1 \input texinfo @c -*-texinfo-*-
2 @c Copyright (c) 1988 1989 1990 1991 1992 1993 Free Software Foundation, Inc.
5 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
6 @c of @set vars. However, you can override filename with makeinfo -o.
12 @settitle Debugging with @value{GDBN}
15 @settitle Debugging with @value{GDBN} (@value{TARGET})
17 @setchapternewpage odd
28 @c readline appendices use @vindex
32 @c Determine the edition number in *three* places by hand:
33 @c 1. First ifinfo section 2. title page 3. top node
34 @c To find the locations, search for !!set
36 @c GDB CHANGELOG CONSULTED BETWEEN:
37 @c Fri Oct 11 23:27:06 1991 John Gilmore (gnu at cygnus.com)
38 @c Sat Dec 22 02:51:40 1990 John Gilmore (gnu at cygint)
40 @c THIS MANUAL REQUIRES TEXINFO-2 macros and info-makers to format properly.
43 @c This is a dir.info fragment to support semi-automated addition of
44 @c manuals to an info tree. zoo@cygnus.com is developing this facility.
47 * Gdb:: The GNU debugger.
54 This file documents the GNU debugger @value{GDBN}.
56 @c !!set edition, date, version
57 This is Edition 4.09, April 1993,
58 of @cite{Debugging with @value{GDBN}: the GNU Source-Level Debugger}
59 for GDB Version @value{GDBVN}.
61 Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993 Free Software Foundation, Inc.
63 Permission is granted to make and distribute verbatim copies of
64 this manual provided the copyright notice and this permission notice
65 are preserved on all copies.
68 Permission is granted to process this file through TeX and print the
69 results, provided the printed document carries copying permission
70 notice identical to this one except for the removal of this paragraph
71 (this paragraph not being relevant to the printed manual).
74 Permission is granted to copy and distribute modified versions of this
75 manual under the conditions for verbatim copying, provided also that the
76 entire resulting derived work is distributed under the terms of a
77 permission notice identical to this one.
79 Permission is granted to copy and distribute translations of this manual
80 into another language, under the above conditions for modified versions.
84 @title Debugging with @value{GDBN}
85 @subtitle The GNU Source-Level Debugger
87 @subtitle (@value{TARGET})
90 @c !!set edition, date, version
91 @subtitle Edition 4.09, for @value{GDBN} version @value{GDBVN}
93 @author by Richard M. Stallman and Roland H. Pesch
97 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@prep.ai.mit.edu.)\par
98 \hfill {\it Debugging with @value{GDBN}}\par
99 \hfill \TeX{}info \texinfoversion\par
100 \hfill pesch\@cygnus.com\par
104 @vskip 0pt plus 1filll
105 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993 Free Software Foundation, Inc.
107 Permission is granted to make and distribute verbatim copies of
108 this manual provided the copyright notice and this permission notice
109 are preserved on all copies.
111 Permission is granted to copy and distribute modified versions of this
112 manual under the conditions for verbatim copying, provided also that the
113 entire resulting derived work is distributed under the terms of a
114 permission notice identical to this one.
116 Permission is granted to copy and distribute translations of this manual
117 into another language, under the above conditions for modified versions.
123 @top Debugging with @value{GDBN}
125 This file describes @value{GDBN}, the GNU symbolic debugger.
127 @c !!set edition, date, version
128 This is Edition 4.09, April 1993, for GDB Version @value{GDBVN}.
131 * Summary:: Summary of @value{GDBN}
133 * New Features:: New features since GDB version 3.5
136 * Sample Session:: A sample @value{GDBN} session
139 * Invocation:: Getting in and out of @value{GDBN}
140 * Commands:: @value{GDBN} commands
141 * Running:: Running programs under @value{GDBN}
142 * Stopping:: Stopping and continuing
143 * Stack:: Examining the stack
144 * Source:: Examining source files
145 * Data:: Examining data
147 * Languages:: Using @value{GDBN} with different languages
150 * C:: C language support
152 @c remnant makeinfo bug, blank line needed after two end-ifs?
154 * Symbols:: Examining the symbol table
155 * Altering:: Altering execution
156 * GDB Files:: @value{GDBN} files
157 * Targets:: Specifying a debugging target
158 * Controlling GDB:: Controlling @value{GDBN}
159 * Sequences:: Canned sequences of commands
161 * Emacs:: Using @value{GDBN} under GNU Emacs
164 * GDB Bugs:: Reporting bugs in @value{GDBN}
165 * Command Line Editing:: Facilities of the readline library
166 * Using History Interactively::
170 @ifclear PRECONFIGURED
171 * Formatting Documentation:: How to format and print GDB documentation
172 * Installing GDB:: Installing GDB
180 @unnumbered Summary of @value{GDBN}
182 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
183 going on ``inside'' another program while it executes---or what another
184 program was doing at the moment it crashed.
186 @value{GDBN} can do four main kinds of things (plus other things in support of
187 these) to help you catch bugs in the act:
191 Start your program, specifying anything that might affect its behavior.
194 Make your program stop on specified conditions.
197 Examine what has happened, when your program has stopped.
200 Change things in your program, so you can experiment with correcting the
201 effects of one bug and go on to learn about another.
206 You can use @value{GDBN} to debug programs written in C or C++.
209 You can use @value{GDBN} to debug programs written in C, C++, and
214 @value{GDBN} can be used to debug programs written in Fortran, although
215 it does not yet support entering expressions, printing values, etc.
216 using Fortran syntax. It may be necessary to refer to some variables
217 with a trailing underscore.
222 * Free Software:: Freely redistributable software
223 * Contributors:: Contributors to GDB
227 @unnumberedsec Free software
229 @value{GDBN} is @dfn{free software}, protected by the GNU General Public License
230 (GPL). The GPL gives you the freedom to copy or adapt a licensed
231 program---but every person getting a copy also gets with it the
232 freedom to modify that copy (which means that they must get access to
233 the source code), and the freedom to distribute further copies.
234 Typical software companies use copyrights to limit your freedoms; the
235 Free Software Foundation uses the GPL to preserve these freedoms.
237 Fundamentally, the General Public License is a license which says that
238 you have these freedoms and that you cannot take these freedoms away
242 @unnumberedsec Contributors to GDB
244 Richard Stallman was the original author of GDB, and of many other GNU
245 programs. Many others have contributed to its development. This
246 section attempts to credit major contributors. One of the virtues of
247 free software is that everyone is free to contribute to it; with
248 regret, we cannot actually acknowledge everyone here. The file
249 @file{ChangeLog} in the GDB distribution approximates a blow-by-blow
252 Changes much prior to version 2.0 are lost in the mists of time.
255 @emph{Plea:} Additions to this section are particularly welcome. If you
256 or your friends (or enemies, to be evenhanded) have been unfairly
257 omitted from this list, we would like to add your names!
260 So that they may not regard their long labor as thankless, we
261 particularly thank those who shepherded GDB through major releases: Fred
262 Fish (release 4.9), Stu Grossman and John Gilmore (releases 4.8, 4.7,
263 4.6, 4.5, 4.4), John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9); Jim
264 Kingdon (releases 3.5, 3.4, 3.3); and Randy Smith (releases 3.2, 3.1,
265 3.0). As major maintainer of GDB for some period, each contributed
266 significantly to the structure, stability, and capabilities of the
269 Richard Stallman, assisted at various times by Pete TerMaat, Chris
270 Hanson, and Richard Mlynarik, handled releases through 2.8.
273 Michael Tiemann is the author of most of the GNU C++ support in GDB,
274 with significant additional contributions from Per Bothner. James
275 Clark wrote the GNU C++ demangler. Early work on C++ was by Peter
276 TerMaat (who also did much general update work leading to release 3.0).
279 GDB 4 uses the BFD subroutine library to examine multiple
280 object-file formats; BFD was a joint project of David V.
281 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
283 David Johnson wrote the original COFF support; Pace Willison did
284 the original support for encapsulated COFF.
286 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
287 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
288 support. Jean-Daniel Fekete contributed Sun 386i support. Chris
289 Hanson improved the HP9000 support. Noboyuki Hikichi and Tomoyuki
290 Hasei contributed Sony/News OS 3 support. David Johnson contributed
291 Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support.
292 Keith Packard contributed NS32K support. Doug Rabson contributed
293 Acorn Risc Machine support. Chris Smith contributed Convex support
294 (and Fortran debugging). Jonathan Stone contributed Pyramid support.
295 Michael Tiemann contributed SPARC support. Tim Tucker contributed
296 support for the Gould NP1 and Gould Powernode. Pace Willison
297 contributed Intel 386 support. Jay Vosburgh contributed Symmetry
300 Rich Schaefer and Peter Schauer helped with support of SunOS shared
303 Jay Fenlason and Roland McGrath ensured that GDB and GAS agree about
304 several machine instruction sets.
306 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped
307 develop remote debugging. Intel Corporation and Wind River Systems
308 contributed remote debugging modules for their products.
310 Brian Fox is the author of the readline libraries providing
311 command-line editing and command history.
313 Andrew Beers of SUNY Buffalo wrote the language-switching code,
315 the Modula-2 support,
317 and contributed the Languages chapter of this manual.
319 Fred Fish wrote most of the support for Unix System Vr4.
321 He also enhanced the command-completion support to cover C++ overloaded
325 Hitachi America, Ltd. sponsored the support for Hitachi microprocessors.
329 @unnumbered New Features since GDB Version 3.5
333 Using the new command @code{target}, you can select at runtime whether
334 you are debugging local files, local processes, standalone systems over
335 a serial port, realtime systems over a TCP/IP connection, etc. The
336 command @code{load} can download programs into a remote system. Serial
337 stubs are available for Motorola 680x0, Intel 80386, and Sparc remote
338 systems; GDB also supports debugging realtime processes running under
339 VxWorks, using SunRPC Remote Procedure Calls over TCP/IP to talk to a
340 debugger stub on the target system. Internally, GDB now uses a function
341 vector to mediate access to different targets; if you need to add your
342 own support for a remote protocol, this makes it much easier.
345 GDB now sports watchpoints as well as breakpoints. You can use a
346 watchpoint to stop execution whenever the value of an expression
347 changes, without having to predict a particular place in your program
348 where this may happen.
351 Commands that issue wide output now insert newlines at places designed
352 to make the output more readable.
354 @item Object Code Formats
355 GDB uses a new library called the Binary File Descriptor (BFD) Library
356 to permit it to switch dynamically, without reconfiguration or
357 recompilation, between different object-file formats. Formats currently
358 supported are COFF, ELF, a.out, Intel 960 b.out, MIPS ECOFF, HPPA SOM
359 (with stabs debugging), and S-records; files may be read as .o files,
360 archive libraries, or core dumps. BFD is available as a subroutine
361 library so that other programs may take advantage of it, and the other
362 GNU binary utilities are being converted to use it.
364 @item Configuration and Ports
365 Compile-time configuration (to select a particular architecture and
366 operating system) is much easier. The script @code{configure} now
367 allows you to configure GDB as either a native debugger or a
368 cross-debugger. @xref{Installing GDB}, for details on how to
372 The user interface to the GDB control variables is simpler,
373 and is consolidated in two commands, @code{set} and @code{show}. Output
374 lines are now broken at readable places, rather than overflowing onto
375 the next line. You can suppress output of machine-level addresses,
376 displaying only source language information.
379 GDB now supports C++ multiple inheritance (if used with a GCC
380 version 2 compiler), and also has limited support for C++ exception
381 handling, with the commands @code{catch} and @code{info catch}: GDB
382 can break when an exception is raised, before the stack is peeled back
383 to the exception handler's context.
387 GDB now has preliminary support for the GNU Modula-2 compiler, currently
388 under development at the State University of New York at Buffalo.
389 Coordinated development of both GDB and the GNU Modula-2 compiler will
390 continue. Other Modula-2 compilers are currently not supported, and
391 attempting to debug programs compiled with them will likely result in an
392 error as the symbol table of the executable is read in.
395 @item Command Rationalization
396 Many GDB commands have been renamed to make them easier to remember
397 and use. In particular, the subcommands of @code{info} and
398 @code{show}/@code{set} are grouped to make the former refer to the state
399 of your program, and the latter refer to the state of GDB itself.
400 @xref{Renamed Commands}, for details on what commands were renamed.
402 @item Shared Libraries
403 GDB 4 can debug programs and core files that use SunOS, SVR4, or IBM RS/6000
407 GDB 4 has a reference card. @xref{Formatting Documentation,,Formatting
408 the Documentation}, for instructions about how to print it.
414 @chapter A Sample @value{GDBN} Session
416 You can use this manual at your leisure to read all about @value{GDBN}.
417 However, a handful of commands are enough to get started using the
418 debugger. This chapter illustrates those commands.
421 In this sample session, we emphasize user input like this: @b{input},
422 to make it easier to pick out from the surrounding output.
425 @c FIXME: this example may not be appropriate for some configs, where
426 @c FIXME...primary interest is in remote use.
428 One of the preliminary versions of GNU @code{m4} (a generic macro
429 processor) exhibits the following bug: sometimes, when we change its
430 quote strings from the default, the commands used to capture one macro
431 definition within another stop working. In the following short @code{m4}
432 session, we define a macro @code{foo} which expands to @code{0000}; we
433 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
434 same thing. However, when we change the open quote string to
435 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
436 procedure fails to define a new synonym @code{baz}:
445 @b{define(bar,defn(`foo'))}
449 @b{changequote(<QUOTE>,<UNQUOTE>)}
451 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
454 m4: End of input: 0: fatal error: EOF in string
458 Let us use @value{GDBN} to try to see what is going on.
461 $ @b{@value{GDBP} m4}
462 @c FIXME: this falsifies the exact text played out, to permit smallbook
463 @c FIXME... format to come out better.
464 GDB is free software and you are welcome to distribute copies
465 of it under certain conditions; type "show copying" to see
467 There is absolutely no warranty for GDB; type "show warranty"
469 GDB @value{GDBVN}, Copyright 1993 Free Software Foundation, Inc...
474 @value{GDBN} reads only enough symbol data to know where to find the rest when
475 needed; as a result, the first prompt comes up very quickly. We now
476 tell @value{GDBN} to use a narrower display width than usual, so that examples
477 will fit in this manual.
480 (@value{GDBP}) @b{set width 70}
484 We need to see how the @code{m4} built-in @code{changequote} works.
485 Having looked at the source, we know the relevant subroutine is
486 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
487 @code{break} command.
490 (@value{GDBP}) @b{break m4_changequote}
491 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
495 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
496 control; as long as control does not reach the @code{m4_changequote}
497 subroutine, the program runs as usual:
500 (@value{GDBP}) @b{run}
501 Starting program: /work/Editorial/gdb/gnu/m4/m4
509 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
510 suspends execution of @code{m4}, displaying information about the
511 context where it stops.
514 @b{changequote(<QUOTE>,<UNQUOTE>)}
516 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
518 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
522 Now we use the command @code{n} (@code{next}) to advance execution to
523 the next line of the current function.
527 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
532 @code{set_quotes} looks like a promising subroutine. We can go into it
533 by using the command @code{s} (@code{step}) instead of @code{next}.
534 @code{step} goes to the next line to be executed in @emph{any}
535 subroutine, so it steps into @code{set_quotes}.
539 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
541 530 if (lquote != def_lquote)
545 The display that shows the subroutine where @code{m4} is now
546 suspended (and its arguments) is called a stack frame display. It
547 shows a summary of the stack. We can use the @code{backtrace}
548 command (which can also be spelled @code{bt}), to see where we are
549 in the stack as a whole: the @code{backtrace} command displays a
550 stack frame for each active subroutine.
553 (@value{GDBP}) @b{bt}
554 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
556 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
558 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
559 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
561 #4 0x79dc in expand_input () at macro.c:40
562 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
566 We will step through a few more lines to see what happens. The first two
567 times, we can use @samp{s}; the next two times we use @code{n} to avoid
568 falling into the @code{xstrdup} subroutine.
572 0x3b5c 532 if (rquote != def_rquote)
574 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
575 def_lquote : xstrdup(lq);
577 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
580 538 len_lquote = strlen(rquote);
584 The last line displayed looks a little odd; we can examine the variables
585 @code{lquote} and @code{rquote} to see if they are in fact the new left
586 and right quotes we specified. We use the command @code{p}
587 (@code{print}) to see their values.
590 (@value{GDBP}) @b{p lquote}
591 $1 = 0x35d40 "<QUOTE>"
592 (@value{GDBP}) @b{p rquote}
593 $2 = 0x35d50 "<UNQUOTE>"
597 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
598 To look at some context, we can display ten lines of source
599 surrounding the current line with the @code{l} (@code{list}) command.
605 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
607 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
610 538 len_lquote = strlen(rquote);
611 539 len_rquote = strlen(lquote);
618 Let us step past the two lines that set @code{len_lquote} and
619 @code{len_rquote}, and then examine the values of those variables.
623 539 len_rquote = strlen(lquote);
626 (@value{GDBP}) @b{p len_lquote}
628 (@value{GDBP}) @b{p len_rquote}
633 That certainly looks wrong, assuming @code{len_lquote} and
634 @code{len_rquote} are meant to be the lengths of @code{lquote} and
635 @code{rquote} respectively. We can set them to better values using
636 the @code{p} command, since it can print the value of
637 any expression---and that expression can include subroutine calls and
641 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
643 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
648 Is that enough to fix the problem of using the new quotes with the
649 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
650 executing with the @code{c} (@code{continue}) command, and then try the
651 example that caused trouble initially:
657 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
664 Success! The new quotes now work just as well as the default ones. The
665 problem seems to have been just the two typos defining the wrong
666 lengths. We allow @code{m4} exit by giving it an EOF as input:
670 Program exited normally.
674 The message @samp{Program exited normally.} is from @value{GDBN}; it
675 indicates @code{m4} has finished executing. We can end our @value{GDBN}
676 session with the @value{GDBN} @code{quit} command.
679 (@value{GDBP}) @b{quit}
684 @chapter Getting In and Out of @value{GDBN}
686 This chapter discusses how to start @value{GDBN}, and how to get out of it.
687 (The essentials: type @samp{@value{GDBP}} to start GDB, and type @kbd{quit}
688 or @kbd{C-d} to exit.)
691 * Invoking GDB:: How to start @value{GDBN}
692 * Quitting GDB:: How to quit @value{GDBN}
693 * Shell Commands:: How to use shell commands inside @value{GDBN}
697 @section Invoking @value{GDBN}
700 For details on starting up @value{GDBP} as a
701 remote debugger attached to a Hitachi microprocessor, see @ref{Hitachi
702 Remote,,@value{GDBN} and Hitachi Microprocessors}.
705 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
706 @value{GDBN} reads commands from the terminal until you tell it to exit.
708 You can also run @code{@value{GDBP}} with a variety of arguments and options,
709 to specify more of your debugging environment at the outset.
712 The command-line options described here are designed
713 to cover a variety of situations; in some environments, some of these
714 options may effectively be unavailable.
717 The most usual way to start @value{GDBN} is with one argument,
718 specifying an executable program:
721 @value{GDBP} @var{program}
726 You can also start with both an executable program and a core file
730 @value{GDBP} @var{program} @var{core}
733 You can, instead, specify a process ID as a second argument, if you want
734 to debug a running process:
737 @value{GDBP} @var{program} 1234
741 would attach @value{GDBN} to process @code{1234} (unless you also have a file
742 named @file{1234}; @value{GDBN} does check for a core file first).
744 Taking advantage of the second command-line argument requires a fairly
745 complete operating system; when you use @value{GDBN} as a remote debugger
746 attached to a bare board, there may not be any notion of ``process'',
747 and there is often no way to get a core dump.
751 You can further control how @value{GDBN} starts up by using command-line
752 options. @value{GDBN} itself can remind you of the options available.
762 to display all available options and briefly describe their use
763 (@samp{@value{GDBP} -h} is a shorter equivalent).
765 All options and command line arguments you give are processed
766 in sequential order. The order makes a difference when the
767 @samp{-x} option is used.
773 * Remote Serial:: @value{GDBN} remote serial protocol
776 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
779 * UDI29K Remote:: @value{GDBN} and the UDI protocol for AMD29K
780 * EB29K Remote:: @value{GDBN} with a remote EB29K
783 * VxWorks Remote:: @value{GDBN} and VxWorks
786 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
789 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
792 * MIPS Remote:: @value{GDBN} and MIPS boards
795 * Simulator:: Simulated CPU target
798 @c remnant makeinfo bug requires this blank line after *two* end-ifblahs:
800 * File Options:: Choosing files
801 * Mode Options:: Choosing modes
809 @subsection Choosing files
812 When @value{GDBN} starts, it reads any arguments other than options as
813 specifying an executable file and core file (or process ID). This is
814 the same as if the arguments were specified by the @samp{-se} and
815 @samp{-c} options respectively. (@value{GDBN} reads the first argument
816 that does not have an associated option flag as equivalent to the
817 @samp{-se} option followed by that argument; and the second argument
818 that does not have an associated option flag, if any, as equivalent to
819 the @samp{-c} option followed by that argument.)
822 When @value{GDBN} starts, it reads any argument other than options as
823 specifying an executable file. This is the same as if the argument was
824 specified by the @samp{-se} option.
827 Many options have both long and short forms; both are shown in the
828 following list. @value{GDBN} also recognizes the long forms if you truncate
829 them, so long as enough of the option is present to be unambiguous.
830 (If you prefer, you can flag option arguments with @samp{--} rather
831 than @samp{-}, though we illustrate the more usual convention.)
834 @item -symbols=@var{file}
836 Read symbol table from file @var{file}.
838 @item -exec=@var{file}
840 Use file @var{file} as the executable file to execute when
845 appropriate, and for examining pure data in conjunction with a core
850 Read symbol table from file @var{file} and use it as the executable
854 @item -core=@var{file}
856 Use file @var{file} as a core dump to examine.
858 @item -c @var{number}
859 Connect to process ID @var{number}, as with the @code{attach} command
860 (unless there is a file in core-dump format named @var{number}, in which
861 case @samp{-c} specifies that file as a core dump to read).
864 @item -command=@var{file}
866 Execute @value{GDBN} commands from file @var{file}. @xref{Command
867 Files,, Command files}.
869 @item -directory=@var{directory}
870 @itemx -d @var{directory}
871 Add @var{directory} to the path to search for source files.
876 @emph{Warning: this option depends on operating system facilities that are not
877 supported on all systems.}@*
878 If memory-mapped files are available on your system through the @code{mmap}
879 system call, you can use this option
880 to have @value{GDBN} write the symbols from your
881 program into a reusable file in the current directory. If the program you are debugging is
882 called @file{/tmp/fred}, the mapped symbol file will be @file{./fred.syms}.
883 Future @value{GDBN} debugging sessions will notice the presence of this file,
884 and will quickly map in symbol information from it, rather than reading
885 the symbol table from the executable program.
887 @c FIXME! Really host, not target?
888 The @file{.syms} file is specific to the host machine where @value{GDBN}
889 is run. It holds an exact image of the internal @value{GDBN} symbol
890 table. It cannot be shared across multiple host platforms.
895 Read each symbol file's entire symbol table immediately, rather than
896 the default, which is to read it incrementally as it is needed.
897 This makes startup slower, but makes future operations faster.
901 The @code{-mapped} and @code{-readnow} options are typically combined in
902 order to build a @file{.syms} file that contains complete symbol
903 information. (@xref{Files,,Commands to specify files}, for information
904 on @file{.syms} files.) A simple GDB invocation to do nothing but build
905 a @file{.syms} file for future use is:
908 gdb -batch -nx -mapped -readnow programname
913 @subsection Choosing modes
915 You can run @value{GDBN} in various alternative modes---for example, in
916 batch mode or quiet mode.
921 Do not execute commands from any initialization files (normally called
922 @file{@value{GDBINIT}}). Normally, the commands in these files are
923 executed after all the command options and arguments have been
924 processed. @xref{Command Files,,Command files}.
928 ``Quiet''. Do not print the introductory and copyright messages. These
929 messages are also suppressed in batch mode.
932 Run in batch mode. Exit with status @code{0} after processing all the
933 command files specified with @samp{-x} (and all commands from
934 initialization files, if not inhibited with @samp{-n}). Exit with
935 nonzero status if an error occurs in executing the @value{GDBN} commands
936 in the command files.
938 Batch mode may be useful for running @value{GDBN} as a filter, for example to
939 download and run a program on another computer; in order to make this
940 more useful, the message
943 Program exited normally.
947 (which is ordinarily issued whenever a program running under @value{GDBN} control
948 terminates) is not issued when running in batch mode.
950 @item -cd=@var{directory}
951 Run @value{GDBN} using @var{directory} as its working directory,
952 instead of the current directory.
955 @item -context @var{authentication}
956 When the Energize programming system starts up @value{GDBN}, it uses this
957 option to trigger an alternate mode of interaction.
958 @var{authentication} is a pair of numeric codes that identify @value{GDBN}
959 as a client in the Energize environment. Avoid this option when you run
960 @value{GDBN} directly from the command line. See @ref{Energize,,Using
961 @value{GDBN} with Energize} for more discussion of using @value{GDBN} with Energize.
967 Emacs sets this option when it runs @value{GDBN} as a subprocess. It tells @value{GDBN}
968 to output the full file name and line number in a standard,
969 recognizable fashion each time a stack frame is displayed (which
970 includes each time your program stops). This recognizable format looks
971 like two @samp{\032} characters, followed by the file name, line number
972 and character position separated by colons, and a newline. The
973 Emacs-to-@value{GDBN} interface program uses the two @samp{\032} characters as
974 a signal to display the source code for the frame.
979 Set the line speed (baud rate or bits per second) of any serial
980 interface used by @value{GDBN} for remote debugging.
982 @item -tty=@var{device}
983 Run using @var{device} for your program's standard input and output.
984 @c FIXME: kingdon thinks there is more to -tty. Investigate.
989 @section Quitting @value{GDBN}
990 @cindex exiting @value{GDBN}
991 @cindex leaving @value{GDBN}
997 To exit @value{GDBN}, use the @code{quit} command (abbreviated @code{q}), or type
998 an end-of-file character (usually @kbd{C-d}).
1002 An interrupt (often @kbd{C-c}) will not exit from @value{GDBN}, but rather
1003 will terminate the action of any @value{GDBN} command that is in progress and
1004 return to @value{GDBN} command level. It is safe to type the interrupt
1005 character at any time because @value{GDBN} does not allow it to take effect
1006 until a time when it is safe.
1009 If you have been using @value{GDBN} to control an attached process or
1010 device, you can release it with the @code{detach} command
1011 (@pxref{Attach, ,Debugging an already-running process}).
1014 @node Shell Commands
1015 @section Shell commands
1017 If you need to execute occasional shell commands during your
1018 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1019 just use the @code{shell} command.
1022 @item shell @var{command string}
1024 @cindex shell escape
1025 Invoke a the standard shell to execute @var{command string}.
1027 If it exists, the environment variable @code{SHELL} determines which
1028 shell to run. Otherwise @value{GDBN} uses @code{/bin/sh}.
1032 The utility @code{make} is often needed in development environments.
1033 You do not have to use the @code{shell} command for this purpose in
1037 @item make @var{make-args}
1039 @cindex calling make
1040 Execute the @code{make} program with the specified
1041 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1045 @chapter @value{GDBN} Commands
1047 You can abbreviate a @value{GDBN} command to the first few letters of the command
1048 name, if that abbreviation is unambiguous; and you can repeat certain
1049 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1050 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1051 show you the alternatives available, if there is more than one possibility).
1054 * Command Syntax:: How to give commands to @value{GDBN}
1055 * Completion:: Command completion
1056 * Help:: How to ask @value{GDBN} for help
1059 @node Command Syntax
1060 @section Command syntax
1062 A @value{GDBN} command is a single line of input. There is no limit on
1063 how long it can be. It starts with a command name, which is followed by
1064 arguments whose meaning depends on the command name. For example, the
1065 command @code{step} accepts an argument which is the number of times to
1066 step, as in @samp{step 5}. You can also use the @code{step} command
1067 with no arguments. Some command names do not allow any arguments.
1069 @cindex abbreviation
1070 @value{GDBN} command names may always be truncated if that abbreviation is
1071 unambiguous. Other possible command abbreviations are listed in the
1072 documentation for individual commands. In some cases, even ambiguous
1073 abbreviations are allowed; for example, @code{s} is specially defined as
1074 equivalent to @code{step} even though there are other commands whose
1075 names start with @code{s}. You can test abbreviations by using them as
1076 arguments to the @code{help} command.
1078 @cindex repeating commands
1080 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1081 repeat the previous command. Certain commands (for example, @code{run})
1082 will not repeat this way; these are commands for which unintentional
1083 repetition might cause trouble and which you are unlikely to want to
1086 The @code{list} and @code{x} commands, when you repeat them with
1087 @key{RET}, construct new arguments rather than repeating
1088 exactly as typed. This permits easy scanning of source or memory.
1090 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1091 output, in a way similar to the common utility @code{more}
1092 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1093 @key{RET} too many in this situation, @value{GDBN} disables command
1094 repetition after any command that generates this sort of display.
1098 Any text from a @kbd{#} to the end of the line is a comment; it does
1099 nothing. This is useful mainly in command files (@pxref{Command
1100 Files,,Command files}).
1103 @section Command completion
1106 @cindex word completion
1107 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1108 only one possibility; it can also show you what the valid possibilities
1109 are for the next word in a command, at any time. This works for @value{GDBN}
1110 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1112 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1113 of a word. If there is only one possibility, @value{GDBN} will fill in the
1114 word, and wait for you to finish the command (or press @key{RET} to
1115 enter it). For example, if you type
1117 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1118 @c complete accuracy in these examples; space introduced for clarity.
1119 @c If texinfo enhancements make it unnecessary, it would be nice to
1120 @c replace " @key" by "@key" in the following...
1122 (@value{GDBP}) info bre @key{TAB}
1126 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1127 the only @code{info} subcommand beginning with @samp{bre}:
1130 (@value{GDBP}) info breakpoints
1134 You can either press @key{RET} at this point, to run the @code{info
1135 breakpoints} command, or backspace and enter something else, if
1136 @samp{breakpoints} does not look like the command you expected. (If you
1137 were sure you wanted @code{info breakpoints} in the first place, you
1138 might as well just type @key{RET} immediately after @samp{info bre},
1139 to exploit command abbreviations rather than command completion).
1141 If there is more than one possibility for the next word when you press
1142 @key{TAB}, @value{GDBN} will sound a bell. You can either supply more
1143 characters and try again, or just press @key{TAB} a second time, and
1144 @value{GDBN} will display all the possible completions for that word. For
1145 example, you might want to set a breakpoint on a subroutine whose name
1146 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1147 just sounds the bell. Typing @key{TAB} again will display all the
1148 function names in your program that begin with those characters, for
1152 (@value{GDBP}) b make_ @key{TAB}
1153 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1154 make_a_section_from_file make_environ
1155 make_abs_section make_function_type
1156 make_blockvector make_pointer_type
1157 make_cleanup make_reference_type
1158 make_command make_symbol_completion_list
1159 (@value{GDBP}) b make_
1163 After displaying the available possibilities, @value{GDBN} copies your
1164 partial input (@samp{b make_} in the example) so you can finish the
1167 If you just want to see the list of alternatives in the first place, you
1168 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1169 means @kbd{@key{META} ?}. You can type this
1171 either by holding down a
1172 key designated as the @key{META} shift on your keyboard (if there is
1173 one) while typing @kbd{?}, or
1175 as @key{ESC} followed by @kbd{?}.
1177 @cindex quotes in commands
1178 @cindex completion of quoted strings
1179 Sometimes the string you need, while logically a ``word'', may contain
1180 parentheses or other characters that @value{GDBN} normally excludes from its
1181 notion of a word. To permit word completion to work in this situation,
1182 you may enclose words in @code{'} (single quote marks) in @value{GDBN} commands.
1185 The most likely situation where you might need this is in typing the
1186 name of a C++ function. This is because C++ allows function overloading
1187 (multiple definitions of the same function, distinguished by argument
1188 type). For example, when you want to set a breakpoint you may need to
1189 distinguish whether you mean the version of @code{name} that takes an
1190 @code{int} parameter, @code{name(int)}, or the version that takes a
1191 @code{float} parameter, @code{name(float)}. To use the word-completion
1192 facilities in this situation, type a single quote @code{'} at the
1193 beginning of the function name. This alerts @value{GDBN} that it may need to
1194 consider more information than usual when you press @key{TAB} or
1195 @kbd{M-?} to request word completion:
1198 (@value{GDBP}) b 'bubble( @key{M-?}
1199 bubble(double,double) bubble(int,int)
1200 (@value{GDBP}) b 'bubble(
1203 In some cases, @value{GDBN} can tell that completing a name will require
1204 quotes. When this happens, @value{GDBN} will insert the quote for you (while
1205 completing as much as it can) if you do not type the quote in the first
1209 (@value{GDBP}) b bub @key{TAB}
1210 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1211 (@value{GDBP}) b 'bubble(
1215 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1216 you have not yet started typing the argument list when you ask for
1217 completion on an overloaded symbol.
1222 @section Getting help
1223 @cindex online documentation
1226 You can always ask @value{GDBN} itself for information on its commands, using the
1227 command @code{help}.
1233 You can use @code{help} (abbreviated @code{h}) with no arguments to
1234 display a short list of named classes of commands:
1238 List of classes of commands:
1240 running -- Running the program
1241 stack -- Examining the stack
1242 data -- Examining data
1243 breakpoints -- Making program stop at certain points
1244 files -- Specifying and examining files
1245 status -- Status inquiries
1246 support -- Support facilities
1247 user-defined -- User-defined commands
1248 aliases -- Aliases of other commands
1249 obscure -- Obscure features
1251 Type "help" followed by a class name for a list of
1252 commands in that class.
1253 Type "help" followed by command name for full
1255 Command name abbreviations are allowed if unambiguous.
1259 @item help @var{class}
1260 Using one of the general help classes as an argument, you can get a
1261 list of the individual commands in that class. For example, here is the
1262 help display for the class @code{status}:
1265 (@value{GDBP}) help status
1270 @c Line break in "show" line falsifies real output, but needed
1271 @c to fit in smallbook page size.
1272 show -- Generic command for showing things set
1274 info -- Generic command for printing status
1276 Type "help" followed by command name for full
1278 Command name abbreviations are allowed if unambiguous.
1282 @item help @var{command}
1283 With a command name as @code{help} argument, @value{GDBN} will display a
1284 short paragraph on how to use that command.
1287 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1288 and @code{show} to inquire about the state of your program, or the state
1289 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1290 manual introduces each of them in the appropriate context. The listings
1291 under @code{info} and under @code{show} in the Index point to
1292 all the sub-commands. @xref{Index}.
1299 This command (abbreviated @code{i}) is for describing the state of your
1300 program. For example, you can list the arguments given to your program
1301 with @code{info args}, list the registers currently in use with @code{info
1302 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1303 You can get a complete list of the @code{info} sub-commands with
1304 @w{@code{help info}}.
1308 In contrast, @code{show} is for describing the state of @value{GDBN} itself.
1309 You can change most of the things you can @code{show}, by using the
1310 related command @code{set}; for example, you can control what number
1311 system is used for displays with @code{set radix}, or simply inquire
1312 which is currently in use with @code{show radix}.
1315 To display all the settable parameters and their current
1316 values, you can use @code{show} with no arguments; you may also use
1317 @code{info set}. Both commands produce the same display.
1318 @c FIXME: "info set" violates the rule that "info" is for state of
1319 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1320 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1324 Here are three miscellaneous @code{show} subcommands, all of which are
1325 exceptional in lacking corresponding @code{set} commands:
1328 @kindex show version
1329 @cindex version number
1331 Show what version of @value{GDBN} is running. You should include this
1332 information in @value{GDBN} bug-reports. If multiple versions of @value{GDBN} are in
1333 use at your site, you may occasionally want to determine which version
1334 of @value{GDBN} you are running; as @value{GDBN} evolves, new commands are introduced,
1335 and old ones may wither away. The version number is also announced
1336 when you start @value{GDBN}.
1338 @kindex show copying
1340 Display information about permission for copying @value{GDBN}.
1342 @kindex show warranty
1344 Display the GNU ``NO WARRANTY'' statement.
1348 @chapter Running Programs Under @value{GDBN}
1350 When you run a program under @value{GDBN}, you must first generate
1351 debugging information when you compile it.
1353 You may start it with its arguments, if any, in an environment of your
1354 choice. You may redirect your program's input and output, debug an
1355 already running process, or kill a child process.
1359 * Compilation:: Compiling for debugging
1360 * Starting:: Starting your program
1362 * Arguments:: Your program's arguments
1363 * Environment:: Your program's environment
1364 * Working Directory:: Your program's working directory
1365 * Input/Output:: Your program's input and output
1366 * Attach:: Debugging an already-running process
1367 * Kill Process:: Killing the child process
1368 * Process Information:: Additional process information
1373 @section Compiling for debugging
1375 In order to debug a program effectively, you need to generate
1376 debugging information when you compile it. This debugging information
1377 is stored in the object file; it describes the data type of each
1378 variable or function and the correspondence between source line numbers
1379 and addresses in the executable code.
1381 To request debugging information, specify the @samp{-g} option when you run
1384 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1385 options together. Using those compilers, you cannot generate optimized
1386 executables containing debugging information.
1388 @value{NGCC}, the GNU C compiler, supports @samp{-g} with or without
1389 @samp{-O}, making it possible to debug optimized code. We recommend
1390 that you @emph{always} use @samp{-g} whenever you compile a program.
1391 You may think your program is correct, but there is no sense in pushing
1394 @cindex optimized code, debugging
1395 @cindex debugging optimized code
1396 When you debug a program compiled with @samp{-g -O}, remember that the
1397 optimizer is rearranging your code; the debugger will show you what is
1398 really there. Do not be too surprised when the execution path does not
1399 exactly match your source file! An extreme example: if you define a
1400 variable, but never use it, @value{GDBN} will never see that
1401 variable---because the compiler optimizes it out of existence.
1403 Some things do not work as well with @samp{-g -O} as with just
1404 @samp{-g}, particularly on machines with instruction scheduling. If in
1405 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1406 please report it as a bug (including a test case!).
1408 Older versions of the GNU C compiler permitted a variant option
1409 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1410 format; if your GNU C compiler has this option, do not use it.
1414 @section Starting your program
1422 Use the @code{run} command to start your program under @value{GDBN}. You must
1423 first specify the program name
1427 with an argument to @value{GDBN} (@pxref{Invocation, ,Getting In and
1428 Out of @value{GDBN}}), or by using the @code{file} or @code{exec-file}
1429 command (@pxref{Files, ,Commands to specify files}).
1434 If you are running your program in an execution environment that
1435 supports processes, @code{run} creates an inferior process and makes
1436 that process run your program. (In environments without processes,
1437 @code{run} jumps to the start of your program.)
1439 The execution of a program is affected by certain information it
1440 receives from its superior. @value{GDBN} provides ways to specify this
1441 information, which you must do @emph{before} starting your program. (You
1442 can change it after starting your program, but such changes will only affect
1443 your program the next time you start it.) This information may be
1444 divided into four categories:
1447 @item The @emph{arguments.}
1448 Specify the arguments to give your program as the arguments of the
1449 @code{run} command. If a shell is available on your target, the shell
1450 is used to pass the arguments, so that you may use normal conventions
1451 (such as wildcard expansion or variable substitution) in describing
1452 the arguments. In Unix systems, you can control which shell is used
1453 with the @code{SHELL} environment variable. @xref{Arguments, ,Your
1454 program's arguments}.
1456 @item The @emph{environment.}
1457 Your program normally inherits its environment from @value{GDBN}, but you can
1458 use the @value{GDBN} commands @code{set environment} and @code{unset
1459 environment} to change parts of the environment that will be given to
1460 your program. @xref{Environment, ,Your program's environment}.
1462 @item The @emph{working directory.}
1463 Your program inherits its working directory from @value{GDBN}. You can set
1464 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1465 @xref{Working Directory, ,Your program's working directory}.
1467 @item The @emph{standard input and output.}
1468 Your program normally uses the same device for standard input and
1469 standard output as @value{GDBN} is using. You can redirect input and output
1470 in the @code{run} command line, or you can use the @code{tty} command to
1471 set a different device for your program.
1472 @xref{Input/Output, ,Your program's input and output}.
1475 @emph{Warning:} While input and output redirection work, you cannot use
1476 pipes to pass the output of the program you are debugging to another
1477 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1482 When you issue the @code{run} command, your program begins to execute
1483 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1484 of how to arrange for your program to stop. Once your program has
1485 stopped, you may calls functions in your program, using the @code{print}
1486 or @code{call} commands. @xref{Data, ,Examining Data}.
1488 If the modification time of your symbol file has changed since the
1489 last time @value{GDBN} read its symbols, @value{GDBN} will discard its symbol table and
1490 re-read it. When it does this, @value{GDBN} tries to retain your current
1495 @section Your program's arguments
1497 @cindex arguments (to your program)
1498 The arguments to your program can be specified by the arguments of the
1499 @code{run} command. They are passed to a shell, which expands wildcard
1500 characters and performs redirection of I/O, and thence to your program.
1501 Your @code{SHELL} environment variable (if it exists) specifies what
1502 shell @value{GDBN} if you do not define @code{SHELL}, @value{GDBN} uses
1505 @code{run} with no arguments uses the same arguments used by the previous
1506 @code{run}, or those set by the @code{set args} command.
1511 Specify the arguments to be used the next time your program is run. If
1512 @code{set args} has no arguments, @code{run} will execute your program
1513 with no arguments. Once you have run your program with arguments,
1514 using @code{set args} before the next @code{run} is the only way to run
1515 it again without arguments.
1519 Show the arguments to give your program when it is started.
1523 @section Your program's environment
1525 @cindex environment (of your program)
1526 The @dfn{environment} consists of a set of environment variables and
1527 their values. Environment variables conventionally record such things as
1528 your user name, your home directory, your terminal type, and your search
1529 path for programs to run. Usually you set up environment variables with
1530 the shell and they are inherited by all the other programs you run. When
1531 debugging, it can be useful to try running your program with a modified
1532 environment without having to start @value{GDBN} over again.
1535 @item path @var{directory}
1537 Add @var{directory} to the front of the @code{PATH} environment variable
1538 (the search path for executables), for both @value{GDBN} and your program.
1539 You may specify several directory names, separated by @samp{:} or
1540 whitespace. If @var{directory} is already in the path, it is moved to
1541 the front, so it will be searched sooner.
1543 You can use the string @samp{$cwd} to refer to whatever is the current
1544 working directory at the time @value{GDBN} searches the path. If you
1545 use @samp{.} instead, it refers to the directory where you executed the
1546 @code{path} command. @value{GDBN} replaces @samp{.} in the
1547 @var{directory} argument (with the current path) before adding
1548 @var{directory} to the search path.
1549 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1550 @c document that, since repeating it would be a no-op.
1554 Display the list of search paths for executables (the @code{PATH}
1555 environment variable).
1557 @item show environment @r{[}@var{varname}@r{]}
1558 @kindex show environment
1559 Print the value of environment variable @var{varname} to be given to
1560 your program when it starts. If you do not supply @var{varname},
1561 print the names and values of all environment variables to be given to
1562 your program. You can abbreviate @code{environment} as @code{env}.
1564 @item set environment @var{varname} @r{[}=@r{]} @var{value}
1565 @kindex set environment
1566 Set environment variable @var{varname} to @var{value}. The value
1567 changes for your program only, not for @value{GDBN} itself. @var{value} may
1568 be any string; the values of environment variables are just strings, and
1569 any interpretation is supplied by your program itself. The @var{value}
1570 parameter is optional; if it is eliminated, the variable is set to a
1572 @c "any string" here does not include leading, trailing
1573 @c blanks. Gnu asks: does anyone care?
1575 For example, this command:
1582 tells a Unix program, when subsequently run, that its user is named
1583 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1584 are not actually required.)
1586 @item unset environment @var{varname}
1587 @kindex unset environment
1588 Remove variable @var{varname} from the environment to be passed to your
1589 program. This is different from @samp{set env @var{varname} =};
1590 @code{unset environment} removes the variable from the environment,
1591 rather than assigning it an empty value.
1594 @emph{Warning:} @value{GDBN} runs your program using the shell indicated
1595 by your @code{SHELL} environment variable if it exists (or
1596 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1597 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1598 @file{.bashrc} for BASH---any variables you set in that file will affect
1599 your program. You may wish to move setting of environment variables to
1600 files that are only run when you sign on, such as @file{.login} or
1603 @node Working Directory
1604 @section Your program's working directory
1606 @cindex working directory (of your program)
1607 Each time you start your program with @code{run}, it inherits its
1608 working directory from the current working directory of @value{GDBN}.
1609 The @value{GDBN} working directory is initially whatever it inherited
1610 from its parent process (typically the shell), but you can specify a new
1611 working directory in @value{GDBN} with the @code{cd} command.
1613 The @value{GDBN} working directory also serves as a default for the commands
1614 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1618 @item cd @var{directory}
1620 Set the @value{GDBN} working directory to @var{directory}.
1624 Print the @value{GDBN} working directory.
1628 @section Your program's input and output
1633 By default, the program you run under @value{GDBN} does input and output to
1634 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal to
1635 its own terminal modes to interact with you, but it records the terminal
1636 modes your program was using and switches back to them when you continue
1637 running your program.
1641 @kindex info terminal
1642 Displays information recorded by @value{GDBN} about the terminal modes your
1646 You can redirect your program's input and/or output using shell
1647 redirection with the @code{run} command. For example,
1654 starts your program, diverting its output to the file @file{outfile}.
1657 @cindex controlling terminal
1658 Another way to specify where your program should do input and output is
1659 with the @code{tty} command. This command accepts a file name as
1660 argument, and causes this file to be the default for future @code{run}
1661 commands. It also resets the controlling terminal for the child
1662 process, for future @code{run} commands. For example,
1669 directs that processes started with subsequent @code{run} commands
1670 default to do input and output on the terminal @file{/dev/ttyb} and have
1671 that as their controlling terminal.
1673 An explicit redirection in @code{run} overrides the @code{tty} command's
1674 effect on the input/output device, but not its effect on the controlling
1677 When you use the @code{tty} command or redirect input in the @code{run}
1678 command, only the input @emph{for your program} is affected. The input
1679 for @value{GDBN} still comes from your terminal.
1682 @section Debugging an already-running process
1687 @item attach @var{process-id}
1688 This command attaches to a running process---one that was started
1689 outside @value{GDBN}. (@code{info files} will show your active
1690 targets.) The command takes as argument a process ID. The usual way to
1691 find out the process-id of a Unix process is with the @code{ps} utility,
1692 or with the @samp{jobs -l} shell command.
1694 @code{attach} will not repeat if you press @key{RET} a second time after
1695 executing the command.
1698 To use @code{attach}, your program must be running in an environment
1699 which supports processes; for example, @code{attach} does not work for
1700 programs on bare-board targets that lack an operating system. You must
1701 also have permission to send the process a signal.
1703 When using @code{attach}, you should first use the @code{file} command
1704 to specify the program running in the process and load its symbol table.
1705 @xref{Files, ,Commands to Specify Files}.
1707 The first thing @value{GDBN} does after arranging to debug the specified
1708 process is to stop it. You can examine and modify an attached process
1709 with all the @value{GDBN} commands that are ordinarily available when you start
1710 processes with @code{run}. You can insert breakpoints; you can step and
1711 continue; you can modify storage. If you would rather the process
1712 continue running, you may use the @code{continue} command after
1713 attaching @value{GDBN} to the process.
1718 When you have finished debugging the attached process, you can use the
1719 @code{detach} command to release it from @value{GDBN} control. Detaching
1720 the process continues its execution. After the @code{detach} command,
1721 that process and @value{GDBN} become completely independent once more, and you
1722 are ready to @code{attach} another process or start one with @code{run}.
1723 @code{detach} will not repeat if you press @key{RET} again after
1724 executing the command.
1727 If you exit @value{GDBN} or use the @code{run} command while you have an attached
1728 process, you kill that process. By default, you will be asked for
1729 confirmation if you try to do either of these things; you can control
1730 whether or not you need to confirm by using the @code{set confirm} command
1731 (@pxref{Messages/Warnings, ,Optional warnings and messages}).
1735 @section Killing the child process
1740 Kill the child process in which your program is running under @value{GDBN}.
1743 This command is useful if you wish to debug a core dump instead of a
1744 running process. @value{GDBN} ignores any core dump file while your program
1748 On some operating systems, a program cannot be executed outside @value{GDBN}
1749 while you have breakpoints set on it inside @value{GDBN}. You can use the
1750 @code{kill} command in this situation to permit running your program
1751 outside the debugger.
1753 The @code{kill} command is also useful if you wish to recompile and
1754 relink your program, since on many systems it is impossible to modify an
1755 executable file while it is running in a process. In this case, when you
1756 next type @code{run}, @value{GDBN} will notice that the file has changed, and
1757 will re-read the symbol table (while trying to preserve your current
1758 breakpoint settings).
1760 @node Process Information
1761 @section Additional process information
1764 @cindex process image
1765 Some operating systems provide a facility called @samp{/proc} that can
1766 be used to examine the image of a running process using file-system
1767 subroutines. If @value{GDBN} is configured for an operating system with this
1768 facility, the command @code{info proc} is available to report on several
1769 kinds of information about the process running your program.
1774 Summarize available information about the process.
1776 @item info proc mappings
1777 @kindex info proc mappings
1778 Report on the address ranges accessible in the program, with information
1779 on whether your program may read, write, or execute each range.
1781 @item info proc times
1782 @kindex info proc times
1783 Starting time, user CPU time, and system CPU time for your program and
1787 @kindex info proc id
1788 Report on the process IDs related to your program: its own process ID,
1789 the ID of its parent, the process group ID, and the session ID.
1791 @item info proc status
1792 @kindex info proc status
1793 General information on the state of the process. If the process is
1794 stopped, this report includes the reason for stopping, and any signal
1798 Show all the above information about the process.
1803 @chapter Stopping and Continuing
1805 The principal purposes of using a debugger are so that you can stop your
1806 program before it terminates; or so that, if your program runs into
1807 trouble, you can investigate and find out why.
1809 Inside @value{GDBN}, your program may stop for any of several reasons, such
1814 a breakpoint, or reaching a new line after a @value{GDBN}
1815 command such as @code{step}. You may then examine and change
1816 variables, set new breakpoints or remove old ones, and then continue
1817 execution. Usually, the messages shown by @value{GDBN} provide ample
1818 explanation of the status of your program---but you can also explicitly
1819 request this information at any time.
1823 @kindex info program
1824 Display information about the status of your program: whether it is
1834 * Breakpoints:: Breakpoints, watchpoints, and exceptions
1837 * Breakpoints:: Breakpoints and watchpoints
1839 @c Remnant makeinfo bug requires blank line after *successful* end-if in menu:
1841 * Continuing and Stepping:: Resuming execution
1847 @c makeinfo node-defaulting requires adjacency of @node and sectioning cmds
1848 @c ...hence distribute @node Breakpoints over two possible @if expansions.
1852 @section Breakpoints, watchpoints, and exceptions
1856 @section Breakpoints and watchpoints
1860 A @dfn{breakpoint} makes your program stop whenever a certain point in
1861 the program is reached. For each breakpoint, you can add various
1862 conditions to control in finer detail whether your program will stop.
1863 You can set breakpoints with the @code{break} command and its variants
1864 (@pxref{Set Breaks, ,Setting breakpoints}), to specify the place where
1865 your program should stop by line number, function name or exact address
1868 In languages with exception handling (such as GNU C++), you can also set
1869 breakpoints where an exception is raised (@pxref{Exception Handling,
1870 ,Breakpoints and exceptions}).
1874 @cindex memory tracing
1875 @cindex breakpoint on memory address
1876 @cindex breakpoint on variable modification
1877 A @dfn{watchpoint} is a special breakpoint that stops your program
1878 when the value of an expression changes. You must use a different
1879 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
1880 watchpoints}), but aside from that, you can manage a watchpoint like
1881 any other breakpoint: you enable, disable, and delete both breakpoints
1882 and watchpoints using the same commands.
1884 You can arrange to have values from your program displayed automatically
1885 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,
1886 ,Automatic display}.
1888 @cindex breakpoint numbers
1889 @cindex numbers for breakpoints
1890 @value{GDBN} assigns a number to each breakpoint or watchpoint when you
1891 create it; these numbers are successive integers starting with one. In
1892 many of the commands for controlling various features of breakpoints you
1893 use the breakpoint number to say which breakpoint you want to change.
1894 Each breakpoint may be @dfn{enabled} or @dfn{disabled}; if disabled, it has
1895 no effect on your program until you enable it again.
1898 * Set Breaks:: Setting breakpoints
1899 * Set Watchpoints:: Setting watchpoints
1901 * Exception Handling:: Breakpoints and exceptions
1904 * Delete Breaks:: Deleting breakpoints
1905 * Disabling:: Disabling breakpoints
1906 * Conditions:: Break conditions
1907 * Break Commands:: Breakpoint command lists
1909 * Breakpoint Menus:: Breakpoint menus
1912 * Error in Breakpoints:: ``Cannot insert breakpoints''
1917 @subsection Setting breakpoints
1919 @c FIXME LMB what does GDB do if no code on line of breakpt?
1920 @c consider in particular declaration with/without initialization.
1922 @c FIXME 2 is there stuff on this already? break at fun start, already init?
1927 @cindex latest breakpoint
1928 Breakpoints are set with the @code{break} command (abbreviated
1929 @code{b}). The debugger convenience variable @samp{$bpnum} records the
1930 number of the beakpoint you've set most recently; see @ref{Convenience
1931 Vars,, Convenience variables}, for a discussion of what you can do with
1932 convenience variables.
1934 You have several ways to say where the breakpoint should go.
1937 @item break @var{function}
1938 Set a breakpoint at entry to function @var{function}.
1940 When using source languages that permit overloading of symbols, such as
1941 C++, @var{function} may refer to more than one possible place to break.
1942 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
1945 @item break +@var{offset}
1946 @itemx break -@var{offset}
1947 Set a breakpoint some number of lines forward or back from the position
1948 at which execution stopped in the currently selected frame.
1950 @item break @var{linenum}
1951 Set a breakpoint at line @var{linenum} in the current source file.
1952 That file is the last file whose source text was printed. This
1953 breakpoint will stop your program just before it executes any of the
1956 @item break @var{filename}:@var{linenum}
1957 Set a breakpoint at line @var{linenum} in source file @var{filename}.
1959 @item break @var{filename}:@var{function}
1960 Set a breakpoint at entry to function @var{function} found in file
1961 @var{filename}. Specifying a file name as well as a function name is
1962 superfluous except when multiple files contain similarly named
1965 @item break *@var{address}
1966 Set a breakpoint at address @var{address}. You can use this to set
1967 breakpoints in parts of your program which do not have debugging
1968 information or source files.
1971 When called without any arguments, @code{break} sets a breakpoint at
1972 the next instruction to be executed in the selected stack frame
1973 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
1974 innermost, this will cause your program to stop as soon as control
1975 returns to that frame. This is similar to the effect of a
1976 @code{finish} command in the frame inside the selected frame---except
1977 that @code{finish} does not leave an active breakpoint. If you use
1978 @code{break} without an argument in the innermost frame, @value{GDBN} will stop
1979 the next time it reaches the current location; this may be useful
1982 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
1983 least one instruction has been executed. If it did not do this, you
1984 would be unable to proceed past a breakpoint without first disabling the
1985 breakpoint. This rule applies whether or not the breakpoint already
1986 existed when your program stopped.
1988 @item break @dots{} if @var{cond}
1989 Set a breakpoint with condition @var{cond}; evaluate the expression
1990 @var{cond} each time the breakpoint is reached, and stop only if the
1991 value is nonzero---that is, if @var{cond} evaluates as true.
1992 @samp{@dots{}} stands for one of the possible arguments described
1993 above (or no argument) specifying where to break. @xref{Conditions,
1994 ,Break conditions}, for more information on breakpoint conditions.
1996 @item tbreak @var{args}
1998 Set a breakpoint enabled only for one stop. @var{args} are the
1999 same as for the @code{break} command, and the breakpoint is set in the same
2000 way, but the breakpoint is automatically disabled after the first time your
2001 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2003 @item rbreak @var{regex}
2005 @cindex regular expression
2006 @c FIXME what kind of regexp?
2007 Set breakpoints on all functions matching the regular expression
2008 @var{regex}. This command
2009 sets an unconditional breakpoint on all matches, printing a list of all
2010 breakpoints it set. Once these breakpoints are set, they are treated
2011 just like the breakpoints set with the @code{break} command. They can
2012 be deleted, disabled, made conditional, etc., in the standard ways.
2015 When debugging C++ programs, @code{rbreak} is useful for setting
2016 breakpoints on overloaded functions that are not members of any special
2020 @kindex info breakpoints
2021 @cindex @code{$_} and @code{info breakpoints}
2022 @item info breakpoints @r{[}@var{n}@r{]}
2023 @itemx info break @r{[}@var{n}@r{]}
2024 @itemx info watchpoints @r{[}@var{n}@r{]}
2025 Print a table of all breakpoints and watchpoints set and not
2026 deleted, with the following columns for each breakpoint:
2029 @item Breakpoint Numbers
2031 Breakpoint or watchpoint.
2033 Whether the breakpoint is marked to be disabled or deleted when hit.
2034 @item Enabled or Disabled
2035 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2036 that are not enabled.
2038 Where the breakpoint is in your program, as a memory address
2040 Where the breakpoint is in the source for your program, as a file and
2045 If a breakpoint is conditional, @code{info break} shows the condition on
2046 the line following the affected breakpoint; breakpoint commands, if any,
2047 are listed after that.
2050 @code{info break} with a breakpoint
2051 number @var{n} as argument lists only that breakpoint. The
2052 convenience variable @code{$_} and the default examining-address for
2053 the @code{x} command are set to the address of the last breakpoint
2054 listed (@pxref{Memory, ,Examining memory}).
2057 @value{GDBN} allows you to set any number of breakpoints at the same place in
2058 your program. There is nothing silly or meaningless about this. When
2059 the breakpoints are conditional, this is even useful
2060 (@pxref{Conditions, ,Break conditions}).
2062 @cindex negative breakpoint numbers
2063 @cindex internal @value{GDBN} breakpoints
2064 @value{GDBN} itself sometimes sets breakpoints in your program for special
2065 purposes, such as proper handling of @code{longjmp} (in C programs).
2066 These internal breakpoints are assigned negative numbers, starting with
2067 @code{-1}; @samp{info breakpoints} does not display them.
2069 You can see these breakpoints with the @value{GDBN} maintenance command
2070 @samp{maint info breakpoints}.
2073 @kindex maint info breakpoints
2074 @item maint info breakpoints
2075 Using the same format as @samp{info breakpoints}, display both the
2076 breakpoints you've set explicitly, and those @value{GDBN} is using for
2077 internal purposes. Internal breakpoints are shown with negative
2078 breakpoint numbers. The type column identifies what kind of breakpoint
2083 Normal, explicitly set breakpoint.
2086 Normal, explicitly set watchpoint.
2089 Internal breakpoint, used to handle correctly stepping through
2090 @code{longjmp} calls.
2092 @item longjmp resume
2093 Internal breakpoint at the target of a @code{longjmp}.
2096 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2099 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2105 @node Set Watchpoints
2106 @subsection Setting watchpoints
2107 @cindex setting watchpoints
2109 You can use a watchpoint to stop execution whenever the value of an
2110 expression changes, without having to predict a particular place
2111 where this may happen.
2113 Watchpoints currently execute two orders of magnitude more slowly than
2114 other breakpoints, but this can well be worth it to catch errors where
2115 you have no clue what part of your program is the culprit. Some
2116 processors provide special hardware to support watchpoint evaluation; future
2117 releases of @value{GDBN} will use such hardware if it is available.
2121 @item watch @var{expr}
2122 Set a watchpoint for an expression.
2124 @kindex info watchpoints
2125 @item info watchpoints
2126 This command prints a list of watchpoints and breakpoints; it is the
2127 same as @code{info break}.
2131 @node Exception Handling
2132 @subsection Breakpoints and exceptions
2133 @cindex exception handlers
2135 Some languages, such as GNU C++, implement exception handling. You can
2136 use @value{GDBN} to examine what caused your program to raise an exception,
2137 and to list the exceptions your program is prepared to handle at a
2138 given point in time.
2141 @item catch @var{exceptions}
2143 You can set breakpoints at active exception handlers by using the
2144 @code{catch} command. @var{exceptions} is a list of names of exceptions
2148 You can use @code{info catch} to list active exception handlers.
2149 @xref{Frame Info, ,Information about a frame}.
2151 There are currently some limitations to exception handling in @value{GDBN}.
2152 These will be corrected in a future release.
2156 If you call a function interactively, @value{GDBN} normally returns
2157 control to you when the function has finished executing. If the call
2158 raises an exception, however, the call may bypass the mechanism that
2159 returns control to you and cause your program to simply continue
2160 running until it hits a breakpoint, catches a signal that @value{GDBN} is
2161 listening for, or exits.
2163 You cannot raise an exception interactively.
2165 You cannot interactively install an exception handler.
2168 @cindex raise exceptions
2169 Sometimes @code{catch} is not the best way to debug exception handling:
2170 if you need to know exactly where an exception is raised, it is better to
2171 stop @emph{before} the exception handler is called, since that way you
2172 can see the stack before any unwinding takes place. If you set a
2173 breakpoint in an exception handler instead, it may not be easy to find
2174 out where the exception was raised.
2176 To stop just before an exception handler is called, you need some
2177 knowledge of the implementation. In the case of GNU C++, exceptions are
2178 raised by calling a library function named @code{__raise_exception}
2179 which has the following ANSI C interface:
2182 /* @var{addr} is where the exception identifier is stored.
2183 ID is the exception identifier. */
2184 void __raise_exception (void **@var{addr}, void *@var{id});
2188 To make the debugger catch all exceptions before any stack
2189 unwinding takes place, set a breakpoint on @code{__raise_exception}
2190 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2192 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2193 that depends on the value of @var{id}, you can stop your program when
2194 a specific exception is raised. You can use multiple conditional
2195 breakpoints to stop your program when any of a number of exceptions are
2200 @subsection Deleting breakpoints
2202 @cindex clearing breakpoints, watchpoints
2203 @cindex deleting breakpoints, watchpoints
2204 It is often necessary to eliminate a breakpoint or watchpoint once it
2205 has done its job and you no longer want your program to stop there. This
2206 is called @dfn{deleting} the breakpoint. A breakpoint that has been
2207 deleted no longer exists; it is forgotten.
2209 With the @code{clear} command you can delete breakpoints according to
2210 where they are in your program. With the @code{delete} command you can
2211 delete individual breakpoints or watchpoints by specifying their
2214 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2215 automatically ignores breakpoints on the first instruction to be executed
2216 when you continue execution without changing the execution address.
2221 Delete any breakpoints at the next instruction to be executed in the
2222 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2223 the innermost frame is selected, this is a good way to delete a
2224 breakpoint where your program just stopped.
2226 @item clear @var{function}
2227 @itemx clear @var{filename}:@var{function}
2228 Delete any breakpoints set at entry to the function @var{function}.
2230 @item clear @var{linenum}
2231 @itemx clear @var{filename}:@var{linenum}
2232 Delete any breakpoints set at or within the code of the specified line.
2234 @item delete @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2235 @cindex delete breakpoints
2238 Delete the breakpoints or watchpoints of the numbers specified as
2239 arguments. If no argument is specified, delete all breakpoints (@value{GDBN}
2240 asks confirmation, unless you have @code{set confirm off}). You
2241 can abbreviate this command as @code{d}.
2245 @subsection Disabling breakpoints
2247 @cindex disabled breakpoints
2248 @cindex enabled breakpoints
2249 Rather than deleting a breakpoint or watchpoint, you might prefer to
2250 @dfn{disable} it. This makes the breakpoint inoperative as if it had
2251 been deleted, but remembers the information on the breakpoint so that
2252 you can @dfn{enable} it again later.
2254 You disable and enable breakpoints and watchpoints with the
2255 @code{enable} and @code{disable} commands, optionally specifying one or
2256 more breakpoint numbers as arguments. Use @code{info break} or
2257 @code{info watch} to print a list of breakpoints or watchpoints if you
2258 do not know which numbers to use.
2260 A breakpoint or watchpoint can have any of four different states of
2265 Enabled. The breakpoint will stop your program. A breakpoint set
2266 with the @code{break} command starts out in this state.
2268 Disabled. The breakpoint has no effect on your program.
2270 Enabled once. The breakpoint will stop your program, but
2271 when it does so it will become disabled. A breakpoint set
2272 with the @code{tbreak} command starts out in this state.
2274 Enabled for deletion. The breakpoint will stop your program, but
2275 immediately after it does so it will be deleted permanently.
2278 You can use the following commands to enable or disable breakpoints and
2282 @item disable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2283 @kindex disable breakpoints
2286 Disable the specified breakpoints---or all breakpoints, if none are
2287 listed. A disabled breakpoint has no effect but is not forgotten. All
2288 options such as ignore-counts, conditions and commands are remembered in
2289 case the breakpoint is enabled again later. You may abbreviate
2290 @code{disable} as @code{dis}.
2292 @item enable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2293 @kindex enable breakpoints
2295 Enable the specified breakpoints (or all defined breakpoints). They
2296 become effective once again in stopping your program.
2298 @item enable @r{[}breakpoints@r{]} once @var{bnums}@dots{}
2299 Enable the specified breakpoints temporarily. Each will be disabled
2300 again the next time it stops your program.
2302 @item enable @r{[}breakpoints@r{]} delete @var{bnums}@dots{}
2303 Enable the specified breakpoints to work once and then die. Each of
2304 the breakpoints will be deleted the next time it stops your program.
2307 Save for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2308 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2309 subsequently, they become disabled or enabled only when you use one of
2310 the commands above. (The command @code{until} can set and delete a
2311 breakpoint of its own, but it will not change the state of your other
2312 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2316 @subsection Break conditions
2317 @cindex conditional breakpoints
2318 @cindex breakpoint conditions
2320 @c FIXME what is scope of break condition expr? Context where wanted?
2321 @c in particular for a watchpoint?
2322 The simplest sort of breakpoint breaks every time your program reaches a
2323 specified place. You can also specify a @dfn{condition} for a
2324 breakpoint. A condition is just a Boolean expression in your
2325 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2326 a condition evaluates the expression each time your program reaches it,
2327 and your program stops only if the condition is @emph{true}.
2329 This is the converse of using assertions for program validation; in that
2330 situation, you want to stop when the assertion is violated---that is,
2331 when the condition is false. In C, if you want to test an assertion expressed
2332 by the condition @var{assert}, you should set the condition
2333 @samp{! @var{assert}} on the appropriate breakpoint.
2335 Conditions are also accepted for watchpoints; you may not need them,
2336 since a watchpoint is inspecting the value of an expression anyhow---but
2337 it might be simpler, say, to just set a watchpoint on a variable name,
2338 and specify a condition that tests whether the new value is an interesting
2341 Break conditions can have side effects, and may even call functions in
2342 your program. This can be useful, for example, to activate functions
2343 that log program progress, or to use your own print functions to
2344 format special data structures. The effects are completely predictable
2345 unless there is another enabled breakpoint at the same address. (In
2346 that case, @value{GDBN} might see the other breakpoint first and stop your
2347 program without checking the condition of this one.) Note that
2348 breakpoint commands are usually more convenient and flexible for the
2349 purpose of performing side effects when a breakpoint is reached
2350 (@pxref{Break Commands, ,Breakpoint command lists}).
2352 Break conditions can be specified when a breakpoint is set, by using
2353 @samp{if} in the arguments to the @code{break} command. @xref{Set
2354 Breaks, ,Setting breakpoints}. They can also be changed at any time
2355 with the @code{condition} command. The @code{watch} command does not
2356 recognize the @code{if} keyword; @code{condition} is the only way to
2357 impose a further condition on a watchpoint.
2360 @item condition @var{bnum} @var{expression}
2362 Specify @var{expression} as the break condition for breakpoint or
2363 watchpoint number @var{bnum}. From now on, this breakpoint will stop
2364 your program only if the value of @var{expression} is true (nonzero, in
2365 C). When you use @code{condition}, @value{GDBN} checks @var{expression}
2366 immediately for syntactic correctness, and to determine whether symbols
2367 in it have referents in the context of your breakpoint.
2368 @c FIXME so what does GDB do if there is no referent? Moreover, what
2369 @c about watchpoints?
2371 not actually evaluate @var{expression} at the time the @code{condition}
2372 command is given, however. @xref{Expressions, ,Expressions}.
2374 @item condition @var{bnum}
2375 Remove the condition from breakpoint number @var{bnum}. It becomes
2376 an ordinary unconditional breakpoint.
2379 @cindex ignore count (of breakpoint)
2380 A special case of a breakpoint condition is to stop only when the
2381 breakpoint has been reached a certain number of times. This is so
2382 useful that there is a special way to do it, using the @dfn{ignore
2383 count} of the breakpoint. Every breakpoint has an ignore count, which
2384 is an integer. Most of the time, the ignore count is zero, and
2385 therefore has no effect. But if your program reaches a breakpoint whose
2386 ignore count is positive, then instead of stopping, it just decrements
2387 the ignore count by one and continues. As a result, if the ignore count
2388 value is @var{n}, the breakpoint will not stop the next @var{n} times it
2392 @item ignore @var{bnum} @var{count}
2394 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
2395 The next @var{count} times the breakpoint is reached, your program's
2396 execution will not stop; other than to decrement the ignore count, @value{GDBN}
2399 To make the breakpoint stop the next time it is reached, specify
2402 When you use @code{continue} to resume execution of your program from a
2403 breakpoint, you can specify an ignore count directly as an argument to
2404 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
2405 Stepping,,Continuing and stepping}.
2407 If a breakpoint has a positive ignore count and a condition, the condition
2408 is not checked. Once the ignore count reaches zero, the condition will
2411 You could achieve the effect of the ignore count with a condition such
2412 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
2413 is decremented each time. @xref{Convenience Vars, ,Convenience
2417 @node Break Commands
2418 @subsection Breakpoint command lists
2420 @cindex breakpoint commands
2421 You can give any breakpoint (or watchpoint) a series of commands to
2422 execute when your program stops due to that breakpoint. For example, you
2423 might want to print the values of certain expressions, or enable other
2427 @item commands @r{[}@var{bnum}@r{]}
2428 @itemx @dots{} @var{command-list} @dots{}
2432 Specify a list of commands for breakpoint number @var{bnum}. The commands
2433 themselves appear on the following lines. Type a line containing just
2434 @code{end} to terminate the commands.
2436 To remove all commands from a breakpoint, type @code{commands} and
2437 follow it immediately with @code{end}; that is, give no commands.
2439 With no @var{bnum} argument, @code{commands} refers to the last
2440 breakpoint or watchpoint set (not to the breakpoint most recently
2444 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
2445 disabled within a @var{command-list}.
2447 You can use breakpoint commands to start your program up again. Simply
2448 use the @code{continue} command, or @code{step}, or any other command
2449 that resumes execution.
2451 Any other commands in the command list, after a command that resumes
2452 execution, are ignored. This is because any time you resume execution
2453 (even with a simple @code{next} or @code{step}), you may encounter
2454 another breakpoint---which could have its own command list, leading to
2455 ambiguities about which list to execute.
2458 If the first command you specify in a command list is @code{silent}, the
2459 usual message about stopping at a breakpoint is not printed. This may
2460 be desirable for breakpoints that are to print a specific message and
2461 then continue. If none of the remaining commands print anything, you
2462 will see no sign that the breakpoint was reached. @code{silent} is
2463 meaningful only at the beginning of a breakpoint command list.
2465 The commands @code{echo}, @code{output}, and @code{printf} allow you to
2466 print precisely controlled output, and are often useful in silent
2467 breakpoints. @xref{Output, ,Commands for controlled output}.
2469 For example, here is how you could use breakpoint commands to print the
2470 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
2476 printf "x is %d\n",x
2481 One application for breakpoint commands is to compensate for one bug so
2482 you can test for another. Put a breakpoint just after the erroneous line
2483 of code, give it a condition to detect the case in which something
2484 erroneous has been done, and give it commands to assign correct values
2485 to any variables that need them. End with the @code{continue} command
2486 so that your program does not stop, and start with the @code{silent}
2487 command so that no output is produced. Here is an example:
2499 @c Do we need to mention this at all? I am sort of tempted to mention
2500 @c it in case people are used to seeing this section of the manual. But
2501 @c for new users it is an annoyance--it documents something which isn't
2502 @c there. -kingdon, 6 Jul 93
2503 Previous versions of @value{GDBN} (4.9 and earlier) would flush pending
2504 input when executing breakpoint commands, if your program used raw mode
2505 for the terminal. This is no longer true.
2508 @c I don't think this is true any longer, now that only readline
2509 @c switches to or from raw mode. In any event, it is a (relatively
2510 @c easily fixable) GDB bug if it switches to or from raw mode except
2511 @c when it has to in order to read input from the terminal. kingdon -6 Jul 93.
2512 One deficiency in the operation of automatically continuing breakpoints
2513 under Unix appears when your program uses raw mode for the terminal.
2514 @value{GDBN} switches back to its own terminal modes (not raw) before executing
2515 commands, and then must switch back to raw mode when your program is
2516 continued. This causes any pending terminal input to be lost.
2517 @c FIXME: revisit below when GNU sys avail.
2518 @c In the GNU system, this will be fixed by changing the behavior of
2521 Under Unix, you can get around this problem by writing actions into
2522 the breakpoint condition rather than in commands. For example,
2525 condition 5 (x = y + 4), 0
2529 specifies a condition expression (@pxref{Expressions, ,Expressions}) that will
2530 change @code{x} as needed, then always have the value zero so your
2531 program will not stop. No input is lost here, because @value{GDBN} evaluates
2532 break conditions without changing the terminal modes. When you want
2533 to have nontrivial conditions for performing the side effects, the
2534 operators @samp{&&}, @samp{||} and @samp{?@dots{}:} may be useful.
2538 @node Breakpoint Menus
2539 @subsection Breakpoint menus
2541 @cindex symbol overloading
2543 Some programming languages (notably C++) permit a single function name
2544 to be defined several times, for application in different contexts.
2545 This is called @dfn{overloading}. When a function name is overloaded,
2546 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
2547 a breakpoint. If you realize this will be a problem, you can use
2548 something like @samp{break @var{function}(@var{types})} to specify which
2549 particular version of the function you want. Otherwise, @value{GDBN} offers
2550 you a menu of numbered choices for different possible breakpoints, and
2551 waits for your selection with the prompt @samp{>}. The first two
2552 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
2553 sets a breakpoint at each definition of @var{function}, and typing
2554 @kbd{0} aborts the @code{break} command without setting any new
2557 For example, the following session excerpt shows an attempt to set a
2558 breakpoint at the overloaded symbol @code{String::after}.
2559 We choose three particular definitions of that function name:
2561 @c FIXME! This is likely to change to show arg type lists, at least
2563 (@value{GDBP}) b String::after
2566 [2] file:String.cc; line number:867
2567 [3] file:String.cc; line number:860
2568 [4] file:String.cc; line number:875
2569 [5] file:String.cc; line number:853
2570 [6] file:String.cc; line number:846
2571 [7] file:String.cc; line number:735
2573 Breakpoint 1 at 0xb26c: file String.cc, line 867.
2574 Breakpoint 2 at 0xb344: file String.cc, line 875.
2575 Breakpoint 3 at 0xafcc: file String.cc, line 846.
2576 Multiple breakpoints were set.
2577 Use the "delete" command to delete unwanted
2584 @node Error in Breakpoints
2585 @subsection ``Cannot insert breakpoints''
2587 @c FIXME: "cannot insert breakpoints" error, v unclear.
2588 @c Q in pending mail to Gilmore. ---pesch@cygnus.com, 26mar91
2589 @c some light may be shed by looking at instances of
2590 @c ONE_PROCESS_WRITETEXT. But error message seems possible otherwise
2591 @c too. pesch, 20sep91
2592 Under some operating systems, breakpoints cannot be used in a program if
2593 any other process is running that program. In this situation,
2594 attempting to run or continue a program with a breakpoint causes @value{GDBN}
2595 to stop the other process.
2597 When this happens, you have three ways to proceed:
2601 Remove or disable the breakpoints, then continue.
2604 Suspend @value{GDBN}, and copy the file containing your program to a new name.
2605 Resume @value{GDBN} and use the @code{exec-file} command to specify that @value{GDBN}
2606 should run your program under that name. Then start your program again.
2608 @c FIXME: RMS commented here "Show example". Maybe when someone
2609 @c explains the first FIXME: in this section...
2612 Relink your program so that the text segment is nonsharable, using the
2613 linker option @samp{-N}. The operating system limitation may not apply
2614 to nonsharable executables.
2618 @node Continuing and Stepping
2619 @section Continuing and stepping
2623 @cindex resuming execution
2624 @dfn{Continuing} means resuming program execution until your program
2625 completes normally. In contrast, @dfn{stepping} means executing just
2626 one more ``step'' of your program, where ``step'' may mean either one
2627 line of source code, or one machine instruction (depending on what
2628 particular command you use). Either when continuing
2629 or when stepping, your program may stop even sooner, due to
2634 a breakpoint or to a signal. (If due to a signal, you may want to use
2635 @code{handle}, or use @samp{signal 0} to resume execution.
2636 @xref{Signals, ,Signals}.)
2640 @item continue @r{[}@var{count}@r{]}
2641 @itemx c @r{[}@var{count}@r{]}
2642 @itemx fg @r{[}@var{count}@r{]}
2646 Resume program execution, at the address where your program last
2647 stopped; any breakpoints set at that address are bypassed. The optional
2648 argument @var{count} means to set the ignore count of a breakpoint which
2649 you are stopped at to @var{count} @minus{} 1, just like the @code{ignore}
2650 command (@pxref{Conditions, ,Break conditions}). This means that the
2651 program does not stop at that breakpoint until the @var{count}th time
2654 The argument @var{count} is meaningful only when your program
2655 stopped due to a breakpoint. At other times, the argument to
2656 @code{continue} is ignored.
2658 The synonyms @code{c} and @code{fg} are provided purely for convenience,
2659 and have exactly the same behavior as @code{continue}.
2662 To resume execution at a different place, you can use @code{return}
2663 (@pxref{Returning, ,Returning from a function}) to go back to the
2664 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
2665 different address}) to go to an arbitrary location in your program.
2667 A typical technique for using stepping is to set a breakpoint
2669 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions})
2672 (@pxref{Breakpoints, ,Breakpoints and watchpoints})
2675 beginning of the function or the section of your program where a
2676 problem is believed to lie, run your program until it stops at that
2677 breakpoint, and then step through the suspect area, examining the
2678 variables that are interesting, until you see the problem happen.
2684 Continue running your program until control reaches a different source
2685 line, then stop it and return control to @value{GDBN}. This command is
2686 abbreviated @code{s}.
2689 @emph{Warning:} If you use the @code{step} command while control is
2690 within a function that was compiled without debugging information,
2691 execution proceeds until control reaches a function that does have
2692 debugging information.
2695 @item step @var{count}
2696 Continue running as in @code{step}, but do so @var{count} times. If a
2697 breakpoint is reached,
2699 or a signal not related to stepping occurs before @var{count} steps,
2701 stepping stops right away.
2703 @item next @r{[}@var{count}@r{]}
2706 Continue to the next source line in the current (innermost) stack frame.
2707 Similar to @code{step}, but any function calls appearing within the line
2708 of code are executed without stopping. Execution stops when control
2709 reaches a different line of code at the stack level which was executing
2710 when the @code{next} command was given. This command is abbreviated
2713 An argument @var{count} is a repeat count, as for @code{step}.
2715 @code{next} within a function that lacks debugging information acts like
2716 @code{step}, but any function calls appearing within the code of the
2717 function are executed without stopping.
2721 Continue running until just after function in the selected stack frame
2722 returns. Print the returned value (if any).
2724 Contrast this with the @code{return} command (@pxref{Returning,
2725 ,Returning from a function}).
2731 Continue running until a source line past the current line, in the
2732 current stack frame, is reached. This command is used to avoid single
2733 stepping through a loop more than once. It is like the @code{next}
2734 command, except that when @code{until} encounters a jump, it
2735 automatically continues execution until the program counter is greater
2736 than the address of the jump.
2738 This means that when you reach the end of a loop after single stepping
2739 though it, @code{until} will cause your program to continue execution
2740 until the loop is exited. In contrast, a @code{next} command at the end
2741 of a loop will simply step back to the beginning of the loop, which
2742 would force you to step through the next iteration.
2744 @code{until} always stops your program if it attempts to exit the current
2747 @code{until} may produce somewhat counterintuitive results if the order
2748 of machine code does not match the order of the source lines. For
2749 example, in the following excerpt from a debugging session, the @code{f}
2750 (@code{frame}) command shows that execution is stopped at line
2751 @code{206}; yet when we use @code{until}, we get to line @code{195}:
2755 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
2757 (@value{GDBP}) until
2758 195 for ( ; argc > 0; NEXTARG) @{
2761 This happened because, for execution efficiency, the compiler had
2762 generated code for the loop closure test at the end, rather than the
2763 start, of the loop---even though the test in a C @code{for}-loop is
2764 written before the body of the loop. The @code{until} command appeared
2765 to step back to the beginning of the loop when it advanced to this
2766 expression; however, it has not really gone to an earlier
2767 statement---not in terms of the actual machine code.
2769 @code{until} with no argument works by means of single
2770 instruction stepping, and hence is slower than @code{until} with an
2773 @item until @var{location}
2774 @item u @var{location}
2775 Continue running your program until either the specified location is
2776 reached, or the current stack frame returns. @var{location} is any of
2777 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
2778 ,Setting breakpoints}). This form of the command uses breakpoints,
2779 and hence is quicker than @code{until} without an argument.
2785 Execute one machine instruction, then stop and return to the debugger.
2787 It is often useful to do @samp{display/i $pc} when stepping by machine
2788 instructions. This will cause the next instruction to be executed to
2789 be displayed automatically at each stop. @xref{Auto Display,
2790 ,Automatic display}.
2792 An argument is a repeat count, as in @code{step}.
2799 Execute one machine instruction, but if it is a function call,
2800 proceed until the function returns.
2802 An argument is a repeat count, as in @code{next}.
2810 A signal is an asynchronous event that can happen in a program. The
2811 operating system defines the possible kinds of signals, and gives each
2812 kind a name and a number. For example, in Unix @code{SIGINT} is the
2813 signal a program gets when you type an interrupt (often @kbd{C-c});
2814 @code{SIGSEGV} is the signal a program gets from referencing a place in
2815 memory far away from all the areas in use; @code{SIGALRM} occurs when
2816 the alarm clock timer goes off (which happens only if your program has
2817 requested an alarm).
2819 @cindex fatal signals
2820 Some signals, including @code{SIGALRM}, are a normal part of the
2821 functioning of your program. Others, such as @code{SIGSEGV}, indicate
2822 errors; these signals are @dfn{fatal} (kill your program immediately) if the
2823 program has not specified in advance some other way to handle the signal.
2824 @code{SIGINT} does not indicate an error in your program, but it is normally
2825 fatal so it can carry out the purpose of the interrupt: to kill the program.
2827 @value{GDBN} has the ability to detect any occurrence of a signal in your
2828 program. You can tell @value{GDBN} in advance what to do for each kind of
2831 @cindex handling signals
2832 Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM}
2833 (so as not to interfere with their role in the functioning of your program)
2834 but to stop your program immediately whenever an error signal happens.
2835 You can change these settings with the @code{handle} command.
2839 @kindex info signals
2840 Print a table of all the kinds of signals and how @value{GDBN} has been told to
2841 handle each one. You can use this to see the signal numbers of all
2842 the defined types of signals.
2844 @item handle @var{signal} @var{keywords}@dots{}
2846 Change the way @value{GDBN} handles signal @var{signal}. @var{signal} can be the
2847 number of a signal or its name (with or without the @samp{SIG} at the
2848 beginning). The @var{keywords} say what change to make.
2852 The keywords allowed by the @code{handle} command can be abbreviated.
2853 Their full names are:
2857 @value{GDBN} should not stop your program when this signal happens. It may
2858 still print a message telling you that the signal has come in.
2861 @value{GDBN} should stop your program when this signal happens. This implies
2862 the @code{print} keyword as well.
2865 @value{GDBN} should print a message when this signal happens.
2868 @value{GDBN} should not mention the occurrence of the signal at all. This
2869 implies the @code{nostop} keyword as well.
2872 @value{GDBN} should allow your program to see this signal; your program will be
2873 able to handle the signal, or may be terminated if the signal is fatal
2877 @value{GDBN} should not allow your program to see this signal.
2881 When a signal stops your program, the signal is not visible until you
2882 continue. Your program will see the signal then, if @code{pass} is in
2883 effect for the signal in question @emph{at that time}. In other words,
2884 after @value{GDBN} reports a signal, you can use the @code{handle}
2885 command with @code{pass} or @code{nopass} to control whether that
2886 signal will be seen by your program when you later continue it.
2888 You can also use the @code{signal} command to prevent your program from
2889 seeing a signal, or cause it to see a signal it normally would not see,
2890 or to give it any signal at any time. For example, if your program stopped
2891 due to some sort of memory reference error, you might store correct
2892 values into the erroneous variables and continue, hoping to see more
2893 execution; but your program would probably terminate immediately as
2894 a result of the fatal signal once it saw the signal. To prevent this,
2895 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
2900 @chapter Examining the Stack
2902 When your program has stopped, the first thing you need to know is where it
2903 stopped and how it got there.
2906 Each time your program performs a function call, the information about
2907 where in your program the call was made from is saved in a block of data
2908 called a @dfn{stack frame}. The frame also contains the arguments of the
2909 call and the local variables of the function that was called. All the
2910 stack frames are allocated in a region of memory called the @dfn{call
2913 When your program stops, the @value{GDBN} commands for examining the
2914 stack allow you to see all of this information.
2916 @cindex selected frame
2917 One of the stack frames is @dfn{selected} by @value{GDBN} and many
2918 @value{GDBN} commands refer implicitly to the selected frame. In
2919 particular, whenever you ask @value{GDBN} for the value of a variable in
2920 your program, the value is found in the selected frame. There are
2921 special @value{GDBN} commands to select whichever frame you are
2924 When your program stops, @value{GDBN} automatically selects the
2925 currently executing frame and describes it briefly as the @code{frame}
2926 command does (@pxref{Frame Info, ,Information about a frame}).
2929 * Frames:: Stack frames
2930 * Backtrace:: Backtraces
2931 * Selection:: Selecting a frame
2932 * Frame Info:: Information on a frame
2934 * MIPS Stack:: MIPS machines and the function stack
2939 @section Stack frames
2943 The call stack is divided up into contiguous pieces called @dfn{stack
2944 frames}, or @dfn{frames} for short; each frame is the data associated
2945 with one call to one function. The frame contains the arguments given
2946 to the function, the function's local variables, and the address at
2947 which the function is executing.
2949 @cindex initial frame
2950 @cindex outermost frame
2951 @cindex innermost frame
2952 When your program is started, the stack has only one frame, that of the
2953 function @code{main}. This is called the @dfn{initial} frame or the
2954 @dfn{outermost} frame. Each time a function is called, a new frame is
2955 made. Each time a function returns, the frame for that function invocation
2956 is eliminated. If a function is recursive, there can be many frames for
2957 the same function. The frame for the function in which execution is
2958 actually occurring is called the @dfn{innermost} frame. This is the most
2959 recently created of all the stack frames that still exist.
2961 @cindex frame pointer
2962 Inside your program, stack frames are identified by their addresses. A
2963 stack frame consists of many bytes, each of which has its own address; each
2964 kind of computer has a convention for choosing one of those bytes whose
2965 address serves as the address of the frame. Usually this address is kept
2966 in a register called the @dfn{frame pointer register} while execution is
2967 going on in that frame.
2969 @cindex frame number
2970 @value{GDBN} assigns numbers to all existing stack frames, starting with
2971 zero for the innermost frame, one for the frame that called it,
2972 and so on upward. These numbers do not really exist in your program;
2973 they are assigned by @value{GDBN} to give you a way of designating stack
2974 frames in @value{GDBN} commands.
2976 @cindex frameless execution
2977 Some compilers provide a way to compile functions so that they operate
2978 without stack frames. (For example, the @code{@value{GCC}} option
2979 @samp{-fomit-frame-pointer} will generate functions without a frame.)
2980 This is occasionally done with heavily used library functions to save
2981 the frame setup time. @value{GDBN} has limited facilities for dealing
2982 with these function invocations. If the innermost function invocation
2983 has no stack frame, @value{GDBN} will nevertheless regard it as though
2984 it had a separate frame, which is numbered zero as usual, allowing
2985 correct tracing of the function call chain. However, @value{GDBN} has
2986 no provision for frameless functions elsewhere in the stack.
2991 A backtrace is a summary of how your program got where it is. It shows one
2992 line per frame, for many frames, starting with the currently executing
2993 frame (frame zero), followed by its caller (frame one), and on up the
3001 Print a backtrace of the entire stack: one line per frame for all
3002 frames in the stack.
3004 You can stop the backtrace at any time by typing the system interrupt
3005 character, normally @kbd{C-c}.
3007 @item backtrace @var{n}
3009 Similar, but print only the innermost @var{n} frames.
3011 @item backtrace -@var{n}
3013 Similar, but print only the outermost @var{n} frames.
3019 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3020 are additional aliases for @code{backtrace}.
3022 Each line in the backtrace shows the frame number and the function name.
3023 The program counter value is also shown---unless you use @code{set
3024 print address off}. The backtrace also shows the source file name and
3025 line number, as well as the arguments to the function. The program
3026 counter value is omitted if it is at the beginning of the code for that
3029 Here is an example of a backtrace. It was made with the command
3030 @samp{bt 3}, so it shows the innermost three frames.
3034 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3036 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3037 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3039 (More stack frames follow...)
3044 The display for frame zero does not begin with a program counter
3045 value, indicating that your program has stopped at the beginning of the
3046 code for line @code{993} of @code{builtin.c}.
3049 @section Selecting a frame
3051 Most commands for examining the stack and other data in your program work on
3052 whichever stack frame is selected at the moment. Here are the commands for
3053 selecting a stack frame; all of them finish by printing a brief description
3054 of the stack frame just selected.
3061 Select frame number @var{n}. Recall that frame zero is the innermost
3062 (currently executing) frame, frame one is the frame that called the
3063 innermost one, and so on. The highest-numbered frame is the one for
3066 @item frame @var{addr}
3068 Select the frame at address @var{addr}. This is useful mainly if the
3069 chaining of stack frames has been damaged by a bug, making it
3070 impossible for @value{GDBN} to assign numbers properly to all frames. In
3071 addition, this can be useful when your program has multiple stacks and
3072 switches between them.
3075 On the SPARC architecture, @code{frame} needs two addresses to
3076 select an arbitrary frame: a frame pointer and a stack pointer.
3077 @c note to future updaters: this is conditioned on a flag
3078 @c FRAME_SPECIFICATION_DYADIC in the tm-*.h files, currently only used
3079 @c by SPARC, hence the specific attribution. Generalize or list all
3080 @c possibilities if more supported machines start doing this.
3085 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3086 advances toward the outermost frame, to higher frame numbers, to frames
3087 that have existed longer. @var{n} defaults to one.
3092 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3093 advances toward the innermost frame, to lower frame numbers, to frames
3094 that were created more recently. @var{n} defaults to one. You may
3095 abbreviate @code{down} as @code{do}.
3098 All of these commands end by printing two lines of output describing the
3099 frame. The first line shows the frame number, the function name, the
3100 arguments, and the source file and line number of execution in that
3101 frame. The second line shows the text of that source line.
3107 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3109 10 read_input_file (argv[i]);
3113 After such a printout, the @code{list} command with no arguments will
3114 print ten lines centered on the point of execution in the frame.
3115 @xref{List, ,Printing source lines}.
3118 @item up-silently @var{n}
3119 @itemx down-silently @var{n}
3120 @kindex down-silently
3122 These two commands are variants of @code{up} and @code{down},
3123 respectively; they differ in that they do their work silently, without
3124 causing display of the new frame. They are intended primarily for use
3125 in @value{GDBN} command scripts, where the output might be unnecessary and
3130 @section Information about a frame
3132 There are several other commands to print information about the selected
3138 When used without any argument, this command does not change which
3139 frame is selected, but prints a brief description of the currently
3140 selected stack frame. It can be abbreviated @code{f}. With an
3141 argument, this command is used to select a stack frame.
3142 @xref{Selection, ,Selecting a frame}.
3148 This command prints a verbose description of the selected stack frame,
3149 including the address of the frame, the addresses of the next frame down
3150 (called by this frame) and the next frame up (caller of this frame), the
3151 language that the source code corresponding to this frame was written in,
3152 the address of the frame's arguments, the program counter saved in it
3153 (the address of execution in the caller frame), and which registers
3154 were saved in the frame. The verbose description is useful when
3155 something has gone wrong that has made the stack format fail to fit
3156 the usual conventions.
3158 @item info frame @var{addr}
3159 @itemx info f @var{addr}
3160 Print a verbose description of the frame at address @var{addr},
3161 without selecting that frame. The selected frame remains unchanged by
3166 Print the arguments of the selected frame, each on a separate line.
3170 Print the local variables of the selected frame, each on a separate
3171 line. These are all variables (declared either static or automatic)
3172 accessible at the point of execution of the selected frame.
3177 @cindex catch exceptions
3178 @cindex exception handlers
3179 Print a list of all the exception handlers that are active in the
3180 current stack frame at the current point of execution. To see other
3181 exception handlers, visit the associated frame (using the @code{up},
3182 @code{down}, or @code{frame} commands); then type @code{info catch}.
3183 @xref{Exception Handling, ,Breakpoints and exceptions}.
3189 @section MIPS machines and the function stack
3191 @cindex stack on MIPS
3193 MIPS based computers use an unusual stack frame, which sometimes
3194 requires @value{GDBN} to search backward in the object code to find the
3195 beginning of a function.
3197 @cindex response time, MIPS debugging
3198 To improve response time (especially for embedded applications, where
3199 @value{GDBN} may be restricted to a slow serial line for this search)
3200 you may want to limit the size of this search, using one of these
3202 @c FIXME! So what happens when GDB does *not* find the beginning of a
3205 @cindex @code{heuristic-fence-post} (MIPS)
3207 @item set heuristic-fence-post @var{limit}
3208 Restrict @var{GDBN} to examining at most @var{limit} bytes in its search
3209 for the beginning of a function. A value of @code{0} (the default)
3210 means there is no limit.
3212 @item show heuristic-fence-post
3213 Display the current limit.
3217 These commands are available @emph{only} when @value{GDBN} is configured
3218 for debugging programs on MIPS processors.
3222 @chapter Examining Source Files
3224 @value{GDBN} can print parts of your program's source, since the debugging
3225 information recorded in the program tells @value{GDBN} what source files were
3226 used to build it. When your program stops, @value{GDBN} spontaneously prints
3227 the line where it stopped. Likewise, when you select a stack frame
3228 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
3229 execution in that frame has stopped. You can print other portions of
3230 source files by explicit command.
3233 If you use @value{GDBN} through its GNU Emacs interface, you may prefer to use
3234 Emacs facilities to view source; @pxref{Emacs, ,Using @value{GDBN} under GNU
3239 * List:: Printing source lines
3241 * Search:: Searching source files
3244 * Source Path:: Specifying source directories
3245 * Machine Code:: Source and machine code
3249 @section Printing source lines
3253 To print lines from a source file, use the @code{list} command
3254 (abbreviated @code{l}). There are several ways to specify what part
3255 of the file you want to print.
3257 Here are the forms of the @code{list} command most commonly used:
3260 @item list @var{linenum}
3261 Print lines centered around line number @var{linenum} in the
3262 current source file.
3264 @item list @var{function}
3265 Print lines centered around the beginning of function
3269 Print more lines. If the last lines printed were printed with a
3270 @code{list} command, this prints lines following the last lines
3271 printed; however, if the last line printed was a solitary line printed
3272 as part of displaying a stack frame (@pxref{Stack, ,Examining the
3273 Stack}), this prints lines centered around that line.
3276 Print lines just before the lines last printed.
3279 By default, @value{GDBN} prints ten source lines with any of these forms of
3280 the @code{list} command. You can change this using @code{set listsize}:
3283 @item set listsize @var{count}
3284 @kindex set listsize
3285 Make the @code{list} command display @var{count} source lines (unless
3286 the @code{list} argument explicitly specifies some other number).
3289 @kindex show listsize
3290 Display the number of lines that @code{list} will currently display by
3294 Repeating a @code{list} command with @key{RET} discards the argument,
3295 so it is equivalent to typing just @code{list}. This is more useful
3296 than listing the same lines again. An exception is made for an
3297 argument of @samp{-}; that argument is preserved in repetition so that
3298 each repetition moves up in the source file.
3301 In general, the @code{list} command expects you to supply zero, one or two
3302 @dfn{linespecs}. Linespecs specify source lines; there are several ways
3303 of writing them but the effect is always to specify some source line.
3304 Here is a complete description of the possible arguments for @code{list}:
3307 @item list @var{linespec}
3308 Print lines centered around the line specified by @var{linespec}.
3310 @item list @var{first},@var{last}
3311 Print lines from @var{first} to @var{last}. Both arguments are
3314 @item list ,@var{last}
3315 Print lines ending with @var{last}.
3317 @item list @var{first},
3318 Print lines starting with @var{first}.
3321 Print lines just after the lines last printed.
3324 Print lines just before the lines last printed.
3327 As described in the preceding table.
3330 Here are the ways of specifying a single source line---all the
3335 Specifies line @var{number} of the current source file.
3336 When a @code{list} command has two linespecs, this refers to
3337 the same source file as the first linespec.
3340 Specifies the line @var{offset} lines after the last line printed.
3341 When used as the second linespec in a @code{list} command that has
3342 two, this specifies the line @var{offset} lines down from the
3346 Specifies the line @var{offset} lines before the last line printed.
3348 @item @var{filename}:@var{number}
3349 Specifies line @var{number} in the source file @var{filename}.
3351 @item @var{function}
3352 @c FIXME: "of the open-brace" is C-centric. When we add other langs...
3353 Specifies the line of the open-brace that begins the body of the
3354 function @var{function}.
3356 @item @var{filename}:@var{function}
3357 Specifies the line of the open-brace that begins the body of the
3358 function @var{function} in the file @var{filename}. You only need the
3359 file name with a function name to avoid ambiguity when there are
3360 identically named functions in different source files.
3362 @item *@var{address}
3363 Specifies the line containing the program address @var{address}.
3364 @var{address} may be any expression.
3369 @section Searching source files
3371 @kindex reverse-search
3373 There are two commands for searching through the current source file for a
3377 @item forward-search @var{regexp}
3378 @itemx search @var{regexp}
3380 @kindex forward-search
3381 The command @samp{forward-search @var{regexp}} checks each line,
3382 starting with the one following the last line listed, for a match for
3383 @var{regexp}. It lists the line that is found. You can use
3384 synonym @samp{search @var{regexp}} or abbreviate the command name as
3387 @item reverse-search @var{regexp}
3388 The command @samp{reverse-search @var{regexp}} checks each line, starting
3389 with the one before the last line listed and going backward, for a match
3390 for @var{regexp}. It lists the line that is found. You can abbreviate
3391 this command as @code{rev}.
3396 @section Specifying source directories
3399 @cindex directories for source files
3400 Executable programs sometimes do not record the directories of the source
3401 files from which they were compiled, just the names. Even when they do,
3402 the directories could be moved between the compilation and your debugging
3403 session. @value{GDBN} has a list of directories to search for source files;
3404 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
3405 it tries all the directories in the list, in the order they are present
3406 in the list, until it finds a file with the desired name. Note that
3407 the executable search path is @emph{not} used for this purpose. Neither is
3408 the current working directory, unless it happens to be in the source
3411 If @value{GDBN} cannot find a source file in the source path, and the object
3412 program records a directory, @value{GDBN} tries that directory too. If the
3413 source path is empty, and there is no record of the compilation
3414 directory, @value{GDBN} will, as a last resort, look in the current
3417 Whenever you reset or rearrange the source path, @value{GDBN} will clear out
3418 any information it has cached about where source files are found, where
3419 each line is in the file, etc.
3422 When you start @value{GDBN}, its source path is empty.
3423 To add other directories, use the @code{directory} command.
3426 @item directory @var{dirname} @dots{}
3427 Add directory @var{dirname} to the front of the source path. Several
3428 directory names may be given to this command, separated by @samp{:} or
3429 whitespace. You may specify a directory that is already in the source
3430 path; this moves it forward, so it will be searched sooner.
3432 You can use the string @samp{$cdir} to refer to the compilation
3433 directory (if one is recorded), and @samp{$cwd} to refer to the current
3434 working directory. @samp{$cwd} is not the same as @samp{.}---the former
3435 tracks the current working directory as it changes during your @value{GDBN}
3436 session, while the latter is immediately expanded to the current
3437 directory at the time you add an entry to the source path.
3440 Reset the source path to empty again. This requires confirmation.
3442 @c RET-repeat for @code{directory} is explicitly disabled, but since
3443 @c repeating it would be a no-op we do not say that. (thanks to RMS)
3445 @item show directories
3446 @kindex show directories
3447 Print the source path: show which directories it contains.
3450 If your source path is cluttered with directories that are no longer of
3451 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
3452 versions of source. You can correct the situation as follows:
3456 Use @code{directory} with no argument to reset the source path to empty.
3459 Use @code{directory} with suitable arguments to reinstall the
3460 directories you want in the source path. You can add all the
3461 directories in one command.
3465 @section Source and machine code
3467 You can use the command @code{info line} to map source lines to program
3468 addresses (and vice versa), and the command @code{disassemble} to display
3469 a range of addresses as machine instructions.
3472 @item info line @var{linespec}
3474 Print the starting and ending addresses of the compiled code for
3475 source line @var{linespec}. You can specify source lines in any of
3476 the ways understood by the @code{list} command (@pxref{List, ,Printing
3480 For example, we can use @code{info line} to discover the location of
3481 the object code for the first line of function
3482 @code{m4_changequote}:
3485 (@value{GDBP}) info line m4_changecom
3486 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
3490 We can also inquire (using @code{*@var{addr}} as the form for
3491 @var{linespec}) what source line covers a particular address:
3493 (@value{GDBP}) info line *0x63ff
3494 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
3497 @cindex @code{$_} and @code{info line}
3498 After @code{info line}, the default address for the @code{x} command
3499 is changed to the starting address of the line, so that @samp{x/i} is
3500 sufficient to begin examining the machine code (@pxref{Memory,
3501 ,Examining memory}). Also, this address is saved as the value of the
3502 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
3508 @cindex assembly instructions
3509 @cindex instructions, assembly
3510 @cindex machine instructions
3511 @cindex listing machine instructions
3512 This specialized command dumps a range of memory as machine
3513 instructions. The default memory range is the function surrounding the
3514 program counter of the selected frame. A single argument to this
3515 command is a program counter value; the function surrounding this value
3516 will be dumped. Two arguments specify a range of addresses (first
3517 inclusive, second exclusive) to dump.
3520 @ifclear H8EXCLUSIVE
3521 We can use @code{disassemble} to inspect the object code
3522 range shown in the last @code{info line} example (the example
3523 shows SPARC machine instructions):
3527 (@value{GDBP}) disas 0x63e4 0x6404
3528 Dump of assembler code from 0x63e4 to 0x6404:
3529 0x63e4 <builtin_init+5340>: ble 0x63f8 <builtin_init+5360>
3530 0x63e8 <builtin_init+5344>: sethi %hi(0x4c00), %o0
3531 0x63ec <builtin_init+5348>: ld [%i1+4], %o0
3532 0x63f0 <builtin_init+5352>: b 0x63fc <builtin_init+5364>
3533 0x63f4 <builtin_init+5356>: ld [%o0+4], %o0
3534 0x63f8 <builtin_init+5360>: or %o0, 0x1a4, %o0
3535 0x63fc <builtin_init+5364>: call 0x9288 <path_search>
3536 0x6400 <builtin_init+5368>: nop
3537 End of assembler dump.
3542 For example, here is the beginning of the output for the
3543 disassembly of a function @code{fact}:
3547 (@value{GDBP}) disas fact
3548 Dump of assembler code for function fact:
3550 0x802c <fact>: 6d f2 mov.w r2,@@-r7
3551 0x802e <fact+2>: 6d f3 mov.w r3,@@-r7
3552 0x8030 <fact+4>: 6d f6 mov.w r6,@@-r7
3553 0x8032 <fact+6>: 0d 76 mov.w r7,r6
3554 0x8034 <fact+8>: 6f 70 00 08 mov.w @@(0x8,r7),r0
3555 0x8038 <fact+12> 19 11 sub.w r1,r1
3563 @chapter Examining Data
3565 @cindex printing data
3566 @cindex examining data
3569 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
3570 @c document because it is nonstandard... Under Epoch it displays in a
3571 @c different window or something like that.
3572 The usual way to examine data in your program is with the @code{print}
3573 command (abbreviated @code{p}), or its synonym @code{inspect}.
3575 It evaluates and prints the value of an expression of the language your
3576 program is written in (@pxref{Languages, ,Using @value{GDBN} with Different
3581 @item print @var{exp}
3582 @itemx print /@var{f} @var{exp}
3583 @var{exp} is an expression (in the source language). By default the
3584 value of @var{exp} is printed in a format appropriate to its data type;
3585 you can choose a different format by specifying @samp{/@var{f}}, where
3586 @var{f} is a letter specifying the format; @pxref{Output Formats,,Output
3590 @itemx print /@var{f}
3591 If you omit @var{exp}, @value{GDBN} displays the last value again (from the
3592 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
3593 conveniently inspect the same value in an alternative format.
3596 A more low-level way of examining data is with the @code{x} command.
3597 It examines data in memory at a specified address and prints it in a
3598 specified format. @xref{Memory, ,Examining memory}.
3600 If you are interested in information about types, or about how the fields
3605 are declared, use the @code{ptype @var{exp}}
3606 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol Table}.
3609 * Expressions:: Expressions
3610 * Variables:: Program variables
3611 * Arrays:: Artificial arrays
3612 * Output Formats:: Output formats
3613 * Memory:: Examining memory
3614 * Auto Display:: Automatic display
3615 * Print Settings:: Print settings
3616 * Value History:: Value history
3617 * Convenience Vars:: Convenience variables
3618 * Registers:: Registers
3620 * Floating Point Hardware:: Floating point hardware
3625 @section Expressions
3628 @code{print} and many other @value{GDBN} commands accept an expression and
3629 compute its value. Any kind of constant, variable or operator defined
3630 by the programming language you are using is valid in an expression in
3631 @value{GDBN}. This includes conditional expressions, function calls, casts
3632 and string constants. It unfortunately does not include symbols defined
3633 by preprocessor @code{#define} commands.
3636 Because C is so widespread, most of the expressions shown in examples in
3637 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
3638 Languages}, for information on how to use expressions in other
3641 In this section, we discuss operators that you can use in @value{GDBN}
3642 expressions regardless of your programming language.
3644 Casts are supported in all languages, not just in C, because it is so
3645 useful to cast a number into a pointer so as to examine a structure
3646 at that address in memory.
3647 @c FIXME: casts supported---Mod2 true?
3650 @value{GDBN} supports these operators in addition to those of programming
3655 @samp{@@} is a binary operator for treating parts of memory as arrays.
3656 @xref{Arrays, ,Artificial arrays}, for more information.
3659 @samp{::} allows you to specify a variable in terms of the file or
3660 function where it is defined. @xref{Variables, ,Program variables}.
3662 @item @{@var{type}@} @var{addr}
3663 @cindex @{@var{type}@}
3664 @cindex type casting memory
3665 @cindex memory, viewing as typed object
3666 @cindex casts, to view memory
3667 Refers to an object of type @var{type} stored at address @var{addr} in
3668 memory. @var{addr} may be any expression whose value is an integer or
3669 pointer (but parentheses are required around binary operators, just as in
3670 a cast). This construct is allowed regardless of what kind of data is
3671 normally supposed to reside at @var{addr}.
3675 @section Program variables
3677 The most common kind of expression to use is the name of a variable
3680 Variables in expressions are understood in the selected stack frame
3681 (@pxref{Selection, ,Selecting a frame}); they must either be global
3682 (or static) or be visible according to the scope rules of the
3683 programming language from the point of execution in that frame. This
3684 means that in the function
3699 you can examine and use the variable @code{a} whenever your program is
3700 executing within the function @code{foo}, but you can only use or
3701 examine the variable @code{b} while your program is executing inside
3702 the block where @code{b} is declared.
3704 @cindex variable name conflict
3705 There is an exception: you can refer to a variable or function whose
3706 scope is a single source file even if the current execution point is not
3707 in this file. But it is possible to have more than one such variable or
3708 function with the same name (in different source files). If that
3709 happens, referring to that name has unpredictable effects. If you wish,
3710 you can specify a static variable in a particular function or file,
3711 using the colon-colon notation:
3715 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
3719 @var{file}::@var{variable}
3720 @var{function}::@var{variable}
3724 Here @var{file} or @var{function} is the name of the context for the
3725 static @var{variable}. In the case of file names, you can use quotes to
3726 make sure @value{GDBN} parses the file name as a single word---for example,
3727 to print a global value of @code{x} defined in @file{f2.c}:
3730 (@value{GDBP}) p 'f2.c'::x
3734 @cindex C++ scope resolution
3735 This use of @samp{::} is very rarely in conflict with the very similar
3736 use of the same notation in C++. @value{GDBN} also supports use of the C++
3737 scope resolution operator in @value{GDBN} expressions.
3738 @c FIXME: Um, so what happens in one of those rare cases where it's in
3742 @cindex wrong values
3743 @cindex variable values, wrong
3745 @emph{Warning:} Occasionally, a local variable may appear to have the
3746 wrong value at certain points in a function---just after entry to a new
3747 scope, and just before exit.
3749 You may see this problem when you are stepping by machine instructions.
3750 This is because on most machines, it takes more than one instruction to
3751 set up a stack frame (including local variable definitions); if you are
3752 stepping by machine instructions, variables may appear to have the wrong
3753 values until the stack frame is completely built. On exit, it usually
3754 also takes more than one machine instruction to destroy a stack frame;
3755 after you begin stepping through that group of instructions, local
3756 variable definitions may be gone.
3759 @section Artificial arrays
3761 @cindex artificial array
3763 It is often useful to print out several successive objects of the
3764 same type in memory; a section of an array, or an array of
3765 dynamically determined size for which only a pointer exists in the
3768 You can do this by referring to a contiguous span of memory as an
3769 @dfn{artificial array}, using the binary operator @samp{@@}. The left
3770 operand of @samp{@@} should be the first element of the desired array,
3771 as an individual object. The right operand should be the desired length
3772 of the array. The result is an array value whose elements are all of
3773 the type of the left argument. The first element is actually the left
3774 argument; the second element comes from bytes of memory immediately
3775 following those that hold the first element, and so on. Here is an
3776 example. If a program says
3779 int *array = (int *) malloc (len * sizeof (int));
3783 you can print the contents of @code{array} with
3789 The left operand of @samp{@@} must reside in memory. Array values made
3790 with @samp{@@} in this way behave just like other arrays in terms of
3791 subscripting, and are coerced to pointers when used in expressions.
3792 Artificial arrays most often appear in expressions via the value history
3793 (@pxref{Value History, ,Value history}), after printing one out.
3795 Sometimes the artificial array mechanism is not quite enough; in
3796 moderately complex data structures, the elements of interest may not
3797 actually be adjacent---for example, if you are interested in the values
3798 of pointers in an array. One useful work-around in this situation is
3799 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
3800 variables}) as a counter in an expression that prints the first
3801 interesting value, and then repeat that expression via @key{RET}. For
3802 instance, suppose you have an array @code{dtab} of pointers to
3803 structures, and you are interested in the values of a field @code{fv}
3804 in each structure. Here is an example of what you might type:
3814 @node Output Formats
3815 @section Output formats
3817 @cindex formatted output
3818 @cindex output formats
3819 By default, @value{GDBN} prints a value according to its data type. Sometimes
3820 this is not what you want. For example, you might want to print a number
3821 in hex, or a pointer in decimal. Or you might want to view data in memory
3822 at a certain address as a character string or as an instruction. To do
3823 these things, specify an @dfn{output format} when you print a value.
3825 The simplest use of output formats is to say how to print a value
3826 already computed. This is done by starting the arguments of the
3827 @code{print} command with a slash and a format letter. The format
3828 letters supported are:
3832 Regard the bits of the value as an integer, and print the integer in
3836 Print as integer in signed decimal.
3839 Print as integer in unsigned decimal.
3842 Print as integer in octal.
3845 Print as integer in binary. The letter @samp{t} stands for ``two''.
3846 @footnote{@samp{b} cannot be used because these format letters are also
3847 used with the @code{x} command, where @samp{b} stands for ``byte'';
3848 @pxref{Memory,,Examining memory}.}
3851 Print as an address, both absolute in hex and as an offset from the
3852 nearest preceding symbol. This format can be used to discover where (in
3853 what function) an unknown address is located:
3856 (@value{GDBP}) p/a 0x54320
3857 $3 = 0x54320 <_initialize_vx+396>
3861 Regard as an integer and print it as a character constant.
3864 Regard the bits of the value as a floating point number and print
3865 using typical floating point syntax.
3868 For example, to print the program counter in hex (@pxref{Registers}), type
3875 Note that no space is required before the slash; this is because command
3876 names in @value{GDBN} cannot contain a slash.
3878 To reprint the last value in the value history with a different format,
3879 you can use the @code{print} command with just a format and no
3880 expression. For example, @samp{p/x} reprints the last value in hex.
3883 @section Examining memory
3885 You can use the command @code{x} (for ``examine'') to examine memory in
3886 any of several formats, independently of your program's data types.
3888 @cindex examining memory
3891 @item x/@var{nfu} @var{addr}
3894 Use the @code{x} command to examine memory.
3897 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
3898 much memory to display and how to format it; @var{addr} is an
3899 expression giving the address where you want to start displaying memory.
3900 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
3901 Several commands set convenient defaults for @var{addr}.
3904 @item @var{n}, the repeat count
3905 The repeat count is a decimal integer; the default is 1. It specifies
3906 how much memory (counting by units @var{u}) to display.
3907 @c This really is **decimal**; unaffected by 'set radix' as of GDB
3910 @item @var{f}, the display format
3911 The display format is one of the formats used by @code{print},
3912 or @samp{s} (null-terminated string) or @samp{i} (machine instruction).
3913 The default is @samp{x} (hexadecimal) initially, or the format from the
3914 last time you used either @code{x} or @code{print}.
3916 @item @var{u}, the unit size
3917 The unit size is any of
3923 Halfwords (two bytes).
3925 Words (four bytes). This is the initial default.
3927 Giant words (eight bytes).
3930 Each time you specify a unit size with @code{x}, that size becomes the
3931 default unit the next time you use @code{x}. (For the @samp{s} and
3932 @samp{i} formats, the unit size is ignored and is normally not written.)
3934 @item @var{addr}, starting display address
3935 @var{addr} is the address where you want @value{GDBN} to begin displaying
3936 memory. The expression need not have a pointer value (though it may);
3937 it is always interpreted as an integer address of a byte of memory.
3938 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
3939 @var{addr} is usually just after the last address examined---but several
3940 other commands also set the default address: @code{info breakpoints} (to
3941 the address of the last breakpoint listed), @code{info line} (to the
3942 starting address of a line), and @code{print} (if you use it to display
3943 a value from memory).
3946 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
3947 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
3948 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
3949 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
3950 @pxref{Registers}) in hexadecimal (@samp{x}).
3952 Since the letters indicating unit sizes are all distinct from the
3953 letters specifying output formats, you do not have to remember whether
3954 unit size or format comes first; either order will work. The output
3955 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
3956 (However, the count @var{n} must come first; @samp{wx4} will not work.)
3958 Even though the unit size @var{u} is ignored for the formats @samp{s}
3959 and @samp{i}, you might still want to use a count @var{n}; for example,
3960 @samp{3i} specifies that you want to see three machine instructions,
3961 including any operands. The command @code{disassemble} gives an
3962 alternative way of inspecting machine instructions; @pxref{Machine
3963 Code,,Source and machine code}.
3965 All the defaults for the arguments to @code{x} are designed to make it
3966 easy to continue scanning memory with minimal specifications each time
3967 you use @code{x}. For example, after you have inspected three machine
3968 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
3969 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
3970 the repeat count @var{n} is used again; the other arguments default as
3971 for successive uses of @code{x}.
3973 @cindex @code{$_}, @code{$__}, and value history
3974 The addresses and contents printed by the @code{x} command are not saved
3975 in the value history because there is often too much of them and they
3976 would get in the way. Instead, @value{GDBN} makes these values available for
3977 subsequent use in expressions as values of the convenience variables
3978 @code{$_} and @code{$__}. After an @code{x} command, the last address
3979 examined is available for use in expressions in the convenience variable
3980 @code{$_}. The contents of that address, as examined, are available in
3981 the convenience variable @code{$__}.
3983 If the @code{x} command has a repeat count, the address and contents saved
3984 are from the last memory unit printed; this is not the same as the last
3985 address printed if several units were printed on the last line of output.
3988 @section Automatic display
3989 @cindex automatic display
3990 @cindex display of expressions
3992 If you find that you want to print the value of an expression frequently
3993 (to see how it changes), you might want to add it to the @dfn{automatic
3994 display list} so that @value{GDBN} will print its value each time your program stops.
3995 Each expression added to the list is given a number to identify it;
3996 to remove an expression from the list, you specify that number.
3997 The automatic display looks like this:
4001 3: bar[5] = (struct hack *) 0x3804
4005 This display shows item numbers, expressions and their current values. As with
4006 displays you request manually using @code{x} or @code{print}, you can
4007 specify the output format you prefer; in fact, @code{display} decides
4008 whether to use @code{print} or @code{x} depending on how elaborate your
4009 format specification is---it uses @code{x} if you specify a unit size,
4010 or one of the two formats (@samp{i} and @samp{s}) that are only
4011 supported by @code{x}; otherwise it uses @code{print}.
4014 @item display @var{exp}
4016 Add the expression @var{exp} to the list of expressions to display
4017 each time your program stops. @xref{Expressions, ,Expressions}.
4019 @code{display} will not repeat if you press @key{RET} again after using it.
4021 @item display/@var{fmt} @var{exp}
4022 For @var{fmt} specifying only a display format and not a size or
4023 count, add the expression @var{exp} to the auto-display list but
4024 arrange to display it each time in the specified format @var{fmt}.
4025 @xref{Output Formats,,Output formats}.
4027 @item display/@var{fmt} @var{addr}
4028 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4029 number of units, add the expression @var{addr} as a memory address to
4030 be examined each time your program stops. Examining means in effect
4031 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4034 For example, @samp{display/i $pc} can be helpful, to see the machine
4035 instruction about to be executed each time execution stops (@samp{$pc}
4036 is a common name for the program counter; @pxref{Registers}).
4039 @item undisplay @var{dnums}@dots{}
4040 @itemx delete display @var{dnums}@dots{}
4041 @kindex delete display
4043 Remove item numbers @var{dnums} from the list of expressions to display.
4045 @code{undisplay} will not repeat if you press @key{RET} after using it.
4046 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4048 @item disable display @var{dnums}@dots{}
4049 @kindex disable display
4050 Disable the display of item numbers @var{dnums}. A disabled display
4051 item is not printed automatically, but is not forgotten. It may be
4052 enabled again later.
4054 @item enable display @var{dnums}@dots{}
4055 @kindex enable display
4056 Enable display of item numbers @var{dnums}. It becomes effective once
4057 again in auto display of its expression, until you specify otherwise.
4060 Display the current values of the expressions on the list, just as is
4061 done when your program stops.
4064 @kindex info display
4065 Print the list of expressions previously set up to display
4066 automatically, each one with its item number, but without showing the
4067 values. This includes disabled expressions, which are marked as such.
4068 It also includes expressions which would not be displayed right now
4069 because they refer to automatic variables not currently available.
4072 If a display expression refers to local variables, then it does not make
4073 sense outside the lexical context for which it was set up. Such an
4074 expression is disabled when execution enters a context where one of its
4075 variables is not defined. For example, if you give the command
4076 @code{display last_char} while inside a function with an argument
4077 @code{last_char}, then this argument will be displayed while your program
4078 continues to stop inside that function. When it stops elsewhere---where
4079 there is no variable @code{last_char}---display is disabled. The next time
4080 your program stops where @code{last_char} is meaningful, you can enable the
4081 display expression once again.
4083 @node Print Settings
4084 @section Print settings
4086 @cindex format options
4087 @cindex print settings
4088 @value{GDBN} provides the following ways to control how arrays, structures,
4089 and symbols are printed.
4092 These settings are useful for debugging programs in any language:
4095 @item set print address
4096 @item set print address on
4097 @kindex set print address
4098 @value{GDBN} will print memory addresses showing the location of stack
4099 traces, structure values, pointer values, breakpoints, and so forth,
4100 even when it also displays the contents of those addresses. The default
4101 is on. For example, this is what a stack frame display looks like, with
4102 @code{set print address on}:
4107 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4109 530 if (lquote != def_lquote)
4113 @item set print address off
4114 Do not print addresses when displaying their contents. For example,
4115 this is the same stack frame displayed with @code{set print address off}:
4119 (@value{GDBP}) set print addr off
4121 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4122 530 if (lquote != def_lquote)
4126 You can use @samp{set print address off} to eliminate all machine
4127 dependent displays from the @value{GDBN} interface. For example, with
4128 @code{print address off}, you should get the same text for backtraces on
4129 all machines---whether or not they involve pointer arguments.
4131 @item show print address
4132 @kindex show print address
4133 Show whether or not addresses are to be printed.
4136 When @value{GDBN} prints a symbolic address, it normally prints the
4137 closest earlier symbol plus an offset. If that symbol does not uniquely
4138 identify the address (for example, it is a name whose scope is a single
4139 source file), you may need to disambiguate. One way to do this is with
4140 @code{info line}, for example @code{info line *0x4537}. Alternately,
4141 you can set @value{GDBN} to print the source file and line number when
4142 it prints a symbolic address:
4145 @item set print symbol-filename on
4146 @kindex set print symbol-filename
4147 Tell @value{GDBN} to print the source file name and line number of a
4148 symbol in the symbolic form of an address.
4150 @item set print symbol-filename off
4151 Do not print source file name and line number of a symbol. This is the
4154 @item show print symbol-filename
4155 @kindex show print symbol-filename
4156 Show whether or not @value{GDBN} will print the source file name and
4157 line number of a symbol in the symbolic form of an address.
4160 Also, you may wish to see the symbolic form only if the address being
4161 printed is reasonably close to the closest earlier symbol:
4164 @item set print max-symbolic-offset @var{max-offset}
4165 @kindex set print max-symbolic-offset
4166 Tell @value{GDBN} to only display the symbolic form of an address if the
4167 offset between the closest earlier symbol and the address is less than
4168 @var{max-offset}. The default is 0, which means to always print the
4169 symbolic form of an address, if any symbol precedes it.
4171 @item show print max-symbolic-offset
4172 @kindex show print max-symbolic-offset
4173 Ask how large the maximum offset is that @value{GDBN} will print in a
4178 @item set print array
4179 @itemx set print array on
4180 @kindex set print array
4181 @value{GDBN} will pretty-print arrays. This format is more convenient to read,
4182 but uses more space. The default is off.
4184 @item set print array off
4185 Return to compressed format for arrays.
4187 @item show print array
4188 @kindex show print array
4189 Show whether compressed or pretty format is selected for displaying
4192 @item set print elements @var{number-of-elements}
4193 @kindex set print elements
4194 If @value{GDBN} is printing a large array, it will stop printing after it has
4195 printed the number of elements set by the @code{set print elements} command.
4196 This limit also applies to the display of strings.
4197 Setting the number of elements to zero means that the printing is unlimited.
4199 @item show print elements
4200 @kindex show print elements
4201 Display the number of elements of a large array that @value{GDBN} will print
4202 before losing patience.
4204 @item set print pretty on
4205 @kindex set print pretty
4206 Cause @value{GDBN} to print structures in an indented format with one member per
4222 @item set print pretty off
4223 Cause @value{GDBN} to print structures in a compact format, like this:
4227 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
4228 meat = 0x54 "Pork"@}
4233 This is the default format.
4235 @item show print pretty
4236 @kindex show print pretty
4237 Show which format @value{GDBN} will use to print structures.
4239 @item set print sevenbit-strings on
4240 @kindex set print sevenbit-strings
4241 Print using only seven-bit characters; if this option is set,
4242 @value{GDBN} will display any eight-bit characters (in strings or character
4243 values) using the notation @code{\}@var{nnn}. For example, @kbd{M-a} is
4244 displayed as @code{\341}.
4246 @item set print sevenbit-strings off
4247 Print using either seven-bit or eight-bit characters, as required. This
4250 @item show print sevenbit-strings
4251 @kindex show print sevenbit-strings
4252 Show whether or not @value{GDBN} will print only seven-bit characters.
4254 @item set print union on
4255 @kindex set print union
4256 Tell @value{GDBN} to print unions which are contained in structures. This is the
4259 @item set print union off
4260 Tell @value{GDBN} not to print unions which are contained in structures.
4262 @item show print union
4263 @kindex show print union
4264 Ask @value{GDBN} whether or not it will print unions which are contained in
4267 For example, given the declarations
4270 typedef enum @{Tree, Bug@} Species;
4271 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
4272 typedef enum @{Caterpillar, Cocoon, Butterfly@}
4283 struct thing foo = @{Tree, @{Acorn@}@};
4287 with @code{set print union on} in effect @samp{p foo} would print
4290 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
4294 and with @code{set print union off} in effect it would print
4297 $1 = @{it = Tree, form = @{...@}@}
4304 These settings are of interest when debugging C++ programs:
4307 @item set print demangle
4308 @itemx set print demangle on
4309 @kindex set print demangle
4310 Print C++ names in their source form rather than in the encoded
4311 (``mangled'') form passed to the assembler and linker for type-safe
4312 linkage. The default is @samp{on}.
4314 @item show print demangle
4315 @kindex show print demangle
4316 Show whether C++ names will be printed in mangled or demangled form.
4318 @item set print asm-demangle
4319 @itemx set print asm-demangle on
4320 @kindex set print asm-demangle
4321 Print C++ names in their source form rather than their mangled form, even
4322 in assembler code printouts such as instruction disassemblies.
4325 @item show print asm-demangle
4326 @kindex show print asm-demangle
4327 Show whether C++ names in assembly listings will be printed in mangled
4330 @item set demangle-style @var{style}
4331 @kindex set demangle-style
4332 @cindex C++ symbol decoding style
4333 @cindex symbol decoding style, C++
4334 Choose among several encoding schemes used by different compilers to
4335 represent C++ names. The choices for @var{style} are currently:
4339 Allow @value{GDBN} to choose a decoding style by inspecting your program.
4342 Decode based on the GNU C++ compiler (@code{g++}) encoding algorithm.
4345 Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm.
4348 Decode using the algorithm in the @cite{C++ Annotated Reference Manual}.
4349 @strong{Warning:} this setting alone is not sufficient to allow
4350 debugging @code{cfront}-generated executables. @value{GDBN} would
4351 require further enhancement to permit that.
4354 @item show demangle-style
4355 @kindex show demangle-style
4356 Display the encoding style currently in use for decoding C++ symbols.
4358 @item set print object
4359 @itemx set print object on
4360 @kindex set print object
4361 When displaying a pointer to an object, identify the @emph{actual}
4362 (derived) type of the object rather than the @emph{declared} type, using
4363 the virtual function table.
4365 @item set print object off
4366 Display only the declared type of objects, without reference to the
4367 virtual function table. This is the default setting.
4369 @item show print object
4370 @kindex show print object
4371 Show whether actual, or declared, object types will be displayed.
4373 @item set print vtbl
4374 @itemx set print vtbl on
4375 @kindex set print vtbl
4376 Pretty print C++ virtual function tables. The default is off.
4378 @item set print vtbl off
4379 Do not pretty print C++ virtual function tables.
4381 @item show print vtbl
4382 @kindex show print vtbl
4383 Show whether C++ virtual function tables are pretty printed, or not.
4388 @section Value history
4390 @cindex value history
4391 Values printed by the @code{print} command are saved in the @value{GDBN} @dfn{value
4392 history} so that you can refer to them in other expressions. Values are
4393 kept until the symbol table is re-read or discarded (for example with
4394 the @code{file} or @code{symbol-file} commands). When the symbol table
4395 changes, the value history is discarded, since the values may contain
4396 pointers back to the types defined in the symbol table.
4400 @cindex history number
4401 The values printed are given @dfn{history numbers} for you to refer to them
4402 by. These are successive integers starting with one. @code{print} shows you
4403 the history number assigned to a value by printing @samp{$@var{num} = }
4404 before the value; here @var{num} is the history number.
4406 To refer to any previous value, use @samp{$} followed by the value's
4407 history number. The way @code{print} labels its output is designed to
4408 remind you of this. Just @code{$} refers to the most recent value in
4409 the history, and @code{$$} refers to the value before that.
4410 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
4411 is the value just prior to @code{$$}, @code{$$1} is equivalent to
4412 @code{$$}, and @code{$$0} is equivalent to @code{$}.
4414 For example, suppose you have just printed a pointer to a structure and
4415 want to see the contents of the structure. It suffices to type
4421 If you have a chain of structures where the component @code{next} points
4422 to the next one, you can print the contents of the next one with this:
4429 You can print successive links in the chain by repeating this
4430 command---which you can do by just typing @key{RET}.
4432 Note that the history records values, not expressions. If the value of
4433 @code{x} is 4 and you type these commands:
4441 then the value recorded in the value history by the @code{print} command
4442 remains 4 even though the value of @code{x} has changed.
4447 Print the last ten values in the value history, with their item numbers.
4448 This is like @samp{p@ $$9} repeated ten times, except that @code{show
4449 values} does not change the history.
4451 @item show values @var{n}
4452 Print ten history values centered on history item number @var{n}.
4455 Print ten history values just after the values last printed. If no more
4456 values are available, produces no display.
4459 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
4460 same effect as @samp{show values +}.
4462 @node Convenience Vars
4463 @section Convenience variables
4465 @cindex convenience variables
4466 @value{GDBN} provides @dfn{convenience variables} that you can use within
4467 @value{GDBN} to hold on to a value and refer to it later. These variables
4468 exist entirely within @value{GDBN}; they are not part of your program, and
4469 setting a convenience variable has no direct effect on further execution
4470 of your program. That is why you can use them freely.
4472 Convenience variables are prefixed with @samp{$}. Any name preceded by
4473 @samp{$} can be used for a convenience variable, unless it is one of
4474 the predefined machine-specific register names (@pxref{Registers}).
4475 (Value history references, in contrast, are @emph{numbers} preceded
4476 by @samp{$}. @xref{Value History, ,Value history}.)
4478 You can save a value in a convenience variable with an assignment
4479 expression, just as you would set a variable in your program.
4483 set $foo = *object_ptr
4487 would save in @code{$foo} the value contained in the object pointed to by
4490 Using a convenience variable for the first time creates it; but its value
4491 is @code{void} until you assign a new value. You can alter the value with
4492 another assignment at any time.
4494 Convenience variables have no fixed types. You can assign a convenience
4495 variable any type of value, including structures and arrays, even if
4496 that variable already has a value of a different type. The convenience
4497 variable, when used as an expression, has the type of its current value.
4500 @item show convenience
4501 @kindex show convenience
4502 Print a list of convenience variables used so far, and their values.
4503 Abbreviated @code{show con}.
4506 One of the ways to use a convenience variable is as a counter to be
4507 incremented or a pointer to be advanced. For example, to print
4508 a field from successive elements of an array of structures:
4512 print bar[$i++]->contents
4513 @i{@dots{} repeat that command by typing @key{RET}.}
4516 Some convenience variables are created automatically by @value{GDBN} and given
4517 values likely to be useful.
4522 The variable @code{$_} is automatically set by the @code{x} command to
4523 the last address examined (@pxref{Memory, ,Examining memory}). Other
4524 commands which provide a default address for @code{x} to examine also
4525 set @code{$_} to that address; these commands include @code{info line}
4526 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
4527 except when set by the @code{x} command, in which case it is a pointer
4528 to the type of @code{$__}.
4532 The variable @code{$__} is automatically set by the @code{x} command
4533 to the value found in the last address examined. Its type is chosen
4534 to match the format in which the data was printed.
4541 You can refer to machine register contents, in expressions, as variables
4542 with names starting with @samp{$}. The names of registers are different
4543 for each machine; use @code{info registers} to see the names used on
4547 @item info registers
4548 @kindex info registers
4549 Print the names and values of all registers except floating-point
4550 registers (in the selected stack frame).
4552 @item info all-registers
4553 @kindex info all-registers
4554 @cindex floating point registers
4555 Print the names and values of all registers, including floating-point
4558 @item info registers @var{regname} @dots{}
4559 Print the relativized value of each specified register @var{regname}.
4560 @var{regname} may be any register name valid on the machine you are using, with
4561 or without the initial @samp{$}.
4564 @value{GDBN} has four ``standard'' register names that are available (in
4565 expressions) on most machines---whenever they do not conflict with an
4566 architecture's canonical mnemonics for registers. The register names
4567 @code{$pc} and @code{$sp} are used for the program counter register and
4568 the stack pointer. @code{$fp} is used for a register that contains a
4569 pointer to the current stack frame, and @code{$ps} is used for a
4570 register that contains the processor status. For example,
4571 you could print the program counter in hex with
4578 or print the instruction to be executed next with
4585 or add four to the stack pointer@footnote{This is a way of removing
4586 one word from the stack, on machines where stacks grow downward in
4587 memory (most machines, nowadays). This assumes that the innermost
4588 stack frame is selected; setting @code{$sp} is not allowed when other
4589 stack frames are selected. To pop entire frames off the stack,
4590 regardless of machine architecture, use @code{return};
4591 @pxref{Returning, ,Returning from a function}.} with
4597 Whenever possible, these four standard register names are available on
4598 your machine even though the machine has different canonical mnemonics,
4599 so long as there is no conflict. The @code{info registers} command
4600 shows the canonical names. For example, on the SPARC, @code{info
4601 registers} displays the processor status register as @code{$psr} but you
4602 can also refer to it as @code{$ps}.
4604 @value{GDBN} always considers the contents of an ordinary register as an
4605 integer when the register is examined in this way. Some machines have
4606 special registers which can hold nothing but floating point; these
4607 registers are considered to have floating point values. There is no way
4608 to refer to the contents of an ordinary register as floating point value
4609 (although you can @emph{print} it as a floating point value with
4610 @samp{print/f $@var{regname}}).
4612 Some registers have distinct ``raw'' and ``virtual'' data formats. This
4613 means that the data format in which the register contents are saved by
4614 the operating system is not the same one that your program normally
4615 sees. For example, the registers of the 68881 floating point
4616 coprocessor are always saved in ``extended'' (raw) format, but all C
4617 programs expect to work with ``double'' (virtual) format. In such
4618 cases, @value{GDBN} normally works with the virtual format only (the format that
4619 makes sense for your program), but the @code{info registers} command
4620 prints the data in both formats.
4622 Normally, register values are relative to the selected stack frame
4623 (@pxref{Selection, ,Selecting a frame}). This means that you get the
4624 value that the register would contain if all stack frames farther in
4625 were exited and their saved registers restored. In order to see the
4626 true contents of hardware registers, you must select the innermost
4627 frame (with @samp{frame 0}).
4629 However, @value{GDBN} must deduce where registers are saved, from the machine
4630 code generated by your compiler. If some registers are not saved, or if
4631 @value{GDBN} is unable to locate the saved registers, the selected stack
4632 frame will make no difference.
4636 @item set rstack_high_address @var{address}
4637 @kindex set rstack_high_address
4638 @cindex AMD 29K register stack
4639 @cindex register stack, AMD29K
4640 On AMD 29000 family processors, registers are saved in a separate
4641 ``register stack''. There is no way for @value{GDBN} to determine the extent
4642 of this stack. Normally, @value{GDBN} just assumes that the stack is ``large
4643 enough''. This may result in @value{GDBN} referencing memory locations that
4644 do not exist. If necessary, you can get around this problem by
4645 specifying the ending address of the register stack with the @code{set
4646 rstack_high_address} command. The argument should be an address, which
4647 you will probably want to precede with @samp{0x} to specify in
4650 @item show rstack_high_address
4651 @kindex show rstack_high_address
4652 Display the current limit of the register stack, on AMD 29000 family
4658 @node Floating Point Hardware
4659 @section Floating point hardware
4660 @cindex floating point
4662 @c FIXME! Really host, not target?
4663 Depending on the host machine architecture, @value{GDBN} may be able to give
4664 you more information about the status of the floating point hardware.
4669 Display hardware-dependent information about the floating
4670 point unit. The exact contents and layout vary depending on the
4671 floating point chip; on some platforms, @samp{info float} is not
4674 @c FIXME: this is a cop-out. Try to get examples, explanations. Only
4675 @c FIXME...supported currently on arm's and 386's. Mark properly with
4676 @c FIXME... m4 macros to isolate general statements from hardware-dep,
4677 @c FIXME... at that point.
4682 @chapter Using @value{GDBN} with Different Languages
4686 Although programming languages generally have common aspects, they are
4687 rarely expressed in the same manner. For instance, in ANSI C,
4688 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
4689 Modula-2, it is accomplished by @code{p^}. Values can also be
4690 represented (and displayed) differently. Hex numbers in C are written
4691 like @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
4694 @cindex working language
4695 Language-specific information is built into @value{GDBN} for some languages,
4696 allowing you to express operations like the above in your program's
4697 native language, and allowing @value{GDBN} to output values in a manner
4698 consistent with the syntax of your program's native language. The
4699 language you use to build expressions, called the @dfn{working
4700 language}, can be selected manually, or @value{GDBN} can set it
4704 * Setting:: Switching between source languages
4705 * Show:: Displaying the language
4707 * Checks:: Type and range checks
4710 * Support:: Supported languages
4714 @section Switching between source languages
4716 There are two ways to control the working language---either have @value{GDBN}
4717 set it automatically, or select it manually yourself. You can use the
4718 @code{set language} command for either purpose. On startup, @value{GDBN}
4719 defaults to setting the language automatically.
4722 * Manually:: Setting the working language manually
4723 * Automatically:: Having @value{GDBN} infer the source language
4727 @subsection Setting the working language
4729 If you allow @value{GDBN} to set the language automatically,
4730 expressions are interpreted the same way in your debugging session and
4733 @kindex set language
4734 If you wish, you may set the language manually. To do this, issue the
4735 command @samp{set language @var{lang}}, where @var{lang} is the name of
4741 @code{c} or @code{modula-2}.
4743 For a list of the supported languages, type @samp{set language}.
4744 @c FIXME: rms: eventually this command should be "help set language".
4747 Setting the language manually prevents @value{GDBN} from updating the working
4748 language automatically. This can lead to confusion if you try
4749 to debug a program when the working language is not the same as the
4750 source language, when an expression is acceptable to both
4751 languages---but means different things. For instance, if the current
4752 source file were written in C, and @value{GDBN} was parsing Modula-2, a
4760 might not have the effect you intended. In C, this means to add
4761 @code{b} and @code{c} and place the result in @code{a}. The result
4762 printed would be the value of @code{a}. In Modula-2, this means to compare
4763 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
4767 @subsection Having @value{GDBN} infer the source language
4769 To have @value{GDBN} set the working language automatically, use @samp{set
4770 language local} or @samp{set language auto}. @value{GDBN} then infers the
4771 language that a program was written in by looking at the name of its
4772 source files, and examining their extensions:
4777 Modula-2 source file
4788 This information is recorded for each function or procedure in a source
4789 file. When your program stops in a frame (usually by encountering a
4790 breakpoint), @value{GDBN} sets the working language to the language recorded
4791 for the function in that frame. If the language for a frame is unknown
4792 (that is, if the function or block corresponding to the frame was
4793 defined in a source file that does not have a recognized extension), the
4794 current working language is not changed, and @value{GDBN} issues a warning.
4796 This may not seem necessary for most programs, which are written
4797 entirely in one source language. However, program modules and libraries
4798 written in one source language can be used by a main program written in
4799 a different source language. Using @samp{set language auto} in this
4800 case frees you from having to set the working language manually.
4803 @section Displaying the language
4805 The following commands will help you find out which language is the
4806 working language, and also what language source files were written in.
4808 @kindex show language
4813 Display the current working language. This is the
4814 language you can use with commands such as @code{print} to
4815 build and compute expressions that may involve variables in your program.
4818 Among the other information listed here (@pxref{Frame Info, ,Information
4819 about a frame}) is the source language for this frame. This is the
4820 language that will become the working language if you ever use an
4821 identifier that is in this frame.
4824 Among the other information listed here (@pxref{Symbols, ,Examining the
4825 Symbol Table}) is the source language of this source file.
4830 @section Type and range checking
4833 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
4834 checking are included, but they do not yet have any effect. This
4835 section documents the intended facilities.
4837 @c FIXME remove warning when type/range code added
4839 Some languages are designed to guard you against making seemingly common
4840 errors through a series of compile- and run-time checks. These include
4841 checking the type of arguments to functions and operators, and making
4842 sure mathematical overflows are caught at run time. Checks such as
4843 these help to ensure a program's correctness once it has been compiled
4844 by eliminating type mismatches, and providing active checks for range
4845 errors when your program is running.
4847 @value{GDBN} can check for conditions like the above if you wish.
4848 Although @value{GDBN} will not check the statements in your program, it
4849 can check expressions entered directly into @value{GDBN} for evaluation via
4850 the @code{print} command, for example. As with the working language,
4851 @value{GDBN} can also decide whether or not to check automatically based on
4852 your program's source language. @xref{Support, ,Supported languages},
4853 for the default settings of supported languages.
4856 * Type Checking:: An overview of type checking
4857 * Range Checking:: An overview of range checking
4860 @cindex type checking
4861 @cindex checks, type
4863 @subsection An overview of type checking
4865 Some languages, such as Modula-2, are strongly typed, meaning that the
4866 arguments to operators and functions have to be of the correct type,
4867 otherwise an error occurs. These checks prevent type mismatch
4868 errors from ever causing any run-time problems. For example,
4876 The second example fails because the @code{CARDINAL} 1 is not
4877 type-compatible with the @code{REAL} 2.3.
4879 For expressions you use in @value{GDBN} commands, you can tell the @value{GDBN}
4880 type checker to skip checking; to treat any mismatches as errors and
4881 abandon the expression; or only issue warnings when type mismatches
4882 occur, but evaluate the expression anyway. When you choose the last of
4883 these, @value{GDBN} evaluates expressions like the second example above, but
4884 also issues a warning.
4886 Even though you may turn type checking off, other type-based reasons may
4887 prevent @value{GDBN} from evaluating an expression. For instance, @value{GDBN} does not
4888 know how to add an @code{int} and a @code{struct foo}. These particular
4889 type errors have nothing to do with the language in use, and usually
4890 arise from expressions, such as the one described above, which make
4891 little sense to evaluate anyway.
4893 Each language defines to what degree it is strict about type. For
4894 instance, both Modula-2 and C require the arguments to arithmetical
4895 operators to be numbers. In C, enumerated types and pointers can be
4896 represented as numbers, so that they are valid arguments to mathematical
4897 operators. @xref{Support, ,Supported languages}, for further
4898 details on specific languages.
4900 @value{GDBN} provides some additional commands for controlling the type checker:
4903 @kindex set check type
4904 @kindex show check type
4906 @item set check type auto
4907 Set type checking on or off based on the current working language.
4908 @xref{Support, ,Supported languages}, for the default settings for
4911 @item set check type on
4912 @itemx set check type off
4913 Set type checking on or off, overriding the default setting for the
4914 current working language. Issue a warning if the setting does not
4915 match the language default. If any type mismatches occur in
4916 evaluating an expression while typechecking is on, @value{GDBN} prints a
4917 message and aborts evaluation of the expression.
4919 @item set check type warn
4920 Cause the type checker to issue warnings, but to always attempt to
4921 evaluate the expression. Evaluating the expression may still
4922 be impossible for other reasons. For example, @value{GDBN} cannot add
4923 numbers and structures.
4926 Show the current setting of the type checker, and whether or not @value{GDBN} is
4927 setting it automatically.
4930 @cindex range checking
4931 @cindex checks, range
4932 @node Range Checking
4933 @subsection An overview of range checking
4935 In some languages (such as Modula-2), it is an error to exceed the
4936 bounds of a type; this is enforced with run-time checks. Such range
4937 checking is meant to ensure program correctness by making sure
4938 computations do not overflow, or indices on an array element access do
4939 not exceed the bounds of the array.
4941 For expressions you use in @value{GDBN} commands, you can tell
4942 @value{GDBN} to treat range errors in one of three ways: ignore them,
4943 always treat them as errors and abandon the expression, or issue
4944 warnings but evaluate the expression anyway.
4946 A range error can result from numerical overflow, from exceeding an
4947 array index bound, or when you type a constant that is not a member
4948 of any type. Some languages, however, do not treat overflows as an
4949 error. In many implementations of C, mathematical overflow causes the
4950 result to ``wrap around'' to lower values---for example, if @var{m} is
4951 the largest integer value, and @var{s} is the smallest, then
4954 @var{m} + 1 @result{} @var{s}
4957 This, too, is specific to individual languages, and in some cases
4958 specific to individual compilers or machines. @xref{Support, ,
4959 Supported languages}, for further details on specific languages.
4961 @value{GDBN} provides some additional commands for controlling the range checker:
4964 @kindex set check range
4965 @kindex show check range
4967 @item set check range auto
4968 Set range checking on or off based on the current working language.
4969 @xref{Support, ,Supported languages}, for the default settings for
4972 @item set check range on
4973 @itemx set check range off
4974 Set range checking on or off, overriding the default setting for the
4975 current working language. A warning is issued if the setting does not
4976 match the language default. If a range error occurs, then a message
4977 is printed and evaluation of the expression is aborted.
4979 @item set check range warn
4980 Output messages when the @value{GDBN} range checker detects a range error,
4981 but attempt to evaluate the expression anyway. Evaluating the
4982 expression may still be impossible for other reasons, such as accessing
4983 memory that the process does not own (a typical example from many UNIX
4987 Show the current setting of the range checker, and whether or not it is
4988 being set automatically by @value{GDBN}.
4993 @section Supported languages
4996 @value{GDBN} 4 supports C, C++, and Modula-2.
4999 @value{GDBN} 4 supports C, and C++.
5001 Some @value{GDBN} features may be used in expressions regardless of the
5002 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
5003 and the @samp{@{type@}addr} construct (@pxref{Expressions,
5004 ,Expressions}) can be used with the constructs of any supported
5007 The following sections detail to what degree each source language is
5008 supported by @value{GDBN}. These sections are not meant to be language
5009 tutorials or references, but serve only as a reference guide to what the
5010 @value{GDBN} expression parser will accept, and what input and output
5011 formats should look like for different languages. There are many good
5012 books written on each of these languages; please look to these for a
5013 language reference or tutorial.
5018 * Modula-2:: Modula-2
5022 @subsection C and C++
5024 @cindex expressions in C or C++
5026 Since C and C++ are so closely related, many features of @value{GDBN} apply
5027 to both languages. Whenever this is the case, we discuss both languages
5031 @c Cancel this below, under same condition, at end of this chapter!
5038 The C++ debugging facilities are jointly implemented by the GNU C++
5039 compiler and @value{GDBN}. Therefore, to debug your C++ code effectively,
5040 you must compile your C++ programs with the GNU C++ compiler,
5045 @chapter C Language Support
5047 @cindex expressions in C
5049 Information specific to the C language is built into @value{GDBN} so that you
5050 can use C expressions while degugging. This also permits @value{GDBN} to
5051 output values in a manner consistent with C conventions.
5054 * C Operators:: C operators
5055 * C Constants:: C constants
5056 * Debugging C:: @value{GDBN} and C
5061 * C Operators:: C and C++ operators
5062 * C Constants:: C and C++ constants
5063 * Cplus expressions:: C++ expressions
5064 * C Defaults:: Default settings for C and C++
5066 * C Checks:: C and C++ type and range checks
5069 * Debugging C:: @value{GDBN} and C
5070 * Debugging C plus plus:: Special features for C++
5075 @cindex C and C++ operators
5077 @subsubsection C and C++ operators
5082 @section C operators
5085 Operators must be defined on values of specific types. For instance,
5086 @code{+} is defined on numbers, but not on structures. Operators are
5087 often defined on groups of types.
5090 For the purposes of C and C++, the following definitions hold:
5095 @emph{Integral types} include @code{int} with any of its storage-class
5096 specifiers; @code{char}; and @code{enum}.
5099 @emph{Floating-point types} include @code{float} and @code{double}.
5102 @emph{Pointer types} include all types defined as @code{(@var{type}
5106 @emph{Scalar types} include all of the above.
5110 The following operators are supported. They are listed here
5111 in order of increasing precedence:
5115 The comma or sequencing operator. Expressions in a comma-separated list
5116 are evaluated from left to right, with the result of the entire
5117 expression being the last expression evaluated.
5120 Assignment. The value of an assignment expression is the value
5121 assigned. Defined on scalar types.
5124 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
5125 and translated to @w{@code{@var{a} = @var{a op b}}}.
5126 @w{@code{@var{op}=}} and @code{=} have the same precendence.
5127 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
5128 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
5131 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
5132 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
5136 Logical @sc{or}. Defined on integral types.
5139 Logical @sc{and}. Defined on integral types.
5142 Bitwise @sc{or}. Defined on integral types.
5145 Bitwise exclusive-@sc{or}. Defined on integral types.
5148 Bitwise @sc{and}. Defined on integral types.
5151 Equality and inequality. Defined on scalar types. The value of these
5152 expressions is 0 for false and non-zero for true.
5154 @item <@r{, }>@r{, }<=@r{, }>=
5155 Less than, greater than, less than or equal, greater than or equal.
5156 Defined on scalar types. The value of these expressions is 0 for false
5157 and non-zero for true.
5160 left shift, and right shift. Defined on integral types.
5163 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
5166 Addition and subtraction. Defined on integral types, floating-point types and
5169 @item *@r{, }/@r{, }%
5170 Multiplication, division, and modulus. Multiplication and division are
5171 defined on integral and floating-point types. Modulus is defined on
5175 Increment and decrement. When appearing before a variable, the
5176 operation is performed before the variable is used in an expression;
5177 when appearing after it, the variable's value is used before the
5178 operation takes place.
5181 Pointer dereferencing. Defined on pointer types. Same precedence as
5185 Address operator. Defined on variables. Same precedence as @code{++}.
5188 For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is
5189 allowed in the C++ language itself: you can use @samp{&(&@var{ref})}
5190 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
5191 where a C++ reference variable (declared with @samp{&@var{ref}}) is
5196 Negative. Defined on integral and floating-point types. Same
5197 precedence as @code{++}.
5200 Logical negation. Defined on integral types. Same precedence as
5204 Bitwise complement operator. Defined on integral types. Same precedence as
5209 Structure member, and pointer-to-structure member. For convenience,
5210 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
5211 pointer based on the stored type information.
5212 Defined on @code{struct} and @code{union} data.
5215 Array indexing. @code{@var{a}[@var{i}]} is defined as
5216 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
5219 Function parameter list. Same precedence as @code{->}.
5223 C++ scope resolution operator. Defined on
5224 @code{struct}, @code{union}, and @code{class} types.
5232 represent the @value{GDBN} scope operator (@pxref{Expressions,
5235 Same precedence as @code{::}, above.
5240 @cindex C and C++ constants
5242 @subsubsection C and C++ constants
5244 @value{GDBN} allows you to express the constants of C and C++ in the
5250 @section C constants
5252 @value{GDBN} allows you to express the constants of C in the
5258 Integer constants are a sequence of digits. Octal constants are
5259 specified by a leading @samp{0} (ie. zero), and hexadecimal constants by
5260 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
5261 @samp{l}, specifying that the constant should be treated as a
5265 Floating point constants are a sequence of digits, followed by a decimal
5266 point, followed by a sequence of digits, and optionally followed by an
5267 exponent. An exponent is of the form:
5268 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
5269 sequence of digits. The @samp{+} is optional for positive exponents.
5272 Enumerated constants consist of enumerated identifiers, or their
5273 integral equivalents.
5276 Character constants are a single character surrounded by single quotes
5277 (@code{'}), or a number---the ordinal value of the corresponding character
5278 (usually its @sc{ASCII} value). Within quotes, the single character may
5279 be represented by a letter or by @dfn{escape sequences}, which are of
5280 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
5281 of the character's ordinal value; or of the form @samp{\@var{x}}, where
5282 @samp{@var{x}} is a predefined special character---for example,
5283 @samp{\n} for newline.
5286 String constants are a sequence of character constants surrounded
5287 by double quotes (@code{"}).
5290 Pointer constants are an integral value. You can also write pointers
5291 to constants using the C operator @samp{&}.
5294 Array constants are comma-separated lists surrounded by braces @samp{@{}
5295 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
5296 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
5297 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
5301 @node Cplus expressions
5302 @subsubsection C++ expressions
5304 @cindex expressions in C++
5305 @value{GDBN} expression handling has a number of extensions to
5306 interpret a significant subset of C++ expressions.
5308 @cindex C++ support, not in @sc{coff}
5309 @cindex @sc{coff} versus C++
5310 @cindex C++ and object formats
5311 @cindex object formats and C++
5312 @cindex a.out and C++
5313 @cindex @sc{ecoff} and C++
5314 @cindex @sc{xcoff} and C++
5315 @cindex @sc{elf}/stabs and C++
5316 @cindex @sc{elf}/@sc{dwarf} and C++
5318 @emph{Warning:} Most of these extensions depend on the use of additional
5319 debugging information in the symbol table, and thus require a rich,
5320 extendable object code format. In particular, if your system uses
5321 a.out, MIPS @sc{ecoff}, RS/6000 @sc{xcoff}, or Sun @sc{elf} with stabs
5322 extensions to the symbol table, these facilities are all available.
5323 Where the object code format is standard @sc{coff}, on the other hand,
5324 most of the C++ support in @value{GDBN} will @emph{not} work, nor can it.
5325 For the standard SVr4 debugging format, @sc{dwarf} in @sc{elf}, the
5326 standard is still evolving, so the C++ support in @value{GDBN} is still
5327 fragile; when this debugging format stabilizes, however, C++ support
5328 will also be available on systems that use it.
5333 @cindex member functions
5335 Member function calls are allowed; you can use expressions like
5338 count = aml->GetOriginal(x, y)
5342 @cindex namespace in C++
5344 While a member function is active (in the selected stack frame), your
5345 expressions have the same namespace available as the member function;
5346 that is, @value{GDBN} allows implicit references to the class instance
5347 pointer @code{this} following the same rules as C++.
5349 @cindex call overloaded functions
5350 @cindex type conversions in C++
5352 You can call overloaded functions; @value{GDBN} will resolve the function
5353 call to the right definition, with one restriction---you must use
5354 arguments of the type required by the function that you want to call.
5355 @value{GDBN} will not perform conversions requiring constructors or
5356 user-defined type operators.
5358 @cindex reference declarations
5360 @value{GDBN} understands variables declared as C++ references; you can use them in
5361 expressions just as you do in C++ source---they are automatically
5364 In the parameter list shown when @value{GDBN} displays a frame, the values of
5365 reference variables are not displayed (unlike other variables); this
5366 avoids clutter, since references are often used for large structures.
5367 The @emph{address} of a reference variable is always shown, unless
5368 you have specified @samp{set print address off}.
5371 @value{GDBN} supports the C++ name resolution operator @code{::}---your
5372 expressions can use it just as expressions in your program do. Since
5373 one scope may be defined in another, you can use @code{::} repeatedly if
5374 necessary, for example in an expression like
5375 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
5376 resolving name scope by reference to source files, in both C and C++
5377 debugging (@pxref{Variables, ,Program variables}).
5381 @subsubsection C and C++ defaults
5382 @cindex C and C++ defaults
5384 If you allow @value{GDBN} to set type and range checking automatically, they
5385 both default to @code{off} whenever the working language changes to
5386 C or C++. This happens regardless of whether you, or @value{GDBN},
5387 selected the working language.
5389 If you allow @value{GDBN} to set the language automatically, it sets the
5390 working language to C or C++ on entering code compiled from a source file
5391 whose name ends with @file{.c}, @file{.C}, or @file{.cc}.
5392 @xref{Automatically, ,Having @value{GDBN} infer the source language}, for
5396 @c Type checking is (a) primarily motivated by Modula-2, and (b)
5397 @c unimplemented. If (b) changes, it might make sense to let this node
5398 @c appear even if Mod-2 does not, but meanwhile ignore it. pesch 16jul93.
5400 @subsubsection C and C++ type and range checks
5401 @cindex C and C++ checks
5403 By default, when @value{GDBN} parses C or C++ expressions, type checking
5404 is not used. However, if you turn type checking on, @value{GDBN} will
5405 consider two variables type equivalent if:
5409 The two variables are structured and have the same structure, union, or
5413 Two two variables have the same type name, or types that have been
5414 declared equivalent through @code{typedef}.
5417 @c leaving this out because neither J Gilmore nor R Pesch understand it.
5420 The two @code{struct}, @code{union}, or @code{enum} variables are
5421 declared in the same declaration. (Note: this may not be true for all C
5426 Range checking, if turned on, is done on mathematical operations. Array
5427 indices are not checked, since they are often used to index a pointer
5428 that is not itself an array.
5434 @subsubsection @value{GDBN} and C
5438 @section @value{GDBN} and C
5441 The @code{set print union} and @code{show print union} commands apply to
5442 the @code{union} type. When set to @samp{on}, any @code{union} that is
5443 inside a @code{struct}
5447 will also be printed.
5448 Otherwise, it will appear as @samp{@{...@}}.
5450 The @code{@@} operator aids in the debugging of dynamic arrays, formed
5451 with pointers and a memory allocation function. @xref{Expressions,
5455 @node Debugging C plus plus
5456 @subsubsection @value{GDBN} features for C++
5458 @cindex commands for C++
5459 Some @value{GDBN} commands are particularly useful with C++, and some are
5460 designed specifically for use with C++. Here is a summary:
5463 @cindex break in overloaded functions
5464 @item @r{breakpoint menus}
5465 When you want a breakpoint in a function whose name is overloaded,
5466 @value{GDBN} breakpoint menus help you specify which function definition
5467 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
5469 @cindex overloading in C++
5470 @item rbreak @var{regex}
5471 Setting breakpoints using regular expressions is helpful for setting
5472 breakpoints on overloaded functions that are not members of any special
5474 @xref{Set Breaks, ,Setting breakpoints}.
5476 @cindex C++ exception handling
5477 @item catch @var{exceptions}
5479 Debug C++ exception handling using these commands. @xref{Exception
5480 Handling, ,Breakpoints and exceptions}.
5483 @item ptype @var{typename}
5484 Print inheritance relationships as well as other information for type
5486 @xref{Symbols, ,Examining the Symbol Table}.
5488 @cindex C++ symbol display
5489 @item set print demangle
5490 @itemx show print demangle
5491 @itemx set print asm-demangle
5492 @itemx show print asm-demangle
5493 Control whether C++ symbols display in their source form, both when
5494 displaying code as C++ source and when displaying disassemblies.
5495 @xref{Print Settings, ,Print settings}.
5497 @item set print object
5498 @itemx show print object
5499 Choose whether to print derived (actual) or declared types of objects.
5500 @xref{Print Settings, ,Print settings}.
5502 @item set print vtbl
5503 @itemx show print vtbl
5504 Control the format for printing virtual function tables.
5505 @xref{Print Settings, ,Print settings}.
5507 @item @r{Overloaded symbol names}
5508 You can specify a particular definition of an overloaded symbol, using
5509 the same notation that is used to declare such symbols in C++: type
5510 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
5511 also use the @value{GDBN} command-line word completion facilities to list the
5512 available choices, or to finish the type list for you.
5513 @xref{Completion,, Command completion}, for details on how to do this.
5516 @c cancels "raisesections" under same conditions near bgn of chapter
5522 @subsection Modula-2
5525 The extensions made to @value{GDBN} to support Modula-2 only support
5526 output from the GNU Modula-2 compiler (which is currently being
5527 developed). Other Modula-2 compilers are not currently supported, and
5528 attempting to debug executables produced by them will most likely
5529 result in an error as @value{GDBN} reads in the executable's symbol
5532 @cindex expressions in Modula-2
5534 * M2 Operators:: Built-in operators
5535 * Built-In Func/Proc:: Built-in functions and procedures
5536 * M2 Constants:: Modula-2 constants
5537 * M2 Defaults:: Default settings for Modula-2
5538 * Deviations:: Deviations from standard Modula-2
5539 * M2 Checks:: Modula-2 type and range checks
5540 * M2 Scope:: The scope operators @code{::} and @code{.}
5541 * GDB/M2:: @value{GDBN} and Modula-2
5545 @subsubsection Operators
5546 @cindex Modula-2 operators
5548 Operators must be defined on values of specific types. For instance,
5549 @code{+} is defined on numbers, but not on structures. Operators are
5550 often defined on groups of types. For the purposes of Modula-2, the
5551 following definitions hold:
5556 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
5560 @emph{Character types} consist of @code{CHAR} and its subranges.
5563 @emph{Floating-point types} consist of @code{REAL}.
5566 @emph{Pointer types} consist of anything declared as @code{POINTER TO
5570 @emph{Scalar types} consist of all of the above.
5573 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
5576 @emph{Boolean types} consist of @code{BOOLEAN}.
5580 The following operators are supported, and appear in order of
5581 increasing precedence:
5585 Function argument or array index separator.
5588 Assignment. The value of @var{var} @code{:=} @var{value} is
5592 Less than, greater than on integral, floating-point, or enumerated
5596 Less than, greater than, less than or equal to, greater than or equal to
5597 on integral, floating-point and enumerated types, or set inclusion on
5598 set types. Same precedence as @code{<}.
5600 @item =@r{, }<>@r{, }#
5601 Equality and two ways of expressing inequality, valid on scalar types.
5602 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
5603 available for inequality, since @code{#} conflicts with the script
5607 Set membership. Defined on set types and the types of their members.
5608 Same precedence as @code{<}.
5611 Boolean disjunction. Defined on boolean types.
5614 Boolean conjuction. Defined on boolean types.
5617 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
5620 Addition and subtraction on integral and floating-point types, or union
5621 and difference on set types.
5624 Multiplication on integral and floating-point types, or set intersection
5628 Division on floating-point types, or symmetric set difference on set
5629 types. Same precedence as @code{*}.
5632 Integer division and remainder. Defined on integral types. Same
5633 precedence as @code{*}.
5636 Negative. Defined on @code{INTEGER} and @code{REAL} data.
5639 Pointer dereferencing. Defined on pointer types.
5642 Boolean negation. Defined on boolean types. Same precedence as
5646 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
5647 precedence as @code{^}.
5650 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
5653 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
5657 @value{GDBN} and Modula-2 scope operators.
5661 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
5662 will treat the use of the operator @code{IN}, or the use of operators
5663 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
5664 @code{<=}, and @code{>=} on sets as an error.
5667 @cindex Modula-2 built-ins
5668 @node Built-In Func/Proc
5669 @subsubsection Built-in functions and procedures
5671 Modula-2 also makes available several built-in procedures and functions.
5672 In describing these, the following metavariables are used:
5677 represents an @code{ARRAY} variable.
5680 represents a @code{CHAR} constant or variable.
5683 represents a variable or constant of integral type.
5686 represents an identifier that belongs to a set. Generally used in the
5687 same function with the metavariable @var{s}. The type of @var{s} should
5688 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}.
5691 represents a variable or constant of integral or floating-point type.
5694 represents a variable or constant of floating-point type.
5700 represents a variable.
5703 represents a variable or constant of one of many types. See the
5704 explanation of the function for details.
5707 All Modula-2 built-in procedures also return a result, described below.
5711 Returns the absolute value of @var{n}.
5714 If @var{c} is a lower case letter, it returns its upper case
5715 equivalent, otherwise it returns its argument
5718 Returns the character whose ordinal value is @var{i}.
5721 Decrements the value in the variable @var{v}. Returns the new value.
5723 @item DEC(@var{v},@var{i})
5724 Decrements the value in the variable @var{v} by @var{i}. Returns the
5727 @item EXCL(@var{m},@var{s})
5728 Removes the element @var{m} from the set @var{s}. Returns the new
5731 @item FLOAT(@var{i})
5732 Returns the floating point equivalent of the integer @var{i}.
5735 Returns the index of the last member of @var{a}.
5738 Increments the value in the variable @var{v}. Returns the new value.
5740 @item INC(@var{v},@var{i})
5741 Increments the value in the variable @var{v} by @var{i}. Returns the
5744 @item INCL(@var{m},@var{s})
5745 Adds the element @var{m} to the set @var{s} if it is not already
5746 there. Returns the new set.
5749 Returns the maximum value of the type @var{t}.
5752 Returns the minimum value of the type @var{t}.
5755 Returns boolean TRUE if @var{i} is an odd number.
5758 Returns the ordinal value of its argument. For example, the ordinal
5759 value of a character is its ASCII value (on machines supporting the
5760 ASCII character set). @var{x} must be of an ordered type, which include
5761 integral, character and enumerated types.
5764 Returns the size of its argument. @var{x} can be a variable or a type.
5766 @item TRUNC(@var{r})
5767 Returns the integral part of @var{r}.
5769 @item VAL(@var{t},@var{i})
5770 Returns the member of the type @var{t} whose ordinal value is @var{i}.
5774 @emph{Warning:} Sets and their operations are not yet supported, so
5775 @value{GDBN} will treat the use of procedures @code{INCL} and @code{EXCL} as
5779 @cindex Modula-2 constants
5781 @subsubsection Constants
5783 @value{GDBN} allows you to express the constants of Modula-2 in the following
5789 Integer constants are simply a sequence of digits. When used in an
5790 expression, a constant is interpreted to be type-compatible with the
5791 rest of the expression. Hexadecimal integers are specified by a
5792 trailing @samp{H}, and octal integers by a trailing @samp{B}.
5795 Floating point constants appear as a sequence of digits, followed by a
5796 decimal point and another sequence of digits. An optional exponent can
5797 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
5798 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
5799 digits of the floating point constant must be valid decimal (base 10)
5803 Character constants consist of a single character enclosed by a pair of
5804 like quotes, either single (@code{'}) or double (@code{"}). They may
5805 also be expressed by their ordinal value (their ASCII value, usually)
5806 followed by a @samp{C}.
5809 String constants consist of a sequence of characters enclosed by a
5810 pair of like quotes, either single (@code{'}) or double (@code{"}).
5811 Escape sequences in the style of C are also allowed. @xref{C
5812 Constants, ,C and C++ constants}, for a brief explanation of escape
5816 Enumerated constants consist of an enumerated identifier.
5819 Boolean constants consist of the identifiers @code{TRUE} and
5823 Pointer constants consist of integral values only.
5826 Set constants are not yet supported.
5830 @subsubsection Modula-2 defaults
5831 @cindex Modula-2 defaults
5833 If type and range checking are set automatically by @value{GDBN}, they
5834 both default to @code{on} whenever the working language changes to
5835 Modula-2. This happens regardless of whether you, or @value{GDBN},
5836 selected the working language.
5838 If you allow @value{GDBN} to set the language automatically, then entering
5839 code compiled from a file whose name ends with @file{.mod} will set the
5840 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
5841 the language automatically}, for further details.
5844 @subsubsection Deviations from standard Modula-2
5845 @cindex Modula-2, deviations from
5847 A few changes have been made to make Modula-2 programs easier to debug.
5848 This is done primarily via loosening its type strictness:
5852 Unlike in standard Modula-2, pointer constants can be formed by
5853 integers. This allows you to modify pointer variables during
5854 debugging. (In standard Modula-2, the actual address contained in a
5855 pointer variable is hidden from you; it can only be modified
5856 through direct assignment to another pointer variable or expression that
5857 returned a pointer.)
5860 C escape sequences can be used in strings and characters to represent
5861 non-printable characters. @value{GDBN} will print out strings with these
5862 escape sequences embedded. Single non-printable characters are
5863 printed using the @samp{CHR(@var{nnn})} format.
5866 The assignment operator (@code{:=}) returns the value of its right-hand
5870 All built-in procedures both modify @emph{and} return their argument.
5874 @subsubsection Modula-2 type and range checks
5875 @cindex Modula-2 checks
5878 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
5881 @c FIXME remove warning when type/range checks added
5883 @value{GDBN} considers two Modula-2 variables type equivalent if:
5887 They are of types that have been declared equivalent via a @code{TYPE
5888 @var{t1} = @var{t2}} statement
5891 They have been declared on the same line. (Note: This is true of the
5892 GNU Modula-2 compiler, but it may not be true of other compilers.)
5895 As long as type checking is enabled, any attempt to combine variables
5896 whose types are not equivalent is an error.
5898 Range checking is done on all mathematical operations, assignment, array
5899 index bounds, and all built-in functions and procedures.
5902 @subsubsection The scope operators @code{::} and @code{.}
5905 @cindex colon, doubled as scope operator
5908 @c Info cannot handle :: but TeX can.
5914 There are a few subtle differences between the Modula-2 scope operator
5915 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
5920 @var{module} . @var{id}
5921 @var{scope} :: @var{id}
5925 where @var{scope} is the name of a module or a procedure,
5926 @var{module} the name of a module, and @var{id} is any declared
5927 identifier within your program, except another module.
5929 Using the @code{::} operator makes @value{GDBN} search the scope
5930 specified by @var{scope} for the identifier @var{id}. If it is not
5931 found in the specified scope, then @value{GDBN} will search all scopes
5932 enclosing the one specified by @var{scope}.
5934 Using the @code{.} operator makes @value{GDBN} search the current scope for
5935 the identifier specified by @var{id} that was imported from the
5936 definition module specified by @var{module}. With this operator, it is
5937 an error if the identifier @var{id} was not imported from definition
5938 module @var{module}, or if @var{id} is not an identifier in
5942 @subsubsection @value{GDBN} and Modula-2
5944 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
5945 Five subcommands of @code{set print} and @code{show print} apply
5946 specifically to C and C++: @samp{vtbl}, @samp{demangle},
5947 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
5948 apply to C++, and the last to the C @code{union} type, which has no direct
5949 analogue in Modula-2.
5951 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
5952 while using any language, is not useful with Modula-2. Its
5953 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
5954 created in Modula-2 as they can in C or C++. However, because an
5955 address can be specified by an integral constant, the construct
5956 @samp{@{@var{type}@}@var{adrexp}} is still useful. (@pxref{Expressions, ,Expressions})
5958 @cindex @code{#} in Modula-2
5959 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
5960 interpreted as the beginning of a comment. Use @code{<>} instead.
5966 @chapter Examining the Symbol Table
5968 The commands described in this section allow you to inquire about the
5969 symbols (names of variables, functions and types) defined in your
5970 program. This information is inherent in the text of your program and
5971 does not change as your program executes. @value{GDBN} finds it in your
5972 program's symbol table, in the file indicated when you started @value{GDBN}
5973 (@pxref{File Options, ,Choosing files}), or by one of the
5974 file-management commands (@pxref{Files, ,Commands to specify files}).
5976 @c FIXME! This might be intentionally specific to C and C++; if so, move
5977 @c to someplace in C section of lang chapter.
5978 @cindex symbol names
5979 @cindex names of symbols
5980 @cindex quoting names
5981 Occasionally, you may need to refer to symbols that contain unusual
5982 characters, which @value{GDBN} ordinarily treats as word delimiters. The
5983 most frequent case is in referring to static variables in other
5984 source files (@pxref{Variables,,Program variables}). File names
5985 are recorded in object files as debugging symbols, but @value{GDBN} would
5986 ordinarily parse a typical file name, like @file{foo.c}, as the three words
5987 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
5988 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
5995 looks up the value of @code{x} in the scope of the file @file{foo.c}.
5998 @item info address @var{symbol}
5999 @kindex info address
6000 Describe where the data for @var{symbol} is stored. For a register
6001 variable, this says which register it is kept in. For a non-register
6002 local variable, this prints the stack-frame offset at which the variable
6005 Note the contrast with @samp{print &@var{symbol}}, which does not work
6006 at all for a register variables, and for a stack local variable prints
6007 the exact address of the current instantiation of the variable.
6009 @item whatis @var{exp}
6011 Print the data type of expression @var{exp}. @var{exp} is not
6012 actually evaluated, and any side-effecting operations (such as
6013 assignments or function calls) inside it do not take place.
6014 @xref{Expressions, ,Expressions}.
6017 Print the data type of @code{$}, the last value in the value history.
6019 @item ptype @var{typename}
6021 Print a description of data type @var{typename}. @var{typename} may be
6022 the name of a type, or for C code it may have the form
6023 @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or
6024 @samp{enum @var{enum-tag}}.
6026 @item ptype @var{exp}
6028 Print a description of the type of expression @var{exp}. @code{ptype}
6029 differs from @code{whatis} by printing a detailed description, instead
6030 of just the name of the type.
6032 For example, for this variable declaration:
6035 struct complex @{double real; double imag;@} v;
6039 the two commands give this output:
6043 (@value{GDBP}) whatis v
6044 type = struct complex
6045 (@value{GDBP}) ptype v
6046 type = struct complex @{
6054 As with @code{whatis}, using @code{ptype} without an argument refers to
6055 the type of @code{$}, the last value in the value history.
6057 @item info types @var{regexp}
6060 Print a brief description of all types whose name matches @var{regexp}
6061 (or all types in your program, if you supply no argument). Each
6062 complete typename is matched as though it were a complete line; thus,
6063 @samp{i type value} gives information on all types in your program whose
6064 name includes the string @code{value}, but @samp{i type ^value$} gives
6065 information only on types whose complete name is @code{value}.
6067 This command differs from @code{ptype} in two ways: first, like
6068 @code{whatis}, it does not print a detailed description; second, it
6069 lists all source files where a type is defined.
6073 Show the name of the current source file---that is, the source file for
6074 the function containing the current point of execution---and the language
6078 @kindex info sources
6079 Print the names of all source files in your program for which there is
6080 debugging information, organized into two lists: files whose symbols
6081 have already been read, and files whose symbols will be read when needed.
6083 @item info functions
6084 @kindex info functions
6085 Print the names and data types of all defined functions.
6087 @item info functions @var{regexp}
6088 Print the names and data types of all defined functions
6089 whose names contain a match for regular expression @var{regexp}.
6090 Thus, @samp{info fun step} finds all functions whose names
6091 include @code{step}; @samp{info fun ^step} finds those whose names
6092 start with @code{step}.
6094 @item info variables
6095 @kindex info variables
6096 Print the names and data types of all variables that are declared
6097 outside of functions (i.e., excluding local variables).
6099 @item info variables @var{regexp}
6100 Print the names and data types of all variables (except for local
6101 variables) whose names contain a match for regular expression
6105 This was never implemented.
6107 @itemx info methods @var{regexp}
6108 @kindex info methods
6109 The @code{info methods} command permits the user to examine all defined
6110 methods within C++ program, or (with the @var{regexp} argument) a
6111 specific set of methods found in the various C++ classes. Many
6112 C++ classes provide a large number of methods. Thus, the output
6113 from the @code{ptype} command can be overwhelming and hard to use. The
6114 @code{info-methods} command filters the methods, printing only those
6115 which match the regular-expression @var{regexp}.
6118 @item maint print symbols @var{filename}
6119 @itemx maint print psymbols @var{filename}
6120 @itemx maint print msymbols @var{filename}
6121 @kindex maint print symbols
6123 @kindex maint print psymbols
6124 @cindex partial symbol dump
6125 Write a dump of debugging symbol data into the file @var{filename}.
6126 These commands are used to debug the @value{GDBN} symbol-reading code. Only
6127 symbols with debugging data are included. If you use @samp{maint print
6128 symbols}, @value{GDBN} includes all the symbols for which it has already
6129 collected full details: that is, @var{filename} reflects symbols for
6130 only those files whose symbols @value{GDBN} has read. You can use the
6131 command @code{info sources} to find out which files these are. If you
6132 use @samp{maint print psymbols} instead, the dump shows information about
6133 symbols that @value{GDBN} only knows partially---that is, symbols defined in
6134 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
6135 @samp{maint print msymbols} dumps just the minimal symbol information
6136 required for each object file from which @value{GDBN} has read some symbols.
6137 @xref{Files, ,Commands to specify files}, for a discussion of how
6138 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
6142 @chapter Altering Execution
6144 Once you think you have found an error in your program, you might want to
6145 find out for certain whether correcting the apparent error would lead to
6146 correct results in the rest of the run. You can find the answer by
6147 experiment, using the @value{GDBN} features for altering execution of the
6150 For example, you can store new values into variables or memory
6153 give your program a signal, restart it
6156 restart your program
6158 at a different address, or even return prematurely from a function to
6162 * Assignment:: Assignment to variables
6163 * Jumping:: Continuing at a different address
6165 * Signaling:: Giving your program a signal
6168 * Returning:: Returning from a function
6169 * Calling:: Calling your program's functions
6170 * Patching:: Patching your program
6174 @section Assignment to variables
6177 @cindex setting variables
6178 To alter the value of a variable, evaluate an assignment expression.
6179 @xref{Expressions, ,Expressions}. For example,
6186 stores the value 4 into the variable @code{x}, and then prints the
6187 value of the assignment expression (which is 4).
6189 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
6190 information on operators in supported languages.
6193 @kindex set variable
6194 @cindex variables, setting
6195 If you are not interested in seeing the value of the assignment, use the
6196 @code{set} command instead of the @code{print} command. @code{set} is
6197 really the same as @code{print} except that the expression's value is
6198 not printed and is not put in the value history (@pxref{Value History,
6199 ,Value history}). The expression is evaluated only for its effects.
6201 If the beginning of the argument string of the @code{set} command
6202 appears identical to a @code{set} subcommand, use the @code{set
6203 variable} command instead of just @code{set}. This command is identical
6204 to @code{set} except for its lack of subcommands. For example, if
6205 your program has a variable @code{width}, you get
6206 an error if you try to set a new value with just @samp{set width=13},
6207 because @value{GDBN} has the command @code{set width}:
6210 (@value{GDBP}) whatis width
6212 (@value{GDBP}) p width
6214 (@value{GDBP}) set width=47
6215 Invalid syntax in expression.
6219 The invalid expression, of course, is @samp{=47}. In
6220 order to actually set the program's variable @code{width}, use
6223 (@value{GDBP}) set var width=47
6226 @value{GDBN} allows more implicit conversions in assignments than C; you can
6227 freely store an integer value into a pointer variable or vice versa,
6228 and you can convert any structure to any other structure that is the
6229 same length or shorter.
6230 @comment FIXME: how do structs align/pad in these conversions?
6231 @comment /pesch@cygnus.com 18dec1990
6233 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
6234 construct to generate a value of specified type at a specified address
6235 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
6236 to memory location @code{0x83040} as an integer (which implies a certain size
6237 and representation in memory), and
6240 set @{int@}0x83040 = 4
6244 stores the value 4 into that memory location.
6247 @section Continuing at a different address
6249 Ordinarily, when you continue your program, you do so at the place where
6250 it stopped, with the @code{continue} command. You can instead continue at
6251 an address of your own choosing, with the following commands:
6254 @item jump @var{linespec}
6256 Resume execution at line @var{linespec}. Execution will stop
6257 immediately if there is a breakpoint there. @xref{List, ,Printing
6258 source lines}, for a description of the different forms of
6261 The @code{jump} command does not change the current stack frame, or
6262 the stack pointer, or the contents of any memory location or any
6263 register other than the program counter. If line @var{linespec} is in
6264 a different function from the one currently executing, the results may
6265 be bizarre if the two functions expect different patterns of arguments or
6266 of local variables. For this reason, the @code{jump} command requests
6267 confirmation if the specified line is not in the function currently
6268 executing. However, even bizarre results are predictable if you are
6269 well acquainted with the machine-language code of your program.
6271 @item jump *@var{address}
6272 Resume execution at the instruction at address @var{address}.
6275 You can get much the same effect as the @code{jump} command by storing a
6276 new value into the register @code{$pc}. The difference is that this
6277 does not start your program running; it only changes the address where it
6278 @emph{will} run when it is continued. For example,
6285 causes the next @code{continue} command or stepping command to execute at
6286 address @code{0x485}, rather than at the address where your program stopped.
6287 @xref{Continuing and Stepping, ,Continuing and stepping}.
6289 The most common occasion to use the @code{jump} command is to back up,
6290 perhaps with more breakpoints set, over a portion of a program that has
6291 already executed, in order to examine its execution in more detail.
6296 @section Giving your program a signal
6299 @item signal @var{signalnum}
6301 Resume execution where your program stopped, but give it immediately the
6302 signal number @var{signalnum}.
6304 Alternatively, if @var{signalnum} is zero, continue execution without
6305 giving a signal. This is useful when your program stopped on account of
6306 a signal and would ordinary see the signal when resumed with the
6307 @code{continue} command; @samp{signal 0} causes it to resume without a
6310 @code{signal} does not repeat when you press @key{RET} a second time
6311 after executing the command.
6317 @section Returning from a function
6321 @itemx return @var{expression}
6322 @cindex returning from a function
6324 You can cancel execution of a function call with the @code{return}
6325 command. If you give an
6326 @var{expression} argument, its value is used as the function's return
6330 When you use @code{return}, @value{GDBN} discards the selected stack frame
6331 (and all frames within it). You can think of this as making the
6332 discarded frame return prematurely. If you wish to specify a value to
6333 be returned, give that value as the argument to @code{return}.
6335 This pops the selected stack frame (@pxref{Selection, ,Selecting a
6336 frame}), and any other frames inside of it, leaving its caller as the
6337 innermost remaining frame. That frame becomes selected. The
6338 specified value is stored in the registers used for returning values
6341 The @code{return} command does not resume execution; it leaves the
6342 program stopped in the state that would exist if the function had just
6343 returned. In contrast, the @code{finish} command (@pxref{Continuing
6344 and Stepping, ,Continuing and stepping}) resumes execution until the
6345 selected stack frame returns naturally.
6348 @section Calling program functions
6350 @cindex calling functions
6353 @item call @var{expr}
6354 Evaluate the expression @var{expr} without displaying @code{void}
6358 You can use this variant of the @code{print} command if you want to
6359 execute a function from your program, but without cluttering the output
6360 with @code{void} returned values. The result is printed and saved in
6361 the value history, if it is not void.
6364 @section Patching programs
6365 @cindex patching binaries
6366 @cindex writing into executables
6368 @cindex writing into corefiles
6371 By default, @value{GDBN} opens the file containing your program's executable
6376 read-only. This prevents accidental alterations
6377 to machine code; but it also prevents you from intentionally patching
6378 your program's binary.
6380 If you'd like to be able to patch the binary, you can specify that
6381 explicitly with the @code{set write} command. For example, you might
6382 want to turn on internal debugging flags, or even to make emergency
6387 @itemx set write off
6389 If you specify @samp{set write on}, @value{GDBN} will open executable
6393 files for both reading and writing; if you specify @samp{set write
6394 off} (the default), @value{GDBN} will open them read-only.
6396 If you have already loaded a file, you must load it again (using the
6401 command) after changing @code{set write}, for your new setting to take
6406 Display whether executable files
6410 will be opened for writing as well as reading.
6414 @chapter @value{GDBN} Files
6416 @value{GDBN} needs to know the file name of the program to be debugged, both in
6417 order to read its symbol table and in order to start your program.
6419 To debug a core dump of a previous run, you must also tell @value{GDBN}
6420 the name of the core dump file.
6424 * Files:: Commands to specify files
6425 * Symbol Errors:: Errors reading symbol files
6429 @section Commands to specify files
6430 @cindex symbol table
6433 @cindex core dump file
6434 The usual way to specify executable and core dump file names is with
6435 the command arguments given when you start @value{GDBN} (@pxref{Invocation,
6436 ,Getting In and Out of @value{GDBN}}.
6439 The usual way to specify an executable file name is with
6440 the command argument given when you start @value{GDBN}, (@pxref{Invocation,
6441 ,Getting In and Out of @value{GDBN}}.
6444 Occasionally it is necessary to change to a different file during a
6445 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
6446 a file you want to use. In these situations the @value{GDBN} commands
6447 to specify new files are useful.
6450 @item file @var{filename}
6451 @cindex executable file
6453 Use @var{filename} as the program to be debugged. It is read for its
6454 symbols and for the contents of pure memory. It is also the program
6455 executed when you use the @code{run} command. If you do not specify a
6456 directory and the file is not found in the @value{GDBN} working directory, @value{GDBN}
6457 uses the environment variable @code{PATH} as a list of directories to
6458 search, just as the shell does when looking for a program to run. You
6459 can change the value of this variable, for both @value{GDBN} and your program,
6460 using the @code{path} command.
6462 On systems with memory-mapped files, an auxiliary symbol table file
6463 @file{@var{filename}.syms} may be available for @var{filename}. If it
6464 is, @value{GDBN} will map in the symbol table from
6465 @file{@var{filename}.syms}, starting up more quickly. See the
6466 descriptions of the options @samp{-mapped} and @samp{-readnow} (available
6467 on the command line, and with the commands @code{file}, @code{symbol-file},
6468 or @code{add-symbol-file}), for more information.
6471 @code{file} with no argument makes @value{GDBN} discard any information it
6472 has on both executable file and the symbol table.
6474 @item exec-file @r{[} @var{filename} @r{]}
6476 Specify that the program to be run (but not the symbol table) is found
6477 in @var{filename}. @value{GDBN} will search the environment variable @code{PATH}
6478 if necessary to locate your program. Omitting @var{filename} means to
6479 discard information on the executable file.
6481 @item symbol-file @r{[} @var{filename} @r{]}
6483 Read symbol table information from file @var{filename}. @code{PATH} is
6484 searched when necessary. Use the @code{file} command to get both symbol
6485 table and program to run from the same file.
6487 @code{symbol-file} with no argument clears out @value{GDBN} information on your
6488 program's symbol table.
6490 The @code{symbol-file} command causes @value{GDBN} to forget the contents of its
6491 convenience variables, the value history, and all breakpoints and
6492 auto-display expressions. This is because they may contain pointers to
6493 the internal data recording symbols and data types, which are part of
6494 the old symbol table data being discarded inside @value{GDBN}.
6496 @code{symbol-file} will not repeat if you press @key{RET} again after
6499 When @value{GDBN} is configured for a particular environment, it will
6500 understand debugging information in whatever format is the standard
6501 generated for that environment; you may use either a GNU compiler, or
6502 other compilers that adhere to the local conventions. Best results are
6503 usually obtained from GNU compilers; for example, using @code{@value{GCC}}
6504 you can generate debugging information for optimized code.
6506 On some kinds of object files, the @code{symbol-file} command does not
6507 normally read the symbol table in full right away. Instead, it scans
6508 the symbol table quickly to find which source files and which symbols
6509 are present. The details are read later, one source file at a time,
6512 The purpose of this two-stage reading strategy is to make @value{GDBN} start up
6513 faster. For the most part, it is invisible except for occasional
6514 pauses while the symbol table details for a particular source file are
6515 being read. (The @code{set verbose} command can turn these pauses
6516 into messages if desired. @xref{Messages/Warnings, ,Optional warnings
6519 We have not implemented the two-stage strategy for COFF yet. When the
6520 symbol table is stored in COFF format, @code{symbol-file} reads the
6521 symbol table data in full right away.
6523 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6524 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6526 @cindex reading symbols immediately
6527 @cindex symbols, reading immediately
6529 @cindex memory-mapped symbol file
6530 @cindex saving symbol table
6531 You can override the @value{GDBN} two-stage strategy for reading symbol
6532 tables by using the @samp{-readnow} option with any of the commands that
6533 load symbol table information, if you want to be sure @value{GDBN} has the
6534 entire symbol table available.
6537 If memory-mapped files are available on your system through the
6538 @code{mmap} system call, you can use another option, @samp{-mapped}, to
6539 cause @value{GDBN} to write the symbols for your program into a reusable
6540 file. Future @value{GDBN} debugging sessions will map in symbol information
6541 from this auxiliary symbol file (if the program has not changed), rather
6542 than spending time reading the symbol table from the executable
6543 program. Using the @samp{-mapped} option has the same effect as
6544 starting @value{GDBN} with the @samp{-mapped} command-line option.
6546 You can use both options together, to make sure the auxiliary symbol
6547 file has all the symbol information for your program.
6549 The auxiliary symbol file for a program called @var{myprog} is called
6550 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
6551 than the corresponding executable), @value{GDBN} will always attempt to use
6552 it when you debug @var{myprog}; no special options or commands are
6555 The @file{.syms} file is specific to the host machine where you run
6556 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
6557 symbol table. It cannot be shared across multiple host platforms.
6559 @c FIXME: for now no mention of directories, since this seems to be in
6560 @c flux. 13mar1992 status is that in theory GDB would look either in
6561 @c current dir or in same dir as myprog; but issues like competing
6562 @c GDB's, or clutter in system dirs, mean that in practice right now
6563 @c only current dir is used. FFish says maybe a special GDB hierarchy
6564 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
6567 @item core-file @r{[} @var{filename} @r{]}
6570 Specify the whereabouts of a core dump file to be used as the ``contents
6571 of memory''. Traditionally, core files contain only some parts of the
6572 address space of the process that generated them; @value{GDBN} can access the
6573 executable file itself for other parts.
6575 @code{core-file} with no argument specifies that no core file is
6578 Note that the core file is ignored when your program is actually running
6579 under @value{GDBN}. So, if you have been running your program and you wish to
6580 debug a core file instead, you must kill the subprocess in which the
6581 program is running. To do this, use the @code{kill} command
6582 (@pxref{Kill Process, ,Killing the child process}).
6585 @item load @var{filename}
6588 Depending on what remote debugging facilities are configured into
6589 @value{GDBN}, the @code{load} command may be available. Where it exists, it
6590 is meant to make @var{filename} (an executable) available for debugging
6591 on the remote system---by downloading, or dynamic linking, for example.
6592 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
6593 the @code{add-symbol-file} command.
6595 If your @value{GDBN} does not have a @code{load} command, attempting to
6596 execute it gets the error message ``@code{You can't do that when your
6597 target is @dots{}}''
6601 On VxWorks, @code{load} will dynamically link @var{filename} on the
6602 current target system as well as adding its symbols in @value{GDBN}.
6606 @cindex download to Nindy-960
6607 With the Nindy interface to an Intel 960 board, @code{load} will
6608 download @var{filename} to the 960 as well as adding its symbols in
6613 @cindex download to H8/300 or H8/500
6614 @cindex H8/300 or H8/500 download
6615 @cindex download to Hitachi SH
6616 @cindex Hitachi SH download
6617 When you select remote debugging to a Hitachi SH, H8/300, or H8/500 board
6618 (@pxref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}),
6619 the @code{load} command downloads your program to the Hitachi board and also
6620 opens it as the current executable target for @value{GDBN} on your host
6621 (like the @code{file} command).
6624 @code{load} will not repeat if you press @key{RET} again after using it.
6627 @item add-symbol-file @var{filename} @var{address}
6628 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6629 @kindex add-symbol-file
6630 @cindex dynamic linking
6631 The @code{add-symbol-file} command reads additional symbol table information
6632 from the file @var{filename}. You would use this command when @var{filename}
6633 has been dynamically loaded (by some other means) into the program that
6634 is running. @var{address} should be the memory address at which the
6635 file has been loaded; @value{GDBN} cannot figure this out for itself.
6636 You can specify @var{address} as an expression.
6638 The symbol table of the file @var{filename} is added to the symbol table
6639 originally read with the @code{symbol-file} command. You can use the
6640 @code{add-symbol-file} command any number of times; the new symbol data thus
6641 read keeps adding to the old. To discard all old symbol data instead,
6642 use the @code{symbol-file} command.
6644 @code{add-symbol-file} will not repeat if you press @key{RET} after using it.
6646 You can use the @samp{-mapped} and @samp{-readnow} options just as with
6647 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
6648 table information for @var{filename}.
6655 @code{info files} and @code{info target} are synonymous; both print
6656 the current target (@pxref{Targets, ,Specifying a Debugging Target}),
6659 names of the executable and core dump files
6662 name of the executable file
6664 currently in use by @value{GDBN}, and the files from which symbols were
6665 loaded. The command @code{help targets} lists all possible targets
6666 rather than current ones.
6669 All file-specifying commands allow both absolute and relative file names
6670 as arguments. @value{GDBN} always converts the file name to an absolute path
6671 name and remembers it that way.
6674 @cindex shared libraries
6675 @value{GDBN} supports SunOS, SVR4, and IBM RS/6000 shared libraries.
6676 @value{GDBN} automatically loads symbol definitions from shared libraries
6677 when you use the @code{run} command, or when you examine a core file.
6678 (Before you issue the @code{run} command, @value{GDBN} will not understand
6679 references to a function in a shared library, however---unless you are
6680 debugging a core file).
6681 @c FIXME: next @value{GDBN} release should permit some refs to undef
6682 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared lib
6686 @itemx info sharedlibrary
6687 @kindex info sharedlibrary
6689 Print the names of the shared libraries which are currently loaded.
6691 @item sharedlibrary @var{regex}
6692 @itemx share @var{regex}
6693 @kindex sharedlibrary
6695 This is an obsolescent command; you can use it to explicitly
6696 load shared object library symbols for files matching a UNIX regular
6697 expression, but as with files loaded automatically, it will only load
6698 shared libraries required by your program for a core file or after
6699 typing @code{run}. If @var{regex} is omitted all shared libraries
6700 required by your program are loaded.
6705 @section Errors reading symbol files
6707 While reading a symbol file, @value{GDBN} will occasionally encounter problems,
6708 such as symbol types it does not recognize, or known bugs in compiler
6709 output. By default, @value{GDBN} does not notify you of such problems, since
6710 they are relatively common and primarily of interest to people
6711 debugging compilers. If you are interested in seeing information
6712 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
6713 only one message about each such type of problem, no matter how many
6714 times the problem occurs; or you can ask @value{GDBN} to print more messages,
6715 to see how many times the problems occur, with the @code{set
6716 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
6719 The messages currently printed, and their meanings, include:
6722 @item inner block not inside outer block in @var{symbol}
6724 The symbol information shows where symbol scopes begin and end
6725 (such as at the start of a function or a block of statements). This
6726 error indicates that an inner scope block is not fully contained
6727 in its outer scope blocks.
6729 @value{GDBN} circumvents the problem by treating the inner block as if it had
6730 the same scope as the outer block. In the error message, @var{symbol}
6731 may be shown as ``@code{(don't know)}'' if the outer block is not a
6734 @item block at @var{address} out of order
6736 The symbol information for symbol scope blocks should occur in
6737 order of increasing addresses. This error indicates that it does not
6740 @value{GDBN} does not circumvent this problem, and will have trouble
6741 locating symbols in the source file whose symbols it is reading. (You
6742 can often determine what source file is affected by specifying
6743 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
6746 @item bad block start address patched
6748 The symbol information for a symbol scope block has a start address
6749 smaller than the address of the preceding source line. This is known
6750 to occur in the SunOS 4.1.1 (and earlier) C compiler.
6752 @value{GDBN} circumvents the problem by treating the symbol scope block as
6753 starting on the previous source line.
6755 @item bad string table offset in symbol @var{n}
6758 Symbol number @var{n} contains a pointer into the string table which is
6759 larger than the size of the string table.
6761 @value{GDBN} circumvents the problem by considering the symbol to have the
6762 name @code{foo}, which may cause other problems if many symbols end up
6765 @item unknown symbol type @code{0x@var{nn}}
6767 The symbol information contains new data types that @value{GDBN} does not yet
6768 know how to read. @code{0x@var{nn}} is the symbol type of the misunderstood
6769 information, in hexadecimal.
6771 @value{GDBN} circumvents the error by ignoring this symbol information. This
6772 will usually allow your program to be debugged, though certain symbols
6773 will not be accessible. If you encounter such a problem and feel like
6774 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint on
6775 @code{complain}, then go up to the function @code{read_dbx_symtab} and
6776 examine @code{*bufp} to see the symbol.
6778 @item stub type has NULL name
6779 @value{GDBN} could not find the full definition for
6788 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
6790 The symbol information for a C++ member function is missing some
6791 information that recent versions of the compiler should have output
6795 @item info mismatch between compiler and debugger
6797 @value{GDBN} could not parse a type specification output by the compiler.
6801 @chapter Specifying a Debugging Target
6802 @cindex debugging target
6805 A @dfn{target} is the execution environment occupied by your program.
6807 Often, @value{GDBN} runs in the same host environment as your program; in
6808 that case, the debugging target is specified as a side effect when you
6809 use the @code{file} or @code{core} commands. When you need more
6810 flexibility---for example, running @value{GDBN} on a physically separate
6811 host, or controlling a standalone system over a serial port or a
6812 realtime system over a TCP/IP connection---you
6817 can use the @code{target} command to specify one of the target types
6818 configured for @value{GDBN} (@pxref{Target Commands, ,Commands for managing
6822 * Active Targets:: Active targets
6823 * Target Commands:: Commands for managing targets
6824 * Remote:: Remote debugging
6827 @node Active Targets
6828 @section Active targets
6829 @cindex stacking targets
6830 @cindex active targets
6831 @cindex multiple targets
6834 There are three classes of targets: processes, core files, and
6835 executable files. @value{GDBN} can work concurrently on up to three active
6836 targets, one in each class. This allows you to (for example) start a
6837 process and inspect its activity without abandoning your work on a core
6840 For example, if you execute @samp{gdb a.out}, then the executable file
6841 @code{a.out} is the only active target. If you designate a core file as
6842 well---presumably from a prior run that crashed and coredumped---then
6843 @value{GDBN} has two active targets and will use them in tandem, looking
6844 first in the corefile target, then in the executable file, to satisfy
6845 requests for memory addresses. (Typically, these two classes of target
6846 are complementary, since core files contain only a program's
6847 read-write memory---variables and so on---plus machine status, while
6848 executable files contain only the program text and initialized data.)
6851 When you type @code{run}, your executable file becomes an active process
6852 target as well. When a process target is active, all @value{GDBN} commands
6853 requesting memory addresses refer to that target; addresses in an
6857 executable file target are obscured while the process
6861 Use the @code{exec-file} command to select a
6862 new executable target (@pxref{Files, ,Commands to specify
6866 Use the @code{core-file} and @code{exec-file} commands to select a
6867 new core file or executable target (@pxref{Files, ,Commands to specify
6868 files}). To specify as a target a process that is already running, use
6869 the @code{attach} command (@pxref{Attach, ,Debugging an
6870 already-running process}).
6873 @node Target Commands
6874 @section Commands for managing targets
6877 @item target @var{type} @var{parameters}
6878 Connects the @value{GDBN} host environment to a target
6883 machine or process. A target is typically a protocol for talking to
6884 debugging facilities. You use the argument @var{type} to specify the
6885 type or protocol of the target machine.
6887 Further @var{parameters} are interpreted by the target protocol, but
6888 typically include things like device names or host names to connect
6889 with, process numbers, and baud rates.
6892 The @code{target} command will not repeat if you press @key{RET} again
6893 after executing the command.
6897 Displays the names of all targets available. To display targets
6898 currently selected, use either @code{info target} or @code{info files}
6899 (@pxref{Files, ,Commands to specify files}).
6901 @item help target @var{name}
6902 Describe a particular target, including any parameters necessary to
6906 Here are some common targets (available, or not, depending on the GDB
6910 @item target exec @var{program}
6912 An executable file. @samp{target exec @var{program}} is the same as
6913 @samp{exec-file @var{program}}.
6916 @item target core @var{filename}
6918 A core dump file. @samp{target core @var{filename}} is the same as
6919 @samp{core-file @var{filename}}.
6923 @item target remote @var{dev}
6924 @kindex target remote
6925 Remote serial target in GDB-specific protocol. The argument @var{dev}
6926 specifies what serial device to use for the connection (e.g.
6927 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}.
6933 CPU simulator. @xref{Simulator,,Simulated CPU Target}.
6937 @item target udi @var{keyword}
6939 Remote AMD29K target, using the AMD UDI protocol. The @var{keyword}
6940 argument specifies which 29K board or simulator to use. @xref{UDI29K
6941 Remote,,@value{GDBN} and the UDI protocol for AMD29K}.
6943 @item target amd-eb @var{dev} @var{speed} @var{PROG}
6944 @kindex target amd-eb
6946 Remote PC-resident AMD EB29K board, attached over serial lines.
6947 @var{dev} is the serial device, as for @code{target remote};
6948 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
6949 name of the program to be debugged, as it appears to DOS on the PC.
6950 @xref{EB29K Remote, ,@value{GDBN} with a remote EB29K}.
6956 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
6957 @ifclear H8EXCLUSIVE
6958 @c Unix only, not currently of interest for H8-only manual
6959 Use special commands @code{device} and @code{speed} to control the serial
6960 line and the communications speed used.
6962 @xref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}.
6966 @item target nindy @var{devicename}
6967 @kindex target nindy
6968 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
6969 the name of the serial device to use for the connection, e.g.
6970 @file{/dev/ttya}. @xref{i960-Nindy Remote, ,@value{GDBN} with a remote i960 (Nindy)}.
6974 @item target st2000 @var{dev} @var{speed}
6975 @kindex target st2000
6976 A Tandem ST2000 phone switch, running Tandem's STDBUG protocol. @var{dev}
6977 is the name of the device attached to the ST2000 serial line;
6978 @var{speed} is the communication line speed. The arguments are not used
6979 if @value{GDBN} is configured to connect to the ST2000 using TCP or Telnet.
6980 @xref{ST2000 Remote,,@value{GDBN} with a Tandem ST2000}.
6984 @item target vxworks @var{machinename}
6985 @kindex target vxworks
6986 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
6987 is the target system's machine name or IP address.
6988 @xref{VxWorks Remote, ,@value{GDBN} and VxWorks}.
6993 Different targets are available on different configurations of @value{GDBN}; your
6994 configuration may have more or fewer targets.
6998 @section Remote debugging
6999 @cindex remote debugging
7001 If you are trying to debug a program running on a machine that cannot run
7002 GDB in the usual way, it is often useful to use remote debugging. For
7003 example, you might use remote debugging on an operating system kernel, or on
7004 a small system which does not have a general purpose operating system
7005 powerful enough to run a full-featured debugger.
7007 Some configurations of GDB have special serial or TCP/IP interfaces
7008 to make this work with particular debugging targets. In addition,
7009 GDB comes with a generic serial protocol (specific to GDB, but
7010 not specific to any particular target system) which you can use if you
7011 write the remote stubs---the code that will run on the remote system to
7012 communicate with GDB.
7014 Other remote targets may be available in your
7015 configuration of GDB; use @code{help targets} to list them.
7018 @c Text on starting up GDB in various specific cases; it goes up front
7019 @c in manuals configured for any of those particular situations, here
7023 * Remote Serial:: @value{GDBN} remote serial protocol
7026 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
7029 * UDI29K Remote:: @value{GDBN} and the UDI protocol for AMD29K
7030 * EB29K Remote:: @value{GDBN} with a remote EB29K
7033 * VxWorks Remote:: @value{GDBN} and VxWorks
7036 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
7039 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
7042 * MIPS Remote:: @value{GDBN} and MIPS boards
7045 * Simulator:: Simulated CPU target
7049 @include remote.texi
7052 @node Controlling GDB
7053 @chapter Controlling @value{GDBN}
7055 You can alter the way @value{GDBN} interacts with you by using
7056 the @code{set} command. For commands controlling how @value{GDBN} displays
7057 data, @pxref{Print Settings, ,Print settings}; other settings are described here.
7061 * Editing:: Command editing
7062 * History:: Command history
7063 * Screen Size:: Screen size
7065 * Messages/Warnings:: Optional warnings and messages
7072 @value{GDBN} indicates its readiness to read a command by printing a string
7073 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
7074 can change the prompt string with the @code{set prompt} command. For
7075 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
7076 the prompt in one of the @value{GDBN} sessions so that you can always tell which
7077 one you are talking to.
7080 @item set prompt @var{newprompt}
7082 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
7085 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
7089 @section Command editing
7091 @cindex command line editing
7093 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
7094 GNU library provides consistent behavior for programs which provide a
7095 command line interface to the user. Advantages are @code{emacs}-style
7096 or @code{vi}-style inline editing of commands, @code{csh}-like history
7097 substitution, and a storage and recall of command history across
7100 You may control the behavior of command line editing in @value{GDBN} with the
7107 @itemx set editing on
7108 Enable command line editing (enabled by default).
7110 @item set editing off
7111 Disable command line editing.
7113 @kindex show editing
7115 Show whether command line editing is enabled.
7119 @section Command history
7121 @value{GDBN} can keep track of the commands you type during your
7122 debugging sessions, so that you can be certain of precisely what
7123 happened. Use these commands to manage the @value{GDBN} command
7127 @cindex history substitution
7128 @cindex history file
7129 @kindex set history filename
7130 @item set history filename @var{fname}
7131 Set the name of the @value{GDBN} command history file to @var{fname}. This is
7132 the file from which @value{GDBN} will read an initial command history
7133 list or to which it will write this list when it exits. This list is
7134 accessed through history expansion or through the history
7135 command editing characters listed below. This file defaults to the
7136 value of the environment variable @code{GDBHISTFILE}, or to
7137 @file{./.gdb_history} if this variable is not set.
7139 @cindex history save
7140 @kindex set history save
7141 @item set history save
7142 @itemx set history save on
7143 Record command history in a file, whose name may be specified with the
7144 @code{set history filename} command. By default, this option is disabled.
7146 @item set history save off
7147 Stop recording command history in a file.
7149 @cindex history size
7150 @kindex set history size
7151 @item set history size @var{size}
7152 Set the number of commands which @value{GDBN} will keep in its history list.
7153 This defaults to the value of the environment variable
7154 @code{HISTSIZE}, or to 256 if this variable is not set.
7157 @cindex history expansion
7158 History expansion assigns special meaning to the character @kbd{!}.
7159 @ifset have-readline-appendices
7160 @xref{Event Designators}.
7163 Since @kbd{!} is also the logical not operator in C, history expansion
7164 is off by default. If you decide to enable history expansion with the
7165 @code{set history expansion on} command, you may sometimes need to
7166 follow @kbd{!} (when it is used as logical not, in an expression) with
7167 a space or a tab to prevent it from being expanded. The readline
7168 history facilities will not attempt substitution on the strings
7169 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
7171 The commands to control history expansion are:
7175 @kindex set history expansion
7176 @item set history expansion on
7177 @itemx set history expansion
7178 Enable history expansion. History expansion is off by default.
7180 @item set history expansion off
7181 Disable history expansion.
7183 The readline code comes with more complete documentation of
7184 editing and history expansion features. Users unfamiliar with @code{emacs}
7185 or @code{vi} may wish to read it.
7186 @ifset have-readline-appendices
7187 @xref{Command Line Editing}.
7191 @kindex show history
7193 @itemx show history filename
7194 @itemx show history save
7195 @itemx show history size
7196 @itemx show history expansion
7197 These commands display the state of the @value{GDBN} history parameters.
7198 @code{show history} by itself displays all four states.
7203 @kindex show commands
7205 Display the last ten commands in the command history.
7207 @item show commands @var{n}
7208 Print ten commands centered on command number @var{n}.
7210 @item show commands +
7211 Print ten commands just after the commands last printed.
7215 @section Screen size
7216 @cindex size of screen
7217 @cindex pauses in output
7219 Certain commands to @value{GDBN} may produce large amounts of
7220 information output to the screen. To help you read all of it,
7221 @value{GDBN} pauses and asks you for input at the end of each page of
7222 output. Type @key{RET} when you want to continue the output, or @kbd{q}
7223 to discard the remaining output. Also, the screen width setting
7224 determines when to wrap lines of output. Depending on what is being
7225 printed, @value{GDBN} tries to break the line at a readable place,
7226 rather than simply letting it overflow onto the following line.
7228 Normally @value{GDBN} knows the size of the screen from the termcap data base
7229 together with the value of the @code{TERM} environment variable and the
7230 @code{stty rows} and @code{stty cols} settings. If this is not correct,
7231 you can override it with the @code{set height} and @code{set
7235 @item set height @var{lpp}
7237 @itemx set width @var{cpl}
7243 These @code{set} commands specify a screen height of @var{lpp} lines and
7244 a screen width of @var{cpl} characters. The associated @code{show}
7245 commands display the current settings.
7247 If you specify a height of zero lines, @value{GDBN} will not pause during output
7248 no matter how long the output is. This is useful if output is to a file
7249 or to an editor buffer.
7251 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
7252 from wrapping its output.
7257 @cindex number representation
7258 @cindex entering numbers
7260 You can always enter numbers in octal, decimal, or hexadecimal in @value{GDBN} by
7261 the usual conventions: octal numbers begin with @samp{0}, decimal
7262 numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}.
7263 Numbers that begin with none of these are, by default, entered in base
7264 10; likewise, the default display for numbers---when no particular
7265 format is specified---is base 10. You can change the default base for
7266 both input and output with the @code{set radix} command.
7270 @item set radix @var{base}
7271 Set the default base for numeric input and display. Supported choices
7272 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
7273 specified either unambiguously or using the current default radix; for
7283 will set the base to decimal. On the other hand, @samp{set radix 10}
7284 will leave the radix unchanged no matter what it was.
7288 Display the current default base for numeric input and display.
7291 @node Messages/Warnings
7292 @section Optional warnings and messages
7294 By default, @value{GDBN} is silent about its inner workings. If you are running
7295 on a slow machine, you may want to use the @code{set verbose} command.
7296 It will make @value{GDBN} tell you when it does a lengthy internal operation, so
7297 you will not think it has crashed.
7299 Currently, the messages controlled by @code{set verbose} are those
7300 which announce that the symbol table for a source file is being read;
7301 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
7305 @item set verbose on
7306 Enables @value{GDBN} output of certain informational messages.
7308 @item set verbose off
7309 Disables @value{GDBN} output of certain informational messages.
7311 @kindex show verbose
7313 Displays whether @code{set verbose} is on or off.
7316 By default, if @value{GDBN} encounters bugs in the symbol table of an object
7317 file, it is silent; but if you are debugging a compiler, you may find
7318 this information useful (@pxref{Symbol Errors, ,Errors reading symbol files}).
7321 @kindex set complaints
7322 @item set complaints @var{limit}
7323 Permits @value{GDBN} to output @var{limit} complaints about each type of unusual
7324 symbols before becoming silent about the problem. Set @var{limit} to
7325 zero to suppress all complaints; set it to a large number to prevent
7326 complaints from being suppressed.
7328 @kindex show complaints
7329 @item show complaints
7330 Displays how many symbol complaints @value{GDBN} is permitted to produce.
7333 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
7334 lot of stupid questions to confirm certain commands. For example, if
7335 you try to run a program which is already running:
7339 The program being debugged has been started already.
7340 Start it from the beginning? (y or n)
7343 If you are willing to unflinchingly face the consequences of your own
7344 commands, you can disable this ``feature'':
7349 @cindex confirmation
7350 @cindex stupid questions
7351 @item set confirm off
7352 Disables confirmation requests.
7354 @item set confirm on
7355 Enables confirmation requests (the default).
7358 @kindex show confirm
7359 Displays state of confirmation requests.
7362 @c FIXME this does not really belong here. But where *does* it belong?
7363 @cindex reloading symbols
7364 Some systems allow individual object files that make up your program to
7365 be replaced without stopping and restarting your program.
7367 For example, in VxWorks you can simply recompile a defective object file
7368 and keep on running.
7370 If you are running on one of these systems, you can allow @value{GDBN} to
7371 reload the symbols for automatically relinked modules:
7374 @kindex set symbol-reloading
7375 @item set symbol-reloading on
7376 Replace symbol definitions for the corresponding source file when an
7377 object file with a particular name is seen again.
7379 @item set symbol-reloading off
7380 Do not replace symbol definitions when re-encountering object files of
7381 the same name. This is the default state; if you are not running on a
7382 system that permits automatically relinking modules, you should leave
7383 @code{symbol-reloading} off, since otherwise @value{GDBN} may discard symbols
7384 when linking large programs, that may contain several modules (from
7385 different directories or libraries) with the same name.
7387 @item show symbol-reloading
7388 Show the current @code{on} or @code{off} setting.
7392 @chapter Canned Sequences of Commands
7394 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
7395 command lists}), @value{GDBN} provides two ways to store sequences of commands
7396 for execution as a unit: user-defined commands and command files.
7399 * Define:: User-defined commands
7400 * Hooks:: User-defined command hooks
7401 * Command Files:: Command files
7402 * Output:: Commands for controlled output
7406 @section User-defined commands
7408 @cindex user-defined command
7409 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to which you
7410 assign a new name as a command. This is done with the @code{define}
7414 @item define @var{commandname}
7416 Define a command named @var{commandname}. If there is already a command
7417 by that name, you are asked to confirm that you want to redefine it.
7419 The definition of the command is made up of other @value{GDBN} command lines,
7420 which are given following the @code{define} command. The end of these
7421 commands is marked by a line containing @code{end}.
7423 @item document @var{commandname}
7425 Give documentation to the user-defined command @var{commandname}. The
7426 command @var{commandname} must already be defined. This command reads
7427 lines of documentation just as @code{define} reads the lines of the
7428 command definition, ending with @code{end}. After the @code{document}
7429 command is finished, @code{help} on command @var{commandname} will print
7430 the documentation you have specified.
7432 You may use the @code{document} command again to change the
7433 documentation of a command. Redefining the command with @code{define}
7434 does not change the documentation.
7436 @item help user-defined
7437 @kindex help user-defined
7438 List all user-defined commands, with the first line of the documentation
7442 @itemx show user @var{commandname}
7444 Display the @value{GDBN} commands used to define @var{commandname} (but not its
7445 documentation). If no @var{commandname} is given, display the
7446 definitions for all user-defined commands.
7449 User-defined commands do not take arguments. When they are executed, the
7450 commands of the definition are not printed. An error in any command
7451 stops execution of the user-defined command.
7453 Commands that would ask for confirmation if used interactively proceed
7454 without asking when used inside a user-defined command. Many @value{GDBN} commands
7455 that normally print messages to say what they are doing omit the messages
7456 when used in a user-defined command.
7459 @section User-defined command hooks
7460 @cindex command files
7462 You may define @emph{hooks}, which are a special kind of user-defined
7463 command. Whenever you run the command @samp{foo}, if the user-defined
7464 command @samp{hook-foo} exists, it is executed (with no arguments)
7465 before that command.
7467 In addition, a pseudo-command, @samp{stop} exists. Defining
7468 (@samp{hook-stop}) makes the associated commands execute every time
7469 execution stops in your program: before breakpoint commands are run,
7470 displays are printed, or the stack frame is printed.
7473 For example, to ignore @code{SIGALRM} signals while
7474 single-stepping, but treat them normally during normal execution,
7479 handle SIGALRM nopass
7486 define hook-continue
7492 You can define a hook for any single-word command in @value{GDBN}, but
7493 not for command aliases; you should define a hook for the basic command
7494 name, e.g. @code{backtrace} rather than @code{bt}.
7495 @c FIXME! So how does Joe User discover whether a command is an alias
7497 If an error occurs during the execution of your hook, execution of
7498 @value{GDBN} commands stops and @value{GDBN} issues a prompt
7499 (before the command that you actually typed had a chance to run).
7501 If you try to define a hook which does not match any known command, you
7502 will get a warning from the @code{define} command.
7505 @section Command files
7507 @cindex command files
7508 A command file for @value{GDBN} is a file of lines that are @value{GDBN} commands. Comments
7509 (lines starting with @kbd{#}) may also be included. An empty line in a
7510 command file does nothing; it does not mean to repeat the last command, as
7511 it would from the terminal.
7514 @cindex @file{@value{GDBINIT}}
7515 When you start @value{GDBN}, it automatically executes commands from its
7516 @dfn{init files}. These are files named @file{@value{GDBINIT}}. @value{GDBN} reads
7517 the init file (if any) in your home directory and then the init file
7518 (if any) in the current working directory. (The init files are not
7519 executed if you use the @samp{-nx} option; @pxref{Mode Options,
7523 @cindex init file name
7524 On some configurations of @value{GDBN}, the init file is known by a
7525 different name (these are typically environments where a specialized
7526 form of GDB may need to coexist with other forms, hence a different name
7527 for the specialized version's init file). These are the environments
7528 with special init file names:
7533 VxWorks (Wind River Systems real-time OS): @samp{.vxgdbinit}
7535 @kindex .os68gdbinit
7537 OS68K (Enea Data Systems real-time OS): @samp{.os68gdbinit}
7541 ES-1800 (Ericsson Telecom AB M68000 emulator): @samp{.esgdbinit}
7545 You can also request the execution of a command file with the
7546 @code{source} command:
7549 @item source @var{filename}
7551 Execute the command file @var{filename}.
7554 The lines in a command file are executed sequentially. They are not
7555 printed as they are executed. An error in any command terminates execution
7556 of the command file.
7558 Commands that would ask for confirmation if used interactively proceed
7559 without asking when used in a command file. Many @value{GDBN} commands that
7560 normally print messages to say what they are doing omit the messages
7561 when called from command files.
7564 @section Commands for controlled output
7566 During the execution of a command file or a user-defined command, normal
7567 @value{GDBN} output is suppressed; the only output that appears is what is
7568 explicitly printed by the commands in the definition. This section
7569 describes three commands useful for generating exactly the output you
7573 @item echo @var{text}
7575 @c I do not consider backslash-space a standard C escape sequence
7576 @c because it is not in ANSI.
7577 Print @var{text}. Nonprinting characters can be included in
7578 @var{text} using C escape sequences, such as @samp{\n} to print a
7579 newline. @strong{No newline will be printed unless you specify one.}
7580 In addition to the standard C escape sequences, a backslash followed
7581 by a space stands for a space. This is useful for displaying a
7582 string with spaces at the beginning or the end, since leading and
7583 trailing spaces are otherwise trimmed from all arguments.
7584 To print @samp{@w{ }and foo =@w{ }}, use the command
7585 @samp{echo \@w{ }and foo = \@w{ }}.
7587 A backslash at the end of @var{text} can be used, as in C, to continue
7588 the command onto subsequent lines. For example,
7591 echo This is some text\n\
7592 which is continued\n\
7593 onto several lines.\n
7596 produces the same output as
7599 echo This is some text\n
7600 echo which is continued\n
7601 echo onto several lines.\n
7604 @item output @var{expression}
7606 Print the value of @var{expression} and nothing but that value: no
7607 newlines, no @samp{$@var{nn} = }. The value is not entered in the
7608 value history either. @xref{Expressions, ,Expressions}, for more information on
7611 @item output/@var{fmt} @var{expression}
7612 Print the value of @var{expression} in format @var{fmt}. You can use
7613 the same formats as for @code{print}. @xref{Output Formats,,Output
7614 formats}, for more information.
7616 @item printf @var{string}, @var{expressions}@dots{}
7618 Print the values of the @var{expressions} under the control of
7619 @var{string}. The @var{expressions} are separated by commas and may be
7620 either numbers or pointers. Their values are printed as specified by
7621 @var{string}, exactly as if your program were to execute the C
7625 printf (@var{string}, @var{expressions}@dots{});
7628 For example, you can print two values in hex like this:
7631 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
7634 The only backslash-escape sequences that you can use in the format
7635 string are the simple ones that consist of backslash followed by a
7641 @chapter Using @value{GDBN} under GNU Emacs
7644 A special interface allows you to use GNU Emacs to view (and
7645 edit) the source files for the program you are debugging with
7648 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
7649 executable file you want to debug as an argument. This command starts
7650 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
7651 created Emacs buffer.
7653 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
7658 All ``terminal'' input and output goes through the Emacs buffer.
7661 This applies both to @value{GDBN} commands and their output, and to the input
7662 and output done by the program you are debugging.
7664 This is useful because it means that you can copy the text of previous
7665 commands and input them again; you can even use parts of the output
7668 All the facilities of Emacs' Shell mode are available for interacting
7669 with your program. In particular, you can send signals the usual
7670 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
7675 @value{GDBN} displays source code through Emacs.
7678 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
7679 source file for that frame and puts an arrow (@samp{=>}) at the
7680 left margin of the current line. Emacs uses a separate buffer for
7681 source display, and splits the screen to show both your @value{GDBN} session
7684 Explicit @value{GDBN} @code{list} or search commands still produce output as
7685 usual, but you probably will have no reason to use them.
7688 @emph{Warning:} If the directory where your program resides is not your
7689 current directory, it can be easy to confuse Emacs about the location of
7690 the source files, in which case the auxiliary display buffer will not
7691 appear to show your source. @value{GDBN} can find programs by searching your
7692 environment's @code{PATH} variable, so the @value{GDBN} input and output
7693 session will proceed normally; but Emacs does not get enough information
7694 back from @value{GDBN} to locate the source files in this situation. To
7695 avoid this problem, either start @value{GDBN} mode from the directory where
7696 your program resides, or specify a full path name when prompted for the
7697 @kbd{M-x gdb} argument.
7699 A similar confusion can result if you use the @value{GDBN} @code{file} command to
7700 switch to debugging a program in some other location, from an existing
7701 @value{GDBN} buffer in Emacs.
7704 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
7705 you need to call @value{GDBN} by a different name (for example, if you keep
7706 several configurations around, with different names) you can set the
7707 Emacs variable @code{gdb-command-name}; for example,
7710 (setq gdb-command-name "mygdb")
7714 (preceded by @kbd{ESC ESC}, or typed in the @code{*scratch*} buffer, or
7715 in your @file{.emacs} file) will make Emacs call the program named
7716 ``@code{mygdb}'' instead.
7718 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
7719 addition to the standard Shell mode commands:
7723 Describe the features of Emacs' @value{GDBN} Mode.
7726 Execute to another source line, like the @value{GDBN} @code{step} command; also
7727 update the display window to show the current file and location.
7730 Execute to next source line in this function, skipping all function
7731 calls, like the @value{GDBN} @code{next} command. Then update the display window
7732 to show the current file and location.
7735 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
7736 display window accordingly.
7739 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
7740 display window accordingly.
7743 Execute until exit from the selected stack frame, like the @value{GDBN}
7744 @code{finish} command.
7747 Continue execution of your program, like the @value{GDBN} @code{continue}
7750 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
7753 Go up the number of frames indicated by the numeric argument
7754 (@pxref{Arguments, , Numeric Arguments, emacs, The GNU Emacs Manual}),
7755 like the @value{GDBN} @code{up} command.
7757 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
7760 Go down the number of frames indicated by the numeric argument, like the
7761 @value{GDBN} @code{down} command.
7763 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
7766 Read the number where the cursor is positioned, and insert it at the end
7767 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
7768 around an address that was displayed earlier, type @kbd{disassemble};
7769 then move the cursor to the address display, and pick up the
7770 argument for @code{disassemble} by typing @kbd{C-x &}.
7772 You can customize this further by defining elements of the list
7773 @code{gdb-print-command}; once it is defined, you can format or
7774 otherwise process numbers picked up by @kbd{C-x &} before they are
7775 inserted. A numeric argument to @kbd{C-x &} will both indicate that you
7776 wish special formatting, and act as an index to pick an element of the
7777 list. If the list element is a string, the number to be inserted is
7778 formatted using the Emacs function @code{format}; otherwise the number
7779 is passed as an argument to the corresponding list element.
7782 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
7783 tells @value{GDBN} to set a breakpoint on the source line point is on.
7785 If you accidentally delete the source-display buffer, an easy way to get
7786 it back is to type the command @code{f} in the @value{GDBN} buffer, to
7787 request a frame display; when you run under Emacs, this will recreate
7788 the source buffer if necessary to show you the context of the current
7791 The source files displayed in Emacs are in ordinary Emacs buffers
7792 which are visiting the source files in the usual way. You can edit
7793 the files with these buffers if you wish; but keep in mind that @value{GDBN}
7794 communicates with Emacs in terms of line numbers. If you add or
7795 delete lines from the text, the line numbers that @value{GDBN} knows will cease
7796 to correspond properly with the code.
7798 @c The following dropped because Epoch is nonstandard. Reactivate
7799 @c if/when v19 does something similar. ---pesch@cygnus.com 19dec1990
7801 @kindex emacs epoch environment
7805 Version 18 of Emacs has a built-in window system called the @code{epoch}
7806 environment. Users of this environment can use a new command,
7807 @code{inspect} which performs identically to @code{print} except that
7808 each value is printed in its own window.
7814 @chapter Using @value{GDBN} with Energize
7817 The Energize Programming System is an integrated development environment
7818 that includes a point-and-click interface to many programming tools.
7819 When you use @value{GDBN} in this environment, you can use the standard
7820 Energize graphical interface to drive @value{GDBN}; you can also, if you
7821 choose, type @value{GDBN} commands as usual in a debugging window. Even if
7822 you use the graphical interface, the debugging window (which uses Emacs,
7823 and resembles the standard Emacs interface to @value{GDBN}) displays the
7824 equivalent commands, so that the history of your debugging session is
7827 When Energize starts up a @value{GDBN} session, it uses one of the
7828 command-line options @samp{-energize} or @samp{-cadillac} (``cadillac''
7829 is the name of the communications protocol used by the Energize system).
7830 This option makes @value{GDBN} run as one of the tools in the Energize Tool
7831 Set: it sends all output to the Energize kernel, and accept input from
7834 See the user manual for the Energize Programming System for
7835 information on how to use the Energize graphical interface and the other
7836 development tools that Energize integrates with @value{GDBN}.
7841 @chapter Reporting Bugs in @value{GDBN}
7842 @cindex bugs in @value{GDBN}
7843 @cindex reporting bugs in @value{GDBN}
7845 Your bug reports play an essential role in making @value{GDBN} reliable.
7847 Reporting a bug may help you by bringing a solution to your problem, or it
7848 may not. But in any case the principal function of a bug report is to help
7849 the entire community by making the next version of @value{GDBN} work better. Bug
7850 reports are your contribution to the maintenance of @value{GDBN}.
7852 In order for a bug report to serve its purpose, you must include the
7853 information that enables us to fix the bug.
7856 * Bug Criteria:: Have you found a bug?
7857 * Bug Reporting:: How to report bugs
7861 @section Have you found a bug?
7862 @cindex bug criteria
7864 If you are not sure whether you have found a bug, here are some guidelines:
7868 @cindex fatal signal
7869 @cindex debugger crash
7870 @cindex crash of debugger
7871 If the debugger gets a fatal signal, for any input whatever, that is a
7872 @value{GDBN} bug. Reliable debuggers never crash.
7875 @cindex error on valid input
7876 If @value{GDBN} produces an error message for valid input, that is a bug.
7879 @cindex invalid input
7880 If @value{GDBN} does not produce an error message for invalid input,
7881 that is a bug. However, you should note that your idea of
7882 ``invalid input'' might be our idea of ``an extension'' or ``support
7883 for traditional practice''.
7886 If you are an experienced user of debugging tools, your suggestions
7887 for improvement of @value{GDBN} are welcome in any case.
7891 @section How to report bugs
7893 @cindex @value{GDBN} bugs, reporting
7895 A number of companies and individuals offer support for GNU products.
7896 If you obtained @value{GDBN} from a support organization, we recommend you
7897 contact that organization first.
7899 You can find contact information for many support companies and
7900 individuals in the file @file{etc/SERVICE} in the GNU Emacs
7903 In any event, we also recommend that you send bug reports for @value{GDBN} to one
7907 bug-gdb@@prep.ai.mit.edu
7908 @{ucbvax|mit-eddie|uunet@}!prep.ai.mit.edu!bug-gdb
7911 @strong{Do not send bug reports to @samp{info-gdb}, or to
7912 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do not want to
7913 receive bug reports. Those that do, have arranged to receive @samp{bug-gdb}.
7915 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
7916 serves as a repeater. The mailing list and the newsgroup carry exactly
7917 the same messages. Often people think of posting bug reports to the
7918 newsgroup instead of mailing them. This appears to work, but it has one
7919 problem which can be crucial: a newsgroup posting often lacks a mail
7920 path back to the sender. Thus, if we need to ask for more information,
7921 we may be unable to reach you. For this reason, it is better to send
7922 bug reports to the mailing list.
7924 As a last resort, send bug reports on paper to:
7928 Free Software Foundation
7933 The fundamental principle of reporting bugs usefully is this:
7934 @strong{report all the facts}. If you are not sure whether to state a
7935 fact or leave it out, state it!
7937 Often people omit facts because they think they know what causes the
7938 problem and assume that some details do not matter. Thus, you might
7939 assume that the name of the variable you use in an example does not matter.
7940 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
7941 stray memory reference which happens to fetch from the location where that
7942 name is stored in memory; perhaps, if the name were different, the contents
7943 of that location would fool the debugger into doing the right thing despite
7944 the bug. Play it safe and give a specific, complete example. That is the
7945 easiest thing for you to do, and the most helpful.
7947 Keep in mind that the purpose of a bug report is to enable us to fix
7948 the bug if it is new to us. It is not as important as what happens if
7949 the bug is already known. Therefore, always write your bug reports on
7950 the assumption that the bug has not been reported previously.
7952 Sometimes people give a few sketchy facts and ask, ``Does this ring a
7953 bell?'' Those bug reports are useless, and we urge everyone to
7954 @emph{refuse to respond to them} except to chide the sender to report
7957 To enable us to fix the bug, you should include all these things:
7961 The version of @value{GDBN}. @value{GDBN} announces it if you start with no
7962 arguments; you can also print it at any time using @code{show version}.
7964 Without this, we will not know whether there is any point in looking for
7965 the bug in the current version of @value{GDBN}.
7968 The type of machine you are using, and the operating system name and
7972 What compiler (and its version) was used to compile @value{GDBN}---e.g.
7973 ``@value{GCC}--2.0''.
7976 What compiler (and its version) was used to compile the program you
7977 are debugging---e.g. ``@value{GCC}--2.0''.
7980 The command arguments you gave the compiler to compile your example and
7981 observe the bug. For example, did you use @samp{-O}? To guarantee
7982 you will not omit something important, list them all. A copy of the
7983 Makefile (or the output from make) is sufficient.
7985 If we were to try to guess the arguments, we would probably guess wrong
7986 and then we might not encounter the bug.
7989 A complete input script, and all necessary source files, that will
7993 A description of what behavior you observe that you believe is
7994 incorrect. For example, ``It gets a fatal signal.''
7996 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we will
7997 certainly notice it. But if the bug is incorrect output, we might not
7998 notice unless it is glaringly wrong. We are human, after all. You
7999 might as well not give us a chance to make a mistake.
8001 Even if the problem you experience is a fatal signal, you should still
8002 say so explicitly. Suppose something strange is going on, such as,
8003 your copy of @value{GDBN} is out of synch, or you have encountered a
8004 bug in the C library on your system. (This has happened!) Your copy
8005 might crash and ours would not. If you told us to expect a crash,
8006 then when ours fails to crash, we would know that the bug was not
8007 happening for us. If you had not told us to expect a crash, then we
8008 would not be able to draw any conclusion from our observations.
8011 If you wish to suggest changes to the @value{GDBN} source, send us context
8012 diffs. If you even discuss something in the @value{GDBN} source, refer to
8013 it by context, not by line number.
8015 The line numbers in our development sources will not match those in your
8016 sources. Your line numbers would convey no useful information to us.
8019 Here are some things that are not necessary:
8023 A description of the envelope of the bug.
8025 Often people who encounter a bug spend a lot of time investigating
8026 which changes to the input file will make the bug go away and which
8027 changes will not affect it.
8029 This is often time consuming and not very useful, because the way we
8030 will find the bug is by running a single example under the debugger
8031 with breakpoints, not by pure deduction from a series of examples.
8032 We recommend that you save your time for something else.
8034 Of course, if you can find a simpler example to report @emph{instead}
8035 of the original one, that is a convenience for us. Errors in the
8036 output will be easier to spot, running under the debugger will take
8039 However, simplification is not vital; if you do not want to do this,
8040 report the bug anyway and send us the entire test case you used.
8043 A patch for the bug.
8045 A patch for the bug does help us if it is a good one. But do not omit
8046 the necessary information, such as the test case, on the assumption that
8047 a patch is all we need. We might see problems with your patch and decide
8048 to fix the problem another way, or we might not understand it at all.
8050 Sometimes with a program as complicated as @value{GDBN} it is very hard to
8051 construct an example that will make the program follow a certain path
8052 through the code. If you do not send us the example, we will not be able
8053 to construct one, so we will not be able to verify that the bug is fixed.
8055 And if we cannot understand what bug you are trying to fix, or why your
8056 patch should be an improvement, we will not install it. A test case will
8057 help us to understand.
8060 A guess about what the bug is or what it depends on.
8062 Such guesses are usually wrong. Even we cannot guess right about such
8063 things without first using the debugger to find the facts.
8066 @c The readline documentation is distributed with the readline code
8067 @c and consists of the two following files:
8070 @c Use -I with makeinfo to point to the appropriate directory,
8071 @c environment var TEXINPUTS with TeX.
8072 @include rluser.texinfo
8073 @include inc-hist.texi
8076 @node Renamed Commands
8077 @appendix Renamed Commands
8079 The following commands were renamed in GDB 4, in order to make the
8080 command set as a whole more consistent and easier to use and remember:
8083 @kindex delete environment
8084 @kindex info copying
8085 @kindex info convenience
8086 @kindex info directories
8087 @kindex info editing
8088 @kindex info history
8089 @kindex info targets
8091 @kindex info version
8092 @kindex info warranty
8093 @kindex set addressprint
8094 @kindex set arrayprint
8095 @kindex set prettyprint
8096 @kindex set screen-height
8097 @kindex set screen-width
8098 @kindex set unionprint
8099 @kindex set vtblprint
8100 @kindex set demangle
8101 @kindex set asm-demangle
8102 @kindex set sevenbit-strings
8103 @kindex set array-max
8105 @kindex set history write
8106 @kindex show addressprint
8107 @kindex show arrayprint
8108 @kindex show prettyprint
8109 @kindex show screen-height
8110 @kindex show screen-width
8111 @kindex show unionprint
8112 @kindex show vtblprint
8113 @kindex show demangle
8114 @kindex show asm-demangle
8115 @kindex show sevenbit-strings
8116 @kindex show array-max
8117 @kindex show caution
8118 @kindex show history write
8123 @c END TEXI2ROFF-KILL
8125 OLD COMMAND NEW COMMAND
8127 --------------- -------------------------------
8128 @c END TEXI2ROFF-KILL
8129 add-syms add-symbol-file
8130 delete environment unset environment
8131 info convenience show convenience
8132 info copying show copying
8133 info directories show directories
8134 info editing show commands
8135 info history show values
8136 info targets help target
8137 info values show values
8138 info version show version
8139 info warranty show warranty
8140 set/show addressprint set/show print address
8141 set/show array-max set/show print elements
8142 set/show arrayprint set/show print array
8143 set/show asm-demangle set/show print asm-demangle
8144 set/show caution set/show confirm
8145 set/show demangle set/show print demangle
8146 set/show history write set/show history save
8147 set/show prettyprint set/show print pretty
8148 set/show screen-height set/show height
8149 set/show screen-width set/show width
8150 set/show sevenbit-strings set/show print sevenbit-strings
8151 set/show unionprint set/show print union
8152 set/show vtblprint set/show print vtbl
8154 unset [No longer an alias for delete]
8160 \vskip \parskip\vskip \baselineskip
8161 \halign{\tt #\hfil &\qquad#&\tt #\hfil\cr
8162 {\bf Old Command} &&{\bf New Command}\cr
8163 add-syms &&add-symbol-file\cr
8164 delete environment &&unset environment\cr
8165 info convenience &&show convenience\cr
8166 info copying &&show copying\cr
8167 info directories &&show directories \cr
8168 info editing &&show commands\cr
8169 info history &&show values\cr
8170 info targets &&help target\cr
8171 info values &&show values\cr
8172 info version &&show version\cr
8173 info warranty &&show warranty\cr
8174 set{\rm / }show addressprint &&set{\rm / }show print address\cr
8175 set{\rm / }show array-max &&set{\rm / }show print elements\cr
8176 set{\rm / }show arrayprint &&set{\rm / }show print array\cr
8177 set{\rm / }show asm-demangle &&set{\rm / }show print asm-demangle\cr
8178 set{\rm / }show caution &&set{\rm / }show confirm\cr
8179 set{\rm / }show demangle &&set{\rm / }show print demangle\cr
8180 set{\rm / }show history write &&set{\rm / }show history save\cr
8181 set{\rm / }show prettyprint &&set{\rm / }show print pretty\cr
8182 set{\rm / }show screen-height &&set{\rm / }show height\cr
8183 set{\rm / }show screen-width &&set{\rm / }show width\cr
8184 set{\rm / }show sevenbit-strings &&set{\rm / }show print sevenbit-strings\cr
8185 set{\rm / }show unionprint &&set{\rm / }show print union\cr
8186 set{\rm / }show vtblprint &&set{\rm / }show print vtbl\cr
8188 unset &&\rm(No longer an alias for delete)\cr
8191 @c END TEXI2ROFF-KILL
8194 @ifclear PRECONFIGURED
8195 @node Formatting Documentation
8196 @appendix Formatting Documentation
8198 @cindex GDB reference card
8199 @cindex reference card
8200 The GDB 4 release includes an already-formatted reference card, ready
8201 for printing with PostScript or GhostScript, in the @file{gdb}
8202 subdirectory of the main source directory@footnote{In
8203 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
8204 release.}. If you can use PostScript or GhostScript with your printer,
8205 you can print the reference card immediately with @file{refcard.ps}.
8207 The release also includes the source for the reference card. You
8208 can format it, using @TeX{}, by typing:
8214 The GDB reference card is designed to print in landscape mode on US
8215 ``letter'' size paper; that is, on a sheet 11 inches wide by 8.5 inches
8216 high. You will need to specify this form of printing as an option to
8217 your @sc{dvi} output program.
8219 @cindex documentation
8221 All the documentation for GDB comes as part of the machine-readable
8222 distribution. The documentation is written in Texinfo format, which is
8223 a documentation system that uses a single source file to produce both
8224 on-line information and a printed manual. You can use one of the Info
8225 formatting commands to create the on-line version of the documentation
8226 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
8228 GDB includes an already formatted copy of the on-line Info version of
8229 this manual in the @file{gdb} subdirectory. The main Info file is
8230 @file{gdb-@var{version-number}/gdb/gdb.info}, and it refers to
8231 subordinate files matching @samp{gdb.info*} in the same directory. If
8232 necessary, you can print out these files, or read them with any editor;
8233 but they are easier to read using the @code{info} subsystem in GNU Emacs
8234 or the standalone @code{info} program, available as part of the GNU
8235 Texinfo distribution.
8237 If you want to format these Info files yourself, you need one of the
8238 Info formatting programs, such as @code{texinfo-format-buffer} or
8241 If you have @code{makeinfo} installed, and are in the top level GDB
8242 source directory (@file{gdb-@value{GDBVN}}, in the case of version @value{GDBVN}), you can
8243 make the Info file by typing:
8250 If you want to typeset and print copies of this manual, you need @TeX{},
8251 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
8252 Texinfo definitions file.
8254 @TeX{} is a typesetting program; it does not print files directly, but
8255 produces output files called @sc{dvi} files. To print a typeset
8256 document, you need a program to print @sc{dvi} files. If your system
8257 has @TeX{} installed, chances are it has such a program. The precise
8258 command to use depends on your system; @kbd{lpr -d} is common; another
8259 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
8260 require a file name without any extension or a @samp{.dvi} extension.
8262 @TeX{} also requires a macro definitions file called
8263 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
8264 written in Texinfo format. On its own, @TeX{} cannot read, much less
8265 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
8266 and is located in the @file{gdb-@var{version-number}/texinfo}
8269 If you have @TeX{} and a @sc{dvi} printer program installed, you can
8270 typeset and print this manual. First switch to the the @file{gdb}
8271 subdirectory of the main source directory (for example, to
8272 @file{gdb-@value{GDBVN}/gdb}) and then type:
8278 @node Installing GDB
8279 @appendix Installing GDB
8280 @cindex configuring GDB
8281 @cindex installation
8283 GDB comes with a @code{configure} script that automates the process
8284 of preparing GDB for installation; you can then use @code{make} to
8285 build the @code{gdb} program.
8287 @c irrelevant in info file; it's as current as the code it lives with.
8288 @footnote{If you have a more recent version of GDB than @value{GDBVN},
8289 look at the @file{README} file in the sources; we may have improved the
8290 installation procedures since publishing this manual.}
8293 The GDB distribution includes all the source code you need for GDB in
8294 a single directory, whose name is usually composed by appending the
8295 version number to @samp{gdb}.
8297 For example, the GDB version @value{GDBVN} distribution is in the
8298 @file{gdb-@value{GDBVN}} directory. That directory contains:
8301 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
8302 script for configuring GDB and all its supporting libraries.
8304 @item gdb-@value{GDBVN}/gdb
8305 the source specific to GDB itself
8307 @item gdb-@value{GDBVN}/bfd
8308 source for the Binary File Descriptor library
8310 @item gdb-@value{GDBVN}/include
8313 @item gdb-@value{GDBVN}/libiberty
8314 source for the @samp{-liberty} free software library
8316 @item gdb-@value{GDBVN}/opcodes
8317 source for the library of opcode tables and disassemblers
8319 @item gdb-@value{GDBVN}/readline
8320 source for the GNU command-line interface
8322 @item gdb-@value{GDBVN}/glob
8323 source for the GNU filename pattern-matching subroutine
8325 @item gdb-@value{GDBVN}/mmalloc
8326 source for the GNU memory-mapped malloc package
8329 The simplest way to configure and build GDB is to run @code{configure}
8330 from the @file{gdb-@var{version-number}} source directory, which in
8331 this example is the @file{gdb-@value{GDBVN}} directory.
8333 First switch to the @file{gdb-@var{version-number}} source directory
8334 if you are not already in it; then run @code{configure}. Pass the
8335 identifier for the platform on which GDB will run as an
8341 cd gdb-@value{GDBVN}
8342 ./configure @var{host}
8347 where @var{host} is an identifier such as @samp{sun4} or
8348 @samp{decstation}, that identifies the platform where GDB will run.
8349 (You can often leave off @var{host}; @code{configure} tries to guess the
8350 correct value by examining your system.)
8352 Running @samp{configure @var{host}} and then running @code{make} builds the
8353 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
8354 libraries, then @code{gdb} itself. The configured source files, and the
8355 binaries, are left in the corresponding source directories.
8357 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
8358 system does not recognize this automatically when you run a different
8359 shell, you may need to run @code{sh} on it explicitly:
8362 sh configure @var{host}
8365 If you run @code{configure} from a directory that contains source
8366 directories for multiple libraries or programs, such as the
8367 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
8368 creates configuration files for every directory level underneath (unless
8369 you tell it not to, with the @samp{--norecursion} option).
8371 You can run the @code{configure} script from any of the
8372 subordinate directories in the GDB distribution if you only want to
8373 configure that subdirectory, but be sure to specify a path to it.
8375 For example, with version @value{GDBVN}, type the following to configure only
8376 the @code{bfd} subdirectory:
8380 cd gdb-@value{GDBVN}/bfd
8381 ../configure @var{host}
8385 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
8386 However, you should make sure that the shell on your path (named by
8387 the @samp{SHELL} environment variable) is publicly readable. Remember
8388 that GDB uses the shell to start your program---some systems refuse to
8389 let GDB debug child processes whose programs are not readable.
8392 * Separate Objdir:: Compiling GDB in another directory
8393 * Config Names:: Specifying names for hosts and targets
8394 * configure Options:: Summary of options for configure
8397 @node Separate Objdir
8398 @section Compiling GDB in another directory
8400 If you want to run GDB versions for several host or target machines,
8401 you need a different @code{gdb} compiled for each combination of
8402 host and target. @code{configure} is designed to make this easy by
8403 allowing you to generate each configuration in a separate subdirectory,
8404 rather than in the source directory. If your @code{make} program
8405 handles the @samp{VPATH} feature (GNU @code{make} does), running
8406 @code{make} in each of these directories builds the @code{gdb}
8407 program specified there.
8409 To build @code{gdb} in a separate directory, run @code{configure}
8410 with the @samp{--srcdir} option to specify where to find the source.
8411 (You also need to specify a path to find @code{configure}
8412 itself from your working directory. If the path to @code{configure}
8413 would be the same as the argument to @samp{--srcdir}, you can leave out
8414 the @samp{--srcdir} option; it will be assumed.)
8416 For example, with version @value{GDBVN}, you can build GDB in a separate
8417 directory for a Sun 4 like this:
8421 cd gdb-@value{GDBVN}
8424 ../gdb-@value{GDBVN}/configure sun4
8429 When @code{configure} builds a configuration using a remote source
8430 directory, it creates a tree for the binaries with the same structure
8431 (and using the same names) as the tree under the source directory. In
8432 the example, you'd find the Sun 4 library @file{libiberty.a} in the
8433 directory @file{gdb-sun4/libiberty}, and GDB itself in
8434 @file{gdb-sun4/gdb}.
8436 One popular reason to build several GDB configurations in separate
8437 directories is to configure GDB for cross-compiling (where GDB
8438 runs on one machine---the host---while debugging programs that run on
8439 another machine---the target). You specify a cross-debugging target by
8440 giving the @samp{--target=@var{target}} option to @code{configure}.
8442 When you run @code{make} to build a program or library, you must run
8443 it in a configured directory---whatever directory you were in when you
8444 called @code{configure} (or one of its subdirectories).
8446 The @code{Makefile} that @code{configure} generates in each source
8447 directory also runs recursively. If you type @code{make} in a source
8448 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
8449 directory configured with @samp{--srcdir=@var{path}/gdb-@value{GDBVN}}), you
8450 will build all the required libraries, and then build GDB.
8452 When you have multiple hosts or targets configured in separate
8453 directories, you can run @code{make} on them in parallel (for example,
8454 if they are NFS-mounted on each of the hosts); they will not interfere
8458 @section Specifying names for hosts and targets
8460 The specifications used for hosts and targets in the @code{configure}
8461 script are based on a three-part naming scheme, but some short predefined
8462 aliases are also supported. The full naming scheme encodes three pieces
8463 of information in the following pattern:
8466 @var{architecture}-@var{vendor}-@var{os}
8469 For example, you can use the alias @code{sun4} as a @var{host} argument,
8470 or as the value for @var{target} in a @code{--target=@var{target}}
8471 option. The equivalent full name is @samp{sparc-sun-sunos4}.
8473 The @code{configure} script accompanying GDB does not provide
8474 any query facility to list all supported host and target names or
8475 aliases. @code{configure} calls the Bourne shell script
8476 @code{config.sub} to map abbreviations to full names; you can read the
8477 script, if you wish, or you can use it to test your guesses on
8478 abbreviations---for example:
8481 % sh config.sub sun4
8482 sparc-sun-sunos4.1.1
8483 % sh config.sub sun3
8485 % sh config.sub decstation
8487 % sh config.sub hp300bsd
8489 % sh config.sub i386v
8491 % sh config.sub i786v
8492 Invalid configuration `i786v': machine `i786v' not recognized
8496 @code{config.sub} is also distributed in the GDB source
8497 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
8499 @node configure Options
8500 @section @code{configure} options
8502 Here is a summary of the @code{configure} options and arguments that
8503 are most often useful for building @value{GDBN}. @code{configure} also has
8504 several other options not listed here. @inforef{What Configure
8505 Does,,configure.info}, for a full explanation of @code{configure}.
8506 @c FIXME: Would this be more, or less, useful as an xref (ref to printed
8507 @c manual in the printed manual, ref to info file only from the info file)?
8510 configure @r{[}--help@r{]}
8511 @r{[}--prefix=@var{dir}@r{]}
8512 @r{[}--srcdir=@var{path}@r{]}
8513 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
8514 @r{[}--target=@var{target}@r{]} @var{host}
8518 You may introduce options with a single @samp{-} rather than
8519 @samp{--} if you prefer; but you may abbreviate option names if you use
8524 Display a quick summary of how to invoke @code{configure}.
8526 @item -prefix=@var{dir}
8527 Configure the source to install programs and files under directory
8530 @item --srcdir=@var{path}
8531 @strong{Warning: using this option requires GNU @code{make}, or another
8532 @code{make} that implements the @code{VPATH} feature.}@*
8533 Use this option to make configurations in directories separate from the
8534 GDB source directories. Among other things, you can use this to
8535 build (or maintain) several configurations simultaneously, in separate
8536 directories. @code{configure} writes configuration specific files in
8537 the current directory, but arranges for them to use the source in the
8538 directory @var{path}. @code{configure} will create directories under
8539 the working directory in parallel to the source directories below
8543 Configure only the directory level where @code{configure} is executed; do not
8544 propagate configuration to subdirectories.
8547 @emph{Remove} files otherwise built during configuration.
8549 @c This does not work (yet if ever). FIXME.
8550 @c @item --parse=@var{lang} @dots{}
8551 @c Configure the GDB expression parser to parse the listed languages.
8552 @c @samp{all} configures GDB for all supported languages. To get a
8553 @c list of all supported languages, omit the argument. Without this
8554 @c option, GDB is configured to parse all supported languages.
8556 @item --target=@var{target}
8557 Configure GDB for cross-debugging programs running on the specified
8558 @var{target}. Without this option, GDB is configured to debug
8559 programs that run on the same machine (@var{host}) as GDB itself.
8561 There is no convenient way to generate a list of all available targets.
8563 @item @var{host} @dots{}
8564 Configure GDB to run on the specified @var{host}.
8566 There is no convenient way to generate a list of all available hosts.
8570 @code{configure} accepts other options, for compatibility with
8571 configuring other GNU tools recursively; but these are the only
8572 options that affect GDB or its supporting libraries.
8581 % I think something like @colophon should be in texinfo. In the
8583 \long\def\colophon{\hbox to0pt{}\vfill
8584 \centerline{The body of this manual is set in}
8585 \centerline{\fontname\tenrm,}
8586 \centerline{with headings in {\bf\fontname\tenbf}}
8587 \centerline{and examples in {\tt\fontname\tentt}.}
8588 \centerline{{\it\fontname\tenit\/},}
8589 \centerline{{\bf\fontname\tenbf}, and}
8590 \centerline{{\sl\fontname\tensl\/}}
8591 \centerline{are used for emphasis.}\vfill}
8593 % Blame: pesch@cygnus.com, 1991.