only for one stop. The catchpoint is automatically deleted after the first time the event is caught. @end table Use the @code{info break} command to list the current catchpoints. @node Delete Breaks @subsection Deleting Breakpoints @cindex clearing breakpoints, watchpoints, catchpoints @cindex deleting breakpoints, watchpoints, catchpoints It is often necessary to eliminate a breakpoint, watchpoint, or catchpoint once it has done its job and you no longer want your program to stop there. This is called @dfn{deleting} the breakpoint. A breakpoint that has been deleted no longer exists; it is forgotten. With the @code{clear} command you can delete breakpoints according to where they are in your program. With the @code{delete} command you can delete individual breakpoints, watchpoints, or catchpoints by specifying their breakpoint numbers. It is not necessary to delete a breakpoint to proceed past it. @value{GDBN} automatically ignores breakpoints on the first instruction to be executed when you continue execution without changing the execution address. @table @code @kindex clear @item clear Delete any breakpoints at the next instruction to be executed in the selected stack frame (@pxref{Selection, ,Selecting a Frame}). When the innermost frame is selected, this is a good way to delete a breakpoint where your program just stopped. @item clear @var{location} Delete any breakpoints set at the specified @var{location}. @xref{Specify Location}, for the various forms of @var{location}; the most useful ones are listed below: @table @code @item clear @var{function} @itemx clear @var{filename}:@var{function} Delete any breakpoints set at entry to the named @var{function}. @item clear @var{linenum} @itemx clear @var{filename}:@var{linenum} Delete any breakpoints set at or within the code of the specified @var{linenum} of the specified @var{filename}. @end table @cindex delete breakpoints @kindex delete @kindex d @r{(@code{delete})} @item delete @r{[}breakpoints@r{]} @r{[}@var{list}@dots{}@r{]} Delete the breakpoints, watchpoints, or catchpoints of the breakpoint list specified as argument. If no argument is specified, delete all breakpoints (@value{GDBN} asks confirmation, unless you have @code{set confirm off}). You can abbreviate this command as @code{d}. @end table @node Disabling @subsection Disabling Breakpoints @cindex enable/disable a breakpoint Rather than deleting a breakpoint, watchpoint, or catchpoint, you might prefer to @dfn{disable} it. This makes the breakpoint inoperative as if it had been deleted, but remembers the information on the breakpoint so that you can @dfn{enable} it again later. You disable and enable breakpoints, watchpoints, and catchpoints with the @code{enable} and @code{disable} commands, optionally specifying one or more breakpoint numbers as arguments. Use @code{info break} to print a list of all breakpoints, watchpoints, and catchpoints if you do not know which numbers to use. Disabling and enabling a breakpoint that has multiple locations affects all of its locations. A breakpoint, watchpoint, or catchpoint can have any of several different states of enablement: @itemize @bullet @item Enabled. The breakpoint stops your program. A breakpoint set with the @code{break} command starts out in this state. @item Disabled. The breakpoint has no effect on your program. @item Enabled once. The breakpoint stops your program, but then becomes disabled. @item Enabled for a count. The breakpoint stops your program for the next N times, then becomes disabled. @item Enabled for deletion. The breakpoint stops your program, but immediately after it does so it is deleted permanently. A breakpoint set with the @code{tbreak} command starts out in this state. @end itemize You can use the following commands to enable or disable breakpoints, watchpoints, and catchpoints: @table @code @kindex disable @kindex dis @r{(@code{disable})} @item disable @r{[}breakpoints@r{]} @r{[}@var{list}@dots{}@r{]} Disable the specified breakpoints---or all breakpoints, if none are listed. A disabled breakpoint has no effect but is not forgotten. All options such as ignore-counts, conditions and commands are remembered in case the breakpoint is enabled again later. You may abbreviate @code{disable} as @code{dis}. @kindex enable @item enable @r{[}breakpoints@r{]} @r{[}@var{list}@dots{}@r{]} Enable the specified breakpoints (or all defined breakpoints). They become effective once again in stopping your program. @item enable @r{[}breakpoints@r{]} once @var{list}@dots{} Enable the specified breakpoints temporarily. @value{GDBN} disables any of these breakpoints immediately after stopping your program. @item enable @r{[}breakpoints@r{]} count @var{count} @var{list}@dots{} Enable the specified breakpoints temporarily. @value{GDBN} records @var{count} with each of the specified breakpoints, and decrements a breakpoint's count when it is hit. When any count reaches 0, @value{GDBN} disables that breakpoint. If a breakpoint has an ignore count (@pxref{Conditions, ,Break Conditions}), that will be decremented to 0 before @var{count} is affected. @item enable @r{[}breakpoints@r{]} delete @var{list}@dots{} Enable the specified breakpoints to work once, then die. @value{GDBN} deletes any of these breakpoints as soon as your program stops there. Breakpoints set by the @code{tbreak} command start out in this state. @end table @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is @c confusing: tbreak is also initially enabled. Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks, ,Setting Breakpoints}), breakpoints that you set are initially enabled; subsequently, they become disabled or enabled only when you use one of the commands above. (The command @code{until} can set and delete a breakpoint of its own, but it does not change the state of your other breakpoints; see @ref{Continuing and Stepping, ,Continuing and Stepping}.) @node Conditions @subsection Break Conditions @cindex conditional breakpoints @cindex breakpoint conditions @c FIXME what is scope of break condition expr? Context where wanted? @c in particular for a watchpoint? The simplest sort of breakpoint breaks every time your program reaches a specified place. You can also specify a @dfn{condition} for a breakpoint. A condition is just a Boolean expression in your programming language (@pxref{Expressions, ,Expressions}). A breakpoint with a condition evaluates the expression each time your program reaches it, and your program stops only if the condition is @emph{true}. This is the converse of using assertions for program validation; in that situation, you want to stop when the assertion is violated---that is, when the condition is false. In C, if you want to test an assertion expressed by the condition @var{assert}, you should set the condition @samp{! @var{assert}} on the appropriate breakpoint. Conditions are also accepted for watchpoints; you may not need them, since a watchpoint is inspecting the value of an expression anyhow---but it might be simpler, say, to just set a watchpoint on a variable name, and specify a condition that tests whether the new value is an interesting one. Break conditions can have side effects, and may even call functions in your program. This can be useful, for example, to activate functions that log program progress, or to use your own print functions to format special data structures. The effects are completely predictable unless there is another enabled breakpoint at the same address. (In that case, @value{GDBN} might see the other breakpoint first and stop your program without checking the condition of this one.) Note that breakpoint commands are usually more convenient and flexible than break conditions for the purpose of performing side effects when a breakpoint is reached (@pxref{Break Commands, ,Breakpoint Command Lists}). Breakpoint conditions can also be evaluated on the target's side if the target supports it. Instead of evaluating the conditions locally, @value{GDBN} encodes the expression into an agent expression (@pxref{Agent Expressions}) suitable for execution on the target, independently of @value{GDBN}. Global variables become raw memory locations, locals become stack accesses, and so forth. In this case, @value{GDBN} will only be notified of a breakpoint trigger when its condition evaluates to true. This mechanism may provide faster response times depending on the performance characteristics of the target since it does not need to keep @value{GDBN} informed about every breakpoint trigger, even those with false conditions. Break conditions can be specified when a breakpoint is set, by using @samp{if} in the arguments to the @code{break} command. @xref{Set Breaks, ,Setting Breakpoints}. They can also be changed at any time with the @code{condition} command. You can also use the @code{if} keyword with the @code{watch} command. The @code{catch} command does not recognize the @code{if} keyword; @code{condition} is the only way to impose a further condition on a catchpoint. @table @code @kindex condition @item condition @var{bnum} @var{expression} Specify @var{expression} as the break condition for breakpoint, watchpoint, or catchpoint number @var{bnum}. After you set a condition, breakpoint @var{bnum} stops your program only if the value of @var{expression} is true (nonzero, in C). When you use @code{condition}, @value{GDBN} checks @var{expression} immediately for syntactic correctness, and to determine whether symbols in it have referents in the context of your breakpoint. If @var{expression} uses symbols not referenced in the context of the breakpoint, @value{GDBN} prints an error message: @smallexample No symbol "foo" in current context. @end smallexample @noindent @value{GDBN} does not actually evaluate @var{expression} at the time the @code{condition} command (or a command that sets a breakpoint with a condition, like @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}. @item condition @var{bnum} Remove the condition from breakpoint number @var{bnum}. It becomes an ordinary unconditional breakpoint. @end table @cindex ignore count (of breakpoint) A special case of a breakpoint condition is to stop only when the breakpoint has been reached a certain number of times. This is so useful that there is a special way to do it, using the @dfn{ignore count} of the breakpoint. Every breakpoint has an ignore count, which is an integer. Most of the time, the ignore count is zero, and therefore has no effect. But if your program reaches a breakpoint whose ignore count is positive, then instead of stopping, it just decrements the ignore count by one and continues. As a result, if the ignore count value is @var{n}, the breakpoint does not stop the next @var{n} times your program reaches it. @table @code @kindex ignore @item ignore @var{bnum} @var{count} Set the ignore count of breakpoint number @var{bnum} to @var{count}. The next @var{count} times the breakpoint is reached, your program's execution does not stop; other than to decrement the ignore count, @value{GDBN} takes no action. To make the breakpoint stop the next time it is reached, specify a count of zero. When you use @code{continue} to resume execution of your program from a breakpoint, you can specify an ignore count directly as an argument to @code{continue}, rather than using @code{ignore}. @xref{Continuing and Stepping,,Continuing and Stepping}. If a breakpoint has a positive ignore count and a condition, the condition is not checked. Once the ignore count reaches zero, @value{GDBN} resumes checking the condition. You could achieve the effect of the ignore count with a condition such as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that is decremented each time. @xref{Convenience Vars, ,Convenience Variables}. @end table Ignore counts apply to breakpoints, watchpoints, and catchpoints. @node Break Commands @subsection Breakpoint Command Lists @cindex breakpoint commands You can give any breakpoint (or watchpoint or catchpoint) a series of commands to execute when your program stops due to that breakpoint. For example, you might want to print the values of certain expressions, or enable other breakpoints. @table @code @kindex commands @kindex end@r{ (breakpoint commands)} @item commands @r{[}@var{list}@dots{}@r{]} @itemx @dots{} @var{command-list} @dots{} @itemx end Specify a list of commands for the given breakpoints. The commands themselves appear on the following lines. Type a line containing just @code{end} to terminate the commands. To remove all commands from a breakpoint, type @code{commands} and follow it immediately with @code{end}; that is, give no commands. With no argument, @code{commands} refers to the last breakpoint, watchpoint, or catchpoint set (not to the breakpoint most recently encountered). If the most recent breakpoints were set with a single command, then the @code{commands} will apply to all the breakpoints set by that command. This applies to breakpoints set by @code{rbreak}, and also applies when a single @code{break} command creates multiple breakpoints (@pxref{Ambiguous Expressions,,Ambiguous Expressions}). @end table Pressing @key{RET} as a means of repeating the last @value{GDBN} command is disabled within a @var{command-list}. You can use breakpoint commands to start your program up again. Simply use the @code{continue} command, or @code{step}, or any other command that resumes execution. Any other commands in the command list, after a command that resumes execution, are ignored. This is because any time you resume execution (even with a simple @code{next} or @code{step}), you may encounter another breakpoint---which could have its own command list, leading to ambiguities about which list to execute. @kindex silent If the first command you specify in a command list is @code{silent}, the usual message about stopping at a breakpoint is not printed. This may be desirable for breakpoints that are to print a specific message and then continue. If none of the remaining commands print anything, you see no sign that the breakpoint was reached. @code{silent} is meaningful only at the beginning of a breakpoint command list. The commands @code{echo}, @code{output}, and @code{printf} allow you to print precisely controlled output, and are often useful in silent breakpoints. @xref{Output, ,Commands for Controlled Output}. For example, here is how you could use breakpoint commands to print the value of @code{x} at entry to @code{foo} whenever @code{x} is positive. @smallexample break foo if x>0 commands silent printf "x is %d\n",x cont end @end smallexample One application for breakpoint commands is to compensate for one bug so you can test for another. Put a breakpoint just after the erroneous line of code, give it a condition to detect the case in which something erroneous has been done, and give it commands to assign correct values to any variables that need them. End with the @code{continue} command so that your program does not stop, and start with the @code{silent} command so that no output is produced. Here is an example: @smallexample break 403 commands silent set x = y + 4 cont end @end smallexample @node Dynamic Printf @subsection Dynamic Printf @cindex dynamic printf @cindex dprintf The dynamic printf command @code{dprintf} combines a breakpoint with formatted printing of your program's data to give you the effect of inserting @code{printf} calls into your program on-the-fly, without having to recompile it. In its most basic form, the output goes to the GDB console. However, you can set the variable @code{dprintf-style} for alternate handling. For instance, you can ask to format the output by calling your program's @code{printf} function. This has the advantage that the characters go to the program's output device, so they can recorded in redirects to files and so forth. If you are doing remote debugging with a stub or agent, you can also ask to have the printf handled by the remote agent. In addition to ensuring that the output goes to the remote program's device along with any other output the program might produce, you can also ask that the dprintf remain active even after disconnecting from the remote target. Using the stub/agent is also more efficient, as it can do everything without needing to communicate with @value{GDBN}. @table @code @kindex dprintf @item dprintf @var{location},@var{template},@var{expression}[,@var{expression}@dots{}] Whenever execution reaches @var{location}, print the values of one or more @var{expressions} under the control of the string @var{template}. To print several values, separate them with commas. @item set dprintf-style @var{style} Set the dprintf output to be handled in one of several different styles enumerated below. A change of style affects all existing dynamic printfs immediately. (If you need individual control over the print commands, simply define normal breakpoints with explicitly-supplied command lists.) @table @code @item gdb @kindex dprintf-style gdb Handle the output using the @value{GDBN} @code{printf} command. @item call @kindex dprintf-style call Handle the output by calling a function in your program (normally @code{printf}). @item agent @kindex dprintf-style agent Have the remote debugging agent (such as @code{gdbserver}) handle the output itself. This style is only available for agents that support running commands on the target. @end table @item set dprintf-function @var{function} Set the function to call if the dprintf style is @code{call}. By default its value is @code{printf}. You may set it to any expression. that @value{GDBN} can evaluate to a function, as per the @code{call} command. @item set dprintf-channel @var{channel} Set a ``channel'' for dprintf. If set to a non-empty value, @value{GDBN} will evaluate it as an expression and pass the result as a first argument to the @code{dprintf-function}, in the manner of @code{fprintf} and similar functions. Otherwise, the dprintf format string will be the first argument, in the manner of @code{printf}. As an example, if you wanted @code{dprintf} output to go to a logfile that is a standard I/O stream assigned to the variable @code{mylog}, you could do the following: @example (gdb) set dprintf-style call (gdb) set dprintf-function fprintf (gdb) set dprintf-channel mylog (gdb) dprintf 25,"at line 25, glob=%d\n",glob Dprintf 1 at 0x123456: file main.c, line 25. (gdb) info break 1 dprintf keep y 0x00123456 in main at main.c:25 call (void) fprintf (mylog,"at line 25, glob=%d\n",glob) continue (gdb) @end example Note that the @code{info break} displays the dynamic printf commands as normal breakpoint commands; you can thus easily see the effect of the variable settings. @item set disconnected-dprintf on @itemx set disconnected-dprintf off @kindex set disconnected-dprintf Choose whether @code{dprintf} commands should continue to run if @value{GDBN} has disconnected from the target. This only applies if the @code{dprintf-style} is @code{agent}. @item show disconnected-dprintf off @kindex show disconnected-dprintf Show the current choice for disconnected @code{dprintf}. @end table @value{GDBN} does not check the validity of function and channel, relying on you to supply values that are meaningful for the contexts in which they are being used. For instance, the function and channel may be the values of local variables, but if that is the case, then all enabled dynamic prints must be at locations within the scope of those locals. If evaluation fails, @value{GDBN} will report an error. @node Save Breakpoints @subsection How to save breakpoints to a file To save breakpoint definitions to a file use the @w{@code{save breakpoints}} command. @table @code @kindex save breakpoints @cindex save breakpoints to a file for future sessions @item save breakpoints [@var{filename}] This command saves all current breakpoint definitions together with their commands and ignore counts, into a file @file{@var{filename}} suitable for use in a later debugging session. This includes all types of breakpoints (breakpoints, watchpoints, catchpoints, tracepoints). To read the saved breakpoint definitions, use the @code{source} command (@pxref{Command Files}). Note that watchpoints with expressions involving local variables may fail to be recreated because it may not be possible to access the context where the watchpoint is valid anymore. Because the saved breakpoint definitions are simply a sequence of @value{GDBN} commands that recreate the breakpoints, you can edit the file in your favorite editing program, and remove the breakpoint definitions you're not interested in, or that can no longer be recreated. @end table @node Static Probe Points @subsection Static Probe Points @cindex static probe point, SystemTap @cindex static probe point, DTrace @value{GDBN} supports @dfn{SDT} probes in the code. @acronym{SDT} stands for Statically Defined Tracing, and the probes are designed to have a tiny runtime code and data footprint, and no dynamic relocations. Currently, the following types of probes are supported on ELF-compatible systems: @itemize @bullet @item @code{SystemTap} (@uref{http://sourceware.org/systemtap/}) @acronym{SDT} probes@footnote{See @uref{http://sourceware.org/systemtap/wiki/AddingUserSpaceProbingToApps} for more information on how to add @code{SystemTap} @acronym{SDT} probes in your applications.}. @code{SystemTap} probes are usable from assembly, C and C@t{++} languages@footnote{See @uref{http://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation} for a good reference on how the @acronym{SDT} probes are implemented.}. @item @code{DTrace} (@uref{http://oss.oracle.com/projects/DTrace}) @acronym{USDT} probes. @code{DTrace} probes are usable from C and C@t{++} languages. @end itemize @cindex semaphores on static probe points Some @code{SystemTap} probes have an associated semaphore variable; for instance, this happens automatically if you defined your probe using a DTrace-style @file{.d} file. If your probe has a semaphore, @value{GDBN} will automatically enable it when you specify a breakpoint using the @samp{-probe-stap} notation. But, if you put a breakpoint at a probe's location by some other method (e.g., @code{break file:line}), then @value{GDBN} will not automatically set the semaphore. @code{DTrace} probes do not support semaphores. You can examine the available static static probes using @code{info probes}, with optional arguments: @table @code @kindex info probes @item info probes @r{[}@var{type}@r{]} @r{[}@var{provider} @r{[}@var{name} @r{[}@var{objfile}@r{]}@r{]}@r{]} If given, @var{type} is either @code{stap} for listing @code{SystemTap} probes or @code{dtrace} for listing @code{DTrace} probes. If omitted all probes are listed regardless of their types. If given, @var{provider} is a regular expression used to match against provider names when selecting which probes to list. If omitted, probes by all probes from all providers are listed. If given, @var{name} is a regular expression to match against probe names when selecting which probes to list. If omitted, probe names are not considered when deciding whether to display them. If given, @var{objfile} is a regular expression used to select which object files (executable or shared libraries) to examine. If not given, all object files are considered. @item info probes all List the available static probes, from all types. @end table @cindex enabling and disabling probes Some probe points can be enabled and/or disabled. The effect of enabling or disabling a probe depends on the type of probe being handled. Some @code{DTrace} probes can be enabled or disabled, but @code{SystemTap} probes cannot be disabled. You can enable (or disable) one or more probes using the following commands, with optional arguments: @table @code @kindex enable probes @item enable probes @r{[}@var{provider} @r{[}@var{name} @r{[}@var{objfile}@r{]}@r{]}@r{]} If given, @var{provider} is a regular expression used to match against provider names when selecting which probes to enable. If omitted, all probes from all providers are enabled. If given, @var{name} is a regular expression to match against probe names when selecting which probes to enable. If omitted, probe names are not considered when deciding whether to enable them. If given, @var{objfile} is a regular expression used to select which object files (executable or shared libraries) to examine. If not given, all object files are considered. @kindex disable probes @item disable probes @r{[}@var{provider} @r{[}@var{name} @r{[}@var{objfile}@r{]}@r{]}@r{]} See the @code{enable probes} command above for a description of the optional arguments accepted by this command. @end table @vindex $_probe_arg@r{, convenience variable} A probe may specify up to twelve arguments. These are available at the point at which the probe is defined---that is, when the current PC is at the probe's location. The arguments are available using the convenience variables (@pxref{Convenience Vars}) @code{$_probe_arg0}@dots{}@code{$_probe_arg11}. In @code{SystemTap} probes each probe argument is an integer of the appropriate size; types are not preserved. In @code{DTrace} probes types are preserved provided that they are recognized as such by @value{GDBN}; otherwise the value of the probe argument will be a long integer. The convenience variable @code{$_probe_argc} holds the number of arguments at the current probe point. These variables are always available, but attempts to access them at any location other than a probe point will cause @value{GDBN} to give an error message. @c @ifclear BARETARGET @node Error in Breakpoints @subsection ``Cannot insert breakpoints'' If you request too many active hardware-assisted breakpoints and watchpoints, you will see this error message: @c FIXME: the precise wording of this message may change; the relevant @c source change is not committed yet (Sep 3, 1999). @smallexample Stopped; cannot insert breakpoints. You may have requested too many hardware breakpoints and watchpoints. @end smallexample @noindent This message is printed when you attempt to resume the program, since only then @value{GDBN} knows exactly how many hardware breakpoints and watchpoints it needs to insert. When this message is printed, you need to disable or remove some of the hardware-assisted breakpoints and watchpoints, and then continue. @node Breakpoint-related Warnings @subsection ``Breakpoint address adjusted...'' @cindex breakpoint address adjusted Some processor architectures place constraints on the addresses at which breakpoints may be placed. For architectures thus constrained, @value{GDBN} will attempt to adjust the breakpoint's address to comply with the constraints dictated by the architecture. One example of such an architecture is the Fujitsu FR-V. The FR-V is a VLIW architecture in which a number of RISC-like instructions may be bundled together for parallel execution. The FR-V architecture constrains the location of a breakpoint instruction within such a bundle to the instruction with the lowest address. @value{GDBN} honors this constraint by adjusting a breakpoint's address to the first in the bundle. It is not uncommon for optimized code to have bundles which contain instructions from different source statements, thus it may happen that a breakpoint's address will be adjusted from one source statement to another. Since this adjustment may significantly alter @value{GDBN}'s breakpoint related behavior from what the user expects, a warning is printed when the breakpoint is first set and also when the breakpoint is hit. A warning like the one below is printed when setting a breakpoint that's been subject to address adjustment: @smallexample warning: Breakpoint address adjusted from 0x00010414 to 0x00010410. @end smallexample Such warnings are printed both for user settable and @value{GDBN}'s internal breakpoints. If you see one of these warnings, you should verify that a breakpoint set at the adjusted address will have the desired affect. If not, the breakpoint in question may be removed and other breakpoints may be set which will have the desired behavior. E.g., it may be sufficient to place the breakpoint at a later instruction. A conditional breakpoint may also be useful in some cases to prevent the breakpoint from triggering too often. @value{GDBN} will also issue a warning when stopping at one of these adjusted breakpoints: @smallexample warning: Breakpoint 1 address previously adjusted from 0x00010414 to 0x00010410. @end smallexample When this warning is encountered, it may be too late to take remedial action except in cases where the breakpoint is hit earlier or more frequently than expected. @node Continuing and Stepping @section Continuing and Stepping @cindex stepping @cindex continuing @cindex resuming execution @dfn{Continuing} means resuming program execution until your program completes normally. In contrast, @dfn{stepping} means executing just one more ``step'' of your program, where ``step'' may mean either one line of source code, or one machine instruction (depending on what particular command you use). Either when continuing or when stepping, your program may stop even sooner, due to a breakpoint or a signal. (If it stops due to a signal, you may want to use @code{handle}, or use @samp{signal 0} to resume execution (@pxref{Signals, ,Signals}), or you may step into the signal's handler (@pxref{stepping and signal handlers}).) @table @code @kindex continue @kindex c @r{(@code{continue})} @kindex fg @r{(resume foreground execution)} @item continue @r{[}@var{ignore-count}@r{]} @itemx c @r{[}@var{ignore-count}@r{]} @itemx fg @r{[}@var{ignore-count}@r{]} Resume program execution, at the address where your program last stopped; any breakpoints set at that address are bypassed. The optional argument @var{ignore-count} allows you to specify a further number of times to ignore a breakpoint at this location; its effect is like that of @code{ignore} (@pxref{Conditions, ,Break Conditions}). The argument @var{ignore-count} is meaningful only when your program stopped due to a breakpoint. At other times, the argument to @code{continue} is ignored. The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the debugged program is deemed to be the foreground program) are provided purely for convenience, and have exactly the same behavior as @code{continue}. @end table To resume execution at a different place, you can use @code{return} (@pxref{Returning, ,Returning from a Function}) to go back to the calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a Different Address}) to go to an arbitrary location in your program. A typical technique for using stepping is to set a breakpoint (@pxref{Breakpoints, ,Breakpoints; Watchpoints; and Catchpoints}) at the beginning of the function or the section of your program where a problem is believed to lie, run your program until it stops at that breakpoint, and then step through the suspect area, examining the variables that are interesting, until you see the problem happen. @table @code @kindex step @kindex s @r{(@code{step})} @item step Continue running your program until control reaches a different source line, then stop it and return control to @value{GDBN}. This command is abbreviated @code{s}. @quotation @c "without debugging information" is imprecise; actually "without line @c numbers in the debugging information". (gcc -g1 has debugging info but @c not line numbers). But it seems complex to try to make that @c distinction here. @emph{Warning:} If you use the @code{step} command while control is within a function that was compiled without debugging information, execution proceeds until control reaches a function that does have debugging information. Likewise, it will not step into a function which is compiled without debugging information. To step through functions without debugging information, use the @code{stepi} command, described below. @end quotation The @code{step} command only stops at the first instruction of a source line. This prevents the multiple stops that could otherwise occur in @code{switch} statements, @code{for} loops, etc. @code{step} continues to stop if a function that has debugging information is called within the line. In other words, @code{step} @emph{steps inside} any functions called within the line. Also, the @code{step} command only enters a function if there is line number information for the function. Otherwise it acts like the @code{next} command. This avoids problems when using @code{cc -gl} on @acronym{MIPS} machines. Previously, @code{step} entered subroutines if there was any debugging information about the routine. @item step @var{count} Continue running as in @code{step}, but do so @var{count} times. If a breakpoint is reached, or a signal not related to stepping occurs before @var{count} steps, stepping stops right away. @kindex next @kindex n @r{(@code{next})} @item next @r{[}@var{count}@r{]} Continue to the next source line in the current (innermost) stack frame. This is similar to @code{step}, but function calls that appear within the line of code are executed without stopping. Execution stops when control reaches a different line of code at the original stack level that was executing when you gave the @code{next} command. This command is abbreviated @code{n}. An argument @var{count} is a repeat count, as for @code{step}. @c FIX ME!! Do we delete this, or is there a way it fits in with @c the following paragraph? --- Vctoria @c @c @code{next} within a function that lacks debugging information acts like @c @code{step}, but any function calls appearing within the code of the @c function are executed without stopping. The @code{next} command only stops at the first instruction of a source line. This prevents multiple stops that could otherwise occur in @code{switch} statements, @code{for} loops, etc. @kindex set step-mode @item set step-mode @cindex functions without line info, and stepping @cindex stepping into functions with no line info @itemx set step-mode on The @code{set step-mode on} command causes the @code{step} command to stop at the first instruction of a function which contains no debug line information rather than stepping over it. This is useful in cases where you may be interested in inspecting the machine instructions of a function which has no symbolic info and do not want @value{GDBN} to automatically skip over this function. @item set step-mode off Causes the @code{step} command to step over any functions which contains no debug information. This is the default. @item show step-mode Show whether @value{GDBN} will stop in or step over functions without source line debug information. @kindex finish @kindex fin @r{(@code{finish})} @item finish Continue running until just after function in the selected stack frame returns. Print the returned value (if any). This command can be abbreviated as @code{fin}. Contrast this with the @code{return} command (@pxref{Returning, ,Returning from a Function}). @kindex set print finish @kindex show print finish @item set print finish @r{[}on|off@r{]} @itemx show print finish By default the @code{finish} command will show the value that is returned by the function. This can be disabled using @code{set print finish off}. When disabled, the value is still entered into the value history (@pxref{Value History}), but not displayed. @kindex until @kindex u @r{(@code{until})} @cindex run until specified location @item until @itemx u Continue running until a source line past the current line, in the current stack frame, is reached. This command is used to avoid single stepping through a loop more than once. It is like the @code{next} command, except that when @code{until} encounters a jump, it automatically continues execution until the program counter is greater than the address of the jump. This means that when you reach the end of a loop after single stepping though it, @code{until} makes your program continue execution until it exits the loop. In contrast, a @code{next} command at the end of a loop simply steps back to the beginning of the loop, which forces you to step through the next iteration. @code{until} always stops your program if it attempts to exit the current stack frame. @code{until} may produce somewhat counterintuitive results if the order of machine code does not match the order of the source lines. For example, in the following excerpt from a debugging session, the @code{f} (@code{frame}) command shows that execution is stopped at line @code{206}; yet when we use @code{until}, we get to line @code{195}: @smallexample (@value{GDBP}) f #0 main (argc=4, argv=0xf7fffae8) at m4.c:206 206 expand_input(); (@value{GDBP}) until 195 for ( ; argc > 0; NEXTARG) @{ @end smallexample This happened because, for execution efficiency, the compiler had generated code for the loop closure test at the end, rather than the start, of the loop---even though the test in a C @code{for}-loop is written before the body of the loop. The @code{until} command appeared to step back to the beginning of the loop when it advanced to this expression; however, it has not really gone to an earlier statement---not in terms of the actual machine code. @code{until} with no argument works by means of single instruction stepping, and hence is slower than @code{until} with an argument. @item until @var{location} @itemx u @var{location} Continue running your program until either the specified @var{location} is reached, or the current stack frame returns. The location is any of the forms described in @ref{Specify Location}. This form of the command uses temporary breakpoints, and hence is quicker than @code{until} without an argument. The specified location is actually reached only if it is in the current frame. This implies that @code{until} can be used to skip over recursive function invocations. For instance in the code below, if the current location is line @code{96}, issuing @code{until 99} will execute the program up to line @code{99} in the same invocation of factorial, i.e., after the inner invocations have returned. @smallexample 94 int factorial (int value) 95 @{ 96 if (value > 1) @{ 97 value *= factorial (value - 1); 98 @} 99 return (value); 100 @} @end smallexample @kindex advance @var{location} @item advance @var{location} Continue running the program up to the given @var{location}. An argument is required, which should be of one of the forms described in @ref{Specify Location}. Execution will also stop upon exit from the current stack frame. This command is similar to @code{until}, but @code{advance} will not skip over recursive function calls, and the target location doesn't have to be in the same frame as the current one. @kindex stepi @kindex si @r{(@code{stepi})} @item stepi @itemx stepi @var{arg} @itemx si Execute one machine instruction, then stop and return to the debugger. It is often useful to do @samp{display/i $pc} when stepping by machine instructions. This makes @value{GDBN} automatically display the next instruction to be executed, each time your program stops. @xref{Auto Display,, Automatic Display}. An argument is a repeat count, as in @code{step}. @need 750 @kindex nexti @kindex ni @r{(@code{nexti})} @item nexti @itemx nexti @var{arg} @itemx ni Execute one machine instruction, but if it is a function call, proceed until the function returns. An argument is a repeat count, as in @code{next}. @end table @anchor{range stepping} @cindex range stepping @cindex target-assisted range stepping By default, and if available, @value{GDBN} makes use of target-assisted @dfn{range stepping}. In other words, whenever you use a stepping command (e.g., @code{step}, @code{next}), @value{GDBN} tells the target to step the corresponding range of instruction addresses instead of issuing multiple single-steps. This speeds up line stepping, particularly for remote targets. Ideally, there should be no reason you would want to turn range stepping off. However, it's possible that a bug in the debug info, a bug in the remote stub (for remote targets), or even a bug in @value{GDBN} could make line stepping behave incorrectly when target-assisted range stepping is enabled. You can use the following command to turn off range stepping if necessary: @table @code @kindex set range-stepping @kindex show range-stepping @item set range-stepping @itemx show range-stepping Control whether range stepping is enabled. If @code{on}, and the target supports it, @value{GDBN} tells the target to step a range of addresses itself, instead of issuing multiple single-steps. If @code{off}, @value{GDBN} always issues single-steps, even if range stepping is supported by the target. The default is @code{on}. @end table @node Skipping Over Functions and Files @section Skipping Over Functions and Files @cindex skipping over functions and files The program you are debugging may contain some functions which are uninteresting to debug. The @code{skip} command lets you tell @value{GDBN} to skip a function, all functions in a file or a particular function in a particular file when stepping. For example, consider the following C function: @smallexample 101 int func() 102 @{ 103 foo(boring()); 104 bar(boring()); 105 @} @end smallexample @noindent Suppose you wish to step into the functions @code{foo} and @code{bar}, but you are not interested in stepping through @code{boring}. If you run @code{step} at line 103, you'll enter @code{boring()}, but if you run @code{next}, you'll step over both @code{foo} and @code{boring}! One solution is to @code{step} into @code{boring} and use the @code{finish} command to immediately exit it. But this can become tedious if @code{boring} is called from many places. A more flexible solution is to execute @kbd{skip boring}. This instructs @value{GDBN} never to step into @code{boring}. Now when you execute @code{step} at line 103, you'll step over @code{boring} and directly into @code{foo}. Functions may be skipped by providing either a function name, linespec (@pxref{Specify Location}), regular expression that matches the function's name, file name or a @code{glob}-style pattern that matches the file name. On Posix systems the form of the regular expression is ``Extended Regular Expressions''. See for example @samp{man 7 regex} on @sc{gnu}/Linux systems. On non-Posix systems the form of the regular expression is whatever is provided by the @code{regcomp} function of the underlying system. See for example @samp{man 7 glob} on @sc{gnu}/Linux systems for a description of @code{glob}-style patterns. @table @code @kindex skip @item skip @r{[}@var{options}@r{]} The basic form of the @code{skip} command takes zero or more options that specify what to skip. The @var{options} argument is any useful combination of the following: @table @code @item -file @var{file} @itemx -fi @var{file} Functions in @var{file} will be skipped over when stepping. @item -gfile @var{file-glob-pattern} @itemx -gfi @var{file-glob-pattern} @cindex skipping over files via glob-style patterns Functions in files matching @var{file-glob-pattern} will be skipped over when stepping. @smallexample (gdb) skip -gfi utils/*.c @end smallexample @item -function @var{linespec} @itemx -fu @var{linespec} Functions named by @var{linespec} or the function containing the line named by @var{linespec} will be skipped over when stepping. @xref{Specify Location}. @item -rfunction @var{regexp} @itemx -rfu @var{regexp} @cindex skipping over functions via regular expressions Functions whose name matches @var{regexp} will be skipped over when stepping. This form is useful for complex function names. For example, there is generally no need to step into C@t{++} @code{std::string} constructors or destructors. Plus with C@t{++} templates it can be hard to write out the full name of the function, and often it doesn't matter what the template arguments are. Specifying the function to be skipped as a regular expression makes this easier. @smallexample (gdb) skip -rfu ^std::(allocator|basic_string)<.*>::~?\1 *\( @end smallexample If you want to skip every templated C@t{++} constructor and destructor in the @code{std} namespace you can do: @smallexample (gdb) skip -rfu ^std::([a-zA-z0-9_]+)<.*>::~?\1 *\( @end smallexample @end table If no options are specified, the function you're currently debugging will be skipped. @kindex skip function @item skip function @r{[}@var{linespec}@r{]} After running this command, the function named by @var{linespec} or the function containing the line named by @var{linespec} will be skipped over when stepping. @xref{Specify Location}. If you do not specify @var{linespec}, the function you're currently debugging will be skipped. (If you have a function called @code{file} that you want to skip, use @kbd{skip function file}.) @kindex skip file @item skip file @r{[}@var{filename}@r{]} After running this command, any function whose source lives in @var{filename} will be skipped over when stepping. @smallexample (gdb) skip file boring.c File boring.c will be skipped when stepping. @end smallexample If you do not specify @var{filename}, functions whose source lives in the file you're currently debugging will be skipped. @end table Skips can be listed, deleted, disabled, and enabled, much like breakpoints. These are the commands for managing your list of skips: @table @code @kindex info skip @item info skip @r{[}@var{range}@r{]} Print details about the specified skip(s). If @var{range} is not specified, print a table with details about all functions and files marked for skipping. @code{info skip} prints the following information about each skip: @table @emph @item Identifier A number identifying this skip. @item Enabled or Disabled Enabled skips are marked with @samp{y}. Disabled skips are marked with @samp{n}. @item Glob If the file name is a @samp{glob} pattern this is @samp{y}. Otherwise it is @samp{n}. @item File The name or @samp{glob} pattern of the file to be skipped. If no file is specified this is @samp{<none>}. @item RE If the function name is a @samp{regular expression} this is @samp{y}. Otherwise it is @samp{n}. @item Function The name or regular expression of the function to skip. If no function is specified this is @samp{<none>}. @end table @kindex skip delete @item skip delete @r{[}@var{range}@r{]} Delete the specified skip(s). If @var{range} is not specified, delete all skips. @kindex skip enable @item skip enable @r{[}@var{range}@r{]} Enable the specified skip(s). If @var{range} is not specified, enable all skips. @kindex skip disable @item skip disable @r{[}@var{range}@r{]} Disable the specified skip(s). If @var{range} is not specified, disable all skips. @kindex set debug skip @item set debug skip @r{[}on|off@r{]} Set whether to print the debug output about skipping files and functions. @kindex show debug skip @item show debug skip Show whether the debug output about skipping files and functions is printed. @end table @node Signals @section Signals @cindex signals A signal is an asynchronous event that can happen in a program. The operating system defines the possible kinds of signals, and gives each kind a name and a number. For example, in Unix @code{SIGINT} is the signal a program gets when you type an interrupt character (often @kbd{Ctrl-c}); @code{SIGSEGV} is the signal a program gets from referencing a place in memory far away from all the areas in use; @code{SIGALRM} occurs when the alarm clock timer goes off (which happens only if your program has requested an alarm). @cindex fatal signals Some signals, including @code{SIGALRM}, are a normal part of the functioning of your program. Others, such as @code{SIGSEGV}, indicate errors; these signals are @dfn{fatal} (they kill your program immediately) if the program has not specified in advance some other way to handle the signal. @code{SIGINT} does not indicate an error in your program, but it is normally fatal so it can carry out the purpose of the interrupt: to kill the program. @value{GDBN} has the ability to detect any occurrence of a signal in your program. You can tell @value{GDBN} in advance what to do for each kind of signal. @cindex handling signals Normally, @value{GDBN} is set up to let the non-erroneous signals like @code{SIGALRM} be silently passed to your program (so as not to interfere with their role in the program's functioning) but to stop your program immediately whenever an error signal happens. You can change these settings with the @code{handle} command. @table @code @kindex info signals @kindex info handle @item info signals @itemx info handle Print a table of all the kinds of signals and how @value{GDBN} has been told to handle each one. You can use this to see the signal numbers of all the defined types of signals. @item info signals @var{sig} Similar, but print information only about the specified signal number. @code{info handle} is an alias for @code{info signals}. @item catch signal @r{[}@var{signal}@dots{} @r{|} @samp{all}@r{]} Set a catchpoint for the indicated signals. @xref{Set Catchpoints}, for details about this command. @kindex handle @item handle @var{signal} @r{[}@var{keywords}@dots{}@r{]} Change the way @value{GDBN} handles signal @var{signal}. The @var{signal} can be the number of a signal or its name (with or without the @samp{SIG} at the beginning); a list of signal numbers of the form @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the known signals. Optional arguments @var{keywords}, described below, say what change to make. @end table @c @group The keywords allowed by the @code{handle} command can be abbreviated. Their full names are: @table @code @item nostop @value{GDBN} should not stop your program when this signal happens. It may still print a message telling you that the signal has come in. @item stop @value{GDBN} should stop your program when this signal happens. This implies the @code{print} keyword as well. @item print @value{GDBN} should print a message when this signal happens. @item noprint @value{GDBN} should not mention the occurrence of the signal at all. This implies the @code{nostop} keyword as well. @item pass @itemx noignore @value{GDBN} should allow your program to see this signal; your program can handle the signal, or else it may terminate if the signal is fatal and not handled. @code{pass} and @code{noignore} are synonyms. @item nopass @itemx ignore @value{GDBN} should not allow your program to see this signal. @code{nopass} and @code{ignore} are synonyms. @end table @c @end group When a signal stops your program, the signal is not visible to the program until you continue. Your program sees the signal then, if @code{pass} is in effect for the signal in question @emph{at that time}. In other words, after @value{GDBN} reports a signal, you can use the @code{handle} command with @code{pass} or @code{nopass} to control whether your program sees that signal when you continue. The default is set to @code{nostop}, @code{noprint}, @code{pass} for non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the erroneous signals. You can also use the @code{signal} command to prevent your program from seeing a signal, or cause it to see a signal it normally would not see, or to give it any signal at any time. For example, if your program stopped due to some sort of memory reference error, you might store correct values into the erroneous variables and continue, hoping to see more execution; but your program would probably terminate immediately as a result of the fatal signal once it saw the signal. To prevent this, you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your Program a Signal}. @cindex stepping and signal handlers @anchor{stepping and signal handlers} @value{GDBN} optimizes for stepping the mainline code. If a signal that has @code{handle nostop} and @code{handle pass} set arrives while a stepping command (e.g., @code{stepi}, @code{step}, @code{next}) is in progress, @value{GDBN} lets the signal handler run and then resumes stepping the mainline code once the signal handler returns. In other words, @value{GDBN} steps over the signal handler. This prevents signals that you've specified as not interesting (with @code{handle nostop}) from changing the focus of debugging unexpectedly. Note that the signal handler itself may still hit a breakpoint, stop for another signal that has @code{handle stop} in effect, or for any other event that normally results in stopping the stepping command sooner. Also note that @value{GDBN} still informs you that the program received a signal if @code{handle print} is set. @anchor{stepping into signal handlers} If you set @code{handle pass} for a signal, and your program sets up a handler for it, then issuing a stepping command, such as @code{step} or @code{stepi}, when your program is stopped due to the signal will step @emph{into} the signal handler (if the target supports that). Likewise, if you use the @code{queue-signal} command to queue a signal to be delivered to the current thread when execution of the thread resumes (@pxref{Signaling, ,Giving your Program a Signal}), then a stepping command will step into the signal handler. Here's an example, using @code{stepi} to step to the first instruction of @code{SIGUSR1}'s handler: @smallexample (@value{GDBP}) handle SIGUSR1 Signal Stop Print Pass to program Description SIGUSR1 Yes Yes Yes User defined signal 1 (@value{GDBP}) c Continuing. Program received signal SIGUSR1, User defined signal 1. main () sigusr1.c:28 28 p = 0; (@value{GDBP}) si sigusr1_handler () at sigusr1.c:9 9 @{ @end smallexample The same, but using @code{queue-signal} instead of waiting for the program to receive the signal first: @smallexample (@value{GDBP}) n 28 p = 0; (@value{GDBP}) queue-signal SIGUSR1 (@value{GDBP}) si sigusr1_handler () at sigusr1.c:9 9 @{ (@value{GDBP}) @end smallexample @cindex extra signal information @anchor{extra signal information} On some targets, @value{GDBN} can inspect extra signal information associated with the intercepted signal, before it is actually delivered to the program being debugged. This information is exported by the convenience variable @code{$_siginfo}, and consists of data that is passed by the kernel to the signal handler at the time of the receipt of a signal. The data type of the information itself is target dependent. You can see the data type using the @code{ptype $_siginfo} command. On Unix systems, it typically corresponds to the standard @code{siginfo_t} type, as defined in the @file{signal.h} system header. Here's an example, on a @sc{gnu}/Linux system, printing the stray referenced address that raised a segmentation fault. @smallexample @group (@value{GDBP}) continue Program received signal SIGSEGV, Segmentation fault. 0x0000000000400766 in main () 69 *(int *)p = 0; (@value{GDBP}) ptype $_siginfo type = struct @{ int si_signo; int si_errno; int si_code; union @{ int _pad[28]; struct @{...@} _kill; struct @{...@} _timer; struct @{...@} _rt; struct @{...@} _sigchld; struct @{...@} _sigfault; struct @{...@} _sigpoll; @} _sifields; @} (@value{GDBP}) ptype $_siginfo._sifields._sigfault type = struct @{ void *si_addr; @} (@value{GDBP}) p $_siginfo._sifields._sigfault.si_addr $1 = (void *) 0x7ffff7ff7000 @end group @end smallexample Depending on target support, @code{$_siginfo} may also be writable. @cindex Intel MPX boundary violations @cindex boundary violations, Intel MPX On some targets, a @code{SIGSEGV} can be caused by a boundary violation, i.e., accessing an address outside of the allowed range. In those cases @value{GDBN} may displays additional information, depending on how @value{GDBN} has been told to handle the signal. With @code{handle stop SIGSEGV}, @value{GDBN} displays the violation kind: "Upper" or "Lower", the memory address accessed and the bounds, while with @code{handle nostop SIGSEGV} no additional information is displayed. The usual output of a segfault is: @smallexample Program received signal SIGSEGV, Segmentation fault 0x0000000000400d7c in upper () at i386-mpx-sigsegv.c:68 68 value = *(p + len); @end smallexample While a bound violation is presented as: @smallexample Program received signal SIGSEGV, Segmentation fault Upper bound violation while accessing address 0x7fffffffc3b3 Bounds: [lower = 0x7fffffffc390, upper = 0x7fffffffc3a3] 0x0000000000400d7c in upper () at i386-mpx-sigsegv.c:68 68 value = *(p + len); @end smallexample @node Thread Stops @section Stopping and Starting Multi-thread Programs @cindex stopped threads @cindex threads, stopped @cindex continuing threads @cindex threads, continuing @value{GDBN} supports debugging programs with multiple threads (@pxref{Threads,, Debugging Programs with Multiple Threads}). There are two modes of controlling execution of your program within the debugger. In the default mode, referred to as @dfn{all-stop mode}, when any thread in your program stops (for example, at a breakpoint or while being stepped), all other threads in the program are also stopped by @value{GDBN}. On some targets, @value{GDBN} also supports @dfn{non-stop mode}, in which other threads can continue to run freely while you examine the stopped thread in the debugger. @menu * All-Stop Mode:: All threads stop when GDB takes control * Non-Stop Mode:: Other threads continue to execute * Background Execution:: Running your program asynchronously * Thread-Specific Breakpoints:: Controlling breakpoints * Interrupted System Calls:: GDB may interfere with system calls * Observer Mode:: GDB does not alter program behavior @end menu @node All-Stop Mode @subsection All-Stop Mode @cindex all-stop mode In all-stop mode, whenever your program stops under @value{GDBN} for any reason, @emph{all} threads of execution stop, not just the current thread. This allows you to examine the overall state of the program, including switching between threads, without worrying that things may change underfoot. Conversely, whenever you restart the program, @emph{all} threads start executing. @emph{This is true even when single-stepping} with commands like @code{step} or @code{next}. In particular, @value{GDBN} cannot single-step all threads in lockstep. Since thread scheduling is up to your debugging target's operating system (not controlled by @value{GDBN}), other threads may execute more than one statement while the current thread completes a single step. Moreover, in general other threads stop in the middle of a statement, rather than at a clean statement boundary, when the program stops. You might even find your program stopped in another thread after continuing or even single-stepping. This happens whenever some other thread runs into a breakpoint, a signal, or an exception before the first thread completes whatever you requested. @cindex automatic thread selection @cindex switching threads automatically @cindex threads, automatic switching Whenever @value{GDBN} stops your program, due to a breakpoint or a signal, it automatically selects the thread where that breakpoint or signal happened. @value{GDBN} alerts you to the context switch with a message such as @samp{[Switching to Thread @var{n}]} to identify the thread. On some OSes, you can modify @value{GDBN}'s default behavior by locking the OS scheduler to allow only a single thread to run. @table @code @item set scheduler-locking @var{mode} @cindex scheduler locking mode @cindex lock scheduler Set the scheduler locking mode. It applies to normal execution, record mode, and replay mode. If it is @code{off}, then there is no locking and any thread may run at any time. If @code{on}, then only the current thread may run when the inferior is resumed. The @code{step} mode optimizes for single-stepping; it prevents other threads from preempting the current thread while you are stepping, so that the focus of debugging does not change unexpectedly. Other threads never get a chance to run when you step, and they are completely free to run when you use commands like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another thread hits a breakpoint during its timeslice, @value{GDBN} does not change the current thread away from the thread that you are debugging. The @code{replay} mode behaves like @code{off} in record mode and like @code{on} in replay mode. @item show scheduler-locking Display the current scheduler locking mode. @end table @cindex resume threads of multiple processes simultaneously By default, when you issue one of the execution commands such as @code{continue}, @code{next} or @code{step}, @value{GDBN} allows only threads of the current inferior to run. For example, if @value{GDBN} is attached to two inferiors, each with two threads, the @code{continue} command resumes only the two threads of the current inferior. This is useful, for example, when you debug a program that forks and you want to hold the parent stopped (so that, for instance, it doesn't run to exit), while you debug the child. In other situations, you may not be interested in inspecting the current state of any of the processes @value{GDBN} is attached to, and you may want to resume them all until some breakpoint is hit. In the latter case, you can instruct @value{GDBN} to allow all threads of all the inferiors to run with the @w{@code{set schedule-multiple}} command. @table @code @kindex set schedule-multiple @item set schedule-multiple Set the mode for allowing threads of multiple processes to be resumed when an execution command is issued. When @code{on}, all threads of all processes are allowed to run. When @code{off}, only the threads of the current process are resumed. The default is @code{off}. The @code{scheduler-locking} mode takes precedence when set to @code{on}, or while you are stepping and set to @code{step}. @item show schedule-multiple Display the current mode for resuming the execution of threads of multiple processes. @end table @node Non-Stop Mode @subsection Non-Stop Mode @cindex non-stop mode @c This section is really only a place-holder, and needs to be expanded @c with more details. For some multi-threaded targets, @value{GDBN} supports an optional mode of operation in which you can examine stopped program threads in the debugger while other threads continue to execute freely. This minimizes intrusion when debugging live systems, such as programs where some threads have real-time constraints or must continue to respond to external events. This is referred to as @dfn{non-stop} mode. In non-stop mode, when a thread stops to report a debugging event, @emph{only} that thread is stopped; @value{GDBN} does not stop other threads as well, in contrast to the all-stop mode behavior. Additionally, execution commands such as @code{continue} and @code{step} apply by default only to the current thread in non-stop mode, rather than all threads as in all-stop mode. This allows you to control threads explicitly in ways that are not possible in all-stop mode --- for example, stepping one thread while allowing others to run freely, stepping one thread while holding all others stopped, or stepping several threads independently and simultaneously. To enter non-stop mode, use this sequence of commands before you run or attach to your program: @smallexample # If using the CLI, pagination breaks non-stop. set pagination off # Finally, turn it on! set non-stop on @end smallexample You can use these commands to manipulate the non-stop mode setting: @table @code @kindex set non-stop @item set non-stop on Enable selection of non-stop mode. @item set non-stop off Disable selection of non-stop mode. @kindex show non-stop @item show non-stop Show the current non-stop enablement setting. @end table Note these commands only reflect whether non-stop mode is enabled, not whether the currently-executing program is being run in non-stop mode. In particular, the @code{set non-stop} preference is only consulted when @value{GDBN} starts or connects to the target program, and it is generally not possible to switch modes once debugging has started. Furthermore, since not all targets support non-stop mode, even when you have enabled non-stop mode, @value{GDBN} may still fall back to all-stop operation by default. In non-stop mode, all execution commands apply only to the current thread by default. That is, @code{continue} only continues one thread. To continue all threads, issue @code{continue -a} or @code{c -a}. You can use @value{GDBN}'s background execution commands (@pxref{Background Execution}) to run some threads in the background while you continue to examine or step others from @value{GDBN}. The MI execution commands (@pxref{GDB/MI Program Execution}) are always executed asynchronously in non-stop mode. Suspending execution is done with the @code{interrupt} command when running in the background, or @kbd{Ctrl-c} during foreground execution. In all-stop mode, this stops the whole process; but in non-stop mode the interrupt applies only to the current thread. To stop the whole program, use @code{interrupt -a}. Other execution commands do not currently support the @code{-a} option. In non-stop mode, when a thread stops, @value{GDBN} doesn't automatically make that thread current, as it does in all-stop mode. This is because the thread stop notifications are asynchronous with respect to @value{GDBN}'s command interpreter, and it would be confusing if @value{GDBN} unexpectedly changed to a different thread just as you entered a command to operate on the previously current thread. @node Background Execution @subsection Background Execution @cindex foreground execution @cindex background execution @cindex asynchronous execution @cindex execution, foreground, background and asynchronous @value{GDBN}'s execution commands have two variants: the normal foreground (synchronous) behavior, and a background (asynchronous) behavior. In foreground execution, @value{GDBN} waits for the program to report that some thread has stopped before prompting for another command. In background execution, @value{GDBN} immediately gives a command prompt so that you can issue other commands while your program runs. If the target doesn't support async mode, @value{GDBN} issues an error message if you attempt to use the background execution commands. @cindex @code{&}, background execution of commands To specify background execution, add a @code{&} to the command. For example, the background form of the @code{continue} command is @code{continue&}, or just @code{c&}. The execution commands that accept background execution are: @table @code @kindex run& @item run @xref{Starting, , Starting your Program}. @item attach @kindex attach& @xref{Attach, , Debugging an Already-running Process}. @item step @kindex step& @xref{Continuing and Stepping, step}. @item stepi @kindex stepi& @xref{Continuing and Stepping, stepi}. @item next @kindex next& @xref{Continuing and Stepping, next}. @item nexti @kindex nexti& @xref{Continuing and Stepping, nexti}. @item continue @kindex continue& @xref{Continuing and Stepping, continue}. @item finish @kindex finish& @xref{Continuing and Stepping, finish}. @item until @kindex until& @xref{Continuing and Stepping, until}. @end table Background execution is especially useful in conjunction with non-stop mode for debugging programs with multiple threads; see @ref{Non-Stop Mode}. However, you can also use these commands in the normal all-stop mode with the restriction that you cannot issue another execution command until the previous one finishes. Examples of commands that are valid in all-stop mode while the program is running include @code{help} and @code{info break}. You can interrupt your program while it is running in the background by using the @code{interrupt} command. @table @code @kindex interrupt @item interrupt @itemx interrupt -a Suspend execution of the running program. In all-stop mode, @code{interrupt} stops the whole process, but in non-stop mode, it stops only the current thread. To stop the whole program in non-stop mode, use @code{interrupt -a}. @end table @node Thread-Specific Breakpoints @subsection Thread-Specific Breakpoints When your program has multiple threads (@pxref{Threads,, Debugging Programs with Multiple Threads}), you can choose whether to set breakpoints on all threads, or on a particular thread. @table @code @cindex breakpoints and threads @cindex thread breakpoints @kindex break @dots{} thread @var{thread-id} @item break @var{location} thread @var{thread-id} @itemx break @var{location} thread @var{thread-id} if @dots{} @var{location} specifies source lines; there are several ways of writing them (@pxref{Specify Location}), but the effect is always to specify some source line. Use the qualifier @samp{thread @var{thread-id}} with a breakpoint command to specify that you only want @value{GDBN} to stop the program when a particular thread reaches this breakpoint. The @var{thread-id} specifier is one of the thread identifiers assigned by @value{GDBN}, shown in the first column of the @samp{info threads} display. If you do not specify @samp{thread @var{thread-id}} when you set a breakpoint, the breakpoint applies to @emph{all} threads of your program. You can use the @code{thread} qualifier on conditional breakpoints as well; in this case, place @samp{thread @var{thread-id}} before or after the breakpoint condition, like this: @smallexample (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim @end smallexample @end table Thread-specific breakpoints are automatically deleted when @value{GDBN} detects the corresponding thread is no longer in the thread list. For example: @smallexample (@value{GDBP}) c Thread-specific breakpoint 3 deleted - thread 28 no longer in the thread list. @end smallexample There are several ways for a thread to disappear, such as a regular thread exit, but also when you detach from the process with the @code{detach} command (@pxref{Attach, ,Debugging an Already-running Process}), or if @value{GDBN} loses the remote connection (@pxref{Remote Debugging}), etc. Note that with some targets, @value{GDBN} is only able to detect a thread has exited when the user explictly asks for the thread list with the @code{info threads} command. @node Interrupted System Calls @subsection Interrupted System Calls @cindex thread breakpoints and system calls @cindex system calls and thread breakpoints @cindex premature return from system calls There is an unfortunate side effect when using @value{GDBN} to debug multi-threaded programs. If one thread stops for a breakpoint, or for some other reason, and another thread is blocked in a system call, then the system call may return prematurely. This is a consequence of the interaction between multiple threads and the signals that @value{GDBN} uses to implement breakpoints and other events that stop execution. To handle this problem, your program should check the return value of each system call and react appropriately. This is good programming style anyways. For example, do not write code like this: @smallexample sleep (10); @end smallexample The call to @code{sleep} will return early if a different thread stops at a breakpoint or for some other reason. Instead, write this: @smallexample int unslept = 10; while (unslept > 0) unslept = sleep (unslept); @end smallexample A system call is allowed to return early, so the system is still conforming to its specification. But @value{GDBN} does cause your multi-threaded program to behave differently than it would without @value{GDBN}. Also, @value{GDBN} uses internal breakpoints in the thread library to monitor certain events such as thread creation and thread destruction. When such an event happens, a system call in another thread may return prematurely, even though your program does not appear to stop. @node Observer Mode @subsection Observer Mode If you want to build on non-stop mode and observe program behavior without any chance of disruption by @value{GDBN}, you can set variables to disable all of the debugger's attempts to modify state, whether by writing memory, inserting breakpoints, etc. These operate at a low level, intercepting operations from all commands. When all of these are set to @code{off}, then @value{GDBN} is said to be @dfn{observer mode}. As a convenience, the variable @code{observer} can be set to disable these, plus enable non-stop mode. Note that @value{GDBN} will not prevent you from making nonsensical combinations of these settings. For instance, if you have enabled @code{may-insert-breakpoints} but disabled @code{may-write-memory}, then breakpoints that work by writing trap instructions into the code stream will still not be able to be placed. @table @code @kindex observer @item set observer on @itemx set observer off When set to @code{on}, this disables all the permission variables below (except for @code{insert-fast-tracepoints}), plus enables non-stop debugging. Setting this to @code{off} switches back to normal debugging, though remaining in non-stop mode. @item show observer Show whether observer mode is on or off. @kindex may-write-registers @item set may-write-registers on @itemx set may-write-registers off This controls whether @value{GDBN} will attempt to alter the values of registers, such as with assignment expressions in @code{print}, or the @code{jump} command. It defaults to @code{on}. @item show may-write-registers Show the current permission to write registers. @kindex may-write-memory @item set may-write-memory on @itemx set may-write-memory off This controls whether @value{GDBN} will attempt to alter the contents of memory, such as with assignment expressions in @code{print}. It defaults to @code{on}. @item show may-write-memory Show the current permission to write memory. @kindex may-insert-breakpoints @item set may-insert-breakpoints on @itemx set may-insert-breakpoints off This controls whether @value{GDBN} will attempt to insert breakpoints. This affects all breakpoints, including internal breakpoints defined by @value{GDBN}. It defaults to @code{on}. @item show may-insert-breakpoints Show the current permission to insert breakpoints. @kindex may-insert-tracepoints @item set may-insert-tracepoints on @itemx set may-insert-tracepoints off This controls whether @value{GDBN} will attempt to insert (regular) tracepoints at the beginning of a tracing experiment. It affects only non-fast tracepoints, fast tracepoints being under the control of @code{may-insert-fast-tracepoints}. It defaults to @code{on}. @item show may-insert-tracepoints Show the current permission to insert tracepoints. @kindex may-insert-fast-tracepoints @item set may-insert-fast-tracepoints on @itemx set may-insert-fast-tracepoints off This controls whether @value{GDBN} will attempt to insert fast tracepoints at the beginning of a tracing experiment. It affects only fast tracepoints, regular (non-fast) tracepoints being under the control of @code{may-insert-tracepoints}. It defaults to @code{on}. @item show may-insert-fast-tracepoints Show the current permission to insert fast tracepoints. @kindex may-interrupt @item set may-interrupt on @itemx set may-interrupt off This controls whether @value{GDBN} will attempt to interrupt or stop program execution. When this variable is @code{off}, the @code{interrupt} command will have no effect, nor will @kbd{Ctrl-c}. It defaults to @code{on}. @item show may-interrupt Show the current permission to interrupt or stop the program. @end table @node Reverse Execution @chapter Running programs backward @cindex reverse execution @cindex running programs backward When you are debugging a program, it is not unusual to realize that you have gone too far, and some event of interest has already happened. If the target environment supports it, @value{GDBN} can allow you to ``rewind'' the program by running it backward. A target environment that supports reverse execution should be able to ``undo'' the changes in machine state that have taken place as the program was executing normally. Variables, registers etc.@: should revert to their previous values. Obviously this requires a great deal of sophistication on the part of the target environment; not all target environments can support reverse execution. When a program is executed in reverse, the instructions that have most recently been executed are ``un-executed'', in reverse order. The program counter runs backward, following the previous thread of execution in reverse. As each instruction is ``un-executed'', the values of memory and/or registers that were changed by that instruction are reverted to their previous states. After executing a piece of source code in reverse, all side effects of that code should be ``undone'', and all variables should be returned to their prior values@footnote{ Note that some side effects are easier to undo than others. For instance, memory and registers are relatively easy, but device I/O is hard. Some targets may be able undo things like device I/O, and some may not. The contract between @value{GDBN} and the reverse executing target requires only that the target do something reasonable when @value{GDBN} tells it to execute backwards, and then report the results back to @value{GDBN}. Whatever the target reports back to @value{GDBN}, @value{GDBN} will report back to the user. @value{GDBN} assumes that the memory and registers that the target reports are in a consistent state, but @value{GDBN} accepts whatever it is given. }. On some platforms, @value{GDBN} has built-in support for reverse execution, activated with the @code{record} or @code{record btrace} commands. @xref{Process Record and Replay}. Some remote targets, typically full system emulators, support reverse execution directly without requiring any special command. If you are debugging in a target environment that supports reverse execution, @value{GDBN} provides the following commands. @table @code @kindex reverse-continue @kindex rc @r{(@code{reverse-continue})} @item reverse-continue @r{[}@var{ignore-count}@r{]} @itemx rc @r{[}@var{ignore-count}@r{]} Beginning at the point where your program last stopped, start executing in reverse. Reverse execution will stop for breakpoints and synchronous exceptions (signals), just like normal execution. Behavior of asynchronous signals depends on the target environment. @kindex reverse-step @kindex rs @r{(@code{step})} @item reverse-step @r{[}@var{count}@r{]} Run the program backward until control reaches the start of a different source line; then stop it, and return control to @value{GDBN}. Like the @code{step} command, @code{reverse-step} will only stop at the beginning of a source line. It ``un-executes'' the previously executed source line. If the previous source line included calls to debuggable functions, @code{reverse-step} will step (backward) into the called function, stopping at the beginning of the @emph{last} statement in the called function (typically a return statement). Also, as with the @code{step} command, if non-debuggable functions are called, @code{reverse-step} will run thru them backward without stopping. @kindex reverse-stepi @kindex rsi @r{(@code{reverse-stepi})} @item reverse-stepi @r{[}@var{count}@r{]} Reverse-execute one machine instruction. Note that the instruction to be reverse-executed is @emph{not} the one pointed to by the program counter, but the instruction executed prior to that one. For instance, if the last instruction was a jump, @code{reverse-stepi} will take you back from the destination of the jump to the jump instruction itself. @kindex reverse-next @kindex rn @r{(@code{reverse-next})} @item reverse-next @r{[}@var{count}@r{]} Run backward to the beginning of the previous line executed in the current (innermost) stack frame. If the line contains function calls, they will be ``un-executed'' without stopping. Starting from the first line of a function, @code{reverse-next} will take you back to the caller of that function, @emph{before} the function was called, just as the normal @code{next} command would take you from the last line of a function back to its return to its caller @footnote{Unless the code is too heavily optimized.}. @kindex reverse-nexti @kindex rni @r{(@code{reverse-nexti})} @item reverse-nexti @r{[}@var{count}@r{]} Like @code{nexti}, @code{reverse-nexti} executes a single instruction in reverse, except that called functions are ``un-executed'' atomically. That is, if the previously executed instruction was a return from another function, @code{reverse-nexti} will continue to execute in reverse until the call to that function (from the current stack frame) is reached. @kindex reverse-finish @item reverse-finish Just as the @code{finish} command takes you to the point where the current function returns, @code{reverse-finish} takes you to the point where it was called. Instead of ending up at the end of the current function invocation, you end up at the beginning. @kindex set exec-direction @item set exec-direction Set the direction of target execution. @item set exec-direction reverse @cindex execute forward or backward in time @value{GDBN} will perform all execution commands in reverse, until the exec-direction mode is changed to ``forward''. Affected commands include @code{step, stepi, next, nexti, continue, and finish}. The @code{return} command cannot be used in reverse mode. @item set exec-direction forward @value{GDBN} will perform all execution commands in the normal fashion. This is the default. @end table @node Process Record and Replay @chapter Recording Inferior's Execution and Replaying It @cindex process record and replay @cindex recording inferior's execution and replaying it On some platforms, @value{GDBN} provides a special @dfn{process record and replay} target that can record a log of the process execution, and replay it later with both forward and reverse execution commands. @cindex replay mode When this target is in use, if the execution log includes the record for the next instruction, @value{GDBN} will debug in @dfn{replay mode}. In the replay mode, the inferior does not really execute code instructions. Instead, all the events that normally happen during code execution are taken from the execution log. While code is not really executed in replay mode, the values of registers (including the program counter register) and the memory of the inferior are still changed as they normally would. Their contents are taken from the execution log. @cindex record mode If the record for the next instruction is not in the execution log, @value{GDBN} will debug in @dfn{record mode}. In this mode, the inferior executes normally, and @value{GDBN} records the execution log for future replay. The process record and replay target supports reverse execution (@pxref{Reverse Execution}), even if the platform on which the inferior runs does not. However, the reverse execution is limited in this case by the range of the instructions recorded in the execution log. In other words, reverse execution on platforms that don't support it directly can only be done in the replay mode. When debugging in the reverse direction, @value{GDBN} will work in replay mode as long as the execution log includes the record for the previous instruction; otherwise, it will work in record mode, if the platform supports reverse execution, or stop if not. Currently, process record and replay is supported on ARM, Aarch64, Moxie, PowerPC, PowerPC64, S/390, and x86 (i386/amd64) running GNU/Linux. Process record and replay can be used both when native debugging, and when remote debugging via @code{gdbserver}. For architecture environments that support process record and replay, @value{GDBN} provides the following commands: @table @code @kindex target record @kindex target record-full @kindex target record-btrace @kindex record @kindex record full @kindex record btrace @kindex record btrace bts @kindex record btrace pt @kindex record bts @kindex record pt @kindex rec @kindex rec full @kindex rec btrace @kindex rec btrace bts @kindex rec btrace pt @kindex rec bts @kindex rec pt @item record @var{method} This command starts the process record and replay target. The recording method can be specified as parameter. Without a parameter the command uses the @code{full} recording method. The following recording methods are available: @table @code @item full Full record/replay recording using @value{GDBN}'s software record and replay implementation. This method allows replaying and reverse execution. @item btrace @var{format} Hardware-supported instruction recording, supported on Intel processors. This method does not record data. Further, the data is collected in a ring buffer so old data will be overwritten when the buffer is full. It allows limited reverse execution. Variables and registers are not available during reverse execution. In remote debugging, recording continues on disconnect. Recorded data can be inspected after reconnecting. The recording may be stopped using @code{record stop}. The recording format can be specified as parameter. Without a parameter the command chooses the recording format. The following recording formats are available: @table @code @item bts @cindex branch trace store Use the @dfn{Branch Trace Store} (@acronym{BTS}) recording format. In this format, the processor stores a from/to record for each executed branch in the btrace ring buffer. @item pt @cindex Intel Processor Trace Use the @dfn{Intel Processor Trace} recording format. In this format, the processor stores the execution trace in a compressed form that is afterwards decoded by @value{GDBN}. The trace can be recorded with very low overhead. The compressed trace format also allows small trace buffers to already contain a big number of instructions compared to @acronym{BTS}. Decoding the recorded execution trace, on the other hand, is more expensive than decoding @acronym{BTS} trace. This is mostly due to the increased number of instructions to process. You should increase the buffer-size with care. @end table Not all recording formats may be available on all processors. @end table The process record and replay target can only debug a process that is already running. Therefore, you need first to start the process with the @kbd{run} or @kbd{start} commands, and then start the recording with the @kbd{record @var{method}} command. @cindex displaced stepping, and process record and replay Displaced stepping (@pxref{Maintenance Commands,, displaced stepping}) will be automatically disabled when process record and replay target is started. That's because the process record and replay target doesn't support displaced stepping. @cindex non-stop mode, and process record and replay @cindex asynchronous execution, and process record and replay If the inferior is in the non-stop mode (@pxref{Non-Stop Mode}) or in the asynchronous execution mode (@pxref{Background Execution}), not all recording methods are available. The @code{full} recording method does not support these two modes. @kindex record stop @kindex rec s @item record stop Stop the process record and replay target. When process record and replay target stops, the entire execution log will be deleted and the inferior will either be terminated, or will remain in its final state. When you stop the process record and replay target in record mode (at the end of the execution log), the inferior will be stopped at the next instruction that would have been recorded. In other words, if you record for a while and then stop recording, the inferior process will be left in the same state as if the recording never happened. On the other hand, if the process record and replay target is stopped while in replay mode (that is, not at the end of the execution log, but at some earlier point), the inferior process will become ``live'' at that earlier state, and it will then be possible to continue the usual ``live'' debugging of the process from that state. When the inferior process exits, or @value{GDBN} detaches from it, process record and replay target will automatically stop itself. @kindex record goto @item record goto Go to a specific location in the execution log. There are several ways to specify the location to go to: @table @code @item record goto begin @itemx record goto start Go to the beginning of the execution log. @item record goto end Go to the end of the execution log. @item record goto @var{n} Go to instruction number @var{n} in the execution log. @end table @kindex record save @item record save @var{filename} Save the execution log to a file @file{@var{filename}}. Default filename is @file{gdb_record.@var{process_id}}, where @var{process_id} is the process ID of the inferior. This command may not be available for all recording methods. @kindex record restore @item record restore @var{filename} Restore the execution log from a file @file{@var{filename}}. File must have been created with @code{record save}. @kindex set record full @item set record full insn-number-max @var{limit} @itemx set record full insn-number-max unlimited Set the limit of instructions to be recorded for the @code{full} recording method. Default value is 200000. If @var{limit} is a positive number, then @value{GDBN} will start deleting instructions from the log once the number of the record instructions becomes greater than @var{limit}. For every new recorded instruction, @value{GDBN} will delete the earliest recorded instruction to keep the number of recorded instructions at the limit. (Since deleting recorded instructions loses information, @value{GDBN} lets you control what happens when the limit is reached, by means of the @code{stop-at-limit} option, described below.) If @var{limit} is @code{unlimited} or zero, @value{GDBN} will never delete recorded instructions from the execution log. The number of recorded instructions is limited only by the available memory. @kindex show record full @item show record full insn-number-max Show the limit of instructions to be recorded with the @code{full} recording method. @item set record full stop-at-limit Control the behavior of the @code{full} recording method when the number of recorded instructions reaches the limit. If ON (the default), @value{GDBN} will stop when the limit is reached for the first time and ask you whether you want to stop the inferior or continue running it and recording the execution log. If you decide to continue recording, each new recorded instruction will cause the oldest one to be deleted. If this option is OFF, @value{GDBN} will automatically delete the oldest record to make room for each new one, without asking. @item show record full stop-at-limit Show the current setting of @code{stop-at-limit}. @item set record full memory-query Control the behavior when @value{GDBN} is unable to record memory changes caused by an instruction for the @code{full} recording method. If ON, @value{GDBN} will query whether to stop the inferior in that case. If this option is OFF (the default), @value{GDBN} will automatically ignore the effect of such instructions on memory. Later, when @value{GDBN} replays this execution log, it will mark the log of this instruction as not accessible, and it will not affect the replay results. @item show record full memory-query Show the current setting of @code{memory-query}. @kindex set record btrace The @code{btrace} record target does not trace data. As a convenience, when replaying, @value{GDBN} reads read-only memory off the live program directly, assuming that the addresses of the read-only areas don't change. This for example makes it possible to disassemble code while replaying, but not to print variables. In some cases, being able to inspect variables might be useful. You can use the following command for that: @item set record btrace replay-memory-access Control the behavior of the @code{btrace} recording method when accessing memory during replay. If @code{read-only} (the default), @value{GDBN} will only allow accesses to read-only memory. If @code{read-write}, @value{GDBN} will allow accesses to read-only and to read-write memory. Beware that the accessed memory corresponds to the live target and not necessarily to the current replay position. @item set record btrace cpu @var{identifier} Set the processor to be used for enabling workarounds for processor errata when decoding the trace. Processor errata are defects in processor operation, caused by its design or manufacture. They can cause a trace not to match the specification. This, in turn, may cause trace decode to fail. @value{GDBN} can detect erroneous trace packets and correct them, thus avoiding the decoding failures. These corrections are known as @dfn{errata workarounds}, and are enabled based on the processor on which the trace was recorded. By default, @value{GDBN} attempts to detect the processor automatically, and apply the necessary workarounds for it. However, you may need to specify the processor if @value{GDBN} does not yet support it. This command allows you to do that, and also allows to disable the workarounds. The argument @var{identifier} identifies the @sc{cpu} and is of the form: @code{@var{vendor}:@var{processor identifier}}. In addition, there are two special identifiers, @code{none} and @code{auto} (default). The following vendor identifiers and corresponding processor identifiers are currently supported: @multitable @columnfractions .1 .9 @item @code{intel} @tab @var{family}/@var{model}[/@var{stepping}] @end multitable On GNU/Linux systems, the processor @var{family}, @var{model}, and @var{stepping} can be obtained from @code{/proc/cpuinfo}. If @var{identifier} is @code{auto}, enable errata workarounds for the processor on which the trace was recorded. If @var{identifier} is @code{none}, errata workarounds are disabled. For example, when using an old @value{GDBN} on a new system, decode may fail because @value{GDBN} does not support the new processor. It often suffices to specify an older processor that @value{GDBN} supports. @smallexample (gdb) info record Active record target: record-btrace Recording format: Intel Processor Trace. Buffer size: 16kB. Failed to configure the Intel Processor Trace decoder: unknown cpu. (gdb) set record btrace cpu intel:6/158 (gdb) info record Active record target: record-btrace Recording format: Intel Processor Trace. Buffer size: 16kB. Recorded 84872 instructions in 3189 functions (0 gaps) for thread 1 (...). @end smallexample @kindex show record btrace @item show record btrace replay-memory-access Show the current setting of @code{replay-memory-access}. @item show record btrace cpu Show the processor to be used for enabling trace decode errata workarounds. @kindex set record btrace bts @item set record btrace bts buffer-size @var{size} @itemx set record btrace bts buffer-size unlimited Set the requested ring buffer size for branch tracing in @acronym{BTS} format. Default is 64KB. If @var{size} is a positive number, then @value{GDBN} will try to allocate a buffer of at least @var{size} bytes for each new thread that uses the btrace recording method and the @acronym{BTS} format. The actually obtained buffer size may differ from the requested @var{size}. Use the @code{info record} command to see the actual buffer size for each thread that uses the btrace recording method and the @acronym{BTS} format. If @var{limit} is @code{unlimited} or zero, @value{GDBN} will try to allocate a buffer of 4MB. Bigger buffers mean longer traces. On the other hand, @value{GDBN} will also need longer to process the branch trace data before it can be used. @item show record btrace bts buffer-size @var{size} Show the current setting of the requested ring buffer size for branch tracing in @acronym{BTS} format. @kindex set record btrace pt @item set record btrace pt buffer-size @var{size} @itemx set record btrace pt buffer-size unlimited Set the requested ring buffer size for branch tracing in Intel Processor Trace format. Default is 16KB. If @var{size} is a positive number, then @value{GDBN} will try to allocate a buffer of at least @var{size} bytes for each new thread that uses the btrace recording method and the Intel Processor Trace format. The actually obtained buffer size may differ from the requested @var{size}. Use the @code{info record} command to see the actual buffer size for each thread. If @var{limit} is @code{unlimited} or zero, @value{GDBN} will try to allocate a buffer of 4MB. Bigger buffers mean longer traces. On the other hand, @value{GDBN} will also need longer to process the branch trace data before it can be used. @item show record btrace pt buffer-size @var{size} Show the current setting of the requested ring buffer size for branch tracing in Intel Processor Trace format. @kindex info record @item info record Show various statistics about the recording depending on the recording method: @table @code @item full For the @code{full} recording method, it shows the state of process record and its in-memory execution log buffer, including: @itemize @bullet @item Whether in record mode or replay mode. @item Lowest recorded instruction number (counting from when the current execution log started recording instructions). @item Highest recorded instruction number. @item Current instruction about to be replayed (if in replay mode). @item Number of instructions contained in the execution log. @item Maximum number of instructions that may be contained in the execution log. @end itemize @item btrace For the @code{btrace} recording method, it shows: @itemize @bullet @item Recording format. @item Number of instructions that have been recorded. @item Number of blocks of sequential control-flow formed by the recorded instructions. @item Whether in record mode or replay mode. @end itemize For the @code{bts} recording format, it also shows: @itemize @bullet @item Size of the perf ring buffer. @end itemize For the @code{pt} recording format, it also shows: @itemize @bullet @item Size of the perf ring buffer. @end itemize @end table @kindex record delete @kindex rec del @item record delete When record target runs in replay mode (``in the past''), delete the subsequent execution log and begin to record a new execution log starting from the current address. This means you will abandon the previously recorded ``future'' and begin recording a new ``future''. @kindex record instruction-history @kindex rec instruction-history @item record instruction-history Disassembles instructions from the recorded execution log. By default, ten instructions are disassembled. This can be changed using the @code{set record instruction-history-size} command. Instructions are printed in execution order. It can also print mixed source+disassembly if you specify the the @code{/m} or @code{/s} modifier, and print the raw instructions in hex as well as in symbolic form by specifying the @code{/r} modifier. The current position marker is printed for the instruction at the current program counter value. This instruction can appear multiple times in the trace and the current position marker will be printed every time. To omit the current position marker, specify the @code{/p} modifier. To better align the printed instructions when the trace contains instructions from more than one function, the function name may be omitted by specifying the @code{/f} modifier. Speculatively executed instructions are prefixed with @samp{?}. This feature is not available for all recording formats. There are several ways to specify what part of the execution log to disassemble: @table @code @item record instruction-history @var{insn} Disassembles ten instructions starting from instruction number @var{insn}. @item record instruction-history @var{insn}, +/-@var{n} Disassembles @var{n} instructions around instruction number @var{insn}. If @var{n} is preceded with @code{+}, disassembles @var{n} instructions after instruction number @var{insn}. If @var{n} is preceded with @code{-}, disassembles @var{n} instructions before instruction number @var{insn}. @item record instruction-history Disassembles ten more instructions after the last disassembly. @item record instruction-history - Disassembles ten more instructions before the last disassembly. @item record instruction-history @var{begin}, @var{end} Disassembles instructions beginning with instruction number @var{begin} until instruction number @var{end}. The instruction number @var{end} is included. @end table This command may not be available for all recording methods. @kindex set record @item set record instruction-history-size @var{size} @itemx set record instruction-history-size unlimited Define how many instructions to disassemble in the @code{record instruction-history} command. The default value is 10. A @var{size} of @code{unlimited} means unlimited instructions. @kindex show record @item show record instruction-history-size Show how many instructions to disassemble in the @code{record instruction-history} command. @kindex record function-call-history @kindex rec function-call-history @item record function-call-history Prints the execution history at function granularity. It prints one line for each sequence of instructions that belong to the same function giving the name of that function, the source lines for this instruction sequence (if the @code{/l} modifier is specified), and the instructions numbers that form the sequence (if the @code{/i} modifier is specified). The function names are indented to reflect the call stack depth if the @code{/c} modifier is specified. The @code{/l}, @code{/i}, and @code{/c} modifiers can be given together. @smallexample (@value{GDBP}) @b{list 1, 10} 1 void foo (void) 2 @{ 3 @} 4 5 void bar (void) 6 @{ 7 ... 8 foo (); 9 ... 10 @} (@value{GDBP}) @b{record function-call-history /ilc} 1 bar inst 1,4 at foo.c:6,8 2 foo inst 5,10 at foo.c:2,3 3 bar inst 11,13 at foo.c:9,10 @end smallexample By default, ten lines are printed. This can be changed using the @code{set record function-call-history-size} command. Functions are printed in execution order. There are several ways to specify what to print: @table @code @item record function-call-history @var{func} Prints ten functions starting from function number @var{func}. @item record function-call-history @var{func}, +/-@var{n} Prints @var{n} functions around function number @var{func}. If @var{n} is preceded with @code{+}, prints @var{n} functions after function number @var{func}. If @var{n} is preceded with @code{-}, prints @var{n} functions before function number @var{func}. @item record function-call-history Prints ten more functions after the last ten-line print. @item record function-call-history - Prints ten more functions before the last ten-line print. @item record function-call-history @var{begin}, @var{end} Prints functions beginning with function number @var{begin} until function number @var{end}. The function number @var{end} is included. @end table This command may not be available for all recording methods. @item set record function-call-history-size @var{size} @itemx set record function-call-history-size unlimited Define how many lines to print in the @code{record function-call-history} command. The default value is 10. A size of @code{unlimited} means unlimited lines. @item show record function-call-history-size Show how many lines to print in the @code{record function-call-history} command. @end table @node Stack @chapter Examining the Stack When your program has stopped, the first thing you need to know is where it stopped and how it got there. @cindex call stack Each time your program performs a function call, information about the call is generated. That information includes the location of the call in your program, the arguments of the call, and the local variables of the function being called. The information is saved in a block of data called a @dfn{stack frame}. The stack frames are allocated in a region of memory called the @dfn{call stack}. When your program stops, the @value{GDBN} commands for examining the stack allow you to see all of this information. @cindex selected frame One of the stack frames is @dfn{selected} by @value{GDBN} and many @value{GDBN} commands refer implicitly to the selected frame. In particular, whenever you ask @value{GDBN} for the value of a variable in your program, the value is found in the selected frame. There are special @value{GDBN} commands to select whichever frame you are interested in. @xref{Selection, ,Selecting a Frame}. When your program stops, @value{GDBN} automatically selects the currently executing frame and describes it briefly, similar to the @code{frame} command (@pxref{Frame Info, ,Information about a Frame}). @menu * Frames:: Stack frames * Backtrace:: Backtraces * Selection:: Selecting a frame * Frame Info:: Information on a frame * Frame Apply:: Applying a command to several frames * Frame Filter Management:: Managing frame filters @end menu @node Frames @section Stack Frames @cindex frame, definition @cindex stack frame The call stack is divided up into contiguous pieces called @dfn{stack frames}, or @dfn{frames} for short; each frame is the data associated with one call to one function. The frame contains the arguments given to the function, the function's local variables, and the address at which the function is executing. @cindex initial frame @cindex outermost frame @cindex innermost frame When your program is started, the stack has only one frame, that of the function @code{main}. This is called the @dfn{initial} frame or the @dfn{outermost} frame. Each time a function is called, a new frame is made. Each time a function returns, the frame for that function invocation is eliminated. If a function is recursive, there can be many frames for the same function. The frame for the function in which execution is actually occurring is called the @dfn{innermost} frame. This is the most recently created of all the stack frames that still exist. @cindex frame pointer Inside your program, stack frames are identified by their addresses. A stack frame consists of many bytes, each of which has its own address; each kind of computer has a convention for choosing one byte whose address serves as the address of the frame. Usually this address is kept in a register called the @dfn{frame pointer register} (@pxref{Registers, $fp}) while execution is going on in that frame. @cindex frame level @cindex frame number @value{GDBN} labels each existing stack frame with a @dfn{level}, a number that is zero for the innermost frame, one for the frame that called it, and so on upward. These level numbers give you a way of designating stack frames in @value{GDBN} commands. The terms @dfn{frame number} and @dfn{frame level} can be used interchangeably to describe this number. @c The -fomit-frame-pointer below perennially causes hbox overflow @c underflow problems. @cindex frameless execution Some compilers provide a way to compile functions so that they operate without stack frames. (For example, the @value{NGCC} option @smallexample @samp{-fomit-frame-pointer} @end smallexample generates functions without a frame.) This is occasionally done with heavily used library functions to save the frame setup time. @value{GDBN} has limited facilities for dealing with these function invocations. If the innermost function invocation has no stack frame, @value{GDBN} nevertheless regards it as though it had a separate frame, which is numbered zero as usual, allowing correct tracing of the function call chain. However, @value{GDBN} has no provision for frameless functions elsewhere in the stack. @node Backtrace @section Backtraces @cindex traceback @cindex call stack traces A backtrace is a summary of how your program got where it is. It shows one line per frame, for many frames, starting with the currently executing frame (frame zero), followed by its caller (frame one), and on up the stack. @anchor{backtrace-command} @kindex backtrace @kindex bt @r{(@code{backtrace})} To print a backtrace of the entire stack, use the @code{backtrace} command, or its alias @code{bt}. This command will print one line per frame for frames in the stack. By default, all stack frames are printed. You can stop the backtrace at any time by typing the system interrupt character, normally @kbd{Ctrl-c}. @table @code @item backtrace [@var{option}]@dots{} [@var{qualifier}]@dots{} [@var{count}] @itemx bt [@var{option}]@dots{} [@var{qualifier}]@dots{} [@var{count}] Print the backtrace of the entire stack. The optional @var{count} can be one of the following: @table @code @item @var{n} @itemx @var{n} Print only the innermost @var{n} frames, where @var{n} is a positive number. @item -@var{n} @itemx -@var{n} Print only the outermost @var{n} frames, where @var{n} is a positive number. @end table Options: @table @code @item -full Print the values of the local variables also. This can be combined with the optional @var{count} to limit the number of frames shown. @item -no-filters Do not run Python frame filters on this backtrace. @xref{Frame Filter API}, for more information. Additionally use @ref{disable frame-filter all} to turn off all frame filters. This is only relevant when @value{GDBN} has been configured with @code{Python} support. @item -hide A Python frame filter might decide to ``elide'' some frames. Normally such elided frames are still printed, but they are indented relative to the filtered frames that cause them to be elided. The @code{-hide} option causes elided frames to not be printed at all. @end table The @code{backtrace} command also supports a number of options that allow overriding relevant global print settings as set by @code{set backtrace} and @code{set print} subcommands: @table @code @item -past-main [@code{on}|@code{off}] Set whether backtraces should continue past @code{main}. Related setting: @ref{set backtrace past-main}. @item -past-entry [@code{on}|@code{off}] Set whether backtraces should continue past the entry point of a program. Related setting: @ref{set backtrace past-entry}. @item -entry-values @code{no}|@code{only}|@code{preferred}|@code{if-needed}|@code{both}|@code{compact}|@code{default} Set printing of function arguments at function entry. Related setting: @ref{set print entry-values}. @item -frame-arguments @code{all}|@code{scalars}|@code{none} Set printing of non-scalar frame arguments. Related setting: @ref{set print frame-arguments}. @item -raw-frame-arguments [@code{on}|@code{off}] Set whether to print frame arguments in raw form. Related setting: @ref{set print raw-frame-arguments}. @item -frame-info @code{auto}|@code{source-line}|@code{location}|@code{source-and-location}|@code{location-and-address}|@code{short-location} Set printing of frame information. Related setting: @ref{set print frame-info}. @end table The optional @var{qualifier} is maintained for backward compatibility. It can be one of the following: @table @code @item full Equivalent to the @code{-full} option. @item no-filters Equivalent to the @code{-no-filters} option. @item hide Equivalent to the @code{-hide} option. @end table @end table @kindex where @kindex info stack The names @code{where} and @code{info stack} (abbreviated @code{info s}) are additional aliases for @code{backtrace}. @cindex multiple threads, backtrace In a multi-threaded program, @value{GDBN} by default shows the backtrace only for the current thread. To display the backtrace for several or all of the threads, use the command @code{thread apply} (@pxref{Threads, thread apply}). For example, if you type @kbd{thread apply all backtrace}, @value{GDBN} will display the backtrace for all the threads; this is handy when you debug a core dump of a multi-threaded program. Each line in the backtrace shows the frame number and the function name. The program counter value is also shown---unless you use @code{set print address off}. The backtrace also shows the source file name and line number, as well as the arguments to the function. The program counter value is omitted if it is at the beginning of the code for that line number. Here is an example of a backtrace. It was made with the command @samp{bt 3}, so it shows the innermost three frames. @smallexample @group #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8) at builtin.c:993 #1 0x6e38 in expand_macro (sym=0x2b600, data=...) at macro.c:242 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08) at macro.c:71 (More stack frames follow...) @end group @end smallexample @noindent The display for frame zero does not begin with a program counter value, indicating that your program has stopped at the beginning of the code for line @code{993} of @code{builtin.c}. @noindent The value of parameter @code{data} in frame 1 has been replaced by @code{@dots{}}. By default, @value{GDBN} prints the value of a parameter only if it is a scalar (integer, pointer, enumeration, etc). See command @kbd{set print frame-arguments} in @ref{Print Settings} for more details on how to configure the way function parameter values are printed. The command @kbd{set print frame-info} (@pxref{Print Settings}) controls what frame information is printed. @cindex optimized out, in backtrace @cindex function call arguments, optimized out If your program was compiled with optimizations, some compilers will optimize away arguments passed to functions if those arguments are never used after the call. Such optimizations generate code that passes arguments through registers, but doesn't store those arguments in the stack frame. @value{GDBN} has no way of displaying such arguments in stack frames other than the innermost one. Here's what such a backtrace might look like: @smallexample @group #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8) at builtin.c:993 #1 0x6e38 in expand_macro (sym=<optimized out>) at macro.c:242 #2 0x6840 in expand_token (obs=0x0, t=<optimized out>, td=0xf7fffb08) at macro.c:71 (More stack frames follow...) @end group @end smallexample @noindent The values of arguments that were not saved in their stack frames are shown as @samp{<optimized out>}. If you need to display the values of such optimized-out arguments, either deduce that from other variables whose values depend on the one you are interested in, or recompile without optimizations. @cindex backtrace beyond @code{main} function @cindex program entry point @cindex startup code, and backtrace Most programs have a standard user entry point---a place where system libraries and startup code transition into user code. For C this is @code{main}@footnote{ Note that embedded programs (the so-called ``free-standing'' environment) are not required to have a @code{main} function as the entry point. They could even have multiple entry points.}. When @value{GDBN} finds the entry function in a backtrace it will terminate the backtrace, to avoid tracing into highly system-specific (and generally uninteresting) code. If you need to examine the startup code, or limit the number of levels in a backtrace, you can change this behavior: @table @code @item set backtrace past-main @itemx set backtrace past-main on @anchor{set backtrace past-main} @kindex set backtrace Backtraces will continue past the user entry point. @item set backtrace past-main off Backtraces will stop when they encounter the user entry point. This is the default. @item show backtrace past-main @kindex show backtrace Display the current user entry point backtrace policy. @item set backtrace past-entry @itemx set backtrace past-entry on @anchor{set backtrace past-entry} Backtraces will continue past the internal entry point of an application. This entry point is encoded by the linker when the application is built, and is likely before the user entry point @code{main} (or equivalent) is called. @item set backtrace past-entry off Backtraces will stop when they encounter the internal entry point of an application. This is the default. @item show backtrace past-entry Display the current internal entry point backtrace policy. @item set backtrace limit @var{n} @itemx set backtrace limit 0 @itemx set backtrace limit unlimited @anchor{set backtrace limit} @cindex backtrace limit Limit the backtrace to @var{n} levels. A value of @code{unlimited} or zero means unlimited levels. @item show backtrace limit Display the current limit on backtrace levels. @end table You can control how file names are displayed. @table @code @item set filename-display @itemx set filename-display relative @cindex filename-display Display file names relative to the compilation directory. This is the default. @item set filename-display basename Display only basename of a filename. @item set filename-display absolute Display an absolute filename. @item show filename-display Show the current way to display filenames. @end table @node Selection @section Selecting a Frame Most commands for examining the stack and other data in your program work on whichever stack frame is selected at the moment. Here are the commands for selecting a stack frame; all of them finish by printing a brief description of the stack frame just selected. @table @code @kindex frame@r{, selecting} @kindex f @r{(@code{frame})} @item frame @r{[} @var{frame-selection-spec} @r{]} @item f @r{[} @var{frame-selection-spec} @r{]} The @command{frame} command allows different stack frames to be selected. The @var{frame-selection-spec} can be any of the following: @table @code @kindex frame level @item @var{num} @item level @var{num} Select frame level @var{num}. Recall that frame zero is the innermost (currently executing) frame, frame one is the frame that called the innermost one, and so on. The highest level frame is usually the one for @code{main}. As this is the most common method of navigating the frame stack, the string @command{level} can be omitted. For example, the following two commands are equivalent: @smallexample (@value{GDBP}) frame 3 (@value{GDBP}) frame level 3 @end smallexample @kindex frame address @item address @var{stack-address} Select the frame with stack address @var{stack-address}. The @var{stack-address} for a frame can be seen in the output of @command{info frame}, for example: @smallexample (gdb) info frame Stack level 1, frame at 0x7fffffffda30: rip = 0x40066d in b (amd64-entry-value.cc:59); saved rip 0x4004c5 tail call frame, caller of frame at 0x7fffffffda30 source language c++. Arglist at unknown address. Locals at unknown address, Previous frame's sp is 0x7fffffffda30 @end smallexample The @var{stack-address} for this frame is @code{0x7fffffffda30} as indicated by the line: @smallexample Stack level 1, frame at 0x7fffffffda30: @end smallexample @kindex frame function @item function @var{function-name} Select the stack frame for function @var{function-name}. If there are multiple stack frames for function @var{function-name} then the inner most stack frame is selected. @kindex frame view @item view @var{stack-address} @r{[} @var{pc-addr} @r{]} View a frame that is not part of @value{GDBN}'s backtrace. The frame viewed has stack address @var{stack-addr}, and optionally, a program counter address of @var{pc-addr}. This is useful mainly if the chaining of stack frames has been damaged by a bug, making it impossible for @value{GDBN} to assign numbers properly to all frames. In addition, this can be useful when your program has multiple stacks and switches between them. When viewing a frame outside the current backtrace using @command{frame view} then you can always return to the original stack using one of the previous stack frame selection instructions, for example @command{frame level 0}. @end table @kindex up @item up @var{n} Move @var{n} frames up the stack; @var{n} defaults to 1. For positive numbers @var{n}, this advances toward the outermost frame, to higher frame numbers, to frames that have existed longer. @kindex down @kindex do @r{(@code{down})} @item down @var{n} Move @var{n} frames down the stack; @var{n} defaults to 1. For positive numbers @var{n}, this advances toward the innermost frame, to lower frame numbers, to frames that were created more recently. You may abbreviate @code{down} as @code{do}. @end table All of these commands end by printing two lines of output describing the frame. The first line shows the frame number, the function name, the arguments, and the source file and line number of execution in that frame. The second line shows the text of that source line. @need 1000 For example: @smallexample @group (@value{GDBP}) up #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc) at env.c:10 10 read_input_file (argv[i]); @end group @end smallexample After such a printout, the @code{list} command with no arguments prints ten lines centered on the point of execution in the frame. You can also edit the program at the point of execution with your favorite editing program by typing @code{edit}. @xref{List, ,Printing Source Lines}, for details. @table @code @kindex select-frame @item select-frame @r{[} @var{frame-selection-spec} @r{]} The @code{select-frame} command is a variant of @code{frame} that does not display the new frame after selecting it. This command is intended primarily for use in @value{GDBN} command scripts, where the output might be unnecessary and distracting. The @var{frame-selection-spec} is as for the @command{frame} command described in @ref{Selection, ,Selecting a Frame}. @kindex down-silently @kindex up-silently @item up-silently @var{n} @itemx down-silently @var{n} These two commands are variants of @code{up} and @code{down}, respectively; they differ in that they do their work silently, without causing display of the new frame. They are intended primarily for use in @value{GDBN} command scripts, where the output might be unnecessary and distracting. @end table @node Frame Info @section Information About a Frame There are several other commands to print information about the selected stack frame. @table @code @item frame @itemx f When used without any argument, this command does not change which frame is selected, but prints a brief description of the currently selected stack frame. It can be abbreviated @code{f}. With an argument, this command is used to select a stack frame. @xref{Selection, ,Selecting a Frame}. @kindex info frame @kindex info f @r{(@code{info frame})} @item info frame @itemx info f This command prints a verbose description of the selected stack frame, including: @itemize @bullet @item the address of the frame @item the address of the next frame down (called by this frame) @item the address of the next frame up (caller of this frame) @item the language in which the source code corresponding to this frame is written @item the address of the frame's arguments @item the address of the frame's local variables @item the program counter saved in it (the address of execution in the caller frame) @item which registers were saved in the frame @end itemize @noindent The verbose description is useful when something has gone wrong that has made the stack format fail to fit the usual conventions. @item info frame @r{[} @var{frame-selection-spec} @r{]} @itemx info f @r{[} @var{frame-selection-spec} @r{]} Print a verbose description of the frame selected by @var{frame-selection-spec}. The @var{frame-selection-spec} is the same as for the @command{frame} command (@pxref{Selection, ,Selecting a Frame}). The selected frame remains unchanged by this command. @kindex info args @item info args [-q] Print the arguments of the selected frame, each on a separate line. The optional flag @samp{-q}, which stands for @samp{quiet}, disables printing header information and messages explaining why no argument have been printed. @item info args [-q] [-t @var{type_regexp}] [@var{regexp}] Like @kbd{info args}, but only print the arguments selected with the provided regexp(s). If @var{regexp} is provided, print only the arguments whose names match the regular expression @var{regexp}. If @var{type_regexp} is provided, print only the arguments whose types, as printed by the @code{whatis} command, match the regular expression @var{type_regexp}. If @var{type_regexp} contains space(s), it should be enclosed in quote characters. If needed, use backslash to escape the meaning of special characters or quotes. If both @var{regexp} and @var{type_regexp} are provided, an argument is printed only if its name matches @var{regexp} and its type matches @var{type_regexp}. @item info locals [-q] @kindex info locals Print the local variables of the selected frame, each on a separate line. These are all variables (declared either static or automatic) accessible at the point of execution of the selected frame. The optional flag @samp{-q}, which stands for @samp{quiet}, disables printing header information and messages explaining why no local variables have been printed. @item info locals [-q] [-t @var{type_regexp}] [@var{regexp}] Like @kbd{info locals}, but only print the local variables selected with the provided regexp(s). If @var{regexp} is provided, print only the local variables whose names match the regular expression @var{regexp}. If @var{type_regexp} is provided, print only the local variables whose types, as printed by the @code{whatis} command, match the regular expression @var{type_regexp}. If @var{type_regexp} contains space(s), it should be enclosed in quote characters. If needed, use backslash to escape the meaning of special characters or quotes. If both @var{regexp} and @var{type_regexp} are provided, a local variable is printed only if its name matches @var{regexp} and its type matches @var{type_regexp}. The command @kbd{info locals -q -t @var{type_regexp}} can usefully be combined with the commands @kbd{frame apply} and @kbd{thread apply}. For example, your program might use Resource Acquisition Is Initialization types (RAII) such as @code{lock_something_t}: each local variable of type @code{lock_something_t} automatically places a lock that is destroyed when the variable goes out of scope. You can then list all acquired locks in your program by doing @smallexample thread apply all -s frame apply all -s info locals -q -t lock_something_t @end smallexample @noindent or the equivalent shorter form @smallexample tfaas i lo -q -t lock_something_t @end smallexample @end table @node Frame Apply @section Applying a Command to Several Frames. @anchor{frame apply} @kindex frame apply @cindex apply command to several frames @table @code @item frame apply [all | @var{count} | @var{-count} | level @var{level}@dots{}] [@var{option}]@dots{} @var{command} The @code{frame apply} command allows you to apply the named @var{command} to one or more frames. @table @code @item @code{all} Specify @code{all} to apply @var{command} to all frames. @item @var{count} Use @var{count} to apply @var{command} to the innermost @var{count} frames, where @var{count} is a positive number. @item @var{-count} Use @var{-count} to apply @var{command} to the outermost @var{count} frames, where @var{count} is a positive number. @item @code{level} Use @code{level} to apply @var{command} to the set of frames identified by the @var{level} list. @var{level} is a frame level or a range of frame levels as @var{level1}-@var{level2}. The frame level is the number shown in the first field of the @samp{backtrace} command output. E.g., @samp{2-4 6-8 3} indicates to apply @var{command} for the frames at levels 2, 3, 4, 6, 7, 8, and then again on frame at level 3. @end table Note that the frames on which @code{frame apply} applies a command are also influenced by the @code{set backtrace} settings such as @code{set backtrace past-main} and @code{set backtrace limit N}. @xref{Backtrace,,Backtraces}. The @code{frame apply} command also supports a number of options that allow overriding relevant @code{set backtrace} settings: @table @code @item -past-main [@code{on}|@code{off}] Whether backtraces should continue past @code{main}. Related setting: @ref{set backtrace past-main}. @item -past-entry [@code{on}|@code{off}] Whether backtraces should continue past the entry point of a program. Related setting: @ref{set backtrace past-entry}. @end table By default, @value{GDBN} displays some frame information before the output produced by @var{command}, and an error raised during the execution of a @var{command} will abort @code{frame apply}. The following options can be used to fine-tune these behaviors: @table @code @item -c The flag @code{-c}, which stands for @samp{continue}, causes any errors in @var{command} to be displayed, and the execution of @code{frame apply} then continues. @item -s The flag @code{-s}, which stands for @samp{silent}, causes any errors or empty output produced by a @var{command} to be silently ignored. That is, the execution continues, but the frame information and errors are not printed. @item -q The flag @code{-q} (@samp{quiet}) disables printing the frame information. @end table The following example shows how the flags @code{-c} and @code{-s} are working when applying the command @code{p j} to all frames, where variable @code{j} can only be successfully printed in the outermost @code{#1 main} frame. @smallexample @group (gdb) frame apply all p j #0 some_function (i=5) at fun.c:4 No symbol "j" in current context. (gdb) frame apply all -c p j #0 some_function (i=5) at fun.c:4 No symbol "j" in current context. #1 0x565555fb in main (argc=1, argv=0xffffd2c4) at fun.c:11 $1 = 5 (gdb) frame apply all -s p j #1 0x565555fb in main (argc=1, argv=0xffffd2c4) at fun.c:11 $2 = 5 (gdb) @end group @end smallexample By default, @samp{frame apply}, prints the frame location information before the command output: @smallexample @group (gdb) frame apply all p $sp #0 some_function (i=5) at fun.c:4 $4 = (void *) 0xffffd1e0 #1 0x565555fb in main (argc=1, argv=0xffffd2c4) at fun.c:11 $5 = (void *) 0xffffd1f0 (gdb) @end group @end smallexample If the flag @code{-q} is given, no frame information is printed: @smallexample @group (gdb) frame apply all -q p $sp $12 = (void *) 0xffffd1e0 $13 = (void *) 0xffffd1f0 (gdb) @end group @end smallexample @end table @table @code @kindex faas @cindex apply a command to all frames (ignoring errors and empty output) @item faas @var{command} Shortcut for @code{frame apply all -s @var{command}}. Applies @var{command} on all frames, ignoring errors and empty output. It can for example be used to print a local variable or a function argument without knowing the frame where this variable or argument is, using: @smallexample (@value{GDBP}) faas p some_local_var_i_do_not_remember_where_it_is @end smallexample The @code{faas} command accepts the same options as the @code{frame apply} command. @xref{frame apply}. Note that the command @code{tfaas @var{command}} applies @var{command} on all frames of all threads. See @xref{Threads,,Threads}. @end table @node Frame Filter Management @section Management of Frame Filters. @cindex managing frame filters Frame filters are Python based utilities to manage and decorate the output of frames. @xref{Frame Filter API}, for further information. Managing frame filters is performed by several commands available within @value{GDBN}, detailed here. @table @code @kindex info frame-filter @item info frame-filter Print a list of installed frame filters from all dictionaries, showing their name, priority and enabled status. @kindex disable frame-filter @anchor{disable frame-filter all} @item disable frame-filter @var{filter-dictionary} @var{filter-name} Disable a frame filter in the dictionary matching @var{filter-dictionary} and @var{filter-name}. The @var{filter-dictionary} may be @code{all}, @code{global}, @code{progspace}, or the name of the object file where the frame filter dictionary resides. When @code{all} is specified, all frame filters across all dictionaries are disabled. The @var{filter-name} is the name of the frame filter and is used when @code{all} is not the option for @var{filter-dictionary}. A disabled frame-filter is not deleted, it may be enabled again later. @kindex enable frame-filter @item enable frame-filter @var{filter-dictionary} @var{filter-name} Enable a frame filter in the dictionary matching @var{filter-dictionary} and @var{filter-name}. The @var{filter-dictionary} may be @code{all}, @code{global}, @code{progspace} or the name of the object file where the frame filter dictionary resides. When @code{all} is specified, all frame filters across all dictionaries are enabled. The @var{filter-name} is the name of the frame filter and is used when @code{all} is not the option for @var{filter-dictionary}. Example: @smallexample (gdb) info frame-filter global frame-filters: Priority Enabled Name 1000 No PrimaryFunctionFilter 100 Yes Reverse progspace /build/test frame-filters: Priority Enabled Name 100 Yes ProgspaceFilter objfile /build/test frame-filters: Priority Enabled Name 999 Yes BuildProgramFilter (gdb) disable frame-filter /build/test BuildProgramFilter (gdb) info frame-filter global frame-filters: Priority Enabled Name 1000 No PrimaryFunctionFilter 100 Yes Reverse progspace /build/test frame-filters: Priority Enabled Name 100 Yes ProgspaceFilter objfile /build/test frame-filters: Priority Enabled Name 999 No BuildProgramFilter (gdb) enable frame-filter global PrimaryFunctionFilter (gdb) info frame-filter global frame-filters: Priority Enabled Name 1000 Yes PrimaryFunctionFilter 100 Yes Reverse progspace /build/test frame-filters: Priority Enabled Name 100 Yes ProgspaceFilter objfile /build/test frame-filters: Priority Enabled Name 999 No BuildProgramFilter @end smallexample @kindex set frame-filter priority @item set frame-filter priority @var{filter-dictionary} @var{filter-name} @var{priority} Set the @var{priority} of a frame filter in the dictionary matching @var{filter-dictionary}, and the frame filter name matching @var{filter-name}. The @var{filter-dictionary} may be @code{global}, @code{progspace} or the name of the object file where the frame filter dictionary resides. The @var{priority} is an integer. @kindex show frame-filter priority @item show frame-filter priority @var{filter-dictionary} @var{filter-name} Show the @var{priority} of a frame filter in the dictionary matching @var{filter-dictionary}, and the frame filter name matching @var{filter-name}. The @var{filter-dictionary} may be @code{global}, @code{progspace} or the name of the object file where the frame filter dictionary resides. Example: @smallexample (gdb) info frame-filter global frame-filters: Priority Enabled Name 1000 Yes PrimaryFunctionFilter 100 Yes Reverse progspace /build/test frame-filters: Priority Enabled Name 100 Yes ProgspaceFilter objfile /build/test frame-filters: Priority Enabled Name 999 No BuildProgramFilter (gdb) set frame-filter priority global Reverse 50 (gdb) info frame-filter global frame-filters: Priority Enabled Name 1000 Yes PrimaryFunctionFilter 50 Yes Reverse progspace /build/test frame-filters: Priority Enabled Name 100 Yes ProgspaceFilter objfile /build/test frame-filters: Priority Enabled Name 999 No BuildProgramFilter @end smallexample @end table @node Source @chapter Examining Source Files @value{GDBN} can print parts of your program's source, since the debugging information recorded in the program tells @value{GDBN} what source files were used to build it. When your program stops, @value{GDBN} spontaneously prints the line where it stopped. Likewise, when you select a stack frame (@pxref{Selection, ,Selecting a Frame}), @value{GDBN} prints the line where execution in that frame has stopped. You can print other portions of source files by explicit command. If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}. @menu * List:: Printing source lines * Specify Location:: How to specify code locations * Edit:: Editing source files * Search:: Searching source files * Source Path:: Specifying source directories * Machine Code:: Source and machine code @end menu @node List @section Printing Source Lines @kindex list @kindex l @r{(@code{list})} To print lines from a source file, use the @code{list} command (abbreviated @code{l}). By default, ten lines are printed. There are several ways to specify what part of the file you want to print; see @ref{Specify Location}, for the full list. Here are the forms of the @code{list} command most commonly used: @table @code @item list @var{linenum} Print lines centered around line number @var{linenum} in the current source file. @item list @var{function} Print lines centered around the beginning of function @var{function}. @item list Print more lines. If the last lines printed were printed with a @code{list} command, this prints lines following the last lines printed; however, if the last line printed was a solitary line printed as part of displaying a stack frame (@pxref{Stack, ,Examining the Stack}), this prints lines centered around that line. @item list - Print lines just before the lines last printed. @end table @cindex @code{list}, how many lines to display By default, @value{GDBN} prints ten source lines with any of these forms of the @code{list} command. You can change this using @code{set listsize}: @table @code @kindex set listsize @item set listsize @var{count} @itemx set listsize unlimited Make the @code{list} command display @var{count} source lines (unless the @code{list} argument explicitly specifies some other number). Setting @var{count} to @code{unlimited} or 0 means there's no limit. @kindex show listsize @item show listsize Display the number of lines that @code{list} prints. @end table Repeating a @code{list} command with @key{RET} discards the argument, so it is equivalent to typing just @code{list}. This is more useful than listing the same lines again. An exception is made for an argument of @samp{-}; that argument is preserved in repetition so that each repetition moves up in the source file. In general, the @code{list} command expects you to supply zero, one or two @dfn{locations}. Locations specify source lines; there are several ways of writing them (@pxref{Specify Location}), but the effect is always to specify some source line. Here is a complete description of the possible arguments for @code{list}: @table @code @item list @var{location} Print lines centered around the line specified by @var{location}. @item list @var{first},@var{last} Print lines from @var{first} to @var{last}. Both arguments are locations. When a @code{list} command has two locations, and the source file of the second location is omitted, this refers to the same source file as the first location. @item list ,@var{last} Print lines ending with @var{last}. @item list @var{first}, Print lines starting with @var{first}. @item list + Print lines just after the lines last printed. @item list - Print lines just before the lines last printed. @item list As described in the preceding table. @end table @node Specify Location @section Specifying a Location @cindex specifying location @cindex location @cindex source location @menu * Linespec Locations:: Linespec locations * Explicit Locations:: Explicit locations * Address Locations:: Address locations @end menu Several @value{GDBN} commands accept arguments that specify a location of your program's code. Since @value{GDBN} is a source-level debugger, a location usually specifies some line in the source code. Locations may be specified using three different formats: linespec locations, explicit locations, or address locations. @node Linespec Locations @subsection Linespec Locations @cindex linespec locations A @dfn{linespec} is a colon-separated list of source location parameters such as file name, function name, etc. Here are all the different ways of specifying a linespec: @table @code @item @var{linenum} Specifies the line number @var{linenum} of the current source file. @item -@var{offset} @itemx +@var{offset} Specifies the line @var{offset} lines before or after the @dfn{current line}. For the @code{list} command, the current line is the last one printed; for the breakpoint commands, this is the line at which execution stopped in the currently selected @dfn{stack frame} (@pxref{Frames, ,Frames}, for a description of stack frames.) When used as the second of the two linespecs in a @code{list} command, this specifies the line @var{offset} lines up or down from the first linespec. @item @var{filename}:@var{linenum} Specifies the line @var{linenum} in the source file @var{filename}. If @var{filename} is a relative file name, then it will match any source file name with the same trailing components. For example, if @var{filename} is @samp{gcc/expr.c}, then it will match source file name of @file{/build/trunk/gcc/expr.c}, but not @file{/build/trunk/libcpp/expr.c} or @file{/build/trunk/gcc/x-expr.c}. @item @var{function} Specifies the line that begins the body of the function @var{function}. For example, in C, this is the line with the open brace. By default, in C@t{++} and Ada, @var{function} is interpreted as specifying all functions named @var{function} in all scopes. For C@t{++}, this means in all namespaces and classes. For Ada, this means in all packages. For example, assuming a program with C@t{++} symbols named @code{A::B::func} and @code{B::func}, both commands @w{@kbd{break func}} and @w{@kbd{break B::func}} set a breakpoint on both symbols. Commands that accept a linespec let you override this with the @code{-qualified} option. For example, @w{@kbd{break -qualified func}} sets a breakpoint on a free-function named @code{func} ignoring any C@t{++} class methods and namespace functions called @code{func}. @xref{Explicit Locations}. @item @var{function}:@var{label} Specifies the line where @var{label} appears in @var{function}. @item @var{filename}:@var{function} Specifies the line that begins the body of the function @var{function} in the file @var{filename}. You only need the file name with a function name to avoid ambiguity when there are identically named functions in different source files. @item @var{label} Specifies the line at which the label named @var{label} appears in the function corresponding to the currently selected stack frame. If there is no current selected stack frame (for instance, if the inferior is not running), then @value{GDBN} will not search for a label. @cindex breakpoint at static probe point @item -pstap|-probe-stap @r{[}@var{objfile}:@r{[}@var{provider}:@r{]}@r{]}@var{name} The @sc{gnu}/Linux tool @code{SystemTap} provides a way for applications to embed static probes. @xref{Static Probe Points}, for more information on finding and using static probes. This form of linespec specifies the location of such a static probe. If @var{objfile} is given, only probes coming from that shared library or executable matching @var{objfile} as a regular expression are considered. If @var{provider} is given, then only probes from that provider are considered. If several probes match the spec, @value{GDBN} will insert a breakpoint at each one of those probes. @end table @node Explicit Locations @subsection Explicit Locations @cindex explicit locations @dfn{Explicit locations} allow the user to directly specify the source location's parameters using option-value pairs. Explicit locations are useful when several functions, labels, or file names have the same name (base name for files) in the program's sources. In these cases, explicit locations point to the source line you meant more accurately and unambiguously. Also, using explicit locations might be faster in large programs. For example, the linespec @samp{foo:bar} may refer to a function @code{bar} defined in the file named @file{foo} or the label @code{bar} in a function named @code{foo}. @value{GDBN} must search either the file system or the symbol table to know. The list of valid explicit location options is summarized in the following table: @table @code @item -source @var{filename} The value specifies the source file name. To differentiate between files with the same base name, prepend as many directories as is necessary to uniquely identify the desired file, e.g., @file{foo/bar/baz.c}. Otherwise @value{GDBN} will use the first file it finds with the given base name. This option requires the use of either @code{-function} or @code{-line}. @item -function @var{function} The value specifies the name of a function. Operations on function locations unmodified by other options (such as @code{-label} or @code{-line}) refer to the line that begins the body of the function. In C, for example, this is the line with the open brace. By default, in C@t{++} and Ada, @var{function} is interpreted as specifying all functions named @var{function} in all scopes. For C@t{++}, this means in all namespaces and classes. For Ada, this means in all packages. For example, assuming a program with C@t{++} symbols named @code{A::B::func} and @code{B::func}, both commands @w{@kbd{break -function func}} and @w{@kbd{break -function B::func}} set a breakpoint on both symbols. You can use the @kbd{-qualified} flag to override this (see below). @item -qualified This flag makes @value{GDBN} interpret a function name specified with @kbd{-function} as a complete fully-qualified name. For example, assuming a C@t{++} program with symbols named @code{A::B::func} and @code{B::func}, the @w{@kbd{break -qualified -function B::func}} command sets a breakpoint on @code{B::func}, only. (Note: the @kbd{-qualified} option can precede a linespec as well (@pxref{Linespec Locations}), so the particular example above could be simplified as @w{@kbd{break -qualified B::func}}.) @item -label @var{label} The value specifies the name of a label. When the function name is not specified, the label is searched in the function of the currently selected stack frame. @item -line @var{number} The value specifies a line offset for the location. The offset may either be absolute (@code{-line 3}) or relative (@code{-line +3}), depending on the command. When specified without any other options, the line offset is relative to the current line. @end table Explicit location options may be abbreviated by omitting any non-unique trailing characters from the option name, e.g., @w{@kbd{break -s main.c -li 3}}. @node Address Locations @subsection Address Locations @cindex address locations @dfn{Address locations} indicate a specific program address. They have the generalized form *@var{address}. For line-oriented commands, such as @code{list} and @code{edit}, this specifies a source line that contains @var{address}. For @code{break} and other breakpoint-oriented commands, this can be used to set breakpoints in parts of your program which do not have debugging information or source files. Here @var{address} may be any expression valid in the current working language (@pxref{Languages, working language}) that specifies a code address. In addition, as a convenience, @value{GDBN} extends the semantics of expressions used in locations to cover several situations that frequently occur during debugging. Here are the various forms of @var{address}: @table @code @item @var{expression} Any expression valid in the current working language. @item @var{funcaddr} An address of a function or procedure derived from its name. In C, C@t{++}, Objective-C, Fortran, minimal, and assembly, this is simply the function's name @var{function} (and actually a special case of a valid expression). In Pascal and Modula-2, this is @code{&@var{function}}. In Ada, this is @code{@var{function}'Address} (although the Pascal form also works). This form specifies the address of the function's first instruction, before the stack frame and arguments have been set up. @item '@var{filename}':@var{funcaddr} Like @var{funcaddr} above, but also specifies the name of the source file explicitly. This is useful if the name of the function does not specify the function unambiguously, e.g., if there are several functions with identical names in different source files. @end table @node Edit @section Editing Source Files @cindex editing source files @kindex edit @kindex e @r{(@code{edit})} To edit the lines in a source file, use the @code{edit} command. The editing program of your choice is invoked with the current line set to the active line in the program. Alternatively, there are several ways to specify what part of the file you want to print if you want to see other parts of the program: @table @code @item edit @var{location} Edit the source file specified by @code{location}. Editing starts at that @var{location}, e.g., at the specified source line of the specified file. @xref{Specify Location}, for all the possible forms of the @var{location} argument; here are the forms of the @code{edit} command most commonly used: @table @code @item edit @var{number} Edit the current source file with @var{number} as the active line number. @item edit @var{function} Edit the file containing @var{function} at the beginning of its definition. @end table @end table @subsection Choosing your Editor You can customize @value{GDBN} to use any editor you want @footnote{ The only restriction is that your editor (say @code{ex}), recognizes the following command-line syntax: @smallexample ex +@var{number} file @end smallexample The optional numeric value +@var{number} specifies the number of the line in the file where to start editing.}. By default, it is @file{@value{EDITOR}}, but you can change this by setting the environment variable @code{EDITOR} before using @value{GDBN}. For example, to configure @value{GDBN} to use the @code{vi} editor, you could use these commands with the @code{sh} shell: @smallexample EDITOR=/usr/bin/vi export EDITOR gdb @dots{} @end smallexample or in the @code{csh} shell, @smallexample setenv EDITOR /usr/bin/vi gdb @dots{} @end smallexample @node Search @section Searching Source Files @cindex searching source files There are two commands for searching through the current source file for a regular expression. @table @code @kindex search @kindex forward-search @kindex fo @r{(@code{forward-search})} @item forward-search @var{regexp} @itemx search @var{regexp} The command @samp{forward-search @var{regexp}} checks each line, starting with the one following the last line listed, for a match for @var{regexp}. It lists the line that is found. You can use the synonym @samp{search @var{regexp}} or abbreviate the command name as @code{fo}. @kindex reverse-search @item reverse-search @var{regexp} The command @samp{reverse-search @var{regexp}} checks each line, starting with the one before the last line listed and going backward, for a match for @var{regexp}. It lists the line that is found. You can abbreviate this command as @code{rev}. @end table @node Source Path @section Specifying Source Directories @cindex source path @cindex directories for source files Executable programs sometimes do not record the directories of the source files from which they were compiled, just the names. Even when they do, the directories could be moved between the compilation and your debugging session. @value{GDBN} has a list of directories to search for source files; this is called the @dfn{source path}. Each time @value{GDBN} wants a source file, it tries all the directories in the list, in the order they are present in the list, until it finds a file with the desired name. For example, suppose an executable references the file @file{/usr/src/foo-1.0/lib/foo.c}, does not record a compilation directory, and the @dfn{source path} is @file{/mnt/cross}. @value{GDBN} would look for the source file in the following locations: @enumerate @item @file{/usr/src/foo-1.0/lib/foo.c} @item @file{/mnt/cross/usr/src/foo-1.0/lib/foo.c} @item @file{/mnt/cross/foo.c} @end enumerate If the source file is not present at any of the above locations then an error is printed. @value{GDBN} does not look up the parts of the source file name, such as @file{/mnt/cross/src/foo-1.0/lib/foo.c}. Likewise, the subdirectories of the source path are not searched: if the source path is @file{/mnt/cross}, and the binary refers to @file{foo.c}, @value{GDBN} would not find it under @file{/mnt/cross/usr/src/foo-1.0/lib}. Plain file names, relative file names with leading directories, file names containing dots, etc.@: are all treated as described above, except that non-absolute file names are not looked up literally. If the @dfn{source path} is @file{/mnt/cross}, the source file is recorded as @file{../lib/foo.c}, and no compilation directory is recorded, then @value{GDBN} will search in the following locations: @enumerate @item @file{/mnt/cross/../lib/foo.c} @item @file{/mnt/cross/foo.c} @end enumerate @kindex cdir @kindex cwd @vindex $cdir@r{, convenience variable} @vindex $cwd@r{, convenience variable} @cindex compilation directory @cindex current directory @cindex working directory @cindex directory, current @cindex directory, compilation The @dfn{source path} will always include two special entries @samp{$cdir} and @samp{$cwd}, these refer to the compilation directory (if one is recorded) and the current working directory respectively. @samp{$cdir} causes @value{GDBN} to search within the compilation directory, if one is recorded in the debug information. If no compilation directory is recorded in the debug information then @samp{$cdir} is ignored. @samp{$cwd} is not the same as @samp{.}---the former tracks the current working directory as it changes during your @value{GDBN} session, while the latter is immediately expanded to the current directory at the time you add an entry to the source path. If a compilation directory is recorded in the debug information, and @value{GDBN} has not found the source file after the first search using @dfn{source path}, then @value{GDBN} will combine the compilation directory and the filename, and then search for the source file again using the @dfn{source path}. For example, if the executable records the source file as @file{/usr/src/foo-1.0/lib/foo.c}, the compilation directory is recorded as @file{/project/build}, and the @dfn{source path} is @file{/mnt/cross:$cdir:$cwd} while the current working directory of the @value{GDBN} session is @file{/home/user}, then @value{GDBN} will search for the source file in the following locations: @enumerate @item @file{/usr/src/foo-1.0/lib/foo.c} @item @file{/mnt/cross/usr/src/foo-1.0/lib/foo.c} @item @file{/project/build/usr/src/foo-1.0/lib/foo.c} @item @file{/home/user/usr/src/foo-1.0/lib/foo.c} @item @file{/mnt/cross/project/build/usr/src/foo-1.0/lib/foo.c} @item @file{/project/build/project/build/usr/src/foo-1.0/lib/foo.c} @item @file{/home/user/project/build/usr/src/foo-1.0/lib/foo.c} @item @file{/mnt/cross/foo.c} @item @file{/project/build/foo.c} @item @file{/home/user/foo.c} @end enumerate If the file name in the previous example had been recorded in the executable as a relative path rather than an absolute path, then the first look up would not have occurred, but all of the remaining steps would be similar. When searching for source files on MS-DOS and MS-Windows, where absolute paths start with a drive letter (e.g. @file{C:/project/foo.c}), @value{GDBN} will remove the drive letter from the file name before appending it to a search directory from @dfn{source path}; for instance if the executable references the source file @file{C:/project/foo.c} and @dfn{source path} is set to @file{D:/mnt/cross}, then @value{GDBN} will search in the following locations for the source file: @enumerate @item @file{C:/project/foo.c} @item @file{D:/mnt/cross/project/foo.c} @item @file{D:/mnt/cross/foo.c} @end enumerate Note that the executable search path is @emph{not} used to locate the source files. Whenever you reset or rearrange the source path, @value{GDBN} clears out any information it has cached about where source files are found and where each line is in the file. @kindex directory @kindex dir When you start @value{GDBN}, its source path includes only @samp{$cdir} and @samp{$cwd}, in that order. To add other directories, use the @code{directory} command. The search path is used to find both program source files and @value{GDBN} script files (read using the @samp{-command} option and @samp{source} command). In addition to the source path, @value{GDBN} provides a set of commands that manage a list of source path substitution rules. A @dfn{substitution rule} specifies how to rewrite source directories stored in the program's debug information in case the sources were moved to a different directory between compilation and debugging. A rule is made of two strings, the first specifying what needs to be rewritten in the path, and the second specifying how it should be rewritten. In @ref{set substitute-path}, we name these two parts @var{from} and @var{to} respectively. @value{GDBN} does a simple string replacement of @var{from} with @var{to} at the start of the directory part of the source file name, and uses that result instead of the original file name to look up the sources. Using the previous example, suppose the @file{foo-1.0} tree has been moved from @file{/usr/src} to @file{/mnt/cross}, then you can tell @value{GDBN} to replace @file{/usr/src} in all source path names with @file{/mnt/cross}. The first lookup will then be @file{/mnt/cross/foo-1.0/lib/foo.c} in place of the original location of @file{/usr/src/foo-1.0/lib/foo.c}. To define a source path substitution rule, use the @code{set substitute-path} command (@pxref{set substitute-path}). To avoid unexpected substitution results, a rule is applied only if the @var{from} part of the directory name ends at a directory separator. For instance, a rule substituting @file{/usr/source} into @file{/mnt/cross} will be applied to @file{/usr/source/foo-1.0} but not to @file{/usr/sourceware/foo-2.0}. And because the substitution is applied only at the beginning of the directory name, this rule will not be applied to @file{/root/usr/source/baz.c} either. In many cases, you can achieve the same result using the @code{directory} command. However, @code{set substitute-path} can be more efficient in the case where the sources are organized in a complex tree with multiple subdirectories. With the @code{directory} command, you need to add each subdirectory of your project. If you moved the entire tree while preserving its internal organization, then @code{set substitute-path} allows you to direct the debugger to all the sources with one single command. @code{set substitute-path} is also more than just a shortcut command. The source path is only used if the file at the original location no longer exists. On the other hand, @code{set substitute-path} modifies the debugger behavior to look at the rewritten location instead. So, if for any reason a source file that is not relevant to your executable is located at the original location, a substitution rule is the only method available to point @value{GDBN} at the new location. @cindex @samp{--with-relocated-sources} @cindex default source path substitution You can configure a default source path substitution rule by configuring @value{GDBN} with the @samp{--with-relocated-sources=@var{dir}} option. The @var{dir} should be the name of a directory under @value{GDBN}'s configured prefix (set with @samp{--prefix} or @samp{--exec-prefix}), and directory names in debug information under @var{dir} will be adjusted automatically if the installed @value{GDBN} is moved to a new location. This is useful if @value{GDBN}, libraries or executables with debug information and corresponding source code are being moved together. @table @code @item directory @var{dirname} @dots{} @item dir @var{dirname} @dots{} Add directory @var{dirname} to the front of the source path. Several directory names may be given to this command, separated by @samp{:} (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as part of absolute file names) or whitespace. You may specify a directory that is already in the source path; this moves it forward, so @value{GDBN} searches it sooner. The special strings @samp{$cdir} (to refer to the compilation directory, if one is recorded), and @samp{$cwd} (to refer to the current working directory) can also be included in the list of directories @var{dirname}. Though these will already be in the source path they will be moved forward in the list so @value{GDBN} searches them sooner. @item directory Reset the source path to its default value (@samp{$cdir:$cwd} on Unix systems). This requires confirmation. @c RET-repeat for @code{directory} is explicitly disabled, but since @c repeating it would be a no-op we do not say that. (thanks to RMS) @item set directories @var{path-list} @kindex set directories Set the source path to @var{path-list}. @samp{$cdir:$cwd} are added if missing. @item show directories @kindex show directories Print the source path: show which directories it contains. @anchor{set substitute-path} @item set substitute-path @var{from} @var{to} @kindex set substitute-path Define a source path substitution rule, and add it at the end of the current list of existing substitution rules. If a rule with the same @var{from} was already defined, then the old rule is also deleted. For example, if the file @file{/foo/bar/baz.c} was moved to @file{/mnt/cross/baz.c}, then the command @smallexample (@value{GDBP}) set substitute-path /foo/bar /mnt/cross @end smallexample @noindent will tell @value{GDBN} to replace @samp{/foo/bar} with @samp{/mnt/cross}, which will allow @value{GDBN} to find the file @file{baz.c} even though it was moved. In the case when more than one substitution rule have been defined, the rules are evaluated one by one in the order where they have been defined. The first one matching, if any, is selected to perform the substitution. For instance, if we had entered the following commands: @smallexample (@value{GDBP}) set substitute-path /usr/src/include /mnt/include (@value{GDBP}) set substitute-path /usr/src /mnt/src @end smallexample @noindent @value{GDBN} would then rewrite @file{/usr/src/include/defs.h} into @file{/mnt/include/defs.h} by using the first rule. However, it would use the second rule to rewrite @file{/usr/src/lib/foo.c} into @file{/mnt/src/lib/foo.c}. @item unset substitute-path [path] @kindex unset substitute-path If a path is specified, search the current list of substitution rules for a rule that would rewrite that path. Delete that rule if found. A warning is emitted by the debugger if no rule could be found. If no path is specified, then all substitution rules are deleted. @item show substitute-path [path] @kindex show substitute-path If a path is specified, then print the source path substitution rule which would rewrite that path, if any. If no path is specified, then print all existing source path substitution rules. @end table If your source path is cluttered with directories that are no longer of interest, @value{GDBN} may sometimes cause confusion by finding the wrong versions of source. You can correct the situation as follows: @enumerate @item Use @code{directory} with no argument to reset the source path to its default value. @item Use @code{directory} with suitable arguments to reinstall the directories you want in the source path. You can add all the directories in one command. @end enumerate @node Machine Code @section Source and Machine Code @cindex source line and its code address You can use the command @code{info line} to map source lines to program addresses (and vice versa), and the command @code{disassemble} to display a range of addresses as machine instructions. You can use the command @code{set disassemble-next-line} to set whether to disassemble next source line when execution stops. When run under @sc{gnu} Emacs mode, the @code{info line} command causes the arrow to point to the line specified. Also, @code{info line} prints addresses in symbolic form as well as hex. @table @code @kindex info line @item info line @itemx info line @var{location} Print the starting and ending addresses of the compiled code for source line @var{location}. You can specify source lines in any of the ways documented in @ref{Specify Location}. With no @var{location} information about the current source line is printed. @end table For example, we can use @code{info line} to discover the location of the object code for the first line of function @code{m4_changequote}: @smallexample (@value{GDBP}) info line m4_changequote Line 895 of "builtin.c" starts at pc 0x634c <m4_changequote> and \ ends at 0x6350 <m4_changequote+4>. @end smallexample @noindent @cindex code address and its source line We can also inquire (using @code{*@var{addr}} as the form for @var{location}) what source line covers a particular address: @smallexample (@value{GDBP}) info line *0x63ff Line 926 of "builtin.c" starts at pc 0x63e4 <m4_changequote+152> and \ ends at 0x6404 <m4_changequote+184>. @end smallexample @cindex @code{$_} and @code{info line} @cindex @code{x} command, default address @kindex x@r{(examine), and} info line After @code{info line}, the default address for the @code{x} command is changed to the starting address of the line, so that @samp{x/i} is sufficient to begin examining the machine code (@pxref{Memory, ,Examining Memory}). Also, this address is saved as the value of the convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience Variables}). @cindex info line, repeated calls After @code{info line}, using @code{info line} again without specifying a location will display information about the next source line. @table @code @kindex disassemble @cindex assembly instructions @cindex instructions, assembly @cindex machine instructions @cindex listing machine instructions @item disassemble @itemx disassemble /m @itemx disassemble /s @itemx disassemble /r This specialized command dumps a range of memory as machine instructions. It can also print mixed source+disassembly by specifying the @code{/m} or @code{/s} modifier and print the raw instructions in hex as well as in symbolic form by specifying the @code{/r} modifier. The default memory range is the function surrounding the program counter of the selected frame. A single argument to this command is a program counter value; @value{GDBN} dumps the function surrounding this value. When two arguments are given, they should be separated by a comma, possibly surrounded by whitespace. The arguments specify a range of addresses to dump, in one of two forms: @table @code @item @var{start},@var{end} the addresses from @var{start} (inclusive) to @var{end} (exclusive) @item @var{start},+@var{length} the addresses from @var{start} (inclusive) to @code{@var{start}+@var{length}} (exclusive). @end table @noindent When 2 arguments are specified, the name of the function is also printed (since there could be several functions in the given range). The argument(s) can be any expression yielding a numeric value, such as @samp{0x32c4}, @samp{&main+10} or @samp{$pc - 8}. If the range of memory being disassembled contains current program counter, the instruction at that location is shown with a @code{=>} marker. @end table The following example shows the disassembly of a range of addresses of HP PA-RISC 2.0 code: @smallexample (@value{GDBP}) disas 0x32c4, 0x32e4 Dump of assembler code from 0x32c4 to 0x32e4: 0x32c4 <main+204>: addil 0,dp 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26 0x32cc <main+212>: ldil 0x3000,r31 0x32d0 <main+216>: ble 0x3f8(sr4,r31) 0x32d4 <main+220>: ldo 0(r31),rp 0x32d8 <main+224>: addil -0x800,dp 0x32dc <main+228>: ldo 0x588(r1),r26 0x32e0 <main+232>: ldil 0x3000,r31 End of assembler dump. @end smallexample Here is an example showing mixed source+assembly for Intel x86 with @code{/m} or @code{/s}, when the program is stopped just after function prologue in a non-optimized function with no inline code. @smallexample (@value{GDBP}) disas /m main Dump of assembler code for function main: 5 @{ 0x08048330 <+0>: push %ebp 0x08048331 <+1>: mov %esp,%ebp 0x08048333 <+3>: sub $0x8,%esp 0x08048336 <+6>: and $0xfffffff0,%esp 0x08048339 <+9>: sub $0x10,%esp 6 printf ("Hello.\n"); => 0x0804833c <+12>: movl $0x8048440,(%esp) 0x08048343 <+19>: call 0x8048284 <puts@@plt> 7 return 0; 8 @} 0x08048348 <+24>: mov $0x0,%eax 0x0804834d <+29>: leave 0x0804834e <+30>: ret End of assembler dump. @end smallexample The @code{/m} option is deprecated as its output is not useful when there is either inlined code or re-ordered code. The @code{/s} option is the preferred choice. Here is an example for AMD x86-64 showing the difference between @code{/m} output and @code{/s} output. This example has one inline function defined in a header file, and the code is compiled with @samp{-O2} optimization. Note how the @code{/m} output is missing the disassembly of several instructions that are present in the @code{/s} output. @file{foo.h}: @smallexample int foo (int a) @{ if (a < 0) return a * 2; if (a == 0) return 1; return a + 10; @} @end smallexample @file{foo.c}: @smallexample #include "foo.h" volatile int x, y; int main () @{ x = foo (y); return 0; @} @end smallexample @smallexample (@value{GDBP}) disas /m main Dump of assembler code for function main: 5 @{ 6 x = foo (y); 0x0000000000400400 <+0>: mov 0x200c2e(%rip),%eax # 0x601034 <y> 0x0000000000400417 <+23>: mov %eax,0x200c13(%rip) # 0x601030 <x> 7 return 0; 8 @} 0x000000000040041d <+29>: xor %eax,%eax 0x000000000040041f <+31>: retq 0x0000000000400420 <+32>: add %eax,%eax 0x0000000000400422 <+34>: jmp 0x400417 <main+23> End of assembler dump. (@value{GDBP}) disas /s main Dump of assembler code for function main: foo.c: 5 @{ 6 x = foo (y); 0x0000000000400400 <+0>: mov 0x200c2e(%rip),%eax # 0x601034 <y> foo.h: 4 if (a < 0) 0x0000000000400406 <+6>: test %eax,%eax 0x0000000000400408 <+8>: js 0x400420 <main+32> 6 if (a == 0) 7 return 1; 8 return a + 10; 0x000000000040040a <+10>: lea 0xa(%rax),%edx 0x000000000040040d <+13>: test %eax,%eax 0x000000000040040f <+15>: mov $0x1,%eax 0x0000000000400414 <+20>: cmovne %edx,%eax foo.c: 6 x = foo (y); 0x0000000000400417 <+23>: mov %eax,0x200c13(%rip) # 0x601030 <x> 7 return 0; 8 @} 0x000000000040041d <+29>: xor %eax,%eax 0x000000000040041f <+31>: retq foo.h: 5 return a * 2; 0x0000000000400420 <+32>: add %eax,%eax 0x0000000000400422 <+34>: jmp 0x400417 <main+23> End of assembler dump. @end smallexample Here is another example showing raw instructions in hex for AMD x86-64, @smallexample (gdb) disas /r 0x400281,+10 Dump of assembler code from 0x400281 to 0x40028b: 0x0000000000400281: 38 36 cmp %dh,(%rsi) 0x0000000000400283: 2d 36 34 2e 73 sub $0x732e3436,%eax 0x0000000000400288: 6f outsl %ds:(%rsi),(%dx) 0x0000000000400289: 2e 32 00 xor %cs:(%rax),%al End of assembler dump. @end smallexample Addresses cannot be specified as a location (@pxref{Specify Location}). So, for example, if you want to disassemble function @code{bar} in file @file{foo.c}, you must type @samp{disassemble 'foo.c'::bar} and not @samp{disassemble foo.c:bar}. Some architectures have more than one commonly-used set of instruction mnemonics or other syntax. For programs that were dynamically linked and use shared libraries, instructions that call functions or branch to locations in the shared libraries might show a seemingly bogus location---it's actually a location of the relocation table. On some architectures, @value{GDBN} might be able to resolve these to actual function names. @table @code @kindex set disassembler-options @cindex disassembler options @item set disassembler-options @var{option1}[,@var{option2}@dots{}] This command controls the passing of target specific information to the disassembler. For a list of valid options, please refer to the @code{-M}/@code{--disassembler-options} section of the @samp{objdump} manual and/or the output of @kbd{objdump --help} (@pxref{objdump,,objdump,binutils,The GNU Binary Utilities}). The default value is the empty string. If it is necessary to specify more than one disassembler option, then multiple options can be placed together into a comma separated list. Currently this command is only supported on targets ARM, MIPS, PowerPC and S/390. @kindex show disassembler-options @item show disassembler-options Show the current setting of the disassembler options. @end table @table @code @kindex set disassembly-flavor @cindex Intel disassembly flavor @cindex AT&T disassembly flavor @item set disassembly-flavor @var{instruction-set} Select the instruction set to use when disassembling the program via the @code{disassemble} or @code{x/i} commands. Currently this command is only defined for the Intel x86 family. You can set @var{instruction-set} to either @code{intel} or @code{att}. The default is @code{att}, the AT&T flavor used by default by Unix assemblers for x86-based targets. @kindex show disassembly-flavor @item show disassembly-flavor Show the current setting of the disassembly flavor. @end table @table @code @kindex set disassemble-next-line @kindex show disassemble-next-line @item set disassemble-next-line @itemx show disassemble-next-line Control whether or not @value{GDBN} will disassemble the next source line or instruction when execution stops. If ON, @value{GDBN} will display disassembly of the next source line when execution of the program being debugged stops. This is @emph{in addition} to displaying the source line itself, which @value{GDBN} always does if possible. If the next source line cannot be displayed for some reason (e.g., if @value{GDBN} cannot find the source file, or there's no line info in the debug info), @value{GDBN} will display disassembly of the next @emph{instruction} instead of showing the next source line. If AUTO, @value{GDBN} will display disassembly of next instruction only if the source line cannot be displayed. This setting causes @value{GDBN} to display some feedback when you step through a function with no line info or whose source file is unavailable. The default is OFF, which means never display the disassembly of the next line or instruction. @end table @node Data @chapter Examining Data @cindex printing data @cindex examining data @kindex print @kindex inspect The usual way to examine data in your program is with the @code{print} command (abbreviated @code{p}), or its synonym @code{inspect}. It evaluates and prints the value of an expression of the language your program is written in (@pxref{Languages, ,Using @value{GDBN} with Different Languages}). It may also print the expression using a Python-based pretty-printer (@pxref{Pretty Printing}). @table @code @item print [[@var{options}] --] @var{expr} @itemx print [[@var{options}] --] /@var{f} @var{expr} @var{expr} is an expression (in the source language). By default the value of @var{expr} is printed in a format appropriate to its data type; you can choose a different format by specifying @samp{/@var{f}}, where @var{f} is a letter specifying the format; see @ref{Output Formats,,Output Formats}. @anchor{print options} The @code{print} command supports a number of options that allow overriding relevant global print settings as set by @code{set print} subcommands: @table @code @item -address [@code{on}|@code{off}] Set printing of addresses. Related setting: @ref{set print address}. @item -array [@code{on}|@code{off}] Pretty formatting of arrays. Related setting: @ref{set print array}. @item -array-indexes [@code{on}|@code{off}] Set printing of array indexes. Related setting: @ref{set print array-indexes}. @item -elements @var{number-of-elements}|@code{unlimited} Set limit on string chars or array elements to print. The value @code{unlimited} causes there to be no limit. Related setting: @ref{set print elements}. @item -max-depth @var{depth}|@code{unlimited} Set the threshold after which nested structures are replaced with ellipsis. Related setting: @ref{set print max-depth}. @item -null-stop [@code{on}|@code{off}] Set printing of char arrays to stop at first null char. Related setting: @ref{set print null-stop}. @item -object [@code{on}|@code{off}] Set printing C@t{++} virtual function tables. Related setting: @ref{set print object}. @item -pretty [@code{on}|@code{off}] Set pretty formatting of structures. Related setting: @ref{set print pretty}. @item -raw-values [@code{on}|@code{off}] Set whether to print values in raw form, bypassing any pretty-printers for that value. Related setting: @ref{set print raw-values}. @item -repeats @var{number-of-repeats}|@code{unlimited} Set threshold for repeated print elements. @code{unlimited} causes all elements to be individually printed. Related setting: @ref{set print repeats}. @item -static-members [@code{on}|@code{off}] Set printing C@t{++} static members. Related setting: @ref{set print static-members}. @item -symbol [@code{on}|@code{off}] Set printing of symbol names when printing pointers. Related setting: @ref{set print symbol}. @item -union [@code{on}|@code{off}] Set printing of unions interior to structures. Related setting: @ref{set print union}. @item -vtbl [@code{on}|@code{off}] Set printing of C++ virtual function tables. Related setting: @ref{set print vtbl}. @end table Because the @code{print} command accepts arbitrary expressions which may look like options (including abbreviations), if you specify any command option, then you must use a double dash (@code{--}) to mark the end of option processing. For example, this prints the value of the @code{-p} expression: @smallexample (@value{GDBP}) print -p @end smallexample While this repeats the last value in the value history (see below) with the @code{-pretty} option in effect: @smallexample (@value{GDBP}) print -p -- @end smallexample Here is an example including both on option and an expression: @smallexample @group (@value{GDBP}) print -pretty -- *myptr $1 = @{ next = 0x0, flags = @{ sweet = 1, sour = 1 @}, meat = 0x54 "Pork" @} @end group @end smallexample @item print [@var{options}] @itemx print [@var{options}] /@var{f} @cindex reprint the last value If you omit @var{expr}, @value{GDBN} displays the last value again (from the @dfn{value history}; @pxref{Value History, ,Value History}). This allows you to conveniently inspect the same value in an alternative format. @end table A more low-level way of examining data is with the @code{x} command. It examines data in memory at a specified address and prints it in a specified format. @xref{Memory, ,Examining Memory}. If you are interested in information about types, or about how the fields of a struct or a class are declared, use the @code{ptype @var{exp}} command rather than @code{print}. @xref{Symbols, ,Examining the Symbol Table}. @cindex exploring hierarchical data structures @kindex explore Another way of examining values of expressions and type information is through the Python extension command @code{explore} (available only if the @value{GDBN} build is configured with @code{--with-python}). It offers an interactive way to start at the highest level (or, the most abstract level) of the data type of an expression (or, the data type itself) and explore all the way down to leaf scalar values/fields embedded in the higher level data types. @table @code @item explore @var{arg} @var{arg} is either an expression (in the source language), or a type visible in the current context of the program being debugged. @end table The working of the @code{explore} command can be illustrated with an example. If a data type @code{struct ComplexStruct} is defined in your C program as @smallexample struct SimpleStruct @{ int i; double d; @}; struct ComplexStruct @{ struct SimpleStruct *ss_p; int arr[10]; @}; @end smallexample @noindent followed by variable declarations as @smallexample struct SimpleStruct ss = @{ 10, 1.11 @}; struct ComplexStruct cs = @{ &ss, @{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 @} @}; @end smallexample @noindent then, the value of the variable @code{cs} can be explored using the @code{explore} command as follows. @smallexample (gdb) explore cs The value of `cs' is a struct/class of type `struct ComplexStruct' with the following fields: ss_p = <Enter 0 to explore this field of type `struct SimpleStruct *'> arr = <Enter 1 to explore this field of type `int [10]'> Enter the field number of choice: @end smallexample @noindent Since the fields of @code{cs} are not scalar values, you are being prompted to chose the field you want to explore. Let's say you choose the field @code{ss_p} by entering @code{0}. Then, since this field is a pointer, you will be asked if it is pointing to a single value. From the declaration of @code{cs} above, it is indeed pointing to a single value, hence you enter @code{y}. If you enter @code{n}, then you will be asked if it were pointing to an array of values, in which case this field will be explored as if it were an array. @smallexample `cs.ss_p' is a pointer to a value of type `struct SimpleStruct' Continue exploring it as a pointer to a single value [y/n]: y The value of `*(cs.ss_p)' is a struct/class of type `struct SimpleStruct' with the following fields: i = 10 .. (Value of type `int') d = 1.1100000000000001 .. (Value of type `double') Press enter to return to parent value: @end smallexample @noindent If the field @code{arr} of @code{cs} was chosen for exploration by entering @code{1} earlier, then since it is as array, you will be prompted to enter the index of the element in the array that you want to explore. @smallexample `cs.arr' is an array of `int'. Enter the index of the element you want to explore in `cs.arr': 5 `(cs.arr)[5]' is a scalar value of type `int'. (cs.arr)[5] = 4 Press enter to return to parent value: @end smallexample In general, at any stage of exploration, you can go deeper towards the leaf values by responding to the prompts appropriately, or hit the return key to return to the enclosing data structure (the @i{higher} level data structure). Similar to exploring values, you can use the @code{explore} command to explore types. Instead of specifying a value (which is typically a variable name or an expression valid in the current context of the program being debugged), you specify a type name. If you consider the same example as above, your can explore the type @code{struct ComplexStruct} by passing the argument @code{struct ComplexStruct} to the @code{explore} command. @smallexample (gdb) explore struct ComplexStruct @end smallexample @noindent By responding to the prompts appropriately in the subsequent interactive session, you can explore the type @code{struct ComplexStruct} in a manner similar to how the value @code{cs} was explored in the above example. The @code{explore} command also has two sub-commands, @code{explore value} and @code{explore type}. The former sub-command is a way to explicitly specify that value exploration of the argument is being invoked, while the latter is a way to explicitly specify that type exploration of the argument is being invoked. @table @code @item explore value @var{expr} @cindex explore value This sub-command of @code{explore} explores the value of the expression @var{expr} (if @var{expr} is an expression valid in the current context of the program being debugged). The behavior of this command is identical to that of the behavior of the @code{explore} command being passed the argument @var{expr}. @item explore type @var{arg} @cindex explore type This sub-command of @code{explore} explores the type of @var{arg} (if @var{arg} is a type visible in the current context of program being debugged), or the type of the value/expression @var{arg} (if @var{arg} is an expression valid in the current context of the program being debugged). If @var{arg} is a type, then the behavior of this command is identical to that of the @code{explore} command being passed the argument @var{arg}. If @var{arg} is an expression, then the behavior of this command will be identical to that of the @code{explore} command being passed the type of @var{arg} as the argument. @end table @menu * Expressions:: Expressions * Ambiguous Expressions:: Ambiguous Expressions * Variables:: Program variables * Arrays:: Artificial arrays * Output Formats:: Output formats * Memory:: Examining memory * Auto Display:: Automatic display * Print Settings:: Print settings * Pretty Printing:: Python pretty printing * Value History:: Value history * Convenience Vars:: Convenience variables * Convenience Funs:: Convenience functions * Registers:: Registers * Floating Point Hardware:: Floating point hardware * Vector Unit:: Vector Unit * OS Information:: Auxiliary data provided by operating system * Memory Region Attributes:: Memory region attributes * Dump/Restore Files:: Copy between memory and a file * Core File Generation:: Cause a program dump its core * Character Sets:: Debugging programs that use a different character set than GDB does * Caching Target Data:: Data caching for targets * Searching Memory:: Searching memory for a sequence of bytes * Value Sizes:: Managing memory allocated for values @end menu @node Expressions @section Expressions @cindex expressions @code{print} and many other @value{GDBN} commands accept an expression and compute its value. Any kind of constant, variable or operator defined by the programming language you are using is valid in an expression in @value{GDBN}. This includes conditional expressions, function calls, casts, and string constants. It also includes preprocessor macros, if you compiled your program to include this information; see @ref{Compilation}. @cindex arrays in expressions @value{GDBN} supports array constants in expressions input by the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example, you can use the command @code{print @{1, 2, 3@}} to create an array of three integers. If you pass an array to a function or assign it to a program variable, @value{GDBN} copies the array to memory that is @code{malloc}ed in the target program. Because C is so widespread, most of the expressions shown in examples in this manual are in C. @xref{Languages, , Using @value{GDBN} with Different Languages}, for information on how to use expressions in other languages. In this section, we discuss operators that you can use in @value{GDBN} expressions regardless of your programming language. @cindex casts, in expressions Casts are supported in all languages, not just in C, because it is so useful to cast a number into a pointer in order to examine a structure at that address in memory. @c FIXME: casts supported---Mod2 true? @value{GDBN} supports these operators, in addition to those common to programming languages: @table @code @item @@ @samp{@@} is a binary operator for treating parts of memory as arrays. @xref{Arrays, ,Artificial Arrays}, for more information. @item :: @samp{::} allows you to specify a variable in terms of the file or function where it is defined. @xref{Variables, ,Program Variables}. @cindex @{@var{type}@} @cindex type casting memory @cindex memory, viewing as typed object @cindex casts, to view memory @item @{@var{type}@} @var{addr} Refers to an object of type @var{type} stored at address @var{addr} in memory. The address @var{addr} may be any expression whose value is an integer or pointer (but parentheses are required around binary operators, just as in a cast). This construct is allowed regardless of what kind of data is normally supposed to reside at @var{addr}. @end table @node Ambiguous Expressions @section Ambiguous Expressions @cindex ambiguous expressions Expressions can sometimes contain some ambiguous elements. For instance, some programming languages (notably Ada, C@t{++} and Objective-C) permit a single function name to be defined several times, for application in different contexts. This is called @dfn{overloading}. Another example involving Ada is generics. A @dfn{generic package} is similar to C@t{++} templates and is typically instantiated several times, resulting in the same function name being defined in different contexts. In some cases and depending on the language, it is possible to adjust the expression to remove the ambiguity. For instance in C@t{++}, you can specify the signature of the function you want to break on, as in @kbd{break @var{function}(@var{types})}. In Ada, using the fully qualified name of your function often makes the expression unambiguous as well. When an ambiguity that needs to be resolved is detected, the debugger has the capability to display a menu of numbered choices for each possibility, and then waits for the selection with the prompt @samp{>}. The first option is always @samp{[0] cancel}, and typing @kbd{0 @key{RET}} aborts the current command. If the command in which the expression was used allows more than one choice to be selected, the next option in the menu is @samp{[1] all}, and typing @kbd{1 @key{RET}} selects all possible choices. For example, the following session excerpt shows an attempt to set a breakpoint at the overloaded symbol @code{String::after}. We choose three particular definitions of that function name: @c FIXME! This is likely to change to show arg type lists, at least @smallexample @group (@value{GDBP}) b String::after [0] cancel [1] all [2] file:String.cc; line number:867 [3] file:String.cc; line number:860 [4] file:String.cc; line number:875 [5] file:String.cc; line number:853 [6] file:String.cc; line number:846 [7] file:String.cc; line number:735 > 2 4 6 Breakpoint 1 at 0xb26c: file String.cc, line 867. Breakpoint 2 at 0xb344: file String.cc, line 875. Breakpoint 3 at 0xafcc: file String.cc, line 846. Multiple breakpoints were set. Use the "delete" command to delete unwanted breakpoints. (@value{GDBP}) @end group @end smallexample @table @code @kindex set multiple-symbols @item set multiple-symbols @var{mode} @cindex multiple-symbols menu This option allows you to adjust the debugger behavior when an expression is ambiguous. By default, @var{mode} is set to @code{all}. If the command with which the expression is used allows more than one choice, then @value{GDBN} automatically selects all possible choices. For instance, inserting a breakpoint on a function using an ambiguous name results in a breakpoint inserted on each possible match. However, if a unique choice must be made, then @value{GDBN} uses the menu to help you disambiguate the expression. For instance, printing the address of an overloaded function will result in the use of the menu. When @var{mode} is set to @code{ask}, the debugger always uses the menu when an ambiguity is detected. Finally, when @var{mode} is set to @code{cancel}, the debugger reports an error due to the ambiguity and the command is aborted. @kindex show multiple-symbols @item show multiple-symbols Show the current value of the @code{multiple-symbols} setting. @end table @node Variables @section Program Variables The most common kind of expression to use is the name of a variable in your program. Variables in expressions are understood in the selected stack frame (@pxref{Selection, ,Selecting a Frame}); they must be either: @itemize @bullet @item global (or file-static) @end itemize @noindent or @itemize @bullet @item visible according to the scope rules of the programming language from the point of execution in that frame @end itemize @noindent This means that in the function @smallexample foo (a) int a; @{ bar (a); @{ int b = test (); bar (b); @} @} @end smallexample @noindent you can examine and use the variable @code{a} whenever your program is executing within the function @code{foo}, but you can only use or examine the variable @code{b} while your program is executing inside the block where @code{b} is declared. @cindex variable name conflict There is an exception: you can refer to a variable or function whose scope is a single source file even if the current execution point is not in this file. But it is possible to have more than one such variable or function with the same name (in different source files). If that happens, referring to that name has unpredictable effects. If you wish, you can specify a static variable in a particular function or file by using the colon-colon (@code{::}) notation: @cindex colon-colon, context for variables/functions @ifnotinfo @c info cannot cope with a :: index entry, but why deprive hard copy readers? @cindex @code{::}, context for variables/functions @end ifnotinfo @smallexample @var{file}::@var{variable} @var{function}::@var{variable} @end smallexample @noindent Here @var{file} or @var{function} is the name of the context for the static @var{variable}. In the case of file names, you can use quotes to make sure @value{GDBN} parses the file name as a single word---for example, to print a global value of @code{x} defined in @file{f2.c}: @smallexample (@value{GDBP}) p 'f2.c'::x @end smallexample The @code{::} notation is normally used for referring to static variables, since you typically disambiguate uses of local variables in functions by selecting the appropriate frame and using the simple name of the variable. However, you may also use this notation to refer to local variables in frames enclosing the selected frame: @smallexample void foo (int a) @{ if (a < 10) bar (a); else process (a); /* Stop here */ @} int bar (int a) @{ foo (a + 5); @} @end smallexample @noindent For example, if there is a breakpoint at the commented line, here is what you might see when the program stops after executing the call @code{bar(0)}: @smallexample (@value{GDBP}) p a $1 = 10 (@value{GDBP}) p bar::a $2 = 5 (@value{GDBP}) up 2 #2 0x080483d0 in foo (a=5) at foobar.c:12 (@value{GDBP}) p a $3 = 5 (@value{GDBP}) p bar::a $4 = 0 @end smallexample @cindex C@t{++} scope resolution These uses of @samp{::} are very rarely in conflict with the very similar use of the same notation in C@t{++}. When they are in conflict, the C@t{++} meaning takes precedence; however, this can be overridden by quoting the file or function name with single quotes. For example, suppose the program is stopped in a method of a class that has a field named @code{includefile}, and there is also an include file named @file{includefile} that defines a variable, @code{some_global}. @smallexample (@value{GDBP}) p includefile $1 = 23 (@value{GDBP}) p includefile::some_global A syntax error in expression, near `'. (@value{GDBP}) p 'includefile'::some_global $2 = 27 @end smallexample @cindex wrong values @cindex variable values, wrong @cindex function entry/exit, wrong values of variables @cindex optimized code, wrong values of variables @quotation @emph{Warning:} Occasionally, a local variable may appear to have the wrong value at certain points in a function---just after entry to a new scope, and just before exit. @end quotation You may see this problem when you are stepping by machine instructions. This is because, on most machines, it takes more than one instruction to set up a stack frame (including local variable definitions); if you are stepping by machine instructions, variables may appear to have the wrong values until the stack frame is completely built. On exit, it usually also takes more than one machine instruction to destroy a stack frame; after you begin stepping through that group of instructions, local variable definitions may be gone. This may also happen when the compiler does significant optimizations. To be sure of always seeing accurate values, turn off all optimization when compiling. @cindex ``No symbol "foo" in current context'' Another possible effect of compiler optimizations is to optimize unused variables out of existence, or assign variables to registers (as opposed to memory addresses). Depending on the support for such cases offered by the debug info format used by the compiler, @value{GDBN} might not be able to display values for such local variables. If that happens, @value{GDBN} will print a message like this: @smallexample No symbol "foo" in current context. @end smallexample To solve such problems, either recompile without optimizations, or use a different debug info format, if the compiler supports several such formats. @xref{Compilation}, for more information on choosing compiler options. @xref{C, ,C and C@t{++}}, for more information about debug info formats that are best suited to C@t{++} programs. If you ask to print an object whose contents are unknown to @value{GDBN}, e.g., because its data type is not completely specified by the debug information, @value{GDBN} will say @samp{<incomplete type>}. @xref{Symbols, incomplete type}, for more about this. @cindex no debug info variables If you try to examine or use the value of a (global) variable for which @value{GDBN} has no type information, e.g., because the program includes no debug information, @value{GDBN} displays an error message. @xref{Symbols, unknown type}, for more about unknown types. If you cast the variable to its declared type, @value{GDBN} gets the variable's value using the cast-to type as the variable's type. For example, in a C program: @smallexample (@value{GDBP}) p var 'var' has unknown type; cast it to its declared type (@value{GDBP}) p (float) var $1 = 3.14 @end smallexample If you append @kbd{@@entry} string to a function parameter name you get its value at the time the function got called. If the value is not available an error message is printed. Entry values are available only with some compilers. Entry values are normally also printed at the function parameter list according to @ref{set print entry-values}. @smallexample Breakpoint 1, d (i=30) at gdb.base/entry-value.c:29 29 i++; (gdb) next 30 e (i); (gdb) print i $1 = 31 (gdb) print i@@entry $2 = 30 @end smallexample Strings are identified as arrays of @code{char} values without specified signedness. Arrays of either @code{signed char} or @code{unsigned char} get printed as arrays of 1 byte sized integers. @code{-fsigned-char} or @code{-funsigned-char} @value{NGCC} options have no effect as @value{GDBN} defines literal string type @code{"char"} as @code{char} without a sign. For program code @smallexample char var0[] = "A"; signed char var1[] = "A"; @end smallexample You get during debugging @smallexample (gdb) print var0 $1 = "A" (gdb) print var1 $2 = @{65 'A', 0 '\0'@} @end smallexample @node Arrays @section Artificial Arrays @cindex artificial array @cindex arrays @kindex @@@r{, referencing memory as an array} It is often useful to print out several successive objects of the same type in memory; a section of an array, or an array of dynamically determined size for which only a pointer exists in the program. You can do this by referring to a contiguous span of memory as an @dfn{artificial array}, using the binary operator @samp{@@}. The left operand of @samp{@@} should be the first element of the desired array and be an individual object. The right operand should be the desired length of the array. The result is an array value whose elements are all of the type of the left argument. The first element is actually the left argument; the second element comes from bytes of memory immediately following those that hold the first element, and so on. Here is an example. If a program says @smallexample int *array = (int *) malloc (len * sizeof (int)); @end smallexample @noindent you can print the contents of @code{array} with @smallexample p *array@@len @end smallexample The left operand of @samp{@@} must reside in memory. Array values made with @samp{@@} in this way behave just like other arrays in terms of subscripting, and are coerced to pointers when used in expressions. Artificial arrays most often appear in expressions via the value history (@pxref{Value History, ,Value History}), after printing one out. Another way to create an artificial array is to use a cast. This re-interprets a value as if it were an array. The value need not be in memory: @smallexample (@value{GDBP}) p/x (short[2])0x12345678 $1 = @{0x1234, 0x5678@} @end smallexample As a convenience, if you leave the array length out (as in @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}: @smallexample (@value{GDBP}) p/x (short[])0x12345678 $2 = @{0x1234, 0x5678@} @end smallexample Sometimes the artificial array mechanism is not quite enough; in moderately complex data structures, the elements of interest may not actually be adjacent---for example, if you are interested in the values of pointers in an array. One useful work-around in this situation is to use a convenience variable (@pxref{Convenience Vars, ,Convenience Variables}) as a counter in an expression that prints the first interesting value, and then repeat that expression via @key{RET}. For instance, suppose you have an array @code{dtab} of pointers to structures, and you are interested in the values of a field @code{fv} in each structure. Here is an example of what you might type: @smallexample set $i = 0 p dtab[$i++]->fv @key{RET} @key{RET} @dots{} @end smallexample @node Output Formats @section Output Formats @cindex formatted output @cindex output formats By default, @value{GDBN} prints a value according to its data type. Sometimes this is not what you want. For example, you might want to print a number in hex, or a pointer in decimal. Or you might want to view data in memory at a certain address as a character string or as an instruction. To do these things, specify an @dfn{output format} when you print a value. The simplest use of output formats is to say how to print a value already computed. This is done by starting the arguments of the @code{print} command with a slash and a format letter. The format letters supported are: @table @code @item x Regard the bits of the value as an integer, and print the integer in hexadecimal. @item d Print as integer in signed decimal. @item u Print as integer in unsigned decimal. @item o Print as integer in octal. @item t Print as integer in binary. The letter @samp{t} stands for ``two''. @footnote{@samp{b} cannot be used because these format letters are also used with the @code{x} command, where @samp{b} stands for ``byte''; see @ref{Memory,,Examining Memory}.} @item a @cindex unknown address, locating @cindex locate address Print as an address, both absolute in hexadecimal and as an offset from the nearest preceding symbol. You can use this format used to discover where (in what function) an unknown address is located: @smallexample (@value{GDBP}) p/a 0x54320 $3 = 0x54320 <_initialize_vx+396> @end smallexample @noindent The command @code{info symbol 0x54320} yields similar results. @xref{Symbols, info symbol}. @item c Regard as an integer and print it as a character constant. This prints both the numerical value and its character representation. The character representation is replaced with the octal escape @samp{\nnn} for characters outside the 7-bit @sc{ascii} range. Without this format, @value{GDBN} displays @code{char}, @w{@code{unsigned char}}, and @w{@code{signed char}} data as character constants. Single-byte members of vectors are displayed as integer data. @item f Regard the bits of the value as a floating point number and print using typical floating point syntax. @item s @cindex printing strings @cindex printing byte arrays Regard as a string, if possible. With this format, pointers to single-byte data are displayed as null-terminated strings and arrays of single-byte data are displayed as fixed-length strings. Other values are displayed in their natural types. Without this format, @value{GDBN} displays pointers to and arrays of @code{char}, @w{@code{unsigned char}}, and @w{@code{signed char}} as strings. Single-byte members of a vector are displayed as an integer array. @item z Like @samp{x} formatting, the value is treated as an integer and printed as hexadecimal, but leading zeros are printed to pad the value to the size of the integer type. @item r @cindex raw printing Print using the @samp{raw} formatting. By default, @value{GDBN} will use a Python-based pretty-printer, if one is available (@pxref{Pretty Printing}). This typically results in a higher-level display of the value's contents. The @samp{r} format bypasses any Python pretty-printer which might exist. @end table For example, to print the program counter in hex (@pxref{Registers}), type @smallexample p/x $pc @end smallexample @noindent Note that no space is required before the slash; this is because command names in @value{GDBN} cannot contain a slash. To reprint the last value in the value history with a different format, you can use the @code{print} command with just a format and no expression. For example, @samp{p/x} reprints the last value in hex. @node Memory @section Examining Memory You can use the command @code{x} (for ``examine'') to examine memory in any of several formats, independently of your program's data types. @cindex examining memory @table @code @kindex x @r{(examine memory)} @item x/@var{nfu} @var{addr} @itemx x @var{addr} @itemx x Use the @code{x} command to examine memory. @end table @var{n}, @var{f}, and @var{u} are all optional parameters that specify how much memory to display and how to format it; @var{addr} is an expression giving the address where you want to start displaying memory. If you use defaults for @var{nfu}, you need not type the slash @samp{/}. Several commands set convenient defaults for @var{addr}. @table @r @item @var{n}, the repeat count The repeat count is a decimal integer; the default is 1. It specifies how much memory (counting by units @var{u}) to display. If a negative number is specified, memory is examined backward from @var{addr}. @c This really is **decimal**; unaffected by 'set radix' as of GDB @c 4.1.2. @item @var{f}, the display format The display format is one of the formats used by @code{print} (@samp{x}, @samp{d}, @samp{u}, @samp{o}, @samp{t}, @samp{a}, @samp{c}, @samp{f}, @samp{s}), and in addition @samp{i} (for machine instructions). The default is @samp{x} (hexadecimal) initially. The default changes each time you use either @code{x} or @code{print}. @item @var{u}, the unit size The unit size is any of @table @code @item b Bytes. @item h Halfwords (two bytes). @item w Words (four bytes). This is the initial default. @item g Giant words (eight bytes). @end table Each time you specify a unit size with @code{x}, that size becomes the default unit the next time you use @code{x}. For the @samp{i} format, the unit size is ignored and is normally not written. For the @samp{s} format, the unit size defaults to @samp{b}, unless it is explicitly given. Use @kbd{x /hs} to display 16-bit char strings and @kbd{x /ws} to display 32-bit strings. The next use of @kbd{x /s} will again display 8-bit strings. Note that the results depend on the programming language of the current compilation unit. If the language is C, the @samp{s} modifier will use the UTF-16 encoding while @samp{w} will use UTF-32. The encoding is set by the programming language and cannot be altered. @item @var{addr}, starting display address @var{addr} is the address where you want @value{GDBN} to begin displaying memory. The expression need not have a pointer value (though it may); it is always interpreted as an integer address of a byte of memory. @xref{Expressions, ,Expressions}, for more information on expressions. The default for @var{addr} is usually just after the last address examined---but several other commands also set the default address: @code{info breakpoints} (to the address of the last breakpoint listed), @code{info line} (to the starting address of a line), and @code{print} (if you use it to display a value from memory). @end table For example, @samp{x/3uh 0x54320} is a request to display three halfwords (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}), starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four words (@samp{w}) of memory above the stack pointer (here, @samp{$sp}; @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}). You can also specify a negative repeat count to examine memory backward from the given address. For example, @samp{x/-3uh 0x54320} prints three halfwords (@code{h}) at @code{0x54314}, @code{0x54328}, and @code{0x5431c}. Since the letters indicating unit sizes are all distinct from the letters specifying output formats, you do not have to remember whether unit size or format comes first; either order works. The output specifications @samp{4xw} and @samp{4wx} mean exactly the same thing. (However, the count @var{n} must come first; @samp{wx4} does not work.) Even though the unit size @var{u} is ignored for the formats @samp{s} and @samp{i}, you might still want to use a count @var{n}; for example, @samp{3i} specifies that you want to see three machine instructions, including any operands. For convenience, especially when used with the @code{display} command, the @samp{i} format also prints branch delay slot instructions, if any, beyond the count specified, which immediately follow the last instruction that is within the count. The command @code{disassemble} gives an alternative way of inspecting machine instructions; see @ref{Machine Code,,Source and Machine Code}. If a negative repeat count is specified for the formats @samp{s} or @samp{i}, the command displays null-terminated strings or instructions before the given address as many as the absolute value of the given number. For the @samp{i} format, we use line number information in the debug info to accurately locate instruction boundaries while disassembling backward. If line info is not available, the command stops examining memory with an error message. All the defaults for the arguments to @code{x} are designed to make it easy to continue scanning memory with minimal specifications each time you use @code{x}. For example, after you have inspected three machine instructions with @samp{x/3i @var{addr}}, you can inspect the next seven with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command, the repeat count @var{n} is used again; the other arguments default as for successive uses of @code{x}. When examining machine instructions, the instruction at current program counter is shown with a @code{=>} marker. For example: @smallexample (@value{GDBP}) x/5i $pc-6 0x804837f <main+11>: mov %esp,%ebp 0x8048381 <main+13>: push %ecx 0x8048382 <main+14>: sub $0x4,%esp => 0x8048385 <main+17>: movl $0x8048460,(%esp) 0x804838c <main+24>: call 0x80482d4 <puts@@plt> @end smallexample @cindex @code{$_}, @code{$__}, and value history The addresses and contents printed by the @code{x} command are not saved in the value history because there is often too much of them and they would get in the way. Instead, @value{GDBN} makes these values available for subsequent use in expressions as values of the convenience variables @code{$_} and @code{$__}. After an @code{x} command, the last address examined is available for use in expressions in the convenience variable @code{$_}. The contents of that address, as examined, are available in the convenience variable @code{$__}. If the @code{x} command has a repeat count, the address and contents saved are from the last memory unit printed; this is not the same as the last address printed if several units were printed on the last line of output. @anchor{addressable memory unit} @cindex addressable memory unit Most targets have an addressable memory unit size of 8 bits. This means that to each memory address are associated 8 bits of data. Some targets, however, have other addressable memory unit sizes. Within @value{GDBN} and this document, the term @dfn{addressable memory unit} (or @dfn{memory unit} for short) is used when explicitly referring to a chunk of data of that size. The word @dfn{byte} is used to refer to a chunk of data of 8 bits, regardless of the addressable memory unit size of the target. For most systems, addressable memory unit is a synonym of byte. @cindex remote memory comparison @cindex target memory comparison @cindex verify remote memory image @cindex verify target memory image When you are debugging a program running on a remote target machine (@pxref{Remote Debugging}), you may wish to verify the program's image in the remote machine's memory against the executable file you downloaded to the target. Or, on any target, you may want to check whether the program has corrupted its own read-only sections. The @code{compare-sections} command is provided for such situations. @table @code @kindex compare-sections @item compare-sections @r{[}@var{section-name}@r{|}@code{-r}@r{]} Compare the data of a loadable section @var{section-name} in the executable file of the program being debugged with the same section in the target machine's memory, and report any mismatches. With no arguments, compares all loadable sections. With an argument of @code{-r}, compares all loadable read-only sections. Note: for remote targets, this command can be accelerated if the target supports computing the CRC checksum of a block of memory (@pxref{qCRC packet}). @end table @node Auto Display @section Automatic Display @cindex automatic display @cindex display of expressions If you find that you want to print the value of an expression frequently (to see how it changes), you might want to add it to the @dfn{automatic display list} so that @value{GDBN} prints its value each time your program stops. Each expression added to the list is given a number to identify it; to remove an expression from the list, you specify that number. The automatic display looks like this: @smallexample 2: foo = 38 3: bar[5] = (struct hack *) 0x3804 @end smallexample @noindent This display shows item numbers, expressions and their current values. As with displays you request manually using @code{x} or @code{print}, you can specify the output format you prefer; in fact, @code{display} decides whether to use @code{print} or @code{x} depending your format specification---it uses @code{x} if you specify either the @samp{i} or @samp{s} format, or a unit size; otherwise it uses @code{print}. @table @code @kindex display @item display @var{expr} Add the expression @var{expr} to the list of expressions to display each time your program stops. @xref{Expressions, ,Expressions}. @code{display} does not repeat if you press @key{RET} again after using it. @item display/@var{fmt} @var{expr} For @var{fmt} specifying only a display format and not a size or count, add the expression @var{expr} to the auto-display list but arrange to display it each time in the specified format @var{fmt}. @xref{Output Formats,,Output Formats}. @item display/@var{fmt} @var{addr} For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a number of units, add the expression @var{addr} as a memory address to be examined each time your program stops. Examining means in effect doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining Memory}. @end table For example, @samp{display/i $pc} can be helpful, to see the machine instruction about to be executed each time execution stops (@samp{$pc} is a common name for the program counter; @pxref{Registers, ,Registers}). @table @code @kindex delete display @kindex undisplay @item undisplay @var{dnums}@dots{} @itemx delete display @var{dnums}@dots{} Remove items from the list of expressions to display. Specify the numbers of the displays that you want affected with the command argument @var{dnums}. It can be a single display number, one of the numbers shown in the first field of the @samp{info display} display; or it could be a range of display numbers, as in @code{2-4}. @code{undisplay} does not repeat if you press @key{RET} after using it. (Otherwise you would just get the error @samp{No display number @dots{}}.) @kindex disable display @item disable display @var{dnums}@dots{} Disable the display of item numbers @var{dnums}. A disabled display item is not printed automatically, but is not forgotten. It may be enabled again later. Specify the numbers of the displays that you want affected with the command argument @var{dnums}. It can be a single display number, one of the numbers shown in the first field of the @samp{info display} display; or it could be a range of display numbers, as in @code{2-4}. @kindex enable display @item enable display @var{dnums}@dots{} Enable display of item numbers @var{dnums}. It becomes effective once again in auto display of its expression, until you specify otherwise. Specify the numbers of the displays that you want affected with the command argument @var{dnums}. It can be a single display number, one of the numbers shown in the first field of the @samp{info display} display; or it could be a range of display numbers, as in @code{2-4}. @item display Display the current values of the expressions on the list, just as is done when your program stops. @kindex info display @item info display Print the list of expressions previously set up to display automatically, each one with its item number, but without showing the values. This includes disabled expressions, which are marked as such. It also includes expressions which would not be displayed right now because they refer to automatic variables not currently available. @end table @cindex display disabled out of scope If a display expression refers to local variables, then it does not make sense outside the lexical context for which it was set up. Such an expression is disabled when execution enters a context where one of its variables is not defined. For example, if you give the command @code{display last_char} while inside a function with an argument @code{last_char}, @value{GDBN} displays this argument while your program continues to stop inside that function. When it stops elsewhere---where there is no variable @code{last_char}---the display is disabled automatically. The next time your program stops where @code{last_char} is meaningful, you can enable the display expression once again. @node Print Settings @section Print Settings @cindex format options @cindex print settings @value{GDBN} provides the following ways to control how arrays, structures, and symbols are printed. @noindent These settings are useful for debugging programs in any language: @table @code @kindex set print @anchor{set print address} @item set print address @itemx set print address on @cindex print/don't print memory addresses @value{GDBN} prints memory addresses showing the location of stack traces, structure values, pointer values, breakpoints, and so forth, even when it also displays the contents of those addresses. The default is @code{on}. For example, this is what a stack frame display looks like with @code{set print address on}: @smallexample @group (@value{GDBP}) f #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>") at input.c:530 530 if (lquote != def_lquote) @end group @end smallexample @item set print address off Do not print addresses when displaying their contents. For example, this is the same stack frame displayed with @code{set print address off}: @smallexample @group (@value{GDBP}) set print addr off (@value{GDBP}) f #0 set_quotes (lq="<<", rq=">>") at input.c:530 530 if (lquote != def_lquote) @end group @end smallexample You can use @samp{set print address off} to eliminate all machine dependent displays from the @value{GDBN} interface. For example, with @code{print address off}, you should get the same text for backtraces on all machines---whether or not they involve pointer arguments. @kindex show print @item show print address Show whether or not addresses are to be printed. @end table When @value{GDBN} prints a symbolic address, it normally prints the closest earlier symbol plus an offset. If that symbol does not uniquely identify the address (for example, it is a name whose scope is a single source file), you may need to clarify. One way to do this is with @code{info line}, for example @samp{info line *0x4537}. Alternately, you can set @value{GDBN} to print the source file and line number when it prints a symbolic address: @table @code @item set print symbol-filename on @cindex source file and line of a symbol @cindex symbol, source file and line Tell @value{GDBN} to print the source file name and line number of a symbol in the symbolic form of an address. @item set print symbol-filename off Do not print source file name and line number of a symbol. This is the default. @item show print symbol-filename Show whether or not @value{GDBN} will print the source file name and line number of a symbol in the symbolic form of an address. @end table Another situation where it is helpful to show symbol filenames and line numbers is when disassembling code; @value{GDBN} shows you the line number and source file that corresponds to each instruction. Also, you may wish to see the symbolic form only if the address being printed is reasonably close to the closest earlier symbol: @table @code @item set print max-symbolic-offset @var{max-offset} @itemx set print max-symbolic-offset unlimited @cindex maximum value for offset of closest symbol Tell @value{GDBN} to only display the symbolic form of an address if the offset between the closest earlier symbol and the address is less than @var{max-offset}. The default is @code{unlimited}, which tells @value{GDBN} to always print the symbolic form of an address if any symbol precedes it. Zero is equivalent to @code{unlimited}. @item show print max-symbolic-offset Ask how large the maximum offset is that @value{GDBN} prints in a symbolic address. @end table @cindex wild pointer, interpreting @cindex pointer, finding referent If you have a pointer and you are not sure where it points, try @samp{set print symbol-filename on}. Then you can determine the name and source file location of the variable where it points, using @samp{p/a @var{pointer}}. This interprets the address in symbolic form. For example, here @value{GDBN} shows that a variable @code{ptt} points at another variable @code{t}, defined in @file{hi2.c}: @smallexample (@value{GDBP}) set print symbol-filename on (@value{GDBP}) p/a ptt $4 = 0xe008 <t in hi2.c> @end smallexample @quotation @emph{Warning:} For pointers that point to a local variable, @samp{p/a} does not show the symbol name and filename of the referent, even with the appropriate @code{set print} options turned on. @end quotation You can also enable @samp{/a}-like formatting all the time using @samp{set print symbol on}: @anchor{set print symbol} @table @code @item set print symbol on Tell @value{GDBN} to print the symbol corresponding to an address, if one exists. @item set print symbol off Tell @value{GDBN} not to print the symbol corresponding to an address. In this mode, @value{GDBN} will still print the symbol corresponding to pointers to functions. This is the default. @item show print symbol Show whether @value{GDBN} will display the symbol corresponding to an address. @end table Other settings control how different kinds of objects are printed: @table @code @anchor{set print array} @item set print array @itemx set print array on @cindex pretty print arrays Pretty print arrays. This format is more convenient to read, but uses more space. The default is off. @item set print array off Return to compressed format for arrays. @item show print array Show whether compressed or pretty format is selected for displaying arrays. @cindex print array indexes @anchor{set print array-indexes} @item set print array-indexes @itemx set print array-indexes on Print the index of each element when displaying arrays. May be more convenient to locate a given element in the array or quickly find the index of a given element in that printed array. The default is off. @item set print array-indexes off Stop printing element indexes when displaying arrays. @item show print array-indexes Show whether the index of each element is printed when displaying arrays. @anchor{set print elements} @item set print elements @var{number-of-elements} @itemx set print elements unlimited @cindex number of array elements to print @cindex limit on number of printed array elements Set a limit on how many elements of an array @value{GDBN} will print. If @value{GDBN} is printing a large array, it stops printing after it has printed the number of elements set by the @code{set print elements} command. This limit also applies to the display of strings. When @value{GDBN} starts, this limit is set to 200. Setting @var{number-of-elements} to @code{unlimited} or zero means that the number of elements to print is unlimited. @item show print elements Display the number of elements of a large array that @value{GDBN} will print. If the number is 0, then the printing is unlimited. @anchor{set print frame-arguments} @item set print frame-arguments @var{value} @kindex set print frame-arguments @cindex printing frame argument values @cindex print all frame argument values @cindex print frame argument values for scalars only @cindex do not print frame arguments This command allows to control how the values of arguments are printed when the debugger prints a frame (@pxref{Frames}). The possible values are: @table @code @item all The values of all arguments are printed. @item scalars Print the value of an argument only if it is a scalar. The value of more complex arguments such as arrays, structures, unions, etc, is replaced by @code{@dots{}}. This is the default. Here is an example where only scalar arguments are shown: @smallexample #1 0x08048361 in call_me (i=3, s=@dots{}, ss=0xbf8d508c, u=@dots{}, e=green) at frame-args.c:23 @end smallexample @item none None of the argument values are printed. Instead, the value of each argument is replaced by @code{@dots{}}. In this case, the example above now becomes: @smallexample #1 0x08048361 in call_me (i=@dots{}, s=@dots{}, ss=@dots{}, u=@dots{}, e=@dots{}) at frame-args.c:23 @end smallexample @item presence Only the presence of arguments is indicated by @code{@dots{}}. The @code{@dots{}} are not printed for function without any arguments. None of the argument names and values are printed. In this case, the example above now becomes: @smallexample #1 0x08048361 in call_me (@dots{}) at frame-args.c:23 @end smallexample @end table By default, only scalar arguments are printed. This command can be used to configure the debugger to print the value of all arguments, regardless of their type. However, it is often advantageous to not print the value of more complex parameters. For instance, it reduces the amount of information printed in each frame, making the backtrace more readable. Also, it improves performance when displaying Ada frames, because the computation of large arguments can sometimes be CPU-intensive, especially in large applications. Setting @code{print frame-arguments} to @code{scalars} (the default), @code{none} or @code{presence} avoids this computation, thus speeding up the display of each Ada frame. @item show print frame-arguments Show how the value of arguments should be displayed when printing a frame. @anchor{set print raw-frame-arguments} @item set print raw-frame-arguments on Print frame arguments in raw, non pretty-printed, form. @item set print raw-frame-arguments off Print frame arguments in pretty-printed form, if there is a pretty-printer for the value (@pxref{Pretty Printing}), otherwise print the value in raw form. This is the default. @item show print raw-frame-arguments Show whether to print frame arguments in raw form. @anchor{set print entry-values} @item set print entry-values @var{value} @kindex set print entry-values Set printing of frame argument values at function entry. In some cases @value{GDBN} can determine the value of function argument which was passed by the function caller, even if the value was modified inside the called function and therefore is different. With optimized code, the current value could be unavailable, but the entry value may still be known. The default value is @code{default} (see below for its description). Older @value{GDBN} behaved as with the setting @code{no}. Compilers not supporting this feature will behave in the @code{default} setting the same way as with the @code{no} setting. This functionality is currently supported only by DWARF 2 debugging format and the compiler has to produce @samp{DW_TAG_call_site} tags. With @value{NGCC}, you need to specify @option{-O -g} during compilation, to get this information. The @var{value} parameter can be one of the following: @table @code @item no Print only actual parameter values, never print values from function entry point. @smallexample #0 equal (val=5) #0 different (val=6) #0 lost (val=<optimized out>) #0 born (val=10) #0 invalid (val=<optimized out>) @end smallexample @item only Print only parameter values from function entry point. The actual parameter values are never printed. @smallexample #0 equal (val@@entry=5) #0 different (val@@entry=5) #0 lost (val@@entry=5) #0 born (val@@entry=<optimized out>) #0 invalid (val@@entry=<optimized out>) @end smallexample @item preferred Print only parameter values from function entry point. If value from function entry point is not known while the actual value is known, print the actual value for such parameter. @smallexample #0 equal (val@@entry=5) #0 different (val@@entry=5) #0 lost (val@@entry=5) #0 born (val=10) #0 invalid (val@@entry=<optimized out>) @end smallexample @item if-needed Print actual parameter values. If actual parameter value is not known while value from function entry point is known, print the entry point value for such parameter. @smallexample #0 equal (val=5) #0 different (val=6) #0 lost (val@@entry=5) #0 born (val=10) #0 invalid (val=<optimized out>) @end smallexample @item both Always print both the actual parameter value and its value from function entry point, even if values of one or both are not available due to compiler optimizations. @smallexample #0 equal (val=5, val@@entry=5) #0 different (val=6, val@@entry=5) #0 lost (val=<optimized out>, val@@entry=5) #0 born (val=10, val@@entry=<optimized out>) #0 invalid (val=<optimized out>, val@@entry=<optimized out>) @end smallexample @item compact Print the actual parameter value if it is known and also its value from function entry point if it is known. If neither is known, print for the actual value @code{<optimized out>}. If not in MI mode (@pxref{GDB/MI}) and if both values are known and identical, print the shortened @code{param=param@@entry=VALUE} notation. @smallexample #0 equal (val=val@@entry=5) #0 different (val=6, val@@entry=5) #0 lost (val@@entry=5) #0 born (val=10) #0 invalid (val=<optimized out>) @end smallexample @item default Always print the actual parameter value. Print also its value from function entry point, but only if it is known. If not in MI mode (@pxref{GDB/MI}) and if both values are known and identical, print the shortened @code{param=param@@entry=VALUE} notation. @smallexample #0 equal (val=val@@entry=5) #0 different (val=6, val@@entry=5) #0 lost (val=<optimized out>, val@@entry=5) #0 born (val=10) #0 invalid (val=<optimized out>) @end smallexample @end table For analysis messages on possible failures of frame argument values at function entry resolution see @ref{set debug entry-values}. @item show print entry-values Show the method being used for printing of frame argument values at function entry. @anchor{set print frame-info} @item set print frame-info @var{value} @kindex set print frame-info @cindex printing frame information @cindex frame information, printing This command allows to control the information printed when the debugger prints a frame. See @ref{Frames}, @ref{Backtrace}, for a general explanation about frames and frame information. Note that some other settings (such as @code{set print frame-arguments} and @code{set print address}) are also influencing if and how some frame information is displayed. In particular, the frame program counter is never printed if @code{set print address} is off. The possible values for @code{set print frame-info} are: @table @code @item short-location Print the frame level, the program counter (if not at the beginning of the location source line), the function, the function arguments. @item location Same as @code{short-location} but also print the source file and source line number. @item location-and-address Same as @code{location} but print the program counter even if located at the beginning of the location source line. @item source-line Print the program counter (if not at the beginning of the location source line), the line number and the source line. @item source-and-location Print what @code{location} and @code{source-line} are printing. @item auto The information printed for a frame is decided automatically by the @value{GDBN} command that prints a frame. For example, @code{frame} prints the information printed by @code{source-and-location} while @code{stepi} will switch between @code{source-line} and @code{source-and-location} depending on the program counter. The default value is @code{auto}. @end table @anchor{set print repeats} @item set print repeats @var{number-of-repeats} @itemx set print repeats unlimited @cindex repeated array elements Set the threshold for suppressing display of repeated array elements. When the number of consecutive identical elements of an array exceeds the threshold, @value{GDBN} prints the string @code{"<repeats @var{n} times>"}, where @var{n} is the number of identical repetitions, instead of displaying the identical elements themselves. Setting the threshold to @code{unlimited} or zero will cause all elements to be individually printed. The default threshold is 10. @item show print repeats Display the current threshold for printing repeated identical elements. @anchor{set print max-depth} @item set print max-depth @var{depth} @item set print max-depth unlimited @cindex printing nested structures Set the threshold after which nested structures are replaced with ellipsis, this can make visualising deeply nested structures easier. For example, given this C code @smallexample typedef struct s1 @{ int a; @} s1; typedef struct s2 @{ s1 b; @} s2; typedef struct s3 @{ s2 c; @} s3; typedef struct s4 @{ s3 d; @} s4; s4 var = @{ @{ @{ @{ 3 @} @} @} @}; @end smallexample The following table shows how different values of @var{depth} will effect how @code{var} is printed by @value{GDBN}: @multitable @columnfractions .3 .7 @headitem @var{depth} setting @tab Result of @samp{p var} @item unlimited @tab @code{$1 = @{d = @{c = @{b = @{a = 3@}@}@}@}} @item @code{0} @tab @code{$1 = @{...@}} @item @code{1} @tab @code{$1 = @{d = @{...@}@}} @item @code{2} @tab @code{$1 = @{d = @{c = @{...@}@}@}} @item @code{3} @tab @code{$1 = @{d = @{c = @{b = @{...@}@}@}@}} @item @code{4} @tab @code{$1 = @{d = @{c = @{b = @{a = 3@}@}@}@}} @end multitable To see the contents of structures that have been hidden the user can either increase the print max-depth, or they can print the elements of the structure that are visible, for example @smallexample (gdb) set print max-depth 2 (gdb) p var $1 = @{d = @{c = @{...@}@}@} (gdb) p var.d $2 = @{c = @{b = @{...@}@}@} (gdb) p var.d.c $3 = @{b = @{a = 3@}@} @end smallexample The pattern used to replace nested structures varies based on language, for most languages @code{@{...@}} is used, but Fortran uses @code{(...)}. @item show print max-depth Display the current threshold after which nested structures are replaces with ellipsis. @anchor{set print null-stop} @item set print null-stop @cindex @sc{null} elements in arrays Cause @value{GDBN} to stop printing the characters of an array when the first @sc{null} is encountered. This is useful when large arrays actually contain only short strings. The default is off. @item show print null-stop Show whether @value{GDBN} stops printing an array on the first @sc{null} character. @anchor{set print pretty} @item set print pretty on @cindex print structures in indented form @cindex indentation in structure display Cause @value{GDBN} to print structures in an indented format with one member per line, like this: @smallexample @group $1 = @{ next = 0x0, flags = @{ sweet = 1, sour = 1 @}, meat = 0x54 "Pork" @} @end group @end smallexample @item set print pretty off Cause @value{GDBN} to print structures in a compact format, like this: @smallexample @group $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \ meat = 0x54 "Pork"@} @end group @end smallexample @noindent This is the default format. @item show print pretty Show which format @value{GDBN} is using to print structures. @anchor{set print raw-values} @item set print raw-values on Print values in raw form, without applying the pretty printers for the value. @item set print raw-values off Print values in pretty-printed form, if there is a pretty-printer for the value (@pxref{Pretty Printing}), otherwise print the value in raw form. The default setting is ``off''. @item show print raw-values Show whether to print values in raw form. @item set print sevenbit-strings on @cindex eight-bit characters in strings @cindex octal escapes in strings Print using only seven-bit characters; if this option is set, @value{GDBN} displays any eight-bit characters (in strings or character values) using the notation @code{\}@var{nnn}. This setting is best if you are working in English (@sc{ascii}) and you use the high-order bit of characters as a marker or ``meta'' bit. @item set print sevenbit-strings off Print full eight-bit characters. This allows the use of more international character sets, and is the default. @item show print sevenbit-strings Show whether or not @value{GDBN} is printing only seven-bit characters. @anchor{set print union} @item set print union on @cindex unions in structures, printing Tell @value{GDBN} to print unions which are contained in structures and other unions. This is the default setting. @item set print union off Tell @value{GDBN} not to print unions which are contained in structures and other unions. @value{GDBN} will print @code{"@{...@}"} instead. @item show print union Ask @value{GDBN} whether or not it will print unions which are contained in structures and other unions. For example, given the declarations @smallexample typedef enum @{Tree, Bug@} Species; typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms; typedef enum @{Caterpillar, Cocoon, Butterfly@} Bug_forms; struct thing @{ Species it; union @{ Tree_forms tree; Bug_forms bug; @} form; @}; struct thing foo = @{Tree, @{Acorn@}@}; @end smallexample @noindent with @code{set print union on} in effect @samp{p foo} would print @smallexample $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@} @end smallexample @noindent and with @code{set print union off} in effect it would print @smallexample $1 = @{it = Tree, form = @{...@}@} @end smallexample @noindent @code{set print union} affects programs written in C-like languages and in Pascal. @end table @need 1000 @noindent These settings are of interest when debugging C@t{++} programs: @table @code @cindex demangling C@t{++} names @item set print demangle @itemx set print demangle on Print C@t{++} names in their source form rather than in the encoded (``mangled'') form passed to the assembler and linker for type-safe linkage. The default is on. @item show print demangle Show whether C@t{++} names are printed in mangled or demangled form. @item set print asm-demangle @itemx set print asm-demangle on Print C@t{++} names in their source form rather than their mangled form, even in assembler code printouts such as instruction disassemblies. The default is off. @item show print asm-demangle Show whether C@t{++} names in assembly listings are printed in mangled or demangled form. @cindex C@t{++} symbol decoding style @cindex symbol decoding style, C@t{++} @kindex set demangle-style @item set demangle-style @var{style} Choose among several encoding schemes used by different compilers to represent C@t{++} names. If you omit @var{style}, you will see a list of possible formats. The default value is @var{auto}, which lets @value{GDBN} choose a decoding style by inspecting your program. @item show demangle-style Display the encoding style currently in use for decoding C@t{++} symbols. @anchor{set print object} @item set print object @itemx set print object on @cindex derived type of an object, printing @cindex display derived types When displaying a pointer to an object, identify the @emph{actual} (derived) type of the object rather than the @emph{declared} type, using the virtual function table. Note that the virtual function table is required---this feature can only work for objects that have run-time type identification; a single virtual method in the object's declared type is sufficient. Note that this setting is also taken into account when working with variable objects via MI (@pxref{GDB/MI}). @item set print object off Display only the declared type of objects, without reference to the virtual function table. This is the default setting. @item show print object Show whether actual, or declared, object types are displayed. @anchor{set print static-members} @item set print static-members @itemx set print static-members on @cindex static members of C@t{++} objects Print static members when displaying a C@t{++} object. The default is on. @item set print static-members off Do not print static members when displaying a C@t{++} object. @item show print static-members Show whether C@t{++} static members are printed or not. @item set print pascal_static-members @itemx set print pascal_static-members on @cindex static members of Pascal objects @cindex Pascal objects, static members display Print static members when displaying a Pascal object. The default is on. @item set print pascal_static-members off Do not print static members when displaying a Pascal object. @item show print pascal_static-members Show whether Pascal static members are printed or not. @c These don't work with HP ANSI C++ yet. @anchor{set print vtbl} @item set print vtbl @itemx set print vtbl on @cindex pretty print C@t{++} virtual function tables @cindex virtual functions (C@t{++}) display @cindex VTBL display Pretty print C@t{++} virtual function tables. The default is off. (The @code{vtbl} commands do not work on programs compiled with the HP ANSI C@t{++} compiler (@code{aCC}).) @item set print vtbl off Do not pretty print C@t{++} virtual function tables. @item show print vtbl Show whether C@t{++} virtual function tables are pretty printed, or not. @end table @node Pretty Printing @section Pretty Printing @value{GDBN} provides a mechanism to allow pretty-printing of values using Python code. It greatly simplifies the display of complex objects. This mechanism works for both MI and the CLI. @menu * Pretty-Printer Introduction:: Introduction to pretty-printers * Pretty-Printer Example:: An example pretty-printer * Pretty-Printer Commands:: Pretty-printer commands @end menu @node Pretty-Printer Introduction @subsection Pretty-Printer Introduction When @value{GDBN} prints a value, it first sees if there is a pretty-printer registered for the value. If there is then @value{GDBN} invokes the pretty-printer to print the value. Otherwise the value is printed normally. Pretty-printers are normally named. This makes them easy to manage. The @samp{info pretty-printer} command will list all the installed pretty-printers with their names. If a pretty-printer can handle multiple data types, then its @dfn{subprinters} are the printers for the individual data types. Each such subprinter has its own name. The format of the name is @var{printer-name};@var{subprinter-name}. Pretty-printers are installed by @dfn{registering} them with @value{GDBN}. Typically they are automatically loaded and registered when the corresponding debug information is loaded, thus making them available without having to do anything special. There are three places where a pretty-printer can be registered. @itemize @bullet @item Pretty-printers registered globally are available when debugging all inferiors. @item Pretty-printers registered with a program space are available only when debugging that program. @xref{Progspaces In Python}, for more details on program spaces in Python. @item Pretty-printers registered with an objfile are loaded and unloaded with the corresponding objfile (e.g., shared library). @xref{Objfiles In Python}, for more details on objfiles in Python. @end itemize @xref{Selecting Pretty-Printers}, for further information on how pretty-printers are selected, @xref{Writing a Pretty-Printer}, for implementing pretty printers for new types. @node Pretty-Printer Example @subsection Pretty-Printer Example Here is how a C@t{++} @code{std::string} looks without a pretty-printer: @smallexample (@value{GDBP}) print s $1 = @{ static npos = 4294967295, _M_dataplus = @{ <std::allocator<char>> = @{ <__gnu_cxx::new_allocator<char>> = @{ <No data fields>@}, <No data fields> @}, members of std::basic_string<char, std::char_traits<char>, std::allocator<char> >::_Alloc_hider: _M_p = 0x804a014 "abcd" @} @} @end smallexample With a pretty-printer for @code{std::string} only the contents are printed: @smallexample (@value{GDBP}) print s $2 = "abcd" @end smallexample @node Pretty-Printer Commands @subsection Pretty-Printer Commands @cindex pretty-printer commands @table @code @kindex info pretty-printer @item info pretty-printer [@var{object-regexp} [@var{name-regexp}]] Print the list of installed pretty-printers. This includes disabled pretty-printers, which are marked as such. @var{object-regexp} is a regular expression matching the objects whose pretty-printers to list. Objects can be @code{global}, the program space's file (@pxref{Progspaces In Python}), and the object files within that program space (@pxref{Objfiles In Python}). @xref{Selecting Pretty-Printers}, for details on how @value{GDBN} looks up a printer from these three objects. @var{name-regexp} is a regular expression matching the name of the printers to list. @kindex disable pretty-printer @item disable pretty-printer [@var{object-regexp} [@var{name-regexp}]] Disable pretty-printers matching @var{object-regexp} and @var{name-regexp}. A disabled pretty-printer is not forgotten, it may be enabled again later. @kindex enable pretty-printer @item enable pretty-printer [@var{object-regexp} [@var{name-regexp}]] Enable pretty-printers matching @var{object-regexp} and @var{name-regexp}. @end table Example: Suppose we have three pretty-printers installed: one from library1.so named @code{foo} that prints objects of type @code{foo}, and another from library2.so named @code{bar} that prints two types of objects, @code{bar1} and @code{bar2}. @smallexample (gdb) info pretty-printer library1.so: foo library2.so: bar bar1 bar2 (gdb) info pretty-printer library2 library2.so: bar bar1 bar2 (gdb) disable pretty-printer library1 1 printer disabled 2 of 3 printers enabled (gdb) info pretty-printer library1.so: foo [disabled] library2.so: bar bar1 bar2 (gdb) disable pretty-printer library2 bar;bar1 1 printer disabled 1 of 3 printers enabled (gdb) info pretty-printer library2 library1.so: foo [disabled] library2.so: bar bar1 [disabled] bar2 (gdb) disable pretty-printer library2 bar 1 printer disabled 0 of 3 printers enabled (gdb) info pretty-printer library2 library1.so: foo [disabled] library2.so: bar [disabled] bar1 [disabled] bar2 @end smallexample Note that for @code{bar} the entire printer can be disabled, as can each individual subprinter. Printing values and frame arguments is done by default using the enabled pretty printers. The print option @code{-raw-values} and @value{GDBN} setting @code{set print raw-values} (@pxref{set print raw-values}) can be used to print values without applying the enabled pretty printers. Similarly, the backtrace option @code{-raw-frame-arguments} and @value{GDBN} setting @code{set print raw-frame-arguments} (@pxref{set print raw-frame-arguments}) can be used to ignore the enabled pretty printers when printing frame argument values. @node Value History @section Value History @cindex value history @cindex history of values printed by @value{GDBN} Values printed by the @code{print} command are saved in the @value{GDBN} @dfn{value history}. This allows you to refer to them in other expressions. Values are kept until the symbol table is re-read or discarded (for example with the @code{file} or @code{symbol-file} commands). When the symbol table changes, the value history is discarded, since the values may contain pointers back to the types defined in the symbol table. @cindex @code{$} @cindex @code{$$} @cindex history number The values printed are given @dfn{history numbers} by which you can refer to them. These are successive integers starting with one. @code{print} shows you the history number assigned to a value by printing @samp{$@var{num} = } before the value; here @var{num} is the history number. To refer to any previous value, use @samp{$} followed by the value's history number. The way @code{print} labels its output is designed to remind you of this. Just @code{$} refers to the most recent value in the history, and @code{$$} refers to the value before that. @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2} is the value just prior to @code{$$}, @code{$$1} is equivalent to @code{$$}, and @code{$$0} is equivalent to @code{$}. For example, suppose you have just printed a pointer to a structure and want to see the contents of the structure. It suffices to type @smallexample p *$ @end smallexample If you have a chain of structures where the component @code{next} points to the next one, you can print the contents of the next one with this: @smallexample p *$.next @end smallexample @noindent You can print successive links in the chain by repeating this command---which you can do by just typing @key{RET}. Note that the history records values, not expressions. If the value of @code{x} is 4 and you type these commands: @smallexample print x set x=5 @end smallexample @noindent then the value recorded in the value history by the @code{print} command remains 4 even though the value of @code{x} has changed. @table @code @kindex show values @item show values Print the last ten values in the value history, with their item numbers. This is like @samp{p@ $$9} repeated ten times, except that @code{show values} does not change the history. @item show values @var{n} Print ten history values centered on history item number @var{n}. @item show values + Print ten history values just after the values last printed. If no more values are available, @code{show values +} produces no display. @end table Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the same effect as @samp{show values +}. @node Convenience Vars @section Convenience Variables @cindex convenience variables @cindex user-defined variables @value{GDBN} provides @dfn{convenience variables} that you can use within @value{GDBN} to hold on to a value and refer to it later. These variables exist entirely within @value{GDBN}; they are not part of your program, and setting a convenience variable has no direct effect on further execution of your program. That is why you can use them freely. Convenience variables are prefixed with @samp{$}. Any name preceded by @samp{$} can be used for a convenience variable, unless it is one of the predefined machine-specific register names (@pxref{Registers, ,Registers}). (Value history references, in contrast, are @emph{numbers} preceded by @samp{$}. @xref{Value History, ,Value History}.) You can save a value in a convenience variable with an assignment expression, just as you would set a variable in your program. For example: @smallexample set $foo = *object_ptr @end smallexample @noindent would save in @code{$foo} the value contained in the object pointed to by @code{object_ptr}. Using a convenience variable for the first time creates it, but its value is @code{void} until you assign a new value. You can alter the value with another assignment at any time. Convenience variables have no fixed types. You can assign a convenience variable any type of value, including structures and arrays, even if that variable already has a value of a different type. The convenience variable, when used as an expression, has the type of its current value. @table @code @kindex show convenience @cindex show all user variables and functions @item show convenience Print a list of convenience variables used so far, and their values, as well as a list of the convenience functions. Abbreviated @code{show conv}. @kindex init-if-undefined @cindex convenience variables, initializing @item init-if-undefined $@var{variable} = @var{expression} Set a convenience variable if it has not already been set. This is useful for user-defined commands that keep some state. It is similar, in concept, to using local static variables with initializers in C (except that convenience variables are global). It can also be used to allow users to override default values used in a command script. If the variable is already defined then the expression is not evaluated so any side-effects do not occur. @end table One of the ways to use a convenience variable is as a counter to be incremented or a pointer to be advanced. For example, to print a field from successive elements of an array of structures: @smallexample set $i = 0 print bar[$i++]->contents @end smallexample @noindent Repeat that command by typing @key{RET}. Some convenience variables are created automatically by @value{GDBN} and given values likely to be useful. @table @code @vindex $_@r{, convenience variable} @item $_ The variable @code{$_} is automatically set by the @code{x} command to the last address examined (@pxref{Memory, ,Examining Memory}). Other commands which provide a default address for @code{x} to examine also set @code{$_} to that address; these commands include @code{info line} and @code{info breakpoint}. The type of @code{$_} is @code{void *} except when set by the @code{x} command, in which case it is a pointer to the type of @code{$__}. @vindex $__@r{, convenience variable} @item $__ The variable @code{$__} is automatically set by the @code{x} command to the value found in the last address examined. Its type is chosen to match the format in which the data was printed. @item $_exitcode @vindex $_exitcode@r{, convenience variable} When the program being debugged terminates normally, @value{GDBN} automatically sets this variable to the exit code of the program, and resets @code{$_exitsignal} to @code{void}. @item $_exitsignal @vindex $_exitsignal@r{, convenience variable} When the program being debugged dies due to an uncaught signal, @value{GDBN} automatically sets this variable to that signal's number, and resets @code{$_exitcode} to @code{void}. To distinguish between whether the program being debugged has exited (i.e., @code{$_exitcode} is not @code{void}) or signalled (i.e., @code{$_exitsignal} is not @code{void}), the convenience function @code{$_isvoid} can be used (@pxref{Convenience Funs,, Convenience Functions}). For example, considering the following source code: @smallexample #include <signal.h> int main (int argc, char *argv[]) @{ raise (SIGALRM); return 0; @} @end smallexample A valid way of telling whether the program being debugged has exited or signalled would be: @smallexample (@value{GDBP}) define has_exited_or_signalled Type commands for definition of ``has_exited_or_signalled''. End with a line saying just ``end''. >if $_isvoid ($_exitsignal) >echo The program has exited\n >else >echo The program has signalled\n >end >end (@value{GDBP}) run Starting program: Program terminated with signal SIGALRM, Alarm clock. The program no longer exists. (@value{GDBP}) has_exited_or_signalled The program has signalled @end smallexample As can be seen, @value{GDBN} correctly informs that the program being debugged has signalled, since it calls @code{raise} and raises a @code{SIGALRM} signal. If the program being debugged had not called @code{raise}, then @value{GDBN} would report a normal exit: @smallexample (@value{GDBP}) has_exited_or_signalled The program has exited @end smallexample @item $_exception The variable @code{$_exception} is set to the exception object being thrown at an exception-related catchpoint. @xref{Set Catchpoints}. @item $_ada_exception The variable @code{$_ada_exception} is set to the address of the exception being caught or thrown at an Ada exception-related catchpoint. @xref{Set Catchpoints}. @item $_probe_argc @itemx $_probe_arg0@dots{}$_probe_arg11 Arguments to a static probe. @xref{Static Probe Points}. @item $_sdata @vindex $_sdata@r{, inspect, convenience variable} The variable @code{$_sdata} contains extra collected static tracepoint data. @xref{Tracepoint Actions,,Tracepoint Action Lists}. Note that @code{$_sdata} could be empty, if not inspecting a trace buffer, or if extra static tracepoint data has not been collected. @item $_siginfo @vindex $_siginfo@r{, convenience variable} The variable @code{$_siginfo} contains extra signal information (@pxref{extra signal information}). Note that @code{$_siginfo} could be empty, if the application has not yet received any signals. For example, it will be empty before you execute the @code{run} command. @item $_tlb @vindex $_tlb@r{, convenience variable} The variable @code{$_tlb} is automatically set when debugging applications running on MS-Windows in native mode or connected to gdbserver that supports the @code{qGetTIBAddr} request. @xref{General Query Packets}. This variable contains the address of the thread information block. @item $_inferior The number of the current inferior. @xref{Inferiors Connections and Programs, ,Debugging Multiple Inferiors Connections and Programs}. @item $_thread The thread number of the current thread. @xref{thread numbers}. @item $_gthread The global number of the current thread. @xref{global thread numbers}. @item $_gdb_major @itemx $_gdb_minor @vindex $_gdb_major@r{, convenience variable} @vindex $_gdb_minor@r{, convenience variable} The major and minor version numbers of the running @value{GDBN}. Development snapshots and pretest versions have their minor version incremented by one; thus, @value{GDBN} pretest 9.11.90 will produce the value 12 for @code{$_gdb_minor}. These variables allow you to write scripts that work with different versions of @value{GDBN} without errors caused by features unavailable in some of those versions. @item $_shell_exitcode @itemx $_shell_exitsignal @vindex $_shell_exitcode@r{, convenience variable} @vindex $_shell_exitsignal@r{, convenience variable} @cindex shell command, exit code @cindex shell command, exit signal @cindex exit status of shell commands @value{GDBN} commands such as @code{shell} and @code{|} are launching shell commands. When a launched command terminates, @value{GDBN} automatically maintains the variables @code{$_shell_exitcode} and @code{$_shell_exitsignal} according to the exit status of the last launched command. These variables are set and used similarly to the variables @code{$_exitcode} and @code{$_exitsignal}. @end table @node Convenience Funs @section Convenience Functions @cindex convenience functions @value{GDBN} also supplies some @dfn{convenience functions}. These have a syntax similar to convenience variables. A convenience function can be used in an expression just like an ordinary function; however, a convenience function is implemented internally to @value{GDBN}. These functions do not require @value{GDBN} to be configured with @code{Python} support, which means that they are always available. @table @code @item $_isvoid (@var{expr}) @findex $_isvoid@r{, convenience function} Return one if the expression @var{expr} is @code{void}. Otherwise it returns zero. A @code{void} expression is an expression where the type of the result is @code{void}. For example, you can examine a convenience variable (see @ref{Convenience Vars,, Convenience Variables}) to check whether it is @code{void}: @smallexample (@value{GDBP}) print $_exitcode $1 = void (@value{GDBP}) print $_isvoid ($_exitcode) $2 = 1 (@value{GDBP}) run Starting program: ./a.out [Inferior 1 (process 29572) exited normally] (@value{GDBP}) print $_exitcode $3 = 0 (@value{GDBP}) print $_isvoid ($_exitcode) $4 = 0 @end smallexample In the example above, we used @code{$_isvoid} to check whether @code{$_exitcode} is @code{void} before and after the execution of the program being debugged. Before the execution there is no exit code to be examined, therefore @code{$_exitcode} is @code{void}. After the execution the program being debugged returned zero, therefore @code{$_exitcode} is zero, which means that it is not @code{void} anymore. The @code{void} expression can also be a call of a function from the program being debugged. For example, given the following function: @smallexample void foo (void) @{ @} @end smallexample The result of calling it inside @value{GDBN} is @code{void}: @smallexample (@value{GDBP}) print foo () $1 = void (@value{GDBP}) print $_isvoid (foo ()) $2 = 1 (@value{GDBP}) set $v = foo () (@value{GDBP}) print $v $3 = void (@value{GDBP}) print $_isvoid ($v) $4 = 1 @end smallexample @item $_gdb_setting_str (@var{setting}) @findex $_gdb_setting_str@r{, convenience function} Return the value of the @value{GDBN} @var{setting} as a string. @var{setting} is any setting that can be used in a @code{set} or @code{show} command (@pxref{Controlling GDB}). @smallexample (@value{GDBP}) show print frame-arguments Printing of non-scalar frame arguments is "scalars". (@value{GDBP}) p $_gdb_setting_str("print frame-arguments") $1 = "scalars" (@value{GDBP}) p $_gdb_setting_str("height") $2 = "30" (@value{GDBP}) @end smallexample @item $_gdb_setting (@var{setting}) @findex $_gdb_setting@r{, convenience function} Return the value of the @value{GDBN} @var{setting}. The type of the returned value depends on the setting. The value type for boolean and auto boolean settings is @code{int}. The boolean values @code{off} and @code{on} are converted to the integer values @code{0} and @code{1}. The value @code{auto} is converted to the value @code{-1}. The value type for integer settings is either @code{unsigned int} or @code{int}, depending on the setting. Some integer settings accept an @code{unlimited} value. Depending on the setting, the @code{set} command also accepts the value @code{0} or the value @code{@minus{}1} as a synonym for @code{unlimited}. For example, @code{set height unlimited} is equivalent to @code{set height 0}. Some other settings that accept the @code{unlimited} value use the value @code{0} to literally mean zero. For example, @code{set history size 0} indicates to not record any @value{GDBN} commands in the command history. For such settings, @code{@minus{}1} is the synonym for @code{unlimited}. See the documentation of the corresponding @code{set} command for the numerical value equivalent to @code{unlimited}. The @code{$_gdb_setting} function converts the unlimited value to a @code{0} or a @code{@minus{}1} value according to what the @code{set} command uses. @smallexample @group (@value{GDBP}) p $_gdb_setting_str("height") $1 = "30" (@value{GDBP}) p $_gdb_setting("height") $2 = 30 (@value{GDBP}) set height unlimited (@value{GDBP}) p $_gdb_setting_str("height") $3 = "unlimited" (@value{GDBP}) p $_gdb_setting("height") $4 = 0 @end group @group (@value{GDBP}) p $_gdb_setting_str("history size") $5 = "unlimited" (@value{GDBP}) p $_gdb_setting("history size") $6 = -1 (@value{GDBP}) p $_gdb_setting_str("disassemble-next-line") $7 = "auto" (@value{GDBP}) p $_gdb_setting("disassemble-next-line") $8 = -1 (@value{GDBP}) @end group @end smallexample Other setting types (enum, filename, optional filename, string, string noescape) are returned as string values. @item $_gdb_maint_setting_str (@var{setting}) @findex $_gdb_maint_setting_str@r{, convenience function} Like the @code{$_gdb_setting_str} function, but works with @code{maintenance set} variables. @item $_gdb_maint_setting (@var{setting}) @findex $_gdb_maint_setting@r{, convenience function} Like the @code{$_gdb_setting} function, but works with @code{maintenance set} variables. @end table The following functions require @value{GDBN} to be configured with @code{Python} support. @table @code @item $_memeq(@var{buf1}, @var{buf2}, @var{length}) @findex $_memeq@r{, convenience function} Returns one if the @var{length} bytes at the addresses given by @var{buf1} and @var{buf2} are equal. Otherwise it returns zero. @item $_regex(@var{str}, @var{regex}) @findex $_regex@r{, convenience function} Returns one if the string @var{str} matches the regular expression @var{regex}. Otherwise it returns zero. The syntax of the regular expression is that specified by @code{Python}'s regular expression support. @item $_streq(@var{str1}, @var{str2}) @findex $_streq@r{, convenience function} Returns one if the strings @var{str1} and @var{str2} are equal. Otherwise it returns zero. @item $_strlen(@var{str}) @findex $_strlen@r{, convenience function} Returns the length of string @var{str}. @item $_caller_is(@var{name}@r{[}, @var{number_of_frames}@r{]}) @findex $_caller_is@r{, convenience function} Returns one if the calling function's name is equal to @var{name}. Otherwise it returns zero. If the optional argument @var{number_of_frames} is provided, it is the number of frames up in the stack to look. The default is 1. Example: @smallexample (gdb) backtrace #0 bottom_func () at testsuite/gdb.python/py-caller-is.c:21 #1 0x00000000004005a0 in middle_func () at testsuite/gdb.python/py-caller-is.c:27 #2 0x00000000004005ab in top_func () at testsuite/gdb.python/py-caller-is.c:33 #3 0x00000000004005b6 in main () at testsuite/gdb.python/py-caller-is.c:39 (gdb) print $_caller_is ("middle_func") $1 = 1 (gdb) print $_caller_is ("top_func", 2) $1 = 1 @end smallexample @item $_caller_matches(@var{regexp}@r{[}, @var{number_of_frames}@r{]}) @findex $_caller_matches@r{, convenience function} Returns one if the calling function's name matches the regular expression @var{regexp}. Otherwise it returns zero. If the optional argument @var{number_of_frames} is provided, it is the number of frames up in the stack to look. The default is 1. @item $_any_caller_is(@var{name}@r{[}, @var{number_of_frames}@r{]}) @findex $_any_caller_is@r{, convenience function} Returns one if any calling function's name is equal to @var{name}. Otherwise it returns zero. If the optional argument @var{number_of_frames} is provided, it is the number of frames up in the stack to look. The default is 1. This function differs from @code{$_caller_is} in that this function checks all stack frames from the immediate caller to the frame specified by @var{number_of_frames}, whereas @code{$_caller_is} only checks the frame specified by @var{number_of_frames}. @item $_any_caller_matches(@var{regexp}@r{[}, @var{number_of_frames}@r{]}) @findex $_any_caller_matches@r{, convenience function} Returns one if any calling function's name matches the regular expression @var{regexp}. Otherwise it returns zero. If the optional argument @var{number_of_frames} is provided, it is the number of frames up in the stack to look. The default is 1. This function differs from @code{$_caller_matches} in that this function checks all stack frames from the immediate caller to the frame specified by @var{number_of_frames}, whereas @code{$_caller_matches} only checks the frame specified by @var{number_of_frames}. @item $_as_string(@var{value}) @findex $_as_string@r{, convenience function} Return the string representation of @var{value}. This function is useful to obtain the textual label (enumerator) of an enumeration value. For example, assuming the variable @var{node} is of an enumerated type: @smallexample (gdb) printf "Visiting node of type %s\n", $_as_string(node) Visiting node of type NODE_INTEGER @end smallexample @item $_cimag(@var{value}) @itemx $_creal(@var{value}) @findex $_cimag@r{, convenience function} @findex $_creal@r{, convenience function} Return the imaginary (@code{$_cimag}) or real (@code{$_creal}) part of the complex number @var{value}. The type of the imaginary or real part depends on the type of the complex number, e.g., using @code{$_cimag} on a @code{float complex} will return an imaginary part of type @code{float}. @end table @value{GDBN} provides the ability to list and get help on convenience functions. @table @code @item help function @kindex help function @cindex show all convenience functions Print a list of all convenience functions. @end table @node Registers @section Registers @cindex registers You can refer to machine register contents, in expressions, as variables with names starting with @samp{$}. The names of registers are different for each machine; use @code{info registers} to see the names used on your machine. @table @code @kindex info registers @item info registers Print the names and values of all registers except floating-point and vector registers (in the selected stack frame). @kindex info all-registers @cindex floating point registers @item info all-registers Print the names and values of all registers, including floating-point and vector registers (in the selected stack frame). @item info registers @var{reggroup} @dots{} Print the name and value of the registers in each of the specified @var{reggroup}s. The @var{reggroup} can be any of those returned by @code{maint print reggroups} (@pxref{Maintenance Commands}). @item info registers @var{regname} @dots{} Print the @dfn{relativized} value of each specified register @var{regname}. As discussed in detail below, register values are normally relative to the selected stack frame. The @var{regname} may be any register name valid on the machine you are using, with or without the initial @samp{$}. @end table @anchor{standard registers} @cindex stack pointer register @cindex program counter register @cindex process status register @cindex frame pointer register @cindex standard registers @value{GDBN} has four ``standard'' register names that are available (in expressions) on most machines---whenever they do not conflict with an architecture's canonical mnemonics for registers. The register names @code{$pc} and @code{$sp} are used for the program counter register and the stack pointer. @code{$fp} is used for a register that contains a pointer to the current stack frame, and @code{$ps} is used for a register that contains the processor status. For example, you could print the program counter in hex with @smallexample p/x $pc @end smallexample @noindent or print the instruction to be executed next with @smallexample x/i $pc @end smallexample @noindent or add four to the stack pointer@footnote{This is a way of removing one word from the stack, on machines where stacks grow downward in memory (most machines, nowadays). This assumes that the innermost stack frame is selected; setting @code{$sp} is not allowed when other stack frames are selected. To pop entire frames off the stack, regardless of machine architecture, use @code{return}; see @ref{Returning, ,Returning from a Function}.} with @smallexample set $sp += 4 @end smallexample Whenever possible, these four standard register names are available on your machine even though the machine has different canonical mnemonics, so long as there is no conflict. The @code{info registers} command shows the canonical names. For example, on the SPARC, @code{info registers} displays the processor status register as @code{$psr} but you can also refer to it as @code{$ps}; and on x86-based machines @code{$ps} is an alias for the @sc{eflags} register. @value{GDBN} always considers the contents of an ordinary register as an integer when the register is examined in this way. Some machines have special registers which can hold nothing but floating point; these registers are considered to have floating point values. There is no way to refer to the contents of an ordinary register as floating point value (although you can @emph{print} it as a floating point value with @samp{print/f $@var{regname}}). Some registers have distinct ``raw'' and ``virtual'' data formats. This means that the data format in which the register contents are saved by the operating system is not the same one that your program normally sees. For example, the registers of the 68881 floating point coprocessor are always saved in ``extended'' (raw) format, but all C programs expect to work with ``double'' (virtual) format. In such cases, @value{GDBN} normally works with the virtual format only (the format that makes sense for your program), but the @code{info registers} command prints the data in both formats. @cindex SSE registers (x86) @cindex MMX registers (x86) Some machines have special registers whose contents can be interpreted in several different ways. For example, modern x86-based machines have SSE and MMX registers that can hold several values packed together in several different formats. @value{GDBN} refers to such registers in @code{struct} notation: @smallexample (@value{GDBP}) print $xmm1 $1 = @{ v4_float = @{0, 3.43859137e-038, 1.54142831e-044, 1.821688e-044@}, v2_double = @{9.92129282474342e-303, 2.7585945287983262e-313@}, v16_int8 = "\000\000\000\000\3706;\001\v\000\000\000\r\000\000", v8_int16 = @{0, 0, 14072, 315, 11, 0, 13, 0@}, v4_int32 = @{0, 20657912, 11, 13@}, v2_int64 = @{88725056443645952, 55834574859@}, uint128 = 0x0000000d0000000b013b36f800000000 @} @end smallexample @noindent To set values of such registers, you need to tell @value{GDBN} which view of the register you wish to change, as if you were assigning value to a @code{struct} member: @smallexample (@value{GDBP}) set $xmm1.uint128 = 0x000000000000000000000000FFFFFFFF @end smallexample Normally, register values are relative to the selected stack frame (@pxref{Selection, ,Selecting a Frame}). This means that you get the value that the register would contain if all stack frames farther in were exited and their saved registers restored. In order to see the true contents of hardware registers, you must select the innermost frame (with @samp{frame 0}). @cindex caller-saved registers @cindex call-clobbered registers @cindex volatile registers @cindex <not saved> values Usually ABIs reserve some registers as not needed to be saved by the callee (a.k.a.: ``caller-saved'', ``call-clobbered'' or ``volatile'' registers). It may therefore not be possible for @value{GDBN} to know the value a register had before the call (in other words, in the outer frame), if the register value has since been changed by the callee. @value{GDBN} tries to deduce where the inner frame saved (``callee-saved'') registers, from the debug info, unwind info, or the machine code generated by your compiler. If some register is not saved, and @value{GDBN} knows the register is ``caller-saved'' (via its own knowledge of the ABI, or because the debug/unwind info explicitly says the register's value is undefined), @value{GDBN} displays @w{@samp{<not saved>}} as the register's value. With targets that @value{GDBN} has no knowledge of the register saving convention, if a register was not saved by the callee, then its value and location in the outer frame are assumed to be the same of the inner frame. This is usually harmless, because if the register is call-clobbered, the caller either does not care what is in the register after the call, or has code to restore the value that it does care about. Note, however, that if you change such a register in the outer frame, you may also be affecting the inner frame. Also, the more ``outer'' the frame is you're looking at, the more likely a call-clobbered register's value is to be wrong, in the sense that it doesn't actually represent the value the register had just before the call. @node Floating Point Hardware @section Floating Point Hardware @cindex floating point Depending on the configuration, @value{GDBN} may be able to give you more information about the status of the floating point hardware. @table @code @kindex info float @item info float Display hardware-dependent information about the floating point unit. The exact contents and layout vary depending on the floating point chip. Currently, @samp{info float} is supported on the ARM and x86 machines. @end table @node Vector Unit @section Vector Unit @cindex vector unit Depending on the configuration, @value{GDBN} may be able to give you more information about the status of the vector unit. @table @code @kindex info vector @item info vector Display information about the vector unit. The exact contents and layout vary depending on the hardware. @end table @node OS Information @section Operating System Auxiliary Information @cindex OS information @value{GDBN} provides interfaces to useful OS facilities that can help you debug your program. @cindex auxiliary vector @cindex vector, auxiliary Some operating systems supply an @dfn{auxiliary vector} to programs at startup. This is akin to the arguments and environment that you specify for a program, but contains a system-dependent variety of binary values that tell system libraries important details about the hardware, operating system, and process. Each value's purpose is identified by an integer tag; the meanings are well-known but system-specific. Depending on the configuration and operating system facilities, @value{GDBN} may be able to show you this information. For remote targets, this functionality may further depend on the remote stub's support of the @samp{qXfer:auxv:read} packet, see @ref{qXfer auxiliary vector read}. @table @code @kindex info auxv @item info auxv Display the auxiliary vector of the inferior, which can be either a live process or a core dump file. @value{GDBN} prints each tag value numerically, and also shows names and text descriptions for recognized tags. Some values in the vector are numbers, some bit masks, and some pointers to strings or other data. @value{GDBN} displays each value in the most appropriate form for a recognized tag, and in hexadecimal for an unrecognized tag. @end table On some targets, @value{GDBN} can access operating system-specific information and show it to you. The types of information available will differ depending on the type of operating system running on the target. The mechanism used to fetch the data is described in @ref{Operating System Information}. For remote targets, this functionality depends on the remote stub's support of the @samp{qXfer:osdata:read} packet, see @ref{qXfer osdata read}. @table @code @kindex info os @item info os @var{infotype} Display OS information of the requested type. On @sc{gnu}/Linux, the following values of @var{infotype} are valid: @anchor{linux info os infotypes} @table @code @kindex info os cpus @item cpus Display the list of all CPUs/cores. For each CPU/core, @value{GDBN} prints the available fields from /proc/cpuinfo. For each supported architecture different fields are available. Two common entries are processor which gives CPU number and bogomips; a system constant that is calculated during kernel initialization. @kindex info os files @item files Display the list of open file descriptors on the target. For each file descriptor, @value{GDBN} prints the identifier of the process owning the descriptor, the command of the owning process, the value of the descriptor, and the target of the descriptor. @kindex info os modules @item modules Display the list of all loaded kernel modules on the target. For each module, @value{GDBN} prints the module name, the size of the module in bytes, the number of times the module is used, the dependencies of the module, the status of the module, and the address of the loaded module in memory. @kindex info os msg @item msg Display the list of all System V message queues on the target. For each message queue, @value{GDBN} prints the message queue key, the message queue identifier, the access permissions, the current number of bytes on the queue, the current number of messages on the queue, the processes that last sent and received a message on the queue, the user and group of the owner and creator of the message queue, the times at which a message was last sent and received on the queue, and the time at which the message queue was last changed. @kindex info os processes @item processes Display the list of processes on the target. For each process, @value{GDBN} prints the process identifier, the name of the user, the command corresponding to the process, and the list of processor cores that the process is currently running on. (To understand what these properties mean, for this and the following info types, please consult the general @sc{gnu}/Linux documentation.) @kindex info os procgroups @item procgroups Display the list of process groups on the target. For each process, @value{GDBN} prints the identifier of the process group that it belongs to, the command corresponding to the process group leader, the process identifier, and the command line of the process. The list is sorted first by the process group identifier, then by the process identifier, so that processes belonging to the same process group are grouped together and the process group leader is listed first. @kindex info os semaphores @item semaphores Display the list of all System V semaphore sets on the target. For each semaphore set, @value{GDBN} prints the semaphore set key, the semaphore set identifier, the access permissions, the number of semaphores in the set, the user and group of the owner and creator of the semaphore set, and the times at which the semaphore set was operated upon and changed. @kindex info os shm @item shm Display the list of all System V shared-memory regions on the target. For each shared-memory region, @value{GDBN} prints the region key, the shared-memory identifier, the access permissions, the size of the region, the process that created the region, the process that last attached to or detached from the region, the current number of live attaches to the region, and the times at which the region was last attached to, detach from, and changed. @kindex info os sockets @item sockets Display the list of Internet-domain sockets on the target. For each socket, @value{GDBN} prints the address and port of the local and remote endpoints, the current state of the connection, the creator of the socket, the IP address family of the socket, and the type of the connection. @kindex info os threads @item threads Display the list of threads running on the target. For each thread, @value{GDBN} prints the identifier of the process that the thread belongs to, the command of the process, the thread identifier, and the processor core that it is currently running on. The main thread of a process is not listed. @end table @item info os If @var{infotype} is omitted, then list the possible values for @var{infotype} and the kind of OS information available for each @var{infotype}. If the target does not return a list of possible types, this command will report an error. @end table @node Memory Region Attributes @section Memory Region Attributes @cindex memory region attributes @dfn{Memory region attributes} allow you to describe special handling required by regions of your target's memory. @value{GDBN} uses attributes to determine whether to allow certain types of memory accesses; whether to use specific width accesses; and whether to cache target memory. By default the description of memory regions is fetched from the target (if the current target supports this), but the user can override the fetched regions. Defined memory regions can be individually enabled and disabled. When a memory region is disabled, @value{GDBN} uses the default attributes when accessing memory in that region. Similarly, if no memory regions have been defined, @value{GDBN} uses the default attributes when accessing all memory. When a memory region is defined, it is given a number to identify it; to enable, disable, or remove a memory region, you specify that number. @table @code @kindex mem @item mem @var{lower} @var{upper} @var{attributes}@dots{} Define a memory region bounded by @var{lower} and @var{upper} with attributes @var{attributes}@dots{}, and add it to the list of regions monitored by @value{GDBN}. Note that @var{upper} == 0 is a special case: it is treated as the target's maximum memory address. (0xffff on 16 bit targets, 0xffffffff on 32 bit targets, etc.) @item mem auto Discard any user changes to the memory regions and use target-supplied regions, if available, or no regions if the target does not support. @kindex delete mem @item delete mem @var{nums}@dots{} Remove memory regions @var{nums}@dots{} from the list of regions monitored by @value{GDBN}. @kindex disable mem @item disable mem @var{nums}@dots{} Disable monitoring of memory regions @var{nums}@dots{}. A disabled memory region is not forgotten. It may be enabled again later. @kindex enable mem @item enable mem @var{nums}@dots{} Enable monitoring of memory regions @var{nums}@dots{}. @kindex info mem @item info mem Print a table of all defined memory regions, with the following columns for each region: @table @emph @item Memory Region Number @item Enabled or Disabled. Enabled memory regions are marked with @samp{y}. Disabled memory regions are marked with @samp{n}. @item Lo Address The address defining the inclusive lower bound of the memory region. @item Hi Address The address defining the exclusive upper bound of the memory region. @item Attributes The list of attributes set for this memory region. @end table @end table @subsection Attributes @subsubsection Memory Access Mode The access mode attributes set whether @value{GDBN} may make read or write accesses to a memory region. While these attributes prevent @value{GDBN} from performing invalid memory accesses, they do nothing to prevent the target system, I/O DMA, etc.@: from accessing memory. @table @code @item ro Memory is read only. @item wo Memory is write only. @item rw Memory is read/write. This is the default. @end table @subsubsection Memory Access Size The access size attribute tells @value{GDBN} to use specific sized accesses in the memory region. Often memory mapped device registers require specific sized accesses. If no access size attribute is specified, @value{GDBN} may use accesses of any size. @table @code @item 8 Use 8 bit memory accesses. @item 16 Use 16 bit memory accesses. @item 32 Use 32 bit memory accesses. @item 64 Use 64 bit memory accesses. @end table @c @subsubsection Hardware/Software Breakpoints @c The hardware/software breakpoint attributes set whether @value{GDBN} @c will use hardware or software breakpoints for the internal breakpoints @c used by the step, next, finish, until, etc. commands. @c @c @table @code @c @item hwbreak @c Always use hardware breakpoints @c @item swbreak (default) @c @end table @subsubsection Data Cache The data cache attributes set whether @value{GDBN} will cache target memory. While this generally improves performance by reducing debug protocol overhead, it can lead to incorrect results because @value{GDBN} does not know about volatile variables or memory mapped device registers. @table @code @item cache Enable @value{GDBN} to cache target memory. @item nocache Disable @value{GDBN} from caching target memory. This is the default. @end table @subsection Memory Access Checking @value{GDBN} can be instructed to refuse accesses to memory that is not explicitly described. This can be useful if accessing such regions has undesired effects for a specific target, or to provide better error checking. The following commands control this behaviour. @table @code @kindex set mem inaccessible-by-default @item set mem inaccessible-by-default [on|off] If @code{on} is specified, make @value{GDBN} treat memory not explicitly described by the memory ranges as non-existent and refuse accesses to such memory. The checks are only performed if there's at least one memory range defined. If @code{off} is specified, make @value{GDBN} treat the memory not explicitly described by the memory ranges as RAM. The default value is @code{on}. @kindex show mem inaccessible-by-default @item show mem inaccessible-by-default Show the current handling of accesses to unknown memory. @end table @c @subsubsection Memory Write Verification @c The memory write verification attributes set whether @value{GDBN} @c will re-reads data after each write to verify the write was successful. @c @c @table @code @c @item verify @c @item noverify (default) @c @end table @node Dump/Restore Files @section Copy Between Memory and a File @cindex dump/restore files @cindex append data to a file @cindex dump data to a file @cindex restore data from a file You can use the commands @code{dump}, @code{append}, and @code{restore} to copy data between target memory and a file. The @code{dump} and @code{append} commands write data to a file, and the @code{restore} command reads data from a file back into the inferior's memory. Files may be in binary, Motorola S-record, Intel hex, Tektronix Hex, or Verilog Hex format; however, @value{GDBN} can only append to binary files, and cannot read from Verilog Hex files. @table @code @kindex dump @item dump @r{[}@var{format}@r{]} memory @var{filename} @var{start_addr} @var{end_addr} @itemx dump @r{[}@var{format}@r{]} value @var{filename} @var{expr} Dump the contents of memory from @var{start_addr} to @var{end_addr}, or the value of @var{expr}, to @var{filename} in the given format. The @var{format} parameter may be any one of: @table @code @item binary Raw binary form. @item ihex Intel hex format. @item srec Motorola S-record format. @item tekhex Tektronix Hex format. @item verilog Verilog Hex format. @end table @value{GDBN} uses the same definitions of these formats as the @sc{gnu} binary utilities, like @samp{objdump} and @samp{objcopy}. If @var{format} is omitted, @value{GDBN} dumps the data in raw binary form. @kindex append @item append @r{[}binary@r{]} memory @var{filename} @var{start_addr} @var{end_addr} @itemx append @r{[}binary@r{]} value @var{filename} @var{expr} Append the contents of memory from @var{start_addr} to @var{end_addr}, or the value of @var{expr}, to the file @var{filename}, in raw binary form. (@value{GDBN} can only append data to files in raw binary form.) @kindex restore @item restore @var{filename} @r{[}binary@r{]} @var{bias} @var{start} @var{end} Restore the contents of file @var{filename} into memory. The @code{restore} command can automatically recognize any known @sc{bfd} file format, except for raw binary. To restore a raw binary file you must specify the optional keyword @code{binary} after the filename. If @var{bias} is non-zero, its value will be added to the addresses contained in the file. Binary files always start at address zero, so they will be restored at address @var{bias}. Other bfd files have a built-in location; they will be restored at offset @var{bias} from that location. If @var{start} and/or @var{end} are non-zero, then only data between file offset @var{start} and file offset @var{end} will be restored. These offsets are relative to the addresses in the file, before the @var{bias} argument is applied. @end table @node Core File Generation @section How to Produce a Core File from Your Program @cindex dump core from inferior A @dfn{core file} or @dfn{core dump} is a file that records the memory image of a running process and its process status (register values etc.). Its primary use is post-mortem debugging of a program that crashed while it ran outside a debugger. A program that crashes automatically produces a core file, unless this feature is disabled by the user. @xref{Files}, for information on invoking @value{GDBN} in the post-mortem debugging mode. Occasionally, you may wish to produce a core file of the program you are debugging in order to preserve a snapshot of its state. @value{GDBN} has a special command for that. @table @code @kindex gcore @kindex generate-core-file @item generate-core-file [@var{file}] @itemx gcore [@var{file}] Produce a core dump of the inferior process. The optional argument @var{file} specifies the file name where to put the core dump. If not specified, the file name defaults to @file{core.@var{pid}}, where @var{pid} is the inferior process ID. Note that this command is implemented only for some systems (as of this writing, @sc{gnu}/Linux, FreeBSD, Solaris, and S390). On @sc{gnu}/Linux, this command can take into account the value of the file @file{/proc/@var{pid}/coredump_filter} when generating the core dump (@pxref{set use-coredump-filter}), and by default honors the @code{VM_DONTDUMP} flag for mappings where it is present in the file @file{/proc/@var{pid}/smaps} (@pxref{set dump-excluded-mappings}). @kindex set use-coredump-filter @anchor{set use-coredump-filter} @item set use-coredump-filter on @itemx set use-coredump-filter off Enable or disable the use of the file @file{/proc/@var{pid}/coredump_filter} when generating core dump files. This file is used by the Linux kernel to decide what types of memory mappings will be dumped or ignored when generating a core dump file. @var{pid} is the process ID of a currently running process. To make use of this feature, you have to write in the @file{/proc/@var{pid}/coredump_filter} file a value, in hexadecimal, which is a bit mask representing the memory mapping types. If a bit is set in the bit mask, then the memory mappings of the corresponding types will be dumped; otherwise, they will be ignored. This configuration is inherited by child processes. For more information about the bits that can be set in the @file{/proc/@var{pid}/coredump_filter} file, please refer to the manpage of @code{core(5)}. By default, this option is @code{on}. If this option is turned @code{off}, @value{GDBN} does not read the @file{coredump_filter} file and instead uses the same default value as the Linux kernel in order to decide which pages will be dumped in the core dump file. This value is currently @code{0x33}, which means that bits @code{0} (anonymous private mappings), @code{1} (anonymous shared mappings), @code{4} (ELF headers) and @code{5} (private huge pages) are active. This will cause these memory mappings to be dumped automatically. @kindex set dump-excluded-mappings @anchor{set dump-excluded-mappings} @item set dump-excluded-mappings on @itemx set dump-excluded-mappings off If @code{on} is specified, @value{GDBN} will dump memory mappings marked with the @code{VM_DONTDUMP} flag. This flag is represented in the file @file{/proc/@var{pid}/smaps} with the acronym @code{dd}. The default value is @code{off}. @end table @node Character Sets @section Character Sets @cindex character sets @cindex charset @cindex translating between character sets @cindex host character set @cindex target character set If the program you are debugging uses a different character set to represent characters and strings than the one @value{GDBN} uses itself, @value{GDBN} can automatically translate between the character sets for you. The character set @value{GDBN} uses we call the @dfn{host character set}; the one the inferior program uses we call the @dfn{target character set}. For example, if you are running @value{GDBN} on a @sc{gnu}/Linux system, which uses the ISO Latin 1 character set, but you are using @value{GDBN}'s remote protocol (@pxref{Remote Debugging}) to debug a program running on an IBM mainframe, which uses the @sc{ebcdic} character set, then the host character set is Latin-1, and the target character set is @sc{ebcdic}. If you give @value{GDBN} the command @code{set target-charset EBCDIC-US}, then @value{GDBN} translates between @sc{ebcdic} and Latin 1 as you print character or string values, or use character and string literals in expressions. @value{GDBN} has no way to automatically recognize which character set the inferior program uses; you must tell it, using the @code{set target-charset} command, described below. Here are the commands for controlling @value{GDBN}'s character set support: @table @code @item set target-charset @var{charset} @kindex set target-charset Set the current target character set to @var{charset}. To display the list of supported target character sets, type @kbd{@w{set target-charset @key{TAB}@key{TAB}}}. @item set host-charset @var{charset} @kindex set host-charset Set the current host character set to @var{charset}. By default, @value{GDBN} uses a host character set appropriate to the system it is running on; you can override that default using the @code{set host-charset} command. On some systems, @value{GDBN} cannot automatically determine the appropriate host character set. In this case, @value{GDBN} uses @samp{UTF-8}. @value{GDBN} can only use certain character sets as its host character set. If you type @kbd{@w{set host-charset @key{TAB}@key{TAB}}}, @value{GDBN} will list the host character sets it supports. @item set charset @var{charset} @kindex set charset Set the current host and target character sets to @var{charset}. As above, if you type @kbd{@w{set charset @key{TAB}@key{TAB}}}, @value{GDBN} will list the names of the character sets that can be used for both host and target. @item show charset @kindex show charset Show the names of the current host and target character sets. @item show host-charset @kindex show host-charset Show the name of the current host character set. @item show target-charset @kindex show target-charset Show the name of the current target character set. @item set target-wide-charset @var{charset} @kindex set target-wide-charset Set the current target's wide character set to @var{charset}. This is the character set used by the target's @code{wchar_t} type. To display the list of supported wide character sets, type @kbd{@w{set target-wide-charset @key{TAB}@key{TAB}}}. @item show target-wide-charset @kindex show target-wide-charset Show the name of the current target's wide character set. @end table Here is an example of @value{GDBN}'s character set support in action. Assume that the following source code has been placed in the file @file{charset-test.c}: @smallexample #include <stdio.h> char ascii_hello[] = @{72, 101, 108, 108, 111, 44, 32, 119, 111, 114, 108, 100, 33, 10, 0@}; char ibm1047_hello[] = @{200, 133, 147, 147, 150, 107, 64, 166, 150, 153, 147, 132, 90, 37, 0@}; main () @{ printf ("Hello, world!\n"); @} @end smallexample In this program, @code{ascii_hello} and @code{ibm1047_hello} are arrays containing the string @samp{Hello, world!} followed by a newline, encoded in the @sc{ascii} and @sc{ibm1047} character sets. We compile the program, and invoke the debugger on it: @smallexample $ gcc -g charset-test.c -o charset-test $ gdb -nw charset-test GNU gdb 2001-12-19-cvs Copyright 2001 Free Software Foundation, Inc. @dots{} (@value{GDBP}) @end smallexample We can use the @code{show charset} command to see what character sets @value{GDBN} is currently using to interpret and display characters and strings: @smallexample (@value{GDBP}) show charset The current host and target character set is `ISO-8859-1'. (@value{GDBP}) @end smallexample For the sake of printing this manual, let's use @sc{ascii} as our initial character set: @smallexample (@value{GDBP}) set charset ASCII (@value{GDBP}) show charset The current host and target character set is `ASCII'. (@value{GDBP}) @end smallexample Let's assume that @sc{ascii} is indeed the correct character set for our host system --- in other words, let's assume that if @value{GDBN} prints characters using the @sc{ascii} character set, our terminal will display them properly. Since our current target character set is also @sc{ascii}, the contents of @code{ascii_hello} print legibly: @smallexample (@value{GDBP}) print ascii_hello $1 = 0x401698 "Hello, world!\n" (@value{GDBP}) print ascii_hello[0] $2 = 72 'H' (@value{GDBP}) @end smallexample @value{GDBN} uses the target character set for character and string literals you use in expressions: @smallexample (@value{GDBP}) print '+' $3 = 43 '+' (@value{GDBP}) @end smallexample The @sc{ascii} character set uses the number 43 to encode the @samp{+} character. @value{GDBN} relies on the user to tell it which character set the target program uses. If we print @code{ibm1047_hello} while our target character set is still @sc{ascii}, we get jibberish: @smallexample (@value{GDBP}) print ibm1047_hello $4 = 0x4016a8 "\310\205\223\223\226k@@\246\226\231\223\204Z%" (@value{GDBP}) print ibm1047_hello[0] $5 = 200 '\310' (@value{GDBP}) @end smallexample If we invoke the @code{set target-charset} followed by @key{TAB}@key{TAB}, @value{GDBN} tells us the character sets it supports: @smallexample (@value{GDBP}) set target-charset ASCII EBCDIC-US IBM1047 ISO-8859-1 (@value{GDBP}) set target-charset @end smallexample We can select @sc{ibm1047} as our target character set, and examine the program's strings again. Now the @sc{ascii} string is wrong, but @value{GDBN} translates the contents of @code{ibm1047_hello} from the target character set, @sc{ibm1047}, to the host character set, @sc{ascii}, and they display correctly: @smallexample (@value{GDBP}) set target-charset IBM1047 (@value{GDBP}) show charset The current host character set is `ASCII'. The current target character set is `IBM1047'. (@value{GDBP}) print ascii_hello $6 = 0x401698 "\110\145%%?\054\040\167?\162%\144\041\012" (@value{GDBP}) print ascii_hello[0] $7 = 72 '\110' (@value{GDBP}) print ibm1047_hello $8 = 0x4016a8 "Hello, world!\n" (@value{GDBP}) print ibm1047_hello[0] $9 = 200 'H' (@value{GDBP}) @end smallexample As above, @value{GDBN} uses the target character set for character and string literals you use in expressions: @smallexample (@value{GDBP}) print '+' $10 = 78 '+' (@value{GDBP}) @end smallexample The @sc{ibm1047} character set uses the number 78 to encode the @samp{+} character. @node Caching Target Data @section Caching Data of Targets @cindex caching data of targets @value{GDBN} caches data exchanged between the debugger and a target. Each cache is associated with the address space of the inferior. @xref{Inferiors Connections and Programs}, about inferior and address space. Such caching generally improves performance in remote debugging (@pxref{Remote Debugging}), because it reduces the overhead of the remote protocol by bundling memory reads and writes into large chunks. Unfortunately, simply caching everything would lead to incorrect results, since @value{GDBN} does not necessarily know anything about volatile values, memory-mapped I/O addresses, etc. Furthermore, in non-stop mode (@pxref{Non-Stop Mode}) memory can be changed @emph{while} a gdb command is executing. Therefore, by default, @value{GDBN} only caches data known to be on the stack@footnote{In non-stop mode, it is moderately rare for a running thread to modify the stack of a stopped thread in a way that would interfere with a backtrace, and caching of stack reads provides a significant speed up of remote backtraces.} or in the code segment. Other regions of memory can be explicitly marked as cacheable; @pxref{Memory Region Attributes}. @table @code @kindex set remotecache @item set remotecache on @itemx set remotecache off This option no longer does anything; it exists for compatibility with old scripts. @kindex show remotecache @item show remotecache Show the current state of the obsolete remotecache flag. @kindex set stack-cache @item set stack-cache on @itemx set stack-cache off Enable or disable caching of stack accesses. When @code{on}, use caching. By default, this option is @code{on}. @kindex show stack-cache @item show stack-cache Show the current state of data caching for memory accesses. @kindex set code-cache @item set code-cache on @itemx set code-cache off Enable or disable caching of code segment accesses. When @code{on}, use caching. By default, this option is @code{on}. This improves performance of disassembly in remote debugging. @kindex show code-cache @item show code-cache Show the current state of target memory cache for code segment accesses. @kindex info dcache @item info dcache @r{[}line@r{]} Print the information about the performance of data cache of the current inferior's address space. The information displayed includes the dcache width and depth, and for each cache line, its number, address, and how many times it was referenced. This command is useful for debugging the data cache operation. If a line number is specified, the contents of that line will be printed in hex. @item set dcache size @var{size} @cindex dcache size @kindex set dcache size Set maximum number of entries in dcache (dcache depth above). @item set dcache line-size @var{line-size} @cindex dcache line-size @kindex set dcache line-size Set number of bytes each dcache entry caches (dcache width above). Must be a power of 2. @item show dcache size @kindex show dcache size Show maximum number of dcache entries. @xref{Caching Target Data, info dcache}. @item show dcache line-size @kindex show dcache line-size Show default size of dcache lines. @end table @node Searching Memory @section Search Memory @cindex searching memory Memory can be searched for a particular sequence of bytes with the @code{find} command. @table @code @kindex find @item find @r{[}/@var{sn}@r{]} @var{start_addr}, +@var{len}, @var{val1} @r{[}, @var{val2}, @dots{}@r{]} @itemx find @r{[}/@var{sn}@r{]} @var{start_addr}, @var{end_addr}, @var{val1} @r{[}, @var{val2}, @dots{}@r{]} Search memory for the sequence of bytes specified by @var{val1}, @var{val2}, etc. The search begins at address @var{start_addr} and continues for either @var{len} bytes or through to @var{end_addr} inclusive. @end table @var{s} and @var{n} are optional parameters. They may be specified in either order, apart or together. @table @r @item @var{s}, search query size The size of each search query value. @table @code @item b bytes @item h halfwords (two bytes) @item w words (four bytes) @item g giant words (eight bytes) @end table All values are interpreted in the current language. This means, for example, that if the current source language is C/C@t{++} then searching for the string ``hello'' includes the trailing '\0'. The null terminator can be removed from searching by using casts, e.g.: @samp{@{char[5]@}"hello"}. If the value size is not specified, it is taken from the value's type in the current language. This is useful when one wants to specify the search pattern as a mixture of types. Note that this means, for example, that in the case of C-like languages a search for an untyped 0x42 will search for @samp{(int) 0x42} which is typically four bytes. @item @var{n}, maximum number of finds The maximum number of matches to print. The default is to print all finds. @end table You can use strings as search values. Quote them with double-quotes (@code{"}). The string value is copied into the search pattern byte by byte, regardless of the endianness of the target and the size specification. The address of each match found is printed as well as a count of the number of matches found. The address of the last value found is stored in convenience variable @samp{$_}. A count of the number of matches is stored in @samp{$numfound}. For example, if stopped at the @code{printf} in this function: @smallexample void hello () @{ static char hello[] = "hello-hello"; static struct @{ char c; short s; int i; @} __attribute__ ((packed)) mixed = @{ 'c', 0x1234, 0x87654321 @}; printf ("%s\n", hello); @} @end smallexample @noindent you get during debugging: @smallexample (gdb) find &hello[0], +sizeof(hello), "hello" 0x804956d <hello.1620+6> 1 pattern found (gdb) find &hello[0], +sizeof(hello), 'h', 'e', 'l', 'l', 'o' 0x8049567 <hello.1620> 0x804956d <hello.1620+6> 2 patterns found. (gdb) find &hello[0], +sizeof(hello), @{char[5]@}"hello" 0x8049567 <hello.1620> 0x804956d <hello.1620+6> 2 patterns found. (gdb) find /b1 &hello[0], +sizeof(hello), 'h', 0x65, 'l' 0x8049567 <hello.1620> 1 pattern found (gdb) find &mixed, +sizeof(mixed), (char) 'c', (short) 0x1234, (int) 0x87654321 0x8049560 <mixed.1625> 1 pattern found (gdb) print $numfound $1 = 1 (gdb) print $_ $2 = (void *) 0x8049560 @end smallexample @node Value Sizes @section Value Sizes Whenever @value{GDBN} prints a value memory will be allocated within @value{GDBN} to hold the contents of the value. It is possible in some languages with dynamic typing systems, that an invalid program may indicate a value that is incorrectly large, this in turn may cause @value{GDBN} to try and allocate an overly large amount of memory. @table @code @kindex set max-value-size @item set max-value-size @var{bytes} @itemx set max-value-size unlimited Set the maximum size of memory that @value{GDBN} will allocate for the contents of a value to @var{bytes}, trying to display a value that requires more memory than that will result in an error. Setting this variable does not effect values that have already been allocated within @value{GDBN}, only future allocations. There's a minimum size that @code{max-value-size} can be set to in order that @value{GDBN} can still operate correctly, this minimum is currently 16 bytes. The limit applies to the results of some subexpressions as well as to complete expressions. For example, an expression denoting a simple integer component, such as @code{x.y.z}, may fail if the size of @var{x.y} is dynamic and exceeds @var{bytes}. On the other hand, @value{GDBN} is sometimes clever; the expression @code{A[i]}, where @var{A} is an array variable with non-constant size, will generally succeed regardless of the bounds on @var{A}, as long as the component size is less than @var{bytes}. The default value of @code{max-value-size} is currently 64k. @kindex show max-value-size @item show max-value-size Show the maximum size of memory, in bytes, that @value{GDBN} will allocate for the contents of a value. @end table @node Optimized Code @chapter Debugging Optimized Code @cindex optimized code, debugging @cindex debugging optimized code Almost all compilers support optimization. With optimization disabled, the compiler generates assembly code that corresponds directly to your source code, in a simplistic way. As the compiler applies more powerful optimizations, the generated assembly code diverges from your original source code. With help from debugging information generated by the compiler, @value{GDBN} can map from the running program back to constructs from your original source. @value{GDBN} is more accurate with optimization disabled. If you can recompile without optimization, it is easier to follow the progress of your program during debugging. But, there are many cases where you may need to debug an optimized version. When you debug a program compiled with @samp{-g -O}, remember that the optimizer has rearranged your code; the debugger shows you what is really there. Do not be too surprised when the execution path does not exactly match your source file! An extreme example: if you define a variable, but never use it, @value{GDBN} never sees that variable---because the compiler optimizes it out of existence. Some things do not work as well with @samp{-g -O} as with just @samp{-g}, particularly on machines with instruction scheduling. If in doubt, recompile with @samp{-g} alone, and if this fixes the problem, please report it to us as a bug (including a test case!). @xref{Variables}, for more information about debugging optimized code. @menu * Inline Functions:: How @value{GDBN} presents inlining * Tail Call Frames:: @value{GDBN} analysis of jumps to functions @end menu @node Inline Functions @section Inline Functions @cindex inline functions, debugging @dfn{Inlining} is an optimization that inserts a copy of the function body directly at each call site, instead of jumping to a shared routine. @value{GDBN} displays inlined functions just like non-inlined functions. They appear in backtraces. You can view their arguments and local variables, step into them with @code{step}, skip them with @code{next}, and escape from them with @code{finish}. You can check whether a function was inlined by using the @code{info frame} command. For @value{GDBN} to support inlined functions, the compiler must record information about inlining in the debug information --- @value{NGCC} using the @sc{dwarf 2} format does this, and several other compilers do also. @value{GDBN} only supports inlined functions when using @sc{dwarf 2}. Versions of @value{NGCC} before 4.1 do not emit two required attributes (@samp{DW_AT_call_file} and @samp{DW_AT_call_line}); @value{GDBN} does not display inlined function calls with earlier versions of @value{NGCC}. It instead displays the arguments and local variables of inlined functions as local variables in the caller. The body of an inlined function is directly included at its call site; unlike a non-inlined function, there are no instructions devoted to the call. @value{GDBN} still pretends that the call site and the start of the inlined function are different instructions. Stepping to the call site shows the call site, and then stepping again shows the first line of the inlined function, even though no additional instructions are executed. This makes source-level debugging much clearer; you can see both the context of the call and then the effect of the call. Only stepping by a single instruction using @code{stepi} or @code{nexti} does not do this; single instruction steps always show the inlined body. There are some ways that @value{GDBN} does not pretend that inlined function calls are the same as normal calls: @itemize @bullet @item Setting breakpoints at the call site of an inlined function may not work, because the call site does not contain any code. @value{GDBN} may incorrectly move the breakpoint to the next line of the enclosing function, after the call. This limitation will be removed in a future version of @value{GDBN}; until then, set a breakpoint on an earlier line or inside the inlined function instead. @item @value{GDBN} cannot locate the return value of inlined calls after using the @code{finish} command. This is a limitation of compiler-generated debugging information; after @code{finish}, you can step to the next line and print a variable where your program stored the return value. @end itemize @node Tail Call Frames @section Tail Call Frames @cindex tail call frames, debugging Function @code{B} can call function @code{C} in its very last statement. In unoptimized compilation the call of @code{C} is immediately followed by return instruction at the end of @code{B} code. Optimizing compiler may replace the call and return in function @code{B} into one jump to function @code{C} instead. Such use of a jump instruction is called @dfn{tail call}. During execution of function @code{C}, there will be no indication in the function call stack frames that it was tail-called from @code{B}. If function @code{A} regularly calls function @code{B} which tail-calls function @code{C}, then @value{GDBN} will see @code{A} as the caller of @code{C}. However, in some cases @value{GDBN} can determine that @code{C} was tail-called from @code{B}, and it will then create fictitious call frame for that, with the return address set up as if @code{B} called @code{C} normally. This functionality is currently supported only by DWARF 2 debugging format and the compiler has to produce @samp{DW_TAG_call_site} tags. With @value{NGCC}, you need to specify @option{-O -g} during compilation, to get this information. @kbd{info frame} command (@pxref{Frame Info}) will indicate the tail call frame kind by text @code{tail call frame} such as in this sample @value{GDBN} output: @smallexample (gdb) x/i $pc - 2 0x40066b <b(int, double)+11>: jmp 0x400640 <c(int, double)> (gdb) info frame Stack level 1, frame at 0x7fffffffda30: rip = 0x40066d in b (amd64-entry-value.cc:59); saved rip 0x4004c5 tail call frame, caller of frame at 0x7fffffffda30 source language c++. Arglist at unknown address. Locals at unknown address, Previous frame's sp is 0x7fffffffda30 @end smallexample The detection of all the possible code path executions can find them ambiguous. There is no execution history stored (possible @ref{Reverse Execution} is never used for this purpose) and the last known caller could have reached the known callee by multiple different jump sequences. In such case @value{GDBN} still tries to show at least all the unambiguous top tail callers and all the unambiguous bottom tail calees, if any. @table @code @anchor{set debug entry-values} @item set debug entry-values @kindex set debug entry-values When set to on, enables printing of analysis messages for both frame argument values at function entry and tail calls. It will show all the possible valid tail calls code paths it has considered. It will also print the intersection of them with the final unambiguous (possibly partial or even empty) code path result. @item show debug entry-values @kindex show debug entry-values Show the current state of analysis messages printing for both frame argument values at function entry and tail calls. @end table The analysis messages for tail calls can for example show why the virtual tail call frame for function @code{c} has not been recognized (due to the indirect reference by variable @code{x}): @smallexample static void __attribute__((noinline, noclone)) c (void); void (*x) (void) = c; static void __attribute__((noinline, noclone)) a (void) @{ x++; @} static void __attribute__((noinline, noclone)) c (void) @{ a (); @} int main (void) @{ x (); return 0; @} Breakpoint 1, DW_OP_entry_value resolving cannot find DW_TAG_call_site 0x40039a in main a () at t.c:3 3 static void __attribute__((noinline, noclone)) a (void) @{ x++; @} (gdb) bt #0 a () at t.c:3 #1 0x000000000040039a in main () at t.c:5 @end smallexample Another possibility is an ambiguous virtual tail call frames resolution: @smallexample int i; static void __attribute__((noinline, noclone)) f (void) @{ i++; @} static void __attribute__((noinline, noclone)) e (void) @{ f (); @} static void __attribute__((noinline, noclone)) d (void) @{ f (); @} static void __attribute__((noinline, noclone)) c (void) @{ d (); @} static void __attribute__((noinline, noclone)) b (void) @{ if (i) c (); else e (); @} static void __attribute__((noinline, noclone)) a (void) @{ b (); @} int main (void) @{ a (); return 0; @} tailcall: initial: 0x4004d2(a) 0x4004ce(b) 0x4004b2(c) 0x4004a2(d) tailcall: compare: 0x4004d2(a) 0x4004cc(b) 0x400492(e) tailcall: reduced: 0x4004d2(a) | (gdb) bt #0 f () at t.c:2 #1 0x00000000004004d2 in a () at t.c:8 #2 0x0000000000400395 in main () at t.c:9 @end smallexample @set CALLSEQ1A @code{main@value{ARROW}a@value{ARROW}b@value{ARROW}c@value{ARROW}d@value{ARROW}f} @set CALLSEQ2A @code{main@value{ARROW}a@value{ARROW}b@value{ARROW}e@value{ARROW}f} @c Convert CALLSEQ#A to CALLSEQ#B depending on HAVE_MAKEINFO_CLICK. @ifset HAVE_MAKEINFO_CLICK @set ARROW @click{} @set CALLSEQ1B @clicksequence{@value{CALLSEQ1A}} @set CALLSEQ2B @clicksequence{@value{CALLSEQ2A}} @end ifset @ifclear HAVE_MAKEINFO_CLICK @set ARROW -> @set CALLSEQ1B @value{CALLSEQ1A} @set CALLSEQ2B @value{CALLSEQ2A} @end ifclear Frames #0 and #2 are real, #1 is a virtual tail call frame. The code can have possible execution paths @value{CALLSEQ1B} or @value{CALLSEQ2B}, @value{GDBN} cannot find which one from the inferior state. @code{initial:} state shows some random possible calling sequence @value{GDBN} has found. It then finds another possible calling sequence - that one is prefixed by @code{compare:}. The non-ambiguous intersection of these two is printed as the @code{reduced:} calling sequence. That one could have many further @code{compare:} and @code{reduced:} statements as long as there remain any non-ambiguous sequence entries. For the frame of function @code{b} in both cases there are different possible @code{$pc} values (@code{0x4004cc} or @code{0x4004ce}), therefore this frame is also ambiguous. The only non-ambiguous frame is the one for function @code{a}, therefore this one is displayed to the user while the ambiguous frames are omitted. There can be also reasons why printing of frame argument values at function entry may fail: @smallexample int v; static void __attribute__((noinline, noclone)) c (int i) @{ v++; @} static void __attribute__((noinline, noclone)) a (int i); static void __attribute__((noinline, noclone)) b (int i) @{ a (i); @} static void __attribute__((noinline, noclone)) a (int i) @{ if (i) b (i - 1); else c (0); @} int main (void) @{ a (5); return 0; @} (gdb) bt #0 c (i=i@@entry=0) at t.c:2 #1 0x0000000000400428 in a (DW_OP_entry_value resolving has found function "a" at 0x400420 can call itself via tail calls i=<optimized out>) at t.c:6 #2 0x000000000040036e in main () at t.c:7 @end smallexample @value{GDBN} cannot find out from the inferior state if and how many times did function @code{a} call itself (via function @code{b}) as these calls would be tail calls. Such tail calls would modify the @code{i} variable, therefore @value{GDBN} cannot be sure the value it knows would be right - @value{GDBN} prints @code{<optimized out>} instead. @node Macros @chapter C Preprocessor Macros Some languages, such as C and C@t{++}, provide a way to define and invoke ``preprocessor macros'' which expand into strings of tokens. @value{GDBN} can evaluate expressions containing macro invocations, show the result of macro expansion, and show a macro's definition, including where it was defined. You may need to compile your program specially to provide @value{GDBN} with information about preprocessor macros. Most compilers do not include macros in their debugging information, even when you compile with the @option{-g} flag. @xref{Compilation}. A program may define a macro at one point, remove that definition later, and then provide a different definition after that. Thus, at different points in the program, a macro may have different definitions, or have no definition at all. If there is a current stack frame, @value{GDBN} uses the macros in scope at that frame's source code line. Otherwise, @value{GDBN} uses the macros in scope at the current listing location; see @ref{List}. Whenever @value{GDBN} evaluates an expression, it always expands any macro invocations present in the expression. @value{GDBN} also provides the following commands for working with macros explicitly. @table @code @kindex macro expand @cindex macro expansion, showing the results of preprocessor @cindex preprocessor macro expansion, showing the results of @cindex expanding preprocessor macros @item macro expand @var{expression} @itemx macro exp @var{expression} Show the results of expanding all preprocessor macro invocations in @var{expression}. Since @value{GDBN} simply expands macros, but does not parse the result, @var{expression} need not be a valid expression; it can be any string of tokens. @kindex macro exp1 @item macro expand-once @var{expression} @itemx macro exp1 @var{expression} @cindex expand macro once @i{(This command is not yet implemented.)} Show the results of expanding those preprocessor macro invocations that appear explicitly in @var{expression}. Macro invocations appearing in that expansion are left unchanged. This command allows you to see the effect of a particular macro more clearly, without being confused by further expansions. Since @value{GDBN} simply expands macros, but does not parse the result, @var{expression} need not be a valid expression; it can be any string of tokens. @kindex info macro @cindex macro definition, showing @cindex definition of a macro, showing @cindex macros, from debug info @item info macro [-a|-all] [--] @var{macro} Show the current definition or all definitions of the named @var{macro}, and describe the source location or compiler command-line where that definition was established. The optional double dash is to signify the end of argument processing and the beginning of @var{macro} for non C-like macros where the macro may begin with a hyphen. @kindex info macros @item info macros @var{location} Show all macro definitions that are in effect at the location specified by @var{location}, and describe the source location or compiler command-line where those definitions were established. @kindex macro define @cindex user-defined macros @cindex defining macros interactively @cindex macros, user-defined @item macro define @var{macro} @var{replacement-list} @itemx macro define @var{macro}(@var{arglist}) @var{replacement-list} Introduce a definition for a preprocessor macro named @var{macro}, invocations of which are replaced by the tokens given in @var{replacement-list}. The first form of this command defines an ``object-like'' macro, which takes no arguments; the second form defines a ``function-like'' macro, which takes the arguments given in @var{arglist}. A definition introduced by this command is in scope in every expression evaluated in @value{GDBN}, until it is removed with the @code{macro undef} command, described below. The definition overrides all definitions for @var{macro} present in the program being debugged, as well as any previous user-supplied definition. @kindex macro undef @item macro undef @var{macro} Remove any user-supplied definition for the macro named @var{macro}. This command only affects definitions provided with the @code{macro define} command, described above; it cannot remove definitions present in the program being debugged. @kindex macro list @item macro list List all the macros defined using the @code{macro define} command. @end table @cindex macros, example of debugging with Here is a transcript showing the above commands in action. First, we show our source files: @smallexample $ cat sample.c #include <stdio.h> #include "sample.h" #define M 42 #define ADD(x) (M + x) main () @{ #define N 28 printf ("Hello, world!\n"); #undef N printf ("We're so creative.\n"); #define N 1729 printf ("Goodbye, world!\n"); @} $ cat sample.h #define Q < $ @end smallexample Now, we compile the program using the @sc{gnu} C compiler, @value{NGCC}. We pass the @option{-gdwarf-2}@footnote{This is the minimum. Recent versions of @value{NGCC} support @option{-gdwarf-3} and @option{-gdwarf-4}; we recommend always choosing the most recent version of DWARF.} @emph{and} @option{-g3} flags to ensure the compiler includes information about preprocessor macros in the debugging information. @smallexample $ gcc -gdwarf-2 -g3 sample.c -o sample $ @end smallexample Now, we start @value{GDBN} on our sample program: @smallexample $ gdb -nw sample GNU gdb 2002-05-06-cvs Copyright 2002 Free Software Foundation, Inc. GDB is free software, @dots{} (@value{GDBP}) @end smallexample We can expand macros and examine their definitions, even when the program is not running. @value{GDBN} uses the current listing position to decide which macro definitions are in scope: @smallexample (@value{GDBP}) list main 3 4 #define M 42 5 #define ADD(x) (M + x) 6 7 main () 8 @{ 9 #define N 28 10 printf ("Hello, world!\n"); 11 #undef N 12 printf ("We're so creative.\n"); (@value{GDBP}) info macro ADD Defined at /home/jimb/gdb/macros/play/sample.c:5 #define ADD(x) (M + x) (@value{GDBP}) info macro Q Defined at /home/jimb/gdb/macros/play/sample.h:1 included at /home/jimb/gdb/macros/play/sample.c:2 #define Q < (@value{GDBP}) macro expand ADD(1) expands to: (42 + 1) (@value{GDBP}) macro expand-once ADD(1) expands to: once (M + 1) (@value{GDBP}) @end smallexample In the example above, note that @code{macro expand-once} expands only the macro invocation explicit in the original text --- the invocation of @code{ADD} --- but does not expand the invocation of the macro @code{M}, which was introduced by @code{ADD}. Once the program is running, @value{GDBN} uses the macro definitions in force at the source line of the current stack frame: @smallexample (@value{GDBP}) break main Breakpoint 1 at 0x8048370: file sample.c, line 10. (@value{GDBP}) run Starting program: /home/jimb/gdb/macros/play/sample Breakpoint 1, main () at sample.c:10 10 printf ("Hello, world!\n"); (@value{GDBP}) @end smallexample At line 10, the definition of the macro @code{N} at line 9 is in force: @smallexample (@value{GDBP}) info macro N Defined at /home/jimb/gdb/macros/play/sample.c:9 #define N 28 (@value{GDBP}) macro expand N Q M expands to: 28 < 42 (@value{GDBP}) print N Q M $1 = 1 (@value{GDBP}) @end smallexample As we step over directives that remove @code{N}'s definition, and then give it a new definition, @value{GDBN} finds the definition (or lack thereof) in force at each point: @smallexample (@value{GDBP}) next Hello, world! 12 printf ("We're so creative.\n"); (@value{GDBP}) info macro N The symbol `N' has no definition as a C/C++ preprocessor macro at /home/jimb/gdb/macros/play/sample.c:12 (@value{GDBP}) next We're so creative. 14 printf ("Goodbye, world!\n"); (@value{GDBP}) info macro N Defined at /home/jimb/gdb/macros/play/sample.c:13 #define N 1729 (@value{GDBP}) macro expand N Q M expands to: 1729 < 42 (@value{GDBP}) print N Q M $2 = 0 (@value{GDBP}) @end smallexample In addition to source files, macros can be defined on the compilation command line using the @option{-D@var{name}=@var{value}} syntax. For macros defined in such a way, @value{GDBN} displays the location of their definition as line zero of the source file submitted to the compiler. @smallexample (@value{GDBP}) info macro __STDC__ Defined at /home/jimb/gdb/macros/play/sample.c:0 -D__STDC__=1 (@value{GDBP}) @end smallexample @node Tracepoints @chapter Tracepoints @c This chapter is based on the documentation written by Michael @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni. @cindex tracepoints In some applications, it is not feasible for the debugger to interrupt the program's execution long enough for the developer to learn anything helpful about its behavior. If the program's correctness depends on its real-time behavior, delays introduced by a debugger might cause the program to change its behavior drastically, or perhaps fail, even when the code itself is correct. It is useful to be able to observe the program's behavior without interrupting it. Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can specify locations in the program, called @dfn{tracepoints}, and arbitrary expressions to evaluate when those tracepoints are reached. Later, using the @code{tfind} command, you can examine the values those expressions had when the program hit the tracepoints. The expressions may also denote objects in memory---structures or arrays, for example---whose values @value{GDBN} should record; while visiting a particular tracepoint, you may inspect those objects as if they were in memory at that moment. However, because @value{GDBN} records these values without interacting with you, it can do so quickly and unobtrusively, hopefully not disturbing the program's behavior. The tracepoint facility is currently available only for remote targets. @xref{Targets}. In addition, your remote target must know how to collect trace data. This functionality is implemented in the remote stub; however, none of the stubs distributed with @value{GDBN} support tracepoints as of this writing. The format of the remote packets used to implement tracepoints are described in @ref{Tracepoint Packets}. It is also possible to get trace data from a file, in a manner reminiscent of corefiles; you specify the filename, and use @code{tfind} to search through the file. @xref{Trace Files}, for more details. This chapter describes the tracepoint commands and features. @menu * Set Tracepoints:: * Analyze Collected Data:: * Tracepoint Variables:: * Trace Files:: @end menu @node Set Tracepoints @section Commands to Set Tracepoints Before running such a @dfn{trace experiment}, an arbitrary number of tracepoints can be set. A tracepoint is actually a special type of breakpoint (@pxref{Set Breaks}), so you can manipulate it using standard breakpoint commands. For instance, as with breakpoints, tracepoint numbers are successive integers starting from one, and many of the commands associated with tracepoints take the tracepoint number as their argument, to identify which tracepoint to work on. For each tracepoint, you can specify, in advance, some arbitrary set of data that you want the target to collect in the trace buffer when it hits that tracepoint. The collected data can include registers, local variables, or global data. Later, you can use @value{GDBN} commands to examine the values these data had at the time the tracepoint was hit. Tracepoints do not support every breakpoint feature. Ignore counts on tracepoints have no effect, and tracepoints cannot run @value{GDBN} commands when they are hit. Tracepoints may not be thread-specific either. @cindex fast tracepoints Some targets may support @dfn{fast tracepoints}, which are inserted in a different way (such as with a jump instead of a trap), that is faster but possibly restricted in where they may be installed. @cindex static tracepoints @cindex markers, static tracepoints @cindex probing markers, static tracepoints Regular and fast tracepoints are dynamic tracing facilities, meaning that they can be used to insert tracepoints at (almost) any location in the target. Some targets may also support controlling @dfn{static tracepoints} from @value{GDBN}. With static tracing, a set of instrumentation points, also known as @dfn{markers}, are embedded in the target program, and can be activated or deactivated by name or address. These are usually placed at locations which facilitate investigating what the target is actually doing. @value{GDBN}'s support for static tracing includes being able to list instrumentation points, and attach them with @value{GDBN} defined high level tracepoints that expose the whole range of convenience of @value{GDBN}'s tracepoints support. Namely, support for collecting registers values and values of global or local (to the instrumentation point) variables; tracepoint conditions and trace state variables. The act of installing a @value{GDBN} static tracepoint on an instrumentation point, or marker, is referred to as @dfn{probing} a static tracepoint marker. @code{gdbserver} supports tracepoints on some target systems. @xref{Server,,Tracepoints support in @code{gdbserver}}. This section describes commands to set tracepoints and associated conditions and actions. @menu * Create and Delete Tracepoints:: * Enable and Disable Tracepoints:: * Tracepoint Passcounts:: * Tracepoint Conditions:: * Trace State Variables:: * Tracepoint Actions:: * Listing Tracepoints:: * Listing Static Tracepoint Markers:: * Starting and Stopping Trace Experiments:: * Tracepoint Restrictions:: @end menu @node Create and Delete Tracepoints @subsection Create and Delete Tracepoints @table @code @cindex set tracepoint @kindex trace @item trace @var{location} The @code{trace} command is very similar to the @code{break} command. Its argument @var{location} can be any valid location. @xref{Specify Location}. The @code{trace} command defines a tracepoint, which is a point in the target program where the debugger will briefly stop, collect some data, and then allow the program to continue. Setting a tracepoint or changing its actions takes effect immediately if the remote stub supports the @samp{InstallInTrace} feature (@pxref{install tracepoint in tracing}). If remote stub doesn't support the @samp{InstallInTrace} feature, all these changes don't take effect until the next @code{tstart} command, and once a trace experiment is running, further changes will not have any effect until the next trace experiment starts. In addition, @value{GDBN} supports @dfn{pending tracepoints}---tracepoints whose address is not yet resolved. (This is similar to pending breakpoints.) Pending tracepoints are not downloaded to the target and not installed until they are resolved. The resolution of pending tracepoints requires @value{GDBN} support---when debugging with the remote target, and @value{GDBN} disconnects from the remote stub (@pxref{disconnected tracing}), pending tracepoints can not be resolved (and downloaded to the remote stub) while @value{GDBN} is disconnected. Here are some examples of using the @code{trace} command: @smallexample (@value{GDBP}) @b{trace foo.c:121} // a source file and line number (@value{GDBP}) @b{trace +2} // 2 lines forward (@value{GDBP}) @b{trace my_function} // first source line of function (@value{GDBP}) @b{trace *my_function} // EXACT start address of function (@value{GDBP}) @b{trace *0x2117c4} // an address @end smallexample @noindent You can abbreviate @code{trace} as @code{tr}. @item trace @var{location} if @var{cond} Set a tracepoint with condition @var{cond}; evaluate the expression @var{cond} each time the tracepoint is reached, and collect data only if the value is nonzero---that is, if @var{cond} evaluates as true. @xref{Tracepoint Conditions, ,Tracepoint Conditions}, for more information on tracepoint conditions. @item ftrace @var{location} [ if @var{cond} ] @cindex set fast tracepoint @cindex fast tracepoints, setting @kindex ftrace The @code{ftrace} command sets a fast tracepoint. For targets that support them, fast tracepoints will use a more efficient but possibly less general technique to trigger data collection, such as a jump instruction instead of a trap, or some sort of hardware support. It may not be possible to create a fast tracepoint at the desired location, in which case the command will exit with an explanatory message. @value{GDBN} handles arguments to @code{ftrace} exactly as for @code{trace}. On 32-bit x86-architecture systems, fast tracepoints normally need to be placed at an instruction that is 5 bytes or longer, but can be placed at 4-byte instructions if the low 64K of memory of the target program is available to install trampolines. Some Unix-type systems, such as @sc{gnu}/Linux, exclude low addresses from the program's address space; but for instance with the Linux kernel it is possible to let @value{GDBN} use this area by doing a @command{sysctl} command to set the @code{mmap_min_addr} kernel parameter, as in @example sudo sysctl -w vm.mmap_min_addr=32768 @end example @noindent which sets the low address to 32K, which leaves plenty of room for trampolines. The minimum address should be set to a page boundary. @item strace @var{location} [ if @var{cond} ] @cindex set static tracepoint @cindex static tracepoints, setting @cindex probe static tracepoint marker @kindex strace The @code{strace} command sets a static tracepoint. For targets that support it, setting a static tracepoint probes a static instrumentation point, or marker, found at @var{location}. It may not be possible to set a static tracepoint at the desired location, in which case the command will exit with an explanatory message. @value{GDBN} handles arguments to @code{strace} exactly as for @code{trace}, with the addition that the user can also specify @code{-m @var{marker}} as @var{location}. This probes the marker identified by the @var{marker} string identifier. This identifier depends on the static tracepoint backend library your program is using. You can find all the marker identifiers in the @samp{ID} field of the @code{info static-tracepoint-markers} command output. @xref{Listing Static Tracepoint Markers,,Listing Static Tracepoint Markers}. For example, in the following small program using the UST tracing engine: @smallexample main () @{ trace_mark(ust, bar33, "str %s", "FOOBAZ"); @} @end smallexample @noindent the marker id is composed of joining the first two arguments to the @code{trace_mark} call with a slash, which translates to: @smallexample (@value{GDBP}) info static-tracepoint-markers Cnt Enb ID Address What 1 n ust/bar33 0x0000000000400ddc in main at stexample.c:22 Data: "str %s" [etc...] @end smallexample @noindent so you may probe the marker above with: @smallexample (@value{GDBP}) strace -m ust/bar33 @end smallexample Static tracepoints accept an extra collect action --- @code{collect $_sdata}. This collects arbitrary user data passed in the probe point call to the tracing library. In the UST example above, you'll see that the third argument to @code{trace_mark} is a printf-like format string. The user data is then the result of running that formatting string against the following arguments. Note that @code{info static-tracepoint-markers} command output lists that format string in the @samp{Data:} field. You can inspect this data when analyzing the trace buffer, by printing the $_sdata variable like any other variable available to @value{GDBN}. @xref{Tracepoint Actions,,Tracepoint Action Lists}. @vindex $tpnum @cindex last tracepoint number @cindex recent tracepoint number @cindex tracepoint number The convenience variable @code{$tpnum} records the tracepoint number of the most recently set tracepoint. @kindex delete tracepoint @cindex tracepoint deletion @item delete tracepoint @r{[}@var{num}@r{]} Permanently delete one or more tracepoints. With no argument, the default is to delete all tracepoints. Note that the regular @code{delete} command can remove tracepoints also. Examples: @smallexample (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints (@value{GDBP}) @b{delete trace} // remove all tracepoints @end smallexample @noindent You can abbreviate this command as @code{del tr}. @end table @node Enable and Disable Tracepoints @subsection Enable and Disable Tracepoints These commands are deprecated; they are equivalent to plain @code{disable} and @code{enable}. @table @code @kindex disable tracepoint @item disable tracepoint @r{[}@var{num}@r{]} Disable tracepoint @var{num}, or all tracepoints if no argument @var{num} is given. A disabled tracepoint will have no effect during a trace experiment, but it is not forgotten. You can re-enable a disabled tracepoint using the @code{enable tracepoint} command. If the command is issued during a trace experiment and the debug target has support for disabling tracepoints during a trace experiment, then the change will be effective immediately. Otherwise, it will be applied to the next trace experiment. @kindex enable tracepoint @item enable tracepoint @r{[}@var{num}@r{]} Enable tracepoint @var{num}, or all tracepoints. If this command is issued during a trace experiment and the debug target supports enabling tracepoints during a trace experiment, then the enabled tracepoints will become effective immediately. Otherwise, they will become effective the next time a trace experiment is run. @end table @node Tracepoint Passcounts @subsection Tracepoint Passcounts @table @code @kindex passcount @cindex tracepoint pass count @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]} Set the @dfn{passcount} of a tracepoint. The passcount is a way to automatically stop a trace experiment. If a tracepoint's passcount is @var{n}, then the trace experiment will be automatically stopped on the @var{n}'th time that tracepoint is hit. If the tracepoint number @var{num} is not specified, the @code{passcount} command sets the passcount of the most recently defined tracepoint. If no passcount is given, the trace experiment will run until stopped explicitly by the user. Examples: @smallexample (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// tracepoint 2} (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// most recently defined tracepoint.} (@value{GDBP}) @b{trace foo} (@value{GDBP}) @b{pass 3} (@value{GDBP}) @b{trace bar} (@value{GDBP}) @b{pass 2} (@value{GDBP}) @b{trace baz} (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// executed 3 times OR when bar has} @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// been executed 2 times} @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// OR when baz has been executed 1 time.} @end smallexample @end table @node Tracepoint Conditions @subsection Tracepoint Conditions @cindex conditional tracepoints @cindex tracepoint conditions The simplest sort of tracepoint collects data every time your program reaches a specified place. You can also specify a @dfn{condition} for a tracepoint. A condition is just a Boolean expression in your programming language (@pxref{Expressions, ,Expressions}). A tracepoint with a condition evaluates the expression each time your program reaches it, and data collection happens only if the condition is true. Tracepoint conditions can be specified when a tracepoint is set, by using @samp{if} in the arguments to the @code{trace} command. @xref{Create and Delete Tracepoints, ,Setting Tracepoints}. They can also be set or changed at any time with the @code{condition} command, just as with breakpoints. Unlike breakpoint conditions, @value{GDBN} does not actually evaluate the conditional expression itself. Instead, @value{GDBN} encodes the expression into an agent expression (@pxref{Agent Expressions}) suitable for execution on the target, independently of @value{GDBN}. Global variables become raw memory locations, locals become stack accesses, and so forth. For instance, suppose you have a function that is usually called frequently, but should not be called after an error has occurred. You could use the following tracepoint command to collect data about calls of that function that happen while the error code is propagating through the program; an unconditional tracepoint could end up collecting thousands of useless trace frames that you would have to search through. @smallexample (@value{GDBP}) @kbd{trace normal_operation if errcode > 0} @end smallexample @node Trace State Variables @subsection Trace State Variables @cindex trace state variables A @dfn{trace state variable} is a special type of variable that is created and managed by target-side code. The syntax is the same as that for GDB's convenience variables (a string prefixed with ``$''), but they are stored on the target. They must be created explicitly, using a @code{tvariable} command. They are always 64-bit signed integers. Trace state variables are remembered by @value{GDBN}, and downloaded to the target along with tracepoint information when the trace experiment starts. There are no intrinsic limits on the number of trace state variables, beyond memory limitations of the target. @cindex convenience variables, and trace state variables Although trace state variables are managed by the target, you can use them in print commands and expressions as if they were convenience variables; @value{GDBN} will get the current value from the target while the trace experiment is running. Trace state variables share the same namespace as other ``$'' variables, which means that you cannot have trace state variables with names like @code{$23} or @code{$pc}, nor can you have a trace state variable and a convenience variable with the same name. @table @code @item tvariable $@var{name} [ = @var{expression} ] @kindex tvariable The @code{tvariable} command creates a new trace state variable named @code{$@var{name}}, and optionally gives it an initial value of @var{expression}. The @var{expression} is evaluated when this command is entered; the result will be converted to an integer if possible, otherwise @value{GDBN} will report an error. A subsequent @code{tvariable} command specifying the same name does not create a variable, but instead assigns the supplied initial value to the existing variable of that name, overwriting any previous initial value. The default initial value is 0. @item info tvariables @kindex info tvariables List all the trace state variables along with their initial values. Their current values may also be displayed, if the trace experiment is currently running. @item delete tvariable @r{[} $@var{name} @dots{} @r{]} @kindex delete tvariable Delete the given trace state variables, or all of them if no arguments are specified. @end table @node Tracepoint Actions @subsection Tracepoint Action Lists @table @code @kindex actions @cindex tracepoint actions @item actions @r{[}@var{num}@r{]} This command will prompt for a list of actions to be taken when the tracepoint is hit. If the tracepoint number @var{num} is not specified, this command sets the actions for the one that was most recently defined (so that you can define a tracepoint and then say @code{actions} without bothering about its number). You specify the actions themselves on the following lines, one action at a time, and terminate the actions list with a line containing just @code{end}. So far, the only defined actions are @code{collect}, @code{teval}, and @code{while-stepping}. @code{actions} is actually equivalent to @code{commands} (@pxref{Break Commands, ,Breakpoint Command Lists}), except that only the defined actions are allowed; any other @value{GDBN} command is rejected. @cindex remove actions from a tracepoint To remove all actions from a tracepoint, type @samp{actions @var{num}} and follow it immediately with @samp{end}. @smallexample (@value{GDBP}) @b{collect @var{data}} // collect some data (@value{GDBP}) @b{while-stepping 5} // single-step 5 times, collect data (@value{GDBP}) @b{end} // signals the end of actions. @end smallexample In the following example, the action list begins with @code{collect} commands indicating the things to be collected when the tracepoint is hit. Then, in order to single-step and collect additional data following the tracepoint, a @code{while-stepping} command is used, followed by the list of things to be collected after each step in a sequence of single steps. The @code{while-stepping} command is terminated by its own separate @code{end} command. Lastly, the action list is terminated by an @code{end} command. @smallexample (@value{GDBP}) @b{trace foo} (@value{GDBP}) @b{actions} Enter actions for tracepoint 1, one per line: > collect bar,baz > collect $regs > while-stepping 12 > collect $pc, arr[i] > end end @end smallexample @kindex collect @r{(tracepoints)} @item collect@r{[}/@var{mods}@r{]} @var{expr1}, @var{expr2}, @dots{} Collect values of the given expressions when the tracepoint is hit. This command accepts a comma-separated list of any valid expressions. In addition to global, static, or local variables, the following special arguments are supported: @table @code @item $regs Collect all registers. @item $args Collect all function arguments. @item $locals Collect all local variables. @item $_ret Collect the return address. This is helpful if you want to see more of a backtrace. @emph{Note:} The return address location can not always be reliably determined up front, and the wrong address / registers may end up collected instead. On some architectures the reliability is higher for tracepoints at function entry, while on others it's the opposite. When this happens, backtracing will stop because the return address is found unavailable (unless another collect rule happened to match it). @item $_probe_argc Collects the number of arguments from the static probe at which the tracepoint is located. @xref{Static Probe Points}. @item $_probe_arg@var{n} @var{n} is an integer between 0 and 11. Collects the @var{n}th argument from the static probe at which the tracepoint is located. @xref{Static Probe Points}. @item $_sdata @vindex $_sdata@r{, collect} Collect static tracepoint marker specific data. Only available for static tracepoints. @xref{Tracepoint Actions,,Tracepoint Action Lists}. On the UST static tracepoints library backend, an instrumentation point resembles a @code{printf} function call. The tracing library is able to collect user specified data formatted to a character string using the format provided by the programmer that instrumented the program. Other backends have similar mechanisms. Here's an example of a UST marker call: @smallexample const char master_name[] = "$your_name"; trace_mark(channel1, marker1, "hello %s", master_name) @end smallexample In this case, collecting @code{$_sdata} collects the string @samp{hello $yourname}. When analyzing the trace buffer, you can inspect @samp{$_sdata} like any other variable available to @value{GDBN}. @end table You can give several consecutive @code{collect} commands, each one with a single argument, or one @code{collect} command with several arguments separated by commas; the effect is the same. The optional @var{mods} changes the usual handling of the arguments. @code{s} requests that pointers to chars be handled as strings, in particular collecting the contents of the memory being pointed at, up to the first zero. The upper bound is by default the value of the @code{print elements} variable; if @code{s} is followed by a decimal number, that is the upper bound instead. So for instance @samp{collect/s25 mystr} collects as many as 25 characters at @samp{mystr}. The command @code{info scope} (@pxref{Symbols, info scope}) is particularly useful for figuring out what data to collect. @kindex teval @r{(tracepoints)} @item teval @var{expr1}, @var{expr2}, @dots{} Evaluate the given expressions when the tracepoint is hit. This command accepts a comma-separated list of expressions. The results are discarded, so this is mainly useful for assigning values to trace state variables (@pxref{Trace State Variables}) without adding those values to the trace buffer, as would be the case if the @code{collect} action were used. @kindex while-stepping @r{(tracepoints)} @item while-stepping @var{n} Perform @var{n} single-step instruction traces after the tracepoint, collecting new data after each step. The @code{while-stepping} command is followed by the list of what to collect while stepping (followed by its own @code{end} command): @smallexample > while-stepping 12 > collect $regs, myglobal > end > @end smallexample @noindent Note that @code{$pc} is not automatically collected by @code{while-stepping}; you need to explicitly collect that register if you need it. You may abbreviate @code{while-stepping} as @code{ws} or @code{stepping}. @item set default-collect @var{expr1}, @var{expr2}, @dots{} @kindex set default-collect @cindex default collection action This variable is a list of expressions to collect at each tracepoint hit. It is effectively an additional @code{collect} action prepended to every tracepoint action list. The expressions are parsed individually for each tracepoint, so for instance a variable named @code{xyz} may be interpreted as a global for one tracepoint, and a local for another, as appropriate to the tracepoint's location. @item show default-collect @kindex show default-collect Show the list of expressions that are collected by default at each tracepoint hit. @end table @node Listing Tracepoints @subsection Listing Tracepoints @table @code @kindex info tracepoints @r{[}@var{n}@dots{}@r{]} @kindex info tp @r{[}@var{n}@dots{}@r{]} @cindex information about tracepoints @item info tracepoints @r{[}@var{num}@dots{}@r{]} Display information about the tracepoint @var{num}. If you don't specify a tracepoint number, displays information about all the tracepoints defined so far. The format is similar to that used for @code{info breakpoints}; in fact, @code{info tracepoints} is the same command, simply restricting itself to tracepoints. A tracepoint's listing may include additional information specific to tracing: @itemize @bullet @item its passcount as given by the @code{passcount @var{n}} command @item the state about installed on target of each location @end itemize @smallexample (@value{GDBP}) @b{info trace} Num Type Disp Enb Address What 1 tracepoint keep y 0x0804ab57 in foo() at main.cxx:7 while-stepping 20 collect globfoo, $regs end collect globfoo2 end pass count 1200 2 tracepoint keep y <MULTIPLE> collect $eip 2.1 y 0x0804859c in func4 at change-loc.h:35 installed on target 2.2 y 0xb7ffc480 in func4 at change-loc.h:35 installed on target 2.3 y <PENDING> set_tracepoint 3 tracepoint keep y 0x080485b1 in foo at change-loc.c:29 not installed on target (@value{GDBP}) @end smallexample @noindent This command can be abbreviated @code{info tp}. @end table @node Listing Static Tracepoint Markers @subsection Listing Static Tracepoint Markers @table @code @kindex info static-tracepoint-markers @cindex information about static tracepoint markers @item info static-tracepoint-markers Display information about all static tracepoint markers defined in the program. For each marker, the following columns are printed: @table @emph @item Count An incrementing counter, output to help readability. This is not a stable identifier. @item ID The marker ID, as reported by the target. @item Enabled or Disabled Probed markers are tagged with @samp{y}. @samp{n} identifies marks that are not enabled. @item Address Where the marker is in your program, as a memory address. @item What Where the marker is in the source for your program, as a file and line number. If the debug information included in the program does not allow @value{GDBN} to locate the source of the marker, this column will be left blank. @end table @noindent In addition, the following information may be printed for each marker: @table @emph @item Data User data passed to the tracing library by the marker call. In the UST backend, this is the format string passed as argument to the marker call. @item Static tracepoints probing the marker The list of static tracepoints attached to the marker. @end table @smallexample (@value{GDBP}) info static-tracepoint-markers Cnt ID Enb Address What 1 ust/bar2 y 0x0000000000400e1a in main at stexample.c:25 Data: number1 %d number2 %d Probed by static tracepoints: #2 2 ust/bar33 n 0x0000000000400c87 in main at stexample.c:24 Data: str %s (@value{GDBP}) @end smallexample @end table @node Starting and Stopping Trace Experiments @subsection Starting and Stopping Trace Experiments @table @code @kindex tstart [ @var{notes} ] @cindex start a new trace experiment @cindex collected data discarded @item tstart This command starts the trace experiment, and begins collecting data. It has the side effect of discarding all the data collected in the trace buffer during the previous trace experiment. If any arguments are supplied, they are taken as a note and stored with the trace experiment's state. The notes may be arbitrary text, and are especially useful with disconnected tracing in a multi-user context; the notes can explain what the trace is doing, supply user contact information, and so forth. @kindex tstop [ @var{notes} ] @cindex stop a running trace experiment @item tstop This command stops the trace experiment. If any arguments are supplied, they are recorded with the experiment as a note. This is useful if you are stopping a trace started by someone else, for instance if the trace is interfering with the system's behavior and needs to be stopped quickly. @strong{Note}: a trace experiment and data collection may stop automatically if any tracepoint's passcount is reached (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full. @kindex tstatus @cindex status of trace data collection @cindex trace experiment, status of @item tstatus This command displays the status of the current trace data collection. @end table Here is an example of the commands we described so far: @smallexample (@value{GDBP}) @b{trace gdb_c_test} (@value{GDBP}) @b{actions} Enter actions for tracepoint #1, one per line. > collect $regs,$locals,$args > while-stepping 11 > collect $regs > end > end (@value{GDBP}) @b{tstart} [time passes @dots{}] (@value{GDBP}) @b{tstop} @end smallexample @anchor{disconnected tracing} @cindex disconnected tracing You can choose to continue running the trace experiment even if @value{GDBN} disconnects from the target, voluntarily or involuntarily. For commands such as @code{detach}, the debugger will ask what you want to do with the trace. But for unexpected terminations (@value{GDBN} crash, network outage), it would be unfortunate to lose hard-won trace data, so the variable @code{disconnected-tracing} lets you decide whether the trace should continue running without @value{GDBN}. @table @code @item set disconnected-tracing on @itemx set disconnected-tracing off @kindex set disconnected-tracing Choose whether a tracing run should continue to run if @value{GDBN} has disconnected from the target. Note that @code{detach} or @code{quit} will ask you directly what to do about a running trace no matter what this variable's setting, so the variable is mainly useful for handling unexpected situations, such as loss of the network. @item show disconnected-tracing @kindex show disconnected-tracing Show the current choice for disconnected tracing. @end table When you reconnect to the target, the trace experiment may or may not still be running; it might have filled the trace buffer in the meantime, or stopped for one of the other reasons. If it is running, it will continue after reconnection. Upon reconnection, the target will upload information about the tracepoints in effect. @value{GDBN} will then compare that information to the set of tracepoints currently defined, and attempt to match them up, allowing for the possibility that the numbers may have changed due to creation and deletion in the meantime. If one of the target's tracepoints does not match any in @value{GDBN}, the debugger will create a new tracepoint, so that you have a number with which to specify that tracepoint. This matching-up process is necessarily heuristic, and it may result in useless tracepoints being created; you may simply delete them if they are of no use. @cindex circular trace buffer If your target agent supports a @dfn{circular trace buffer}, then you can run a trace experiment indefinitely without filling the trace buffer; when space runs out, the agent deletes already-collected trace frames, oldest first, until there is enough room to continue collecting. This is especially useful if your tracepoints are being hit too often, and your trace gets terminated prematurely because the buffer is full. To ask for a circular trace buffer, simply set @samp{circular-trace-buffer} to on. You can set this at any time, including during tracing; if the agent can do it, it will change buffer handling on the fly, otherwise it will not take effect until the next run. @table @code @item set circular-trace-buffer on @itemx set circular-trace-buffer off @kindex set circular-trace-buffer Choose whether a tracing run should use a linear or circular buffer for trace data. A linear buffer will not lose any trace data, but may fill up prematurely, while a circular buffer will discard old trace data, but it will have always room for the latest tracepoint hits. @item show circular-trace-buffer @kindex show circular-trace-buffer Show the current choice for the trace buffer. Note that this may not match the agent's current buffer handling, nor is it guaranteed to match the setting that might have been in effect during a past run, for instance if you are looking at frames from a trace file. @end table @table @code @item set trace-buffer-size @var{n} @itemx set trace-buffer-size unlimited @kindex set trace-buffer-size Request that the target use a trace buffer of @var{n} bytes. Not all targets will honor the request; they may have a compiled-in size for the trace buffer, or some other limitation. Set to a value of @code{unlimited} or @code{-1} to let the target use whatever size it likes. This is also the default. @item show trace-buffer-size @kindex show trace-buffer-size Show the current requested size for the trace buffer. Note that this will only match the actual size if the target supports size-setting, and was able to handle the requested size. For instance, if the target can only change buffer size between runs, this variable will not reflect the change until the next run starts. Use @code{tstatus} to get a report of the actual buffer size. @end table @table @code @item set trace-user @var{text} @kindex set trace-user @item show trace-user @kindex show trace-user @item set trace-notes @var{text} @kindex set trace-notes Set the trace run's notes. @item show trace-notes @kindex show trace-notes Show the trace run's notes. @item set trace-stop-notes @var{text} @kindex set trace-stop-notes Set the trace run's stop notes. The handling of the note is as for @code{tstop} arguments; the set command is convenient way to fix a stop note that is mistaken or incomplete. @item show trace-stop-notes @kindex show trace-stop-notes Show the trace run's stop notes. @end table @node Tracepoint Restrictions @subsection Tracepoint Restrictions @cindex tracepoint restrictions There are a number of restrictions on the use of tracepoints. As described above, tracepoint data gathering occurs on the target without interaction from @value{GDBN}. Thus the full capabilities of the debugger are not available during data gathering, and then at data examination time, you will be limited by only having what was collected. The following items describe some common problems, but it is not exhaustive, and you may run into additional difficulties not mentioned here. @itemize @bullet @item Tracepoint expressions are intended to gather objects (lvalues). Thus the full flexibility of GDB's expression evaluator is not available. You cannot call functions, cast objects to aggregate types, access convenience variables or modify values (except by assignment to trace state variables). Some language features may implicitly call functions (for instance Objective-C fields with accessors), and therefore cannot be collected either. @item Collection of local variables, either individually or in bulk with @code{$locals} or @code{$args}, during @code{while-stepping} may behave erratically. The stepping action may enter a new scope (for instance by stepping into a function), or the location of the variable may change (for instance it is loaded into a register). The tracepoint data recorded uses the location information for the variables that is correct for the tracepoint location. When the tracepoint is created, it is not possible, in general, to determine where the steps of a @code{while-stepping} sequence will advance the program---particularly if a conditional branch is stepped. @item Collection of an incompletely-initialized or partially-destroyed object may result in something that @value{GDBN} cannot display, or displays in a misleading way. @item When @value{GDBN} displays a pointer to character it automatically dereferences the pointer to also display characters of the string being pointed to. However, collecting the pointer during tracing does not automatically collect the string. You need to explicitly dereference the pointer and provide size information if you want to collect not only the pointer, but the memory pointed to. For example, @code{*ptr@@50} can be used to collect the 50 element array pointed to by @code{ptr}. @item It is not possible to collect a complete stack backtrace at a tracepoint. Instead, you may collect the registers and a few hundred bytes from the stack pointer with something like @code{*(unsigned char *)$esp@@300} (adjust to use the name of the actual stack pointer register on your target architecture, and the amount of stack you wish to capture). Then the @code{backtrace} command will show a partial backtrace when using a trace frame. The number of stack frames that can be examined depends on the sizes of the frames in the collected stack. Note that if you ask for a block so large that it goes past the bottom of the stack, the target agent may report an error trying to read from an invalid address. @item If you do not collect registers at a tracepoint, @value{GDBN} can infer that the value of @code{$pc} must be the same as the address of the tracepoint and use that when you are looking at a trace frame for that tracepoint. However, this cannot work if the tracepoint has multiple locations (for instance if it was set in a function that was inlined), or if it has a @code{while-stepping} loop. In those cases @value{GDBN} will warn you that it can't infer @code{$pc}, and default it to zero. @end itemize @node Analyze Collected Data @section Using the Collected Data After the tracepoint experiment ends, you use @value{GDBN} commands for examining the trace data. The basic idea is that each tracepoint collects a trace @dfn{snapshot} every time it is hit and another snapshot every time it single-steps. All these snapshots are consecutively numbered from zero and go into a buffer, and you can examine them later. The way you examine them is to @dfn{focus} on a specific trace snapshot. When the remote stub is focused on a trace snapshot, it will respond to all @value{GDBN} requests for memory and registers by reading from the buffer which belongs to that snapshot, rather than from @emph{real} memory or registers of the program being debugged. This means that @strong{all} @value{GDBN} commands (@code{print}, @code{info registers}, @code{backtrace}, etc.) will behave as if we were currently debugging the program state as it was when the tracepoint occurred. Any requests for data that are not in the buffer will fail. @menu * tfind:: How to select a trace snapshot * tdump:: How to display all data for a snapshot * save tracepoints:: How to save tracepoints for a future run @end menu @node tfind @subsection @code{tfind @var{n}} @kindex tfind @cindex select trace snapshot @cindex find trace snapshot The basic command for selecting a trace snapshot from the buffer is @code{tfind @var{n}}, which finds trace snapshot number @var{n}, counting from zero. If no argument @var{n} is given, the next snapshot is selected. Here are the various forms of using the @code{tfind} command. @table @code @item tfind start Find the first snapshot in the buffer. This is a synonym for @code{tfind 0} (since 0 is the number of the first snapshot). @item tfind none Stop debugging trace snapshots, resume @emph{live} debugging. @item tfind end Same as @samp{tfind none}. @item tfind No argument means find the next trace snapshot or find the first one if no trace snapshot is selected. @item tfind - Find the previous trace snapshot before the current one. This permits retracing earlier steps. @item tfind tracepoint @var{num} Find the next snapshot associated with tracepoint @var{num}. Search proceeds forward from the last examined trace snapshot. If no argument @var{num} is given, it means find the next snapshot collected for the same tracepoint as the current snapshot. @item tfind pc @var{addr} Find the next snapshot associated with the value @var{addr} of the program counter. Search proceeds forward from the last examined trace snapshot. If no argument @var{addr} is given, it means find the next snapshot with the same value of PC as the current snapshot. @item tfind outside @var{addr1}, @var{addr2} Find the next snapshot whose PC is outside the given range of addresses (exclusive). @item tfind range @var{addr1}, @var{addr2} Find the next snapshot whose PC is between @var{addr1} and @var{addr2} (inclusive). @item tfind line @r{[}@var{file}:@r{]}@var{n} Find the next snapshot associated with the source line @var{n}. If the optional argument @var{file} is given, refer to line @var{n} in that source file. Search proceeds forward from the last examined trace snapshot. If no argument @var{n} is given, it means find the next line other than the one currently being examined; thus saying @code{tfind line} repeatedly can appear to have the same effect as stepping from line to line in a @emph{live} debugging session. @end table The default arguments for the @code{tfind} commands are specifically designed to make it easy to scan through the trace buffer. For instance, @code{tfind} with no argument selects the next trace snapshot, and @code{tfind -} with no argument selects the previous trace snapshot. So, by giving one @code{tfind} command, and then simply hitting @key{RET} repeatedly you can examine all the trace snapshots in order. Or, by saying @code{tfind -} and then hitting @key{RET} repeatedly you can examine the snapshots in reverse order. The @code{tfind line} command with no argument selects the snapshot for the next source line executed. The @code{tfind pc} command with no argument selects the next snapshot with the same program counter (PC) as the current frame. The @code{tfind tracepoint} command with no argument selects the next trace snapshot collected by the same tracepoint as the current one. In addition to letting you scan through the trace buffer manually, these commands make it easy to construct @value{GDBN} scripts that scan through the trace buffer and print out whatever collected data you are interested in. Thus, if we want to examine the PC, FP, and SP registers from each trace frame in the buffer, we can say this: @smallexample (@value{GDBP}) @b{tfind start} (@value{GDBP}) @b{while ($trace_frame != -1)} > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \ $trace_frame, $pc, $sp, $fp > tfind > end Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14 @end smallexample Or, if we want to examine the variable @code{X} at each source line in the buffer: @smallexample (@value{GDBP}) @b{tfind start} (@value{GDBP}) @b{while ($trace_frame != -1)} > printf "Frame %d, X == %d\n", $trace_frame, X > tfind line > end Frame 0, X = 1 Frame 7, X = 2 Frame 13, X = 255 @end smallexample @node tdump @subsection @code{tdump} @kindex tdump @cindex dump all data collected at tracepoint @cindex tracepoint data, display This command takes no arguments. It prints all the data collected at the current trace snapshot. @smallexample (@value{GDBP}) @b{trace 444} (@value{GDBP}) @b{actions} Enter actions for tracepoint #2, one per line: > collect $regs, $locals, $args, gdb_long_test > end (@value{GDBP}) @b{tstart} (@value{GDBP}) @b{tfind line 444} #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66) at gdb_test.c:444 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", ) (@value{GDBP}) @b{tdump} Data collected at tracepoint 2, trace frame 1: d0 0xc4aa0085 -995491707 d1 0x18 24 d2 0x80 128 d3 0x33 51 d4 0x71aea3d 119204413 d5 0x22 34 d6 0xe0 224 d7 0x380035 3670069 a0 0x19e24a 1696330 a1 0x3000668 50333288 a2 0x100 256 a3 0x322000 3284992 a4 0x3000698 50333336 a5 0x1ad3cc 1758156 fp 0x30bf3c 0x30bf3c sp 0x30bf34 0x30bf34 ps 0x0 0 pc 0x20b2c8 0x20b2c8 fpcontrol 0x0 0 fpstatus 0x0 0 fpiaddr 0x0 0 p = 0x20e5b4 "gdb-test" p1 = (void *) 0x11 p2 = (void *) 0x22 p3 = (void *) 0x33 p4 = (void *) 0x44 p5 = (void *) 0x55 p6 = (void *) 0x66 gdb_long_test = 17 '\021' (@value{GDBP}) @end smallexample @code{tdump} works by scanning the tracepoint's current collection actions and printing the value of each expression listed. So @code{tdump} can fail, if after a run, you change the tracepoint's actions to mention variables that were not collected during the run. Also, for tracepoints with @code{while-stepping} loops, @code{tdump} uses the collected value of @code{$pc} to distinguish between trace frames that were collected at the tracepoint hit, and frames that were collected while stepping. This allows it to correctly choose whether to display the basic list of collections, or the collections from the body of the while-stepping loop. However, if @code{$pc} was not collected, then @code{tdump} will always attempt to dump using the basic collection list, and may fail if a while-stepping frame does not include all the same data that is collected at the tracepoint hit. @c This is getting pretty arcane, example would be good. @node save tracepoints @subsection @code{save tracepoints @var{filename}} @kindex save tracepoints @kindex save-tracepoints @cindex save tracepoints for future sessions This command saves all current tracepoint definitions together with their actions and passcounts, into a file @file{@var{filename}} suitable for use in a later debugging session. To read the saved tracepoint definitions, use the @code{source} command (@pxref{Command Files}). The @w{@code{save-tracepoints}} command is a deprecated alias for @w{@code{save tracepoints}} @node Tracepoint Variables @section Convenience Variables for Tracepoints @cindex tracepoint variables @cindex convenience variables for tracepoints @table @code @vindex $trace_frame @item (int) $trace_frame The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no snapshot is selected. @vindex $tracepoint @item (int) $tracepoint The tracepoint for the current trace snapshot. @vindex $trace_line @item (int) $trace_line The line number for the current trace snapshot. @vindex $trace_file @item (char []) $trace_file The source file for the current trace snapshot. @vindex $trace_func @item (char []) $trace_func The name of the function containing @code{$tracepoint}. @end table Note: @code{$trace_file} is not suitable for use in @code{printf}, use @code{output} instead. Here's a simple example of using these convenience variables for stepping through all the trace snapshots and printing some of their data. Note that these are not the same as trace state variables, which are managed by the target. @smallexample (@value{GDBP}) @b{tfind start} (@value{GDBP}) @b{while $trace_frame != -1} > output $trace_file > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint > tfind > end @end smallexample @node Trace Files @section Using Trace Files @cindex trace files In some situations, the target running a trace experiment may no longer be available; perhaps it crashed, or the hardware was needed for a different activity. To handle these cases, you can arrange to dump the trace data into a file, and later use that file as a source of trace data, via the @code{target tfile} command. @table @code @kindex tsave @item tsave [ -r ] @var{filename} @itemx tsave [-ctf] @var{dirname} Save the trace data to @var{filename}. By default, this command assumes that @var{filename} refers to the host filesystem, so if necessary @value{GDBN} will copy raw trace data up from the target and then save it. If the target supports it, you can also supply the optional argument @code{-r} (``remote'') to direct the target to save the data directly into @var{filename} in its own filesystem, which may be more efficient if the trace buffer is very large. (Note, however, that @code{target tfile} can only read from files accessible to the host.) By default, this command will save trace frame in tfile format. You can supply the optional argument @code{-ctf} to save data in CTF format. The @dfn{Common Trace Format} (CTF) is proposed as a trace format that can be shared by multiple debugging and tracing tools. Please go to @indicateurl{http://www.efficios.com/ctf} to get more information. @kindex target tfile @kindex tfile @kindex target ctf @kindex ctf @item target tfile @var{filename} @itemx target ctf @var{dirname} Use the file named @var{filename} or directory named @var{dirname} as a source of trace data. Commands that examine data work as they do with a live target, but it is not possible to run any new trace experiments. @code{tstatus} will report the state of the trace run at the moment the data was saved, as well as the current trace frame you are examining. Both @var{filename} and @var{dirname} must be on a filesystem accessible to the host. @smallexample (@value{GDBP}) target ctf ctf.ctf (@value{GDBP}) tfind Found trace frame 0, tracepoint 2 39 ++a; /* set tracepoint 1 here */ (@value{GDBP}) tdump Data collected at tracepoint 2, trace frame 0: i = 0 a = 0 b = 1 '\001' c = @{"123", "456", "789", "123", "456", "789"@} d = @{@{@{a = 1, b = 2@}, @{a = 3, b = 4@}@}, @{@{a = 5, b = 6@}, @{a = 7, b = 8@}@}@} (@value{GDBP}) p b $1 = 1 @end smallexample @end table @node Overlays @chapter Debugging Programs That Use Overlays @cindex overlays If your program is too large to fit completely in your target system's memory, you can sometimes use @dfn{overlays} to work around this problem. @value{GDBN} provides some support for debugging programs that use overlays. @menu * How Overlays Work:: A general explanation of overlays. * Overlay Commands:: Managing overlays in @value{GDBN}. * Automatic Overlay Debugging:: @value{GDBN} can find out which overlays are mapped by asking the inferior. * Overlay Sample Program:: A sample program using overlays. @end menu @node How Overlays Work @section How Overlays Work @cindex mapped overlays @cindex unmapped overlays @cindex load address, overlay's @cindex mapped address @cindex overlay area Suppose you have a computer whose instruction address space is only 64 kilobytes long, but which has much more memory which can be accessed by other means: special instructions, segment registers, or memory management hardware, for example. Suppose further that you want to adapt a program which is larger than 64 kilobytes to run on this system. One solution is to identify modules of your program which are relatively independent, and need not call each other directly; call these modules @dfn{overlays}. Separate the overlays from the main program, and place their machine code in the larger memory. Place your main program in instruction memory, but leave at least enough space there to hold the largest overlay as well. Now, to call a function located in an overlay, you must first copy that overlay's machine code from the large memory into the space set aside for it in the instruction memory, and then jump to its entry point there. @c NB: In the below the mapped area's size is greater or equal to the @c size of all overlays. This is intentional to remind the developer @c that overlays don't necessarily need to be the same size. @smallexample @group Data Instruction Larger Address Space Address Space Address Space +-----------+ +-----------+ +-----------+ | | | | | | +-----------+ +-----------+ +-----------+<-- overlay 1 | program | | main | .----| overlay 1 | load address | variables | | program | | +-----------+ | and heap | | | | | | +-----------+ | | | +-----------+<-- overlay 2 | | +-----------+ | | | load address +-----------+ | | | .-| overlay 2 | | | | | | | mapped --->+-----------+ | | +-----------+ address | | | | | | | overlay | <-' | | | | area | <---' +-----------+<-- overlay 3 | | <---. | | load address +-----------+ `--| overlay 3 | | | | | +-----------+ | | +-----------+ | | +-----------+ @anchor{A code overlay}A code overlay @end group @end smallexample The diagram (@pxref{A code overlay}) shows a system with separate data and instruction address spaces. To map an overlay, the program copies its code from the larger address space to the instruction address space. Since the overlays shown here all use the same mapped address, only one may be mapped at a time. For a system with a single address space for data and instructions, the diagram would be similar, except that the program variables and heap would share an address space with the main program and the overlay area. An overlay loaded into instruction memory and ready for use is called a @dfn{mapped} overlay; its @dfn{mapped address} is its address in the instruction memory. An overlay not present (or only partially present) in instruction memory is called @dfn{unmapped}; its @dfn{load address} is its address in the larger memory. The mapped address is also called the @dfn{virtual memory address}, or @dfn{VMA}; the load address is also called the @dfn{load memory address}, or @dfn{LMA}. Unfortunately, overlays are not a completely transparent way to adapt a program to limited instruction memory. They introduce a new set of global constraints you must keep in mind as you design your program: @itemize @bullet @item Before calling or returning to a function in an overlay, your program must make sure that overlay is actually mapped. Otherwise, the call or return will transfer control to the right address, but in the wrong overlay, and your program will probably crash. @item If the process of mapping an overlay is expensive on your system, you will need to choose your overlays carefully to minimize their effect on your program's performance. @item The executable file you load onto your system must contain each overlay's instructions, appearing at the overlay's load address, not its mapped address. However, each overlay's instructions must be relocated and its symbols defined as if the overlay were at its mapped address. You can use GNU linker scripts to specify different load and relocation addresses for pieces of your program; see @ref{Overlay Description,,, ld.info, Using ld: the GNU linker}. @item The procedure for loading executable files onto your system must be able to load their contents into the larger address space as well as the instruction and data spaces. @end itemize The overlay system described above is rather simple, and could be improved in many ways: @itemize @bullet @item If your system has suitable bank switch registers or memory management hardware, you could use those facilities to make an overlay's load area contents simply appear at their mapped address in instruction space. This would probably be faster than copying the overlay to its mapped area in the usual way. @item If your overlays are small enough, you could set aside more than one overlay area, and have more than one overlay mapped at a time. @item You can use overlays to manage data, as well as instructions. In general, data overlays are even less transparent to your design than code overlays: whereas code overlays only require care when you call or return to functions, data overlays require care every time you access the data. Also, if you change the contents of a data overlay, you must copy its contents back out to its load address before you can copy a different data overlay into the same mapped area. @end itemize @node Overlay Commands @section Overlay Commands To use @value{GDBN}'s overlay support, each overlay in your program must correspond to a separate section of the executable file. The section's virtual memory address and load memory address must be the overlay's mapped and load addresses. Identifying overlays with sections allows @value{GDBN} to determine the appropriate address of a function or variable, depending on whether the overlay is mapped or not. @value{GDBN}'s overlay commands all start with the word @code{overlay}; you can abbreviate this as @code{ov} or @code{ovly}. The commands are: @table @code @item overlay off @kindex overlay Disable @value{GDBN}'s overlay support. When overlay support is disabled, @value{GDBN} assumes that all functions and variables are always present at their mapped addresses. By default, @value{GDBN}'s overlay support is disabled. @item overlay manual @cindex manual overlay debugging Enable @dfn{manual} overlay debugging. In this mode, @value{GDBN} relies on you to tell it which overlays are mapped, and which are not, using the @code{overlay map-overlay} and @code{overlay unmap-overlay} commands described below. @item overlay map-overlay @var{overlay} @itemx overlay map @var{overlay} @cindex map an overlay Tell @value{GDBN} that @var{overlay} is now mapped; @var{overlay} must be the name of the object file section containing the overlay. When an overlay is mapped, @value{GDBN} assumes it can find the overlay's functions and variables at their mapped addresses. @value{GDBN} assumes that any other overlays whose mapped ranges overlap that of @var{overlay} are now unmapped. @item overlay unmap-overlay @var{overlay} @itemx overlay unmap @var{overlay} @cindex unmap an overlay Tell @value{GDBN} that @var{overlay} is no longer mapped; @var{overlay} must be the name of the object file section containing the overlay. When an overlay is unmapped, @value{GDBN} assumes it can find the overlay's functions and variables at their load addresses. @item overlay auto Enable @dfn{automatic} overlay debugging. In this mode, @value{GDBN} consults a data structure the overlay manager maintains in the inferior to see which overlays are mapped. For details, see @ref{Automatic Overlay Debugging}. @item overlay load-target @itemx overlay load @cindex reloading the overlay table Re-read the overlay table from the inferior. Normally, @value{GDBN} re-reads the table @value{GDBN} automatically each time the inferior stops, so this command should only be necessary if you have changed the overlay mapping yourself using @value{GDBN}. This command is only useful when using automatic overlay debugging. @item overlay list-overlays @itemx overlay list @cindex listing mapped overlays Display a list of the overlays currently mapped, along with their mapped addresses, load addresses, and sizes. @end table Normally, when @value{GDBN} prints a code address, it includes the name of the function the address falls in: @smallexample (@value{GDBP}) print main $3 = @{int ()@} 0x11a0 <main> @end smallexample @noindent When overlay debugging is enabled, @value{GDBN} recognizes code in unmapped overlays, and prints the names of unmapped functions with asterisks around them. For example, if @code{foo} is a function in an unmapped overlay, @value{GDBN} prints it this way: @smallexample (@value{GDBP}) overlay list No sections are mapped. (@value{GDBP}) print foo $5 = @{int (int)@} 0x100000 <*foo*> @end smallexample @noindent When @code{foo}'s overlay is mapped, @value{GDBN} prints the function's name normally: @smallexample (@value{GDBP}) overlay list Section .ov.foo.text, loaded at 0x100000 - 0x100034, mapped at 0x1016 - 0x104a (@value{GDBP}) print foo $6 = @{int (int)@} 0x1016 <foo> @end smallexample When overlay debugging is enabled, @value{GDBN} can find the correct address for functions and variables in an overlay, whether or not the overlay is mapped. This allows most @value{GDBN} commands, like @code{break} and @code{disassemble}, to work normally, even on unmapped code. However, @value{GDBN}'s breakpoint support has some limitations: @itemize @bullet @item @cindex breakpoints in overlays @cindex overlays, setting breakpoints in You can set breakpoints in functions in unmapped overlays, as long as @value{GDBN} can write to the overlay at its load address. @item @value{GDBN} can not set hardware or simulator-based breakpoints in unmapped overlays. However, if you set a breakpoint at the end of your overlay manager (and tell @value{GDBN} which overlays are now mapped, if you are using manual overlay management), @value{GDBN} will re-set its breakpoints properly. @end itemize @node Automatic Overlay Debugging @section Automatic Overlay Debugging @cindex automatic overlay debugging @value{GDBN} can automatically track which overlays are mapped and which are not, given some simple co-operation from the overlay manager in the inferior. If you enable automatic overlay debugging with the @code{overlay auto} command (@pxref{Overlay Commands}), @value{GDBN} looks in the inferior's memory for certain variables describing the current state of the overlays. Here are the variables your overlay manager must define to support @value{GDBN}'s automatic overlay debugging: @table @asis @item @code{_ovly_table}: This variable must be an array of the following structures: @smallexample struct @{ /* The overlay's mapped address. */ unsigned long vma; /* The size of the overlay, in bytes. */ unsigned long size; /* The overlay's load address. */ unsigned long lma; /* Non-zero if the overlay is currently mapped; zero otherwise. */ unsigned long mapped; @} @end smallexample @item @code{_novlys}: This variable must be a four-byte signed integer, holding the total number of elements in @code{_ovly_table}. @end table To decide whether a particular overlay is mapped or not, @value{GDBN} looks for an entry in @w{@code{_ovly_table}} whose @code{vma} and @code{lma} members equal the VMA and LMA of the overlay's section in the executable file. When @value{GDBN} finds a matching entry, it consults the entry's @code{mapped} member to determine whether the overlay is currently mapped. In addition, your overlay manager may define a function called @code{_ovly_debug_event}. If this function is defined, @value{GDBN} will silently set a breakpoint there. If the overlay manager then calls this function whenever it has changed the overlay table, this will enable @value{GDBN} to accurately keep track of which overlays are in program memory, and update any breakpoints that may be set in overlays. This will allow breakpoints to work even if the overlays are kept in ROM or other non-writable memory while they are not being executed. @node Overlay Sample Program @section Overlay Sample Program @cindex overlay example program When linking a program which uses overlays, you must place the overlays at their load addresses, while relocating them to run at their mapped addresses. To do this, you must write a linker script (@pxref{Overlay Description,,, ld.info, Using ld: the GNU linker}). Unfortunately, since linker scripts are specific to a particular host system, target architecture, and target memory layout, this manual cannot provide portable sample code demonstrating @value{GDBN}'s overlay support. However, the @value{GDBN} source distribution does contain an overlaid program, with linker scripts for a few systems, as part of its test suite. The program consists of the following files from @file{gdb/testsuite/gdb.base}: @table @file @item overlays.c The main program file. @item ovlymgr.c A simple overlay manager, used by @file{overlays.c}. @item foo.c @itemx bar.c @itemx baz.c @itemx grbx.c Overlay modules, loaded and used by @file{overlays.c}. @item d10v.ld @itemx m32r.ld Linker scripts for linking the test program on the @code{d10v-elf} and @code{m32r-elf} targets. @end table You can build the test program using the @code{d10v-elf} GCC cross-compiler like this: @smallexample $ d10v-elf-gcc -g -c overlays.c $ d10v-elf-gcc -g -c ovlymgr.c $ d10v-elf-gcc -g -c foo.c $ d10v-elf-gcc -g -c bar.c $ d10v-elf-gcc -g -c baz.c $ d10v-elf-gcc -g -c grbx.c $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \ baz.o grbx.o -Wl,-Td10v.ld -o overlays @end smallexample The build process is identical for any other architecture, except that you must substitute the appropriate compiler and linker script for the target system for @code{d10v-elf-gcc} and @code{d10v.ld}. @node Languages @chapter Using @value{GDBN} with Different Languages @cindex languages Although programming languages generally have common aspects, they are rarely expressed in the same manner. For instance, in ANSI C, dereferencing a pointer @code{p} is accomplished by @code{*p}, but in Modula-2, it is accomplished by @code{p^}. Values can also be represented (and displayed) differently. Hex numbers in C appear as @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}. @cindex working language Language-specific information is built into @value{GDBN} for some languages, allowing you to express operations like the above in your program's native language, and allowing @value{GDBN} to output values in a manner consistent with the syntax of your program's native language. The language you use to build expressions is called the @dfn{working language}. @menu * Setting:: Switching between source languages * Show:: Displaying the language * Checks:: Type and range checks * Supported Languages:: Supported languages * Unsupported Languages:: Unsupported languages @end menu @node Setting @section Switching Between Source Languages There are two ways to control the working language---either have @value{GDBN} set it automatically, or select it manually yourself. You can use the @code{set language} command for either purpose. On startup, @value{GDBN} defaults to setting the language automatically. The working language is used to determine how expressions you type are interpreted, how values are printed, etc. In addition to the working language, every source file that @value{GDBN} knows about has its own working language. For some object file formats, the compiler might indicate which language a particular source file is in. However, most of the time @value{GDBN} infers the language from the name of the file. The language of a source file controls whether C@t{++} names are demangled---this way @code{backtrace} can show each frame appropriately for its own language. There is no way to set the language of a source file from within @value{GDBN}, but you can set the language associated with a filename extension. @xref{Show, , Displaying the Language}. This is most commonly a problem when you use a program, such as @code{cfront} or @code{f2c}, that generates C but is written in another language. In that case, make the program use @code{#line} directives in its C output; that way @value{GDBN} will know the correct language of the source code of the original program, and will display that source code, not the generated C code. @menu * Filenames:: Filename extensions and languages. * Manually:: Setting the working language manually * Automatically:: Having @value{GDBN} infer the source language @end menu @node Filenames @subsection List of Filename Extensions and Languages If a source file name ends in one of the following extensions, then @value{GDBN} infers that its language is the one indicated. @table @file @item .ada @itemx .ads @itemx .adb @itemx .a Ada source file. @item .c C source file @item .C @itemx .cc @itemx .cp @itemx .cpp @itemx .cxx @itemx .c++ C@t{++} source file @item .d D source file @item .m Objective-C source file @item .f @itemx .F Fortran source file @item .mod Modula-2 source file @item .s @itemx .S Assembler source file. This actually behaves almost like C, but @value{GDBN} does not skip over function prologues when stepping. @end table In addition, you may set the language associated with a filename extension. @xref{Show, , Displaying the Language}. @node Manually @subsection Setting the Working Language If you allow @value{GDBN} to set the language automatically, expressions are interpreted the same way in your debugging session and your program. @kindex set language If you wish, you may set the language manually. To do this, issue the command @samp{set language @var{lang}}, where @var{lang} is the name of a language, such as @code{c} or @code{modula-2}. For a list of the supported languages, type @samp{set language}. Setting the language manually prevents @value{GDBN} from updating the working language automatically. This can lead to confusion if you try to debug a program when the working language is not the same as the source language, when an expression is acceptable to both languages---but means different things. For instance, if the current source file were written in C, and @value{GDBN} was parsing Modula-2, a command such as: @smallexample print a = b + c @end smallexample @noindent might not have the effect you intended. In C, this means to add @code{b} and @code{c} and place the result in @code{a}. The result printed would be the value of @code{a}. In Modula-2, this means to compare @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value. @node Automatically @subsection Having @value{GDBN} Infer the Source Language To have @value{GDBN} set the working language automatically, use @samp{set language local} or @samp{set language auto}. @value{GDBN} then infers the working language. That is, when your program stops in a frame (usually by encountering a breakpoint), @value{GDBN} sets the working language to the language recorded for the function in that frame. If the language for a frame is unknown (that is, if the function or block corresponding to the frame was defined in a source file that does not have a recognized extension), the current working language is not changed, and @value{GDBN} issues a warning. This may not seem necessary for most programs, which are written entirely in one source language. However, program modules and libraries written in one source language can be used by a main program written in a different source language. Using @samp{set language auto} in this case frees you from having to set the working language manually. @node Show @section Displaying the Language The following commands help you find out which language is the working language, and also what language source files were written in. @table @code @item show language @anchor{show language} @kindex show language Display the current working language. This is the language you can use with commands such as @code{print} to build and compute expressions that may involve variables in your program. @item info frame @kindex info frame@r{, show the source language} Display the source language for this frame. This language becomes the working language if you use an identifier from this frame. @xref{Frame Info, ,Information about a Frame}, to identify the other information listed here. @item info source @kindex info source@r{, show the source language} Display the source language of this source file. @xref{Symbols, ,Examining the Symbol Table}, to identify the other information listed here. @end table In unusual circumstances, you may have source files with extensions not in the standard list. You can then set the extension associated with a language explicitly: @table @code @item set extension-language @var{ext} @var{language} @kindex set extension-language Tell @value{GDBN} that source files with extension @var{ext} are to be assumed as written in the source language @var{language}. @item info extensions @kindex info extensions List all the filename extensions and the associated languages. @end table @node Checks @section Type and Range Checking Some languages are designed to guard you against making seemingly common errors through a series of compile- and run-time checks. These include checking the type of arguments to functions and operators and making sure mathematical overflows are caught at run time. Checks such as these help to ensure a program's correctness once it has been compiled by eliminating type mismatches and providing active checks for range errors when your program is running. By default @value{GDBN} checks for these errors according to the rules of the current source language. Although @value{GDBN} does not check the statements in your program, it can check expressions entered directly into @value{GDBN} for evaluation via the @code{print} command, for example. @menu * Type Checking:: An overview of type checking * Range Checking:: An overview of range checking @end menu @cindex type checking @cindex checks, type @node Type Checking @subsection An Overview of Type Checking Some languages, such as C and C@t{++}, are strongly typed, meaning that the arguments to operators and functions have to be of the correct type, otherwise an error occurs. These checks prevent type mismatch errors from ever causing any run-time problems. For example, @smallexample int klass::my_method(char *b) @{ return b ? 1 : 2; @} (@value{GDBP}) print obj.my_method (0) $1 = 2 @exdent but (@value{GDBP}) print obj.my_method (0x1234) Cannot resolve method klass::my_method to any overloaded instance @end smallexample The second example fails because in C@t{++} the integer constant @samp{0x1234} is not type-compatible with the pointer parameter type. For the expressions you use in @value{GDBN} commands, you can tell @value{GDBN} to not enforce strict type checking or to treat any mismatches as errors and abandon the expression; When type checking is disabled, @value{GDBN} successfully evaluates expressions like the second example above. Even if type checking is off, there may be other reasons related to type that prevent @value{GDBN} from evaluating an expression. For instance, @value{GDBN} does not know how to add an @code{int} and a @code{struct foo}. These particular type errors have nothing to do with the language in use and usually arise from expressions which make little sense to evaluate anyway. @value{GDBN} provides some additional commands for controlling type checking: @kindex set check type @kindex show check type @table @code @item set check type on @itemx set check type off Set strict type checking on or off. If any type mismatches occur in evaluating an expression while type checking is on, @value{GDBN} prints a message and aborts evaluation of the expression. @item show check type Show the current setting of type checking and whether @value{GDBN} is enforcing strict type checking rules. @end table @cindex range checking @cindex checks, range @node Range Checking @subsection An Overview of Range Checking In some languages (such as Modula-2), it is an error to exceed the bounds of a type; this is enforced with run-time checks. Such range checking is meant to ensure program correctness by making sure computations do not overflow, or indices on an array element access do not exceed the bounds of the array. For expressions you use in @value{GDBN} commands, you can tell @value{GDBN} to treat range errors in one of three ways: ignore them, always treat them as errors and abandon the expression, or issue warnings but evaluate the expression anyway. A range error can result from numerical overflow, from exceeding an array index bound, or when you type a constant that is not a member of any type. Some languages, however, do not treat overflows as an error. In many implementations of C, mathematical overflow causes the result to ``wrap around'' to lower values---for example, if @var{m} is the largest integer value, and @var{s} is the smallest, then @smallexample @var{m} + 1 @result{} @var{s} @end smallexample This, too, is specific to individual languages, and in some cases specific to individual compilers or machines. @xref{Supported Languages, , Supported Languages}, for further details on specific languages. @value{GDBN} provides some additional commands for controlling the range checker: @kindex set check range @kindex show check range @table @code @item set check range auto Set range checking on or off based on the current working language. @xref{Supported Languages, ,Supported Languages}, for the default settings for each language. @item set check range on @itemx set check range off Set range checking on or off, overriding the default setting for the current working language. A warning is issued if the setting does not match the language default. If a range error occurs and range checking is on, then a message is printed and evaluation of the expression is aborted. @item set check range warn Output messages when the @value{GDBN} range checker detects a range error, but attempt to evaluate the expression anyway. Evaluating the expression may still be impossible for other reasons, such as accessing memory that the process does not own (a typical example from many Unix systems). @item show range Show the current setting of the range checker, and whether or not it is being set automatically by @value{GDBN}. @end table @node Supported Languages @section Supported Languages @value{GDBN} supports C, C@t{++}, D, Go, Objective-C, Fortran, OpenCL C, Pascal, Rust, assembly, Modula-2, and Ada. @c This is false ... Some @value{GDBN} features may be used in expressions regardless of the language you use: the @value{GDBN} @code{@@} and @code{::} operators, and the @samp{@{type@}addr} construct (@pxref{Expressions, ,Expressions}) can be used with the constructs of any supported language. The following sections detail to what degree each source language is supported by @value{GDBN}. These sections are not meant to be language tutorials or references, but serve only as a reference guide to what the @value{GDBN} expression parser accepts, and what input and output formats should look like for different languages. There are many good books written on each of these languages; please look to these for a language reference or tutorial. @menu * C:: C and C@t{++} * D:: D * Go:: Go * Objective-C:: Objective-C * OpenCL C:: OpenCL C * Fortran:: Fortran * Pascal:: Pascal * Rust:: Rust * Modula-2:: Modula-2 * Ada:: Ada @end menu @node C @subsection C and C@t{++} @cindex C and C@t{++} @cindex expressions in C or C@t{++} Since C and C@t{++} are so closely related, many features of @value{GDBN} apply to both languages. Whenever this is the case, we discuss those languages together. @cindex C@t{++} @cindex @code{g++}, @sc{gnu} C@t{++} compiler @cindex @sc{gnu} C@t{++} The C@t{++} debugging facilities are jointly implemented by the C@t{++} compiler and @value{GDBN}. Therefore, to debug your C@t{++} code effectively, you must compile your C@t{++} programs with a supported C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++} compiler (@code{aCC}). @menu * C Operators:: C and C@t{++} operators * C Constants:: C and C@t{++} constants * C Plus Plus Expressions:: C@t{++} expressions * C Defaults:: Default settings for C and C@t{++} * C Checks:: C and C@t{++} type and range checks * Debugging C:: @value{GDBN} and C * Debugging C Plus Plus:: @value{GDBN} features for C@t{++} * Decimal Floating Point:: Numbers in Decimal Floating Point format @end menu @node C Operators @subsubsection C and C@t{++} Operators @cindex C and C@t{++} operators Operators must be defined on values of specific types. For instance, @code{+} is defined on numbers, but not on structures. Operators are often defined on groups of types. For the purposes of C and C@t{++}, the following definitions hold: @itemize @bullet @item @emph{Integral types} include @code{int} with any of its storage-class specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}. @item @emph{Floating-point types} include @code{float}, @code{double}, and @code{long double} (if supported by the target platform). @item @emph{Pointer types} include all types defined as @code{(@var{type} *)}. @item @emph{Scalar types} include all of the above. @end itemize @noindent The following operators are supported. They are listed here in order of increasing precedence: @table @code @item , The comma or sequencing operator. Expressions in a comma-separated list are evaluated from left to right, with the result of the entire expression being the last expression evaluated. @item = Assignment. The value of an assignment expression is the value assigned. Defined on scalar types. @item @var{op}= Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}}, and translated to @w{@code{@var{a} = @var{a op b}}}. @w{@code{@var{op}=}} and @code{=} have the same precedence. The operator @var{op} is any one of the operators @code{|}, @code{^}, @code{&}, @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}. @item ?: The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought of as: if @var{a} then @var{b} else @var{c}. The argument @var{a} should be of an integral type. @item || Logical @sc{or}. Defined on integral types. @item && Logical @sc{and}. Defined on integral types. @item | Bitwise @sc{or}. Defined on integral types. @item ^ Bitwise exclusive-@sc{or}. Defined on integral types. @item & Bitwise @sc{and}. Defined on integral types. @item ==@r{, }!= Equality and inequality. Defined on scalar types. The value of these expressions is 0 for false and non-zero for true. @item <@r{, }>@r{, }<=@r{, }>= Less than, greater than, less than or equal, greater than or equal. Defined on scalar types. The value of these expressions is 0 for false and non-zero for true. @item <<@r{, }>> left shift, and right shift. Defined on integral types. @item @@ The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}). @item +@r{, }- Addition and subtraction. Defined on integral types, floating-point types and pointer types. @item *@r{, }/@r{, }% Multiplication, division, and modulus. Multiplication and division are defined on integral and floating-point types. Modulus is defined on integral types. @item ++@r{, }-- Increment and decrement. When appearing before a variable, the operation is performed before the variable is used in an expression; when appearing after it, the variable's value is used before the operation takes place. @item * Pointer dereferencing. Defined on pointer types. Same precedence as @code{++}. @item & Address operator. Defined on variables. Same precedence as @code{++}. For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})} to examine the address where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is stored. @item - Negative. Defined on integral and floating-point types. Same precedence as @code{++}. @item ! Logical negation. Defined on integral types. Same precedence as @code{++}. @item ~ Bitwise complement operator. Defined on integral types. Same precedence as @code{++}. @item .@r{, }-> Structure member, and pointer-to-structure member. For convenience, @value{GDBN} regards the two as equivalent, choosing whether to dereference a pointer based on the stored type information. Defined on @code{struct} and @code{union} data. @item .*@r{, }->* Dereferences of pointers to members. @item [] Array indexing. @code{@var{a}[@var{i}]} is defined as @code{*(@var{a}+@var{i})}. Same precedence as @code{->}. @item () Function parameter list. Same precedence as @code{->}. @item :: C@t{++} scope resolution operator. Defined on @code{struct}, @code{union}, and @code{class} types. @item :: Doubled colons also represent the @value{GDBN} scope operator (@pxref{Expressions, ,Expressions}). Same precedence as @code{::}, above. @end table If an operator is redefined in the user code, @value{GDBN} usually attempts to invoke the redefined version instead of using the operator's predefined meaning. @node C Constants @subsubsection C and C@t{++} Constants @cindex C and C@t{++} constants @value{GDBN} allows you to express the constants of C and C@t{++} in the following ways: @itemize @bullet @item Integer constants are a sequence of digits. Octal constants are specified by a leading @samp{0} (i.e.@: zero), and hexadecimal constants by a leading @samp{0x} or @samp{0X}. Constants may also end with a letter @samp{l}, specifying that the constant should be treated as a @code{long} value. @item Floating point constants are a sequence of digits, followed by a decimal point, followed by a sequence of digits, and optionally followed by an exponent. An exponent is of the form: @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another sequence of digits. The @samp{+} is optional for positive exponents. A floating-point constant may also end with a letter @samp{f} or @samp{F}, specifying that the constant should be treated as being of the @code{float} (as opposed to the default @code{double}) type; or with a letter @samp{l} or @samp{L}, which specifies a @code{long double} constant. @item Enumerated constants consist of enumerated identifiers, or their integral equivalents. @item Character constants are a single character surrounded by single quotes (@code{'}), or a number---the ordinal value of the corresponding character (usually its @sc{ascii} value). Within quotes, the single character may be represented by a letter or by @dfn{escape sequences}, which are of the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation of the character's ordinal value; or of the form @samp{\@var{x}}, where @samp{@var{x}} is a predefined special character---for example, @samp{\n} for newline. Wide character constants can be written by prefixing a character constant with @samp{L}, as in C. For example, @samp{L'x'} is the wide form of @samp{x}. The target wide character set is used when computing the value of this constant (@pxref{Character Sets}). @item String constants are a sequence of character constants surrounded by double quotes (@code{"}). Any valid character constant (as described above) may appear. Double quotes within the string must be preceded by a backslash, so for instance @samp{"a\"b'c"} is a string of five characters. Wide string constants can be written by prefixing a string constant with @samp{L}, as in C. The target wide character set is used when computing the value of this constant (@pxref{Character Sets}). @item Pointer constants are an integral value. You can also write pointers to constants using the C operator @samp{&}. @item Array constants are comma-separated lists surrounded by braces @samp{@{} and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array, and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers. @end itemize @node C Plus Plus Expressions @subsubsection C@t{++} Expressions @cindex expressions in C@t{++} @value{GDBN} expression handling can interpret most C@t{++} expressions. @cindex debugging C@t{++} programs @cindex C@t{++} compilers @cindex debug formats and C@t{++} @cindex @value{NGCC} and C@t{++} @quotation @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the proper compiler and the proper debug format. Currently, @value{GDBN} works best when debugging C@t{++} code that is compiled with the most recent version of @value{NGCC} possible. The DWARF debugging format is preferred; @value{NGCC} defaults to this on most popular platforms. Other compilers and/or debug formats are likely to work badly or not at all when using @value{GDBN} to debug C@t{++} code. @xref{Compilation}. @end quotation @enumerate @cindex member functions @item Member function calls are allowed; you can use expressions like @smallexample count = aml->GetOriginal(x, y) @end smallexample @vindex this@r{, inside C@t{++} member functions} @cindex namespace in C@t{++} @item While a member function is active (in the selected stack frame), your expressions have the same namespace available as the member function; that is, @value{GDBN} allows implicit references to the class instance pointer @code{this} following the same rules as C@t{++}. @code{using} declarations in the current scope are also respected by @value{GDBN}. @cindex call overloaded functions @cindex overloaded functions, calling @cindex type conversions in C@t{++} @item You can call overloaded functions; @value{GDBN} resolves the function call to the right definition, with some restrictions. @value{GDBN} does not perform overload resolution involving user-defined type conversions, calls to constructors, or instantiations of templates that do not exist in the program. It also cannot handle ellipsis argument lists or default arguments. It does perform integral conversions and promotions, floating-point promotions, arithmetic conversions, pointer conversions, conversions of class objects to base classes, and standard conversions such as those of functions or arrays to pointers; it requires an exact match on the number of function arguments. Overload resolution is always performed, unless you have specified @code{set overload-resolution off}. @xref{Debugging C Plus Plus, ,@value{GDBN} Features for C@t{++}}. You must specify @code{set overload-resolution off} in order to use an explicit function signature to call an overloaded function, as in @smallexample p 'foo(char,int)'('x', 13) @end smallexample The @value{GDBN} command-completion facility can simplify this; see @ref{Completion, ,Command Completion}. @cindex reference declarations @item @value{GDBN} understands variables declared as C@t{++} lvalue or rvalue references; you can use them in expressions just as you do in C@t{++} source---they are automatically dereferenced. In the parameter list shown when @value{GDBN} displays a frame, the values of reference variables are not displayed (unlike other variables); this avoids clutter, since references are often used for large structures. The @emph{address} of a reference variable is always shown, unless you have specified @samp{set print address off}. @item @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your expressions can use it just as expressions in your program do. Since one scope may be defined in another, you can use @code{::} repeatedly if necessary, for example in an expression like @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows resolving name scope by reference to source files, in both C and C@t{++} debugging (@pxref{Variables, ,Program Variables}). @item @value{GDBN} performs argument-dependent lookup, following the C@t{++} specification. @end enumerate @node C Defaults @subsubsection C and C@t{++} Defaults @cindex C and C@t{++} defaults If you allow @value{GDBN} to set range checking automatically, it defaults to @code{off} whenever the working language changes to C or C@t{++}. This happens regardless of whether you or @value{GDBN} selects the working language. If you allow @value{GDBN} to set the language automatically, it recognizes source files whose names end with @file{.c}, @file{.C}, or @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of these files, it sets the working language to C or C@t{++}. @xref{Automatically, ,Having @value{GDBN} Infer the Source Language}, for further details. @node C Checks @subsubsection C and C@t{++} Type and Range Checks @cindex C and C@t{++} checks By default, when @value{GDBN} parses C or C@t{++} expressions, strict type checking is used. However, if you turn type checking off, @value{GDBN} will allow certain non-standard conversions, such as promoting integer constants to pointers. Range checking, if turned on, is done on mathematical operations. Array indices are not checked, since they are often used to index a pointer that is not itself an array. @node Debugging C @subsubsection @value{GDBN} and C The @code{set print union} and @code{show print union} commands apply to the @code{union} type. When set to @samp{on}, any @code{union} that is inside a @code{struct} or @code{class} is also printed. Otherwise, it appears as @samp{@{...@}}. The @code{@@} operator aids in the debugging of dynamic arrays, formed with pointers and a memory allocation function. @xref{Expressions, ,Expressions}. @node Debugging C Plus Plus @subsubsection @value{GDBN} Features for C@t{++} @cindex commands for C@t{++} Some @value{GDBN} commands are particularly useful with C@t{++}, and some are designed specifically for use with C@t{++}. Here is a summary: @table @code @cindex break in overloaded functions @item @r{breakpoint menus} When you want a breakpoint in a function whose name is overloaded, @value{GDBN} has the capability to display a menu of possible breakpoint locations to help you specify which function definition you want. @xref{Ambiguous Expressions,,Ambiguous Expressions}. @cindex overloading in C@t{++} @item rbreak @var{regex} Setting breakpoints using regular expressions is helpful for setting breakpoints on overloaded functions that are not members of any special classes. @xref{Set Breaks, ,Setting Breakpoints}. @cindex C@t{++} exception handling @item catch throw @itemx catch rethrow @itemx catch catch Debug C@t{++} exception handling using these commands. @xref{Set Catchpoints, , Setting Catchpoints}. @cindex inheritance @item ptype @var{typename} Print inheritance relationships as well as other information for type @var{typename}. @xref{Symbols, ,Examining the Symbol Table}. @item info vtbl @var{expression}. The @code{info vtbl} command can be used to display the virtual method tables of the object computed by @var{expression}. This shows one entry per virtual table; there may be multiple virtual tables when multiple inheritance is in use. @cindex C@t{++} demangling @item demangle @var{name} Demangle @var{name}. @xref{Symbols}, for a more complete description of the @code{demangle} command. @cindex C@t{++} symbol display @item set print demangle @itemx show print demangle @itemx set print asm-demangle @itemx show print asm-demangle Control whether C@t{++} symbols display in their source form, both when displaying code as C@t{++} source and when displaying disassemblies. @xref{Print Settings, ,Print Settings}. @item set print object @itemx show print object Choose whether to print derived (actual) or declared types of objects. @xref{Print Settings, ,Print Settings}. @item set print vtbl @itemx show print vtbl Control the format for printing virtual function tables. @xref{Print Settings, ,Print Settings}. (The @code{vtbl} commands do not work on programs compiled with the HP ANSI C@t{++} compiler (@code{aCC}).) @kindex set overload-resolution @cindex overloaded functions, overload resolution @item set overload-resolution on Enable overload resolution for C@t{++} expression evaluation. The default is on. For overloaded functions, @value{GDBN} evaluates the arguments and searches for a function whose signature matches the argument types, using the standard C@t{++} conversion rules (see @ref{C Plus Plus Expressions, ,C@t{++} Expressions}, for details). If it cannot find a match, it emits a message. @item set overload-resolution off Disable overload resolution for C@t{++} expression evaluation. For overloaded functions that are not class member functions, @value{GDBN} chooses the first function of the specified name that it finds in the symbol table, whether or not its arguments are of the correct type. For overloaded functions that are class member functions, @value{GDBN} searches for a function whose signature @emph{exactly} matches the argument types. @kindex show overload-resolution @item show overload-resolution Show the current setting of overload resolution. @item @r{Overloaded symbol names} You can specify a particular definition of an overloaded symbol, using the same notation that is used to declare such symbols in C@t{++}: type @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can also use the @value{GDBN} command-line word completion facilities to list the available choices, or to finish the type list for you. @xref{Completion,, Command Completion}, for details on how to do this. @item @r{Breakpoints in functions with ABI tags} The GNU C@t{++} compiler introduced the notion of ABI ``tags'', which correspond to changes in the ABI of a type, function, or variable that would not otherwise be reflected in a mangled name. See @url{https://developers.redhat.com/blog/2015/02/05/gcc5-and-the-c11-abi/} for more detail. The ABI tags are visible in C@t{++} demangled names. For example, a function that returns a std::string: @smallexample std::string function(int); @end smallexample @noindent when compiled for the C++11 ABI is marked with the @code{cxx11} ABI tag, and @value{GDBN} displays the symbol like this: @smallexample function[abi:cxx11](int) @end smallexample You can set a breakpoint on such functions simply as if they had no tag. For example: @smallexample (gdb) b function(int) Breakpoint 2 at 0x40060d: file main.cc, line 10. (gdb) info breakpoints Num Type Disp Enb Address What 1 breakpoint keep y 0x0040060d in function[abi:cxx11](int) at main.cc:10 @end smallexample On the rare occasion you need to disambiguate between different ABI tags, you can do so by simply including the ABI tag in the function name, like: @smallexample (@value{GDBP}) b ambiguous[abi:other_tag](int) @end smallexample @end table @node Decimal Floating Point @subsubsection Decimal Floating Point format @cindex decimal floating point format @value{GDBN} can examine, set and perform computations with numbers in decimal floating point format, which in the C language correspond to the @code{_Decimal32}, @code{_Decimal64} and @code{_Decimal128} types as specified by the extension to support decimal floating-point arithmetic. There are two encodings in use, depending on the architecture: BID (Binary Integer Decimal) for x86 and x86-64, and DPD (Densely Packed Decimal) for PowerPC and S/390. @value{GDBN} will use the appropriate encoding for the configured target. Because of a limitation in @file{libdecnumber}, the library used by @value{GDBN} to manipulate decimal floating point numbers, it is not possible to convert (using a cast, for example) integers wider than 32-bit to decimal float. In addition, in order to imitate @value{GDBN}'s behaviour with binary floating point computations, error checking in decimal float operations ignores underflow, overflow and divide by zero exceptions. In the PowerPC architecture, @value{GDBN} provides a set of pseudo-registers to inspect @code{_Decimal128} values stored in floating point registers. See @ref{PowerPC,,PowerPC} for more details. @node D @subsection D @cindex D @value{GDBN} can be used to debug programs written in D and compiled with GDC, LDC or DMD compilers. Currently @value{GDBN} supports only one D specific feature --- dynamic arrays. @node Go @subsection Go @cindex Go (programming language) @value{GDBN} can be used to debug programs written in Go and compiled with @file{gccgo} or @file{6g} compilers. Here is a summary of the Go-specific features and restrictions: @table @code @cindex current Go package @item The current Go package The name of the current package does not need to be specified when specifying global variables and functions. For example, given the program: @example package main var myglob = "Shall we?" func main () @{ // ... @} @end example When stopped inside @code{main} either of these work: @example (gdb) p myglob (gdb) p main.myglob @end example @cindex builtin Go types @item Builtin Go types The @code{string} type is recognized by @value{GDBN} and is printed as a string. @cindex builtin Go functions @item Builtin Go functions The @value{GDBN} expression parser recognizes the @code{unsafe.Sizeof} function and handles it internally. @cindex restrictions on Go expressions @item Restrictions on Go expressions All Go operators are supported except @code{&^}. The Go @code{_} ``blank identifier'' is not supported. Automatic dereferencing of pointers is not supported. @end table @node Objective-C @subsection Objective-C @cindex Objective-C This section provides information about some commands and command options that are useful for debugging Objective-C code. See also @ref{Symbols, info classes}, and @ref{Symbols, info selectors}, for a few more commands specific to Objective-C support. @menu * Method Names in Commands:: * The Print Command with Objective-C:: @end menu @node Method Names in Commands @subsubsection Method Names in Commands The following commands have been extended to accept Objective-C method names as line specifications: @kindex clear@r{, and Objective-C} @kindex break@r{, and Objective-C} @kindex info line@r{, and Objective-C} @kindex jump@r{, and Objective-C} @kindex list@r{, and Objective-C} @itemize @item @code{clear} @item @code{break} @item @code{info line} @item @code{jump} @item @code{list} @end itemize A fully qualified Objective-C method name is specified as @smallexample -[@var{Class} @var{methodName}] @end smallexample where the minus sign is used to indicate an instance method and a plus sign (not shown) is used to indicate a class method. The class name @var{Class} and method name @var{methodName} are enclosed in brackets, similar to the way messages are specified in Objective-C source code. For example, to set a breakpoint at the @code{create} instance method of class @code{Fruit} in the program currently being debugged, enter: @smallexample break -[Fruit create] @end smallexample To list ten program lines around the @code{initialize} class method, enter: @smallexample list +[NSText initialize] @end smallexample In the current version of @value{GDBN}, the plus or minus sign is required. In future versions of @value{GDBN}, the plus or minus sign will be optional, but you can use it to narrow the search. It is also possible to specify just a method name: @smallexample break create @end smallexample You must specify the complete method name, including any colons. If your program's source files contain more than one @code{create} method, you'll be presented with a numbered list of classes that implement that method. Indicate your choice by number, or type @samp{0} to exit if none apply. As another example, to clear a breakpoint established at the @code{makeKeyAndOrderFront:} method of the @code{NSWindow} class, enter: @smallexample clear -[NSWindow makeKeyAndOrderFront:] @end smallexample @node The Print Command with Objective-C @subsubsection The Print Command With Objective-C @cindex Objective-C, print objects @kindex print-object @kindex po @r{(@code{print-object})} The print command has also been extended to accept methods. For example: @smallexample print -[@var{object} hash] @end smallexample @cindex print an Objective-C object description @cindex @code{_NSPrintForDebugger}, and printing Objective-C objects @noindent will tell @value{GDBN} to send the @code{hash} message to @var{object} and print the result. Also, an additional command has been added, @code{print-object} or @code{po} for short, which is meant to print the description of an object. However, this command may only work with certain Objective-C libraries that have a particular hook function, @code{_NSPrintForDebugger}, defined. @node OpenCL C @subsection OpenCL C @cindex OpenCL C This section provides information about @value{GDBN}s OpenCL C support. @menu * OpenCL C Datatypes:: * OpenCL C Expressions:: * OpenCL C Operators:: @end menu @node OpenCL C Datatypes @subsubsection OpenCL C Datatypes @cindex OpenCL C Datatypes @value{GDBN} supports the builtin scalar and vector datatypes specified by OpenCL 1.1. In addition the half- and double-precision floating point data types of the @code{cl_khr_fp16} and @code{cl_khr_fp64} OpenCL extensions are also known to @value{GDBN}. @node OpenCL C Expressions @subsubsection OpenCL C Expressions @cindex OpenCL C Expressions @value{GDBN} supports accesses to vector components including the access as lvalue where possible. Since OpenCL C is based on C99 most C expressions supported by @value{GDBN} can be used as well. @node OpenCL C Operators @subsubsection OpenCL C Operators @cindex OpenCL C Operators @value{GDBN} supports the operators specified by OpenCL 1.1 for scalar and vector data types. @node Fortran @subsection Fortran @cindex Fortran-specific support in @value{GDBN} @value{GDBN} can be used to debug programs written in Fortran, but it currently supports only the features of Fortran 77 language. @cindex trailing underscore, in Fortran symbols Some Fortran compilers (@sc{gnu} Fortran 77 and Fortran 95 compilers among them) append an underscore to the names of variables and functions. When you debug programs compiled by those compilers, you will need to refer to variables and functions with a trailing underscore. @menu * Fortran Operators:: Fortran operators and expressions * Fortran Defaults:: Default settings for Fortran * Special Fortran Commands:: Special @value{GDBN} commands for Fortran @end menu @node Fortran Operators @subsubsection Fortran Operators and Expressions @cindex Fortran operators and expressions Operators must be defined on values of specific types. For instance, @code{+} is defined on numbers, but not on characters or other non- arithmetic types. Operators are often defined on groups of types. @table @code @item ** The exponentiation operator. It raises the first operand to the power of the second one. @item : The range operator. Normally used in the form of array(low:high) to represent a section of array. @item % The access component operator. Normally used to access elements in derived types. Also suitable for unions. As unions aren't part of regular Fortran, this can only happen when accessing a register that uses a gdbarch-defined union type. @item :: The scope operator. Normally used to access variables in modules or to set breakpoints on subroutines nested in modules or in other subroutines (internal subroutines). @end table @node Fortran Defaults @subsubsection Fortran Defaults @cindex Fortran Defaults Fortran symbols are usually case-insensitive, so @value{GDBN} by default uses case-insensitive matches for Fortran symbols. You can change that with the @samp{set case-insensitive} command, see @ref{Symbols}, for the details. @node Special Fortran Commands @subsubsection Special Fortran Commands @cindex Special Fortran commands @value{GDBN} has some commands to support Fortran-specific features, such as displaying common blocks. @table @code @cindex @code{COMMON} blocks, Fortran @kindex info common @item info common @r{[}@var{common-name}@r{]} This command prints the values contained in the Fortran @code{COMMON} block whose name is @var{common-name}. With no argument, the names of all @code{COMMON} blocks visible at the current program location are printed. @end table @node Pascal @subsection Pascal @cindex Pascal support in @value{GDBN}, limitations Debugging Pascal programs which use sets, subranges, file variables, or nested functions does not currently work. @value{GDBN} does not support entering expressions, printing values, or similar features using Pascal syntax. The Pascal-specific command @code{set print pascal_static-members} controls whether static members of Pascal objects are displayed. @xref{Print Settings, pascal_static-members}. @node Rust @subsection Rust @value{GDBN} supports the @url{https://www.rust-lang.org/, Rust Programming Language}. Type- and value-printing, and expression parsing, are reasonably complete. However, there are a few peculiarities and holes to be aware of. @itemize @bullet @item Linespecs (@pxref{Specify Location}) are never relative to the current crate. Instead, they act as if there were a global namespace of crates, somewhat similar to the way @code{extern crate} behaves. That is, if @value{GDBN} is stopped at a breakpoint in a function in crate @samp{A}, module @samp{B}, then @code{break B::f} will attempt to set a breakpoint in a function named @samp{f} in a crate named @samp{B}. As a consequence of this approach, linespecs also cannot refer to items using @samp{self::} or @samp{super::}. @item Because @value{GDBN} implements Rust name-lookup semantics in expressions, it will sometimes prepend the current crate to a name. For example, if @value{GDBN} is stopped at a breakpoint in the crate @samp{K}, then @code{print ::x::y} will try to find the symbol @samp{K::x::y}. However, since it is useful to be able to refer to other crates when debugging, @value{GDBN} provides the @code{extern} extension to circumvent this. To use the extension, just put @code{extern} before a path expression to refer to the otherwise unavailable ``global'' scope. In the above example, if you wanted to refer to the symbol @samp{y} in the crate @samp{x}, you would use @code{print extern x::y}. @item The Rust expression evaluator does not support ``statement-like'' expressions such as @code{if} or @code{match}, or lambda expressions. @item Tuple expressions are not implemented. @item The Rust expression evaluator does not currently implement the @code{Drop} trait. Objects that may be created by the evaluator will never be destroyed. @item @value{GDBN} does not implement type inference for generics. In order to call generic functions or otherwise refer to generic items, you will have to specify the type parameters manually. @item @value{GDBN} currently uses the C@t{++} demangler for Rust. In most cases this does not cause any problems. However, in an expression context, completing a generic function name will give syntactically invalid results. This happens because Rust requires the @samp{::} operator between the function name and its generic arguments. For example, @value{GDBN} might provide a completion like @code{crate::f<u32>}, where the parser would require @code{crate::f::<u32>}. @item As of this writing, the Rust compiler (version 1.8) has a few holes in the debugging information it generates. These holes prevent certain features from being implemented by @value{GDBN}: @itemize @bullet @item Method calls cannot be made via traits. @item Operator overloading is not implemented. @item When debugging in a monomorphized function, you cannot use the generic type names. @item The type @code{Self} is not available. @item @code{use} statements are not available, so some names may not be available in the crate. @end itemize @end itemize @node Modula-2 @subsection Modula-2 @cindex Modula-2, @value{GDBN} support The extensions made to @value{GDBN} to support Modula-2 only support output from the @sc{gnu} Modula-2 compiler (which is currently being developed). Other Modula-2 compilers are not currently supported, and attempting to debug executables produced by them is most likely to give an error as @value{GDBN} reads in the executable's symbol table. @cindex expressions in Modula-2 @menu * M2 Operators:: Built-in operators * Built-In Func/Proc:: Built-in functions and procedures * M2 Constants:: Modula-2 constants * M2 Types:: Modula-2 types * M2 Defaults:: Default settings for Modula-2 * Deviations:: Deviations from standard Modula-2 * M2 Checks:: Modula-2 type and range checks * M2 Scope:: The scope operators @code{::} and @code{.} * GDB/M2:: @value{GDBN} and Modula-2 @end menu @node M2 Operators @subsubsection Operators @cindex Modula-2 operators Operators must be defined on values of specific types. For instance, @code{+} is defined on numbers, but not on structures. Operators are often defined on groups of types. For the purposes of Modula-2, the following definitions hold: @itemize @bullet @item @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and their subranges. @item @emph{Character types} consist of @code{CHAR} and its subranges. @item @emph{Floating-point types} consist of @code{REAL}. @item @emph{Pointer types} consist of anything declared as @code{POINTER TO @var{type}}. @item @emph{Scalar types} consist of all of the above. @item @emph{Set types} consist of @code{SET} and @code{BITSET} types. @item @emph{Boolean types} consist of @code{BOOLEAN}. @end itemize @noindent The following operators are supported, and appear in order of increasing precedence: @table @code @item , Function argument or array index separator. @item := Assignment. The value of @var{var} @code{:=} @var{value} is @var{value}. @item <@r{, }> Less than, greater than on integral, floating-point, or enumerated types. @item <=@r{, }>= Less than or equal to, greater than or equal to on integral, floating-point and enumerated types, or set inclusion on set types. Same precedence as @code{<}. @item =@r{, }<>@r{, }# Equality and two ways of expressing inequality, valid on scalar types. Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is available for inequality, since @code{#} conflicts with the script comment character. @item IN Set membership. Defined on set types and the types of their members. Same precedence as @code{<}. @item OR Boolean disjunction. Defined on boolean types. @item AND@r{, }& Boolean conjunction. Defined on boolean types. @item @@ The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}). @item +@r{, }- Addition and subtraction on integral and floating-point types, or union and difference on set types. @item * Multiplication on integral and floating-point types, or set intersection on set types. @item / Division on floating-point types, or symmetric set difference on set types. Same precedence as @code{*}. @item DIV@r{, }MOD Integer division and remainder. Defined on integral types. Same precedence as @code{*}. @item - Negative. Defined on @code{INTEGER} and @code{REAL} data. @item ^ Pointer dereferencing. Defined on pointer types. @item NOT Boolean negation. Defined on boolean types. Same precedence as @code{^}. @item . @code{RECORD} field selector. Defined on @code{RECORD} data. Same precedence as @code{^}. @item [] Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}. @item () Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence as @code{^}. @item ::@r{, }. @value{GDBN} and Modula-2 scope operators. @end table @quotation @emph{Warning:} Set expressions and their operations are not yet supported, so @value{GDBN} treats the use of the operator @code{IN}, or the use of operators @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#}, @code{<=}, and @code{>=} on sets as an error. @end quotation @node Built-In Func/Proc @subsubsection Built-in Functions and Procedures @cindex Modula-2 built-ins Modula-2 also makes available several built-in procedures and functions. In describing these, the following metavariables are used: @table @var @item a represents an @code{ARRAY} variable. @item c represents a @code{CHAR} constant or variable. @item i represents a variable or constant of integral type. @item m represents an identifier that belongs to a set. Generally used in the same function with the metavariable @var{s}. The type of @var{s} should be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}). @item n represents a variable or constant of integral or floating-point type. @item r represents a variable or constant of floating-point type. @item t represents a type. @item v represents a variable. @item x represents a variable or constant of one of many types. See the explanation of the function for details. @end table All Modula-2 built-in procedures also return a result, described below. @table @code @item ABS(@var{n}) Returns the absolute value of @var{n}. @item CAP(@var{c}) If @var{c} is a lower case letter, it returns its upper case equivalent, otherwise it returns its argument. @item CHR(@var{i}) Returns the character whose ordinal value is @var{i}. @item DEC(@var{v}) Decrements the value in the variable @var{v} by one. Returns the new value. @item DEC(@var{v},@var{i}) Decrements the value in the variable @var{v} by @var{i}. Returns the new value. @item EXCL(@var{m},@var{s}) Removes the element @var{m} from the set @var{s}. Returns the new set. @item FLOAT(@var{i}) Returns the floating point equivalent of the integer @var{i}. @item HIGH(@var{a}) Returns the index of the last member of @var{a}. @item INC(@var{v}) Increments the value in the variable @var{v} by one. Returns the new value. @item INC(@var{v},@var{i}) Increments the value in the variable @var{v} by @var{i}. Returns the new value. @item INCL(@var{m},@var{s}) Adds the element @var{m} to the set @var{s} if it is not already there. Returns the new set. @item MAX(@var{t}) Returns the maximum value of the type @var{t}. @item MIN(@var{t}) Returns the minimum value of the type @var{t}. @item ODD(@var{i}) Returns boolean TRUE if @var{i} is an odd number. @item ORD(@var{x}) Returns the ordinal value of its argument. For example, the ordinal value of a character is its @sc{ascii} value (on machines supporting the @sc{ascii} character set). The argument @var{x} must be of an ordered type, which include integral, character and enumerated types. @item SIZE(@var{x}) Returns the size of its argument. The argument @var{x} can be a variable or a type. @item TRUNC(@var{r}) Returns the integral part of @var{r}. @item TSIZE(@var{x}) Returns the size of its argument. The argument @var{x} can be a variable or a type. @item VAL(@var{t},@var{i}) Returns the member of the type @var{t} whose ordinal value is @var{i}. @end table @quotation @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as an error. @end quotation @cindex Modula-2 constants @node M2 Constants @subsubsection Constants @value{GDBN} allows you to express the constants of Modula-2 in the following ways: @itemize @bullet @item Integer constants are simply a sequence of digits. When used in an expression, a constant is interpreted to be type-compatible with the rest of the expression. Hexadecimal integers are specified by a trailing @samp{H}, and octal integers by a trailing @samp{B}. @item Floating point constants appear as a sequence of digits, followed by a decimal point and another sequence of digits. An optional exponent can then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the digits of the floating point constant must be valid decimal (base 10) digits. @item Character constants consist of a single character enclosed by a pair of like quotes, either single (@code{'}) or double (@code{"}). They may also be expressed by their ordinal value (their @sc{ascii} value, usually) followed by a @samp{C}. @item String constants consist of a sequence of characters enclosed by a pair of like quotes, either single (@code{'}) or double (@code{"}). Escape sequences in the style of C are also allowed. @xref{C Constants, ,C and C@t{++} Constants}, for a brief explanation of escape sequences. @item Enumerated constants consist of an enumerated identifier. @item Boolean constants consist of the identifiers @code{TRUE} and @code{FALSE}. @item Pointer constants consist of integral values only. @item Set constants are not yet supported. @end itemize @node M2 Types @subsubsection Modula-2 Types @cindex Modula-2 types Currently @value{GDBN} can print the following data types in Modula-2 syntax: array types, record types, set types, pointer types, procedure types, enumerated types, subrange types and base types. You can also print the contents of variables declared using these type. This section gives a number of simple source code examples together with sample @value{GDBN} sessions. The first example contains the following section of code: @smallexample VAR s: SET OF CHAR ; r: [20..40] ; @end smallexample @noindent and you can request @value{GDBN} to interrogate the type and value of @code{r} and @code{s}. @smallexample (@value{GDBP}) print s @{'A'..'C', 'Z'@} (@value{GDBP}) ptype s SET OF CHAR (@value{GDBP}) print r 21 (@value{GDBP}) ptype r [20..40] @end smallexample @noindent Likewise if your source code declares @code{s} as: @smallexample VAR s: SET ['A'..'Z'] ; @end smallexample @noindent then you may query the type of @code{s} by: @smallexample (@value{GDBP}) ptype s type = SET ['A'..'Z'] @end smallexample @noindent Note that at present you cannot interactively manipulate set expressions using the debugger. The following example shows how you might declare an array in Modula-2 and how you can interact with @value{GDBN} to print its type and contents: @smallexample VAR s: ARRAY [-10..10] OF CHAR ; @end smallexample @smallexample (@value{GDBP}) ptype s ARRAY [-10..10] OF CHAR @end smallexample Note that the array handling is not yet complete and although the type is printed correctly, expression handling still assumes that all arrays have a lower bound of zero and not @code{-10} as in the example above. Here are some more type related Modula-2 examples: @smallexample TYPE colour = (blue, red, yellow, green) ; t = [blue..yellow] ; VAR s: t ; BEGIN s := blue ; @end smallexample @noindent The @value{GDBN} interaction shows how you can query the data type and value of a variable. @smallexample (@value{GDBP}) print s $1 = blue (@value{GDBP}) ptype t type = [blue..yellow] @end smallexample @noindent In this example a Modula-2 array is declared and its contents displayed. Observe that the contents are written in the same way as their @code{C} counterparts. @smallexample VAR s: ARRAY [1..5] OF CARDINAL ; BEGIN s[1] := 1 ; @end smallexample @smallexample (@value{GDBP}) print s $1 = @{1, 0, 0, 0, 0@} (@value{GDBP}) ptype s type = ARRAY [1..5] OF CARDINAL @end smallexample The Modula-2 language interface to @value{GDBN} also understands pointer types as shown in this example: @smallexample VAR s: POINTER TO ARRAY [1..5] OF CARDINAL ; BEGIN NEW(s) ; s^[1] := 1 ; @end smallexample @noindent and you can request that @value{GDBN} describes the type of @code{s}. @smallexample (@value{GDBP}) ptype s type = POINTER TO ARRAY [1..5] OF CARDINAL @end smallexample @value{GDBN} handles compound types as we can see in this example. Here we combine array types, record types, pointer types and subrange types: @smallexample TYPE foo = RECORD f1: CARDINAL ; f2: CHAR ; f3: myarray ; END ; myarray = ARRAY myrange OF CARDINAL ; myrange = [-2..2] ; VAR s: POINTER TO ARRAY myrange OF foo ; @end smallexample @noindent and you can ask @value{GDBN} to describe the type of @code{s} as shown below. @smallexample (@value{GDBP}) ptype s type = POINTER TO ARRAY [-2..2] OF foo = RECORD f1 : CARDINAL; f2 : CHAR; f3 : ARRAY [-2..2] OF CARDINAL; END @end smallexample @node M2 Defaults @subsubsection Modula-2 Defaults @cindex Modula-2 defaults If type and range checking are set automatically by @value{GDBN}, they both default to @code{on} whenever the working language changes to Modula-2. This happens regardless of whether you or @value{GDBN} selected the working language. If you allow @value{GDBN} to set the language automatically, then entering code compiled from a file whose name ends with @file{.mod} sets the working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} Infer the Source Language}, for further details. @node Deviations @subsubsection Deviations from Standard Modula-2 @cindex Modula-2, deviations from A few changes have been made to make Modula-2 programs easier to debug. This is done primarily via loosening its type strictness: @itemize @bullet @item Unlike in standard Modula-2, pointer constants can be formed by integers. This allows you to modify pointer variables during debugging. (In standard Modula-2, the actual address contained in a pointer variable is hidden from you; it can only be modified through direct assignment to another pointer variable or expression that returned a pointer.) @item C escape sequences can be used in strings and characters to represent non-printable characters. @value{GDBN} prints out strings with these escape sequences embedded. Single non-printable characters are printed using the @samp{CHR(@var{nnn})} format. @item The assignment operator (@code{:=}) returns the value of its right-hand argument. @item All built-in procedures both modify @emph{and} return their argument. @end itemize @node M2 Checks @subsubsection Modula-2 Type and Range Checks @cindex Modula-2 checks @quotation @emph{Warning:} in this release, @value{GDBN} does not yet perform type or range checking. @end quotation @c FIXME remove warning when type/range checks added @value{GDBN} considers two Modula-2 variables type equivalent if: @itemize @bullet @item They are of types that have been declared equivalent via a @code{TYPE @var{t1} = @var{t2}} statement @item They have been declared on the same line. (Note: This is true of the @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.) @end itemize As long as type checking is enabled, any attempt to combine variables whose types are not equivalent is an error. Range checking is done on all mathematical operations, assignment, array index bounds, and all built-in functions and procedures. @node M2 Scope @subsubsection The Scope Operators @code{::} and @code{.} @cindex scope @cindex @code{.}, Modula-2 scope operator @cindex colon, doubled as scope operator @ifinfo @vindex colon-colon@r{, in Modula-2} @c Info cannot handle :: but TeX can. @end ifinfo @ifnotinfo @vindex ::@r{, in Modula-2} @end ifnotinfo There are a few subtle differences between the Modula-2 scope operator (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have similar syntax: @smallexample @var{module} . @var{id} @var{scope} :: @var{id} @end smallexample @noindent where @var{scope} is the name of a module or a procedure, @var{module} the name of a module, and @var{id} is any declared identifier within your program, except another module. Using the @code{::} operator makes @value{GDBN} search the scope specified by @var{scope} for the identifier @var{id}. If it is not found in the specified scope, then @value{GDBN} searches all scopes enclosing the one specified by @var{scope}. Using the @code{.} operator makes @value{GDBN} search the current scope for the identifier specified by @var{id} that was imported from the definition module specified by @var{module}. With this operator, it is an error if the identifier @var{id} was not imported from definition module @var{module}, or if @var{id} is not an identifier in @var{module}. @node GDB/M2 @subsubsection @value{GDBN} and Modula-2 Some @value{GDBN} commands have little use when debugging Modula-2 programs. Five subcommands of @code{set print} and @code{show print} apply specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle}, @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four apply to C@t{++}, and the last to the C @code{union} type, which has no direct analogue in Modula-2. The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available with any language, is not useful with Modula-2. Its intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be created in Modula-2 as they can in C or C@t{++}. However, because an address can be specified by an integral constant, the construct @samp{@{@var{type}@}@var{adrexp}} is still useful. @cindex @code{#} in Modula-2 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is interpreted as the beginning of a comment. Use @code{<>} instead. @node Ada @subsection Ada @cindex Ada The extensions made to @value{GDBN} for Ada only support output from the @sc{gnu} Ada (GNAT) compiler. Other Ada compilers are not currently supported, and attempting to debug executables produced by them is most likely to be difficult. @cindex expressions in Ada @menu * Ada Mode Intro:: General remarks on the Ada syntax and semantics supported by Ada mode in @value{GDBN}. * Omissions from Ada:: Restrictions on the Ada expression syntax. * Additions to Ada:: Extensions of the Ada expression syntax. * Overloading support for Ada:: Support for expressions involving overloaded subprograms. * Stopping Before Main Program:: Debugging the program during elaboration. * Ada Exceptions:: Ada Exceptions * Ada Tasks:: Listing and setting breakpoints in tasks. * Ada Tasks and Core Files:: Tasking Support when Debugging Core Files * Ravenscar Profile:: Tasking Support when using the Ravenscar Profile * Ada Settings:: New settable GDB parameters for Ada. * Ada Glitches:: Known peculiarities of Ada mode. @end menu @node Ada Mode Intro @subsubsection Introduction @cindex Ada mode, general The Ada mode of @value{GDBN} supports a fairly large subset of Ada expression syntax, with some extensions. The philosophy behind the design of this subset is @itemize @bullet @item That @value{GDBN} should provide basic literals and access to operations for arithmetic, dereferencing, field selection, indexing, and subprogram calls, leaving more sophisticated computations to subprograms written into the program (which therefore may be called from @value{GDBN}). @item That type safety and strict adherence to Ada language restrictions are not particularly important to the @value{GDBN} user. @item That brevity is important to the @value{GDBN} user. @end itemize Thus, for brevity, the debugger acts as if all names declared in user-written packages are directly visible, even if they are not visible according to Ada rules, thus making it unnecessary to fully qualify most names with their packages, regardless of context. Where this causes ambiguity, @value{GDBN} asks the user's intent. The debugger will start in Ada mode if it detects an Ada main program. As for other languages, it will enter Ada mode when stopped in a program that was translated from an Ada source file. While in Ada mode, you may use `@t{--}' for comments. This is useful mostly for documenting command files. The standard @value{GDBN} comment (@samp{#}) still works at the beginning of a line in Ada mode, but not in the middle (to allow based literals). @node Omissions from Ada @subsubsection Omissions from Ada @cindex Ada, omissions from Here are the notable omissions from the subset: @itemize @bullet @item Only a subset of the attributes are supported: @itemize @minus @item @t{'First}, @t{'Last}, and @t{'Length} on array objects (not on types and subtypes). @item @t{'Min} and @t{'Max}. @item @t{'Pos} and @t{'Val}. @item @t{'Tag}. @item @t{'Range} on array objects (not subtypes), but only as the right operand of the membership (@code{in}) operator. @item @t{'Access}, @t{'Unchecked_Access}, and @t{'Unrestricted_Access} (a GNAT extension). @item @t{'Address}. @end itemize @item The names in @code{Characters.Latin_1} are not available and concatenation is not implemented. Thus, escape characters in strings are not currently available. @item Equality tests (@samp{=} and @samp{/=}) on arrays test for bitwise equality of representations. They will generally work correctly for strings and arrays whose elements have integer or enumeration types. They may not work correctly for arrays whose element types have user-defined equality, for arrays of real values (in particular, IEEE-conformant floating point, because of negative zeroes and NaNs), and for arrays whose elements contain unused bits with indeterminate values. @item The other component-by-component array operations (@code{and}, @code{or}, @code{xor}, @code{not}, and relational tests other than equality) are not implemented. @item @cindex array aggregates (Ada) @cindex record aggregates (Ada) @cindex aggregates (Ada) There is limited support for array and record aggregates. They are permitted only on the right sides of assignments, as in these examples: @smallexample (@value{GDBP}) set An_Array := (1, 2, 3, 4, 5, 6) (@value{GDBP}) set An_Array := (1, others => 0) (@value{GDBP}) set An_Array := (0|4 => 1, 1..3 => 2, 5 => 6) (@value{GDBP}) set A_2D_Array := ((1, 2, 3), (4, 5, 6), (7, 8, 9)) (@value{GDBP}) set A_Record := (1, "Peter", True); (@value{GDBP}) set A_Record := (Name => "Peter", Id => 1, Alive => True) @end smallexample Changing a discriminant's value by assigning an aggregate has an undefined effect if that discriminant is used within the record. However, you can first modify discriminants by directly assigning to them (which normally would not be allowed in Ada), and then performing an aggregate assignment. For example, given a variable @code{A_Rec} declared to have a type such as: @smallexample type Rec (Len : Small_Integer := 0) is record Id : Integer; Vals : IntArray (1 .. Len); end record; @end smallexample you can assign a value with a different size of @code{Vals} with two assignments: @smallexample (@value{GDBP}) set A_Rec.Len := 4 (@value{GDBP}) set A_Rec := (Id => 42, Vals => (1, 2, 3, 4)) @end smallexample As this example also illustrates, @value{GDBN} is very loose about the usual rules concerning aggregates. You may leave out some of the components of an array or record aggregate (such as the @code{Len} component in the assignment to @code{A_Rec} above); they will retain their original values upon assignment. You may freely use dynamic values as indices in component associations. You may even use overlapping or redundant component associations, although which component values are assigned in such cases is not defined. @item Calls to dispatching subprograms are not implemented. @item The overloading algorithm is much more limited (i.e., less selective) than that of real Ada. It makes only limited use of the context in which a subexpression appears to resolve its meaning, and it is much looser in its rules for allowing type matches. As a result, some function calls will be ambiguous, and the user will be asked to choose the proper resolution. @item The @code{new} operator is not implemented. @item Entry calls are not implemented. @item Aside from printing, arithmetic operations on the native VAX floating-point formats are not supported. @item It is not possible to slice a packed array. @item The names @code{True} and @code{False}, when not part of a qualified name, are interpreted as if implicitly prefixed by @code{Standard}, regardless of context. Should your program redefine these names in a package or procedure (at best a dubious practice), you will have to use fully qualified names to access their new definitions. @end itemize @node Additions to Ada @subsubsection Additions to Ada @cindex Ada, deviations from As it does for other languages, @value{GDBN} makes certain generic extensions to Ada (@pxref{Expressions}): @itemize @bullet @item If the expression @var{E} is a variable residing in memory (typically a local variable or array element) and @var{N} is a positive integer, then @code{@var{E}@@@var{N}} displays the values of @var{E} and the @var{N}-1 adjacent variables following it in memory as an array. In Ada, this operator is generally not necessary, since its prime use is in displaying parts of an array, and slicing will usually do this in Ada. However, there are occasional uses when debugging programs in which certain debugging information has been optimized away. @item @code{@var{B}::@var{var}} means ``the variable named @var{var} that appears in function or file @var{B}.'' When @var{B} is a file name, you must typically surround it in single quotes. @item The expression @code{@{@var{type}@} @var{addr}} means ``the variable of type @var{type} that appears at address @var{addr}.'' @item A name starting with @samp{$} is a convenience variable (@pxref{Convenience Vars}) or a machine register (@pxref{Registers}). @end itemize In addition, @value{GDBN} provides a few other shortcuts and outright additions specific to Ada: @itemize @bullet @item The assignment statement is allowed as an expression, returning its right-hand operand as its value. Thus, you may enter @smallexample (@value{GDBP}) set x := y + 3 (@value{GDBP}) print A(tmp := y + 1) @end smallexample @item The semicolon is allowed as an ``operator,'' returning as its value the value of its right-hand operand. This allows, for example, complex conditional breaks: @smallexample (@value{GDBP}) break f (@value{GDBP}) condition 1 (report(i); k += 1; A(k) > 100) @end smallexample @item Rather than use catenation and symbolic character names to introduce special characters into strings, one may instead use a special bracket notation, which is also used to print strings. A sequence of characters of the form @samp{["@var{XX}"]} within a string or character literal denotes the (single) character whose numeric encoding is @var{XX} in hexadecimal. The sequence of characters @samp{["""]} also denotes a single quotation mark in strings. For example, @smallexample "One line.["0a"]Next line.["0a"]" @end smallexample @noindent contains an ASCII newline character (@code{Ada.Characters.Latin_1.LF}) after each period. @item The subtype used as a prefix for the attributes @t{'Pos}, @t{'Min}, and @t{'Max} is optional (and is ignored in any case). For example, it is valid to write @smallexample (@value{GDBP}) print 'max(x, y) @end smallexample @item When printing arrays, @value{GDBN} uses positional notation when the array has a lower bound of 1, and uses a modified named notation otherwise. For example, a one-dimensional array of three integers with a lower bound of 3 might print as @smallexample (3 => 10, 17, 1) @end smallexample @noindent That is, in contrast to valid Ada, only the first component has a @code{=>} clause. @item You may abbreviate attributes in expressions with any unique, multi-character subsequence of their names (an exact match gets preference). For example, you may use @t{a'len}, @t{a'gth}, or @t{a'lh} in place of @t{a'length}. @item @cindex quoting Ada internal identifiers Since Ada is case-insensitive, the debugger normally maps identifiers you type to lower case. The GNAT compiler uses upper-case characters for some of its internal identifiers, which are normally of no interest to users. For the rare occasions when you actually have to look at them, enclose them in angle brackets to avoid the lower-case mapping. For example, @smallexample (@value{GDBP}) print <JMPBUF_SAVE>[0] @end smallexample @item Printing an object of class-wide type or dereferencing an access-to-class-wide value will display all the components of the object's specific type (as indicated by its run-time tag). Likewise, component selection on such a value will operate on the specific type of the object. @end itemize @node Overloading support for Ada @subsubsection Overloading support for Ada @cindex overloading, Ada The debugger supports limited overloading. Given a subprogram call in which the function symbol has multiple definitions, it will use the number of actual parameters and some information about their types to attempt to narrow the set of definitions. It also makes very limited use of context, preferring procedures to functions in the context of the @code{call} command, and functions to procedures elsewhere. If, after narrowing, the set of matching definitions still contains more than one definition, @value{GDBN} will display a menu to query which one it should use, for instance: @smallexample (@value{GDBP}) print f(1) Multiple matches for f [0] cancel [1] foo.f (integer) return boolean at foo.adb:23 [2] foo.f (foo.new_integer) return boolean at foo.adb:28 > @end smallexample In this case, just select one menu entry either to cancel expression evaluation (type @kbd{0} and press @key{RET}) or to continue evaluation with a specific instance (type the corresponding number and press @key{RET}). Here are a couple of commands to customize @value{GDBN}'s behavior in this case: @table @code @kindex set ada print-signatures @item set ada print-signatures Control whether parameter types and return types are displayed in overloads selection menus. It is @code{on} by default. @xref{Overloading support for Ada}. @kindex show ada print-signatures @item show ada print-signatures Show the current setting for displaying parameter types and return types in overloads selection menu. @xref{Overloading support for Ada}. @end table @node Stopping Before Main Program @subsubsection Stopping at the Very Beginning @cindex breakpointing Ada elaboration code It is sometimes necessary to debug the program during elaboration, and before reaching the main procedure. As defined in the Ada Reference Manual, the elaboration code is invoked from a procedure called @code{adainit}. To run your program up to the beginning of elaboration, simply use the following two commands: @code{tbreak adainit} and @code{run}. @node Ada Exceptions @subsubsection Ada Exceptions A command is provided to list all Ada exceptions: @table @code @kindex info exceptions @item info exceptions @itemx info exceptions @var{regexp} The @code{info exceptions} command allows you to list all Ada exceptions defined within the program being debugged, as well as their addresses. With a regular expression, @var{regexp}, as argument, only those exceptions whose names match @var{regexp} are listed. @end table Below is a small example, showing how the command can be used, first without argument, and next with a regular expression passed as an argument. @smallexample (@value{GDBP}) info exceptions All defined Ada exceptions: constraint_error: 0x613da0 program_error: 0x613d20 storage_error: 0x613ce0 tasking_error: 0x613ca0 const.aint_global_e: 0x613b00 (@value{GDBP}) info exceptions const.aint All Ada exceptions matching regular expression "const.aint": constraint_error: 0x613da0 const.aint_global_e: 0x613b00 @end smallexample It is also possible to ask @value{GDBN} to stop your program's execution when an exception is raised. For more details, see @ref{Set Catchpoints}. @node Ada Tasks @subsubsection Extensions for Ada Tasks @cindex Ada, tasking Support for Ada tasks is analogous to that for threads (@pxref{Threads}). @value{GDBN} provides the following task-related commands: @table @code @kindex info tasks @item info tasks This command shows a list of current Ada tasks, as in the following example: @smallexample @iftex @leftskip=0.5cm @end iftex (@value{GDBP}) info tasks ID TID P-ID Pri State Name 1 8088000 0 15 Child Activation Wait main_task 2 80a4000 1 15 Accept Statement b 3 809a800 1 15 Child Activation Wait a * 4 80ae800 3 15 Runnable c @end smallexample @noindent In this listing, the asterisk before the last task indicates it to be the task currently being inspected. @table @asis @item ID Represents @value{GDBN}'s internal task number. @item TID The Ada task ID. @item P-ID The parent's task ID (@value{GDBN}'s internal task number). @item Pri The base priority of the task. @item State Current state of the task. @table @code @item Unactivated The task has been created but has not been activated. It cannot be executing. @item Runnable The task is not blocked for any reason known to Ada. (It may be waiting for a mutex, though.) It is conceptually "executing" in normal mode. @item Terminated The task is terminated, in the sense of ARM 9.3 (5). Any dependents that were waiting on terminate alternatives have been awakened and have terminated themselves. @item Child Activation Wait The task is waiting for created tasks to complete activation. @item Accept Statement The task is waiting on an accept or selective wait statement. @item Waiting on entry call The task is waiting on an entry call. @item Async Select Wait The task is waiting to start the abortable part of an asynchronous select statement. @item Delay Sleep The task is waiting on a select statement with only a delay alternative open. @item Child Termination Wait The task is sleeping having completed a master within itself, and is waiting for the tasks dependent on that master to become terminated or waiting on a terminate Phase. @item Wait Child in Term Alt The task is sleeping waiting for tasks on terminate alternatives to finish terminating. @item Accepting RV with @var{taskno} The task is accepting a rendez-vous with the task @var{taskno}. @end table @item Name Name of the task in the program. @end table @kindex info task @var{taskno} @item info task @var{taskno} This command shows detailed informations on the specified task, as in the following example: @smallexample @iftex @leftskip=0.5cm @end iftex (@value{GDBP}) info tasks ID TID P-ID Pri State Name 1 8077880 0 15 Child Activation Wait main_task * 2 807c468 1 15 Runnable task_1 (@value{GDBP}) info task 2 Ada Task: 0x807c468 Name: "task_1" Thread: 0 LWP: 0x1fac Parent: 1 ("main_task") Base Priority: 15 State: Runnable @end smallexample @item task @kindex task@r{ (Ada)} @cindex current Ada task ID This command prints the ID and name of the current task. @smallexample @iftex @leftskip=0.5cm @end iftex (@value{GDBP}) info tasks ID TID P-ID Pri State Name 1 8077870 0 15 Child Activation Wait main_task * 2 807c458 1 15 Runnable some_task (@value{GDBP}) task [Current task is 2 "some_task"] @end smallexample @item task @var{taskno} @cindex Ada task switching This command is like the @code{thread @var{thread-id}} command (@pxref{Threads}). It switches the context of debugging from the current task to the given task. @smallexample @iftex @leftskip=0.5cm @end iftex (@value{GDBP}) info tasks ID TID P-ID Pri State Name 1 8077870 0 15 Child Activation Wait main_task * 2 807c458 1 15 Runnable some_task (@value{GDBP}) task 1 [Switching to task 1 "main_task"] #0 0x8067726 in pthread_cond_wait () (@value{GDBP}) bt #0 0x8067726 in pthread_cond_wait () #1 0x8056714 in system.os_interface.pthread_cond_wait () #2 0x805cb63 in system.task_primitives.operations.sleep () #3 0x806153e in system.tasking.stages.activate_tasks () #4 0x804aacc in un () at un.adb:5 @end smallexample @item break @var{location} task @var{taskno} @itemx break @var{location} task @var{taskno} if @dots{} @cindex breakpoints and tasks, in Ada @cindex task breakpoints, in Ada @kindex break @dots{} task @var{taskno}@r{ (Ada)} These commands are like the @code{break @dots{} thread @dots{}} command (@pxref{Thread Stops}). The @var{location} argument specifies source lines, as described in @ref{Specify Location}. Use the qualifier @samp{task @var{taskno}} with a breakpoint command to specify that you only want @value{GDBN} to stop the program when a particular Ada task reaches this breakpoint. The @var{taskno} is one of the numeric task identifiers assigned by @value{GDBN}, shown in the first column of the @samp{info tasks} display. If you do not specify @samp{task @var{taskno}} when you set a breakpoint, the breakpoint applies to @emph{all} tasks of your program. You can use the @code{task} qualifier on conditional breakpoints as well; in this case, place @samp{task @var{taskno}} before the breakpoint condition (before the @code{if}). For example, @smallexample @iftex @leftskip=0.5cm @end iftex (@value{GDBP}) info tasks ID TID P-ID Pri State Name 1 140022020 0 15 Child Activation Wait main_task 2 140045060 1 15 Accept/Select Wait t2 3 140044840 1 15 Runnable t1 * 4 140056040 1 15 Runnable t3 (@value{GDBP}) b 15 task 2 Breakpoint 5 at 0x120044cb0: file test_task_debug.adb, line 15. (@value{GDBP}) cont Continuing. task # 1 running task # 2 running Breakpoint 5, test_task_debug () at test_task_debug.adb:15 15 flush; (@value{GDBP}) info tasks ID TID P-ID Pri State Name 1 140022020 0 15 Child Activation Wait main_task * 2 140045060 1 15 Runnable t2 3 140044840 1 15 Runnable t1 4 140056040 1 15 Delay Sleep t3 @end smallexample @end table @node Ada Tasks and Core Files @subsubsection Tasking Support when Debugging Core Files @cindex Ada tasking and core file debugging When inspecting a core file, as opposed to debugging a live program, tasking support may be limited or even unavailable, depending on the platform being used. For instance, on x86-linux, the list of tasks is available, but task switching is not supported. On certain platforms, the debugger needs to perform some memory writes in order to provide Ada tasking support. When inspecting a core file, this means that the core file must be opened with read-write privileges, using the command @samp{"set write on"} (@pxref{Patching}). Under these circumstances, you should make a backup copy of the core file before inspecting it with @value{GDBN}. @node Ravenscar Profile @subsubsection Tasking Support when using the Ravenscar Profile @cindex Ravenscar Profile The @dfn{Ravenscar Profile} is a subset of the Ada tasking features, specifically designed for systems with safety-critical real-time requirements. @table @code @kindex set ravenscar task-switching on @cindex task switching with program using Ravenscar Profile @item set ravenscar task-switching on Allows task switching when debugging a program that uses the Ravenscar Profile. This is the default. @kindex set ravenscar task-switching off @item set ravenscar task-switching off Turn off task switching when debugging a program that uses the Ravenscar Profile. This is mostly intended to disable the code that adds support for the Ravenscar Profile, in case a bug in either @value{GDBN} or in the Ravenscar runtime is preventing @value{GDBN} from working properly. To be effective, this command should be run before the program is started. @kindex show ravenscar task-switching @item show ravenscar task-switching Show whether it is possible to switch from task to task in a program using the Ravenscar Profile. @end table @node Ada Settings @subsubsection Ada Settings @cindex Ada settings @table @code @kindex set varsize-limit @item set varsize-limit @var{size} Prevent @value{GDBN} from attempting to evaluate objects whose size is above the given limit (@var{size}) when those sizes are computed from run-time quantities. This is typically the case when the object has a variable size, such as an array whose bounds are not known at compile time for example. Setting @var{size} to @code{unlimited} removes the size limitation. By default, the limit is about 65KB. The purpose of having such a limit is to prevent @value{GDBN} from trying to grab enormous chunks of virtual memory when asked to evaluate a quantity whose bounds have been corrupted or have not yet been fully initialized. The limit applies to the results of some subexpressions as well as to complete expressions. For example, an expression denoting a simple integer component, such as @code{x.y.z}, may fail if the size of @code{x.y} is variable and exceeds @code{size}. On the other hand, @value{GDBN} is sometimes clever; the expression @code{A(i)}, where @code{A} is an array variable with non-constant size, will generally succeed regardless of the bounds on @code{A}, as long as the component size is less than @var{size}. @kindex show varsize-limit @item show varsize-limit Show the limit on types whose size is determined by run-time quantities. @end table @node Ada Glitches @subsubsection Known Peculiarities of Ada Mode @cindex Ada, problems Besides the omissions listed previously (@pxref{Omissions from Ada}), we know of several problems with and limitations of Ada mode in @value{GDBN}, some of which will be fixed with planned future releases of the debugger and the GNU Ada compiler. @itemize @bullet @item Static constants that the compiler chooses not to materialize as objects in storage are invisible to the debugger. @item Named parameter associations in function argument lists are ignored (the argument lists are treated as positional). @item Many useful library packages are currently invisible to the debugger. @item Fixed-point arithmetic, conversions, input, and output is carried out using floating-point arithmetic, and may give results that only approximate those on the host machine. @item The GNAT compiler never generates the prefix @code{Standard} for any of the standard symbols defined by the Ada language. @value{GDBN} knows about this: it will strip the prefix from names when you use it, and will never look for a name you have so qualified among local symbols, nor match against symbols in other packages or subprograms. If you have defined entities anywhere in your program other than parameters and local variables whose simple names match names in @code{Standard}, GNAT's lack of qualification here can cause confusion. When this happens, you can usually resolve the confusion by qualifying the problematic names with package @code{Standard} explicitly. @end itemize Older versions of the compiler sometimes generate erroneous debugging information, resulting in the debugger incorrectly printing the value of affected entities. In some cases, the debugger is able to work around an issue automatically. In other cases, the debugger is able to work around the issue, but the work-around has to be specifically enabled. @kindex set ada trust-PAD-over-XVS @kindex show ada trust-PAD-over-XVS @table @code @item set ada trust-PAD-over-XVS on Configure GDB to strictly follow the GNAT encoding when computing the value of Ada entities, particularly when @code{PAD} and @code{PAD___XVS} types are involved (see @code{ada/exp_dbug.ads} in the GCC sources for a complete description of the encoding used by the GNAT compiler). This is the default. @item set ada trust-PAD-over-XVS off This is related to the encoding using by the GNAT compiler. If @value{GDBN} sometimes prints the wrong value for certain entities, changing @code{ada trust-PAD-over-XVS} to @code{off} activates a work-around which may fix the issue. It is always safe to set @code{ada trust-PAD-over-XVS} to @code{off}, but this incurs a slight performance penalty, so it is recommended to leave this setting to @code{on} unless necessary. @end table @cindex GNAT descriptive types @cindex GNAT encoding Internally, the debugger also relies on the compiler following a number of conventions known as the @samp{GNAT Encoding}, all documented in @file{gcc/ada/exp_dbug.ads} in the GCC sources. This encoding describes how the debugging information should be generated for certain types. In particular, this convention makes use of @dfn{descriptive types}, which are artificial types generated purely to help the debugger. These encodings were defined at a time when the debugging information format used was not powerful enough to describe some of the more complex types available in Ada. Since DWARF allows us to express nearly all Ada features, the long-term goal is to slowly replace these descriptive types by their pure DWARF equivalent. To facilitate that transition, a new maintenance option is available to force the debugger to ignore those descriptive types. It allows the user to quickly evaluate how well @value{GDBN} works without them. @table @code @kindex maint ada set ignore-descriptive-types @item maintenance ada set ignore-descriptive-types [on|off] Control whether the debugger should ignore descriptive types. The default is not to ignore descriptives types (@code{off}). @kindex maint ada show ignore-descriptive-types @item maintenance ada show ignore-descriptive-types Show if descriptive types are ignored by @value{GDBN}. @end table @node Unsupported Languages @section Unsupported Languages @cindex unsupported languages @cindex minimal language In addition to the other fully-supported programming languages, @value{GDBN} also provides a pseudo-language, called @code{minimal}. It does not represent a real programming language, but provides a set of capabilities close to what the C or assembly languages provide. This should allow most simple operations to be performed while debugging an application that uses a language currently not supported by @value{GDBN}. If the language is set to @code{auto}, @value{GDBN} will automatically select this language if the current frame corresponds to an unsupported language. @node Symbols @chapter Examining the Symbol Table The commands described in this chapter allow you to inquire about the symbols (names of variables, functions and types) defined in your program. This information is inherent in the text of your program and does not change as your program executes. @value{GDBN} finds it in your program's symbol table, in the file indicated when you started @value{GDBN} (@pxref{File Options, ,Choosing Files}), or by one of the file-management commands (@pxref{Files, ,Commands to Specify Files}). @cindex symbol names @cindex names of symbols @cindex quoting names @anchor{quoting names} Occasionally, you may need to refer to symbols that contain unusual characters, which @value{GDBN} ordinarily treats as word delimiters. The most frequent case is in referring to static variables in other source files (@pxref{Variables,,Program Variables}). File names are recorded in object files as debugging symbols, but @value{GDBN} would ordinarily parse a typical file name, like @file{foo.c}, as the three words @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize @samp{foo.c} as a single symbol, enclose it in single quotes; for example, @smallexample p 'foo.c'::x @end smallexample @noindent looks up the value of @code{x} in the scope of the file @file{foo.c}. @table @code @cindex case-insensitive symbol names @cindex case sensitivity in symbol names @kindex set case-sensitive @item set case-sensitive on @itemx set case-sensitive off @itemx set case-sensitive auto Normally, when @value{GDBN} looks up symbols, it matches their names with case sensitivity determined by the current source language. Occasionally, you may wish to control that. The command @code{set case-sensitive} lets you do that by specifying @code{on} for case-sensitive matches or @code{off} for case-insensitive ones. If you specify @code{auto}, case sensitivity is reset to the default suitable for the source language. The default is case-sensitive matches for all languages except for Fortran, for which the default is case-insensitive matches. @kindex show case-sensitive @item show case-sensitive This command shows the current setting of case sensitivity for symbols lookups. @kindex set print type methods @item set print type methods @itemx set print type methods on @itemx set print type methods off Normally, when @value{GDBN} prints a class, it displays any methods declared in that class. You can control this behavior either by passing the appropriate flag to @code{ptype}, or using @command{set print type methods}. Specifying @code{on} will cause @value{GDBN} to display the methods; this is the default. Specifying @code{off} will cause @value{GDBN} to omit the methods. @kindex show print type methods @item show print type methods This command shows the current setting of method display when printing classes. @kindex set print type nested-type-limit @item set print type nested-type-limit @var{limit} @itemx set print type nested-type-limit unlimited Set the limit of displayed nested types that the type printer will show. A @var{limit} of @code{unlimited} or @code{-1} will show all nested definitions. By default, the type printer will not show any nested types defined in classes. @kindex show print type nested-type-limit @item show print type nested-type-limit This command shows the current display limit of nested types when printing classes. @kindex set print type typedefs @item set print type typedefs @itemx set print type typedefs on @itemx set print type typedefs off Normally, when @value{GDBN} prints a class, it displays any typedefs defined in that class. You can control this behavior either by passing the appropriate flag to @code{ptype}, or using @command{set print type typedefs}. Specifying @code{on} will cause @value{GDBN} to display the typedef definitions; this is the default. Specifying @code{off} will cause @value{GDBN} to omit the typedef definitions. Note that this controls whether the typedef definition itself is printed, not whether typedef names are substituted when printing other types. @kindex show print type typedefs @item show print type typedefs This command shows the current setting of typedef display when printing classes. @kindex info address @cindex address of a symbol @item info address @var{symbol} Describe where the data for @var{symbol} is stored. For a register variable, this says which register it is kept in. For a non-register local variable, this prints the stack-frame offset at which the variable is always stored. Note the contrast with @samp{print &@var{symbol}}, which does not work at all for a register variable, and for a stack local variable prints the exact address of the current instantiation of the variable. @kindex info symbol @cindex symbol from address @cindex closest symbol and offset for an address @item info symbol @var{addr} Print the name of a symbol which is stored at the address @var{addr}. If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the nearest symbol and an offset from it: @smallexample (@value{GDBP}) info symbol 0x54320 _initialize_vx + 396 in section .text @end smallexample @noindent This is the opposite of the @code{info address} command. You can use it to find out the name of a variable or a function given its address. For dynamically linked executables, the name of executable or shared library containing the symbol is also printed: @smallexample (@value{GDBP}) info symbol 0x400225 _start + 5 in section .text of /tmp/a.out (@value{GDBP}) info symbol 0x2aaaac2811cf __read_nocancel + 6 in section .text of /usr/lib64/libc.so.6 @end smallexample @kindex demangle @cindex demangle @item demangle @r{[}-l @var{language}@r{]} @r{[}@var{--}@r{]} @var{name} Demangle @var{name}. If @var{language} is provided it is the name of the language to demangle @var{name} in. Otherwise @var{name} is demangled in the current language. The @samp{--} option specifies the end of options, and is useful when @var{name} begins with a dash. The parameter @code{demangle-style} specifies how to interpret the kind of mangling used. @xref{Print Settings}. @kindex whatis @item whatis[/@var{flags}] [@var{arg}] Print the data type of @var{arg}, which can be either an expression or a name of a data type. With no argument, print the data type of @code{$}, the last value in the value history. If @var{arg} is an expression (@pxref{Expressions, ,Expressions}), it is not actually evaluated, and any side-effecting operations (such as assignments or function calls) inside it do not take place. If @var{arg} is a variable or an expression, @code{whatis} prints its literal type as it is used in the source code. If the type was defined using a @code{typedef}, @code{whatis} will @emph{not} print the data type underlying the @code{typedef}. If the type of the variable or the expression is a compound data type, such as @code{struct} or @code{class}, @code{whatis} never prints their fields or methods. It just prints the @code{struct}/@code{class} name (a.k.a.@: its @dfn{tag}). If you want to see the members of such a compound data type, use @code{ptype}. If @var{arg} is a type name that was defined using @code{typedef}, @code{whatis} @dfn{unrolls} only one level of that @code{typedef}. Unrolling means that @code{whatis} will show the underlying type used in the @code{typedef} declaration of @var{arg}. However, if that underlying type is also a @code{typedef}, @code{whatis} will not unroll it. For C code, the type names may also have the form @samp{class @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or @samp{enum @var{enum-tag}}. @var{flags} can be used to modify how the type is displayed. Available flags are: @table @code @item r Display in ``raw'' form. Normally, @value{GDBN} substitutes template parameters and typedefs defined in a class when printing the class' members. The @code{/r} flag disables this. @item m Do not print methods defined in the class. @item M Print methods defined in the class. This is the default, but the flag exists in case you change the default with @command{set print type methods}. @item t Do not print typedefs defined in the class. Note that this controls whether the typedef definition itself is printed, not whether typedef names are substituted when printing other types. @item T Print typedefs defined in the class. This is the default, but the flag exists in case you change the default with @command{set print type typedefs}. @item o Print the offsets and sizes of fields in a struct, similar to what the @command{pahole} tool does. This option implies the @code{/tm} flags. For example, given the following declarations: @smallexample struct tuv @{ int a1; char *a2; int a3; @}; struct xyz @{ int f1; char f2; void *f3; struct tuv f4; @}; union qwe @{ struct tuv fff1; struct xyz fff2; @}; struct tyu @{ int a1 : 1; int a2 : 3; int a3 : 23; char a4 : 2; int64_t a5; int a6 : 5; int64_t a7 : 3; @}; @end smallexample Issuing a @kbd{ptype /o struct tuv} command would print: @smallexample (@value{GDBP}) ptype /o struct tuv /* offset | size */ type = struct tuv @{ /* 0 | 4 */ int a1; /* XXX 4-byte hole */ /* 8 | 8 */ char *a2; /* 16 | 4 */ int a3; /* total size (bytes): 24 */ @} @end smallexample Notice the format of the first column of comments. There, you can find two parts separated by the @samp{|} character: the @emph{offset}, which indicates where the field is located inside the struct, in bytes, and the @emph{size} of the field. Another interesting line is the marker of a @emph{hole} in the struct, indicating that it may be possible to pack the struct and make it use less space by reorganizing its fields. It is also possible to print offsets inside an union: @smallexample (@value{GDBP}) ptype /o union qwe /* offset | size */ type = union qwe @{ /* 24 */ struct tuv @{ /* 0 | 4 */ int a1; /* XXX 4-byte hole */ /* 8 | 8 */ char *a2; /* 16 | 4 */ int a3; /* total size (bytes): 24 */ @} fff1; /* 40 */ struct xyz @{ /* 0 | 4 */ int f1; /* 4 | 1 */ char f2; /* XXX 3-byte hole */ /* 8 | 8 */ void *f3; /* 16 | 24 */ struct tuv @{ /* 16 | 4 */ int a1; /* XXX 4-byte hole */ /* 24 | 8 */ char *a2; /* 32 | 4 */ int a3; /* total size (bytes): 24 */ @} f4; /* total size (bytes): 40 */ @} fff2; /* total size (bytes): 40 */ @} @end smallexample In this case, since @code{struct tuv} and @code{struct xyz} occupy the same space (because we are dealing with an union), the offset is not printed for them. However, you can still examine the offset of each of these structures' fields. Another useful scenario is printing the offsets of a struct containing bitfields: @smallexample (@value{GDBP}) ptype /o struct tyu /* offset | size */ type = struct tyu @{ /* 0:31 | 4 */ int a1 : 1; /* 0:28 | 4 */ int a2 : 3; /* 0: 5 | 4 */ int a3 : 23; /* 3: 3 | 1 */ signed char a4 : 2; /* XXX 3-bit hole */ /* XXX 4-byte hole */ /* 8 | 8 */ int64_t a5; /* 16: 0 | 4 */ int a6 : 5; /* 16: 5 | 8 */ int64_t a7 : 3; "/* XXX 7-byte padding */ /* total size (bytes): 24 */ @} @end smallexample Note how the offset information is now extended to also include the first bit of the bitfield. @end table @kindex ptype @item ptype[/@var{flags}] [@var{arg}] @code{ptype} accepts the same arguments as @code{whatis}, but prints a detailed description of the type, instead of just the name of the type. @xref{Expressions, ,Expressions}. Contrary to @code{whatis}, @code{ptype} always unrolls any @code{typedef}s in its argument declaration, whether the argument is a variable, expression, or a data type. This means that @code{ptype} of a variable or an expression will not print literally its type as present in the source code---use @code{whatis} for that. @code{typedef}s at the pointer or reference targets are also unrolled. Only @code{typedef}s of fields, methods and inner @code{class typedef}s of @code{struct}s, @code{class}es and @code{union}s are not unrolled even with @code{ptype}. For example, for this variable declaration: @smallexample typedef double real_t; struct complex @{ real_t real; double imag; @}; typedef struct complex complex_t; complex_t var; real_t *real_pointer_var; @end smallexample @noindent the two commands give this output: @smallexample @group (@value{GDBP}) whatis var type = complex_t (@value{GDBP}) ptype var type = struct complex @{ real_t real; double imag; @} (@value{GDBP}) whatis complex_t type = struct complex (@value{GDBP}) whatis struct complex type = struct complex (@value{GDBP}) ptype struct complex type = struct complex @{ real_t real; double imag; @} (@value{GDBP}) whatis real_pointer_var type = real_t * (@value{GDBP}) ptype real_pointer_var type = double * @end group @end smallexample @noindent As with @code{whatis}, using @code{ptype} without an argument refers to the type of @code{$}, the last value in the value history. @cindex incomplete type Sometimes, programs use opaque data types or incomplete specifications of complex data structure. If the debug information included in the program does not allow @value{GDBN} to display a full declaration of the data type, it will say @samp{<incomplete type>}. For example, given these declarations: @smallexample struct foo; struct foo *fooptr; @end smallexample @noindent but no definition for @code{struct foo} itself, @value{GDBN} will say: @smallexample (@value{GDBP}) ptype foo $1 = <incomplete type> @end smallexample @noindent ``Incomplete type'' is C terminology for data types that are not completely specified. @cindex unknown type Othertimes, information about a variable's type is completely absent from the debug information included in the program. This most often happens when the program or library where the variable is defined includes no debug information at all. @value{GDBN} knows the variable exists from inspecting the linker/loader symbol table (e.g., the ELF dynamic symbol table), but such symbols do not contain type information. Inspecting the type of a (global) variable for which @value{GDBN} has no type information shows: @smallexample (@value{GDBP}) ptype var type = <data variable, no debug info> @end smallexample @xref{Variables, no debug info variables}, for how to print the values of such variables. @kindex info types @item info types [-q] [@var{regexp}] Print a brief description of all types whose names match the regular expression @var{regexp} (or all types in your program, if you supply no argument). Each complete typename is matched as though it were a complete line; thus, @samp{i type value} gives information on all types in your program whose names include the string @code{value}, but @samp{i type ^value$} gives information only on types whose complete name is @code{value}. In programs using different languages, @value{GDBN} chooses the syntax to print the type description according to the @samp{set language} value: using @samp{set language auto} (see @ref{Automatically, ,Set Language Automatically}) means to use the language of the type, other values mean to use the manually specified language (see @ref{Manually, ,Set Language Manually}). This command differs from @code{ptype} in two ways: first, like @code{whatis}, it does not print a detailed description; second, it lists all source files and line numbers where a type is defined. The output from @samp{into types} is proceeded with a header line describing what types are being listed. The optional flag @samp{-q}, which stands for @samp{quiet}, disables printing this header information. @kindex info type-printers @item info type-printers Versions of @value{GDBN} that ship with Python scripting enabled may have ``type printers'' available. When using @command{ptype} or @command{whatis}, these printers are consulted when the name of a type is needed. @xref{Type Printing API}, for more information on writing type printers. @code{info type-printers} displays all the available type printers. @kindex enable type-printer @kindex disable type-printer @item enable type-printer @var{name}@dots{} @item disable type-printer @var{name}@dots{} These commands can be used to enable or disable type printers. @kindex info scope @cindex local variables @item info scope @var{location} List all the variables local to a particular scope. This command accepts a @var{location} argument---a function name, a source line, or an address preceded by a @samp{*}, and prints all the variables local to the scope defined by that location. (@xref{Specify Location}, for details about supported forms of @var{location}.) For example: @smallexample (@value{GDBP}) @b{info scope command_line_handler} Scope for command_line_handler: Symbol rl is an argument at stack/frame offset 8, length 4. Symbol linebuffer is in static storage at address 0x150a18, length 4. Symbol linelength is in static storage at address 0x150a1c, length 4. Symbol p is a local variable in register $esi, length 4. Symbol p1 is a local variable in register $ebx, length 4. Symbol nline is a local variable in register $edx, length 4. Symbol repeat is a local variable at frame offset -8, length 4. @end smallexample @noindent This command is especially useful for determining what data to collect during a @dfn{trace experiment}, see @ref{Tracepoint Actions, collect}. @kindex info source @item info source Show information about the current source file---that is, the source file for the function containing the current point of execution: @itemize @bullet @item the name of the source file, and the directory containing it, @item the directory it was compiled in, @item its length, in lines, @item which programming language it is written in, @item if the debug information provides it, the program that compiled the file (which may include, e.g., the compiler version and command line arguments), @item whether the executable includes debugging information for that file, and if so, what format the information is in (e.g., STABS, Dwarf 2, etc.), and @item whether the debugging information includes information about preprocessor macros. @end itemize @kindex info sources @item info sources Print the names of all source files in your program for which there is debugging information, organized into two lists: files whose symbols have already been read, and files whose symbols will be read when needed. @item info sources [-dirname | -basename] [--] [@var{regexp}] Like @samp{info sources}, but only print the names of the files matching the provided @var{regexp}. By default, the @var{regexp} is used to match anywhere in the filename. If @code{-dirname}, only files having a dirname matching @var{regexp} are shown. If @code{-basename}, only files having a basename matching @var{regexp} are shown. The matching is case-sensitive, except on operating systems that have case-insensitive filesystem (e.g., MS-Windows). @kindex info functions @item info functions [-q] [-n] Print the names and data types of all defined functions. Similarly to @samp{info types}, this command groups its output by source files and annotates each function definition with its source line number. In programs using different languages, @value{GDBN} chooses the syntax to print the function name and type according to the @samp{set language} value: using @samp{set language auto} (see @ref{Automatically, ,Set Language Automatically}) means to use the language of the function, other values mean to use the manually specified language (see @ref{Manually, ,Set Language Manually}). The @samp{-n} flag excludes @dfn{non-debugging symbols} from the results. A non-debugging symbol is a symbol that comes from the executable's symbol table, not from the debug information (for example, DWARF) associated with the executable. The optional flag @samp{-q}, which stands for @samp{quiet}, disables printing header information and messages explaining why no functions have been printed. @item info functions [-q] [-n] [-t @var{type_regexp}] [@var{regexp}] Like @samp{info functions}, but only print the names and data types of the functions selected with the provided regexp(s). If @var{regexp} is provided, print only the functions whose names match the regular expression @var{regexp}. Thus, @samp{info fun step} finds all functions whose names include @code{step}; @samp{info fun ^step} finds those whose names start with @code{step}. If a function name contains characters that conflict with the regular expression language (e.g.@: @samp{operator*()}), they may be quoted with a backslash. If @var{type_regexp} is provided, print only the functions whose types, as printed by the @code{whatis} command, match the regular expression @var{type_regexp}. If @var{type_regexp} contains space(s), it should be enclosed in quote characters. If needed, use backslash to escape the meaning of special characters or quotes. Thus, @samp{info fun -t '^int ('} finds the functions that return an integer; @samp{info fun -t '(.*int.*'} finds the functions that have an argument type containing int; @samp{info fun -t '^int (' ^step} finds the functions whose names start with @code{step} and that return int. If both @var{regexp} and @var{type_regexp} are provided, a function is printed only if its name matches @var{regexp} and its type matches @var{type_regexp}. @kindex info variables @item info variables [-q] [-n] Print the names and data types of all variables that are defined outside of functions (i.e.@: excluding local variables). The printed variables are grouped by source files and annotated with their respective source line numbers. In programs using different languages, @value{GDBN} chooses the syntax to print the variable name and type according to the @samp{set language} value: using @samp{set language auto} (see @ref{Automatically, ,Set Language Automatically}) means to use the language of the variable, other values mean to use the manually specified language (see @ref{Manually, ,Set Language Manually}). The @samp{-n} flag excludes non-debugging symbols from the results. The optional flag @samp{-q}, which stands for @samp{quiet}, disables printing header information and messages explaining why no variables have been printed. @item info variables [-q] [-n] [-t @var{type_regexp}] [@var{regexp}] Like @kbd{info variables}, but only print the variables selected with the provided regexp(s). If @var{regexp} is provided, print only the variables whose names match the regular expression @var{regexp}. If @var{type_regexp} is provided, print only the variables whose types, as printed by the @code{whatis} command, match the regular expression @var{type_regexp}. If @var{type_regexp} contains space(s), it should be enclosed in quote characters. If needed, use backslash to escape the meaning of special characters or quotes. If both @var{regexp} and @var{type_regexp} are provided, an argument is printed only if its name matches @var{regexp} and its type matches @var{type_regexp}. @kindex info modules @cindex modules @item info modules @r{[}-q@r{]} @r{[}@var{regexp}@r{]} List all Fortran modules in the program, or all modules matching the optional regular expression @var{regexp}. The optional flag @samp{-q}, which stands for @samp{quiet}, disables printing header information and messages explaining why no modules have been printed. @kindex info module @cindex Fortran modules, information about @cindex functions and variables by Fortran module @cindex module functions and variables @item info module functions @r{[}-q@r{]} @r{[}-m @var{module-regexp}@r{]} @r{[}-t @var{type-regexp}@r{]} @r{[}@var{regexp}@r{]} @itemx info module variables @r{[}-q@r{]} @r{[}-m @var{module-regexp}@r{]} @r{[}-t @var{type-regexp}@r{]} @r{[}@var{regexp}@r{]} List all functions or variables within all Fortran modules. The set of functions or variables listed can be limited by providing some or all of the optional regular expressions. If @var{module-regexp} is provided, then only Fortran modules matching @var{module-regexp} will be searched. Only functions or variables whose type matches the optional regular expression @var{type-regexp} will be listed. And only functions or variables whose name matches the optional regular expression @var{regexp} will be listed. The optional flag @samp{-q}, which stands for @samp{quiet}, disables printing header information and messages explaining why no functions or variables have been printed. @kindex info classes @cindex Objective-C, classes and selectors @item info classes @itemx info classes @var{regexp} Display all Objective-C classes in your program, or (with the @var{regexp} argument) all those matching a particular regular expression. @kindex info selectors @item info selectors @itemx info selectors @var{regexp} Display all Objective-C selectors in your program, or (with the @var{regexp} argument) all those matching a particular regular expression. @ignore This was never implemented. @kindex info methods @item info methods @itemx info methods @var{regexp} The @code{info methods} command permits the user to examine all defined methods within C@t{++} program, or (with the @var{regexp} argument) a specific set of methods found in the various C@t{++} classes. Many C@t{++} classes provide a large number of methods. Thus, the output from the @code{ptype} command can be overwhelming and hard to use. The @code{info-methods} command filters the methods, printing only those which match the regular-expression @var{regexp}. @end ignore @cindex opaque data types @kindex set opaque-type-resolution @item set opaque-type-resolution on Tell @value{GDBN} to resolve opaque types. An opaque type is a type declared as a pointer to a @code{struct}, @code{class}, or @code{union}---for example, @code{struct MyType *}---that is used in one source file although the full declaration of @code{struct MyType} is in another source file. The default is on. A change in the setting of this subcommand will not take effect until the next time symbols for a file are loaded. @item set opaque-type-resolution off Tell @value{GDBN} not to resolve opaque types. In this case, the type is printed as follows: @smallexample @{<no data fields>@} @end smallexample @kindex show opaque-type-resolution @item show opaque-type-resolution Show whether opaque types are resolved or not. @kindex set print symbol-loading @cindex print messages when symbols are loaded @item set print symbol-loading @itemx set print symbol-loading full @itemx set print symbol-loading brief @itemx set print symbol-loading off The @code{set print symbol-loading} command allows you to control the printing of messages when @value{GDBN} loads symbol information. By default a message is printed for the executable and one for each shared library, and normally this is what you want. However, when debugging apps with large numbers of shared libraries these messages can be annoying. When set to @code{brief} a message is printed for each executable, and when @value{GDBN} loads a collection of shared libraries at once it will only print one message regardless of the number of shared libraries. When set to @code{off} no messages are printed. @kindex show print symbol-loading @item show print symbol-loading Show whether messages will be printed when a @value{GDBN} command entered from the keyboard causes symbol information to be loaded. @kindex maint print symbols @cindex symbol dump @kindex maint print psymbols @cindex partial symbol dump @kindex maint print msymbols @cindex minimal symbol dump @item maint print symbols @r{[}-pc @var{address}@r{]} @r{[}@var{filename}@r{]} @itemx maint print symbols @r{[}-objfile @var{objfile}@r{]} @r{[}-source @var{source}@r{]} @r{[}--@r{]} @r{[}@var{filename}@r{]} @itemx maint print psymbols @r{[}-objfile @var{objfile}@r{]} @r{[}-pc @var{address}@r{]} @r{[}--@r{]} @r{[}@var{filename}@r{]} @itemx maint print psymbols @r{[}-objfile @var{objfile}@r{]} @r{[}-source @var{source}@r{]} @r{[}--@r{]} @r{[}@var{filename}@r{]} @itemx maint print msymbols @r{[}-objfile @var{objfile}@r{]} @r{[}--@r{]} @r{[}@var{filename}@r{]} Write a dump of debugging symbol data into the file @var{filename} or the terminal if @var{filename} is unspecified. If @code{-objfile @var{objfile}} is specified, only dump symbols for that objfile. If @code{-pc @var{address}} is specified, only dump symbols for the file with code at that address. Note that @var{address} may be a symbol like @code{main}. If @code{-source @var{source}} is specified, only dump symbols for that source file. These commands are used to debug the @value{GDBN} symbol-reading code. These commands do not modify internal @value{GDBN} state, therefore @samp{maint print symbols} will only print symbols for already expanded symbol tables. You can use the command @code{info sources} to find out which files these are. If you use @samp{maint print psymbols} instead, the dump shows information about symbols that @value{GDBN} only knows partially---that is, symbols defined in files that @value{GDBN} has skimmed, but not yet read completely. Finally, @samp{maint print msymbols} just dumps ``minimal symbols'', e.g., ``ELF symbols''. @xref{Files, ,Commands to Specify Files}, for a discussion of how @value{GDBN} reads symbols (in the description of @code{symbol-file}). @kindex maint info symtabs @kindex maint info psymtabs @cindex listing @value{GDBN}'s internal symbol tables @cindex symbol tables, listing @value{GDBN}'s internal @cindex full symbol tables, listing @value{GDBN}'s internal @cindex partial symbol tables, listing @value{GDBN}'s internal @item maint info symtabs @r{[} @var{regexp} @r{]} @itemx maint info psymtabs @r{[} @var{regexp} @r{]} List the @code{struct symtab} or @code{struct partial_symtab} structures whose names match @var{regexp}. If @var{regexp} is not given, list them all. The output includes expressions which you can copy into a @value{GDBN} debugging this one to examine a particular structure in more detail. For example: @smallexample (@value{GDBP}) maint info psymtabs dwarf2read @{ objfile /home/gnu/build/gdb/gdb ((struct objfile *) 0x82e69d0) @{ psymtab /home/gnu/src/gdb/dwarf2read.c ((struct partial_symtab *) 0x8474b10) readin no fullname (null) text addresses 0x814d3c8 -- 0x8158074 globals (* (struct partial_symbol **) 0x8507a08 @@ 9) statics (* (struct partial_symbol **) 0x40e95b78 @@ 2882) dependencies (none) @} @} (@value{GDBP}) maint info symtabs (@value{GDBP}) @end smallexample @noindent We see that there is one partial symbol table whose filename contains the string @samp{dwarf2read}, belonging to the @samp{gdb} executable; and we see that @value{GDBN} has not read in any symtabs yet at all. If we set a breakpoint on a function, that will cause @value{GDBN} to read the symtab for the compilation unit containing that function: @smallexample (@value{GDBP}) break dwarf2_psymtab_to_symtab Breakpoint 1 at 0x814e5da: file /home/gnu/src/gdb/dwarf2read.c, line 1574. (@value{GDBP}) maint info symtabs @{ objfile /home/gnu/build/gdb/gdb ((struct objfile *) 0x82e69d0) @{ symtab /home/gnu/src/gdb/dwarf2read.c ((struct symtab *) 0x86c1f38) dirname (null) fullname (null) blockvector ((struct blockvector *) 0x86c1bd0) (primary) linetable ((struct linetable *) 0x8370fa0) debugformat DWARF 2 @} @} (@value{GDBP}) @end smallexample @kindex maint info line-table @cindex listing @value{GDBN}'s internal line tables @cindex line tables, listing @value{GDBN}'s internal @item maint info line-table @r{[} @var{regexp} @r{]} List the @code{struct linetable} from all @code{struct symtab} instances whose name matches @var{regexp}. If @var{regexp} is not given, list the @code{struct linetable} from all @code{struct symtab}. @kindex maint set symbol-cache-size @cindex symbol cache size @item maint set symbol-cache-size @var{size} Set the size of the symbol cache to @var{size}. The default size is intended to be good enough for debugging most applications. This option exists to allow for experimenting with different sizes. @kindex maint show symbol-cache-size @item maint show symbol-cache-size Show the size of the symbol cache. @kindex maint print symbol-cache @cindex symbol cache, printing its contents @item maint print symbol-cache Print the contents of the symbol cache. This is useful when debugging symbol cache issues. @kindex maint print symbol-cache-statistics @cindex symbol cache, printing usage statistics @item maint print symbol-cache-statistics Print symbol cache usage statistics. This helps determine how well the cache is being utilized. @kindex maint flush-symbol-cache @cindex symbol cache, flushing @item maint flush-symbol-cache Flush the contents of the symbol cache, all entries are removed. This command is useful when debugging the symbol cache. It is also useful when collecting performance data. @end table @node Altering @chapter Altering Execution Once you think you have found an error in your program, you might want to find out for certain whether correcting the apparent error would lead to correct results in the rest of the run. You can find the answer by experiment, using the @value{GDBN} features for altering execution of the program. For example, you can store new values into variables or memory locations, give your program a signal, restart it at a different address, or even return prematurely from a function. @menu * Assignment:: Assignment to variables * Jumping:: Continuing at a different address * Signaling:: Giving your program a signal * Returning:: Returning from a function * Calling:: Calling your program's functions * Patching:: Patching your program * Compiling and Injecting Code:: Compiling and injecting code in @value{GDBN} @end menu @node Assignment @section Assignment to Variables @cindex assignment @cindex setting variables To alter the value of a variable, evaluate an assignment expression. @xref{Expressions, ,Expressions}. For example, @smallexample print x=4 @end smallexample @noindent stores the value 4 into the variable @code{x}, and then prints the value of the assignment expression (which is 4). @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more information on operators in supported languages. @kindex set variable @cindex variables, setting If you are not interested in seeing the value of the assignment, use the @code{set} command instead of the @code{print} command. @code{set} is really the same as @code{print} except that the expression's value is not printed and is not put in the value history (@pxref{Value History, ,Value History}). The expression is evaluated only for its effects. If the beginning of the argument string of the @code{set} command appears identical to a @code{set} subcommand, use the @code{set variable} command instead of just @code{set}. This command is identical to @code{set} except for its lack of subcommands. For example, if your program has a variable @code{width}, you get an error if you try to set a new value with just @samp{set width=13}, because @value{GDBN} has the command @code{set width}: @smallexample (@value{GDBP}) whatis width type = double (@value{GDBP}) p width $4 = 13 (@value{GDBP}) set width=47 Invalid syntax in expression. @end smallexample @noindent The invalid expression, of course, is @samp{=47}. In order to actually set the program's variable @code{width}, use @smallexample (@value{GDBP}) set var width=47 @end smallexample Because the @code{set} command has many subcommands that can conflict with the names of program variables, it is a good idea to use the @code{set variable} command instead of just @code{set}. For example, if your program has a variable @code{g}, you run into problems if you try to set a new value with just @samp{set g=4}, because @value{GDBN} has the command @code{set gnutarget}, abbreviated @code{set g}: @smallexample @group (@value{GDBP}) whatis g type = double (@value{GDBP}) p g $1 = 1 (@value{GDBP}) set g=4 (@value{GDBP}) p g $2 = 1 (@value{GDBP}) r The program being debugged has been started already. Start it from the beginning? (y or n) y Starting program: /home/smith/cc_progs/a.out "/home/smith/cc_progs/a.out": can't open to read symbols: Invalid bfd target. (@value{GDBP}) show g The current BFD target is "=4". @end group @end smallexample @noindent The program variable @code{g} did not change, and you silently set the @code{gnutarget} to an invalid value. In order to set the variable @code{g}, use @smallexample (@value{GDBP}) set var g=4 @end smallexample @value{GDBN} allows more implicit conversions in assignments than C; you can freely store an integer value into a pointer variable or vice versa, and you can convert any structure to any other structure that is the same length or shorter. @comment FIXME: how do structs align/pad in these conversions? @comment /doc@cygnus.com 18dec1990 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}} construct to generate a value of specified type at a specified address (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers to memory location @code{0x83040} as an integer (which implies a certain size and representation in memory), and @smallexample set @{int@}0x83040 = 4 @end smallexample @noindent stores the value 4 into that memory location. @node Jumping @section Continuing at a Different Address Ordinarily, when you continue your program, you do so at the place where it stopped, with the @code{continue} command. You can instead continue at an address of your own choosing, with the following commands: @table @code @kindex jump @kindex j @r{(@code{jump})} @item jump @var{location} @itemx j @var{location} Resume execution at @var{location}. Execution stops again immediately if there is a breakpoint there. @xref{Specify Location}, for a description of the different forms of @var{location}. It is common practice to use the @code{tbreak} command in conjunction with @code{jump}. @xref{Set Breaks, ,Setting Breakpoints}. The @code{jump} command does not change the current stack frame, or the stack pointer, or the contents of any memory location or any register other than the program counter. If @var{location} is in a different function from the one currently executing, the results may be bizarre if the two functions expect different patterns of arguments or of local variables. For this reason, the @code{jump} command requests confirmation if the specified line is not in the function currently executing. However, even bizarre results are predictable if you are well acquainted with the machine-language code of your program. @end table On many systems, you can get much the same effect as the @code{jump} command by storing a new value into the register @code{$pc}. The difference is that this does not start your program running; it only changes the address of where it @emph{will} run when you continue. For example, @smallexample set $pc = 0x485 @end smallexample @noindent makes the next @code{continue} command or stepping command execute at address @code{0x485}, rather than at the address where your program stopped. @xref{Continuing and Stepping, ,Continuing and Stepping}. The most common occasion to use the @code{jump} command is to back up---perhaps with more breakpoints set---over a portion of a program that has already executed, in order to examine its execution in more detail. @c @group @node Signaling @section Giving your Program a Signal @cindex deliver a signal to a program @table @code @kindex signal @item signal @var{signal} Resume execution where your program is stopped, but immediately give it the signal @var{signal}. The @var{signal} can be the name or the number of a signal. For example, on many systems @code{signal 2} and @code{signal SIGINT} are both ways of sending an interrupt signal. Alternatively, if @var{signal} is zero, continue execution without giving a signal. This is useful when your program stopped on account of a signal and would ordinarily see the signal when resumed with the @code{continue} command; @samp{signal 0} causes it to resume without a signal. @emph{Note:} When resuming a multi-threaded program, @var{signal} is delivered to the currently selected thread, not the thread that last reported a stop. This includes the situation where a thread was stopped due to a signal. So if you want to continue execution suppressing the signal that stopped a thread, you should select that same thread before issuing the @samp{signal 0} command. If you issue the @samp{signal 0} command with another thread as the selected one, @value{GDBN} detects that and asks for confirmation. Invoking the @code{signal} command is not the same as invoking the @code{kill} utility from the shell. Sending a signal with @code{kill} causes @value{GDBN} to decide what to do with the signal depending on the signal handling tables (@pxref{Signals}). The @code{signal} command passes the signal directly to your program. @code{signal} does not repeat when you press @key{RET} a second time after executing the command. @kindex queue-signal @item queue-signal @var{signal} Queue @var{signal} to be delivered immediately to the current thread when execution of the thread resumes. The @var{signal} can be the name or the number of a signal. For example, on many systems @code{signal 2} and @code{signal SIGINT} are both ways of sending an interrupt signal. The handling of the signal must be set to pass the signal to the program, otherwise @value{GDBN} will report an error. You can control the handling of signals from @value{GDBN} with the @code{handle} command (@pxref{Signals}). Alternatively, if @var{signal} is zero, any currently queued signal for the current thread is discarded and when execution resumes no signal will be delivered. This is useful when your program stopped on account of a signal and would ordinarily see the signal when resumed with the @code{continue} command. This command differs from the @code{signal} command in that the signal is just queued, execution is not resumed. And @code{queue-signal} cannot be used to pass a signal whose handling state has been set to @code{nopass} (@pxref{Signals}). @end table @c @end group @xref{stepping into signal handlers}, for information on how stepping commands behave when the thread has a signal queued. @node Returning @section Returning from a Function @table @code @cindex returning from a function @kindex return @item return @itemx return @var{expression} You can cancel execution of a function call with the @code{return} command. If you give an @var{expression} argument, its value is used as the function's return value. @end table When you use @code{return}, @value{GDBN} discards the selected stack frame (and all frames within it). You can think of this as making the discarded frame return prematurely. If you wish to specify a value to be returned, give that value as the argument to @code{return}. This pops the selected stack frame (@pxref{Selection, ,Selecting a Frame}), and any other frames inside of it, leaving its caller as the innermost remaining frame. That frame becomes selected. The specified value is stored in the registers used for returning values of functions. The @code{return} command does not resume execution; it leaves the program stopped in the state that would exist if the function had just returned. In contrast, the @code{finish} command (@pxref{Continuing and Stepping, ,Continuing and Stepping}) resumes execution until the selected stack frame returns naturally. @value{GDBN} needs to know how the @var{expression} argument should be set for the inferior. The concrete registers assignment depends on the OS ABI and the type being returned by the selected stack frame. For example it is common for OS ABI to return floating point values in FPU registers while integer values in CPU registers. Still some ABIs return even floating point values in CPU registers. Larger integer widths (such as @code{long long int}) also have specific placement rules. @value{GDBN} already knows the OS ABI from its current target so it needs to find out also the type being returned to make the assignment into the right register(s). Normally, the selected stack frame has debug info. @value{GDBN} will always use the debug info instead of the implicit type of @var{expression} when the debug info is available. For example, if you type @kbd{return -1}, and the function in the current stack frame is declared to return a @code{long long int}, @value{GDBN} transparently converts the implicit @code{int} value of -1 into a @code{long long int}: @smallexample Breakpoint 1, func () at gdb.base/return-nodebug.c:29 29 return 31; (@value{GDBP}) return -1 Make func return now? (y or n) y #0 0x004004f6 in main () at gdb.base/return-nodebug.c:43 43 printf ("result=%lld\n", func ()); (@value{GDBP}) @end smallexample However, if the selected stack frame does not have a debug info, e.g., if the function was compiled without debug info, @value{GDBN} has to find out the type to return from user. Specifying a different type by mistake may set the value in different inferior registers than the caller code expects. For example, typing @kbd{return -1} with its implicit type @code{int} would set only a part of a @code{long long int} result for a debug info less function (on 32-bit architectures). Therefore the user is required to specify the return type by an appropriate cast explicitly: @smallexample Breakpoint 2, 0x0040050b in func () (@value{GDBP}) return -1 Return value type not available for selected stack frame. Please use an explicit cast of the value to return. (@value{GDBP}) return (long long int) -1 Make selected stack frame return now? (y or n) y #0 0x00400526 in main () (@value{GDBP}) @end smallexample @node Calling @section Calling Program Functions @table @code @cindex calling functions @cindex inferior functions, calling @item print @var{expr} Evaluate the expression @var{expr} and display the resulting value. The expression may include calls to functions in the program being debugged. @kindex call @item call @var{expr} Evaluate the expression @var{expr} without displaying @code{void} returned values. You can use this variant of the @code{print} command if you want to execute a function from your program that does not return anything (a.k.a.@: @dfn{a void function}), but without cluttering the output with @code{void} returned values that @value{GDBN} will otherwise print. If the result is not void, it is printed and saved in the value history. @end table It is possible for the function you call via the @code{print} or @code{call} command to generate a signal (e.g., if there's a bug in the function, or if you passed it incorrect arguments). What happens in that case is controlled by the @code{set unwindonsignal} command. Similarly, with a C@t{++} program it is possible for the function you call via the @code{print} or @code{call} command to generate an exception that is not handled due to the constraints of the dummy frame. In this case, any exception that is raised in the frame, but has an out-of-frame exception handler will not be found. GDB builds a dummy-frame for the inferior function call, and the unwinder cannot seek for exception handlers outside of this dummy-frame. What happens in that case is controlled by the @code{set unwind-on-terminating-exception} command. @table @code @item set unwindonsignal @kindex set unwindonsignal @cindex unwind stack in called functions @cindex call dummy stack unwinding Set unwinding of the stack if a signal is received while in a function that @value{GDBN} called in the program being debugged. If set to on, @value{GDBN} unwinds the stack it created for the call and restores the context to what it was before the call. If set to off (the default), @value{GDBN} stops in the frame where the signal was received. @item show unwindonsignal @kindex show unwindonsignal Show the current setting of stack unwinding in the functions called by @value{GDBN}. @item set unwind-on-terminating-exception @kindex set unwind-on-terminating-exception @cindex unwind stack in called functions with unhandled exceptions @cindex call dummy stack unwinding on unhandled exception. Set unwinding of the stack if a C@t{++} exception is raised, but left unhandled while in a function that @value{GDBN} called in the program being debugged. If set to on (the default), @value{GDBN} unwinds the stack it created for the call and restores the context to what it was before the call. If set to off, @value{GDBN} the exception is delivered to the default C@t{++} exception handler and the inferior terminated. @item show unwind-on-terminating-exception @kindex show unwind-on-terminating-exception Show the current setting of stack unwinding in the functions called by @value{GDBN}. @item set may-call-functions @kindex set may-call-functions @cindex disabling calling functions in the program @cindex calling functions in the program, disabling Set permission to call functions in the program. This controls whether @value{GDBN} will attempt to call functions in the program, such as with expressions in the @code{print} command. It defaults to @code{on}. To call a function in the program, @value{GDBN} has to temporarily modify the state of the inferior. This has potentially undesired side effects. Also, having @value{GDBN} call nested functions is likely to be erroneous and may even crash the program being debugged. You can avoid such hazards by forbidding @value{GDBN} from calling functions in the program being debugged. If calling functions in the program is forbidden, GDB will throw an error when a command (such as printing an expression) starts a function call in the program. @item show may-call-functions @kindex show may-call-functions Show permission to call functions in the program. @end table @subsection Calling functions with no debug info @cindex no debug info functions Sometimes, a function you wish to call is missing debug information. In such case, @value{GDBN} does not know the type of the function, including the types of the function's parameters. To avoid calling the inferior function incorrectly, which could result in the called function functioning erroneously and even crash, @value{GDBN} refuses to call the function unless you tell it the type of the function. For prototyped (i.e.@: ANSI/ISO style) functions, there are two ways to do that. The simplest is to cast the call to the function's declared return type. For example: @smallexample (@value{GDBP}) p getenv ("PATH") 'getenv' has unknown return type; cast the call to its declared return type (@value{GDBP}) p (char *) getenv ("PATH") $1 = 0x7fffffffe7ba "/usr/local/bin:/"... @end smallexample Casting the return type of a no-debug function is equivalent to casting the function to a pointer to a prototyped function that has a prototype that matches the types of the passed-in arguments, and calling that. I.e., the call above is equivalent to: @smallexample (@value{GDBP}) p ((char * (*) (const char *)) getenv) ("PATH") @end smallexample @noindent and given this prototyped C or C++ function with float parameters: @smallexample float multiply (float v1, float v2) @{ return v1 * v2; @} @end smallexample @noindent these calls are equivalent: @smallexample (@value{GDBP}) p (float) multiply (2.0f, 3.0f) (@value{GDBP}) p ((float (*) (float, float)) multiply) (2.0f, 3.0f) @end smallexample If the function you wish to call is declared as unprototyped (i.e.@: old K&R style), you must use the cast-to-function-pointer syntax, so that @value{GDBN} knows that it needs to apply default argument promotions (promote float arguments to double). @xref{ABI, float promotion}. For example, given this unprototyped C function with float parameters, and no debug info: @smallexample float multiply_noproto (v1, v2) float v1, v2; @{ return v1 * v2; @} @end smallexample @noindent you call it like this: @smallexample (@value{GDBP}) p ((float (*) ()) multiply_noproto) (2.0f, 3.0f) @end smallexample @node Patching @section Patching Programs @cindex patching binaries @cindex writing into executables @cindex writing into corefiles By default, @value{GDBN} opens the file containing your program's executable code (or the corefile) read-only. This prevents accidental alterations to machine code; but it also prevents you from intentionally patching your program's binary. If you'd like to be able to patch the binary, you can specify that explicitly with the @code{set write} command. For example, you might want to turn on internal debugging flags, or even to make emergency repairs. @table @code @kindex set write @item set write on @itemx set write off If you specify @samp{set write on}, @value{GDBN} opens executable and core files for both reading and writing; if you specify @kbd{set write off} (the default), @value{GDBN} opens them read-only. If you have already loaded a file, you must load it again (using the @code{exec-file} or @code{core-file} command) after changing @code{set write}, for your new setting to take effect. @item show write @kindex show write Display whether executable files and core files are opened for writing as well as reading. @end table @node Compiling and Injecting Code @section Compiling and injecting code in @value{GDBN} @cindex injecting code @cindex writing into executables @cindex compiling code @value{GDBN} supports on-demand compilation and code injection into programs running under @value{GDBN}. GCC 5.0 or higher built with @file{libcc1.so} must be installed for this functionality to be enabled. This functionality is implemented with the following commands. @table @code @kindex compile code @item compile code @var{source-code} @itemx compile code -raw @var{--} @var{source-code} Compile @var{source-code} with the compiler language found as the current language in @value{GDBN} (@pxref{Languages}). If compilation and injection is not supported with the current language specified in @value{GDBN}, or the compiler does not support this feature, an error message will be printed. If @var{source-code} compiles and links successfully, @value{GDBN} will load the object-code emitted, and execute it within the context of the currently selected inferior. It is important to note that the compiled code is executed immediately. After execution, the compiled code is removed from @value{GDBN} and any new types or variables you have defined will be deleted. The command allows you to specify @var{source-code} in two ways. The simplest method is to provide a single line of code to the command. E.g.: @smallexample compile code printf ("hello world\n"); @end smallexample If you specify options on the command line as well as source code, they may conflict. The @samp{--} delimiter can be used to separate options from actual source code. E.g.: @smallexample compile code -r -- printf ("hello world\n"); @end smallexample Alternatively you can enter source code as multiple lines of text. To enter this mode, invoke the @samp{compile code} command without any text following the command. This will start the multiple-line editor and allow you to type as many lines of source code as required. When you have completed typing, enter @samp{end} on its own line to exit the editor. @smallexample compile code >printf ("hello\n"); >printf ("world\n"); >end @end smallexample Specifying @samp{-raw}, prohibits @value{GDBN} from wrapping the provided @var{source-code} in a callable scope. In this case, you must specify the entry point of the code by defining a function named @code{_gdb_expr_}. The @samp{-raw} code cannot access variables of the inferior. Using @samp{-raw} option may be needed for example when @var{source-code} requires @samp{#include} lines which may conflict with inferior symbols otherwise. @kindex compile file @item compile file @var{filename} @itemx compile file -raw @var{filename} Like @code{compile code}, but take the source code from @var{filename}. @smallexample compile file /home/user/example.c @end smallexample @end table @table @code @item compile print [[@var{options}] --] @var{expr} @itemx compile print [[@var{options}] --] /@var{f} @var{expr} Compile and execute @var{expr} with the compiler language found as the current language in @value{GDBN} (@pxref{Languages}). By default the value of @var{expr} is printed in a format appropriate to its data type; you can choose a different format by specifying @samp{/@var{f}}, where @var{f} is a letter specifying the format; see @ref{Output Formats,,Output Formats}. The @code{compile print} command accepts the same options as the @code{print} command; see @ref{print options}. @item compile print [[@var{options}] --] @itemx compile print [[@var{options}] --] /@var{f} @cindex reprint the last value Alternatively you can enter the expression (source code producing it) as multiple lines of text. To enter this mode, invoke the @samp{compile print} command without any text following the command. This will start the multiple-line editor. @end table @noindent The process of compiling and injecting the code can be inspected using: @table @code @anchor{set debug compile} @item set debug compile @cindex compile command debugging info Turns on or off display of @value{GDBN} process of compiling and injecting the code. The default is off. @item show debug compile Displays the current state of displaying @value{GDBN} process of compiling and injecting the code. @anchor{set debug compile-cplus-types} @item set debug compile-cplus-types @cindex compile C@t{++} type conversion Turns on or off the display of C@t{++} type conversion debugging information. The default is off. @item show debug compile-cplus-types Displays the current state of displaying debugging information for C@t{++} type conversion. @end table @subsection Compilation options for the @code{compile} command @value{GDBN} needs to specify the right compilation options for the code to be injected, in part to make its ABI compatible with the inferior and in part to make the injected code compatible with @value{GDBN}'s injecting process. @noindent The options used, in increasing precedence: @table @asis @item target architecture and OS options (@code{gdbarch}) These options depend on target processor type and target operating system, usually they specify at least 32-bit (@code{-m32}) or 64-bit (@code{-m64}) compilation option. @item compilation options recorded in the target @value{NGCC} (since version 4.7) stores the options used for compilation into @code{DW_AT_producer} part of DWARF debugging information according to the @value{NGCC} option @code{-grecord-gcc-switches}. One has to explicitly specify @code{-g} during inferior compilation otherwise @value{NGCC} produces no DWARF. This feature is only relevant for platforms where @code{-g} produces DWARF by default, otherwise one may try to enforce DWARF by using @code{-gdwarf-4}. @item compilation options set by @code{set compile-args} @end table @noindent You can override compilation options using the following command: @table @code @item set compile-args @cindex compile command options override Set compilation options used for compiling and injecting code with the @code{compile} commands. These options override any conflicting ones from the target architecture and/or options stored during inferior compilation. @item show compile-args Displays the current state of compilation options override. This does not show all the options actually used during compilation, use @ref{set debug compile} for that. @end table @subsection Caveats when using the @code{compile} command There are a few caveats to keep in mind when using the @code{compile} command. As the caveats are different per language, the table below highlights specific issues on a per language basis. @table @asis @item C code examples and caveats When the language in @value{GDBN} is set to @samp{C}, the compiler will attempt to compile the source code with a @samp{C} compiler. The source code provided to the @code{compile} command will have much the same access to variables and types as it normally would if it were part of the program currently being debugged in @value{GDBN}. Below is a sample program that forms the basis of the examples that follow. This program has been compiled and loaded into @value{GDBN}, much like any other normal debugging session. @smallexample void function1 (void) @{ int i = 42; printf ("function 1\n"); @} void function2 (void) @{ int j = 12; function1 (); @} int main(void) @{ int k = 6; int *p; function2 (); return 0; @} @end smallexample For the purposes of the examples in this section, the program above has been compiled, loaded into @value{GDBN}, stopped at the function @code{main}, and @value{GDBN} is awaiting input from the user. To access variables and types for any program in @value{GDBN}, the program must be compiled and packaged with debug information. The @code{compile} command is not an exception to this rule. Without debug information, you can still use the @code{compile} command, but you will be very limited in what variables and types you can access. So with that in mind, the example above has been compiled with debug information enabled. The @code{compile} command will have access to all variables and types (except those that may have been optimized out). Currently, as @value{GDBN} has stopped the program in the @code{main} function, the @code{compile} command would have access to the variable @code{k}. You could invoke the @code{compile} command and type some source code to set the value of @code{k}. You can also read it, or do anything with that variable you would normally do in @code{C}. Be aware that changes to inferior variables in the @code{compile} command are persistent. In the following example: @smallexample compile code k = 3; @end smallexample @noindent the variable @code{k} is now 3. It will retain that value until something else in the example program changes it, or another @code{compile} command changes it. Normal scope and access rules apply to source code compiled and injected by the @code{compile} command. In the example, the variables @code{j} and @code{k} are not accessible yet, because the program is currently stopped in the @code{main} function, where these variables are not in scope. Therefore, the following command @smallexample compile code j = 3; @end smallexample @noindent will result in a compilation error message. Once the program is continued, execution will bring these variables in scope, and they will become accessible; then the code you specify via the @code{compile} command will be able to access them. You can create variables and types with the @code{compile} command as part of your source code. Variables and types that are created as part of the @code{compile} command are not visible to the rest of the program for the duration of its run. This example is valid: @smallexample compile code int ff = 5; printf ("ff is %d\n", ff); @end smallexample However, if you were to type the following into @value{GDBN} after that command has completed: @smallexample compile code printf ("ff is %d\n'', ff); @end smallexample @noindent a compiler error would be raised as the variable @code{ff} no longer exists. Object code generated and injected by the @code{compile} command is removed when its execution ends. Caution is advised when assigning to program variables values of variables created by the code submitted to the @code{compile} command. This example is valid: @smallexample compile code int ff = 5; k = ff; @end smallexample The value of the variable @code{ff} is assigned to @code{k}. The variable @code{k} does not require the existence of @code{ff} to maintain the value it has been assigned. However, pointers require particular care in assignment. If the source code compiled with the @code{compile} command changed the address of a pointer in the example program, perhaps to a variable created in the @code{compile} command, that pointer would point to an invalid location when the command exits. The following example would likely cause issues with your debugged program: @smallexample compile code int ff = 5; p = &ff; @end smallexample In this example, @code{p} would point to @code{ff} when the @code{compile} command is executing the source code provided to it. However, as variables in the (example) program persist with their assigned values, the variable @code{p} would point to an invalid location when the command exists. A general rule should be followed in that you should either assign @code{NULL} to any assigned pointers, or restore a valid location to the pointer before the command exits. Similar caution must be exercised with any structs, unions, and typedefs defined in @code{compile} command. Types defined in the @code{compile} command will no longer be available in the next @code{compile} command. Therefore, if you cast a variable to a type defined in the @code{compile} command, care must be taken to ensure that any future need to resolve the type can be achieved. @smallexample (gdb) compile code static struct a @{ int a; @} v = @{ 42 @}; argv = &v; (gdb) compile code printf ("%d\n", ((struct a *) argv)->a); gdb command line:1:36: error: dereferencing pointer to incomplete type ‘struct a’ Compilation failed. (gdb) compile code struct a @{ int a; @}; printf ("%d\n", ((struct a *) argv)->a); 42 @end smallexample Variables that have been optimized away by the compiler are not accessible to the code submitted to the @code{compile} command. Access to those variables will generate a compiler error which @value{GDBN} will print to the console. @end table @subsection Compiler search for the @code{compile} command @value{GDBN} needs to find @value{NGCC} for the inferior being debugged which may not be obvious for remote targets of different architecture than where @value{GDBN} is running. Environment variable @code{PATH} on @value{GDBN} host is searched for @value{NGCC} binary matching the target architecture and operating system. This search can be overriden by @code{set compile-gcc} @value{GDBN} command below. @code{PATH} is taken from shell that executed @value{GDBN}, it is not the value set by @value{GDBN} command @code{set environment}). @xref{Environment}. Specifically @code{PATH} is searched for binaries matching regular expression @code{@var{arch}(-[^-]*)?-@var{os}-gcc} according to the inferior target being debugged. @var{arch} is processor name --- multiarch is supported, so for example both @code{i386} and @code{x86_64} targets look for pattern @code{(x86_64|i.86)} and both @code{s390} and @code{s390x} targets look for pattern @code{s390x?}. @var{os} is currently supported only for pattern @code{linux(-gnu)?}. On Posix hosts the compiler driver @value{GDBN} needs to find also shared library @file{libcc1.so} from the compiler. It is searched in default shared library search path (overridable with usual environment variable @code{LD_LIBRARY_PATH}), unrelated to @code{PATH} or @code{set compile-gcc} settings. Contrary to it @file{libcc1plugin.so} is found according to the installation of the found compiler --- as possibly specified by the @code{set compile-gcc} command. @table @code @item set compile-gcc @cindex compile command driver filename override Set compilation command used for compiling and injecting code with the @code{compile} commands. If this option is not set (it is set to an empty string), the search described above will occur --- that is the default. @item show compile-gcc Displays the current compile command @value{NGCC} driver filename. If set, it is the main command @command{gcc}, found usually for example under name @file{x86_64-linux-gnu-gcc}. @end table @node GDB Files @chapter @value{GDBN} Files @value{GDBN} needs to know the file name of the program to be debugged, both in order to read its symbol table and in order to start your program. To debug a core dump of a previous run, you must also tell @value{GDBN} the name of the core dump file. @menu * Files:: Commands to specify files * File Caching:: Information about @value{GDBN}'s file caching * Separate Debug Files:: Debugging information in separate files * MiniDebugInfo:: Debugging information in a special section * Index Files:: Index files speed up GDB * Symbol Errors:: Errors reading symbol files * Data Files:: GDB data files @end menu @node Files @section Commands to Specify Files @cindex symbol table @cindex core dump file You may want to specify executable and core dump file names. The usual way to do this is at start-up time, using the arguments to @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and Out of @value{GDBN}}). Occasionally it is necessary to change to a different file during a @value{GDBN} session. Or you may run @value{GDBN} and forget to specify a file you want to use. Or you are debugging a remote target via @code{gdbserver} (@pxref{Server, file, Using the @code{gdbserver} Program}). In these situations the @value{GDBN} commands to specify new files are useful. @table @code @cindex executable file @kindex file @item file @var{filename} Use @var{filename} as the program to be debugged. It is read for its symbols and for the contents of pure memory. It is also the program executed when you use the @code{run} command. If you do not specify a directory and the file is not found in the @value{GDBN} working directory, @value{GDBN} uses the environment variable @code{PATH} as a list of directories to search, just as the shell does when looking for a program to run. You can change the value of this variable, for both @value{GDBN} and your program, using the @code{path} command. @cindex unlinked object files @cindex patching object files You can load unlinked object @file{.o} files into @value{GDBN} using the @code{file} command. You will not be able to ``run'' an object file, but you can disassemble functions and inspect variables. Also, if the underlying BFD functionality supports it, you could use @kbd{gdb -write} to patch object files using this technique. Note that @value{GDBN} can neither interpret nor modify relocations in this case, so branches and some initialized variables will appear to go to the wrong place. But this feature is still handy from time to time. @item file @code{file} with no argument makes @value{GDBN} discard any information it has on both executable file and the symbol table. @kindex exec-file @item exec-file @r{[} @var{filename} @r{]} Specify that the program to be run (but not the symbol table) is found in @var{filename}. @value{GDBN} searches the environment variable @code{PATH} if necessary to locate your program. Omitting @var{filename} means to discard information on the executable file. @kindex symbol-file @item symbol-file @r{[} @var{filename} @r{[} -o @var{offset} @r{]]} Read symbol table information from file @var{filename}. @code{PATH} is searched when necessary. Use the @code{file} command to get both symbol table and program to run from the same file. If an optional @var{offset} is specified, it is added to the start address of each section in the symbol file. This is useful if the program is relocated at runtime, such as the Linux kernel with kASLR enabled. @code{symbol-file} with no argument clears out @value{GDBN} information on your program's symbol table. The @code{symbol-file} command causes @value{GDBN} to forget the contents of some breakpoints and auto-display expressions. This is because they may contain pointers to the internal data recording symbols and data types, which are part of the old symbol table data being discarded inside @value{GDBN}. @code{symbol-file} does not repeat if you press @key{RET} again after executing it once. When @value{GDBN} is configured for a particular environment, it understands debugging information in whatever format is the standard generated for that environment; you may use either a @sc{gnu} compiler, or other compilers that adhere to the local conventions. Best results are usually obtained from @sc{gnu} compilers; for example, using @code{@value{NGCC}} you can generate debugging information for optimized code. For most kinds of object files, with the exception of old SVR3 systems using COFF, the @code{symbol-file} command does not normally read the symbol table in full right away. Instead, it scans the symbol table quickly to find which source files and which symbols are present. The details are read later, one source file at a time, as they are needed. The purpose of this two-stage reading strategy is to make @value{GDBN} start up faster. For the most part, it is invisible except for occasional pauses while the symbol table details for a particular source file are being read. (The @code{set verbose} command can turn these pauses into messages if desired. @xref{Messages/Warnings, ,Optional Warnings and Messages}.) We have not implemented the two-stage strategy for COFF yet. When the symbol table is stored in COFF format, @code{symbol-file} reads the symbol table data in full right away. Note that ``stabs-in-COFF'' still does the two-stage strategy, since the debug info is actually in stabs format. @kindex readnow @cindex reading symbols immediately @cindex symbols, reading immediately @item symbol-file @r{[} -readnow @r{]} @var{filename} @itemx file @r{[} -readnow @r{]} @var{filename} You can override the @value{GDBN} two-stage strategy for reading symbol tables by using the @samp{-readnow} option with any of the commands that load symbol table information, if you want to be sure @value{GDBN} has the entire symbol table available. @cindex @code{-readnever}, option for symbol-file command @cindex never read symbols @cindex symbols, never read @item symbol-file @r{[} -readnever @r{]} @var{filename} @itemx file @r{[} -readnever @r{]} @var{filename} You can instruct @value{GDBN} to never read the symbolic information contained in @var{filename} by using the @samp{-readnever} option. @xref{--readnever}. @c FIXME: for now no mention of directories, since this seems to be in @c flux. 13mar1992 status is that in theory GDB would look either in @c current dir or in same dir as myprog; but issues like competing @c GDB's, or clutter in system dirs, mean that in practice right now @c only current dir is used. FFish says maybe a special GDB hierarchy @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol @c files. @kindex core-file @item core-file @r{[}@var{filename}@r{]} @itemx core Specify the whereabouts of a core dump file to be used as the ``contents of memory''. Traditionally, core files contain only some parts of the address space of the process that generated them; @value{GDBN} can access the executable file itself for other parts. @code{core-file} with no argument specifies that no core file is to be used. Note that the core file is ignored when your program is actually running under @value{GDBN}. So, if you have been running your program and you wish to debug a core file instead, you must kill the subprocess in which the program is running. To do this, use the @code{kill} command (@pxref{Kill Process, ,Killing the Child Process}). @kindex add-symbol-file @cindex dynamic linking @item add-symbol-file @var{filename} @r{[} -readnow @r{|} -readnever @r{]} @r{[} -o @var{offset} @r{]} @r{[} @var{textaddress} @r{]} @r{[} -s @var{section} @var{address} @dots{} @r{]} The @code{add-symbol-file} command reads additional symbol table information from the file @var{filename}. You would use this command when @var{filename} has been dynamically loaded (by some other means) into the program that is running. The @var{textaddress} parameter gives the memory address at which the file's text section has been loaded. You can additionally specify the base address of other sections using an arbitrary number of @samp{-s @var{section} @var{address}} pairs. If a section is omitted, @value{GDBN} will use its default addresses as found in @var{filename}. Any @var{address} or @var{textaddress} can be given as an expression. If an optional @var{offset} is specified, it is added to the start address of each section, except those for which the address was specified explicitly. The symbol table of the file @var{filename} is added to the symbol table originally read with the @code{symbol-file} command. You can use the @code{add-symbol-file} command any number of times; the new symbol data thus read is kept in addition to the old. Changes can be reverted using the command @code{remove-symbol-file}. @cindex relocatable object files, reading symbols from @cindex object files, relocatable, reading symbols from @cindex reading symbols from relocatable object files @cindex symbols, reading from relocatable object files @cindex @file{.o} files, reading symbols from Although @var{filename} is typically a shared library file, an executable file, or some other object file which has been fully relocated for loading into a process, you can also load symbolic information from relocatable @file{.o} files, as long as: @itemize @bullet @item the file's symbolic information refers only to linker symbols defined in that file, not to symbols defined by other object files, @item every section the file's symbolic information refers to has actually been loaded into the inferior, as it appears in the file, and @item you can determine the address at which every section was loaded, and provide these to the @code{add-symbol-file} command. @end itemize @noindent Some embedded operating systems, like Sun Chorus and VxWorks, can load relocatable files into an already running program; such systems typically make the requirements above easy to meet. However, it's important to recognize that many native systems use complex link procedures (@code{.linkonce} section factoring and C@t{++} constructor table assembly, for example) that make the requirements difficult to meet. In general, one cannot assume that using @code{add-symbol-file} to read a relocatable object file's symbolic information will have the same effect as linking the relocatable object file into the program in the normal way. @code{add-symbol-file} does not repeat if you press @key{RET} after using it. @kindex remove-symbol-file @item remove-symbol-file @var{filename} @item remove-symbol-file -a @var{address} Remove a symbol file added via the @code{add-symbol-file} command. The file to remove can be identified by its @var{filename} or by an @var{address} that lies within the boundaries of this symbol file in memory. Example: @smallexample (gdb) add-symbol-file /home/user/gdb/mylib.so 0x7ffff7ff9480 add symbol table from file "/home/user/gdb/mylib.so" at .text_addr = 0x7ffff7ff9480 (y or n) y Reading symbols from /home/user/gdb/mylib.so... (gdb) remove-symbol-file -a 0x7ffff7ff9480 Remove symbol table from file "/home/user/gdb/mylib.so"? (y or n) y (gdb) @end smallexample @code{remove-symbol-file} does not repeat if you press @key{RET} after using it. @kindex add-symbol-file-from-memory @cindex @code{syscall DSO} @cindex load symbols from memory @item add-symbol-file-from-memory @var{address} Load symbols from the given @var{address} in a dynamically loaded object file whose image is mapped directly into the inferior's memory. For example, the Linux kernel maps a @code{syscall DSO} into each process's address space; this DSO provides kernel-specific code for some system calls. The argument can be any expression whose evaluation yields the address of the file's shared object file header. For this command to work, you must have used @code{symbol-file} or @code{exec-file} commands in advance. @kindex section @item section @var{section} @var{addr} The @code{section} command changes the base address of the named @var{section} of the exec file to @var{addr}. This can be used if the exec file does not contain section addresses, (such as in the @code{a.out} format), or when the addresses specified in the file itself are wrong. Each section must be changed separately. The @code{info files} command, described below, lists all the sections and their addresses. @kindex info files @kindex info target @item info files @itemx info target @code{info files} and @code{info target} are synonymous; both print the current target (@pxref{Targets, ,Specifying a Debugging Target}), including the names of the executable and core dump files currently in use by @value{GDBN}, and the files from which symbols were loaded. The command @code{help target} lists all possible targets rather than current ones. @kindex maint info sections @item maint info sections Another command that can give you extra information about program sections is @code{maint info sections}. In addition to the section information displayed by @code{info files}, this command displays the flags and file offset of each section in the executable and core dump files. In addition, @code{maint info sections} provides the following command options (which may be arbitrarily combined): @table @code @item ALLOBJ Display sections for all loaded object files, including shared libraries. @item @var{sections} Display info only for named @var{sections}. @item @var{section-flags} Display info only for sections for which @var{section-flags} are true. The section flags that @value{GDBN} currently knows about are: @table @code @item ALLOC Section will have space allocated in the process when loaded. Set for all sections except those containing debug information. @item LOAD Section will be loaded from the file into the child process memory. Set for pre-initialized code and data, clear for @code{.bss} sections. @item RELOC Section needs to be relocated before loading. @item READONLY Section cannot be modified by the child process. @item CODE Section contains executable code only. @item DATA Section contains data only (no executable code). @item ROM Section will reside in ROM. @item CONSTRUCTOR Section contains data for constructor/destructor lists. @item HAS_CONTENTS Section is not empty. @item NEVER_LOAD An instruction to the linker to not output the section. @item COFF_SHARED_LIBRARY A notification to the linker that the section contains COFF shared library information. @item IS_COMMON Section contains common symbols. @end table @end table @kindex set trust-readonly-sections @cindex read-only sections @item set trust-readonly-sections on Tell @value{GDBN} that readonly sections in your object file really are read-only (i.e.@: that their contents will not change). In that case, @value{GDBN} can fetch values from these sections out of the object file, rather than from the target program. For some targets (notably embedded ones), this can be a significant enhancement to debugging performance. The default is off. @item set trust-readonly-sections off Tell @value{GDBN} not to trust readonly sections. This means that the contents of the section might change while the program is running, and must therefore be fetched from the target when needed. @item show trust-readonly-sections Show the current setting of trusting readonly sections. @end table All file-specifying commands allow both absolute and relative file names as arguments. @value{GDBN} always converts the file name to an absolute file name and remembers it that way. @cindex shared libraries @anchor{Shared Libraries} @value{GDBN} supports @sc{gnu}/Linux, MS-Windows, SunOS, Darwin/Mach-O, SVr4, IBM RS/6000 AIX, QNX Neutrino, FDPIC (FR-V), and DSBT (TIC6X) shared libraries. On MS-Windows @value{GDBN} must be linked with the Expat library to support shared libraries. @xref{Expat}. @value{GDBN} automatically loads symbol definitions from shared libraries when you use the @code{run} command, or when you examine a core file. (Before you issue the @code{run} command, @value{GDBN} does not understand references to a function in a shared library, however---unless you are debugging a core file). @c FIXME: some @value{GDBN} release may permit some refs to undef @c FIXME...symbols---eg in a break cmd---assuming they are from a shared @c FIXME...lib; check this from time to time when updating manual There are times, however, when you may wish to not automatically load symbol definitions from shared libraries, such as when they are particularly large or there are many of them. To control the automatic loading of shared library symbols, use the commands: @table @code @kindex set auto-solib-add @item set auto-solib-add @var{mode} If @var{mode} is @code{on}, symbols from all shared object libraries will be loaded automatically when the inferior begins execution, you attach to an independently started inferior, or when the dynamic linker informs @value{GDBN} that a new library has been loaded. If @var{mode} is @code{off}, symbols must be loaded manually, using the @code{sharedlibrary} command. The default value is @code{on}. @cindex memory used for symbol tables If your program uses lots of shared libraries with debug info that takes large amounts of memory, you can decrease the @value{GDBN} memory footprint by preventing it from automatically loading the symbols from shared libraries. To that end, type @kbd{set auto-solib-add off} before running the inferior, then load each library whose debug symbols you do need with @kbd{sharedlibrary @var{regexp}}, where @var{regexp} is a regular expression that matches the libraries whose symbols you want to be loaded. @kindex show auto-solib-add @item show auto-solib-add Display the current autoloading mode. @end table @cindex load shared library To explicitly load shared library symbols, use the @code{sharedlibrary} command: @table @code @kindex info sharedlibrary @kindex info share @item info share @var{regex} @itemx info sharedlibrary @var{regex} Print the names of the shared libraries which are currently loaded that match @var{regex}. If @var{regex} is omitted then print all shared libraries that are loaded. @kindex info dll @item info dll @var{regex} This is an alias of @code{info sharedlibrary}. @kindex sharedlibrary @kindex share @item sharedlibrary @var{regex} @itemx share @var{regex} Load shared object library symbols for files matching a Unix regular expression. As with files loaded automatically, it only loads shared libraries required by your program for a core file or after typing @code{run}. If @var{regex} is omitted all shared libraries required by your program are loaded. @item nosharedlibrary @kindex nosharedlibrary @cindex unload symbols from shared libraries Unload all shared object library symbols. This discards all symbols that have been loaded from all shared libraries. Symbols from shared libraries that were loaded by explicit user requests are not discarded. @end table Sometimes you may wish that @value{GDBN} stops and gives you control when any of shared library events happen. The best way to do this is to use @code{catch load} and @code{catch unload} (@pxref{Set Catchpoints}). @value{GDBN} also supports the the @code{set stop-on-solib-events} command for this. This command exists for historical reasons. It is less useful than setting a catchpoint, because it does not allow for conditions or commands as a catchpoint does. @table @code @item set stop-on-solib-events @kindex set stop-on-solib-events This command controls whether @value{GDBN} should give you control when the dynamic linker notifies it about some shared library event. The most common event of interest is loading or unloading of a new shared library. @item show stop-on-solib-events @kindex show stop-on-solib-events Show whether @value{GDBN} stops and gives you control when shared library events happen. @end table Shared libraries are also supported in many cross or remote debugging configurations. @value{GDBN} needs to have access to the target's libraries; this can be accomplished either by providing copies of the libraries on the host system, or by asking @value{GDBN} to automatically retrieve the libraries from the target. If copies of the target libraries are provided, they need to be the same as the target libraries, although the copies on the target can be stripped as long as the copies on the host are not. @cindex where to look for shared libraries For remote debugging, you need to tell @value{GDBN} where the target libraries are, so that it can load the correct copies---otherwise, it may try to load the host's libraries. @value{GDBN} has two variables to specify the search directories for target libraries. @table @code @cindex prefix for executable and shared library file names @cindex system root, alternate @kindex set solib-absolute-prefix @kindex set sysroot @item set sysroot @var{path} Use @var{path} as the system root for the program being debugged. Any absolute shared library paths will be prefixed with @var{path}; many runtime loaders store the absolute paths to the shared library in the target program's memory. When starting processes remotely, and when attaching to already-running processes (local or remote), their executable filenames will be prefixed with @var{path} if reported to @value{GDBN} as absolute by the operating system. If you use @code{set sysroot} to find executables and shared libraries, they need to be laid out in the same way that they are on the target, with e.g.@: a @file{/bin}, @file{/lib} and @file{/usr/lib} hierarchy under @var{path}. If @var{path} starts with the sequence @file{target:} and the target system is remote then @value{GDBN} will retrieve the target binaries from the remote system. This is only supported when using a remote target that supports the @code{remote get} command (@pxref{File Transfer,,Sending files to a remote system}). The part of @var{path} following the initial @file{target:} (if present) is used as system root prefix on the remote file system. If @var{path} starts with the sequence @file{remote:} this is converted to the sequence @file{target:} by @code{set sysroot}@footnote{Historically the functionality to retrieve binaries from the remote system was provided by prefixing @var{path} with @file{remote:}}. If you want to specify a local system root using a directory that happens to be named @file{target:} or @file{remote:}, you need to use some equivalent variant of the name like @file{./target:}. For targets with an MS-DOS based filesystem, such as MS-Windows and SymbianOS, @value{GDBN} tries prefixing a few variants of the target absolute file name with @var{path}. But first, on Unix hosts, @value{GDBN} converts all backslash directory separators into forward slashes, because the backslash is not a directory separator on Unix: @smallexample c:\foo\bar.dll @result{} c:/foo/bar.dll @end smallexample Then, @value{GDBN} attempts prefixing the target file name with @var{path}, and looks for the resulting file name in the host file system: @smallexample c:/foo/bar.dll @result{} /path/to/sysroot/c:/foo/bar.dll @end smallexample If that does not find the binary, @value{GDBN} tries removing the @samp{:} character from the drive spec, both for convenience, and, for the case of the host file system not supporting file names with colons: @smallexample c:/foo/bar.dll @result{} /path/to/sysroot/c/foo/bar.dll @end smallexample This makes it possible to have a system root that mirrors a target with more than one drive. E.g., you may want to setup your local copies of the target system shared libraries like so (note @samp{c} vs @samp{z}): @smallexample @file{/path/to/sysroot/c/sys/bin/foo.dll} @file{/path/to/sysroot/c/sys/bin/bar.dll} @file{/path/to/sysroot/z/sys/bin/bar.dll} @end smallexample @noindent and point the system root at @file{/path/to/sysroot}, so that @value{GDBN} can find the correct copies of both @file{c:\sys\bin\foo.dll}, and @file{z:\sys\bin\bar.dll}. If that still does not find the binary, @value{GDBN} tries removing the whole drive spec from the target file name: @smallexample c:/foo/bar.dll @result{} /path/to/sysroot/foo/bar.dll @end smallexample This last lookup makes it possible to not care about the drive name, if you don't want or need to. The @code{set solib-absolute-prefix} command is an alias for @code{set sysroot}. @cindex default system root @cindex @samp{--with-sysroot} You can set the default system root by using the configure-time @samp{--with-sysroot} option. If the system root is inside @value{GDBN}'s configured binary prefix (set with @samp{--prefix} or @samp{--exec-prefix}), then the default system root will be updated automatically if the installed @value{GDBN} is moved to a new location. @kindex show sysroot @item show sysroot Display the current executable and shared library prefix. @kindex set solib-search-path @item set solib-search-path @var{path} If this variable is set, @var{path} is a colon-separated list of directories to search for shared libraries. @samp{solib-search-path} is used after @samp{sysroot} fails to locate the library, or if the path to the library is relative instead of absolute. If you want to use @samp{solib-search-path} instead of @samp{sysroot}, be sure to set @samp{sysroot} to a nonexistent directory to prevent @value{GDBN} from finding your host's libraries. @samp{sysroot} is preferred; setting it to a nonexistent directory may interfere with automatic loading of shared library symbols. @kindex show solib-search-path @item show solib-search-path Display the current shared library search path. @cindex DOS file-name semantics of file names. @kindex set target-file-system-kind (unix|dos-based|auto) @kindex show target-file-system-kind @item set target-file-system-kind @var{kind} Set assumed file system kind for target reported file names. Shared library file names as reported by the target system may not make sense as is on the system @value{GDBN} is running on. For example, when remote debugging a target that has MS-DOS based file system semantics, from a Unix host, the target may be reporting to @value{GDBN} a list of loaded shared libraries with file names such as @file{c:\Windows\kernel32.dll}. On Unix hosts, there's no concept of drive letters, so the @samp{c:\} prefix is not normally understood as indicating an absolute file name, and neither is the backslash normally considered a directory separator character. In that case, the native file system would interpret this whole absolute file name as a relative file name with no directory components. This would make it impossible to point @value{GDBN} at a copy of the remote target's shared libraries on the host using @code{set sysroot}, and impractical with @code{set solib-search-path}. Setting @code{target-file-system-kind} to @code{dos-based} tells @value{GDBN} to interpret such file names similarly to how the target would, and to map them to file names valid on @value{GDBN}'s native file system semantics. The value of @var{kind} can be @code{"auto"}, in addition to one of the supported file system kinds. In that case, @value{GDBN} tries to determine the appropriate file system variant based on the current target's operating system (@pxref{ABI, ,Configuring the Current ABI}). The supported file system settings are: @table @code @item unix Instruct @value{GDBN} to assume the target file system is of Unix kind. Only file names starting the forward slash (@samp{/}) character are considered absolute, and the directory separator character is also the forward slash. @item dos-based Instruct @value{GDBN} to assume the target file system is DOS based. File names starting with either a forward slash, or a drive letter followed by a colon (e.g., @samp{c:}), are considered absolute, and both the slash (@samp{/}) and the backslash (@samp{\\}) characters are considered directory separators. @item auto Instruct @value{GDBN} to use the file system kind associated with the target operating system (@pxref{ABI, ,Configuring the Current ABI}). This is the default. @end table @end table @cindex file name canonicalization @cindex base name differences When processing file names provided by the user, @value{GDBN} frequently needs to compare them to the file names recorded in the program's debug info. Normally, @value{GDBN} compares just the @dfn{base names} of the files as strings, which is reasonably fast even for very large programs. (The base name of a file is the last portion of its name, after stripping all the leading directories.) This shortcut in comparison is based upon the assumption that files cannot have more than one base name. This is usually true, but references to files that use symlinks or similar filesystem facilities violate that assumption. If your program records files using such facilities, or if you provide file names to @value{GDBN} using symlinks etc., you can set @code{basenames-may-differ} to @code{true} to instruct @value{GDBN} to completely canonicalize each pair of file names it needs to compare. This will make file-name comparisons accurate, but at a price of a significant slowdown. @table @code @item set basenames-may-differ @kindex set basenames-may-differ Set whether a source file may have multiple base names. @item show basenames-may-differ @kindex show basenames-may-differ Show whether a source file may have multiple base names. @end table @node File Caching @section File Caching @cindex caching of opened files @cindex caching of bfd objects To speed up file loading, and reduce memory usage, @value{GDBN} will reuse the @code{bfd} objects used to track open files. @xref{Top, , BFD, bfd, The Binary File Descriptor Library}. The following commands allow visibility and control of the caching behavior. @table @code @kindex maint info bfds @item maint info bfds This prints information about each @code{bfd} object that is known to @value{GDBN}. @kindex maint set bfd-sharing @kindex maint show bfd-sharing @kindex bfd caching @item maint set bfd-sharing @item maint show bfd-sharing Control whether @code{bfd} objects can be shared. When sharing is enabled @value{GDBN} reuses already open @code{bfd} objects rather than reopening the same file. Turning sharing off does not cause already shared @code{bfd} objects to be unshared, but all future files that are opened will create a new @code{bfd} object. Similarly, re-enabling sharing does not cause multiple existing @code{bfd} objects to be collapsed into a single shared @code{bfd} object. @kindex set debug bfd-cache @var{level} @kindex bfd caching @item set debug bfd-cache @var{level} Turns on debugging of the bfd cache, setting the level to @var{level}. @kindex show debug bfd-cache @kindex bfd caching @item show debug bfd-cache Show the current debugging level of the bfd cache. @end table @node Separate Debug Files @section Debugging Information in Separate Files @cindex separate debugging information files @cindex debugging information in separate files @cindex @file{.debug} subdirectories @cindex debugging information directory, global @cindex global debugging information directories @cindex build ID, and separate debugging files @cindex @file{.build-id} directory @value{GDBN} allows you to put a program's debugging information in a file separate from the executable itself, in a way that allows @value{GDBN} to find and load the debugging information automatically. Since debugging information can be very large---sometimes larger than the executable code itself---some systems distribute debugging information for their executables in separate files, which users can install only when they need to debug a problem. @value{GDBN} supports two ways of specifying the separate debug info file: @itemize @bullet @item The executable contains a @dfn{debug link} that specifies the name of the separate debug info file. The separate debug file's name is usually @file{@var{executable}.debug}, where @var{executable} is the name of the corresponding executable file without leading directories (e.g., @file{ls.debug} for @file{/usr/bin/ls}). In addition, the debug link specifies a 32-bit @dfn{Cyclic Redundancy Check} (CRC) checksum for the debug file, which @value{GDBN} uses to validate that the executable and the debug file came from the same build. @item The executable contains a @dfn{build ID}, a unique bit string that is also present in the corresponding debug info file. (This is supported only on some operating systems, when using the ELF or PE file formats for binary files and the @sc{gnu} Binutils.) For more details about this feature, see the description of the @option{--build-id} command-line option in @ref{Options, , Command Line Options, ld, The GNU Linker}. The debug info file's name is not specified explicitly by the build ID, but can be computed from the build ID, see below. @end itemize Depending on the way the debug info file is specified, @value{GDBN} uses two different methods of looking for the debug file: @itemize @bullet @item For the ``debug link'' method, @value{GDBN} looks up the named file in the directory of the executable file, then in a subdirectory of that directory named @file{.debug}, and finally under each one of the global debug directories, in a subdirectory whose name is identical to the leading directories of the executable's absolute file name. (On MS-Windows/MS-DOS, the drive letter of the executable's leading directories is converted to a one-letter subdirectory, i.e.@: @file{d:/usr/bin/} is converted to @file{/d/usr/bin/}, because Windows filesystems disallow colons in file names.) @item For the ``build ID'' method, @value{GDBN} looks in the @file{.build-id} subdirectory of each one of the global debug directories for a file named @file{@var{nn}/@var{nnnnnnnn}.debug}, where @var{nn} are the first 2 hex characters of the build ID bit string, and @var{nnnnnnnn} are the rest of the bit string. (Real build ID strings are 32 or more hex characters, not 10.) @end itemize So, for example, suppose you ask @value{GDBN} to debug @file{/usr/bin/ls}, which has a debug link that specifies the file @file{ls.debug}, and a build ID whose value in hex is @code{abcdef1234}. If the list of the global debug directories includes @file{/usr/lib/debug}, then @value{GDBN} will look for the following debug information files, in the indicated order: @itemize @minus @item @file{/usr/lib/debug/.build-id/ab/cdef1234.debug} @item @file{/usr/bin/ls.debug} @item @file{/usr/bin/.debug/ls.debug} @item @file{/usr/lib/debug/usr/bin/ls.debug}. @end itemize @anchor{debug-file-directory} Global debugging info directories default to what is set by @value{GDBN} configure option @option{--with-separate-debug-dir}. During @value{GDBN} run you can also set the global debugging info directories, and view the list @value{GDBN} is currently using. @table @code @kindex set debug-file-directory @item set debug-file-directory @var{directories} Set the directories which @value{GDBN} searches for separate debugging information files to @var{directory}. Multiple path components can be set concatenating them by a path separator. @kindex show debug-file-directory @item show debug-file-directory Show the directories @value{GDBN} searches for separate debugging information files. @end table @cindex @code{.gnu_debuglink} sections @cindex debug link sections A debug link is a special section of the executable file named @code{.gnu_debuglink}. The section must contain: @itemize @item A filename, with any leading directory components removed, followed by a zero byte, @item zero to three bytes of padding, as needed to reach the next four-byte boundary within the section, and @item a four-byte CRC checksum, stored in the same endianness used for the executable file itself. The checksum is computed on the debugging information file's full contents by the function given below, passing zero as the @var{crc} argument. @end itemize Any executable file format can carry a debug link, as long as it can contain a section named @code{.gnu_debuglink} with the contents described above. @cindex @code{.note.gnu.build-id} sections @cindex build ID sections The build ID is a special section in the executable file (and in other ELF binary files that @value{GDBN} may consider). This section is often named @code{.note.gnu.build-id}, but that name is not mandatory. It contains unique identification for the built files---the ID remains the same across multiple builds of the same build tree. The default algorithm SHA1 produces 160 bits (40 hexadecimal characters) of the content for the build ID string. The same section with an identical value is present in the original built binary with symbols, in its stripped variant, and in the separate debugging information file. The debugging information file itself should be an ordinary executable, containing a full set of linker symbols, sections, and debugging information. The sections of the debugging information file should have the same names, addresses, and sizes as the original file, but they need not contain any data---much like a @code{.bss} section in an ordinary executable. The @sc{gnu} binary utilities (Binutils) package includes the @samp{objcopy} utility that can produce the separated executable / debugging information file pairs using the following commands: @smallexample @kbd{objcopy --only-keep-debug foo foo.debug} @kbd{strip -g foo} @end smallexample @noindent These commands remove the debugging information from the executable file @file{foo} and place it in the file @file{foo.debug}. You can use the first, second or both methods to link the two files: @itemize @bullet @item The debug link method needs the following additional command to also leave behind a debug link in @file{foo}: @smallexample @kbd{objcopy --add-gnu-debuglink=foo.debug foo} @end smallexample Ulrich Drepper's @file{elfutils} package, starting with version 0.53, contains a version of the @code{strip} command such that the command @kbd{strip foo -f foo.debug} has the same functionality as the two @code{objcopy} commands and the @code{ln -s} command above, together. @item Build ID gets embedded into the main executable using @code{ld --build-id} or the @value{NGCC} counterpart @code{gcc -Wl,--build-id}. Build ID support plus compatibility fixes for debug files separation are present in @sc{gnu} binary utilities (Binutils) package since version 2.18. @end itemize @noindent @cindex CRC algorithm definition The CRC used in @code{.gnu_debuglink} is the CRC-32 defined in IEEE 802.3 using the polynomial: @c TexInfo requires naked braces for multi-digit exponents for Tex @c output, but this causes HTML output to barf. HTML has to be set using @c raw commands. So we end up having to specify this equation in 2 @c different ways! @ifhtml @display @html <em>x</em><sup>32</sup> + <em>x</em><sup>26</sup> + <em>x</em><sup>23</sup> + <em>x</em><sup>22</sup> + <em>x</em><sup>16</sup> + <em>x</em><sup>12</sup> + <em>x</em><sup>11</sup> + <em>x</em><sup>10</sup> + <em>x</em><sup>8</sup> + <em>x</em><sup>7</sup> + <em>x</em><sup>5</sup> + <em>x</em><sup>4</sup> + <em>x</em><sup>2</sup> + <em>x</em> + 1 @end html @end display @end ifhtml @ifnothtml @display @math{x^{32} + x^{26} + x^{23} + x^{22} + x^{16} + x^{12} + x^{11}} @math{+ x^{10} + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1} @end display @end ifnothtml The function is computed byte at a time, taking the least significant bit of each byte first. The initial pattern @code{0xffffffff} is used, to ensure leading zeros affect the CRC and the final result is inverted to ensure trailing zeros also affect the CRC. @emph{Note:} This is the same CRC polynomial as used in handling the @dfn{Remote Serial Protocol} @code{qCRC} packet (@pxref{qCRC packet}). However in the case of the Remote Serial Protocol, the CRC is computed @emph{most} significant bit first, and the result is not inverted, so trailing zeros have no effect on the CRC value. To complete the description, we show below the code of the function which produces the CRC used in @code{.gnu_debuglink}. Inverting the initially supplied @code{crc} argument means that an initial call to this function passing in zero will start computing the CRC using @code{0xffffffff}. @kindex gnu_debuglink_crc32 @smallexample unsigned long gnu_debuglink_crc32 (unsigned long crc, unsigned char *buf, size_t len) @{ static const unsigned long crc32_table[256] = @{ 0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de, 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924, 0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01, 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f, 0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236, 0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713, 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9, 0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d @}; unsigned char *end; crc = ~crc & 0xffffffff; for (end = buf + len; buf < end; ++buf) crc = crc32_table[(crc ^ *buf) & 0xff] ^ (crc >> 8); return ~crc & 0xffffffff; @} @end smallexample @noindent This computation does not apply to the ``build ID'' method. @node MiniDebugInfo @section Debugging information in a special section @cindex separate debug sections @cindex @samp{.gnu_debugdata} section Some systems ship pre-built executables and libraries that have a special @samp{.gnu_debugdata} section. This feature is called @dfn{MiniDebugInfo}. This section holds an LZMA-compressed object and is used to supply extra symbols for backtraces. The intent of this section is to provide extra minimal debugging information for use in simple backtraces. It is not intended to be a replacement for full separate debugging information (@pxref{Separate Debug Files}). The example below shows the intended use; however, @value{GDBN} does not currently put restrictions on what sort of debugging information might be included in the section. @value{GDBN} has support for this extension. If the section exists, then it is used provided that no other source of debugging information can be found, and that @value{GDBN} was configured with LZMA support. This section can be easily created using @command{objcopy} and other standard utilities: @smallexample # Extract the dynamic symbols from the main binary, there is no need # to also have these in the normal symbol table. nm -D @var{binary} --format=posix --defined-only \ | awk '@{ print $1 @}' | sort > dynsyms # Extract all the text (i.e. function) symbols from the debuginfo. # (Note that we actually also accept "D" symbols, for the benefit # of platforms like PowerPC64 that use function descriptors.) nm @var{binary} --format=posix --defined-only \ | awk '@{ if ($2 == "T" || $2 == "t" || $2 == "D") print $1 @}' \ | sort > funcsyms # Keep all the function symbols not already in the dynamic symbol # table. comm -13 dynsyms funcsyms > keep_symbols # Separate full debug info into debug binary. objcopy --only-keep-debug @var{binary} debug # Copy the full debuginfo, keeping only a minimal set of symbols and # removing some unnecessary sections. objcopy -S --remove-section .gdb_index --remove-section .comment \ --keep-symbols=keep_symbols debug mini_debuginfo # Drop the full debug info from the original binary. strip --strip-all -R .comment @var{binary} # Inject the compressed data into the .gnu_debugdata section of the # original binary. xz mini_debuginfo objcopy --add-section .gnu_debugdata=mini_debuginfo.xz @var{binary} @end smallexample @node Index Files @section Index Files Speed Up @value{GDBN} @cindex index files @cindex @samp{.gdb_index} section When @value{GDBN} finds a symbol file, it scans the symbols in the file in order to construct an internal symbol table. This lets most @value{GDBN} operations work quickly---at the cost of a delay early on. For large programs, this delay can be quite lengthy, so @value{GDBN} provides a way to build an index, which speeds up startup. For convenience, @value{GDBN} comes with a program, @command{gdb-add-index}, which can be used to add the index to a symbol file. It takes the symbol file as its only argument: @smallexample $ gdb-add-index symfile @end smallexample @xref{gdb-add-index}. It is also possible to do the work manually. Here is what @command{gdb-add-index} does behind the curtains. The index is stored as a section in the symbol file. @value{GDBN} can write the index to a file, then you can put it into the symbol file using @command{objcopy}. To create an index file, use the @code{save gdb-index} command: @table @code @item save gdb-index [-dwarf-5] @var{directory} @kindex save gdb-index Create index files for all symbol files currently known by @value{GDBN}. For each known @var{symbol-file}, this command by default creates it produces a single file @file{@var{symbol-file}.gdb-index}. If you invoke this command with the @option{-dwarf-5} option, it produces 2 files: @file{@var{symbol-file}.debug_names} and @file{@var{symbol-file}.debug_str}. The files are created in the given @var{directory}. @end table Once you have created an index file you can merge it into your symbol file, here named @file{symfile}, using @command{objcopy}: @smallexample $ objcopy --add-section .gdb_index=symfile.gdb-index \ --set-section-flags .gdb_index=readonly symfile symfile @end smallexample Or for @code{-dwarf-5}: @smallexample $ objcopy --dump-section .debug_str=symfile.debug_str.new symfile $ cat symfile.debug_str >>symfile.debug_str.new $ objcopy --add-section .debug_names=symfile.gdb-index \ --set-section-flags .debug_names=readonly \ --update-section .debug_str=symfile.debug_str.new symfile symfile @end smallexample @value{GDBN} will normally ignore older versions of @file{.gdb_index} sections that have been deprecated. Usually they are deprecated because they are missing a new feature or have performance issues. To tell @value{GDBN} to use a deprecated index section anyway specify @code{set use-deprecated-index-sections on}. The default is @code{off}. This can speed up startup, but may result in some functionality being lost. @xref{Index Section Format}. @emph{Warning:} Setting @code{use-deprecated-index-sections} to @code{on} must be done before gdb reads the file. The following will not work: @smallexample $ gdb -ex "set use-deprecated-index-sections on" <program> @end smallexample Instead you must do, for example, @smallexample $ gdb -iex "set use-deprecated-index-sections on" <program> @end smallexample There are currently some limitation on indices. They only work when using DWARF debugging information, not stabs. And, only the @code{-dwarf-5} index works for programs using Ada. @subsection Automatic symbol index cache @cindex automatic symbol index cache It is possible for @value{GDBN} to automatically save a copy of this index in a cache on disk and retrieve it from there when loading the same binary in the future. This feature can be turned on with @kbd{set index-cache on}. The following commands can be used to tweak the behavior of the index cache. @table @code @kindex set index-cache @item set index-cache on @itemx set index-cache off Enable or disable the use of the symbol index cache. @item set index-cache directory @var{directory} @kindex show index-cache @itemx show index-cache directory Set/show the directory where index files will be saved. The default value for this directory depends on the host platform. On most systems, the index is cached in the @file{gdb} subdirectory of the directory pointed to by the @env{XDG_CACHE_HOME} environment variable, if it is defined, else in the @file{.cache/gdb} subdirectory of your home directory. However, on some systems, the default may differ according to local convention. There is no limit on the disk space used by index cache. It is perfectly safe to delete the content of that directory to free up disk space. @item show index-cache stats Print the number of cache hits and misses since the launch of @value{GDBN}. @end table @node Symbol Errors @section Errors Reading Symbol Files While reading a symbol file, @value{GDBN} occasionally encounters problems, such as symbol types it does not recognize, or known bugs in compiler output. By default, @value{GDBN} does not notify you of such problems, since they are relatively common and primarily of interest to people debugging compilers. If you are interested in seeing information about ill-constructed symbol tables, you can either ask @value{GDBN} to print only one message about each such type of problem, no matter how many times the problem occurs; or you can ask @value{GDBN} to print more messages, to see how many times the problems occur, with the @code{set complaints} command (@pxref{Messages/Warnings, ,Optional Warnings and Messages}). The messages currently printed, and their meanings, include: @table @code @item inner block not inside outer block in @var{symbol} The symbol information shows where symbol scopes begin and end (such as at the start of a function or a block of statements). This error indicates that an inner scope block is not fully contained in its outer scope blocks. @value{GDBN} circumvents the problem by treating the inner block as if it had the same scope as the outer block. In the error message, @var{symbol} may be shown as ``@code{(don't know)}'' if the outer block is not a function. @item block at @var{address} out of order The symbol information for symbol scope blocks should occur in order of increasing addresses. This error indicates that it does not do so. @value{GDBN} does not circumvent this problem, and has trouble locating symbols in the source file whose symbols it is reading. (You can often determine what source file is affected by specifying @code{set verbose on}. @xref{Messages/Warnings, ,Optional Warnings and Messages}.) @item bad block start address patched The symbol information for a symbol scope block has a start address smaller than the address of the preceding source line. This is known to occur in the SunOS 4.1.1 (and earlier) C compiler. @value{GDBN} circumvents the problem by treating the symbol scope block as starting on the previous source line. @item bad string table offset in symbol @var{n} @cindex foo Symbol number @var{n} contains a pointer into the string table which is larger than the size of the string table. @value{GDBN} circumvents the problem by considering the symbol to have the name @code{foo}, which may cause other problems if many symbols end up with this name. @item unknown symbol type @code{0x@var{nn}} The symbol information contains new data types that @value{GDBN} does not yet know how to read. @code{0x@var{nn}} is the symbol type of the uncomprehended information, in hexadecimal. @value{GDBN} circumvents the error by ignoring this symbol information. This usually allows you to debug your program, though certain symbols are not accessible. If you encounter such a problem and feel like debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint on @code{complain}, then go up to the function @code{read_dbx_symtab} and examine @code{*bufp} to see the symbol. @item stub type has NULL name @value{GDBN} could not find the full definition for a struct or class. @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{} The symbol information for a C@t{++} member function is missing some information that recent versions of the compiler should have output for it. @item info mismatch between compiler and debugger @value{GDBN} could not parse a type specification output by the compiler. @end table @node Data Files @section GDB Data Files @cindex prefix for data files @value{GDBN} will sometimes read an auxiliary data file. These files are kept in a directory known as the @dfn{data directory}. You can set the data directory's name, and view the name @value{GDBN} is currently using. @table @code @kindex set data-directory @item set data-directory @var{directory} Set the directory which @value{GDBN} searches for auxiliary data files to @var{directory}. @kindex show data-directory @item show data-directory Show the directory @value{GDBN} searches for auxiliary data files. @end table @cindex default data directory @cindex @samp{--with-gdb-datadir} You can set the default data directory by using the configure-time @samp{--with-gdb-datadir} option. If the data directory is inside @value{GDBN}'s configured binary prefix (set with @samp{--prefix} or @samp{--exec-prefix}), then the default data directory will be updated automatically if the installed @value{GDBN} is moved to a new location. The data directory may also be specified with the @code{--data-directory} command line option. @xref{Mode Options}. @node Targets @chapter Specifying a Debugging Target @cindex debugging target A @dfn{target} is the execution environment occupied by your program. Often, @value{GDBN} runs in the same host environment as your program; in that case, the debugging target is specified as a side effect when you use the @code{file} or @code{core} commands. When you need more flexibility---for example, running @value{GDBN} on a physically separate host, or controlling a standalone system over a serial port or a realtime system over a TCP/IP connection---you can use the @code{target} command to specify one of the target types configured for @value{GDBN} (@pxref{Target Commands, ,Commands for Managing Targets}). @cindex target architecture It is possible to build @value{GDBN} for several different @dfn{target architectures}. When @value{GDBN} is built like that, you can choose one of the available architectures with the @kbd{set architecture} command. @table @code @kindex set architecture @kindex show architecture @item set architecture @var{arch} This command sets the current target architecture to @var{arch}. The value of @var{arch} can be @code{"auto"}, in addition to one of the supported architectures. @item show architecture Show the current target architecture. @item set processor @itemx processor @kindex set processor @kindex show processor These are alias commands for, respectively, @code{set architecture} and @code{show architecture}. @end table @menu * Active Targets:: Active targets * Target Commands:: Commands for managing targets * Byte Order:: Choosing target byte order @end menu @node Active Targets @section Active Targets @cindex stacking targets @cindex active targets @cindex multiple targets There are multiple classes of targets such as: processes, executable files or recording sessions. Core files belong to the process class, making core file and process mutually exclusive. Otherwise, @value{GDBN} can work concurrently on multiple active targets, one in each class. This allows you to (for example) start a process and inspect its activity, while still having access to the executable file after the process finishes. Or if you start process recording (@pxref{Reverse Execution}) and @code{reverse-step} there, you are presented a virtual layer of the recording target, while the process target remains stopped at the chronologically last point of the process execution. Use the @code{core-file} and @code{exec-file} commands to select a new core file or executable target (@pxref{Files, ,Commands to Specify Files}). To specify as a target a process that is already running, use the @code{attach} command (@pxref{Attach, ,Debugging an Already-running Process}). @node Target Commands @section Commands for Managing Targets @table @code @item target @var{type} @var{parameters} Connects the @value{GDBN} host environment to a target machine or process. A target is typically a protocol for talking to debugging facilities. You use the argument @var{type} to specify the type or protocol of the target machine. Further @var{parameters} are interpreted by the target protocol, but typically include things like device names or host names to connect with, process numbers, and baud rates. The @code{target} command does not repeat if you press @key{RET} again after executing the command. @kindex help target @item help target Displays the names of all targets available. To display targets currently selected, use either @code{info target} or @code{info files} (@pxref{Files, ,Commands to Specify Files}). @item help target @var{name} Describe a particular target, including any parameters necessary to select it. @kindex set gnutarget @item set gnutarget @var{args} @value{GDBN} uses its own library BFD to read your files. @value{GDBN} knows whether it is reading an @dfn{executable}, a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format with the @code{set gnutarget} command. Unlike most @code{target} commands, with @code{gnutarget} the @code{target} refers to a program, not a machine. @quotation @emph{Warning:} To specify a file format with @code{set gnutarget}, you must know the actual BFD name. @end quotation @noindent @xref{Files, , Commands to Specify Files}. @kindex show gnutarget @item show gnutarget Use the @code{show gnutarget} command to display what file format @code{gnutarget} is set to read. If you have not set @code{gnutarget}, @value{GDBN} will determine the file format for each file automatically, and @code{show gnutarget} displays @samp{The current BFD target is "auto"}. @end table @cindex common targets Here are some common targets (available, or not, depending on the GDB configuration): @table @code @kindex target @item target exec @var{program} @cindex executable file target An executable file. @samp{target exec @var{program}} is the same as @samp{exec-file @var{program}}. @item target core @var{filename} @cindex core dump file target A core dump file. @samp{target core @var{filename}} is the same as @samp{core-file @var{filename}}. @item target remote @var{medium} @cindex remote target A remote system connected to @value{GDBN} via a serial line or network connection. This command tells @value{GDBN} to use its own remote protocol over @var{medium} for debugging. @xref{Remote Debugging}. For example, if you have a board connected to @file{/dev/ttya} on the machine running @value{GDBN}, you could say: @smallexample target remote /dev/ttya @end smallexample @code{target remote} supports the @code{load} command. This is only useful if you have some other way of getting the stub to the target system, and you can put it somewhere in memory where it won't get clobbered by the download. @item target sim @r{[}@var{simargs}@r{]} @dots{} @cindex built-in simulator target Builtin CPU simulator. @value{GDBN} includes simulators for most architectures. In general, @smallexample target sim load run @end smallexample @noindent works; however, you cannot assume that a specific memory map, device drivers, or even basic I/O is available, although some simulators do provide these. For info about any processor-specific simulator details, see the appropriate section in @ref{Embedded Processors, ,Embedded Processors}. @item target native @cindex native target Setup for local/native process debugging. Useful to make the @code{run} command spawn native processes (likewise @code{attach}, etc.@:) even when @code{set auto-connect-native-target} is @code{off} (@pxref{set auto-connect-native-target}). @end table Different targets are available on different configurations of @value{GDBN}; your configuration may have more or fewer targets. Many remote targets require you to download the executable's code once you've successfully established a connection. You may wish to control various aspects of this process. @table @code @item set hash @kindex set hash@r{, for remote monitors} @cindex hash mark while downloading This command controls whether a hash mark @samp{#} is displayed while downloading a file to the remote monitor. If on, a hash mark is displayed after each S-record is successfully downloaded to the monitor. @item show hash @kindex show hash@r{, for remote monitors} Show the current status of displaying the hash mark. @item set debug monitor @kindex set debug monitor @cindex display remote monitor communications Enable or disable display of communications messages between @value{GDBN} and the remote monitor. @item show debug monitor @kindex show debug monitor Show the current status of displaying communications between @value{GDBN} and the remote monitor. @end table @table @code @kindex load @var{filename} @var{offset} @item load @var{filename} @var{offset} @anchor{load} Depending on what remote debugging facilities are configured into @value{GDBN}, the @code{load} command may be available. Where it exists, it is meant to make @var{filename} (an executable) available for debugging on the remote system---by downloading, or dynamic linking, for example. @code{load} also records the @var{filename} symbol table in @value{GDBN}, like the @code{add-symbol-file} command. If your @value{GDBN} does not have a @code{load} command, attempting to execute it gets the error message ``@code{You can't do that when your target is @dots{}}'' The file is loaded at whatever address is specified in the executable. For some object file formats, you can specify the load address when you link the program; for other formats, like a.out, the object file format specifies a fixed address. @c FIXME! This would be a good place for an xref to the GNU linker doc. It is also possible to tell @value{GDBN} to load the executable file at a specific offset described by the optional argument @var{offset}. When @var{offset} is provided, @var{filename} must also be provided. Depending on the remote side capabilities, @value{GDBN} may be able to load programs into flash memory. @code{load} does not repeat if you press @key{RET} again after using it. @end table @table @code @kindex flash-erase @item flash-erase @anchor{flash-erase} Erases all known flash memory regions on the target. @end table @node Byte Order @section Choosing Target Byte Order @cindex choosing target byte order @cindex target byte order Some types of processors, such as the @acronym{MIPS}, PowerPC, and Renesas SH, offer the ability to run either big-endian or little-endian byte orders. Usually the executable or symbol will include a bit to designate the endian-ness, and you will not need to worry about which to use. However, you may still find it useful to adjust @value{GDBN}'s idea of processor endian-ness manually. @table @code @kindex set endian @item set endian big Instruct @value{GDBN} to assume the target is big-endian. @item set endian little Instruct @value{GDBN} to assume the target is little-endian. @item set endian auto Instruct @value{GDBN} to use the byte order associated with the executable. @item show endian Display @value{GDBN}'s current idea of the target byte order. @end table If the @code{set endian auto} mode is in effect and no executable has been selected, then the endianness used is the last one chosen either by one of the @code{set endian big} and @code{set endian little} commands or by inferring from the last executable used. If no endianness has been previously chosen, then the default for this mode is inferred from the target @value{GDBN} has been built for, and is @code{little} if the name of the target CPU has an @code{el} suffix and @code{big} otherwise. Note that these commands merely adjust interpretation of symbolic data on the host, and that they have absolutely no effect on the target system. @node Remote Debugging @chapter Debugging Remote Programs @cindex remote debugging If you are trying to debug a program running on a machine that cannot run @value{GDBN} in the usual way, it is often useful to use remote debugging. For example, you might use remote debugging on an operating system kernel, or on a small system which does not have a general purpose operating system powerful enough to run a full-featured debugger. Some configurations of @value{GDBN} have special serial or TCP/IP interfaces to make this work with particular debugging targets. In addition, @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN}, but not specific to any particular target system) which you can use if you write the remote stubs---the code that runs on the remote system to communicate with @value{GDBN}. Other remote targets may be available in your configuration of @value{GDBN}; use @code{help target} to list them. @menu * Connecting:: Connecting to a remote target * File Transfer:: Sending files to a remote system * Server:: Using the gdbserver program * Remote Configuration:: Remote configuration * Remote Stub:: Implementing a remote stub @end menu @node Connecting @section Connecting to a Remote Target @cindex remote debugging, connecting @cindex @code{gdbserver}, connecting @cindex remote debugging, types of connections @cindex @code{gdbserver}, types of connections @cindex @code{gdbserver}, @code{target remote} mode @cindex @code{gdbserver}, @code{target extended-remote} mode This section describes how to connect to a remote target, including the types of connections and their differences, how to set up executable and symbol files on the host and target, and the commands used for connecting to and disconnecting from the remote target. @subsection Types of Remote Connections @value{GDBN} supports two types of remote connections, @code{target remote} mode and @code{target extended-remote} mode. Note that many remote targets support only @code{target remote} mode. There are several major differences between the two types of connections, enumerated here: @table @asis @cindex remote debugging, detach and program exit @item Result of detach or program exit @strong{With target remote mode:} When the debugged program exits or you detach from it, @value{GDBN} disconnects from the target. When using @code{gdbserver}, @code{gdbserver} will exit. @strong{With target extended-remote mode:} When the debugged program exits or you detach from it, @value{GDBN} remains connected to the target, even though no program is running. You can rerun the program, attach to a running program, or use @code{monitor} commands specific to the target. When using @code{gdbserver} in this case, it does not exit unless it was invoked using the @option{--once} option. If the @option{--once} option was not used, you can ask @code{gdbserver} to exit using the @code{monitor exit} command (@pxref{Monitor Commands for gdbserver}). @item Specifying the program to debug For both connection types you use the @code{file} command to specify the program on the host system. If you are using @code{gdbserver} there are some differences in how to specify the location of the program on the target. @strong{With target remote mode:} You must either specify the program to debug on the @code{gdbserver} command line or use the @option{--attach} option (@pxref{Attaching to a program,,Attaching to a Running Program}). @cindex @option{--multi}, @code{gdbserver} option @strong{With target extended-remote mode:} You may specify the program to debug on the @code{gdbserver} command line, or you can load the program or attach to it using @value{GDBN} commands after connecting to @code{gdbserver}. @anchor{--multi Option in Types of Remote Connnections} You can start @code{gdbserver} without supplying an initial command to run or process ID to attach. To do this, use the @option{--multi} command line option. Then you can connect using @code{target extended-remote} and start the program you want to debug (see below for details on using the @code{run} command in this scenario). Note that the conditions under which @code{gdbserver} terminates depend on how @value{GDBN} connects to it (@code{target remote} or @code{target extended-remote}). The @option{--multi} option to @code{gdbserver} has no influence on that. @item The @code{run} command @strong{With target remote mode:} The @code{run} command is not supported. Once a connection has been established, you can use all the usual @value{GDBN} commands to examine and change data. The remote program is already running, so you can use commands like @kbd{step} and @kbd{continue}. @strong{With target extended-remote mode:} The @code{run} command is supported. The @code{run} command uses the value set by @code{set remote exec-file} (@pxref{set remote exec-file}) to select the program to run. Command line arguments are supported, except for wildcard expansion and I/O redirection (@pxref{Arguments}). If you specify the program to debug on the command line, then the @code{run} command is not required to start execution, and you can resume using commands like @kbd{step} and @kbd{continue} as with @code{target remote} mode. @anchor{Attaching in Types of Remote Connections} @item Attaching @strong{With target remote mode:} The @value{GDBN} command @code{attach} is not supported. To attach to a running program using @code{gdbserver}, you must use the @option{--attach} option (@pxref{Running gdbserver}). @strong{With target extended-remote mode:} To attach to a running program, you may use the @code{attach} command after the connection has been established. If you are using @code{gdbserver}, you may also invoke @code{gdbserver} using the @option{--attach} option (@pxref{Running gdbserver}). Some remote targets allow @value{GDBN} to determine the executable file running in the process the debugger is attaching to. In such a case, @value{GDBN} uses the value of @code{exec-file-mismatch} to handle a possible mismatch between the executable file name running in the process and the name of the current exec-file loaded by @value{GDBN} (@pxref{set exec-file-mismatch}). @end table @anchor{Host and target files} @subsection Host and Target Files @cindex remote debugging, symbol files @cindex symbol files, remote debugging @value{GDBN}, running on the host, needs access to symbol and debugging information for your program running on the target. This requires access to an unstripped copy of your program, and possibly any associated symbol files. Note that this section applies equally to both @code{target remote} mode and @code{target extended-remote} mode. Some remote targets (@pxref{qXfer executable filename read}, and @pxref{Host I/O Packets}) allow @value{GDBN} to access program files over the same connection used to communicate with @value{GDBN}. With such a target, if the remote program is unstripped, the only command you need is @code{target remote} (or @code{target extended-remote}). If the remote program is stripped, or the target does not support remote program file access, start up @value{GDBN} using the name of the local unstripped copy of your program as the first argument, or use the @code{file} command. Use @code{set sysroot} to specify the location (on the host) of target libraries (unless your @value{GDBN} was compiled with the correct sysroot using @code{--with-sysroot}). Alternatively, you may use @code{set solib-search-path} to specify how @value{GDBN} locates target libraries. The symbol file and target libraries must exactly match the executable and libraries on the target, with one exception: the files on the host system should not be stripped, even if the files on the target system are. Mismatched or missing files will lead to confusing results during debugging. On @sc{gnu}/Linux targets, mismatched or missing files may also prevent @code{gdbserver} from debugging multi-threaded programs. @subsection Remote Connection Commands @cindex remote connection commands @value{GDBN} can communicate with the target over a serial line, a local Unix domain socket, or over an @acronym{IP} network using @acronym{TCP} or @acronym{UDP}. In each case, @value{GDBN} uses the same protocol for debugging your program; only the medium carrying the debugging packets varies. The @code{target remote} and @code{target extended-remote} commands establish a connection to the target. Both commands accept the same arguments, which indicate the medium to use: @table @code @item target remote @var{serial-device} @itemx target extended-remote @var{serial-device} @cindex serial line, @code{target remote} Use @var{serial-device} to communicate with the target. For example, to use a serial line connected to the device named @file{/dev/ttyb}: @smallexample target remote /dev/ttyb @end smallexample If you're using a serial line, you may want to give @value{GDBN} the @samp{--baud} option, or use the @code{set serial baud} command (@pxref{Remote Configuration, set serial baud}) before the @code{target} command. @item target remote @var{local-socket} @itemx target extended-remote @var{local-socket} @cindex local socket, @code{target remote} @cindex Unix domain socket Use @var{local-socket} to communicate with the target. For example, to use a local Unix domain socket bound to the file system entry @file{/tmp/gdb-socket0}: @smallexample target remote /tmp/gdb-socket0 @end smallexample Note that this command has the same form as the command to connect to a serial line. @value{GDBN} will automatically determine which kind of file you have specified and will make the appropriate kind of connection. This feature is not available if the host system does not support Unix domain sockets. @item target remote @code{@var{host}:@var{port}} @itemx target remote @code{@var{[host]}:@var{port}} @itemx target remote @code{tcp:@var{host}:@var{port}} @itemx target remote @code{tcp:@var{[host]}:@var{port}} @itemx target remote @code{tcp4:@var{host}:@var{port}} @itemx target remote @code{tcp6:@var{host}:@var{port}} @itemx target remote @code{tcp6:@var{[host]}:@var{port}} @itemx target extended-remote @code{@var{host}:@var{port}} @itemx target extended-remote @code{@var{[host]}:@var{port}} @itemx target extended-remote @code{tcp:@var{host}:@var{port}} @itemx target extended-remote @code{tcp:@var{[host]}:@var{port}} @itemx target extended-remote @code{tcp4:@var{host}:@var{port}} @itemx target extended-remote @code{tcp6:@var{host}:@var{port}} @itemx target extended-remote @code{tcp6:@var{[host]}:@var{port}} @cindex @acronym{TCP} port, @code{target remote} Debug using a @acronym{TCP} connection to @var{port} on @var{host}. The @var{host} may be either a host name, a numeric @acronym{IPv4} address, or a numeric @acronym{IPv6} address (with or without the square brackets to separate the address from the port); @var{port} must be a decimal number. The @var{host} could be the target machine itself, if it is directly connected to the net, or it might be a terminal server which in turn has a serial line to the target. For example, to connect to port 2828 on a terminal server named @code{manyfarms}: @smallexample target remote manyfarms:2828 @end smallexample To connect to port 2828 on a terminal server whose address is @code{2001:0db8:85a3:0000:0000:8a2e:0370:7334}, you can either use the square bracket syntax: @smallexample target remote [2001:0db8:85a3:0000:0000:8a2e:0370:7334]:2828 @end smallexample @noindent or explicitly specify the @acronym{IPv6} protocol: @smallexample target remote tcp6:2001:0db8:85a3:0000:0000:8a2e:0370:7334:2828 @end smallexample This last example may be confusing to the reader, because there is no visible separation between the hostname and the port number. Therefore, we recommend the user to provide @acronym{IPv6} addresses using square brackets for clarity. However, it is important to mention that for @value{GDBN} there is no ambiguity: the number after the last colon is considered to be the port number. If your remote target is actually running on the same machine as your debugger session (e.g.@: a simulator for your target running on the same host), you can omit the hostname. For example, to connect to port 1234 on your local machine: @smallexample target remote :1234 @end smallexample @noindent Note that the colon is still required here. @item target remote @code{udp:@var{host}:@var{port}} @itemx target remote @code{udp:@var{[host]}:@var{port}} @itemx target remote @code{udp4:@var{host}:@var{port}} @itemx target remote @code{udp6:@var{[host]}:@var{port}} @itemx target extended-remote @code{udp:@var{host}:@var{port}} @itemx target extended-remote @code{udp:@var{host}:@var{port}} @itemx target extended-remote @code{udp:@var{[host]}:@var{port}} @itemx target extended-remote @code{udp4:@var{host}:@var{port}} @itemx target extended-remote @code{udp6:@var{host}:@var{port}} @itemx target extended-remote @code{udp6:@var{[host]}:@var{port}} @cindex @acronym{UDP} port, @code{target remote} Debug using @acronym{UDP} packets to @var{port} on @var{host}. For example, to connect to @acronym{UDP} port 2828 on a terminal server named @code{manyfarms}: @smallexample target remote udp:manyfarms:2828 @end smallexample When using a @acronym{UDP} connection for remote debugging, you should keep in mind that the `U' stands for ``Unreliable''. @acronym{UDP} can silently drop packets on busy or unreliable networks, which will cause havoc with your debugging session. @item target remote | @var{command} @itemx target extended-remote | @var{command} @cindex pipe, @code{target remote} to Run @var{command} in the background and communicate with it using a pipe. The @var{command} is a shell command, to be parsed and expanded by the system's command shell, @code{/bin/sh}; it should expect remote protocol packets on its standard input, and send replies on its standard output. You could use this to run a stand-alone simulator that speaks the remote debugging protocol, to make net connections using programs like @code{ssh}, or for other similar tricks. If @var{command} closes its standard output (perhaps by exiting), @value{GDBN} will try to send it a @code{SIGTERM} signal. (If the program has already exited, this will have no effect.) @end table @cindex interrupting remote programs @cindex remote programs, interrupting Whenever @value{GDBN} is waiting for the remote program, if you type the interrupt character (often @kbd{Ctrl-c}), @value{GDBN} attempts to stop the program. This may or may not succeed, depending in part on the hardware and the serial drivers the remote system uses. If you type the interrupt character once again, @value{GDBN} displays this prompt: @smallexample Interrupted while waiting for the program. Give up (and stop debugging it)? (y or n) @end smallexample In @code{target remote} mode, if you type @kbd{y}, @value{GDBN} abandons the remote debugging session. (If you decide you want to try again later, you can use @kbd{target remote} again to connect once more.) If you type @kbd{n}, @value{GDBN} goes back to waiting. In @code{target extended-remote} mode, typing @kbd{n} will leave @value{GDBN} connected to the target. @table @code @kindex detach (remote) @item detach When you have finished debugging the remote program, you can use the @code{detach} command to release it from @value{GDBN} control. Detaching from the target normally resumes its execution, but the results will depend on your particular remote stub. After the @code{detach} command in @code{target remote} mode, @value{GDBN} is free to connect to another target. In @code{target extended-remote} mode, @value{GDBN} is still connected to the target. @kindex disconnect @item disconnect The @code{disconnect} command closes the connection to the target, and the target is generally not resumed. It will wait for @value{GDBN} (this instance or another one) to connect and continue debugging. After the @code{disconnect} command, @value{GDBN} is again free to connect to another target. @cindex send command to remote monitor @cindex extend @value{GDBN} for remote targets @cindex add new commands for external monitor @kindex monitor @item monitor @var{cmd} This command allows you to send arbitrary commands directly to the remote monitor. Since @value{GDBN} doesn't care about the commands it sends like this, this command is the way to extend @value{GDBN}---you can add new commands that only the external monitor will understand and implement. @end table @node File Transfer @section Sending files to a remote system @cindex remote target, file transfer @cindex file transfer @cindex sending files to remote systems Some remote targets offer the ability to transfer files over the same connection used to communicate with @value{GDBN}. This is convenient for targets accessible through other means, e.g.@: @sc{gnu}/Linux systems running @code{gdbserver} over a network interface. For other targets, e.g.@: embedded devices with only a single serial port, this may be the only way to upload or download files. Not all remote targets support these commands. @table @code @kindex remote put @item remote put @var{hostfile} @var{targetfile} Copy file @var{hostfile} from the host system (the machine running @value{GDBN}) to @var{targetfile} on the target system. @kindex remote get @item remote get @var{targetfile} @var{hostfile} Copy file @var{targetfile} from the target system to @var{hostfile} on the host system. @kindex remote delete @item remote delete @var{targetfile} Delete @var{targetfile} from the target system. @end table @node Server @section Using the @code{gdbserver} Program @kindex gdbserver @cindex remote connection without stubs @code{gdbserver} is a control program for Unix-like systems, which allows you to connect your program with a remote @value{GDBN} via @code{target remote} or @code{target extended-remote}---but without linking in the usual debugging stub. @code{gdbserver} is not a complete replacement for the debugging stubs, because it requires essentially the same operating-system facilities that @value{GDBN} itself does. In fact, a system that can run @code{gdbserver} to connect to a remote @value{GDBN} could also run @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless, because it is a much smaller program than @value{GDBN} itself. It is also easier to port than all of @value{GDBN}, so you may be able to get started more quickly on a new system by using @code{gdbserver}. Finally, if you develop code for real-time systems, you may find that the tradeoffs involved in real-time operation make it more convenient to do as much development work as possible on another system, for example by cross-compiling. You can use @code{gdbserver} to make a similar choice for debugging. @value{GDBN} and @code{gdbserver} communicate via either a serial line or a TCP connection, using the standard @value{GDBN} remote serial protocol. @quotation @emph{Warning:} @code{gdbserver} does not have any built-in security. Do not run @code{gdbserver} connected to any public network; a @value{GDBN} connection to @code{gdbserver} provides access to the target system with the same privileges as the user running @code{gdbserver}. @end quotation @anchor{Running gdbserver} @subsection Running @code{gdbserver} @cindex arguments, to @code{gdbserver} @cindex @code{gdbserver}, command-line arguments Run @code{gdbserver} on the target system. You need a copy of the program you want to debug, including any libraries it requires. @code{gdbserver} does not need your program's symbol table, so you can strip the program if necessary to save space. @value{GDBN} on the host system does all the symbol handling. To use the server, you must tell it how to communicate with @value{GDBN}; the name of your program; and the arguments for your program. The usual syntax is: @smallexample target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ] @end smallexample @var{comm} is either a device name (to use a serial line), or a TCP hostname and portnumber, or @code{-} or @code{stdio} to use stdin/stdout of @code{gdbserver}. For example, to debug Emacs with the argument @samp{foo.txt} and communicate with @value{GDBN} over the serial port @file{/dev/com1}: @smallexample target> gdbserver /dev/com1 emacs foo.txt @end smallexample @code{gdbserver} waits passively for the host @value{GDBN} to communicate with it. To use a TCP connection instead of a serial line: @smallexample target> gdbserver host:2345 emacs foo.txt @end smallexample The only difference from the previous example is the first argument, specifying that you are communicating with the host @value{GDBN} via TCP. The @samp{host:2345} argument means that @code{gdbserver} is to expect a TCP connection from machine @samp{host} to local TCP port 2345. (Currently, the @samp{host} part is ignored.) You can choose any number you want for the port number as long as it does not conflict with any TCP ports already in use on the target system (for example, @code{23} is reserved for @code{telnet}).@footnote{If you choose a port number that conflicts with another service, @code{gdbserver} prints an error message and exits.} You must use the same port number with the host @value{GDBN} @code{target remote} command. The @code{stdio} connection is useful when starting @code{gdbserver} with ssh: @smallexample (gdb) target remote | ssh -T hostname gdbserver - hello @end smallexample The @samp{-T} option to ssh is provided because we don't need a remote pty, and we don't want escape-character handling. Ssh does this by default when a command is provided, the flag is provided to make it explicit. You could elide it if you want to. Programs started with stdio-connected gdbserver have @file{/dev/null} for @code{stdin}, and @code{stdout},@code{stderr} are sent back to gdb for display through a pipe connected to gdbserver. Both @code{stdout} and @code{stderr} use the same pipe. @anchor{Attaching to a program} @subsubsection Attaching to a Running Program @cindex attach to a program, @code{gdbserver} @cindex @option{--attach}, @code{gdbserver} option On some targets, @code{gdbserver} can also attach to running programs. This is accomplished via the @code{--attach} argument. The syntax is: @smallexample target> gdbserver --attach @var{comm} @var{pid} @end smallexample @var{pid} is the process ID of a currently running process. It isn't necessary to point @code{gdbserver} at a binary for the running process. In @code{target extended-remote} mode, you can also attach using the @value{GDBN} attach command (@pxref{Attaching in Types of Remote Connections}). @pindex pidof You can debug processes by name instead of process ID if your target has the @code{pidof} utility: @smallexample target> gdbserver --attach @var{comm} `pidof @var{program}` @end smallexample In case more than one copy of @var{program} is running, or @var{program} has multiple threads, most versions of @code{pidof} support the @code{-s} option to only return the first process ID. @subsubsection TCP port allocation lifecycle of @code{gdbserver} This section applies only when @code{gdbserver} is run to listen on a TCP port. @code{gdbserver} normally terminates after all of its debugged processes have terminated in @kbd{target remote} mode. On the other hand, for @kbd{target extended-remote}, @code{gdbserver} stays running even with no processes left. @value{GDBN} normally terminates the spawned debugged process on its exit, which normally also terminates @code{gdbserver} in the @kbd{target remote} mode. Therefore, when the connection drops unexpectedly, and @value{GDBN} cannot ask @code{gdbserver} to kill its debugged processes, @code{gdbserver} stays running even in the @kbd{target remote} mode. When @code{gdbserver} stays running, @value{GDBN} can connect to it again later. Such reconnecting is useful for features like @ref{disconnected tracing}. For completeness, at most one @value{GDBN} can be connected at a time. @cindex @option{--once}, @code{gdbserver} option By default, @code{gdbserver} keeps the listening TCP port open, so that subsequent connections are possible. However, if you start @code{gdbserver} with the @option{--once} option, it will stop listening for any further connection attempts after connecting to the first @value{GDBN} session. This means no further connections to @code{gdbserver} will be possible after the first one. It also means @code{gdbserver} will terminate after the first connection with remote @value{GDBN} has closed, even for unexpectedly closed connections and even in the @kbd{target extended-remote} mode. The @option{--once} option allows reusing the same port number for connecting to multiple instances of @code{gdbserver} running on the same host, since each instance closes its port after the first connection. @anchor{Other Command-Line Arguments for gdbserver} @subsubsection Other Command-Line Arguments for @code{gdbserver} You can use the @option{--multi} option to start @code{gdbserver} without specifying a program to debug or a process to attach to. Then you can attach in @code{target extended-remote} mode and run or attach to a program. For more information, @pxref{--multi Option in Types of Remote Connnections}. @cindex @option{--debug}, @code{gdbserver} option The @option{--debug} option tells @code{gdbserver} to display extra status information about the debugging process. @cindex @option{--remote-debug}, @code{gdbserver} option The @option{--remote-debug} option tells @code{gdbserver} to display remote protocol debug output. @cindex @option{--debug-file}, @code{gdbserver} option @cindex @code{gdbserver}, send all debug output to a single file The @option{--debug-file=@var{filename}} option tells @code{gdbserver} to write any debug output to the given @var{filename}. These options are intended for @code{gdbserver} development and for bug reports to the developers. @cindex @option{--debug-format}, @code{gdbserver} option The @option{--debug-format=option1[,option2,...]} option tells @code{gdbserver} to include additional information in each output. Possible options are: @table @code @item none Turn off all extra information in debugging output. @item all Turn on all extra information in debugging output. @item timestamps Include a timestamp in each line of debugging output. @end table Options are processed in order. Thus, for example, if @option{none} appears last then no additional information is added to debugging output. @cindex @option{--wrapper}, @code{gdbserver} option The @option{--wrapper} option specifies a wrapper to launch programs for debugging. The option should be followed by the name of the wrapper, then any command-line arguments to pass to the wrapper, then @kbd{--} indicating the end of the wrapper arguments. @code{gdbserver} runs the specified wrapper program with a combined command line including the wrapper arguments, then the name of the program to debug, then any arguments to the program. The wrapper runs until it executes your program, and then @value{GDBN} gains control. You can use any program that eventually calls @code{execve} with its arguments as a wrapper. Several standard Unix utilities do this, e.g.@: @code{env} and @code{nohup}. Any Unix shell script ending with @code{exec "$@@"} will also work. For example, you can use @code{env} to pass an environment variable to the debugged program, without setting the variable in @code{gdbserver}'s environment: @smallexample $ gdbserver --wrapper env LD_PRELOAD=libtest.so -- :2222 ./testprog @end smallexample @cindex @option{--selftest} The @option{--selftest} option runs the self tests in @code{gdbserver}: @smallexample $ gdbserver --selftest Ran 2 unit tests, 0 failed @end smallexample These tests are disabled in release. @subsection Connecting to @code{gdbserver} The basic procedure for connecting to the remote target is: @itemize @item Run @value{GDBN} on the host system. @item Make sure you have the necessary symbol files (@pxref{Host and target files}). Load symbols for your application using the @code{file} command before you connect. Use @code{set sysroot} to locate target libraries (unless your @value{GDBN} was compiled with the correct sysroot using @code{--with-sysroot}). @item Connect to your target (@pxref{Connecting,,Connecting to a Remote Target}). For TCP connections, you must start up @code{gdbserver} prior to using the @code{target} command. Otherwise you may get an error whose text depends on the host system, but which usually looks something like @samp{Connection refused}. Don't use the @code{load} command in @value{GDBN} when using @code{target remote} mode, since the program is already on the target. @end itemize @anchor{Monitor Commands for gdbserver} @subsection Monitor Commands for @code{gdbserver} @cindex monitor commands, for @code{gdbserver} During a @value{GDBN} session using @code{gdbserver}, you can use the @code{monitor} command to send special requests to @code{gdbserver}. Here are the available commands. @table @code @item monitor help List the available monitor commands. @item monitor set debug 0 @itemx monitor set debug 1 Disable or enable general debugging messages. @item monitor set remote-debug 0 @itemx monitor set remote-debug 1 Disable or enable specific debugging messages associated with the remote protocol (@pxref{Remote Protocol}). @item monitor set debug-file filename @itemx monitor set debug-file Send any debug output to the given file, or to stderr. @item monitor set debug-format option1@r{[},option2,...@r{]} Specify additional text to add to debugging messages. Possible options are: @table @code @item none Turn off all extra information in debugging output. @item all Turn on all extra information in debugging output. @item timestamps Include a timestamp in each line of debugging output. @end table Options are processed in order. Thus, for example, if @option{none} appears last then no additional information is added to debugging output. @item monitor set libthread-db-search-path [PATH] @cindex gdbserver, search path for @code{libthread_db} When this command is issued, @var{path} is a colon-separated list of directories to search for @code{libthread_db} (@pxref{Threads,,set libthread-db-search-path}). If you omit @var{path}, @samp{libthread-db-search-path} will be reset to its default value. The special entry @samp{$pdir} for @samp{libthread-db-search-path} is not supported in @code{gdbserver}. @item monitor exit Tell gdbserver to exit immediately. This command should be followed by @code{disconnect} to close the debugging session. @code{gdbserver} will detach from any attached processes and kill any processes it created. Use @code{monitor exit} to terminate @code{gdbserver} at the end of a multi-process mode debug session. @end table @subsection Tracepoints support in @code{gdbserver} @cindex tracepoints support in @code{gdbserver} On some targets, @code{gdbserver} supports tracepoints, fast tracepoints and static tracepoints. For fast or static tracepoints to work, a special library called the @dfn{in-process agent} (IPA), must be loaded in the inferior process. This library is built and distributed as an integral part of @code{gdbserver}. In addition, support for static tracepoints requires building the in-process agent library with static tracepoints support. At present, the UST (LTTng Userspace Tracer, @url{http://lttng.org/ust}) tracing engine is supported. This support is automatically available if UST development headers are found in the standard include path when @code{gdbserver} is built, or if @code{gdbserver} was explicitly configured using @option{--with-ust} to point at such headers. You can explicitly disable the support using @option{--with-ust=no}. There are several ways to load the in-process agent in your program: @table @code @item Specifying it as dependency at link time You can link your program dynamically with the in-process agent library. On most systems, this is accomplished by adding @code{-linproctrace} to the link command. @item Using the system's preloading mechanisms You can force loading the in-process agent at startup time by using your system's support for preloading shared libraries. Many Unixes support the concept of preloading user defined libraries. In most cases, you do that by specifying @code{LD_PRELOAD=libinproctrace.so} in the environment. See also the description of @code{gdbserver}'s @option{--wrapper} command line option. @item Using @value{GDBN} to force loading the agent at run time On some systems, you can force the inferior to load a shared library, by calling a dynamic loader function in the inferior that takes care of dynamically looking up and loading a shared library. On most Unix systems, the function is @code{dlopen}. You'll use the @code{call} command for that. For example: @smallexample (@value{GDBP}) call dlopen ("libinproctrace.so", ...) @end smallexample Note that on most Unix systems, for the @code{dlopen} function to be available, the program needs to be linked with @code{-ldl}. @end table On systems that have a userspace dynamic loader, like most Unix systems, when you connect to @code{gdbserver} using @code{target remote}, you'll find that the program is stopped at the dynamic loader's entry point, and no shared library has been loaded in the program's address space yet, including the in-process agent. In that case, before being able to use any of the fast or static tracepoints features, you need to let the loader run and load the shared libraries. The simplest way to do that is to run the program to the main procedure. E.g., if debugging a C or C@t{++} program, start @code{gdbserver} like so: @smallexample $ gdbserver :9999 myprogram @end smallexample Start GDB and connect to @code{gdbserver} like so, and run to main: @smallexample $ gdb myprogram (@value{GDBP}) target remote myhost:9999 0x00007f215893ba60 in ?? () from /lib64/ld-linux-x86-64.so.2 (@value{GDBP}) b main (@value{GDBP}) continue @end smallexample The in-process tracing agent library should now be loaded into the process; you can confirm it with the @code{info sharedlibrary} command, which will list @file{libinproctrace.so} as loaded in the process. You are now ready to install fast tracepoints, list static tracepoint markers, probe static tracepoints markers, and start tracing. @node Remote Configuration @section Remote Configuration @kindex set remote @kindex show remote This section documents the configuration options available when debugging remote programs. For the options related to the File I/O extensions of the remote protocol, see @ref{system, system-call-allowed}. @table @code @item set remoteaddresssize @var{bits} @cindex address size for remote targets @cindex bits in remote address Set the maximum size of address in a memory packet to the specified number of bits. @value{GDBN} will mask off the address bits above that number, when it passes addresses to the remote target. The default value is the number of bits in the target's address. @item show remoteaddresssize Show the current value of remote address size in bits. @item set serial baud @var{n} @cindex baud rate for remote targets Set the baud rate for the remote serial I/O to @var{n} baud. The value is used to set the speed of the serial port used for debugging remote targets. @item show serial baud Show the current speed of the remote connection. @item set serial parity @var{parity} Set the parity for the remote serial I/O. Supported values of @var{parity} are: @code{even}, @code{none}, and @code{odd}. The default is @code{none}. @item show serial parity Show the current parity of the serial port. @item set remotebreak @cindex interrupt remote programs @cindex BREAK signal instead of Ctrl-C @anchor{set remotebreak} If set to on, @value{GDBN} sends a @code{BREAK} signal to the remote when you type @kbd{Ctrl-c} to interrupt the program running on the remote. If set to off, @value{GDBN} sends the @samp{Ctrl-C} character instead. The default is off, since most remote systems expect to see @samp{Ctrl-C} as the interrupt signal. @item show remotebreak Show whether @value{GDBN} sends @code{BREAK} or @samp{Ctrl-C} to interrupt the remote program. @item set remoteflow on @itemx set remoteflow off @kindex set remoteflow Enable or disable hardware flow control (@code{RTS}/@code{CTS}) on the serial port used to communicate to the remote target. @item show remoteflow @kindex show remoteflow Show the current setting of hardware flow control. @item set remotelogbase @var{base} Set the base (a.k.a.@: radix) of logging serial protocol communications to @var{base}. Supported values of @var{base} are: @code{ascii}, @code{octal}, and @code{hex}. The default is @code{ascii}. @item show remotelogbase Show the current setting of the radix for logging remote serial protocol. @item set remotelogfile @var{file} @cindex record serial communications on file Record remote serial communications on the named @var{file}. The default is not to record at all. @item show remotelogfile Show the current setting of the file name on which to record the serial communications. @item set remotetimeout @var{num} @cindex timeout for serial communications @cindex remote timeout Set the timeout limit to wait for the remote target to respond to @var{num} seconds. The default is 2 seconds. @item show remotetimeout Show the current number of seconds to wait for the remote target responses. @cindex limit hardware breakpoints and watchpoints @cindex remote target, limit break- and watchpoints @anchor{set remote hardware-watchpoint-limit} @anchor{set remote hardware-breakpoint-limit} @item set remote hardware-watchpoint-limit @var{limit} @itemx set remote hardware-breakpoint-limit @var{limit} Restrict @value{GDBN} to using @var{limit} remote hardware watchpoints or breakpoints. The @var{limit} can be set to 0 to disable hardware watchpoints or breakpoints, and @code{unlimited} for unlimited watchpoints or breakpoints. @item show remote hardware-watchpoint-limit @itemx show remote hardware-breakpoint-limit Show the current limit for the number of hardware watchpoints or breakpoints that @value{GDBN} can use. @cindex limit hardware watchpoints length @cindex remote target, limit watchpoints length @anchor{set remote hardware-watchpoint-length-limit} @item set remote hardware-watchpoint-length-limit @var{limit} Restrict @value{GDBN} to using @var{limit} bytes for the maximum length of a remote hardware watchpoint. A @var{limit} of 0 disables hardware watchpoints and @code{unlimited} allows watchpoints of any length. @item show remote hardware-watchpoint-length-limit Show the current limit (in bytes) of the maximum length of a remote hardware watchpoint. @item set remote exec-file @var{filename} @itemx show remote exec-file @anchor{set remote exec-file} @cindex executable file, for remote target Select the file used for @code{run} with @code{target extended-remote}. This should be set to a filename valid on the target system. If it is not set, the target will use a default filename (e.g.@: the last program run). @item set remote interrupt-sequence @cindex interrupt remote programs @cindex select Ctrl-C, BREAK or BREAK-g Allow the user to select one of @samp{Ctrl-C}, a @code{BREAK} or @samp{BREAK-g} as the sequence to the remote target in order to interrupt the execution. @samp{Ctrl-C} is a default. Some system prefers @code{BREAK} which is high level of serial line for some certain time. Linux kernel prefers @samp{BREAK-g}, a.k.a Magic SysRq g. It is @code{BREAK} signal followed by character @code{g}. @item show interrupt-sequence Show which of @samp{Ctrl-C}, @code{BREAK} or @code{BREAK-g} is sent by @value{GDBN} to interrupt the remote program. @code{BREAK-g} is BREAK signal followed by @code{g} and also known as Magic SysRq g. @item set remote interrupt-on-connect @cindex send interrupt-sequence on start Specify whether interrupt-sequence is sent to remote target when @value{GDBN} connects to it. This is mostly needed when you debug Linux kernel. Linux kernel expects @code{BREAK} followed by @code{g} which is known as Magic SysRq g in order to connect @value{GDBN}. @item show interrupt-on-connect Show whether interrupt-sequence is sent to remote target when @value{GDBN} connects to it. @kindex set tcp @kindex show tcp @item set tcp auto-retry on @cindex auto-retry, for remote TCP target Enable auto-retry for remote TCP connections. This is useful if the remote debugging agent is launched in parallel with @value{GDBN}; there is a race condition because the agent may not become ready to accept the connection before @value{GDBN} attempts to connect. When auto-retry is enabled, if the initial attempt to connect fails, @value{GDBN} reattempts to establish the connection using the timeout specified by @code{set tcp connect-timeout}. @item set tcp auto-retry off Do not auto-retry failed TCP connections. @item show tcp auto-retry Show the current auto-retry setting. @item set tcp connect-timeout @var{seconds} @itemx set tcp connect-timeout unlimited @cindex connection timeout, for remote TCP target @cindex timeout, for remote target connection Set the timeout for establishing a TCP connection to the remote target to @var{seconds}. The timeout affects both polling to retry failed connections (enabled by @code{set tcp auto-retry on}) and waiting for connections that are merely slow to complete, and represents an approximate cumulative value. If @var{seconds} is @code{unlimited}, there is no timeout and @value{GDBN} will keep attempting to establish a connection forever, unless interrupted with @kbd{Ctrl-c}. The default is 15 seconds. @item show tcp connect-timeout Show the current connection timeout setting. @end table @cindex remote packets, enabling and disabling The @value{GDBN} remote protocol autodetects the packets supported by your debugging stub. If you need to override the autodetection, you can use these commands to enable or disable individual packets. Each packet can be set to @samp{on} (the remote target supports this packet), @samp{off} (the remote target does not support this packet), or @samp{auto} (detect remote target support for this packet). They all default to @samp{auto}. For more information about each packet, see @ref{Remote Protocol}. During normal use, you should not have to use any of these commands. If you do, that may be a bug in your remote debugging stub, or a bug in @value{GDBN}. You may want to report the problem to the @value{GDBN} developers. For each packet @var{name}, the command to enable or disable the packet is @code{set remote @var{name}-packet}. The available settings are: @multitable @columnfractions 0.28 0.32 0.25 @item Command Name @tab Remote Packet @tab Related Features @item @code{fetch-register} @tab @code{p} @tab @code{info registers} @item @code{set-register} @tab @code{P} @tab @code{set} @item @code{binary-download} @tab @code{X} @tab @code{load}, @code{set} @item @code{read-aux-vector} @tab @code{qXfer:auxv:read} @tab @code{info auxv} @item @code{symbol-lookup} @tab @code{qSymbol} @tab Detecting multiple threads @item @code{attach} @tab @code{vAttach} @tab @code{attach} @item @code{verbose-resume} @tab @code{vCont} @tab Stepping or resuming multiple threads @item @code{run} @tab @code{vRun} @tab @code{run} @item @code{software-breakpoint} @tab @code{Z0} @tab @code{break} @item @code{hardware-breakpoint} @tab @code{Z1} @tab @code{hbreak} @item @code{write-watchpoint} @tab @code{Z2} @tab @code{watch} @item @code{read-watchpoint} @tab @code{Z3} @tab @code{rwatch} @item @code{access-watchpoint} @tab @code{Z4} @tab @code{awatch} @item @code{pid-to-exec-file} @tab @code{qXfer:exec-file:read} @tab @code{attach}, @code{run} @item @code{target-features} @tab @code{qXfer:features:read} @tab @code{set architecture} @item @code{library-info} @tab @code{qXfer:libraries:read} @tab @code{info sharedlibrary} @item @code{memory-map} @tab @code{qXfer:memory-map:read} @tab @code{info mem} @item @code{read-sdata-object} @tab @code{qXfer:sdata:read} @tab @code{print $_sdata} @item @code{read-siginfo-object} @tab @code{qXfer:siginfo:read} @tab @code{print $_siginfo} @item @code{write-siginfo-object} @tab @code{qXfer:siginfo:write} @tab @code{set $_siginfo} @item @code{threads} @tab @code{qXfer:threads:read} @tab @code{info threads} @item @code{get-thread-local-@*storage-address} @tab @code{qGetTLSAddr} @tab Displaying @code{__thread} variables @item @code{get-thread-information-block-address} @tab @code{qGetTIBAddr} @tab Display MS-Windows Thread Information Block. @item @code{search-memory} @tab @code{qSearch:memory} @tab @code{find} @item @code{supported-packets} @tab @code{qSupported} @tab Remote communications parameters @item @code{catch-syscalls} @tab @code{QCatchSyscalls} @tab @code{catch syscall} @item @code{pass-signals} @tab @code{QPassSignals} @tab @code{handle @var{signal}} @item @code{program-signals} @tab @code{QProgramSignals} @tab @code{handle @var{signal}} @item @code{hostio-close-packet} @tab @code{vFile:close} @tab @code{remote get}, @code{remote put} @item @code{hostio-open-packet} @tab @code{vFile:open} @tab @code{remote get}, @code{remote put} @item @code{hostio-pread-packet} @tab @code{vFile:pread} @tab @code{remote get}, @code{remote put} @item @code{hostio-pwrite-packet} @tab @code{vFile:pwrite} @tab @code{remote get}, @code{remote put} @item @code{hostio-unlink-packet} @tab @code{vFile:unlink} @tab @code{remote delete} @item @code{hostio-readlink-packet} @tab @code{vFile:readlink} @tab Host I/O @item @code{hostio-fstat-packet} @tab @code{vFile:fstat} @tab Host I/O @item @code{hostio-setfs-packet} @tab @code{vFile:setfs} @tab Host I/O @item @code{noack-packet} @tab @code{QStartNoAckMode} @tab Packet acknowledgment @item @code{osdata} @tab @code{qXfer:osdata:read} @tab @code{info os} @item @code{query-attached} @tab @code{qAttached} @tab Querying remote process attach state. @item @code{trace-buffer-size} @tab @code{QTBuffer:size} @tab @code{set trace-buffer-size} @item @code{trace-status} @tab @code{qTStatus} @tab @code{tstatus} @item @code{traceframe-info} @tab @code{qXfer:traceframe-info:read} @tab Traceframe info @item @code{install-in-trace} @tab @code{InstallInTrace} @tab Install tracepoint in tracing @item @code{disable-randomization} @tab @code{QDisableRandomization} @tab @code{set disable-randomization} @item @code{startup-with-shell} @tab @code{QStartupWithShell} @tab @code{set startup-with-shell} @item @code{environment-hex-encoded} @tab @code{QEnvironmentHexEncoded} @tab @code{set environment} @item @code{environment-unset} @tab @code{QEnvironmentUnset} @tab @code{unset environment} @item @code{environment-reset} @tab @code{QEnvironmentReset} @tab @code{Reset the inferior environment (i.e., unset user-set variables)} @item @code{set-working-dir} @tab @code{QSetWorkingDir} @tab @code{set cwd} @item @code{conditional-breakpoints-packet} @tab @code{Z0 and Z1} @tab @code{Support for target-side breakpoint condition evaluation} @item @code{multiprocess-extensions} @tab @code{multiprocess extensions} @tab Debug multiple processes and remote process PID awareness @item @code{swbreak-feature} @tab @code{swbreak stop reason} @tab @code{break} @item @code{hwbreak-feature} @tab @code{hwbreak stop reason} @tab @code{hbreak} @item @code{fork-event-feature} @tab @code{fork stop reason} @tab @code{fork} @item @code{vfork-event-feature} @tab @code{vfork stop reason} @tab @code{vfork} @item @code{exec-event-feature} @tab @code{exec stop reason} @tab @code{exec} @item @code{thread-events} @tab @code{QThreadEvents} @tab Tracking thread lifetime. @item @code{no-resumed-stop-reply} @tab @code{no resumed thread left stop reply} @tab Tracking thread lifetime. @end multitable @node Remote Stub @section Implementing a Remote Stub @cindex debugging stub, example @cindex remote stub, example @cindex stub example, remote debugging The stub files provided with @value{GDBN} implement the target side of the communication protocol, and the @value{GDBN} side is implemented in the @value{GDBN} source file @file{remote.c}. Normally, you can simply allow these subroutines to communicate, and ignore the details. (If you're implementing your own stub file, you can still ignore the details: start with one of the existing stub files. @file{sparc-stub.c} is the best organized, and therefore the easiest to read.) @cindex remote serial debugging, overview To debug a program running on another machine (the debugging @dfn{target} machine), you must first arrange for all the usual prerequisites for the program to run by itself. For example, for a C program, you need: @enumerate @item A startup routine to set up the C runtime environment; these usually have a name like @file{crt0}. The startup routine may be supplied by your hardware supplier, or you may have to write your own. @item A C subroutine library to support your program's subroutine calls, notably managing input and output. @item A way of getting your program to the other machine---for example, a download program. These are often supplied by the hardware manufacturer, but you may have to write your own from hardware documentation. @end enumerate The next step is to arrange for your program to use a serial port to communicate with the machine where @value{GDBN} is running (the @dfn{host} machine). In general terms, the scheme looks like this: @table @emph @item On the host, @value{GDBN} already understands how to use this protocol; when everything else is set up, you can simply use the @samp{target remote} command (@pxref{Targets,,Specifying a Debugging Target}). @item On the target, you must link with your program a few special-purpose subroutines that implement the @value{GDBN} remote serial protocol. The file containing these subroutines is called a @dfn{debugging stub}. On certain remote targets, you can use an auxiliary program @code{gdbserver} instead of linking a stub into your program. @xref{Server,,Using the @code{gdbserver} Program}, for details. @end table The debugging stub is specific to the architecture of the remote machine; for example, use @file{sparc-stub.c} to debug programs on @sc{sparc} boards. @cindex remote serial stub list These working remote stubs are distributed with @value{GDBN}: @table @code @item i386-stub.c @cindex @file{i386-stub.c} @cindex Intel @cindex i386 For Intel 386 and compatible architectures. @item m68k-stub.c @cindex @file{m68k-stub.c} @cindex Motorola 680x0 @cindex m680x0 For Motorola 680x0 architectures. @item sh-stub.c @cindex @file{sh-stub.c} @cindex Renesas @cindex SH For Renesas SH architectures. @item sparc-stub.c @cindex @file{sparc-stub.c} @cindex Sparc For @sc{sparc} architectures. @item sparcl-stub.c @cindex @file{sparcl-stub.c} @cindex Fujitsu @cindex SparcLite For Fujitsu @sc{sparclite} architectures. @end table The @file{README} file in the @value{GDBN} distribution may list other recently added stubs. @menu * Stub Contents:: What the stub can do for you * Bootstrapping:: What you must do for the stub * Debug Session:: Putting it all together @end menu @node Stub Contents @subsection What the Stub Can Do for You @cindex remote serial stub The debugging stub for your architecture supplies these three subroutines: @table @code @item set_debug_traps @findex set_debug_traps @cindex remote serial stub, initialization This routine arranges for @code{handle_exception} to run when your program stops. You must call this subroutine explicitly in your program's startup code. @item handle_exception @findex handle_exception @cindex remote serial stub, main routine This is the central workhorse, but your program never calls it explicitly---the setup code arranges for @code{handle_exception} to run when a trap is triggered. @code{handle_exception} takes control when your program stops during execution (for example, on a breakpoint), and mediates communications with @value{GDBN} on the host machine. This is where the communications protocol is implemented; @code{handle_exception} acts as the @value{GDBN} representative on the target machine. It begins by sending summary information on the state of your program, then continues to execute, retrieving and transmitting any information @value{GDBN} needs, until you execute a @value{GDBN} command that makes your program resume; at that point, @code{handle_exception} returns control to your own code on the target machine. @item breakpoint @cindex @code{breakpoint} subroutine, remote Use this auxiliary subroutine to make your program contain a breakpoint. Depending on the particular situation, this may be the only way for @value{GDBN} to get control. For instance, if your target machine has some sort of interrupt button, you won't need to call this; pressing the interrupt button transfers control to @code{handle_exception}---in effect, to @value{GDBN}. On some machines, simply receiving characters on the serial port may also trigger a trap; again, in that situation, you don't need to call @code{breakpoint} from your own program---simply running @samp{target remote} from the host @value{GDBN} session gets control. Call @code{breakpoint} if none of these is true, or if you simply want to make certain your program stops at a predetermined point for the start of your debugging session. @end table @node Bootstrapping @subsection What You Must Do for the Stub @cindex remote stub, support routines The debugging stubs that come with @value{GDBN} are set up for a particular chip architecture, but they have no information about the rest of your debugging target machine. First of all you need to tell the stub how to communicate with the serial port. @table @code @item int getDebugChar() @findex getDebugChar Write this subroutine to read a single character from the serial port. It may be identical to @code{getchar} for your target system; a different name is used to allow you to distinguish the two if you wish. @item void putDebugChar(int) @findex putDebugChar Write this subroutine to write a single character to the serial port. It may be identical to @code{putchar} for your target system; a different name is used to allow you to distinguish the two if you wish. @end table @cindex control C, and remote debugging @cindex interrupting remote targets If you want @value{GDBN} to be able to stop your program while it is running, you need to use an interrupt-driven serial driver, and arrange for it to stop when it receives a @code{^C} (@samp{\003}, the control-C character). That is the character which @value{GDBN} uses to tell the remote system to stop. Getting the debugging target to return the proper status to @value{GDBN} probably requires changes to the standard stub; one quick and dirty way is to just execute a breakpoint instruction (the ``dirty'' part is that @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}). Other routines you need to supply are: @table @code @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address}) @findex exceptionHandler Write this function to install @var{exception_address} in the exception handling tables. You need to do this because the stub does not have any way of knowing what the exception handling tables on your target system are like (for example, the processor's table might be in @sc{rom}, containing entries which point to a table in @sc{ram}). The @var{exception_number} specifies the exception which should be changed; its meaning is architecture-dependent (for example, different numbers might represent divide by zero, misaligned access, etc). When this exception occurs, control should be transferred directly to @var{exception_address}, and the processor state (stack, registers, and so on) should be just as it is when a processor exception occurs. So if you want to use a jump instruction to reach @var{exception_address}, it should be a simple jump, not a jump to subroutine. For the 386, @var{exception_address} should be installed as an interrupt gate so that interrupts are masked while the handler runs. The gate should be at privilege level 0 (the most privileged level). The @sc{sparc} and 68k stubs are able to mask interrupts themselves without help from @code{exceptionHandler}. @item void flush_i_cache() @findex flush_i_cache On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the instruction cache, if any, on your target machine. If there is no instruction cache, this subroutine may be a no-op. On target machines that have instruction caches, @value{GDBN} requires this function to make certain that the state of your program is stable. @end table @noindent You must also make sure this library routine is available: @table @code @item void *memset(void *, int, int) @findex memset This is the standard library function @code{memset} that sets an area of memory to a known value. If you have one of the free versions of @code{libc.a}, @code{memset} can be found there; otherwise, you must either obtain it from your hardware manufacturer, or write your own. @end table If you do not use the GNU C compiler, you may need other standard library subroutines as well; this varies from one stub to another, but in general the stubs are likely to use any of the common library subroutines which @code{@value{NGCC}} generates as inline code. @node Debug Session @subsection Putting it All Together @cindex remote serial debugging summary In summary, when your program is ready to debug, you must follow these steps. @enumerate @item Make sure you have defined the supporting low-level routines (@pxref{Bootstrapping,,What You Must Do for the Stub}): @display @code{getDebugChar}, @code{putDebugChar}, @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}. @end display @item Insert these lines in your program's startup code, before the main procedure is called: @smallexample set_debug_traps(); breakpoint(); @end smallexample On some machines, when a breakpoint trap is raised, the hardware automatically makes the PC point to the instruction after the breakpoint. If your machine doesn't do that, you may need to adjust @code{handle_exception} to arrange for it to return to the instruction after the breakpoint on this first invocation, so that your program doesn't keep hitting the initial breakpoint instead of making progress. @item For the 680x0 stub only, you need to provide a variable called @code{exceptionHook}. Normally you just use: @smallexample void (*exceptionHook)() = 0; @end smallexample @noindent but if before calling @code{set_debug_traps}, you set it to point to a function in your program, that function is called when @code{@value{GDBN}} continues after stopping on a trap (for example, bus error). The function indicated by @code{exceptionHook} is called with one parameter: an @code{int} which is the exception number. @item Compile and link together: your program, the @value{GDBN} debugging stub for your target architecture, and the supporting subroutines. @item Make sure you have a serial connection between your target machine and the @value{GDBN} host, and identify the serial port on the host. @item @c The "remote" target now provides a `load' command, so we should @c document that. FIXME. Download your program to your target machine (or get it there by whatever means the manufacturer provides), and start it. @item Start @value{GDBN} on the host, and connect to the target (@pxref{Connecting,,Connecting to a Remote Target}). @end enumerate @node Configurations @chapter Configuration-Specific Information While nearly all @value{GDBN} commands are available for all native and cross versions of the debugger, there are some exceptions. This chapter describes things that are only available in certain configurations. There are three major categories of configurations: native configurations, where the host and target are the same, embedded operating system configurations, which are usually the same for several different processor architectures, and bare embedded processors, which are quite different from each other. @menu * Native:: * Embedded OS:: * Embedded Processors:: * Architectures:: @end menu @node Native @section Native This section describes details specific to particular native configurations. @menu * BSD libkvm Interface:: Debugging BSD kernel memory images * Process Information:: Process information * DJGPP Native:: Features specific to the DJGPP port * Cygwin Native:: Features specific to the Cygwin port * Hurd Native:: Features specific to @sc{gnu} Hurd * Darwin:: Features specific to Darwin * FreeBSD:: Features specific to FreeBSD @end menu @node BSD libkvm Interface @subsection BSD libkvm Interface @cindex libkvm @cindex kernel memory image @cindex kernel crash dump BSD-derived systems (FreeBSD/NetBSD/OpenBSD) have a kernel memory interface that provides a uniform interface for accessing kernel virtual memory images, including live systems and crash dumps. @value{GDBN} uses this interface to allow you to debug live kernels and kernel crash dumps on many native BSD configurations. This is implemented as a special @code{kvm} debugging target. For debugging a live system, load the currently running kernel into @value{GDBN} and connect to the @code{kvm} target: @smallexample (@value{GDBP}) @b{target kvm} @end smallexample For debugging crash dumps, provide the file name of the crash dump as an argument: @smallexample (@value{GDBP}) @b{target kvm /var/crash/bsd.0} @end smallexample Once connected to the @code{kvm} target, the following commands are available: @table @code @kindex kvm @item kvm pcb Set current context from the @dfn{Process Control Block} (PCB) address. @item kvm proc Set current context from proc address. This command isn't available on modern FreeBSD systems. @end table @node Process Information @subsection Process Information @cindex /proc @cindex examine process image @cindex process info via @file{/proc} Some operating systems provide interfaces to fetch additional information about running processes beyond memory and per-thread register state. If @value{GDBN} is configured for an operating system with a supported interface, the command @code{info proc} is available to report information about the process running your program, or about any process running on your system. One supported interface is a facility called @samp{/proc} that can be used to examine the image of a running process using file-system subroutines. This facility is supported on @sc{gnu}/Linux and Solaris systems. On FreeBSD systems, system control nodes are used to query process information. In addition, some systems may provide additional process information in core files. Note that a core file may include a subset of the information available from a live process. Process information is currently available from cores created on @sc{gnu}/Linux and FreeBSD systems. @table @code @kindex info proc @cindex process ID @item info proc @itemx info proc @var{process-id} Summarize available information about a process. If a process ID is specified by @var{process-id}, display information about that process; otherwise display information about the program being debugged. The summary includes the debugged process ID, the command line used to invoke it, its current working directory, and its executable file's absolute file name. On some systems, @var{process-id} can be of the form @samp{[@var{pid}]/@var{tid}} which specifies a certain thread ID within a process. If the optional @var{pid} part is missing, it means a thread from the process being debugged (the leading @samp{/} still needs to be present, or else @value{GDBN} will interpret the number as a process ID rather than a thread ID). @item info proc cmdline @cindex info proc cmdline Show the original command line of the process. This command is supported on @sc{gnu}/Linux and FreeBSD. @item info proc cwd @cindex info proc cwd Show the current working directory of the process. This command is supported on @sc{gnu}/Linux and FreeBSD. @item info proc exe @cindex info proc exe Show the name of executable of the process. This command is supported on @sc{gnu}/Linux and FreeBSD. @item info proc files @cindex info proc files Show the file descriptors open by the process. For each open file descriptor, @value{GDBN} shows its number, type (file, directory, character device, socket), file pointer offset, and the name of the resource open on the descriptor. The resource name can be a file name (for files, directories, and devices) or a protocol followed by socket address (for network connections). This command is supported on FreeBSD. This example shows the open file descriptors for a process using a tty for standard input and output as well as two network sockets: @smallexample (gdb) info proc files 22136 process 22136 Open files: FD Type Offset Flags Name text file - r-------- /usr/bin/ssh ctty chr - rw------- /dev/pts/20 cwd dir - r-------- /usr/home/john root dir - r-------- / 0 chr 0x32933a4 rw------- /dev/pts/20 1 chr 0x32933a4 rw------- /dev/pts/20 2 chr 0x32933a4 rw------- /dev/pts/20 3 socket 0x0 rw----n-- tcp4 10.0.1.2:53014 -> 10.0.1.10:22 4 socket 0x0 rw------- unix stream:/tmp/ssh-FIt89oAzOn5f/agent.2456 @end smallexample @item info proc mappings @cindex memory address space mappings Report the memory address space ranges accessible in a process. On Solaris and FreeBSD systems, each memory range includes information on whether the process has read, write, or execute access rights to each range. On @sc{gnu}/Linux and FreeBSD systems, each memory range includes the object file which is mapped to that range. @item info proc stat @itemx info proc status @cindex process detailed status information Show additional process-related information, including the user ID and group ID; virtual memory usage; the signals that are pending, blocked, and ignored; its TTY; its consumption of system and user time; its stack size; its @samp{nice} value; etc. These commands are supported on @sc{gnu}/Linux and FreeBSD. For @sc{gnu}/Linux systems, see the @samp{proc} man page for more information (type @kbd{man 5 proc} from your shell prompt). For FreeBSD systems, @code{info proc stat} is an alias for @code{info proc status}. @item info proc all Show all the information about the process described under all of the above @code{info proc} subcommands. @ignore @comment These sub-options of 'info proc' were not included when @comment procfs.c was re-written. Keep their descriptions around @comment against the day when someone finds the time to put them back in. @kindex info proc times @item info proc times Starting time, user CPU time, and system CPU time for your program and its children. @kindex info proc id @item info proc id Report on the process IDs related to your program: its own process ID, the ID of its parent, the process group ID, and the session ID. @end ignore @item set procfs-trace @kindex set procfs-trace @cindex @code{procfs} API calls This command enables and disables tracing of @code{procfs} API calls. @item show procfs-trace @kindex show procfs-trace Show the current state of @code{procfs} API call tracing. @item set procfs-file @var{file} @kindex set procfs-file Tell @value{GDBN} to write @code{procfs} API trace to the named @var{file}. @value{GDBN} appends the trace info to the previous contents of the file. The default is to display the trace on the standard output. @item show procfs-file @kindex show procfs-file Show the file to which @code{procfs} API trace is written. @item proc-trace-entry @itemx proc-trace-exit @itemx proc-untrace-entry @itemx proc-untrace-exit @kindex proc-trace-entry @kindex proc-trace-exit @kindex proc-untrace-entry @kindex proc-untrace-exit These commands enable and disable tracing of entries into and exits from the @code{syscall} interface. @item info pidlist @kindex info pidlist @cindex process list, QNX Neutrino For QNX Neutrino only, this command displays the list of all the processes and all the threads within each process. @item info meminfo @kindex info meminfo @cindex mapinfo list, QNX Neutrino For QNX Neutrino only, this command displays the list of all mapinfos. @end table @node DJGPP Native @subsection Features for Debugging @sc{djgpp} Programs @cindex @sc{djgpp} debugging @cindex native @sc{djgpp} debugging @cindex MS-DOS-specific commands @cindex DPMI @sc{djgpp} is a port of the @sc{gnu} development tools to MS-DOS and MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on top of real-mode DOS systems and their emulations. @value{GDBN} supports native debugging of @sc{djgpp} programs, and defines a few commands specific to the @sc{djgpp} port. This subsection describes those commands. @table @code @kindex info dos @item info dos This is a prefix of @sc{djgpp}-specific commands which print information about the target system and important OS structures. @kindex sysinfo @cindex MS-DOS system info @cindex free memory information (MS-DOS) @item info dos sysinfo This command displays assorted information about the underlying platform: the CPU type and features, the OS version and flavor, the DPMI version, and the available conventional and DPMI memory. @cindex GDT @cindex LDT @cindex IDT @cindex segment descriptor tables @cindex descriptor tables display @item info dos gdt @itemx info dos ldt @itemx info dos idt These 3 commands display entries from, respectively, Global, Local, and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor tables are data structures which store a descriptor for each segment that is currently in use. The segment's selector is an index into a descriptor table; the table entry for that index holds the descriptor's base address and limit, and its attributes and access rights. A typical @sc{djgpp} program uses 3 segments: a code segment, a data segment (used for both data and the stack), and a DOS segment (which allows access to DOS/BIOS data structures and absolute addresses in conventional memory). However, the DPMI host will usually define additional segments in order to support the DPMI environment. @cindex garbled pointers These commands allow to display entries from the descriptor tables. Without an argument, all entries from the specified table are displayed. An argument, which should be an integer expression, means display a single entry whose index is given by the argument. For example, here's a convenient way to display information about the debugged program's data segment: @smallexample @exdent @code{(@value{GDBP}) info dos ldt $ds} @exdent @code{0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)} @end smallexample @noindent This comes in handy when you want to see whether a pointer is outside the data segment's limit (i.e.@: @dfn{garbled}). @cindex page tables display (MS-DOS) @item info dos pde @itemx info dos pte These two commands display entries from, respectively, the Page Directory and the Page Tables. Page Directories and Page Tables are data structures which control how virtual memory addresses are mapped into physical addresses. A Page Table includes an entry for every page of memory that is mapped into the program's address space; there may be several Page Tables, each one holding up to 4096 entries. A Page Directory has up to 4096 entries, one each for every Page Table that is currently in use. Without an argument, @kbd{info dos pde} displays the entire Page Directory, and @kbd{info dos pte} displays all the entries in all of the Page Tables. An argument, an integer expression, given to the @kbd{info dos pde} command means display only that entry from the Page Directory table. An argument given to the @kbd{info dos pte} command means display entries from a single Page Table, the one pointed to by the specified entry in the Page Directory. @cindex direct memory access (DMA) on MS-DOS These commands are useful when your program uses @dfn{DMA} (Direct Memory Access), which needs physical addresses to program the DMA controller. These commands are supported only with some DPMI servers. @cindex physical address from linear address @item info dos address-pte @var{addr} This command displays the Page Table entry for a specified linear address. The argument @var{addr} is a linear address which should already have the appropriate segment's base address added to it, because this command accepts addresses which may belong to @emph{any} segment. For example, here's how to display the Page Table entry for the page where a variable @code{i} is stored: @smallexample @exdent @code{(@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i} @exdent @code{Page Table entry for address 0x11a00d30:} @exdent @code{Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30} @end smallexample @noindent This says that @code{i} is stored at offset @code{0xd30} from the page whose physical base address is @code{0x02698000}, and shows all the attributes of that page. Note that you must cast the addresses of variables to a @code{char *}, since otherwise the value of @code{__djgpp_base_address}, the base address of all variables and functions in a @sc{djgpp} program, will be added using the rules of C pointer arithmetics: if @code{i} is declared an @code{int}, @value{GDBN} will add 4 times the value of @code{__djgpp_base_address} to the address of @code{i}. Here's another example, it displays the Page Table entry for the transfer buffer: @smallexample @exdent @code{(@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)} @exdent @code{Page Table entry for address 0x29110:} @exdent @code{Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110} @end smallexample @noindent (The @code{+ 3} offset is because the transfer buffer's address is the 3rd member of the @code{_go32_info_block} structure.) The output clearly shows that this DPMI server maps the addresses in conventional memory 1:1, i.e.@: the physical (@code{0x00029000} + @code{0x110}) and linear (@code{0x29110}) addresses are identical. This command is supported only with some DPMI servers. @end table @cindex DOS serial data link, remote debugging In addition to native debugging, the DJGPP port supports remote debugging via a serial data link. The following commands are specific to remote serial debugging in the DJGPP port of @value{GDBN}. @table @code @kindex set com1base @kindex set com1irq @kindex set com2base @kindex set com2irq @kindex set com3base @kindex set com3irq @kindex set com4base @kindex set com4irq @item set com1base @var{addr} This command sets the base I/O port address of the @file{COM1} serial port. @item set com1irq @var{irq} This command sets the @dfn{Interrupt Request} (@code{IRQ}) line to use for the @file{COM1} serial port. There are similar commands @samp{set com2base}, @samp{set com3irq}, etc.@: for setting the port address and the @code{IRQ} lines for the other 3 COM ports. @kindex show com1base @kindex show com1irq @kindex show com2base @kindex show com2irq @kindex show com3base @kindex show com3irq @kindex show com4base @kindex show com4irq The related commands @samp{show com1base}, @samp{show com1irq} etc.@: display the current settings of the base address and the @code{IRQ} lines used by the COM ports. @item info serial @kindex info serial @cindex DOS serial port status This command prints the status of the 4 DOS serial ports. For each port, it prints whether it's active or not, its I/O base address and IRQ number, whether it uses a 16550-style FIFO, its baudrate, and the counts of various errors encountered so far. @end table @node Cygwin Native @subsection Features for Debugging MS Windows PE Executables @cindex MS Windows debugging @cindex native Cygwin debugging @cindex Cygwin-specific commands @value{GDBN} supports native debugging of MS Windows programs, including DLLs with and without symbolic debugging information. @cindex Ctrl-BREAK, MS-Windows @cindex interrupt debuggee on MS-Windows MS-Windows programs that call @code{SetConsoleMode} to switch off the special meaning of the @samp{Ctrl-C} keystroke cannot be interrupted by typing @kbd{C-c}. For this reason, @value{GDBN} on MS-Windows supports @kbd{C-@key{BREAK}} as an alternative interrupt key sequence, which can be used to interrupt the debuggee even if it ignores @kbd{C-c}. There are various additional Cygwin-specific commands, described in this section. Working with DLLs that have no debugging symbols is described in @ref{Non-debug DLL Symbols}. @table @code @kindex info w32 @item info w32 This is a prefix of MS Windows-specific commands which print information about the target system and important OS structures. @item info w32 selector This command displays information returned by the Win32 API @code{GetThreadSelectorEntry} function. It takes an optional argument that is evaluated to a long value to give the information about this given selector. Without argument, this command displays information about the six segment registers. @item info w32 thread-information-block This command displays thread specific information stored in the Thread Information Block (readable on the X86 CPU family using @code{$fs} selector for 32-bit programs and @code{$gs} for 64-bit programs). @kindex signal-event @item signal-event @var{id} This command signals an event with user-provided @var{id}. Used to resume crashing process when attached to it using MS-Windows JIT debugging (AeDebug). To use it, create or edit the following keys in @code{HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\AeDebug} and/or @code{HKLM\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\AeDebug} (for x86_64 versions): @itemize @minus @item @code{Debugger} (REG_SZ) --- a command to launch the debugger. Suggested command is: @code{@var{fully-qualified-path-to-gdb.exe} -ex "attach %ld" -ex "signal-event %ld" -ex "continue"}. The first @code{%ld} will be replaced by the process ID of the crashing process, the second @code{%ld} will be replaced by the ID of the event that blocks the crashing process, waiting for @value{GDBN} to attach. @item @code{Auto} (REG_SZ) --- either @code{1} or @code{0}. @code{1} will make the system run debugger specified by the Debugger key automatically, @code{0} will cause a dialog box with ``OK'' and ``Cancel'' buttons to appear, which allows the user to either terminate the crashing process (OK) or debug it (Cancel). @end itemize @kindex set cygwin-exceptions @cindex debugging the Cygwin DLL @cindex Cygwin DLL, debugging @item set cygwin-exceptions @var{mode} If @var{mode} is @code{on}, @value{GDBN} will break on exceptions that happen inside the Cygwin DLL. If @var{mode} is @code{off}, @value{GDBN} will delay recognition of exceptions, and may ignore some exceptions which seem to be caused by internal Cygwin DLL ``bookkeeping''. This option is meant primarily for debugging the Cygwin DLL itself; the default value is @code{off} to avoid annoying @value{GDBN} users with false @code{SIGSEGV} signals. @kindex show cygwin-exceptions @item show cygwin-exceptions Displays whether @value{GDBN} will break on exceptions that happen inside the Cygwin DLL itself. @kindex set new-console @item set new-console @var{mode} If @var{mode} is @code{on} the debuggee will be started in a new console on next start. If @var{mode} is @code{off}, the debuggee will be started in the same console as the debugger. @kindex show new-console @item show new-console Displays whether a new console is used when the debuggee is started. @kindex set new-group @item set new-group @var{mode} This boolean value controls whether the debuggee should start a new group or stay in the same group as the debugger. This affects the way the Windows OS handles @samp{Ctrl-C}. @kindex show new-group @item show new-group Displays current value of new-group boolean. @kindex set debugevents @item set debugevents This boolean value adds debug output concerning kernel events related to the debuggee seen by the debugger. This includes events that signal thread and process creation and exit, DLL loading and unloading, console interrupts, and debugging messages produced by the Windows @code{OutputDebugString} API call. @kindex set debugexec @item set debugexec This boolean value adds debug output concerning execute events (such as resume thread) seen by the debugger. @kindex set debugexceptions @item set debugexceptions This boolean value adds debug output concerning exceptions in the debuggee seen by the debugger. @kindex set debugmemory @item set debugmemory This boolean value adds debug output concerning debuggee memory reads and writes by the debugger. @kindex set shell @item set shell This boolean values specifies whether the debuggee is called via a shell or directly (default value is on). @kindex show shell @item show shell Displays if the debuggee will be started with a shell. @end table @menu * Non-debug DLL Symbols:: Support for DLLs without debugging symbols @end menu @node Non-debug DLL Symbols @subsubsection Support for DLLs without Debugging Symbols @cindex DLLs with no debugging symbols @cindex Minimal symbols and DLLs Very often on windows, some of the DLLs that your program relies on do not include symbolic debugging information (for example, @file{kernel32.dll}). When @value{GDBN} doesn't recognize any debugging symbols in a DLL, it relies on the minimal amount of symbolic information contained in the DLL's export table. This section describes working with such symbols, known internally to @value{GDBN} as ``minimal symbols''. Note that before the debugged program has started execution, no DLLs will have been loaded. The easiest way around this problem is simply to start the program --- either by setting a breakpoint or letting the program run once to completion. @subsubsection DLL Name Prefixes In keeping with the naming conventions used by the Microsoft debugging tools, DLL export symbols are made available with a prefix based on the DLL name, for instance @code{KERNEL32!CreateFileA}. The plain name is also entered into the symbol table, so @code{CreateFileA} is often sufficient. In some cases there will be name clashes within a program (particularly if the executable itself includes full debugging symbols) necessitating the use of the fully qualified name when referring to the contents of the DLL. Use single-quotes around the name to avoid the exclamation mark (``!'') being interpreted as a language operator. Note that the internal name of the DLL may be all upper-case, even though the file name of the DLL is lower-case, or vice-versa. Since symbols within @value{GDBN} are @emph{case-sensitive} this may cause some confusion. If in doubt, try the @code{info functions} and @code{info variables} commands or even @code{maint print msymbols} (@pxref{Symbols}). Here's an example: @smallexample (@value{GDBP}) info function CreateFileA All functions matching regular expression "CreateFileA": Non-debugging symbols: 0x77e885f4 CreateFileA 0x77e885f4 KERNEL32!CreateFileA @end smallexample @smallexample (@value{GDBP}) info function ! All functions matching regular expression "!": Non-debugging symbols: 0x6100114c cygwin1!__assert 0x61004034 cygwin1!_dll_crt0@@0 0x61004240 cygwin1!dll_crt0(per_process *) [etc...] @end smallexample @subsubsection Working with Minimal Symbols Symbols extracted from a DLL's export table do not contain very much type information. All that @value{GDBN} can do is guess whether a symbol refers to a function or variable depending on the linker section that contains the symbol. Also note that the actual contents of the memory contained in a DLL are not available unless the program is running. This means that you cannot examine the contents of a variable or disassemble a function within a DLL without a running program. Variables are generally treated as pointers and dereferenced automatically. For this reason, it is often necessary to prefix a variable name with the address-of operator (``&'') and provide explicit type information in the command. Here's an example of the type of problem: @smallexample (@value{GDBP}) print 'cygwin1!__argv' 'cygwin1!__argv' has unknown type; cast it to its declared type @end smallexample @smallexample (@value{GDBP}) x 'cygwin1!__argv' 'cygwin1!__argv' has unknown type; cast it to its declared type @end smallexample And two possible solutions: @smallexample (@value{GDBP}) print ((char **)'cygwin1!__argv')[0] $2 = 0x22fd98 "/cygdrive/c/mydirectory/myprogram" @end smallexample @smallexample (@value{GDBP}) x/2x &'cygwin1!__argv' 0x610c0aa8 <cygwin1!__argv>: 0x10021608 0x00000000 (@value{GDBP}) x/x 0x10021608 0x10021608: 0x0022fd98 (@value{GDBP}) x/s 0x0022fd98 0x22fd98: "/cygdrive/c/mydirectory/myprogram" @end smallexample Setting a break point within a DLL is possible even before the program starts execution. However, under these circumstances, @value{GDBN} can't examine the initial instructions of the function in order to skip the function's frame set-up code. You can work around this by using ``*&'' to set the breakpoint at a raw memory address: @smallexample (@value{GDBP}) break *&'python22!PyOS_Readline' Breakpoint 1 at 0x1e04eff0 @end smallexample The author of these extensions is not entirely convinced that setting a break point within a shared DLL like @file{kernel32.dll} is completely safe. @node Hurd Native @subsection Commands Specific to @sc{gnu} Hurd Systems @cindex @sc{gnu} Hurd debugging This subsection describes @value{GDBN} commands specific to the @sc{gnu} Hurd native debugging. @table @code @item set signals @itemx set sigs @kindex set signals@r{, Hurd command} @kindex set sigs@r{, Hurd command} This command toggles the state of inferior signal interception by @value{GDBN}. Mach exceptions, such as breakpoint traps, are not affected by this command. @code{sigs} is a shorthand alias for @code{signals}. @item show signals @itemx show sigs @kindex show signals@r{, Hurd command} @kindex show sigs@r{, Hurd command} Show the current state of intercepting inferior's signals. @item set signal-thread @itemx set sigthread @kindex set signal-thread @kindex set sigthread This command tells @value{GDBN} which thread is the @code{libc} signal thread. That thread is run when a signal is delivered to a running process. @code{set sigthread} is the shorthand alias of @code{set signal-thread}. @item show signal-thread @itemx show sigthread @kindex show signal-thread @kindex show sigthread These two commands show which thread will run when the inferior is delivered a signal. @item set stopped @kindex set stopped@r{, Hurd command} This commands tells @value{GDBN} that the inferior process is stopped, as with the @code{SIGSTOP} signal. The stopped process can be continued by delivering a signal to it. @item show stopped @kindex show stopped@r{, Hurd command} This command shows whether @value{GDBN} thinks the debuggee is stopped. @item set exceptions @kindex set exceptions@r{, Hurd command} Use this command to turn off trapping of exceptions in the inferior. When exception trapping is off, neither breakpoints nor single-stepping will work. To restore the default, set exception trapping on. @item show exceptions @kindex show exceptions@r{, Hurd command} Show the current state of trapping exceptions in the inferior. @item set task pause @kindex set task@r{, Hurd commands} @cindex task attributes (@sc{gnu} Hurd) @cindex pause current task (@sc{gnu} Hurd) This command toggles task suspension when @value{GDBN} has control. Setting it to on takes effect immediately, and the task is suspended whenever @value{GDBN} gets control. Setting it to off will take effect the next time the inferior is continued. If this option is set to off, you can use @code{set thread default pause on} or @code{set thread pause on} (see below) to pause individual threads. @item show task pause @kindex show task@r{, Hurd commands} Show the current state of task suspension. @item set task detach-suspend-count @cindex task suspend count @cindex detach from task, @sc{gnu} Hurd This command sets the suspend count the task will be left with when @value{GDBN} detaches from it. @item show task detach-suspend-count Show the suspend count the task will be left with when detaching. @item set task exception-port @itemx set task excp @cindex task exception port, @sc{gnu} Hurd This command sets the task exception port to which @value{GDBN} will forward exceptions. The argument should be the value of the @dfn{send rights} of the task. @code{set task excp} is a shorthand alias. @item set noninvasive @cindex noninvasive task options This command switches @value{GDBN} to a mode that is the least invasive as far as interfering with the inferior is concerned. This is the same as using @code{set task pause}, @code{set exceptions}, and @code{set signals} to values opposite to the defaults. @item info send-rights @itemx info receive-rights @itemx info port-rights @itemx info port-sets @itemx info dead-names @itemx info ports @itemx info psets @cindex send rights, @sc{gnu} Hurd @cindex receive rights, @sc{gnu} Hurd @cindex port rights, @sc{gnu} Hurd @cindex port sets, @sc{gnu} Hurd @cindex dead names, @sc{gnu} Hurd These commands display information about, respectively, send rights, receive rights, port rights, port sets, and dead names of a task. There are also shorthand aliases: @code{info ports} for @code{info port-rights} and @code{info psets} for @code{info port-sets}. @item set thread pause @kindex set thread@r{, Hurd command} @cindex thread properties, @sc{gnu} Hurd @cindex pause current thread (@sc{gnu} Hurd) This command toggles current thread suspension when @value{GDBN} has control. Setting it to on takes effect immediately, and the current thread is suspended whenever @value{GDBN} gets control. Setting it to off will take effect the next time the inferior is continued. Normally, this command has no effect, since when @value{GDBN} has control, the whole task is suspended. However, if you used @code{set task pause off} (see above), this command comes in handy to suspend only the current thread. @item show thread pause @kindex show thread@r{, Hurd command} This command shows the state of current thread suspension. @item set thread run This command sets whether the current thread is allowed to run. @item show thread run Show whether the current thread is allowed to run. @item set thread detach-suspend-count @cindex thread suspend count, @sc{gnu} Hurd @cindex detach from thread, @sc{gnu} Hurd This command sets the suspend count @value{GDBN} will leave on a thread when detaching. This number is relative to the suspend count found by @value{GDBN} when it notices the thread; use @code{set thread takeover-suspend-count} to force it to an absolute value. @item show thread detach-suspend-count Show the suspend count @value{GDBN} will leave on the thread when detaching. @item set thread exception-port @itemx set thread excp Set the thread exception port to which to forward exceptions. This overrides the port set by @code{set task exception-port} (see above). @code{set thread excp} is the shorthand alias. @item set thread takeover-suspend-count Normally, @value{GDBN}'s thread suspend counts are relative to the value @value{GDBN} finds when it notices each thread. This command changes the suspend counts to be absolute instead. @item set thread default @itemx show thread default @cindex thread default settings, @sc{gnu} Hurd Each of the above @code{set thread} commands has a @code{set thread default} counterpart (e.g., @code{set thread default pause}, @code{set thread default exception-port}, etc.). The @code{thread default} variety of commands sets the default thread properties for all threads; you can then change the properties of individual threads with the non-default commands. @end table @node Darwin @subsection Darwin @cindex Darwin @value{GDBN} provides the following commands specific to the Darwin target: @table @code @item set debug darwin @var{num} @kindex set debug darwin When set to a non zero value, enables debugging messages specific to the Darwin support. Higher values produce more verbose output. @item show debug darwin @kindex show debug darwin Show the current state of Darwin messages. @item set debug mach-o @var{num} @kindex set debug mach-o When set to a non zero value, enables debugging messages while @value{GDBN} is reading Darwin object files. (@dfn{Mach-O} is the file format used on Darwin for object and executable files.) Higher values produce more verbose output. This is a command to diagnose problems internal to @value{GDBN} and should not be needed in normal usage. @item show debug mach-o @kindex show debug mach-o Show the current state of Mach-O file messages. @item set mach-exceptions on @itemx set mach-exceptions off @kindex set mach-exceptions On Darwin, faults are first reported as a Mach exception and are then mapped to a Posix signal. Use this command to turn on trapping of Mach exceptions in the inferior. This might be sometimes useful to better understand the cause of a fault. The default is off. @item show mach-exceptions @kindex show mach-exceptions Show the current state of exceptions trapping. @end table @node FreeBSD @subsection FreeBSD @cindex FreeBSD When the ABI of a system call is changed in the FreeBSD kernel, this is implemented by leaving a compatibility system call using the old ABI at the existing number and allocating a new system call number for the version using the new ABI. As a convenience, when a system call is caught by name (@pxref{catch syscall}), compatibility system calls are also caught. For example, FreeBSD 12 introduced a new variant of the @code{kevent} system call and catching the @code{kevent} system call by name catches both variants: @smallexample (@value{GDBP}) catch syscall kevent Catchpoint 1 (syscalls 'freebsd11_kevent' [363] 'kevent' [560]) (@value{GDBP}) @end smallexample @node Embedded OS @section Embedded Operating Systems This section describes configurations involving the debugging of embedded operating systems that are available for several different architectures. @value{GDBN} includes the ability to debug programs running on various real-time operating systems. @node Embedded Processors @section Embedded Processors This section goes into details specific to particular embedded configurations. @cindex send command to simulator Whenever a specific embedded processor has a simulator, @value{GDBN} allows to send an arbitrary command to the simulator. @table @code @item sim @var{command} @kindex sim@r{, a command} Send an arbitrary @var{command} string to the simulator. Consult the documentation for the specific simulator in use for information about acceptable commands. @end table @menu * ARC:: Synopsys ARC * ARM:: ARM * M68K:: Motorola M68K * MicroBlaze:: Xilinx MicroBlaze * MIPS Embedded:: MIPS Embedded * OpenRISC 1000:: OpenRISC 1000 (or1k) * PowerPC Embedded:: PowerPC Embedded * AVR:: Atmel AVR * CRIS:: CRIS * Super-H:: Renesas Super-H @end menu @node ARC @subsection Synopsys ARC @cindex Synopsys ARC @cindex ARC specific commands @cindex ARC600 @cindex ARC700 @cindex ARC EM @cindex ARC HS @value{GDBN} provides the following ARC-specific commands: @table @code @item set debug arc @kindex set debug arc Control the level of ARC specific debug messages. Use 0 for no messages (the default), 1 for debug messages, and 2 for even more debug messages. @item show debug arc @kindex show debug arc Show the level of ARC specific debugging in operation. @item maint print arc arc-instruction @var{address} @kindex maint print arc arc-instruction Print internal disassembler information about instruction at a given address. @end table @node ARM @subsection ARM @value{GDBN} provides the following ARM-specific commands: @table @code @item set arm disassembler @kindex set arm This commands selects from a list of disassembly styles. The @code{"std"} style is the standard style. @item show arm disassembler @kindex show arm Show the current disassembly style. @item set arm apcs32 @cindex ARM 32-bit mode This command toggles ARM operation mode between 32-bit and 26-bit. @item show arm apcs32 Display the current usage of the ARM 32-bit mode. @item set arm fpu @var{fputype} This command sets the ARM floating-point unit (FPU) type. The argument @var{fputype} can be one of these: @table @code @item auto Determine the FPU type by querying the OS ABI. @item softfpa Software FPU, with mixed-endian doubles on little-endian ARM processors. @item fpa GCC-compiled FPA co-processor. @item softvfp Software FPU with pure-endian doubles. @item vfp VFP co-processor. @end table @item show arm fpu Show the current type of the FPU. @item set arm abi This command forces @value{GDBN} to use the specified ABI. @item show arm abi Show the currently used ABI. @item set arm fallback-mode (arm|thumb|auto) @value{GDBN} uses the symbol table, when available, to determine whether instructions are ARM or Thumb. This command controls @value{GDBN}'s default behavior when the symbol table is not available. The default is @samp{auto}, which causes @value{GDBN} to use the current execution mode (from the @code{T} bit in the @code{CPSR} register). @item show arm fallback-mode Show the current fallback instruction mode. @item set arm force-mode (arm|thumb|auto) This command overrides use of the symbol table to determine whether instructions are ARM or Thumb. The default is @samp{auto}, which causes @value{GDBN} to use the symbol table and then the setting of @samp{set arm fallback-mode}. @item show arm force-mode Show the current forced instruction mode. @item set debug arm Toggle whether to display ARM-specific debugging messages from the ARM target support subsystem. @item show debug arm Show whether ARM-specific debugging messages are enabled. @end table @table @code @item target sim @r{[}@var{simargs}@r{]} @dots{} The @value{GDBN} ARM simulator accepts the following optional arguments. @table @code @item --swi-support=@var{type} Tell the simulator which SWI interfaces to support. The argument @var{type} may be a comma separated list of the following values. The default value is @code{all}. @table @code @item none @item demon @item angel @item redboot @item all @end table @end table @end table @node M68K @subsection M68k The Motorola m68k configuration includes ColdFire support. @node MicroBlaze @subsection MicroBlaze @cindex Xilinx MicroBlaze @cindex XMD, Xilinx Microprocessor Debugger The MicroBlaze is a soft-core processor supported on various Xilinx FPGAs, such as Spartan or Virtex series. Boards with these processors usually have JTAG ports which connect to a host system running the Xilinx Embedded Development Kit (EDK) or Software Development Kit (SDK). This host system is used to download the configuration bitstream to the target FPGA. The Xilinx Microprocessor Debugger (XMD) program communicates with the target board using the JTAG interface and presents a @code{gdbserver} interface to the board. By default @code{xmd} uses port @code{1234}. (While it is possible to change this default port, it requires the use of undocumented @code{xmd} commands. Contact Xilinx support if you need to do this.) Use these GDB commands to connect to the MicroBlaze target processor. @table @code @item target remote :1234 Use this command to connect to the target if you are running @value{GDBN} on the same system as @code{xmd}. @item target remote @var{xmd-host}:1234 Use this command to connect to the target if it is connected to @code{xmd} running on a different system named @var{xmd-host}. @item load Use this command to download a program to the MicroBlaze target. @item set debug microblaze @var{n} Enable MicroBlaze-specific debugging messages if non-zero. @item show debug microblaze @var{n} Show MicroBlaze-specific debugging level. @end table @node MIPS Embedded @subsection @acronym{MIPS} Embedded @noindent @value{GDBN} supports these special commands for @acronym{MIPS} targets: @table @code @item set mipsfpu double @itemx set mipsfpu single @itemx set mipsfpu none @itemx set mipsfpu auto @itemx show mipsfpu @kindex set mipsfpu @kindex show mipsfpu @cindex @acronym{MIPS} remote floating point @cindex floating point, @acronym{MIPS} remote If your target board does not support the @acronym{MIPS} floating point coprocessor, you should use the command @samp{set mipsfpu none} (if you need this, you may wish to put the command in your @value{GDBN} init file). This tells @value{GDBN} how to find the return value of functions which return floating point values. It also allows @value{GDBN} to avoid saving the floating point registers when calling functions on the board. If you are using a floating point coprocessor with only single precision floating point support, as on the @sc{r4650} processor, use the command @samp{set mipsfpu single}. The default double precision floating point coprocessor may be selected using @samp{set mipsfpu double}. In previous versions the only choices were double precision or no floating point, so @samp{set mipsfpu on} will select double precision and @samp{set mipsfpu off} will select no floating point. As usual, you can inquire about the @code{mipsfpu} variable with @samp{show mipsfpu}. @end table @node OpenRISC 1000 @subsection OpenRISC 1000 @cindex OpenRISC 1000 @noindent The OpenRISC 1000 provides a free RISC instruction set architecture. It is mainly provided as a soft-core which can run on Xilinx, Altera and other FPGA's. @value{GDBN} for OpenRISC supports the below commands when connecting to a target: @table @code @kindex target sim @item target sim Runs the builtin CPU simulator which can run very basic programs but does not support most hardware functions like MMU. For more complex use cases the user is advised to run an external target, and connect using @samp{target remote}. Example: @code{target sim} @item set debug or1k Toggle whether to display OpenRISC-specific debugging messages from the OpenRISC target support subsystem. @item show debug or1k Show whether OpenRISC-specific debugging messages are enabled. @end table @node PowerPC Embedded @subsection PowerPC Embedded @cindex DVC register @value{GDBN} supports using the DVC (Data Value Compare) register to implement in hardware simple hardware watchpoint conditions of the form: @smallexample (@value{GDBP}) watch @var{ADDRESS|VARIABLE} \ if @var{ADDRESS|VARIABLE} == @var{CONSTANT EXPRESSION} @end smallexample The DVC register will be automatically used when @value{GDBN} detects such pattern in a condition expression, and the created watchpoint uses one debug register (either the @code{exact-watchpoints} option is on and the variable is scalar, or the variable has a length of one byte). This feature is available in native @value{GDBN} running on a Linux kernel version 2.6.34 or newer. When running on PowerPC embedded processors, @value{GDBN} automatically uses ranged hardware watchpoints, unless the @code{exact-watchpoints} option is on, in which case watchpoints using only one debug register are created when watching variables of scalar types. You can create an artificial array to watch an arbitrary memory region using one of the following commands (@pxref{Expressions}): @smallexample (@value{GDBP}) watch *((char *) @var{address})@@@var{length} (@value{GDBP}) watch @{char[@var{length}]@} @var{address} @end smallexample PowerPC embedded processors support masked watchpoints. See the discussion about the @code{mask} argument in @ref{Set Watchpoints}. @cindex ranged breakpoint PowerPC embedded processors support hardware accelerated @dfn{ranged breakpoints}. A ranged breakpoint stops execution of the inferior whenever it executes an instruction at any address within the range it specifies. To set a ranged breakpoint in @value{GDBN}, use the @code{break-range} command. @value{GDBN} provides the following PowerPC-specific commands: @table @code @kindex break-range @item break-range @var{start-location}, @var{end-location} Set a breakpoint for an address range given by @var{start-location} and @var{end-location}, which can specify a function name, a line number, an offset of lines from the current line or from the start location, or an address of an instruction (see @ref{Specify Location}, for a list of all the possible ways to specify a @var{location}.) The breakpoint will stop execution of the inferior whenever it executes an instruction at any address within the specified range, (including @var{start-location} and @var{end-location}.) @kindex set powerpc @item set powerpc soft-float @itemx show powerpc soft-float Force @value{GDBN} to use (or not use) a software floating point calling convention. By default, @value{GDBN} selects the calling convention based on the selected architecture and the provided executable file. @item set powerpc vector-abi @itemx show powerpc vector-abi Force @value{GDBN} to use the specified calling convention for vector arguments and return values. The valid options are @samp{auto}; @samp{generic}, to avoid vector registers even if they are present; @samp{altivec}, to use AltiVec registers; and @samp{spe} to use SPE registers. By default, @value{GDBN} selects the calling convention based on the selected architecture and the provided executable file. @item set powerpc exact-watchpoints @itemx show powerpc exact-watchpoints Allow @value{GDBN} to use only one debug register when watching a variable of scalar type, thus assuming that the variable is accessed through the address of its first byte. @end table @node AVR @subsection Atmel AVR @cindex AVR When configured for debugging the Atmel AVR, @value{GDBN} supports the following AVR-specific commands: @table @code @item info io_registers @kindex info io_registers@r{, AVR} @cindex I/O registers (Atmel AVR) This command displays information about the AVR I/O registers. For each register, @value{GDBN} prints its number and value. @end table @node CRIS @subsection CRIS @cindex CRIS When configured for debugging CRIS, @value{GDBN} provides the following CRIS-specific commands: @table @code @item set cris-version @var{ver} @cindex CRIS version Set the current CRIS version to @var{ver}, either @samp{10} or @samp{32}. The CRIS version affects register names and sizes. This command is useful in case autodetection of the CRIS version fails. @item show cris-version Show the current CRIS version. @item set cris-dwarf2-cfi @cindex DWARF-2 CFI and CRIS Set the usage of DWARF-2 CFI for CRIS debugging. The default is @samp{on}. Change to @samp{off} when using @code{gcc-cris} whose version is below @code{R59}. @item show cris-dwarf2-cfi Show the current state of using DWARF-2 CFI. @item set cris-mode @var{mode} @cindex CRIS mode Set the current CRIS mode to @var{mode}. It should only be changed when debugging in guru mode, in which case it should be set to @samp{guru} (the default is @samp{normal}). @item show cris-mode Show the current CRIS mode. @end table @node Super-H @subsection Renesas Super-H @cindex Super-H For the Renesas Super-H processor, @value{GDBN} provides these commands: @table @code @item set sh calling-convention @var{convention} @kindex set sh calling-convention Set the calling-convention used when calling functions from @value{GDBN}. Allowed values are @samp{gcc}, which is the default setting, and @samp{renesas}. With the @samp{gcc} setting, functions are called using the @value{NGCC} calling convention. If the DWARF-2 information of the called function specifies that the function follows the Renesas calling convention, the function is called using the Renesas calling convention. If the calling convention is set to @samp{renesas}, the Renesas calling convention is always used, regardless of the DWARF-2 information. This can be used to override the default of @samp{gcc} if debug information is missing, or the compiler does not emit the DWARF-2 calling convention entry for a function. @item show sh calling-convention @kindex show sh calling-convention Show the current calling convention setting. @end table @node Architectures @section Architectures This section describes characteristics of architectures that affect all uses of @value{GDBN} with the architecture, both native and cross. @menu * AArch64:: * i386:: * Alpha:: * MIPS:: * HPPA:: HP PA architecture * PowerPC:: * Nios II:: * Sparc64:: * S12Z:: @end menu @node AArch64 @subsection AArch64 @cindex AArch64 support When @value{GDBN} is debugging the AArch64 architecture, it provides the following special commands: @table @code @item set debug aarch64 @kindex set debug aarch64 This command determines whether AArch64 architecture-specific debugging messages are to be displayed. @item show debug aarch64 Show whether AArch64 debugging messages are displayed. @end table @subsubsection AArch64 SVE. @cindex AArch64 SVE. When @value{GDBN} is debugging the AArch64 architecture, if the Scalable Vector Extension (SVE) is present, then @value{GDBN} will provide the vector registers @code{$z0} through @code{$z31}, vector predicate registers @code{$p0} through @code{$p15}, and the @code{$ffr} register. In addition, the pseudo register @code{$vg} will be provided. This is the vector granule for the current thread and represents the number of 64-bit chunks in an SVE @code{z} register. If the vector length changes, then the @code{$vg} register will be updated, but the lengths of the @code{z} and @code{p} registers will not change. This is a known limitation of @value{GDBN} and does not affect the execution of the target process. @subsubsection AArch64 Pointer Authentication. @cindex AArch64 Pointer Authentication. When @value{GDBN} is debugging the AArch64 architecture, and the program is using the v8.3-A feature Pointer Authentication (PAC), then whenever the link register @code{$lr} is pointing to an PAC function its value will be masked. When GDB prints a backtrace, any addresses that required unmasking will be postfixed with the marker [PAC]. When using the MI, this is printed as part of the @code{addr_flags} field. @node i386 @subsection x86 Architecture-specific Issues @table @code @item set struct-convention @var{mode} @kindex set struct-convention @cindex struct return convention @cindex struct/union returned in registers Set the convention used by the inferior to return @code{struct}s and @code{union}s from functions to @var{mode}. Possible values of @var{mode} are @code{"pcc"}, @code{"reg"}, and @code{"default"} (the default). @code{"default"} or @code{"pcc"} means that @code{struct}s are returned on the stack, while @code{"reg"} means that a @code{struct} or a @code{union} whose size is 1, 2, 4, or 8 bytes will be returned in a register. @item show struct-convention @kindex show struct-convention Show the current setting of the convention to return @code{struct}s from functions. @end table @subsubsection Intel @dfn{Memory Protection Extensions} (MPX). @cindex Intel Memory Protection Extensions (MPX). Memory Protection Extension (MPX) adds the bound registers @samp{BND0} @footnote{The register named with capital letters represent the architecture registers.} through @samp{BND3}. Bound registers store a pair of 64-bit values which are the lower bound and upper bound. Bounds are effective addresses or memory locations. The upper bounds are architecturally represented in 1's complement form. A bound having lower bound = 0, and upper bound = 0 (1's complement of all bits set) will allow access to the entire address space. @samp{BND0} through @samp{BND3} are represented in @value{GDBN} as @samp{bnd0raw} through @samp{bnd3raw}. Pseudo registers @samp{bnd0} through @samp{bnd3} display the upper bound performing the complement of one operation on the upper bound value, i.e.@ when upper bound in @samp{bnd0raw} is 0 in the @value{GDBN} @samp{bnd0} it will be @code{0xfff@dots{}}. In this sense it can also be noted that the upper bounds are inclusive. As an example, assume that the register BND0 holds bounds for a pointer having access allowed for the range between 0x32 and 0x71. The values present on bnd0raw and bnd registers are presented as follows: @smallexample bnd0raw = @{0x32, 0xffffffff8e@} bnd0 = @{lbound = 0x32, ubound = 0x71@} : size 64 @end smallexample This way the raw value can be accessed via bnd0raw@dots{}bnd3raw. Any change on bnd0@dots{}bnd3 or bnd0raw@dots{}bnd3raw is reflect on its counterpart. When the bnd0@dots{}bnd3 registers are displayed via Python, the display includes the memory size, in bits, accessible to the pointer. Bounds can also be stored in bounds tables, which are stored in application memory. These tables store bounds for pointers by specifying the bounds pointer's value along with its bounds. Evaluating and changing bounds located in bound tables is therefore interesting while investigating bugs on MPX context. @value{GDBN} provides commands for this purpose: @table @code @item show mpx bound @var{pointer} @kindex show mpx bound Display bounds of the given @var{pointer}. @item set mpx bound @var{pointer}, @var{lbound}, @var{ubound} @kindex set mpx bound Set the bounds of a pointer in the bound table. This command takes three parameters: @var{pointer} is the pointers whose bounds are to be changed, @var{lbound} and @var{ubound} are new values for lower and upper bounds respectively. @end table When you call an inferior function on an Intel MPX enabled program, GDB sets the inferior's bound registers to the init (disabled) state before calling the function. As a consequence, bounds checks for the pointer arguments passed to the function will always pass. This is necessary because when you call an inferior function, the program is usually in the middle of the execution of other function. Since at that point bound registers are in an arbitrary state, not clearing them would lead to random bound violations in the called function. You can still examine the influence of the bound registers on the execution of the called function by stopping the execution of the called function at its prologue, setting bound registers, and continuing the execution. For example: @smallexample $ break *upper Breakpoint 2 at 0x4009de: file i386-mpx-call.c, line 47. $ print upper (a, b, c, d, 1) Breakpoint 2, upper (a=0x0, b=0x6e0000005b, c=0x0, d=0x0, len=48).... $ print $bnd0 @{lbound = 0x0, ubound = ffffffff@} : size -1 @end smallexample At this last step the value of bnd0 can be changed for investigation of bound violations caused along the execution of the call. In order to know how to set the bound registers or bound table for the call consult the ABI. @node Alpha @subsection Alpha See the following section. @node MIPS @subsection @acronym{MIPS} @cindex stack on Alpha @cindex stack on @acronym{MIPS} @cindex Alpha stack @cindex @acronym{MIPS} stack Alpha- and @acronym{MIPS}-based computers use an unusual stack frame, which sometimes requires @value{GDBN} to search backward in the object code to find the beginning of a function. @cindex response time, @acronym{MIPS} debugging To improve response time (especially for embedded applications, where @value{GDBN} may be restricted to a slow serial line for this search) you may want to limit the size of this search, using one of these commands: @table @code @cindex @code{heuristic-fence-post} (Alpha, @acronym{MIPS}) @item set heuristic-fence-post @var{limit} Restrict @value{GDBN} to examining at most @var{limit} bytes in its search for the beginning of a function. A value of @var{0} (the default) means there is no limit. However, except for @var{0}, the larger the limit the more bytes @code{heuristic-fence-post} must search and therefore the longer it takes to run. You should only need to use this command when debugging a stripped executable. @item show heuristic-fence-post Display the current limit. @end table @noindent These commands are available @emph{only} when @value{GDBN} is configured for debugging programs on Alpha or @acronym{MIPS} processors. Several @acronym{MIPS}-specific commands are available when debugging @acronym{MIPS} programs: @table @code @item set mips abi @var{arg} @kindex set mips abi @cindex set ABI for @acronym{MIPS} Tell @value{GDBN} which @acronym{MIPS} ABI is used by the inferior. Possible values of @var{arg} are: @table @samp @item auto The default ABI associated with the current binary (this is the default). @item o32 @item o64 @item n32 @item n64 @item eabi32 @item eabi64 @end table @item show mips abi @kindex show mips abi Show the @acronym{MIPS} ABI used by @value{GDBN} to debug the inferior. @item set mips compression @var{arg} @kindex set mips compression @cindex code compression, @acronym{MIPS} Tell @value{GDBN} which @acronym{MIPS} compressed @acronym{ISA, Instruction Set Architecture} encoding is used by the inferior. @value{GDBN} uses this for code disassembly and other internal interpretation purposes. This setting is only referred to when no executable has been associated with the debugging session or the executable does not provide information about the encoding it uses. Otherwise this setting is automatically updated from information provided by the executable. Possible values of @var{arg} are @samp{mips16} and @samp{micromips}. The default compressed @acronym{ISA} encoding is @samp{mips16}, as executables containing @acronym{MIPS16} code frequently are not identified as such. This setting is ``sticky''; that is, it retains its value across debugging sessions until reset either explicitly with this command or implicitly from an executable. The compiler and/or assembler typically add symbol table annotations to identify functions compiled for the @acronym{MIPS16} or @acronym{microMIPS} @acronym{ISA}s. If these function-scope annotations are present, @value{GDBN} uses them in preference to the global compressed @acronym{ISA} encoding setting. @item show mips compression @kindex show mips compression Show the @acronym{MIPS} compressed @acronym{ISA} encoding used by @value{GDBN} to debug the inferior. @item set mipsfpu @itemx show mipsfpu @xref{MIPS Embedded, set mipsfpu}. @item set mips mask-address @var{arg} @kindex set mips mask-address @cindex @acronym{MIPS} addresses, masking This command determines whether the most-significant 32 bits of 64-bit @acronym{MIPS} addresses are masked off. The argument @var{arg} can be @samp{on}, @samp{off}, or @samp{auto}. The latter is the default setting, which lets @value{GDBN} determine the correct value. @item show mips mask-address @kindex show mips mask-address Show whether the upper 32 bits of @acronym{MIPS} addresses are masked off or not. @item set remote-mips64-transfers-32bit-regs @kindex set remote-mips64-transfers-32bit-regs This command controls compatibility with 64-bit @acronym{MIPS} targets that transfer data in 32-bit quantities. If you have an old @acronym{MIPS} 64 target that transfers 32 bits for some registers, like @sc{sr} and @sc{fsr}, and 64 bits for other registers, set this option to @samp{on}. @item show remote-mips64-transfers-32bit-regs @kindex show remote-mips64-transfers-32bit-regs Show the current setting of compatibility with older @acronym{MIPS} 64 targets. @item set debug mips @kindex set debug mips This command turns on and off debugging messages for the @acronym{MIPS}-specific target code in @value{GDBN}. @item show debug mips @kindex show debug mips Show the current setting of @acronym{MIPS} debugging messages. @end table @node HPPA @subsection HPPA @cindex HPPA support When @value{GDBN} is debugging the HP PA architecture, it provides the following special commands: @table @code @item set debug hppa @kindex set debug hppa This command determines whether HPPA architecture-specific debugging messages are to be displayed. @item show debug hppa Show whether HPPA debugging messages are displayed. @item maint print unwind @var{address} @kindex maint print unwind@r{, HPPA} This command displays the contents of the unwind table entry at the given @var{address}. @end table @node PowerPC @subsection PowerPC @cindex PowerPC architecture When @value{GDBN} is debugging the PowerPC architecture, it provides a set of pseudo-registers to enable inspection of 128-bit wide Decimal Floating Point numbers stored in the floating point registers. These values must be stored in two consecutive registers, always starting at an even register like @code{f0} or @code{f2}. The pseudo-registers go from @code{$dl0} through @code{$dl15}, and are formed by joining the even/odd register pairs @code{f0} and @code{f1} for @code{$dl0}, @code{f2} and @code{f3} for @code{$dl1} and so on. For POWER7 processors, @value{GDBN} provides a set of pseudo-registers, the 64-bit wide Extended Floating Point Registers (@samp{f32} through @samp{f63}). @node Nios II @subsection Nios II @cindex Nios II architecture When @value{GDBN} is debugging the Nios II architecture, it provides the following special commands: @table @code @item set debug nios2 @kindex set debug nios2 This command turns on and off debugging messages for the Nios II target code in @value{GDBN}. @item show debug nios2 @kindex show debug nios2 Show the current setting of Nios II debugging messages. @end table @node Sparc64 @subsection Sparc64 @cindex Sparc64 support @cindex Application Data Integrity @subsubsection ADI Support The M7 processor supports an Application Data Integrity (ADI) feature that detects invalid data accesses. When software allocates memory and enables ADI on the allocated memory, it chooses a 4-bit version number, sets the version in the upper 4 bits of the 64-bit pointer to that data, and stores the 4-bit version in every cacheline of that data. Hardware saves the latter in spare bits in the cache and memory hierarchy. On each load and store, the processor compares the upper 4 VA (virtual address) bits to the cacheline's version. If there is a mismatch, the processor generates a version mismatch trap which can be either precise or disrupting. The trap is an error condition which the kernel delivers to the process as a SIGSEGV signal. Note that only 64-bit applications can use ADI and need to be built with ADI-enabled. Values of the ADI version tags, which are in granularity of a cacheline (64 bytes), can be viewed or modified. @table @code @kindex adi examine @item adi (examine | x) [ / @var{n} ] @var{addr} The @code{adi examine} command displays the value of one ADI version tag per cacheline. @var{n} is a decimal integer specifying the number in bytes; the default is 1. It specifies how much ADI version information, at the ratio of 1:ADI block size, to display. @var{addr} is the address in user address space where you want @value{GDBN} to begin displaying the ADI version tags. Below is an example of displaying ADI versions of variable "shmaddr". @smallexample (@value{GDBP}) adi x/100 shmaddr 0xfff800010002c000: 0 0 @end smallexample @kindex adi assign @item adi (assign | a) [ / @var{n} ] @var{addr} = @var{tag} The @code{adi assign} command is used to assign new ADI version tag to an address. @var{n} is a decimal integer specifying the number in bytes; the default is 1. It specifies how much ADI version information, at the ratio of 1:ADI block size, to modify. @var{addr} is the address in user address space where you want @value{GDBN} to begin modifying the ADI version tags. @var{tag} is the new ADI version tag. For example, do the following to modify then verify ADI versions of variable "shmaddr": @smallexample (@value{GDBP}) adi a/100 shmaddr = 7 (@value{GDBP}) adi x/100 shmaddr 0xfff800010002c000: 7 7 @end smallexample @end table @node S12Z @subsection S12Z @cindex S12Z support When @value{GDBN} is debugging the S12Z architecture, it provides the following special command: @table @code @item maint info bdccsr @kindex maint info bdccsr@r{, S12Z} This command displays the current value of the microprocessor's BDCCSR register. @end table @node Controlling GDB @chapter Controlling @value{GDBN} You can alter the way @value{GDBN} interacts with you by using the @code{set} command. For commands controlling how @value{GDBN} displays data, see @ref{Print Settings, ,Print Settings}. Other settings are described here. @menu * Prompt:: Prompt * Editing:: Command editing * Command History:: Command history * Screen Size:: Screen size * Output Styling:: Output styling * Numbers:: Numbers * ABI:: Configuring the current ABI * Auto-loading:: Automatically loading associated files * Messages/Warnings:: Optional warnings and messages * Debugging Output:: Optional messages about internal happenings * Other Misc Settings:: Other Miscellaneous Settings @end menu @node Prompt @section Prompt @cindex prompt @value{GDBN} indicates its readiness to read a command by printing a string called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You can change the prompt string with the @code{set prompt} command. For instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change the prompt in one of the @value{GDBN} sessions so that you can always tell which one you are talking to. @emph{Note:} @code{set prompt} does not add a space for you after the prompt you set. This allows you to set a prompt which ends in a space or a prompt that does not. @table @code @kindex set prompt @item set prompt @var{newprompt} Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth. @kindex show prompt @item show prompt Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}} @end table Versions of @value{GDBN} that ship with Python scripting enabled have prompt extensions. The commands for interacting with these extensions are: @table @code @kindex set extended-prompt @item set extended-prompt @var{prompt} Set an extended prompt that allows for substitutions. @xref{gdb.prompt}, for a list of escape sequences that can be used for substitution. Any escape sequences specified as part of the prompt string are replaced with the corresponding strings each time the prompt is displayed. For example: @smallexample set extended-prompt Current working directory: \w (gdb) @end smallexample Note that when an extended-prompt is set, it takes control of the @var{prompt_hook} hook. @xref{prompt_hook}, for further information. @kindex show extended-prompt @item show extended-prompt Prints the extended prompt. Any escape sequences specified as part of the prompt string with @code{set extended-prompt}, are replaced with the corresponding strings each time the prompt is displayed. @end table @node Editing @section Command Editing @cindex readline @cindex command line editing @value{GDBN} reads its input commands via the @dfn{Readline} interface. This @sc{gnu} library provides consistent behavior for programs which provide a command line interface to the user. Advantages are @sc{gnu} Emacs-style or @dfn{vi}-style inline editing of commands, @code{csh}-like history substitution, and a storage and recall of command history across debugging sessions. You may control the behavior of command line editing in @value{GDBN} with the command @code{set}. @table @code @kindex set editing @cindex editing @item set editing @itemx set editing on Enable command line editing (enabled by default). @item set editing off Disable command line editing. @kindex show editing @item show editing Show whether command line editing is enabled. @end table @ifset SYSTEM_READLINE @xref{Command Line Editing, , , rluserman, GNU Readline Library}, @end ifset @ifclear SYSTEM_READLINE @xref{Command Line Editing}, @end ifclear for more details about the Readline interface. Users unfamiliar with @sc{gnu} Emacs or @code{vi} are encouraged to read that chapter. @cindex Readline application name @value{GDBN} sets the Readline application name to @samp{gdb}. This is useful for conditions in @file{.inputrc}. @cindex operate-and-get-next @value{GDBN} defines a bindable Readline command, @code{operate-and-get-next}. This is bound to @kbd{C-o} by default. This command accepts the current line for execution and fetches the next line relative to the current line from the history for editing. Any argument is ignored. @node Command History @section Command History @cindex command history @value{GDBN} can keep track of the commands you type during your debugging sessions, so that you can be certain of precisely what happened. Use these commands to manage the @value{GDBN} command history facility. @value{GDBN} uses the @sc{gnu} History library, a part of the Readline package, to provide the history facility. @ifset SYSTEM_READLINE @xref{Using History Interactively, , , history, GNU History Library}, @end ifset @ifclear SYSTEM_READLINE @xref{Using History Interactively}, @end ifclear for the detailed description of the History library. To issue a command to @value{GDBN} without affecting certain aspects of the state which is seen by users, prefix it with @samp{server } (@pxref{Server Prefix}). This means that this command will not affect the command history, nor will it affect @value{GDBN}'s notion of which command to repeat if @key{RET} is pressed on a line by itself. @cindex @code{server}, command prefix The server prefix does not affect the recording of values into the value history; to print a value without recording it into the value history, use the @code{output} command instead of the @code{print} command. Here is the description of @value{GDBN} commands related to command history. @table @code @cindex history substitution @cindex history file @kindex set history filename @cindex @env{GDBHISTFILE}, environment variable @item set history filename @r{[}@var{fname}@r{]} Set the name of the @value{GDBN} command history file to @var{fname}. This is the file where @value{GDBN} reads an initial command history list, and where it writes the command history from this session when it exits. You can access this list through history expansion or through the history command editing characters listed below. This file defaults to the value of the environment variable @code{GDBHISTFILE}, or to @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable is not set. The @code{GDBHISTFILE} environment variable is read after processing any @value{GDBN} initialization files (@pxref{Startup}) and after processing any commands passed using command line options (for example, @code{-ex}). If the @var{fname} argument is not given, or if the @code{GDBHISTFILE} is the empty string then @value{GDBN} will neither try to load an existing history file, nor will it try to save the history on exit. @cindex save command history @kindex set history save @item set history save @itemx set history save on Record command history in a file, whose name may be specified with the @code{set history filename} command. By default, this option is disabled. The command history will be recorded when @value{GDBN} exits. If @code{set history filename} is set to the empty string then history saving is disabled, even when @code{set history save} is @code{on}. @item set history save off Don't record the command history into the file specified by @code{set history filename} when @value{GDBN} exits. @cindex history size @kindex set history size @cindex @env{GDBHISTSIZE}, environment variable @item set history size @var{size} @itemx set history size unlimited Set the number of commands which @value{GDBN} keeps in its history list. This defaults to the value of the environment variable @env{GDBHISTSIZE}, or to 256 if this variable is not set. Non-numeric values of @env{GDBHISTSIZE} are ignored. If @var{size} is @code{unlimited} or if @env{GDBHISTSIZE} is either a negative number or the empty string, then the number of commands @value{GDBN} keeps in the history list is unlimited. The @code{GDBHISTSIZE} environment variable is read after processing any @value{GDBN} initialization files (@pxref{Startup}) and after processing any commands passed using command line options (for example, @code{-ex}). @cindex remove duplicate history @kindex set history remove-duplicates @item set history remove-duplicates @var{count} @itemx set history remove-duplicates unlimited Control the removal of duplicate history entries in the command history list. If @var{count} is non-zero, @value{GDBN} will look back at the last @var{count} history entries and remove the first entry that is a duplicate of the current entry being added to the command history list. If @var{count} is @code{unlimited} then this lookbehind is unbounded. If @var{count} is 0, then removal of duplicate history entries is disabled. Only history entries added during the current session are considered for removal. This option is set to 0 by default. @end table History expansion assigns special meaning to the character @kbd{!}. @ifset SYSTEM_READLINE @xref{Event Designators, , , history, GNU History Library}, @end ifset @ifclear SYSTEM_READLINE @xref{Event Designators}, @end ifclear for more details. @cindex history expansion, turn on/off Since @kbd{!} is also the logical not operator in C, history expansion is off by default. If you decide to enable history expansion with the @code{set history expansion on} command, you may sometimes need to follow @kbd{!} (when it is used as logical not, in an expression) with a space or a tab to prevent it from being expanded. The readline history facilities do not attempt substitution on the strings @kbd{!=} and @kbd{!(}, even when history expansion is enabled. The commands to control history expansion are: @table @code @item set history expansion on @itemx set history expansion @kindex set history expansion Enable history expansion. History expansion is off by default. @item set history expansion off Disable history expansion. @c @group @kindex show history @item show history @itemx show history filename @itemx show history save @itemx show history size @itemx show history expansion These commands display the state of the @value{GDBN} history parameters. @code{show history} by itself displays all four states. @c @end group @end table @table @code @kindex show commands @cindex show last commands @cindex display command history @item show commands Display the last ten commands in the command history. @item show commands @var{n} Print ten commands centered on command number @var{n}. @item show commands + Print ten commands just after the commands last printed. @end table @node Screen Size @section Screen Size @cindex size of screen @cindex screen size @cindex pagination @cindex page size @cindex pauses in output Certain commands to @value{GDBN} may produce large amounts of information output to the screen. To help you read all of it, @value{GDBN} pauses and asks you for input at the end of each page of output. Type @key{RET} when you want to see one more page of output, @kbd{q} to discard the remaining output, or @kbd{c} to continue without paging for the rest of the current command. Also, the screen width setting determines when to wrap lines of output. Depending on what is being printed, @value{GDBN} tries to break the line at a readable place, rather than simply letting it overflow onto the following line. Normally @value{GDBN} knows the size of the screen from the terminal driver software. For example, on Unix @value{GDBN} uses the termcap data base together with the value of the @code{TERM} environment variable and the @code{stty rows} and @code{stty cols} settings. If this is not correct, you can override it with the @code{set height} and @code{set width} commands: @table @code @kindex set height @kindex set width @kindex show width @kindex show height @item set height @var{lpp} @itemx set height unlimited @itemx show height @itemx set width @var{cpl} @itemx set width unlimited @itemx show width These @code{set} commands specify a screen height of @var{lpp} lines and a screen width of @var{cpl} characters. The associated @code{show} commands display the current settings. If you specify a height of either @code{unlimited} or zero lines, @value{GDBN} does not pause during output no matter how long the output is. This is useful if output is to a file or to an editor buffer. Likewise, you can specify @samp{set width unlimited} or @samp{set width 0} to prevent @value{GDBN} from wrapping its output. @item set pagination on @itemx set pagination off @kindex set pagination Turn the output pagination on or off; the default is on. Turning pagination off is the alternative to @code{set height unlimited}. Note that running @value{GDBN} with the @option{--batch} option (@pxref{Mode Options, -batch}) also automatically disables pagination. @item show pagination @kindex show pagination Show the current pagination mode. @end table @node Output Styling @section Output Styling @cindex styling @cindex colors @kindex set style @kindex show style @value{GDBN} can style its output on a capable terminal. This is enabled by default on most systems, but disabled by default when in batch mode (@pxref{Mode Options}). Various style settings are available; and styles can also be disabled entirely. @table @code @item set style enabled @samp{on|off} Enable or disable all styling. The default is host-dependent, with most hosts defaulting to @samp{on}. @item show style enabled Show the current state of styling. @item set style sources @samp{on|off} Enable or disable source code styling. This affects whether source code, such as the output of the @code{list} command, is styled. Note that source styling only works if styling in general is enabled, and if @value{GDBN} was linked with the GNU Source Highlight library. The default is @samp{on}. @item show style sources Show the current state of source code styling. @end table Subcommands of @code{set style} control specific forms of styling. These subcommands all follow the same pattern: each style-able object can be styled with a foreground color, a background color, and an intensity. For example, the style of file names can be controlled using the @code{set style filename} group of commands: @table @code @item set style filename background @var{color} Set the background to @var{color}. Valid colors are @samp{none} (meaning the terminal's default color), @samp{black}, @samp{red}, @samp{green}, @samp{yellow}, @samp{blue}, @samp{magenta}, @samp{cyan}, and@samp{white}. @item set style filename foreground @var{color} Set the foreground to @var{color}. Valid colors are @samp{none} (meaning the terminal's default color), @samp{black}, @samp{red}, @samp{green}, @samp{yellow}, @samp{blue}, @samp{magenta}, @samp{cyan}, and@samp{white}. @item set style filename intensity @var{value} Set the intensity to @var{value}. Valid intensities are @samp{normal} (the default), @samp{bold}, and @samp{dim}. @end table The @code{show style} command and its subcommands are styling a style name in their output using its own style. So, use @command{show style} to see the complete list of styles, their characteristics and the visual aspect of each style. The style-able objects are: @table @code @item filename Control the styling of file names. By default, this style's foreground color is green. @item function Control the styling of function names. These are managed with the @code{set style function} family of commands. By default, this style's foreground color is yellow. @item variable Control the styling of variable names. These are managed with the @code{set style variable} family of commands. By default, this style's foreground color is cyan. @item address Control the styling of addresses. These are managed with the @code{set style address} family of commands. By default, this style's foreground color is blue. @item title Control the styling of titles. These are managed with the @code{set style title} family of commands. By default, this style's intensity is bold. Commands are using the title style to improve the readability of large output. For example, the commands @command{apropos} and @command{help} are using the title style for the command names. @item highlight Control the styling of highlightings. These are managed with the @code{set style highlight} family of commands. By default, this style's foreground color is red. Commands are using the highlight style to draw the user attention to some specific parts of their output. For example, the command @command{apropos -v REGEXP} uses the highlight style to mark the documentation parts matching @var{regexp}. @item tui-border Control the styling of the TUI border. Note that, unlike other styling options, only the color of the border can be controlled via @code{set style}. This was done for compatibility reasons, as TUI controls to set the border's intensity predated the addition of general styling to @value{GDBN}. @xref{TUI Configuration}. @item tui-active-border Control the styling of the active TUI border; that is, the TUI window that has the focus. @end table @node Numbers @section Numbers @cindex number representation @cindex entering numbers You can always enter numbers in octal, decimal, or hexadecimal in @value{GDBN} by the usual conventions: octal numbers begin with @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}. Numbers that neither begin with @samp{0} or @samp{0x}, nor end with a @samp{.} are, by default, entered in base 10; likewise, the default display for numbers---when no particular format is specified---is base 10. You can change the default base for both input and output with the commands described below. @table @code @kindex set input-radix @item set input-radix @var{base} Set the default base for numeric input. Supported choices for @var{base} are decimal 8, 10, or 16. The base must itself be specified either unambiguously or using the current input radix; for example, any of @smallexample set input-radix 012 set input-radix 10. set input-radix 0xa @end smallexample @noindent sets the input base to decimal. On the other hand, @samp{set input-radix 10} leaves the input radix unchanged, no matter what it was, since @samp{10}, being without any leading or trailing signs of its base, is interpreted in the current radix. Thus, if the current radix is 16, @samp{10} is interpreted in hex, i.e.@: as 16 decimal, which doesn't change the radix. @kindex set output-radix @item set output-radix @var{base} Set the default base for numeric display. Supported choices for @var{base} are decimal 8, 10, or 16. The base must itself be specified either unambiguously or using the current input radix. @kindex show input-radix @item show input-radix Display the current default base for numeric input. @kindex show output-radix @item show output-radix Display the current default base for numeric display. @item set radix @r{[}@var{base}@r{]} @itemx show radix @kindex set radix @kindex show radix These commands set and show the default base for both input and output of numbers. @code{set radix} sets the radix of input and output to the same base; without an argument, it resets the radix back to its default value of 10. @end table @node ABI @section Configuring the Current ABI @value{GDBN} can determine the @dfn{ABI} (Application Binary Interface) of your application automatically. However, sometimes you need to override its conclusions. Use these commands to manage @value{GDBN}'s view of the current ABI. @cindex OS ABI @kindex set osabi @kindex show osabi @cindex Newlib OS ABI and its influence on the longjmp handling One @value{GDBN} configuration can debug binaries for multiple operating system targets, either via remote debugging or native emulation. @value{GDBN} will autodetect the @dfn{OS ABI} (Operating System ABI) in use, but you can override its conclusion using the @code{set osabi} command. One example where this is useful is in debugging of binaries which use an alternate C library (e.g.@: @sc{uClibc} for @sc{gnu}/Linux) which does not have the same identifying marks that the standard C library for your platform provides. When @value{GDBN} is debugging the AArch64 architecture, it provides a ``Newlib'' OS ABI. This is useful for handling @code{setjmp} and @code{longjmp} when debugging binaries that use the @sc{newlib} C library. The ``Newlib'' OS ABI can be selected by @code{set osabi Newlib}. @table @code @item show osabi Show the OS ABI currently in use. @item set osabi With no argument, show the list of registered available OS ABI's. @item set osabi @var{abi} Set the current OS ABI to @var{abi}. @end table @cindex float promotion Generally, the way that an argument of type @code{float} is passed to a function depends on whether the function is prototyped. For a prototyped (i.e.@: ANSI/ISO style) function, @code{float} arguments are passed unchanged, according to the architecture's convention for @code{float}. For unprototyped (i.e.@: K&R style) functions, @code{float} arguments are first promoted to type @code{double} and then passed. Unfortunately, some forms of debug information do not reliably indicate whether a function is prototyped. If @value{GDBN} calls a function that is not marked as prototyped, it consults @kbd{set coerce-float-to-double}. @table @code @kindex set coerce-float-to-double @item set coerce-float-to-double @itemx set coerce-float-to-double on Arguments of type @code{float} will be promoted to @code{double} when passed to an unprototyped function. This is the default setting. @item set coerce-float-to-double off Arguments of type @code{float} will be passed directly to unprototyped functions. @kindex show coerce-float-to-double @item show coerce-float-to-double Show the current setting of promoting @code{float} to @code{double}. @end table @kindex set cp-abi @kindex show cp-abi @value{GDBN} needs to know the ABI used for your program's C@t{++} objects. The correct C@t{++} ABI depends on which C@t{++} compiler was used to build your application. @value{GDBN} only fully supports programs with a single C@t{++} ABI; if your program contains code using multiple C@t{++} ABI's or if @value{GDBN} can not identify your program's ABI correctly, you can tell @value{GDBN} which ABI to use. Currently supported ABI's include ``gnu-v2'', for @code{g++} versions before 3.0, ``gnu-v3'', for @code{g++} versions 3.0 and later, and ``hpaCC'' for the HP ANSI C@t{++} compiler. Other C@t{++} compilers may use the ``gnu-v2'' or ``gnu-v3'' ABI's as well. The default setting is ``auto''. @table @code @item show cp-abi Show the C@t{++} ABI currently in use. @item set cp-abi With no argument, show the list of supported C@t{++} ABI's. @item set cp-abi @var{abi} @itemx set cp-abi auto Set the current C@t{++} ABI to @var{abi}, or return to automatic detection. @end table @node Auto-loading @section Automatically loading associated files @cindex auto-loading @value{GDBN} sometimes reads files with commands and settings automatically, without being explicitly told so by the user. We call this feature @dfn{auto-loading}. While auto-loading is useful for automatically adapting @value{GDBN} to the needs of your project, it can sometimes produce unexpected results or introduce security risks (e.g., if the file comes from untrusted sources). @menu * Init File in the Current Directory:: @samp{set/show/info auto-load local-gdbinit} * libthread_db.so.1 file:: @samp{set/show/info auto-load libthread-db} * Auto-loading safe path:: @samp{set/show/info auto-load safe-path} * Auto-loading verbose mode:: @samp{set/show debug auto-load} @end menu There are various kinds of files @value{GDBN} can automatically load. In addition to these files, @value{GDBN} supports auto-loading code written in various extension languages. @xref{Auto-loading extensions}. Note that loading of these associated files (including the local @file{.gdbinit} file) requires accordingly configured @code{auto-load safe-path} (@pxref{Auto-loading safe path}). For these reasons, @value{GDBN} includes commands and options to let you control when to auto-load files and which files should be auto-loaded. @table @code @anchor{set auto-load off} @kindex set auto-load off @item set auto-load off Globally disable loading of all auto-loaded files. You may want to use this command with the @samp{-iex} option (@pxref{Option -init-eval-command}) such as: @smallexample $ @kbd{gdb -iex "set auto-load off" untrusted-executable corefile} @end smallexample Be aware that system init file (@pxref{System-wide configuration}) and init files from your home directory (@pxref{Home Directory Init File}) still get read (as they come from generally trusted directories). To prevent @value{GDBN} from auto-loading even those init files, use the @option{-nx} option (@pxref{Mode Options}), in addition to @code{set auto-load no}. @anchor{show auto-load} @kindex show auto-load @item show auto-load Show whether auto-loading of each specific @samp{auto-load} file(s) is enabled or disabled. @smallexample (gdb) show auto-load gdb-scripts: Auto-loading of canned sequences of commands scripts is on. libthread-db: Auto-loading of inferior specific libthread_db is on. local-gdbinit: Auto-loading of .gdbinit script from current directory is on. python-scripts: Auto-loading of Python scripts is on. safe-path: List of directories from which it is safe to auto-load files is $debugdir:$datadir/auto-load. scripts-directory: List of directories from which to load auto-loaded scripts is $debugdir:$datadir/auto-load. @end smallexample @anchor{info auto-load} @kindex info auto-load @item info auto-load Print whether each specific @samp{auto-load} file(s) have been auto-loaded or not. @smallexample (gdb) info auto-load gdb-scripts: Loaded Script Yes /home/user/gdb/gdb-gdb.gdb libthread-db: No auto-loaded libthread-db. local-gdbinit: Local .gdbinit file "/home/user/gdb/.gdbinit" has been loaded. python-scripts: Loaded Script Yes /home/user/gdb/gdb-gdb.py @end smallexample @end table These are @value{GDBN} control commands for the auto-loading: @multitable @columnfractions .5 .5 @item @xref{set auto-load off}. @tab Disable auto-loading globally. @item @xref{show auto-load}. @tab Show setting of all kinds of files. @item @xref{info auto-load}. @tab Show state of all kinds of files. @item @xref{set auto-load gdb-scripts}. @tab Control for @value{GDBN} command scripts. @item @xref{show auto-load gdb-scripts}. @tab Show setting of @value{GDBN} command scripts. @item @xref{info auto-load gdb-scripts}. @tab Show state of @value{GDBN} command scripts. @item @xref{set auto-load python-scripts}. @tab Control for @value{GDBN} Python scripts. @item @xref{show auto-load python-scripts}. @tab Show setting of @value{GDBN} Python scripts. @item @xref{info auto-load python-scripts}. @tab Show state of @value{GDBN} Python scripts. @item @xref{set auto-load guile-scripts}. @tab Control for @value{GDBN} Guile scripts. @item @xref{show auto-load guile-scripts}. @tab Show setting of @value{GDBN} Guile scripts. @item @xref{info auto-load guile-scripts}. @tab Show state of @value{GDBN} Guile scripts. @item @xref{set auto-load scripts-directory}. @tab Control for @value{GDBN} auto-loaded scripts location. @item @xref{show auto-load scripts-directory}. @tab Show @value{GDBN} auto-loaded scripts location. @item @xref{add-auto-load-scripts-directory}. @tab Add directory for auto-loaded scripts location list. @item @xref{set auto-load local-gdbinit}. @tab Control for init file in the current directory. @item @xref{show auto-load local-gdbinit}. @tab Show setting of init file in the current directory. @item @xref{info auto-load local-gdbinit}. @tab Show state of init file in the current directory. @item @xref{set auto-load libthread-db}. @tab Control for thread debugging library. @item @xref{show auto-load libthread-db}. @tab Show setting of thread debugging library. @item @xref{info auto-load libthread-db}. @tab Show state of thread debugging library. @item @xref{set auto-load safe-path}. @tab Control directories trusted for automatic loading. @item @xref{show auto-load safe-path}. @tab Show directories trusted for automatic loading. @item @xref{add-auto-load-safe-path}. @tab Add directory trusted for automatic loading. @end multitable @node Init File in the Current Directory @subsection Automatically loading init file in the current directory @cindex auto-loading init file in the current directory By default, @value{GDBN} reads and executes the canned sequences of commands from init file (if any) in the current working directory, see @ref{Init File in the Current Directory during Startup}. Note that loading of this local @file{.gdbinit} file also requires accordingly configured @code{auto-load safe-path} (@pxref{Auto-loading safe path}). @table @code @anchor{set auto-load local-gdbinit} @kindex set auto-load local-gdbinit @item set auto-load local-gdbinit [on|off] Enable or disable the auto-loading of canned sequences of commands (@pxref{Sequences}) found in init file in the current directory. @anchor{show auto-load local-gdbinit} @kindex show auto-load local-gdbinit @item show auto-load local-gdbinit Show whether auto-loading of canned sequences of commands from init file in the current directory is enabled or disabled. @anchor{info auto-load local-gdbinit} @kindex info auto-load local-gdbinit @item info auto-load local-gdbinit Print whether canned sequences of commands from init file in the current directory have been auto-loaded. @end table @node libthread_db.so.1 file @subsection Automatically loading thread debugging library @cindex auto-loading libthread_db.so.1 This feature is currently present only on @sc{gnu}/Linux native hosts. @value{GDBN} reads in some cases thread debugging library from places specific to the inferior (@pxref{set libthread-db-search-path}). The special @samp{libthread-db-search-path} entry @samp{$sdir} is processed without checking this @samp{set auto-load libthread-db} switch as system libraries have to be trusted in general. In all other cases of @samp{libthread-db-search-path} entries @value{GDBN} checks first if @samp{set auto-load libthread-db} is enabled before trying to open such thread debugging library. Note that loading of this debugging library also requires accordingly configured @code{auto-load safe-path} (@pxref{Auto-loading safe path}). @table @code @anchor{set auto-load libthread-db} @kindex set auto-load libthread-db @item set auto-load libthread-db [on|off] Enable or disable the auto-loading of inferior specific thread debugging library. @anchor{show auto-load libthread-db} @kindex show auto-load libthread-db @item show auto-load libthread-db Show whether auto-loading of inferior specific thread debugging library is enabled or disabled. @anchor{info auto-load libthread-db} @kindex info auto-load libthread-db @item info auto-load libthread-db Print the list of all loaded inferior specific thread debugging libraries and for each such library print list of inferior @var{pid}s using it. @end table @node Auto-loading safe path @subsection Security restriction for auto-loading @cindex auto-loading safe-path As the files of inferior can come from untrusted source (such as submitted by an application user) @value{GDBN} does not always load any files automatically. @value{GDBN} provides the @samp{set auto-load safe-path} setting to list directories trusted for loading files not explicitly requested by user. Each directory can also be a shell wildcard pattern. If the path is not set properly you will see a warning and the file will not get loaded: @smallexample $ ./gdb -q ./gdb Reading symbols from /home/user/gdb/gdb... warning: File "/home/user/gdb/gdb-gdb.gdb" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load". warning: File "/home/user/gdb/gdb-gdb.py" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load". @end smallexample @noindent To instruct @value{GDBN} to go ahead and use the init files anyway, invoke @value{GDBN} like this: @smallexample $ gdb -q -iex "set auto-load safe-path /home/user/gdb" ./gdb @end smallexample The list of trusted directories is controlled by the following commands: @table @code @anchor{set auto-load safe-path} @kindex set auto-load safe-path @item set auto-load safe-path @r{[}@var{directories}@r{]} Set the list of directories (and their subdirectories) trusted for automatic loading and execution of scripts. You can also enter a specific trusted file. Each directory can also be a shell wildcard pattern; wildcards do not match directory separator - see @code{FNM_PATHNAME} for system function @code{fnmatch} (@pxref{Wildcard Matching, fnmatch, , libc, GNU C Library Reference Manual}). If you omit @var{directories}, @samp{auto-load safe-path} will be reset to its default value as specified during @value{GDBN} compilation. The list of directories uses path separator (@samp{:} on GNU and Unix systems, @samp{;} on MS-Windows and MS-DOS) to separate directories, similarly to the @env{PATH} environment variable. @anchor{show auto-load safe-path} @kindex show auto-load safe-path @item show auto-load safe-path Show the list of directories trusted for automatic loading and execution of scripts. @anchor{add-auto-load-safe-path} @kindex add-auto-load-safe-path @item add-auto-load-safe-path Add an entry (or list of entries) to the list of directories trusted for automatic loading and execution of scripts. Multiple entries may be delimited by the host platform path separator in use. @end table This variable defaults to what @code{--with-auto-load-dir} has been configured to (@pxref{with-auto-load-dir}). @file{$debugdir} and @file{$datadir} substitution applies the same as for @ref{set auto-load scripts-directory}. The default @code{set auto-load safe-path} value can be also overriden by @value{GDBN} configuration option @option{--with-auto-load-safe-path}. Setting this variable to @file{/} disables this security protection, corresponding @value{GDBN} configuration option is @option{--without-auto-load-safe-path}. This variable is supposed to be set to the system directories writable by the system superuser only. Users can add their source directories in init files in their home directories (@pxref{Home Directory Init File}). See also deprecated init file in the current directory (@pxref{Init File in the Current Directory during Startup}). To force @value{GDBN} to load the files it declined to load in the previous example, you could use one of the following ways: @table @asis @item @file{~/.gdbinit}: @samp{add-auto-load-safe-path ~/src/gdb} Specify this trusted directory (or a file) as additional component of the list. You have to specify also any existing directories displayed by by @samp{show auto-load safe-path} (such as @samp{/usr:/bin} in this example). @item @kbd{gdb -iex "set auto-load safe-path /usr:/bin:~/src/gdb" @dots{}} Specify this directory as in the previous case but just for a single @value{GDBN} session. @item @kbd{gdb -iex "set auto-load safe-path /" @dots{}} Disable auto-loading safety for a single @value{GDBN} session. This assumes all the files you debug during this @value{GDBN} session will come from trusted sources. @item @kbd{./configure --without-auto-load-safe-path} During compilation of @value{GDBN} you may disable any auto-loading safety. This assumes all the files you will ever debug with this @value{GDBN} come from trusted sources. @end table On the other hand you can also explicitly forbid automatic files loading which also suppresses any such warning messages: @table @asis @item @kbd{gdb -iex "set auto-load no" @dots{}} You can use @value{GDBN} command-line option for a single @value{GDBN} session. @item @file{~/.gdbinit}: @samp{set auto-load no} Disable auto-loading globally for the user (@pxref{Home Directory Init File}). While it is improbable, you could also use system init file instead (@pxref{System-wide configuration}). @end table This setting applies to the file names as entered by user. If no entry matches @value{GDBN} tries as a last resort to also resolve all the file names into their canonical form (typically resolving symbolic links) and compare the entries again. @value{GDBN} already canonicalizes most of the filenames on its own before starting the comparison so a canonical form of directories is recommended to be entered. @node Auto-loading verbose mode @subsection Displaying files tried for auto-load @cindex auto-loading verbose mode For better visibility of all the file locations where you can place scripts to be auto-loaded with inferior --- or to protect yourself against accidental execution of untrusted scripts --- @value{GDBN} provides a feature for printing all the files attempted to be loaded. Both existing and non-existing files may be printed. For example the list of directories from which it is safe to auto-load files (@pxref{Auto-loading safe path}) applies also to canonicalized filenames which may not be too obvious while setting it up. @smallexample (gdb) set debug auto-load on (gdb) file ~/src/t/true auto-load: Loading canned sequences of commands script "/tmp/true-gdb.gdb" for objfile "/tmp/true". auto-load: Updating directories of "/usr:/opt". auto-load: Using directory "/usr". auto-load: Using directory "/opt". warning: File "/tmp/true-gdb.gdb" auto-loading has been declined by your `auto-load safe-path' set to "/usr:/opt". @end smallexample @table @code @anchor{set debug auto-load} @kindex set debug auto-load @item set debug auto-load [on|off] Set whether to print the filenames attempted to be auto-loaded. @anchor{show debug auto-load} @kindex show debug auto-load @item show debug auto-load Show whether printing of the filenames attempted to be auto-loaded is turned on or off. @end table @node Messages/Warnings @section Optional Warnings and Messages @cindex verbose operation @cindex optional warnings By default, @value{GDBN} is silent about its inner workings. If you are running on a slow machine, you may want to use the @code{set verbose} command. This makes @value{GDBN} tell you when it does a lengthy internal operation, so you will not think it has crashed. Currently, the messages controlled by @code{set verbose} are those which announce that the symbol table for a source file is being read; see @code{symbol-file} in @ref{Files, ,Commands to Specify Files}. @table @code @kindex set verbose @item set verbose on Enables @value{GDBN} output of certain informational messages. @item set verbose off Disables @value{GDBN} output of certain informational messages. @kindex show verbose @item show verbose Displays whether @code{set verbose} is on or off. @end table By default, if @value{GDBN} encounters bugs in the symbol table of an object file, it is silent; but if you are debugging a compiler, you may find this information useful (@pxref{Symbol Errors, ,Errors Reading Symbol Files}). @table @code @kindex set complaints @item set complaints @var{limit} Permits @value{GDBN} to output @var{limit} complaints about each type of unusual symbols before becoming silent about the problem. Set @var{limit} to zero to suppress all complaints; set it to a large number to prevent complaints from being suppressed. @kindex show complaints @item show complaints Displays how many symbol complaints @value{GDBN} is permitted to produce. @end table @anchor{confirmation requests} By default, @value{GDBN} is cautious, and asks what sometimes seems to be a lot of stupid questions to confirm certain commands. For example, if you try to run a program which is already running: @smallexample (@value{GDBP}) run The program being debugged has been started already. Start it from the beginning? (y or n) @end smallexample If you are willing to unflinchingly face the consequences of your own commands, you can disable this ``feature'': @table @code @kindex set confirm @cindex flinching @cindex confirmation @cindex stupid questions @item set confirm off Disables confirmation requests. Note that running @value{GDBN} with the @option{--batch} option (@pxref{Mode Options, -batch}) also automatically disables confirmation requests. @item set confirm on Enables confirmation requests (the default). @kindex show confirm @item show confirm Displays state of confirmation requests. @end table @cindex command tracing If you need to debug user-defined commands or sourced files you may find it useful to enable @dfn{command tracing}. In this mode each command will be printed as it is executed, prefixed with one or more @samp{+} symbols, the quantity denoting the call depth of each command. @table @code @kindex set trace-commands @cindex command scripts, debugging @item set trace-commands on Enable command tracing. @item set trace-commands off Disable command tracing. @item show trace-commands Display the current state of command tracing. @end table @node Debugging Output @section Optional Messages about Internal Happenings @cindex optional debugging messages @value{GDBN} has commands that enable optional debugging messages from various @value{GDBN} subsystems; normally these commands are of interest to @value{GDBN} maintainers, or when reporting a bug. This section documents those commands. @table @code @kindex set exec-done-display @item set exec-done-display Turns on or off the notification of asynchronous commands' completion. When on, @value{GDBN} will print a message when an asynchronous command finishes its execution. The default is off. @kindex show exec-done-display @item show exec-done-display Displays the current setting of asynchronous command completion notification. @kindex set debug @cindex ARM AArch64 @item set debug aarch64 Turns on or off display of debugging messages related to ARM AArch64. The default is off. @kindex show debug @item show debug aarch64 Displays the current state of displaying debugging messages related to ARM AArch64. @cindex gdbarch debugging info @cindex architecture debugging info @item set debug arch Turns on or off display of gdbarch debugging info. The default is off @item show debug arch Displays the current state of displaying gdbarch debugging info. @item set debug aix-solib @cindex AIX shared library debugging Control display of debugging messages from the AIX shared library support module. The default is off. @item show debug aix-thread Show the current state of displaying AIX shared library debugging messages. @item set debug aix-thread @cindex AIX threads Display debugging messages about inner workings of the AIX thread module. @item show debug aix-thread Show the current state of AIX thread debugging info display. @item set debug check-physname @cindex physname Check the results of the ``physname'' computation. When reading DWARF debugging information for C@t{++}, @value{GDBN} attempts to compute each entity's name. @value{GDBN} can do this computation in two different ways, depending on exactly what information is present. When enabled, this setting causes @value{GDBN} to compute the names both ways and display any discrepancies. @item show debug check-physname Show the current state of ``physname'' checking. @item set debug coff-pe-read @cindex COFF/PE exported symbols Control display of debugging messages related to reading of COFF/PE exported symbols. The default is off. @item show debug coff-pe-read Displays the current state of displaying debugging messages related to reading of COFF/PE exported symbols. @item set debug dwarf-die @cindex DWARF DIEs Dump DWARF DIEs after they are read in. The value is the number of nesting levels to print. A value of zero turns off the display. @item show debug dwarf-die Show the current state of DWARF DIE debugging. @item set debug dwarf-line @cindex DWARF Line Tables Turns on or off display of debugging messages related to reading DWARF line tables. The default is 0 (off). A value of 1 provides basic information. A value greater than 1 provides more verbose information. @item show debug dwarf-line Show the current state of DWARF line table debugging. @item set debug dwarf-read @cindex DWARF Reading Turns on or off display of debugging messages related to reading DWARF debug info. The default is 0 (off). A value of 1 provides basic information. A value greater than 1 provides more verbose information. @item show debug dwarf-read Show the current state of DWARF reader debugging. @item set debug displaced @cindex displaced stepping debugging info Turns on or off display of @value{GDBN} debugging info for the displaced stepping support. The default is off. @item show debug displaced Displays the current state of displaying @value{GDBN} debugging info related to displaced stepping. @item set debug event @cindex event debugging info Turns on or off display of @value{GDBN} event debugging info. The default is off. @item show debug event Displays the current state of displaying @value{GDBN} event debugging info. @item set debug expression @cindex expression debugging info Turns on or off display of debugging info about @value{GDBN} expression parsing. The default is off. @item show debug expression Displays the current state of displaying debugging info about @value{GDBN} expression parsing. @item set debug fbsd-lwp @cindex FreeBSD LWP debug messages Turns on or off debugging messages from the FreeBSD LWP debug support. @item show debug fbsd-lwp Show the current state of FreeBSD LWP debugging messages. @item set debug fbsd-nat @cindex FreeBSD native target debug messages Turns on or off debugging messages from the FreeBSD native target. @item show debug fbsd-nat Show the current state of FreeBSD native target debugging messages. @item set debug frame @cindex frame debugging info Turns on or off display of @value{GDBN} frame debugging info. The default is off. @item show debug frame Displays the current state of displaying @value{GDBN} frame debugging info. @item set debug gnu-nat @cindex @sc{gnu}/Hurd debug messages Turn on or off debugging messages from the @sc{gnu}/Hurd debug support. @item show debug gnu-nat Show the current state of @sc{gnu}/Hurd debugging messages. @item set debug infrun @cindex inferior debugging info Turns on or off display of @value{GDBN} debugging info for running the inferior. The default is off. @file{infrun.c} contains GDB's runtime state machine used for implementing operations such as single-stepping the inferior. @item show debug infrun Displays the current state of @value{GDBN} inferior debugging. @item set debug jit @cindex just-in-time compilation, debugging messages Turn on or off debugging messages from JIT debug support. @item show debug jit Displays the current state of @value{GDBN} JIT debugging. @item set debug lin-lwp @cindex @sc{gnu}/Linux LWP debug messages @cindex Linux lightweight processes Turn on or off debugging messages from the Linux LWP debug support. @item show debug lin-lwp Show the current state of Linux LWP debugging messages. @item set debug linux-namespaces @cindex @sc{gnu}/Linux namespaces debug messages Turn on or off debugging messages from the Linux namespaces debug support. @item show debug linux-namespaces Show the current state of Linux namespaces debugging messages. @item set debug mach-o @cindex Mach-O symbols processing Control display of debugging messages related to Mach-O symbols processing. The default is off. @item show debug mach-o Displays the current state of displaying debugging messages related to reading of COFF/PE exported symbols. @item set debug notification @cindex remote async notification debugging info Turn on or off debugging messages about remote async notification. The default is off. @item show debug notification Displays the current state of remote async notification debugging messages. @item set debug observer @cindex observer debugging info Turns on or off display of @value{GDBN} observer debugging. This includes info such as the notification of observable events. @item show debug observer Displays the current state of observer debugging. @item set debug overload @cindex C@t{++} overload debugging info Turns on or off display of @value{GDBN} C@t{++} overload debugging info. This includes info such as ranking of functions, etc. The default is off. @item show debug overload Displays the current state of displaying @value{GDBN} C@t{++} overload debugging info. @cindex expression parser, debugging info @cindex debug expression parser @item set debug parser Turns on or off the display of expression parser debugging output. Internally, this sets the @code{yydebug} variable in the expression parser. @xref{Tracing, , Tracing Your Parser, bison, Bison}, for details. The default is off. @item show debug parser Show the current state of expression parser debugging. @cindex packets, reporting on stdout @cindex serial connections, debugging @cindex debug remote protocol @cindex remote protocol debugging @cindex display remote packets @item set debug remote Turns on or off display of reports on all packets sent back and forth across the serial line to the remote machine. The info is printed on the @value{GDBN} standard output stream. The default is off. @item show debug remote Displays the state of display of remote packets. @item set debug remote-packet-max-chars Sets the maximum number of characters to display for each remote packet when @code{set debug remote} is on. This is useful to prevent @value{GDBN} from displaying lengthy remote packets and polluting the console. The default value is @code{512}, which means @value{GDBN} will truncate each remote packet after 512 bytes. Setting this option to @code{unlimited} will disable truncation and will output the full length of the remote packets. @item show debug remote-packet-max-chars Displays the number of bytes to output for remote packet debugging. @item set debug separate-debug-file Turns on or off display of debug output about separate debug file search. @item show debug separate-debug-file Displays the state of separate debug file search debug output. @item set debug serial Turns on or off display of @value{GDBN} serial debugging info. The default is off. @item show debug serial Displays the current state of displaying @value{GDBN} serial debugging info. @item set debug solib-frv @cindex FR-V shared-library debugging Turn on or off debugging messages for FR-V shared-library code. @item show debug solib-frv Display the current state of FR-V shared-library code debugging messages. @item set debug symbol-lookup @cindex symbol lookup Turns on or off display of debugging messages related to symbol lookup. The default is 0 (off). A value of 1 provides basic information. A value greater than 1 provides more verbose information. @item show debug symbol-lookup Show the current state of symbol lookup debugging messages. @item set debug symfile @cindex symbol file functions Turns on or off display of debugging messages related to symbol file functions. The default is off. @xref{Files}. @item show debug symfile Show the current state of symbol file debugging messages. @item set debug symtab-create @cindex symbol table creation Turns on or off display of debugging messages related to symbol table creation. The default is 0 (off). A value of 1 provides basic information. A value greater than 1 provides more verbose information. @item show debug symtab-create Show the current state of symbol table creation debugging. @item set debug target @cindex target debugging info Turns on or off display of @value{GDBN} target debugging info. This info includes what is going on at the target level of GDB, as it happens. The default is 0. Set it to 1 to track events, and to 2 to also track the value of large memory transfers. @item show debug target Displays the current state of displaying @value{GDBN} target debugging info. @item set debug timestamp @cindex timestamping debugging info Turns on or off display of timestamps with @value{GDBN} debugging info. When enabled, seconds and microseconds are displayed before each debugging message. @item show debug timestamp Displays the current state of displaying timestamps with @value{GDBN} debugging info. @item set debug varobj @cindex variable object debugging info Turns on or off display of @value{GDBN} variable object debugging info. The default is off. @item show debug varobj Displays the current state of displaying @value{GDBN} variable object debugging info. @item set debug xml @cindex XML parser debugging Turn on or off debugging messages for built-in XML parsers. @item show debug xml Displays the current state of XML debugging messages. @end table @node Other Misc Settings @section Other Miscellaneous Settings @cindex miscellaneous settings @table @code @kindex set interactive-mode @item set interactive-mode If @code{on}, forces @value{GDBN} to assume that GDB was started in a terminal. In practice, this means that @value{GDBN} should wait for the user to answer queries generated by commands entered at the command prompt. If @code{off}, forces @value{GDBN} to operate in the opposite mode, and it uses the default answers to all queries. If @code{auto} (the default), @value{GDBN} tries to determine whether its standard input is a terminal, and works in interactive-mode if it is, non-interactively otherwise. In the vast majority of cases, the debugger should be able to guess correctly which mode should be used. But this setting can be useful in certain specific cases, such as running a MinGW @value{GDBN} inside a cygwin window. @kindex show interactive-mode @item show interactive-mode Displays whether the debugger is operating in interactive mode or not. @end table @node Extending GDB @chapter Extending @value{GDBN} @cindex extending GDB @value{GDBN} provides several mechanisms for extension. @value{GDBN} also provides the ability to automatically load extensions when it reads a file for debugging. This allows the user to automatically customize @value{GDBN} for the program being debugged. @menu * Sequences:: Canned Sequences of @value{GDBN} Commands * Python:: Extending @value{GDBN} using Python * Guile:: Extending @value{GDBN} using Guile * Auto-loading extensions:: Automatically loading extensions * Multiple Extension Languages:: Working with multiple extension languages * Aliases:: Creating new spellings of existing commands @end menu To facilitate the use of extension languages, @value{GDBN} is capable of evaluating the contents of a file. When doing so, @value{GDBN} can recognize which extension language is being used by looking at the filename extension. Files with an unrecognized filename extension are always treated as a @value{GDBN} Command Files. @xref{Command Files,, Command files}. You can control how @value{GDBN} evaluates these files with the following setting: @table @code @kindex set script-extension @kindex show script-extension @item set script-extension off All scripts are always evaluated as @value{GDBN} Command Files. @item set script-extension soft The debugger determines the scripting language based on filename extension. If this scripting language is supported, @value{GDBN} evaluates the script using that language. Otherwise, it evaluates the file as a @value{GDBN} Command File. @item set script-extension strict The debugger determines the scripting language based on filename extension, and evaluates the script using that language. If the language is not supported, then the evaluation fails. @item show script-extension Display the current value of the @code{script-extension} option. @end table @ifset SYSTEM_GDBINIT_DIR This setting is not used for files in the system-wide gdbinit directory. Files in that directory must have an extension matching their language, or have a @file{.gdb} extension to be interpreted as regular @value{GDBN} commands. @xref{Startup}. @end ifset @node Sequences @section Canned Sequences of Commands Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint Command Lists}), @value{GDBN} provides two ways to store sequences of commands for execution as a unit: user-defined commands and command files. @menu * Define:: How to define your own commands * Hooks:: Hooks for user-defined commands * Command Files:: How to write scripts of commands to be stored in a file * Output:: Commands for controlled output * Auto-loading sequences:: Controlling auto-loaded command files @end menu @node Define @subsection User-defined Commands @cindex user-defined command @cindex arguments, to user-defined commands A @dfn{user-defined command} is a sequence of @value{GDBN} commands to which you assign a new name as a command. This is done with the @code{define} command. User commands may accept an unlimited number of arguments separated by whitespace. Arguments are accessed within the user command via @code{$arg0@dots{}$argN}. A trivial example: @smallexample define adder print $arg0 + $arg1 + $arg2 end @end smallexample @noindent To execute the command use: @smallexample adder 1 2 3 @end smallexample @noindent This defines the command @code{adder}, which prints the sum of its three arguments. Note the arguments are text substitutions, so they may reference variables, use complex expressions, or even perform inferior functions calls. @cindex argument count in user-defined commands @cindex how many arguments (user-defined commands) In addition, @code{$argc} may be used to find out how many arguments have been passed. @smallexample define adder if $argc == 2 print $arg0 + $arg1 end if $argc == 3 print $arg0 + $arg1 + $arg2 end end @end smallexample Combining with the @code{eval} command (@pxref{eval}) makes it easier to process a variable number of arguments: @smallexample define adder set $i = 0 set $sum = 0 while $i < $argc eval "set $sum = $sum + $arg%d", $i set $i = $i + 1 end print $sum end @end smallexample @table @code @kindex define @item define @var{commandname} Define a command named @var{commandname}. If there is already a command by that name, you are asked to confirm that you want to redefine it. The argument @var{commandname} may be a bare command name consisting of letters, numbers, dashes, dots, and underscores. It may also start with any predefined or user-defined prefix command. For example, @samp{define target my-target} creates a user-defined @samp{target my-target} command. The definition of the command is made up of other @value{GDBN} command lines, which are given following the @code{define} command. The end of these commands is marked by a line containing @code{end}. @kindex document @kindex end@r{ (user-defined commands)} @item document @var{commandname} Document the user-defined command @var{commandname}, so that it can be accessed by @code{help}. The command @var{commandname} must already be defined. This command reads lines of documentation just as @code{define} reads the lines of the command definition, ending with @code{end}. After the @code{document} command is finished, @code{help} on command @var{commandname} displays the documentation you have written. You may use the @code{document} command again to change the documentation of a command. Redefining the command with @code{define} does not change the documentation. @kindex define-prefix @item define-prefix @var{commandname} Define or mark the command @var{commandname} as a user-defined prefix command. Once marked, @var{commandname} can be used as prefix command by the @code{define} command. Note that @code{define-prefix} can be used with a not yet defined @var{commandname}. In such a case, @var{commandname} is defined as an empty user-defined command. In case you redefine a command that was marked as a user-defined prefix command, the subcommands of the redefined command are kept (and @value{GDBN} indicates so to the user). Example: @example (gdb) define-prefix abc (gdb) define-prefix abc def (gdb) define abc def Type commands for definition of "abc def". End with a line saying just "end". >echo command initial def\n >end (gdb) define abc def ghi Type commands for definition of "abc def ghi". End with a line saying just "end". >echo command ghi\n >end (gdb) define abc def Keeping subcommands of prefix command "def". Redefine command "def"? (y or n) y Type commands for definition of "abc def". End with a line saying just "end". >echo command def\n >end (gdb) abc def ghi command ghi (gdb) abc def command def (gdb) @end example @kindex dont-repeat @cindex don't repeat command @item dont-repeat Used inside a user-defined command, this tells @value{GDBN} that this command should not be repeated when the user hits @key{RET} (@pxref{Command Syntax, repeat last command}). @kindex help user-defined @item help user-defined List all user-defined commands and all python commands defined in class COMMAND_USER. The first line of the documentation or docstring is included (if any). @kindex show user @item show user @itemx show user @var{commandname} Display the @value{GDBN} commands used to define @var{commandname} (but not its documentation). If no @var{commandname} is given, display the definitions for all user-defined commands. This does not work for user-defined python commands. @cindex infinite recursion in user-defined commands @kindex show max-user-call-depth @kindex set max-user-call-depth @item show max-user-call-depth @itemx set max-user-call-depth The value of @code{max-user-call-depth} controls how many recursion levels are allowed in user-defined commands before @value{GDBN} suspects an infinite recursion and aborts the command. This does not apply to user-defined python commands. @end table In addition to the above commands, user-defined commands frequently use control flow commands, described in @ref{Command Files}. When user-defined commands are executed, the commands of the definition are not printed. An error in any command stops execution of the user-defined command. If used interactively, commands that would ask for confirmation proceed without asking when used inside a user-defined command. Many @value{GDBN} commands that normally print messages to say what they are doing omit the messages when used in a user-defined command. @node Hooks @subsection User-defined Command Hooks @cindex command hooks @cindex hooks, for commands @cindex hooks, pre-command @kindex hook You may define @dfn{hooks}, which are a special kind of user-defined command. Whenever you run the command @samp{foo}, if the user-defined command @samp{hook-foo} exists, it is executed (with no arguments) before that command. @cindex hooks, post-command @kindex hookpost A hook may also be defined which is run after the command you executed. Whenever you run the command @samp{foo}, if the user-defined command @samp{hookpost-foo} exists, it is executed (with no arguments) after that command. Post-execution hooks may exist simultaneously with pre-execution hooks, for the same command. It is valid for a hook to call the command which it hooks. If this occurs, the hook is not re-executed, thereby avoiding infinite recursion. @c It would be nice if hookpost could be passed a parameter indicating @c if the command it hooks executed properly or not. FIXME! @kindex stop@r{, a pseudo-command} In addition, a pseudo-command, @samp{stop} exists. Defining (@samp{hook-stop}) makes the associated commands execute every time execution stops in your program: before breakpoint commands are run, displays are printed, or the stack frame is printed. For example, to ignore @code{SIGALRM} signals while single-stepping, but treat them normally during normal execution, you could define: @smallexample define hook-stop handle SIGALRM nopass end define hook-run handle SIGALRM pass end define hook-continue handle SIGALRM pass end @end smallexample As a further example, to hook at the beginning and end of the @code{echo} command, and to add extra text to the beginning and end of the message, you could define: @smallexample define hook-echo echo <<<--- end define hookpost-echo echo --->>>\n end (@value{GDBP}) echo Hello World <<<---Hello World--->>> (@value{GDBP}) @end smallexample You can define a hook for any single-word command in @value{GDBN}, but not for command aliases; you should define a hook for the basic command name, e.g.@: @code{backtrace} rather than @code{bt}. @c FIXME! So how does Joe User discover whether a command is an alias @c or not? You can hook a multi-word command by adding @code{hook-} or @code{hookpost-} to the last word of the command, e.g.@: @samp{define target hook-remote} to add a hook to @samp{target remote}. If an error occurs during the execution of your hook, execution of @value{GDBN} commands stops and @value{GDBN} issues a prompt (before the command that you actually typed had a chance to run). If you try to define a hook which does not match any known command, you get a warning from the @code{define} command. @node Command Files @subsection Command Files @cindex command files @cindex scripting commands A command file for @value{GDBN} is a text file made of lines that are @value{GDBN} commands. Comments (lines starting with @kbd{#}) may also be included. An empty line in a command file does nothing; it does not mean to repeat the last command, as it would from the terminal. You can request the execution of a command file with the @code{source} command. Note that the @code{source} command is also used to evaluate scripts that are not Command Files. The exact behavior can be configured using the @code{script-extension} setting. @xref{Extending GDB,, Extending GDB}. @table @code @kindex source @cindex execute commands from a file @item source [-s] [-v] @var{filename} Execute the command file @var{filename}. @end table The lines in a command file are generally executed sequentially, unless the order of execution is changed by one of the @emph{flow-control commands} described below. The commands are not printed as they are executed. An error in any command terminates execution of the command file and control is returned to the console. @value{GDBN} first searches for @var{filename} in the current directory. If the file is not found there, and @var{filename} does not specify a directory, then @value{GDBN} also looks for the file on the source search path (specified with the @samp{directory} command); except that @file{$cdir} is not searched because the compilation directory is not relevant to scripts. If @code{-s} is specified, then @value{GDBN} searches for @var{filename} on the search path even if @var{filename} specifies a directory. The search is done by appending @var{filename} to each element of the search path. So, for example, if @var{filename} is @file{mylib/myscript} and the search path contains @file{/home/user} then @value{GDBN} will look for the script @file{/home/user/mylib/myscript}. The search is also done if @var{filename} is an absolute path. For example, if @var{filename} is @file{/tmp/myscript} and the search path contains @file{/home/user} then @value{GDBN} will look for the script @file{/home/user/tmp/myscript}. For DOS-like systems, if @var{filename} contains a drive specification, it is stripped before concatenation. For example, if @var{filename} is @file{d:myscript} and the search path contains @file{c:/tmp} then @value{GDBN} will look for the script @file{c:/tmp/myscript}. If @code{-v}, for verbose mode, is given then @value{GDBN} displays each command as it is executed. The option must be given before @var{filename}, and is interpreted as part of the filename anywhere else. Commands that would ask for confirmation if used interactively proceed without asking when used in a command file. Many @value{GDBN} commands that normally print messages to say what they are doing omit the messages when called from command files. @value{GDBN} also accepts command input from standard input. In this mode, normal output goes to standard output and error output goes to standard error. Errors in a command file supplied on standard input do not terminate execution of the command file---execution continues with the next command. @smallexample gdb < cmds > log 2>&1 @end smallexample (The syntax above will vary depending on the shell used.) This example will execute commands from the file @file{cmds}. All output and errors would be directed to @file{log}. Since commands stored on command files tend to be more general than commands typed interactively, they frequently need to deal with complicated situations, such as different or unexpected values of variables and symbols, changes in how the program being debugged is built, etc. @value{GDBN} provides a set of flow-control commands to deal with these complexities. Using these commands, you can write complex scripts that loop over data structures, execute commands conditionally, etc. @table @code @kindex if @kindex else @item if @itemx else This command allows to include in your script conditionally executed commands. The @code{if} command takes a single argument, which is an expression to evaluate. It is followed by a series of commands that are executed only if the expression is true (its value is nonzero). There can then optionally be an @code{else} line, followed by a series of commands that are only executed if the expression was false. The end of the list is marked by a line containing @code{end}. @kindex while @item while This command allows to write loops. Its syntax is similar to @code{if}: the command takes a single argument, which is an expression to evaluate, and must be followed by the commands to execute, one per line, terminated by an @code{end}. These commands are called the @dfn{body} of the loop. The commands in the body of @code{while} are executed repeatedly as long as the expression evaluates to true. @kindex loop_break @item loop_break This command exits the @code{while} loop in whose body it is included. Execution of the script continues after that @code{while}s @code{end} line. @kindex loop_continue @item loop_continue This command skips the execution of the rest of the body of commands in the @code{while} loop in whose body it is included. Execution branches to the beginning of the @code{while} loop, where it evaluates the controlling expression. @kindex end@r{ (if/else/while commands)} @item end Terminate the block of commands that are the body of @code{if}, @code{else}, or @code{while} flow-control commands. @end table @node Output @subsection Commands for Controlled Output During the execution of a command file or a user-defined command, normal @value{GDBN} output is suppressed; the only output that appears is what is explicitly printed by the commands in the definition. This section describes three commands useful for generating exactly the output you want. @table @code @kindex echo @item echo @var{text} @c I do not consider backslash-space a standard C escape sequence @c because it is not in ANSI. Print @var{text}. Nonprinting characters can be included in @var{text} using C escape sequences, such as @samp{\n} to print a newline. @strong{No newline is printed unless you specify one.} In addition to the standard C escape sequences, a backslash followed by a space stands for a space. This is useful for displaying a string with spaces at the beginning or the end, since leading and trailing spaces are otherwise trimmed from all arguments. To print @samp{@w{ }and foo =@w{ }}, use the command @samp{echo \@w{ }and foo = \@w{ }}. A backslash at the end of @var{text} can be used, as in C, to continue the command onto subsequent lines. For example, @smallexample echo This is some text\n\ which is continued\n\ onto several lines.\n @end smallexample produces the same output as @smallexample echo This is some text\n echo which is continued\n echo onto several lines.\n @end smallexample @kindex output @item output @var{expression} Print the value of @var{expression} and nothing but that value: no newlines, no @samp{$@var{nn} = }. The value is not entered in the value history either. @xref{Expressions, ,Expressions}, for more information on expressions. @item output/@var{fmt} @var{expression} Print the value of @var{expression} in format @var{fmt}. You can use the same formats as for @code{print}. @xref{Output Formats,,Output Formats}, for more information. @kindex printf @item printf @var{template}, @var{expressions}@dots{} Print the values of one or more @var{expressions} under the control of the string @var{template}. To print several values, make @var{expressions} be a comma-separated list of individual expressions, which may be either numbers or pointers. Their values are printed as specified by @var{template}, exactly as a C program would do by executing the code below: @smallexample printf (@var{template}, @var{expressions}@dots{}); @end smallexample As in @code{C} @code{printf}, ordinary characters in @var{template} are printed verbatim, while @dfn{conversion specification} introduced by the @samp{%} character cause subsequent @var{expressions} to be evaluated, their values converted and formatted according to type and style information encoded in the conversion specifications, and then printed. For example, you can print two values in hex like this: @smallexample printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo @end smallexample @code{printf} supports all the standard @code{C} conversion specifications, including the flags and modifiers between the @samp{%} character and the conversion letter, with the following exceptions: @itemize @bullet @item The argument-ordering modifiers, such as @samp{2$}, are not supported. @item The modifier @samp{*} is not supported for specifying precision or width. @item The @samp{'} flag (for separation of digits into groups according to @code{LC_NUMERIC'}) is not supported. @item The type modifiers @samp{hh}, @samp{j}, @samp{t}, and @samp{z} are not supported. @item The conversion letter @samp{n} (as in @samp{%n}) is not supported. @item The conversion letters @samp{a} and @samp{A} are not supported. @end itemize @noindent Note that the @samp{ll} type modifier is supported only if the underlying @code{C} implementation used to build @value{GDBN} supports the @code{long long int} type, and the @samp{L} type modifier is supported only if @code{long double} type is available. As in @code{C}, @code{printf} supports simple backslash-escape sequences, such as @code{\n}, @samp{\t}, @samp{\\}, @samp{\"}, @samp{\a}, and @samp{\f}, that consist of backslash followed by a single character. Octal and hexadecimal escape sequences are not supported. Additionally, @code{printf} supports conversion specifications for DFP (@dfn{Decimal Floating Point}) types using the following length modifiers together with a floating point specifier. letters: @itemize @bullet @item @samp{H} for printing @code{Decimal32} types. @item @samp{D} for printing @code{Decimal64} types. @item @samp{DD} for printing @code{Decimal128} types. @end itemize If the underlying @code{C} implementation used to build @value{GDBN} has support for the three length modifiers for DFP types, other modifiers such as width and precision will also be available for @value{GDBN} to use. In case there is no such @code{C} support, no additional modifiers will be available and the value will be printed in the standard way. Here's an example of printing DFP types using the above conversion letters: @smallexample printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl @end smallexample @anchor{eval} @kindex eval @item eval @var{template}, @var{expressions}@dots{} Convert the values of one or more @var{expressions} under the control of the string @var{template} to a command line, and call it. @end table @node Auto-loading sequences @subsection Controlling auto-loading native @value{GDBN} scripts @cindex native script auto-loading When a new object file is read (for example, due to the @code{file} command, or because the inferior has loaded a shared library), @value{GDBN} will look for the command file @file{@var{objfile}-gdb.gdb}. @xref{Auto-loading extensions}. Auto-loading can be enabled or disabled, and the list of auto-loaded scripts can be printed. @table @code @anchor{set auto-load gdb-scripts} @kindex set auto-load gdb-scripts @item set auto-load gdb-scripts [on|off] Enable or disable the auto-loading of canned sequences of commands scripts. @anchor{show auto-load gdb-scripts} @kindex show auto-load gdb-scripts @item show auto-load gdb-scripts Show whether auto-loading of canned sequences of commands scripts is enabled or disabled. @anchor{info auto-load gdb-scripts} @kindex info auto-load gdb-scripts @cindex print list of auto-loaded canned sequences of commands scripts @item info auto-load gdb-scripts [@var{regexp}] Print the list of all canned sequences of commands scripts that @value{GDBN} auto-loaded. @end table If @var{regexp} is supplied only canned sequences of commands scripts with matching names are printed. @c Python docs live in a separate file. @include python.texi @c Guile docs live in a separate file. @include guile.texi @node Auto-loading extensions @section Auto-loading extensions @cindex auto-loading extensions @value{GDBN} provides two mechanisms for automatically loading extensions when a new object file is read (for example, due to the @code{file} command, or because the inferior has loaded a shared library): @file{@var{objfile}-gdb.@var{ext}} and the @code{.debug_gdb_scripts} section of modern file formats like ELF. @menu * objfile-gdb.ext file: objfile-gdbdotext file. The @file{@var{objfile}-gdb.@var{ext}} file * .debug_gdb_scripts section: dotdebug_gdb_scripts section. The @code{.debug_gdb_scripts} section * Which flavor to choose?:: @end menu The auto-loading feature is useful for supplying application-specific debugging commands and features. Auto-loading can be enabled or disabled, and the list of auto-loaded scripts can be printed. See the @samp{auto-loading} section of each extension language for more information. For @value{GDBN} command files see @ref{Auto-loading sequences}. For Python files see @ref{Python Auto-loading}. Note that loading of this script file also requires accordingly configured @code{auto-load safe-path} (@pxref{Auto-loading safe path}). @node objfile-gdbdotext file @subsection The @file{@var{objfile}-gdb.@var{ext}} file @cindex @file{@var{objfile}-gdb.gdb} @cindex @file{@var{objfile}-gdb.py} @cindex @file{@var{objfile}-gdb.scm} When a new object file is read, @value{GDBN} looks for a file named @file{@var{objfile}-gdb.@var{ext}} (we call it @var{script-name} below), where @var{objfile} is the object file's name and where @var{ext} is the file extension for the extension language: @table @code @item @file{@var{objfile}-gdb.gdb} GDB's own command language @item @file{@var{objfile}-gdb.py} Python @item @file{@var{objfile}-gdb.scm} Guile @end table @var{script-name} is formed by ensuring that the file name of @var{objfile} is absolute, following all symlinks, and resolving @code{.} and @code{..} components, and appending the @file{-gdb.@var{ext}} suffix. If this file exists and is readable, @value{GDBN} will evaluate it as a script in the specified extension language. If this file does not exist, then @value{GDBN} will look for @var{script-name} file in all of the directories as specified below. Note that loading of these files requires an accordingly configured @code{auto-load safe-path} (@pxref{Auto-loading safe path}). For object files using @file{.exe} suffix @value{GDBN} tries to load first the scripts normally according to its @file{.exe} filename. But if no scripts are found @value{GDBN} also tries script filenames matching the object file without its @file{.exe} suffix. This @file{.exe} stripping is case insensitive and it is attempted on any platform. This makes the script filenames compatible between Unix and MS-Windows hosts. @table @code @anchor{set auto-load scripts-directory} @kindex set auto-load scripts-directory @item set auto-load scripts-directory @r{[}@var{directories}@r{]} Control @value{GDBN} auto-loaded scripts location. Multiple directory entries may be delimited by the host platform path separator in use (@samp{:} on Unix, @samp{;} on MS-Windows and MS-DOS). Each entry here needs to be covered also by the security setting @code{set auto-load safe-path} (@pxref{set auto-load safe-path}). @anchor{with-auto-load-dir} This variable defaults to @file{$debugdir:$datadir/auto-load}. The default @code{set auto-load safe-path} value can be also overriden by @value{GDBN} configuration option @option{--with-auto-load-dir}. Any reference to @file{$debugdir} will get replaced by @var{debug-file-directory} value (@pxref{Separate Debug Files}) and any reference to @file{$datadir} will get replaced by @var{data-directory} which is determined at @value{GDBN} startup (@pxref{Data Files}). @file{$debugdir} and @file{$datadir} must be placed as a directory component --- either alone or delimited by @file{/} or @file{\} directory separators, depending on the host platform. The list of directories uses path separator (@samp{:} on GNU and Unix systems, @samp{;} on MS-Windows and MS-DOS) to separate directories, similarly to the @env{PATH} environment variable. @anchor{show auto-load scripts-directory} @kindex show auto-load scripts-directory @item show auto-load scripts-directory Show @value{GDBN} auto-loaded scripts location. @anchor{add-auto-load-scripts-directory} @kindex add-auto-load-scripts-directory @item add-auto-load-scripts-directory @r{[}@var{directories}@dots{}@r{]} Add an entry (or list of entries) to the list of auto-loaded scripts locations. Multiple entries may be delimited by the host platform path separator in use. @end table @value{GDBN} does not track which files it has already auto-loaded this way. @value{GDBN} will load the associated script every time the corresponding @var{objfile} is opened. So your @file{-gdb.@var{ext}} file should be careful to avoid errors if it is evaluated more than once. @node dotdebug_gdb_scripts section @subsection The @code{.debug_gdb_scripts} section @cindex @code{.debug_gdb_scripts} section For systems using file formats like ELF and COFF, when @value{GDBN} loads a new object file it will look for a special section named @code{.debug_gdb_scripts}. If this section exists, its contents is a list of null-terminated entries specifying scripts to load. Each entry begins with a non-null prefix byte that specifies the kind of entry, typically the extension language and whether the script is in a file or inlined in @code{.debug_gdb_scripts}. The following entries are supported: @table @code @item SECTION_SCRIPT_ID_PYTHON_FILE = 1 @item SECTION_SCRIPT_ID_SCHEME_FILE = 3 @item SECTION_SCRIPT_ID_PYTHON_TEXT = 4 @item SECTION_SCRIPT_ID_SCHEME_TEXT = 6 @end table @subsubsection Script File Entries If the entry specifies a file, @value{GDBN} will look for the file first in the current directory and then along the source search path (@pxref{Source Path, ,Specifying Source Directories}), except that @file{$cdir} is not searched, since the compilation directory is not relevant to scripts. File entries can be placed in section @code{.debug_gdb_scripts} with, for example, this GCC macro for Python scripts. @example /* Note: The "MS" section flags are to remove duplicates. */ #define DEFINE_GDB_PY_SCRIPT(script_name) \ asm("\ .pushsection \".debug_gdb_scripts\", \"MS\",@@progbits,1\n\ .byte 1 /* Python */\n\ .asciz \"" script_name "\"\n\ .popsection \n\ "); @end example @noindent For Guile scripts, replace @code{.byte 1} with @code{.byte 3}. Then one can reference the macro in a header or source file like this: @example DEFINE_GDB_PY_SCRIPT ("my-app-scripts.py") @end example The script name may include directories if desired. Note that loading of this script file also requires accordingly configured @code{auto-load safe-path} (@pxref{Auto-loading safe path}). If the macro invocation is put in a header, any application or library using this header will get a reference to the specified script, and with the use of @code{"MS"} attributes on the section, the linker will remove duplicates. @subsubsection Script Text Entries Script text entries allow to put the executable script in the entry itself instead of loading it from a file. The first line of the entry, everything after the prefix byte and up to the first newline (@code{0xa}) character, is the script name, and must not contain any kind of space character, e.g., spaces or tabs. The rest of the entry, up to the trailing null byte, is the script to execute in the specified language. The name needs to be unique among all script names, as @value{GDBN} executes each script only once based on its name. Here is an example from file @file{py-section-script.c} in the @value{GDBN} testsuite. @example #include "symcat.h" #include "gdb/section-scripts.h" asm( ".pushsection \".debug_gdb_scripts\", \"MS\",@@progbits,1\n" ".byte " XSTRING (SECTION_SCRIPT_ID_PYTHON_TEXT) "\n" ".ascii \"gdb.inlined-script\\n\"\n" ".ascii \"class test_cmd (gdb.Command):\\n\"\n" ".ascii \" def __init__ (self):\\n\"\n" ".ascii \" super (test_cmd, self).__init__ (" "\\\"test-cmd\\\", gdb.COMMAND_OBSCURE)\\n\"\n" ".ascii \" def invoke (self, arg, from_tty):\\n\"\n" ".ascii \" print (\\\"test-cmd output, arg = %s\\\" % arg)\\n\"\n" ".ascii \"test_cmd ()\\n\"\n" ".byte 0\n" ".popsection\n" ); @end example Loading of inlined scripts requires a properly configured @code{auto-load safe-path} (@pxref{Auto-loading safe path}). The path to specify in @code{auto-load safe-path} is the path of the file containing the @code{.debug_gdb_scripts} section. @node Which flavor to choose? @subsection Which flavor to choose? Given the multiple ways of auto-loading extensions, it might not always be clear which one to choose. This section provides some guidance. @noindent Benefits of the @file{-gdb.@var{ext}} way: @itemize @bullet @item Can be used with file formats that don't support multiple sections. @item Ease of finding scripts for public libraries. Scripts specified in the @code{.debug_gdb_scripts} section are searched for in the source search path. For publicly installed libraries, e.g., @file{libstdc++}, there typically isn't a source directory in which to find the script. @item Doesn't require source code additions. @end itemize @noindent Benefits of the @code{.debug_gdb_scripts} way: @itemize @bullet @item Works with static linking. Scripts for libraries done the @file{-gdb.@var{ext}} way require an objfile to trigger their loading. When an application is statically linked the only objfile available is the executable, and it is cumbersome to attach all the scripts from all the input libraries to the executable's @file{-gdb.@var{ext}} script. @item Works with classes that are entirely inlined. Some classes can be entirely inlined, and thus there may not be an associated shared library to attach a @file{-gdb.@var{ext}} script to. @item Scripts needn't be copied out of the source tree. In some circumstances, apps can be built out of large collections of internal libraries, and the build infrastructure necessary to install the @file{-gdb.@var{ext}} scripts in a place where @value{GDBN} can find them is cumbersome. It may be easier to specify the scripts in the @code{.debug_gdb_scripts} section as relative paths, and add a path to the top of the source tree to the source search path. @end itemize @node Multiple Extension Languages @section Multiple Extension Languages The Guile and Python extension languages do not share any state, and generally do not interfere with each other. There are some things to be aware of, however. @subsection Python comes first Python was @value{GDBN}'s first extension language, and to avoid breaking existing behaviour Python comes first. This is generally solved by the ``first one wins'' principle. @value{GDBN} maintains a list of enabled extension languages, and when it makes a call to an extension language, (say to pretty-print a value), it tries each in turn until an extension language indicates it has performed the request (e.g., has returned the pretty-printed form of a value). This extends to errors while performing such requests: If an error happens while, for example, trying to pretty-print an object then the error is reported and any following extension languages are not tried. @node Aliases @section Creating new spellings of existing commands @cindex aliases for commands It is often useful to define alternate spellings of existing commands. For example, if a new @value{GDBN} command defined in Python has a long name to type, it is handy to have an abbreviated version of it that involves less typing. @value{GDBN} itself uses aliases. For example @samp{s} is an alias of the @samp{step} command even though it is otherwise an ambiguous abbreviation of other commands like @samp{set} and @samp{show}. Aliases are also used to provide shortened or more common versions of multi-word commands. For example, @value{GDBN} provides the @samp{tty} alias of the @samp{set inferior-tty} command. You can define a new alias with the @samp{alias} command. @table @code @kindex alias @item alias [-a] [--] @var{ALIAS} = @var{COMMAND} @end table @var{ALIAS} specifies the name of the new alias. Each word of @var{ALIAS} must consist of letters, numbers, dashes and underscores. @var{COMMAND} specifies the name of an existing command that is being aliased. The @samp{-a} option specifies that the new alias is an abbreviation of the command. Abbreviations are not shown in command lists displayed by the @samp{help} command. The @samp{--} option specifies the end of options, and is useful when @var{ALIAS} begins with a dash. Here is a simple example showing how to make an abbreviation of a command so that there is less to type. Suppose you were tired of typing @samp{disas}, the current shortest unambiguous abbreviation of the @samp{disassemble} command and you wanted an even shorter version named @samp{di}. The following will accomplish this. @smallexample (gdb) alias -a di = disas @end smallexample Note that aliases are different from user-defined commands. With a user-defined command, you also need to write documentation for it with the @samp{document} command. An alias automatically picks up the documentation of the existing command. Here is an example where we make @samp{elms} an abbreviation of @samp{elements} in the @samp{set print elements} command. This is to show that you can make an abbreviation of any part of a command. @smallexample (gdb) alias -a set print elms = set print elements (gdb) alias -a show print elms = show print elements (gdb) set p elms 20 (gdb) show p elms Limit on string chars or array elements to print is 200. @end smallexample Note that if you are defining an alias of a @samp{set} command, and you want to have an alias for the corresponding @samp{show} command, then you need to define the latter separately. Unambiguously abbreviated commands are allowed in @var{COMMAND} and @var{ALIAS}, just as they are normally. @smallexample (gdb) alias -a set pr elms = set p ele @end smallexample Finally, here is an example showing the creation of a one word alias for a more complex command. This creates alias @samp{spe} of the command @samp{set print elements}. @smallexample (gdb) alias spe = set print elements (gdb) spe 20 @end smallexample @node Interpreters @chapter Command Interpreters @cindex command interpreters @value{GDBN} supports multiple command interpreters, and some command infrastructure to allow users or user interface writers to switch between interpreters or run commands in other interpreters. @value{GDBN} currently supports two command interpreters, the console interpreter (sometimes called the command-line interpreter or @sc{cli}) and the machine interface interpreter (or @sc{gdb/mi}). This manual describes both of these interfaces in great detail. By default, @value{GDBN} will start with the console interpreter. However, the user may choose to start @value{GDBN} with another interpreter by specifying the @option{-i} or @option{--interpreter} startup options. Defined interpreters include: @table @code @item console @cindex console interpreter The traditional console or command-line interpreter. This is the most often used interpreter with @value{GDBN}. With no interpreter specified at runtime, @value{GDBN} will use this interpreter. @item mi @cindex mi interpreter The newest @sc{gdb/mi} interface (currently @code{mi3}). Used primarily by programs wishing to use @value{GDBN} as a backend for a debugger GUI or an IDE. For more information, see @ref{GDB/MI, ,The @sc{gdb/mi} Interface}. @item mi3 @cindex mi3 interpreter The @sc{gdb/mi} interface introduced in @value{GDBN} 9.1. @item mi2 @cindex mi2 interpreter The @sc{gdb/mi} interface introduced in @value{GDBN} 6.0. @item mi1 @cindex mi1 interpreter The @sc{gdb/mi} interface introduced in @value{GDBN} 5.1. @end table @cindex invoke another interpreter @kindex interpreter-exec You may execute commands in any interpreter from the current interpreter using the appropriate command. If you are running the console interpreter, simply use the @code{interpreter-exec} command: @smallexample interpreter-exec mi "-data-list-register-names" @end smallexample @sc{gdb/mi} has a similar command, although it is only available in versions of @value{GDBN} which support @sc{gdb/mi} version 2 (or greater). Note that @code{interpreter-exec} only changes the interpreter for the duration of the specified command. It does not change the interpreter permanently. @cindex start a new independent interpreter Although you may only choose a single interpreter at startup, it is possible to run an independent interpreter on a specified input/output device (usually a tty). For example, consider a debugger GUI or IDE that wants to provide a @value{GDBN} console view. It may do so by embedding a terminal emulator widget in its GUI, starting @value{GDBN} in the traditional command-line mode with stdin/stdout/stderr redirected to that terminal, and then creating an MI interpreter running on a specified input/output device. The console interpreter created by @value{GDBN} at startup handles commands the user types in the terminal widget, while the GUI controls and synchronizes state with @value{GDBN} using the separate MI interpreter. To start a new secondary @dfn{user interface} running MI, use the @code{new-ui} command: @kindex new-ui @cindex new user interface @smallexample new-ui @var{interpreter} @var{tty} @end smallexample The @var{interpreter} parameter specifies the interpreter to run. This accepts the same values as the @code{interpreter-exec} command. For example, @samp{console}, @samp{mi}, @samp{mi2}, etc. The @var{tty} parameter specifies the name of the bidirectional file the interpreter uses for input/output, usually the name of a pseudoterminal slave on Unix systems. For example: @smallexample (@value{GDBP}) new-ui mi /dev/pts/9 @end smallexample @noindent runs an MI interpreter on @file{/dev/pts/9}. @node TUI @chapter @value{GDBN} Text User Interface @cindex TUI @cindex Text User Interface @menu * TUI Overview:: TUI overview * TUI Keys:: TUI key bindings * TUI Single Key Mode:: TUI single key mode * TUI Commands:: TUI-specific commands * TUI Configuration:: TUI configuration variables @end menu The @value{GDBN} Text User Interface (TUI) is a terminal interface which uses the @code{curses} library to show the source file, the assembly output, the program registers and @value{GDBN} commands in separate text windows. The TUI mode is supported only on platforms where a suitable version of the @code{curses} library is available. The TUI mode is enabled by default when you invoke @value{GDBN} as @samp{@value{GDBP} -tui}. You can also switch in and out of TUI mode while @value{GDBN} runs by using various TUI commands and key bindings, such as @command{tui enable} or @kbd{C-x C-a}. @xref{TUI Commands, ,TUI Commands}, and @ref{TUI Keys, ,TUI Key Bindings}. @node TUI Overview @section TUI Overview In TUI mode, @value{GDBN} can display several text windows: @table @emph @item command This window is the @value{GDBN} command window with the @value{GDBN} prompt and the @value{GDBN} output. The @value{GDBN} input is still managed using readline. @item source The source window shows the source file of the program. The current line and active breakpoints are displayed in this window. @item assembly The assembly window shows the disassembly output of the program. @item register This window shows the processor registers. Registers are highlighted when their values change. @end table The source and assembly windows show the current program position by highlighting the current line and marking it with a @samp{>} marker. Breakpoints are indicated with two markers. The first marker indicates the breakpoint type: @table @code @item B Breakpoint which was hit at least once. @item b Breakpoint which was never hit. @item H Hardware breakpoint which was hit at least once. @item h Hardware breakpoint which was never hit. @end table The second marker indicates whether the breakpoint is enabled or not: @table @code @item + Breakpoint is enabled. @item - Breakpoint is disabled. @end table The source, assembly and register windows are updated when the current thread changes, when the frame changes, or when the program counter changes. These windows are not all visible at the same time. The command window is always visible. The others can be arranged in several layouts: @itemize @bullet @item source only, @item assembly only, @item source and assembly, @item source and registers, or @item assembly and registers. @end itemize These are the standard layouts, but other layouts can be defined. A status line above the command window shows the following information: @table @emph @item target Indicates the current @value{GDBN} target. (@pxref{Targets, ,Specifying a Debugging Target}). @item process Gives the current process or thread number. When no process is being debugged, this field is set to @code{No process}. @item function Gives the current function name for the selected frame. The name is demangled if demangling is turned on (@pxref{Print Settings}). When there is no symbol corresponding to the current program counter, the string @code{??} is displayed. @item line Indicates the current line number for the selected frame. When the current line number is not known, the string @code{??} is displayed. @item pc Indicates the current program counter address. @end table @node TUI Keys @section TUI Key Bindings @cindex TUI key bindings The TUI installs several key bindings in the readline keymaps @ifset SYSTEM_READLINE (@pxref{Command Line Editing, , , rluserman, GNU Readline Library}). @end ifset @ifclear SYSTEM_READLINE (@pxref{Command Line Editing}). @end ifclear The following key bindings are installed for both TUI mode and the @value{GDBN} standard mode. @table @kbd @kindex C-x C-a @item C-x C-a @kindex C-x a @itemx C-x a @kindex C-x A @itemx C-x A Enter or leave the TUI mode. When leaving the TUI mode, the curses window management stops and @value{GDBN} operates using its standard mode, writing on the terminal directly. When reentering the TUI mode, control is given back to the curses windows. The screen is then refreshed. This key binding uses the bindable Readline function @code{tui-switch-mode}. @kindex C-x 1 @item C-x 1 Use a TUI layout with only one window. The layout will either be @samp{source} or @samp{assembly}. When the TUI mode is not active, it will switch to the TUI mode. Think of this key binding as the Emacs @kbd{C-x 1} binding. This key binding uses the bindable Readline function @code{tui-delete-other-windows}. @kindex C-x 2 @item C-x 2 Use a TUI layout with at least two windows. When the current layout already has two windows, the next layout with two windows is used. When a new layout is chosen, one window will always be common to the previous layout and the new one. Think of it as the Emacs @kbd{C-x 2} binding. This key binding uses the bindable Readline function @code{tui-change-windows}. @kindex C-x o @item C-x o Change the active window. The TUI associates several key bindings (like scrolling and arrow keys) with the active window. This command gives the focus to the next TUI window. Think of it as the Emacs @kbd{C-x o} binding. This key binding uses the bindable Readline function @code{tui-other-window}. @kindex C-x s @item C-x s Switch in and out of the TUI SingleKey mode that binds single keys to @value{GDBN} commands (@pxref{TUI Single Key Mode}). This key binding uses the bindable Readline function @code{next-keymap}. @end table The following key bindings only work in the TUI mode: @table @asis @kindex PgUp @item @key{PgUp} Scroll the active window one page up. @kindex PgDn @item @key{PgDn} Scroll the active window one page down. @kindex Up @item @key{Up} Scroll the active window one line up. @kindex Down @item @key{Down} Scroll the active window one line down. @kindex Left @item @key{Left} Scroll the active window one column left. @kindex Right @item @key{Right} Scroll the active window one column right. @kindex C-L @item @kbd{C-L} Refresh the screen. @end table Because the arrow keys scroll the active window in the TUI mode, they are not available for their normal use by readline unless the command window has the focus. When another window is active, you must use other readline key bindings such as @kbd{C-p}, @kbd{C-n}, @kbd{C-b} and @kbd{C-f} to control the command window. @node TUI Single Key Mode @section TUI Single Key Mode @cindex TUI single key mode The TUI also provides a @dfn{SingleKey} mode, which binds several frequently used @value{GDBN} commands to single keys. Type @kbd{C-x s} to switch into this mode, where the following key bindings are used: @table @kbd @kindex c @r{(SingleKey TUI key)} @item c continue @kindex d @r{(SingleKey TUI key)} @item d down @kindex f @r{(SingleKey TUI key)} @item f finish @kindex n @r{(SingleKey TUI key)} @item n next @kindex o @r{(SingleKey TUI key)} @item o nexti. The shortcut letter @samp{o} stands for ``step Over''. @kindex q @r{(SingleKey TUI key)} @item q exit the SingleKey mode. @kindex r @r{(SingleKey TUI key)} @item r run @kindex s @r{(SingleKey TUI key)} @item s step @kindex i @r{(SingleKey TUI key)} @item i stepi. The shortcut letter @samp{i} stands for ``step Into''. @kindex u @r{(SingleKey TUI key)} @item u up @kindex v @r{(SingleKey TUI key)} @item v info locals @kindex w @r{(SingleKey TUI key)} @item w where @end table Other keys temporarily switch to the @value{GDBN} command prompt. The key that was pressed is inserted in the editing buffer so that it is possible to type most @value{GDBN} commands without interaction with the TUI SingleKey mode. Once the command is entered the TUI SingleKey mode is restored. The only way to permanently leave this mode is by typing @kbd{q} or @kbd{C-x s}. @cindex SingleKey keymap name If @value{GDBN} was built with Readline 8.0 or later, the TUI SingleKey keymap will be named @samp{SingleKey}. This can be used in @file{.inputrc} to add additional bindings to this keymap. @node TUI Commands @section TUI-specific Commands @cindex TUI commands The TUI has specific commands to control the text windows. These commands are always available, even when @value{GDBN} is not in the TUI mode. When @value{GDBN} is in the standard mode, most of these commands will automatically switch to the TUI mode. Note that if @value{GDBN}'s @code{stdout} is not connected to a terminal, or @value{GDBN} has been started with the machine interface interpreter (@pxref{GDB/MI, ,The @sc{gdb/mi} Interface}), most of these commands will fail with an error, because it would not be possible or desirable to enable curses window management. @table @code @item tui enable @kindex tui enable Activate TUI mode. The last active TUI window layout will be used if TUI mode has previously been used in the current debugging session, otherwise a default layout is used. @item tui disable @kindex tui disable Disable TUI mode, returning to the console interpreter. @item info win @kindex info win List and give the size of all displayed windows. @item tui new-layout @var{name} @var{window} @var{weight} @r{[}@var{window} @var{weight}@dots{}@r{]} @kindex tui new-layout Create a new TUI layout. The new layout will be named @var{name}, and can be accessed using the @code{layout} command (see below). Each @var{window} parameter is either the name of a window to display, or a window description. The windows will be displayed from top to bottom in the order listed. The names of the windows are the same as the ones given to the @code{focus} command (see below); additional, the @code{status} window can be specified. Note that, because it is of fixed height, the weight assigned to the status window is of no importance. It is conventional to use @samp{0} here. A window description looks a bit like an invocation of @code{tui new-layout}, and is of the form @{@r{[}@code{-horizontal}@r{]}@var{window} @var{weight} @r{[}@var{window} @var{weight}@dots{}@r{]}@}. This specifies a sub-layout. If @code{-horizontal} is given, the windows in this description will be arranged side-by-side, rather than top-to-bottom. Each @var{weight} is an integer. It is the weight of this window relative to all the other windows in the layout. These numbers are used to calculate how much of the screen is given to each window. For example: @example (gdb) tui new-layout example src 1 regs 1 status 0 cmd 1 @end example Here, the new layout is called @samp{example}. It shows the source and register windows, followed by the status window, and then finally the command window. The non-status windows all have the same weight, so the terminal will be split into three roughly equal sections. Here is a more complex example, showing a horizontal layout: @example (gdb) tui new-layout example @{-horizontal src 1 asm 1@} 2 status 0 cmd 1 @end example This will result in side-by-side source and assembly windows; with the status and command window being beneath these, filling the entire width of the terminal. Because they have weight 2, the source and assembly windows will be twice the height of the command window. @item layout @var{name} @kindex layout Changes which TUI windows are displayed. The @var{name} parameter controls which layout is shown. It can be either one of the built-in layout names, or the name of a layout defined by the user using @code{tui new-layout}. The built-in layouts are as follows: @table @code @item next Display the next layout. @item prev Display the previous layout. @item src Display the source and command windows. @item asm Display the assembly and command windows. @item split Display the source, assembly, and command windows. @item regs When in @code{src} layout display the register, source, and command windows. When in @code{asm} or @code{split} layout display the register, assembler, and command windows. @end table @item focus @var{name} @kindex focus Changes which TUI window is currently active for scrolling. The @var{name} parameter can be any of the following: @table @code @item next Make the next window active for scrolling. @item prev Make the previous window active for scrolling. @item src Make the source window active for scrolling. @item asm Make the assembly window active for scrolling. @item regs Make the register window active for scrolling. @item cmd Make the command window active for scrolling. @end table @item refresh @kindex refresh Refresh the screen. This is similar to typing @kbd{C-L}. @item tui reg @var{group} @kindex tui reg Changes the register group displayed in the tui register window to @var{group}. If the register window is not currently displayed this command will cause the register window to be displayed. The list of register groups, as well as their order is target specific. The following groups are available on most targets: @table @code @item next Repeatedly selecting this group will cause the display to cycle through all of the available register groups. @item prev Repeatedly selecting this group will cause the display to cycle through all of the available register groups in the reverse order to @var{next}. @item general Display the general registers. @item float Display the floating point registers. @item system Display the system registers. @item vector Display the vector registers. @item all Display all registers. @end table @item update @kindex update Update the source window and the current execution point. @item winheight @var{name} +@var{count} @itemx winheight @var{name} -@var{count} @kindex winheight Change the height of the window @var{name} by @var{count} lines. Positive counts increase the height, while negative counts decrease it. The @var{name} parameter can be one of @code{src} (the source window), @code{cmd} (the command window), @code{asm} (the disassembly window), or @code{regs} (the register display window). @end table @node TUI Configuration @section TUI Configuration Variables @cindex TUI configuration variables Several configuration variables control the appearance of TUI windows. @table @code @item set tui border-kind @var{kind} @kindex set tui border-kind Select the border appearance for the source, assembly and register windows. The possible values are the following: @table @code @item space Use a space character to draw the border. @item ascii Use @sc{ascii} characters @samp{+}, @samp{-} and @samp{|} to draw the border. @item acs Use the Alternate Character Set to draw the border. The border is drawn using character line graphics if the terminal supports them. @end table @item set tui border-mode @var{mode} @kindex set tui border-mode @itemx set tui active-border-mode @var{mode} @kindex set tui active-border-mode Select the display attributes for the borders of the inactive windows or the active window. The @var{mode} can be one of the following: @table @code @item normal Use normal attributes to display the border. @item standout Use standout mode. @item reverse Use reverse video mode. @item half Use half bright mode. @item half-standout Use half bright and standout mode. @item bold Use extra bright or bold mode. @item bold-standout Use extra bright or bold and standout mode. @end table @item set tui tab-width @var{nchars} @kindex set tui tab-width @kindex tabset Set the width of tab stops to be @var{nchars} characters. This setting affects the display of TAB characters in the source and assembly windows. @item set tui compact-source @r{[}on@r{|}off@r{]} @kindex set tui compact-source Set whether the TUI source window is displayed in ``compact'' form. The default display uses more space for line numbers and starts the source text at the next tab stop; the compact display uses only as much space as is needed for the line numbers in the current file, and only a single space to separate the line numbers from the source. @end table Note that the colors of the TUI borders can be controlled using the appropriate @code{set style} commands. @xref{Output Styling}. @node Emacs @chapter Using @value{GDBN} under @sc{gnu} Emacs @cindex Emacs @cindex @sc{gnu} Emacs A special interface allows you to use @sc{gnu} Emacs to view (and edit) the source files for the program you are debugging with @value{GDBN}. To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the executable file you want to debug as an argument. This command starts @value{GDBN} as a subprocess of Emacs, with input and output through a newly created Emacs buffer. @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.) Running @value{GDBN} under Emacs can be just like running @value{GDBN} normally except for two things: @itemize @bullet @item All ``terminal'' input and output goes through an Emacs buffer, called the GUD buffer. This applies both to @value{GDBN} commands and their output, and to the input and output done by the program you are debugging. This is useful because it means that you can copy the text of previous commands and input them again; you can even use parts of the output in this way. All the facilities of Emacs' Shell mode are available for interacting with your program. In particular, you can send signals the usual way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a stop. @item @value{GDBN} displays source code through Emacs. Each time @value{GDBN} displays a stack frame, Emacs automatically finds the source file for that frame and puts an arrow (@samp{=>}) at the left margin of the current line. Emacs uses a separate buffer for source display, and splits the screen to show both your @value{GDBN} session and the source. Explicit @value{GDBN} @code{list} or search commands still produce output as usual, but you probably have no reason to use them from Emacs. @end itemize We call this @dfn{text command mode}. Emacs 22.1, and later, also uses a graphical mode, enabled by default, which provides further buffers that can control the execution and describe the state of your program. @xref{GDB Graphical Interface,,, Emacs, The @sc{gnu} Emacs Manual}. If you specify an absolute file name when prompted for the @kbd{M-x gdb} argument, then Emacs sets your current working directory to where your program resides. If you only specify the file name, then Emacs sets your current working directory to the directory associated with the previous buffer. In this case, @value{GDBN} may find your program by searching your environment's @code{PATH} variable, but on some operating systems it might not find the source. So, although the @value{GDBN} input and output session proceeds normally, the auxiliary buffer does not display the current source and line of execution. The initial working directory of @value{GDBN} is printed on the top line of the GUD buffer and this serves as a default for the commands that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to Specify Files}. By default, @kbd{M-x gdb} calls the program called @file{gdb}. If you need to call @value{GDBN} by a different name (for example, if you keep several configurations around, with different names) you can customize the Emacs variable @code{gud-gdb-command-name} to run the one you want. In the GUD buffer, you can use these special Emacs commands in addition to the standard Shell mode commands: @table @kbd @item C-h m Describe the features of Emacs' GUD Mode. @item C-c C-s Execute to another source line, like the @value{GDBN} @code{step} command; also update the display window to show the current file and location. @item C-c C-n Execute to next source line in this function, skipping all function calls, like the @value{GDBN} @code{next} command. Then update the display window to show the current file and location. @item C-c C-i Execute one instruction, like the @value{GDBN} @code{stepi} command; update display window accordingly. @item C-c C-f Execute until exit from the selected stack frame, like the @value{GDBN} @code{finish} command. @item C-c C-r Continue execution of your program, like the @value{GDBN} @code{continue} command. @item C-c < Go up the number of frames indicated by the numeric argument (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}), like the @value{GDBN} @code{up} command. @item C-c > Go down the number of frames indicated by the numeric argument, like the @value{GDBN} @code{down} command. @end table In any source file, the Emacs command @kbd{C-x @key{SPC}} (@code{gud-break}) tells @value{GDBN} to set a breakpoint on the source line point is on. In text command mode, if you type @kbd{M-x speedbar}, Emacs displays a separate frame which shows a backtrace when the GUD buffer is current. Move point to any frame in the stack and type @key{RET} to make it become the current frame and display the associated source in the source buffer. Alternatively, click @kbd{Mouse-2} to make the selected frame become the current one. In graphical mode, the speedbar displays watch expressions. If you accidentally delete the source-display buffer, an easy way to get it back is to type the command @code{f} in the @value{GDBN} buffer, to request a frame display; when you run under Emacs, this recreates the source buffer if necessary to show you the context of the current frame. The source files displayed in Emacs are in ordinary Emacs buffers which are visiting the source files in the usual way. You can edit the files with these buffers if you wish; but keep in mind that @value{GDBN} communicates with Emacs in terms of line numbers. If you add or delete lines from the text, the line numbers that @value{GDBN} knows cease to correspond properly with the code. A more detailed description of Emacs' interaction with @value{GDBN} is given in the Emacs manual (@pxref{Debuggers,,, Emacs, The @sc{gnu} Emacs Manual}). @node GDB/MI @chapter The @sc{gdb/mi} Interface @unnumberedsec Function and Purpose @cindex @sc{gdb/mi}, its purpose @sc{gdb/mi} is a line based machine oriented text interface to @value{GDBN} and is activated by specifying using the @option{--interpreter} command line option (@pxref{Mode Options}). It is specifically intended to support the development of systems which use the debugger as just one small component of a larger system. This chapter is a specification of the @sc{gdb/mi} interface. It is written in the form of a reference manual. Note that @sc{gdb/mi} is still under construction, so some of the features described below are incomplete and subject to change (@pxref{GDB/MI Development and Front Ends, , @sc{gdb/mi} Development and Front Ends}). @unnumberedsec Notation and Terminology @cindex notational conventions, for @sc{gdb/mi} This chapter uses the following notation: @itemize @bullet @item @code{|} separates two alternatives. @item @code{[ @var{something} ]} indicates that @var{something} is optional: it may or may not be given. @item @code{( @var{group} )*} means that @var{group} inside the parentheses may repeat zero or more times. @item @code{( @var{group} )+} means that @var{group} inside the parentheses may repeat one or more times. @item @code{"@var{string}"} means a literal @var{string}. @end itemize @ignore @heading Dependencies @end ignore @menu * GDB/MI General Design:: * GDB/MI Command Syntax:: * GDB/MI Compatibility with CLI:: * GDB/MI Development and Front Ends:: * GDB/MI Output Records:: * GDB/MI Simple Examples:: * GDB/MI Command Description Format:: * GDB/MI Breakpoint Commands:: * GDB/MI Catchpoint Commands:: * GDB/MI Program Context:: * GDB/MI Thread Commands:: * GDB/MI Ada Tasking Commands:: * GDB/MI Program Execution:: * GDB/MI Stack Manipulation:: * GDB/MI Variable Objects:: * GDB/MI Data Manipulation:: * GDB/MI Tracepoint Commands:: * GDB/MI Symbol Query:: * GDB/MI File Commands:: @ignore * GDB/MI Kod Commands:: * GDB/MI Memory Overlay Commands:: * GDB/MI Signal Handling Commands:: @end ignore * GDB/MI Target Manipulation:: * GDB/MI File Transfer Commands:: * GDB/MI Ada Exceptions Commands:: * GDB/MI Support Commands:: * GDB/MI Miscellaneous Commands:: @end menu @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI General Design @section @sc{gdb/mi} General Design @cindex GDB/MI General Design Interaction of a @sc{GDB/MI} frontend with @value{GDBN} involves three parts---commands sent to @value{GDBN}, responses to those commands and notifications. Each command results in exactly one response, indicating either successful completion of the command, or an error. For the commands that do not resume the target, the response contains the requested information. For the commands that resume the target, the response only indicates whether the target was successfully resumed. Notifications is the mechanism for reporting changes in the state of the target, or in @value{GDBN} state, that cannot conveniently be associated with a command and reported as part of that command response. The important examples of notifications are: @itemize @bullet @item Exec notifications. These are used to report changes in target state---when a target is resumed, or stopped. It would not be feasible to include this information in response of resuming commands, because one resume commands can result in multiple events in different threads. Also, quite some time may pass before any event happens in the target, while a frontend needs to know whether the resuming command itself was successfully executed. @item Console output, and status notifications. Console output notifications are used to report output of CLI commands, as well as diagnostics for other commands. Status notifications are used to report the progress of a long-running operation. Naturally, including this information in command response would mean no output is produced until the command is finished, which is undesirable. @item General notifications. Commands may have various side effects on the @value{GDBN} or target state beyond their official purpose. For example, a command may change the selected thread. Although such changes can be included in command response, using notification allows for more orthogonal frontend design. @end itemize There's no guarantee that whenever an MI command reports an error, @value{GDBN} or the target are in any specific state, and especially, the state is not reverted to the state before the MI command was processed. Therefore, whenever an MI command results in an error, we recommend that the frontend refreshes all the information shown in the user interface. @menu * Context management:: * Asynchronous and non-stop modes:: * Thread groups:: @end menu @node Context management @subsection Context management @subsubsection Threads and Frames In most cases when @value{GDBN} accesses the target, this access is done in context of a specific thread and frame (@pxref{Frames}). Often, even when accessing global data, the target requires that a thread be specified. The CLI interface maintains the selected thread and frame, and supplies them to target on each command. This is convenient, because a command line user would not want to specify that information explicitly on each command, and because user interacts with @value{GDBN} via a single terminal, so no confusion is possible as to what thread and frame are the current ones. In the case of MI, the concept of selected thread and frame is less useful. First, a frontend can easily remember this information itself. Second, a graphical frontend can have more than one window, each one used for debugging a different thread, and the frontend might want to access additional threads for internal purposes. This increases the risk that by relying on implicitly selected thread, the frontend may be operating on a wrong one. Therefore, each MI command should explicitly specify which thread and frame to operate on. To make it possible, each MI command accepts the @samp{--thread} and @samp{--frame} options, the value to each is @value{GDBN} global identifier for thread and frame to operate on. Usually, each top-level window in a frontend allows the user to select a thread and a frame, and remembers the user selection for further operations. However, in some cases @value{GDBN} may suggest that the current thread or frame be changed. For example, when stopping on a breakpoint it is reasonable to switch to the thread where breakpoint is hit. For another example, if the user issues the CLI @samp{thread} or @samp{frame} commands via the frontend, it is desirable to change the frontend's selection to the one specified by user. @value{GDBN} communicates the suggestion to change current thread and frame using the @samp{=thread-selected} notification. Note that historically, MI shares the selected thread with CLI, so frontends used the @code{-thread-select} to execute commands in the right context. However, getting this to work right is cumbersome. The simplest way is for frontend to emit @code{-thread-select} command before every command. This doubles the number of commands that need to be sent. The alternative approach is to suppress @code{-thread-select} if the selected thread in @value{GDBN} is supposed to be identical to the thread the frontend wants to operate on. However, getting this optimization right can be tricky. In particular, if the frontend sends several commands to @value{GDBN}, and one of the commands changes the selected thread, then the behaviour of subsequent commands will change. So, a frontend should either wait for response from such problematic commands, or explicitly add @code{-thread-select} for all subsequent commands. No frontend is known to do this exactly right, so it is suggested to just always pass the @samp{--thread} and @samp{--frame} options. @subsubsection Language The execution of several commands depends on which language is selected. By default, the current language (@pxref{show language}) is used. But for commands known to be language-sensitive, it is recommended to use the @samp{--language} option. This option takes one argument, which is the name of the language to use while executing the command. For instance: @smallexample -data-evaluate-expression --language c "sizeof (void*)" ^done,value="4" (gdb) @end smallexample The valid language names are the same names accepted by the @samp{set language} command (@pxref{Manually}), excluding @samp{auto}, @samp{local} or @samp{unknown}. @node Asynchronous and non-stop modes @subsection Asynchronous command execution and non-stop mode On some targets, @value{GDBN} is capable of processing MI commands even while the target is running. This is called @dfn{asynchronous command execution} (@pxref{Background Execution}). The frontend may specify a preference for asynchronous execution using the @code{-gdb-set mi-async 1} command, which should be emitted before either running the executable or attaching to the target. After the frontend has started the executable or attached to the target, it can find if asynchronous execution is enabled using the @code{-list-target-features} command. @table @code @item -gdb-set mi-async on @item -gdb-set mi-async off Set whether MI is in asynchronous mode. When @code{off}, which is the default, MI execution commands (e.g., @code{-exec-continue}) are foreground commands, and @value{GDBN} waits for the program to stop before processing further commands. When @code{on}, MI execution commands are background execution commands (e.g., @code{-exec-continue} becomes the equivalent of the @code{c&} CLI command), and so @value{GDBN} is capable of processing MI commands even while the target is running. @item -gdb-show mi-async Show whether MI asynchronous mode is enabled. @end table Note: In @value{GDBN} version 7.7 and earlier, this option was called @code{target-async} instead of @code{mi-async}, and it had the effect of both putting MI in asynchronous mode and making CLI background commands possible. CLI background commands are now always possible ``out of the box'' if the target supports them. The old spelling is kept as a deprecated alias for backwards compatibility. Even if @value{GDBN} can accept a command while target is running, many commands that access the target do not work when the target is running. Therefore, asynchronous command execution is most useful when combined with non-stop mode (@pxref{Non-Stop Mode}). Then, it is possible to examine the state of one thread, while other threads are running. When a given thread is running, MI commands that try to access the target in the context of that thread may not work, or may work only on some targets. In particular, commands that try to operate on thread's stack will not work, on any target. Commands that read memory, or modify breakpoints, may work or not work, depending on the target. Note that even commands that operate on global state, such as @code{print}, @code{set}, and breakpoint commands, still access the target in the context of a specific thread, so frontend should try to find a stopped thread and perform the operation on that thread (using the @samp{--thread} option). Which commands will work in the context of a running thread is highly target dependent. However, the two commands @code{-exec-interrupt}, to stop a thread, and @code{-thread-info}, to find the state of a thread, will always work. @node Thread groups @subsection Thread groups @value{GDBN} may be used to debug several processes at the same time. On some platforms, @value{GDBN} may support debugging of several hardware systems, each one having several cores with several different processes running on each core. This section describes the MI mechanism to support such debugging scenarios. The key observation is that regardless of the structure of the target, MI can have a global list of threads, because most commands that accept the @samp{--thread} option do not need to know what process that thread belongs to. Therefore, it is not necessary to introduce neither additional @samp{--process} option, nor an notion of the current process in the MI interface. The only strictly new feature that is required is the ability to find how the threads are grouped into processes. To allow the user to discover such grouping, and to support arbitrary hierarchy of machines/cores/processes, MI introduces the concept of a @dfn{thread group}. Thread group is a collection of threads and other thread groups. A thread group always has a string identifier, a type, and may have additional attributes specific to the type. A new command, @code{-list-thread-groups}, returns the list of top-level thread groups, which correspond to processes that @value{GDBN} is debugging at the moment. By passing an identifier of a thread group to the @code{-list-thread-groups} command, it is possible to obtain the members of specific thread group. To allow the user to easily discover processes, and other objects, he wishes to debug, a concept of @dfn{available thread group} is introduced. Available thread group is an thread group that @value{GDBN} is not debugging, but that can be attached to, using the @code{-target-attach} command. The list of available top-level thread groups can be obtained using @samp{-list-thread-groups --available}. In general, the content of a thread group may be only retrieved only after attaching to that thread group. Thread groups are related to inferiors (@pxref{Inferiors Connections and Programs}). Each inferior corresponds to a thread group of a special type @samp{process}, and some additional operations are permitted on such thread groups. @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Command Syntax @section @sc{gdb/mi} Command Syntax @menu * GDB/MI Input Syntax:: * GDB/MI Output Syntax:: @end menu @node GDB/MI Input Syntax @subsection @sc{gdb/mi} Input Syntax @cindex input syntax for @sc{gdb/mi} @cindex @sc{gdb/mi}, input syntax @table @code @item @var{command} @expansion{} @code{@var{cli-command} | @var{mi-command}} @item @var{cli-command} @expansion{} @code{[ @var{token} ] @var{cli-command} @var{nl}}, where @var{cli-command} is any existing @value{GDBN} CLI command. @item @var{mi-command} @expansion{} @code{[ @var{token} ] "-" @var{operation} ( " " @var{option} )* @code{[} " --" @code{]} ( " " @var{parameter} )* @var{nl}} @item @var{token} @expansion{} "any sequence of digits" @item @var{option} @expansion{} @code{"-" @var{parameter} [ " " @var{parameter} ]} @item @var{parameter} @expansion{} @code{@var{non-blank-sequence} | @var{c-string}} @item @var{operation} @expansion{} @emph{any of the operations described in this chapter} @item @var{non-blank-sequence} @expansion{} @emph{anything, provided it doesn't contain special characters such as "-", @var{nl}, """ and of course " "} @item @var{c-string} @expansion{} @code{""" @var{seven-bit-iso-c-string-content} """} @item @var{nl} @expansion{} @code{CR | CR-LF} @end table @noindent Notes: @itemize @bullet @item The CLI commands are still handled by the @sc{mi} interpreter; their output is described below. @item The @code{@var{token}}, when present, is passed back when the command finishes. @item Some @sc{mi} commands accept optional arguments as part of the parameter list. Each option is identified by a leading @samp{-} (dash) and may be followed by an optional argument parameter. Options occur first in the parameter list and can be delimited from normal parameters using @samp{--} (this is useful when some parameters begin with a dash). @end itemize Pragmatics: @itemize @bullet @item We want easy access to the existing CLI syntax (for debugging). @item We want it to be easy to spot a @sc{mi} operation. @end itemize @node GDB/MI Output Syntax @subsection @sc{gdb/mi} Output Syntax @cindex output syntax of @sc{gdb/mi} @cindex @sc{gdb/mi}, output syntax The output from @sc{gdb/mi} consists of zero or more out-of-band records followed, optionally, by a single result record. This result record is for the most recent command. The sequence of output records is terminated by @samp{(gdb)}. If an input command was prefixed with a @code{@var{token}} then the corresponding output for that command will also be prefixed by that same @var{token}. @table @code @item @var{output} @expansion{} @code{( @var{out-of-band-record} )* [ @var{result-record} ] "(gdb)" @var{nl}} @item @var{result-record} @expansion{} @code{ [ @var{token} ] "^" @var{result-class} ( "," @var{result} )* @var{nl}} @item @var{out-of-band-record} @expansion{} @code{@var{async-record} | @var{stream-record}} @item @var{async-record} @expansion{} @code{@var{exec-async-output} | @var{status-async-output} | @var{notify-async-output}} @item @var{exec-async-output} @expansion{} @code{[ @var{token} ] "*" @var{async-output nl}} @item @var{status-async-output} @expansion{} @code{[ @var{token} ] "+" @var{async-output nl}} @item @var{notify-async-output} @expansion{} @code{[ @var{token} ] "=" @var{async-output nl}} @item @var{async-output} @expansion{} @code{@var{async-class} ( "," @var{result} )*} @item @var{result-class} @expansion{} @code{"done" | "running" | "connected" | "error" | "exit"} @item @var{async-class} @expansion{} @code{"stopped" | @var{others}} (where @var{others} will be added depending on the needs---this is still in development). @item @var{result} @expansion{} @code{ @var{variable} "=" @var{value}} @item @var{variable} @expansion{} @code{ @var{string} } @item @var{value} @expansion{} @code{ @var{const} | @var{tuple} | @var{list} } @item @var{const} @expansion{} @code{@var{c-string}} @item @var{tuple} @expansion{} @code{ "@{@}" | "@{" @var{result} ( "," @var{result} )* "@}" } @item @var{list} @expansion{} @code{ "[]" | "[" @var{value} ( "," @var{value} )* "]" | "[" @var{result} ( "," @var{result} )* "]" } @item @var{stream-record} @expansion{} @code{@var{console-stream-output} | @var{target-stream-output} | @var{log-stream-output}} @item @var{console-stream-output} @expansion{} @code{"~" @var{c-string nl}} @item @var{target-stream-output} @expansion{} @code{"@@" @var{c-string nl}} @item @var{log-stream-output} @expansion{} @code{"&" @var{c-string nl}} @item @var{nl} @expansion{} @code{CR | CR-LF} @item @var{token} @expansion{} @emph{any sequence of digits}. @end table @noindent Notes: @itemize @bullet @item All output sequences end in a single line containing a period. @item The @code{@var{token}} is from the corresponding request. Note that for all async output, while the token is allowed by the grammar and may be output by future versions of @value{GDBN} for select async output messages, it is generally omitted. Frontends should treat all async output as reporting general changes in the state of the target and there should be no need to associate async output to any prior command. @item @cindex status output in @sc{gdb/mi} @var{status-async-output} contains on-going status information about the progress of a slow operation. It can be discarded. All status output is prefixed by @samp{+}. @item @cindex async output in @sc{gdb/mi} @var{exec-async-output} contains asynchronous state change on the target (stopped, started, disappeared). All async output is prefixed by @samp{*}. @item @cindex notify output in @sc{gdb/mi} @var{notify-async-output} contains supplementary information that the client should handle (e.g., a new breakpoint information). All notify output is prefixed by @samp{=}. @item @cindex console output in @sc{gdb/mi} @var{console-stream-output} is output that should be displayed as is in the console. It is the textual response to a CLI command. All the console output is prefixed by @samp{~}. @item @cindex target output in @sc{gdb/mi} @var{target-stream-output} is the output produced by the target program. All the target output is prefixed by @samp{@@}. @item @cindex log output in @sc{gdb/mi} @var{log-stream-output} is output text coming from @value{GDBN}'s internals, for instance messages that should be displayed as part of an error log. All the log output is prefixed by @samp{&}. @item @cindex list output in @sc{gdb/mi} New @sc{gdb/mi} commands should only output @var{lists} containing @var{values}. @end itemize @xref{GDB/MI Stream Records, , @sc{gdb/mi} Stream Records}, for more details about the various output records. @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Compatibility with CLI @section @sc{gdb/mi} Compatibility with CLI @cindex compatibility, @sc{gdb/mi} and CLI @cindex @sc{gdb/mi}, compatibility with CLI For the developers convenience CLI commands can be entered directly, but there may be some unexpected behaviour. For example, commands that query the user will behave as if the user replied yes, breakpoint command lists are not executed and some CLI commands, such as @code{if}, @code{when} and @code{define}, prompt for further input with @samp{>}, which is not valid MI output. This feature may be removed at some stage in the future and it is recommended that front ends use the @code{-interpreter-exec} command (@pxref{-interpreter-exec}). @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Development and Front Ends @section @sc{gdb/mi} Development and Front Ends @cindex @sc{gdb/mi} development The application which takes the MI output and presents the state of the program being debugged to the user is called a @dfn{front end}. Since @sc{gdb/mi} is used by a variety of front ends to @value{GDBN}, changes to the MI interface may break existing usage. This section describes how the protocol changes and how to request previous version of the protocol when it does. Some changes in MI need not break a carefully designed front end, and for these the MI version will remain unchanged. The following is a list of changes that may occur within one level, so front ends should parse MI output in a way that can handle them: @itemize @bullet @item New MI commands may be added. @item New fields may be added to the output of any MI command. @item The range of values for fields with specified values, e.g., @code{in_scope} (@pxref{-var-update}) may be extended. @c The format of field's content e.g type prefix, may change so parse it @c at your own risk. Yes, in general? @c The order of fields may change? Shouldn't really matter but it might @c resolve inconsistencies. @end itemize If the changes are likely to break front ends, the MI version level will be increased by one. The new versions of the MI protocol are not compatible with the old versions. Old versions of MI remain available, allowing front ends to keep using them until they are modified to use the latest MI version. Since @code{--interpreter=mi} always points to the latest MI version, it is recommended that front ends request a specific version of MI when launching @value{GDBN} (e.g. @code{--interpreter=mi2}) to make sure they get an interpreter with the MI version they expect. The following table gives a summary of the the released versions of the MI interface: the version number, the version of GDB in which it first appeared and the breaking changes compared to the previous version. @multitable @columnfractions .05 .05 .9 @headitem MI version @tab GDB version @tab Breaking changes @item @center 1 @tab @center 5.1 @tab None @item @center 2 @tab @center 6.0 @tab @itemize @item The @code{-environment-pwd}, @code{-environment-directory} and @code{-environment-path} commands now returns values using the MI output syntax, rather than CLI output syntax. @item @code{-var-list-children}'s @code{children} result field is now a list, rather than a tuple. @item @code{-var-update}'s @code{changelist} result field is now a list, rather than a tuple. @end itemize @item @center 3 @tab @center 9.1 @tab @itemize @item The output of information about multi-location breakpoints has changed in the responses to the @code{-break-insert} and @code{-break-info} commands, as well as in the @code{=breakpoint-created} and @code{=breakpoint-modified} events. The multiple locations are now placed in a @code{locations} field, whose value is a list. @end itemize @end multitable If your front end cannot yet migrate to a more recent version of the MI protocol, you can nevertheless selectively enable specific features available in those recent MI versions, using the following commands: @table @code @item -fix-multi-location-breakpoint-output Use the output for multi-location breakpoints which was introduced by MI 3, even when using MI versions 2 or 1. This command has no effect when using MI version 3 or later. @end table The best way to avoid unexpected changes in MI that might break your front end is to make your project known to @value{GDBN} developers and follow development on @email{gdb@@sourceware.org} and @email{gdb-patches@@sourceware.org}. @cindex mailing lists @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Output Records @section @sc{gdb/mi} Output Records @menu * GDB/MI Result Records:: * GDB/MI Stream Records:: * GDB/MI Async Records:: * GDB/MI Breakpoint Information:: * GDB/MI Frame Information:: * GDB/MI Thread Information:: * GDB/MI Ada Exception Information:: @end menu @node GDB/MI Result Records @subsection @sc{gdb/mi} Result Records @cindex result records in @sc{gdb/mi} @cindex @sc{gdb/mi}, result records In addition to a number of out-of-band notifications, the response to a @sc{gdb/mi} command includes one of the following result indications: @table @code @findex ^done @item "^done" [ "," @var{results} ] The synchronous operation was successful, @code{@var{results}} are the return values. @item "^running" @findex ^running This result record is equivalent to @samp{^done}. Historically, it was output instead of @samp{^done} if the command has resumed the target. This behaviour is maintained for backward compatibility, but all frontends should treat @samp{^done} and @samp{^running} identically and rely on the @samp{*running} output record to determine which threads are resumed. @item "^connected" @findex ^connected @value{GDBN} has connected to a remote target. @item "^error" "," "msg=" @var{c-string} [ "," "code=" @var{c-string} ] @findex ^error The operation failed. The @code{msg=@var{c-string}} variable contains the corresponding error message. If present, the @code{code=@var{c-string}} variable provides an error code on which consumers can rely on to detect the corresponding error condition. At present, only one error code is defined: @table @samp @item "undefined-command" Indicates that the command causing the error does not exist. @end table @item "^exit" @findex ^exit @value{GDBN} has terminated. @end table @node GDB/MI Stream Records @subsection @sc{gdb/mi} Stream Records @cindex @sc{gdb/mi}, stream records @cindex stream records in @sc{gdb/mi} @value{GDBN} internally maintains a number of output streams: the console, the target, and the log. The output intended for each of these streams is funneled through the @sc{gdb/mi} interface using @dfn{stream records}. Each stream record begins with a unique @dfn{prefix character} which identifies its stream (@pxref{GDB/MI Output Syntax, , @sc{gdb/mi} Output Syntax}). In addition to the prefix, each stream record contains a @code{@var{string-output}}. This is either raw text (with an implicit new line) or a quoted C string (which does not contain an implicit newline). @table @code @item "~" @var{string-output} The console output stream contains text that should be displayed in the CLI console window. It contains the textual responses to CLI commands. @item "@@" @var{string-output} The target output stream contains any textual output from the running target. This is only present when GDB's event loop is truly asynchronous, which is currently only the case for remote targets. @item "&" @var{string-output} The log stream contains debugging messages being produced by @value{GDBN}'s internals. @end table @node GDB/MI Async Records @subsection @sc{gdb/mi} Async Records @cindex async records in @sc{gdb/mi} @cindex @sc{gdb/mi}, async records @dfn{Async} records are used to notify the @sc{gdb/mi} client of additional changes that have occurred. Those changes can either be a consequence of @sc{gdb/mi} commands (e.g., a breakpoint modified) or a result of target activity (e.g., target stopped). The following is the list of possible async records: @table @code @item *running,thread-id="@var{thread}" The target is now running. The @var{thread} field can be the global thread ID of the the thread that is now running, and it can be @samp{all} if all threads are running. The frontend should assume that no interaction with a running thread is possible after this notification is produced. The frontend should not assume that this notification is output only once for any command. @value{GDBN} may emit this notification several times, either for different threads, because it cannot resume all threads together, or even for a single thread, if the thread must be stepped though some code before letting it run freely. @item *stopped,reason="@var{reason}",thread-id="@var{id}",stopped-threads="@var{stopped}",core="@var{core}" The target has stopped. The @var{reason} field can have one of the following values: @table @code @item breakpoint-hit A breakpoint was reached. @item watchpoint-trigger A watchpoint was triggered. @item read-watchpoint-trigger A read watchpoint was triggered. @item access-watchpoint-trigger An access watchpoint was triggered. @item function-finished An -exec-finish or similar CLI command was accomplished. @item location-reached An -exec-until or similar CLI command was accomplished. @item watchpoint-scope A watchpoint has gone out of scope. @item end-stepping-range An -exec-next, -exec-next-instruction, -exec-step, -exec-step-instruction or similar CLI command was accomplished. @item exited-signalled The inferior exited because of a signal. @item exited The inferior exited. @item exited-normally The inferior exited normally. @item signal-received A signal was received by the inferior. @item solib-event The inferior has stopped due to a library being loaded or unloaded. This can happen when @code{stop-on-solib-events} (@pxref{Files}) is set or when a @code{catch load} or @code{catch unload} catchpoint is in use (@pxref{Set Catchpoints}). @item fork The inferior has forked. This is reported when @code{catch fork} (@pxref{Set Catchpoints}) has been used. @item vfork The inferior has vforked. This is reported in when @code{catch vfork} (@pxref{Set Catchpoints}) has been used. @item syscall-entry The inferior entered a system call. This is reported when @code{catch syscall} (@pxref{Set Catchpoints}) has been used. @item syscall-return The inferior returned from a system call. This is reported when @code{catch syscall} (@pxref{Set Catchpoints}) has been used. @item exec The inferior called @code{exec}. This is reported when @code{catch exec} (@pxref{Set Catchpoints}) has been used. @end table The @var{id} field identifies the global thread ID of the thread that directly caused the stop -- for example by hitting a breakpoint. Depending on whether all-stop mode is in effect (@pxref{All-Stop Mode}), @value{GDBN} may either stop all threads, or only the thread that directly triggered the stop. If all threads are stopped, the @var{stopped} field will have the value of @code{"all"}. Otherwise, the value of the @var{stopped} field will be a list of thread identifiers. Presently, this list will always include a single thread, but frontend should be prepared to see several threads in the list. The @var{core} field reports the processor core on which the stop event has happened. This field may be absent if such information is not available. @item =thread-group-added,id="@var{id}" @itemx =thread-group-removed,id="@var{id}" A thread group was either added or removed. The @var{id} field contains the @value{GDBN} identifier of the thread group. When a thread group is added, it generally might not be associated with a running process. When a thread group is removed, its id becomes invalid and cannot be used in any way. @item =thread-group-started,id="@var{id}",pid="@var{pid}" A thread group became associated with a running program, either because the program was just started or the thread group was attached to a program. The @var{id} field contains the @value{GDBN} identifier of the thread group. The @var{pid} field contains process identifier, specific to the operating system. @item =thread-group-exited,id="@var{id}"[,exit-code="@var{code}"] A thread group is no longer associated with a running program, either because the program has exited, or because it was detached from. The @var{id} field contains the @value{GDBN} identifier of the thread group. The @var{code} field is the exit code of the inferior; it exists only when the inferior exited with some code. @item =thread-created,id="@var{id}",group-id="@var{gid}" @itemx =thread-exited,id="@var{id}",group-id="@var{gid}" A thread either was created, or has exited. The @var{id} field contains the global @value{GDBN} identifier of the thread. The @var{gid} field identifies the thread group this thread belongs to. @item =thread-selected,id="@var{id}"[,frame="@var{frame}"] Informs that the selected thread or frame were changed. This notification is not emitted as result of the @code{-thread-select} or @code{-stack-select-frame} commands, but is emitted whenever an MI command that is not documented to change the selected thread and frame actually changes them. In particular, invoking, directly or indirectly (via user-defined command), the CLI @code{thread} or @code{frame} commands, will generate this notification. Changing the thread or frame from another user interface (see @ref{Interpreters}) will also generate this notification. The @var{frame} field is only present if the newly selected thread is stopped. See @ref{GDB/MI Frame Information} for the format of its value. We suggest that in response to this notification, front ends highlight the selected thread and cause subsequent commands to apply to that thread. @item =library-loaded,... Reports that a new library file was loaded by the program. This notification has 5 fields---@var{id}, @var{target-name}, @var{host-name}, @var{symbols-loaded} and @var{ranges}. The @var{id} field is an opaque identifier of the library. For remote debugging case, @var{target-name} and @var{host-name} fields give the name of the library file on the target, and on the host respectively. For native debugging, both those fields have the same value. The @var{symbols-loaded} field is emitted only for backward compatibility and should not be relied on to convey any useful information. The @var{thread-group} field, if present, specifies the id of the thread group in whose context the library was loaded. If the field is absent, it means the library was loaded in the context of all present thread groups. The @var{ranges} field specifies the ranges of addresses belonging to this library. @item =library-unloaded,... Reports that a library was unloaded by the program. This notification has 3 fields---@var{id}, @var{target-name} and @var{host-name} with the same meaning as for the @code{=library-loaded} notification. The @var{thread-group} field, if present, specifies the id of the thread group in whose context the library was unloaded. If the field is absent, it means the library was unloaded in the context of all present thread groups. @item =traceframe-changed,num=@var{tfnum},tracepoint=@var{tpnum} @itemx =traceframe-changed,end Reports that the trace frame was changed and its new number is @var{tfnum}. The number of the tracepoint associated with this trace frame is @var{tpnum}. @item =tsv-created,name=@var{name},initial=@var{initial} Reports that the new trace state variable @var{name} is created with initial value @var{initial}. @item =tsv-deleted,name=@var{name} @itemx =tsv-deleted Reports that the trace state variable @var{name} is deleted or all trace state variables are deleted. @item =tsv-modified,name=@var{name},initial=@var{initial}[,current=@var{current}] Reports that the trace state variable @var{name} is modified with the initial value @var{initial}. The current value @var{current} of trace state variable is optional and is reported if the current value of trace state variable is known. @item =breakpoint-created,bkpt=@{...@} @itemx =breakpoint-modified,bkpt=@{...@} @itemx =breakpoint-deleted,id=@var{number} Reports that a breakpoint was created, modified, or deleted, respectively. Only user-visible breakpoints are reported to the MI user. The @var{bkpt} argument is of the same form as returned by the various breakpoint commands; @xref{GDB/MI Breakpoint Commands}. The @var{number} is the ordinal number of the breakpoint. Note that if a breakpoint is emitted in the result record of a command, then it will not also be emitted in an async record. @item =record-started,thread-group="@var{id}",method="@var{method}"[,format="@var{format}"] @itemx =record-stopped,thread-group="@var{id}" Execution log recording was either started or stopped on an inferior. The @var{id} is the @value{GDBN} identifier of the thread group corresponding to the affected inferior. The @var{method} field indicates the method used to record execution. If the method in use supports multiple recording formats, @var{format} will be present and contain the currently used format. @xref{Process Record and Replay}, for existing method and format values. @item =cmd-param-changed,param=@var{param},value=@var{value} Reports that a parameter of the command @code{set @var{param}} is changed to @var{value}. In the multi-word @code{set} command, the @var{param} is the whole parameter list to @code{set} command. For example, In command @code{set check type on}, @var{param} is @code{check type} and @var{value} is @code{on}. @item =memory-changed,thread-group=@var{id},addr=@var{addr},len=@var{len}[,type="code"] Reports that bytes from @var{addr} to @var{data} + @var{len} were written in an inferior. The @var{id} is the identifier of the thread group corresponding to the affected inferior. The optional @code{type="code"} part is reported if the memory written to holds executable code. @end table @node GDB/MI Breakpoint Information @subsection @sc{gdb/mi} Breakpoint Information When @value{GDBN} reports information about a breakpoint, a tracepoint, a watchpoint, or a catchpoint, it uses a tuple with the following fields: @table @code @item number The breakpoint number. @item type The type of the breakpoint. For ordinary breakpoints this will be @samp{breakpoint}, but many values are possible. @item catch-type If the type of the breakpoint is @samp{catchpoint}, then this indicates the exact type of catchpoint. @item disp This is the breakpoint disposition---either @samp{del}, meaning that the breakpoint will be deleted at the next stop, or @samp{keep}, meaning that the breakpoint will not be deleted. @item enabled This indicates whether the breakpoint is enabled, in which case the value is @samp{y}, or disabled, in which case the value is @samp{n}. Note that this is not the same as the field @code{enable}. @item addr The address of the breakpoint. This may be a hexidecimal number, giving the address; or the string @samp{<PENDING>}, for a pending breakpoint; or the string @samp{<MULTIPLE>}, for a breakpoint with multiple locations. This field will not be present if no address can be determined. For example, a watchpoint does not have an address. @item addr_flags Optional field containing any flags related to the address. These flags are architecture-dependent; see @ref{Architectures} for their meaning for a particular CPU. @item func If known, the function in which the breakpoint appears. If not known, this field is not present. @item filename The name of the source file which contains this function, if known. If not known, this field is not present. @item fullname The full file name of the source file which contains this function, if known. If not known, this field is not present. @item line The line number at which this breakpoint appears, if known. If not known, this field is not present. @item at If the source file is not known, this field may be provided. If provided, this holds the address of the breakpoint, possibly followed by a symbol name. @item pending If this breakpoint is pending, this field is present and holds the text used to set the breakpoint, as entered by the user. @item evaluated-by Where this breakpoint's condition is evaluated, either @samp{host} or @samp{target}. @item thread If this is a thread-specific breakpoint, then this identifies the thread in which the breakpoint can trigger. @item task If this breakpoint is restricted to a particular Ada task, then this field will hold the task identifier. @item cond If the breakpoint is conditional, this is the condition expression. @item ignore The ignore count of the breakpoint. @item enable The enable count of the breakpoint. @item traceframe-usage FIXME. @item static-tracepoint-marker-string-id For a static tracepoint, the name of the static tracepoint marker. @item mask For a masked watchpoint, this is the mask. @item pass A tracepoint's pass count. @item original-location The location of the breakpoint as originally specified by the user. This field is optional. @item times The number of times the breakpoint has been hit. @item installed This field is only given for tracepoints. This is either @samp{y}, meaning that the tracepoint is installed, or @samp{n}, meaning that it is not. @item what Some extra data, the exact contents of which are type-dependent. @item locations This field is present if the breakpoint has multiple locations. It is also exceptionally present if the breakpoint is enabled and has a single, disabled location. The value is a list of locations. The format of a location is described below. @end table A location in a multi-location breakpoint is represented as a tuple with the following fields: @table @code @item number The location number as a dotted pair, like @samp{1.2}. The first digit is the number of the parent breakpoint. The second digit is the number of the location within that breakpoint. @item enabled This indicates whether the location is enabled, in which case the value is @samp{y}, or disabled, in which case the value is @samp{n}. Note that this is not the same as the field @code{enable}. @item addr The address of this location as an hexidecimal number. @item addr_flags Optional field containing any flags related to the address. These flags are architecture-dependent; see @ref{Architectures} for their meaning for a particular CPU. @item func If known, the function in which the location appears. If not known, this field is not present. @item file The name of the source file which contains this location, if known. If not known, this field is not present. @item fullname The full file name of the source file which contains this location, if known. If not known, this field is not present. @item line The line number at which this location appears, if known. If not known, this field is not present. @item thread-groups The thread groups this location is in. @end table For example, here is what the output of @code{-break-insert} (@pxref{GDB/MI Breakpoint Commands}) might be: @smallexample -> -break-insert main <- ^done,bkpt=@{number="1",type="breakpoint",disp="keep", enabled="y",addr="0x08048564",func="main",file="myprog.c", fullname="/home/nickrob/myprog.c",line="68",thread-groups=["i1"], times="0"@} <- (gdb) @end smallexample @node GDB/MI Frame Information @subsection @sc{gdb/mi} Frame Information Response from many MI commands includes an information about stack frame. This information is a tuple that may have the following fields: @table @code @item level The level of the stack frame. The innermost frame has the level of zero. This field is always present. @item func The name of the function corresponding to the frame. This field may be absent if @value{GDBN} is unable to determine the function name. @item addr The code address for the frame. This field is always present. @item addr_flags Optional field containing any flags related to the address. These flags are architecture-dependent; see @ref{Architectures} for their meaning for a particular CPU. @item file The name of the source files that correspond to the frame's code address. This field may be absent. @item line The source line corresponding to the frames' code address. This field may be absent. @item from The name of the binary file (either executable or shared library) the corresponds to the frame's code address. This field may be absent. @end table @node GDB/MI Thread Information @subsection @sc{gdb/mi} Thread Information Whenever @value{GDBN} has to report an information about a thread, it uses a tuple with the following fields. The fields are always present unless stated otherwise. @table @code @item id The global numeric id assigned to the thread by @value{GDBN}. @item target-id The target-specific string identifying the thread. @item details Additional information about the thread provided by the target. It is supposed to be human-readable and not interpreted by the frontend. This field is optional. @item name The name of the thread. If the user specified a name using the @code{thread name} command, then this name is given. Otherwise, if @value{GDBN} can extract the thread name from the target, then that name is given. If @value{GDBN} cannot find the thread name, then this field is omitted. @item state The execution state of the thread, either @samp{stopped} or @samp{running}, depending on whether the thread is presently running. @item frame The stack frame currently executing in the thread. This field is only present if the thread is stopped. Its format is documented in @ref{GDB/MI Frame Information}. @item core The value of this field is an integer number of the processor core the thread was last seen on. This field is optional. @end table @node GDB/MI Ada Exception Information @subsection @sc{gdb/mi} Ada Exception Information Whenever a @code{*stopped} record is emitted because the program stopped after hitting an exception catchpoint (@pxref{Set Catchpoints}), @value{GDBN} provides the name of the exception that was raised via the @code{exception-name} field. Also, for exceptions that were raised with an exception message, @value{GDBN} provides that message via the @code{exception-message} field. @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Simple Examples @section Simple Examples of @sc{gdb/mi} Interaction @cindex @sc{gdb/mi}, simple examples This subsection presents several simple examples of interaction using the @sc{gdb/mi} interface. In these examples, @samp{->} means that the following line is passed to @sc{gdb/mi} as input, while @samp{<-} means the output received from @sc{gdb/mi}. Note the line breaks shown in the examples are here only for readability, they don't appear in the real output. @subheading Setting a Breakpoint Setting a breakpoint generates synchronous output which contains detailed information of the breakpoint. @smallexample -> -break-insert main <- ^done,bkpt=@{number="1",type="breakpoint",disp="keep", enabled="y",addr="0x08048564",func="main",file="myprog.c", fullname="/home/nickrob/myprog.c",line="68",thread-groups=["i1"], times="0"@} <- (gdb) @end smallexample @subheading Program Execution Program execution generates asynchronous records and MI gives the reason that execution stopped. @smallexample -> -exec-run <- ^running <- (gdb) <- *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0", frame=@{addr="0x08048564",func="main", args=[@{name="argc",value="1"@},@{name="argv",value="0xbfc4d4d4"@}], file="myprog.c",fullname="/home/nickrob/myprog.c",line="68", arch="i386:x86_64"@} <- (gdb) -> -exec-continue <- ^running <- (gdb) <- *stopped,reason="exited-normally" <- (gdb) @end smallexample @subheading Quitting @value{GDBN} Quitting @value{GDBN} just prints the result class @samp{^exit}. @smallexample -> (gdb) <- -gdb-exit <- ^exit @end smallexample Please note that @samp{^exit} is printed immediately, but it might take some time for @value{GDBN} to actually exit. During that time, @value{GDBN} performs necessary cleanups, including killing programs being debugged or disconnecting from debug hardware, so the frontend should wait till @value{GDBN} exits and should only forcibly kill @value{GDBN} if it fails to exit in reasonable time. @subheading A Bad Command Here's what happens if you pass a non-existent command: @smallexample -> -rubbish <- ^error,msg="Undefined MI command: rubbish" <- (gdb) @end smallexample @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Command Description Format @section @sc{gdb/mi} Command Description Format The remaining sections describe blocks of commands. Each block of commands is laid out in a fashion similar to this section. @subheading Motivation The motivation for this collection of commands. @subheading Introduction A brief introduction to this collection of commands as a whole. @subheading Commands For each command in the block, the following is described: @subsubheading Synopsis @smallexample -command @var{args}@dots{} @end smallexample @subsubheading Result @subsubheading @value{GDBN} Command The corresponding @value{GDBN} CLI command(s), if any. @subsubheading Example Example(s) formatted for readability. Some of the described commands have not been implemented yet and these are labeled N.A.@: (not available). @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Breakpoint Commands @section @sc{gdb/mi} Breakpoint Commands @cindex breakpoint commands for @sc{gdb/mi} @cindex @sc{gdb/mi}, breakpoint commands This section documents @sc{gdb/mi} commands for manipulating breakpoints. @subheading The @code{-break-after} Command @findex -break-after @subsubheading Synopsis @smallexample -break-after @var{number} @var{count} @end smallexample The breakpoint number @var{number} is not in effect until it has been hit @var{count} times. To see how this is reflected in the output of the @samp{-break-list} command, see the description of the @samp{-break-list} command below. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{ignore}. @subsubheading Example @smallexample (gdb) -break-insert main ^done,bkpt=@{number="1",type="breakpoint",disp="keep", enabled="y",addr="0x000100d0",func="main",file="hello.c", fullname="/home/foo/hello.c",line="5",thread-groups=["i1"], times="0"@} (gdb) -break-after 1 3 ~ ^done (gdb) -break-list ^done,BreakpointTable=@{nr_rows="1",nr_cols="6", hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@}, @{width="14",alignment="-1",col_name="type",colhdr="Type"@}, @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@}, @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@}, @{width="10",alignment="-1",col_name="addr",colhdr="Address"@}, @{width="40",alignment="2",col_name="what",colhdr="What"@}], body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y", addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c", line="5",thread-groups=["i1"],times="0",ignore="3"@}]@} (gdb) @end smallexample @ignore @subheading The @code{-break-catch} Command @findex -break-catch @end ignore @subheading The @code{-break-commands} Command @findex -break-commands @subsubheading Synopsis @smallexample -break-commands @var{number} [ @var{command1} ... @var{commandN} ] @end smallexample Specifies the CLI commands that should be executed when breakpoint @var{number} is hit. The parameters @var{command1} to @var{commandN} are the commands. If no command is specified, any previously-set commands are cleared. @xref{Break Commands}. Typical use of this functionality is tracing a program, that is, printing of values of some variables whenever breakpoint is hit and then continuing. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{commands}. @subsubheading Example @smallexample (gdb) -break-insert main ^done,bkpt=@{number="1",type="breakpoint",disp="keep", enabled="y",addr="0x000100d0",func="main",file="hello.c", fullname="/home/foo/hello.c",line="5",thread-groups=["i1"], times="0"@} (gdb) -break-commands 1 "print v" "continue" ^done (gdb) @end smallexample @subheading The @code{-break-condition} Command @findex -break-condition @subsubheading Synopsis @smallexample -break-condition @var{number} @var{expr} @end smallexample Breakpoint @var{number} will stop the program only if the condition in @var{expr} is true. The condition becomes part of the @samp{-break-list} output (see the description of the @samp{-break-list} command below). @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{condition}. @subsubheading Example @smallexample (gdb) -break-condition 1 1 ^done (gdb) -break-list ^done,BreakpointTable=@{nr_rows="1",nr_cols="6", hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@}, @{width="14",alignment="-1",col_name="type",colhdr="Type"@}, @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@}, @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@}, @{width="10",alignment="-1",col_name="addr",colhdr="Address"@}, @{width="40",alignment="2",col_name="what",colhdr="What"@}], body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y", addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c", line="5",cond="1",thread-groups=["i1"],times="0",ignore="3"@}]@} (gdb) @end smallexample @subheading The @code{-break-delete} Command @findex -break-delete @subsubheading Synopsis @smallexample -break-delete ( @var{breakpoint} )+ @end smallexample Delete the breakpoint(s) whose number(s) are specified in the argument list. This is obviously reflected in the breakpoint list. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{delete}. @subsubheading Example @smallexample (gdb) -break-delete 1 ^done (gdb) -break-list ^done,BreakpointTable=@{nr_rows="0",nr_cols="6", hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@}, @{width="14",alignment="-1",col_name="type",colhdr="Type"@}, @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@}, @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@}, @{width="10",alignment="-1",col_name="addr",colhdr="Address"@}, @{width="40",alignment="2",col_name="what",colhdr="What"@}], body=[]@} (gdb) @end smallexample @subheading The @code{-break-disable} Command @findex -break-disable @subsubheading Synopsis @smallexample -break-disable ( @var{breakpoint} )+ @end smallexample Disable the named @var{breakpoint}(s). The field @samp{enabled} in the break list is now set to @samp{n} for the named @var{breakpoint}(s). @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{disable}. @subsubheading Example @smallexample (gdb) -break-disable 2 ^done (gdb) -break-list ^done,BreakpointTable=@{nr_rows="1",nr_cols="6", hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@}, @{width="14",alignment="-1",col_name="type",colhdr="Type"@}, @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@}, @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@}, @{width="10",alignment="-1",col_name="addr",colhdr="Address"@}, @{width="40",alignment="2",col_name="what",colhdr="What"@}], body=[bkpt=@{number="2",type="breakpoint",disp="keep",enabled="n", addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c", line="5",thread-groups=["i1"],times="0"@}]@} (gdb) @end smallexample @subheading The @code{-break-enable} Command @findex -break-enable @subsubheading Synopsis @smallexample -break-enable ( @var{breakpoint} )+ @end smallexample Enable (previously disabled) @var{breakpoint}(s). @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{enable}. @subsubheading Example @smallexample (gdb) -break-enable 2 ^done (gdb) -break-list ^done,BreakpointTable=@{nr_rows="1",nr_cols="6", hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@}, @{width="14",alignment="-1",col_name="type",colhdr="Type"@}, @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@}, @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@}, @{width="10",alignment="-1",col_name="addr",colhdr="Address"@}, @{width="40",alignment="2",col_name="what",colhdr="What"@}], body=[bkpt=@{number="2",type="breakpoint",disp="keep",enabled="y", addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c", line="5",thread-groups=["i1"],times="0"@}]@} (gdb) @end smallexample @subheading The @code{-break-info} Command @findex -break-info @subsubheading Synopsis @smallexample -break-info @var{breakpoint} @end smallexample @c REDUNDANT??? Get information about a single breakpoint. The result is a table of breakpoints. @xref{GDB/MI Breakpoint Information}, for details on the format of each breakpoint in the table. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{info break @var{breakpoint}}. @subsubheading Example N.A. @subheading The @code{-break-insert} Command @findex -break-insert @anchor{-break-insert} @subsubheading Synopsis @smallexample -break-insert [ -t ] [ -h ] [ -f ] [ -d ] [ -a ] [ -c @var{condition} ] [ -i @var{ignore-count} ] [ -p @var{thread-id} ] [ @var{location} ] @end smallexample @noindent If specified, @var{location}, can be one of: @table @var @item linespec location A linespec location. @xref{Linespec Locations}. @item explicit location An explicit location. @sc{gdb/mi} explicit locations are analogous to the CLI's explicit locations using the option names listed below. @xref{Explicit Locations}. @table @samp @item --source @var{filename} The source file name of the location. This option requires the use of either @samp{--function} or @samp{--line}. @item --function @var{function} The name of a function or method. @item --label @var{label} The name of a label. @item --line @var{lineoffset} An absolute or relative line offset from the start of the location. @end table @item address location An address location, *@var{address}. @xref{Address Locations}. @end table @noindent The possible optional parameters of this command are: @table @samp @item -t Insert a temporary breakpoint. @item -h Insert a hardware breakpoint. @item -f If @var{location} cannot be parsed (for example if it refers to unknown files or functions), create a pending breakpoint. Without this flag, @value{GDBN} will report an error, and won't create a breakpoint, if @var{location} cannot be parsed. @item -d Create a disabled breakpoint. @item -a Create a tracepoint. @xref{Tracepoints}. When this parameter is used together with @samp{-h}, a fast tracepoint is created. @item -c @var{condition} Make the breakpoint conditional on @var{condition}. @item -i @var{ignore-count} Initialize the @var{ignore-count}. @item -p @var{thread-id} Restrict the breakpoint to the thread with the specified global @var{thread-id}. @end table @subsubheading Result @xref{GDB/MI Breakpoint Information}, for details on the format of the resulting breakpoint. Note: this format is open to change. @c An out-of-band breakpoint instead of part of the result? @subsubheading @value{GDBN} Command The corresponding @value{GDBN} commands are @samp{break}, @samp{tbreak}, @samp{hbreak}, and @samp{thbreak}. @c and @samp{rbreak}. @subsubheading Example @smallexample (gdb) -break-insert main ^done,bkpt=@{number="1",addr="0x0001072c",file="recursive2.c", fullname="/home/foo/recursive2.c,line="4",thread-groups=["i1"], times="0"@} (gdb) -break-insert -t foo ^done,bkpt=@{number="2",addr="0x00010774",file="recursive2.c", fullname="/home/foo/recursive2.c,line="11",thread-groups=["i1"], times="0"@} (gdb) -break-list ^done,BreakpointTable=@{nr_rows="2",nr_cols="6", hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@}, @{width="14",alignment="-1",col_name="type",colhdr="Type"@}, @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@}, @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@}, @{width="10",alignment="-1",col_name="addr",colhdr="Address"@}, @{width="40",alignment="2",col_name="what",colhdr="What"@}], body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y", addr="0x0001072c", func="main",file="recursive2.c", fullname="/home/foo/recursive2.c,"line="4",thread-groups=["i1"], times="0"@}, bkpt=@{number="2",type="breakpoint",disp="del",enabled="y", addr="0x00010774",func="foo",file="recursive2.c", fullname="/home/foo/recursive2.c",line="11",thread-groups=["i1"], times="0"@}]@} (gdb) @c -break-insert -r foo.* @c ~int foo(int, int); @c ^done,bkpt=@{number="3",addr="0x00010774",file="recursive2.c, @c "fullname="/home/foo/recursive2.c",line="11",thread-groups=["i1"], @c times="0"@} @c (gdb) @end smallexample @subheading The @code{-dprintf-insert} Command @findex -dprintf-insert @subsubheading Synopsis @smallexample -dprintf-insert [ -t ] [ -f ] [ -d ] [ -c @var{condition} ] [ -i @var{ignore-count} ] [ -p @var{thread-id} ] [ @var{location} ] [ @var{format} ] [ @var{argument} ] @end smallexample @noindent If supplied, @var{location} may be specified the same way as for the @code{-break-insert} command. @xref{-break-insert}. The possible optional parameters of this command are: @table @samp @item -t Insert a temporary breakpoint. @item -f If @var{location} cannot be parsed (for example, if it refers to unknown files or functions), create a pending breakpoint. Without this flag, @value{GDBN} will report an error, and won't create a breakpoint, if @var{location} cannot be parsed. @item -d Create a disabled breakpoint. @item -c @var{condition} Make the breakpoint conditional on @var{condition}. @item -i @var{ignore-count} Set the ignore count of the breakpoint (@pxref{Conditions, ignore count}) to @var{ignore-count}. @item -p @var{thread-id} Restrict the breakpoint to the thread with the specified global @var{thread-id}. @end table @subsubheading Result @xref{GDB/MI Breakpoint Information}, for details on the format of the resulting breakpoint. @c An out-of-band breakpoint instead of part of the result? @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{dprintf}. @subsubheading Example @smallexample (gdb) 4-dprintf-insert foo "At foo entry\n" 4^done,bkpt=@{number="1",type="dprintf",disp="keep",enabled="y", addr="0x000000000040061b",func="foo",file="mi-dprintf.c", fullname="mi-dprintf.c",line="25",thread-groups=["i1"], times="0",script=@{"printf \"At foo entry\\n\"","continue"@}, original-location="foo"@} (gdb) 5-dprintf-insert 26 "arg=%d, g=%d\n" arg g 5^done,bkpt=@{number="2",type="dprintf",disp="keep",enabled="y", addr="0x000000000040062a",func="foo",file="mi-dprintf.c", fullname="mi-dprintf.c",line="26",thread-groups=["i1"], times="0",script=@{"printf \"arg=%d, g=%d\\n\", arg, g","continue"@}, original-location="mi-dprintf.c:26"@} (gdb) @end smallexample @subheading The @code{-break-list} Command @findex -break-list @subsubheading Synopsis @smallexample -break-list @end smallexample Displays the list of inserted breakpoints, showing the following fields: @table @samp @item Number number of the breakpoint @item Type type of the breakpoint: @samp{breakpoint} or @samp{watchpoint} @item Disposition should the breakpoint be deleted or disabled when it is hit: @samp{keep} or @samp{nokeep} @item Enabled is the breakpoint enabled or no: @samp{y} or @samp{n} @item Address memory location at which the breakpoint is set @item What logical location of the breakpoint, expressed by function name, file name, line number @item Thread-groups list of thread groups to which this breakpoint applies @item Times number of times the breakpoint has been hit @end table If there are no breakpoints or watchpoints, the @code{BreakpointTable} @code{body} field is an empty list. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{info break}. @subsubheading Example @smallexample (gdb) -break-list ^done,BreakpointTable=@{nr_rows="2",nr_cols="6", hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@}, @{width="14",alignment="-1",col_name="type",colhdr="Type"@}, @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@}, @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@}, @{width="10",alignment="-1",col_name="addr",colhdr="Address"@}, @{width="40",alignment="2",col_name="what",colhdr="What"@}], body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y", addr="0x000100d0",func="main",file="hello.c",line="5",thread-groups=["i1"], times="0"@}, bkpt=@{number="2",type="breakpoint",disp="keep",enabled="y", addr="0x00010114",func="foo",file="hello.c",fullname="/home/foo/hello.c", line="13",thread-groups=["i1"],times="0"@}]@} (gdb) @end smallexample Here's an example of the result when there are no breakpoints: @smallexample (gdb) -break-list ^done,BreakpointTable=@{nr_rows="0",nr_cols="6", hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@}, @{width="14",alignment="-1",col_name="type",colhdr="Type"@}, @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@}, @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@}, @{width="10",alignment="-1",col_name="addr",colhdr="Address"@}, @{width="40",alignment="2",col_name="what",colhdr="What"@}], body=[]@} (gdb) @end smallexample @subheading The @code{-break-passcount} Command @findex -break-passcount @subsubheading Synopsis @smallexample -break-passcount @var{tracepoint-number} @var{passcount} @end smallexample Set the passcount for tracepoint @var{tracepoint-number} to @var{passcount}. If the breakpoint referred to by @var{tracepoint-number} is not a tracepoint, error is emitted. This corresponds to CLI command @samp{passcount}. @subheading The @code{-break-watch} Command @findex -break-watch @subsubheading Synopsis @smallexample -break-watch [ -a | -r ] @end smallexample Create a watchpoint. With the @samp{-a} option it will create an @dfn{access} watchpoint, i.e., a watchpoint that triggers either on a read from or on a write to the memory location. With the @samp{-r} option, the watchpoint created is a @dfn{read} watchpoint, i.e., it will trigger only when the memory location is accessed for reading. Without either of the options, the watchpoint created is a regular watchpoint, i.e., it will trigger when the memory location is accessed for writing. @xref{Set Watchpoints, , Setting Watchpoints}. Note that @samp{-break-list} will report a single list of watchpoints and breakpoints inserted. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} commands are @samp{watch}, @samp{awatch}, and @samp{rwatch}. @subsubheading Example Setting a watchpoint on a variable in the @code{main} function: @smallexample (gdb) -break-watch x ^done,wpt=@{number="2",exp="x"@} (gdb) -exec-continue ^running (gdb) *stopped,reason="watchpoint-trigger",wpt=@{number="2",exp="x"@}, value=@{old="-268439212",new="55"@}, frame=@{func="main",args=[],file="recursive2.c", fullname="/home/foo/bar/recursive2.c",line="5",arch="i386:x86_64"@} (gdb) @end smallexample Setting a watchpoint on a variable local to a function. @value{GDBN} will stop the program execution twice: first for the variable changing value, then for the watchpoint going out of scope. @smallexample (gdb) -break-watch C ^done,wpt=@{number="5",exp="C"@} (gdb) -exec-continue ^running (gdb) *stopped,reason="watchpoint-trigger", wpt=@{number="5",exp="C"@},value=@{old="-276895068",new="3"@}, frame=@{func="callee4",args=[], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13", arch="i386:x86_64"@} (gdb) -exec-continue ^running (gdb) *stopped,reason="watchpoint-scope",wpnum="5", frame=@{func="callee3",args=[@{name="strarg", value="0x11940 \"A string argument.\""@}], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18", arch="i386:x86_64"@} (gdb) @end smallexample Listing breakpoints and watchpoints, at different points in the program execution. Note that once the watchpoint goes out of scope, it is deleted. @smallexample (gdb) -break-watch C ^done,wpt=@{number="2",exp="C"@} (gdb) -break-list ^done,BreakpointTable=@{nr_rows="2",nr_cols="6", hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@}, @{width="14",alignment="-1",col_name="type",colhdr="Type"@}, @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@}, @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@}, @{width="10",alignment="-1",col_name="addr",colhdr="Address"@}, @{width="40",alignment="2",col_name="what",colhdr="What"@}], body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y", addr="0x00010734",func="callee4", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c"line="8",thread-groups=["i1"], times="1"@}, bkpt=@{number="2",type="watchpoint",disp="keep", enabled="y",addr="",what="C",thread-groups=["i1"],times="0"@}]@} (gdb) -exec-continue ^running (gdb) *stopped,reason="watchpoint-trigger",wpt=@{number="2",exp="C"@}, value=@{old="-276895068",new="3"@}, frame=@{func="callee4",args=[], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13", arch="i386:x86_64"@} (gdb) -break-list ^done,BreakpointTable=@{nr_rows="2",nr_cols="6", hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@}, @{width="14",alignment="-1",col_name="type",colhdr="Type"@}, @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@}, @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@}, @{width="10",alignment="-1",col_name="addr",colhdr="Address"@}, @{width="40",alignment="2",col_name="what",colhdr="What"@}], body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y", addr="0x00010734",func="callee4", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",thread-groups=["i1"], times="1"@}, bkpt=@{number="2",type="watchpoint",disp="keep", enabled="y",addr="",what="C",thread-groups=["i1"],times="-5"@}]@} (gdb) -exec-continue ^running ^done,reason="watchpoint-scope",wpnum="2", frame=@{func="callee3",args=[@{name="strarg", value="0x11940 \"A string argument.\""@}], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18", arch="i386:x86_64"@} (gdb) -break-list ^done,BreakpointTable=@{nr_rows="1",nr_cols="6", hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@}, @{width="14",alignment="-1",col_name="type",colhdr="Type"@}, @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@}, @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@}, @{width="10",alignment="-1",col_name="addr",colhdr="Address"@}, @{width="40",alignment="2",col_name="what",colhdr="What"@}], body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y", addr="0x00010734",func="callee4", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8", thread-groups=["i1"],times="1"@}]@} (gdb) @end smallexample @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Catchpoint Commands @section @sc{gdb/mi} Catchpoint Commands This section documents @sc{gdb/mi} commands for manipulating catchpoints. @menu * Shared Library GDB/MI Catchpoint Commands:: * Ada Exception GDB/MI Catchpoint Commands:: * C++ Exception GDB/MI Catchpoint Commands:: @end menu @node Shared Library GDB/MI Catchpoint Commands @subsection Shared Library @sc{gdb/mi} Catchpoints @subheading The @code{-catch-load} Command @findex -catch-load @subsubheading Synopsis @smallexample -catch-load [ -t ] [ -d ] @var{regexp} @end smallexample Add a catchpoint for library load events. If the @samp{-t} option is used, the catchpoint is a temporary one (@pxref{Set Breaks, ,Setting Breakpoints}). If the @samp{-d} option is used, the catchpoint is created in a disabled state. The @samp{regexp} argument is a regular expression used to match the name of the loaded library. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{catch load}. @subsubheading Example @smallexample -catch-load -t foo.so ^done,bkpt=@{number="1",type="catchpoint",disp="del",enabled="y", what="load of library matching foo.so",catch-type="load",times="0"@} (gdb) @end smallexample @subheading The @code{-catch-unload} Command @findex -catch-unload @subsubheading Synopsis @smallexample -catch-unload [ -t ] [ -d ] @var{regexp} @end smallexample Add a catchpoint for library unload events. If the @samp{-t} option is used, the catchpoint is a temporary one (@pxref{Set Breaks, ,Setting Breakpoints}). If the @samp{-d} option is used, the catchpoint is created in a disabled state. The @samp{regexp} argument is a regular expression used to match the name of the unloaded library. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{catch unload}. @subsubheading Example @smallexample -catch-unload -d bar.so ^done,bkpt=@{number="2",type="catchpoint",disp="keep",enabled="n", what="load of library matching bar.so",catch-type="unload",times="0"@} (gdb) @end smallexample @node Ada Exception GDB/MI Catchpoint Commands @subsection Ada Exception @sc{gdb/mi} Catchpoints The following @sc{gdb/mi} commands can be used to create catchpoints that stop the execution when Ada exceptions are being raised. @subheading The @code{-catch-assert} Command @findex -catch-assert @subsubheading Synopsis @smallexample -catch-assert [ -c @var{condition}] [ -d ] [ -t ] @end smallexample Add a catchpoint for failed Ada assertions. The possible optional parameters for this command are: @table @samp @item -c @var{condition} Make the catchpoint conditional on @var{condition}. @item -d Create a disabled catchpoint. @item -t Create a temporary catchpoint. @end table @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{catch assert}. @subsubheading Example @smallexample -catch-assert ^done,bkptno="5",bkpt=@{number="5",type="breakpoint",disp="keep", enabled="y",addr="0x0000000000404888",what="failed Ada assertions", thread-groups=["i1"],times="0", original-location="__gnat_debug_raise_assert_failure"@} (gdb) @end smallexample @subheading The @code{-catch-exception} Command @findex -catch-exception @subsubheading Synopsis @smallexample -catch-exception [ -c @var{condition}] [ -d ] [ -e @var{exception-name} ] [ -t ] [ -u ] @end smallexample Add a catchpoint stopping when Ada exceptions are raised. By default, the command stops the program when any Ada exception gets raised. But it is also possible, by using some of the optional parameters described below, to create more selective catchpoints. The possible optional parameters for this command are: @table @samp @item -c @var{condition} Make the catchpoint conditional on @var{condition}. @item -d Create a disabled catchpoint. @item -e @var{exception-name} Only stop when @var{exception-name} is raised. This option cannot be used combined with @samp{-u}. @item -t Create a temporary catchpoint. @item -u Stop only when an unhandled exception gets raised. This option cannot be used combined with @samp{-e}. @end table @subsubheading @value{GDBN} Command The corresponding @value{GDBN} commands are @samp{catch exception} and @samp{catch exception unhandled}. @subsubheading Example @smallexample -catch-exception -e Program_Error ^done,bkptno="4",bkpt=@{number="4",type="breakpoint",disp="keep", enabled="y",addr="0x0000000000404874", what="`Program_Error' Ada exception", thread-groups=["i1"], times="0",original-location="__gnat_debug_raise_exception"@} (gdb) @end smallexample @subheading The @code{-catch-handlers} Command @findex -catch-handlers @subsubheading Synopsis @smallexample -catch-handlers [ -c @var{condition}] [ -d ] [ -e @var{exception-name} ] [ -t ] @end smallexample Add a catchpoint stopping when Ada exceptions are handled. By default, the command stops the program when any Ada exception gets handled. But it is also possible, by using some of the optional parameters described below, to create more selective catchpoints. The possible optional parameters for this command are: @table @samp @item -c @var{condition} Make the catchpoint conditional on @var{condition}. @item -d Create a disabled catchpoint. @item -e @var{exception-name} Only stop when @var{exception-name} is handled. @item -t Create a temporary catchpoint. @end table @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{catch handlers}. @subsubheading Example @smallexample -catch-handlers -e Constraint_Error ^done,bkptno="4",bkpt=@{number="4",type="breakpoint",disp="keep", enabled="y",addr="0x0000000000402f68", what="`Constraint_Error' Ada exception handlers",thread-groups=["i1"], times="0",original-location="__gnat_begin_handler"@} (gdb) @end smallexample @node C++ Exception GDB/MI Catchpoint Commands @subsection C@t{++} Exception @sc{gdb/mi} Catchpoints The following @sc{gdb/mi} commands can be used to create catchpoints that stop the execution when C@t{++} exceptions are being throw, rethrown, or caught. @subheading The @code{-catch-throw} Command @findex -catch-throw @subsubheading Synopsis @smallexample -catch-throw [ -t ] [ -r @var{regexp}] @end smallexample Stop when the debuggee throws a C@t{++} exception. If @var{regexp} is given, then only exceptions whose type matches the regular expression will be caught. If @samp{-t} is given, then the catchpoint is enabled only for one stop, the catchpoint is automatically deleted after stopping once for the event. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} commands are @samp{catch throw} and @samp{tcatch throw} (@pxref{Set Catchpoints}). @subsubheading Example @smallexample -catch-throw -r exception_type ^done,bkpt=@{number="1",type="catchpoint",disp="keep",enabled="y", what="exception throw",catch-type="throw", thread-groups=["i1"], regexp="exception_type",times="0"@} (gdb) -exec-run ^running (gdb) ~"\n" ~"Catchpoint 1 (exception thrown), 0x00007ffff7ae00ed in __cxa_throw () from /lib64/libstdc++.so.6\n" *stopped,bkptno="1",reason="breakpoint-hit",disp="keep", frame=@{addr="0x00007ffff7ae00ed",func="__cxa_throw", args=[],from="/lib64/libstdc++.so.6",arch="i386:x86-64"@}, thread-id="1",stopped-threads="all",core="6" (gdb) @end smallexample @subheading The @code{-catch-rethrow} Command @findex -catch-rethrow @subsubheading Synopsis @smallexample -catch-rethrow [ -t ] [ -r @var{regexp}] @end smallexample Stop when a C@t{++} exception is re-thrown. If @var{regexp} is given, then only exceptions whose type matches the regular expression will be caught. If @samp{-t} is given, then the catchpoint is enabled only for one stop, the catchpoint is automatically deleted after the first event is caught. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} commands are @samp{catch rethrow} and @samp{tcatch rethrow} (@pxref{Set Catchpoints}). @subsubheading Example @smallexample -catch-rethrow -r exception_type ^done,bkpt=@{number="1",type="catchpoint",disp="keep",enabled="y", what="exception rethrow",catch-type="rethrow", thread-groups=["i1"], regexp="exception_type",times="0"@} (gdb) -exec-run ^running (gdb) ~"\n" ~"Catchpoint 1 (exception rethrown), 0x00007ffff7ae00ed in __cxa_rethrow () from /lib64/libstdc++.so.6\n" *stopped,bkptno="1",reason="breakpoint-hit",disp="keep", frame=@{addr="0x00007ffff7ae00ed",func="__cxa_rethrow", args=[],from="/lib64/libstdc++.so.6",arch="i386:x86-64"@}, thread-id="1",stopped-threads="all",core="6" (gdb) @end smallexample @subheading The @code{-catch-catch} Command @findex -catch-catch @subsubheading Synopsis @smallexample -catch-catch [ -t ] [ -r @var{regexp}] @end smallexample Stop when the debuggee catches a C@t{++} exception. If @var{regexp} is given, then only exceptions whose type matches the regular expression will be caught. If @samp{-t} is given, then the catchpoint is enabled only for one stop, the catchpoint is automatically deleted after the first event is caught. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} commands are @samp{catch catch} and @samp{tcatch catch} (@pxref{Set Catchpoints}). @subsubheading Example @smallexample -catch-catch -r exception_type ^done,bkpt=@{number="1",type="catchpoint",disp="keep",enabled="y", what="exception catch",catch-type="catch", thread-groups=["i1"], regexp="exception_type",times="0"@} (gdb) -exec-run ^running (gdb) ~"\n" ~"Catchpoint 1 (exception caught), 0x00007ffff7ae00ed in __cxa_begin_catch () from /lib64/libstdc++.so.6\n" *stopped,bkptno="1",reason="breakpoint-hit",disp="keep", frame=@{addr="0x00007ffff7ae00ed",func="__cxa_begin_catch", args=[],from="/lib64/libstdc++.so.6",arch="i386:x86-64"@}, thread-id="1",stopped-threads="all",core="6" (gdb) @end smallexample @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Program Context @section @sc{gdb/mi} Program Context @subheading The @code{-exec-arguments} Command @findex -exec-arguments @subsubheading Synopsis @smallexample -exec-arguments @var{args} @end smallexample Set the inferior program arguments, to be used in the next @samp{-exec-run}. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{set args}. @subsubheading Example @smallexample (gdb) -exec-arguments -v word ^done (gdb) @end smallexample @ignore @subheading The @code{-exec-show-arguments} Command @findex -exec-show-arguments @subsubheading Synopsis @smallexample -exec-show-arguments @end smallexample Print the arguments of the program. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{show args}. @subsubheading Example N.A. @end ignore @subheading The @code{-environment-cd} Command @findex -environment-cd @subsubheading Synopsis @smallexample -environment-cd @var{pathdir} @end smallexample Set @value{GDBN}'s working directory. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{cd}. @subsubheading Example @smallexample (gdb) -environment-cd /kwikemart/marge/ezannoni/flathead-dev/devo/gdb ^done (gdb) @end smallexample @subheading The @code{-environment-directory} Command @findex -environment-directory @subsubheading Synopsis @smallexample -environment-directory [ -r ] [ @var{pathdir} ]+ @end smallexample Add directories @var{pathdir} to beginning of search path for source files. If the @samp{-r} option is used, the search path is reset to the default search path. If directories @var{pathdir} are supplied in addition to the @samp{-r} option, the search path is first reset and then addition occurs as normal. Multiple directories may be specified, separated by blanks. Specifying multiple directories in a single command results in the directories added to the beginning of the search path in the same order they were presented in the command. If blanks are needed as part of a directory name, double-quotes should be used around the name. In the command output, the path will show up separated by the system directory-separator character. The directory-separator character must not be used in any directory name. If no directories are specified, the current search path is displayed. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{dir}. @subsubheading Example @smallexample (gdb) -environment-directory /kwikemart/marge/ezannoni/flathead-dev/devo/gdb ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd" (gdb) -environment-directory "" ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd" (gdb) -environment-directory -r /home/jjohnstn/src/gdb /usr/src ^done,source-path="/home/jjohnstn/src/gdb:/usr/src:$cdir:$cwd" (gdb) -environment-directory -r ^done,source-path="$cdir:$cwd" (gdb) @end smallexample @subheading The @code{-environment-path} Command @findex -environment-path @subsubheading Synopsis @smallexample -environment-path [ -r ] [ @var{pathdir} ]+ @end smallexample Add directories @var{pathdir} to beginning of search path for object files. If the @samp{-r} option is used, the search path is reset to the original search path that existed at gdb start-up. If directories @var{pathdir} are supplied in addition to the @samp{-r} option, the search path is first reset and then addition occurs as normal. Multiple directories may be specified, separated by blanks. Specifying multiple directories in a single command results in the directories added to the beginning of the search path in the same order they were presented in the command. If blanks are needed as part of a directory name, double-quotes should be used around the name. In the command output, the path will show up separated by the system directory-separator character. The directory-separator character must not be used in any directory name. If no directories are specified, the current path is displayed. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{path}. @subsubheading Example @smallexample (gdb) -environment-path ^done,path="/usr/bin" (gdb) -environment-path /kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb /bin ^done,path="/kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb:/bin:/usr/bin" (gdb) -environment-path -r /usr/local/bin ^done,path="/usr/local/bin:/usr/bin" (gdb) @end smallexample @subheading The @code{-environment-pwd} Command @findex -environment-pwd @subsubheading Synopsis @smallexample -environment-pwd @end smallexample Show the current working directory. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{pwd}. @subsubheading Example @smallexample (gdb) -environment-pwd ^done,cwd="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb" (gdb) @end smallexample @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Thread Commands @section @sc{gdb/mi} Thread Commands @subheading The @code{-thread-info} Command @findex -thread-info @subsubheading Synopsis @smallexample -thread-info [ @var{thread-id} ] @end smallexample Reports information about either a specific thread, if the @var{thread-id} parameter is present, or about all threads. @var{thread-id} is the thread's global thread ID. When printing information about all threads, also reports the global ID of the current thread. @subsubheading @value{GDBN} Command The @samp{info thread} command prints the same information about all threads. @subsubheading Result The result contains the following attributes: @table @samp @item threads A list of threads. The format of the elements of the list is described in @ref{GDB/MI Thread Information}. @item current-thread-id The global id of the currently selected thread. This field is omitted if there is no selected thread (for example, when the selected inferior is not running, and therefore has no threads) or if a @var{thread-id} argument was passed to the command. @end table @subsubheading Example @smallexample -thread-info ^done,threads=[ @{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)", frame=@{level="0",addr="0xffffe410",func="__kernel_vsyscall", args=[]@},state="running"@}, @{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)", frame=@{level="0",addr="0x0804891f",func="foo", args=[@{name="i",value="10"@}], file="/tmp/a.c",fullname="/tmp/a.c",line="158",arch="i386:x86_64"@}, state="running"@}], current-thread-id="1" (gdb) @end smallexample @subheading The @code{-thread-list-ids} Command @findex -thread-list-ids @subsubheading Synopsis @smallexample -thread-list-ids @end smallexample Produces a list of the currently known global @value{GDBN} thread ids. At the end of the list it also prints the total number of such threads. This command is retained for historical reasons, the @code{-thread-info} command should be used instead. @subsubheading @value{GDBN} Command Part of @samp{info threads} supplies the same information. @subsubheading Example @smallexample (gdb) -thread-list-ids ^done,thread-ids=@{thread-id="3",thread-id="2",thread-id="1"@}, current-thread-id="1",number-of-threads="3" (gdb) @end smallexample @subheading The @code{-thread-select} Command @findex -thread-select @subsubheading Synopsis @smallexample -thread-select @var{thread-id} @end smallexample Make thread with global thread number @var{thread-id} the current thread. It prints the number of the new current thread, and the topmost frame for that thread. This command is deprecated in favor of explicitly using the @samp{--thread} option to each command. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{thread}. @subsubheading Example @smallexample (gdb) -exec-next ^running (gdb) *stopped,reason="end-stepping-range",thread-id="2",line="187", file="../../../devo/gdb/testsuite/gdb.threads/linux-dp.c" (gdb) -thread-list-ids ^done, thread-ids=@{thread-id="3",thread-id="2",thread-id="1"@}, number-of-threads="3" (gdb) -thread-select 3 ^done,new-thread-id="3", frame=@{level="0",func="vprintf", args=[@{name="format",value="0x8048e9c \"%*s%c %d %c\\n\""@}, @{name="arg",value="0x2"@}],file="vprintf.c",line="31",arch="i386:x86_64"@} (gdb) @end smallexample @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Ada Tasking Commands @section @sc{gdb/mi} Ada Tasking Commands @subheading The @code{-ada-task-info} Command @findex -ada-task-info @subsubheading Synopsis @smallexample -ada-task-info [ @var{task-id} ] @end smallexample Reports information about either a specific Ada task, if the @var{task-id} parameter is present, or about all Ada tasks. @subsubheading @value{GDBN} Command The @samp{info tasks} command prints the same information about all Ada tasks (@pxref{Ada Tasks}). @subsubheading Result The result is a table of Ada tasks. The following columns are defined for each Ada task: @table @samp @item current This field exists only for the current thread. It has the value @samp{*}. @item id The identifier that @value{GDBN} uses to refer to the Ada task. @item task-id The identifier that the target uses to refer to the Ada task. @item thread-id The global thread identifier of the thread corresponding to the Ada task. This field should always exist, as Ada tasks are always implemented on top of a thread. But if @value{GDBN} cannot find this corresponding thread for any reason, the field is omitted. @item parent-id This field exists only when the task was created by another task. In this case, it provides the ID of the parent task. @item priority The base priority of the task. @item state The current state of the task. For a detailed description of the possible states, see @ref{Ada Tasks}. @item name The name of the task. @end table @subsubheading Example @smallexample -ada-task-info ^done,tasks=@{nr_rows="3",nr_cols="8", hdr=[@{width="1",alignment="-1",col_name="current",colhdr=""@}, @{width="3",alignment="1",col_name="id",colhdr="ID"@}, @{width="9",alignment="1",col_name="task-id",colhdr="TID"@}, @{width="4",alignment="1",col_name="thread-id",colhdr=""@}, @{width="4",alignment="1",col_name="parent-id",colhdr="P-ID"@}, @{width="3",alignment="1",col_name="priority",colhdr="Pri"@}, @{width="22",alignment="-1",col_name="state",colhdr="State"@}, @{width="1",alignment="2",col_name="name",colhdr="Name"@}], body=[@{current="*",id="1",task-id=" 644010",thread-id="1",priority="48", state="Child Termination Wait",name="main_task"@}]@} (gdb) @end smallexample @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Program Execution @section @sc{gdb/mi} Program Execution These are the asynchronous commands which generate the out-of-band record @samp{*stopped}. Currently @value{GDBN} only really executes asynchronously with remote targets and this interaction is mimicked in other cases. @subheading The @code{-exec-continue} Command @findex -exec-continue @subsubheading Synopsis @smallexample -exec-continue [--reverse] [--all|--thread-group N] @end smallexample Resumes the execution of the inferior program, which will continue to execute until it reaches a debugger stop event. If the @samp{--reverse} option is specified, execution resumes in reverse until it reaches a stop event. Stop events may include @itemize @bullet @item breakpoints or watchpoints @item signals or exceptions @item the end of the process (or its beginning under @samp{--reverse}) @item the end or beginning of a replay log if one is being used. @end itemize In all-stop mode (@pxref{All-Stop Mode}), may resume only one thread, or all threads, depending on the value of the @samp{scheduler-locking} variable. If @samp{--all} is specified, all threads (in all inferiors) will be resumed. The @samp{--all} option is ignored in all-stop mode. If the @samp{--thread-group} options is specified, then all threads in that thread group are resumed. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} corresponding is @samp{continue}. @subsubheading Example @smallexample -exec-continue ^running (gdb) @@Hello world *stopped,reason="breakpoint-hit",disp="keep",bkptno="2",frame=@{ func="foo",args=[],file="hello.c",fullname="/home/foo/bar/hello.c", line="13",arch="i386:x86_64"@} (gdb) @end smallexample @subheading The @code{-exec-finish} Command @findex -exec-finish @subsubheading Synopsis @smallexample -exec-finish [--reverse] @end smallexample Resumes the execution of the inferior program until the current function is exited. Displays the results returned by the function. If the @samp{--reverse} option is specified, resumes the reverse execution of the inferior program until the point where current function was called. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{finish}. @subsubheading Example Function returning @code{void}. @smallexample -exec-finish ^running (gdb) @@hello from foo *stopped,reason="function-finished",frame=@{func="main",args=[], file="hello.c",fullname="/home/foo/bar/hello.c",line="7",arch="i386:x86_64"@} (gdb) @end smallexample Function returning other than @code{void}. The name of the internal @value{GDBN} variable storing the result is printed, together with the value itself. @smallexample -exec-finish ^running (gdb) *stopped,reason="function-finished",frame=@{addr="0x000107b0",func="foo", args=[@{name="a",value="1"],@{name="b",value="9"@}@}, file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"@}, gdb-result-var="$1",return-value="0" (gdb) @end smallexample @subheading The @code{-exec-interrupt} Command @findex -exec-interrupt @subsubheading Synopsis @smallexample -exec-interrupt [--all|--thread-group N] @end smallexample Interrupts the background execution of the target. Note how the token associated with the stop message is the one for the execution command that has been interrupted. The token for the interrupt itself only appears in the @samp{^done} output. If the user is trying to interrupt a non-running program, an error message will be printed. Note that when asynchronous execution is enabled, this command is asynchronous just like other execution commands. That is, first the @samp{^done} response will be printed, and the target stop will be reported after that using the @samp{*stopped} notification. In non-stop mode, only the context thread is interrupted by default. All threads (in all inferiors) will be interrupted if the @samp{--all} option is specified. If the @samp{--thread-group} option is specified, all threads in that group will be interrupted. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{interrupt}. @subsubheading Example @smallexample (gdb) 111-exec-continue 111^running (gdb) 222-exec-interrupt 222^done (gdb) 111*stopped,signal-name="SIGINT",signal-meaning="Interrupt", frame=@{addr="0x00010140",func="foo",args=[],file="try.c", fullname="/home/foo/bar/try.c",line="13",arch="i386:x86_64"@} (gdb) (gdb) -exec-interrupt ^error,msg="mi_cmd_exec_interrupt: Inferior not executing." (gdb) @end smallexample @subheading The @code{-exec-jump} Command @findex -exec-jump @subsubheading Synopsis @smallexample -exec-jump @var{location} @end smallexample Resumes execution of the inferior program at the location specified by parameter. @xref{Specify Location}, for a description of the different forms of @var{location}. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{jump}. @subsubheading Example @smallexample -exec-jump foo.c:10 *running,thread-id="all" ^running @end smallexample @subheading The @code{-exec-next} Command @findex -exec-next @subsubheading Synopsis @smallexample -exec-next [--reverse] @end smallexample Resumes execution of the inferior program, stopping when the beginning of the next source line is reached. If the @samp{--reverse} option is specified, resumes reverse execution of the inferior program, stopping at the beginning of the previous source line. If you issue this command on the first line of a function, it will take you back to the caller of that function, to the source line where the function was called. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{next}. @subsubheading Example @smallexample -exec-next ^running (gdb) *stopped,reason="end-stepping-range",line="8",file="hello.c" (gdb) @end smallexample @subheading The @code{-exec-next-instruction} Command @findex -exec-next-instruction @subsubheading Synopsis @smallexample -exec-next-instruction [--reverse] @end smallexample Executes one machine instruction. If the instruction is a function call, continues until the function returns. If the program stops at an instruction in the middle of a source line, the address will be printed as well. If the @samp{--reverse} option is specified, resumes reverse execution of the inferior program, stopping at the previous instruction. If the previously executed instruction was a return from another function, it will continue to execute in reverse until the call to that function (from the current stack frame) is reached. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{nexti}. @subsubheading Example @smallexample (gdb) -exec-next-instruction ^running (gdb) *stopped,reason="end-stepping-range", addr="0x000100d4",line="5",file="hello.c" (gdb) @end smallexample @subheading The @code{-exec-return} Command @findex -exec-return @subsubheading Synopsis @smallexample -exec-return @end smallexample Makes current function return immediately. Doesn't execute the inferior. Displays the new current frame. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{return}. @subsubheading Example @smallexample (gdb) 200-break-insert callee4 200^done,bkpt=@{number="1",addr="0x00010734", file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8"@} (gdb) 000-exec-run 000^running (gdb) 000*stopped,reason="breakpoint-hit",disp="keep",bkptno="1", frame=@{func="callee4",args=[], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8", arch="i386:x86_64"@} (gdb) 205-break-delete 205^done (gdb) 111-exec-return 111^done,frame=@{level="0",func="callee3", args=[@{name="strarg", value="0x11940 \"A string argument.\""@}], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18", arch="i386:x86_64"@} (gdb) @end smallexample @subheading The @code{-exec-run} Command @findex -exec-run @subsubheading Synopsis @smallexample -exec-run [ --all | --thread-group N ] [ --start ] @end smallexample Starts execution of the inferior from the beginning. The inferior executes until either a breakpoint is encountered or the program exits. In the latter case the output will include an exit code, if the program has exited exceptionally. When neither the @samp{--all} nor the @samp{--thread-group} option is specified, the current inferior is started. If the @samp{--thread-group} option is specified, it should refer to a thread group of type @samp{process}, and that thread group will be started. If the @samp{--all} option is specified, then all inferiors will be started. Using the @samp{--start} option instructs the debugger to stop the execution at the start of the inferior's main subprogram, following the same behavior as the @code{start} command (@pxref{Starting}). @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{run}. @subsubheading Examples @smallexample (gdb) -break-insert main ^done,bkpt=@{number="1",addr="0x0001072c",file="recursive2.c",line="4"@} (gdb) -exec-run ^running (gdb) *stopped,reason="breakpoint-hit",disp="keep",bkptno="1", frame=@{func="main",args=[],file="recursive2.c", fullname="/home/foo/bar/recursive2.c",line="4",arch="i386:x86_64"@} (gdb) @end smallexample @noindent Program exited normally: @smallexample (gdb) -exec-run ^running (gdb) x = 55 *stopped,reason="exited-normally" (gdb) @end smallexample @noindent Program exited exceptionally: @smallexample (gdb) -exec-run ^running (gdb) x = 55 *stopped,reason="exited",exit-code="01" (gdb) @end smallexample Another way the program can terminate is if it receives a signal such as @code{SIGINT}. In this case, @sc{gdb/mi} displays this: @smallexample (gdb) *stopped,reason="exited-signalled",signal-name="SIGINT", signal-meaning="Interrupt" @end smallexample @c @subheading -exec-signal @subheading The @code{-exec-step} Command @findex -exec-step @subsubheading Synopsis @smallexample -exec-step [--reverse] @end smallexample Resumes execution of the inferior program, stopping when the beginning of the next source line is reached, if the next source line is not a function call. If it is, stop at the first instruction of the called function. If the @samp{--reverse} option is specified, resumes reverse execution of the inferior program, stopping at the beginning of the previously executed source line. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{step}. @subsubheading Example Stepping into a function: @smallexample -exec-step ^running (gdb) *stopped,reason="end-stepping-range", frame=@{func="foo",args=[@{name="a",value="10"@}, @{name="b",value="0"@}],file="recursive2.c", fullname="/home/foo/bar/recursive2.c",line="11",arch="i386:x86_64"@} (gdb) @end smallexample Regular stepping: @smallexample -exec-step ^running (gdb) *stopped,reason="end-stepping-range",line="14",file="recursive2.c" (gdb) @end smallexample @subheading The @code{-exec-step-instruction} Command @findex -exec-step-instruction @subsubheading Synopsis @smallexample -exec-step-instruction [--reverse] @end smallexample Resumes the inferior which executes one machine instruction. If the @samp{--reverse} option is specified, resumes reverse execution of the inferior program, stopping at the previously executed instruction. The output, once @value{GDBN} has stopped, will vary depending on whether we have stopped in the middle of a source line or not. In the former case, the address at which the program stopped will be printed as well. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{stepi}. @subsubheading Example @smallexample (gdb) -exec-step-instruction ^running (gdb) *stopped,reason="end-stepping-range", frame=@{func="foo",args=[],file="try.c", fullname="/home/foo/bar/try.c",line="10",arch="i386:x86_64"@} (gdb) -exec-step-instruction ^running (gdb) *stopped,reason="end-stepping-range", frame=@{addr="0x000100f4",func="foo",args=[],file="try.c", fullname="/home/foo/bar/try.c",line="10",arch="i386:x86_64"@} (gdb) @end smallexample @subheading The @code{-exec-until} Command @findex -exec-until @subsubheading Synopsis @smallexample -exec-until [ @var{location} ] @end smallexample Executes the inferior until the @var{location} specified in the argument is reached. If there is no argument, the inferior executes until a source line greater than the current one is reached. The reason for stopping in this case will be @samp{location-reached}. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{until}. @subsubheading Example @smallexample (gdb) -exec-until recursive2.c:6 ^running (gdb) x = 55 *stopped,reason="location-reached",frame=@{func="main",args=[], file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="6", arch="i386:x86_64"@} (gdb) @end smallexample @ignore @subheading -file-clear Is this going away???? @end ignore @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Stack Manipulation @section @sc{gdb/mi} Stack Manipulation Commands @subheading The @code{-enable-frame-filters} Command @findex -enable-frame-filters @smallexample -enable-frame-filters @end smallexample @value{GDBN} allows Python-based frame filters to affect the output of the MI commands relating to stack traces. As there is no way to implement this in a fully backward-compatible way, a front end must request that this functionality be enabled. Once enabled, this feature cannot be disabled. Note that if Python support has not been compiled into @value{GDBN}, this command will still succeed (and do nothing). @subheading The @code{-stack-info-frame} Command @findex -stack-info-frame @subsubheading Synopsis @smallexample -stack-info-frame @end smallexample Get info on the selected frame. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{info frame} or @samp{frame} (without arguments). @subsubheading Example @smallexample (gdb) -stack-info-frame ^done,frame=@{level="1",addr="0x0001076c",func="callee3", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17", arch="i386:x86_64"@} (gdb) @end smallexample @subheading The @code{-stack-info-depth} Command @findex -stack-info-depth @subsubheading Synopsis @smallexample -stack-info-depth [ @var{max-depth} ] @end smallexample Return the depth of the stack. If the integer argument @var{max-depth} is specified, do not count beyond @var{max-depth} frames. @subsubheading @value{GDBN} Command There's no equivalent @value{GDBN} command. @subsubheading Example For a stack with frame levels 0 through 11: @smallexample (gdb) -stack-info-depth ^done,depth="12" (gdb) -stack-info-depth 4 ^done,depth="4" (gdb) -stack-info-depth 12 ^done,depth="12" (gdb) -stack-info-depth 11 ^done,depth="11" (gdb) -stack-info-depth 13 ^done,depth="12" (gdb) @end smallexample @anchor{-stack-list-arguments} @subheading The @code{-stack-list-arguments} Command @findex -stack-list-arguments @subsubheading Synopsis @smallexample -stack-list-arguments [ --no-frame-filters ] [ --skip-unavailable ] @var{print-values} [ @var{low-frame} @var{high-frame} ] @end smallexample Display a list of the arguments for the frames between @var{low-frame} and @var{high-frame} (inclusive). If @var{low-frame} and @var{high-frame} are not provided, list the arguments for the whole call stack. If the two arguments are equal, show the single frame at the corresponding level. It is an error if @var{low-frame} is larger than the actual number of frames. On the other hand, @var{high-frame} may be larger than the actual number of frames, in which case only existing frames will be returned. If @var{print-values} is 0 or @code{--no-values}, print only the names of the variables; if it is 1 or @code{--all-values}, print also their values; and if it is 2 or @code{--simple-values}, print the name, type and value for simple data types, and the name and type for arrays, structures and unions. If the option @code{--no-frame-filters} is supplied, then Python frame filters will not be executed. If the @code{--skip-unavailable} option is specified, arguments that are not available are not listed. Partially available arguments are still displayed, however. Use of this command to obtain arguments in a single frame is deprecated in favor of the @samp{-stack-list-variables} command. @subsubheading @value{GDBN} Command @value{GDBN} does not have an equivalent command. @code{gdbtk} has a @samp{gdb_get_args} command which partially overlaps with the functionality of @samp{-stack-list-arguments}. @subsubheading Example @smallexample (gdb) -stack-list-frames ^done, stack=[ frame=@{level="0",addr="0x00010734",func="callee4", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8", arch="i386:x86_64"@}, frame=@{level="1",addr="0x0001076c",func="callee3", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17", arch="i386:x86_64"@}, frame=@{level="2",addr="0x0001078c",func="callee2", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="22", arch="i386:x86_64"@}, frame=@{level="3",addr="0x000107b4",func="callee1", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="27", arch="i386:x86_64"@}, frame=@{level="4",addr="0x000107e0",func="main", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="32", arch="i386:x86_64"@}] (gdb) -stack-list-arguments 0 ^done, stack-args=[ frame=@{level="0",args=[]@}, frame=@{level="1",args=[name="strarg"]@}, frame=@{level="2",args=[name="intarg",name="strarg"]@}, frame=@{level="3",args=[name="intarg",name="strarg",name="fltarg"]@}, frame=@{level="4",args=[]@}] (gdb) -stack-list-arguments 1 ^done, stack-args=[ frame=@{level="0",args=[]@}, frame=@{level="1", args=[@{name="strarg",value="0x11940 \"A string argument.\""@}]@}, frame=@{level="2",args=[ @{name="intarg",value="2"@}, @{name="strarg",value="0x11940 \"A string argument.\""@}]@}, @{frame=@{level="3",args=[ @{name="intarg",value="2"@}, @{name="strarg",value="0x11940 \"A string argument.\""@}, @{name="fltarg",value="3.5"@}]@}, frame=@{level="4",args=[]@}] (gdb) -stack-list-arguments 0 2 2 ^done,stack-args=[frame=@{level="2",args=[name="intarg",name="strarg"]@}] (gdb) -stack-list-arguments 1 2 2 ^done,stack-args=[frame=@{level="2", args=[@{name="intarg",value="2"@}, @{name="strarg",value="0x11940 \"A string argument.\""@}]@}] (gdb) @end smallexample @c @subheading -stack-list-exception-handlers @anchor{-stack-list-frames} @subheading The @code{-stack-list-frames} Command @findex -stack-list-frames @subsubheading Synopsis @smallexample -stack-list-frames [ --no-frame-filters @var{low-frame} @var{high-frame} ] @end smallexample List the frames currently on the stack. For each frame it displays the following info: @table @samp @item @var{level} The frame number, 0 being the topmost frame, i.e., the innermost function. @item @var{addr} The @code{$pc} value for that frame. @item @var{func} Function name. @item @var{file} File name of the source file where the function lives. @item @var{fullname} The full file name of the source file where the function lives. @item @var{line} Line number corresponding to the @code{$pc}. @item @var{from} The shared library where this function is defined. This is only given if the frame's function is not known. @item @var{arch} Frame's architecture. @end table If invoked without arguments, this command prints a backtrace for the whole stack. If given two integer arguments, it shows the frames whose levels are between the two arguments (inclusive). If the two arguments are equal, it shows the single frame at the corresponding level. It is an error if @var{low-frame} is larger than the actual number of frames. On the other hand, @var{high-frame} may be larger than the actual number of frames, in which case only existing frames will be returned. If the option @code{--no-frame-filters} is supplied, then Python frame filters will not be executed. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} commands are @samp{backtrace} and @samp{where}. @subsubheading Example Full stack backtrace: @smallexample (gdb) -stack-list-frames ^done,stack= [frame=@{level="0",addr="0x0001076c",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="11", arch="i386:x86_64"@}, frame=@{level="1",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"@}, frame=@{level="2",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"@}, frame=@{level="3",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"@}, frame=@{level="4",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"@}, frame=@{level="5",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"@}, frame=@{level="6",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"@}, frame=@{level="7",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"@}, frame=@{level="8",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"@}, frame=@{level="9",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"@}, frame=@{level="10",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"@}, frame=@{level="11",addr="0x00010738",func="main", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="4", arch="i386:x86_64"@}] (gdb) @end smallexample Show frames between @var{low_frame} and @var{high_frame}: @smallexample (gdb) -stack-list-frames 3 5 ^done,stack= [frame=@{level="3",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"@}, frame=@{level="4",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"@}, frame=@{level="5",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"@}] (gdb) @end smallexample Show a single frame: @smallexample (gdb) -stack-list-frames 3 3 ^done,stack= [frame=@{level="3",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14", arch="i386:x86_64"@}] (gdb) @end smallexample @subheading The @code{-stack-list-locals} Command @findex -stack-list-locals @anchor{-stack-list-locals} @subsubheading Synopsis @smallexample -stack-list-locals [ --no-frame-filters ] [ --skip-unavailable ] @var{print-values} @end smallexample Display the local variable names for the selected frame. If @var{print-values} is 0 or @code{--no-values}, print only the names of the variables; if it is 1 or @code{--all-values}, print also their values; and if it is 2 or @code{--simple-values}, print the name, type and value for simple data types, and the name and type for arrays, structures and unions. In this last case, a frontend can immediately display the value of simple data types and create variable objects for other data types when the user wishes to explore their values in more detail. If the option @code{--no-frame-filters} is supplied, then Python frame filters will not be executed. If the @code{--skip-unavailable} option is specified, local variables that are not available are not listed. Partially available local variables are still displayed, however. This command is deprecated in favor of the @samp{-stack-list-variables} command. @subsubheading @value{GDBN} Command @samp{info locals} in @value{GDBN}, @samp{gdb_get_locals} in @code{gdbtk}. @subsubheading Example @smallexample (gdb) -stack-list-locals 0 ^done,locals=[name="A",name="B",name="C"] (gdb) -stack-list-locals --all-values ^done,locals=[@{name="A",value="1"@},@{name="B",value="2"@}, @{name="C",value="@{1, 2, 3@}"@}] -stack-list-locals --simple-values ^done,locals=[@{name="A",type="int",value="1"@}, @{name="B",type="int",value="2"@},@{name="C",type="int [3]"@}] (gdb) @end smallexample @anchor{-stack-list-variables} @subheading The @code{-stack-list-variables} Command @findex -stack-list-variables @subsubheading Synopsis @smallexample -stack-list-variables [ --no-frame-filters ] [ --skip-unavailable ] @var{print-values} @end smallexample Display the names of local variables and function arguments for the selected frame. If @var{print-values} is 0 or @code{--no-values}, print only the names of the variables; if it is 1 or @code{--all-values}, print also their values; and if it is 2 or @code{--simple-values}, print the name, type and value for simple data types, and the name and type for arrays, structures and unions. If the option @code{--no-frame-filters} is supplied, then Python frame filters will not be executed. If the @code{--skip-unavailable} option is specified, local variables and arguments that are not available are not listed. Partially available arguments and local variables are still displayed, however. @subsubheading Example @smallexample (gdb) -stack-list-variables --thread 1 --frame 0 --all-values ^done,variables=[@{name="x",value="11"@},@{name="s",value="@{a = 1, b = 2@}"@}] (gdb) @end smallexample @subheading The @code{-stack-select-frame} Command @findex -stack-select-frame @subsubheading Synopsis @smallexample -stack-select-frame @var{framenum} @end smallexample Change the selected frame. Select a different frame @var{framenum} on the stack. This command in deprecated in favor of passing the @samp{--frame} option to every command. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} commands are @samp{frame}, @samp{up}, @samp{down}, @samp{select-frame}, @samp{up-silent}, and @samp{down-silent}. @subsubheading Example @smallexample (gdb) -stack-select-frame 2 ^done (gdb) @end smallexample @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Variable Objects @section @sc{gdb/mi} Variable Objects @ignore @subheading Motivation for Variable Objects in @sc{gdb/mi} For the implementation of a variable debugger window (locals, watched expressions, etc.), we are proposing the adaptation of the existing code used by @code{Insight}. The two main reasons for that are: @enumerate 1 @item It has been proven in practice (it is already on its second generation). @item It will shorten development time (needless to say how important it is now). @end enumerate The original interface was designed to be used by Tcl code, so it was slightly changed so it could be used through @sc{gdb/mi}. This section describes the @sc{gdb/mi} operations that will be available and gives some hints about their use. @emph{Note}: In addition to the set of operations described here, we expect the @sc{gui} implementation of a variable window to require, at least, the following operations: @itemize @bullet @item @code{-gdb-show} @code{output-radix} @item @code{-stack-list-arguments} @item @code{-stack-list-locals} @item @code{-stack-select-frame} @end itemize @end ignore @subheading Introduction to Variable Objects @cindex variable objects in @sc{gdb/mi} Variable objects are "object-oriented" MI interface for examining and changing values of expressions. Unlike some other MI interfaces that work with expressions, variable objects are specifically designed for simple and efficient presentation in the frontend. A variable object is identified by string name. When a variable object is created, the frontend specifies the expression for that variable object. The expression can be a simple variable, or it can be an arbitrary complex expression, and can even involve CPU registers. After creating a variable object, the frontend can invoke other variable object operations---for example to obtain or change the value of a variable object, or to change display format. Variable objects have hierarchical tree structure. Any variable object that corresponds to a composite type, such as structure in C, has a number of child variable objects, for example corresponding to each element of a structure. A child variable object can itself have children, recursively. Recursion ends when we reach leaf variable objects, which always have built-in types. Child variable objects are created only by explicit request, so if a frontend is not interested in the children of a particular variable object, no child will be created. For a leaf variable object it is possible to obtain its value as a string, or set the value from a string. String value can be also obtained for a non-leaf variable object, but it's generally a string that only indicates the type of the object, and does not list its contents. Assignment to a non-leaf variable object is not allowed. A frontend does not need to read the values of all variable objects each time the program stops. Instead, MI provides an update command that lists all variable objects whose values has changed since the last update operation. This considerably reduces the amount of data that must be transferred to the frontend. As noted above, children variable objects are created on demand, and only leaf variable objects have a real value. As result, gdb will read target memory only for leaf variables that frontend has created. The automatic update is not always desirable. For example, a frontend might want to keep a value of some expression for future reference, and never update it. For another example, fetching memory is relatively slow for embedded targets, so a frontend might want to disable automatic update for the variables that are either not visible on the screen, or ``closed''. This is possible using so called ``frozen variable objects''. Such variable objects are never implicitly updated. Variable objects can be either @dfn{fixed} or @dfn{floating}. For the fixed variable object, the expression is parsed when the variable object is created, including associating identifiers to specific variables. The meaning of expression never changes. For a floating variable object the values of variables whose names appear in the expressions are re-evaluated every time in the context of the current frame. Consider this example: @smallexample void do_work(...) @{ struct work_state state; if (...) do_work(...); @} @end smallexample If a fixed variable object for the @code{state} variable is created in this function, and we enter the recursive call, the variable object will report the value of @code{state} in the top-level @code{do_work} invocation. On the other hand, a floating variable object will report the value of @code{state} in the current frame. If an expression specified when creating a fixed variable object refers to a local variable, the variable object becomes bound to the thread and frame in which the variable object is created. When such variable object is updated, @value{GDBN} makes sure that the thread/frame combination the variable object is bound to still exists, and re-evaluates the variable object in context of that thread/frame. The following is the complete set of @sc{gdb/mi} operations defined to access this functionality: @multitable @columnfractions .4 .6 @item @strong{Operation} @tab @strong{Description} @item @code{-enable-pretty-printing} @tab enable Python-based pretty-printing @item @code{-var-create} @tab create a variable object @item @code{-var-delete} @tab delete the variable object and/or its children @item @code{-var-set-format} @tab set the display format of this variable @item @code{-var-show-format} @tab show the display format of this variable @item @code{-var-info-num-children} @tab tells how many children this object has @item @code{-var-list-children} @tab return a list of the object's children @item @code{-var-info-type} @tab show the type of this variable object @item @code{-var-info-expression} @tab print parent-relative expression that this variable object represents @item @code{-var-info-path-expression} @tab print full expression that this variable object represents @item @code{-var-show-attributes} @tab is this variable editable? does it exist here? @item @code{-var-evaluate-expression} @tab get the value of this variable @item @code{-var-assign} @tab set the value of this variable @item @code{-var-update} @tab update the variable and its children @item @code{-var-set-frozen} @tab set frozenness attribute @item @code{-var-set-update-range} @tab set range of children to display on update @end multitable In the next subsection we describe each operation in detail and suggest how it can be used. @subheading Description And Use of Operations on Variable Objects @subheading The @code{-enable-pretty-printing} Command @findex -enable-pretty-printing @smallexample -enable-pretty-printing @end smallexample @value{GDBN} allows Python-based visualizers to affect the output of the MI variable object commands. However, because there was no way to implement this in a fully backward-compatible way, a front end must request that this functionality be enabled. Once enabled, this feature cannot be disabled. Note that if Python support has not been compiled into @value{GDBN}, this command will still succeed (and do nothing). This feature is currently (as of @value{GDBN} 7.0) experimental, and may work differently in future versions of @value{GDBN}. @subheading The @code{-var-create} Command @findex -var-create @subsubheading Synopsis @smallexample -var-create @{@var{name} | "-"@} @{@var{frame-addr} | "*" | "@@"@} @var{expression} @end smallexample This operation creates a variable object, which allows the monitoring of a variable, the result of an expression, a memory cell or a CPU register. The @var{name} parameter is the string by which the object can be referenced. It must be unique. If @samp{-} is specified, the varobj system will generate a string ``varNNNNNN'' automatically. It will be unique provided that one does not specify @var{name} of that format. The command fails if a duplicate name is found. The frame under which the expression should be evaluated can be specified by @var{frame-addr}. A @samp{*} indicates that the current frame should be used. A @samp{@@} indicates that a floating variable object must be created. @var{expression} is any expression valid on the current language set (must not begin with a @samp{*}), or one of the following: @itemize @bullet @item @samp{*@var{addr}}, where @var{addr} is the address of a memory cell @item @samp{*@var{addr}-@var{addr}} --- a memory address range (TBD) @item @samp{$@var{regname}} --- a CPU register name @end itemize @cindex dynamic varobj A varobj's contents may be provided by a Python-based pretty-printer. In this case the varobj is known as a @dfn{dynamic varobj}. Dynamic varobjs have slightly different semantics in some cases. If the @code{-enable-pretty-printing} command is not sent, then @value{GDBN} will never create a dynamic varobj. This ensures backward compatibility for existing clients. @subsubheading Result This operation returns attributes of the newly-created varobj. These are: @table @samp @item name The name of the varobj. @item numchild The number of children of the varobj. This number is not necessarily reliable for a dynamic varobj. Instead, you must examine the @samp{has_more} attribute. @item value The varobj's scalar value. For a varobj whose type is some sort of aggregate (e.g., a @code{struct}), or for a dynamic varobj, this value will not be interesting. @item type The varobj's type. This is a string representation of the type, as would be printed by the @value{GDBN} CLI. If @samp{print object} (@pxref{Print Settings, set print object}) is set to @code{on}, the @emph{actual} (derived) type of the object is shown rather than the @emph{declared} one. @item thread-id If a variable object is bound to a specific thread, then this is the thread's global identifier. @item has_more For a dynamic varobj, this indicates whether there appear to be any children available. For a non-dynamic varobj, this will be 0. @item dynamic This attribute will be present and have the value @samp{1} if the varobj is a dynamic varobj. If the varobj is not a dynamic varobj, then this attribute will not be present. @item displayhint A dynamic varobj can supply a display hint to the front end. The value comes directly from the Python pretty-printer object's @code{display_hint} method. @xref{Pretty Printing API}. @end table Typical output will look like this: @smallexample name="@var{name}",numchild="@var{N}",type="@var{type}",thread-id="@var{M}", has_more="@var{has_more}" @end smallexample @subheading The @code{-var-delete} Command @findex -var-delete @subsubheading Synopsis @smallexample -var-delete [ -c ] @var{name} @end smallexample Deletes a previously created variable object and all of its children. With the @samp{-c} option, just deletes the children. Returns an error if the object @var{name} is not found. @subheading The @code{-var-set-format} Command @findex -var-set-format @subsubheading Synopsis @smallexample -var-set-format @var{name} @var{format-spec} @end smallexample Sets the output format for the value of the object @var{name} to be @var{format-spec}. @anchor{-var-set-format} The syntax for the @var{format-spec} is as follows: @smallexample @var{format-spec} @expansion{} @{binary | decimal | hexadecimal | octal | natural | zero-hexadecimal@} @end smallexample The natural format is the default format choosen automatically based on the variable type (like decimal for an @code{int}, hex for pointers, etc.). The zero-hexadecimal format has a representation similar to hexadecimal but with padding zeroes to the left of the value. For example, a 32-bit hexadecimal value of 0x1234 would be represented as 0x00001234 in the zero-hexadecimal format. For a variable with children, the format is set only on the variable itself, and the children are not affected. @subheading The @code{-var-show-format} Command @findex -var-show-format @subsubheading Synopsis @smallexample -var-show-format @var{name} @end smallexample Returns the format used to display the value of the object @var{name}. @smallexample @var{format} @expansion{} @var{format-spec} @end smallexample @subheading The @code{-var-info-num-children} Command @findex -var-info-num-children @subsubheading Synopsis @smallexample -var-info-num-children @var{name} @end smallexample Returns the number of children of a variable object @var{name}: @smallexample numchild=@var{n} @end smallexample Note that this number is not completely reliable for a dynamic varobj. It will return the current number of children, but more children may be available. @subheading The @code{-var-list-children} Command @findex -var-list-children @subsubheading Synopsis @smallexample -var-list-children [@var{print-values}] @var{name} [@var{from} @var{to}] @end smallexample @anchor{-var-list-children} Return a list of the children of the specified variable object and create variable objects for them, if they do not already exist. With a single argument or if @var{print-values} has a value of 0 or @code{--no-values}, print only the names of the variables; if @var{print-values} is 1 or @code{--all-values}, also print their values; and if it is 2 or @code{--simple-values} print the name and value for simple data types and just the name for arrays, structures and unions. @var{from} and @var{to}, if specified, indicate the range of children to report. If @var{from} or @var{to} is less than zero, the range is reset and all children will be reported. Otherwise, children starting at @var{from} (zero-based) and up to and excluding @var{to} will be reported. If a child range is requested, it will only affect the current call to @code{-var-list-children}, but not future calls to @code{-var-update}. For this, you must instead use @code{-var-set-update-range}. The intent of this approach is to enable a front end to implement any update approach it likes; for example, scrolling a view may cause the front end to request more children with @code{-var-list-children}, and then the front end could call @code{-var-set-update-range} with a different range to ensure that future updates are restricted to just the visible items. For each child the following results are returned: @table @var @item name Name of the variable object created for this child. @item exp The expression to be shown to the user by the front end to designate this child. For example this may be the name of a structure member. For a dynamic varobj, this value cannot be used to form an expression. There is no way to do this at all with a dynamic varobj. For C/C@t{++} structures there are several pseudo children returned to designate access qualifiers. For these pseudo children @var{exp} is @samp{public}, @samp{private}, or @samp{protected}. In this case the type and value are not present. A dynamic varobj will not report the access qualifying pseudo-children, regardless of the language. This information is not available at all with a dynamic varobj. @item numchild Number of children this child has. For a dynamic varobj, this will be 0. @item type The type of the child. If @samp{print object} (@pxref{Print Settings, set print object}) is set to @code{on}, the @emph{actual} (derived) type of the object is shown rather than the @emph{declared} one. @item value If values were requested, this is the value. @item thread-id If this variable object is associated with a thread, this is the thread's global thread id. Otherwise this result is not present. @item frozen If the variable object is frozen, this variable will be present with a value of 1. @item displayhint A dynamic varobj can supply a display hint to the front end. The value comes directly from the Python pretty-printer object's @code{display_hint} method. @xref{Pretty Printing API}. @item dynamic This attribute will be present and have the value @samp{1} if the varobj is a dynamic varobj. If the varobj is not a dynamic varobj, then this attribute will not be present. @end table The result may have its own attributes: @table @samp @item displayhint A dynamic varobj can supply a display hint to the front end. The value comes directly from the Python pretty-printer object's @code{display_hint} method. @xref{Pretty Printing API}. @item has_more This is an integer attribute which is nonzero if there are children remaining after the end of the selected range. @end table @subsubheading Example @smallexample (gdb) -var-list-children n ^done,numchild=@var{n},children=[child=@{name=@var{name},exp=@var{exp}, numchild=@var{n},type=@var{type}@},@r{(repeats N times)}] (gdb) -var-list-children --all-values n ^done,numchild=@var{n},children=[child=@{name=@var{name},exp=@var{exp}, numchild=@var{n},value=@var{value},type=@var{type}@},@r{(repeats N times)}] @end smallexample @subheading The @code{-var-info-type} Command @findex -var-info-type @subsubheading Synopsis @smallexample -var-info-type @var{name} @end smallexample Returns the type of the specified variable @var{name}. The type is returned as a string in the same format as it is output by the @value{GDBN} CLI: @smallexample type=@var{typename} @end smallexample @subheading The @code{-var-info-expression} Command @findex -var-info-expression @subsubheading Synopsis @smallexample -var-info-expression @var{name} @end smallexample Returns a string that is suitable for presenting this variable object in user interface. The string is generally not valid expression in the current language, and cannot be evaluated. For example, if @code{a} is an array, and variable object @code{A} was created for @code{a}, then we'll get this output: @smallexample (gdb) -var-info-expression A.1 ^done,lang="C",exp="1" @end smallexample @noindent Here, the value of @code{lang} is the language name, which can be found in @ref{Supported Languages}. Note that the output of the @code{-var-list-children} command also includes those expressions, so the @code{-var-info-expression} command is of limited use. @subheading The @code{-var-info-path-expression} Command @findex -var-info-path-expression @subsubheading Synopsis @smallexample -var-info-path-expression @var{name} @end smallexample Returns an expression that can be evaluated in the current context and will yield the same value that a variable object has. Compare this with the @code{-var-info-expression} command, which result can be used only for UI presentation. Typical use of the @code{-var-info-path-expression} command is creating a watchpoint from a variable object. This command is currently not valid for children of a dynamic varobj, and will give an error when invoked on one. For example, suppose @code{C} is a C@t{++} class, derived from class @code{Base}, and that the @code{Base} class has a member called @code{m_size}. Assume a variable @code{c} is has the type of @code{C} and a variable object @code{C} was created for variable @code{c}. Then, we'll get this output: @smallexample (gdb) -var-info-path-expression C.Base.public.m_size ^done,path_expr=((Base)c).m_size) @end smallexample @subheading The @code{-var-show-attributes} Command @findex -var-show-attributes @subsubheading Synopsis @smallexample -var-show-attributes @var{name} @end smallexample List attributes of the specified variable object @var{name}: @smallexample status=@var{attr} [ ( ,@var{attr} )* ] @end smallexample @noindent where @var{attr} is @code{@{ @{ editable | noneditable @} | TBD @}}. @subheading The @code{-var-evaluate-expression} Command @findex -var-evaluate-expression @subsubheading Synopsis @smallexample -var-evaluate-expression [-f @var{format-spec}] @var{name} @end smallexample Evaluates the expression that is represented by the specified variable object and returns its value as a string. The format of the string can be specified with the @samp{-f} option. The possible values of this option are the same as for @code{-var-set-format} (@pxref{-var-set-format}). If the @samp{-f} option is not specified, the current display format will be used. The current display format can be changed using the @code{-var-set-format} command. @smallexample value=@var{value} @end smallexample Note that one must invoke @code{-var-list-children} for a variable before the value of a child variable can be evaluated. @subheading The @code{-var-assign} Command @findex -var-assign @subsubheading Synopsis @smallexample -var-assign @var{name} @var{expression} @end smallexample Assigns the value of @var{expression} to the variable object specified by @var{name}. The object must be @samp{editable}. If the variable's value is altered by the assign, the variable will show up in any subsequent @code{-var-update} list. @subsubheading Example @smallexample (gdb) -var-assign var1 3 ^done,value="3" (gdb) -var-update * ^done,changelist=[@{name="var1",in_scope="true",type_changed="false"@}] (gdb) @end smallexample @subheading The @code{-var-update} Command @findex -var-update @subsubheading Synopsis @smallexample -var-update [@var{print-values}] @{@var{name} | "*"@} @end smallexample Reevaluate the expressions corresponding to the variable object @var{name} and all its direct and indirect children, and return the list of variable objects whose values have changed; @var{name} must be a root variable object. Here, ``changed'' means that the result of @code{-var-evaluate-expression} before and after the @code{-var-update} is different. If @samp{*} is used as the variable object names, all existing variable objects are updated, except for frozen ones (@pxref{-var-set-frozen}). The option @var{print-values} determines whether both names and values, or just names are printed. The possible values of this option are the same as for @code{-var-list-children} (@pxref{-var-list-children}). It is recommended to use the @samp{--all-values} option, to reduce the number of MI commands needed on each program stop. With the @samp{*} parameter, if a variable object is bound to a currently running thread, it will not be updated, without any diagnostic. If @code{-var-set-update-range} was previously used on a varobj, then only the selected range of children will be reported. @code{-var-update} reports all the changed varobjs in a tuple named @samp{changelist}. Each item in the change list is itself a tuple holding: @table @samp @item name The name of the varobj. @item value If values were requested for this update, then this field will be present and will hold the value of the varobj. @item in_scope @anchor{-var-update} This field is a string which may take one of three values: @table @code @item "true" The variable object's current value is valid. @item "false" The variable object does not currently hold a valid value but it may hold one in the future if its associated expression comes back into scope. @item "invalid" The variable object no longer holds a valid value. This can occur when the executable file being debugged has changed, either through recompilation or by using the @value{GDBN} @code{file} command. The front end should normally choose to delete these variable objects. @end table In the future new values may be added to this list so the front should be prepared for this possibility. @xref{GDB/MI Development and Front Ends, ,@sc{GDB/MI} Development and Front Ends}. @item type_changed This is only present if the varobj is still valid. If the type changed, then this will be the string @samp{true}; otherwise it will be @samp{false}. When a varobj's type changes, its children are also likely to have become incorrect. Therefore, the varobj's children are automatically deleted when this attribute is @samp{true}. Also, the varobj's update range, when set using the @code{-var-set-update-range} command, is unset. @item new_type If the varobj's type changed, then this field will be present and will hold the new type. @item new_num_children For a dynamic varobj, if the number of children changed, or if the type changed, this will be the new number of children. The @samp{numchild} field in other varobj responses is generally not valid for a dynamic varobj -- it will show the number of children that @value{GDBN} knows about, but because dynamic varobjs lazily instantiate their children, this will not reflect the number of children which may be available. The @samp{new_num_children} attribute only reports changes to the number of children known by @value{GDBN}. This is the only way to detect whether an update has removed children (which necessarily can only happen at the end of the update range). @item displayhint The display hint, if any. @item has_more This is an integer value, which will be 1 if there are more children available outside the varobj's update range. @item dynamic This attribute will be present and have the value @samp{1} if the varobj is a dynamic varobj. If the varobj is not a dynamic varobj, then this attribute will not be present. @item new_children If new children were added to a dynamic varobj within the selected update range (as set by @code{-var-set-update-range}), then they will be listed in this attribute. @end table @subsubheading Example @smallexample (gdb) -var-assign var1 3 ^done,value="3" (gdb) -var-update --all-values var1 ^done,changelist=[@{name="var1",value="3",in_scope="true", type_changed="false"@}] (gdb) @end smallexample @subheading The @code{-var-set-frozen} Command @findex -var-set-frozen @anchor{-var-set-frozen} @subsubheading Synopsis @smallexample -var-set-frozen @var{name} @var{flag} @end smallexample Set the frozenness flag on the variable object @var{name}. The @var{flag} parameter should be either @samp{1} to make the variable frozen or @samp{0} to make it unfrozen. If a variable object is frozen, then neither itself, nor any of its children, are implicitly updated by @code{-var-update} of a parent variable or by @code{-var-update *}. Only @code{-var-update} of the variable itself will update its value and values of its children. After a variable object is unfrozen, it is implicitly updated by all subsequent @code{-var-update} operations. Unfreezing a variable does not update it, only subsequent @code{-var-update} does. @subsubheading Example @smallexample (gdb) -var-set-frozen V 1 ^done (gdb) @end smallexample @subheading The @code{-var-set-update-range} command @findex -var-set-update-range @anchor{-var-set-update-range} @subsubheading Synopsis @smallexample -var-set-update-range @var{name} @var{from} @var{to} @end smallexample Set the range of children to be returned by future invocations of @code{-var-update}. @var{from} and @var{to} indicate the range of children to report. If @var{from} or @var{to} is less than zero, the range is reset and all children will be reported. Otherwise, children starting at @var{from} (zero-based) and up to and excluding @var{to} will be reported. @subsubheading Example @smallexample (gdb) -var-set-update-range V 1 2 ^done @end smallexample @subheading The @code{-var-set-visualizer} command @findex -var-set-visualizer @anchor{-var-set-visualizer} @subsubheading Synopsis @smallexample -var-set-visualizer @var{name} @var{visualizer} @end smallexample Set a visualizer for the variable object @var{name}. @var{visualizer} is the visualizer to use. The special value @samp{None} means to disable any visualizer in use. If not @samp{None}, @var{visualizer} must be a Python expression. This expression must evaluate to a callable object which accepts a single argument. @value{GDBN} will call this object with the value of the varobj @var{name} as an argument (this is done so that the same Python pretty-printing code can be used for both the CLI and MI). When called, this object must return an object which conforms to the pretty-printing interface (@pxref{Pretty Printing API}). The pre-defined function @code{gdb.default_visualizer} may be used to select a visualizer by following the built-in process (@pxref{Selecting Pretty-Printers}). This is done automatically when a varobj is created, and so ordinarily is not needed. This feature is only available if Python support is enabled. The MI command @code{-list-features} (@pxref{GDB/MI Support Commands}) can be used to check this. @subsubheading Example Resetting the visualizer: @smallexample (gdb) -var-set-visualizer V None ^done @end smallexample Reselecting the default (type-based) visualizer: @smallexample (gdb) -var-set-visualizer V gdb.default_visualizer ^done @end smallexample Suppose @code{SomeClass} is a visualizer class. A lambda expression can be used to instantiate this class for a varobj: @smallexample (gdb) -var-set-visualizer V "lambda val: SomeClass()" ^done @end smallexample @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Data Manipulation @section @sc{gdb/mi} Data Manipulation @cindex data manipulation, in @sc{gdb/mi} @cindex @sc{gdb/mi}, data manipulation This section describes the @sc{gdb/mi} commands that manipulate data: examine memory and registers, evaluate expressions, etc. For details about what an addressable memory unit is, @pxref{addressable memory unit}. @c REMOVED FROM THE INTERFACE. @c @subheading -data-assign @c Change the value of a program variable. Plenty of side effects. @c @subsubheading GDB Command @c set variable @c @subsubheading Example @c N.A. @subheading The @code{-data-disassemble} Command @findex -data-disassemble @subsubheading Synopsis @smallexample -data-disassemble [ -s @var{start-addr} -e @var{end-addr} ] | [ -a @var{addr} ] | [ -f @var{filename} -l @var{linenum} [ -n @var{lines} ] ] -- @var{mode} @end smallexample @noindent Where: @table @samp @item @var{start-addr} is the beginning address (or @code{$pc}) @item @var{end-addr} is the end address @item @var{addr} is an address anywhere within (or the name of) the function to disassemble. If an address is specified, the whole function surrounding that address will be disassembled. If a name is specified, the whole function with that name will be disassembled. @item @var{filename} is the name of the file to disassemble @item @var{linenum} is the line number to disassemble around @item @var{lines} is the number of disassembly lines to be produced. If it is -1, the whole function will be disassembled, in case no @var{end-addr} is specified. If @var{end-addr} is specified as a non-zero value, and @var{lines} is lower than the number of disassembly lines between @var{start-addr} and @var{end-addr}, only @var{lines} lines are displayed; if @var{lines} is higher than the number of lines between @var{start-addr} and @var{end-addr}, only the lines up to @var{end-addr} are displayed. @item @var{mode} is one of: @itemize @bullet @item 0 disassembly only @item 1 mixed source and disassembly (deprecated) @item 2 disassembly with raw opcodes @item 3 mixed source and disassembly with raw opcodes (deprecated) @item 4 mixed source and disassembly @item 5 mixed source and disassembly with raw opcodes @end itemize Modes 1 and 3 are deprecated. The output is ``source centric'' which hasn't proved useful in practice. @xref{Machine Code}, for a discussion of the difference between @code{/m} and @code{/s} output of the @code{disassemble} command. @end table @subsubheading Result The result of the @code{-data-disassemble} command will be a list named @samp{asm_insns}, the contents of this list depend on the @var{mode} used with the @code{-data-disassemble} command. For modes 0 and 2 the @samp{asm_insns} list contains tuples with the following fields: @table @code @item address The address at which this instruction was disassembled. @item func-name The name of the function this instruction is within. @item offset The decimal offset in bytes from the start of @samp{func-name}. @item inst The text disassembly for this @samp{address}. @item opcodes This field is only present for modes 2, 3 and 5. This contains the raw opcode bytes for the @samp{inst} field. @end table For modes 1, 3, 4 and 5 the @samp{asm_insns} list contains tuples named @samp{src_and_asm_line}, each of which has the following fields: @table @code @item line The line number within @samp{file}. @item file The file name from the compilation unit. This might be an absolute file name or a relative file name depending on the compile command used. @item fullname Absolute file name of @samp{file}. It is converted to a canonical form using the source file search path (@pxref{Source Path, ,Specifying Source Directories}) and after resolving all the symbolic links. If the source file is not found this field will contain the path as present in the debug information. @item line_asm_insn This is a list of tuples containing the disassembly for @samp{line} in @samp{file}. The fields of each tuple are the same as for @code{-data-disassemble} in @var{mode} 0 and 2, so @samp{address}, @samp{func-name}, @samp{offset}, @samp{inst}, and optionally @samp{opcodes}. @end table Note that whatever included in the @samp{inst} field, is not manipulated directly by @sc{gdb/mi}, i.e., it is not possible to adjust its format. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{disassemble}. @subsubheading Example Disassemble from the current value of @code{$pc} to @code{$pc + 20}: @smallexample (gdb) -data-disassemble -s $pc -e "$pc + 20" -- 0 ^done, asm_insns=[ @{address="0x000107c0",func-name="main",offset="4", inst="mov 2, %o0"@}, @{address="0x000107c4",func-name="main",offset="8", inst="sethi %hi(0x11800), %o2"@}, @{address="0x000107c8",func-name="main",offset="12", inst="or %o2, 0x140, %o1\t! 0x11940 <_lib_version+8>"@}, @{address="0x000107cc",func-name="main",offset="16", inst="sethi %hi(0x11800), %o2"@}, @{address="0x000107d0",func-name="main",offset="20", inst="or %o2, 0x168, %o4\t! 0x11968 <_lib_version+48>"@}] (gdb) @end smallexample Disassemble the whole @code{main} function. Line 32 is part of @code{main}. @smallexample -data-disassemble -f basics.c -l 32 -- 0 ^done,asm_insns=[ @{address="0x000107bc",func-name="main",offset="0", inst="save %sp, -112, %sp"@}, @{address="0x000107c0",func-name="main",offset="4", inst="mov 2, %o0"@}, @{address="0x000107c4",func-name="main",offset="8", inst="sethi %hi(0x11800), %o2"@}, [@dots{}] @{address="0x0001081c",func-name="main",offset="96",inst="ret "@}, @{address="0x00010820",func-name="main",offset="100",inst="restore "@}] (gdb) @end smallexample Disassemble 3 instructions from the start of @code{main}: @smallexample (gdb) -data-disassemble -f basics.c -l 32 -n 3 -- 0 ^done,asm_insns=[ @{address="0x000107bc",func-name="main",offset="0", inst="save %sp, -112, %sp"@}, @{address="0x000107c0",func-name="main",offset="4", inst="mov 2, %o0"@}, @{address="0x000107c4",func-name="main",offset="8", inst="sethi %hi(0x11800), %o2"@}] (gdb) @end smallexample Disassemble 3 instructions from the start of @code{main} in mixed mode: @smallexample (gdb) -data-disassemble -f basics.c -l 32 -n 3 -- 1 ^done,asm_insns=[ src_and_asm_line=@{line="31", file="../../../src/gdb/testsuite/gdb.mi/basics.c", fullname="/absolute/path/to/src/gdb/testsuite/gdb.mi/basics.c", line_asm_insn=[@{address="0x000107bc", func-name="main",offset="0",inst="save %sp, -112, %sp"@}]@}, src_and_asm_line=@{line="32", file="../../../src/gdb/testsuite/gdb.mi/basics.c", fullname="/absolute/path/to/src/gdb/testsuite/gdb.mi/basics.c", line_asm_insn=[@{address="0x000107c0", func-name="main",offset="4",inst="mov 2, %o0"@}, @{address="0x000107c4",func-name="main",offset="8", inst="sethi %hi(0x11800), %o2"@}]@}] (gdb) @end smallexample @subheading The @code{-data-evaluate-expression} Command @findex -data-evaluate-expression @subsubheading Synopsis @smallexample -data-evaluate-expression @var{expr} @end smallexample Evaluate @var{expr} as an expression. The expression could contain an inferior function call. The function call will execute synchronously. If the expression contains spaces, it must be enclosed in double quotes. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} commands are @samp{print}, @samp{output}, and @samp{call}. In @code{gdbtk} only, there's a corresponding @samp{gdb_eval} command. @subsubheading Example In the following example, the numbers that precede the commands are the @dfn{tokens} described in @ref{GDB/MI Command Syntax, ,@sc{gdb/mi} Command Syntax}. Notice how @sc{gdb/mi} returns the same tokens in its output. @smallexample 211-data-evaluate-expression A 211^done,value="1" (gdb) 311-data-evaluate-expression &A 311^done,value="0xefffeb7c" (gdb) 411-data-evaluate-expression A+3 411^done,value="4" (gdb) 511-data-evaluate-expression "A + 3" 511^done,value="4" (gdb) @end smallexample @subheading The @code{-data-list-changed-registers} Command @findex -data-list-changed-registers @subsubheading Synopsis @smallexample -data-list-changed-registers @end smallexample Display a list of the registers that have changed. @subsubheading @value{GDBN} Command @value{GDBN} doesn't have a direct analog for this command; @code{gdbtk} has the corresponding command @samp{gdb_changed_register_list}. @subsubheading Example On a PPC MBX board: @smallexample (gdb) -exec-continue ^running (gdb) *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",frame=@{ func="main",args=[],file="try.c",fullname="/home/foo/bar/try.c", line="5",arch="powerpc"@} (gdb) -data-list-changed-registers ^done,changed-registers=["0","1","2","4","5","6","7","8","9", "10","11","13","14","15","16","17","18","19","20","21","22","23", "24","25","26","27","28","30","31","64","65","66","67","69"] (gdb) @end smallexample @subheading The @code{-data-list-register-names} Command @findex -data-list-register-names @subsubheading Synopsis @smallexample -data-list-register-names [ ( @var{regno} )+ ] @end smallexample Show a list of register names for the current target. If no arguments are given, it shows a list of the names of all the registers. If integer numbers are given as arguments, it will print a list of the names of the registers corresponding to the arguments. To ensure consistency between a register name and its number, the output list may include empty register names. @subsubheading @value{GDBN} Command @value{GDBN} does not have a command which corresponds to @samp{-data-list-register-names}. In @code{gdbtk} there is a corresponding command @samp{gdb_regnames}. @subsubheading Example For the PPC MBX board: @smallexample (gdb) -data-list-register-names ^done,register-names=["r0","r1","r2","r3","r4","r5","r6","r7", "r8","r9","r10","r11","r12","r13","r14","r15","r16","r17","r18", "r19","r20","r21","r22","r23","r24","r25","r26","r27","r28","r29", "r30","r31","f0","f1","f2","f3","f4","f5","f6","f7","f8","f9", "f10","f11","f12","f13","f14","f15","f16","f17","f18","f19","f20", "f21","f22","f23","f24","f25","f26","f27","f28","f29","f30","f31", "", "pc","ps","cr","lr","ctr","xer"] (gdb) -data-list-register-names 1 2 3 ^done,register-names=["r1","r2","r3"] (gdb) @end smallexample @subheading The @code{-data-list-register-values} Command @findex -data-list-register-values @subsubheading Synopsis @smallexample -data-list-register-values [ @code{--skip-unavailable} ] @var{fmt} [ ( @var{regno} )*] @end smallexample Display the registers' contents. The format according to which the registers' contents are to be returned is given by @var{fmt}, followed by an optional list of numbers specifying the registers to display. A missing list of numbers indicates that the contents of all the registers must be returned. The @code{--skip-unavailable} option indicates that only the available registers are to be returned. Allowed formats for @var{fmt} are: @table @code @item x Hexadecimal @item o Octal @item t Binary @item d Decimal @item r Raw @item N Natural @end table @subsubheading @value{GDBN} Command The corresponding @value{GDBN} commands are @samp{info reg}, @samp{info all-reg}, and (in @code{gdbtk}) @samp{gdb_fetch_registers}. @subsubheading Example For a PPC MBX board (note: line breaks are for readability only, they don't appear in the actual output): @smallexample (gdb) -data-list-register-values r 64 65 ^done,register-values=[@{number="64",value="0xfe00a300"@}, @{number="65",value="0x00029002"@}] (gdb) -data-list-register-values x ^done,register-values=[@{number="0",value="0xfe0043c8"@}, @{number="1",value="0x3fff88"@},@{number="2",value="0xfffffffe"@}, @{number="3",value="0x0"@},@{number="4",value="0xa"@}, @{number="5",value="0x3fff68"@},@{number="6",value="0x3fff58"@}, @{number="7",value="0xfe011e98"@},@{number="8",value="0x2"@}, @{number="9",value="0xfa202820"@},@{number="10",value="0xfa202808"@}, @{number="11",value="0x1"@},@{number="12",value="0x0"@}, @{number="13",value="0x4544"@},@{number="14",value="0xffdfffff"@}, @{number="15",value="0xffffffff"@},@{number="16",value="0xfffffeff"@}, @{number="17",value="0xefffffed"@},@{number="18",value="0xfffffffe"@}, @{number="19",value="0xffffffff"@},@{number="20",value="0xffffffff"@}, @{number="21",value="0xffffffff"@},@{number="22",value="0xfffffff7"@}, @{number="23",value="0xffffffff"@},@{number="24",value="0xffffffff"@}, @{number="25",value="0xffffffff"@},@{number="26",value="0xfffffffb"@}, @{number="27",value="0xffffffff"@},@{number="28",value="0xf7bfffff"@}, @{number="29",value="0x0"@},@{number="30",value="0xfe010000"@}, @{number="31",value="0x0"@},@{number="32",value="0x0"@}, @{number="33",value="0x0"@},@{number="34",value="0x0"@}, @{number="35",value="0x0"@},@{number="36",value="0x0"@}, @{number="37",value="0x0"@},@{number="38",value="0x0"@}, @{number="39",value="0x0"@},@{number="40",value="0x0"@}, @{number="41",value="0x0"@},@{number="42",value="0x0"@}, @{number="43",value="0x0"@},@{number="44",value="0x0"@}, @{number="45",value="0x0"@},@{number="46",value="0x0"@}, @{number="47",value="0x0"@},@{number="48",value="0x0"@}, @{number="49",value="0x0"@},@{number="50",value="0x0"@}, @{number="51",value="0x0"@},@{number="52",value="0x0"@}, @{number="53",value="0x0"@},@{number="54",value="0x0"@}, @{number="55",value="0x0"@},@{number="56",value="0x0"@}, @{number="57",value="0x0"@},@{number="58",value="0x0"@}, @{number="59",value="0x0"@},@{number="60",value="0x0"@}, @{number="61",value="0x0"@},@{number="62",value="0x0"@}, @{number="63",value="0x0"@},@{number="64",value="0xfe00a300"@}, @{number="65",value="0x29002"@},@{number="66",value="0x202f04b5"@}, @{number="67",value="0xfe0043b0"@},@{number="68",value="0xfe00b3e4"@}, @{number="69",value="0x20002b03"@}] (gdb) @end smallexample @subheading The @code{-data-read-memory} Command @findex -data-read-memory This command is deprecated, use @code{-data-read-memory-bytes} instead. @subsubheading Synopsis @smallexample -data-read-memory [ -o @var{byte-offset} ] @var{address} @var{word-format} @var{word-size} @var{nr-rows} @var{nr-cols} [ @var{aschar} ] @end smallexample @noindent where: @table @samp @item @var{address} An expression specifying the address of the first memory word to be read. Complex expressions containing embedded white space should be quoted using the C convention. @item @var{word-format} The format to be used to print the memory words. The notation is the same as for @value{GDBN}'s @code{print} command (@pxref{Output Formats, ,Output Formats}). @item @var{word-size} The size of each memory word in bytes. @item @var{nr-rows} The number of rows in the output table. @item @var{nr-cols} The number of columns in the output table. @item @var{aschar} If present, indicates that each row should include an @sc{ascii} dump. The value of @var{aschar} is used as a padding character when a byte is not a member of the printable @sc{ascii} character set (printable @sc{ascii} characters are those whose code is between 32 and 126, inclusively). @item @var{byte-offset} An offset to add to the @var{address} before fetching memory. @end table This command displays memory contents as a table of @var{nr-rows} by @var{nr-cols} words, each word being @var{word-size} bytes. In total, @code{@var{nr-rows} * @var{nr-cols} * @var{word-size}} bytes are read (returned as @samp{total-bytes}). Should less than the requested number of bytes be returned by the target, the missing words are identified using @samp{N/A}. The number of bytes read from the target is returned in @samp{nr-bytes} and the starting address used to read memory in @samp{addr}. The address of the next/previous row or page is available in @samp{next-row} and @samp{prev-row}, @samp{next-page} and @samp{prev-page}. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{x}. @code{gdbtk} has @samp{gdb_get_mem} memory read command. @subsubheading Example Read six bytes of memory starting at @code{bytes+6} but then offset by @code{-6} bytes. Format as three rows of two columns. One byte per word. Display each word in hex. @smallexample (gdb) 9-data-read-memory -o -6 -- bytes+6 x 1 3 2 9^done,addr="0x00001390",nr-bytes="6",total-bytes="6", next-row="0x00001396",prev-row="0x0000138e",next-page="0x00001396", prev-page="0x0000138a",memory=[ @{addr="0x00001390",data=["0x00","0x01"]@}, @{addr="0x00001392",data=["0x02","0x03"]@}, @{addr="0x00001394",data=["0x04","0x05"]@}] (gdb) @end smallexample Read two bytes of memory starting at address @code{shorts + 64} and display as a single word formatted in decimal. @smallexample (gdb) 5-data-read-memory shorts+64 d 2 1 1 5^done,addr="0x00001510",nr-bytes="2",total-bytes="2", next-row="0x00001512",prev-row="0x0000150e", next-page="0x00001512",prev-page="0x0000150e",memory=[ @{addr="0x00001510",data=["128"]@}] (gdb) @end smallexample Read thirty two bytes of memory starting at @code{bytes+16} and format as eight rows of four columns. Include a string encoding with @samp{x} used as the non-printable character. @smallexample (gdb) 4-data-read-memory bytes+16 x 1 8 4 x 4^done,addr="0x000013a0",nr-bytes="32",total-bytes="32", next-row="0x000013c0",prev-row="0x0000139c", next-page="0x000013c0",prev-page="0x00001380",memory=[ @{addr="0x000013a0",data=["0x10","0x11","0x12","0x13"],ascii="xxxx"@}, @{addr="0x000013a4",data=["0x14","0x15","0x16","0x17"],ascii="xxxx"@}, @{addr="0x000013a8",data=["0x18","0x19","0x1a","0x1b"],ascii="xxxx"@}, @{addr="0x000013ac",data=["0x1c","0x1d","0x1e","0x1f"],ascii="xxxx"@}, @{addr="0x000013b0",data=["0x20","0x21","0x22","0x23"],ascii=" !\"#"@}, @{addr="0x000013b4",data=["0x24","0x25","0x26","0x27"],ascii="$%&'"@}, @{addr="0x000013b8",data=["0x28","0x29","0x2a","0x2b"],ascii="()*+"@}, @{addr="0x000013bc",data=["0x2c","0x2d","0x2e","0x2f"],ascii=",-./"@}] (gdb) @end smallexample @subheading The @code{-data-read-memory-bytes} Command @findex -data-read-memory-bytes @subsubheading Synopsis @smallexample -data-read-memory-bytes [ -o @var{offset} ] @var{address} @var{count} @end smallexample @noindent where: @table @samp @item @var{address} An expression specifying the address of the first addressable memory unit to be read. Complex expressions containing embedded white space should be quoted using the C convention. @item @var{count} The number of addressable memory units to read. This should be an integer literal. @item @var{offset} The offset relative to @var{address} at which to start reading. This should be an integer literal. This option is provided so that a frontend is not required to first evaluate address and then perform address arithmetics itself. @end table This command attempts to read all accessible memory regions in the specified range. First, all regions marked as unreadable in the memory map (if one is defined) will be skipped. @xref{Memory Region Attributes}. Second, @value{GDBN} will attempt to read the remaining regions. For each one, if reading full region results in an errors, @value{GDBN} will try to read a subset of the region. In general, every single memory unit in the region may be readable or not, and the only way to read every readable unit is to try a read at every address, which is not practical. Therefore, @value{GDBN} will attempt to read all accessible memory units at either beginning or the end of the region, using a binary division scheme. This heuristic works well for reading across a memory map boundary. Note that if a region has a readable range that is neither at the beginning or the end, @value{GDBN} will not read it. The result record (@pxref{GDB/MI Result Records}) that is output of the command includes a field named @samp{memory} whose content is a list of tuples. Each tuple represent a successfully read memory block and has the following fields: @table @code @item begin The start address of the memory block, as hexadecimal literal. @item end The end address of the memory block, as hexadecimal literal. @item offset The offset of the memory block, as hexadecimal literal, relative to the start address passed to @code{-data-read-memory-bytes}. @item contents The contents of the memory block, in hex. @end table @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{x}. @subsubheading Example @smallexample (gdb) -data-read-memory-bytes &a 10 ^done,memory=[@{begin="0xbffff154",offset="0x00000000", end="0xbffff15e", contents="01000000020000000300"@}] (gdb) @end smallexample @subheading The @code{-data-write-memory-bytes} Command @findex -data-write-memory-bytes @subsubheading Synopsis @smallexample -data-write-memory-bytes @var{address} @var{contents} -data-write-memory-bytes @var{address} @var{contents} @r{[}@var{count}@r{]} @end smallexample @noindent where: @table @samp @item @var{address} An expression specifying the address of the first addressable memory unit to be written. Complex expressions containing embedded white space should be quoted using the C convention. @item @var{contents} The hex-encoded data to write. It is an error if @var{contents} does not represent an integral number of addressable memory units. @item @var{count} Optional argument indicating the number of addressable memory units to be written. If @var{count} is greater than @var{contents}' length, @value{GDBN} will repeatedly write @var{contents} until it fills @var{count} memory units. @end table @subsubheading @value{GDBN} Command There's no corresponding @value{GDBN} command. @subsubheading Example @smallexample (gdb) -data-write-memory-bytes &a "aabbccdd" ^done (gdb) @end smallexample @smallexample (gdb) -data-write-memory-bytes &a "aabbccdd" 16e ^done (gdb) @end smallexample @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Tracepoint Commands @section @sc{gdb/mi} Tracepoint Commands The commands defined in this section implement MI support for tracepoints. For detailed introduction, see @ref{Tracepoints}. @subheading The @code{-trace-find} Command @findex -trace-find @subsubheading Synopsis @smallexample -trace-find @var{mode} [@var{parameters}@dots{}] @end smallexample Find a trace frame using criteria defined by @var{mode} and @var{parameters}. The following table lists permissible modes and their parameters. For details of operation, see @ref{tfind}. @table @samp @item none No parameters are required. Stops examining trace frames. @item frame-number An integer is required as parameter. Selects tracepoint frame with that index. @item tracepoint-number An integer is required as parameter. Finds next trace frame that corresponds to tracepoint with the specified number. @item pc An address is required as parameter. Finds next trace frame that corresponds to any tracepoint at the specified address. @item pc-inside-range Two addresses are required as parameters. Finds next trace frame that corresponds to a tracepoint at an address inside the specified range. Both bounds are considered to be inside the range. @item pc-outside-range Two addresses are required as parameters. Finds next trace frame that corresponds to a tracepoint at an address outside the specified range. Both bounds are considered to be inside the range. @item line Line specification is required as parameter. @xref{Specify Location}. Finds next trace frame that corresponds to a tracepoint at the specified location. @end table If @samp{none} was passed as @var{mode}, the response does not have fields. Otherwise, the response may have the following fields: @table @samp @item found This field has either @samp{0} or @samp{1} as the value, depending on whether a matching tracepoint was found. @item traceframe The index of the found traceframe. This field is present iff the @samp{found} field has value of @samp{1}. @item tracepoint The index of the found tracepoint. This field is present iff the @samp{found} field has value of @samp{1}. @item frame The information about the frame corresponding to the found trace frame. This field is present only if a trace frame was found. @xref{GDB/MI Frame Information}, for description of this field. @end table @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{tfind}. @subheading -trace-define-variable @findex -trace-define-variable @subsubheading Synopsis @smallexample -trace-define-variable @var{name} [ @var{value} ] @end smallexample Create trace variable @var{name} if it does not exist. If @var{value} is specified, sets the initial value of the specified trace variable to that value. Note that the @var{name} should start with the @samp{$} character. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{tvariable}. @subheading The @code{-trace-frame-collected} Command @findex -trace-frame-collected @subsubheading Synopsis @smallexample -trace-frame-collected [--var-print-values @var{var_pval}] [--comp-print-values @var{comp_pval}] [--registers-format @var{regformat}] [--memory-contents] @end smallexample This command returns the set of collected objects, register names, trace state variable names, memory ranges and computed expressions that have been collected at a particular trace frame. The optional parameters to the command affect the output format in different ways. See the output description table below for more details. The reported names can be used in the normal manner to create varobjs and inspect the objects themselves. The items returned by this command are categorized so that it is clear which is a variable, which is a register, which is a trace state variable, which is a memory range and which is a computed expression. For instance, if the actions were @smallexample collect myVar, myArray[myIndex], myObj.field, myPtr->field, myCount + 2 collect *(int*)0xaf02bef0@@40 @end smallexample @noindent the object collected in its entirety would be @code{myVar}. The object @code{myArray} would be partially collected, because only the element at index @code{myIndex} would be collected. The remaining objects would be computed expressions. An example output would be: @smallexample (gdb) -trace-frame-collected ^done, explicit-variables=[@{name="myVar",value="1"@}], computed-expressions=[@{name="myArray[myIndex]",value="0"@}, @{name="myObj.field",value="0"@}, @{name="myPtr->field",value="1"@}, @{name="myCount + 2",value="3"@}, @{name="$tvar1 + 1",value="43970027"@}], registers=[@{number="0",value="0x7fe2c6e79ec8"@}, @{number="1",value="0x0"@}, @{number="2",value="0x4"@}, ... @{number="125",value="0x0"@}], tvars=[@{name="$tvar1",current="43970026"@}], memory=[@{address="0x0000000000602264",length="4"@}, @{address="0x0000000000615bc0",length="4"@}] (gdb) @end smallexample Where: @table @code @item explicit-variables The set of objects that have been collected in their entirety (as opposed to collecting just a few elements of an array or a few struct members). For each object, its name and value are printed. The @code{--var-print-values} option affects how or whether the value field is output. If @var{var_pval} is 0, then print only the names; if it is 1, print also their values; and if it is 2, print the name, type and value for simple data types, and the name and type for arrays, structures and unions. @item computed-expressions The set of computed expressions that have been collected at the current trace frame. The @code{--comp-print-values} option affects this set like the @code{--var-print-values} option affects the @code{explicit-variables} set. See above. @item registers The registers that have been collected at the current trace frame. For each register collected, the name and current value are returned. The value is formatted according to the @code{--registers-format} option. See the @command{-data-list-register-values} command for a list of the allowed formats. The default is @samp{x}. @item tvars The trace state variables that have been collected at the current trace frame. For each trace state variable collected, the name and current value are returned. @item memory The set of memory ranges that have been collected at the current trace frame. Its content is a list of tuples. Each tuple represents a collected memory range and has the following fields: @table @code @item address The start address of the memory range, as hexadecimal literal. @item length The length of the memory range, as decimal literal. @item contents The contents of the memory block, in hex. This field is only present if the @code{--memory-contents} option is specified. @end table @end table @subsubheading @value{GDBN} Command There is no corresponding @value{GDBN} command. @subsubheading Example @subheading -trace-list-variables @findex -trace-list-variables @subsubheading Synopsis @smallexample -trace-list-variables @end smallexample Return a table of all defined trace variables. Each element of the table has the following fields: @table @samp @item name The name of the trace variable. This field is always present. @item initial The initial value. This is a 64-bit signed integer. This field is always present. @item current The value the trace variable has at the moment. This is a 64-bit signed integer. This field is absent iff current value is not defined, for example if the trace was never run, or is presently running. @end table @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{tvariables}. @subsubheading Example @smallexample (gdb) -trace-list-variables ^done,trace-variables=@{nr_rows="1",nr_cols="3", hdr=[@{width="15",alignment="-1",col_name="name",colhdr="Name"@}, @{width="11",alignment="-1",col_name="initial",colhdr="Initial"@}, @{width="11",alignment="-1",col_name="current",colhdr="Current"@}], body=[variable=@{name="$trace_timestamp",initial="0"@} variable=@{name="$foo",initial="10",current="15"@}]@} (gdb) @end smallexample @subheading -trace-save @findex -trace-save @subsubheading Synopsis @smallexample -trace-save [ -r ] [ -ctf ] @var{filename} @end smallexample Saves the collected trace data to @var{filename}. Without the @samp{-r} option, the data is downloaded from the target and saved in a local file. With the @samp{-r} option the target is asked to perform the save. By default, this command will save the trace in the tfile format. You can supply the optional @samp{-ctf} argument to save it the CTF format. See @ref{Trace Files} for more information about CTF. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{tsave}. @subheading -trace-start @findex -trace-start @subsubheading Synopsis @smallexample -trace-start @end smallexample Starts a tracing experiment. The result of this command does not have any fields. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{tstart}. @subheading -trace-status @findex -trace-status @subsubheading Synopsis @smallexample -trace-status @end smallexample Obtains the status of a tracing experiment. The result may include the following fields: @table @samp @item supported May have a value of either @samp{0}, when no tracing operations are supported, @samp{1}, when all tracing operations are supported, or @samp{file} when examining trace file. In the latter case, examining of trace frame is possible but new tracing experiement cannot be started. This field is always present. @item running May have a value of either @samp{0} or @samp{1} depending on whether tracing experiement is in progress on target. This field is present if @samp{supported} field is not @samp{0}. @item stop-reason Report the reason why the tracing was stopped last time. This field may be absent iff tracing was never stopped on target yet. The value of @samp{request} means the tracing was stopped as result of the @code{-trace-stop} command. The value of @samp{overflow} means the tracing buffer is full. The value of @samp{disconnection} means tracing was automatically stopped when @value{GDBN} has disconnected. The value of @samp{passcount} means tracing was stopped when a tracepoint was passed a maximal number of times for that tracepoint. This field is present if @samp{supported} field is not @samp{0}. @item stopping-tracepoint The number of tracepoint whose passcount as exceeded. This field is present iff the @samp{stop-reason} field has the value of @samp{passcount}. @item frames @itemx frames-created The @samp{frames} field is a count of the total number of trace frames in the trace buffer, while @samp{frames-created} is the total created during the run, including ones that were discarded, such as when a circular trace buffer filled up. Both fields are optional. @item buffer-size @itemx buffer-free These fields tell the current size of the tracing buffer and the remaining space. These fields are optional. @item circular The value of the circular trace buffer flag. @code{1} means that the trace buffer is circular and old trace frames will be discarded if necessary to make room, @code{0} means that the trace buffer is linear and may fill up. @item disconnected The value of the disconnected tracing flag. @code{1} means that tracing will continue after @value{GDBN} disconnects, @code{0} means that the trace run will stop. @item trace-file The filename of the trace file being examined. This field is optional, and only present when examining a trace file. @end table @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{tstatus}. @subheading -trace-stop @findex -trace-stop @subsubheading Synopsis @smallexample -trace-stop @end smallexample Stops a tracing experiment. The result of this command has the same fields as @code{-trace-status}, except that the @samp{supported} and @samp{running} fields are not output. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{tstop}. @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Symbol Query @section @sc{gdb/mi} Symbol Query Commands @ignore @subheading The @code{-symbol-info-address} Command @findex -symbol-info-address @subsubheading Synopsis @smallexample -symbol-info-address @var{symbol} @end smallexample Describe where @var{symbol} is stored. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{info address}. @subsubheading Example N.A. @subheading The @code{-symbol-info-file} Command @findex -symbol-info-file @subsubheading Synopsis @smallexample -symbol-info-file @end smallexample Show the file for the symbol. @subsubheading @value{GDBN} Command There's no equivalent @value{GDBN} command. @code{gdbtk} has @samp{gdb_find_file}. @subsubheading Example N.A. @end ignore @subheading The @code{-symbol-info-functions} Command @findex -symbol-info-functions @anchor{-symbol-info-functions} @subsubheading Synopsis @smallexample -symbol-info-functions [--include-nondebug] [--type @var{type_regexp}] [--name @var{name_regexp}] [--max-results @var{limit}] @end smallexample @noindent Return a list containing the names and types for all global functions taken from the debug information. The functions are grouped by source file, and shown with the line number on which each function is defined. The @code{--include-nondebug} option causes the output to include code symbols from the symbol table. The options @code{--type} and @code{--name} allow the symbols returned to be filtered based on either the name of the function, or the type signature of the function. The option @code{--max-results} restricts the command to return no more than @var{limit} results. If exactly @var{limit} results are returned then there might be additional results available if a higher limit is used. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{info functions}. @subsubheading Example @smallexample @group (gdb) -symbol-info-functions ^done,symbols= @{debug= [@{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[@{line="36", name="f4", type="void (int *)", description="void f4(int *);"@}, @{line="42", name="main", type="int ()", description="int main();"@}, @{line="30", name="f1", type="my_int_t (int, int)", description="static my_int_t f1(int, int);"@}]@}, @{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", symbols=[@{line="33", name="f2", type="float (another_float_t)", description="float f2(another_float_t);"@}, @{line="39", name="f3", type="int (another_int_t)", description="int f3(another_int_t);"@}, @{line="27", name="f1", type="another_float_t (int)", description="static another_float_t f1(int);"@}]@}]@} @end group @group (gdb) -symbol-info-functions --name f1 ^done,symbols= @{debug= [@{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[@{line="30", name="f1", type="my_int_t (int, int)", description="static my_int_t f1(int, int);"@}]@}, @{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", symbols=[@{line="27", name="f1", type="another_float_t (int)", description="static another_float_t f1(int);"@}]@}]@} @end group @group (gdb) -symbol-info-functions --type void ^done,symbols= @{debug= [@{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[@{line="36", name="f4", type="void (int *)", description="void f4(int *);"@}]@}]@} @end group @group (gdb) -symbol-info-functions --include-nondebug ^done,symbols= @{debug= [@{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[@{line="36", name="f4", type="void (int *)", description="void f4(int *);"@}, @{line="42", name="main", type="int ()", description="int main();"@}, @{line="30", name="f1", type="my_int_t (int, int)", description="static my_int_t f1(int, int);"@}]@}, @{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", symbols=[@{line="33", name="f2", type="float (another_float_t)", description="float f2(another_float_t);"@}, @{line="39", name="f3", type="int (another_int_t)", description="int f3(another_int_t);"@}, @{line="27", name="f1", type="another_float_t (int)", description="static another_float_t f1(int);"@}]@}], nondebug= [@{address="0x0000000000400398",name="_init"@}, @{address="0x00000000004003b0",name="_start"@}, ... ]@} @end group @end smallexample @subheading The @code{-symbol-info-module-functions} Command @findex -symbol-info-module-functions @anchor{-symbol-info-module-functions} @subsubheading Synopsis @smallexample -symbol-info-module-functions [--module @var{module_regexp}] [--name @var{name_regexp}] [--type @var{type_regexp}] @end smallexample @noindent Return a list containing the names of all known functions within all know Fortran modules. The functions are grouped by source file and containing module, and shown with the line number on which each function is defined. The option @code{--module} only returns results for modules matching @var{module_regexp}. The option @code{--name} only returns functions whose name matches @var{name_regexp}, and @code{--type} only returns functions whose type matches @var{type_regexp}. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{info module functions}. @subsubheading Example @smallexample @group (gdb) -symbol-info-module-functions ^done,symbols= [@{module="mod1", files=[@{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", symbols=[@{line="21",name="mod1::check_all",type="void (void)", description="void mod1::check_all(void);"@}]@}]@}, @{module="mod2", files=[@{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", symbols=[@{line="30",name="mod2::check_var_i",type="void (void)", description="void mod2::check_var_i(void);"@}]@}]@}, @{module="mod3", files=[@{filename="/projec/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", fullname="/projec/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", symbols=[@{line="21",name="mod3::check_all",type="void (void)", description="void mod3::check_all(void);"@}, @{line="27",name="mod3::check_mod2",type="void (void)", description="void mod3::check_mod2(void);"@}]@}]@}, @{module="modmany", files=[@{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", symbols=[@{line="35",name="modmany::check_some",type="void (void)", description="void modmany::check_some(void);"@}]@}]@}, @{module="moduse", files=[@{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", symbols=[@{line="44",name="moduse::check_all",type="void (void)", description="void moduse::check_all(void);"@}, @{line="49",name="moduse::check_var_x",type="void (void)", description="void moduse::check_var_x(void);"@}]@}]@}] @end group @end smallexample @subheading The @code{-symbol-info-module-variables} Command @findex -symbol-info-module-variables @anchor{-symbol-info-module-variables} @subsubheading Synopsis @smallexample -symbol-info-module-variables [--module @var{module_regexp}] [--name @var{name_regexp}] [--type @var{type_regexp}] @end smallexample @noindent Return a list containing the names of all known variables within all know Fortran modules. The variables are grouped by source file and containing module, and shown with the line number on which each variable is defined. The option @code{--module} only returns results for modules matching @var{module_regexp}. The option @code{--name} only returns variables whose name matches @var{name_regexp}, and @code{--type} only returns variables whose type matches @var{type_regexp}. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{info module variables}. @subsubheading Example @smallexample @group (gdb) -symbol-info-module-variables ^done,symbols= [@{module="mod1", files=[@{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", symbols=[@{line="18",name="mod1::var_const",type="integer(kind=4)", description="integer(kind=4) mod1::var_const;"@}, @{line="17",name="mod1::var_i",type="integer(kind=4)", description="integer(kind=4) mod1::var_i;"@}]@}]@}, @{module="mod2", files=[@{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", symbols=[@{line="28",name="mod2::var_i",type="integer(kind=4)", description="integer(kind=4) mod2::var_i;"@}]@}]@}, @{module="mod3", files=[@{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", symbols=[@{line="18",name="mod3::mod1",type="integer(kind=4)", description="integer(kind=4) mod3::mod1;"@}, @{line="17",name="mod3::mod2",type="integer(kind=4)", description="integer(kind=4) mod3::mod2;"@}, @{line="19",name="mod3::var_i",type="integer(kind=4)", description="integer(kind=4) mod3::var_i;"@}]@}]@}, @{module="modmany", files=[@{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", symbols=[@{line="33",name="modmany::var_a",type="integer(kind=4)", description="integer(kind=4) modmany::var_a;"@}, @{line="33",name="modmany::var_b",type="integer(kind=4)", description="integer(kind=4) modmany::var_b;"@}, @{line="33",name="modmany::var_c",type="integer(kind=4)", description="integer(kind=4) modmany::var_c;"@}, @{line="33",name="modmany::var_i",type="integer(kind=4)", description="integer(kind=4) modmany::var_i;"@}]@}]@}, @{module="moduse", files=[@{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", symbols=[@{line="42",name="moduse::var_x",type="integer(kind=4)", description="integer(kind=4) moduse::var_x;"@}, @{line="42",name="moduse::var_y",type="integer(kind=4)", description="integer(kind=4) moduse::var_y;"@}]@}]@}] @end group @end smallexample @subheading The @code{-symbol-info-modules} Command @findex -symbol-info-modules @anchor{-symbol-info-modules} @subsubheading Synopsis @smallexample -symbol-info-modules [--name @var{name_regexp}] [--max-results @var{limit}] @end smallexample @noindent Return a list containing the names of all known Fortran modules. The modules are grouped by source file, and shown with the line number on which each modules is defined. The option @code{--name} allows the modules returned to be filtered based the name of the module. The option @code{--max-results} restricts the command to return no more than @var{limit} results. If exactly @var{limit} results are returned then there might be additional results available if a higher limit is used. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{info modules}. @subsubheading Example @smallexample @group (gdb) -symbol-info-modules ^done,symbols= @{debug= [@{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", symbols=[@{line="16",name="mod1"@}, @{line="22",name="mod2"@}]@}, @{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", symbols=[@{line="16",name="mod3"@}, @{line="22",name="modmany"@}, @{line="26",name="moduse"@}]@}]@} @end group @group (gdb) -symbol-info-modules --name mod[123] ^done,symbols= @{debug= [@{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90", symbols=[@{line="16",name="mod1"@}, @{line="22",name="mod2"@}]@}, @{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90", symbols=[@{line="16",name="mod3"@}]@}]@} @end group @end smallexample @subheading The @code{-symbol-info-types} Command @findex -symbol-info-types @anchor{-symbol-info-types} @subsubheading Synopsis @smallexample -symbol-info-types [--name @var{name_regexp}] [--max-results @var{limit}] @end smallexample @noindent Return a list of all defined types. The types are grouped by source file, and shown with the line number on which each user defined type is defined. Some base types are not defined in the source code but are added to the debug information by the compiler, for example @code{int}, @code{float}, etc.; these types do not have an associated line number. The option @code{--name} allows the list of types returned to be filtered by name. The option @code{--max-results} restricts the command to return no more than @var{limit} results. If exactly @var{limit} results are returned then there might be additional results available if a higher limit is used. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{info types}. @subsubheading Example @smallexample @group (gdb) -symbol-info-types ^done,symbols= @{debug= [@{filename="gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[@{name="float"@}, @{name="int"@}, @{line="27",name="typedef int my_int_t;"@}]@}, @{filename="gdb.mi/mi-sym-info-2.c", fullname="/project/gdb.mi/mi-sym-info-2.c", symbols=[@{line="24",name="typedef float another_float_t;"@}, @{line="23",name="typedef int another_int_t;"@}, @{name="float"@}, @{name="int"@}]@}]@} @end group @group (gdb) -symbol-info-types --name _int_ ^done,symbols= @{debug= [@{filename="gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[@{line="27",name="typedef int my_int_t;"@}]@}, @{filename="gdb.mi/mi-sym-info-2.c", fullname="/project/gdb.mi/mi-sym-info-2.c", symbols=[@{line="23",name="typedef int another_int_t;"@}]@}]@} @end group @end smallexample @subheading The @code{-symbol-info-variables} Command @findex -symbol-info-variables @anchor{-symbol-info-variables} @subsubheading Synopsis @smallexample -symbol-info-variables [--include-nondebug] [--type @var{type_regexp}] [--name @var{name_regexp}] [--max-results @var{limit}] @end smallexample @noindent Return a list containing the names and types for all global variables taken from the debug information. The variables are grouped by source file, and shown with the line number on which each variable is defined. The @code{--include-nondebug} option causes the output to include data symbols from the symbol table. The options @code{--type} and @code{--name} allow the symbols returned to be filtered based on either the name of the variable, or the type of the variable. The option @code{--max-results} restricts the command to return no more than @var{limit} results. If exactly @var{limit} results are returned then there might be additional results available if a higher limit is used. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{info variables}. @subsubheading Example @smallexample @group (gdb) -symbol-info-variables ^done,symbols= @{debug= [@{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[@{line="25",name="global_f1",type="float", description="static float global_f1;"@}, @{line="24",name="global_i1",type="int", description="static int global_i1;"@}]@}, @{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", symbols=[@{line="21",name="global_f2",type="int", description="int global_f2;"@}, @{line="20",name="global_i2",type="int", description="int global_i2;"@}, @{line="19",name="global_f1",type="float", description="static float global_f1;"@}, @{line="18",name="global_i1",type="int", description="static int global_i1;"@}]@}]@} @end group @group (gdb) -symbol-info-variables --name f1 ^done,symbols= @{debug= [@{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[@{line="25",name="global_f1",type="float", description="static float global_f1;"@}]@}, @{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", symbols=[@{line="19",name="global_f1",type="float", description="static float global_f1;"@}]@}]@} @end group @group (gdb) -symbol-info-variables --type float ^done,symbols= @{debug= [@{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[@{line="25",name="global_f1",type="float", description="static float global_f1;"@}]@}, @{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", symbols=[@{line="19",name="global_f1",type="float", description="static float global_f1;"@}]@}]@} @end group @group (gdb) -symbol-info-variables --include-nondebug ^done,symbols= @{debug= [@{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c", symbols=[@{line="25",name="global_f1",type="float", description="static float global_f1;"@}, @{line="24",name="global_i1",type="int", description="static int global_i1;"@}]@}, @{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c", symbols=[@{line="21",name="global_f2",type="int", description="int global_f2;"@}, @{line="20",name="global_i2",type="int", description="int global_i2;"@}, @{line="19",name="global_f1",type="float", description="static float global_f1;"@}, @{line="18",name="global_i1",type="int", description="static int global_i1;"@}]@}], nondebug= [@{address="0x00000000004005d0",name="_IO_stdin_used"@}, @{address="0x00000000004005d8",name="__dso_handle"@} ... ]@} @end group @end smallexample @ignore @subheading The @code{-symbol-info-line} Command @findex -symbol-info-line @subsubheading Synopsis @smallexample -symbol-info-line @end smallexample Show the core addresses of the code for a source line. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{info line}. @code{gdbtk} has the @samp{gdb_get_line} and @samp{gdb_get_file} commands. @subsubheading Example N.A. @subheading The @code{-symbol-info-symbol} Command @findex -symbol-info-symbol @subsubheading Synopsis @smallexample -symbol-info-symbol @var{addr} @end smallexample Describe what symbol is at location @var{addr}. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{info symbol}. @subsubheading Example N.A. @subheading The @code{-symbol-list-functions} Command @findex -symbol-list-functions @subsubheading Synopsis @smallexample -symbol-list-functions @end smallexample List the functions in the executable. @subsubheading @value{GDBN} Command @samp{info functions} in @value{GDBN}, @samp{gdb_listfunc} and @samp{gdb_search} in @code{gdbtk}. @subsubheading Example N.A. @end ignore @subheading The @code{-symbol-list-lines} Command @findex -symbol-list-lines @subsubheading Synopsis @smallexample -symbol-list-lines @var{filename} @end smallexample Print the list of lines that contain code and their associated program addresses for the given source filename. The entries are sorted in ascending PC order. @subsubheading @value{GDBN} Command There is no corresponding @value{GDBN} command. @subsubheading Example @smallexample (gdb) -symbol-list-lines basics.c ^done,lines=[@{pc="0x08048554",line="7"@},@{pc="0x0804855a",line="8"@}] (gdb) @end smallexample @ignore @subheading The @code{-symbol-list-types} Command @findex -symbol-list-types @subsubheading Synopsis @smallexample -symbol-list-types @end smallexample List all the type names. @subsubheading @value{GDBN} Command The corresponding commands are @samp{info types} in @value{GDBN}, @samp{gdb_search} in @code{gdbtk}. @subsubheading Example N.A. @subheading The @code{-symbol-list-variables} Command @findex -symbol-list-variables @subsubheading Synopsis @smallexample -symbol-list-variables @end smallexample List all the global and static variable names. @subsubheading @value{GDBN} Command @samp{info variables} in @value{GDBN}, @samp{gdb_search} in @code{gdbtk}. @subsubheading Example N.A. @subheading The @code{-symbol-locate} Command @findex -symbol-locate @subsubheading Synopsis @smallexample -symbol-locate @end smallexample @subsubheading @value{GDBN} Command @samp{gdb_loc} in @code{gdbtk}. @subsubheading Example N.A. @subheading The @code{-symbol-type} Command @findex -symbol-type @subsubheading Synopsis @smallexample -symbol-type @var{variable} @end smallexample Show type of @var{variable}. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{ptype}, @code{gdbtk} has @samp{gdb_obj_variable}. @subsubheading Example N.A. @end ignore @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI File Commands @section @sc{gdb/mi} File Commands This section describes the GDB/MI commands to specify executable file names and to read in and obtain symbol table information. @subheading The @code{-file-exec-and-symbols} Command @findex -file-exec-and-symbols @subsubheading Synopsis @smallexample -file-exec-and-symbols @var{file} @end smallexample Specify the executable file to be debugged. This file is the one from which the symbol table is also read. If no file is specified, the command clears the executable and symbol information. If breakpoints are set when using this command with no arguments, @value{GDBN} will produce error messages. Otherwise, no output is produced, except a completion notification. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{file}. @subsubheading Example @smallexample (gdb) -file-exec-and-symbols /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx ^done (gdb) @end smallexample @subheading The @code{-file-exec-file} Command @findex -file-exec-file @subsubheading Synopsis @smallexample -file-exec-file @var{file} @end smallexample Specify the executable file to be debugged. Unlike @samp{-file-exec-and-symbols}, the symbol table is @emph{not} read from this file. If used without argument, @value{GDBN} clears the information about the executable file. No output is produced, except a completion notification. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{exec-file}. @subsubheading Example @smallexample (gdb) -file-exec-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx ^done (gdb) @end smallexample @ignore @subheading The @code{-file-list-exec-sections} Command @findex -file-list-exec-sections @subsubheading Synopsis @smallexample -file-list-exec-sections @end smallexample List the sections of the current executable file. @subsubheading @value{GDBN} Command The @value{GDBN} command @samp{info file} shows, among the rest, the same information as this command. @code{gdbtk} has a corresponding command @samp{gdb_load_info}. @subsubheading Example N.A. @end ignore @subheading The @code{-file-list-exec-source-file} Command @findex -file-list-exec-source-file @subsubheading Synopsis @smallexample -file-list-exec-source-file @end smallexample List the line number, the current source file, and the absolute path to the current source file for the current executable. The macro information field has a value of @samp{1} or @samp{0} depending on whether or not the file includes preprocessor macro information. @subsubheading @value{GDBN} Command The @value{GDBN} equivalent is @samp{info source} @subsubheading Example @smallexample (gdb) 123-file-list-exec-source-file 123^done,line="1",file="foo.c",fullname="/home/bar/foo.c,macro-info="1" (gdb) @end smallexample @subheading The @code{-file-list-exec-source-files} Command @findex -file-list-exec-source-files @subsubheading Synopsis @smallexample -file-list-exec-source-files @end smallexample List the source files for the current executable. It will always output both the filename and fullname (absolute file name) of a source file. @subsubheading @value{GDBN} Command The @value{GDBN} equivalent is @samp{info sources}. @code{gdbtk} has an analogous command @samp{gdb_listfiles}. @subsubheading Example @smallexample (gdb) -file-list-exec-source-files ^done,files=[ @{file=foo.c,fullname=/home/foo.c@}, @{file=/home/bar.c,fullname=/home/bar.c@}, @{file=gdb_could_not_find_fullpath.c@}] (gdb) @end smallexample @subheading The @code{-file-list-shared-libraries} Command @findex -file-list-shared-libraries @subsubheading Synopsis @smallexample -file-list-shared-libraries [ @var{regexp} ] @end smallexample List the shared libraries in the program. With a regular expression @var{regexp}, only those libraries whose names match @var{regexp} are listed. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{info shared}. The fields have a similar meaning to the @code{=library-loaded} notification. The @code{ranges} field specifies the multiple segments belonging to this library. Each range has the following fields: @table @samp @item from The address defining the inclusive lower bound of the segment. @item to The address defining the exclusive upper bound of the segment. @end table @subsubheading Example @smallexample (gdb) -file-list-exec-source-files ^done,shared-libraries=[ @{id="/lib/libfoo.so",target-name="/lib/libfoo.so",host-name="/lib/libfoo.so",symbols-loaded="1",thread-group="i1",ranges=[@{from="0x72815989",to="0x728162c0"@}]@}, @{id="/lib/libbar.so",target-name="/lib/libbar.so",host-name="/lib/libbar.so",symbols-loaded="1",thread-group="i1",ranges=[@{from="0x76ee48c0",to="0x76ee9160"@}]@}] (gdb) @end smallexample @ignore @subheading The @code{-file-list-symbol-files} Command @findex -file-list-symbol-files @subsubheading Synopsis @smallexample -file-list-symbol-files @end smallexample List symbol files. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{info file} (part of it). @subsubheading Example N.A. @end ignore @subheading The @code{-file-symbol-file} Command @findex -file-symbol-file @subsubheading Synopsis @smallexample -file-symbol-file @var{file} @end smallexample Read symbol table info from the specified @var{file} argument. When used without arguments, clears @value{GDBN}'s symbol table info. No output is produced, except for a completion notification. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{symbol-file}. @subsubheading Example @smallexample (gdb) -file-symbol-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx ^done (gdb) @end smallexample @ignore @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Memory Overlay Commands @section @sc{gdb/mi} Memory Overlay Commands The memory overlay commands are not implemented. @c @subheading -overlay-auto @c @subheading -overlay-list-mapping-state @c @subheading -overlay-list-overlays @c @subheading -overlay-map @c @subheading -overlay-off @c @subheading -overlay-on @c @subheading -overlay-unmap @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Signal Handling Commands @section @sc{gdb/mi} Signal Handling Commands Signal handling commands are not implemented. @c @subheading -signal-handle @c @subheading -signal-list-handle-actions @c @subheading -signal-list-signal-types @end ignore @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Target Manipulation @section @sc{gdb/mi} Target Manipulation Commands @subheading The @code{-target-attach} Command @findex -target-attach @subsubheading Synopsis @smallexample -target-attach @var{pid} | @var{gid} | @var{file} @end smallexample Attach to a process @var{pid} or a file @var{file} outside of @value{GDBN}, or a thread group @var{gid}. If attaching to a thread group, the id previously returned by @samp{-list-thread-groups --available} must be used. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{attach}. @subsubheading Example @smallexample (gdb) -target-attach 34 =thread-created,id="1" *stopped,thread-id="1",frame=@{addr="0xb7f7e410",func="bar",args=[]@} ^done (gdb) @end smallexample @ignore @subheading The @code{-target-compare-sections} Command @findex -target-compare-sections @subsubheading Synopsis @smallexample -target-compare-sections [ @var{section} ] @end smallexample Compare data of section @var{section} on target to the exec file. Without the argument, all sections are compared. @subsubheading @value{GDBN} Command The @value{GDBN} equivalent is @samp{compare-sections}. @subsubheading Example N.A. @end ignore @subheading The @code{-target-detach} Command @findex -target-detach @subsubheading Synopsis @smallexample -target-detach [ @var{pid} | @var{gid} ] @end smallexample Detach from the remote target which normally resumes its execution. If either @var{pid} or @var{gid} is specified, detaches from either the specified process, or specified thread group. There's no output. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{detach}. @subsubheading Example @smallexample (gdb) -target-detach ^done (gdb) @end smallexample @subheading The @code{-target-disconnect} Command @findex -target-disconnect @subsubheading Synopsis @smallexample -target-disconnect @end smallexample Disconnect from the remote target. There's no output and the target is generally not resumed. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{disconnect}. @subsubheading Example @smallexample (gdb) -target-disconnect ^done (gdb) @end smallexample @subheading The @code{-target-download} Command @findex -target-download @subsubheading Synopsis @smallexample -target-download @end smallexample Loads the executable onto the remote target. It prints out an update message every half second, which includes the fields: @table @samp @item section The name of the section. @item section-sent The size of what has been sent so far for that section. @item section-size The size of the section. @item total-sent The total size of what was sent so far (the current and the previous sections). @item total-size The size of the overall executable to download. @end table @noindent Each message is sent as status record (@pxref{GDB/MI Output Syntax, , @sc{gdb/mi} Output Syntax}). In addition, it prints the name and size of the sections, as they are downloaded. These messages include the following fields: @table @samp @item section The name of the section. @item section-size The size of the section. @item total-size The size of the overall executable to download. @end table @noindent At the end, a summary is printed. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{load}. @subsubheading Example Note: each status message appears on a single line. Here the messages have been broken down so that they can fit onto a page. @smallexample (gdb) -target-download +download,@{section=".text",section-size="6668",total-size="9880"@} +download,@{section=".text",section-sent="512",section-size="6668", total-sent="512",total-size="9880"@} +download,@{section=".text",section-sent="1024",section-size="6668", total-sent="1024",total-size="9880"@} +download,@{section=".text",section-sent="1536",section-size="6668", total-sent="1536",total-size="9880"@} +download,@{section=".text",section-sent="2048",section-size="6668", total-sent="2048",total-size="9880"@} +download,@{section=".text",section-sent="2560",section-size="6668", total-sent="2560",total-size="9880"@} +download,@{section=".text",section-sent="3072",section-size="6668", total-sent="3072",total-size="9880"@} +download,@{section=".text",section-sent="3584",section-size="6668", total-sent="3584",total-size="9880"@} +download,@{section=".text",section-sent="4096",section-size="6668", total-sent="4096",total-size="9880"@} +download,@{section=".text",section-sent="4608",section-size="6668", total-sent="4608",total-size="9880"@} +download,@{section=".text",section-sent="5120",section-size="6668", total-sent="5120",total-size="9880"@} +download,@{section=".text",section-sent="5632",section-size="6668", total-sent="5632",total-size="9880"@} +download,@{section=".text",section-sent="6144",section-size="6668", total-sent="6144",total-size="9880"@} +download,@{section=".text",section-sent="6656",section-size="6668", total-sent="6656",total-size="9880"@} +download,@{section=".init",section-size="28",total-size="9880"@} +download,@{section=".fini",section-size="28",total-size="9880"@} +download,@{section=".data",section-size="3156",total-size="9880"@} +download,@{section=".data",section-sent="512",section-size="3156", total-sent="7236",total-size="9880"@} +download,@{section=".data",section-sent="1024",section-size="3156", total-sent="7748",total-size="9880"@} +download,@{section=".data",section-sent="1536",section-size="3156", total-sent="8260",total-size="9880"@} +download,@{section=".data",section-sent="2048",section-size="3156", total-sent="8772",total-size="9880"@} +download,@{section=".data",section-sent="2560",section-size="3156", total-sent="9284",total-size="9880"@} +download,@{section=".data",section-sent="3072",section-size="3156", total-sent="9796",total-size="9880"@} ^done,address="0x10004",load-size="9880",transfer-rate="6586", write-rate="429" (gdb) @end smallexample @ignore @subheading The @code{-target-exec-status} Command @findex -target-exec-status @subsubheading Synopsis @smallexample -target-exec-status @end smallexample Provide information on the state of the target (whether it is running or not, for instance). @subsubheading @value{GDBN} Command There's no equivalent @value{GDBN} command. @subsubheading Example N.A. @subheading The @code{-target-list-available-targets} Command @findex -target-list-available-targets @subsubheading Synopsis @smallexample -target-list-available-targets @end smallexample List the possible targets to connect to. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{help target}. @subsubheading Example N.A. @subheading The @code{-target-list-current-targets} Command @findex -target-list-current-targets @subsubheading Synopsis @smallexample -target-list-current-targets @end smallexample Describe the current target. @subsubheading @value{GDBN} Command The corresponding information is printed by @samp{info file} (among other things). @subsubheading Example N.A. @subheading The @code{-target-list-parameters} Command @findex -target-list-parameters @subsubheading Synopsis @smallexample -target-list-parameters @end smallexample @c ???? @end ignore @subsubheading @value{GDBN} Command No equivalent. @subsubheading Example N.A. @subheading The @code{-target-flash-erase} Command @findex -target-flash-erase @subsubheading Synopsis @smallexample -target-flash-erase @end smallexample Erases all known flash memory regions on the target. The corresponding @value{GDBN} command is @samp{flash-erase}. The output is a list of flash regions that have been erased, with starting addresses and memory region sizes. @smallexample (gdb) -target-flash-erase ^done,erased-regions=@{address="0x0",size="0x40000"@} (gdb) @end smallexample @subheading The @code{-target-select} Command @findex -target-select @subsubheading Synopsis @smallexample -target-select @var{type} @var{parameters @dots{}} @end smallexample Connect @value{GDBN} to the remote target. This command takes two args: @table @samp @item @var{type} The type of target, for instance @samp{remote}, etc. @item @var{parameters} Device names, host names and the like. @xref{Target Commands, , Commands for Managing Targets}, for more details. @end table The output is a connection notification, followed by the address at which the target program is, in the following form: @smallexample ^connected,addr="@var{address}",func="@var{function name}", args=[@var{arg list}] @end smallexample @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{target}. @subsubheading Example @smallexample (gdb) -target-select remote /dev/ttya ^connected,addr="0xfe00a300",func="??",args=[] (gdb) @end smallexample @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI File Transfer Commands @section @sc{gdb/mi} File Transfer Commands @subheading The @code{-target-file-put} Command @findex -target-file-put @subsubheading Synopsis @smallexample -target-file-put @var{hostfile} @var{targetfile} @end smallexample Copy file @var{hostfile} from the host system (the machine running @value{GDBN}) to @var{targetfile} on the target system. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{remote put}. @subsubheading Example @smallexample (gdb) -target-file-put localfile remotefile ^done (gdb) @end smallexample @subheading The @code{-target-file-get} Command @findex -target-file-get @subsubheading Synopsis @smallexample -target-file-get @var{targetfile} @var{hostfile} @end smallexample Copy file @var{targetfile} from the target system to @var{hostfile} on the host system. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{remote get}. @subsubheading Example @smallexample (gdb) -target-file-get remotefile localfile ^done (gdb) @end smallexample @subheading The @code{-target-file-delete} Command @findex -target-file-delete @subsubheading Synopsis @smallexample -target-file-delete @var{targetfile} @end smallexample Delete @var{targetfile} from the target system. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{remote delete}. @subsubheading Example @smallexample (gdb) -target-file-delete remotefile ^done (gdb) @end smallexample @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Ada Exceptions Commands @section Ada Exceptions @sc{gdb/mi} Commands @subheading The @code{-info-ada-exceptions} Command @findex -info-ada-exceptions @subsubheading Synopsis @smallexample -info-ada-exceptions [ @var{regexp}] @end smallexample List all Ada exceptions defined within the program being debugged. With a regular expression @var{regexp}, only those exceptions whose names match @var{regexp} are listed. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{info exceptions}. @subsubheading Result The result is a table of Ada exceptions. The following columns are defined for each exception: @table @samp @item name The name of the exception. @item address The address of the exception. @end table @subsubheading Example @smallexample -info-ada-exceptions aint ^done,ada-exceptions=@{nr_rows="2",nr_cols="2", hdr=[@{width="1",alignment="-1",col_name="name",colhdr="Name"@}, @{width="1",alignment="-1",col_name="address",colhdr="Address"@}], body=[@{name="constraint_error",address="0x0000000000613da0"@}, @{name="const.aint_global_e",address="0x0000000000613b00"@}]@} @end smallexample @subheading Catching Ada Exceptions The commands describing how to ask @value{GDBN} to stop when a program raises an exception are described at @ref{Ada Exception GDB/MI Catchpoint Commands}. @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Support Commands @section @sc{gdb/mi} Support Commands Since new commands and features get regularly added to @sc{gdb/mi}, some commands are available to help front-ends query the debugger about support for these capabilities. Similarly, it is also possible to query @value{GDBN} about target support of certain features. @subheading The @code{-info-gdb-mi-command} Command @cindex @code{-info-gdb-mi-command} @findex -info-gdb-mi-command @subsubheading Synopsis @smallexample -info-gdb-mi-command @var{cmd_name} @end smallexample Query support for the @sc{gdb/mi} command named @var{cmd_name}. Note that the dash (@code{-}) starting all @sc{gdb/mi} commands is technically not part of the command name (@pxref{GDB/MI Input Syntax}), and thus should be omitted in @var{cmd_name}. However, for ease of use, this command also accepts the form with the leading dash. @subsubheading @value{GDBN} Command There is no corresponding @value{GDBN} command. @subsubheading Result The result is a tuple. There is currently only one field: @table @samp @item exists This field is equal to @code{"true"} if the @sc{gdb/mi} command exists, @code{"false"} otherwise. @end table @subsubheading Example Here is an example where the @sc{gdb/mi} command does not exist: @smallexample -info-gdb-mi-command unsupported-command ^done,command=@{exists="false"@} @end smallexample @noindent And here is an example where the @sc{gdb/mi} command is known to the debugger: @smallexample -info-gdb-mi-command symbol-list-lines ^done,command=@{exists="true"@} @end smallexample @subheading The @code{-list-features} Command @findex -list-features @cindex supported @sc{gdb/mi} features, list Returns a list of particular features of the MI protocol that this version of gdb implements. A feature can be a command, or a new field in an output of some command, or even an important bugfix. While a frontend can sometimes detect presence of a feature at runtime, it is easier to perform detection at debugger startup. The command returns a list of strings, with each string naming an available feature. Each returned string is just a name, it does not have any internal structure. The list of possible feature names is given below. Example output: @smallexample (gdb) -list-features ^done,result=["feature1","feature2"] @end smallexample The current list of features is: @ftable @samp @item frozen-varobjs Indicates support for the @code{-var-set-frozen} command, as well as possible presence of the @code{frozen} field in the output of @code{-varobj-create}. @item pending-breakpoints Indicates support for the @option{-f} option to the @code{-break-insert} command. @item python Indicates Python scripting support, Python-based pretty-printing commands, and possible presence of the @samp{display_hint} field in the output of @code{-var-list-children} @item thread-info Indicates support for the @code{-thread-info} command. @item data-read-memory-bytes Indicates support for the @code{-data-read-memory-bytes} and the @code{-data-write-memory-bytes} commands. @item breakpoint-notifications Indicates that changes to breakpoints and breakpoints created via the CLI will be announced via async records. @item ada-task-info Indicates support for the @code{-ada-task-info} command. @item language-option Indicates that all @sc{gdb/mi} commands accept the @option{--language} option (@pxref{Context management}). @item info-gdb-mi-command Indicates support for the @code{-info-gdb-mi-command} command. @item undefined-command-error-code Indicates support for the "undefined-command" error code in error result records, produced when trying to execute an undefined @sc{gdb/mi} command (@pxref{GDB/MI Result Records}). @item exec-run-start-option Indicates that the @code{-exec-run} command supports the @option{--start} option (@pxref{GDB/MI Program Execution}). @item data-disassemble-a-option Indicates that the @code{-data-disassemble} command supports the @option{-a} option (@pxref{GDB/MI Data Manipulation}). @end ftable @subheading The @code{-list-target-features} Command @findex -list-target-features Returns a list of particular features that are supported by the target. Those features affect the permitted MI commands, but unlike the features reported by the @code{-list-features} command, the features depend on which target GDB is using at the moment. Whenever a target can change, due to commands such as @code{-target-select}, @code{-target-attach} or @code{-exec-run}, the list of target features may change, and the frontend should obtain it again. Example output: @smallexample (gdb) -list-target-features ^done,result=["async"] @end smallexample The current list of features is: @table @samp @item async Indicates that the target is capable of asynchronous command execution, which means that @value{GDBN} will accept further commands while the target is running. @item reverse Indicates that the target is capable of reverse execution. @xref{Reverse Execution}, for more information. @end table @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% @node GDB/MI Miscellaneous Commands @section Miscellaneous @sc{gdb/mi} Commands @c @subheading -gdb-complete @subheading The @code{-gdb-exit} Command @findex -gdb-exit @subsubheading Synopsis @smallexample -gdb-exit @end smallexample Exit @value{GDBN} immediately. @subsubheading @value{GDBN} Command Approximately corresponds to @samp{quit}. @subsubheading Example @smallexample (gdb) -gdb-exit ^exit @end smallexample @ignore @subheading The @code{-exec-abort} Command @findex -exec-abort @subsubheading Synopsis @smallexample -exec-abort @end smallexample Kill the inferior running program. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{kill}. @subsubheading Example N.A. @end ignore @subheading The @code{-gdb-set} Command @findex -gdb-set @subsubheading Synopsis @smallexample -gdb-set @end smallexample Set an internal @value{GDBN} variable. @c IS THIS A DOLLAR VARIABLE? OR SOMETHING LIKE ANNOTATE ????? @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{set}. @subsubheading Example @smallexample (gdb) -gdb-set $foo=3 ^done (gdb) @end smallexample @subheading The @code{-gdb-show} Command @findex -gdb-show @subsubheading Synopsis @smallexample -gdb-show @end smallexample Show the current value of a @value{GDBN} variable. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{show}. @subsubheading Example @smallexample (gdb) -gdb-show annotate ^done,value="0" (gdb) @end smallexample @c @subheading -gdb-source @subheading The @code{-gdb-version} Command @findex -gdb-version @subsubheading Synopsis @smallexample -gdb-version @end smallexample Show version information for @value{GDBN}. Used mostly in testing. @subsubheading @value{GDBN} Command The @value{GDBN} equivalent is @samp{show version}. @value{GDBN} by default shows this information when you start an interactive session. @subsubheading Example @c This example modifies the actual output from GDB to avoid overfull @c box in TeX. @smallexample (gdb) -gdb-version ~GNU gdb 5.2.1 ~Copyright 2000 Free Software Foundation, Inc. ~GDB is free software, covered by the GNU General Public License, and ~you are welcome to change it and/or distribute copies of it under ~ certain conditions. ~Type "show copying" to see the conditions. ~There is absolutely no warranty for GDB. Type "show warranty" for ~ details. ~This GDB was configured as "--host=sparc-sun-solaris2.5.1 --target=ppc-eabi". ^done (gdb) @end smallexample @subheading The @code{-list-thread-groups} Command @findex -list-thread-groups @subheading Synopsis @smallexample -list-thread-groups [ --available ] [ --recurse 1 ] [ @var{group} ... ] @end smallexample Lists thread groups (@pxref{Thread groups}). When a single thread group is passed as the argument, lists the children of that group. When several thread group are passed, lists information about those thread groups. Without any parameters, lists information about all top-level thread groups. Normally, thread groups that are being debugged are reported. With the @samp{--available} option, @value{GDBN} reports thread groups available on the target. The output of this command may have either a @samp{threads} result or a @samp{groups} result. The @samp{thread} result has a list of tuples as value, with each tuple describing a thread (@pxref{GDB/MI Thread Information}). The @samp{groups} result has a list of tuples as value, each tuple describing a thread group. If top-level groups are requested (that is, no parameter is passed), or when several groups are passed, the output always has a @samp{groups} result. The format of the @samp{group} result is described below. To reduce the number of roundtrips it's possible to list thread groups together with their children, by passing the @samp{--recurse} option and the recursion depth. Presently, only recursion depth of 1 is permitted. If this option is present, then every reported thread group will also include its children, either as @samp{group} or @samp{threads} field. In general, any combination of option and parameters is permitted, with the following caveats: @itemize @bullet @item When a single thread group is passed, the output will typically be the @samp{threads} result. Because threads may not contain anything, the @samp{recurse} option will be ignored. @item When the @samp{--available} option is passed, limited information may be available. In particular, the list of threads of a process might be inaccessible. Further, specifying specific thread groups might not give any performance advantage over listing all thread groups. The frontend should assume that @samp{-list-thread-groups --available} is always an expensive operation and cache the results. @end itemize The @samp{groups} result is a list of tuples, where each tuple may have the following fields: @table @code @item id Identifier of the thread group. This field is always present. The identifier is an opaque string; frontends should not try to convert it to an integer, even though it might look like one. @item type The type of the thread group. At present, only @samp{process} is a valid type. @item pid The target-specific process identifier. This field is only present for thread groups of type @samp{process} and only if the process exists. @item exit-code The exit code of this group's last exited thread, formatted in octal. This field is only present for thread groups of type @samp{process} and only if the process is not running. @item num_children The number of children this thread group has. This field may be absent for an available thread group. @item threads This field has a list of tuples as value, each tuple describing a thread. It may be present if the @samp{--recurse} option is specified, and it's actually possible to obtain the threads. @item cores This field is a list of integers, each identifying a core that one thread of the group is running on. This field may be absent if such information is not available. @item executable The name of the executable file that corresponds to this thread group. The field is only present for thread groups of type @samp{process}, and only if there is a corresponding executable file. @end table @subheading Example @smallexample @value{GDBP} -list-thread-groups ^done,groups=[@{id="17",type="process",pid="yyy",num_children="2"@}] -list-thread-groups 17 ^done,threads=[@{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)", frame=@{level="0",addr="0xffffe410",func="__kernel_vsyscall",args=[]@},state="running"@}, @{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)", frame=@{level="0",addr="0x0804891f",func="foo",args=[@{name="i",value="10"@}], file="/tmp/a.c",fullname="/tmp/a.c",line="158",arch="i386:x86_64"@},state="running"@}]] -list-thread-groups --available ^done,groups=[@{id="17",type="process",pid="yyy",num_children="2",cores=[1,2]@}] -list-thread-groups --available --recurse 1 ^done,groups=[@{id="17", types="process",pid="yyy",num_children="2",cores=[1,2], threads=[@{id="1",target-id="Thread 0xb7e14b90",cores=[1]@}, @{id="2",target-id="Thread 0xb7e14b90",cores=[2]@}]@},..] -list-thread-groups --available --recurse 1 17 18 ^done,groups=[@{id="17", types="process",pid="yyy",num_children="2",cores=[1,2], threads=[@{id="1",target-id="Thread 0xb7e14b90",cores=[1]@}, @{id="2",target-id="Thread 0xb7e14b90",cores=[2]@}]@},...] @end smallexample @subheading The @code{-info-os} Command @findex -info-os @subsubheading Synopsis @smallexample -info-os [ @var{type} ] @end smallexample If no argument is supplied, the command returns a table of available operating-system-specific information types. If one of these types is supplied as an argument @var{type}, then the command returns a table of data of that type. The types of information available depend on the target operating system. @subsubheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{info os}. @subsubheading Example When run on a @sc{gnu}/Linux system, the output will look something like this: @smallexample @value{GDBP} -info-os ^done,OSDataTable=@{nr_rows="10",nr_cols="3", hdr=[@{width="10",alignment="-1",col_name="col0",colhdr="Type"@}, @{width="10",alignment="-1",col_name="col1",colhdr="Description"@}, @{width="10",alignment="-1",col_name="col2",colhdr="Title"@}], body=[item=@{col0="cpus",col1="Listing of all cpus/cores on the system", col2="CPUs"@}, item=@{col0="files",col1="Listing of all file descriptors", col2="File descriptors"@}, item=@{col0="modules",col1="Listing of all loaded kernel modules", col2="Kernel modules"@}, item=@{col0="msg",col1="Listing of all message queues", col2="Message queues"@}, item=@{col0="processes",col1="Listing of all processes", col2="Processes"@}, item=@{col0="procgroups",col1="Listing of all process groups", col2="Process groups"@}, item=@{col0="semaphores",col1="Listing of all semaphores", col2="Semaphores"@}, item=@{col0="shm",col1="Listing of all shared-memory regions", col2="Shared-memory regions"@}, item=@{col0="sockets",col1="Listing of all internet-domain sockets", col2="Sockets"@}, item=@{col0="threads",col1="Listing of all threads", col2="Threads"@}] @value{GDBP} -info-os processes ^done,OSDataTable=@{nr_rows="190",nr_cols="4", hdr=[@{width="10",alignment="-1",col_name="col0",colhdr="pid"@}, @{width="10",alignment="-1",col_name="col1",colhdr="user"@}, @{width="10",alignment="-1",col_name="col2",colhdr="command"@}, @{width="10",alignment="-1",col_name="col3",colhdr="cores"@}], body=[item=@{col0="1",col1="root",col2="/sbin/init",col3="0"@}, item=@{col0="2",col1="root",col2="[kthreadd]",col3="1"@}, item=@{col0="3",col1="root",col2="[ksoftirqd/0]",col3="0"@}, ... item=@{col0="26446",col1="stan",col2="bash",col3="0"@}, item=@{col0="28152",col1="stan",col2="bash",col3="1"@}]@} (gdb) @end smallexample (Note that the MI output here includes a @code{"Title"} column that does not appear in command-line @code{info os}; this column is useful for MI clients that want to enumerate the types of data, such as in a popup menu, but is needless clutter on the command line, and @code{info os} omits it.) @subheading The @code{-add-inferior} Command @findex -add-inferior @subheading Synopsis @smallexample -add-inferior @end smallexample Creates a new inferior (@pxref{Inferiors Connections and Programs}). The created inferior is not associated with any executable. Such association may be established with the @samp{-file-exec-and-symbols} command (@pxref{GDB/MI File Commands}). The command response has a single field, @samp{inferior}, whose value is the identifier of the thread group corresponding to the new inferior. @subheading Example @smallexample @value{GDBP} -add-inferior ^done,inferior="i3" @end smallexample @subheading The @code{-interpreter-exec} Command @findex -interpreter-exec @subheading Synopsis @smallexample -interpreter-exec @var{interpreter} @var{command} @end smallexample @anchor{-interpreter-exec} Execute the specified @var{command} in the given @var{interpreter}. @subheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{interpreter-exec}. @subheading Example @smallexample (gdb) -interpreter-exec console "break main" &"During symbol reading, couldn't parse type; debugger out of date?.\n" &"During symbol reading, bad structure-type format.\n" ~"Breakpoint 1 at 0x8074fc6: file ../../src/gdb/main.c, line 743.\n" ^done (gdb) @end smallexample @subheading The @code{-inferior-tty-set} Command @findex -inferior-tty-set @subheading Synopsis @smallexample -inferior-tty-set /dev/pts/1 @end smallexample Set terminal for future runs of the program being debugged. @subheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{set inferior-tty} /dev/pts/1. @subheading Example @smallexample (gdb) -inferior-tty-set /dev/pts/1 ^done (gdb) @end smallexample @subheading The @code{-inferior-tty-show} Command @findex -inferior-tty-show @subheading Synopsis @smallexample -inferior-tty-show @end smallexample Show terminal for future runs of program being debugged. @subheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{show inferior-tty}. @subheading Example @smallexample (gdb) -inferior-tty-set /dev/pts/1 ^done (gdb) -inferior-tty-show ^done,inferior_tty_terminal="/dev/pts/1" (gdb) @end smallexample @subheading The @code{-enable-timings} Command @findex -enable-timings @subheading Synopsis @smallexample -enable-timings [yes | no] @end smallexample Toggle the printing of the wallclock, user and system times for an MI command as a field in its output. This command is to help frontend developers optimize the performance of their code. No argument is equivalent to @samp{yes}. @subheading @value{GDBN} Command No equivalent. @subheading Example @smallexample (gdb) -enable-timings ^done (gdb) -break-insert main ^done,bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y", addr="0x080484ed",func="main",file="myprog.c", fullname="/home/nickrob/myprog.c",line="73",thread-groups=["i1"], times="0"@}, time=@{wallclock="0.05185",user="0.00800",system="0.00000"@} (gdb) -enable-timings no ^done (gdb) -exec-run ^running (gdb) *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0", frame=@{addr="0x080484ed",func="main",args=[@{name="argc",value="1"@}, @{name="argv",value="0xbfb60364"@}],file="myprog.c", fullname="/home/nickrob/myprog.c",line="73",arch="i386:x86_64"@} (gdb) @end smallexample @subheading The @code{-complete} Command @findex -complete @subheading Synopsis @smallexample -complete @var{command} @end smallexample Show a list of completions for partially typed CLI @var{command}. This command is intended for @sc{gdb/mi} frontends that cannot use two separate CLI and MI channels --- for example: because of lack of PTYs like on Windows or because @value{GDBN} is used remotely via a SSH connection. @subheading Result The result consists of two or three fields: @table @samp @item completion This field contains the completed @var{command}. If @var{command} has no known completions, this field is omitted. @item matches This field contains a (possibly empty) array of matches. It is always present. @item max_completions_reached This field contains @code{1} if number of known completions is above @code{max-completions} limit (@pxref{Completion}), otherwise it contains @code{0}. It is always present. @end table @subheading @value{GDBN} Command The corresponding @value{GDBN} command is @samp{complete}. @subheading Example @smallexample (gdb) -complete br ^done,completion="break", matches=["break","break-range"], max_completions_reached="0" (gdb) -complete "b ma" ^done,completion="b ma", matches=["b madvise","b main"],max_completions_reached="0" (gdb) -complete "b push_b" ^done,completion="b push_back(", matches=[ "b A::push_back(void*)", "b std::string::push_back(char)", "b std::vector<int, std::allocator<int> >::push_back(int&&)"], max_completions_reached="0" (gdb) -complete "nonexist" ^done,matches=[],max_completions_reached="0" (gdb) @end smallexample @node Annotations @chapter @value{GDBN} Annotations This chapter describes annotations in @value{GDBN}. Annotations were designed to interface @value{GDBN} to graphical user interfaces or other similar programs which want to interact with @value{GDBN} at a relatively high level. The annotation mechanism has largely been superseded by @sc{gdb/mi} (@pxref{GDB/MI}). @ignore This is Edition @value{EDITION}, @value{DATE}. @end ignore @menu * Annotations Overview:: What annotations are; the general syntax. * Server Prefix:: Issuing a command without affecting user state. * Prompting:: Annotations marking @value{GDBN}'s need for input. * Errors:: Annotations for error messages. * Invalidation:: Some annotations describe things now invalid. * Annotations for Running:: Whether the program is running, how it stopped, etc. * Source Annotations:: Annotations describing source code. @end menu @node Annotations Overview @section What is an Annotation? @cindex annotations Annotations start with a newline character, two @samp{control-z} characters, and the name of the annotation. If there is no additional information associated with this annotation, the name of the annotation is followed immediately by a newline. If there is additional information, the name of the annotation is followed by a space, the additional information, and a newline. The additional information cannot contain newline characters. Any output not beginning with a newline and two @samp{control-z} characters denotes literal output from @value{GDBN}. Currently there is no need for @value{GDBN} to output a newline followed by two @samp{control-z} characters, but if there was such a need, the annotations could be extended with an @samp{escape} annotation which means those three characters as output. The annotation @var{level}, which is specified using the @option{--annotate} command line option (@pxref{Mode Options}), controls how much information @value{GDBN} prints together with its prompt, values of expressions, source lines, and other types of output. Level 0 is for no annotations, level 1 is for use when @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 3 is the maximum annotation suitable for programs that control @value{GDBN}, and level 2 annotations have been made obsolete (@pxref{Limitations, , Limitations of the Annotation Interface, annotate, GDB's Obsolete Annotations}). @table @code @kindex set annotate @item set annotate @var{level} The @value{GDBN} command @code{set annotate} sets the level of annotations to the specified @var{level}. @item show annotate @kindex show annotate Show the current annotation level. @end table This chapter describes level 3 annotations. A simple example of starting up @value{GDBN} with annotations is: @smallexample $ @kbd{gdb --annotate=3} GNU gdb 6.0 Copyright 2003 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "i386-pc-linux-gnu" ^Z^Zpre-prompt (@value{GDBP}) ^Z^Zprompt @kbd{quit} ^Z^Zpost-prompt $ @end smallexample Here @samp{quit} is input to @value{GDBN}; the rest is output from @value{GDBN}. The three lines beginning @samp{^Z^Z} (where @samp{^Z} denotes a @samp{control-z} character) are annotations; the rest is output from @value{GDBN}. @node Server Prefix @section The Server Prefix @cindex server prefix If you prefix a command with @samp{server } then it will not affect the command history, nor will it affect @value{GDBN}'s notion of which command to repeat if @key{RET} is pressed on a line by itself. This means that commands can be run behind a user's back by a front-end in a transparent manner. The @code{server } prefix does not affect the recording of values into the value history; to print a value without recording it into the value history, use the @code{output} command instead of the @code{print} command. Using this prefix also disables confirmation requests (@pxref{confirmation requests}). @node Prompting @section Annotation for @value{GDBN} Input @cindex annotations for prompts When @value{GDBN} prompts for input, it annotates this fact so it is possible to know when to send output, when the output from a given command is over, etc. Different kinds of input each have a different @dfn{input type}. Each input type has three annotations: a @code{pre-} annotation, which denotes the beginning of any prompt which is being output, a plain annotation, which denotes the end of the prompt, and then a @code{post-} annotation which denotes the end of any echo which may (or may not) be associated with the input. For example, the @code{prompt} input type features the following annotations: @smallexample ^Z^Zpre-prompt ^Z^Zprompt ^Z^Zpost-prompt @end smallexample The input types are @table @code @findex pre-prompt annotation @findex prompt annotation @findex post-prompt annotation @item prompt When @value{GDBN} is prompting for a command (the main @value{GDBN} prompt). @findex pre-commands annotation @findex commands annotation @findex post-commands annotation @item commands When @value{GDBN} prompts for a set of commands, like in the @code{commands} command. The annotations are repeated for each command which is input. @findex pre-overload-choice annotation @findex overload-choice annotation @findex post-overload-choice annotation @item overload-choice When @value{GDBN} wants the user to select between various overloaded functions. @findex pre-query annotation @findex query annotation @findex post-query annotation @item query When @value{GDBN} wants the user to confirm a potentially dangerous operation. @findex pre-prompt-for-continue annotation @findex prompt-for-continue annotation @findex post-prompt-for-continue annotation @item prompt-for-continue When @value{GDBN} is asking the user to press return to continue. Note: Don't expect this to work well; instead use @code{set height 0} to disable prompting. This is because the counting of lines is buggy in the presence of annotations. @end table @node Errors @section Errors @cindex annotations for errors, warnings and interrupts @findex quit annotation @smallexample ^Z^Zquit @end smallexample This annotation occurs right before @value{GDBN} responds to an interrupt. @findex error annotation @smallexample ^Z^Zerror @end smallexample This annotation occurs right before @value{GDBN} responds to an error. Quit and error annotations indicate that any annotations which @value{GDBN} was in the middle of may end abruptly. For example, if a @code{value-history-begin} annotation is followed by a @code{error}, one cannot expect to receive the matching @code{value-history-end}. One cannot expect not to receive it either, however; an error annotation does not necessarily mean that @value{GDBN} is immediately returning all the way to the top level. @findex error-begin annotation A quit or error annotation may be preceded by @smallexample ^Z^Zerror-begin @end smallexample Any output between that and the quit or error annotation is the error message. Warning messages are not yet annotated. @c If we want to change that, need to fix warning(), type_error(), @c range_error(), and possibly other places. @node Invalidation @section Invalidation Notices @cindex annotations for invalidation messages The following annotations say that certain pieces of state may have changed. @table @code @findex frames-invalid annotation @item ^Z^Zframes-invalid The frames (for example, output from the @code{backtrace} command) may have changed. @findex breakpoints-invalid annotation @item ^Z^Zbreakpoints-invalid The breakpoints may have changed. For example, the user just added or deleted a breakpoint. @end table @node Annotations for Running @section Running the Program @cindex annotations for running programs @findex starting annotation @findex stopping annotation When the program starts executing due to a @value{GDBN} command such as @code{step} or @code{continue}, @smallexample ^Z^Zstarting @end smallexample is output. When the program stops, @smallexample ^Z^Zstopped @end smallexample is output. Before the @code{stopped} annotation, a variety of annotations describe how the program stopped. @table @code @findex exited annotation @item ^Z^Zexited @var{exit-status} The program exited, and @var{exit-status} is the exit status (zero for successful exit, otherwise nonzero). @findex signalled annotation @findex signal-name annotation @findex signal-name-end annotation @findex signal-string annotation @findex signal-string-end annotation @item ^Z^Zsignalled The program exited with a signal. After the @code{^Z^Zsignalled}, the annotation continues: @smallexample @var{intro-text} ^Z^Zsignal-name @var{name} ^Z^Zsignal-name-end @var{middle-text} ^Z^Zsignal-string @var{string} ^Z^Zsignal-string-end @var{end-text} @end smallexample @noindent where @var{name} is the name of the signal, such as @code{SIGILL} or @code{SIGSEGV}, and @var{string} is the explanation of the signal, such as @code{Illegal Instruction} or @code{Segmentation fault}. The arguments @var{intro-text}, @var{middle-text}, and @var{end-text} are for the user's benefit and have no particular format. @findex signal annotation @item ^Z^Zsignal The syntax of this annotation is just like @code{signalled}, but @value{GDBN} is just saying that the program received the signal, not that it was terminated with it. @findex breakpoint annotation @item ^Z^Zbreakpoint @var{number} The program hit breakpoint number @var{number}. @findex watchpoint annotation @item ^Z^Zwatchpoint @var{number} The program hit watchpoint number @var{number}. @end table @node Source Annotations @section Displaying Source @cindex annotations for source display @findex source annotation The following annotation is used instead of displaying source code: @smallexample ^Z^Zsource @var{filename}:@var{line}:@var{character}:@var{middle}:@var{addr} @end smallexample where @var{filename} is an absolute file name indicating which source file, @var{line} is the line number within that file (where 1 is the first line in the file), @var{character} is the character position within the file (where 0 is the first character in the file) (for most debug formats this will necessarily point to the beginning of a line), @var{middle} is @samp{middle} if @var{addr} is in the middle of the line, or @samp{beg} if @var{addr} is at the beginning of the line, and @var{addr} is the address in the target program associated with the source which is being displayed. The @var{addr} is in the form @samp{0x} followed by one or more lowercase hex digits (note that this does not depend on the language). @node JIT Interface @chapter JIT Compilation Interface @cindex just-in-time compilation @cindex JIT compilation interface This chapter documents @value{GDBN}'s @dfn{just-in-time} (JIT) compilation interface. A JIT compiler is a program or library that generates native executable code at runtime and executes it, usually in order to achieve good performance while maintaining platform independence. Programs that use JIT compilation are normally difficult to debug because portions of their code are generated at runtime, instead of being loaded from object files, which is where @value{GDBN} normally finds the program's symbols and debug information. In order to debug programs that use JIT compilation, @value{GDBN} has an interface that allows the program to register in-memory symbol files with @value{GDBN} at runtime. If you are using @value{GDBN} to debug a program that uses this interface, then it should work transparently so long as you have not stripped the binary. If you are developing a JIT compiler, then the interface is documented in the rest of this chapter. At this time, the only known client of this interface is the LLVM JIT. Broadly speaking, the JIT interface mirrors the dynamic loader interface. The JIT compiler communicates with @value{GDBN} by writing data into a global variable and calling a function at a well-known symbol. When @value{GDBN} attaches, it reads a linked list of symbol files from the global variable to find existing code, and puts a breakpoint in the function so that it can find out about additional code. @menu * Declarations:: Relevant C struct declarations * Registering Code:: Steps to register code * Unregistering Code:: Steps to unregister code * Custom Debug Info:: Emit debug information in a custom format @end menu @node Declarations @section JIT Declarations These are the relevant struct declarations that a C program should include to implement the interface: @smallexample typedef enum @{ JIT_NOACTION = 0, JIT_REGISTER_FN, JIT_UNREGISTER_FN @} jit_actions_t; struct jit_code_entry @{ struct jit_code_entry *next_entry; struct jit_code_entry *prev_entry; const char *symfile_addr; uint64_t symfile_size; @}; struct jit_descriptor @{ uint32_t version; /* This type should be jit_actions_t, but we use uint32_t to be explicit about the bitwidth. */ uint32_t action_flag; struct jit_code_entry *relevant_entry; struct jit_code_entry *first_entry; @}; /* GDB puts a breakpoint in this function. */ void __attribute__((noinline)) __jit_debug_register_code() @{ @}; /* Make sure to specify the version statically, because the debugger may check the version before we can set it. */ struct jit_descriptor __jit_debug_descriptor = @{ 1, 0, 0, 0 @}; @end smallexample If the JIT is multi-threaded, then it is important that the JIT synchronize any modifications to this global data properly, which can easily be done by putting a global mutex around modifications to these structures. @node Registering Code @section Registering Code To register code with @value{GDBN}, the JIT should follow this protocol: @itemize @bullet @item Generate an object file in memory with symbols and other desired debug information. The file must include the virtual addresses of the sections. @item Create a code entry for the file, which gives the start and size of the symbol file. @item Add it to the linked list in the JIT descriptor. @item Point the relevant_entry field of the descriptor at the entry. @item Set @code{action_flag} to @code{JIT_REGISTER} and call @code{__jit_debug_register_code}. @end itemize When @value{GDBN} is attached and the breakpoint fires, @value{GDBN} uses the @code{relevant_entry} pointer so it doesn't have to walk the list looking for new code. However, the linked list must still be maintained in order to allow @value{GDBN} to attach to a running process and still find the symbol files. @node Unregistering Code @section Unregistering Code If code is freed, then the JIT should use the following protocol: @itemize @bullet @item Remove the code entry corresponding to the code from the linked list. @item Point the @code{relevant_entry} field of the descriptor at the code entry. @item Set @code{action_flag} to @code{JIT_UNREGISTER} and call @code{__jit_debug_register_code}. @end itemize If the JIT frees or recompiles code without unregistering it, then @value{GDBN} and the JIT will leak the memory used for the associated symbol files. @node Custom Debug Info @section Custom Debug Info @cindex custom JIT debug info @cindex JIT debug info reader Generating debug information in platform-native file formats (like ELF or COFF) may be an overkill for JIT compilers; especially if all the debug info is used for is displaying a meaningful backtrace. The issue can be resolved by having the JIT writers decide on a debug info format and also provide a reader that parses the debug info generated by the JIT compiler. This section gives a brief overview on writing such a parser. More specific details can be found in the source file @file{gdb/jit-reader.in}, which is also installed as a header at @file{@var{includedir}/gdb/jit-reader.h} for easy inclusion. The reader is implemented as a shared object (so this functionality is not available on platforms which don't allow loading shared objects at runtime). Two @value{GDBN} commands, @code{jit-reader-load} and @code{jit-reader-unload} are provided, to be used to load and unload the readers from a preconfigured directory. Once loaded, the shared object is used the parse the debug information emitted by the JIT compiler. @menu * Using JIT Debug Info Readers:: How to use supplied readers correctly * Writing JIT Debug Info Readers:: Creating a debug-info reader @end menu @node Using JIT Debug Info Readers @subsection Using JIT Debug Info Readers @kindex jit-reader-load @kindex jit-reader-unload Readers can be loaded and unloaded using the @code{jit-reader-load} and @code{jit-reader-unload} commands. @table @code @item jit-reader-load @var{reader} Load the JIT reader named @var{reader}, which is a shared object specified as either an absolute or a relative file name. In the latter case, @value{GDBN} will try to load the reader from a pre-configured directory, usually @file{@var{libdir}/gdb/} on a UNIX system (here @var{libdir} is the system library directory, often @file{/usr/local/lib}). Only one reader can be active at a time; trying to load a second reader when one is already loaded will result in @value{GDBN} reporting an error. A new JIT reader can be loaded by first unloading the current one using @code{jit-reader-unload} and then invoking @code{jit-reader-load}. @item jit-reader-unload Unload the currently loaded JIT reader. @end table @node Writing JIT Debug Info Readers @subsection Writing JIT Debug Info Readers @cindex writing JIT debug info readers As mentioned, a reader is essentially a shared object conforming to a certain ABI. This ABI is described in @file{jit-reader.h}. @file{jit-reader.h} defines the structures, macros and functions required to write a reader. It is installed (along with @value{GDBN}), in @file{@var{includedir}/gdb} where @var{includedir} is the system include directory. Readers need to be released under a GPL compatible license. A reader can be declared as released under such a license by placing the macro @code{GDB_DECLARE_GPL_COMPATIBLE_READER} in a source file. The entry point for readers is the symbol @code{gdb_init_reader}, which is expected to be a function with the prototype @findex gdb_init_reader @smallexample extern struct gdb_reader_funcs *gdb_init_reader (void); @end smallexample @cindex @code{struct gdb_reader_funcs} @code{struct gdb_reader_funcs} contains a set of pointers to callback functions. These functions are executed to read the debug info generated by the JIT compiler (@code{read}), to unwind stack frames (@code{unwind}) and to create canonical frame IDs (@code{get_frame_id}). It also has a callback that is called when the reader is being unloaded (@code{destroy}). The struct looks like this @smallexample struct gdb_reader_funcs @{ /* Must be set to GDB_READER_INTERFACE_VERSION. */ int reader_version; /* For use by the reader. */ void *priv_data; gdb_read_debug_info *read; gdb_unwind_frame *unwind; gdb_get_frame_id *get_frame_id; gdb_destroy_reader *destroy; @}; @end smallexample @cindex @code{struct gdb_symbol_callbacks} @cindex @code{struct gdb_unwind_callbacks} The callbacks are provided with another set of callbacks by @value{GDBN} to do their job. For @code{read}, these callbacks are passed in a @code{struct gdb_symbol_callbacks} and for @code{unwind} and @code{get_frame_id}, in a @code{struct gdb_unwind_callbacks}. @code{struct gdb_symbol_callbacks} has callbacks to create new object files and new symbol tables inside those object files. @code{struct gdb_unwind_callbacks} has callbacks to read registers off the current frame and to write out the values of the registers in the previous frame. Both have a callback (@code{target_read}) to read bytes off the target's address space. @node In-Process Agent @chapter In-Process Agent @cindex debugging agent The traditional debugging model is conceptually low-speed, but works fine, because most bugs can be reproduced in debugging-mode execution. However, as multi-core or many-core processors are becoming mainstream, and multi-threaded programs become more and more popular, there should be more and more bugs that only manifest themselves at normal-mode execution, for example, thread races, because debugger's interference with the program's timing may conceal the bugs. On the other hand, in some applications, it is not feasible for the debugger to interrupt the program's execution long enough for the developer to learn anything helpful about its behavior. If the program's correctness depends on its real-time behavior, delays introduced by a debugger might cause the program to fail, even when the code itself is correct. It is useful to be able to observe the program's behavior without interrupting it. Therefore, traditional debugging model is too intrusive to reproduce some bugs. In order to reduce the interference with the program, we can reduce the number of operations performed by debugger. The @dfn{In-Process Agent}, a shared library, is running within the same process with inferior, and is able to perform some debugging operations itself. As a result, debugger is only involved when necessary, and performance of debugging can be improved accordingly. Note that interference with program can be reduced but can't be removed completely, because the in-process agent will still stop or slow down the program. The in-process agent can interpret and execute Agent Expressions (@pxref{Agent Expressions}) during performing debugging operations. The agent expressions can be used for different purposes, such as collecting data in tracepoints, and condition evaluation in breakpoints. @anchor{Control Agent} You can control whether the in-process agent is used as an aid for debugging with the following commands: @table @code @kindex set agent on @item set agent on Causes the in-process agent to perform some operations on behalf of the debugger. Just which operations requested by the user will be done by the in-process agent depends on the its capabilities. For example, if you request to evaluate breakpoint conditions in the in-process agent, and the in-process agent has such capability as well, then breakpoint conditions will be evaluated in the in-process agent. @kindex set agent off @item set agent off Disables execution of debugging operations by the in-process agent. All of the operations will be performed by @value{GDBN}. @kindex show agent @item show agent Display the current setting of execution of debugging operations by the in-process agent. @end table @menu * In-Process Agent Protocol:: @end menu @node In-Process Agent Protocol @section In-Process Agent Protocol @cindex in-process agent protocol The in-process agent is able to communicate with both @value{GDBN} and GDBserver (@pxref{In-Process Agent}). This section documents the protocol used for communications between @value{GDBN} or GDBserver and the IPA. In general, @value{GDBN} or GDBserver sends commands (@pxref{IPA Protocol Commands}) and data to in-process agent, and then in-process agent replies back with the return result of the command, or some other information. The data sent to in-process agent is composed of primitive data types, such as 4-byte or 8-byte type, and composite types, which are called objects (@pxref{IPA Protocol Objects}). @menu * IPA Protocol Objects:: * IPA Protocol Commands:: @end menu @node IPA Protocol Objects @subsection IPA Protocol Objects @cindex ipa protocol objects The commands sent to and results received from agent may contain some complex data types called @dfn{objects}. The in-process agent is running on the same machine with @value{GDBN} or GDBserver, so it doesn't have to handle as much differences between two ends as remote protocol (@pxref{Remote Protocol}) tries to handle. However, there are still some differences of two ends in two processes: @enumerate @item word size. On some 64-bit machines, @value{GDBN} or GDBserver can be compiled as a 64-bit executable, while in-process agent is a 32-bit one. @item ABI. Some machines may have multiple types of ABI, @value{GDBN} or GDBserver is compiled with one, and in-process agent is compiled with the other one. @end enumerate Here are the IPA Protocol Objects: @enumerate @item agent expression object. It represents an agent expression (@pxref{Agent Expressions}). @anchor{agent expression object} @item tracepoint action object. It represents a tracepoint action (@pxref{Tracepoint Actions,,Tracepoint Action Lists}) to collect registers, memory, static trace data and to evaluate expression. @anchor{tracepoint action object} @item tracepoint object. It represents a tracepoint (@pxref{Tracepoints}). @anchor{tracepoint object} @end enumerate The following table describes important attributes of each IPA protocol object: @multitable @columnfractions .30 .20 .50 @headitem Name @tab Size @tab Description @item @emph{agent expression object} @tab @tab @item length @tab 4 @tab length of bytes code @item byte code @tab @var{length} @tab contents of byte code @item @emph{tracepoint action for collecting memory} @tab @tab @item 'M' @tab 1 @tab type of tracepoint action @item addr @tab 8 @tab if @var{basereg} is @samp{-1}, @var{addr} is the address of the lowest byte to collect, otherwise @var{addr} is the offset of @var{basereg} for memory collecting. @item len @tab 8 @tab length of memory for collecting @item basereg @tab 4 @tab the register number containing the starting memory address for collecting. @item @emph{tracepoint action for collecting registers} @tab @tab @item 'R' @tab 1 @tab type of tracepoint action @item @emph{tracepoint action for collecting static trace data} @tab @tab @item 'L' @tab 1 @tab type of tracepoint action @item @emph{tracepoint action for expression evaluation} @tab @tab @item 'X' @tab 1 @tab type of tracepoint action @item agent expression @tab length of @tab @ref{agent expression object} @item @emph{tracepoint object} @tab @tab @item number @tab 4 @tab number of tracepoint @item address @tab 8 @tab address of tracepoint inserted on @item type @tab 4 @tab type of tracepoint @item enabled @tab 1 @tab enable or disable of tracepoint @item step_count @tab 8 @tab step @item pass_count @tab 8 @tab pass @item numactions @tab 4 @tab number of tracepoint actions @item hit count @tab 8 @tab hit count @item trace frame usage @tab 8 @tab trace frame usage @item compiled_cond @tab 8 @tab compiled condition @item orig_size @tab 8 @tab orig size @item condition @tab 4 if condition is NULL otherwise length of @ref{agent expression object} @tab zero if condition is NULL, otherwise is @ref{agent expression object} @item actions @tab variable @tab numactions number of @ref{tracepoint action object} @end multitable @node IPA Protocol Commands @subsection IPA Protocol Commands @cindex ipa protocol commands The spaces in each command are delimiters to ease reading this commands specification. They don't exist in real commands. @table @samp @item FastTrace:@var{tracepoint_object} @var{gdb_jump_pad_head} Installs a new fast tracepoint described by @var{tracepoint_object} (@pxref{tracepoint object}). The @var{gdb_jump_pad_head}, 8-byte long, is the head of @dfn{jumppad}, which is used to jump to data collection routine in IPA finally. Replies: @table @samp @item OK @var{target_address} @var{gdb_jump_pad_head} @var{fjump_size} @var{fjump} @var{target_address} is address of tracepoint in the inferior. The @var{gdb_jump_pad_head} is updated head of jumppad. Both of @var{target_address} and @var{gdb_jump_pad_head} are 8-byte long. The @var{fjump} contains a sequence of instructions jump to jumppad entry. The @var{fjump_size}, 4-byte long, is the size of @var{fjump}. @item E @var{NN} for an error @end table @item close Closes the in-process agent. This command is sent when @value{GDBN} or GDBserver is about to kill inferiors. @item qTfSTM @xref{qTfSTM}. @item qTsSTM @xref{qTsSTM}. @item qTSTMat @xref{qTSTMat}. @item probe_marker_at:@var{address} Asks in-process agent to probe the marker at @var{address}. Replies: @table @samp @item E @var{NN} for an error @end table @item unprobe_marker_at:@var{address} Asks in-process agent to unprobe the marker at @var{address}. @end table @node GDB Bugs @chapter Reporting Bugs in @value{GDBN} @cindex bugs in @value{GDBN} @cindex reporting bugs in @value{GDBN} Your bug reports play an essential role in making @value{GDBN} reliable. Reporting a bug may help you by bringing a solution to your problem, or it may not. But in any case the principal function of a bug report is to help the entire community by making the next version of @value{GDBN} work better. Bug reports are your contribution to the maintenance of @value{GDBN}. In order for a bug report to serve its purpose, you must include the information that enables us to fix the bug. @menu * Bug Criteria:: Have you found a bug? * Bug Reporting:: How to report bugs @end menu @node Bug Criteria @section Have You Found a Bug? @cindex bug criteria If you are not sure whether you have found a bug, here are some guidelines: @itemize @bullet @cindex fatal signal @cindex debugger crash @cindex crash of debugger @item If the debugger gets a fatal signal, for any input whatever, that is a @value{GDBN} bug. Reliable debuggers never crash. @cindex error on valid input @item If @value{GDBN} produces an error message for valid input, that is a bug. (Note that if you're cross debugging, the problem may also be somewhere in the connection to the target.) @cindex invalid input @item If @value{GDBN} does not produce an error message for invalid input, that is a bug. However, you should note that your idea of ``invalid input'' might be our idea of ``an extension'' or ``support for traditional practice''. @item If you are an experienced user of debugging tools, your suggestions for improvement of @value{GDBN} are welcome in any case. @end itemize @node Bug Reporting @section How to Report Bugs @cindex bug reports @cindex @value{GDBN} bugs, reporting A number of companies and individuals offer support for @sc{gnu} products. If you obtained @value{GDBN} from a support organization, we recommend you contact that organization first. You can find contact information for many support companies and individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs distribution. @c should add a web page ref... @ifset BUGURL @ifset BUGURL_DEFAULT In any event, we also recommend that you submit bug reports for @value{GDBN}. The preferred method is to submit them directly using @uref{http://www.gnu.org/software/gdb/bugs/, @value{GDBN}'s Bugs web page}. Alternatively, the @email{bug-gdb@@gnu.org, e-mail gateway} can be used. @strong{Do not send bug reports to @samp{info-gdb}, or to @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do not want to receive bug reports. Those that do have arranged to receive @samp{bug-gdb}. The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which serves as a repeater. The mailing list and the newsgroup carry exactly the same messages. Often people think of posting bug reports to the newsgroup instead of mailing them. This appears to work, but it has one problem which can be crucial: a newsgroup posting often lacks a mail path back to the sender. Thus, if we need to ask for more information, we may be unable to reach you. For this reason, it is better to send bug reports to the mailing list. @end ifset @ifclear BUGURL_DEFAULT In any event, we also recommend that you submit bug reports for @value{GDBN} to @value{BUGURL}. @end ifclear @end ifset The fundamental principle of reporting bugs usefully is this: @strong{report all the facts}. If you are not sure whether to state a fact or leave it out, state it! Often people omit facts because they think they know what causes the problem and assume that some details do not matter. Thus, you might assume that the name of the variable you use in an example does not matter. Well, probably it does not, but one cannot be sure. Perhaps the bug is a stray memory reference which happens to fetch from the location where that name is stored in memory; perhaps, if the name were different, the contents of that location would fool the debugger into doing the right thing despite the bug. Play it safe and give a specific, complete example. That is the easiest thing for you to do, and the most helpful. Keep in mind that the purpose of a bug report is to enable us to fix the bug. It may be that the bug has been reported previously, but neither you nor we can know that unless your bug report is complete and self-contained. Sometimes people give a few sketchy facts and ask, ``Does this ring a bell?'' Those bug reports are useless, and we urge everyone to @emph{refuse to respond to them} except to chide the sender to report bugs properly. To enable us to fix the bug, you should include all these things: @itemize @bullet @item The version of @value{GDBN}. @value{GDBN} announces it if you start with no arguments; you can also print it at any time using @code{show version}. Without this, we will not know whether there is any point in looking for the bug in the current version of @value{GDBN}. @item The type of machine you are using, and the operating system name and version number. @item The details of the @value{GDBN} build-time configuration. @value{GDBN} shows these details if you invoke it with the @option{--configuration} command-line option, or if you type @code{show configuration} at @value{GDBN}'s prompt. @item What compiler (and its version) was used to compile @value{GDBN}---e.g.@: ``@value{GCC}--2.8.1''. @item What compiler (and its version) was used to compile the program you are debugging---e.g.@: ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP C Compiler''. For @value{NGCC}, you can say @kbd{@value{GCC} --version} to get this information; for other compilers, see the documentation for those compilers. @item The command arguments you gave the compiler to compile your example and observe the bug. For example, did you use @samp{-O}? To guarantee you will not omit something important, list them all. A copy of the Makefile (or the output from make) is sufficient. If we were to try to guess the arguments, we would probably guess wrong and then we might not encounter the bug. @item A complete input script, and all necessary source files, that will reproduce the bug. @item A description of what behavior you observe that you believe is incorrect. For example, ``It gets a fatal signal.'' Of course, if the bug is that @value{GDBN} gets a fatal signal, then we will certainly notice it. But if the bug is incorrect output, we might not notice unless it is glaringly wrong. You might as well not give us a chance to make a mistake. Even if the problem you experience is a fatal signal, you should still say so explicitly. Suppose something strange is going on, such as, your copy of @value{GDBN} is out of synch, or you have encountered a bug in the C library on your system. (This has happened!) Your copy might crash and ours would not. If you told us to expect a crash, then when ours fails to crash, we would know that the bug was not happening for us. If you had not told us to expect a crash, then we would not be able to draw any conclusion from our observations. @pindex script @cindex recording a session script To collect all this information, you can use a session recording program such as @command{script}, which is available on many Unix systems. Just run your @value{GDBN} session inside @command{script} and then include the @file{typescript} file with your bug report. Another way to record a @value{GDBN} session is to run @value{GDBN} inside Emacs and then save the entire buffer to a file. @item If you wish to suggest changes to the @value{GDBN} source, send us context diffs. If you even discuss something in the @value{GDBN} source, refer to it by context, not by line number. The line numbers in our development sources will not match those in your sources. Your line numbers would convey no useful information to us. @end itemize Here are some things that are not necessary: @itemize @bullet @item A description of the envelope of the bug. Often people who encounter a bug spend a lot of time investigating which changes to the input file will make the bug go away and which changes will not affect it. This is often time consuming and not very useful, because the way we will find the bug is by running a single example under the debugger with breakpoints, not by pure deduction from a series of examples. We recommend that you save your time for something else. Of course, if you can find a simpler example to report @emph{instead} of the original one, that is a convenience for us. Errors in the output will be easier to spot, running under the debugger will take less time, and so on. However, simplification is not vital; if you do not want to do this, report the bug anyway and send us the entire test case you used. @item A patch for the bug. A patch for the bug does help us if it is a good one. But do not omit the necessary information, such as the test case, on the assumption that a patch is all we need. We might see problems with your patch and decide to fix the problem another way, or we might not understand it at all. Sometimes with a program as complicated as @value{GDBN} it is very hard to construct an example that will make the program follow a certain path through the code. If you do not send us the example, we will not be able to construct one, so we will not be able to verify that the bug is fixed. And if we cannot understand what bug you are trying to fix, or why your patch should be an improvement, we will not install it. A test case will help us to understand. @item A guess about what the bug is or what it depends on. Such guesses are usually wrong. Even we cannot guess right about such things without first using the debugger to find the facts. @end itemize @c The readline documentation is distributed with the readline code @c and consists of the two following files: @c rluser.texi @c hsuser.texi @c Use -I with makeinfo to point to the appropriate directory, @c environment var TEXINPUTS with TeX. @ifclear SYSTEM_READLINE @include rluser.texi @include hsuser.texi @end ifclear @node In Memoriam @appendix In Memoriam The @value{GDBN} project mourns the loss of the following long-time contributors: @table @code @item Fred Fish Fred was a long-standing contributor to @value{GDBN} (1991-2006), and to Free Software in general. Outside of @value{GDBN}, he was known in the Amiga world for his series of Fish Disks, and the GeekGadget project. @item Michael Snyder Michael was one of the Global Maintainers of the @value{GDBN} project, with contributions recorded as early as 1996, until 2011. In addition to his day to day participation, he was a large driving force behind adding Reverse Debugging to @value{GDBN}. @end table Beyond their technical contributions to the project, they were also enjoyable members of the Free Software Community. We will miss them. @node Formatting Documentation @appendix Formatting Documentation @cindex @value{GDBN} reference card @cindex reference card The @value{GDBN} 4 release includes an already-formatted reference card, ready for printing with PostScript or Ghostscript, in the @file{gdb} subdirectory of the main source directory@footnote{In @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN} release.}. If you can use PostScript or Ghostscript with your printer, you can print the reference card immediately with @file{refcard.ps}. The release also includes the source for the reference card. You can format it, using @TeX{}, by typing: @smallexample make refcard.dvi @end smallexample The @value{GDBN} reference card is designed to print in @dfn{landscape} mode on US ``letter'' size paper; that is, on a sheet 11 inches wide by 8.5 inches high. You will need to specify this form of printing as an option to your @sc{dvi} output program. @cindex documentation All the documentation for @value{GDBN} comes as part of the machine-readable distribution. The documentation is written in Texinfo format, which is a documentation system that uses a single source file to produce both on-line information and a printed manual. You can use one of the Info formatting commands to create the on-line version of the documentation and @TeX{} (or @code{texi2roff}) to typeset the printed version. @value{GDBN} includes an already formatted copy of the on-line Info version of this manual in the @file{gdb} subdirectory. The main Info file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to subordinate files matching @samp{gdb.info*} in the same directory. If necessary, you can print out these files, or read them with any editor; but they are easier to read using the @code{info} subsystem in @sc{gnu} Emacs or the standalone @code{info} program, available as part of the @sc{gnu} Texinfo distribution. If you want to format these Info files yourself, you need one of the Info formatting programs, such as @code{texinfo-format-buffer} or @code{makeinfo}. If you have @code{makeinfo} installed, and are in the top level @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of version @value{GDBVN}), you can make the Info file by typing: @smallexample cd gdb make gdb.info @end smallexample If you want to typeset and print copies of this manual, you need @TeX{}, a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the Texinfo definitions file. @TeX{} is a typesetting program; it does not print files directly, but produces output files called @sc{dvi} files. To print a typeset document, you need a program to print @sc{dvi} files. If your system has @TeX{} installed, chances are it has such a program. The precise command to use depends on your system; @kbd{lpr -d} is common; another (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may require a file name without any extension or a @samp{.dvi} extension. @TeX{} also requires a macro definitions file called @file{texinfo.tex}. This file tells @TeX{} how to typeset a document written in Texinfo format. On its own, @TeX{} cannot either read or typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB and is located in the @file{gdb-@var{version-number}/texinfo} directory. If you have @TeX{} and a @sc{dvi} printer program installed, you can typeset and print this manual. First switch to the @file{gdb} subdirectory of the main source directory (for example, to @file{gdb-@value{GDBVN}/gdb}) and type: @smallexample make gdb.dvi @end smallexample Then give @file{gdb.dvi} to your @sc{dvi} printing program. @node Installing GDB @appendix Installing @value{GDBN} @cindex installation @menu * Requirements:: Requirements for building @value{GDBN} * Running Configure:: Invoking the @value{GDBN} @file{configure} script * Separate Objdir:: Compiling @value{GDBN} in another directory * Config Names:: Specifying names for hosts and targets * Configure Options:: Summary of options for configure * System-wide configuration:: Having a system-wide init file @end menu @node Requirements @section Requirements for Building @value{GDBN} @cindex building @value{GDBN}, requirements for Building @value{GDBN} requires various tools and packages to be available. Other packages will be used only if they are found. @heading Tools/Packages Necessary for Building @value{GDBN} @table @asis @item C@t{++}11 compiler @value{GDBN} is written in C@t{++}11. It should be buildable with any recent C@t{++}11 compiler, e.g.@: GCC. @item GNU make @value{GDBN}'s build system relies on features only found in the GNU make program. Other variants of @code{make} will not work. @end table @heading Tools/Packages Optional for Building @value{GDBN} @table @asis @item Expat @anchor{Expat} @value{GDBN} can use the Expat XML parsing library. This library may be included with your operating system distribution; if it is not, you can get the latest version from @url{http://expat.sourceforge.net}. The @file{configure} script will search for this library in several standard locations; if it is installed in an unusual path, you can use the @option{--with-libexpat-prefix} option to specify its location. Expat is used for: @itemize @bullet @item Remote protocol memory maps (@pxref{Memory Map Format}) @item Target descriptions (@pxref{Target Descriptions}) @item Remote shared library lists (@xref{Library List Format}, or alternatively @pxref{Library List Format for SVR4 Targets}) @item MS-Windows shared libraries (@pxref{Shared Libraries}) @item Traceframe info (@pxref{Traceframe Info Format}) @item Branch trace (@pxref{Branch Trace Format}, @pxref{Branch Trace Configuration Format}) @end itemize @item Guile @value{GDBN} can be scripted using GNU Guile. @xref{Guile}. By default, @value{GDBN} will be compiled if the Guile libraries are installed and are found by @file{configure}. You can use the @code{--with-guile} option to request Guile, and pass either the Guile version number or the file name of the relevant @code{pkg-config} program to choose a particular version of Guile. @item iconv @value{GDBN}'s features related to character sets (@pxref{Character Sets}) require a functioning @code{iconv} implementation. If you are on a GNU system, then this is provided by the GNU C Library. Some other systems also provide a working @code{iconv}. If @value{GDBN} is using the @code{iconv} program which is installed in a non-standard place, you will need to tell @value{GDBN} where to find it. This is done with @option{--with-iconv-bin} which specifies the directory that contains the @code{iconv} program. This program is run in order to make a list of the available character sets. On systems without @code{iconv}, you can install GNU Libiconv. If Libiconv is installed in a standard place, @value{GDBN} will automatically use it if it is needed. If you have previously installed Libiconv in a non-standard place, you can use the @option{--with-libiconv-prefix} option to @file{configure}. @value{GDBN}'s top-level @file{configure} and @file{Makefile} will arrange to build Libiconv if a directory named @file{libiconv} appears in the top-most source directory. If Libiconv is built this way, and if the operating system does not provide a suitable @code{iconv} implementation, then the just-built library will automatically be used by @value{GDBN}. One easy way to set this up is to download GNU Libiconv, unpack it inside the top-level directory of the @value{GDBN} source tree, and then rename the directory holding the Libiconv source code to @samp{libiconv}. @item lzma @value{GDBN} can support debugging sections that are compressed with the LZMA library. @xref{MiniDebugInfo}. If this library is not included with your operating system, you can find it in the xz package at @url{http://tukaani.org/xz/}. If the LZMA library is available in the usual place, then the @file{configure} script will use it automatically. If it is installed in an unusual path, you can use the @option{--with-lzma-prefix} option to specify its location. @item MPFR @anchor{MPFR} @value{GDBN} can use the GNU MPFR multiple-precision floating-point library. This library may be included with your operating system distribution; if it is not, you can get the latest version from @url{http://www.mpfr.org}. The @file{configure} script will search for this library in several standard locations; if it is installed in an unusual path, you can use the @option{--with-libmpfr-prefix} option to specify its location. GNU MPFR is used to emulate target floating-point arithmetic during expression evaluation when the target uses different floating-point formats than the host. If GNU MPFR it is not available, @value{GDBN} will fall back to using host floating-point arithmetic. @item Python @value{GDBN} can be scripted using Python language. @xref{Python}. By default, @value{GDBN} will be compiled if the Python libraries are installed and are found by @file{configure}. You can use the @code{--with-python} option to request Python, and pass either the file name of the relevant @code{python} executable, or the name of the directory in which Python is installed, to choose a particular installation of Python. @item zlib @cindex compressed debug sections @value{GDBN} will use the @samp{zlib} library, if available, to read compressed debug sections. Some linkers, such as GNU gold, are capable of producing binaries with compressed debug sections. If @value{GDBN} is compiled with @samp{zlib}, it will be able to read the debug information in such binaries. The @samp{zlib} library is likely included with your operating system distribution; if it is not, you can get the latest version from @url{http://zlib.net}. @end table @node Running Configure @section Invoking the @value{GDBN} @file{configure} Script @cindex configuring @value{GDBN} @value{GDBN} comes with a @file{configure} script that automates the process of preparing @value{GDBN} for installation; you can then use @code{make} to build the @code{gdb} program. @iftex @c irrelevant in info file; it's as current as the code it lives with. @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN}, look at the @file{README} file in the sources; we may have improved the installation procedures since publishing this manual.} @end iftex The @value{GDBN} distribution includes all the source code you need for @value{GDBN} in a single directory, whose name is usually composed by appending the version number to @samp{gdb}. For example, the @value{GDBN} version @value{GDBVN} distribution is in the @file{gdb-@value{GDBVN}} directory. That directory contains: @table @code @item gdb-@value{GDBVN}/configure @r{(and supporting files)} script for configuring @value{GDBN} and all its supporting libraries @item gdb-@value{GDBVN}/gdb the source specific to @value{GDBN} itself @item gdb-@value{GDBVN}/bfd source for the Binary File Descriptor library @item gdb-@value{GDBVN}/include @sc{gnu} include files @item gdb-@value{GDBVN}/libiberty source for the @samp{-liberty} free software library @item gdb-@value{GDBVN}/opcodes source for the library of opcode tables and disassemblers @item gdb-@value{GDBVN}/readline source for the @sc{gnu} command-line interface @end table There may be other subdirectories as well. The simplest way to configure and build @value{GDBN} is to run @file{configure} from the @file{gdb-@var{version-number}} source directory, which in this example is the @file{gdb-@value{GDBVN}} directory. First switch to the @file{gdb-@var{version-number}} source directory if you are not already in it; then run @file{configure}. Pass the identifier for the platform on which @value{GDBN} will run as an argument. For example: @smallexample cd gdb-@value{GDBVN} ./configure make @end smallexample Running @samp{configure} and then running @code{make} builds the included supporting libraries, then @code{gdb} itself. The configured source files, and the binaries, are left in the corresponding source directories. @need 750 @file{configure} is a Bourne-shell (@code{/bin/sh}) script; if your system does not recognize this automatically when you run a different shell, you may need to run @code{sh} on it explicitly: @smallexample sh configure @end smallexample You should run the @file{configure} script from the top directory in the source tree, the @file{gdb-@var{version-number}} directory. If you run @file{configure} from one of the subdirectories, you will configure only that subdirectory. That is usually not what you want. In particular, if you run the first @file{configure} from the @file{gdb} subdirectory of the @file{gdb-@var{version-number}} directory, you will omit the configuration of @file{bfd}, @file{readline}, and other sibling directories of the @file{gdb} subdirectory. This leads to build errors about missing include files such as @file{bfd/bfd.h}. You can install @code{@value{GDBN}} anywhere. The best way to do this is to pass the @code{--prefix} option to @code{configure}, and then install it with @code{make install}. @node Separate Objdir @section Compiling @value{GDBN} in Another Directory If you want to run @value{GDBN} versions for several host or target machines, you need a different @code{gdb} compiled for each combination of host and target. @file{configure} is designed to make this easy by allowing you to generate each configuration in a separate subdirectory, rather than in the source directory. If your @code{make} program handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running @code{make} in each of these directories builds the @code{gdb} program specified there. To build @code{gdb} in a separate directory, run @file{configure} with the @samp{--srcdir} option to specify where to find the source. (You also need to specify a path to find @file{configure} itself from your working directory. If the path to @file{configure} would be the same as the argument to @samp{--srcdir}, you can leave out the @samp{--srcdir} option; it is assumed.) For example, with version @value{GDBVN}, you can build @value{GDBN} in a separate directory for a Sun 4 like this: @smallexample @group cd gdb-@value{GDBVN} mkdir ../gdb-sun4 cd ../gdb-sun4 ../gdb-@value{GDBVN}/configure make @end group @end smallexample When @file{configure} builds a configuration using a remote source directory, it creates a tree for the binaries with the same structure (and using the same names) as the tree under the source directory. In the example, you'd find the Sun 4 library @file{libiberty.a} in the directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in @file{gdb-sun4/gdb}. Make sure that your path to the @file{configure} script has just one instance of @file{gdb} in it. If your path to @file{configure} looks like @file{../gdb-@value{GDBVN}/gdb/configure}, you are configuring only one subdirectory of @value{GDBN}, not the whole package. This leads to build errors about missing include files such as @file{bfd/bfd.h}. One popular reason to build several @value{GDBN} configurations in separate directories is to configure @value{GDBN} for cross-compiling (where @value{GDBN} runs on one machine---the @dfn{host}---while debugging programs that run on another machine---the @dfn{target}). You specify a cross-debugging target by giving the @samp{--target=@var{target}} option to @file{configure}. When you run @code{make} to build a program or library, you must run it in a configured directory---whatever directory you were in when you called @file{configure} (or one of its subdirectories). The @code{Makefile} that @file{configure} generates in each source directory also runs recursively. If you type @code{make} in a source directory such as @file{gdb-@value{GDBVN}} (or in a separate configured directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you will build all the required libraries, and then build GDB. When you have multiple hosts or targets configured in separate directories, you can run @code{make} on them in parallel (for example, if they are NFS-mounted on each of the hosts); they will not interfere with each other. @node Config Names @section Specifying Names for Hosts and Targets The specifications used for hosts and targets in the @file{configure} script are based on a three-part naming scheme, but some short predefined aliases are also supported. The full naming scheme encodes three pieces of information in the following pattern: @smallexample @var{architecture}-@var{vendor}-@var{os} @end smallexample For example, you can use the alias @code{sun4} as a @var{host} argument, or as the value for @var{target} in a @code{--target=@var{target}} option. The equivalent full name is @samp{sparc-sun-sunos4}. The @file{configure} script accompanying @value{GDBN} does not provide any query facility to list all supported host and target names or aliases. @file{configure} calls the Bourne shell script @code{config.sub} to map abbreviations to full names; you can read the script, if you wish, or you can use it to test your guesses on abbreviations---for example: @smallexample % sh config.sub i386-linux i386-pc-linux-gnu % sh config.sub alpha-linux alpha-unknown-linux-gnu % sh config.sub hp9k700 hppa1.1-hp-hpux % sh config.sub sun4 sparc-sun-sunos4.1.1 % sh config.sub sun3 m68k-sun-sunos4.1.1 % sh config.sub i986v Invalid configuration `i986v': machine `i986v' not recognized @end smallexample @noindent @code{config.sub} is also distributed in the @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}). @node Configure Options @section @file{configure} Options Here is a summary of the @file{configure} options and arguments that are most often useful for building @value{GDBN}. @file{configure} also has several other options not listed here. @inforef{Running configure scripts,,autoconf.info}, for a full explanation of @file{configure}. @smallexample configure @r{[}--help@r{]} @r{[}--prefix=@var{dir}@r{]} @r{[}--exec-prefix=@var{dir}@r{]} @r{[}--srcdir=@var{dirname}@r{]} @r{[}--target=@var{target}@r{]} @end smallexample @noindent You may introduce options with a single @samp{-} rather than @samp{--} if you prefer; but you may abbreviate option names if you use @samp{--}. @table @code @item --help Display a quick summary of how to invoke @file{configure}. @item --prefix=@var{dir} Configure the source to install programs and files under directory @file{@var{dir}}. @item --exec-prefix=@var{dir} Configure the source to install programs under directory @file{@var{dir}}. @c avoid splitting the warning from the explanation: @need 2000 @item --srcdir=@var{dirname} Use this option to make configurations in directories separate from the @value{GDBN} source directories. Among other things, you can use this to build (or maintain) several configurations simultaneously, in separate directories. @file{configure} writes configuration-specific files in the current directory, but arranges for them to use the source in the directory @var{dirname}. @file{configure} creates directories under the working directory in parallel to the source directories below @var{dirname}. @item --target=@var{target} Configure @value{GDBN} for cross-debugging programs running on the specified @var{target}. Without this option, @value{GDBN} is configured to debug programs that run on the same machine (@var{host}) as @value{GDBN} itself. There is no convenient way to generate a list of all available targets. Also see the @code{--enable-targets} option, below. @end table There are many other options that are specific to @value{GDBN}. This lists just the most common ones; there are some very specialized options not described here. @table @code @item --enable-targets=@r{[}@var{target}@r{]}@dots{} @itemx --enable-targets=all Configure @value{GDBN} for cross-debugging programs running on the specified list of targets. The special value @samp{all} configures @value{GDBN} for debugging programs running on any target it supports. @item --with-gdb-datadir=@var{path} Set the @value{GDBN}-specific data directory. @value{GDBN} will look here for certain supporting files or scripts. This defaults to the @file{gdb} subdirectory of @samp{datadir} (which can be set using @code{--datadir}). @item --with-relocated-sources=@var{dir} Sets up the default source path substitution rule so that directory names recorded in debug information will be automatically adjusted for any directory under @var{dir}. @var{dir} should be a subdirectory of @value{GDBN}'s configured prefix, the one mentioned in the @code{--prefix} or @code{--exec-prefix} options to configure. This option is useful if GDB is supposed to be moved to a different place after it is built. @item --enable-64-bit-bfd Enable 64-bit support in BFD on 32-bit hosts. @item --disable-gdbmi Build @value{GDBN} without the GDB/MI machine interface (@pxref{GDB/MI}). @item --enable-tui Build @value{GDBN} with the text-mode full-screen user interface (TUI). Requires a curses library (ncurses and cursesX are also supported). @item --with-curses Use the curses library instead of the termcap library, for text-mode terminal operations. @item --with-debuginfod Build @value{GDBN} with libdebuginfod, the debuginfod client library. Used to automatically fetch source files and separate debug files from debuginfod servers using the associated executable's build ID. Enabled by default if libdebuginfod is installed and found at configure time. debuginfod is packaged with elfutils, starting with version 0.178. You can get the latest version from `https://sourceware.org/elfutils/'. @item --with-libunwind-ia64 Use the libunwind library for unwinding function call stack on ia64 target platforms. See http://www.nongnu.org/libunwind/index.html for details. @item --with-system-readline Use the readline library installed on the host, rather than the library supplied as part of @value{GDBN}. Readline 7 or newer is required; this is enforced by the build system. @item --with-system-zlib Use the zlib library installed on the host, rather than the library supplied as part of @value{GDBN}. @item --with-expat Build @value{GDBN} with Expat, a library for XML parsing. (Done by default if libexpat is installed and found at configure time.) This library is used to read XML files supplied with @value{GDBN}. If it is unavailable, some features, such as remote protocol memory maps, target descriptions, and shared library lists, that are based on XML files, will not be available in @value{GDBN}. If your host does not have libexpat installed, you can get the latest version from `http://expat.sourceforge.net'. @item --with-libiconv-prefix@r{[}=@var{dir}@r{]} Build @value{GDBN} with GNU libiconv, a character set encoding conversion library. This is not done by default, as on GNU systems the @code{iconv} that is built in to the C library is sufficient. If your host does not have a working @code{iconv}, you can get the latest version of GNU iconv from `https://www.gnu.org/software/libiconv/'. @value{GDBN}'s build system also supports building GNU libiconv as part of the overall build. @xref{Requirements}. @item --with-lzma Build @value{GDBN} with LZMA, a compression library. (Done by default if liblzma is installed and found at configure time.) LZMA is used by @value{GDBN}'s "mini debuginfo" feature, which is only useful on platforms using the ELF object file format. If your host does not have liblzma installed, you can get the latest version from `https://tukaani.org/xz/'. @item --with-mpfr Build @value{GDBN} with GNU MPFR, a library for multiple-precision floating-point computation with correct rounding. (Done by default if GNU MPFR is installed and found at configure time.) This library is used to emulate target floating-point arithmetic during expression evaluation when the target uses different floating-point formats than the host. If GNU MPFR is not available, @value{GDBN} will fall back to using host floating-point arithmetic. If your host does not have GNU MPFR installed, you can get the latest version from `http://www.mpfr.org'. @item --with-python@r{[}=@var{python}@r{]} Build @value{GDBN} with Python scripting support. (Done by default if libpython is present and found at configure time.) Python makes @value{GDBN} scripting much more powerful than the restricted CLI scripting language. If your host does not have Python installed, you can find it on `http://www.python.org/download/'. The oldest version of Python supported by GDB is 2.6. The optional argument @var{python} is used to find the Python headers and libraries. It can be either the name of a Python executable, or the name of the directory in which Python is installed. @item --with-guile[=GUILE]' Build @value{GDBN} with GNU Guile scripting support. (Done by default if libguile is present and found at configure time.) If your host does not have Guile installed, you can find it at `https://www.gnu.org/software/guile/'. The optional argument GUILE can be a version number, which will cause @code{configure} to try to use that version of Guile; or the file name of a @code{pkg-config} executable, which will be queried to find the information needed to compile and link against Guile. @item --without-included-regex Don't use the regex library included with @value{GDBN} (as part of the libiberty library). This is the default on hosts with version 2 of the GNU C library. @item --with-sysroot=@var{dir} Use @var{dir} as the default system root directory for libraries whose file names begin with @file{/lib}' or @file{/usr/lib'}. (The value of @var{dir} can be modified at run time by using the @command{set sysroot} command.) If @var{dir} is under the @value{GDBN} configured prefix (set with @code{--prefix} or @code{--exec-prefix options}, the default system root will be automatically adjusted if and when @value{GDBN} is moved to a different location. @item --with-system-gdbinit=@var{file} Configure @value{GDBN} to automatically load a system-wide init file. @var{file} should be an absolute file name. If @var{file} is in a directory under the configured prefix, and @value{GDBN} is moved to another location after being built, the location of the system-wide init file will be adjusted accordingly. @item --with-system-gdbinit-dir=@var{directory} Configure @value{GDBN} to automatically load init files from a system-wide directory. @var{directory} should be an absolute directory name. If @var{directory} is in a directory under the configured prefix, and @value{GDBN} is moved to another location after being built, the location of the system-wide init directory will be adjusted accordingly. @item --enable-build-warnings When building the @value{GDBN} sources, ask the compiler to warn about any code which looks even vaguely suspicious. It passes many different warning flags, depending on the exact version of the compiler you are using. @item --enable-werror Treat compiler warnings as werrors. It adds the @code{-Werror} flag to the compiler, which will fail the compilation if the compiler outputs any warning messages. @item --enable-ubsan Enable the GCC undefined behavior sanitizer. This is disabled by default, but passing @code{--enable-ubsan=yes} or @code{--enable-ubsan=auto} to @code{configure} will enable it. The undefined behavior sanitizer checks for C@t{++} undefined behavior. It has a performance cost, so if you are looking at @value{GDBN}'s performance, you should disable it. The undefined behavior sanitizer was first introduced in GCC 4.9. @end table @node System-wide configuration @section System-wide configuration and settings @cindex system-wide init file @value{GDBN} can be configured to have a system-wide init file and a system-wide init file directory; this file and files in that directory (if they have a recognized file extension) will be read and executed at startup (@pxref{Startup, , What @value{GDBN} does during startup}). Here are the corresponding configure options: @table @code @item --with-system-gdbinit=@var{file} Specify that the default location of the system-wide init file is @var{file}. @item --with-system-gdbinit-dir=@var{directory} Specify that the default location of the system-wide init file directory is @var{directory}. @end table If @value{GDBN} has been configured with the option @option{--prefix=$prefix}, they may be subject to relocation. Two possible cases: @itemize @bullet @item If the default location of this init file/directory contains @file{$prefix}, it will be subject to relocation. Suppose that the configure options are @option{--prefix=$prefix --with-system-gdbinit=$prefix/etc/gdbinit}; if @value{GDBN} is moved from @file{$prefix} to @file{$install}, the system init file is looked for as @file{$install/etc/gdbinit} instead of @file{$prefix/etc/gdbinit}. @item By contrast, if the default location does not contain the prefix, it will not be relocated. E.g.@: if @value{GDBN} has been configured with @option{--prefix=/usr/local --with-system-gdbinit=/usr/share/gdb/gdbinit}, then @value{GDBN} will always look for @file{/usr/share/gdb/gdbinit}, wherever @value{GDBN} is installed. @end itemize If the configured location of the system-wide init file (as given by the @option{--with-system-gdbinit} option at configure time) is in the data-directory (as specified by @option{--with-gdb-datadir} at configure time) or in one of its subdirectories, then @value{GDBN} will look for the system-wide init file in the directory specified by the @option{--data-directory} command-line option. Note that the system-wide init file is only read once, during @value{GDBN} initialization. If the data-directory is changed after @value{GDBN} has started with the @code{set data-directory} command, the file will not be reread. This applies similarly to the system-wide directory specified in @option{--with-system-gdbinit-dir}. Any supported scripting language can be used for these init files, as long as the file extension matches the scripting language. To be interpreted as regular @value{GDBN} commands, the files needs to have a @file{.gdb} extension. @menu * System-wide Configuration Scripts:: Installed System-wide Configuration Scripts @end menu @node System-wide Configuration Scripts @subsection Installed System-wide Configuration Scripts @cindex system-wide configuration scripts The @file{system-gdbinit} directory, located inside the data-directory (as specified by @option{--with-gdb-datadir} at configure time) contains a number of scripts which can be used as system-wide init files. To automatically source those scripts at startup, @value{GDBN} should be configured with @option{--with-system-gdbinit}. Otherwise, any user should be able to source them by hand as needed. The following scripts are currently available: @itemize @bullet @item @file{elinos.py} @pindex elinos.py @cindex ELinOS system-wide configuration script This script is useful when debugging a program on an ELinOS target. It takes advantage of the environment variables defined in a standard ELinOS environment in order to determine the location of the system shared libraries, and then sets the @samp{solib-absolute-prefix} and @samp{solib-search-path} variables appropriately. @item @file{wrs-linux.py} @pindex wrs-linux.py @cindex Wind River Linux system-wide configuration script This script is useful when debugging a program on a target running Wind River Linux. It expects the @env{ENV_PREFIX} to be set to the host-side sysroot used by the target system. @end itemize @node Maintenance Commands @appendix Maintenance Commands @cindex maintenance commands @cindex internal commands In addition to commands intended for @value{GDBN} users, @value{GDBN} includes a number of commands intended for @value{GDBN} developers, that are not documented elsewhere in this manual. These commands are provided here for reference. (For commands that turn on debugging messages, see @ref{Debugging Output}.) @table @code @kindex maint agent @kindex maint agent-eval @item maint agent @r{[}-at @var{location}@r{,}@r{]} @var{expression} @itemx maint agent-eval @r{[}-at @var{location}@r{,}@r{]} @var{expression} Translate the given @var{expression} into remote agent bytecodes. This command is useful for debugging the Agent Expression mechanism (@pxref{Agent Expressions}). The @samp{agent} version produces an expression useful for data collection, such as by tracepoints, while @samp{maint agent-eval} produces an expression that evaluates directly to a result. For instance, a collection expression for @code{globa + globb} will include bytecodes to record four bytes of memory at each of the addresses of @code{globa} and @code{globb}, while discarding the result of the addition, while an evaluation expression will do the addition and return the sum. If @code{-at} is given, generate remote agent bytecode for @var{location}. If not, generate remote agent bytecode for current frame PC address. @kindex maint agent-printf @item maint agent-printf @var{format},@var{expr},... Translate the given format string and list of argument expressions into remote agent bytecodes and display them as a disassembled list. This command is useful for debugging the agent version of dynamic printf (@pxref{Dynamic Printf}). @kindex maint info breakpoints @item @anchor{maint info breakpoints}maint info breakpoints Using the same format as @samp{info breakpoints}, display both the breakpoints you've set explicitly, and those @value{GDBN} is using for internal purposes. Internal breakpoints are shown with negative breakpoint numbers. The type column identifies what kind of breakpoint is shown: @table @code @item breakpoint Normal, explicitly set breakpoint. @item watchpoint Normal, explicitly set watchpoint. @item longjmp Internal breakpoint, used to handle correctly stepping through @code{longjmp} calls. @item longjmp resume Internal breakpoint at the target of a @code{longjmp}. @item until Temporary internal breakpoint used by the @value{GDBN} @code{until} command. @item finish Temporary internal breakpoint used by the @value{GDBN} @code{finish} command. @item shlib events Shared library events. @end table @kindex maint info btrace @item maint info btrace Pint information about raw branch tracing data. @kindex maint btrace packet-history @item maint btrace packet-history Print the raw branch trace packets that are used to compute the execution history for the @samp{record btrace} command. Both the information and the format in which it is printed depend on the btrace recording format. @table @code @item bts For the BTS recording format, print a list of blocks of sequential code. For each block, the following information is printed: @table @asis @item Block number Newer blocks have higher numbers. The oldest block has number zero. @item Lowest @samp{PC} @item Highest @samp{PC} @end table @item pt For the Intel Processor Trace recording format, print a list of Intel Processor Trace packets. For each packet, the following information is printed: @table @asis @item Packet number Newer packets have higher numbers. The oldest packet has number zero. @item Trace offset The packet's offset in the trace stream. @item Packet opcode and payload @end table @end table @kindex maint btrace clear-packet-history @item maint btrace clear-packet-history Discards the cached packet history printed by the @samp{maint btrace packet-history} command. The history will be computed again when needed. @kindex maint btrace clear @item maint btrace clear Discard the branch trace data. The data will be fetched anew and the branch trace will be recomputed when needed. This implicitly truncates the branch trace to a single branch trace buffer. When updating branch trace incrementally, the branch trace available to @value{GDBN} may be bigger than a single branch trace buffer. @kindex maint set btrace pt skip-pad @item maint set btrace pt skip-pad @kindex maint show btrace pt skip-pad @item maint show btrace pt skip-pad Control whether @value{GDBN} will skip PAD packets when computing the packet history. @kindex set displaced-stepping @kindex show displaced-stepping @cindex displaced stepping support @cindex out-of-line single-stepping @item set displaced-stepping @itemx show displaced-stepping Control whether or not @value{GDBN} will do @dfn{displaced stepping} if the target supports it. Displaced stepping is a way to single-step over breakpoints without removing them from the inferior, by executing an out-of-line copy of the instruction that was originally at the breakpoint location. It is also known as out-of-line single-stepping. @table @code @item set displaced-stepping on If the target architecture supports it, @value{GDBN} will use displaced stepping to step over breakpoints. @item set displaced-stepping off @value{GDBN} will not use displaced stepping to step over breakpoints, even if such is supported by the target architecture. @cindex non-stop mode, and @samp{set displaced-stepping} @item set displaced-stepping auto This is the default mode. @value{GDBN} will use displaced stepping only if non-stop mode is active (@pxref{Non-Stop Mode}) and the target architecture supports displaced stepping. @end table @kindex maint check-psymtabs @item maint check-psymtabs Check the consistency of currently expanded psymtabs versus symtabs. Use this to check, for example, whether a symbol is in one but not the other. @kindex maint check-symtabs @item maint check-symtabs Check the consistency of currently expanded symtabs. @kindex maint expand-symtabs @item maint expand-symtabs [@var{regexp}] Expand symbol tables. If @var{regexp} is specified, only expand symbol tables for file names matching @var{regexp}. @kindex maint set catch-demangler-crashes @kindex maint show catch-demangler-crashes @cindex demangler crashes @item maint set catch-demangler-crashes [on|off] @itemx maint show catch-demangler-crashes Control whether @value{GDBN} should attempt to catch crashes in the symbol name demangler. The default is to attempt to catch crashes. If enabled, the first time a crash is caught, a core file is created, the offending symbol is displayed and the user is presented with the option to terminate the current session. @kindex maint cplus first_component @item maint cplus first_component @var{name} Print the first C@t{++} class/namespace component of @var{name}. @kindex maint cplus namespace @item maint cplus namespace Print the list of possible C@t{++} namespaces. @kindex maint deprecate @kindex maint undeprecate @cindex deprecated commands @item maint deprecate @var{command} @r{[}@var{replacement}@r{]} @itemx maint undeprecate @var{command} Deprecate or undeprecate the named @var{command}. Deprecated commands cause @value{GDBN} to issue a warning when you use them. The optional argument @var{replacement} says which newer command should be used in favor of the deprecated one; if it is given, @value{GDBN} will mention the replacement as part of the warning. @kindex maint dump-me @item maint dump-me @cindex @code{SIGQUIT} signal, dump core of @value{GDBN} Cause a fatal signal in the debugger and force it to dump its core. This is supported only on systems which support aborting a program with the @code{SIGQUIT} signal. @kindex maint internal-error @kindex maint internal-warning @kindex maint demangler-warning @cindex demangler crashes @item maint internal-error @r{[}@var{message-text}@r{]} @itemx maint internal-warning @r{[}@var{message-text}@r{]} @itemx maint demangler-warning @r{[}@var{message-text}@r{]} Cause @value{GDBN} to call the internal function @code{internal_error}, @code{internal_warning} or @code{demangler_warning} and hence behave as though an internal problem has been detected. In addition to reporting the internal problem, these functions give the user the opportunity to either quit @value{GDBN} or (for @code{internal_error} and @code{internal_warning}) create a core file of the current @value{GDBN} session. These commands take an optional parameter @var{message-text} that is used as the text of the error or warning message. Here's an example of using @code{internal-error}: @smallexample (@value{GDBP}) @kbd{maint internal-error testing, 1, 2} @dots{}/maint.c:121: internal-error: testing, 1, 2 A problem internal to GDB has been detected. Further debugging may prove unreliable. Quit this debugging session? (y or n) @kbd{n} Create a core file? (y or n) @kbd{n} (@value{GDBP}) @end smallexample @cindex @value{GDBN} internal error @cindex internal errors, control of @value{GDBN} behavior @cindex demangler crashes @kindex maint set internal-error @kindex maint show internal-error @kindex maint set internal-warning @kindex maint show internal-warning @kindex maint set demangler-warning @kindex maint show demangler-warning @item maint set internal-error @var{action} [ask|yes|no] @itemx maint show internal-error @var{action} @itemx maint set internal-warning @var{action} [ask|yes|no] @itemx maint show internal-warning @var{action} @itemx maint set demangler-warning @var{action} [ask|yes|no] @itemx maint show demangler-warning @var{action} When @value{GDBN} reports an internal problem (error or warning) it gives the user the opportunity to both quit @value{GDBN} and create a core file of the current @value{GDBN} session. These commands let you override the default behaviour for each particular @var{action}, described in the table below. @table @samp @item quit You can specify that @value{GDBN} should always (yes) or never (no) quit. The default is to ask the user what to do. @item corefile You can specify that @value{GDBN} should always (yes) or never (no) create a core file. The default is to ask the user what to do. Note that there is no @code{corefile} option for @code{demangler-warning}: demangler warnings always create a core file and this cannot be disabled. @end table @kindex maint packet @item maint packet @var{text} If @value{GDBN} is talking to an inferior via the serial protocol, then this command sends the string @var{text} to the inferior, and displays the response packet. @value{GDBN} supplies the initial @samp{$} character, the terminating @samp{#} character, and the checksum. @kindex maint print architecture @item maint print architecture @r{[}@var{file}@r{]} Print the entire architecture configuration. The optional argument @var{file} names the file where the output goes. @kindex maint print c-tdesc @r{[}@var{file}@r{]} @item maint print c-tdesc Print the target description (@pxref{Target Descriptions}) as a C source file. By default, the target description is for the current target, but if the optional argument @var{file} is provided, that file is used to produce the description. The @var{file} should be an XML document, of the form described in @ref{Target Description Format}. The created source file is built into @value{GDBN} when @value{GDBN} is built again. This command is used by developers after they add or modify XML target descriptions. @kindex maint check xml-descriptions @item maint check xml-descriptions @var{dir} Check that the target descriptions dynamically created by @value{GDBN} equal the descriptions created from XML files found in @var{dir}. @anchor{maint check libthread-db} @kindex maint check libthread-db @item maint check libthread-db Run integrity checks on the current inferior's thread debugging library. This exercises all @code{libthread_db} functionality used by @value{GDBN} on GNU/Linux systems, and by extension also exercises the @code{proc_service} functions provided by @value{GDBN} that @code{libthread_db} uses. Note that parts of the test may be skipped on some platforms when debugging core files. @kindex maint print dummy-frames @item maint print dummy-frames Prints the contents of @value{GDBN}'s internal dummy-frame stack. @smallexample (@value{GDBP}) @kbd{b add} @dots{} (@value{GDBP}) @kbd{print add(2,3)} Breakpoint 2, add (a=2, b=3) at @dots{} 58 return (a + b); The program being debugged stopped while in a function called from GDB. @dots{} (@value{GDBP}) @kbd{maint print dummy-frames} 0xa8206d8: id=@{stack=0xbfffe734,code=0xbfffe73f,!special@}, ptid=process 9353 (@value{GDBP}) @end smallexample Takes an optional file parameter. @kindex maint print registers @kindex maint print raw-registers @kindex maint print cooked-registers @kindex maint print register-groups @kindex maint print remote-registers @item maint print registers @r{[}@var{file}@r{]} @itemx maint print raw-registers @r{[}@var{file}@r{]} @itemx maint print cooked-registers @r{[}@var{file}@r{]} @itemx maint print register-groups @r{[}@var{file}@r{]} @itemx maint print remote-registers @r{[}@var{file}@r{]} Print @value{GDBN}'s internal register data structures. The command @code{maint print raw-registers} includes the contents of the raw register cache; the command @code{maint print cooked-registers} includes the (cooked) value of all registers, including registers which aren't available on the target nor visible to user; the command @code{maint print register-groups} includes the groups that each register is a member of; and the command @code{maint print remote-registers} includes the remote target's register numbers and offsets in the `G' packets. These commands take an optional parameter, a file name to which to write the information. @kindex maint print reggroups @item maint print reggroups @r{[}@var{file}@r{]} Print @value{GDBN}'s internal register group data structures. The optional argument @var{file} tells to what file to write the information. The register groups info looks like this: @smallexample (@value{GDBP}) @kbd{maint print reggroups} Group Type general user float user all user vector user system user save internal restore internal @end smallexample @kindex flushregs @item flushregs This command forces @value{GDBN} to flush its internal register cache. @kindex maint print objfiles @cindex info for known object files @item maint print objfiles @r{[}@var{regexp}@r{]} Print a dump of all known object files. If @var{regexp} is specified, only print object files whose names match @var{regexp}. For each object file, this command prints its name, address in memory, and all of its psymtabs and symtabs. @kindex maint print user-registers @cindex user registers @item maint print user-registers List all currently available @dfn{user registers}. User registers typically provide alternate names for actual hardware registers. They include the four ``standard'' registers @code{$fp}, @code{$pc}, @code{$sp}, and @code{$ps}. @xref{standard registers}. User registers can be used in expressions in the same way as the canonical register names, but only the latter are listed by the @code{info registers} and @code{maint print registers} commands. @kindex maint print section-scripts @cindex info for known .debug_gdb_scripts-loaded scripts @item maint print section-scripts [@var{regexp}] Print a dump of scripts specified in the @code{.debug_gdb_section} section. If @var{regexp} is specified, only print scripts loaded by object files matching @var{regexp}. For each script, this command prints its name as specified in the objfile, and the full path if known. @xref{dotdebug_gdb_scripts section}. @kindex maint print statistics @cindex bcache statistics @item maint print statistics This command prints, for each object file in the program, various data about that object file followed by the byte cache (@dfn{bcache}) statistics for the object file. The objfile data includes the number of minimal, partial, full, and stabs symbols, the number of types defined by the objfile, the number of as yet unexpanded psym tables, the number of line tables and string tables, and the amount of memory used by the various tables. The bcache statistics include the counts, sizes, and counts of duplicates of all and unique objects, max, average, and median entry size, total memory used and its overhead and savings, and various measures of the hash table size and chain lengths. @kindex maint print target-stack @cindex target stack description @item maint print target-stack A @dfn{target} is an interface between the debugger and a particular kind of file or process. Targets can be stacked in @dfn{strata}, so that more than one target can potentially respond to a request. In particular, memory accesses will walk down the stack of targets until they find a target that is interested in handling that particular address. This command prints a short description of each layer that was pushed on the @dfn{target stack}, starting from the top layer down to the bottom one. @kindex maint print type @cindex type chain of a data type @item maint print type @var{expr} Print the type chain for a type specified by @var{expr}. The argument can be either a type name or a symbol. If it is a symbol, the type of that symbol is described. The type chain produced by this command is a recursive definition of the data type as stored in @value{GDBN}'s data structures, including its flags and contained types. @kindex maint selftest @cindex self tests @item maint selftest @r{[}@var{filter}@r{]} Run any self tests that were compiled in to @value{GDBN}. This will print a message showing how many tests were run, and how many failed. If a @var{filter} is passed, only the tests with @var{filter} in their name will by ran. @kindex maint info selftests @cindex self tests @item maint info selftests List the selftests compiled in to @value{GDBN}. @kindex maint set dwarf always-disassemble @kindex maint show dwarf always-disassemble @item maint set dwarf always-disassemble @item maint show dwarf always-disassemble Control the behavior of @code{info address} when using DWARF debugging information. The default is @code{off}, which means that @value{GDBN} should try to describe a variable's location in an easily readable format. When @code{on}, @value{GDBN} will instead display the DWARF location expression in an assembly-like format. Note that some locations are too complex for @value{GDBN} to describe simply; in this case you will always see the disassembly form. Here is an example of the resulting disassembly: @smallexample (gdb) info addr argc Symbol "argc" is a complex DWARF expression: 1: DW_OP_fbreg 0 @end smallexample For more information on these expressions, see @uref{http://www.dwarfstd.org/, the DWARF standard}. @kindex maint set dwarf max-cache-age @kindex maint show dwarf max-cache-age @item maint set dwarf max-cache-age @itemx maint show dwarf max-cache-age Control the DWARF compilation unit cache. @cindex DWARF compilation units cache In object files with inter-compilation-unit references, such as those produced by the GCC option @samp{-feliminate-dwarf2-dups}, the DWARF reader needs to frequently refer to previously read compilation units. This setting controls how long a compilation unit will remain in the cache if it is not referenced. A higher limit means that cached compilation units will be stored in memory longer, and more total memory will be used. Setting it to zero disables caching, which will slow down @value{GDBN} startup, but reduce memory consumption. @kindex maint set dwarf unwinders @kindex maint show dwarf unwinders @item maint set dwarf unwinders @itemx maint show dwarf unwinders Control use of the DWARF frame unwinders. @cindex DWARF frame unwinders Many targets that support DWARF debugging use @value{GDBN}'s DWARF frame unwinders to build the backtrace. Many of these targets will also have a second mechanism for building the backtrace for use in cases where DWARF information is not available, this second mechanism is often an analysis of a function's prologue. In order to extend testing coverage of the second level stack unwinding mechanisms it is helpful to be able to disable the DWARF stack unwinders, this can be done with this switch. In normal use of @value{GDBN} disabling the DWARF unwinders is not advisable, there are cases that are better handled through DWARF than prologue analysis, and the debug experience is likely to be better with the DWARF frame unwinders enabled. If DWARF frame unwinders are not supported for a particular target architecture, then enabling this flag does not cause them to be used. @kindex maint set worker-threads @kindex maint show worker-threads @item maint set worker-threads @item maint show worker-threads Control the number of worker threads that may be used by @value{GDBN}. On capable hosts, @value{GDBN} may use multiple threads to speed up certain CPU-intensive operations, such as demangling symbol names. While the number of threads used by @value{GDBN} may vary, this command can be used to set an upper bound on this number. The default is @code{unlimited}, which lets @value{GDBN} choose a reasonable number. Note that this only controls worker threads started by @value{GDBN} itself; libraries used by @value{GDBN} may start threads of their own. @kindex maint set profile @kindex maint show profile @cindex profiling GDB @item maint set profile @itemx maint show profile Control profiling of @value{GDBN}. Profiling will be disabled until you use the @samp{maint set profile} command to enable it. When you enable profiling, the system will begin collecting timing and execution count data; when you disable profiling or exit @value{GDBN}, the results will be written to a log file. Remember that if you use profiling, @value{GDBN} will overwrite the profiling log file (often called @file{gmon.out}). If you have a record of important profiling data in a @file{gmon.out} file, be sure to move it to a safe location. Configuring with @samp{--enable-profiling} arranges for @value{GDBN} to be compiled with the @samp{-pg} compiler option. @kindex maint set show-debug-regs @kindex maint show show-debug-regs @cindex hardware debug registers @item maint set show-debug-regs @itemx maint show show-debug-regs Control whether to show variables that mirror the hardware debug registers. Use @code{on} to enable, @code{off} to disable. If enabled, the debug registers values are shown when @value{GDBN} inserts or removes a hardware breakpoint or watchpoint, and when the inferior triggers a hardware-assisted breakpoint or watchpoint. @kindex maint set show-all-tib @kindex maint show show-all-tib @item maint set show-all-tib @itemx maint show show-all-tib Control whether to show all non zero areas within a 1k block starting at thread local base, when using the @samp{info w32 thread-information-block} command. @kindex maint set target-async @kindex maint show target-async @item maint set target-async @itemx maint show target-async This controls whether @value{GDBN} targets operate in synchronous or asynchronous mode (@pxref{Background Execution}). Normally the default is asynchronous, if it is available; but this can be changed to more easily debug problems occurring only in synchronous mode. @kindex maint set target-non-stop @var{mode} [on|off|auto] @kindex maint show target-non-stop @item maint set target-non-stop @itemx maint show target-non-stop This controls whether @value{GDBN} targets always operate in non-stop mode even if @code{set non-stop} is @code{off} (@pxref{Non-Stop Mode}). The default is @code{auto}, meaning non-stop mode is enabled if supported by the target. @table @code @item maint set target-non-stop auto This is the default mode. @value{GDBN} controls the target in non-stop mode if the target supports it. @item maint set target-non-stop on @value{GDBN} controls the target in non-stop mode even if the target does not indicate support. @item maint set target-non-stop off @value{GDBN} does not control the target in non-stop mode even if the target supports it. @end table @kindex maint set tui-resize-message @kindex maint show tui-resize-message @item maint set tui-resize-message @item maint show tui-resize-message Control whether @value{GDBN} displays a message each time the terminal is resized when in TUI mode. The default is @code{off}, which means that @value{GDBN} is silent during resizes. When @code{on}, @value{GDBN} will display a message after a resize is completed; the message will include a number indicating how many times the terminal has been resized. This setting is intended for use by the test suite, where it would otherwise be difficult to determine when a resize and refresh has been completed. @kindex maint set per-command @kindex maint show per-command @item maint set per-command @itemx maint show per-command @cindex resources used by commands @value{GDBN} can display the resources used by each command. This is useful in debugging performance problems. @table @code @item maint set per-command space [on|off] @itemx maint show per-command space Enable or disable the printing of the memory used by GDB for each command. If enabled, @value{GDBN} will display how much memory each command took, following the command's own output. This can also be requested by invoking @value{GDBN} with the @option{--statistics} command-line switch (@pxref{Mode Options}). @item maint set per-command time [on|off] @itemx maint show per-command time Enable or disable the printing of the execution time of @value{GDBN} for each command. If enabled, @value{GDBN} will display how much time it took to execute each command, following the command's own output. Both CPU time and wallclock time are printed. Printing both is useful when trying to determine whether the cost is CPU or, e.g., disk/network latency. Note that the CPU time printed is for @value{GDBN} only, it does not include the execution time of the inferior because there's no mechanism currently to compute how much time was spent by @value{GDBN} and how much time was spent by the program been debugged. This can also be requested by invoking @value{GDBN} with the @option{--statistics} command-line switch (@pxref{Mode Options}). @item maint set per-command symtab [on|off] @itemx maint show per-command symtab Enable or disable the printing of basic symbol table statistics for each command. If enabled, @value{GDBN} will display the following information: @enumerate a @item number of symbol tables @item number of primary symbol tables @item number of blocks in the blockvector @end enumerate @end table @kindex maint set check-libthread-db @kindex maint show check-libthread-db @item maint set check-libthread-db [on|off] @itemx maint show check-libthread-db Control whether @value{GDBN} should run integrity checks on inferior specific thread debugging libraries as they are loaded. The default is not to perform such checks. If any check fails @value{GDBN} will unload the library and continue searching for a suitable candidate as described in @ref{set libthread-db-search-path}. For more information about the tests, see @ref{maint check libthread-db}. @kindex maint space @cindex memory used by commands @item maint space @var{value} An alias for @code{maint set per-command space}. A non-zero value enables it, zero disables it. @kindex maint time @cindex time of command execution @item maint time @var{value} An alias for @code{maint set per-command time}. A non-zero value enables it, zero disables it. @kindex maint translate-address @item maint translate-address @r{[}@var{section}@r{]} @var{addr} Find the symbol stored at the location specified by the address @var{addr} and an optional section name @var{section}. If found, @value{GDBN} prints the name of the closest symbol and an offset from the symbol's location to the specified address. This is similar to the @code{info address} command (@pxref{Symbols}), except that this command also allows to find symbols in other sections. If section was not specified, the section in which the symbol was found is also printed. For dynamically linked executables, the name of executable or shared library containing the symbol is printed as well. @kindex maint test-options @item maint test-options require-delimiter @itemx maint test-options unknown-is-error @itemx maint test-options unknown-is-operand These commands are used by the testsuite to validate the command options framework. The @code{require-delimiter} variant requires a double-dash delimiter to indicate end of options. The @code{unknown-is-error} and @code{unknown-is-operand} do not. The @code{unknown-is-error} variant throws an error on unknown option, while @code{unknown-is-operand} treats unknown options as the start of the command's operands. When run, the commands output the result of the processed options. When completed, the commands store the internal result of completion in a variable exposed by the @code{maint show test-options-completion-result} command. @kindex maint show test-options-completion-result @item maint show test-options-completion-result Shows the result of completing the @code{maint test-options} subcommands. This is used by the testsuite to validate completion support in the command options framework. @kindex maint set test-settings @kindex maint show test-settings @item maint set test-settings @var{kind} @itemx maint show test-settings @var{kind} These are representative commands for each @var{kind} of setting type @value{GDBN} supports. They are used by the testsuite for exercising the settings infrastructure. @kindex maint with @item maint with @var{setting} [@var{value}] [-- @var{command}] Like the @code{with} command, but works with @code{maintenance set} variables. This is used by the testsuite to exercise the @code{with} command's infrastructure. @end table The following command is useful for non-interactive invocations of @value{GDBN}, such as in the test suite. @table @code @item set watchdog @var{nsec} @kindex set watchdog @cindex watchdog timer @cindex timeout for commands Set the maximum number of seconds @value{GDBN} will wait for the target operation to finish. If this time expires, @value{GDBN} reports and error and the command is aborted. @item show watchdog Show the current setting of the target wait timeout. @end table @node Remote Protocol @appendix @value{GDBN} Remote Serial Protocol @menu * Overview:: * Packets:: * Stop Reply Packets:: * General Query Packets:: * Architecture-Specific Protocol Details:: * Tracepoint Packets:: * Host I/O Packets:: * Interrupts:: * Notification Packets:: * Remote Non-Stop:: * Packet Acknowledgment:: * Examples:: * File-I/O Remote Protocol Extension:: * Library List Format:: * Library List Format for SVR4 Targets:: * Memory Map Format:: * Thread List Format:: * Traceframe Info Format:: * Branch Trace Format:: * Branch Trace Configuration Format:: @end menu @node Overview @section Overview There may be occasions when you need to know something about the protocol---for example, if there is only one serial port to your target machine, you might want your program to do something special if it recognizes a packet meant for @value{GDBN}. In the examples below, @samp{->} and @samp{<-} are used to indicate transmitted and received data, respectively. @cindex protocol, @value{GDBN} remote serial @cindex serial protocol, @value{GDBN} remote @cindex remote serial protocol All @value{GDBN} commands and responses (other than acknowledgments and notifications, see @ref{Notification Packets}) are sent as a @var{packet}. A @var{packet} is introduced with the character @samp{$}, the actual @var{packet-data}, and the terminating character @samp{#} followed by a two-digit @var{checksum}: @smallexample @code{$}@var{packet-data}@code{#}@var{checksum} @end smallexample @noindent @cindex checksum, for @value{GDBN} remote @noindent The two-digit @var{checksum} is computed as the modulo 256 sum of all characters between the leading @samp{$} and the trailing @samp{#} (an eight bit unsigned checksum). Implementors should note that prior to @value{GDBN} 5.0 the protocol specification also included an optional two-digit @var{sequence-id}: @smallexample @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum} @end smallexample @cindex sequence-id, for @value{GDBN} remote @noindent That @var{sequence-id} was appended to the acknowledgment. @value{GDBN} has never output @var{sequence-id}s. Stubs that handle packets added since @value{GDBN} 5.0 must not accept @var{sequence-id}. When either the host or the target machine receives a packet, the first response expected is an acknowledgment: either @samp{+} (to indicate the package was received correctly) or @samp{-} (to request retransmission): @smallexample -> @code{$}@var{packet-data}@code{#}@var{checksum} <- @code{+} @end smallexample @noindent The @samp{+}/@samp{-} acknowledgments can be disabled once a connection is established. @xref{Packet Acknowledgment}, for details. The host (@value{GDBN}) sends @var{command}s, and the target (the debugging stub incorporated in your program) sends a @var{response}. In the case of step and continue @var{command}s, the response is only sent when the operation has completed, and the target has again stopped all threads in all attached processes. This is the default all-stop mode behavior, but the remote protocol also supports @value{GDBN}'s non-stop execution mode; see @ref{Remote Non-Stop}, for details. @var{packet-data} consists of a sequence of characters with the exception of @samp{#} and @samp{$} (see @samp{X} packet for additional exceptions). @cindex remote protocol, field separator Fields within the packet should be separated using @samp{,} @samp{;} or @samp{:}. Except where otherwise noted all numbers are represented in @sc{hex} with leading zeros suppressed. Implementors should note that prior to @value{GDBN} 5.0, the character @samp{:} could not appear as the third character in a packet (as it would potentially conflict with the @var{sequence-id}). @cindex remote protocol, binary data @anchor{Binary Data} Binary data in most packets is encoded either as two hexadecimal digits per byte of binary data. This allowed the traditional remote protocol to work over connections which were only seven-bit clean. Some packets designed more recently assume an eight-bit clean connection, and use a more efficient encoding to send and receive binary data. The binary data representation uses @code{7d} (@sc{ascii} @samp{@}}) as an escape character. Any escaped byte is transmitted as the escape character followed by the original character XORed with @code{0x20}. For example, the byte @code{0x7d} would be transmitted as the two bytes @code{0x7d 0x5d}. The bytes @code{0x23} (@sc{ascii} @samp{#}), @code{0x24} (@sc{ascii} @samp{$}), and @code{0x7d} (@sc{ascii} @samp{@}}) must always be escaped. Responses sent by the stub must also escape @code{0x2a} (@sc{ascii} @samp{*}), so that it is not interpreted as the start of a run-length encoded sequence (described next). Response @var{data} can be run-length encoded to save space. Run-length encoding replaces runs of identical characters with one instance of the repeated character, followed by a @samp{*} and a repeat count. The repeat count is itself sent encoded, to avoid binary characters in @var{data}: a value of @var{n} is sent as @code{@var{n}+29}. For a repeat count greater or equal to 3, this produces a printable @sc{ascii} character, e.g.@: a space (@sc{ascii} code 32) for a repeat count of 3. (This is because run-length encoding starts to win for counts 3 or more.) Thus, for example, @samp{0* } is a run-length encoding of ``0000'': the space character after @samp{*} means repeat the leading @code{0} @w{@code{32 - 29 = 3}} more times. The printable characters @samp{#} and @samp{$} or with a numeric value greater than 126 must not be used. Runs of six repeats (@samp{#}) or seven repeats (@samp{$}) can be expanded using a repeat count of only five (@samp{"}). For example, @samp{00000000} can be encoded as @samp{0*"00}. The error response returned for some packets includes a two character error number. That number is not well defined. @cindex empty response, for unsupported packets For any @var{command} not supported by the stub, an empty response (@samp{$#00}) should be returned. That way it is possible to extend the protocol. A newer @value{GDBN} can tell if a packet is supported based on that response. At a minimum, a stub is required to support the @samp{g} and @samp{G} commands for register access, and the @samp{m} and @samp{M} commands for memory access. Stubs that only control single-threaded targets can implement run control with the @samp{c} (continue), and @samp{s} (step) commands. Stubs that support multi-threading targets should support the @samp{vCont} command. All other commands are optional. @node Packets @section Packets The following table provides a complete list of all currently defined @var{command}s and their corresponding response @var{data}. @xref{File-I/O Remote Protocol Extension}, for details about the File I/O extension of the remote protocol. Each packet's description has a template showing the packet's overall syntax, followed by an explanation of the packet's meaning. We include spaces in some of the templates for clarity; these are not part of the packet's syntax. No @value{GDBN} packet uses spaces to separate its components. For example, a template like @samp{foo @var{bar} @var{baz}} describes a packet beginning with the three ASCII bytes @samp{foo}, followed by a @var{bar}, followed directly by a @var{baz}. @value{GDBN} does not transmit a space character between the @samp{foo} and the @var{bar}, or between the @var{bar} and the @var{baz}. @cindex @var{thread-id}, in remote protocol @anchor{thread-id syntax} Several packets and replies include a @var{thread-id} field to identify a thread. Normally these are positive numbers with a target-specific interpretation, formatted as big-endian hex strings. A @var{thread-id} can also be a literal @samp{-1} to indicate all threads, or @samp{0} to pick any thread. In addition, the remote protocol supports a multiprocess feature in which the @var{thread-id} syntax is extended to optionally include both process and thread ID fields, as @samp{p@var{pid}.@var{tid}}. The @var{pid} (process) and @var{tid} (thread) components each have the format described above: a positive number with target-specific interpretation formatted as a big-endian hex string, literal @samp{-1} to indicate all processes or threads (respectively), or @samp{0} to indicate an arbitrary process or thread. Specifying just a process, as @samp{p@var{pid}}, is equivalent to @samp{p@var{pid}.-1}. It is an error to specify all processes but a specific thread, such as @samp{p-1.@var{tid}}. Note that the @samp{p} prefix is @emph{not} used for those packets and replies explicitly documented to include a process ID, rather than a @var{thread-id}. The multiprocess @var{thread-id} syntax extensions are only used if both @value{GDBN} and the stub report support for the @samp{multiprocess} feature using @samp{qSupported}. @xref{multiprocess extensions}, for more information. Note that all packet forms beginning with an upper- or lower-case letter, other than those described here, are reserved for future use. Here are the packet descriptions. @table @samp @item ! @cindex @samp{!} packet @anchor{extended mode} Enable extended mode. In extended mode, the remote server is made persistent. The @samp{R} packet is used to restart the program being debugged. Reply: @table @samp @item OK The remote target both supports and has enabled extended mode. @end table @item ? @cindex @samp{?} packet @anchor{? packet} Indicate the reason the target halted. The reply is the same as for step and continue. This packet has a special interpretation when the target is in non-stop mode; see @ref{Remote Non-Stop}. Reply: @xref{Stop Reply Packets}, for the reply specifications. @item A @var{arglen},@var{argnum},@var{arg},@dots{} @cindex @samp{A} packet Initialized @code{argv[]} array passed into program. @var{arglen} specifies the number of bytes in the hex encoded byte stream @var{arg}. See @code{gdbserver} for more details. Reply: @table @samp @item OK The arguments were set. @item E @var{NN} An error occurred. @end table @item b @var{baud} @cindex @samp{b} packet (Don't use this packet; its behavior is not well-defined.) Change the serial line speed to @var{baud}. JTC: @emph{When does the transport layer state change? When it's received, or after the ACK is transmitted. In either case, there are problems if the command or the acknowledgment packet is dropped.} Stan: @emph{If people really wanted to add something like this, and get it working for the first time, they ought to modify ser-unix.c to send some kind of out-of-band message to a specially-setup stub and have the switch happen "in between" packets, so that from remote protocol's point of view, nothing actually happened.} @item B @var{addr},@var{mode} @cindex @samp{B} packet Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a breakpoint at @var{addr}. Don't use this packet. Use the @samp{Z} and @samp{z} packets instead (@pxref{insert breakpoint or watchpoint packet}). @cindex @samp{bc} packet @anchor{bc} @item bc Backward continue. Execute the target system in reverse. No parameter. @xref{Reverse Execution}, for more information. Reply: @xref{Stop Reply Packets}, for the reply specifications. @cindex @samp{bs} packet @anchor{bs} @item bs Backward single step. Execute one instruction in reverse. No parameter. @xref{Reverse Execution}, for more information. Reply: @xref{Stop Reply Packets}, for the reply specifications. @item c @r{[}@var{addr}@r{]} @cindex @samp{c} packet Continue at @var{addr}, which is the address to resume. If @var{addr} is omitted, resume at current address. This packet is deprecated for multi-threading support. @xref{vCont packet}. Reply: @xref{Stop Reply Packets}, for the reply specifications. @item C @var{sig}@r{[};@var{addr}@r{]} @cindex @samp{C} packet Continue with signal @var{sig} (hex signal number). If @samp{;@var{addr}} is omitted, resume at same address. This packet is deprecated for multi-threading support. @xref{vCont packet}. Reply: @xref{Stop Reply Packets}, for the reply specifications. @item d @cindex @samp{d} packet Toggle debug flag. Don't use this packet; instead, define a general set packet (@pxref{General Query Packets}). @item D @itemx D;@var{pid} @cindex @samp{D} packet The first form of the packet is used to detach @value{GDBN} from the remote system. It is sent to the remote target before @value{GDBN} disconnects via the @code{detach} command. The second form, including a process ID, is used when multiprocess protocol extensions are enabled (@pxref{multiprocess extensions}), to detach only a specific process. The @var{pid} is specified as a big-endian hex string. Reply: @table @samp @item OK for success @item E @var{NN} for an error @end table @item F @var{RC},@var{EE},@var{CF};@var{XX} @cindex @samp{F} packet A reply from @value{GDBN} to an @samp{F} packet sent by the target. This is part of the File-I/O protocol extension. @xref{File-I/O Remote Protocol Extension}, for the specification. @item g @anchor{read registers packet} @cindex @samp{g} packet Read general registers. Reply: @table @samp @item @var{XX@dots{}} Each byte of register data is described by two hex digits. The bytes with the register are transmitted in target byte order. The size of each register and their position within the @samp{g} packet are determined by the @value{GDBN} internal gdbarch functions @code{DEPRECATED_REGISTER_RAW_SIZE} and @code{gdbarch_register_name}. When reading registers from a trace frame (@pxref{Analyze Collected Data,,Using the Collected Data}), the stub may also return a string of literal @samp{x}'s in place of the register data digits, to indicate that the corresponding register has not been collected, thus its value is unavailable. For example, for an architecture with 4 registers of 4 bytes each, the following reply indicates to @value{GDBN} that registers 0 and 2 have not been collected, while registers 1 and 3 have been collected, and both have zero value: @smallexample -> @code{g} <- @code{xxxxxxxx00000000xxxxxxxx00000000} @end smallexample @item E @var{NN} for an error. @end table @item G @var{XX@dots{}} @cindex @samp{G} packet Write general registers. @xref{read registers packet}, for a description of the @var{XX@dots{}} data. Reply: @table @samp @item OK for success @item E @var{NN} for an error @end table @item H @var{op} @var{thread-id} @cindex @samp{H} packet Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g}, @samp{G}, et.al.). Depending on the operation to be performed, @var{op} should be @samp{c} for step and continue operations (note that this is deprecated, supporting the @samp{vCont} command is a better option), and @samp{g} for other operations. The thread designator @var{thread-id} has the format and interpretation described in @ref{thread-id syntax}. Reply: @table @samp @item OK for success @item E @var{NN} for an error @end table @c FIXME: JTC: @c 'H': How restrictive (or permissive) is the thread model. If a @c thread is selected and stopped, are other threads allowed @c to continue to execute? As I mentioned above, I think the @c semantics of each command when a thread is selected must be @c described. For example: @c @c 'g': If the stub supports threads and a specific thread is @c selected, returns the register block from that thread; @c otherwise returns current registers. @c @c 'G' If the stub supports threads and a specific thread is @c selected, sets the registers of the register block of @c that thread; otherwise sets current registers. @item i @r{[}@var{addr}@r{[},@var{nnn}@r{]]} @anchor{cycle step packet} @cindex @samp{i} packet Step the remote target by a single clock cycle. If @samp{,@var{nnn}} is present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle step starting at that address. @item I @cindex @samp{I} packet Signal, then cycle step. @xref{step with signal packet}. @xref{cycle step packet}. @item k @cindex @samp{k} packet Kill request. The exact effect of this packet is not specified. For a bare-metal target, it may power cycle or reset the target system. For that reason, the @samp{k} packet has no reply. For a single-process target, it may kill that process if possible. A multiple-process target may choose to kill just one process, or all that are under @value{GDBN}'s control. For more precise control, use the vKill packet (@pxref{vKill packet}). If the target system immediately closes the connection in response to @samp{k}, @value{GDBN} does not consider the lack of packet acknowledgment to be an error, and assumes the kill was successful. If connected using @kbd{target extended-remote}, and the target does not close the connection in response to a kill request, @value{GDBN} probes the target state as if a new connection was opened (@pxref{? packet}). @item m @var{addr},@var{length} @cindex @samp{m} packet Read @var{length} addressable memory units starting at address @var{addr} (@pxref{addressable memory unit}). Note that @var{addr} may not be aligned to any particular boundary. The stub need not use any particular size or alignment when gathering data from memory for the response; even if @var{addr} is word-aligned and @var{length} is a multiple of the word size, the stub is free to use byte accesses, or not. For this reason, this packet may not be suitable for accessing memory-mapped I/O devices. @cindex alignment of remote memory accesses @cindex size of remote memory accesses @cindex memory, alignment and size of remote accesses Reply: @table @samp @item @var{XX@dots{}} Memory contents; each byte is transmitted as a two-digit hexadecimal number. The reply may contain fewer addressable memory units than requested if the server was able to read only part of the region of memory. @item E @var{NN} @var{NN} is errno @end table @item M @var{addr},@var{length}:@var{XX@dots{}} @cindex @samp{M} packet Write @var{length} addressable memory units starting at address @var{addr} (@pxref{addressable memory unit}). The data is given by @var{XX@dots{}}; each byte is transmitted as a two-digit hexadecimal number. Reply: @table @samp @item OK for success @item E @var{NN} for an error (this includes the case where only part of the data was written). @end table @item p @var{n} @cindex @samp{p} packet Read the value of register @var{n}; @var{n} is in hex. @xref{read registers packet}, for a description of how the returned register value is encoded. Reply: @table @samp @item @var{XX@dots{}} the register's value @item E @var{NN} for an error @item @w{} Indicating an unrecognized @var{query}. @end table @item P @var{n@dots{}}=@var{r@dots{}} @anchor{write register packet} @cindex @samp{P} packet Write register @var{n@dots{}} with value @var{r@dots{}}. The register number @var{n} is in hexadecimal, and @var{r@dots{}} contains two hex digits for each byte in the register (target byte order). Reply: @table @samp @item OK for success @item E @var{NN} for an error @end table @item q @var{name} @var{params}@dots{} @itemx Q @var{name} @var{params}@dots{} @cindex @samp{q} packet @cindex @samp{Q} packet General query (@samp{q}) and set (@samp{Q}). These packets are described fully in @ref{General Query Packets}. @item r @cindex @samp{r} packet Reset the entire system. Don't use this packet; use the @samp{R} packet instead. @item R @var{XX} @cindex @samp{R} packet Restart the program being debugged. The @var{XX}, while needed, is ignored. This packet is only available in extended mode (@pxref{extended mode}). The @samp{R} packet has no reply. @item s @r{[}@var{addr}@r{]} @cindex @samp{s} packet Single step, resuming at @var{addr}. If @var{addr} is omitted, resume at same address. This packet is deprecated for multi-threading support. @xref{vCont packet}. Reply: @xref{Stop Reply Packets}, for the reply specifications. @item S @var{sig}@r{[};@var{addr}@r{]} @anchor{step with signal packet} @cindex @samp{S} packet Step with signal. This is analogous to the @samp{C} packet, but requests a single-step, rather than a normal resumption of execution. This packet is deprecated for multi-threading support. @xref{vCont packet}. Reply: @xref{Stop Reply Packets}, for the reply specifications. @item t @var{addr}:@var{PP},@var{MM} @cindex @samp{t} packet Search backwards starting at address @var{addr} for a match with pattern @var{PP} and mask @var{MM}, both of which are are 4 byte long. There must be at least 3 digits in @var{addr}. @item T @var{thread-id} @cindex @samp{T} packet Find out if the thread @var{thread-id} is alive. @xref{thread-id syntax}. Reply: @table @samp @item OK thread is still alive @item E @var{NN} thread is dead @end table @item v Packets starting with @samp{v} are identified by a multi-letter name, up to the first @samp{;} or @samp{?} (or the end of the packet). @item vAttach;@var{pid} @cindex @samp{vAttach} packet Attach to a new process with the specified process ID @var{pid}. The process ID is a hexadecimal integer identifying the process. In all-stop mode, all threads in the attached process are stopped; in non-stop mode, it may be attached without being stopped if that is supported by the target. @c In non-stop mode, on a successful vAttach, the stub should set the @c current thread to a thread of the newly-attached process. After @c attaching, GDB queries for the attached process's thread ID with qC. @c Also note that, from a user perspective, whether or not the @c target is stopped on attach in non-stop mode depends on whether you @c use the foreground or background version of the attach command, not @c on what vAttach does; GDB does the right thing with respect to either @c stopping or restarting threads. This packet is only available in extended mode (@pxref{extended mode}). Reply: @table @samp @item E @var{nn} for an error @item @r{Any stop packet} for success in all-stop mode (@pxref{Stop Reply Packets}) @item OK for success in non-stop mode (@pxref{Remote Non-Stop}) @end table @item vCont@r{[};@var{action}@r{[}:@var{thread-id}@r{]]}@dots{} @cindex @samp{vCont} packet @anchor{vCont packet} Resume the inferior, specifying different actions for each thread. For each inferior thread, the leftmost action with a matching @var{thread-id} is applied. Threads that don't match any action remain in their current state. Thread IDs are specified using the syntax described in @ref{thread-id syntax}. If multiprocess extensions (@pxref{multiprocess extensions}) are supported, actions can be specified to match all threads in a process by using the @samp{p@var{pid}.-1} form of the @var{thread-id}. An action with no @var{thread-id} matches all threads. Specifying no actions is an error. Currently supported actions are: @table @samp @item c Continue. @item C @var{sig} Continue with signal @var{sig}. The signal @var{sig} should be two hex digits. @item s Step. @item S @var{sig} Step with signal @var{sig}. The signal @var{sig} should be two hex digits. @item t Stop. @item r @var{start},@var{end} Step once, and then keep stepping as long as the thread stops at addresses between @var{start} (inclusive) and @var{end} (exclusive). The remote stub reports a stop reply when either the thread goes out of the range or is stopped due to an unrelated reason, such as hitting a breakpoint. @xref{range stepping}. If the range is empty (@var{start} == @var{end}), then the action becomes equivalent to the @samp{s} action. In other words, single-step once, and report the stop (even if the stepped instruction jumps to @var{start}). (A stop reply may be sent at any point even if the PC is still within the stepping range; for example, it is valid to implement this packet in a degenerate way as a single instruction step operation.) @end table The optional argument @var{addr} normally associated with the @samp{c}, @samp{C}, @samp{s}, and @samp{S} packets is not supported in @samp{vCont}. The @samp{t} action is only relevant in non-stop mode (@pxref{Remote Non-Stop}) and may be ignored by the stub otherwise. A stop reply should be generated for any affected thread not already stopped. When a thread is stopped by means of a @samp{t} action, the corresponding stop reply should indicate that the thread has stopped with signal @samp{0}, regardless of whether the target uses some other signal as an implementation detail. The server must ignore @samp{c}, @samp{C}, @samp{s}, @samp{S}, and @samp{r} actions for threads that are already running. Conversely, the server must ignore @samp{t} actions for threads that are already stopped. @emph{Note:} In non-stop mode, a thread is considered running until @value{GDBN} acknowledges an asynchronous stop notification for it with the @samp{vStopped} packet (@pxref{Remote Non-Stop}). The stub must support @samp{vCont} if it reports support for multiprocess extensions (@pxref{multiprocess extensions}). Reply: @xref{Stop Reply Packets}, for the reply specifications. @item vCont? @cindex @samp{vCont?} packet Request a list of actions supported by the @samp{vCont} packet. Reply: @table @samp @item vCont@r{[};@var{action}@dots{}@r{]} The @samp{vCont} packet is supported. Each @var{action} is a supported command in the @samp{vCont} packet. @item @w{} The @samp{vCont} packet is not supported. @end table @anchor{vCtrlC packet} @item vCtrlC @cindex @samp{vCtrlC} packet Interrupt remote target as if a control-C was pressed on the remote terminal. This is the equivalent to reacting to the @code{^C} (@samp{\003}, the control-C character) character in all-stop mode while the target is running, except this works in non-stop mode. @xref{interrupting remote targets}, for more info on the all-stop variant. Reply: @table @samp @item E @var{nn} for an error @item OK for success @end table @item vFile:@var{operation}:@var{parameter}@dots{} @cindex @samp{vFile} packet Perform a file operation on the target system. For details, see @ref{Host I/O Packets}. @item vFlashErase:@var{addr},@var{length} @cindex @samp{vFlashErase} packet Direct the stub to erase @var{length} bytes of flash starting at @var{addr}. The region may enclose any number of flash blocks, but its start and end must fall on block boundaries, as indicated by the flash block size appearing in the memory map (@pxref{Memory Map Format}). @value{GDBN} groups flash memory programming operations together, and sends a @samp{vFlashDone} request after each group; the stub is allowed to delay erase operation until the @samp{vFlashDone} packet is received. Reply: @table @samp @item OK for success @item E @var{NN} for an error @end table @item vFlashWrite:@var{addr}:@var{XX@dots{}} @cindex @samp{vFlashWrite} packet Direct the stub to write data to flash address @var{addr}. The data is passed in binary form using the same encoding as for the @samp{X} packet (@pxref{Binary Data}). The memory ranges specified by @samp{vFlashWrite} packets preceding a @samp{vFlashDone} packet must not overlap, and must appear in order of increasing addresses (although @samp{vFlashErase} packets for higher addresses may already have been received; the ordering is guaranteed only between @samp{vFlashWrite} packets). If a packet writes to an address that was neither erased by a preceding @samp{vFlashErase} packet nor by some other target-specific method, the results are unpredictable. Reply: @table @samp @item OK for success @item E.memtype for vFlashWrite addressing non-flash memory @item E @var{NN} for an error @end table @item vFlashDone @cindex @samp{vFlashDone} packet Indicate to the stub that flash programming operation is finished. The stub is permitted to delay or batch the effects of a group of @samp{vFlashErase} and @samp{vFlashWrite} packets until a @samp{vFlashDone} packet is received. The contents of the affected regions of flash memory are unpredictable until the @samp{vFlashDone} request is completed. @item vKill;@var{pid} @cindex @samp{vKill} packet @anchor{vKill packet} Kill the process with the specified process ID @var{pid}, which is a hexadecimal integer identifying the process. This packet is used in preference to @samp{k} when multiprocess protocol extensions are supported; see @ref{multiprocess extensions}. Reply: @table @samp @item E @var{nn} for an error @item OK for success @end table @item vMustReplyEmpty @cindex @samp{vMustReplyEmpty} packet The correct reply to an unknown @samp{v} packet is to return the empty string, however, some older versions of @command{gdbserver} would incorrectly return @samp{OK} for unknown @samp{v} packets. The @samp{vMustReplyEmpty} is used as a feature test to check how @command{gdbserver} handles unknown packets, it is important that this packet be handled in the same way as other unknown @samp{v} packets. If this packet is handled differently to other unknown @samp{v} packets then it is possible that @value{GDBN} may run into problems in other areas, specifically around use of @samp{vFile:setfs:}. @item vRun;@var{filename}@r{[};@var{argument}@r{]}@dots{} @cindex @samp{vRun} packet Run the program @var{filename}, passing it each @var{argument} on its command line. The file and arguments are hex-encoded strings. If @var{filename} is an empty string, the stub may use a default program (e.g.@: the last program run). The program is created in the stopped state. @c FIXME: What about non-stop mode? This packet is only available in extended mode (@pxref{extended mode}). Reply: @table @samp @item E @var{nn} for an error @item @r{Any stop packet} for success (@pxref{Stop Reply Packets}) @end table @item vStopped @cindex @samp{vStopped} packet @xref{Notification Packets}. @item X @var{addr},@var{length}:@var{XX@dots{}} @anchor{X packet} @cindex @samp{X} packet Write data to memory, where the data is transmitted in binary. Memory is specified by its address @var{addr} and number of addressable memory units @var{length} (@pxref{addressable memory unit}); @samp{@var{XX}@dots{}} is binary data (@pxref{Binary Data}). Reply: @table @samp @item OK for success @item E @var{NN} for an error @end table @item z @var{type},@var{addr},@var{kind} @itemx Z @var{type},@var{addr},@var{kind} @anchor{insert breakpoint or watchpoint packet} @cindex @samp{z} packet @cindex @samp{Z} packets Insert (@samp{Z}) or remove (@samp{z}) a @var{type} breakpoint or watchpoint starting at address @var{address} of kind @var{kind}. Each breakpoint and watchpoint packet @var{type} is documented separately. @emph{Implementation notes: A remote target shall return an empty string for an unrecognized breakpoint or watchpoint packet @var{type}. A remote target shall support either both or neither of a given @samp{Z@var{type}@dots{}} and @samp{z@var{type}@dots{}} packet pair. To avoid potential problems with duplicate packets, the operations should be implemented in an idempotent way.} @item z0,@var{addr},@var{kind} @itemx Z0,@var{addr},@var{kind}@r{[};@var{cond_list}@dots{}@r{]}@r{[};cmds:@var{persist},@var{cmd_list}@dots{}@r{]} @cindex @samp{z0} packet @cindex @samp{Z0} packet Insert (@samp{Z0}) or remove (@samp{z0}) a software breakpoint at address @var{addr} of type @var{kind}. A software breakpoint is implemented by replacing the instruction at @var{addr} with a software breakpoint or trap instruction. The @var{kind} is target-specific and typically indicates the size of the breakpoint in bytes that should be inserted. E.g., the @sc{arm} and @sc{mips} can insert either a 2 or 4 byte breakpoint. Some architectures have additional meanings for @var{kind} (@pxref{Architecture-Specific Protocol Details}); if no architecture-specific value is being used, it should be @samp{0}. @var{kind} is hex-encoded. @var{cond_list} is an optional list of conditional expressions in bytecode form that should be evaluated on the target's side. These are the conditions that should be taken into consideration when deciding if the breakpoint trigger should be reported back to @value{GDBN}. See also the @samp{swbreak} stop reason (@pxref{swbreak stop reason}) for how to best report a software breakpoint event to @value{GDBN}. The @var{cond_list} parameter is comprised of a series of expressions, concatenated without separators. Each expression has the following form: @table @samp @item X @var{len},@var{expr} @var{len} is the length of the bytecode expression and @var{expr} is the actual conditional expression in bytecode form. @end table The optional @var{cmd_list} parameter introduces commands that may be run on the target, rather than being reported back to @value{GDBN}. The parameter starts with a numeric flag @var{persist}; if the flag is nonzero, then the breakpoint may remain active and the commands continue to be run even when @value{GDBN} disconnects from the target. Following this flag is a series of expressions concatenated with no separators. Each expression has the following form: @table @samp @item X @var{len},@var{expr} @var{len} is the length of the bytecode expression and @var{expr} is the actual commands expression in bytecode form. @end table @emph{Implementation note: It is possible for a target to copy or move code that contains software breakpoints (e.g., when implementing overlays). The behavior of this packet, in the presence of such a target, is not defined.} Reply: @table @samp @item OK success @item @w{} not supported @item E @var{NN} for an error @end table @item z1,@var{addr},@var{kind} @itemx Z1,@var{addr},@var{kind}@r{[};@var{cond_list}@dots{}@r{]}@r{[};cmds:@var{persist},@var{cmd_list}@dots{}@r{]} @cindex @samp{z1} packet @cindex @samp{Z1} packet Insert (@samp{Z1}) or remove (@samp{z1}) a hardware breakpoint at address @var{addr}. A hardware breakpoint is implemented using a mechanism that is not dependent on being able to modify the target's memory. The @var{kind}, @var{cond_list}, and @var{cmd_list} arguments have the same meaning as in @samp{Z0} packets. @emph{Implementation note: A hardware breakpoint is not affected by code movement.} Reply: @table @samp @item OK success @item @w{} not supported @item E @var{NN} for an error @end table @item z2,@var{addr},@var{kind} @itemx Z2,@var{addr},@var{kind} @cindex @samp{z2} packet @cindex @samp{Z2} packet Insert (@samp{Z2}) or remove (@samp{z2}) a write watchpoint at @var{addr}. The number of bytes to watch is specified by @var{kind}. Reply: @table @samp @item OK success @item @w{} not supported @item E @var{NN} for an error @end table @item z3,@var{addr},@var{kind} @itemx Z3,@var{addr},@var{kind} @cindex @samp{z3} packet @cindex @samp{Z3} packet Insert (@samp{Z3}) or remove (@samp{z3}) a read watchpoint at @var{addr}. The number of bytes to watch is specified by @var{kind}. Reply: @table @samp @item OK success @item @w{} not supported @item E @var{NN} for an error @end table @item z4,@var{addr},@var{kind} @itemx Z4,@var{addr},@var{kind} @cindex @samp{z4} packet @cindex @samp{Z4} packet Insert (@samp{Z4}) or remove (@samp{z4}) an access watchpoint at @var{addr}. The number of bytes to watch is specified by @var{kind}. Reply: @table @samp @item OK success @item @w{} not supported @item E @var{NN} for an error @end table @end table @node Stop Reply Packets @section Stop Reply Packets @cindex stop reply packets The @samp{C}, @samp{c}, @samp{S}, @samp{s}, @samp{vCont}, @samp{vAttach}, @samp{vRun}, @samp{vStopped}, and @samp{?} packets can receive any of the below as a reply. Except for @samp{?} and @samp{vStopped}, that reply is only returned when the target halts. In the below the exact meaning of @dfn{signal number} is defined by the header @file{include/gdb/signals.h} in the @value{GDBN} source code. In non-stop mode, the server will simply reply @samp{OK} to commands such as @samp{vCont}; any stop will be the subject of a future notification. @xref{Remote Non-Stop}. As in the description of request packets, we include spaces in the reply templates for clarity; these are not part of the reply packet's syntax. No @value{GDBN} stop reply packet uses spaces to separate its components. @table @samp @item S @var{AA} The program received signal number @var{AA} (a two-digit hexadecimal number). This is equivalent to a @samp{T} response with no @var{n}:@var{r} pairs. @item T @var{AA} @var{n1}:@var{r1};@var{n2}:@var{r2};@dots{} @cindex @samp{T} packet reply The program received signal number @var{AA} (a two-digit hexadecimal number). This is equivalent to an @samp{S} response, except that the @samp{@var{n}:@var{r}} pairs can carry values of important registers and other information directly in the stop reply packet, reducing round-trip latency. Single-step and breakpoint traps are reported this way. Each @samp{@var{n}:@var{r}} pair is interpreted as follows: @itemize @bullet @item If @var{n} is a hexadecimal number, it is a register number, and the corresponding @var{r} gives that register's value. The data @var{r} is a series of bytes in target byte order, with each byte given by a two-digit hex number. @item If @var{n} is @samp{thread}, then @var{r} is the @var{thread-id} of the stopped thread, as specified in @ref{thread-id syntax}. @item If @var{n} is @samp{core}, then @var{r} is the hexadecimal number of the core on which the stop event was detected. @item If @var{n} is a recognized @dfn{stop reason}, it describes a more specific event that stopped the target. The currently defined stop reasons are listed below. The @var{aa} should be @samp{05}, the trap signal. At most one stop reason should be present. @item Otherwise, @value{GDBN} should ignore this @samp{@var{n}:@var{r}} pair and go on to the next; this allows us to extend the protocol in the future. @end itemize The currently defined stop reasons are: @table @samp @item watch @itemx rwatch @itemx awatch The packet indicates a watchpoint hit, and @var{r} is the data address, in hex. @item syscall_entry @itemx syscall_return The packet indicates a syscall entry or return, and @var{r} is the syscall number, in hex. @cindex shared library events, remote reply @item library The packet indicates that the loaded libraries have changed. @value{GDBN} should use @samp{qXfer:libraries:read} to fetch a new list of loaded libraries. The @var{r} part is ignored. @cindex replay log events, remote reply @item replaylog The packet indicates that the target cannot continue replaying logged execution events, because it has reached the end (or the beginning when executing backward) of the log. The value of @var{r} will be either @samp{begin} or @samp{end}. @xref{Reverse Execution}, for more information. @item swbreak @anchor{swbreak stop reason} The packet indicates a software breakpoint instruction was executed, irrespective of whether it was @value{GDBN} that planted the breakpoint or the breakpoint is hardcoded in the program. The @var{r} part must be left empty. On some architectures, such as x86, at the architecture level, when a breakpoint instruction executes the program counter points at the breakpoint address plus an offset. On such targets, the stub is responsible for adjusting the PC to point back at the breakpoint address. This packet should not be sent by default; older @value{GDBN} versions did not support it. @value{GDBN} requests it, by supplying an appropriate @samp{qSupported} feature (@pxref{qSupported}). The remote stub must also supply the appropriate @samp{qSupported} feature indicating support. This packet is required for correct non-stop mode operation. @item hwbreak The packet indicates the target stopped for a hardware breakpoint. The @var{r} part must be left empty. The same remarks about @samp{qSupported} and non-stop mode above apply. @cindex fork events, remote reply @item fork The packet indicates that @code{fork} was called, and @var{r} is the thread ID of the new child process. Refer to @ref{thread-id syntax} for the format of the @var{thread-id} field. This packet is only applicable to targets that support fork events. This packet should not be sent by default; older @value{GDBN} versions did not support it. @value{GDBN} requests it, by supplying an appropriate @samp{qSupported} feature (@pxref{qSupported}). The remote stub must also supply the appropriate @samp{qSupported} feature indicating support. @cindex vfork events, remote reply @item vfork The packet indicates that @code{vfork} was called, and @var{r} is the thread ID of the new child process. Refer to @ref{thread-id syntax} for the format of the @var{thread-id} field. This packet is only applicable to targets that support vfork events. This packet should not be sent by default; older @value{GDBN} versions did not support it. @value{GDBN} requests it, by supplying an appropriate @samp{qSupported} feature (@pxref{qSupported}). The remote stub must also supply the appropriate @samp{qSupported} feature indicating support. @cindex vforkdone events, remote reply @item vforkdone The packet indicates that a child process created by a vfork has either called @code{exec} or terminated, so that the address spaces of the parent and child process are no longer shared. The @var{r} part is ignored. This packet is only applicable to targets that support vforkdone events. This packet should not be sent by default; older @value{GDBN} versions did not support it. @value{GDBN} requests it, by supplying an appropriate @samp{qSupported} feature (@pxref{qSupported}). The remote stub must also supply the appropriate @samp{qSupported} feature indicating support. @cindex exec events, remote reply @item exec The packet indicates that @code{execve} was called, and @var{r} is the absolute pathname of the file that was executed, in hex. This packet is only applicable to targets that support exec events. This packet should not be sent by default; older @value{GDBN} versions did not support it. @value{GDBN} requests it, by supplying an appropriate @samp{qSupported} feature (@pxref{qSupported}). The remote stub must also supply the appropriate @samp{qSupported} feature indicating support. @cindex thread create event, remote reply @anchor{thread create event} @item create The packet indicates that the thread was just created. The new thread is stopped until @value{GDBN} sets it running with a resumption packet (@pxref{vCont packet}). This packet should not be sent by default; @value{GDBN} requests it with the @ref{QThreadEvents} packet. See also the @samp{w} (@pxref{thread exit event}) remote reply below. The @var{r} part is ignored. @end table @item W @var{AA} @itemx W @var{AA} ; process:@var{pid} The process exited, and @var{AA} is the exit status. This is only applicable to certain targets. The second form of the response, including the process ID of the exited process, can be used only when @value{GDBN} has reported support for multiprocess protocol extensions; see @ref{multiprocess extensions}. Both @var{AA} and @var{pid} are formatted as big-endian hex strings. @item X @var{AA} @itemx X @var{AA} ; process:@var{pid} The process terminated with signal @var{AA}. The second form of the response, including the process ID of the terminated process, can be used only when @value{GDBN} has reported support for multiprocess protocol extensions; see @ref{multiprocess extensions}. Both @var{AA} and @var{pid} are formatted as big-endian hex strings. @anchor{thread exit event} @cindex thread exit event, remote reply @item w @var{AA} ; @var{tid} The thread exited, and @var{AA} is the exit status. This response should not be sent by default; @value{GDBN} requests it with the @ref{QThreadEvents} packet. See also @ref{thread create event} above. @var{AA} is formatted as a big-endian hex string. @item N There are no resumed threads left in the target. In other words, even though the process is alive, the last resumed thread has exited. For example, say the target process has two threads: thread 1 and thread 2. The client leaves thread 1 stopped, and resumes thread 2, which subsequently exits. At this point, even though the process is still alive, and thus no @samp{W} stop reply is sent, no thread is actually executing either. The @samp{N} stop reply thus informs the client that it can stop waiting for stop replies. This packet should not be sent by default; older @value{GDBN} versions did not support it. @value{GDBN} requests it, by supplying an appropriate @samp{qSupported} feature (@pxref{qSupported}). The remote stub must also supply the appropriate @samp{qSupported} feature indicating support. @item O @var{XX}@dots{} @samp{@var{XX}@dots{}} is hex encoding of @sc{ascii} data, to be written as the program's console output. This can happen at any time while the program is running and the debugger should continue to wait for @samp{W}, @samp{T}, etc. This reply is not permitted in non-stop mode. @item F @var{call-id},@var{parameter}@dots{} @var{call-id} is the identifier which says which host system call should be called. This is just the name of the function. Translation into the correct system call is only applicable as it's defined in @value{GDBN}. @xref{File-I/O Remote Protocol Extension}, for a list of implemented system calls. @samp{@var{parameter}@dots{}} is a list of parameters as defined for this very system call. The target replies with this packet when it expects @value{GDBN} to call a host system call on behalf of the target. @value{GDBN} replies with an appropriate @samp{F} packet and keeps up waiting for the next reply packet from the target. The latest @samp{C}, @samp{c}, @samp{S} or @samp{s} action is expected to be continued. @xref{File-I/O Remote Protocol Extension}, for more details. @end table @node General Query Packets @section General Query Packets @cindex remote query requests Packets starting with @samp{q} are @dfn{general query packets}; packets starting with @samp{Q} are @dfn{general set packets}. General query and set packets are a semi-unified form for retrieving and sending information to and from the stub. The initial letter of a query or set packet is followed by a name indicating what sort of thing the packet applies to. For example, @value{GDBN} may use a @samp{qSymbol} packet to exchange symbol definitions with the stub. These packet names follow some conventions: @itemize @bullet @item The name must not contain commas, colons or semicolons. @item Most @value{GDBN} query and set packets have a leading upper case letter. @item The names of custom vendor packets should use a company prefix, in lower case, followed by a period. For example, packets designed at the Acme Corporation might begin with @samp{qacme.foo} (for querying foos) or @samp{Qacme.bar} (for setting bars). @end itemize The name of a query or set packet should be separated from any parameters by a @samp{:}; the parameters themselves should be separated by @samp{,} or @samp{;}. Stubs must be careful to match the full packet name, and check for a separator or the end of the packet, in case two packet names share a common prefix. New packets should not begin with @samp{qC}, @samp{qP}, or @samp{qL}@footnote{The @samp{qP} and @samp{qL} packets predate these conventions, and have arguments without any terminator for the packet name; we suspect they are in widespread use in places that are difficult to upgrade. The @samp{qC} packet has no arguments, but some existing stubs (e.g.@: RedBoot) are known to not check for the end of the packet.}. Like the descriptions of the other packets, each description here has a template showing the packet's overall syntax, followed by an explanation of the packet's meaning. We include spaces in some of the templates for clarity; these are not part of the packet's syntax. No @value{GDBN} packet uses spaces to separate its components. Here are the currently defined query and set packets: @table @samp @item QAgent:1 @itemx QAgent:0 Turn on or off the agent as a helper to perform some debugging operations delegated from @value{GDBN} (@pxref{Control Agent}). @item QAllow:@var{op}:@var{val}@dots{} @cindex @samp{QAllow} packet Specify which operations @value{GDBN} expects to request of the target, as a semicolon-separated list of operation name and value pairs. Possible values for @var{op} include @samp{WriteReg}, @samp{WriteMem}, @samp{InsertBreak}, @samp{InsertTrace}, @samp{InsertFastTrace}, and @samp{Stop}. @var{val} is either 0, indicating that @value{GDBN} will not request the operation, or 1, indicating that it may. (The target can then use this to set up its own internals optimally, for instance if the debugger never expects to insert breakpoints, it may not need to install its own trap handler.) @item qC @cindex current thread, remote request @cindex @samp{qC} packet Return the current thread ID. Reply: @table @samp @item QC @var{thread-id} Where @var{thread-id} is a thread ID as documented in @ref{thread-id syntax}. @item @r{(anything else)} Any other reply implies the old thread ID. @end table @item qCRC:@var{addr},@var{length} @cindex CRC of memory block, remote request @cindex @samp{qCRC} packet @anchor{qCRC packet} Compute the CRC checksum of a block of memory using CRC-32 defined in IEEE 802.3. The CRC is computed byte at a time, taking the most significant bit of each byte first. The initial pattern code @code{0xffffffff} is used to ensure leading zeros affect the CRC. @emph{Note:} This is the same CRC used in validating separate debug files (@pxref{Separate Debug Files, , Debugging Information in Separate Files}). However the algorithm is slightly different. When validating separate debug files, the CRC is computed taking the @emph{least} significant bit of each byte first, and the final result is inverted to detect trailing zeros. Reply: @table @samp @item E @var{NN} An error (such as memory fault) @item C @var{crc32} The specified memory region's checksum is @var{crc32}. @end table @item QDisableRandomization:@var{value} @cindex disable address space randomization, remote request @cindex @samp{QDisableRandomization} packet Some target operating systems will randomize the virtual address space of the inferior process as a security feature, but provide a feature to disable such randomization, e.g.@: to allow for a more deterministic debugging experience. On such systems, this packet with a @var{value} of 1 directs the target to disable address space randomization for processes subsequently started via @samp{vRun} packets, while a packet with a @var{value} of 0 tells the target to enable address space randomization. This packet is only available in extended mode (@pxref{extended mode}). Reply: @table @samp @item OK The request succeeded. @item E @var{nn} An error occurred. The error number @var{nn} is given as hex digits. @item @w{} An empty reply indicates that @samp{QDisableRandomization} is not supported by the stub. @end table This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). This should only be done on targets that actually support disabling address space randomization. @item QStartupWithShell:@var{value} @cindex startup with shell, remote request @cindex @samp{QStartupWithShell} packet On UNIX-like targets, it is possible to start the inferior using a shell program. This is the default behavior on both @value{GDBN} and @command{gdbserver} (@pxref{set startup-with-shell}). This packet is used to inform @command{gdbserver} whether it should start the inferior using a shell or not. If @var{value} is @samp{0}, @command{gdbserver} will not use a shell to start the inferior. If @var{value} is @samp{1}, @command{gdbserver} will use a shell to start the inferior. All other values are considered an error. This packet is only available in extended mode (@pxref{extended mode}). Reply: @table @samp @item OK The request succeeded. @item E @var{nn} An error occurred. The error number @var{nn} is given as hex digits. @end table This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). This should only be done on targets that actually support starting the inferior using a shell. Use of this packet is controlled by the @code{set startup-with-shell} command; @pxref{set startup-with-shell}. @item QEnvironmentHexEncoded:@var{hex-value} @anchor{QEnvironmentHexEncoded} @cindex set environment variable, remote request @cindex @samp{QEnvironmentHexEncoded} packet On UNIX-like targets, it is possible to set environment variables that will be passed to the inferior during the startup process. This packet is used to inform @command{gdbserver} of an environment variable that has been defined by the user on @value{GDBN} (@pxref{set environment}). The packet is composed by @var{hex-value}, an hex encoded representation of the @var{name=value} format representing an environment variable. The name of the environment variable is represented by @var{name}, and the value to be assigned to the environment variable is represented by @var{value}. If the variable has no value (i.e., the value is @code{null}), then @var{value} will not be present. This packet is only available in extended mode (@pxref{extended mode}). Reply: @table @samp @item OK The request succeeded. @end table This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). This should only be done on targets that actually support passing environment variables to the starting inferior. This packet is related to the @code{set environment} command; @pxref{set environment}. @item QEnvironmentUnset:@var{hex-value} @anchor{QEnvironmentUnset} @cindex unset environment variable, remote request @cindex @samp{QEnvironmentUnset} packet On UNIX-like targets, it is possible to unset environment variables before starting the inferior in the remote target. This packet is used to inform @command{gdbserver} of an environment variable that has been unset by the user on @value{GDBN} (@pxref{unset environment}). The packet is composed by @var{hex-value}, an hex encoded representation of the name of the environment variable to be unset. This packet is only available in extended mode (@pxref{extended mode}). Reply: @table @samp @item OK The request succeeded. @end table This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). This should only be done on targets that actually support passing environment variables to the starting inferior. This packet is related to the @code{unset environment} command; @pxref{unset environment}. @item QEnvironmentReset @anchor{QEnvironmentReset} @cindex reset environment, remote request @cindex @samp{QEnvironmentReset} packet On UNIX-like targets, this packet is used to reset the state of environment variables in the remote target before starting the inferior. In this context, reset means unsetting all environment variables that were previously set by the user (i.e., were not initially present in the environment). It is sent to @command{gdbserver} before the @samp{QEnvironmentHexEncoded} (@pxref{QEnvironmentHexEncoded}) and the @samp{QEnvironmentUnset} (@pxref{QEnvironmentUnset}) packets. This packet is only available in extended mode (@pxref{extended mode}). Reply: @table @samp @item OK The request succeeded. @end table This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). This should only be done on targets that actually support passing environment variables to the starting inferior. @item QSetWorkingDir:@r{[}@var{directory}@r{]} @anchor{QSetWorkingDir packet} @cindex set working directory, remote request @cindex @samp{QSetWorkingDir} packet This packet is used to inform the remote server of the intended current working directory for programs that are going to be executed. The packet is composed by @var{directory}, an hex encoded representation of the directory that the remote inferior will use as its current working directory. If @var{directory} is an empty string, the remote server should reset the inferior's current working directory to its original, empty value. This packet is only available in extended mode (@pxref{extended mode}). Reply: @table @samp @item OK The request succeeded. @end table @item qfThreadInfo @itemx qsThreadInfo @cindex list active threads, remote request @cindex @samp{qfThreadInfo} packet @cindex @samp{qsThreadInfo} packet Obtain a list of all active thread IDs from the target (OS). Since there may be too many active threads to fit into one reply packet, this query works iteratively: it may require more than one query/reply sequence to obtain the entire list of threads. The first query of the sequence will be the @samp{qfThreadInfo} query; subsequent queries in the sequence will be the @samp{qsThreadInfo} query. NOTE: This packet replaces the @samp{qL} query (see below). Reply: @table @samp @item m @var{thread-id} A single thread ID @item m @var{thread-id},@var{thread-id}@dots{} a comma-separated list of thread IDs @item l (lower case letter @samp{L}) denotes end of list. @end table In response to each query, the target will reply with a list of one or more thread IDs, separated by commas. @value{GDBN} will respond to each reply with a request for more thread ids (using the @samp{qs} form of the query), until the target responds with @samp{l} (lower-case ell, for @dfn{last}). Refer to @ref{thread-id syntax}, for the format of the @var{thread-id} fields. @emph{Note: @value{GDBN} will send the @code{qfThreadInfo} query during the initial connection with the remote target, and the very first thread ID mentioned in the reply will be stopped by @value{GDBN} in a subsequent message. Therefore, the stub should ensure that the first thread ID in the @code{qfThreadInfo} reply is suitable for being stopped by @value{GDBN}.} @item qGetTLSAddr:@var{thread-id},@var{offset},@var{lm} @cindex get thread-local storage address, remote request @cindex @samp{qGetTLSAddr} packet Fetch the address associated with thread local storage specified by @var{thread-id}, @var{offset}, and @var{lm}. @var{thread-id} is the thread ID associated with the thread for which to fetch the TLS address. @xref{thread-id syntax}. @var{offset} is the (big endian, hex encoded) offset associated with the thread local variable. (This offset is obtained from the debug information associated with the variable.) @var{lm} is the (big endian, hex encoded) OS/ABI-specific encoding of the load module associated with the thread local storage. For example, a @sc{gnu}/Linux system will pass the link map address of the shared object associated with the thread local storage under consideration. Other operating environments may choose to represent the load module differently, so the precise meaning of this parameter will vary. Reply: @table @samp @item @var{XX}@dots{} Hex encoded (big endian) bytes representing the address of the thread local storage requested. @item E @var{nn} An error occurred. The error number @var{nn} is given as hex digits. @item @w{} An empty reply indicates that @samp{qGetTLSAddr} is not supported by the stub. @end table @item qGetTIBAddr:@var{thread-id} @cindex get thread information block address @cindex @samp{qGetTIBAddr} packet Fetch address of the Windows OS specific Thread Information Block. @var{thread-id} is the thread ID associated with the thread. Reply: @table @samp @item @var{XX}@dots{} Hex encoded (big endian) bytes representing the linear address of the thread information block. @item E @var{nn} An error occured. This means that either the thread was not found, or the address could not be retrieved. @item @w{} An empty reply indicates that @samp{qGetTIBAddr} is not supported by the stub. @end table @item qL @var{startflag} @var{threadcount} @var{nextthread} Obtain thread information from RTOS. Where: @var{startflag} (one hex digit) is one to indicate the first query and zero to indicate a subsequent query; @var{threadcount} (two hex digits) is the maximum number of threads the response packet can contain; and @var{nextthread} (eight hex digits), for subsequent queries (@var{startflag} is zero), is returned in the response as @var{argthread}. Don't use this packet; use the @samp{qfThreadInfo} query instead (see above). Reply: @table @samp @item qM @var{count} @var{done} @var{argthread} @var{thread}@dots{} Where: @var{count} (two hex digits) is the number of threads being returned; @var{done} (one hex digit) is zero to indicate more threads and one indicates no further threads; @var{argthreadid} (eight hex digits) is @var{nextthread} from the request packet; @var{thread}@dots{} is a sequence of thread IDs, @var{threadid} (eight hex digits), from the target. See @code{remote.c:parse_threadlist_response()}. @end table @item qOffsets @cindex section offsets, remote request @cindex @samp{qOffsets} packet Get section offsets that the target used when relocating the downloaded image. Reply: @table @samp @item Text=@var{xxx};Data=@var{yyy}@r{[};Bss=@var{zzz}@r{]} Relocate the @code{Text} section by @var{xxx} from its original address. Relocate the @code{Data} section by @var{yyy} from its original address. If the object file format provides segment information (e.g.@: @sc{elf} @samp{PT_LOAD} program headers), @value{GDBN} will relocate entire segments by the supplied offsets. @emph{Note: while a @code{Bss} offset may be included in the response, @value{GDBN} ignores this and instead applies the @code{Data} offset to the @code{Bss} section.} @item TextSeg=@var{xxx}@r{[};DataSeg=@var{yyy}@r{]} Relocate the first segment of the object file, which conventionally contains program code, to a starting address of @var{xxx}. If @samp{DataSeg} is specified, relocate the second segment, which conventionally contains modifiable data, to a starting address of @var{yyy}. @value{GDBN} will report an error if the object file does not contain segment information, or does not contain at least as many segments as mentioned in the reply. Extra segments are kept at fixed offsets relative to the last relocated segment. @end table @item qP @var{mode} @var{thread-id} @cindex thread information, remote request @cindex @samp{qP} packet Returns information on @var{thread-id}. Where: @var{mode} is a hex encoded 32 bit mode; @var{thread-id} is a thread ID (@pxref{thread-id syntax}). Don't use this packet; use the @samp{qThreadExtraInfo} query instead (see below). Reply: see @code{remote.c:remote_unpack_thread_info_response()}. @item QNonStop:1 @itemx QNonStop:0 @cindex non-stop mode, remote request @cindex @samp{QNonStop} packet @anchor{QNonStop} Enter non-stop (@samp{QNonStop:1}) or all-stop (@samp{QNonStop:0}) mode. @xref{Remote Non-Stop}, for more information. Reply: @table @samp @item OK The request succeeded. @item E @var{nn} An error occurred. The error number @var{nn} is given as hex digits. @item @w{} An empty reply indicates that @samp{QNonStop} is not supported by the stub. @end table This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). Use of this packet is controlled by the @code{set non-stop} command; @pxref{Non-Stop Mode}. @item QCatchSyscalls:1 @r{[};@var{sysno}@r{]}@dots{} @itemx QCatchSyscalls:0 @cindex catch syscalls from inferior, remote request @cindex @samp{QCatchSyscalls} packet @anchor{QCatchSyscalls} Enable (@samp{QCatchSyscalls:1}) or disable (@samp{QCatchSyscalls:0}) catching syscalls from the inferior process. For @samp{QCatchSyscalls:1}, each listed syscall @var{sysno} (encoded in hex) should be reported to @value{GDBN}. If no syscall @var{sysno} is listed, every system call should be reported. Note that if a syscall not in the list is reported, @value{GDBN} will still filter the event according to its own list from all corresponding @code{catch syscall} commands. However, it is more efficient to only report the requested syscalls. Multiple @samp{QCatchSyscalls:1} packets do not combine; any earlier @samp{QCatchSyscalls:1} list is completely replaced by the new list. If the inferior process execs, the state of @samp{QCatchSyscalls} is kept for the new process too. On targets where exec may affect syscall numbers, for example with exec between 32 and 64-bit processes, the client should send a new packet with the new syscall list. Reply: @table @samp @item OK The request succeeded. @item E @var{nn} An error occurred. @var{nn} are hex digits. @item @w{} An empty reply indicates that @samp{QCatchSyscalls} is not supported by the stub. @end table Use of this packet is controlled by the @code{set remote catch-syscalls} command (@pxref{Remote Configuration, set remote catch-syscalls}). This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). @item QPassSignals: @var{signal} @r{[};@var{signal}@r{]}@dots{} @cindex pass signals to inferior, remote request @cindex @samp{QPassSignals} packet @anchor{QPassSignals} Each listed @var{signal} should be passed directly to the inferior process. Signals are numbered identically to continue packets and stop replies (@pxref{Stop Reply Packets}). Each @var{signal} list item should be strictly greater than the previous item. These signals do not need to stop the inferior, or be reported to @value{GDBN}. All other signals should be reported to @value{GDBN}. Multiple @samp{QPassSignals} packets do not combine; any earlier @samp{QPassSignals} list is completely replaced by the new list. This packet improves performance when using @samp{handle @var{signal} nostop noprint pass}. Reply: @table @samp @item OK The request succeeded. @item E @var{nn} An error occurred. The error number @var{nn} is given as hex digits. @item @w{} An empty reply indicates that @samp{QPassSignals} is not supported by the stub. @end table Use of this packet is controlled by the @code{set remote pass-signals} command (@pxref{Remote Configuration, set remote pass-signals}). This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). @item QProgramSignals: @var{signal} @r{[};@var{signal}@r{]}@dots{} @cindex signals the inferior may see, remote request @cindex @samp{QProgramSignals} packet @anchor{QProgramSignals} Each listed @var{signal} may be delivered to the inferior process. Others should be silently discarded. In some cases, the remote stub may need to decide whether to deliver a signal to the program or not without @value{GDBN} involvement. One example of that is while detaching --- the program's threads may have stopped for signals that haven't yet had a chance of being reported to @value{GDBN}, and so the remote stub can use the signal list specified by this packet to know whether to deliver or ignore those pending signals. This does not influence whether to deliver a signal as requested by a resumption packet (@pxref{vCont packet}). Signals are numbered identically to continue packets and stop replies (@pxref{Stop Reply Packets}). Each @var{signal} list item should be strictly greater than the previous item. Multiple @samp{QProgramSignals} packets do not combine; any earlier @samp{QProgramSignals} list is completely replaced by the new list. Reply: @table @samp @item OK The request succeeded. @item E @var{nn} An error occurred. The error number @var{nn} is given as hex digits. @item @w{} An empty reply indicates that @samp{QProgramSignals} is not supported by the stub. @end table Use of this packet is controlled by the @code{set remote program-signals} command (@pxref{Remote Configuration, set remote program-signals}). This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). @anchor{QThreadEvents} @item QThreadEvents:1 @itemx QThreadEvents:0 @cindex thread create/exit events, remote request @cindex @samp{QThreadEvents} packet Enable (@samp{QThreadEvents:1}) or disable (@samp{QThreadEvents:0}) reporting of thread create and exit events. @xref{thread create event}, for the reply specifications. For example, this is used in non-stop mode when @value{GDBN} stops a set of threads and synchronously waits for the their corresponding stop replies. Without exit events, if one of the threads exits, @value{GDBN} would hang forever not knowing that it should no longer expect a stop for that same thread. @value{GDBN} does not enable this feature unless the stub reports that it supports it by including @samp{QThreadEvents+} in its @samp{qSupported} reply. Reply: @table @samp @item OK The request succeeded. @item E @var{nn} An error occurred. The error number @var{nn} is given as hex digits. @item @w{} An empty reply indicates that @samp{QThreadEvents} is not supported by the stub. @end table Use of this packet is controlled by the @code{set remote thread-events} command (@pxref{Remote Configuration, set remote thread-events}). @item qRcmd,@var{command} @cindex execute remote command, remote request @cindex @samp{qRcmd} packet @var{command} (hex encoded) is passed to the local interpreter for execution. Invalid commands should be reported using the output string. Before the final result packet, the target may also respond with a number of intermediate @samp{O@var{output}} console output packets. @emph{Implementors should note that providing access to a stubs's interpreter may have security implications}. Reply: @table @samp @item OK A command response with no output. @item @var{OUTPUT} A command response with the hex encoded output string @var{OUTPUT}. @item E @var{NN} Indicate a badly formed request. @item @w{} An empty reply indicates that @samp{qRcmd} is not recognized. @end table (Note that the @code{qRcmd} packet's name is separated from the command by a @samp{,}, not a @samp{:}, contrary to the naming conventions above. Please don't use this packet as a model for new packets.) @item qSearch:memory:@var{address};@var{length};@var{search-pattern} @cindex searching memory, in remote debugging @ifnotinfo @cindex @samp{qSearch:memory} packet @end ifnotinfo @cindex @samp{qSearch memory} packet @anchor{qSearch memory} Search @var{length} bytes at @var{address} for @var{search-pattern}. Both @var{address} and @var{length} are encoded in hex; @var{search-pattern} is a sequence of bytes, also hex encoded. Reply: @table @samp @item 0 The pattern was not found. @item 1,address The pattern was found at @var{address}. @item E @var{NN} A badly formed request or an error was encountered while searching memory. @item @w{} An empty reply indicates that @samp{qSearch:memory} is not recognized. @end table @item QStartNoAckMode @cindex @samp{QStartNoAckMode} packet @anchor{QStartNoAckMode} Request that the remote stub disable the normal @samp{+}/@samp{-} protocol acknowledgments (@pxref{Packet Acknowledgment}). Reply: @table @samp @item OK The stub has switched to no-acknowledgment mode. @value{GDBN} acknowledges this response, but neither the stub nor @value{GDBN} shall send or expect further @samp{+}/@samp{-} acknowledgments in the current connection. @item @w{} An empty reply indicates that the stub does not support no-acknowledgment mode. @end table @item qSupported @r{[}:@var{gdbfeature} @r{[};@var{gdbfeature}@r{]}@dots{} @r{]} @cindex supported packets, remote query @cindex features of the remote protocol @cindex @samp{qSupported} packet @anchor{qSupported} Tell the remote stub about features supported by @value{GDBN}, and query the stub for features it supports. This packet allows @value{GDBN} and the remote stub to take advantage of each others' features. @samp{qSupported} also consolidates multiple feature probes at startup, to improve @value{GDBN} performance---a single larger packet performs better than multiple smaller probe packets on high-latency links. Some features may enable behavior which must not be on by default, e.g.@: because it would confuse older clients or stubs. Other features may describe packets which could be automatically probed for, but are not. These features must be reported before @value{GDBN} will use them. This ``default unsupported'' behavior is not appropriate for all packets, but it helps to keep the initial connection time under control with new versions of @value{GDBN} which support increasing numbers of packets. Reply: @table @samp @item @var{stubfeature} @r{[};@var{stubfeature}@r{]}@dots{} The stub supports or does not support each returned @var{stubfeature}, depending on the form of each @var{stubfeature} (see below for the possible forms). @item @w{} An empty reply indicates that @samp{qSupported} is not recognized, or that no features needed to be reported to @value{GDBN}. @end table The allowed forms for each feature (either a @var{gdbfeature} in the @samp{qSupported} packet, or a @var{stubfeature} in the response) are: @table @samp @item @var{name}=@var{value} The remote protocol feature @var{name} is supported, and associated with the specified @var{value}. The format of @var{value} depends on the feature, but it must not include a semicolon. @item @var{name}+ The remote protocol feature @var{name} is supported, and does not need an associated value. @item @var{name}- The remote protocol feature @var{name} is not supported. @item @var{name}? The remote protocol feature @var{name} may be supported, and @value{GDBN} should auto-detect support in some other way when it is needed. This form will not be used for @var{gdbfeature} notifications, but may be used for @var{stubfeature} responses. @end table Whenever the stub receives a @samp{qSupported} request, the supplied set of @value{GDBN} features should override any previous request. This allows @value{GDBN} to put the stub in a known state, even if the stub had previously been communicating with a different version of @value{GDBN}. The following values of @var{gdbfeature} (for the packet sent by @value{GDBN}) are defined: @table @samp @item multiprocess This feature indicates whether @value{GDBN} supports multiprocess extensions to the remote protocol. @value{GDBN} does not use such extensions unless the stub also reports that it supports them by including @samp{multiprocess+} in its @samp{qSupported} reply. @xref{multiprocess extensions}, for details. @item xmlRegisters This feature indicates that @value{GDBN} supports the XML target description. If the stub sees @samp{xmlRegisters=} with target specific strings separated by a comma, it will report register description. @item qRelocInsn This feature indicates whether @value{GDBN} supports the @samp{qRelocInsn} packet (@pxref{Tracepoint Packets,,Relocate instruction reply packet}). @item swbreak This feature indicates whether @value{GDBN} supports the swbreak stop reason in stop replies. @xref{swbreak stop reason}, for details. @item hwbreak This feature indicates whether @value{GDBN} supports the hwbreak stop reason in stop replies. @xref{swbreak stop reason}, for details. @item fork-events This feature indicates whether @value{GDBN} supports fork event extensions to the remote protocol. @value{GDBN} does not use such extensions unless the stub also reports that it supports them by including @samp{fork-events+} in its @samp{qSupported} reply. @item vfork-events This feature indicates whether @value{GDBN} supports vfork event extensions to the remote protocol. @value{GDBN} does not use such extensions unless the stub also reports that it supports them by including @samp{vfork-events+} in its @samp{qSupported} reply. @item exec-events This feature indicates whether @value{GDBN} supports exec event extensions to the remote protocol. @value{GDBN} does not use such extensions unless the stub also reports that it supports them by including @samp{exec-events+} in its @samp{qSupported} reply. @item vContSupported This feature indicates whether @value{GDBN} wants to know the supported actions in the reply to @samp{vCont?} packet. @end table Stubs should ignore any unknown values for @var{gdbfeature}. Any @value{GDBN} which sends a @samp{qSupported} packet supports receiving packets of unlimited length (earlier versions of @value{GDBN} may reject overly long responses). Additional values for @var{gdbfeature} may be defined in the future to let the stub take advantage of new features in @value{GDBN}, e.g.@: incompatible improvements in the remote protocol---the @samp{multiprocess} feature is an example of such a feature. The stub's reply should be independent of the @var{gdbfeature} entries sent by @value{GDBN}; first @value{GDBN} describes all the features it supports, and then the stub replies with all the features it supports. Similarly, @value{GDBN} will silently ignore unrecognized stub feature responses, as long as each response uses one of the standard forms. Some features are flags. A stub which supports a flag feature should respond with a @samp{+} form response. Other features require values, and the stub should respond with an @samp{=} form response. Each feature has a default value, which @value{GDBN} will use if @samp{qSupported} is not available or if the feature is not mentioned in the @samp{qSupported} response. The default values are fixed; a stub is free to omit any feature responses that match the defaults. Not all features can be probed, but for those which can, the probing mechanism is useful: in some cases, a stub's internal architecture may not allow the protocol layer to know some information about the underlying target in advance. This is especially common in stubs which may be configured for multiple targets. These are the currently defined stub features and their properties: @multitable @columnfractions 0.35 0.2 0.12 0.2 @c NOTE: The first row should be @headitem, but we do not yet require @c a new enough version of Texinfo (4.7) to use @headitem. @item Feature Name @tab Value Required @tab Default @tab Probe Allowed @item @samp{PacketSize} @tab Yes @tab @samp{-} @tab No @item @samp{qXfer:auxv:read} @tab No @tab @samp{-} @tab Yes @item @samp{qXfer:btrace:read} @tab No @tab @samp{-} @tab Yes @item @samp{qXfer:btrace-conf:read} @tab No @tab @samp{-} @tab Yes @item @samp{qXfer:exec-file:read} @tab No @tab @samp{-} @tab Yes @item @samp{qXfer:features:read} @tab No @tab @samp{-} @tab Yes @item @samp{qXfer:libraries:read} @tab No @tab @samp{-} @tab Yes @item @samp{qXfer:libraries-svr4:read} @tab No @tab @samp{-} @tab Yes @item @samp{augmented-libraries-svr4-read} @tab No @tab @samp{-} @tab No @item @samp{qXfer:memory-map:read} @tab No @tab @samp{-} @tab Yes @item @samp{qXfer:sdata:read} @tab No @tab @samp{-} @tab Yes @item @samp{qXfer:siginfo:read} @tab No @tab @samp{-} @tab Yes @item @samp{qXfer:siginfo:write} @tab No @tab @samp{-} @tab Yes @item @samp{qXfer:threads:read} @tab No @tab @samp{-} @tab Yes @item @samp{qXfer:traceframe-info:read} @tab No @tab @samp{-} @tab Yes @item @samp{qXfer:uib:read} @tab No @tab @samp{-} @tab Yes @item @samp{qXfer:fdpic:read} @tab No @tab @samp{-} @tab Yes @item @samp{Qbtrace:off} @tab Yes @tab @samp{-} @tab Yes @item @samp{Qbtrace:bts} @tab Yes @tab @samp{-} @tab Yes @item @samp{Qbtrace:pt} @tab Yes @tab @samp{-} @tab Yes @item @samp{Qbtrace-conf:bts:size} @tab Yes @tab @samp{-} @tab Yes @item @samp{Qbtrace-conf:pt:size} @tab Yes @tab @samp{-} @tab Yes @item @samp{QNonStop} @tab No @tab @samp{-} @tab Yes @item @samp{QCatchSyscalls} @tab No @tab @samp{-} @tab Yes @item @samp{QPassSignals} @tab No @tab @samp{-} @tab Yes @item @samp{QStartNoAckMode} @tab No @tab @samp{-} @tab Yes @item @samp{multiprocess} @tab No @tab @samp{-} @tab No @item @samp{ConditionalBreakpoints} @tab No @tab @samp{-} @tab No @item @samp{ConditionalTracepoints} @tab No @tab @samp{-} @tab No @item @samp{ReverseContinue} @tab No @tab @samp{-} @tab No @item @samp{ReverseStep} @tab No @tab @samp{-} @tab No @item @samp{TracepointSource} @tab No @tab @samp{-} @tab No @item @samp{QAgent} @tab No @tab @samp{-} @tab No @item @samp{QAllow} @tab No @tab @samp{-} @tab No @item @samp{QDisableRandomization} @tab No @tab @samp{-} @tab No @item @samp{EnableDisableTracepoints} @tab No @tab @samp{-} @tab No @item @samp{QTBuffer:size} @tab No @tab @samp{-} @tab No @item @samp{tracenz} @tab No @tab @samp{-} @tab No @item @samp{BreakpointCommands} @tab No @tab @samp{-} @tab No @item @samp{swbreak} @tab No @tab @samp{-} @tab No @item @samp{hwbreak} @tab No @tab @samp{-} @tab No @item @samp{fork-events} @tab No @tab @samp{-} @tab No @item @samp{vfork-events} @tab No @tab @samp{-} @tab No @item @samp{exec-events} @tab No @tab @samp{-} @tab No @item @samp{QThreadEvents} @tab No @tab @samp{-} @tab No @item @samp{no-resumed} @tab No @tab @samp{-} @tab No @end multitable These are the currently defined stub features, in more detail: @table @samp @cindex packet size, remote protocol @item PacketSize=@var{bytes} The remote stub can accept packets up to at least @var{bytes} in length. @value{GDBN} will send packets up to this size for bulk transfers, and will never send larger packets. This is a limit on the data characters in the packet, including the frame and checksum. There is no trailing NUL byte in a remote protocol packet; if the stub stores packets in a NUL-terminated format, it should allow an extra byte in its buffer for the NUL. If this stub feature is not supported, @value{GDBN} guesses based on the size of the @samp{g} packet response. @item qXfer:auxv:read The remote stub understands the @samp{qXfer:auxv:read} packet (@pxref{qXfer auxiliary vector read}). @item qXfer:btrace:read The remote stub understands the @samp{qXfer:btrace:read} packet (@pxref{qXfer btrace read}). @item qXfer:btrace-conf:read The remote stub understands the @samp{qXfer:btrace-conf:read} packet (@pxref{qXfer btrace-conf read}). @item qXfer:exec-file:read The remote stub understands the @samp{qXfer:exec-file:read} packet (@pxref{qXfer executable filename read}). @item qXfer:features:read The remote stub understands the @samp{qXfer:features:read} packet (@pxref{qXfer target description read}). @item qXfer:libraries:read The remote stub understands the @samp{qXfer:libraries:read} packet (@pxref{qXfer library list read}). @item qXfer:libraries-svr4:read The remote stub understands the @samp{qXfer:libraries-svr4:read} packet (@pxref{qXfer svr4 library list read}). @item augmented-libraries-svr4-read The remote stub understands the augmented form of the @samp{qXfer:libraries-svr4:read} packet (@pxref{qXfer svr4 library list read}). @item qXfer:memory-map:read The remote stub understands the @samp{qXfer:memory-map:read} packet (@pxref{qXfer memory map read}). @item qXfer:sdata:read The remote stub understands the @samp{qXfer:sdata:read} packet (@pxref{qXfer sdata read}). @item qXfer:siginfo:read The remote stub understands the @samp{qXfer:siginfo:read} packet (@pxref{qXfer siginfo read}). @item qXfer:siginfo:write The remote stub understands the @samp{qXfer:siginfo:write} packet (@pxref{qXfer siginfo write}). @item qXfer:threads:read The remote stub understands the @samp{qXfer:threads:read} packet (@pxref{qXfer threads read}). @item qXfer:traceframe-info:read The remote stub understands the @samp{qXfer:traceframe-info:read} packet (@pxref{qXfer traceframe info read}). @item qXfer:uib:read The remote stub understands the @samp{qXfer:uib:read} packet (@pxref{qXfer unwind info block}). @item qXfer:fdpic:read The remote stub understands the @samp{qXfer:fdpic:read} packet (@pxref{qXfer fdpic loadmap read}). @item QNonStop The remote stub understands the @samp{QNonStop} packet (@pxref{QNonStop}). @item QCatchSyscalls The remote stub understands the @samp{QCatchSyscalls} packet (@pxref{QCatchSyscalls}). @item QPassSignals The remote stub understands the @samp{QPassSignals} packet (@pxref{QPassSignals}). @item QStartNoAckMode The remote stub understands the @samp{QStartNoAckMode} packet and prefers to operate in no-acknowledgment mode. @xref{Packet Acknowledgment}. @item multiprocess @anchor{multiprocess extensions} @cindex multiprocess extensions, in remote protocol The remote stub understands the multiprocess extensions to the remote protocol syntax. The multiprocess extensions affect the syntax of thread IDs in both packets and replies (@pxref{thread-id syntax}), and add process IDs to the @samp{D} packet and @samp{W} and @samp{X} replies. Note that reporting this feature indicates support for the syntactic extensions only, not that the stub necessarily supports debugging of more than one process at a time. The stub must not use multiprocess extensions in packet replies unless @value{GDBN} has also indicated it supports them in its @samp{qSupported} request. @item qXfer:osdata:read The remote stub understands the @samp{qXfer:osdata:read} packet ((@pxref{qXfer osdata read}). @item ConditionalBreakpoints The target accepts and implements evaluation of conditional expressions defined for breakpoints. The target will only report breakpoint triggers when such conditions are true (@pxref{Conditions, ,Break Conditions}). @item ConditionalTracepoints The remote stub accepts and implements conditional expressions defined for tracepoints (@pxref{Tracepoint Conditions}). @item ReverseContinue The remote stub accepts and implements the reverse continue packet (@pxref{bc}). @item ReverseStep The remote stub accepts and implements the reverse step packet (@pxref{bs}). @item TracepointSource The remote stub understands the @samp{QTDPsrc} packet that supplies the source form of tracepoint definitions. @item QAgent The remote stub understands the @samp{QAgent} packet. @item QAllow The remote stub understands the @samp{QAllow} packet. @item QDisableRandomization The remote stub understands the @samp{QDisableRandomization} packet. @item StaticTracepoint @cindex static tracepoints, in remote protocol The remote stub supports static tracepoints. @item InstallInTrace @anchor{install tracepoint in tracing} The remote stub supports installing tracepoint in tracing. @item EnableDisableTracepoints The remote stub supports the @samp{QTEnable} (@pxref{QTEnable}) and @samp{QTDisable} (@pxref{QTDisable}) packets that allow tracepoints to be enabled and disabled while a trace experiment is running. @item QTBuffer:size The remote stub supports the @samp{QTBuffer:size} (@pxref{QTBuffer-size}) packet that allows to change the size of the trace buffer. @item tracenz @cindex string tracing, in remote protocol The remote stub supports the @samp{tracenz} bytecode for collecting strings. See @ref{Bytecode Descriptions} for details about the bytecode. @item BreakpointCommands @cindex breakpoint commands, in remote protocol The remote stub supports running a breakpoint's command list itself, rather than reporting the hit to @value{GDBN}. @item Qbtrace:off The remote stub understands the @samp{Qbtrace:off} packet. @item Qbtrace:bts The remote stub understands the @samp{Qbtrace:bts} packet. @item Qbtrace:pt The remote stub understands the @samp{Qbtrace:pt} packet. @item Qbtrace-conf:bts:size The remote stub understands the @samp{Qbtrace-conf:bts:size} packet. @item Qbtrace-conf:pt:size The remote stub understands the @samp{Qbtrace-conf:pt:size} packet. @item swbreak The remote stub reports the @samp{swbreak} stop reason for memory breakpoints. @item hwbreak The remote stub reports the @samp{hwbreak} stop reason for hardware breakpoints. @item fork-events The remote stub reports the @samp{fork} stop reason for fork events. @item vfork-events The remote stub reports the @samp{vfork} stop reason for vfork events and vforkdone events. @item exec-events The remote stub reports the @samp{exec} stop reason for exec events. @item vContSupported The remote stub reports the supported actions in the reply to @samp{vCont?} packet. @item QThreadEvents The remote stub understands the @samp{QThreadEvents} packet. @item no-resumed The remote stub reports the @samp{N} stop reply. @end table @item qSymbol:: @cindex symbol lookup, remote request @cindex @samp{qSymbol} packet Notify the target that @value{GDBN} is prepared to serve symbol lookup requests. Accept requests from the target for the values of symbols. Reply: @table @samp @item OK The target does not need to look up any (more) symbols. @item qSymbol:@var{sym_name} The target requests the value of symbol @var{sym_name} (hex encoded). @value{GDBN} may provide the value by using the @samp{qSymbol:@var{sym_value}:@var{sym_name}} message, described below. @end table @item qSymbol:@var{sym_value}:@var{sym_name} Set the value of @var{sym_name} to @var{sym_value}. @var{sym_name} (hex encoded) is the name of a symbol whose value the target has previously requested. @var{sym_value} (hex) is the value for symbol @var{sym_name}. If @value{GDBN} cannot supply a value for @var{sym_name}, then this field will be empty. Reply: @table @samp @item OK The target does not need to look up any (more) symbols. @item qSymbol:@var{sym_name} The target requests the value of a new symbol @var{sym_name} (hex encoded). @value{GDBN} will continue to supply the values of symbols (if available), until the target ceases to request them. @end table @item qTBuffer @itemx QTBuffer @itemx QTDisconnected @itemx QTDP @itemx QTDPsrc @itemx QTDV @itemx qTfP @itemx qTfV @itemx QTFrame @itemx qTMinFTPILen @xref{Tracepoint Packets}. @item qThreadExtraInfo,@var{thread-id} @cindex thread attributes info, remote request @cindex @samp{qThreadExtraInfo} packet Obtain from the target OS a printable string description of thread attributes for the thread @var{thread-id}; see @ref{thread-id syntax}, for the forms of @var{thread-id}. This string may contain anything that the target OS thinks is interesting for @value{GDBN} to tell the user about the thread. The string is displayed in @value{GDBN}'s @code{info threads} display. Some examples of possible thread extra info strings are @samp{Runnable}, or @samp{Blocked on Mutex}. Reply: @table @samp @item @var{XX}@dots{} Where @samp{@var{XX}@dots{}} is a hex encoding of @sc{ascii} data, comprising the printable string containing the extra information about the thread's attributes. @end table (Note that the @code{qThreadExtraInfo} packet's name is separated from the command by a @samp{,}, not a @samp{:}, contrary to the naming conventions above. Please don't use this packet as a model for new packets.) @item QTNotes @itemx qTP @itemx QTSave @itemx qTsP @itemx qTsV @itemx QTStart @itemx QTStop @itemx QTEnable @itemx QTDisable @itemx QTinit @itemx QTro @itemx qTStatus @itemx qTV @itemx qTfSTM @itemx qTsSTM @itemx qTSTMat @xref{Tracepoint Packets}. @item qXfer:@var{object}:read:@var{annex}:@var{offset},@var{length} @cindex read special object, remote request @cindex @samp{qXfer} packet @anchor{qXfer read} Read uninterpreted bytes from the target's special data area identified by the keyword @var{object}. Request @var{length} bytes starting at @var{offset} bytes into the data. The content and encoding of @var{annex} is specific to @var{object}; it can supply additional details about what data to access. Reply: @table @samp @item m @var{data} Data @var{data} (@pxref{Binary Data}) has been read from the target. There may be more data at a higher address (although it is permitted to return @samp{m} even for the last valid block of data, as long as at least one byte of data was read). It is possible for @var{data} to have fewer bytes than the @var{length} in the request. @item l @var{data} Data @var{data} (@pxref{Binary Data}) has been read from the target. There is no more data to be read. It is possible for @var{data} to have fewer bytes than the @var{length} in the request. @item l The @var{offset} in the request is at the end of the data. There is no more data to be read. @item E00 The request was malformed, or @var{annex} was invalid. @item E @var{nn} The offset was invalid, or there was an error encountered reading the data. The @var{nn} part is a hex-encoded @code{errno} value. @item @w{} An empty reply indicates the @var{object} string was not recognized by the stub, or that the object does not support reading. @end table Here are the specific requests of this form defined so far. All the @samp{qXfer:@var{object}:read:@dots{}} requests use the same reply formats, listed above. @table @samp @item qXfer:auxv:read::@var{offset},@var{length} @anchor{qXfer auxiliary vector read} Access the target's @dfn{auxiliary vector}. @xref{OS Information, auxiliary vector}. Note @var{annex} must be empty. This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). @item qXfer:btrace:read:@var{annex}:@var{offset},@var{length} @anchor{qXfer btrace read} Return a description of the current branch trace. @xref{Branch Trace Format}. The annex part of the generic @samp{qXfer} packet may have one of the following values: @table @code @item all Returns all available branch trace. @item new Returns all available branch trace if the branch trace changed since the last read request. @item delta Returns the new branch trace since the last read request. Adds a new block to the end of the trace that begins at zero and ends at the source location of the first branch in the trace buffer. This extra block is used to stitch traces together. If the trace buffer overflowed, returns an error indicating the overflow. @end table This packet is not probed by default; the remote stub must request it by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). @item qXfer:btrace-conf:read::@var{offset},@var{length} @anchor{qXfer btrace-conf read} Return a description of the current branch trace configuration. @xref{Branch Trace Configuration Format}. This packet is not probed by default; the remote stub must request it by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). @item qXfer:exec-file:read:@var{annex}:@var{offset},@var{length} @anchor{qXfer executable filename read} Return the full absolute name of the file that was executed to create a process running on the remote system. The annex specifies the numeric process ID of the process to query, encoded as a hexadecimal number. If the annex part is empty the remote stub should return the filename corresponding to the currently executing process. This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). @item qXfer:features:read:@var{annex}:@var{offset},@var{length} @anchor{qXfer target description read} Access the @dfn{target description}. @xref{Target Descriptions}. The annex specifies which XML document to access. The main description is always loaded from the @samp{target.xml} annex. This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). @item qXfer:libraries:read:@var{annex}:@var{offset},@var{length} @anchor{qXfer library list read} Access the target's list of loaded libraries. @xref{Library List Format}. The annex part of the generic @samp{qXfer} packet must be empty (@pxref{qXfer read}). Targets which maintain a list of libraries in the program's memory do not need to implement this packet; it is designed for platforms where the operating system manages the list of loaded libraries. This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). @item qXfer:libraries-svr4:read:@var{annex}:@var{offset},@var{length} @anchor{qXfer svr4 library list read} Access the target's list of loaded libraries when the target is an SVR4 platform. @xref{Library List Format for SVR4 Targets}. The annex part of the generic @samp{qXfer} packet must be empty unless the remote stub indicated it supports the augmented form of this packet by supplying an appropriate @samp{qSupported} response (@pxref{qXfer read}, @ref{qSupported}). This packet is optional for better performance on SVR4 targets. @value{GDBN} uses memory read packets to read the SVR4 library list otherwise. This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). If the remote stub indicates it supports the augmented form of this packet then the annex part of the generic @samp{qXfer} packet may contain a semicolon-separated list of @samp{@var{name}=@var{value}} arguments. The currently supported arguments are: @table @code @item start=@var{address} A hexadecimal number specifying the address of the @samp{struct link_map} to start reading the library list from. If unset or zero then the first @samp{struct link_map} in the library list will be chosen as the starting point. @item prev=@var{address} A hexadecimal number specifying the address of the @samp{struct link_map} immediately preceding the @samp{struct link_map} specified by the @samp{start} argument. If unset or zero then the remote stub will expect that no @samp{struct link_map} exists prior to the starting point. @end table Arguments that are not understood by the remote stub will be silently ignored. @item qXfer:memory-map:read::@var{offset},@var{length} @anchor{qXfer memory map read} Access the target's @dfn{memory-map}. @xref{Memory Map Format}. The annex part of the generic @samp{qXfer} packet must be empty (@pxref{qXfer read}). This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). @item qXfer:sdata:read::@var{offset},@var{length} @anchor{qXfer sdata read} Read contents of the extra collected static tracepoint marker information. The annex part of the generic @samp{qXfer} packet must be empty (@pxref{qXfer read}). @xref{Tracepoint Actions,,Tracepoint Action Lists}. This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). @item qXfer:siginfo:read::@var{offset},@var{length} @anchor{qXfer siginfo read} Read contents of the extra signal information on the target system. The annex part of the generic @samp{qXfer} packet must be empty (@pxref{qXfer read}). This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). @item qXfer:threads:read::@var{offset},@var{length} @anchor{qXfer threads read} Access the list of threads on target. @xref{Thread List Format}. The annex part of the generic @samp{qXfer} packet must be empty (@pxref{qXfer read}). This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). @item qXfer:traceframe-info:read::@var{offset},@var{length} @anchor{qXfer traceframe info read} Return a description of the current traceframe's contents. @xref{Traceframe Info Format}. The annex part of the generic @samp{qXfer} packet must be empty (@pxref{qXfer read}). This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). @item qXfer:uib:read:@var{pc}:@var{offset},@var{length} @anchor{qXfer unwind info block} Return the unwind information block for @var{pc}. This packet is used on OpenVMS/ia64 to ask the kernel unwind information. This packet is not probed by default. @item qXfer:fdpic:read:@var{annex}:@var{offset},@var{length} @anchor{qXfer fdpic loadmap read} Read contents of @code{loadmap}s on the target system. The annex, either @samp{exec} or @samp{interp}, specifies which @code{loadmap}, executable @code{loadmap} or interpreter @code{loadmap} to read. This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). @item qXfer:osdata:read::@var{offset},@var{length} @anchor{qXfer osdata read} Access the target's @dfn{operating system information}. @xref{Operating System Information}. @end table @item qXfer:@var{object}:write:@var{annex}:@var{offset}:@var{data}@dots{} @cindex write data into object, remote request @anchor{qXfer write} Write uninterpreted bytes into the target's special data area identified by the keyword @var{object}, starting at @var{offset} bytes into the data. The binary-encoded data (@pxref{Binary Data}) to be written is given by @var{data}@dots{}. The content and encoding of @var{annex} is specific to @var{object}; it can supply additional details about what data to access. Reply: @table @samp @item @var{nn} @var{nn} (hex encoded) is the number of bytes written. This may be fewer bytes than supplied in the request. @item E00 The request was malformed, or @var{annex} was invalid. @item E @var{nn} The offset was invalid, or there was an error encountered writing the data. The @var{nn} part is a hex-encoded @code{errno} value. @item @w{} An empty reply indicates the @var{object} string was not recognized by the stub, or that the object does not support writing. @end table Here are the specific requests of this form defined so far. All the @samp{qXfer:@var{object}:write:@dots{}} requests use the same reply formats, listed above. @table @samp @item qXfer:siginfo:write::@var{offset}:@var{data}@dots{} @anchor{qXfer siginfo write} Write @var{data} to the extra signal information on the target system. The annex part of the generic @samp{qXfer} packet must be empty (@pxref{qXfer write}). This packet is not probed by default; the remote stub must request it, by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}). @end table @item qXfer:@var{object}:@var{operation}:@dots{} Requests of this form may be added in the future. When a stub does not recognize the @var{object} keyword, or its support for @var{object} does not recognize the @var{operation} keyword, the stub must respond with an empty packet. @item qAttached:@var{pid} @cindex query attached, remote request @cindex @samp{qAttached} packet Return an indication of whether the remote server attached to an existing process or created a new process. When the multiprocess protocol extensions are supported (@pxref{multiprocess extensions}), @var{pid} is an integer in hexadecimal format identifying the target process. Otherwise, @value{GDBN} will omit the @var{pid} field and the query packet will be simplified as @samp{qAttached}. This query is used, for example, to know whether the remote process should be detached or killed when a @value{GDBN} session is ended with the @code{quit} command. Reply: @table @samp @item 1 The remote server attached to an existing process. @item 0 The remote server created a new process. @item E @var{NN} A badly formed request or an error was encountered. @end table @item Qbtrace:bts Enable branch tracing for the current thread using Branch Trace Store. Reply: @table @samp @item OK Branch tracing has been enabled. @item E.errtext A badly formed request or an error was encountered. @end table @item Qbtrace:pt Enable branch tracing for the current thread using Intel Processor Trace. Reply: @table @samp @item OK Branch tracing has been enabled. @item E.errtext A badly formed request or an error was encountered. @end table @item Qbtrace:off Disable branch tracing for the current thread. Reply: @table @samp @item OK Branch tracing has been disabled. @item E.errtext A badly formed request or an error was encountered. @end table @item Qbtrace-conf:bts:size=@var{value} Set the requested ring buffer size for new threads that use the btrace recording method in bts format. Reply: @table @samp @item OK The ring buffer size has been set. @item E.errtext A badly formed request or an error was encountered. @end table @item Qbtrace-conf:pt:size=@var{value} Set the requested ring buffer size for new threads that use the btrace recording method in pt format. Reply: @table @samp @item OK The ring buffer size has been set. @item E.errtext A badly formed request or an error was encountered. @end table @end table @node Architecture-Specific Protocol Details @section Architecture-Specific Protocol Details This section describes how the remote protocol is applied to specific target architectures. Also see @ref{Standard Target Features}, for details of XML target descriptions for each architecture. @menu * ARM-Specific Protocol Details:: * MIPS-Specific Protocol Details:: @end menu @node ARM-Specific Protocol Details @subsection @acronym{ARM}-specific Protocol Details @menu * ARM Breakpoint Kinds:: @end menu @node ARM Breakpoint Kinds @subsubsection @acronym{ARM} Breakpoint Kinds @cindex breakpoint kinds, @acronym{ARM} These breakpoint kinds are defined for the @samp{Z0} and @samp{Z1} packets. @table @r @item 2 16-bit Thumb mode breakpoint. @item 3 32-bit Thumb mode (Thumb-2) breakpoint. @item 4 32-bit @acronym{ARM} mode breakpoint. @end table @node MIPS-Specific Protocol Details @subsection @acronym{MIPS}-specific Protocol Details @menu * MIPS Register packet Format:: * MIPS Breakpoint Kinds:: @end menu @node MIPS Register packet Format @subsubsection @acronym{MIPS} Register Packet Format @cindex register packet format, @acronym{MIPS} The following @code{g}/@code{G} packets have previously been defined. In the below, some thirty-two bit registers are transferred as sixty-four bits. Those registers should be zero/sign extended (which?) to fill the space allocated. Register bytes are transferred in target byte order. The two nibbles within a register byte are transferred most-significant -- least-significant. @table @r @item MIPS32 All registers are transferred as thirty-two bit quantities in the order: 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point registers; fsr; fir; fp. @item MIPS64 All registers are transferred as sixty-four bit quantities (including thirty-two bit registers such as @code{sr}). The ordering is the same as @code{MIPS32}. @end table @node MIPS Breakpoint Kinds @subsubsection @acronym{MIPS} Breakpoint Kinds @cindex breakpoint kinds, @acronym{MIPS} These breakpoint kinds are defined for the @samp{Z0} and @samp{Z1} packets. @table @r @item 2 16-bit @acronym{MIPS16} mode breakpoint. @item 3 16-bit @acronym{microMIPS} mode breakpoint. @item 4 32-bit standard @acronym{MIPS} mode breakpoint. @item 5 32-bit @acronym{microMIPS} mode breakpoint. @end table @node Tracepoint Packets @section Tracepoint Packets @cindex tracepoint packets @cindex packets, tracepoint Here we describe the packets @value{GDBN} uses to implement tracepoints (@pxref{Tracepoints}). @table @samp @item QTDP:@var{n}:@var{addr}:@var{ena}:@var{step}:@var{pass}[:F@var{flen}][:X@var{len},@var{bytes}]@r{[}-@r{]} @cindex @samp{QTDP} packet Create a new tracepoint, number @var{n}, at @var{addr}. If @var{ena} is @samp{E}, then the tracepoint is enabled; if it is @samp{D}, then the tracepoint is disabled. The @var{step} gives the tracepoint's step count, and @var{pass} gives its pass count. If an @samp{F} is present, then the tracepoint is to be a fast tracepoint, and the @var{flen} is the number of bytes that the target should copy elsewhere to make room for the tracepoint. If an @samp{X} is present, it introduces a tracepoint condition, which consists of a hexadecimal length, followed by a comma and hex-encoded bytes, in a manner similar to action encodings as described below. If the trailing @samp{-} is present, further @samp{QTDP} packets will follow to specify this tracepoint's actions. Replies: @table @samp @item OK The packet was understood and carried out. @item qRelocInsn @xref{Tracepoint Packets,,Relocate instruction reply packet}. @item @w{} The packet was not recognized. @end table @item QTDP:-@var{n}:@var{addr}:@r{[}S@r{]}@var{action}@dots{}@r{[}-@r{]} Define actions to be taken when a tracepoint is hit. The @var{n} and @var{addr} must be the same as in the initial @samp{QTDP} packet for this tracepoint. This packet may only be sent immediately after another @samp{QTDP} packet that ended with a @samp{-}. If the trailing @samp{-} is present, further @samp{QTDP} packets will follow, specifying more actions for this tracepoint. In the series of action packets for a given tracepoint, at most one can have an @samp{S} before its first @var{action}. If such a packet is sent, it and the following packets define ``while-stepping'' actions. Any prior packets define ordinary actions --- that is, those taken when the tracepoint is first hit. If no action packet has an @samp{S}, then all the packets in the series specify ordinary tracepoint actions. The @samp{@var{action}@dots{}} portion of the packet is a series of actions, concatenated without separators. Each action has one of the following forms: @table @samp @item R @var{mask} Collect the registers whose bits are set in @var{mask}, a hexadecimal number whose @var{i}'th bit is set if register number @var{i} should be collected. (The least significant bit is numbered zero.) Note that @var{mask} may be any number of digits long; it may not fit in a 32-bit word. @item M @var{basereg},@var{offset},@var{len} Collect @var{len} bytes of memory starting at the address in register number @var{basereg}, plus @var{offset}. If @var{basereg} is @samp{-1}, then the range has a fixed address: @var{offset} is the address of the lowest byte to collect. The @var{basereg}, @var{offset}, and @var{len} parameters are all unsigned hexadecimal values (the @samp{-1} value for @var{basereg} is a special case). @item X @var{len},@var{expr} Evaluate @var{expr}, whose length is @var{len}, and collect memory as it directs. The agent expression @var{expr} is as described in @ref{Agent Expressions}. Each byte of the expression is encoded as a two-digit hex number in the packet; @var{len} is the number of bytes in the expression (and thus one-half the number of hex digits in the packet). @end table Any number of actions may be packed together in a single @samp{QTDP} packet, as long as the packet does not exceed the maximum packet length (400 bytes, for many stubs). There may be only one @samp{R} action per tracepoint, and it must precede any @samp{M} or @samp{X} actions. Any registers referred to by @samp{M} and @samp{X} actions must be collected by a preceding @samp{R} action. (The ``while-stepping'' actions are treated as if they were attached to a separate tracepoint, as far as these restrictions are concerned.) Replies: @table @samp @item OK The packet was understood and carried out. @item qRelocInsn @xref{Tracepoint Packets,,Relocate instruction reply packet}. @item @w{} The packet was not recognized. @end table @item QTDPsrc:@var{n}:@var{addr}:@var{type}:@var{start}:@var{slen}:@var{bytes} @cindex @samp{QTDPsrc} packet Specify a source string of tracepoint @var{n} at address @var{addr}. This is useful to get accurate reproduction of the tracepoints originally downloaded at the beginning of the trace run. The @var{type} is the name of the tracepoint part, such as @samp{cond} for the tracepoint's conditional expression (see below for a list of types), while @var{bytes} is the string, encoded in hexadecimal. @var{start} is the offset of the @var{bytes} within the overall source string, while @var{slen} is the total length of the source string. This is intended for handling source strings that are longer than will fit in a single packet. @c Add detailed example when this info is moved into a dedicated @c tracepoint descriptions section. The available string types are @samp{at} for the location, @samp{cond} for the conditional, and @samp{cmd} for an action command. @value{GDBN} sends a separate packet for each command in the action list, in the same order in which the commands are stored in the list. The target does not need to do anything with source strings except report them back as part of the replies to the @samp{qTfP}/@samp{qTsP} query packets. Although this packet is optional, and @value{GDBN} will only send it if the target replies with @samp{TracepointSource} @xref{General Query Packets}, it makes both disconnected tracing and trace files much easier to use. Otherwise the user must be careful that the tracepoints in effect while looking at trace frames are identical to the ones in effect during the trace run; even a small discrepancy could cause @samp{tdump} not to work, or a particular trace frame not be found. @item QTDV:@var{n}:@var{value}:@var{builtin}:@var{name} @cindex define trace state variable, remote request @cindex @samp{QTDV} packet Create a new trace state variable, number @var{n}, with an initial value of @var{value}, which is a 64-bit signed integer. Both @var{n} and @var{value} are encoded as hexadecimal values. @value{GDBN} has the option of not using this packet for initial values of zero; the target should simply create the trace state variables as they are mentioned in expressions. The value @var{builtin} should be 1 (one) if the trace state variable is builtin and 0 (zero) if it is not builtin. @value{GDBN} only sets @var{builtin} to 1 if a previous @samp{qTfV} or @samp{qTsV} packet had it set. The contents of @var{name} is the hex-encoded name (without the leading @samp{$}) of the trace state variable. @item QTFrame:@var{n} @cindex @samp{QTFrame} packet Select the @var{n}'th tracepoint frame from the buffer, and use the register and memory contents recorded there to answer subsequent request packets from @value{GDBN}. A successful reply from the stub indicates that the stub has found the requested frame. The response is a series of parts, concatenated without separators, describing the frame we selected. Each part has one of the following forms: @table @samp @item F @var{f} The selected frame is number @var{n} in the trace frame buffer; @var{f} is a hexadecimal number. If @var{f} is @samp{-1}, then there was no frame matching the criteria in the request packet. @item T @var{t} The selected trace frame records a hit of tracepoint number @var{t}; @var{t} is a hexadecimal number. @end table @item QTFrame:pc:@var{addr} Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the currently selected frame whose PC is @var{addr}; @var{addr} is a hexadecimal number. @item QTFrame:tdp:@var{t} Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the currently selected frame that is a hit of tracepoint @var{t}; @var{t} is a hexadecimal number. @item QTFrame:range:@var{start}:@var{end} Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the currently selected frame whose PC is between @var{start} (inclusive) and @var{end} (inclusive); @var{start} and @var{end} are hexadecimal numbers. @item QTFrame:outside:@var{start}:@var{end} Like @samp{QTFrame:range:@var{start}:@var{end}}, but select the first frame @emph{outside} the given range of addresses (exclusive). @item qTMinFTPILen @cindex @samp{qTMinFTPILen} packet This packet requests the minimum length of instruction at which a fast tracepoint (@pxref{Set Tracepoints}) may be placed. For instance, on the 32-bit x86 architecture, it is possible to use a 4-byte jump, but it depends on the target system being able to create trampolines in the first 64K of memory, which might or might not be possible for that system. So the reply to this packet will be 4 if it is able to arrange for that. Replies: @table @samp @item 0 The minimum instruction length is currently unknown. @item @var{length} The minimum instruction length is @var{length}, where @var{length} is a hexadecimal number greater or equal to 1. A reply of 1 means that a fast tracepoint may be placed on any instruction regardless of size. @item E An error has occurred. @item @w{} An empty reply indicates that the request is not supported by the stub. @end table @item QTStart @cindex @samp{QTStart} packet Begin the tracepoint experiment. Begin collecting data from tracepoint hits in the trace frame buffer. This packet supports the @samp{qRelocInsn} reply (@pxref{Tracepoint Packets,,Relocate instruction reply packet}). @item QTStop @cindex @samp{QTStop} packet End the tracepoint experiment. Stop collecting trace frames. @item QTEnable:@var{n}:@var{addr} @anchor{QTEnable} @cindex @samp{QTEnable} packet Enable tracepoint @var{n} at address @var{addr} in a started tracepoint experiment. If the tracepoint was previously disabled, then collection of data from it will resume. @item QTDisable:@var{n}:@var{addr} @anchor{QTDisable} @cindex @samp{QTDisable} packet Disable tracepoint @var{n} at address @var{addr} in a started tracepoint experiment. No more data will be collected from the tracepoint unless @samp{QTEnable:@var{n}:@var{addr}} is subsequently issued. @item QTinit @cindex @samp{QTinit} packet Clear the table of tracepoints, and empty the trace frame buffer. @item QTro:@var{start1},@var{end1}:@var{start2},@var{end2}:@dots{} @cindex @samp{QTro} packet Establish the given ranges of memory as ``transparent''. The stub will answer requests for these ranges from memory's current contents, if they were not collected as part of the tracepoint hit. @value{GDBN} uses this to mark read-only regions of memory, like those containing program code. Since these areas never change, they should still have the same contents they did when the tracepoint was hit, so there's no reason for the stub to refuse to provide their contents. @item QTDisconnected:@var{value} @cindex @samp{QTDisconnected} packet Set the choice to what to do with the tracing run when @value{GDBN} disconnects from the target. A @var{value} of 1 directs the target to continue the tracing run, while 0 tells the target to stop tracing if @value{GDBN} is no longer in the picture. @item qTStatus @cindex @samp{qTStatus} packet Ask the stub if there is a trace experiment running right now. The reply has the form: @table @samp @item T@var{running}@r{[};@var{field}@r{]}@dots{} @var{running} is a single digit @code{1} if the trace is presently running, or @code{0} if not. It is followed by semicolon-separated optional fields that an agent may use to report additional status. @end table If the trace is not running, the agent may report any of several explanations as one of the optional fields: @table @samp @item tnotrun:0 No trace has been run yet. @item tstop[:@var{text}]:0 The trace was stopped by a user-originated stop command. The optional @var{text} field is a user-supplied string supplied as part of the stop command (for instance, an explanation of why the trace was stopped manually). It is hex-encoded. @item tfull:0 The trace stopped because the trace buffer filled up. @item tdisconnected:0 The trace stopped because @value{GDBN} disconnected from the target. @item tpasscount:@var{tpnum} The trace stopped because tracepoint @var{tpnum} exceeded its pass count. @item terror:@var{text}:@var{tpnum} The trace stopped because tracepoint @var{tpnum} had an error. The string @var{text} is available to describe the nature of the error (for instance, a divide by zero in the condition expression); it is hex encoded. @item tunknown:0 The trace stopped for some other reason. @end table Additional optional fields supply statistical and other information. Although not required, they are extremely useful for users monitoring the progress of a trace run. If a trace has stopped, and these numbers are reported, they must reflect the state of the just-stopped trace. @table @samp @item tframes:@var{n} The number of trace frames in the buffer. @item tcreated:@var{n} The total number of trace frames created during the run. This may be larger than the trace frame count, if the buffer is circular. @item tsize:@var{n} The total size of the trace buffer, in bytes. @item tfree:@var{n} The number of bytes still unused in the buffer. @item circular:@var{n} The value of the circular trace buffer flag. @code{1} means that the trace buffer is circular and old trace frames will be discarded if necessary to make room, @code{0} means that the trace buffer is linear and may fill up. @item disconn:@var{n} The value of the disconnected tracing flag. @code{1} means that tracing will continue after @value{GDBN} disconnects, @code{0} means that the trace run will stop. @end table @item qTP:@var{tp}:@var{addr} @cindex tracepoint status, remote request @cindex @samp{qTP} packet Ask the stub for the current state of tracepoint number @var{tp} at address @var{addr}. Replies: @table @samp @item V@var{hits}:@var{usage} The tracepoint has been hit @var{hits} times so far during the trace run, and accounts for @var{usage} in the trace buffer. Note that @code{while-stepping} steps are not counted as separate hits, but the steps' space consumption is added into the usage number. @end table @item qTV:@var{var} @cindex trace state variable value, remote request @cindex @samp{qTV} packet Ask the stub for the value of the trace state variable number @var{var}. Replies: @table @samp @item V@var{value} The value of the variable is @var{value}. This will be the current value of the variable if the user is examining a running target, or a saved value if the variable was collected in the trace frame that the user is looking at. Note that multiple requests may result in different reply values, such as when requesting values while the program is running. @item U The value of the variable is unknown. This would occur, for example, if the user is examining a trace frame in which the requested variable was not collected. @end table @item qTfP @cindex @samp{qTfP} packet @itemx qTsP @cindex @samp{qTsP} packet These packets request data about tracepoints that are being used by the target. @value{GDBN} sends @code{qTfP} to get the first piece of data, and multiple @code{qTsP} to get additional pieces. Replies to these packets generally take the form of the @code{QTDP} packets that define tracepoints. (FIXME add detailed syntax) @item qTfV @cindex @samp{qTfV} packet @itemx qTsV @cindex @samp{qTsV} packet These packets request data about trace state variables that are on the target. @value{GDBN} sends @code{qTfV} to get the first vari of data, and multiple @code{qTsV} to get additional variables. Replies to these packets follow the syntax of the @code{QTDV} packets that define trace state variables. @item qTfSTM @itemx qTsSTM @anchor{qTfSTM} @anchor{qTsSTM} @cindex @samp{qTfSTM} packet @cindex @samp{qTsSTM} packet These packets request data about static tracepoint markers that exist in the target program. @value{GDBN} sends @code{qTfSTM} to get the first piece of data, and multiple @code{qTsSTM} to get additional pieces. Replies to these packets take the following form: Reply: @table @samp @item m @var{address}:@var{id}:@var{extra} A single marker @item m @var{address}:@var{id}:@var{extra},@var{address}:@var{id}:@var{extra}@dots{} a comma-separated list of markers @item l (lower case letter @samp{L}) denotes end of list. @item E @var{nn} An error occurred. The error number @var{nn} is given as hex digits. @item @w{} An empty reply indicates that the request is not supported by the stub. @end table The @var{address} is encoded in hex; @var{id} and @var{extra} are strings encoded in hex. In response to each query, the target will reply with a list of one or more markers, separated by commas. @value{GDBN} will respond to each reply with a request for more markers (using the @samp{qs} form of the query), until the target responds with @samp{l} (lower-case ell, for @dfn{last}). @item qTSTMat:@var{address} @anchor{qTSTMat} @cindex @samp{qTSTMat} packet This packets requests data about static tracepoint markers in the target program at @var{address}. Replies to this packet follow the syntax of the @samp{qTfSTM} and @code{qTsSTM} packets that list static tracepoint markers. @item QTSave:@var{filename} @cindex @samp{QTSave} packet This packet directs the target to save trace data to the file name @var{filename} in the target's filesystem. The @var{filename} is encoded as a hex string; the interpretation of the file name (relative vs absolute, wild cards, etc) is up to the target. @item qTBuffer:@var{offset},@var{len} @cindex @samp{qTBuffer} packet Return up to @var{len} bytes of the current contents of trace buffer, starting at @var{offset}. The trace buffer is treated as if it were a contiguous collection of traceframes, as per the trace file format. The reply consists as many hex-encoded bytes as the target can deliver in a packet; it is not an error to return fewer than were asked for. A reply consisting of just @code{l} indicates that no bytes are available. @item QTBuffer:circular:@var{value} This packet directs the target to use a circular trace buffer if @var{value} is 1, or a linear buffer if the value is 0. @item QTBuffer:size:@var{size} @anchor{QTBuffer-size} @cindex @samp{QTBuffer size} packet This packet directs the target to make the trace buffer be of size @var{size} if possible. A value of @code{-1} tells the target to use whatever size it prefers. @item QTNotes:@r{[}@var{type}:@var{text}@r{]}@r{[};@var{type}:@var{text}@r{]}@dots{} @cindex @samp{QTNotes} packet This packet adds optional textual notes to the trace run. Allowable types include @code{user}, @code{notes}, and @code{tstop}, the @var{text} fields are arbitrary strings, hex-encoded. @end table @subsection Relocate instruction reply packet When installing fast tracepoints in memory, the target may need to relocate the instruction currently at the tracepoint address to a different address in memory. For most instructions, a simple copy is enough, but, for example, call instructions that implicitly push the return address on the stack, and relative branches or other PC-relative instructions require offset adjustment, so that the effect of executing the instruction at a different address is the same as if it had executed in the original location. In response to several of the tracepoint packets, the target may also respond with a number of intermediate @samp{qRelocInsn} request packets before the final result packet, to have @value{GDBN} handle this relocation operation. If a packet supports this mechanism, its documentation will explicitly say so. See for example the above descriptions for the @samp{QTStart} and @samp{QTDP} packets. The format of the request is: @table @samp @item qRelocInsn:@var{from};@var{to} This requests @value{GDBN} to copy instruction at address @var{from} to address @var{to}, possibly adjusted so that executing the instruction at @var{to} has the same effect as executing it at @var{from}. @value{GDBN} writes the adjusted instruction to target memory starting at @var{to}. @end table Replies: @table @samp @item qRelocInsn:@var{adjusted_size} Informs the stub the relocation is complete. The @var{adjusted_size} is the length in bytes of resulting relocated instruction sequence. @item E @var{NN} A badly formed request was detected, or an error was encountered while relocating the instruction. @end table @node Host I/O Packets @section Host I/O Packets @cindex Host I/O, remote protocol @cindex file transfer, remote protocol The @dfn{Host I/O} packets allow @value{GDBN} to perform I/O operations on the far side of a remote link. For example, Host I/O is used to upload and download files to a remote target with its own filesystem. Host I/O uses the same constant values and data structure layout as the target-initiated File-I/O protocol. However, the Host I/O packets are structured differently. The target-initiated protocol relies on target memory to store parameters and buffers. Host I/O requests are initiated by @value{GDBN}, and the target's memory is not involved. @xref{File-I/O Remote Protocol Extension}, for more details on the target-initiated protocol. The Host I/O request packets all encode a single operation along with its arguments. They have this format: @table @samp @item vFile:@var{operation}: @var{parameter}@dots{} @var{operation} is the name of the particular request; the target should compare the entire packet name up to the second colon when checking for a supported operation. The format of @var{parameter} depends on the operation. Numbers are always passed in hexadecimal. Negative numbers have an explicit minus sign (i.e.@: two's complement is not used). Strings (e.g.@: filenames) are encoded as a series of hexadecimal bytes. The last argument to a system call may be a buffer of escaped binary data (@pxref{Binary Data}). @end table The valid responses to Host I/O packets are: @table @samp @item F @var{result} [, @var{errno}] [; @var{attachment}] @var{result} is the integer value returned by this operation, usually non-negative for success and -1 for errors. If an error has occured, @var{errno} will be included in the result specifying a value defined by the File-I/O protocol (@pxref{Errno Values}). For operations which return data, @var{attachment} supplies the data as a binary buffer. Binary buffers in response packets are escaped in the normal way (@pxref{Binary Data}). See the individual packet documentation for the interpretation of @var{result} and @var{attachment}. @item @w{} An empty response indicates that this operation is not recognized. @end table These are the supported Host I/O operations: @table @samp @item vFile:open: @var{filename}, @var{flags}, @var{mode} Open a file at @var{filename} and return a file descriptor for it, or return -1 if an error occurs. The @var{filename} is a string, @var{flags} is an integer indicating a mask of open flags (@pxref{Open Flags}), and @var{mode} is an integer indicating a mask of mode bits to use if the file is created (@pxref{mode_t Values}). @xref{open}, for details of the open flags and mode values. @item vFile:close: @var{fd} Close the open file corresponding to @var{fd} and return 0, or -1 if an error occurs. @item vFile:pread: @var{fd}, @var{count}, @var{offset} Read data from the open file corresponding to @var{fd}. Up to @var{count} bytes will be read from the file, starting at @var{offset} relative to the start of the file. The target may read fewer bytes; common reasons include packet size limits and an end-of-file condition. The number of bytes read is returned. Zero should only be returned for a successful read at the end of the file, or if @var{count} was zero. The data read should be returned as a binary attachment on success. If zero bytes were read, the response should include an empty binary attachment (i.e.@: a trailing semicolon). The return value is the number of target bytes read; the binary attachment may be longer if some characters were escaped. @item vFile:pwrite: @var{fd}, @var{offset}, @var{data} Write @var{data} (a binary buffer) to the open file corresponding to @var{fd}. Start the write at @var{offset} from the start of the file. Unlike many @code{write} system calls, there is no separate @var{count} argument; the length of @var{data} in the packet is used. @samp{vFile:pwrite} returns the number of bytes written, which may be shorter than the length of @var{data}, or -1 if an error occurred. @item vFile:fstat: @var{fd} Get information about the open file corresponding to @var{fd}. On success the information is returned as a binary attachment and the return value is the size of this attachment in bytes. If an error occurs the return value is -1. The format of the returned binary attachment is as described in @ref{struct stat}. @item vFile:unlink: @var{filename} Delete the file at @var{filename} on the target. Return 0, or -1 if an error occurs. The @var{filename} is a string. @item vFile:readlink: @var{filename} Read value of symbolic link @var{filename} on the target. Return the number of bytes read, or -1 if an error occurs. The data read should be returned as a binary attachment on success. If zero bytes were read, the response should include an empty binary attachment (i.e.@: a trailing semicolon). The return value is the number of target bytes read; the binary attachment may be longer if some characters were escaped. @item vFile:setfs: @var{pid} Select the filesystem on which @code{vFile} operations with @var{filename} arguments will operate. This is required for @value{GDBN} to be able to access files on remote targets where the remote stub does not share a common filesystem with the inferior(s). If @var{pid} is nonzero, select the filesystem as seen by process @var{pid}. If @var{pid} is zero, select the filesystem as seen by the remote stub. Return 0 on success, or -1 if an error occurs. If @code{vFile:setfs:} indicates success, the selected filesystem remains selected until the next successful @code{vFile:setfs:} operation. @end table @node Interrupts @section Interrupts @cindex interrupts (remote protocol) @anchor{interrupting remote targets} In all-stop mode, when a program on the remote target is running, @value{GDBN} may attempt to interrupt it by sending a @samp{Ctrl-C}, @code{BREAK} or a @code{BREAK} followed by @code{g}, control of which is specified via @value{GDBN}'s @samp{interrupt-sequence}. The precise meaning of @code{BREAK} is defined by the transport mechanism and may, in fact, be undefined. @value{GDBN} does not currently define a @code{BREAK} mechanism for any of the network interfaces except for TCP, in which case @value{GDBN} sends the @code{telnet} BREAK sequence. @samp{Ctrl-C}, on the other hand, is defined and implemented for all transport mechanisms. It is represented by sending the single byte @code{0x03} without any of the usual packet overhead described in the Overview section (@pxref{Overview}). When a @code{0x03} byte is transmitted as part of a packet, it is considered to be packet data and does @emph{not} represent an interrupt. E.g., an @samp{X} packet (@pxref{X packet}), used for binary downloads, may include an unescaped @code{0x03} as part of its packet. @code{BREAK} followed by @code{g} is also known as Magic SysRq g. When Linux kernel receives this sequence from serial port, it stops execution and connects to gdb. In non-stop mode, because packet resumptions are asynchronous (@pxref{vCont packet}), @value{GDBN} is always free to send a remote command to the remote stub, even when the target is running. For that reason, @value{GDBN} instead sends a regular packet (@pxref{vCtrlC packet}) with the usual packet framing instead of the single byte @code{0x03}. Stubs are not required to recognize these interrupt mechanisms and the precise meaning associated with receipt of the interrupt is implementation defined. If the target supports debugging of multiple threads and/or processes, it should attempt to interrupt all currently-executing threads and processes. If the stub is successful at interrupting the running program, it should send one of the stop reply packets (@pxref{Stop Reply Packets}) to @value{GDBN} as a result of successfully stopping the program in all-stop mode, and a stop reply for each stopped thread in non-stop mode. Interrupts received while the program is stopped are queued and the program will be interrupted when it is resumed next time. @node Notification Packets @section Notification Packets @cindex notification packets @cindex packets, notification The @value{GDBN} remote serial protocol includes @dfn{notifications}, packets that require no acknowledgment. Both the GDB and the stub may send notifications (although the only notifications defined at present are sent by the stub). Notifications carry information without incurring the round-trip latency of an acknowledgment, and so are useful for low-impact communications where occasional packet loss is not a problem. A notification packet has the form @samp{% @var{data} # @var{checksum}}, where @var{data} is the content of the notification, and @var{checksum} is a checksum of @var{data}, computed and formatted as for ordinary @value{GDBN} packets. A notification's @var{data} never contains @samp{$}, @samp{%} or @samp{#} characters. Upon receiving a notification, the recipient sends no @samp{+} or @samp{-} to acknowledge the notification's receipt or to report its corruption. Every notification's @var{data} begins with a name, which contains no colon characters, followed by a colon character. Recipients should silently ignore corrupted notifications and notifications they do not understand. Recipients should restart timeout periods on receipt of a well-formed notification, whether or not they understand it. Senders should only send the notifications described here when this protocol description specifies that they are permitted. In the future, we may extend the protocol to permit existing notifications in new contexts; this rule helps older senders avoid confusing newer recipients. (Older versions of @value{GDBN} ignore bytes received until they see the @samp{$} byte that begins an ordinary packet, so new stubs may transmit notifications without fear of confusing older clients. There are no notifications defined for @value{GDBN} to send at the moment, but we assume that most older stubs would ignore them, as well.) Each notification is comprised of three parts: @table @samp @item @var{name}:@var{event} The notification packet is sent by the side that initiates the exchange (currently, only the stub does that), with @var{event} carrying the specific information about the notification, and @var{name} specifying the name of the notification. @item @var{ack} The acknowledge sent by the other side, usually @value{GDBN}, to acknowledge the exchange and request the event. @end table The purpose of an asynchronous notification mechanism is to report to @value{GDBN} that something interesting happened in the remote stub. The remote stub may send notification @var{name}:@var{event} at any time, but @value{GDBN} acknowledges the notification when appropriate. The notification event is pending before @value{GDBN} acknowledges. Only one notification at a time may be pending; if additional events occur before @value{GDBN} has acknowledged the previous notification, they must be queued by the stub for later synchronous transmission in response to @var{ack} packets from @value{GDBN}. Because the notification mechanism is unreliable, the stub is permitted to resend a notification if it believes @value{GDBN} may not have received it. Specifically, notifications may appear when @value{GDBN} is not otherwise reading input from the stub, or when @value{GDBN} is expecting to read a normal synchronous response or a @samp{+}/@samp{-} acknowledgment to a packet it has sent. Notification packets are distinct from any other communication from the stub so there is no ambiguity. After receiving a notification, @value{GDBN} shall acknowledge it by sending a @var{ack} packet as a regular, synchronous request to the stub. Such acknowledgment is not required to happen immediately, as @value{GDBN} is permitted to send other, unrelated packets to the stub first, which the stub should process normally. Upon receiving a @var{ack} packet, if the stub has other queued events to report to @value{GDBN}, it shall respond by sending a normal @var{event}. @value{GDBN} shall then send another @var{ack} packet to solicit further responses; again, it is permitted to send other, unrelated packets as well which the stub should process normally. If the stub receives a @var{ack} packet and there are no additional @var{event} to report, the stub shall return an @samp{OK} response. At this point, @value{GDBN} has finished processing a notification and the stub has completed sending any queued events. @value{GDBN} won't accept any new notifications until the final @samp{OK} is received . If further notification events occur, the stub shall send a new notification, @value{GDBN} shall accept the notification, and the process shall be repeated. The process of asynchronous notification can be illustrated by the following example: @smallexample <- @code{%Stop:T0505:98e7ffbf;04:4ce6ffbf;08:b1b6e54c;thread:p7526.7526;core:0;} @code{...} -> @code{vStopped} <- @code{T0505:68f37db7;04:40f37db7;08:63850408;thread:p7526.7528;core:0;} -> @code{vStopped} <- @code{T0505:68e3fdb6;04:40e3fdb6;08:63850408;thread:p7526.7529;core:0;} -> @code{vStopped} <- @code{OK} @end smallexample The following notifications are defined: @multitable @columnfractions 0.12 0.12 0.38 0.38 @item Notification @tab Ack @tab Event @tab Description @item Stop @tab vStopped @tab @var{reply}. The @var{reply} has the form of a stop reply, as described in @ref{Stop Reply Packets}. Refer to @ref{Remote Non-Stop}, for information on how these notifications are acknowledged by @value{GDBN}. @tab Report an asynchronous stop event in non-stop mode. @end multitable @node Remote Non-Stop @section Remote Protocol Support for Non-Stop Mode @value{GDBN}'s remote protocol supports non-stop debugging of multi-threaded programs, as described in @ref{Non-Stop Mode}. If the stub supports non-stop mode, it should report that to @value{GDBN} by including @samp{QNonStop+} in its @samp{qSupported} response (@pxref{qSupported}). @value{GDBN} typically sends a @samp{QNonStop} packet only when establishing a new connection with the stub. Entering non-stop mode does not alter the state of any currently-running threads, but targets must stop all threads in any already-attached processes when entering all-stop mode. @value{GDBN} uses the @samp{?} packet as necessary to probe the target state after a mode change. In non-stop mode, when an attached process encounters an event that would otherwise be reported with a stop reply, it uses the asynchronous notification mechanism (@pxref{Notification Packets}) to inform @value{GDBN}. In contrast to all-stop mode, where all threads in all processes are stopped when a stop reply is sent, in non-stop mode only the thread reporting the stop event is stopped. That is, when reporting a @samp{S} or @samp{T} response to indicate completion of a step operation, hitting a breakpoint, or a fault, only the affected thread is stopped; any other still-running threads continue to run. When reporting a @samp{W} or @samp{X} response, all running threads belonging to other attached processes continue to run. In non-stop mode, the target shall respond to the @samp{?} packet as follows. First, any incomplete stop reply notification/@samp{vStopped} sequence in progress is abandoned. The target must begin a new sequence reporting stop events for all stopped threads, whether or not it has previously reported those events to @value{GDBN}. The first stop reply is sent as a synchronous reply to the @samp{?} packet, and subsequent stop replies are sent as responses to @samp{vStopped} packets using the mechanism described above. The target must not send asynchronous stop reply notifications until the sequence is complete. If all threads are running when the target receives the @samp{?} packet, or if the target is not attached to any process, it shall respond @samp{OK}. If the stub supports non-stop mode, it should also support the @samp{swbreak} stop reason if software breakpoints are supported, and the @samp{hwbreak} stop reason if hardware breakpoints are supported (@pxref{swbreak stop reason}). This is because given the asynchronous nature of non-stop mode, between the time a thread hits a breakpoint and the time the event is finally processed by @value{GDBN}, the breakpoint may have already been removed from the target. Due to this, @value{GDBN} needs to be able to tell whether a trap stop was caused by a delayed breakpoint event, which should be ignored, as opposed to a random trap signal, which should be reported to the user. Note the @samp{swbreak} feature implies that the target is responsible for adjusting the PC when a software breakpoint triggers, if necessary, such as on the x86 architecture. @node Packet Acknowledgment @section Packet Acknowledgment @cindex acknowledgment, for @value{GDBN} remote @cindex packet acknowledgment, for @value{GDBN} remote By default, when either the host or the target machine receives a packet, the first response expected is an acknowledgment: either @samp{+} (to indicate the package was received correctly) or @samp{-} (to request retransmission). This mechanism allows the @value{GDBN} remote protocol to operate over unreliable transport mechanisms, such as a serial line. In cases where the transport mechanism is itself reliable (such as a pipe or TCP connection), the @samp{+}/@samp{-} acknowledgments are redundant. It may be desirable to disable them in that case to reduce communication overhead, or for other reasons. This can be accomplished by means of the @samp{QStartNoAckMode} packet; @pxref{QStartNoAckMode}. When in no-acknowledgment mode, neither the stub nor @value{GDBN} shall send or expect @samp{+}/@samp{-} protocol acknowledgments. The packet and response format still includes the normal checksum, as described in @ref{Overview}, but the checksum may be ignored by the receiver. If the stub supports @samp{QStartNoAckMode} and prefers to operate in no-acknowledgment mode, it should report that to @value{GDBN} by including @samp{QStartNoAckMode+} in its response to @samp{qSupported}; @pxref{qSupported}. If @value{GDBN} also supports @samp{QStartNoAckMode} and it has not been disabled via the @code{set remote noack-packet off} command (@pxref{Remote Configuration}), @value{GDBN} may then send a @samp{QStartNoAckMode} packet to the stub. Only then may the stub actually turn off packet acknowledgments. @value{GDBN} sends a final @samp{+} acknowledgment of the stub's @samp{OK} response, which can be safely ignored by the stub. Note that @code{set remote noack-packet} command only affects negotiation between @value{GDBN} and the stub when subsequent connections are made; it does not affect the protocol acknowledgment state for any current connection. Since @samp{+}/@samp{-} acknowledgments are enabled by default when a new connection is established, there is also no protocol request to re-enable the acknowledgments for the current connection, once disabled. @node Examples @section Examples Example sequence of a target being re-started. Notice how the restart does not get any direct output: @smallexample -> @code{R00} <- @code{+} @emph{target restarts} -> @code{?} <- @code{+} <- @code{T001:1234123412341234} -> @code{+} @end smallexample Example sequence of a target being stepped by a single instruction: @smallexample -> @code{G1445@dots{}} <- @code{+} -> @code{s} <- @code{+} @emph{time passes} <- @code{T001:1234123412341234} -> @code{+} -> @code{g} <- @code{+} <- @code{1455@dots{}} -> @code{+} @end smallexample @node File-I/O Remote Protocol Extension @section File-I/O Remote Protocol Extension @cindex File-I/O remote protocol extension @menu * File-I/O Overview:: * Protocol Basics:: * The F Request Packet:: * The F Reply Packet:: * The Ctrl-C Message:: * Console I/O:: * List of Supported Calls:: * Protocol-specific Representation of Datatypes:: * Constants:: * File-I/O Examples:: @end menu @node File-I/O Overview @subsection File-I/O Overview @cindex file-i/o overview The @dfn{File I/O remote protocol extension} (short: File-I/O) allows the target to use the host's file system and console I/O to perform various system calls. System calls on the target system are translated into a remote protocol packet to the host system, which then performs the needed actions and returns a response packet to the target system. This simulates file system operations even on targets that lack file systems. The protocol is defined to be independent of both the host and target systems. It uses its own internal representation of datatypes and values. Both @value{GDBN} and the target's @value{GDBN} stub are responsible for translating the system-dependent value representations into the internal protocol representations when data is transmitted. The communication is synchronous. A system call is possible only when @value{GDBN} is waiting for a response from the @samp{C}, @samp{c}, @samp{S} or @samp{s} packets. While @value{GDBN} handles the request for a system call, the target is stopped to allow deterministic access to the target's memory. Therefore File-I/O is not interruptible by target signals. On the other hand, it is possible to interrupt File-I/O by a user interrupt (@samp{Ctrl-C}) within @value{GDBN}. The target's request to perform a host system call does not finish the latest @samp{C}, @samp{c}, @samp{S} or @samp{s} action. That means, after finishing the system call, the target returns to continuing the previous activity (continue, step). No additional continue or step request from @value{GDBN} is required. @smallexample (@value{GDBP}) continue <- target requests 'system call X' target is stopped, @value{GDBN} executes system call -> @value{GDBN} returns result ... target continues, @value{GDBN} returns to wait for the target <- target hits breakpoint and sends a Txx packet @end smallexample The protocol only supports I/O on the console and to regular files on the host file system. Character or block special devices, pipes, named pipes, sockets or any other communication method on the host system are not supported by this protocol. File I/O is not supported in non-stop mode. @node Protocol Basics @subsection Protocol Basics @cindex protocol basics, file-i/o The File-I/O protocol uses the @code{F} packet as the request as well as reply packet. Since a File-I/O system call can only occur when @value{GDBN} is waiting for a response from the continuing or stepping target, the File-I/O request is a reply that @value{GDBN} has to expect as a result of a previous @samp{C}, @samp{c}, @samp{S} or @samp{s} packet. This @code{F} packet contains all information needed to allow @value{GDBN} to call the appropriate host system call: @itemize @bullet @item A unique identifier for the requested system call. @item All parameters to the system call. Pointers are given as addresses in the target memory address space. Pointers to strings are given as pointer/length pair. Numerical values are given as they are. Numerical control flags are given in a protocol-specific representation. @end itemize At this point, @value{GDBN} has to perform the following actions. @itemize @bullet @item If the parameters include pointer values to data needed as input to a system call, @value{GDBN} requests this data from the target with a standard @code{m} packet request. This additional communication has to be expected by the target implementation and is handled as any other @code{m} packet. @item @value{GDBN} translates all value from protocol representation to host representation as needed. Datatypes are coerced into the host types. @item @value{GDBN} calls the system call. @item It then coerces datatypes back to protocol representation. @item If the system call is expected to return data in buffer space specified by pointer parameters to the call, the data is transmitted to the target using a @code{M} or @code{X} packet. This packet has to be expected by the target implementation and is handled as any other @code{M} or @code{X} packet. @end itemize Eventually @value{GDBN} replies with another @code{F} packet which contains all necessary information for the target to continue. This at least contains @itemize @bullet @item Return value. @item @code{errno}, if has been changed by the system call. @item ``Ctrl-C'' flag. @end itemize After having done the needed type and value coercion, the target continues the latest continue or step action. @node The F Request Packet @subsection The @code{F} Request Packet @cindex file-i/o request packet @cindex @code{F} request packet The @code{F} request packet has the following format: @table @samp @item F@var{call-id},@var{parameter@dots{}} @var{call-id} is the identifier to indicate the host system call to be called. This is just the name of the function. @var{parameter@dots{}} are the parameters to the system call. Parameters are hexadecimal integer values, either the actual values in case of scalar datatypes, pointers to target buffer space in case of compound datatypes and unspecified memory areas, or pointer/length pairs in case of string parameters. These are appended to the @var{call-id} as a comma-delimited list. All values are transmitted in ASCII string representation, pointer/length pairs separated by a slash. @end table @node The F Reply Packet @subsection The @code{F} Reply Packet @cindex file-i/o reply packet @cindex @code{F} reply packet The @code{F} reply packet has the following format: @table @samp @item F@var{retcode},@var{errno},@var{Ctrl-C flag};@var{call-specific attachment} @var{retcode} is the return code of the system call as hexadecimal value. @var{errno} is the @code{errno} set by the call, in protocol-specific representation. This parameter can be omitted if the call was successful. @var{Ctrl-C flag} is only sent if the user requested a break. In this case, @var{errno} must be sent as well, even if the call was successful. The @var{Ctrl-C flag} itself consists of the character @samp{C}: @smallexample F0,0,C @end smallexample @noindent or, if the call was interrupted before the host call has been performed: @smallexample F-1,4,C @end smallexample @noindent assuming 4 is the protocol-specific representation of @code{EINTR}. @end table @node The Ctrl-C Message @subsection The @samp{Ctrl-C} Message @cindex ctrl-c message, in file-i/o protocol If the @samp{Ctrl-C} flag is set in the @value{GDBN} reply packet (@pxref{The F Reply Packet}), the target should behave as if it had gotten a break message. The meaning for the target is ``system call interrupted by @code{SIGINT}''. Consequentially, the target should actually stop (as with a break message) and return to @value{GDBN} with a @code{T02} packet. It's important for the target to know in which state the system call was interrupted. There are two possible cases: @itemize @bullet @item The system call hasn't been performed on the host yet. @item The system call on the host has been finished. @end itemize These two states can be distinguished by the target by the value of the returned @code{errno}. If it's the protocol representation of @code{EINTR}, the system call hasn't been performed. This is equivalent to the @code{EINTR} handling on POSIX systems. In any other case, the target may presume that the system call has been finished --- successfully or not --- and should behave as if the break message arrived right after the system call. @value{GDBN} must behave reliably. If the system call has not been called yet, @value{GDBN} may send the @code{F} reply immediately, setting @code{EINTR} as @code{errno} in the packet. If the system call on the host has been finished before the user requests a break, the full action must be finished by @value{GDBN}. This requires sending @code{M} or @code{X} packets as necessary. The @code{F} packet may only be sent when either nothing has happened or the full action has been completed. @node Console I/O @subsection Console I/O @cindex console i/o as part of file-i/o By default and if not explicitly closed by the target system, the file descriptors 0, 1 and 2 are connected to the @value{GDBN} console. Output on the @value{GDBN} console is handled as any other file output operation (@code{write(1, @dots{})} or @code{write(2, @dots{})}). Console input is handled by @value{GDBN} so that after the target read request from file descriptor 0 all following typing is buffered until either one of the following conditions is met: @itemize @bullet @item The user types @kbd{Ctrl-c}. The behaviour is as explained above, and the @code{read} system call is treated as finished. @item The user presses @key{RET}. This is treated as end of input with a trailing newline. @item The user types @kbd{Ctrl-d}. This is treated as end of input. No trailing character (neither newline nor @samp{Ctrl-D}) is appended to the input. @end itemize If the user has typed more characters than fit in the buffer given to the @code{read} call, the trailing characters are buffered in @value{GDBN} until either another @code{read(0, @dots{})} is requested by the target, or debugging is stopped at the user's request. @node List of Supported Calls @subsection List of Supported Calls @cindex list of supported file-i/o calls @menu * open:: * close:: * read:: * write:: * lseek:: * rename:: * unlink:: * stat/fstat:: * gettimeofday:: * isatty:: * system:: @end menu @node open @unnumberedsubsubsec open @cindex open, file-i/o system call @table @asis @item Synopsis: @smallexample int open(const char *pathname, int flags); int open(const char *pathname, int flags, mode_t mode); @end smallexample @item Request: @samp{Fopen,@var{pathptr}/@var{len},@var{flags},@var{mode}} @noindent @var{flags} is the bitwise @code{OR} of the following values: @table @code @item O_CREAT If the file does not exist it will be created. The host rules apply as far as file ownership and time stamps are concerned. @item O_EXCL When used with @code{O_CREAT}, if the file already exists it is an error and open() fails. @item O_TRUNC If the file already exists and the open mode allows writing (@code{O_RDWR} or @code{O_WRONLY} is given) it will be truncated to zero length. @item O_APPEND The file is opened in append mode. @item O_RDONLY The file is opened for reading only. @item O_WRONLY The file is opened for writing only. @item O_RDWR The file is opened for reading and writing. @end table @noindent Other bits are silently ignored. @noindent @var{mode} is the bitwise @code{OR} of the following values: @table @code @item S_IRUSR User has read permission. @item S_IWUSR User has write permission. @item S_IRGRP Group has read permission. @item S_IWGRP Group has write permission. @item S_IROTH Others have read permission. @item S_IWOTH Others have write permission. @end table @noindent Other bits are silently ignored. @item Return value: @code{open} returns the new file descriptor or -1 if an error occurred. @item Errors: @table @code @item EEXIST @var{pathname} already exists and @code{O_CREAT} and @code{O_EXCL} were used. @item EISDIR @var{pathname} refers to a directory. @item EACCES The requested access is not allowed. @item ENAMETOOLONG @var{pathname} was too long. @item ENOENT A directory component in @var{pathname} does not exist. @item ENODEV @var{pathname} refers to a device, pipe, named pipe or socket. @item EROFS @var{pathname} refers to a file on a read-only filesystem and write access was requested. @item EFAULT @var{pathname} is an invalid pointer value. @item ENOSPC No space on device to create the file. @item EMFILE The process already has the maximum number of files open. @item ENFILE The limit on the total number of files open on the system has been reached. @item EINTR The call was interrupted by the user. @end table @end table @node close @unnumberedsubsubsec close @cindex close, file-i/o system call @table @asis @item Synopsis: @smallexample int close(int fd); @end smallexample @item Request: @samp{Fclose,@var{fd}} @item Return value: @code{close} returns zero on success, or -1 if an error occurred. @item Errors: @table @code @item EBADF @var{fd} isn't a valid open file descriptor. @item EINTR The call was interrupted by the user. @end table @end table @node read @unnumberedsubsubsec read @cindex read, file-i/o system call @table @asis @item Synopsis: @smallexample int read(int fd, void *buf, unsigned int count); @end smallexample @item Request: @samp{Fread,@var{fd},@var{bufptr},@var{count}} @item Return value: On success, the number of bytes read is returned. Zero indicates end of file. If count is zero, read returns zero as well. On error, -1 is returned. @item Errors: @table @code @item EBADF @var{fd} is not a valid file descriptor or is not open for reading. @item EFAULT @var{bufptr} is an invalid pointer value. @item EINTR The call was interrupted by the user. @end table @end table @node write @unnumberedsubsubsec write @cindex write, file-i/o system call @table @asis @item Synopsis: @smallexample int write(int fd, const void *buf, unsigned int count); @end smallexample @item Request: @samp{Fwrite,@var{fd},@var{bufptr},@var{count}} @item Return value: On success, the number of bytes written are returned. Zero indicates nothing was written. On error, -1 is returned. @item Errors: @table @code @item EBADF @var{fd} is not a valid file descriptor or is not open for writing. @item EFAULT @var{bufptr} is an invalid pointer value. @item EFBIG An attempt was made to write a file that exceeds the host-specific maximum file size allowed. @item ENOSPC No space on device to write the data. @item EINTR The call was interrupted by the user. @end table @end table @node lseek @unnumberedsubsubsec lseek @cindex lseek, file-i/o system call @table @asis @item Synopsis: @smallexample long lseek (int fd, long offset, int flag); @end smallexample @item Request: @samp{Flseek,@var{fd},@var{offset},@var{flag}} @var{flag} is one of: @table @code @item SEEK_SET The offset is set to @var{offset} bytes. @item SEEK_CUR The offset is set to its current location plus @var{offset} bytes. @item SEEK_END The offset is set to the size of the file plus @var{offset} bytes. @end table @item Return value: On success, the resulting unsigned offset in bytes from the beginning of the file is returned. Otherwise, a value of -1 is returned. @item Errors: @table @code @item EBADF @var{fd} is not a valid open file descriptor. @item ESPIPE @var{fd} is associated with the @value{GDBN} console. @item EINVAL @var{flag} is not a proper value. @item EINTR The call was interrupted by the user. @end table @end table @node rename @unnumberedsubsubsec rename @cindex rename, file-i/o system call @table @asis @item Synopsis: @smallexample int rename(const char *oldpath, const char *newpath); @end smallexample @item Request: @samp{Frename,@var{oldpathptr}/@var{len},@var{newpathptr}/@var{len}} @item Return value: On success, zero is returned. On error, -1 is returned. @item Errors: @table @code @item EISDIR @var{newpath} is an existing directory, but @var{oldpath} is not a directory. @item EEXIST @var{newpath} is a non-empty directory. @item EBUSY @var{oldpath} or @var{newpath} is a directory that is in use by some process. @item EINVAL An attempt was made to make a directory a subdirectory of itself. @item ENOTDIR A component used as a directory in @var{oldpath} or new path is not a directory. Or @var{oldpath} is a directory and @var{newpath} exists but is not a directory. @item EFAULT @var{oldpathptr} or @var{newpathptr} are invalid pointer values. @item EACCES No access to the file or the path of the file. @item ENAMETOOLONG @var{oldpath} or @var{newpath} was too long. @item ENOENT A directory component in @var{oldpath} or @var{newpath} does not exist. @item EROFS The file is on a read-only filesystem. @item ENOSPC The device containing the file has no room for the new directory entry. @item EINTR The call was interrupted by the user. @end table @end table @node unlink @unnumberedsubsubsec unlink @cindex unlink, file-i/o system call @table @asis @item Synopsis: @smallexample int unlink(const char *pathname); @end smallexample @item Request: @samp{Funlink,@var{pathnameptr}/@var{len}} @item Return value: On success, zero is returned. On error, -1 is returned. @item Errors: @table @code @item EACCES No access to the file or the path of the file. @item EPERM The system does not allow unlinking of directories. @item EBUSY The file @var{pathname} cannot be unlinked because it's being used by another process. @item EFAULT @var{pathnameptr} is an invalid pointer value. @item ENAMETOOLONG @var{pathname} was too long. @item ENOENT A directory component in @var{pathname} does not exist. @item ENOTDIR A component of the path is not a directory. @item EROFS The file is on a read-only filesystem. @item EINTR The call was interrupted by the user. @end table @end table @node stat/fstat @unnumberedsubsubsec stat/fstat @cindex fstat, file-i/o system call @cindex stat, file-i/o system call @table @asis @item Synopsis: @smallexample int stat(const char *pathname, struct stat *buf); int fstat(int fd, struct stat *buf); @end smallexample @item Request: @samp{Fstat,@var{pathnameptr}/@var{len},@var{bufptr}}@* @samp{Ffstat,@var{fd},@var{bufptr}} @item Return value: On success, zero is returned. On error, -1 is returned. @item Errors: @table @code @item EBADF @var{fd} is not a valid open file. @item ENOENT A directory component in @var{pathname} does not exist or the path is an empty string. @item ENOTDIR A component of the path is not a directory. @item EFAULT @var{pathnameptr} is an invalid pointer value. @item EACCES No access to the file or the path of the file. @item ENAMETOOLONG @var{pathname} was too long. @item EINTR The call was interrupted by the user. @end table @end table @node gettimeofday @unnumberedsubsubsec gettimeofday @cindex gettimeofday, file-i/o system call @table @asis @item Synopsis: @smallexample int gettimeofday(struct timeval *tv, void *tz); @end smallexample @item Request: @samp{Fgettimeofday,@var{tvptr},@var{tzptr}} @item Return value: On success, 0 is returned, -1 otherwise. @item Errors: @table @code @item EINVAL @var{tz} is a non-NULL pointer. @item EFAULT @var{tvptr} and/or @var{tzptr} is an invalid pointer value. @end table @end table @node isatty @unnumberedsubsubsec isatty @cindex isatty, file-i/o system call @table @asis @item Synopsis: @smallexample int isatty(int fd); @end smallexample @item Request: @samp{Fisatty,@var{fd}} @item Return value: Returns 1 if @var{fd} refers to the @value{GDBN} console, 0 otherwise. @item Errors: @table @code @item EINTR The call was interrupted by the user. @end table @end table Note that the @code{isatty} call is treated as a special case: it returns 1 to the target if the file descriptor is attached to the @value{GDBN} console, 0 otherwise. Implementing through system calls would require implementing @code{ioctl} and would be more complex than needed. @node system @unnumberedsubsubsec system @cindex system, file-i/o system call @table @asis @item Synopsis: @smallexample int system(const char *command); @end smallexample @item Request: @samp{Fsystem,@var{commandptr}/@var{len}} @item Return value: If @var{len} is zero, the return value indicates whether a shell is available. A zero return value indicates a shell is not available. For non-zero @var{len}, the value returned is -1 on error and the return status of the command otherwise. Only the exit status of the command is returned, which is extracted from the host's @code{system} return value by calling @code{WEXITSTATUS(retval)}. In case @file{/bin/sh} could not be executed, 127 is returned. @item Errors: @table @code @item EINTR The call was interrupted by the user. @end table @end table @value{GDBN} takes over the full task of calling the necessary host calls to perform the @code{system} call. The return value of @code{system} on the host is simplified before it's returned to the target. Any termination signal information from the child process is discarded, and the return value consists entirely of the exit status of the called command. Due to security concerns, the @code{system} call is by default refused by @value{GDBN}. The user has to allow this call explicitly with the @code{set remote system-call-allowed 1} command. @table @code @item set remote system-call-allowed @kindex set remote system-call-allowed Control whether to allow the @code{system} calls in the File I/O protocol for the remote target. The default is zero (disabled). @item show remote system-call-allowed @kindex show remote system-call-allowed Show whether the @code{system} calls are allowed in the File I/O protocol. @end table @node Protocol-specific Representation of Datatypes @subsection Protocol-specific Representation of Datatypes @cindex protocol-specific representation of datatypes, in file-i/o protocol @menu * Integral Datatypes:: * Pointer Values:: * Memory Transfer:: * struct stat:: * struct timeval:: @end menu @node Integral Datatypes @unnumberedsubsubsec Integral Datatypes @cindex integral datatypes, in file-i/o protocol The integral datatypes used in the system calls are @code{int}, @code{unsigned int}, @code{long}, @code{unsigned long}, @code{mode_t}, and @code{time_t}. @code{int}, @code{unsigned int}, @code{mode_t} and @code{time_t} are implemented as 32 bit values in this protocol. @code{long} and @code{unsigned long} are implemented as 64 bit types. @xref{Limits}, for corresponding MIN and MAX values (similar to those in @file{limits.h}) to allow range checking on host and target. @code{time_t} datatypes are defined as seconds since the Epoch. All integral datatypes transferred as part of a memory read or write of a structured datatype e.g.@: a @code{struct stat} have to be given in big endian byte order. @node Pointer Values @unnumberedsubsubsec Pointer Values @cindex pointer values, in file-i/o protocol Pointers to target data are transmitted as they are. An exception is made for pointers to buffers for which the length isn't transmitted as part of the function call, namely strings. Strings are transmitted as a pointer/length pair, both as hex values, e.g.@: @smallexample @code{1aaf/12} @end smallexample @noindent which is a pointer to data of length 18 bytes at position 0x1aaf. The length is defined as the full string length in bytes, including the trailing null byte. For example, the string @code{"hello world"} at address 0x123456 is transmitted as @smallexample @code{123456/d} @end smallexample @node Memory Transfer @unnumberedsubsubsec Memory Transfer @cindex memory transfer, in file-i/o protocol Structured data which is transferred using a memory read or write (for example, a @code{struct stat}) is expected to be in a protocol-specific format with all scalar multibyte datatypes being big endian. Translation to this representation needs to be done both by the target before the @code{F} packet is sent, and by @value{GDBN} before it transfers memory to the target. Transferred pointers to structured data should point to the already-coerced data at any time. @node struct stat @unnumberedsubsubsec struct stat @cindex struct stat, in file-i/o protocol The buffer of type @code{struct stat} used by the target and @value{GDBN} is defined as follows: @smallexample struct stat @{ unsigned int st_dev; /* device */ unsigned int st_ino; /* inode */ mode_t st_mode; /* protection */ unsigned int st_nlink; /* number of hard links */ unsigned int st_uid; /* user ID of owner */ unsigned int st_gid; /* group ID of owner */ unsigned int st_rdev; /* device type (if inode device) */ unsigned long st_size; /* total size, in bytes */ unsigned long st_blksize; /* blocksize for filesystem I/O */ unsigned long st_blocks; /* number of blocks allocated */ time_t st_atime; /* time of last access */ time_t st_mtime; /* time of last modification */ time_t st_ctime; /* time of last change */ @}; @end smallexample The integral datatypes conform to the definitions given in the appropriate section (see @ref{Integral Datatypes}, for details) so this structure is of size 64 bytes. The values of several fields have a restricted meaning and/or range of values. @table @code @item st_dev A value of 0 represents a file, 1 the console. @item st_ino No valid meaning for the target. Transmitted unchanged. @item st_mode Valid mode bits are described in @ref{Constants}. Any other bits have currently no meaning for the target. @item st_uid @itemx st_gid @itemx st_rdev No valid meaning for the target. Transmitted unchanged. @item st_atime @itemx st_mtime @itemx st_ctime These values have a host and file system dependent accuracy. Especially on Windows hosts, the file system may not support exact timing values. @end table The target gets a @code{struct stat} of the above representation and is responsible for coercing it to the target representation before continuing. Note that due to size differences between the host, target, and protocol representations of @code{struct stat} members, these members could eventually get truncated on the target. @node struct timeval @unnumberedsubsubsec struct timeval @cindex struct timeval, in file-i/o protocol The buffer of type @code{struct timeval} used by the File-I/O protocol is defined as follows: @smallexample struct timeval @{ time_t tv_sec; /* second */ long tv_usec; /* microsecond */ @}; @end smallexample The integral datatypes conform to the definitions given in the appropriate section (see @ref{Integral Datatypes}, for details) so this structure is of size 8 bytes. @node Constants @subsection Constants @cindex constants, in file-i/o protocol The following values are used for the constants inside of the protocol. @value{GDBN} and target are responsible for translating these values before and after the call as needed. @menu * Open Flags:: * mode_t Values:: * Errno Values:: * Lseek Flags:: * Limits:: @end menu @node Open Flags @unnumberedsubsubsec Open Flags @cindex open flags, in file-i/o protocol All values are given in hexadecimal representation. @smallexample O_RDONLY 0x0 O_WRONLY 0x1 O_RDWR 0x2 O_APPEND 0x8 O_CREAT 0x200 O_TRUNC 0x400 O_EXCL 0x800 @end smallexample @node mode_t Values @unnumberedsubsubsec mode_t Values @cindex mode_t values, in file-i/o protocol All values are given in octal representation. @smallexample S_IFREG 0100000 S_IFDIR 040000 S_IRUSR 0400 S_IWUSR 0200 S_IXUSR 0100 S_IRGRP 040 S_IWGRP 020 S_IXGRP 010 S_IROTH 04 S_IWOTH 02 S_IXOTH 01 @end smallexample @node Errno Values @unnumberedsubsubsec Errno Values @cindex errno values, in file-i/o protocol All values are given in decimal representation. @smallexample EPERM 1 ENOENT 2 EINTR 4 EBADF 9 EACCES 13 EFAULT 14 EBUSY 16 EEXIST 17 ENODEV 19 ENOTDIR 20 EISDIR 21 EINVAL 22 ENFILE 23 EMFILE 24 EFBIG 27 ENOSPC 28 ESPIPE 29 EROFS 30 ENAMETOOLONG 91 EUNKNOWN 9999 @end smallexample @code{EUNKNOWN} is used as a fallback error value if a host system returns any error value not in the list of supported error numbers. @node Lseek Flags @unnumberedsubsubsec Lseek Flags @cindex lseek flags, in file-i/o protocol @smallexample SEEK_SET 0 SEEK_CUR 1 SEEK_END 2 @end smallexample @node Limits @unnumberedsubsubsec Limits @cindex limits, in file-i/o protocol All values are given in decimal representation. @smallexample INT_MIN -2147483648 INT_MAX 2147483647 UINT_MAX 4294967295 LONG_MIN -9223372036854775808 LONG_MAX 9223372036854775807 ULONG_MAX 18446744073709551615 @end smallexample @node File-I/O Examples @subsection File-I/O Examples @cindex file-i/o examples Example sequence of a write call, file descriptor 3, buffer is at target address 0x1234, 6 bytes should be written: @smallexample <- @code{Fwrite,3,1234,6} @emph{request memory read from target} -> @code{m1234,6} <- XXXXXX @emph{return "6 bytes written"} -> @code{F6} @end smallexample Example sequence of a read call, file descriptor 3, buffer is at target address 0x1234, 6 bytes should be read: @smallexample <- @code{Fread,3,1234,6} @emph{request memory write to target} -> @code{X1234,6:XXXXXX} @emph{return "6 bytes read"} -> @code{F6} @end smallexample Example sequence of a read call, call fails on the host due to invalid file descriptor (@code{EBADF}): @smallexample <- @code{Fread,3,1234,6} -> @code{F-1,9} @end smallexample Example sequence of a read call, user presses @kbd{Ctrl-c} before syscall on host is called: @smallexample <- @code{Fread,3,1234,6} -> @code{F-1,4,C} <- @code{T02} @end smallexample Example sequence of a read call, user presses @kbd{Ctrl-c} after syscall on host is called: @smallexample <- @code{Fread,3,1234,6} -> @code{X1234,6:XXXXXX} <- @code{T02} @end smallexample @node Library List Format @section Library List Format @cindex library list format, remote protocol On some platforms, a dynamic loader (e.g.@: @file{ld.so}) runs in the same process as your application to manage libraries. In this case, @value{GDBN} can use the loader's symbol table and normal memory operations to maintain a list of shared libraries. On other platforms, the operating system manages loaded libraries. @value{GDBN} can not retrieve the list of currently loaded libraries through memory operations, so it uses the @samp{qXfer:libraries:read} packet (@pxref{qXfer library list read}) instead. The remote stub queries the target's operating system and reports which libraries are loaded. The @samp{qXfer:libraries:read} packet returns an XML document which lists loaded libraries and their offsets. Each library has an associated name and one or more segment or section base addresses, which report where the library was loaded in memory. For the common case of libraries that are fully linked binaries, the library should have a list of segments. If the target supports dynamic linking of a relocatable object file, its library XML element should instead include a list of allocated sections. The segment or section bases are start addresses, not relocation offsets; they do not depend on the library's link-time base addresses. @value{GDBN} must be linked with the Expat library to support XML library lists. @xref{Expat}. A simple memory map, with one loaded library relocated by a single offset, looks like this: @smallexample <library-list> <library name="/lib/libc.so.6"> <segment address="0x10000000"/> </library> </library-list> @end smallexample Another simple memory map, with one loaded library with three allocated sections (.text, .data, .bss), looks like this: @smallexample <library-list> <library name="sharedlib.o"> <section address="0x10000000"/> <section address="0x20000000"/> <section address="0x30000000"/> </library> </library-list> @end smallexample The format of a library list is described by this DTD: @smallexample  <!ELEMENT library-list (library)*> <!ATTLIST library-list version CDATA #FIXED "1.0"> <!ELEMENT library (segment*, section*)> <!ATTLIST library name CDATA #REQUIRED> <!ELEMENT segment EMPTY> <!ATTLIST segment address CDATA #REQUIRED> <!ELEMENT section EMPTY> <!ATTLIST section address CDATA #REQUIRED> @end smallexample In addition, segments and section descriptors cannot be mixed within a single library element, and you must supply at least one segment or section for each library. @node Library List Format for SVR4 Targets @section Library List Format for SVR4 Targets @cindex library list format, remote protocol On SVR4 platforms @value{GDBN} can use the symbol table of a dynamic loader (e.g.@: @file{ld.so}) and normal memory operations to maintain a list of shared libraries. Still a special library list provided by this packet is more efficient for the @value{GDBN} remote protocol. The @samp{qXfer:libraries-svr4:read} packet returns an XML document which lists loaded libraries and their SVR4 linker parameters. For each library on SVR4 target, the following parameters are reported: @itemize @minus @item @code{name}, the absolute file name from the @code{l_name} field of @code{struct link_map}. @item @code{lm} with address of @code{struct link_map} used for TLS (Thread Local Storage) access. @item @code{l_addr}, the displacement as read from the field @code{l_addr} of @code{struct link_map}. For prelinked libraries this is not an absolute memory address. It is a displacement of absolute memory address against address the file was prelinked to during the library load. @item @code{l_ld}, which is memory address of the @code{PT_DYNAMIC} segment @end itemize Additionally the single @code{main-lm} attribute specifies address of @code{struct link_map} used for the main executable. This parameter is used for TLS access and its presence is optional. @value{GDBN} must be linked with the Expat library to support XML SVR4 library lists. @xref{Expat}. A simple memory map, with two loaded libraries (which do not use prelink), looks like this: @smallexample <library-list-svr4 version="1.0" main-lm="0xe4f8f8"> <library name="/lib/ld-linux.so.2" lm="0xe4f51c" l_addr="0xe2d000" l_ld="0xe4eefc"/> <library name="/lib/libc.so.6" lm="0xe4fbe8" l_addr="0x154000" l_ld="0x152350"/> </library-list-svr> @end smallexample The format of an SVR4 library list is described by this DTD: @smallexample  <!ELEMENT library-list-svr4 (library)*> <!ATTLIST library-list-svr4 version CDATA #FIXED "1.0"> <!ATTLIST library-list-svr4 main-lm CDATA #IMPLIED> <!ELEMENT library EMPTY> <!ATTLIST library name CDATA #REQUIRED> <!ATTLIST library lm CDATA #REQUIRED> <!ATTLIST library l_addr CDATA #REQUIRED> <!ATTLIST library l_ld CDATA #REQUIRED> @end smallexample @node Memory Map Format @section Memory Map Format @cindex memory map format To be able to write into flash memory, @value{GDBN} needs to obtain a memory map from the target. This section describes the format of the memory map. The memory map is obtained using the @samp{qXfer:memory-map:read} (@pxref{qXfer memory map read}) packet and is an XML document that lists memory regions. @value{GDBN} must be linked with the Expat library to support XML memory maps. @xref{Expat}. The top-level structure of the document is shown below: @smallexample <?xml version="1.0"?> <!DOCTYPE memory-map PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN" "http://sourceware.org/gdb/gdb-memory-map.dtd"> <memory-map> region... </memory-map> @end smallexample Each region can be either: @itemize @item A region of RAM starting at @var{addr} and extending for @var{length} bytes from there: @smallexample <memory type="ram" start="@var{addr}" length="@var{length}"/> @end smallexample @item A region of read-only memory: @smallexample <memory type="rom" start="@var{addr}" length="@var{length}"/> @end smallexample @item A region of flash memory, with erasure blocks @var{blocksize} bytes in length: @smallexample <memory type="flash" start="@var{addr}" length="@var{length}"> <property name="blocksize">@var{blocksize}</property> </memory> @end smallexample @end itemize Regions must not overlap. @value{GDBN} assumes that areas of memory not covered by the memory map are RAM, and uses the ordinary @samp{M} and @samp{X} packets to write to addresses in such ranges. The formal DTD for memory map format is given below: @smallexample       <!ELEMENT memory-map (memory)*> <!ATTLIST memory-map version CDATA #FIXED "1.0.0"> <!ELEMENT memory (property)*>  <!ATTLIST memory type (ram|rom|flash) #REQUIRED start CDATA #REQUIRED length CDATA #REQUIRED>  <!ELEMENT property (#PCDATA | property)*> <!ATTLIST property name (blocksize) #REQUIRED> @end smallexample @node Thread List Format @section Thread List Format @cindex thread list format To efficiently update the list of threads and their attributes, @value{GDBN} issues the @samp{qXfer:threads:read} packet (@pxref{qXfer threads read}) and obtains the XML document with the following structure: @smallexample <?xml version="1.0"?> <threads> <thread id="id" core="0" name="name"> ... description ... </thread> </threads> @end smallexample Each @samp{thread} element must have the @samp{id} attribute that identifies the thread (@pxref{thread-id syntax}). The @samp{core} attribute, if present, specifies which processor core the thread was last executing on. The @samp{name} attribute, if present, specifies the human-readable name of the thread. The content of the of @samp{thread} element is interpreted as human-readable auxiliary information. The @samp{handle} attribute, if present, is a hex encoded representation of the thread handle. @node Traceframe Info Format @section Traceframe Info Format @cindex traceframe info format To be able to know which objects in the inferior can be examined when inspecting a tracepoint hit, @value{GDBN} needs to obtain the list of memory ranges, registers and trace state variables that have been collected in a traceframe. This list is obtained using the @samp{qXfer:traceframe-info:read} (@pxref{qXfer traceframe info read}) packet and is an XML document. @value{GDBN} must be linked with the Expat library to support XML traceframe info discovery. @xref{Expat}. The top-level structure of the document is shown below: @smallexample <?xml version="1.0"?> <!DOCTYPE traceframe-info PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN" "http://sourceware.org/gdb/gdb-traceframe-info.dtd"> <traceframe-info> block... </traceframe-info> @end smallexample Each traceframe block can be either: @itemize @item A region of collected memory starting at @var{addr} and extending for @var{length} bytes from there: @smallexample <memory start="@var{addr}" length="@var{length}"/> @end smallexample @item A block indicating trace state variable numbered @var{number} has been collected: @smallexample <tvar id="@var{number}"/> @end smallexample @end itemize The formal DTD for the traceframe info format is given below: @smallexample <!ELEMENT traceframe-info (memory | tvar)* > <!ATTLIST traceframe-info version CDATA #FIXED "1.0"> <!ELEMENT memory EMPTY> <!ATTLIST memory start CDATA #REQUIRED length CDATA #REQUIRED> <!ELEMENT tvar> <!ATTLIST tvar id CDATA #REQUIRED> @end smallexample @node Branch Trace Format @section Branch Trace Format @cindex branch trace format In order to display the branch trace of an inferior thread, @value{GDBN} needs to obtain the list of branches. This list is represented as list of sequential code blocks that are connected via branches. The code in each block has been executed sequentially. This list is obtained using the @samp{qXfer:btrace:read} (@pxref{qXfer btrace read}) packet and is an XML document. @value{GDBN} must be linked with the Expat library to support XML traceframe info discovery. @xref{Expat}. The top-level structure of the document is shown below: @smallexample <?xml version="1.0"?> <!DOCTYPE btrace PUBLIC "+//IDN gnu.org//DTD GDB Branch Trace V1.0//EN" "http://sourceware.org/gdb/gdb-btrace.dtd"> <btrace> block... </btrace> @end smallexample @itemize @item A block of sequentially executed instructions starting at @var{begin} and ending at @var{end}: @smallexample <block begin="@var{begin}" end="@var{end}"/> @end smallexample @end itemize The formal DTD for the branch trace format is given below: @smallexample <!ELEMENT btrace (block* | pt) > <!ATTLIST btrace version CDATA #FIXED "1.0"> <!ELEMENT block EMPTY> <!ATTLIST block begin CDATA #REQUIRED end CDATA #REQUIRED> <!ELEMENT pt (pt-config?, raw?)> <!ELEMENT pt-config (cpu?)> <!ELEMENT cpu EMPTY> <!ATTLIST cpu vendor CDATA #REQUIRED family CDATA #REQUIRED model CDATA #REQUIRED stepping CDATA #REQUIRED> <!ELEMENT raw (#PCDATA)> @end smallexample @node Branch Trace Configuration Format @section Branch Trace Configuration Format @cindex branch trace configuration format For each inferior thread, @value{GDBN} can obtain the branch trace configuration using the @samp{qXfer:btrace-conf:read} (@pxref{qXfer btrace-conf read}) packet. The configuration describes the branch trace format and configuration settings for that format. The following information is described: @table @code @item bts This thread uses the @dfn{Branch Trace Store} (@acronym{BTS}) format. @table @code @item size The size of the @acronym{BTS} ring buffer in bytes. @end table @item pt This thread uses the @dfn{Intel Processor Trace} (@acronym{Intel PT}) format. @table @code @item size The size of the @acronym{Intel PT} ring buffer in bytes. @end table @end table @value{GDBN} must be linked with the Expat library to support XML branch trace configuration discovery. @xref{Expat}. The formal DTD for the branch trace configuration format is given below: @smallexample <!ELEMENT btrace-conf (bts?, pt?)> <!ATTLIST btrace-conf version CDATA #FIXED "1.0"> <!ELEMENT bts EMPTY> <!ATTLIST bts size CDATA #IMPLIED> <!ELEMENT pt EMPTY> <!ATTLIST pt size CDATA #IMPLIED> @end smallexample @include agentexpr.texi @node Target Descriptions @appendix Target Descriptions @cindex target descriptions One of the challenges of using @value{GDBN} to debug embedded systems is that there are so many minor variants of each processor architecture in use. It is common practice for vendors to start with a standard processor core --- ARM, PowerPC, or @acronym{MIPS}, for example --- and then make changes to adapt it to a particular market niche. Some architectures have hundreds of variants, available from dozens of vendors. This leads to a number of problems: @itemize @bullet @item With so many different customized processors, it is difficult for the @value{GDBN} maintainers to keep up with the changes. @item Since individual variants may have short lifetimes or limited audiences, it may not be worthwhile to carry information about every variant in the @value{GDBN} source tree. @item When @value{GDBN} does support the architecture of the embedded system at hand, the task of finding the correct architecture name to give the @command{set architecture} command can be error-prone. @end itemize To address these problems, the @value{GDBN} remote protocol allows a target system to not only identify itself to @value{GDBN}, but to actually describe its own features. This lets @value{GDBN} support processor variants it has never seen before --- to the extent that the descriptions are accurate, and that @value{GDBN} understands them. @value{GDBN} must be linked with the Expat library to support XML target descriptions. @xref{Expat}. @menu * Retrieving Descriptions:: How descriptions are fetched from a target. * Target Description Format:: The contents of a target description. * Predefined Target Types:: Standard types available for target descriptions. * Enum Target Types:: How to define enum target types. * Standard Target Features:: Features @value{GDBN} knows about. @end menu @node Retrieving Descriptions @section Retrieving Descriptions Target descriptions can be read from the target automatically, or specified by the user manually. The default behavior is to read the description from the target. @value{GDBN} retrieves it via the remote protocol using @samp{qXfer} requests (@pxref{General Query Packets, qXfer}). The @var{annex} in the @samp{qXfer} packet will be @samp{target.xml}. The contents of the @samp{target.xml} annex are an XML document, of the form described in @ref{Target Description Format}. Alternatively, you can specify a file to read for the target description. If a file is set, the target will not be queried. The commands to specify a file are: @table @code @cindex set tdesc filename @item set tdesc filename @var{path} Read the target description from @var{path}. @cindex unset tdesc filename @item unset tdesc filename Do not read the XML target description from a file. @value{GDBN} will use the description supplied by the current target. @cindex show tdesc filename @item show tdesc filename Show the filename to read for a target description, if any. @end table @node Target Description Format @section Target Description Format @cindex target descriptions, XML format A target description annex is an @uref{http://www.w3.org/XML/, XML} document which complies with the Document Type Definition provided in the @value{GDBN} sources in @file{gdb/features/gdb-target.dtd}. This means you can use generally available tools like @command{xmllint} to check that your feature descriptions are well-formed and valid. However, to help people unfamiliar with XML write descriptions for their targets, we also describe the grammar here. Target descriptions can identify the architecture of the remote target and (for some architectures) provide information about custom register sets. They can also identify the OS ABI of the remote target. @value{GDBN} can use this information to autoconfigure for your target, or to warn you if you connect to an unsupported target. Here is a simple target description: @smallexample <target version="1.0"> <architecture>i386:x86-64</architecture> </target> @end smallexample @noindent This minimal description only says that the target uses the x86-64 architecture. A target description has the following overall form, with [ ] marking optional elements and @dots{} marking repeatable elements. The elements are explained further below. @smallexample <?xml version="1.0"?> <!DOCTYPE target SYSTEM "gdb-target.dtd"> <target version="1.0"> @r{[}@var{architecture}@r{]} @r{[}@var{osabi}@r{]} @r{[}@var{compatible}@r{]} @r{[}@var{feature}@dots{}@r{]} </target> @end smallexample @noindent The description is generally insensitive to whitespace and line breaks, under the usual common-sense rules. The XML version declaration and document type declaration can generally be omitted (@value{GDBN} does not require them), but specifying them may be useful for XML validation tools. The @samp{version} attribute for @samp{<target>} may also be omitted, but we recommend including it; if future versions of @value{GDBN} use an incompatible revision of @file{gdb-target.dtd}, they will detect and report the version mismatch. @subsection Inclusion @cindex target descriptions, inclusion @cindex XInclude @ifnotinfo @cindex <xi:include> @end ifnotinfo It can sometimes be valuable to split a target description up into several different annexes, either for organizational purposes, or to share files between different possible target descriptions. You can divide a description into multiple files by replacing any element of the target description with an inclusion directive of the form: @smallexample <xi:include href="@var{document}"/> @end smallexample @noindent When @value{GDBN} encounters an element of this form, it will retrieve the named XML @var{document}, and replace the inclusion directive with the contents of that document. If the current description was read using @samp{qXfer}, then so will be the included document; @var{document} will be interpreted as the name of an annex. If the current description was read from a file, @value{GDBN} will look for @var{document} as a file in the same directory where it found the original description. @subsection Architecture @cindex <architecture> An @samp{<architecture>} element has this form: @smallexample <architecture>@var{arch}</architecture> @end smallexample @var{arch} is one of the architectures from the set accepted by @code{set architecture} (@pxref{Targets, ,Specifying a Debugging Target}). @subsection OS ABI @cindex @code{<osabi>} This optional field was introduced in @value{GDBN} version 7.0. Previous versions of @value{GDBN} ignore it. An @samp{<osabi>} element has this form: @smallexample <osabi>@var{abi-name}</osabi> @end smallexample @var{abi-name} is an OS ABI name from the same selection accepted by @w{@code{set osabi}} (@pxref{ABI, ,Configuring the Current ABI}). @subsection Compatible Architecture @cindex @code{<compatible>} This optional field was introduced in @value{GDBN} version 7.0. Previous versions of @value{GDBN} ignore it. A @samp{<compatible>} element has this form: @smallexample <compatible>@var{arch}</compatible> @end smallexample @var{arch} is one of the architectures from the set accepted by @code{set architecture} (@pxref{Targets, ,Specifying a Debugging Target}). A @samp{<compatible>} element is used to specify that the target is able to run binaries in some other than the main target architecture given by the @samp{<architecture>} element. For example, on the Cell Broadband Engine, the main architecture is @code{powerpc:common} or @code{powerpc:common64}, but the system is able to run binaries in the @code{spu} architecture as well. The way to describe this capability with @samp{<compatible>} is as follows: @smallexample <architecture>powerpc:common</architecture> <compatible>spu</compatible> @end smallexample @subsection Features @cindex <feature> Each @samp{<feature>} describes some logical portion of the target system. Features are currently used to describe available CPU registers and the types of their contents. A @samp{<feature>} element has this form: @smallexample <feature name="@var{name}"> @r{[}@var{type}@dots{}@r{]} @var{reg}@dots{} </feature> @end smallexample @noindent Each feature's name should be unique within the description. The name of a feature does not matter unless @value{GDBN} has some special knowledge of the contents of that feature; if it does, the feature should have its standard name. @xref{Standard Target Features}. @subsection Types Any register's value is a collection of bits which @value{GDBN} must interpret. The default interpretation is a two's complement integer, but other types can be requested by name in the register description. Some predefined types are provided by @value{GDBN} (@pxref{Predefined Target Types}), and the description can define additional composite and enum types. Each type element must have an @samp{id} attribute, which gives a unique (within the containing @samp{<feature>}) name to the type. Types must be defined before they are used. @cindex <vector> Some targets offer vector registers, which can be treated as arrays of scalar elements. These types are written as @samp{<vector>} elements, specifying the array element type, @var{type}, and the number of elements, @var{count}: @smallexample <vector id="@var{id}" type="@var{type}" count="@var{count}"/> @end smallexample @cindex <union> If a register's value is usefully viewed in multiple ways, define it with a union type containing the useful representations. The @samp{<union>} element contains one or more @samp{<field>} elements, each of which has a @var{name} and a @var{type}: @smallexample <union id="@var{id}"> <field name="@var{name}" type="@var{type}"/> @dots{} </union> @end smallexample @cindex <struct> @cindex <flags> If a register's value is composed from several separate values, define it with either a structure type or a flags type. A flags type may only contain bitfields. A structure type may either contain only bitfields or contain no bitfields. If the value contains only bitfields, its total size in bytes must be specified. Non-bitfield values have a @var{name} and @var{type}. @smallexample <struct id="@var{id}"> <field name="@var{name}" type="@var{type}"/> @dots{} </struct> @end smallexample Both @var{name} and @var{type} values are required. No implicit padding is added. Bitfield values have a @var{name}, @var{start}, @var{end} and @var{type}. @smallexample <struct id="@var{id}" size="@var{size}"> <field name="@var{name}" start="@var{start}" end="@var{end}" type="@var{type}"/> @dots{} </struct> @end smallexample @smallexample <flags id="@var{id}" size="@var{size}"> <field name="@var{name}" start="@var{start}" end="@var{end}" type="@var{type}"/> @dots{} </flags> @end smallexample The @var{name} value is required. Bitfield values may be named with the empty string, @samp{""}, in which case the field is ``filler'' and its value is not printed. Not all bits need to be specified, so ``filler'' fields are optional. The @var{start} and @var{end} values are required, and @var{type} is optional. The field's @var{start} must be less than or equal to its @var{end}, and zero represents the least significant bit. The default value of @var{type} is @code{bool} for single bit fields, and an unsigned integer otherwise. Which to choose? Structures or flags? Registers defined with @samp{flags} have these advantages over defining them with @samp{struct}: @itemize @bullet @item Arithmetic may be performed on them as if they were integers. @item They are printed in a more readable fashion. @end itemize Registers defined with @samp{struct} have one advantage over defining them with @samp{flags}: @itemize @bullet @item One can fetch individual fields like in @samp{C}. @smallexample (gdb) print $my_struct_reg.field3 $1 = 42 @end smallexample @end itemize @subsection Registers @cindex <reg> Each register is represented as an element with this form: @smallexample <reg name="@var{name}" bitsize="@var{size}" @r{[}regnum="@var{num}"@r{]} @r{[}save-restore="@var{save-restore}"@r{]} @r{[}type="@var{type}"@r{]} @r{[}group="@var{group}"@r{]}/> @end smallexample @noindent The components are as follows: @table @var @item name The register's name; it must be unique within the target description. @item bitsize The register's size, in bits. @item regnum The register's number. If omitted, a register's number is one greater than that of the previous register (either in the current feature or in a preceding feature); the first register in the target description defaults to zero. This register number is used to read or write the register; e.g.@: it is used in the remote @code{p} and @code{P} packets, and registers appear in the @code{g} and @code{G} packets in order of increasing register number. @item save-restore Whether the register should be preserved across inferior function calls; this must be either @code{yes} or @code{no}. The default is @code{yes}, which is appropriate for most registers except for some system control registers; this is not related to the target's ABI. @item type The type of the register. It may be a predefined type, a type defined in the current feature, or one of the special types @code{int} and @code{float}. @code{int} is an integer type of the correct size for @var{bitsize}, and @code{float} is a floating point type (in the architecture's normal floating point format) of the correct size for @var{bitsize}. The default is @code{int}. @item group The register group to which this register belongs. It can be one of the standard register groups @code{general}, @code{float}, @code{vector} or an arbitrary string. Group names should be limited to alphanumeric characters. If a group name is made up of multiple words the words may be separated by hyphens; e.g.@: @code{special-group} or @code{ultra-special-group}. If no @var{group} is specified, @value{GDBN} will not display the register in @code{info registers}. @end table @node Predefined Target Types @section Predefined Target Types @cindex target descriptions, predefined types Type definitions in the self-description can build up composite types from basic building blocks, but can not define fundamental types. Instead, standard identifiers are provided by @value{GDBN} for the fundamental types. The currently supported types are: @table @code @item bool Boolean type, occupying a single bit. @item int8 @itemx int16 @itemx int24 @itemx int32 @itemx int64 @itemx int128 Signed integer types holding the specified number of bits. @item uint8 @itemx uint16 @itemx uint24 @itemx uint32 @itemx uint64 @itemx uint128 Unsigned integer types holding the specified number of bits. @item code_ptr @itemx data_ptr Pointers to unspecified code and data. The program counter and any dedicated return address register may be marked as code pointers; printing a code pointer converts it into a symbolic address. The stack pointer and any dedicated address registers may be marked as data pointers. @item ieee_single Single precision IEEE floating point. @item ieee_double Double precision IEEE floating point. @item arm_fpa_ext The 12-byte extended precision format used by ARM FPA registers. @item i387_ext The 10-byte extended precision format used by x87 registers. @item i386_eflags 32bit @sc{eflags} register used by x86. @item i386_mxcsr 32bit @sc{mxcsr} register used by x86. @end table @node Enum Target Types @section Enum Target Types @cindex target descriptions, enum types Enum target types are useful in @samp{struct} and @samp{flags} register descriptions. @xref{Target Description Format}. Enum types have a name, size and a list of name/value pairs. @smallexample <enum id="@var{id}" size="@var{size}"> <evalue name="@var{name}" value="@var{value}"/> @dots{} </enum> @end smallexample Enums must be defined before they are used. @smallexample <enum id="levels_type" size="4"> <evalue name="low" value="0"/> <evalue name="high" value="1"/> </enum> <flags id="flags_type" size="4"> <field name="X" start="0"/> <field name="LEVEL" start="1" end="1" type="levels_type"/> </flags> <reg name="flags" bitsize="32" type="flags_type"/> @end smallexample Given that description, a value of 3 for the @samp{flags} register would be printed as: @smallexample (gdb) info register flags flags 0x3 [ X LEVEL=high ] @end smallexample @node Standard Target Features @section Standard Target Features @cindex target descriptions, standard features A target description must contain either no registers or all the target's registers. If the description contains no registers, then @value{GDBN} will assume a default register layout, selected based on the architecture. If the description contains any registers, the default layout will not be used; the standard registers must be described in the target description, in such a way that @value{GDBN} can recognize them. This is accomplished by giving specific names to feature elements which contain standard registers. @value{GDBN} will look for features with those names and verify that they contain the expected registers; if any known feature is missing required registers, or if any required feature is missing, @value{GDBN} will reject the target description. You can add additional registers to any of the standard features --- @value{GDBN} will display them just as if they were added to an unrecognized feature. This section lists the known features and their expected contents. Sample XML documents for these features are included in the @value{GDBN} source tree, in the directory @file{gdb/features}. Names recognized by @value{GDBN} should include the name of the company or organization which selected the name, and the overall architecture to which the feature applies; so e.g.@: the feature containing ARM core registers is named @samp{org.gnu.gdb.arm.core}. The names of registers are not case sensitive for the purpose of recognizing standard features, but @value{GDBN} will only display registers using the capitalization used in the description. @menu * AArch64 Features:: * ARC Features:: * ARM Features:: * i386 Features:: * MicroBlaze Features:: * MIPS Features:: * M68K Features:: * NDS32 Features:: * Nios II Features:: * OpenRISC 1000 Features:: * PowerPC Features:: * RISC-V Features:: * RX Features:: * S/390 and System z Features:: * Sparc Features:: * TIC6x Features:: @end menu @node AArch64 Features @subsection AArch64 Features @cindex target descriptions, AArch64 features The @samp{org.gnu.gdb.aarch64.core} feature is required for AArch64 targets. It should contain registers @samp{x0} through @samp{x30}, @samp{sp}, @samp{pc}, and @samp{cpsr}. The @samp{org.gnu.gdb.aarch64.fpu} feature is optional. If present, it should contain registers @samp{v0} through @samp{v31}, @samp{fpsr}, and @samp{fpcr}. The @samp{org.gnu.gdb.aarch64.sve} feature is optional. If present, it should contain registers @samp{z0} through @samp{z31}, @samp{p0} through @samp{p15}, @samp{ffr} and @samp{vg}. The @samp{org.gnu.gdb.aarch64.pauth} feature is optional. If present, it should contain registers @samp{pauth_dmask} and @samp{pauth_cmask}. @node ARC Features @subsection ARC Features @cindex target descriptions, ARC Features ARC processors are highly configurable, so even core registers and their number are not completely predetermined. In addition flags and PC registers which are important to @value{GDBN} are not ``core'' registers in ARC. It is required that one of the core registers features is present. @samp{org.gnu.gdb.arc.aux-minimal} feature is mandatory. The @samp{org.gnu.gdb.arc.core.v2} feature is required for ARC EM and ARC HS targets with a normal register file. It should contain registers @samp{r0} through @samp{r25}, @samp{gp}, @samp{fp}, @samp{sp}, @samp{r30}, @samp{blink}, @samp{lp_count} and @samp{pcl}. This feature may contain register @samp{ilink} and any of extension core registers @samp{r32} through @samp{r59/acch}. @samp{ilink} and extension core registers are not available to read/write, when debugging GNU/Linux applications, thus @samp{ilink} is made optional. The @samp{org.gnu.gdb.arc.core-reduced.v2} feature is required for ARC EM and ARC HS targets with a reduced register file. It should contain registers @samp{r0} through @samp{r3}, @samp{r10} through @samp{r15}, @samp{gp}, @samp{fp}, @samp{sp}, @samp{r30}, @samp{blink}, @samp{lp_count} and @samp{pcl}. This feature may contain register @samp{ilink} and any of extension core registers @samp{r32} through @samp{r59/acch}. The @samp{org.gnu.gdb.arc.core.arcompact} feature is required for ARCompact targets with a normal register file. It should contain registers @samp{r0} through @samp{r25}, @samp{gp}, @samp{fp}, @samp{sp}, @samp{r30}, @samp{blink}, @samp{lp_count} and @samp{pcl}. This feature may contain registers @samp{ilink1}, @samp{ilink2} and any of extension core registers @samp{r32} through @samp{r59/acch}. @samp{ilink1} and @samp{ilink2} and extension core registers are not available when debugging GNU/Linux applications. The only difference with @samp{org.gnu.gdb.arc.core.v2} feature is in the names of @samp{ilink1} and @samp{ilink2} registers and that @samp{r30} is mandatory in ARC v2, but @samp{ilink2} is optional on ARCompact. The @samp{org.gnu.gdb.arc.aux-minimal} feature is required for all ARC targets. It should contain registers @samp{pc} and @samp{status32}. @node ARM Features @subsection ARM Features @cindex target descriptions, ARM features The @samp{org.gnu.gdb.arm.core} feature is required for non-M-profile ARM targets. It should contain registers @samp{r0} through @samp{r13}, @samp{sp}, @samp{lr}, @samp{pc}, and @samp{cpsr}. For M-profile targets (e.g. Cortex-M3), the @samp{org.gnu.gdb.arm.core} feature is replaced by @samp{org.gnu.gdb.arm.m-profile}. It should contain registers @samp{r0} through @samp{r13}, @samp{sp}, @samp{lr}, @samp{pc}, and @samp{xpsr}. The @samp{org.gnu.gdb.arm.fpa} feature is optional. If present, it should contain registers @samp{f0} through @samp{f7} and @samp{fps}. The @samp{org.gnu.gdb.xscale.iwmmxt} feature is optional. If present, it should contain at least registers @samp{wR0} through @samp{wR15} and @samp{wCGR0} through @samp{wCGR3}. The @samp{wCID}, @samp{wCon},


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