diff options
| -rwxr-xr-x | gdb/doc/gdb-all.texi | 8438 |
1 files changed, 8438 insertions, 0 deletions
diff --git a/gdb/doc/gdb-all.texi b/gdb/doc/gdb-all.texi new file mode 100755 index 0000000..f9ae8ad --- /dev/null +++ b/gdb/doc/gdb-all.texi @@ -0,0 +1,8438 @@ + +\input texinfo @c -*-texinfo-*- +@c Copyright (c) 1988 1989 1990 1991 1992 Free Software Foundation, Inc. +@c %**start of header +@setfilename gdb.info +@settitle Using GDB (v4) +@setchapternewpage odd +@input smpklug.texi +@smallbook +@cropmarks +@c %**end of header + +@finalout +@syncodeindex ky cp + +@c ===> NOTE! <== +@c Determine the edition number in *three* places by hand: +@c 1. First ifinfo section 2. title page 3. top node +@c To find the locations, search for !!set + +@c The following is for Pesch for his RCS system. +@c This revision number *not* the same as the Edition number. +@tex +\def\$#1${{#1}} % Kluge: collect RCS revision info without $...$ +\xdef\manvers{\$Revision$} % For use in headers, footers too +@end tex + +@c FOR UPDATES LEADING TO THIS DRAFT, GDB CHANGELOG CONSULTED BETWEEN: +@c Fri Oct 11 23:27:06 1991 John Gilmore (gnu at cygnus.com) +@c Sat Dec 22 02:51:40 1990 John Gilmore (gnu at cygint) + +@c THIS MANUAL REQUIRES TEXINFO-2 macros and info-makers to format properly. + +@ifinfo +@format +START-INFO-DIR-ENTRY +* Gdb: (gdb). The GNU debugger. +END-INFO-DIR-ENTRY +@end format +@end ifinfo +@c +@ifinfo +This file documents the GNU debugger GDB. + +@c !!set edition, date, version +This is Edition 4.01, January 1992, +of @cite{Using GDB: A Guide to the GNU Source-Level Debugger} +for GDB Version 4.4.4. + +Copyright (C) 1988, 1989, 1990, 1991 1992 Free Software Foundation, Inc. + +Permission is granted to make and distribute verbatim copies of +this manual provided the copyright notice and this permission notice +are preserved on all copies. + +@ignore +Permission is granted to process this file through TeX and print the +results, provided the printed document carries copying permission +notice identical to this one except for the removal of this paragraph +(this paragraph not being relevant to the printed manual). + +@end ignore +Permission is granted to copy and distribute modified versions of this +manual under the conditions for verbatim copying, provided also that the +section entitled ``GNU General Public License'' is included exactly as +in the original, and provided that the entire resulting derived work is +distributed under the terms of a permission notice identical to this +one. + +Permission is granted to copy and distribute translations of this manual +into another language, under the above conditions for modified versions, +except that the section entitled ``GNU General Public License'' may be +included in a translation approved by the Free Software Foundation +instead of in the original English. +@end ifinfo + +@titlepage +@title Using GDB +@subtitle A Guide to the GNU Source-Level Debugger +@sp 1 +@c !!set edition, date, version +@subtitle Edition 4.01, for GDB version 4.4.4 +@subtitle January 1992 +@author by Richard M. Stallman and Roland H. Pesch +@page +@tex +{\parskip=0pt +\hfill rms\@ai.mit.edu, pesch\@cygnus.com\par +\hfill {\it Using GDB}, \manvers\par +\hfill \TeX{}info \texinfoversion\par +} +@end tex + +@vskip 0pt plus 1filll +Copyright @copyright{} 1988, 1989, 1990, 1991, 1992 Free Software Foundation, Inc. + +Permission is granted to make and distribute verbatim copies of +this manual provided the copyright notice and this permission notice +are preserved on all copies. + +Permission is granted to copy and distribute modified versions of this +manual under the conditions for verbatim copying, provided also that the +section entitled ``GNU General Public License'' is included exactly as +in the original, and provided that the entire resulting derived work is +distributed under the terms of a permission notice identical to this +one. + +Permission is granted to copy and distribute translations of this manual +into another language, under the above conditions for modified versions, +except that the section entitled ``GNU General Public License'' may be +included in a translation approved by the Free Software Foundation +instead of in the original English. +@end titlepage +@page + +@ifinfo +@node Top, Summary, (dir), (dir) +@top GDB, the GNU symbolic debugger + +This file describes GDB, the GNU symbolic debugger. + +@c !!set edition, date, version +This is Edition 4.01, January 1992, for GDB Version 4.4.4. +@end ifinfo + +@menu +* Summary:: Summary of GDB +* New Features:: New features since GDB version 3.5 +* Sample Session:: A Sample GDB session +* Invocation:: Getting in and out of GDB +* Commands:: GDB commands +* Running:: Running programs under GDB +* Stopping:: Stopping and continuing +* Stack:: Examining the stack +* Source:: Examining source files +* Data:: Examining data +* Languages:: Using GDB with different languages +* Symbols:: Examining the symbol table +* Altering:: Altering execution +* GDB Files:: GDB's files +* Targets:: Specifying a debugging target +* Controlling GDB:: Controlling GDB +* Sequences:: Canned sequences of commands +* Emacs:: Using GDB under GNU Emacs +* GDB Bugs:: Reporting bugs in GDB +* Renamed Commands:: +* Installing GDB:: Installing GDB +* Copying:: GNU GENERAL PUBLIC LICENSE +* Index:: Index + + --- The Detailed Node Listing --- + +Summary of GDB + +* Free Software:: Free Software +* Contributors:: Contributors to GDB + +Getting In and Out of GDB + +* Invoking GDB:: Starting GDB +* Leaving GDB:: Leaving GDB +* Shell Commands:: Shell Commands + +Starting GDB + +* File Options:: Choosing Files +* Mode Options:: Choosing Modes + +GDB Commands + +* Command Syntax:: Command Syntax +* Help:: Getting Help + +Running Programs Under GDB + +* 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 + +Stopping and Continuing + +* Breakpoints:: Breakpoints, Watchpoints, and Exceptions +* Continuing and Stepping:: Resuming Execution +* Signals:: Signals + +Breakpoints, Watchpoints, and Exceptions + +* Set Breaks:: Setting Breakpoints +* Set Watchpoints:: Setting Watchpoints +* Exception Handling:: Breakpoints and Exceptions +* Delete Breaks:: Deleting Breakpoints +* Disabling:: Disabling Breakpoints +* Conditions:: Break Conditions +* Break Commands:: Breakpoint Command Lists +* Breakpoint Menus:: Breakpoint Menus +* Error in Breakpoints:: ``Cannot insert breakpoints'' + +Examining the Stack + +* Frames:: Stack Frames +* Backtrace:: Backtraces +* Selection:: Selecting a Frame +* Frame Info:: Information on a Frame + +Examining Source Files + +* List:: Printing Source Lines +* Search:: Searching Source Files +* Source Path:: Specifying Source Directories +* Machine Code:: Source and Machine Code + +Examining Data + +* Expressions:: Expressions +* Variables:: Program Variables +* Arrays:: Artificial Arrays +* Output formats:: Output formats +* Memory:: Examining Memory +* Auto Display:: Automatic Display +* Print Settings:: Print Settings +* Value History:: Value History +* Convenience Vars:: Convenience Variables +* Registers:: Registers +* Floating Point Hardware:: Floating Point Hardware + +Using GDB with Different Languages + +* Setting:: Switching between source languages +* Show:: Displaying the language +* Checks:: Type and Range checks +* Support:: Supported languages + +Switching between source languages + +* Manually:: Setting the working language manually +* Automatically:: Having GDB infer the source language + +Type and range Checking + +* Type Checking:: An overview of type checking +* Range Checking:: An overview of range checking + +Supported Languages + +* C:: C and C++ +* Modula-2:: Modula-2 + +C and C++ + +* C Operators:: C and C++ Operators +* C Constants:: C and C++ Constants +* Cplusplus expressions:: C++ Expressions +* C Defaults:: Default settings for C and C++ +* C Checks:: C and C++ Type and Range Checks +* Debugging C:: GDB and C +* Debugging C plus plus:: Special features for C++ + +Modula-2 + +* M2 Operators:: Built-in operators +* Built-In Func/Proc:: Built-in Functions and Procedures +* M2 Constants:: Modula-2 Constants +* 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:: GDB and Modula-2 + +Altering Execution + +* 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 + +GDB's Files + +* Files:: Commands to Specify Files +* Symbol Errors:: Errors Reading Symbol Files + +Specifying a Debugging Target + +* Active Targets:: Active Targets +* Target Commands:: Commands for Managing Targets +* Remote:: Remote Debugging + +Remote Debugging + +* i960-Nindy Remote:: GDB with a Remote i960 (Nindy) +* EB29K Remote:: GDB with a Remote EB29K +* VxWorks Remote:: GDB and VxWorks + +GDB with a Remote i960 (Nindy) + +* Nindy Startup:: Startup with Nindy +* Nindy Options:: Options for Nindy +* Nindy reset:: Nindy Reset Command + +GDB with a Remote EB29K + +* Comms (EB29K):: Communications Setup +* gdb-EB29K:: EB29K cross-debugging +* Remote Log:: Remote Log + +GDB and VxWorks + +* VxWorks connection:: Connecting to VxWorks +* VxWorks download:: VxWorks Download +* VxWorks attach:: Running Tasks + +Controlling GDB + +* Prompt:: Prompt +* Editing:: Command Editing +* History:: Command History +* Screen Size:: Screen Size +* Numbers:: Numbers +* Messages/Warnings:: Optional Warnings and Messages + +Canned Sequences of Commands + +* Define:: User-Defined Commands +* Command Files:: Command Files +* Output:: Commands for Controlled Output + +Reporting Bugs in GDB + +* Bug Criteria:: Have You Found a Bug? +* Bug Reporting:: How to Report Bugs + +Installing GDB + +* Separate Objdir:: Compiling GDB in another directory +* Config Names:: Specifying names for hosts and targets +* configure Options:: Summary of options for configure +* Formatting Documentation:: How to format and print GDB documentation +@end menu + +@node Summary, New Features, Top, Top +@unnumbered Summary of GDB + +The purpose of a debugger such as GDB 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. + +GDB 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 GDB to debug programs written in C, C++, and Modula-2. +Fortran support will be added when a GNU Fortran compiler is ready. + +@menu +* Free Software:: Free Software +* Contributors:: Contributors to GDB +@end menu + +@node Free Software, Contributors, Summary, Summary +@unnumberedsec Free Software + +GDB is @dfn{free software}, protected by the 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. + +For full details, @pxref{Copying, ,GNU GENERAL PUBLIC LICENSE}. + +@node Contributors, , Free Software, Summary +@unnumberedsec Contributors to GDB + +Richard Stallman was the original author of GDB, and of many other 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 GDB 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; let's 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 long labor as thankless, we +particularly thank those who shepherded GDB through major releases: Stu +Grossman and John Gilmore (release 4.4), John Gilmore (releases 4.3, 4.2, +4.1, 4.0, and 3.9); Jim Kingdon (releases 3.5, 3.4, 3.3); and Randy +Smith (releases 3.2, 3.1, 3.0). As major maintainer of GDB for some +period, each contributed significantly to the structure, stability, and +capabilities of the entire debugger. + +Richard Stallman, assisted at various times by Pete TerMaat, Chris +Hanson, and Richard Mlynarik, handled releases through 2.8. + +Michael Tiemann is the author of most of the GNU C++ support in GDB, +with significant additional contributions from Per Bothner. James +Clark wrote the GNU C++ demangler. Early work on C++ was by Peter +TerMaat (who also did much general update work leading to release 3.0). + +GDB 4 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. + +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. +Keith Packard contributed NS32K support. Doug Rabson contributed +Acorn Risc Machine 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. + +Rich Schaefer and Peter Schauer helped with support of SunOS shared +libraries. + +Jay Fenlason and Roland McGrath ensured that GDB and GAS agree about +several machine instruction sets. + +Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped +develop remote debugging. Intel Corporation and Wind River Systems +contributed remote debugging modules for their products. + +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 and +the Modula-2 support, and contributed the Languages chapter of this +manual. + +@node New Features, Sample Session, Summary, Top +@unnumbered New Features since GDB version 3.5 + +@table @emph +@item Targets +Using the new command @code{target}, you can select at runtime whether +you are debugging local files, local processes, standalone systems over +a serial port, realtime systems over a TCP/IP connection, etc. The +command @code{load} can download programs into a remote system. Serial +stubs are available for Motorola 680x0 and Intel 80386 remote systems; +GDB also supports debugging realtime processes running under +VxWorks, using SunRPC Remote Procedure Calls over TCP/IP to talk to a +debugger stub on the target system. Internally, GDB now uses a +function vector to mediate access to different targets; if you need to +add your own support for a remote protocol, this makes it much easier. + +@item Watchpoints +GDB now sports watchpoints as well as breakpoints. You can use a +watchpoint to stop execution whenever the value of an expression +changes, without having to predict a particular place in your program +where this may happen. + +@item Wide Output +Commands that issue wide output now insert newlines at places designed +to make the output more readable. + +@item Object Code Formats +GDB uses a new library called the Binary File Descriptor (BFD) +Library to permit it to switch dynamically, without reconfiguration or +recompilation, between different object-file formats. Formats currently +supported are COFF, a.out, and the Intel 960 b.out; files may be read as +.o's, archive libraries, or core dumps. BFD is available as a +subroutine library so that other programs may take advantage of it, and +the other GNU binary utilities are being converted to use it. + +@item Configuration and Ports +Compile-time configuration (to select a particular architecture and +operating system) is much easier. The script @code{configure} now +allows you to configure GDB as either a native debugger or a +cross-debugger. @xref{Installing GDB}, for details on how to +configure and on what architectures are now available. + +@item Interaction +The user interface to GDB's control variables has been simplified +and consolidated in two commands, @code{set} and @code{show}. Output +lines are now broken at readable places, rather than overflowing onto +the next line. You can suppress output of machine-level addresses, +displaying only source language information. + +@item C++ +GDB now supports C++ multiple inheritance (if used with a GCC +version 2 compiler), and also has limited support for C++ exception +handling, with the commands @code{catch} and @code{info catch}: GDB +can break when an exception is raised, before the stack is peeled back +to the exception handler's context. + +@item Modula-2 +GDB now has preliminary support for the GNU Modula-2 compiler, +currently under development at the State University of New York at +Buffalo. Coordinated development of both GDB and the GNU Modula-2 +compiler will continue into 1992. Other Modula-2 compilers are +currently not supported, and attempting to debug programs compiled with +them will likely result in an error as the symbol table of the +executable is read in. + +@item Command Rationalization +Many GDB commands have been renamed to make them easier to remember +and use. In particular, the subcommands of @code{info} and +@code{show}/@code{set} are grouped to make the former refer to the state +of your program, and the latter refer to the state of GDB itself. +@xref{Renamed Commands}, for details on what commands were renamed. + +@item Shared Libraries +GDB 4 can debug programs and core files that use SunOS shared +libraries. + +@item Reference Card +GDB 4 has a reference card. @xref{Formatting Documentation} for +instructions on printing it. + +@item Work in Progress +Kernel debugging for BSD and Mach systems; Tahoe and HPPA architecture +support. +@end table + +@node Sample Session, Invocation, New Features, Top +@chapter A Sample GDB Session + +You can use this manual at your leisure to read all about GDB. +However, a handful of commands are enough to get started using the +debugger. This chapter illustrates these commands. + +@iftex +In this sample session, we emphasize user input like this: @i{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 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's +definition in 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 +$ @i{cd gnu/m4} +$ @i{./m4} +@i{define(foo,0000)} + +@i{foo} +0000 +@i{define(bar,defn(`foo'))} + +@i{bar} +0000 +@i{changequote(<QUOTE>,<UNQUOTE>)} + +@i{define(baz,defn(<QUOTE>foo<UNQUOTE>))} +@i{baz} +@i{C-d} +m4: End of input: 0: fatal error: EOF in string +@end smallexample + +@noindent +Let's use GDB to try to see what's going on. + +@smallexample +$ @i{gdb m4} +@c FIXME: this falsifies the exact text played out, to permit smallbook +@c FIXME... format to come out better. +GDB 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 GDB; type "show warranty" +for details. +GDB 4.4.4, Copyright 1992 Free Software Foundation, Inc... +(gdb) +@end smallexample + +@noindent +GDB 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 GDB to use a narrower display width than usual, so that examples +will fit in this manual. + +@smallexample +(gdb) @i{set width 70} +@end smallexample + +@noindent +Let's 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 GDB's +@code{break} command. + +@smallexample +(gdb) @i{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 GDB +control; as long as control does not reach the @code{m4_changequote} +subroutine, the program runs as usual: + +@smallexample +(gdb) @i{run} +Starting program: /work/Editorial/gdb/gnu/m4/m4 +@i{define(foo,0000)} + +@i{foo} +0000 +@end smallexample + +@noindent +To trigger the breakpoint, we call @code{changequote}. GDB +suspends execution of @code{m4}, displaying information about the +context where it stops. + +@smallexample +@i{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 +(gdb) @i{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 +(gdb) @i{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 +(gdb) @i{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 +Let's 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 +(gdb) @i{s} +0x3b5c 532 if (rquote != def_rquote) +(gdb) @i{s} +0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \ +def_lquote : xstrdup(lq); +(gdb) @i{n} +536 rquote = (rq == nil || *rq == '\0') ? def_rquote\ + : xstrdup(rq); +(gdb) @i{n} +538 len_lquote = strlen(rquote); +@end smallexample + +@noindent +The last line displayed looks a little odd; let's examine the variables +@code{lquote} and @code{rquote} to see if they are in fact the new left +and right quotes we specified. We can use the command @code{p} +(@code{print}) to see their values. + +@smallexample +(gdb) @i{p lquote} +$1 = 0x35d40 "<QUOTE>" +(gdb) @i{p rquote} +$2 = 0x35d50 "<UNQUOTE>" +@end smallexample + +@noindent +@code{lquote} and @code{rquote} are indeed the new left and right quotes. +Let's look at some context; we can display ten lines of source +surrounding the current line, with the @code{l} (@code{list}) command. + +@smallexample +(gdb) @i{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's step past the two lines that set @code{len_lquote} and +@code{len_rquote}, and then examine the values of those variables. + +@smallexample +(gdb) @i{n} +539 len_rquote = strlen(lquote); +(gdb) @i{n} +540 @} +(gdb) @i{p len_lquote} +$3 = 9 +(gdb) @i{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. Let's try setting them to better values. +We can use the @code{p} command for this, since it'll print the value of +any expression---and that expression can include subroutine calls and +assignments. + +@smallexample +(gdb) p @i{len_lquote=strlen(lquote)} +$5 = 7 +(gdb) p @i{len_rquote=strlen(rquote)} +$6 = 9 +@end smallexample + +@noindent +Let's see if that fixes 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 +(gdb) @i{c} +Continuing. + +@i{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'll let @code{m4} exit by giving it an EOF as input. + +@smallexample +@i{C-d} +Program exited normally. +@end smallexample + +@noindent +The message @samp{Program exited normally.} is from GDB; it +indicates @code{m4} has finished executing. We can end our GDB +session with the GDB @code{quit} command. + +@smallexample +(gdb) @i{quit} +@end smallexample + +@node Invocation, Commands, Sample Session, Top +@chapter Getting In and Out of GDB + +This chapter discusses how to start GDB, and how to get out of it. +(The essentials: type @samp{gdb} to start GDB, and type @kbd{quit} +or @kbd{C-d} to exit.) + +@menu +* Invoking GDB:: Starting GDB +* Leaving GDB:: Leaving GDB +* Shell Commands:: Shell Commands +@end menu + +@node Invoking GDB, Leaving GDB, Invocation, Invocation +@section Starting GDB + +Start GDB with the shell command @code{gdb}. Once it's running, +GDB reads commands from the terminal until you tell it to exit. + +You can also run @code{gdb} 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 GDB is with one argument or two, +specifying an executable program as the argument: + +@example +gdb @var{program} +@end example + +@noindent +You can also start with both an executable program and a core file +specified: + +@example +gdb @var{program} @var{core} +@end example + +You can, instead, specify a process ID as a second argument, if you want +to debug a running process: + +@example +gdb @var{program} 1234 +@end example + +@noindent +would attach GDB to process @code{1234} (unless you also have a file +named @file{1234}; GDB does check for a core file first). + +Taking advantage of the second command-line argument requires a fairly +complete operating system; when you use GDB 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. + +@noindent +You can further control how GDB starts up by using command-line +options. GDB itself can remind you of the options available. + +@noindent +Type + +@example +gdb -help +@end example + +@noindent +to display all available options and briefly describe their use +(@samp{gdb -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 +@end menu + +@node File Options, Mode Options, Invoking GDB, Invoking GDB +@subsection Choosing Files + +When GDB 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} options respectively. (GDB 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} option followed by that argument.) + +Many options have both long and short forms; both are shown in the +following list. GDB 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.) + +@table @code +@item -symbols=@var{file} +@itemx -s @var{file} +Read symbol table from file @var{file}. + +@item -exec=@var{file} +@itemx -e @var{file} +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} +Read symbol table from file @var{file} and use it as the executable +file. + +@item -core=@var{file} +@itemx -c @var{file} +Use file @var{file} as a core dump to examine. + +@item -command=@var{file} +@itemx -x @var{file} +Execute GDB commands from file @var{file}. @xref{Command Files}. + +@item -directory=@var{directory} +@itemx -d @var{directory} +Add @var{directory} to the path to search for source files. +@end table + +@node Mode Options, , File Options, Invoking GDB +@subsection Choosing Modes + +You can run GDB in various alternative modes---for example, in +batch mode or quiet mode. + +@table @code +@item -nx +@itemx -n +Do not execute commands from any @file{.gdbinit} initialization files. +Normally, the commands in these files are executed after all the +command options and arguments have been processed. +@xref{Command Files}. + +@item -quiet +@itemx -q +``Quiet''. Do not print the introductory and copyright messages. These +messages are also suppressed in batch mode. + +@item -batch +Run in batch mode. Exit with status @code{0} after processing all the command +files specified with @samp{-x} (and @file{.gdbinit}, if not inhibited). +Exit with nonzero status if an error occurs in executing the GDB +commands in the command files. + +Batch mode may be useful for running GDB as a filter, for example to +download and run a program on another computer; in order to make this +more useful, the message + +@example +Program exited normally. +@end example + +@noindent +(which is ordinarily issued whenever a program running under GDB control +terminates) is not issued when running in batch mode. + +@item -cd=@var{directory} +Run GDB using @var{directory} as its working directory, +instead of the current directory. + +@item -fullname +@itemx -f +Emacs sets this option when it runs GDB as a subprocess. It tells GDB +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-GDB interface program uses the two @samp{\032} characters as +a signal to display the source code for the frame. + +@item -b @var{bps} +Set the line speed (baud rate or bits per second) of any serial +interface used by GDB for remote debugging. + +@item -tty=@var{device} +Run using @var{device} for your program's standard input and output. +@c FIXME: kingdon thinks there is more to -tty. Investigate. +@end table + +@node Leaving GDB, Shell Commands, Invoking GDB, Invocation +@section Leaving GDB +@cindex exiting GDB + +@table @code +@item quit +@kindex quit +@kindex q +To exit GDB, use the @code{quit} command (abbreviated @code{q}), or type +an end-of-file character (usually @kbd{C-d}). +@end table + +@cindex interrupt +An interrupt (often @kbd{C-c}) will not exit from GDB, but rather +will terminate the action of any GDB command that is in progress and +return to GDB command level. It is safe to type the interrupt +character at any time because GDB does not allow it to take effect +until a time when it is safe. + +If you have been using GDB 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, , Leaving GDB, Invocation +@section Shell Commands + +If you need to execute occasional shell commands during your +debugging session, there is no need to leave or suspend GDB; you can +just use the @code{shell} command. + +@table @code +@item shell @var{command string} +@kindex shell +@cindex shell escape +Directs GDB to invoke an inferior shell to execute @var{command +string}. If it exists, the environment variable @code{SHELL} is used +for the name of the shell to run. Otherwise GDB uses +@code{/bin/sh}. +@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 GDB: + +@table @code +@item make @var{make-args} +@kindex make +@cindex calling make +Causes GDB to execute an inferior @code{make} program with the specified +arguments. This is equivalent to @samp{shell make @var{make-args}}. +@end table + +@node Commands, Running, Invocation, Top +@chapter GDB Commands + +You can abbreviate GDB command if that abbreviation is unambiguous; +and you can repeat certain GDB commands by typing just @key{RET}. + +@menu +* Command Syntax:: Command Syntax +* Help:: Getting Help +@end menu + +@node Command Syntax, Help, Commands, Commands +@section Command Syntax + +A GDB 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 command names do not allow any arguments. + +@cindex abbreviation +GDB 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 +A blank line as input to GDB (typing just @key{RET}) means to +repeat the previous command. Certain commands (for example, @code{run}) +will not repeat this way; these are commands for which unintentional +repetition might cause trouble and which you are unlikely to want to +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. + +GDB 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}). Since it is easy to press one @key{RET} too many +in this situation, GDB disables command repetition after any command +that generates this sort of display. + +@kindex # +@cindex comment +A line of input starting with @kbd{#} is a comment; it does nothing. +This is useful mainly in command files (@pxref{Command Files}). + +@node Help, , Command Syntax, Commands +@section Getting Help +@cindex online documentation +@kindex help + +You can always ask GDB itself for information on its commands, using the +command @code{help}. + +@table @code +@item help +@itemx h +@kindex h +You can use @code{help} (abbreviated @code{h}) with no arguments to +display a short list of named classes of commands: + +@smallexample +(gdb) help +List of classes of commands: + +running -- Running the program +stack -- Examining the stack +data -- Examining data +breakpoints -- Making program stop at certain points +files -- Specifying and examining files +status -- Status inquiries +support -- Support facilities +user-defined -- User-defined commands +aliases -- Aliases of other commands +obscure -- Obscure features + +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. +(gdb) +@end smallexample + +@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 +(gdb) help status +Status inquiries. + +List of commands: + +show -- Generic command for showing things set with "set" +info -- Generic command for printing status + +Type "help" followed by command name for full +documentation. +Command name abbreviations are allowed if unambiguous. +(gdb) +@end smallexample + +@item help @var{command} +With a command name as @code{help} argument, GDB will display a +short paragraph on how to use that command. +@end table + +In addition to @code{help}, you can use the GDB commands @code{info} +and @code{show} to inquire about the state of your program, or the state +of GDB 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 Index point to +all the sub-commands. @xref{Index}. + +@c @group +@table @code +@item info +@kindex info +@kindex i +This command (abbreviated @code{i}) is for describing the state of your +program; for example, it can list the arguments given to your program +(@code{info args}), the registers currently in use (@code{info +registers}), or the breakpoints you have set (@code{info breakpoints}). +You can get a complete list of the @code{info} sub-commands with +@w{@code{help info}}. + +@kindex show +@item show +In contrast, @code{show} is for describing the state of GDB 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 three miscellaneous @code{show} subcommands, all of which are +exceptional in lacking corresponding @code{set} commands: + +@table @code +@kindex show version +@cindex version number +@item show version +Show what version of GDB is running. You should include this +information in GDB bug-reports. If multiple versions of GDB are in +use at your site, you may occasionally want to make sure what version +of GDB you are running; as GDB evolves, new commands are introduced, +and old ones may wither away. The version number is also announced +when you start GDB with no arguments. + +@kindex show copying +@item show copying +Display information about permission for copying GDB. + +@kindex show warranty +@item show warranty +Display the GNU ``NO WARRANTY'' statement. +@end table + +@node Running, Stopping, Commands, Top +@chapter Running Programs Under GDB + +To debug a program, you must run it under GDB. + +@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 +@end menu + +@node Compilation, Starting, Running, Running +@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. + +Many C compilers are unable to handle the @samp{-g} and @samp{-O} +options together. Using those compilers, you cannot generate optimized +executables containing debugging information. + +gcc, the GNU C 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. + +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 as a bug (including a test case!). + +Older versions of the GNU C compiler permitted a variant option +@w{@samp{-gg}} for debugging information. GDB no longer supports this +format; if your GNU C compiler has this option, do not use it. + +@ignore +@comment As far as I know, there are no cases in which GDB will +@comment produce strange output in this case. (but no promises). +If your program includes archives made with the @code{ar} program, and +if the object files used as input to @code{ar} were compiled without the +@samp{-g} option and have names longer than 15 characters, GDB will get +confused reading your program's symbol table. No error message will be +given, but GDB may behave strangely. The reason for this problem is a +deficiency in the Unix archive file format, which cannot represent file +names longer than 15 characters. + +To avoid this problem, compile the archive members with the @samp{-g} +option or use shorter file names. Alternatively, use a version of GNU +@code{ar} dated more recently than August 1989. +@end ignore + +@node Starting, Arguments, Compilation, Running +@section Starting your Program +@cindex starting +@cindex running + +@table @code +@item run +@itemx r +@kindex run +Use the @code{run} command to start your program under GDB. You must +first specify the program name +(except on VxWorks) +with an argument to +GDB (@pxref{Invocation, ,Getting In and Out of GDB}), 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 environments without processes, +@code{run} jumps to the start of your program.) + +The execution of a program is affected by certain information it +receives from its superior. GDB provides ways to specify this +information, which you must do @i{before} starting your program. (You +can change it after starting your program, but such changes will only affect +your program the next time you start it.) This information may be +divided into four categories: + +@table @asis +@item The @i{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. @xref{Arguments, ,Your +Program's Arguments}. + +@item The @i{environment.} +Your program normally inherits its environment from GDB, but you can +use the GDB commands @code{set environment} and @code{unset +environment} to change parts of the environment that will be given to +your program. @xref{Environment, ,Your Program's Environment}. + +@item The @i{working directory.} +Your program inherits its working directory from GDB. You can set +GDB's working directory with the @code{cd} command in GDB. +@xref{Working Directory, ,Your Program's Working Directory}. + +@item The @i{standard input and output.} +Your program normally uses the same device for standard input and +standard output as GDB 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, GDB is likely to wind up debugging the +wrong program. +@end table + +@c FIXME: Rewrite following paragraph, especially its third sentence. +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 been started by the @code{run} command (and then stopped), +you may evaluate expressions that involve calls to 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 GDB read its symbols, GDB will discard its symbol table and +re-read it. When it does this, GDB tries to retain your current +breakpoints. + +@node Arguments, Environment, Starting, Running +@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. +GDB uses the shell indicated by your environment variable +@code{SHELL} if it exists; otherwise, GDB uses @code{/bin/sh}. + +@code{run} with no arguments uses the same arguments used by the previous +@code{run}, or those set by the @code{set args} command. + +@kindex set args +@table @code +@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} will execute 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. + +@item show args +@kindex show args +Show the arguments to give your program when it is started. +@end table + +@node Environment, Working Directory, Arguments, Running +@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 GDB over again. + +@table @code +@item path @var{directory} +@kindex path +Add @var{directory} to the front of the @code{PATH} environment variable +(the search path for executables), for both GDB and your program. +You may specify several directory names, separated by @samp{:} or +whitespace. If @var{directory} is already in the path, it is moved to +the front, so it will be searched sooner. + +You can use the string @samp{$cwd} to refer to whatever is the current +working directory at the time GDB searches the path. If you use +@samp{.} instead, it refers to the directory where you executed the +@code{path} command. GDB fills in the current path where needed in +the @var{directory} argument, before adding it 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. + +@item show paths +@kindex show paths +Display the list of search paths for executables (the @code{PATH} +environment variable). + +@item show environment @r{[}@var{varname}@r{]} +@kindex show environment +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}. + +@item set environment @var{varname} @r{[}=@r{]} @var{value} +@kindex set environment +Sets environment variable @var{varname} to @var{value}. The value +changes for your program only, not for GDB itself. @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: + +@example +set env USER = foo +@end example + +@noindent +tells a Unix 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.) + +@item unset environment @var{varname} +@kindex unset environment +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. +@end table + +@node Working Directory, Input/Output, Environment, Running +@section Your Program's Working Directory + +@cindex working directory (of your program) +Each time you start your program with @code{run}, it inherits its +working directory from the current working directory of GDB. GDB's +working directory is initially whatever it inherited from its parent +process (typically the shell), but you can specify a new working +directory in GDB with the @code{cd} command. + +The GDB working directory also serves as a default for the commands +that specify files for GDB to operate on. @xref{Files, ,Commands to +Specify Files}. + +@table @code +@item cd @var{directory} +@kindex cd +Set GDB's working directory to @var{directory}. + +@item pwd +@kindex pwd +Print GDB's working directory. +@end table + +@node Input/Output, Attach, Working Directory, Running +@section Your Program's Input and Output + +@cindex redirection +@cindex i/o +@cindex terminal +By default, the program you run under GDB does input and output to +the same terminal that GDB uses. GDB 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 +@item info terminal +@kindex info terminal +Displays GDB's recorded information 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, + +@example +run > outfile +@end example + +@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, + +@example +tty /dev/ttyb +@end example + +@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 GDB still comes from your terminal. + +@node Attach, Kill Process, Input/Output, Running +@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 GDB. +(@code{info files} will show your active targets.) The command takes as +argument a process ID. The usual way to find out the process-id of +a Unix process is with the @code{ps} utility, or with the @samp{jobs -l} +shell command. + +@code{attach} will not repeat if you press @key{RET} a second time after +executing the command. +@end table + +To use @code{attach}, you must be debugging in an environment which +supports processes. You must also have permission to send the process a +signal, and it must have the same effective user ID as the GDB +process. + +When using @code{attach}, you should first use the @code{file} command +to specify the program running in the process and load its symbol table. +@xref{Files, ,Commands to Specify Files}. + +The first thing GDB does after arranging to debug the specified +process is to stop it. You can examine and modify an attached process +with all the GDB 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 GDB to the process. + +@table @code +@item detach +@kindex detach +When you have finished debugging the attached process, you can use the +@code{detach} command to release it from GDB's control. Detaching +the process continues its execution. After the @code{detach} command, +that process and GDB become completely independent once more, and you +are ready to @code{attach} another process or start one with @code{run}. +@code{detach} will not repeat if you press @key{RET} again after +executing the command. +@end table + +If you exit GDB or use the @code{run} command while you have an attached +process, you kill that process. By default, you will be asked 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, , Attach, Running +@c @group +@section Killing the Child Process + +@table @code +@item kill +@kindex kill +Kill the child process in which your program is running under GDB. +@end table + +This command is useful if you wish to debug a core dump instead of a +running process. GDB ignores any core dump file while your program +is running. +@c @end group + +On some operating systems, a program cannot be executed outside GDB +while you have breakpoints set on it inside GDB. 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}, GDB will notice that the file has changed, and +will re-read the symbol table (while trying to preserve your current +breakpoint settings). + +@node Stopping, Stack, Running, Top +@chapter Stopping and Continuing + +The principal purpose of using a debugger is 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 GDB, your program may stop for any of several reasons, such +as a signal, a breakpoint, or reaching a new line after a GDB +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 GDB provide ample +explanation of the status of your program---but you can also explicitly +request this information at any time. + +@table @code +@item info program +@kindex 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 Exceptions +* Continuing and Stepping:: Resuming Execution +* Signals:: Signals +@end menu + +@node Breakpoints, Continuing and Stepping, Stopping, Stopping +@section Breakpoints, Watchpoints, and Exceptions + +@cindex breakpoints +A @dfn{breakpoint} makes your program stop whenever a certain point in +the program is reached. For each breakpoint, you can add various +conditions to control in finer detail whether your program will stop. +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. In languages with exception handling (such as GNU +C++), you can also set breakpoints where an exception is raised +(@pxref{Exception Handling, ,Breakpoints and Exceptions}). + +@cindex watchpoints +A @dfn{watchpoint} is a special breakpoint that stops your program +when the value of an expression changes. 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. + +Each breakpoint or watchpoint is assigned a number when it is created; +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. + +@menu +* Set Breaks:: Setting Breakpoints +* Set Watchpoints:: Setting Watchpoints +* Exception Handling:: Breakpoints and Exceptions +* Delete Breaks:: Deleting Breakpoints +* Disabling:: Disabling Breakpoints +* Conditions:: Break Conditions +* Break Commands:: Breakpoint Command Lists +* Breakpoint Menus:: Breakpoint Menus +* Error in Breakpoints:: +@end menu + +@node Set Breaks, Set Watchpoints, Breakpoints, Breakpoints +@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 +Breakpoints are set with the @code{break} command (abbreviated @code{b}). + +You have several ways to say where the breakpoint should go. + +@table @code +@item break @var{function} +Set a breakpoint at entry to function @var{function}. When using source +languages that permit overloading of symbols, such as C++, +@var{function} may refer to more than one possible place to break. +@xref{Breakpoint Menus}, for a discussion of that situation. + +@item break +@var{offset} +@itemx break -@var{offset} +Set a breakpoint some number of lines forward or back from the position +at which execution stopped in the currently selected frame. + +@item break @var{linenum} +Set a breakpoint at line @var{linenum} in the current source file. +That file is the last file whose source text was printed. This +breakpoint will stop your program just before it executes any of the +code on that line. + +@item break @var{filename}:@var{linenum} +Set a breakpoint at line @var{linenum} in source file @var{filename}. + +@item break @var{filename}:@var{function} +Set a breakpoint at entry to function @var{function} found in file +@var{filename}. Specifying a file name as well as a function name is +superfluous except when multiple files contain similarly named +functions. + +@item break *@var{address} +Set a breakpoint at address @var{address}. You can use this to set +breakpoints in parts of your program which do not have debugging +information or source files. + +@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 will cause your program to 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, GDB will stop +the next time it reaches the current location; this may be useful +inside loops. + +GDB 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. + +@item tbreak @var{args} +@kindex tbreak +Set a breakpoint enabled only for one stop. @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 disabled after the first time your +program stops there. @xref{Disabling, ,Disabling Breakpoints}. + +@item rbreak @var{regex} +@kindex rbreak +@cindex regular expression +@c FIXME what kind of regexp? +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. They can +be deleted, disabled, made conditional, etc., in the standard ways. + +When debugging C++ programs, @code{rbreak} is useful for setting +breakpoints on overloaded functions that are not members of any special +classes. + +@kindex info breakpoints +@cindex @code{$_} and @code{info breakpoints} +@item info breakpoints @r{[}@var{n}@r{]} +@item info break @r{[}@var{n}@r{]} +Print a list of all breakpoints (but not watchpoints) set and not +deleted, showing their numbers, where in your program they are, and any +special features in use for them. Disabled breakpoints are included in +the list, but marked as disabled. @code{info break} with a breakpoint +number @var{n} as argument lists only that breakpoint. The +convenience variable @code{$_} and the default examining-address for +the @code{x} command are set to the address of the last breakpoint +listed (@pxref{Memory, ,Examining Memory}). The equivalent command +for watchpoints is @code{info watch}. +@end table + +GDB 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}). + +@node Set Watchpoints, Exception Handling, Set Breaks, Breakpoints +@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. + +Watchpoints currently execute two orders of magnitude more slowly than +other breakpoints, but this can well be worth it to catch errors where +you have no clue what part of your program is the culprit. Some +processors provide special hardware to support watchpoint evaluation; future +releases of GDB will use such hardware if it is available. + +@table @code +@kindex watch +@item watch @var{expr} +Set a watchpoint for an expression. + +@kindex info watchpoints +@item info watchpoints +This command prints a list of watchpoints; it is otherwise similar to +@code{info break}. +@end table + +@node Exception Handling, Delete Breaks, Set Watchpoints, Breakpoints +@subsection Breakpoints and Exceptions +@cindex exception handlers + +Some languages, such as GNU C++, implement exception handling. You can +use GDB to examine what caused your program to raise an exception, +and to list the exceptions your program is prepared to handle at a +given point in time. + +@table @code +@item catch @var{exceptions} +@kindex catch +You can set breakpoints at active exception handlers by using the +@code{catch} command. @var{exceptions} is a list of names of exceptions +to catch. +@end table + +You can use @code{info catch} to list active exception handlers. +@xref{Frame Info, ,Information About a Frame}. + +There are currently some limitations to exception handling in GDB. +These will be corrected in a future release. + +@itemize @bullet +@item +If you call a function interactively, GDB 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 to simply continue +running until it hits a breakpoint, catches a signal that GDB is +listening for, or exits. +@item +You cannot raise an exception interactively. +@item +You cannot interactively install an exception handler. +@end itemize + +@cindex raise exceptions +Sometimes @code{catch} is not the best way to debug exception handling: +if you need to know exactly where an exception is raised, it is better to +stop @emph{before} the exception handler is called, since that way you +can see the stack before any unwinding takes place. If you set a +breakpoint in an exception handler instead, it may not be easy to find +out where the exception was raised. + +To stop just before an exception handler is called, you need some +knowledge of the implementation. In the case of GNU C++, exceptions are +raised by calling a library function named @code{__raise_exception} +which has the following ANSI C interface: + +@example + /* @var{addr} is where the exception identifier is stored. + ID is the exception identifier. */ + void __raise_exception (void **@var{addr}, void *@var{id}); +@end example + +@noindent +To make the debugger catch all exceptions before any stack +unwinding takes place, set a breakpoint on @code{__raise_exception} +(@pxref{Breakpoints, ,Breakpoints Watchpoints and Exceptions}). + +With a conditional breakpoint (@pxref{Conditions, ,Break Conditions}) +that depends on the value of @var{id}, you can stop your program when +a specific exception is raised. You can use multiple conditional +breakpoints to stop your program when any of a number of exceptions are +raised. + +@node Delete Breaks, Disabling, Exception Handling, Breakpoints +@subsection Deleting Breakpoints + +@cindex clearing breakpoints, watchpoints +@cindex deleting breakpoints, watchpoints +It is often necessary to eliminate a breakpoint or watchpoint 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 or watchpoints by specifying their +breakpoint numbers. + +It is not necessary to delete a breakpoint to proceed past it. GDB +automatically ignores breakpoints on the first instruction to be executed +when you continue execution without changing the execution address. + +@table @code +@item clear +@kindex 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{function} +@itemx clear @var{filename}:@var{function} +Delete any breakpoints set at entry to the function @var{function}. + +@item clear @var{linenum} +@itemx clear @var{filename}:@var{linenum} +Delete any breakpoints set at or within the code of the specified line. + +@item delete @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]} +@cindex delete breakpoints +@kindex delete +@kindex d +Delete the breakpoints or watchpoints of the numbers specified as +arguments. If no argument is specified, delete all breakpoints (GDB +asks confirmation, unless you have @code{set confirm off}). You +can abbreviate this command as @code{d}. +@end table + +@node Disabling, Conditions, Delete Breaks, Breakpoints +@subsection Disabling Breakpoints + +@cindex disabled breakpoints +@cindex enabled breakpoints +Rather than deleting a breakpoint or watchpoint, 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 and watchpoints with the +@code{enable} and @code{disable} commands, optionally specifying one or +more breakpoint numbers as arguments. Use @code{info break} or +@code{info watch} to print a list of breakpoints or watchpoints if you +do not know which numbers to use. + +A breakpoint or watchpoint can have any of four different states of +enablement: + +@itemize @bullet +@item +Enabled. The breakpoint will stop 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 will stop your program, but +when it does so it will become disabled. A breakpoint set +with the @code{tbreak} command starts out in this state. +@item +Enabled for deletion. The breakpoint will stop your program, but +immediately after it does so it will be deleted permanently. +@end itemize + +You can use the following commands to enable or disable breakpoints and +watchpoints: + +@table @code +@item disable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]} +@kindex disable breakpoints +@kindex disable +@kindex dis +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}. + +@item enable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]} +@kindex enable breakpoints +@kindex enable +Enable the specified breakpoints (or all defined breakpoints). They +become effective once again in stopping your program. + +@item enable @r{[}breakpoints@r{]} once @var{bnums}@dots{} +Enable the specified breakpoints temporarily. Each will be disabled +again the next time it stops your program. + +@item enable @r{[}breakpoints@r{]} delete @var{bnums}@dots{} +Enable the specified breakpoints to work once and then die. Each of +the breakpoints will be deleted the next time it stops your program. +@end table + +Save 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 will not change the state of +your other breakpoints; @pxref{Continuing and Stepping, ,Continuing and Stepping}.) + +@node Conditions, Break Commands, Disabling, Breakpoints +@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, GDB 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 for the +purpose of performing side effects when a breakpoint is reached +(@pxref{Break Commands, ,Breakpoint Command Lists}). + +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. The @code{watch} command does not +recognize the @code{if} keyword; @code{condition} is the only way to +impose a further condition on a watchpoint. + +@table @code +@item condition @var{bnum} @var{expression} +@kindex condition +Specify @var{expression} as the break condition for breakpoint or +watchpoint number @var{bnum}. From now on, this breakpoint will stop +your program only if the value of @var{expression} is true (nonzero, in +C). When you use @code{condition}, GDB checks @var{expression} +immediately for syntactic correctness, and to determine whether symbols +in it have referents in the context of your breakpoint. +@c FIXME so what does GDB do if there is no referent? Moreover, what +@c about watchpoints? +GDB does +not actually evaluate @var{expression} at the time the @code{condition} +command 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 will not stop the next @var{n} times it +is reached. + +@table @code +@item ignore @var{bnum} @var{count} +@kindex ignore +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 will not stop; other than to decrement the ignore count, GDB +takes no action. + +To make the breakpoint stop the next time it is reached, specify +a count of zero. + +@item continue @var{count} +@itemx c @var{count} +@itemx fg @var{count} +@kindex continue @var{count} +Continue execution of your program, setting the ignore count of the +breakpoint where your program stopped to @var{count} minus one. +Thus, your program will not stop at this breakpoint until the +@var{count}'th time it is reached. + +An argument to this command is meaningful only when your program stopped +due to a breakpoint. At other times, the argument to @code{continue} is +ignored. + +The synonym @code{fg} is provided purely for convenience, and has +exactly the same behavior as other forms of the command. +@end table + +If a breakpoint has a positive ignore count and a condition, the condition +is not checked. Once the ignore count reaches zero, the condition will +be checked. + +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}. + +@node Break Commands, Breakpoint Menus, Conditions, Breakpoints +@subsection Breakpoint Command Lists + +@cindex breakpoint commands +You can give any breakpoint (or watchpoint) 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 +@item commands @r{[}@var{bnum}@r{]} +@itemx @dots{} @var{command-list} @dots{} +@itemx end +@kindex commands +@kindex end +Specify a list of commands for breakpoint number @var{bnum}. 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 @var{bnum} argument, @code{commands} refers to the last +breakpoint or watchpoint set (not to the breakpoint most recently +encountered). +@end table + +Pressing @key{RET} as a means of repeating the last GDB 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. Subsequent commands in the command list are +ignored. + +@kindex silent +If the first command specified 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 the remaining commands too print nothing, you will see no sign that +the breakpoint was reached at all. @code{silent} is meaningful only +at the beginning of a breakpoint command list. + +The commands @code{echo} and @code{output} that allow you to print +precisely controlled output 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. + +@example +break foo if x>0 +commands +silent +echo x is\040 +output x +echo \n +cont +end +@end example + +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: + +@example +break 403 +commands +silent +set x = y + 4 +cont +end +@end example + +@cindex lost output +One deficiency in the operation of automatically continuing breakpoints +under Unix appears when your program uses raw mode for the terminal. +GDB switches back to its own terminal modes (not raw) before executing +commands, and then must switch back to raw mode when your program is +continued. This causes any pending terminal input to be lost. +@c FIXME: revisit below when GNU sys avail. +@c In the GNU system, this will be fixed by changing the behavior of +@c terminal modes. + +Under Unix, you can get around this problem by writing actions into +the breakpoint condition rather than in commands. For example + +@example +condition 5 (x = y + 4), 0 +@end example + +@noindent +specifies a condition expression (@pxref{Expressions, ,Expressions}) that will +change @code{x} as needed, then always have the value zero so your +program will not stop. No input is lost here, because GDB evaluates +break conditions without changing the terminal modes. When you want +to have nontrivial conditions for performing the side effects, the +operators @samp{&&}, @samp{||} and @samp{?@dots{}:} may be useful. + +@node Breakpoint Menus, Error in Breakpoints, Break Commands, Breakpoints +@subsection Breakpoint Menus +@cindex overloading +@cindex symbol overloading + +Some programming languages (notably C++) permit a single function name +to be defined several times, for application in different contexts. +This is called @dfn{overloading}. When a function name is overloaded, +@samp{break @var{function}} is not enough to tell GDB where you +want a breakpoint. GDB offers you a menu of numbered choices for +different possible breakpoints, and waits for your selection with the +prompt @samp{>}. The first two options are always @samp{[0] cancel} +and @samp{[1] all}. Typing @kbd{1} sets a breakpoint at each +definition of @var{function}, and typing @kbd{0} aborts the +@code{break} command without setting any new breakpoints. + +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: + +@example +(gdb) 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. +(gdb) +@end example + +@node Error in Breakpoints, , Breakpoint Menus, Breakpoints +@subsection ``Cannot Insert Breakpoints'' + +@c FIXME: "cannot insert breakpoints" error, v unclear. +@c Q in pending mail to Gilmore. ---pesch@cygnus.com, 26mar91 +@c some light may be shed by looking at instances of +@c ONE_PROCESS_WRITETEXT. But error seems possible otherwise +@c too. pesch, 20sep91 +Under some operating systems, breakpoints cannot be used in a program if +any other process is running that program. In this situation, +attempting to run or continue a program with a breakpoint causes GDB +to stop the other process. + +When this happens, you have three ways to proceed: + +@enumerate +@item +Remove or disable the breakpoints, then continue. + +@item +Suspend GDB, and copy the file containing your program to a new name. +Resume GDB and use the @code{exec-file} command to specify that GDB +should run your program under that name. Then start your program again. + +@c FIXME: RMS commented here "Show example". Maybe when someone +@c explains the first FIXME: in this section... + +@item +Relink your program so that the text segment is nonsharable, using the +linker option @samp{-N}. The operating system limitation may not apply +to nonsharable executables. +@end enumerate + +@node Continuing and Stepping, Signals, Breakpoints, Stopping +@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 to a signal. (If due to a signal, you may want to use @code{handle}, +or use @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.) + +@table @code +@item continue @r{[}@var{ignore-count}@r{]} +@kindex continue +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}). + +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. +@end table + +A typical technique for using stepping is to set a breakpoint +(@pxref{Breakpoints, ,Breakpoints Watchpoints and Exceptions}) 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 +@item step +@kindex step +@kindex s +Continue running your program until control reaches a different source +line, then stop it and return control to GDB. This command is +abbreviated @code{s}. + +@quotation +@emph{Warning:} If you use the @code{step} command while control is +within a function that was compiled without debugging information, +execution will proceed until control reaches another function. +@end quotation + +@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. + +@item next @r{[}@var{count}@r{]} +@kindex next +@kindex n +Continue to the next source line in the current (innermost) stack frame. +Similar to @code{step}, but any function calls appearing within the line +of code are executed without stopping. Execution stops when control +reaches a different line of code at the stack level which was executing +when the @code{next} command was given. This command is abbreviated +@code{n}. + +An argument @var{count} is a repeat count, as for @code{step}. + +@code{next} within a function that lacks debugging information acts like +@code{step}, but any function calls appearing within the code of the +function are executed without stopping. + +@item finish +@kindex finish +Continue running until just after function in the selected stack frame +returns. Print the returned value (if any). + +Contrast this with the @code{return} command (@pxref{Returning, +,Returning from a Function}). + +@item until +@kindex until +@item u +@kindex 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} will cause your program to continue execution +until the loop is exited. In contrast, a @code{next} command at the end +of a loop will simply step back to the beginning of the loop, which +would force 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}: + +@example +(gdb) f +#0 main (argc=4, argv=0xf7fffae8) at m4.c:206 +206 expand_input(); +(gdb) until +195 for ( ; argc > 0; NEXTARG) @{ +@end example + +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} +@item u @var{location} +Continue running your program until either the specified location is +reached, or the current stack frame returns. @var{location} is any of +the forms of argument acceptable to @code{break} (@pxref{Set Breaks, +,Setting Breakpoints}). This form of the command uses breakpoints, +and hence is quicker than @code{until} without an argument. + +@item stepi +@itemx si +@kindex stepi +@kindex 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 will cause the next instruction to be executed to +be displayed automatically at each stop. @xref{Auto Display, +,Automatic Display}. + +An argument is a repeat count, as in @code{step}. + +@item nexti +@itemx ni +@kindex nexti +@kindex 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 + +@node Signals, , Continuing and Stepping, Stopping +@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 (often @kbd{C-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} (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. + +GDB has the ability to detect any occurrence of a signal in your +program. You can tell GDB in advance what to do for each kind of +signal. + +@cindex handling signals +Normally, GDB is set up to ignore non-erroneous signals like @code{SIGALRM} +(so as not to interfere with their role in the functioning of your program) +but to stop your program immediately whenever an error signal happens. +You can change these settings with the @code{handle} command. + +@table @code +@item info signals +@kindex info signals +Print a table of all the kinds of signals and how GDB has been told to +handle each one. You can use this to see the signal numbers of all +the defined types of signals. + +@item handle @var{signal} @var{keywords}@dots{} +@kindex handle +Change the way GDB handles signal @var{signal}. @var{signal} can be the +number of a signal or its name (with or without the @samp{SIG} at the +beginning). The @var{keywords} 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 +GDB 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 +GDB should stop your program when this signal happens. This implies +the @code{print} keyword as well. + +@item print +GDB should print a message when this signal happens. + +@item noprint +GDB should not mention the occurrence of the signal at all. This +implies the @code{nostop} keyword as well. + +@item pass +GDB should allow your program to see this signal; your program will be +able to handle the signal, or may be terminated if the signal is fatal +and not handled. + +@item nopass +GDB should not allow your program to see this signal. +@end table +@c @end group + +When a signal has been set to stop your program, your program cannot see the +signal until you continue. It will see the signal then, if @code{pass} is +in effect for the signal in question @i{at that time}. In other words, +after GDB reports a signal, you can use the @code{handle} command with +@code{pass} or @code{nopass} to control whether that signal will be seen by +your program when you later continue it. + +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}. + +@node Stack, Source, Stopping, Top +@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, the information about +where in your program the call was made from is saved in a block of data +called a @dfn{stack frame}. The frame also contains the arguments of the +call and the local variables of the function that was called. All the +stack frames are allocated in a region of memory called the @dfn{call +stack}. + +When your program stops, the GDB 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 GDB and many GDB commands +refer implicitly to the selected frame. In particular, whenever you ask +GDB for the value of a variable in your program, the value is found in the +selected frame. There are special GDB commands to select whichever frame +you are interested in. + +When your program stops, GDB automatically selects the currently executing +frame and describes it briefly as the @code{frame} command does +(@pxref{Frame Info, ,Information About a Frame}). + +@menu +* Frames:: Stack Frames +* Backtrace:: Backtraces +* Selection:: Selecting a Frame +* Frame Info:: Information on a Frame +@end menu + +@node Frames, Backtrace, Stack, Stack +@section Stack Frames + +@cindex frame +@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 of those bytes whose +address serves as the address of the frame. Usually this address is kept +in a register called the @dfn{frame pointer register} while execution is +going on in that frame. + +@cindex frame number +GDB assigns numbers to all existing stack frames, starting with +zero for the innermost frame, one for the frame that called it, +and so on upward. These numbers do not really exist in your program; +they are assigned by GDB to give you a way of designating stack +frames in GDB commands. + +@cindex frameless execution +Some compilers allow functions to be compiled so that they operate +without stack frames. (For example, the @code{gcc} option +@samp{-fomit-frame-pointer} will generate functions without a frame.) +This is occasionally done with heavily used library functions to save +the frame setup time. GDB has limited facilities for dealing with +these function invocations. If the innermost function invocation has no +stack frame, GDB will nevertheless regard it as though it had a +separate frame, which is numbered zero as usual, allowing correct +tracing of the function call chain. However, GDB has no provision +for frameless functions elsewhere in the stack. + +@node Backtrace, Selection, Frames, Stack +@section Backtraces + +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. + +@table @code +@item backtrace +@itemx bt +@kindex backtrace +@kindex bt +Print a backtrace of the entire stack: one line per frame for all +frames in the stack. + +You can stop the backtrace at any time by typing the system interrupt +character, normally @kbd{C-c}. + +@item backtrace @var{n} +@itemx bt @var{n} +Similar, but print only the innermost @var{n} frames. + +@item backtrace -@var{n} +@itemx bt -@var{n} +Similar, but print only the outermost @var{n} frames. +@end table + +@kindex where +@kindex info stack +@kindex info s +The names @code{where} and @code{info stack} (abbreviated @code{info s}) +are additional aliases for @code{backtrace}. + +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) 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}. + +@node Selection, Frame Info, Backtrace, Stack +@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 +@item frame @var{n} +@itemx f @var{n} +@kindex frame +@kindex f +Select frame number @var{n}. 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-numbered frame is @code{main}'s +frame. + +@item frame @var{addr} +@itemx f @var{addr} +Select the frame at address @var{addr}. This is useful mainly if the +chaining of stack frames has been damaged by a bug, making it +impossible for GDB to assign numbers properly to all frames. In +addition, this can be useful when your program has multiple stacks and +switches between them. + +On the SPARC architecture, @code{frame} needs two addresses to +select an arbitrary frame: a frame pointer and a stack pointer. +@c note to future updaters: this is conditioned on a flag +@c FRAME_SPECIFICATION_DYADIC in the tm-*.h files, currently only used +@c by SPARC, hence the specific attribution. Generalize or list all +@c possibilities if more supported machines start doing this. + +@item up @var{n} +@kindex up +Move @var{n} frames up the stack. For positive numbers @var{n}, this +advances toward the outermost frame, to higher frame numbers, to frames +that have existed longer. @var{n} defaults to one. + +@item down @var{n} +@kindex down +@kindex do +Move @var{n} frames down the stack. For positive numbers @var{n}, this +advances toward the innermost frame, to lower frame numbers, to frames +that were created more recently. @var{n} defaults to one. 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. For +example: + +@smallexample +@group +(gdb) 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 will +print ten lines centered on the point of execution in the frame. +@xref{List, ,Printing Source Lines}. + +@table @code +@item up-silently @var{n} +@itemx down-silently @var{n} +@kindex down-silently +@kindex up-silently +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 GDB command scripts, where the output might be unnecessary and +distracting. +@end table + +@node Frame Info, , Selection, Stack +@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 +(@pxref{Selection, ,Selecting a Frame}). + +@item info frame +@itemx info f +@kindex info frame +@kindex info f +This command prints a verbose description of the selected stack frame, +including the address of the frame, the addresses of the next frame down +(called by this frame) and the next frame up (caller of this frame), the +language that the source code corresponding to this frame was written in, +the address of the frame's arguments, the program counter saved in it +(the address of execution in the caller frame), and which registers +were saved in the frame. 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 @var{addr} +@itemx info f @var{addr} +Print a verbose description of the frame at address @var{addr}, +without selecting that frame. The selected frame remains unchanged by +this command. + +@item info args +@kindex info args +Print the arguments of the selected frame, each on a separate line. + +@item info locals +@kindex info locals +Print the local variables of the selected frame, each on a separate +line. These are all variables declared static or automatic within all +program blocks that execution in this frame is currently inside of. + +@item info catch +@kindex info catch +@cindex catch exceptions +@cindex exception handlers +Print a list of all the exception handlers that are active in the +current stack frame at the current point of execution. To see other +exception handlers, visit the associated frame (using the @code{up}, +@code{down}, or @code{frame} commands); then type @code{info catch}. +@xref{Exception Handling, ,Breakpoints and Exceptions}. +@end table + +@node Source, Data, Stack, Top +@chapter Examining Source Files + +GDB can print parts of your program's source, since the debugging +information recorded in your program tells GDB what source files were +used to build it. When your program stops, GDB spontaneously prints +the line where it stopped. Likewise, when you select a stack frame +(@pxref{Selection, ,Selecting a Frame}), GDB prints the line where +execution in that frame has stopped. You can print other portions of +source files by explicit command. + +If you use GDB through its GNU Emacs interface, you may prefer to use +Emacs facilities to view source; @pxref{Emacs, ,Using GDB under GNU +Emacs}. + +@menu +* List:: Printing Source Lines +* Search:: Searching Source Files +* Source Path:: Specifying Source Directories +* Machine Code:: Source and Machine Code +@end menu + +@node List, Search, Source, Source +@section Printing Source Lines + +@kindex list +@kindex l +To print lines from a source file, use the @code{list} command +(abbreviated @code{l}). There are several ways to specify what part +of the file you want to print. + +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 + +By default, GDB prints ten source lines with any of these forms of +the @code{list} command. You can change this using @code{set listsize}: + +@table @code +@item set listsize @var{count} +@kindex set listsize +Make the @code{list} command display @var{count} source lines (unless +the @code{list} argument explicitly specifies some other number). + +@item show listsize +@kindex show listsize +Display the number of lines that @code{list} will currently display by +default. +@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. + +@cindex linespec +In general, the @code{list} command expects you to supply zero, one or two +@dfn{linespecs}. Linespecs specify source lines; there are several ways +of writing them 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{linespec} +Print lines centered around the line specified by @var{linespec}. + +@item list @var{first},@var{last} +Print lines from @var{first} to @var{last}. Both arguments are +linespecs. + +@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 + +Here are the ways of specifying a single source line---all the +kinds of linespec. + +@table @code +@item @var{number} +Specifies line @var{number} of the current source file. +When a @code{list} command has two linespecs, this refers to +the same source file as the first linespec. + +@item +@var{offset} +Specifies the line @var{offset} lines after the last line printed. +When used as the second linespec in a @code{list} command that has +two, this specifies the line @var{offset} lines down from the +first linespec. + +@item -@var{offset} +Specifies the line @var{offset} lines before the last line printed. + +@item @var{filename}:@var{number} +Specifies line @var{number} in the source file @var{filename}. + +@item @var{function} +@c FIXME: "of the open-brace" is C-centric. When we add other langs... +Specifies the line of the open-brace that begins the body of the +function @var{function}. + +@item @var{filename}:@var{function} +Specifies the line of the open-brace 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{address} +Specifies the line containing the program address @var{address}. +@var{address} may be any expression. +@end table + +@node Search, Source Path, List, Source +@section Searching Source Files +@cindex searching +@kindex reverse-search + +There are two commands for searching through the current source file for a +regular expression. + +@table @code +@item forward-search @var{regexp} +@itemx search @var{regexp} +@kindex search +@kindex forward-search +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 +synonym @samp{search @var{regexp}} or abbreviate the command name as +@code{fo}. + +@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, Machine Code, Search, Source +@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. GDB has a list of directories to search for source files; +this is called the @dfn{source path}. Each time GDB 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. Note that +the executable search path is @emph{not} used for this purpose. Neither is +the current working directory, unless it happens to be in the source +path. + +If GDB cannot find a source file in the source path, and the object +program records a directory, GDB tries that directory too. If the +source path is empty, and there is no record of the compilation +directory, GDB will, as a last resort, look in the current +directory. + +Whenever you reset or rearrange the source path, GDB will clear out +any information it has cached about where source files are found, where +each line is in the file, etc. + +@kindex directory +When you start GDB, its source path is empty. +To add other directories, use the @code{directory} command. + +@table @code +@item directory @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{:} or +whitespace. You may specify a directory that is already in the source +path; this moves it forward, so it will be searched sooner. + +You can use the string @samp{$cdir} to refer to the compilation +directory (if one is recorded), and @samp{$cwd} to refer to the current +working directory. @samp{$cwd} is not the same as @samp{.}---the former +tracks the current working directory as it changes during your GDB +session, while the latter is immediately expanded to the current +directory at the time you add an entry to the source path. + +@item directory +Reset the source path to empty again. 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 show directories +@kindex show directories +Print the source path: show which directories it contains. +@end table + +If your source path is cluttered with directories that are no longer of +interest, GDB 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 empty. + +@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, , Source Path, Source +@section Source and Machine Code + +You can use the command @code{info line} to map source lines to program +addresses (and viceversa), and the command @code{disassemble} to display +a range of addresses as machine instructions. + +@table @code +@item info line @var{linespec} +@kindex info line +Print the starting and ending addresses of the compiled code for +source line @var{linespec}. You can specify source lines in any of +the ways understood by the @code{list} command (@pxref{List, ,Printing +Source Lines}). +@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 +(gdb) info line m4_changecom +Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350. +@end smallexample + +@noindent +We can also inquire (using @code{*@var{addr}} as the form for +@var{linespec}) what source line covers a particular address: +@smallexample +(gdb) info line *0x63ff +Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404. +@end smallexample + +@cindex @code{$_} and @code{info line} +After @code{info line}, the default address for the @code{x} command +is changed to the starting address of the line, so that @samp{x/i} is +sufficient to begin examining the machine code (@pxref{Memory, +,Examining Memory}). Also, this address is saved as the value of the +convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience +Variables}). + +@table @code +@kindex disassemble +@item disassemble +This specialized command dumps a range of memory as machine +instructions. 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; the function surrounding this value +will be dumped. Two arguments specify a range of addresses (first +inclusive, second exclusive) to dump. +@end table + +We can use @code{disassemble} to inspect the object code +range shown in the last @code{info line} example: + +@smallexample +(gdb) disas 0x63e4 0x6404 +Dump of assembler code from 0x63e4 to 0x6404: +0x63e4 builtin_init+5340: ble 0x63f8 builtin_init+5360 +0x63e8 builtin_init+5344: sethi %hi(0x4c00), %o0 +0x63ec builtin_init+5348: ld [%i1+4], %o0 +0x63f0 builtin_init+5352: b 0x63fc builtin_init+5364 +0x63f4 builtin_init+5356: ld [%o0+4], %o0 +0x63f8 builtin_init+5360: or %o0, 0x1a4, %o0 +0x63fc builtin_init+5364: call 0x9288 path_search +0x6400 builtin_init+5368: nop +End of assembler dump. +@end smallexample + +@node Data, Languages, Source, Top +@chapter Examining Data + +@cindex printing data +@cindex examining data +@kindex print +@kindex inspect +@c "inspect" is not quite a synonym if you are using Epoch, which we do not +@c document because it is nonstandard... Under Epoch it displays in a +@c different window or something like that. +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 GDB with Different +Languages}). + +@table @code +@item print @var{exp} +@itemx print /@var{f} @var{exp} +@var{exp} is an expression (in the source language). By default +the value of @var{exp} 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; @pxref{Output formats}. + +@item print +@itemx print /@var{f} +If you omit @var{exp}, GDB 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 class are declared, use the @code{ptype @var{exp}} +command rather than @code{print}. @xref{Symbols, ,Examining the Symbol Table}. + +@menu +* Expressions:: Expressions +* Variables:: Program Variables +* Arrays:: Artificial Arrays +* Output formats:: Output formats +* Memory:: Examining Memory +* Auto Display:: Automatic Display +* Print Settings:: Print Settings +* Value History:: Value History +* Convenience Vars:: Convenience Variables +* Registers:: Registers +* Floating Point Hardware:: Floating Point Hardware +@end menu + +@node Expressions, Variables, Data, Data +@section Expressions + +@cindex expressions +@code{print} and many other GDB commands accept an expression and +compute its value. Any kind of constant, variable or operator defined +by the programming language you are using is legal in an expression in +GDB. This includes conditional expressions, function calls, casts +and string constants. It unfortunately does not include symbols defined +by preprocessor @code{#define} commands. + +Because C is so widespread, most of the expressions shown in examples in +this manual are in C. @xref{Languages, , Using GDB with Different +Languages}, for information on how to use expressions in other +languages. + +In this section, we discuss operators that you can use in GDB +expressions regardless of your programming language. + +Casts are supported in all languages, not just in C, because it is so +useful to cast a number into a pointer so as to examine a structure +at that address in memory. +@c FIXME: casts supported---Mod2 true? + +GDB supports these operators in addition to those of 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}. + +@item @{@var{type}@} @var{addr} +Refers to an object of type @var{type} stored at address @var{addr} in +memory. @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 Variables, Arrays, Expressions, Data +@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 either be global +(or static) or be visible according to the scope rules of the +programming language from the point of execution in that frame. This +means that in the function + +@example +foo (a) + int a; +@{ + bar (a); + @{ + int b = test (); + bar (b); + @} +@} +@end example + +@noindent +the variable @code{a} is usable whenever your program is executing +within the function @code{foo}, but the variable @code{b} is visible +only while your program is executing inside the block in which @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 variable in a particular file, using the colon-colon notation: + +@cindex colon-colon +@iftex +@c info cannot cope with a :: index entry, but why deprive hard copy readers? +@kindex :: +@end iftex +@example +@var{file}::@var{variable} +@end example + +@noindent +Here @var{file} is the name of the source file whose variable you want. + +@cindex C++ scope resolution +This use of @samp{::} is very rarely in conflict with the very similar +use of the same notation in C++. GDB also supports use of the C++ +scope resolution operator in GDB expressions. + +@cindex wrong values +@cindex variable values, wrong +@quotation +@emph{Warning:} Occasionally, a local variable may appear to have the +wrong value at certain points in a function---just after entry to the +function, and just before exit. 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 function 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. +@end quotation + +@node Arrays, Output formats, Variables, Data +@section Artificial Arrays + +@cindex artificial array +@kindex @@ +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. + +This can be done by constructing an @dfn{artificial array} with the +binary operator @samp{@@}. The left operand of @samp{@@} should be +the first element of the desired array, as 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 + +@example +int *array = (int *) malloc (len * sizeof (int)); +@end example + +@noindent +you can print the contents of @code{array} with + +@example +p *array@@len +@end example + +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.) + +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: + +@example +set $i = 0 +p dtab[$i++]->fv +@key{RET} +@key{RET} +@dots{} +@end example + +@node Output formats, Memory, Arrays, Data +@section Output formats + +@cindex formatted output +@cindex output formats +By default, GDB 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''. + +@item a +Print as an address, both absolute in hex and as an offset from the +nearest preceding symbol. This format can be used to discover where (in +what function) an unknown address is located: + +@example +(gdb) p/a 0x54320 +$3 = 0x54320 <_initialize_vx+396> +@end example + +@item c +Regard as an integer and print it as a character constant. + +@item f +Regard the bits of the value as a floating point number and print +using typical floating point syntax. +@end table + +For example, to print the program counter in hex (@pxref{Registers}), type + +@example +p/x $pc +@end example + +@noindent +Note that no space is required before the slash; this is because command +names in GDB 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, Auto Display, Output formats, Data +@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 +@item x/@var{nfu} @var{addr} +@itemx x @var{addr} +@itemx x +Use the command @code{x} 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. +@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}, +or @samp{s} (null-terminated string) or @samp{i} (machine instruction). +The default is @samp{x} (hexadecimal) initially, or the format from the +last time you used 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{s} and +@samp{i} formats, the unit size is ignored and is normally not written.) + +@item @var{addr}, starting display address +@var{addr} is the address where you want GDB 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}) in hexadecimal (@samp{x}). + +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 will work. The output +specifications @samp{4xw} and @samp{4wx} mean exactly the same thing. +(However, the count @var{n} must come first; @samp{wx4} will 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. The command @code{disassemble} gives an +alternative way of inspecting machine instructions; @pxref{Machine +Code}. + +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}. + +@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, GDB 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. + +@node Auto Display, Print Settings, Memory, Data +@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 GDB will print 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: + +@example +2: foo = 38 +3: bar[5] = (struct hack *) 0x3804 +@end example + +@noindent +showing 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 on how elaborate your +format specification is---it uses @code{x} if you specify a unit size, +or one of the two formats (@samp{i} and @samp{s}) that are only +supported by @code{x}; otherwise it uses @code{print}. + +@table @code +@item display @var{exp} +@kindex display +Add the expression @var{exp} to the list of expressions to display +each time your program stops. @xref{Expressions, ,Expressions}. + +@code{display} will not repeat if you press @key{RET} again after using it. + +@item display/@var{fmt} @var{exp} +For @var{fmt} specifying only a display format and not a size or +count, add the expression @var{exp} to the auto-display list but +arranges to display it each time in the specified format @var{fmt}. +@xref{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}). + +@table @code +@item undisplay @var{dnums}@dots{} +@itemx delete display @var{dnums}@dots{} +@kindex delete display +@kindex undisplay +Remove item numbers @var{dnums} from the list of expressions to display. + +@code{undisplay} will not repeat if you press @key{RET} after using it. +(Otherwise you would just get the error @samp{No display number @dots{}}.) + +@item disable display @var{dnums}@dots{} +@kindex disable display +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. + +@item enable display @var{dnums}@dots{} +@kindex enable display +Enable display of item numbers @var{dnums}. It becomes effective once +again in auto display of its expression, until you specify otherwise. + +@item display +Display the current values of the expressions on the list, just as is +done when your program stops. + +@item info display +@kindex 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 + +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}, then this argument will be displayed while your program +continues to stop inside that function. When it stops elsewhere---where +there is no variable @code{last_char}---display is disabled. The next time +your program stops where @code{last_char} is meaningful, you can enable the +display expression once again. + +@node Print Settings, Value History, Auto Display, Data +@section Print Settings + +@cindex format options +@cindex print settings +GDB 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 +@item set print address +@item set print address on +@kindex set print address +GDB will print 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 on. For example, this is what a stack frame display looks like, with +@code{set print address on}: + +@smallexample +@group +(gdb) 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}: + +@example +@group +(gdb) set print addr off +(gdb) f +#0 set_quotes (lq="<<", rq=">>") at input.c:530 +530 if (lquote != def_lquote) +@end group +@end example + +@item show print address +@kindex show print address +Show whether or not addresses are to be printed. + +@item set print array +@itemx set print array on +@kindex set print array +GDB will 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 +@kindex show print array +Show whether compressed or pretty format is selected for displaying +arrays. + +@item set print elements @var{number-of-elements} +@kindex set print elements +If GDB is printing a large array, it will stop 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. + +@item show print elements +@kindex show print elements +Display the number of elements of a large array that GDB will print +before losing patience. + +@item set print pretty on +@kindex set print pretty +Cause GDB to print structures in an indented format with one member per +line, like this: + +@example +@group +$1 = @{ + next = 0x0, + flags = @{ + sweet = 1, + sour = 1 + @}, + meat = 0x54 "Pork" +@} +@end group +@end example + +@item set print pretty off +Cause GDB 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 +@kindex show print pretty +Show which format GDB will use to print structures. + +@item set print sevenbit-strings on +@kindex set print sevenbit-strings +Print using only seven-bit characters; if this option is set, +GDB will display any eight-bit characters (in strings or character +values) using the notation @code{\}@var{nnn}. For example, @kbd{M-a} is +displayed as @code{\341}. + +@item set print sevenbit-strings off +Print using either seven-bit or eight-bit characters, as required. This +is the default. + +@item show print sevenbit-strings +@kindex show print sevenbit-strings +Show whether or not GDB will print only seven-bit characters. + +@item set print union on +@kindex set print union +Tell GDB to print unions which are contained in structures. This is the +default setting. + +@item set print union off +Tell GDB not to print unions which are contained in structures. + +@item show print union +@kindex show print union +Ask GDB whether or not it will print unions which are contained in +structures. + +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 +@end table + +@noindent +These settings are of interest when debugging C++ programs: + +@table @code +@item set print demangle +@itemx set print demangle on +@kindex set print demangle +Print C++ names in their source form rather than in the mangled form +in which they are passed to the assembler and linker for type-safe linkage. +The default is on. + +@item show print demangle +@kindex show print demangle +Show whether C++ names will be printed in mangled or demangled form. + +@item set print asm-demangle +@itemx set print asm-demangle on +@kindex set print asm-demangle +Print C++ 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 +@kindex show print asm-demangle +Show whether C++ names in assembly listings will be printed in mangled +or demangled form. + +@item set print object +@itemx set print object on +@kindex set print object +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. + +@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 +@kindex show print object +Show whether actual, or declared, object types will be displayed. + +@item set print vtbl +@itemx set print vtbl on +@kindex set print vtbl +Pretty print C++ virtual function tables. The default is off. + +@item set print vtbl off +Do not pretty print C++ virtual function tables. + +@item show print vtbl +@kindex show print vtbl +Show whether C++ virtual function tables are pretty printed, or not. +@end table + +@node Value History, Convenience Vars, Print Settings, Data +@section Value History + +@cindex value history +Values printed by the @code{print} command are saved in GDB's @dfn{value +history} so that you can 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{$$} +@cindex history number +The values printed are given @dfn{history numbers} for you to refer to them +by. These are successive integers starting with one. @code{print} shows you +the history number assigned to a value by printing @samp{$@var{num} = } +before the value; here @var{num} is the history number. + +To refer to any previous value, use @samp{$} followed by the value's +history number. The way @code{print} labels its output is designed to +remind you of this. Just @code{$} refers to the most recent value in +the history, and @code{$$} 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{$}. + +For example, suppose you have just printed a pointer to a structure and +want to see the contents of the structure. It suffices to type + +@example +p *$ +@end example + +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: + +@example +p *$.next +@end example + +@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: + +@example +print x +set x=5 +@end example + +@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, 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, Registers, Value History, Data +@section Convenience Variables + +@cindex convenience variables +GDB provides @dfn{convenience variables} that you can use within +GDB to hold on to a value and refer to it later. These variables +exist entirely within GDB; 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}). +(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. Example: + +@example +set $foo = *object_ptr +@end example + +@noindent +would save in @code{$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 +@item show convenience +@kindex show convenience +Print a list of convenience variables used so far, and their values. +Abbreviated @code{show con}. +@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: + +@example +set $i = 0 +print bar[$i++]->contents +@i{@dots{} repeat that command by typing @key{RET}.} +@end example + +Some convenience variables are created automatically by GDB and given +values likely to be useful. + +@table @code +@item $_ +@kindex $_ +The variable @code{$_} 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{$__}. + +@item $__ +@kindex $__ +The variable @code{$__} 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. +@end table + +@node Registers, Floating Point Hardware, Convenience Vars, Data +@section Registers + +@cindex registers +You can refer to machine register contents, in expressions, as variables +with names starting with @samp{$}. The names of registers are different +for each machine; use @code{info registers} to see the names used on +your machine. + +@table @code +@item info registers +@kindex info registers +Print the names and values of all registers except floating-point +registers (in the selected stack frame). + +@item info all-registers +@kindex info all-registers +@cindex floating point registers +Print the names and values of all registers, including floating-point +registers. + +@item info registers @var{regname} +Print the relativized value of register @var{regname}. @var{regname} +may be any register name valid on the machine you are using, with +or without the initial @samp{$}. +@end table + +GDB 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 + +@example +p/x $pc +@end example + +@noindent +or print the instruction to be executed next with + +@example +x/i $pc +@end example + +@noindent +or add four to the stack pointer @footnote{This is a way of removing +one word from the stack, on machines where stacks grow downward in +memory (most machines, nowadays). This assumes that the innermost +stack frame is selected; setting @code{$sp} is not allowed when other +stack frames are selected. To pop entire frames off the stack, +regardless of machine architecture, use @code{return}; +@pxref{Returning, ,Returning from a Function}.} with + +@example +set $sp += 4 +@end example + +Whenever possible, these four standard register names are available on +your machine even though the machine has different canonical mnemonics, +so long as there is no conflict. The @code{info registers} command +shows the canonical names. For example, on the SPARC, @code{info +registers} displays the processor status register as @code{$psr} but you +can also refer to it as @code{$ps}. + +GDB 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, GDB 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. + +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}). + +However, GDB must deduce where registers are saved, from the machine +code generated by your compiler. If some registers are not saved, or if +GDB is unable to locate the saved registers, the selected stack +frame will make no difference. + +@node Floating Point Hardware, , Registers, Data +@section Floating Point Hardware +@cindex floating point + +Depending on the host machine architecture, GDB may be able to give +you more information about the status of the floating point hardware. + +@table @code +@item info float +@kindex info float +If available, provides hardware-dependent information about the floating +point unit. The exact contents and layout vary depending on the +floating point chip. +@end table +@c FIXME: this is a cop-out. Try to get examples, explanations. Only +@c FIXME...supported currently on arm's and 386's. Mark properly with +@c FIXME... m4 macros to isolate general statements from hardware-dep, +@c FIXME... at that point. + +@node Languages, Symbols, Data, Top +@chapter Using GDB 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 are written +like @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}. + +@cindex working language +Language-specific information is built into GDB for some languages, +allowing you to express operations like the above in your program's +native language, and allowing GDB to output values in a manner +consistent with the syntax of your program's native language. The +language you use to build expressions, called the @dfn{working +language}, can be selected manually, or GDB can set it +automatically. + +@menu +* Setting:: Switching between source languages +* Show:: Displaying the language +* Checks:: Type and Range checks +* Support:: Supported languages +@end menu + +@node Setting, Show, Languages, Languages +@section Switching between source languages + +There are two ways to control the working language---either have GDB +set it automatically, or select it manually yourself. You can use the +@code{set language} command for either purpose. On startup, GDB +defaults to setting the language automatically. + +@menu +* Manually:: Setting the working language manually +* Automatically:: Having GDB infer the source language +@end menu + +@node Manually, Automatically, Setting, Setting +@subsection Setting the working language + +@kindex set language +To set the language, issue the command @samp{set language @var{lang}}, +where @var{lang} is the name of a language: @code{c} or @code{modula-2}. +For a list of the supported languages, type @samp{set language}. + +Setting the language manually prevents GDB 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 GDB was parsing Modula-2, a +command such as: + +@example +print a = b + c +@end example + +@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. + +If you allow GDB to set the language automatically, then +you can count on expressions evaluating the same way in your debugging +session and in your program. + +@node Automatically, , Manually, Setting +@subsection Having GDB infer the source language + +To have GDB set the working language automatically, use @samp{set +language local} or @samp{set language auto}. GDB then infers the +language that a program was written in by looking at the name of its +source files, and examining their extensions: + +@table @file +@item *.mod +Modula-2 source file + +@item *.c +@itemx *.cc +C or C++ source file. +@end table + +This information is recorded for each function or procedure in a source +file. When your program stops in a frame (usually by encountering a +breakpoint), GDB 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 GDB 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, Checks, Setting, Languages +@section Displaying the language + +The following commands will help you find out which language is the +working language, and also what language source files were written in. + +@kindex show language +@kindex info frame +@kindex info source +@table @code +@item 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 +Among the other information listed here (@pxref{Frame Info, ,Information +about a Frame}) is the source language for this frame. This is the +language that will become the working language if you ever use an +identifier that is in this frame. + +@item info source +Among the other information listed here (@pxref{Symbols, ,Examining the +Symbol Table}) is the source language of this source file. +@end table + +@node Checks, Support, Show, Languages +@section Type and range Checking + +@quotation +@emph{Warning:} In this release, the GDB commands for type and range +checking are included, but they do not yet have any effect. This +section documents the intended facilities. +@end quotation +@c FIXME remove warning when type/range code added + +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. + +GDB can check for conditions like the above if you wish. +Although GDB will not check the statements in your program, it +can check expressions entered directly into GDB for evaluation via +the @code{print} command, for example. As with the working language, +GDB can also decide whether or not to check automatically based on +your program's source language. @xref{Support, ,Supported Languages}, +for the default settings of supported languages. + +@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, Range Checking, Checks, Checks +@subsection An overview of type checking + +Some languages, such as Modula-2, 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, + +@example +1 + 2 @result{} 3 +@exdent but +@error{} 1 + 2.3 +@end example + +The second example fails because the @code{CARDINAL} 1 is not +type-compatible with the @code{REAL} 2.3. + +For expressions you use in GDB commands, you can tell the GDB +type checker to skip checking; to treat any mismatches as errors and +abandon the expression; or only issue warnings when type mismatches +occur, but evaluate the expression anyway. When you choose the last of +these, GDB evaluates expressions like the second example above, but +also issues a warning. + +Even though you may turn type checking off, other type-based reasons may +prevent GDB from evaluating an expression. For instance, GDB 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, such as the one described above, which make +little sense to evaluate anyway. + +Each language defines to what degree it is strict about type. For +instance, both Modula-2 and C require the arguments to arithmetical +operators to be numbers. In C, enumerated types and pointers can be +represented as numbers, so that they are valid arguments to mathematical +operators. @xref{Support, ,Supported Languages}, for further +details on specific languages. + +GDB provides some additional commands for controlling the type checker: + +@kindex set check +@kindex set check type +@kindex show check type +@table @code +@item set check type auto +Set type checking on or off based on the current working language. +@xref{Support, ,Supported Languages}, for the default settings for +each language. + +@item set check type on +@itemx set check type off +Set type checking on or off, overriding the default setting for the +current working language. Issue a warning if the setting does not +match the language's default. If any type mismatches occur in +evaluating an expression while typechecking is on, GDB prints a +message and aborts evaluation of the expression. + +@item set check type warn +Cause the type checker to issue warnings, but to always attempt to +evaluate the expression. Evaluating the expression may still +be impossible for other reasons. For example, GDB cannot add +numbers and structures. + +@item show type +Show the current setting of the type checker, and whether or not GDB is +setting it automatically. +@end table + +@cindex range checking +@cindex checks, range +@node Range Checking, , Type Checking, Checks +@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 GDB commands, you can tell GDB to +ignore range errors; to always treat them as errors and abandon the +expression; or to issue warnings when a range error occurs but evaluate +the expression anyway. + +A range error can result from numerical overflow, from exceeding an +array index bound, or when you type in 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 + +@example +@var{m} + 1 @result{} @var{s} +@end example + +This, too, is specific to individual languages, and in some cases +specific to individual compilers or machines. @xref{Support, , +Supported Languages}, for further details on specific languages. + +GDB provides some additional commands for controlling the range checker: + +@kindex set check +@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{Support, ,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's default. If a range error occurs, then a message +is printed and evaluation of the expression is aborted. + +@item set check range warn +Output messages when the GDB 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 GDB. +@end table + +@node Support, , Checks, Languages +@section Supported Languages + +GDB 4 supports C, C++, and Modula-2. The syntax for C and C++ is so +closely related that GDB does not distinguish the two. Some GDB +features may be used in expressions regardless of the language you +use: the GDB @code{@@} and @code{::} operators, and the +@samp{@{type@}addr} construct (@pxref{Expressions, ,Expressions}) can be +used with the constructs of any of the supported languages. + +The following sections detail to what degree each of these +source languages is supported by GDB. These sections are +not meant to be language tutorials or references, but serve only as a +reference guide to what the GDB expression parser will accept, 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++ +* Modula-2:: Modula-2 +@end menu + +@node C, Modula-2, Support, Support +@subsection C and C++ +@cindex C and C++ + +@cindex expressions in C or C++ +Since C and C++ are so closely related, GDB does not distinguish +between them when interpreting the expressions recognized in GDB +commands. + +@cindex C++ +@kindex g++ +@cindex GNU C++ +The C++ debugging facilities are jointly implemented by the GNU C++ +compiler and GDB. Therefore, to debug your C++ code effectively, +you must compile your C++ programs with the GNU C++ compiler, +@code{g++}. + +@menu +* C Operators:: C and C++ Operators +* C Constants:: C and C++ Constants +* Cplusplus expressions:: C++ Expressions +* C Defaults:: Default settings for C and C++ +* C Checks:: C and C++ Type and Range Checks +* Debugging C:: GDB and C +* Debugging C plus plus:: Special features for C++ +@end menu + +@cindex C and C++ operators +@node C Operators, C Constants, C, C +@subsubsection C and C++ 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++, the +following definitions hold: + +@itemize @bullet +@item +@emph{Integral types} include @code{int} with any of its storage-class +specifiers, @code{char}, and @code{enum}s. + +@item +@emph{Floating-point types} include @code{float} and @code{double}. + +@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 precendence. +@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}. @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 GDB ``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{++}. + +@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, +GDB regards the two as equivalent, choosing whether to dereference a +pointer based on the stored type information. +Defined on @code{struct}s and @code{union}s. + +@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++ scope resolution operator. Defined on +@code{struct}, @code{union}, and @code{class} types. + +@item :: +The GDB scope operator (@pxref{Expressions, ,Expressions}). Same precedence as +@code{::}, above. +@end table + +@cindex C and C++ constants +@node C Constants, Cplusplus expressions, C Operators, C +@subsubsection C and C++ Constants + +GDB allows you to express the constants of C and C++ in the +following ways: + +@itemize @bullet +@item +Integer constants are a sequence of digits. Octal constants are +specified by a leading @samp{0} (ie. 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. + +@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. + +@item +String constants are a sequence of character constants surrounded +by double quotes (@code{"}). + +@item +Pointer constants are an integral value. +@end itemize + +@node Cplusplus expressions, C Defaults, C Constants, C +@subsubsection C++ Expressions + +@cindex expressions in C++ +GDB's expression handling has the following extensions to +interpret a significant subset of C++ expressions: + +@enumerate + +@cindex member functions +@item +Member function calls are allowed; you can use expressions like + +@example +count = aml->GetOriginal(x, y) +@end example + +@kindex this +@cindex namespace in C++ +@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, GDB allows implicit references to the class instance +pointer @code{this} following the same rules as C++. + +@cindex call overloaded functions +@cindex type conversions in C++ +@item +You can call overloaded functions; GDB will resolve the function +call to the right definition, with one restriction---you must use +arguments of the type required by the function that you want to call. +GDB will not perform conversions requiring constructors or +user-defined type operators. + +@cindex reference declarations +@item +GDB understands variables declared as C++ references; you can use them in +expressions just as you do in C++ source---they are automatically +dereferenced. + +In the parameter list shown when GDB 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 +GDB supports the C++ 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}}. GDB also allows +resolving name scope by reference to source files, in both C and C++ +debugging (@pxref{Variables, ,Program Variables}). +@end enumerate + +@node C Defaults, C Checks, Cplusplus expressions, C +@subsubsection C and C++ Defaults +@cindex C and C++ defaults + +If you allow GDB to set type and range checking automatically, they +both default to @code{off} whenever the working language changes to +C/C++. This happens regardless of whether you, or GDB, +selected the working language. + +If you allow GDB to set the language automatically, it sets the +working language to C/C++ on entering code compiled from a source file +whose name ends with @file{.c} or @file{.cc}. +@xref{Automatically, ,Having GDB infer the source language}, for +further details. + +@node C Checks, Debugging C, C Defaults, C +@subsubsection C and C++ Type and Range Checks +@cindex C and C++ checks + +@quotation +@emph{Warning:} in this release, GDB does not yet perform type or +range checking. +@end quotation +@c FIXME remove warning when type/range checks added + +By default, when GDB parses C or C++ expressions, type checking +is not used. However, if you turn type checking on, GDB will +consider two variables type equivalent if: + +@itemize @bullet +@item +The two variables are structured and have the same structure, union, or +enumerated tag. + +@item +Two two variables have the same type name, or types that have been +declared equivalent through @code{typedef}. + +@ignore +@c leaving this out because neither J Gilmore nor R Pesch understand it. +@c FIXME--beers? +@item +The two @code{struct}, @code{union}, or @code{enum} variables are +declared in the same declaration. (Note: this may not be true for all C +compilers.) +@end ignore +@end itemize + +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, Debugging C plus plus, C Checks, C +@subsubsection GDB 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} will also be printed. +Otherwise, it will appear as @samp{@{...@}}. + +The @code{@@} operator aids in the debugging of dynamic arrays, formed +with pointers and a memory allocation function. (@pxref{Expressions, ,Expressions}) + +@node Debugging C plus plus, , Debugging C, C +@subsubsection GDB Commands for C++ + +@cindex commands for C++ +Some GDB commands are particularly useful with C++, and some are +designed specifically for use with C++. 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, +GDB's breakpoint menus help you specify which function definition +you want. @xref{Breakpoint Menus}. + +@cindex overloading in C++ +@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++ exception handling +@item catch @var{exceptions} +@itemx info catch +Debug C++ exception handling using these commands. @xref{Exception +Handling, ,Breakpoints and Exceptions}. + +@cindex inheritance +@item ptype @var{typename} +Print inheritance relationships as well as other information for type +@var{typename}. +@xref{Symbols, ,Examining the Symbol Table}. + +@cindex C++ symbol display +@item set print demangle +@itemx show print demangle +@itemx set print asm-demangle +@itemx show print asm-demangle +Control whether C++ symbols display in their source form, both when +displaying code as C++ 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}. +@end table + +@node Modula-2, , C, Support +@subsection Modula-2 +@cindex Modula-2 + +The extensions made to GDB to support Modula-2 support output +from the 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 will most likely result in an error +as GDB 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 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:: GDB and Modula-2 +@end menu + +@node M2 Operators, Built-In Func/Proc, Modula-2, Modula-2 +@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}s and @code{BITSET}s. + +@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, greater than, 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 GDB 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 conjuction. Defined on boolean types. + +@item @@ +The GDB ``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}s and @code{REAL}s. + +@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}s. Same +precedence as @code{^}. + +@item [] +Array indexing. Defined on @code{ARRAY}s. Same precedence as @code{^}. + +@item () +Procedure argument list. Defined on @code{PROCEDURE}s. Same precedence +as @code{^}. + +@item ::@r{, }. +GDB and Modula-2 scope operators. +@end table + +@quotation +@emph{Warning:} Sets and their operations are not yet supported, so GDB +will treat 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 + +@cindex Modula-2 built-ins +@node Built-In Func/Proc, M2 Constants, M2 Operators, Modula-2 +@subsubsection Built-in Functions and Procedures + +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}. 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}. 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 ASCII value (on machines supporting the +ASCII character set). @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. @var{x} can be a variable or a type. + +@item TRUNC(@var{r}) +Returns the integral part of @var{r}. + +@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 +GDB will treat the use of procedures @code{INCL} and @code{EXCL} as +an error. +@end quotation + +@cindex Modula-2 constants +@node M2 Constants, M2 Defaults, Built-In Func/Proc, Modula-2 +@subsubsection Constants + +GDB 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 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++ 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 Defaults, Deviations, M2 Constants, Modula-2 +@subsubsection Modula-2 Defaults +@cindex Modula-2 defaults + +If type and range checking are set automatically by GDB, they +both default to @code{on} whenever the working language changes to +Modula-2. This happens regardless of whether you, or GDB, +selected the working language. + +If you allow GDB to set the language automatically, then entering +code compiled from a file whose name ends with @file{.mod} will set the +working language to Modula-2. @xref{Automatically, ,Having GDB set +the language automatically}, for further details. + +@node Deviations, M2 Checks, M2 Defaults, Modula-2 +@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. GDB will print 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, M2 Scope, Deviations, Modula-2 +@subsubsection Modula-2 Type and Range Checks +@cindex Modula-2 checks + +@quotation +@emph{Warning:} in this release, GDB does not yet perform type or +range checking. +@end quotation +@c FIXME remove warning when type/range checks added + +GDB 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 +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, GDB/M2, M2 Checks, Modula-2 +@subsubsection The scope operators @code{::} and @code{.} +@cindex scope +@kindex . +@cindex colon, doubled as scope operator +@ifinfo +@kindex colon-colon +@c Info cannot handoe :: but TeX can. +@end ifinfo +@iftex +@kindex :: +@end iftex + +There are a few subtle differences between the Modula-2 scope operator +(@code{.}) and the GDB scope operator (@code{::}). The two have +similar syntax: + +@example + +@var{module} . @var{id} +@var{scope} :: @var{id} +@end example + +@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 GDB search the scope +specified by @var{scope} for the identifier @var{id}. If it is not +found in the specified scope, then GDB will search all scopes +enclosing the one specified by @var{scope}. + +Using the @code{.} operator makes GDB 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, , M2 Scope, Modula-2 +@subsubsection GDB and Modula-2 + +Some GDB 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++: @samp{vtbl}, @samp{demangle}, +@samp{asm-demangle}, @samp{object}, and @samp{union}. The first four +apply to C++, and the last to C's @code{union} type, which has no direct +analogue in Modula-2. + +The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available +while using 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++. However, because an +address can be specified by an integral constant, the construct +@samp{@{@var{type}@}@var{adrexp}} is still useful. (@pxref{Expressions, ,Expressions}) + +@cindex @code{#} in Modula-2 +In GDB scripts, the Modula-2 inequality operator @code{#} is +interpreted as the beginning of a comment. Use @code{<>} instead. + +@node Symbols, Altering, Languages, Top +@chapter Examining the Symbol Table + +The commands described in this section 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. GDB finds it in your +program's symbol table, in the file indicated when you started GDB +(@pxref{File Options, ,Choosing Files}), or by one of the +file-management commands (@pxref{Files, ,Commands to Specify Files}). + +@table @code +@item info address @var{symbol} +@kindex info address +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 variables, and for a stack local variable prints +the exact address of the current instantiation of the variable. + +@item whatis @var{exp} +@kindex whatis +Print the data type of expression @var{exp}. @var{exp} is not +actually evaluated, and any side-effecting operations (such as +assignments or function calls) inside it do not take place. +@xref{Expressions, ,Expressions}. + +@item whatis +Print the data type of @code{$}, the last value in the value history. + +@item ptype @var{typename} +@kindex ptype +Print a description of data type @var{typename}. @var{typename} may be +the name of a type, or for C code it may have the form +@samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or +@samp{enum @var{enum-tag}}. + +@item ptype @var{exp} +@itemx ptype +Print a description of the type of expression @var{exp}. @code{ptype} +differs from @code{whatis} by printing a detailed description, instead +of just the name of the type. For example, if your program declares a +variable as + +@example +struct complex @{double real; double imag;@} v; +@end example + +@noindent +compare the output of the two commands: + +@example +@group +(gdb) whatis v +type = struct complex +(gdb) ptype v +type = struct complex @{ + double real; + double imag; +@} +@end group +@end example + +@noindent +As with @code{whatis}, using @code{ptype} without an argument refers to +the type of @code{$}, the last value in the value history. + +@item info types @var{regexp} +@itemx info types +@kindex info types +Print a brief description of all types whose name matches @var{regexp} +(or all types in your program, if you supply no argument). Each +complete typename is matched as though it were a complete line; thus, +@samp{i type value} gives information on all types in your program whose +name includes the string @code{value}, but @samp{i type ^value$} gives +information only on types whose complete name is @code{value}. + +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 where a type is defined. + +@item info source +@kindex info source +Show the name of the current source file---that is, the source file for +the function containing the current point of execution---and the language +it was written in. + +@item info sources +@kindex 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 functions +@kindex info functions +Print the names and data types of all defined functions. + +@item info functions @var{regexp} +Print the names and data types of all defined functions +whose names contain a match for 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}. + +@item info variables +@kindex info variables +Print the names and data types of all variables that are declared +outside of functions (i.e., excluding local variables). + +@item info variables @var{regexp} +Print the names and data types of all variables (except for local +variables) whose names contain a match for regular expression +@var{regexp}. + +@ignore +This was never implemented. +@item info methods +@itemx info methods @var{regexp} +@kindex info methods +The @code{info methods} command permits the user to examine all defined +methods within C++ program, or (with the @var{regexp} argument) a +specific set of methods found in the various C++ classes. Many +C++ 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 + +@item printsyms @var{filename} +@itemx printpsyms @var{filename} +@kindex printsyms +@cindex symbol dump +@kindex printsyms +@cindex partial symbol dump +Write a dump of debugging symbol data into the file @var{filename}. +These commands are used to debug the GDB symbol-reading code. Only +symbols with debugging data are included. If you use @code{printsyms}, +GDB includes all the symbols for which it has already collected full +details: that is, @var{filename} reflects symbols for only those files +whose symbols GDB has read. You can use the command @code{info +sources} to find out which files these are. If you use +@code{printpsyms}, the dump also shows information about symbols that +GDB only knows partially---that is, symbols defined in files that +GDB has skimmed, but not yet read completely. The description of +@code{symbol-file} describes how GDB reads symbols; both commands +are described under @ref{Files, ,Commands to Specify Files}. +@end table + +@node Altering, GDB Files, Symbols, Top +@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 GDB 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 to its caller. + +@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 +@end menu + +@node Assignment, Jumping, Altering, Altering +@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, + +@example +print x=4 +@end example + +@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 GDB 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, a +program might well have a variable @code{width}---which leads to +an error if we try to set a new value with just @samp{set width=13}, as +we might if @code{set width} did not happen to be a GDB command: + +@example +(gdb) whatis width +type = double +(gdb) p width +$4 = 13 +(gdb) set width=47 +Invalid syntax in expression. +@end example + +@noindent +The invalid expression, of course, is @samp{=47}. What we can do in +order to actually set our program's variable @code{width} is + +@example +(gdb) set var width=47 +@end example + +GDB allows more implicit conversions in assignments than C; you can +freely store an integer value into a pointer variable or vice versa, +and any structure can be converted to any other structure that is the +same length or shorter. +@comment FIXME: how do structs align/pad in these conversions? +@comment /pesch@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 + +@example +set @{int@}0x83040 = 4 +@end example + +@noindent +stores the value 4 into that memory location. + +@node Jumping, Signaling, Assignment, Altering +@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 +@item jump @var{linespec} +@kindex jump +Resume execution at line @var{linespec}. Execution will stop +immediately if there is a breakpoint there. @xref{List, ,Printing +Source Lines}, for a description of the different forms of +@var{linespec}. + +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 line @var{linespec} 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. + +@item jump *@var{address} +Resume execution at the instruction at address @var{address}. +@end table + +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 where it +@emph{will} run when it is continued. For example, + +@example +set $pc = 0x485 +@end example + +@noindent +causes the next @code{continue} command or stepping command to 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. + +@node Signaling, Returning, Jumping, Altering +@c @group +@section Giving your program a Signal + +@table @code +@item signal @var{signalnum} +@kindex signal +Resume execution where your program stopped, but give it immediately the +signal number @var{signalnum}. + +Alternatively, if @var{signalnum} is zero, continue execution without +giving a signal. This is useful when your program stopped on account of +a signal and would ordinary see the signal when resumed with the +@code{continue} command; @samp{signal 0} causes it to resume without a +signal. + +@code{signal} does not repeat when you press @key{RET} a second time +after executing the command. +@end table +@c @end group + +@node Returning, Calling, Signaling, Altering +@section Returning from a Function + +@table @code +@item return +@itemx return @var{expression} +@cindex returning from a function +@kindex return +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}, GDB 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. + +@node Calling, Patching, Returning, Altering +@section Calling your Program's Functions + +@cindex calling functions +@kindex call +@table @code +@item call @var{expr} +Evaluate the expression @var{expr} without displaying @code{void} +returned values. +@end table + +You can use this variant of the @code{print} command if you want to +execute a function from your program, but without cluttering the output +with @code{void} returned values. The result is printed and saved in +the value history, if it is not void. + +@node Patching, , Calling, Altering +@section Patching your Program +@cindex patching binaries +@cindex writing into executables +@cindex writing into corefiles + +By default, GDB 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 +@item set write on +@itemx set write off +@kindex set write +If you specify @samp{set write on}, GDB will open executable and +core files for both reading and writing; if you specify @samp{set write +off} (the default), GDB will open 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 will be opened for +writing as well as reading. +@end table + +@node GDB Files, Targets, Altering, Top +@chapter GDB's Files + +GDB 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, GDB must be told the file name of +the core dump. + +@menu +* Files:: Commands to Specify Files +* Symbol Errors:: Errors Reading Symbol Files +@end menu + +@node Files, Symbol Errors, GDB Files, GDB Files +@section Commands to Specify Files +@cindex core dump file +@cindex symbol table + +The usual way to specify executable and core dump file names is with +the command arguments given when you start GDB, (@pxref{Invocation, +,Getting In and Out of GDB}. + +Occasionally it is necessary to change to a different file during a +GDB session. Or you may run GDB and forget to specify the files you +want to use. In these situations the GDB commands to specify new files +are useful. + +@table @code +@item file @var{filename} +@cindex executable file +@kindex file +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 GDB's working directory, GDB +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 GDB and your program, +using the @code{path} command. + +@item file +@code{file} with no argument makes GDB discard any information it +has on both executable file and the symbol table. + +@item exec-file @r{[} @var{filename} @r{]} +@kindex exec-file +Specify that the program to be run (but not the symbol table) is found +in @var{filename}. GDB will search the environment variable @code{PATH} +if necessary to locate your program. Omitting @var{filename} means to +discard information on the executable file. + +@item symbol-file @r{[} @var{filename} @r{]} +@kindex symbol-file +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. + +@code{symbol-file} with no argument clears out GDB's information on your +program's symbol table. + +The @code{symbol-file} command causes GDB to forget the contents of its +convenience variables, the value history, and all 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 GDB. + +@code{symbol-file} will not repeat if you press @key{RET} again after +executing it once. + +On some kinds of object files, the @code{symbol-file} command does not +actually 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 GDB 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}.) + +When the symbol table is stored in COFF format, @code{symbol-file} does +read the symbol table data in full right away. We have not implemented +the two-stage strategy for COFF yet. + +When GDB is configured for a particular environment, it will +understand debugging information in whatever format is the standard +generated for that environment; you may use either a GNU compiler, or +other compilers that adhere to the local conventions. Best results are +usually obtained from GNU compilers; for example, using @code{gcc} +you can generate debugging information for optimized code. + +@item core-file @r{[} @var{filename} @r{]} +@kindex core +@kindex core-file +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; GDB 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 GDB. 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}). + +@item load @var{filename} +@kindex load +Depending on what remote debugging facilities are configured into +GDB, 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 @var{filename}'s symbol table in GDB, like +the @code{add-symbol-file} command. + +If @code{load} is not available on your GDB, attempting to execute +it gets the error message ``@code{You can't do that when your target is +@dots{}}'' + +On VxWorks, @code{load} will dynamically link @var{filename} on the +current target system as well as adding its symbols in GDB. + +@cindex download to Nindy-960 +With the Nindy interface to an Intel 960 board, @code{load} will +download @var{filename} to the 960 as well as adding its symbols in +GDB. + + +@code{load} will not repeat if you press @key{RET} again after using it. + +@item add-symbol-file @var{filename} @var{address} +@kindex add-symbol-file +@cindex dynamic linking +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. @var{address} should be the memory address at which the +file has been loaded; GDB cannot figure this out for itself. + +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 keeps adding to the old. To discard all old symbol data instead, +use the @code{symbol-file} command. + +@code{add-symbol-file} will not repeat if you press @key{RET} after using it. + +@item info files +@itemx info target +@kindex info files +@kindex info target +@code{info files} and @code{info target} are synonymous; both print +the current targets (@pxref{Targets, ,Specifying a Debugging Target}), +including the names of the executable and core dump files currently in +use by GDB, and the files from which symbols were loaded. The command +@code{help targets} lists all possible targets rather than current +ones. + +@end table + +All file-specifying commands allow both absolute and relative file names +as arguments. GDB always converts the file name to an absolute path +name and remembers it that way. + +@cindex shared libraries + +GDB supports the SunOS shared library format. GDB 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, GDB will not understand references to a +function in a shared library, however---unless you are debugging a core +file). +@c FIXME: next GDB release should permit some refs to undef +@c FIXME...symbols---eg in a break cmd---assuming they are from a shared lib + +@table @code +@item info share +@itemx info sharedlibrary +@kindex info sharedlibrary +@kindex info share +Print the names of the shared libraries which are currently loaded. + +@item sharedlibrary @var{regex} +@itemx share @var{regex} +@kindex sharedlibrary +@kindex share +This is an obsolescent command; you can use it to explicitly +load shared object library symbols for files matching a UNIX regular +expression, but as with files loaded automatically, it will only load +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. +@end table + +@node Symbol Errors, , Files, GDB Files +@section Errors Reading Symbol Files + +While reading a symbol file, GDB will occasionally encounter problems, +such as symbol types it does not recognize, or known bugs in compiler +output. By default, GDB 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 GDB to print +only one message about each such type of problem, no matter how many +times the problem occurs; or you can ask GDB 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, are: + +@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. + +GDB 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. + +GDB does not circumvent this problem, and will have trouble locating +symbols in the source file whose symbols being read. (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. + +GDB 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. + +GDB 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 GDB does not yet +know how to read. @code{0x@var{nn}} is the symbol type of the misunderstood +information, in hexadecimal. + +GDB circumvents the error by ignoring this symbol information. This +will usually allow your program to be debugged, though certain symbols +will not be accessible. If you encounter such a problem and feel like +debugging it, you can debug @code{gdb} 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 +GDB 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++ member function is missing some +information that recent versions of the compiler should have output +for it. + +@item info mismatch between compiler and debugger + +GDB could not parse a type specification output by the compiler. +@end table + +@node Targets, Controlling GDB, GDB Files, Top +@chapter Specifying a Debugging Target +@cindex debugging target +@kindex target + +A @dfn{target} is the execution environment occupied by your program. +Often, GDB 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 GDB 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 GDB +(@pxref{Target Commands, ,Commands for Managing Targets}). + +@menu +* Active Targets:: Active Targets +* Target Commands:: Commands for Managing Targets +* Remote:: Remote Debugging +@end menu + +@node Active Targets, Target Commands, Targets, Targets +@section Active Targets +@cindex stacking targets +@cindex active targets +@cindex multiple targets + +There are three classes of targets: processes, core files, and +executable files. GDB can work concurrently on up to three active +targets, one in each class. This allows you to (for example) start a +process and inspect its activity without abandoning your work on a core +file. + +If, for example, you execute @samp{gdb a.out}, then the executable file +@code{a.out} is the only active target. If you designate a core file as +well---presumably from a prior run that crashed and coredumped---then +GDB has two active targets and will use them in tandem, looking +first in the corefile target, then in the executable file, to satisfy +requests for memory addresses. (Typically, these two classes of target +are complementary, since core files contain only a program's +read-write memory---variables and so on---plus machine status, while +executable files contain only the program text and initialized data.) + +When you type @code{run}, your executable file becomes an active process +target as well. When a process target is active, all GDB commands +requesting memory addresses refer to that target; addresses in an active +core file or executable file target are obscured while the process +target is active. + +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, Remote, Active Targets, Targets +@section Commands for Managing Targets + +@table @code +@item target @var{type} @var{parameters} +Connects the GDB 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 will not repeat if you press @key{RET} again +after executing the command. + +@item help target +@kindex 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. +@end table + +Here are some common targets (available, or not, depending on the GDB +configuration): + +@table @code +@item target exec @var{prog} +@kindex target exec +An executable file. @samp{target exec @var{prog}} is the same as +@samp{exec-file @var{prog}}. + +@item target core @var{filename} +@kindex target core +A core dump file. @samp{target core @var{filename}} is the same as +@samp{core-file @var{filename}}. + +@item target remote @var{dev} +@kindex target remote +Remote serial target in GDB-specific protocol. The argument @var{dev} +specifies what serial device to use for the connection (e.g. +@file{/dev/ttya}). @xref{Remote, ,Remote Debugging}. + +@item target amd-eb @var{dev} @var{speed} @var{PROG} +@kindex target amd-eb +@cindex AMD EB29K +Remote PC-resident AMD EB29K board, attached over serial lines. +@var{dev} is the serial device, as for @code{target remote}; +@var{speed} allows you to specify the linespeed; and @var{PROG} is the +name of the program to be debugged, as it appears to DOS on the PC. +@xref{EB29K Remote, ,GDB with a Remote EB29K}. + +@item target nindy @var{devicename} +@kindex target nindy +An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is +the name of the serial device to use for the connection, e.g. +@file{/dev/ttya}. @xref{i960-Nindy Remote, ,GDB with a Remote i960 (Nindy)}. + +@item target vxworks @var{machinename} +@kindex target vxworks +A VxWorks system, attached via TCP/IP. The argument @var{machinename} +is the target system's machine name or IP address. +@xref{VxWorks Remote, ,GDB and VxWorks}. +@end table + +Different targets are available on different configurations of GDB; your +configuration may have more or fewer targets. + +@node Remote, , Target Commands, Targets +@section Remote Debugging +@cindex remote debugging + +If you are trying to debug a program running on a machine that cannot run +GDB 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 GDB have special serial or TCP/IP interfaces +to make this work with particular debugging targets. In addition, +GDB comes with a generic serial protocol (specific to GDB, but +not specific to any particular target system) which you can use if you +write the remote stubs---the code that will run on the remote system to +communicate with GDB. + +To use the GDB remote serial protocol, the program to be debugged on +the remote machine needs to contain a debugging stub which talks to +GDB over the serial line. Several working remote stubs are +distributed with GDB; see the @file{README} file in the GDB +distribution for more information. + +For details of this communication protocol, see the comments in the +GDB source file @file{remote.c}. + +To start remote debugging, first run GDB and specify as an executable file +the program that is running in the remote machine. This tells GDB how +to find your program's symbols and the contents of its pure text. Then +establish communication using the @code{target remote} command with a device +name as an argument. For example: + +@example +target remote /dev/ttyb +@end example + +@noindent +if the serial line is connected to the device named @file{/dev/ttyb}. This +will stop the remote machine if it is not already stopped. + +Now you can use all the usual commands to examine and change data and to +step and continue the remote program. + +To resume the remote program and stop debugging it, use the @code{detach} +command. + +Other remote targets may be available in your +configuration of GDB; use @code{help targets} to list them. + +@menu +* i960-Nindy Remote:: GDB with a Remote i960 (Nindy) +* EB29K Remote:: GDB with a Remote EB29K +* VxWorks Remote:: GDB and VxWorks + +@end menu +@node i960-Nindy Remote, EB29K Remote, Remote, Remote +@subsection GDB with a Remote i960 (Nindy) + +@cindex Nindy +@cindex i960 +@dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When +GDB is configured to control a remote Intel 960 using Nindy, you can +tell GDB how to connect to the 960 in several ways: + +@itemize @bullet +@item +Through command line options specifying serial port, version of the +Nindy protocol, and communications speed; + +@item +By responding to a prompt on startup; + +@item +By using the @code{target} command at any point during your GDB +session. @xref{Target Commands, ,Commands for Managing Targets}. + +@end itemize + +@menu +* Nindy Startup:: Startup with Nindy +* Nindy Options:: Options for Nindy +* Nindy reset:: Nindy Reset Command +@end menu + +@node Nindy Startup, Nindy Options, i960-Nindy Remote, i960-Nindy Remote +@subsubsection Startup with Nindy + +If you simply start @code{gdb} without using any command-line +options, you are prompted for what serial port to use, @emph{before} you +reach the ordinary GDB prompt: + +@example +Attach /dev/ttyNN -- specify NN, or "quit" to quit: +@end example + +@noindent +Respond to the prompt with whatever suffix (after @samp{/dev/tty}) +identifies the serial port you want to use. You can, if you choose, +simply start up with no Nindy connection by responding to the prompt +with an empty line. If you do this, and later wish to attach to Nindy, +use @code{target} (@pxref{Target Commands, ,Commands for Managing Targets}). + +@node Nindy Options, Nindy reset, Nindy Startup, i960-Nindy Remote +@subsubsection Options for Nindy + +These are the startup options for beginning your GDB session with a +Nindy-960 board attached: + +@table @code +@item -r @var{port} +Specify the serial port name of a serial interface to be used to connect +to the target system. This option is only available when GDB is +configured for the Intel 960 target architecture. You may specify +@var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a +device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique +suffix for a specific @code{tty} (e.g. @samp{-r a}). + +@item -O +(An uppercase letter ``O'', not a zero.) Specify that GDB should use +the ``old'' Nindy monitor protocol to connect to the target system. +This option is only available when GDB is configured for the Intel 960 +target architecture. + +@quotation +@emph{Warning:} if you specify @samp{-O}, but are actually trying to +connect to a target system that expects the newer protocol, the connection +will fail, appearing to be a speed mismatch. GDB will repeatedly +attempt to reconnect at several different line speeds. You can abort +this process with an interrupt. +@end quotation + +@item -brk +Specify that GDB should first send a @code{BREAK} signal to the target +system, in an attempt to reset it, before connecting to a Nindy target. + +@quotation +@emph{Warning:} Many target systems do not have the hardware that this +requires; it only works with a few boards. +@end quotation +@end table + +The standard @samp{-b} option controls the line speed used on the serial +port. + +@c @group +@node Nindy reset, , Nindy Options, i960-Nindy Remote +@subsubsection Nindy Reset Command + +@table @code +@item reset +@kindex reset +For a Nindy target, this command sends a ``break'' to the remote target +system; this is only useful if the target has been equipped with a +circuit to perform a hard reset (or some other interesting action) when +a break is detected. +@end table +@c @end group + +@node EB29K Remote, VxWorks Remote, i960-Nindy Remote, Remote +@subsection GDB with a Remote EB29K + +@cindex EB29K board +@cindex running 29K programs + +To use GDB from a Unix system to run programs on AMD's EB29K +board in a PC, you must first connect a serial cable between the PC +and a serial port on the Unix system. In the following, we assume +you've hooked the cable between the PC's @file{COM1} port and +@file{/dev/ttya} on the Unix system. + +@menu +* Comms (EB29K):: Communications Setup +* gdb-EB29K:: EB29K cross-debugging +* Remote Log:: Remote Log +@end menu + +@node Comms (EB29K), gdb-EB29K, EB29K Remote, EB29K Remote +@subsubsection Communications Setup + +The next step is to set up the PC's port, by doing something like the +following in DOS on the PC: + +@example +C:\> MODE com1:9600,n,8,1,none +@end example + +@noindent +This example---run on an MS DOS 4.0 system---sets the PC port to 9600 +bps, no parity, eight data bits, one stop bit, and no ``retry'' action; +you must match the communications parameters when establishing the Unix +end of the connection as well. +@c FIXME: Who knows what this "no retry action" crud from the DOS manual may +@c mean? It's optional; leave it out? ---pesch@cygnus.com, 25feb91 + +To give control of the PC to the Unix side of the serial line, type +the following at the DOS console: + +@example +C:\> CTTY com1 +@end example + +@noindent +(Later, if you wish to return control to the DOS console, you can use +the command @code{CTTY con}---but you must send it over the device that +had control, in our example over the @file{COM1} serial line). + +From the Unix host, use a communications program such as @code{tip} or +@code{cu} to communicate with the PC; for example, + +@example +cu -s 9600 -l /dev/ttya +@end example + +@noindent +The @code{cu} options shown specify, respectively, the linespeed and the +serial port to use. If you use @code{tip} instead, your command line +may look something like the following: + +@example +tip -9600 /dev/ttya +@end example + +@noindent +Your system may define a different name where our example uses +@file{/dev/ttya} as the argument to @code{tip}. The communications +parameters, including which port to use, are associated with the +@code{tip} argument in the ``remote'' descriptions file---normally the +system table @file{/etc/remote}. +@c FIXME: What if anything needs doing to match the "n,8,1,none" part of +@c the DOS side's comms setup? cu can support -o (odd +@c parity), -e (even parity)---apparently no settings for no parity or +@c for character size. Taken from stty maybe...? John points out tip +@c can set these as internal variables, eg ~s parity=none; man stty +@c suggests that it *might* work to stty these options with stdin or +@c stdout redirected... ---pesch@cygnus.com, 25feb91 + +@kindex EBMON +Using the @code{tip} or @code{cu} connection, change the DOS working +directory to the directory containing a copy of your 29K program, then +start the PC program @code{EBMON} (an EB29K control program supplied +with your board by AMD). You should see an initial display from +@code{EBMON} similar to the one that follows, ending with the +@code{EBMON} prompt @samp{#}--- + +@example +C:\> G: + +G:\> CD \usr\joe\work29k + +G:\USR\JOE\WORK29K> EBMON +Am29000 PC Coprocessor Board Monitor, version 3.0-18 +Copyright 1990 Advanced Micro Devices, Inc. +Written by Gibbons and Associates, Inc. + +Enter '?' or 'H' for help + +PC Coprocessor Type = EB29K +I/O Base = 0x208 +Memory Base = 0xd0000 + +Data Memory Size = 2048KB +Available I-RAM Range = 0x8000 to 0x1fffff +Available D-RAM Range = 0x80002000 to 0x801fffff + +PageSize = 0x400 +Register Stack Size = 0x800 +Memory Stack Size = 0x1800 + +CPU PRL = 0x3 +Am29027 Available = No +Byte Write Available = Yes + +# ~. +@end example + +Then exit the @code{cu} or @code{tip} program (done in the example by +typing @code{~.} at the @code{EBMON} prompt). @code{EBMON} will keep +running, ready for GDB to take over. + +For this example, we've assumed what is probably the most convenient +way to make sure the same 29K program is on both the PC and the Unix +system: a PC/NFS connection that establishes ``drive @code{G:}'' on the +PC as a file system on the Unix host. If you do not have PC/NFS or +something similar connecting the two systems, you must arrange some +other way---perhaps floppy-disk transfer---of getting the 29K program +from the Unix system to the PC; GDB will @emph{not} download it over the +serial line. + +@node gdb-EB29K, Remote Log, Comms (EB29K), EB29K Remote +@subsubsection EB29K cross-debugging + +Finally, @code{cd} to the directory containing an image of your 29K +program on the Unix system, and start GDB---specifying as argument the +name of your 29K program: + +@example +cd /usr/joe/work29k +gdb myfoo +@end example + +Now you can use the @code{target} command: + +@example +target amd-eb /dev/ttya 9600 MYFOO +@c FIXME: test above 'target amd-eb' as spelled, with caps! caps are meant to +@c emphasize that this is the name as seen by DOS (since I think DOS is +@c single-minded about case of letters). ---pesch@cygnus.com, 25feb91 +@end example + +@noindent +In this example, we've assumed your program is in a file called +@file{myfoo}. Note that the filename given as the last argument to +@code{target amd-eb} should be the name of the program as it appears to DOS. +In our example this is simply @code{MYFOO}, but in general it can include +a DOS path, and depending on your transfer mechanism may not resemble +the name on the Unix side. + +At this point, you can set any breakpoints you wish; when you are ready +to see your program run on the 29K board, use the GDB command +@code{run}. + +To stop debugging the remote program, use the GDB @code{detach} +command. + +To return control of the PC to its console, use @code{tip} or @code{cu} +once again, after your GDB session has concluded, to attach to +@code{EBMON}. You can then type the command @code{q} to shut down +@code{EBMON}, returning control to the DOS command-line interpreter. +Type @code{CTTY con} to return command input to the main DOS console, +and type @kbd{~.} to leave @code{tip} or @code{cu}. + +@node Remote Log, , gdb-EB29K, EB29K Remote +@subsubsection Remote Log +@kindex eb.log +@cindex log file for EB29K + +The @code{target amd-eb} command creates a file @file{eb.log} in the +current working directory, to help debug problems with the connection. +@file{eb.log} records all the output from @code{EBMON}, including echoes +of the commands sent to it. Running @samp{tail -f} on this file in +another window often helps to understand trouble with @code{EBMON}, or +unexpected events on the PC side of the connection. + +@node VxWorks Remote, , EB29K Remote, Remote +@subsection GDB and VxWorks +@cindex VxWorks + +GDB enables developers to spawn and debug tasks running on networked +VxWorks targets from a Unix host. Already-running tasks spawned from +the VxWorks shell can also be debugged. GDB uses code that runs on +both the UNIX host and on the VxWorks target. The program +@code{gdb} is installed and executed on the UNIX host. + +The following information on connecting to VxWorks was current when +this manual was produced; newer releases of VxWorks may use revised +procedures. + +The remote debugging interface (RDB) routines are installed and executed +on the VxWorks target. These routines are included in the VxWorks library +@file{rdb.a} and are incorporated into the system image when source-level +debugging is enabled in the VxWorks configuration. + +@kindex INCLUDE_RDB +If you wish, you can define @code{INCLUDE_RDB} in the VxWorks +configuration file @file{configAll.h} to include the RDB interface +routines and spawn the source debugging task @code{tRdbTask} when +VxWorks is booted. For more information on configuring and remaking +VxWorks, see the manufacturer's manual. + +Once you have included the RDB interface in your VxWorks system image +and set your Unix execution search path to find GDB, you are ready +to run GDB. From your UNIX host, type: + +@smallexample +% gdb +@end smallexample + +GDB will come up showing the prompt: + +@smallexample +(gdb) +@end smallexample + +@menu +* VxWorks connection:: Connecting to VxWorks +* VxWorks download:: VxWorks Download +* VxWorks attach:: Running Tasks +@end menu + +@node VxWorks connection, VxWorks download, VxWorks Remote, VxWorks Remote +@subsubsection Connecting to VxWorks + +The GDB command @code{target} lets you connect to a VxWorks target on the +network. To connect to a target whose host name is ``@code{tt}'', type: + +@smallexample +(gdb) target vxworks tt +@end smallexample + +GDB will display a message similar to the following: + +@smallexample +Attaching remote machine across net... Success! +@end smallexample + +GDB will then attempt to read the symbol tables of any object modules +loaded into the VxWorks target since it was last booted. GDB locates +these files by searching the directories listed in the command search +path (@pxref{Environment, ,Your Program's Environment}); if it fails +to find an object file, it will display a message such as: + +@smallexample +prog.o: No such file or directory. +@end smallexample + +This will cause the @code{target} command to abort. When this happens, +you should add the appropriate directory to the search path, with the +GDB command @code{path}, and execute the @code{target} command +again. + +@node VxWorks download, VxWorks attach, VxWorks connection, VxWorks Remote +@subsubsection VxWorks Download + +@cindex download to VxWorks +If you have connected to the VxWorks target and you want to debug an +object that has not yet been loaded, you can use the GDB @code{load} +command to download a file from UNIX to VxWorks incrementally. The +object file given as an argument to the @code{load} command is actually +opened twice: first by the VxWorks target in order to download the code, +then by GDB in order to read the symbol table. This can lead to +problems if the current working directories on the two systems differ. +It is simplest to set the working directory on both systems to the +directory in which the object file resides, and then to reference the +file by its name, without any path. Thus, to load a program +@file{prog.o}, residing in @file{wherever/vw/demo/rdb}, on VxWorks type: + +@smallexample +-> cd "wherever/vw/demo/rdb" +@end smallexample + +On GDB type: + +@smallexample +(gdb) cd wherever/vw/demo/rdb +(gdb) load prog.o +@end smallexample + +GDB will display a response similar to the following: + +@smallexample +Reading symbol data from wherever/vw/demo/rdb/prog.o... done. +@end smallexample + +You can also use the @code{load} command to reload an object module +after editing and recompiling the corresponding source file. Note that +this will cause GDB to delete all currently-defined breakpoints, +auto-displays, and convenience variables, and to clear the value +history. (This is necessary in order to preserve the integrity of +debugger data structures that reference the target system's symbol +table.) + +@node VxWorks attach, , VxWorks download, VxWorks Remote +@subsubsection Running Tasks + +@cindex running VxWorks tasks +You can also attach to an existing task using the @code{attach} command as +follows: + +@smallexample +(gdb) attach @var{task} +@end smallexample + +@noindent +where @var{task} is the VxWorks hexadecimal task ID. The task can be running +or suspended when you attach to it. If running, it will be suspended at +the time of attachment. + + +@node Controlling GDB, Sequences, Targets, Top +@chapter Controlling GDB + +You can alter many aspects of GDB's interaction with you by using +the @code{set} command. For commands controlling how GDB displays +data, @pxref{Print Settings, ,Print Settings}; other settings are described here. + +@menu +* Prompt:: Prompt +* Editing:: Command Editing +* History:: Command History +* Screen Size:: Screen Size +* Numbers:: Numbers +* Messages/Warnings:: Optional Warnings and Messages +@end menu + +@node Prompt, Editing, Controlling GDB, Controlling GDB +@section Prompt +@cindex prompt + +GDB indicates its readiness to read a command by printing a string +called the @dfn{prompt}. This string is normally @samp{(gdb)}. You +can change the prompt string with the @code{set prompt} command. For +instance, when debugging GDB with GDB, it is useful to change +the prompt in one of the GDBs so that you can always tell which +one you are talking to. + +@table @code +@item set prompt @var{newprompt} +@kindex set prompt +Directs GDB 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 + +@node Editing, History, Prompt, Controlling GDB +@section Command Editing +@cindex readline +@cindex command line editing + +GDB reads its input commands via the @dfn{readline} interface. This +GNU library provides consistent behavior for programs which provide a +command line interface to the user. Advantages are @code{emacs}-style +or @code{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 GDB 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 + +@node History, Screen Size, Editing, Controlling GDB +@section Command History + +@table @code +@cindex history substitution +@cindex history file +@kindex set history filename +@item set history filename @var{fname} +Set the name of the GDB command history file to @var{fname}. This is +the file from which GDB will read an initial command history +list or to which it will write this list when it exits. This list is +accessed 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} if this variable is not set. + +@cindex history save +@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. + +@item set history save off +Stop recording command history in a file. + +@cindex history size +@kindex set history size +@item set history size @var{size} +Set the number of commands which GDB will keep in its history list. +This defaults to the value of the environment variable +@code{HISTSIZE}, or to 256 if this variable is not set. +@end table + +@cindex history expansion +History expansion assigns special meaning to the character @kbd{!}. +@iftex +@xref{Event Designators}. +@end iftex +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 will not attempt substitution on the strings +@kbd{!=} and @kbd{!(}, even when history expansion is enabled. + +The commands to control history expansion are: + +@table @code + +@kindex set history expansion +@item set history expansion on +@itemx set history expansion +Enable history expansion. History expansion is off by default. + +@item set history expansion off +Disable history expansion. + +The readline code comes with more complete documentation of +editing and history expansion features. Users unfamiliar with @code{emacs} +or @code{vi} may wish to read it. +@iftex +@xref{Command Line Editing}. +@end iftex + +@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 GDB history parameters. +@code{show history} by itself displays all four states. +@c @end group +@end table + +@table @code +@kindex show commands +@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, Numbers, History, Controlling GDB +@section Screen Size +@cindex size of screen +@cindex pauses in output + +Certain commands to GDB may produce large amounts of information +output to the screen. To help you read all of it, GDB pauses and +asks you for input at the end of each page of output. Type @key{RET} +when you want to continue the output. GDB also uses the screen +width setting to determine when to wrap lines of output. Depending on +what is being printed, it tries to break the line at a readable place, +rather than simply letting it overflow onto the following line. + +Normally GDB knows the size of the screen from 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 +@item set height @var{lpp} +@itemx show height +@itemx set width @var{cpl} +@itemx show width +@kindex set height +@kindex set width +@kindex show width +@kindex show height +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 zero lines, GDB will 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. +@end table + +@node Numbers, Messages/Warnings, Screen Size, Controlling GDB +@section Numbers +@cindex number representation +@cindex entering numbers + +You can always enter numbers in octal, decimal, or hexadecimal in GDB by +the usual conventions: octal numbers begin with @samp{0}, decimal +numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}. +Numbers that begin with none of these 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 @code{set radix} command. + +@table @code +@kindex set radix +@item set radix @var{base} +Set the default base for numeric input and display. Supported choices +for @var{base} are decimal 2, 8, 10, 16. @var{base} must itself be +specified either unambiguously or using the current default radix; for +example, any of + +@example +set radix 1010 +set radix 012 +set radix 10. +set radix 0xa +@end example + +@noindent +will set the base to decimal. On the other hand, @samp{set radix 10} +will leave the radix unchanged no matter what it was. + +@kindex show radix +@item show radix +Display the current default base for numeric input and display. +@end table + +@node Messages/Warnings, , Numbers, Controlling GDB +@section Optional Warnings and Messages + +By default, GDB is silent about its inner workings. If you are running +on a slow machine, you may want to use the @code{set verbose} command. +It will make GDB 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 +(@pxref{Files, ,Commands to Specify Files}, in the description of the +command @code{symbol-file}). +@c The following is the right way to do it, but emacs 18.55 does not support +@c @ref, and neither the emacs lisp manual version of texinfmt or makeinfo +@c is released. +@ignore +see @code{symbol-file} in @ref{Files, ,Commands to Specify Files}). +@end ignore + +@table @code +@kindex set verbose +@item set verbose on +Enables GDB's output of certain informational messages. + +@item set verbose off +Disables GDB's 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 GDB 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 GDB 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 GDB is permitted to produce. +@end table + +By default, GDB is cautious, and asks what sometimes seem to be a +lot of stupid questions to confirm certain commands. For example, if +you try to run a program which is already running: + +@example +(gdb) run +The program being debugged has been started already. +Start it from the beginning? (y or n) +@end example + +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. + +@item set confirm on +Enables confirmation requests (the default). + +@item show confirm +@kindex show confirm +Displays state of confirmation requests. +@end table + +@c FIXME this does not really belong here. But where *does* it belong? +@cindex reloading symbols +Some systems allow individual object files that make up your program to +be replaced without stopping and restarting your program. +For example, in VxWorks you can simply recompile a defective object file +and keep on running. +If you are running on one of these systems, you can allow GDB to +reload the symbols for automatically relinked modules: + +@table @code +@kindex set symbol-reloading +@item set symbol-reloading on +Replace symbol definitions for the corresponding source file when an +object file with a particular name is seen again. + +@item set symbol-reloading off +Do not replace symbol definitions when re-encountering object files of +the same name. This is the default state; if you are not running on a +system that permits automatically relinking modules, you should leave +@code{symbol-reloading} off, since otherwise GDB may discard symbols +when linking large programs, that may contain several modules (from +different directories or libraries) with the same name. + +@item show symbol-reloading +Show the current @code{on} or @code{off} setting. +@end table + +@node Sequences, Emacs, Controlling GDB, Top +@chapter Canned Sequences of Commands + +Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint +Command Lists}), GDB provides two ways to store sequences of commands +for execution as a unit: user-defined commands and command files. + +@menu +* Define:: User-Defined Commands +* Command Files:: Command Files +* Output:: Commands for Controlled Output +@end menu + +@node Define, Command Files, Sequences, Sequences +@section User-Defined Commands + +@cindex user-defined command +A @dfn{user-defined command} is a sequence of GDB commands to which you +assign a new name as a command. This is done with the @code{define} +command. + +@table @code +@item define @var{commandname} +@kindex define +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 definition of the command is made up of other GDB command lines, +which are given following the @code{define} command. The end of these +commands is marked by a line containing @code{end}. + +@item document @var{commandname} +@kindex document +Give documentation to the user-defined command @var{commandname}. 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} will print +the documentation you have specified. + +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. + +@item help user-defined +@kindex help user-defined +List all user-defined commands, with the first line of the documentation +(if any) for each. + +@item info user +@itemx info user @var{commandname} +@kindex info user +Display the GDB commands used to define @var{commandname} (but not its +documentation). If no @var{commandname} is given, display the +definitions for all user-defined commands. +@end table + +User-defined commands do not take arguments. When they are executed, the +commands of the definition are not printed. An error in any command +stops execution of the user-defined command. + +Commands that would ask for confirmation if used interactively proceed +without asking when used inside a user-defined command. Many GDB commands +that normally print messages to say what they are doing omit the messages +when used in a user-defined command. + +@node Command Files, Output, Define, Sequences +@section Command Files + +@cindex command files +A command file for GDB is a file of lines that are GDB 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. + +@cindex init file +@cindex @file{.gdbinit} +When you start GDB, it automatically executes commands from its +@dfn{init files}. These are files named @file{.gdbinit}. GDB reads +the init file (if any) in your home directory and then the init file +(if any) in the current working directory. (The init files are not +executed if you use the @samp{-nx} option; @pxref{Mode Options, +,Choosing Modes}.) You can also request the execution of a command +file with the @code{source} command: + +@table @code +@item source @var{filename} +@kindex source +Execute the command file @var{filename}. +@end table + +The lines in a command file are executed sequentially. They are not +printed as they are executed. An error in any command terminates execution +of the command file. + +Commands that would ask for confirmation if used interactively proceed +without asking when used in a command file. Many GDB commands that +normally print messages to say what they are doing omit the messages +when called from command files. + +@node Output, , Command Files, Sequences +@section Commands for Controlled Output + +During the execution of a command file or a user-defined command, normal +GDB 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 +@item echo @var{text} +@kindex echo +@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 will be 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 outputting 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, + +@example +echo This is some text\n\ +which is continued\n\ +onto several lines.\n +@end example + +produces the same output as + +@example +echo This is some text\n +echo which is continued\n +echo onto several lines.\n +@end example + +@item output @var{expression} +@kindex output +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}; @pxref{Output formats}, for more +information. + +@item printf @var{string}, @var{expressions}@dots{} +@kindex printf +Print the values of the @var{expressions} under the control of +@var{string}. The @var{expressions} are separated by commas and may +be either numbers or pointers. Their values are printed as specified +by @var{string}, exactly as if your program were to execute + +@example +printf (@var{string}, @var{expressions}@dots{}); +@end example + +For example, you can print two values in hex like this: + +@example +printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo +@end example + +The only backslash-escape sequences that you can use in the format +string are the simple ones that consist of backslash followed by a +letter. +@end table + +@node Emacs, GDB Bugs, Sequences, Top +@chapter Using GDB under GNU Emacs + +@cindex emacs +A special interface allows you to use GNU Emacs to view (and +edit) the source files for the program you are debugging with +GDB. + +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 +GDB as a subprocess of Emacs, with input and output through a newly +created Emacs buffer. + +Using GDB under Emacs is just like using GDB normally except for two +things: + +@itemize @bullet +@item +All ``terminal'' input and output goes through the Emacs buffer. +@end itemize + +This applies both to GDB 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. + +@itemize @bullet +@item +GDB displays source code through Emacs. +@end itemize + +Each time GDB 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 window to show both your GDB session +and the source. + +Explicit GDB @code{list} or search commands still produce output as +usual, but you probably will have no reason to use them. + +@quotation +@emph{Warning:} If the directory where your program resides is not your +current directory, it can be easy to confuse Emacs about the location of +the source files, in which case the auxiliary display buffer will not +appear to show your source. GDB can find programs by searching your +environment's @code{PATH} variable, so the GDB input and output +session will proceed normally; but Emacs does not get enough information +back from GDB to locate the source files in this situation. To +avoid this problem, either start GDB mode from the directory where +your program resides, or specify a full path name when prompted for the +@kbd{M-x gdb} argument. + +A similar confusion can result if you use the GDB @code{file} command to +switch to debugging a program in some other location, from an existing +GDB buffer in Emacs. +@end quotation + +By default, @kbd{M-x gdb} calls the program called @file{gdb}. If +you need to call GDB by a different name (for example, if you keep +several configurations around, with different names) you can set the +Emacs variable @code{gdb-command-name}; for example, + +@example +(setq gdb-command-name "mygdb") +@end example + +@noindent +(preceded by @kbd{ESC ESC}, or typed in the @code{*scratch*} buffer, or +in your @file{.emacs} file) will make Emacs call the program named +``@code{mygdb}'' instead. + +In the GDB I/O 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' GDB Mode. + +@item M-s +Execute to another source line, like the GDB @code{step} command; also +update the display window to show the current file and location. + +@item M-n +Execute to next source line in this function, skipping all function +calls, like the GDB @code{next} command. Then update the display window +to show the current file and location. + +@item M-i +Execute one instruction, like the GDB @code{stepi} command; update +display window accordingly. + +@item M-x gdb-nexti +Execute to next instruction, using the GDB @code{nexti} command; update +display window accordingly. + +@item C-c C-f +Execute until exit from the selected stack frame, like the GDB +@code{finish} command. + +@item M-c +Continue execution of your program, like the GDB @code{continue} +command. + +@emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}. + +@item M-u +Go up the number of frames indicated by the numeric argument +(@pxref{Arguments, , Numeric Arguments, emacs, The GNU Emacs Manual}), +like the GDB @code{up} command. + +@emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}. + +@item M-d +Go down the number of frames indicated by the numeric argument, like the +GDB @code{down} command. + +@emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}. + +@item C-x & +Read the number where the cursor is positioned, and insert it at the end +of the GDB I/O buffer. For example, if you wish to disassemble code +around an address that was displayed earlier, type @kbd{disassemble}; +then move the cursor to the address display, and pick up the +argument for @code{disassemble} by typing @kbd{C-x &}. + +You can customize this further on the fly by defining elements of the list +@code{gdb-print-command}; once it is defined, you can format or +otherwise process numbers picked up by @kbd{C-x &} before they are +inserted. A numeric argument to @kbd{C-x &} will both indicate that you +wish special formatting, and act as an index to pick an element of the +list. If the list element is a string, the number to be inserted is +formatted using the Emacs function @code{format}; otherwise the number +is passed as an argument to the corresponding list element. +@end table + +In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break}) +tells GDB to set a breakpoint on the source line point is on. + +If you accidentally delete the source-display buffer, an easy way to get +it back is to type the command @code{f} in the GDB buffer, to +request a frame display; when you run under Emacs, this will recreate +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 GDB +communicates with Emacs in terms of line numbers. If you add or +delete lines from the text, the line numbers that GDB knows will cease +to correspond properly to the code. + +@c The following dropped because Epoch is nonstandard. Reactivate +@c if/when v19 does something similar. ---pesch@cygnus.com 19dec1990 +@ignore +@kindex emacs epoch environment +@kindex epoch +@kindex inspect + +Version 18 of Emacs has a built-in window system called the @code{epoch} +environment. Users of this environment can use a new command, +@code{inspect} which performs identically to @code{print} except that +each value is printed in its own window. +@end ignore + +@node GDB Bugs, Renamed Commands, Emacs, Top +@chapter Reporting Bugs in GDB +@cindex Bugs in GDB +@cindex Reporting Bugs in GDB + +Your bug reports play an essential role in making GDB 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 GDB work better. Bug +reports are your contribution to the maintenance of GDB. + +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, Bug Reporting, GDB Bugs, GDB Bugs +@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 +@item +@cindex Fatal Signal +@cindex Core Dump +If the debugger gets a fatal signal, for any input whatever, that is a +GDB bug. Reliable debuggers never crash. + +@item +@cindex error on Valid Input +If GDB produces an error message for valid input, that is a bug. + +@item +@cindex Invalid Input +If GDB 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 GDB are welcome in any case. +@end itemize + +@node Bug Reporting, , Bug Criteria, GDB Bugs +@section How to Report Bugs +@cindex Bug Reports +@cindex GDB Bugs, Reporting + +A number of companies and individuals offer support for GNU products. +If you obtained GDB from a support organization, we recommend you +contact that organization first. + +Contact information for many support companies and individuals is +available in the file @file{etc/SERVICE} in the GNU Emacs distribution. + +In any event, we also recommend that you send bug reports for GDB to one +of these addresses: + +@example +bug-gdb@@prep.ai.mit.edu +@{ucbvax|mit-eddie|uunet@}!prep.ai.mit.edu!bug-gdb +@end example + +@strong{Do not send bug reports to @samp{info-gdb}, or to +@samp{help-gdb}, or to any newsgroups.} Most users of GDB 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. + +As a last resort, send bug reports on paper to: + +@example +GNU Debugger Bugs +Free Software Foundation +545 Tech Square +Cambridge, MA 02139 +@end example + +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 if it is new to us. It is not as important as what happens if +the bug is already known. Therefore, always write your bug reports on +the assumption that the bug has not been reported previously. + +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 GDB. GDB 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 GDB. + +@item +The type of machine you are using, and the operating system name and +version number. + +@item +What compiler (and its version) was used to compile GDB---e.g. +``gcc-2.0''. + +@item +What compiler (and its version) was used to compile the program you +are debugging---e.g. ``gcc-2.0''. + +@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 GDB 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. We are human, after all. 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 GDB 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. + +@item +If you wish to suggest changes to the GDB source, send us context +diffs. If you even discuss something in the GDB 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, etc. + +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 GDB 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 Note: no need to update nodes for rdl-apps.texi since it appears +@c *only* in the TeX version of the manual. +@c Note: eventually, make a cross reference to the readline Info nodes. +@iftex +@c appendices describing GNU readline. Distributed with readline code. +@include rluser.texinfo +@include inc-hist.texi +@end iftex + +@node Renamed Commands, Installing GDB, GDB Bugs, Top +@appendix Renamed Commands + +The following commands were renamed in GDB 4, in order to make the +command set as a whole more consistent and easier to use and remember: + +@kindex add-syms +@kindex delete environment +@kindex info copying +@kindex info convenience +@kindex info directories +@kindex info editing +@kindex info history +@kindex info targets +@kindex info values +@kindex info version +@kindex info warranty +@kindex set addressprint +@kindex set arrayprint +@kindex set prettyprint +@kindex set screen-height +@kindex set screen-width +@kindex set unionprint +@kindex set vtblprint +@kindex set demangle +@kindex set asm-demangle +@kindex set sevenbit-strings +@kindex set array-max +@kindex set caution +@kindex set history write +@kindex show addressprint +@kindex show arrayprint +@kindex show prettyprint +@kindex show screen-height +@kindex show screen-width +@kindex show unionprint +@kindex show vtblprint +@kindex show demangle +@kindex show asm-demangle +@kindex show sevenbit-strings +@kindex show array-max +@kindex show caution +@kindex show history write +@kindex unset + +@c TEXI2ROFF-KILL +@ifinfo +@c END TEXI2ROFF-KILL +@example +OLD COMMAND NEW COMMAND +@c TEXI2ROFF-KILL +--------------- ------------------------------- +@c END TEXI2ROFF-KILL +add-syms add-symbol-file +delete environment unset environment +info convenience show convenience +info copying show copying +info directories show directories +info editing show commands +info history show values +info targets help target +info values show values +info version show version +info warranty show warranty +set/show addressprint set/show print address +set/show array-max set/show print elements +set/show arrayprint set/show print array +set/show asm-demangle set/show print asm-demangle +set/show caution set/show confirm +set/show demangle set/show print demangle +set/show history write set/show history save +set/show prettyprint set/show print pretty +set/show screen-height set/show height +set/show screen-width set/show width +set/show sevenbit-strings set/show print sevenbit-strings +set/show unionprint set/show print union +set/show vtblprint set/show print vtbl + +unset [No longer an alias for delete] +@end example +@c TEXI2ROFF-KILL +@end ifinfo + +@tex +\vskip \parskip\vskip \baselineskip +\halign{\tt #\hfil &\qquad#&\tt #\hfil\cr +{\bf Old Command} &&{\bf New Command}\cr +add-syms &&add-symbol-file\cr +delete environment &&unset environment\cr +info convenience &&show convenience\cr +info copying &&show copying\cr +info directories &&show directories \cr +info editing &&show commands\cr +info history &&show values\cr +info targets &&help target\cr +info values &&show values\cr +info version &&show version\cr +info warranty &&show warranty\cr +set{\rm / }show addressprint &&set{\rm / }show print address\cr +set{\rm / }show array-max &&set{\rm / }show print elements\cr +set{\rm / }show arrayprint &&set{\rm / }show print array\cr +set{\rm / }show asm-demangle &&set{\rm / }show print asm-demangle\cr +set{\rm / }show caution &&set{\rm / }show confirm\cr +set{\rm / }show demangle &&set{\rm / }show print demangle\cr +set{\rm / }show history write &&set{\rm / }show history save\cr +set{\rm / }show prettyprint &&set{\rm / }show print pretty\cr +set{\rm / }show screen-height &&set{\rm / }show height\cr +set{\rm / }show screen-width &&set{\rm / }show width\cr +set{\rm / }show sevenbit-strings &&set{\rm / }show print sevenbit-strings\cr +set{\rm / }show unionprint &&set{\rm / }show print union\cr +set{\rm / }show vtblprint &&set{\rm / }show print vtbl\cr +\cr +unset &&\rm(No longer an alias for delete)\cr +} +@end tex +@c END TEXI2ROFF-KILL + +@node Installing GDB, Copying, Renamed Commands, Top +@appendix Installing GDB +@cindex configuring GDB +@cindex installation + +@iftex +@c irrelevant in info file; it's as current as the code it lives with. +@quotation +@emph{Warning:} These installation instructions are current as of +GDB version 4.4.4. If you're installing a more recent release +of GDB, we may have improved the installation procedures since +printing this manual; see the @file{README} file included in your +release for the most recent instructions. +@end quotation +@end iftex + +GDB comes with a @code{configure} script that automates the process +of preparing GDB for installation; you can then use @code{make} to +build the program. + +The GDB distribution includes all the source code you need for GDB in +a single directory, whose name is usually composed by appending the +version number to @samp{gdb}. + +For example, the GDB version 4.4.4 distribution is in the @file{gdb-4.4.4} +directory. That directory contains: + +@table @code +@item gdb-4.4.4/configure @r{(and supporting files)} +script for configuring GDB and all its supporting libraries. + +@item gdb-4.4.4/gdb +the source specific to GDB itself + +@item gdb-4.4.4/bfd +source for the Binary File Descriptor Library + +@item gdb-4.4.4/include +GNU include files + +@item gdb-4.4.4/libiberty +source for the @samp{-liberty} free software library + +@item gdb-4.4.4/readline +source for the GNU command-line interface +@end table + +The simplest way to configure and build GDB is to run @code{configure} +from the @file{gdb-@var{version-number}} source directory, which in +this example is the @file{gdb-4.4.4} directory. + +First switch to the @file{gdb-@var{version-number}} source directory +if you are not already in it; then run @code{configure}. Pass the +identifier for the platform on which GDB will run as an +argument. + +For example: + +@example +cd gdb-4.4.4 +./configure @var{host} +make +@end example + +@noindent +where @var{host} is an identifier such as @samp{sun4} or +@samp{decstation}, that identifies the platform where GDB will run. + +These @code{configure} and @code{make} commands build the three libraries @file{bfd}, +@file{readline}, and @file{libiberty}, then @code{gdb} itself. The +configured source files, and the binaries, are left in the +corresponding source directories. + +@code{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: + +@example +sh configure @var{host} +@end example + +If you run @code{configure} from a directory that contains source +directories for multiple libraries or programs, such as the +@file{gdb-4.4.4} source directory for version 4.4.4, @code{configure} +creates configuration files for every directory level underneath (unless +you tell it not to, with the @samp{--norecursion} option). + +You can run the @code{configure} script from any of the +subordinate directories in the GDB distribution, if you only want to +configure that subdirectory; but be sure to specify a path to it. + +For example, with version 4.4.4, type the following to configure only +the @code{bfd} subdirectory: + +@example +@group +cd gdb-4.4.4/bfd +../configure @var{host} +@end group +@end example + +You can install @code{gdb} anywhere; it has no hardwired paths. +However, you should make sure that the shell on your path (named by +the @samp{SHELL} environment variable) is publicly readable. Remember +that GDB uses the shell to start your program---some systems refuse to +let GDB debug child processes whose programs are not readable. + +@menu +* Separate Objdir:: Compiling GDB in another directory +* Config Names:: Specifying names for hosts and targets +* configure Options:: Summary of options for configure +* Formatting Documentation:: How to format and print GDB documentation +@end menu + +@node Separate Objdir, Config Names, Installing GDB, Installing GDB +@section Compiling GDB in Another Directory + +If you want to run GDB versions for several host or target machines, +you'll need a different @code{gdb} compiled for each combination of +host and target. @code{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 (GNU @code{make} does), running +@code{make} in each of these directories then builds the @code{gdb} +program specified there. + +To build @code{gdb} in a separate directory, run @code{configure} +with the @samp{--srcdir} option to specify where to find the source. +(Remember, you'll also need to specify a path to find @code{configure} +itself from your working directory.) + +For example, with version 4.4.4, you can build GDB in a separate +directory for a Sun 4 like this: + +@example +@group +cd gdb-4.4.4 +mkdir ../gdb-sun4 +cd ../gdb-sun4 +../gdb-4.4.4/configure --srcdir=../gdb-4.4.4 sun4 +make +@end group +@end example + +When @code{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 GDB itself in +@file{gdb-sun4/gdb}. + +One popular use for building several GDB configurations in separate +directories is to configure GDB for cross-compiling (where GDB +runs on one machine---the host---while debugging programs that run on +another machine---the target). You specify a cross-debugging target by +giving the @samp{--target=@var{target}} option to @code{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 @code{configure} (or one of its subdirectories). + +The @code{Makefile} generated by @code{configure} for each source +directory also runs recursively. If you type @code{make} in a source +directory such as @file{gdb-4.4.4} (or in a separate configured +directory configured with @samp{--srcdir=@var{path}/gdb-4.4.4}), you +will build all the required libraries, 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, configure Options, Separate Objdir, Installing GDB +@section Specifying Names for Hosts and Targets + +The specifications used for hosts and targets in the @code{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: + +@example +@var{architecture}-@var{vendor}-@var{os} +@end example + +For example, you can use the alias @code{sun4} as a @var{host} argument +or in a @code{--target=@var{target}} option, but the equivalent full name +is @samp{sparc-sun-sunos4}. + +The following table shows all the architectures, hosts, and OS +prefixes that @code{configure} recognizes in GDB version 4.4.4. Entries +in the ``OS prefix'' column ending in a @samp{*} may be followed by a +release number. + +@c FIXME! Update for gdb 4.4 +@c TEXI2ROFF-KILL +@ifinfo +@c END TEXI2ROFF-KILL +@example + +ARCHITECTURE VENDOR OS prefix +@c TEXI2ROFF-KILL +------------+--------------------------+--------------------------- +@c END TEXI2ROFF-KILL + | | + 580 | altos hp | aix* msdos* + a29k | amd ibm | amigados newsos* + alliant | amdahl intel | aout nindy* + arm | aout isi | bout osf* + c1 | apollo little | bsd* sco* + c2 | att mips | coff sunos* + cray2 | bcs motorola | ctix* svr4 + h8300 | bout ncr | dgux* sym* + i386 | bull next | dynix* sysv* + i860 | cbm nyu | ebmon ultrix* + i960 | coff sco | esix* unicos* + m68000 | convergent sequent | hds unos* + m68k | convex sgi | hpux* uts + m88k | cray sony | irix* v88r* + mips | dec sun | isc* vms* + ns32k | encore unicom | kern vxworks* + pyramid | gould utek | mach* + romp | hitachi wrs | + rs6000 | | + sparc | | + tahoe | | + tron | | + vax | | + xmp | | + ymp | | +@end example + +@c TEXI2ROFF-KILL +@end ifinfo +@tex +%\vskip\parskip +\vskip \baselineskip +\hfil\vbox{\offinterlineskip +\halign{\strut\tt #\hfil\ &\vrule#&\strut\ \tt #\hfil\ &\strut\ \tt #\hfil +\ &\vrule#&\strut\ \tt #\hfil\ &\strut\ \tt #\hfil \cr +{\bf Architecture} &&{\bf Vendor} &&&{\bf OS prefix}\cr +\multispan7\hrulefill\cr + 580 && altos & hp && aix* & msdos* \cr + a29k && amd & ibm && amigados & newsos* \cr + alliant && amdahl & intel && aout & nindy* \cr + arm && aout & isi && bout & osf* \cr + c1 && apollo & little && bsd* & sco* \cr + c2 && att & mips && coff & sunos* \cr + cray2 && bcs & motorola && ctix* & svr4 \cr + h8300 && bout & ncr && dgux* & sym* \cr + i386 && bull & next && dynix* & sysv* \cr + i860 && cbm & nyu && ebmon & ultrix* \cr + i960 && coff & sco && esix* & unicos* \cr + m68000 && convergent& sequent && hds & unos* \cr + m68k && convex & sgi && hpux* & uts \cr + m88k && cray & sony && irix* & v88r* \cr + mips && dec & sun && isc* & vms* \cr + ns32k && encore & unicom && kern & vxworks* \cr + pyramid && gould & utek && mach* & \cr + romp && hitachi & wrs && & \cr + rs6000 && & && & \cr + sparc && & && & \cr + tahoe && & && & \cr + tron && & && & \cr + vax && & && & \cr + xmp && & && & \cr + ymp && & && & \cr +}\hfil} +@end tex +@c END TEXI2ROFF-KILL + +@quotation +@emph{Warning:} @code{configure} can represent a very large number of +combinations of architecture, vendor, and OS. There is by no means +support available for all possible combinations! +@end quotation + +The @code{configure} script accompanying GDB does not provide +any query facility to list all supported host and target names or +aliases. @code{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: + +@example +% sh config.sub sun4 +sparc-sun-sunos4 +% sh config.sub sun3 +m68k-sun-sunos4 +% sh config.sub decstation +mips-dec-ultrix +% sh config.sub hp300bsd +m68k-hp-bsd +% sh config.sub i386v +i386-none-sysv +% sh config.sub i786v +*** Configuration "i786v" not recognized +@end example + +@noindent +@code{config.sub} is also distributed in the GDB source +directory (@file{gdb-4.4.4}, for version 4.4.4). + +@node configure Options, Formatting Documentation, Config Names, Installing GDB +@section @code{configure} Options + +Here is a summary of all the @code{configure} options and arguments that +you might use for building GDB: + +@example +configure @r{[}--destdir=@var{dir}@r{]} @r{[}--srcdir=@var{path}@r{]} + @r{[}--norecursion@r{]} @r{[}--rm@r{]} + @r{[}--target=@var{target}@r{]} @var{host} +@end example + +@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 --destdir=@var{dir} +@var{dir} is an installation directory @emph{path prefix}. After you +configure with this option, @code{make install} will install GDB as +@file{@var{dir}/bin/gdb}, and the libraries in @file{@var{dir}/lib}. +If you specify @samp{--destdir=/usr/local}, for example, @code{make +install} creates @file{/usr/local/bin/gdb}. + +@item --srcdir=@var{path} +Use this option to make configurations in directories separate from the +GDB source directories. Among other things, you can use this to +build (or maintain) several configurations simultaneously, in separate +directories. @code{configure} writes configuration specific files in +the current directory, but arranges for them to use the source in the +directory @var{path}. @code{configure} will create directories under +the working directory in parallel to the source directories below +@var{path}. + +@item --norecursion +Configure only the directory level where @code{configure} is executed; do not +propagate configuration to subdirectories. + +@item --rm +Remove the configuration that the other arguments specify. + +@c This does not work (yet if ever). FIXME. +@c @item --parse=@var{lang} @dots{} +@c Configure the GDB expression parser to parse the listed languages. +@c @samp{all} configures GDB for all supported languages. To get a +@c list of all supported languages, omit the argument. Without this +@c option, GDB is configured to parse all supported languages. + +@item --target=@var{target} +Configure GDB for cross-debugging programs running on the specified +@var{target}. Without this option, GDB is configured to debug +programs that run on the same machine (@var{host}) as GDB itself. + +There is no convenient way to generate a list of all available targets. + +@item @var{host} @dots{} +Configure GDB to run on the specified @var{host}. + +There is no convenient way to generate a list of all available hosts. +@end table + +@noindent +@code{configure} accepts other options, for compatibility with +configuring other GNU tools recursively; but these are the only +options that affect GDB or its supporting libraries. + +@node Formatting Documentation, , configure Options, Installing GDB +@section Formatting the Documentation + +All the documentation for GDB, including this manual, comes as part of +the 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. + +GDB 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-@var{version-number}/gdb/gdb.info}, and it refers to +subordinate files matching @samp{gdb.info*} in the same directory. + +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 GDB +source directory (@file{gdb-4.4.4}, in the case of version 4.4.4), you can +make the Info file by typing: + +@example +cd gdb +make gdb.info +@end example + +If you want to typeset and print copies of this manual, you need +@TeX{}, a printing program such as @code{lpr}, and @file{texinfo.tex}, +the Texinfo definitions file. + +@TeX{} is 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 +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 read, much less +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 the @file{gdb} +subdirectory of the main source directory (for example, to +@file{gdb-4.4.4/gdb}) and then type: + +@example +make gdb.dvi +@end example + +@cindex GDB reference card +@cindex reference card +In addition to the manual, the GDB 4 release includes a three-column +reference card. Format the GDB reference card by typing: + +@example +make refcard.dvi +@end example + +The GDB reference card is designed to print in 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. + +The GDB 4 release includes an already-formatted reference card, ready +for printing on a PostScript or GhostScript printer, in the @file{gdb} +subdirectory of the main source directory---in +@file{gdb-4.2/gdb/refcard.ps} of the version 4.2 release. If you have +a PostScript or GhostScript printer, you can print the reference card +by just sending @file{refcard.ps} to the printer. + +@node Copying, Index, Installing GDB, Top +@unnumbered GNU GENERAL PUBLIC LICENSE +@center Version 2, June 1991 + +@display +Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc. +675 Mass Ave, Cambridge, MA 02139, USA + +Everyone is permitted to copy and distribute verbatim copies +of this license document, but changing it is not allowed. +@end display + +@unnumberedsec Preamble + + The licenses for most software are designed to take away your +freedom to share and change it. By contrast, the GNU General Public +License is intended to guarantee your freedom to share and change free +software---to make sure the software is free for all its users. This +General Public License applies to most of the Free Software +Foundation's software and to any other program whose authors commit to +using it. (Some other Free Software Foundation software is covered by +the GNU Library General Public License instead.) You can apply it to +your programs, too. + + When we speak of free software, we are referring to freedom, not +price. Our General Public Licenses are designed to make sure that you +have the freedom to distribute copies of free software (and charge for +this service if you wish), that you receive source code or can get it +if you want it, that you can change the software or use pieces of it +in new free programs; and that you know you can do these things. + + To protect your rights, we need to make restrictions that forbid +anyone to deny you these rights or to ask you to surrender the rights. +These restrictions translate to certain responsibilities for you if you +distribute copies of the software, or if you modify it. + + For example, if you distribute copies of such a program, whether +gratis or for a fee, you must give the recipients all the rights that +you have. You must make sure that they, too, receive or can get the +source code. And you must show them these terms so they know their +rights. + + We protect your rights with two steps: (1) copyright the software, and +(2) offer you this license which gives you legal permission to copy, +distribute and/or modify the software. + + Also, for each author's protection and ours, we want to make certain +that everyone understands that there is no warranty for this free +software. If the software is modified by someone else and passed on, we +want its recipients to know that what they have is not the original, so +that any problems introduced by others will not reflect on the original +authors' reputations. + + Finally, any free program is threatened constantly by software +patents. We wish to avoid the danger that redistributors of a free +program will individually obtain patent licenses, in effect making the +program proprietary. To prevent this, we have made it clear that any +patent must be licensed for everyone's free use or not licensed at all. + + The precise terms and conditions for copying, distribution and +modification follow. + +@iftex +@unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION +@end iftex +@ifinfo +@center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION +@end ifinfo + +@enumerate +@item +This License applies to any program or other work which contains +a notice placed by the copyright holder saying it may be distributed +under the terms of this General Public License. The ``Program'', below, +refers to any such program or work, and a ``work based on the Program'' +means either the Program or any derivative work under copyright law: +that is to say, a work containing the Program or a portion of it, +either verbatim or with modifications and/or translated into another +language. (Hereinafter, translation is included without limitation in +the term ``modification''.) Each licensee is addressed as ``you''. + +Activities other than copying, distribution and modification are not +covered by this License; they are outside its scope. The act of +running the Program is not restricted, and the output from the Program +is covered only if its contents constitute a work based on the +Program (independent of having been made by running the Program). +Whether that is true depends on what the Program does. + +@item +You may copy and distribute verbatim copies of the Program's +source code as you receive it, in any medium, provided that you +conspicuously and appropriately publish on each copy an appropriate +copyright notice and disclaimer of warranty; keep intact all the +notices that refer to this License and to the absence of any warranty; +and give any other recipients of the Program a copy of this License +along with the Program. + +You may charge a fee for the physical act of transferring a copy, and +you may at your option offer warranty protection in exchange for a fee. + +@item +You may modify your copy or copies of the Program or any portion +of it, thus forming a work based on the Program, and copy and +distribute such modifications or work under the terms of Section 1 +above, provided that you also meet all of these conditions: + +@enumerate a +@item +You must cause the modified files to carry prominent notices +stating that you changed the files and the date of any change. + +@item +You must cause any work that you distribute or publish, that in +whole or in part contains or is derived from the Program or any +part thereof, to be licensed as a whole at no charge to all third +parties under the terms of this License. + +@item +If the modified program normally reads commands interactively +when run, you must cause it, when started running for such +interactive use in the most ordinary way, to print or display an +announcement including an appropriate copyright notice and a +notice that there is no warranty (or else, saying that you provide +a warranty) and that users may redistribute the program under +these conditions, and telling the user how to view a copy of this +License. (Exception: if the Program itself is interactive but +does not normally print such an announcement, your work based on +the Program is not required to print an announcement.) +@end enumerate + +These requirements apply to the modified work as a whole. If +identifiable sections of that work are not derived from the Program, +and can be reasonably considered independent and separate works in +themselves, then this License, and its terms, do not apply to those +sections when you distribute them as separate works. But when you +distribute the same sections as part of a whole which is a work based +on the Program, the distribution of the whole must be on the terms of +this License, whose permissions for other licensees extend to the +entire whole, and thus to each and every part regardless of who wrote it. + +Thus, it is not the intent of this section to claim rights or contest +your rights to work written entirely by you; rather, the intent is to +exercise the right to control the distribution of derivative or +collective works based on the Program. + +In addition, mere aggregation of another work not based on the Program +with the Program (or with a work based on the Program) on a volume of +a storage or distribution medium does not bring the other work under +the scope of this License. + +@item +You may copy and distribute the Program (or a work based on it, +under Section 2) in object code or executable form under the terms of +Sections 1 and 2 above provided that you also do one of the following: + +@enumerate a +@item +Accompany it with the complete corresponding machine-readable +source code, which must be distributed under the terms of Sections +1 and 2 above on a medium customarily used for software interchange; or, + +@item +Accompany it with a written offer, valid for at least three +years, to give any third party, for a charge no more than your +cost of physically performing source distribution, a complete +machine-readable copy of the corresponding source code, to be +distributed under the terms of Sections 1 and 2 above on a medium +customarily used for software interchange; or, + +@item +Accompany it with the information you received as to the offer +to distribute corresponding source code. (This alternative is +allowed only for noncommercial distribution and only if you +received the program in object code or executable form with such +an offer, in accord with Subsection b above.) +@end enumerate + +The source code for a work means the preferred form of the work for +making modifications to it. For an executable work, complete source +code means all the source code for all modules it contains, plus any +associated interface definition files, plus the scripts used to +control compilation and installation of the executable. However, as a +special exception, the source code distributed need not include +anything that is normally distributed (in either source or binary +form) with the major components (compiler, kernel, and so on) of the +operating system on which the executable runs, unless that component +itself accompanies the executable. + +If distribution of executable or object code is made by offering +access to copy from a designated place, then offering equivalent +access to copy the source code from the same place counts as +distribution of the source code, even though third parties are not +compelled to copy the source along with the object code. + +@item +You may not copy, modify, sublicense, or distribute the Program +except as expressly provided under this License. Any attempt +otherwise to copy, modify, sublicense or distribute the Program is +void, and will automatically terminate your rights under this License. +However, parties who have received copies, or rights, from you under +this License will not have their licenses terminated so long as such +parties remain in full compliance. + +@item +You are not required to accept this License, since you have not +signed it. However, nothing else grants you permission to modify or +distribute the Program or its derivative works. These actions are +prohibited by law if you do not accept this License. Therefore, by +modifying or distributing the Program (or any work based on the +Program), you indicate your acceptance of this License to do so, and +all its terms and conditions for copying, distributing or modifying +the Program or works based on it. + +@item +Each time you redistribute the Program (or any work based on the +Program), the recipient automatically receives a license from the +original licensor to copy, distribute or modify the Program subject to +these terms and conditions. You may not impose any further +restrictions on the recipients' exercise of the rights granted herein. +You are not responsible for enforcing compliance by third parties to +this License. + +@item +If, as a consequence of a court judgment or allegation of patent +infringement or for any other reason (not limited to patent issues), +conditions are imposed on you (whether by court order, agreement or +otherwise) that contradict the conditions of this License, they do not +excuse you from the conditions of this License. If you cannot +distribute so as to satisfy simultaneously your obligations under this +License and any other pertinent obligations, then as a consequence you +may not distribute the Program at all. For example, if a patent +license would not permit royalty-free redistribution of the Program by +all those who receive copies directly or indirectly through you, then +the only way you could satisfy both it and this License would be to +refrain entirely from distribution of the Program. + +If any portion of this section is held invalid or unenforceable under +any particular circumstance, the balance of the section is intended to +apply and the section as a whole is intended to apply in other +circumstances. + +It is not the purpose of this section to induce you to infringe any +patents or other property right claims or to contest validity of any +such claims; this section has the sole purpose of protecting the +integrity of the free software distribution system, which is +implemented by public license practices. Many people have made +generous contributions to the wide range of software distributed +through that system in reliance on consistent application of that +system; it is up to the author/donor to decide if he or she is willing +to distribute software through any other system and a licensee cannot +impose that choice. + +This section is intended to make thoroughly clear what is believed to +be a consequence of the rest of this License. + +@item +If the distribution and/or use of the Program is restricted in +certain countries either by patents or by copyrighted interfaces, the +original copyright holder who places the Program under this License +may add an explicit geographical distribution limitation excluding +those countries, so that distribution is permitted only in or among +countries not thus excluded. In such case, this License incorporates +the limitation as if written in the body of this License. + +@item +The Free Software Foundation may publish revised and/or new versions +of the General Public License from time to time. Such new versions will +be similar in spirit to the present version, but may differ in detail to +address new problems or concerns. + +Each version is given a distinguishing version number. If the Program +specifies a version number of this License which applies to it and ``any +later version'', you have the option of following the terms and conditions +either of that version or of any later version published by the Free +Software Foundation. If the Program does not specify a version number of +this License, you may choose any version ever published by the Free Software +Foundation. + +@item +If you wish to incorporate parts of the Program into other free +programs whose distribution conditions are different, write to the author +to ask for permission. For software which is copyrighted by the Free +Software Foundation, write to the Free Software Foundation; we sometimes +make exceptions for this. Our decision will be guided by the two goals +of preserving the free status of all derivatives of our free software and +of promoting the sharing and reuse of software generally. + +@iftex +@heading NO WARRANTY +@end iftex +@ifinfo +@center NO WARRANTY +@end ifinfo + +@item +BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY +FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN +OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES +PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED +OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF +MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS +TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE +PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, +REPAIR OR CORRECTION. + +@item +IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING +WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR +REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, +INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING +OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED +TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY +YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER +PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE +POSSIBILITY OF SUCH DAMAGES. +@end enumerate + +@iftex +@heading END OF TERMS AND CONDITIONS +@end iftex +@ifinfo +@center END OF TERMS AND CONDITIONS +@end ifinfo + +@page +@unnumberedsec Applying These Terms to Your New Programs + + If you develop a new program, and you want it to be of the greatest +possible use to the public, the best way to achieve this is to make it +free software which everyone can redistribute and change under these terms. + + To do so, attach the following notices to the program. It is safest +to attach them to the start of each source file to most effectively +convey the exclusion of warranty; and each file should have at least +the ``copyright'' line and a pointer to where the full notice is found. + +@smallexample +@var{one line to give the program's name and an idea of what it does.} +Copyright (C) 19@var{yy} @var{name of author} + +This program is free software; you can redistribute it and/or +modify it under the terms of the GNU General Public License +as published by the Free Software Foundation; either version 2 +of the License, or (at your option) any later version. + +This program is distributed in the hope that it will be useful, +but WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +GNU General Public License for more details. + +You should have received a copy of the GNU General Public License +along with this program; if not, write to the +Free Software Foundation, Inc., 675 Mass Ave, +Cambridge, MA 02139, USA. +@end smallexample + +Also add information on how to contact you by electronic and paper mail. + +If the program is interactive, make it output a short notice like this +when it starts in an interactive mode: + +@smallexample +Gnomovision version 69, Copyright (C) 19@var{yy} @var{name of author} +Gnomovision comes with ABSOLUTELY NO WARRANTY; for details +type `show w'. This is free software, and you are welcome +to redistribute it under certain conditions; type `show c' +for details. +@end smallexample + +The hypothetical commands @samp{show w} and @samp{show c} should show +the appropriate parts of the General Public License. Of course, the +commands you use may be called something other than @samp{show w} and +@samp{show c}; they could even be mouse-clicks or menu items---whatever +suits your program. + +You should also get your employer (if you work as a programmer) or your +school, if any, to sign a ``copyright disclaimer'' for the program, if +necessary. Here is a sample; alter the names: + +@example +Yoyodyne, Inc., hereby disclaims all copyright +interest in the program `Gnomovision' +(which makes passes at compilers) written +by James Hacker. + +@var{signature of Ty Coon}, 1 April 1989 +Ty Coon, President of Vice +@end example + +This General Public License does not permit incorporating your program into +proprietary programs. If your program is a subroutine library, you may +consider it more useful to permit linking proprietary applications with the +library. If this is what you want to do, use the GNU Library General +Public License instead of this License. + +@node Index, , Copying, Top +@unnumbered Index + +@printindex cp + +@tex +% I think something like @colophon should be in texinfo. In the +% meantime: +\long\def\colophon{\hbox to0pt{}\vfill +\centerline{The body of this manual is set in} +\centerline{\fontname\tenrm,} +\centerline{with headings in {\bf\fontname\tenbf}} +\centerline{and examples in {\tt\fontname\tentt}.} +\centerline{{\it\fontname\tenit\/},} +\centerline{{\bf\fontname\tenbf}, and} +\centerline{{\sl\fontname\tensl\/}} +\centerline{are used for emphasis.}\vfill} +\page\colophon +% Blame: pesch@cygnus.com, 1991. +@end tex + +@contents +@bye |