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diff --git a/gdb/doc/gdb-all.texi b/gdb/doc/gdb-all.texi index e2162da..e69de29 100755 --- a/gdb/doc/gdb-all.texi +++ b/gdb/doc/gdb-all.texi @@ -1,8437 +0,0 @@ - -\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 -@c @smallbook -@c @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; see @ref{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 |