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.
9 @include gdb-config.texi
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 section entitled ``GNU General Public License'' is included exactly as
77 in the original, and provided that the entire resulting derived work is
78 distributed under the terms of a permission notice identical to this
81 Permission is granted to copy and distribute translations of this manual
82 into another language, under the above conditions for modified versions,
83 except that the section entitled ``GNU General Public License'' may be
84 included in a translation approved by the Free Software Foundation
85 instead of in the original English.
89 @title Debugging with @value{GDBN}
90 @subtitle The GNU Source-Level Debugger
92 @subtitle (@value{TARGET})
95 @c !!set edition, date, version
96 @subtitle Edition 4.09, for @value{GDBN} version @value{GDBVN}
98 @author by Richard M. Stallman and Roland H. Pesch
102 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@prep.ai.mit.edu.)\par
103 \hfill {\it Debugging with @value{GDBN}}\par
104 \hfill \TeX{}info \texinfoversion\par
105 \hfill pesch\@cygnus.com\par
109 @vskip 0pt plus 1filll
110 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993 Free Software Foundation, Inc.
112 Permission is granted to make and distribute verbatim copies of
113 this manual provided the copyright notice and this permission notice
114 are preserved on all copies.
116 Permission is granted to copy and distribute modified versions of this
117 manual under the conditions for verbatim copying, provided also that the
118 section entitled ``GNU General Public License'' is included exactly as
119 in the original, and provided that the entire resulting derived work is
120 distributed under the terms of a permission notice identical to this
123 Permission is granted to copy and distribute translations of this manual
124 into another language, under the above conditions for modified versions,
125 except that the section entitled ``GNU General Public License'' may be
126 included in a translation approved by the Free Software Foundation
127 instead of in the original English.
133 @top Debugging with @value{GDBN}
135 This file describes @value{GDBN}, the GNU symbolic debugger.
137 @c !!set edition, date, version
138 This is Edition 4.09, April 1993, for GDB Version @value{GDBVN}.
141 * Summary:: Summary of @value{GDBN}
143 * New Features:: New features since GDB version 3.5
146 * Sample Session:: A sample @value{GDBN} session
149 * Invocation:: Getting in and out of @value{GDBN}
150 * Commands:: @value{GDBN} commands
151 * Running:: Running programs under @value{GDBN}
152 * Stopping:: Stopping and continuing
153 * Stack:: Examining the stack
154 * Source:: Examining source files
155 * Data:: Examining data
157 * Languages:: Using @value{GDBN} with different languages
160 * C:: C language support
162 @c remnant makeinfo bug, blank line needed after two end-ifs?
164 * Symbols:: Examining the symbol table
165 * Altering:: Altering execution
166 * GDB Files:: @value{GDBN} files
167 * Targets:: Specifying a debugging target
168 * Controlling GDB:: Controlling @value{GDBN}
169 * Sequences:: Canned sequences of commands
171 * Emacs:: Using @value{GDBN} under GNU Emacs
174 * GDB Bugs:: Reporting bugs in @value{GDBN}
175 * Command Line Editing:: Facilities of the readline library
176 * Using History Interactively::
180 @ifclear PRECONFIGURED
181 * Formatting Documentation:: How to format and print GDB documentation
182 * Installing GDB:: Installing GDB
184 @ifclear AGGLOMERATION
185 * Copying:: GNU GENERAL PUBLIC LICENSE
193 @unnumbered Summary of @value{GDBN}
195 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
196 going on ``inside'' another program while it executes---or what another
197 program was doing at the moment it crashed.
199 @value{GDBN} can do four main kinds of things (plus other things in support of
200 these) to help you catch bugs in the act:
204 Start your program, specifying anything that might affect its behavior.
207 Make your program stop on specified conditions.
210 Examine what has happened, when your program has stopped.
213 Change things in your program, so you can experiment with correcting the
214 effects of one bug and go on to learn about another.
218 You can use @value{GDBN} to debug programs written in C, C++, and Modula-2.
219 Fortran support will be added when a GNU Fortran compiler is ready.
223 * Free Software:: Freely redistributable software
224 * Contributors:: Contributors to GDB
228 @unnumberedsec Free software
230 @value{GDBN} is @dfn{free software}, protected by the GNU General Public License
231 (GPL). The GPL gives you the freedom to copy or adapt a licensed
232 program---but every person getting a copy also gets with it the
233 freedom to modify that copy (which means that they must get access to
234 the source code), and the freedom to distribute further copies.
235 Typical software companies use copyrights to limit your freedoms; the
236 Free Software Foundation uses the GPL to preserve these freedoms.
238 Fundamentally, the General Public License is a license which says that
239 you have these freedoms and that you cannot take these freedoms away
242 @ifclear AGGLOMERATION
243 For full details, @pxref{Copying, ,GNU GENERAL PUBLIC LICENSE}.
247 @unnumberedsec Contributors to GDB
249 Richard Stallman was the original author of GDB, and of many other GNU
250 programs. Many others have contributed to its development. This
251 section attempts to credit major contributors. One of the virtues of
252 free software is that everyone is free to contribute to it; with
253 regret, we cannot actually acknowledge everyone here. The file
254 @file{ChangeLog} in the GDB distribution approximates a blow-by-blow
257 Changes much prior to version 2.0 are lost in the mists of time.
260 @emph{Plea:} Additions to this section are particularly welcome. If you
261 or your friends (or enemies, to be evenhanded) have been unfairly
262 omitted from this list, we would like to add your names!
265 So that they may not regard their long labor as thankless, we
266 particularly thank those who shepherded GDB through major releases: Stu
267 Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, 4.4), John Gilmore
268 (releases 4.3, 4.2, 4.1, 4.0, and 3.9); Jim Kingdon (releases 3.5, 3.4,
269 3.3); and Randy Smith (releases 3.2, 3.1, 3.0). As major maintainer of
270 GDB for some period, each contributed significantly to the structure,
271 stability, and capabilities of the entire debugger.
273 Richard Stallman, assisted at various times by Pete TerMaat, Chris
274 Hanson, and Richard Mlynarik, handled releases through 2.8.
277 Michael Tiemann is the author of most of the GNU C++ support in GDB,
278 with significant additional contributions from Per Bothner. James
279 Clark wrote the GNU C++ demangler. Early work on C++ was by Peter
280 TerMaat (who also did much general update work leading to release 3.0).
283 GDB 4 uses the BFD subroutine library to examine multiple
284 object-file formats; BFD was a joint project of David V.
285 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
287 David Johnson wrote the original COFF support; Pace Willison did
288 the original support for encapsulated COFF.
290 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
291 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
292 support. Jean-Daniel Fekete contributed Sun 386i support. Chris
293 Hanson improved the HP9000 support. Noboyuki Hikichi and Tomoyuki
294 Hasei contributed Sony/News OS 3 support. David Johnson contributed
295 Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support.
296 Keith Packard contributed NS32K support. Doug Rabson contributed
297 Acorn Risc Machine support. Chris Smith contributed Convex support
298 (and Fortran debugging). Jonathan Stone contributed Pyramid support.
299 Michael Tiemann contributed SPARC support. Tim Tucker contributed
300 support for the Gould NP1 and Gould Powernode. Pace Willison
301 contributed Intel 386 support. Jay Vosburgh contributed Symmetry
304 Rich Schaefer and Peter Schauer helped with support of SunOS shared
307 Jay Fenlason and Roland McGrath ensured that GDB and GAS agree about
308 several machine instruction sets.
310 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped
311 develop remote debugging. Intel Corporation and Wind River Systems
312 contributed remote debugging modules for their products.
314 Brian Fox is the author of the readline libraries providing
315 command-line editing and command history.
317 Andrew Beers of SUNY Buffalo wrote the language-switching code and
318 the Modula-2 support, and contributed the Languages chapter of this
321 Fred Fish wrote most of the support for Unix System Vr4.
323 He also enhanced the command-completion support to cover C++ overloaded
327 Hitachi America, Ltd. sponsored the support for Hitachi microprocessors.
331 @unnumbered New Features since GDB Version 3.5
335 Using the new command @code{target}, you can select at runtime whether
336 you are debugging local files, local processes, standalone systems over
337 a serial port, realtime systems over a TCP/IP connection, etc. The
338 command @code{load} can download programs into a remote system. Serial
339 stubs are available for Motorola 680x0, Intel 80386, and Sparc remote
340 systems; GDB also supports debugging realtime processes running under
341 VxWorks, using SunRPC Remote Procedure Calls over TCP/IP to talk to a
342 debugger stub on the target system. Internally, GDB now uses a function
343 vector to mediate access to different targets; if you need to add your
344 own support for a remote protocol, this makes it much easier.
347 GDB now sports watchpoints as well as breakpoints. You can use a
348 watchpoint to stop execution whenever the value of an expression
349 changes, without having to predict a particular place in your program
350 where this may happen.
353 Commands that issue wide output now insert newlines at places designed
354 to make the output more readable.
356 @item Object Code Formats
357 GDB uses a new library called the Binary File Descriptor (BFD)
358 Library to permit it to switch dynamically, without reconfiguration or
359 recompilation, between different object-file formats. Formats currently
360 supported are COFF, a.out, and the Intel 960 b.out; files may be read as
361 .o files, archive libraries, or core dumps. BFD is available as a
362 subroutine library so that other programs may take advantage of it, and
363 the other GNU binary utilities are being converted to use it.
365 @item Configuration and Ports
366 Compile-time configuration (to select a particular architecture and
367 operating system) is much easier. The script @code{configure} now
368 allows you to configure GDB as either a native debugger or a
369 cross-debugger. @xref{Installing GDB}, for details on how to
373 The user interface to the GDB control variables is simpler,
374 and is consolidated in two commands, @code{set} and @code{show}. Output
375 lines are now broken at readable places, rather than overflowing onto
376 the next line. You can suppress output of machine-level addresses,
377 displaying only source language information.
380 GDB now supports C++ multiple inheritance (if used with a GCC
381 version 2 compiler), and also has limited support for C++ exception
382 handling, with the commands @code{catch} and @code{info catch}: GDB
383 can break when an exception is raised, before the stack is peeled back
384 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.
394 @item Command Rationalization
395 Many GDB commands have been renamed to make them easier to remember
396 and use. In particular, the subcommands of @code{info} and
397 @code{show}/@code{set} are grouped to make the former refer to the state
398 of your program, and the latter refer to the state of GDB itself.
399 @xref{Renamed Commands}, for details on what commands were renamed.
401 @item Shared Libraries
402 GDB 4 can debug programs and core files that use SunOS, SVR4, or IBM RS/6000
406 GDB 4 has a reference card. @xref{Formatting Documentation,,Formatting
407 the Documentation}, for instructions about how to print it.
409 @item Work in Progress
410 Kernel debugging for BSD and Mach systems; Tahoe and HPPA architecture
417 @chapter A Sample @value{GDBN} Session
419 You can use this manual at your leisure to read all about @value{GDBN}.
420 However, a handful of commands are enough to get started using the
421 debugger. This chapter illustrates those commands.
424 In this sample session, we emphasize user input like this: @b{input},
425 to make it easier to pick out from the surrounding output.
428 @c FIXME: this example may not be appropriate for some configs, where
429 @c FIXME...primary interest is in remote use.
431 One of the preliminary versions of GNU @code{m4} (a generic macro
432 processor) exhibits the following bug: sometimes, when we change its
433 quote strings from the default, the commands used to capture one macro
434 definition within another stop working. In the following short @code{m4}
435 session, we define a macro @code{foo} which expands to @code{0000}; we
436 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
437 same thing. However, when we change the open quote string to
438 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
439 procedure fails to define a new synonym @code{baz}:
448 @b{define(bar,defn(`foo'))}
452 @b{changequote(<QUOTE>,<UNQUOTE>)}
454 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
457 m4: End of input: 0: fatal error: EOF in string
461 Let us use @value{GDBN} to try to see what is going on.
464 $ @b{@value{GDBP} m4}
465 @c FIXME: this falsifies the exact text played out, to permit smallbook
466 @c FIXME... format to come out better.
467 GDB is free software and you are welcome to distribute copies
468 of it under certain conditions; type "show copying" to see
470 There is absolutely no warranty for GDB; type "show warranty"
472 GDB @value{GDBVN}, Copyright 1993 Free Software Foundation, Inc...
477 @value{GDBN} reads only enough symbol data to know where to find the rest when
478 needed; as a result, the first prompt comes up very quickly. We now
479 tell @value{GDBN} to use a narrower display width than usual, so that examples
480 will fit in this manual.
483 (@value{GDBP}) @b{set width 70}
487 We need to see how the @code{m4} built-in @code{changequote} works.
488 Having looked at the source, we know the relevant subroutine is
489 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
490 @code{break} command.
493 (@value{GDBP}) @b{break m4_changequote}
494 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
498 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
499 control; as long as control does not reach the @code{m4_changequote}
500 subroutine, the program runs as usual:
503 (@value{GDBP}) @b{run}
504 Starting program: /work/Editorial/gdb/gnu/m4/m4
512 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
513 suspends execution of @code{m4}, displaying information about the
514 context where it stops.
517 @b{changequote(<QUOTE>,<UNQUOTE>)}
519 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
521 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
525 Now we use the command @code{n} (@code{next}) to advance execution to
526 the next line of the current function.
530 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
535 @code{set_quotes} looks like a promising subroutine. We can go into it
536 by using the command @code{s} (@code{step}) instead of @code{next}.
537 @code{step} goes to the next line to be executed in @emph{any}
538 subroutine, so it steps into @code{set_quotes}.
542 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
544 530 if (lquote != def_lquote)
548 The display that shows the subroutine where @code{m4} is now
549 suspended (and its arguments) is called a stack frame display. It
550 shows a summary of the stack. We can use the @code{backtrace}
551 command (which can also be spelled @code{bt}), to see where we are
552 in the stack as a whole: the @code{backtrace} command displays a
553 stack frame for each active subroutine.
556 (@value{GDBP}) @b{bt}
557 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
559 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
561 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
562 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
564 #4 0x79dc in expand_input () at macro.c:40
565 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
569 We will step through a few more lines to see what happens. The first two
570 times, we can use @samp{s}; the next two times we use @code{n} to avoid
571 falling into the @code{xstrdup} subroutine.
575 0x3b5c 532 if (rquote != def_rquote)
577 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
578 def_lquote : xstrdup(lq);
580 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
583 538 len_lquote = strlen(rquote);
587 The last line displayed looks a little odd; we can examine the variables
588 @code{lquote} and @code{rquote} to see if they are in fact the new left
589 and right quotes we specified. We use the command @code{p}
590 (@code{print}) to see their values.
593 (@value{GDBP}) @b{p lquote}
594 $1 = 0x35d40 "<QUOTE>"
595 (@value{GDBP}) @b{p rquote}
596 $2 = 0x35d50 "<UNQUOTE>"
600 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
601 To look at some context, we can display ten lines of source
602 surrounding the current line with the @code{l} (@code{list}) command.
608 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
610 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
613 538 len_lquote = strlen(rquote);
614 539 len_rquote = strlen(lquote);
621 Let us step past the two lines that set @code{len_lquote} and
622 @code{len_rquote}, and then examine the values of those variables.
626 539 len_rquote = strlen(lquote);
629 (@value{GDBP}) @b{p len_lquote}
631 (@value{GDBP}) @b{p len_rquote}
636 That certainly looks wrong, assuming @code{len_lquote} and
637 @code{len_rquote} are meant to be the lengths of @code{lquote} and
638 @code{rquote} respectively. We can set them to better values using
639 the @code{p} command, since it can print the value of
640 any expression---and that expression can include subroutine calls and
644 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
646 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
651 Is that enough to fix the problem of using the new quotes with the
652 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
653 executing with the @code{c} (@code{continue}) command, and then try the
654 example that caused trouble initially:
660 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
667 Success! The new quotes now work just as well as the default ones. The
668 problem seems to have been just the two typos defining the wrong
669 lengths. We allow @code{m4} exit by giving it an EOF as input:
673 Program exited normally.
677 The message @samp{Program exited normally.} is from @value{GDBN}; it
678 indicates @code{m4} has finished executing. We can end our @value{GDBN}
679 session with the @value{GDBN} @code{quit} command.
682 (@value{GDBP}) @b{quit}
687 @chapter Getting In and Out of @value{GDBN}
689 This chapter discusses how to start @value{GDBN}, and how to get out of it.
690 (The essentials: type @samp{@value{GDBP}} to start GDB, and type @kbd{quit}
691 or @kbd{C-d} to exit.)
694 * Invoking GDB:: How to start @value{GDBN}
695 * Quitting GDB:: How to quit @value{GDBN}
696 * Shell Commands:: How to use shell commands inside @value{GDBN}
700 @section Invoking @value{GDBN}
703 For details on starting up @value{GDBP} as a
704 remote debugger attached to a Hitachi microprocessor, see @ref{Hitachi
705 Remote,,@value{GDBN} and Hitachi Microprocessors}.
708 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
709 @value{GDBN} reads commands from the terminal until you tell it to exit.
711 You can also run @code{@value{GDBP}} with a variety of arguments and options,
712 to specify more of your debugging environment at the outset.
715 The command-line options described here are designed
716 to cover a variety of situations; in some environments, some of these
717 options may effectively be unavailable.
720 The most usual way to start @value{GDBN} is with one argument,
721 specifying an executable program:
724 @value{GDBP} @var{program}
729 You can also start with both an executable program and a core file
733 @value{GDBP} @var{program} @var{core}
736 You can, instead, specify a process ID as a second argument, if you want
737 to debug a running process:
740 @value{GDBP} @var{program} 1234
744 would attach @value{GDBN} to process @code{1234} (unless you also have a file
745 named @file{1234}; @value{GDBN} does check for a core file first).
747 Taking advantage of the second command-line argument requires a fairly
748 complete operating system; when you use @value{GDBN} as a remote debugger
749 attached to a bare board, there may not be any notion of ``process'',
750 and there is often no way to get a core dump.
754 You can further control how @value{GDBN} starts up by using command-line
755 options. @value{GDBN} itself can remind you of the options available.
765 to display all available options and briefly describe their use
766 (@samp{@value{GDBP} -h} is a shorter equivalent).
768 All options and command line arguments you give are processed
769 in sequential order. The order makes a difference when the
770 @samp{-x} option is used.
776 * Remote Serial:: @value{GDBN} remote serial protocol
779 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
782 * UDI29K Remote:: @value{GDBN} and the UDI protocol for AMD29K
783 * EB29K Remote:: @value{GDBN} with a remote EB29K
786 * VxWorks Remote:: @value{GDBN} and VxWorks
789 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
792 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
795 * MIPS Remote:: @value{GDBN} and MIPS boards
798 * Simulator:: Simulated CPU target
801 @c remnant makeinfo bug requires this blank line after *two* end-ifblahs:
803 * File Options:: Choosing files
804 * Mode Options:: Choosing modes
808 @include gdbinv-s.texi
812 @subsection Choosing files
815 When @value{GDBN} starts, it reads any arguments other than options as
816 specifying an executable file and core file (or process ID). This is
817 the same as if the arguments were specified by the @samp{-se} and
818 @samp{-c} options respectively. (@value{GDBN} reads the first argument
819 that does not have an associated option flag as equivalent to the
820 @samp{-se} option followed by that argument; and the second argument
821 that does not have an associated option flag, if any, as equivalent to
822 the @samp{-c} option followed by that argument.)
825 When @value{GDBN} starts, it reads any argument other than options as
826 specifying an executable file. This is the same as if the argument was
827 specified by the @samp{-se} option.
830 Many options have both long and short forms; both are shown in the
831 following list. @value{GDBN} also recognizes the long forms if you truncate
832 them, so long as enough of the option is present to be unambiguous.
833 (If you prefer, you can flag option arguments with @samp{--} rather
834 than @samp{-}, though we illustrate the more usual convention.)
837 @item -symbols=@var{file}
839 Read symbol table from file @var{file}.
841 @item -exec=@var{file}
843 Use file @var{file} as the executable file to execute when
848 appropriate, and for examining pure data in conjunction with a core
853 Read symbol table from file @var{file} and use it as the executable
857 @item -core=@var{file}
859 Use file @var{file} as a core dump to examine.
862 @item -command=@var{file}
864 Execute @value{GDBN} commands from file @var{file}. @xref{Command
865 Files,, Command files}.
867 @item -directory=@var{directory}
868 @itemx -d @var{directory}
869 Add @var{directory} to the path to search for source files.
874 @emph{Warning: this option depends on operating system facilities that are not
875 supported on all systems.}@*
876 If memory-mapped files are available on your system through the @code{mmap}
877 system call, you can use this option
878 to have @value{GDBN} write the symbols from your
879 program into a reusable file in the current directory. If the program you are debugging is
880 called @file{/tmp/fred}, the mapped symbol file will be @file{./fred.syms}.
881 Future @value{GDBN} debugging sessions will notice the presence of this file,
882 and will quickly map in symbol information from it, rather than reading
883 the symbol table from the executable program.
885 @c FIXME! Really host, not target?
886 The @file{.syms} file is specific to the host machine where @value{GDBN}
887 is run. It holds an exact image of the internal @value{GDBN} symbol
888 table. It cannot be shared across multiple host platforms.
893 Read each symbol file's entire symbol table immediately, rather than
894 the default, which is to read it incrementally as it is needed.
895 This makes startup slower, but makes future operations faster.
899 The @code{-mapped} and @code{-readnow} options are typically combined in
900 order to build a @file{.syms} file that contains complete symbol
901 information. (@xref{Files,,Commands to specify files}, for information
902 on @file{.syms} files.) A simple GDB invocation to do nothing but build
903 a @file{.syms} file for future use is:
906 gdb -batch -nx -mapped -readnow programname
911 @subsection Choosing modes
913 You can run @value{GDBN} in various alternative modes---for example, in
914 batch mode or quiet mode.
919 Do not execute commands from any @file{@value{GDBINIT}} initialization files.
920 Normally, the commands in these files are executed after all the
921 command options and arguments have been processed.
922 @xref{Command Files,,Command files}.
926 ``Quiet''. Do not print the introductory and copyright messages. These
927 messages are also suppressed in batch mode.
930 Run in batch mode. Exit with status @code{0} after processing all the command
931 files specified with @samp{-x} (and @file{@value{GDBINIT}}, if not inhibited).
932 Exit with nonzero status if an error occurs in executing the @value{GDBN}
933 commands in the command files.
935 Batch mode may be useful for running @value{GDBN} as a filter, for example to
936 download and run a program on another computer; in order to make this
937 more useful, the message
940 Program exited normally.
944 (which is ordinarily issued whenever a program running under @value{GDBN} control
945 terminates) is not issued when running in batch mode.
947 @item -cd=@var{directory}
948 Run @value{GDBN} using @var{directory} as its working directory,
949 instead of the current directory.
952 @item -context @var{authentication}
953 When the Energize programming system starts up @value{GDBN}, it uses this
954 option to trigger an alternate mode of interaction.
955 @var{authentication} is a pair of numeric codes that identify @value{GDBN}
956 as a client in the Energize environment. Avoid this option when you run
957 @value{GDBN} directly from the command line. See @ref{Energize,,Using
958 @value{GDBN} with Energize} for more discussion of using @value{GDBN} with Energize.
964 Emacs sets this option when it runs @value{GDBN} as a subprocess. It tells @value{GDBN}
965 to output the full file name and line number in a standard,
966 recognizable fashion each time a stack frame is displayed (which
967 includes each time your program stops). This recognizable format looks
968 like two @samp{\032} characters, followed by the file name, line number
969 and character position separated by colons, and a newline. The
970 Emacs-to-@value{GDBN} interface program uses the two @samp{\032} characters as
971 a signal to display the source code for the frame.
976 Set the line speed (baud rate or bits per second) of any serial
977 interface used by @value{GDBN} for remote debugging.
979 @item -tty=@var{device}
980 Run using @var{device} for your program's standard input and output.
981 @c FIXME: kingdon thinks there is more to -tty. Investigate.
986 @section Quitting @value{GDBN}
987 @cindex exiting @value{GDBN}
988 @cindex leaving @value{GDBN}
994 To exit @value{GDBN}, use the @code{quit} command (abbreviated @code{q}), or type
995 an end-of-file character (usually @kbd{C-d}).
999 An interrupt (often @kbd{C-c}) will not exit from @value{GDBN}, but rather
1000 will terminate the action of any @value{GDBN} command that is in progress and
1001 return to @value{GDBN} command level. It is safe to type the interrupt
1002 character at any time because @value{GDBN} does not allow it to take effect
1003 until a time when it is safe.
1006 If you have been using @value{GDBN} to control an attached process or
1007 device, you can release it with the @code{detach} command
1008 (@pxref{Attach, ,Debugging an already-running process}).
1011 @node Shell Commands
1012 @section Shell commands
1014 If you need to execute occasional shell commands during your
1015 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1016 just use the @code{shell} command.
1019 @item shell @var{command string}
1021 @cindex shell escape
1022 Invoke a the standard shell to execute @var{command string}.
1024 If it exists, the environment variable @code{SHELL} determines which
1025 shell to run. Otherwise @value{GDBN} uses @code{/bin/sh}.
1029 The utility @code{make} is often needed in development environments.
1030 You do not have to use the @code{shell} command for this purpose in
1034 @item make @var{make-args}
1036 @cindex calling make
1037 Execute the @code{make} program with the specified
1038 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1042 @chapter @value{GDBN} Commands
1044 You can abbreviate a @value{GDBN} command to the first few letters of the command
1045 name, if that abbreviation is unambiguous; and you can repeat certain
1046 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1047 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1048 show you the alternatives available, if there is more than one possibility).
1051 * Command Syntax:: How to give commands to @value{GDBN}
1052 * Completion:: Command completion
1053 * Help:: How to ask @value{GDBN} for help
1056 @node Command Syntax
1057 @section Command syntax
1059 A @value{GDBN} command is a single line of input. There is no limit on
1060 how long it can be. It starts with a command name, which is followed by
1061 arguments whose meaning depends on the command name. For example, the
1062 command @code{step} accepts an argument which is the number of times to
1063 step, as in @samp{step 5}. You can also use the @code{step} command
1064 with no arguments. Some command names do not allow any arguments.
1066 @cindex abbreviation
1067 @value{GDBN} command names may always be truncated if that abbreviation is
1068 unambiguous. Other possible command abbreviations are listed in the
1069 documentation for individual commands. In some cases, even ambiguous
1070 abbreviations are allowed; for example, @code{s} is specially defined as
1071 equivalent to @code{step} even though there are other commands whose
1072 names start with @code{s}. You can test abbreviations by using them as
1073 arguments to the @code{help} command.
1075 @cindex repeating commands
1077 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1078 repeat the previous command. Certain commands (for example, @code{run})
1079 will not repeat this way; these are commands for which unintentional
1080 repetition might cause trouble and which you are unlikely to want to
1083 The @code{list} and @code{x} commands, when you repeat them with
1084 @key{RET}, construct new arguments rather than repeating
1085 exactly as typed. This permits easy scanning of source or memory.
1087 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1088 output, in a way similar to the common utility @code{more}
1089 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1090 @key{RET} too many in this situation, @value{GDBN} disables command
1091 repetition after any command that generates this sort of display.
1095 Any text from a @kbd{#} to the end of the line is a comment; it does
1096 nothing. This is useful mainly in command files (@pxref{Command
1097 Files,,Command files}).
1100 @section Command completion
1103 @cindex word completion
1104 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1105 only one possibility; it can also show you what the valid possibilities
1106 are for the next word in a command, at any time. This works for @value{GDBN}
1107 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1109 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1110 of a word. If there is only one possibility, @value{GDBN} will fill in the
1111 word, and wait for you to finish the command (or press @key{RET} to
1112 enter it). For example, if you type
1114 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1115 @c complete accuracy in these examples; space introduced for clarity.
1116 @c If texinfo enhancements make it unnecessary, it would be nice to
1117 @c replace " @key" by "@key" in the following...
1119 (@value{GDBP}) info bre @key{TAB}
1123 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1124 the only @code{info} subcommand beginning with @samp{bre}:
1127 (@value{GDBP}) info breakpoints
1131 You can either press @key{RET} at this point, to run the @code{info
1132 breakpoints} command, or backspace and enter something else, if
1133 @samp{breakpoints} does not look like the command you expected. (If you
1134 were sure you wanted @code{info breakpoints} in the first place, you
1135 might as well just type @key{RET} immediately after @samp{info bre},
1136 to exploit command abbreviations rather than command completion).
1138 If there is more than one possibility for the next word when you press
1139 @key{TAB}, @value{GDBN} will sound a bell. You can either supply more
1140 characters and try again, or just press @key{TAB} a second time, and
1141 @value{GDBN} will display all the possible completions for that word. For
1142 example, you might want to set a breakpoint on a subroutine whose name
1143 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1144 just sounds the bell. Typing @key{TAB} again will display all the
1145 function names in your program that begin with those characters, for
1149 (@value{GDBP}) b make_ @key{TAB}
1150 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1151 make_a_section_from_file make_environ
1152 make_abs_section make_function_type
1153 make_blockvector make_pointer_type
1154 make_cleanup make_reference_type
1155 make_command make_symbol_completion_list
1156 (@value{GDBP}) b make_
1160 After displaying the available possibilities, @value{GDBN} copies your
1161 partial input (@samp{b make_} in the example) so you can finish the
1164 If you just want to see the list of alternatives in the first place, you
1165 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1166 means @kbd{@key{META} ?}. You can type this
1168 either by holding down a
1169 key designated as the @key{META} shift on your keyboard (if there is
1170 one) while typing @kbd{?}, or
1172 as @key{ESC} followed by @kbd{?}.
1174 @cindex quotes in commands
1175 @cindex completion of quoted strings
1176 Sometimes the string you need, while logically a ``word'', may contain
1177 parentheses or other characters that @value{GDBN} normally excludes from its
1178 notion of a word. To permit word completion to work in this situation,
1179 you may enclose words in @code{'} (single quote marks) in @value{GDBN} commands.
1182 The most likely situation where you might need this is in typing the
1183 name of a C++ function. This is because C++ allows function overloading
1184 (multiple definitions of the same function, distinguished by argument
1185 type). For example, when you want to set a breakpoint you may need to
1186 distinguish whether you mean the version of @code{name} that takes an
1187 @code{int} parameter, @code{name(int)}, or the version that takes a
1188 @code{float} parameter, @code{name(float)}. To use the word-completion
1189 facilities in this situation, type a single quote @code{'} at the
1190 beginning of the function name. This alerts @value{GDBN} that it may need to
1191 consider more information than usual when you press @key{TAB} or
1192 @kbd{M-?} to request word completion:
1195 (@value{GDBP}) b 'bubble( @key{M-?}
1196 bubble(double,double) bubble(int,int)
1197 (@value{GDBP}) b 'bubble(
1200 In some cases, @value{GDBN} can tell that completing a name will require
1201 quotes. When this happens, @value{GDBN} will insert the quote for you (while
1202 completing as much as it can) if you do not type the quote in the first
1206 (@value{GDBP}) b bub @key{TAB}
1207 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1208 (@value{GDBP}) b 'bubble(
1212 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1213 you have not yet started typing the argument list when you ask for
1214 completion on an overloaded symbol.
1219 @section Getting help
1220 @cindex online documentation
1223 You can always ask @value{GDBN} itself for information on its commands, using the
1224 command @code{help}.
1230 You can use @code{help} (abbreviated @code{h}) with no arguments to
1231 display a short list of named classes of commands:
1235 List of classes of commands:
1237 running -- Running the program
1238 stack -- Examining the stack
1239 data -- Examining data
1240 breakpoints -- Making program stop at certain points
1241 files -- Specifying and examining files
1242 status -- Status inquiries
1243 support -- Support facilities
1244 user-defined -- User-defined commands
1245 aliases -- Aliases of other commands
1246 obscure -- Obscure features
1248 Type "help" followed by a class name for a list of
1249 commands in that class.
1250 Type "help" followed by command name for full
1252 Command name abbreviations are allowed if unambiguous.
1256 @item help @var{class}
1257 Using one of the general help classes as an argument, you can get a
1258 list of the individual commands in that class. For example, here is the
1259 help display for the class @code{status}:
1262 (@value{GDBP}) help status
1267 @c Line break in "show" line falsifies real output, but needed
1268 @c to fit in smallbook page size.
1269 show -- Generic command for showing things set
1271 info -- Generic command for printing status
1273 Type "help" followed by command name for full
1275 Command name abbreviations are allowed if unambiguous.
1279 @item help @var{command}
1280 With a command name as @code{help} argument, @value{GDBN} will display a
1281 short paragraph on how to use that command.
1284 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1285 and @code{show} to inquire about the state of your program, or the state
1286 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1287 manual introduces each of them in the appropriate context. The listings
1288 under @code{info} and under @code{show} in the Index point to
1289 all the sub-commands. @xref{Index}.
1296 This command (abbreviated @code{i}) is for describing the state of your
1297 program. For example, you can list the arguments given to your program
1298 with @code{info args}, list the registers currently in use with @code{info
1299 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1300 You can get a complete list of the @code{info} sub-commands with
1301 @w{@code{help info}}.
1305 In contrast, @code{show} is for describing the state of @value{GDBN} itself.
1306 You can change most of the things you can @code{show}, by using the
1307 related command @code{set}; for example, you can control what number
1308 system is used for displays with @code{set radix}, or simply inquire
1309 which is currently in use with @code{show radix}.
1312 To display all the settable parameters and their current
1313 values, you can use @code{show} with no arguments; you may also use
1314 @code{info set}. Both commands produce the same display.
1315 @c FIXME: "info set" violates the rule that "info" is for state of
1316 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1317 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1321 Here are three miscellaneous @code{show} subcommands, all of which are
1322 exceptional in lacking corresponding @code{set} commands:
1325 @kindex show version
1326 @cindex version number
1328 Show what version of @value{GDBN} is running. You should include this
1329 information in @value{GDBN} bug-reports. If multiple versions of @value{GDBN} are in
1330 use at your site, you may occasionally want to determine which version
1331 of @value{GDBN} you are running; as @value{GDBN} evolves, new commands are introduced,
1332 and old ones may wither away. The version number is also announced
1333 when you start @value{GDBN} with no arguments.
1335 @kindex show copying
1337 Display information about permission for copying @value{GDBN}.
1339 @kindex show warranty
1341 Display the GNU ``NO WARRANTY'' statement.
1345 @chapter Running Programs Under @value{GDBN}
1347 When you run a program under @value{GDBN}, you must first generate
1348 debugging information when you compile it.
1350 You may start it with its arguments, if any, in an environment of your
1351 choice. You may redirect your program's input and output, debug an
1352 already running process, or kill a child process.
1356 * Compilation:: Compiling for debugging
1357 * Starting:: Starting your program
1359 * Arguments:: Your program's arguments
1360 * Environment:: Your program's environment
1361 * Working Directory:: Your program's working directory
1362 * Input/Output:: Your program's input and output
1363 * Attach:: Debugging an already-running process
1364 * Kill Process:: Killing the child process
1365 * Process Information:: Additional process information
1370 @section Compiling for debugging
1372 In order to debug a program effectively, you need to generate
1373 debugging information when you compile it. This debugging information
1374 is stored in the object file; it describes the data type of each
1375 variable or function and the correspondence between source line numbers
1376 and addresses in the executable code.
1378 To request debugging information, specify the @samp{-g} option when you run
1381 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1382 options together. Using those compilers, you cannot generate optimized
1383 executables containing debugging information.
1385 @value{NGCC}, the GNU C compiler, supports @samp{-g} with or without
1386 @samp{-O}, making it possible to debug optimized code. We recommend
1387 that you @emph{always} use @samp{-g} whenever you compile a program.
1388 You may think your program is correct, but there is no sense in pushing
1391 @cindex optimized code, debugging
1392 @cindex debugging optimized code
1393 When you debug a program compiled with @samp{-g -O}, remember that the
1394 optimizer is rearranging your code; the debugger will show you what is
1395 really there. Do not be too surprised when the execution path does not
1396 exactly match your source file! An extreme example: if you define a
1397 variable, but never use it, @value{GDBN} will never see that
1398 variable---because the compiler optimizes it out of existence.
1400 Some things do not work as well with @samp{-g -O} as with just
1401 @samp{-g}, particularly on machines with instruction scheduling. If in
1402 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1403 please report it as a bug (including a test case!).
1405 Older versions of the GNU C compiler permitted a variant option
1406 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1407 format; if your GNU C compiler has this option, do not use it.
1410 @comment As far as I know, there are no cases in which @value{GDBN} will
1411 @comment produce strange output in this case. (but no promises).
1412 If your program includes archives made with the @code{ar} program, and
1413 if the object files used as input to @code{ar} were compiled without the
1414 @samp{-g} option and have names longer than 15 characters, @value{GDBN} will get
1415 confused reading your program's symbol table. No error message will be
1416 given, but @value{GDBN} may behave strangely. The reason for this problem is a
1417 deficiency in the Unix archive file format, which cannot represent file
1418 names longer than 15 characters.
1420 To avoid this problem, compile the archive members with the @samp{-g}
1421 option or use shorter file names. Alternatively, use a version of GNU
1422 @code{ar} dated more recently than August 1989.
1426 @section Starting your program
1434 Use the @code{run} command to start your program under @value{GDBN}. You must
1435 first specify the program name
1439 with an argument to @value{GDBN} (@pxref{Invocation, ,Getting In and
1440 Out of @value{GDBN}}), or by using the @code{file} or @code{exec-file}
1441 command (@pxref{Files, ,Commands to specify files}).
1446 If you are running your program in an execution environment that
1447 supports processes, @code{run} creates an inferior process and makes
1448 that process run your program. (In environments without processes,
1449 @code{run} jumps to the start of your program.)
1451 The execution of a program is affected by certain information it
1452 receives from its superior. @value{GDBN} provides ways to specify this
1453 information, which you must do @emph{before} starting your program. (You
1454 can change it after starting your program, but such changes will only affect
1455 your program the next time you start it.) This information may be
1456 divided into four categories:
1459 @item The @emph{arguments.}
1460 Specify the arguments to give your program as the arguments of the
1461 @code{run} command. If a shell is available on your target, the shell
1462 is used to pass the arguments, so that you may use normal conventions
1463 (such as wildcard expansion or variable substitution) in describing
1464 the arguments. In Unix systems, you can control which shell is used
1465 with the @code{SHELL} environment variable. @xref{Arguments, ,Your
1466 program's arguments}.
1468 @item The @emph{environment.}
1469 Your program normally inherits its environment from @value{GDBN}, but you can
1470 use the @value{GDBN} commands @code{set environment} and @code{unset
1471 environment} to change parts of the environment that will be given to
1472 your program. @xref{Environment, ,Your program's environment}.
1474 @item The @emph{working directory.}
1475 Your program inherits its working directory from @value{GDBN}. You can set
1476 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1477 @xref{Working Directory, ,Your program's working directory}.
1479 @item The @emph{standard input and output.}
1480 Your program normally uses the same device for standard input and
1481 standard output as @value{GDBN} is using. You can redirect input and output
1482 in the @code{run} command line, or you can use the @code{tty} command to
1483 set a different device for your program.
1484 @xref{Input/Output, ,Your program's input and output}.
1487 @emph{Warning:} While input and output redirection work, you cannot use
1488 pipes to pass the output of the program you are debugging to another
1489 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1494 When you issue the @code{run} command, your program begins to execute
1495 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1496 of how to arrange for your program to stop. Once your program has
1497 stopped, you may calls functions in your program, using the @code{print}
1498 or @code{call} commands. @xref{Data, ,Examining Data}.
1500 If the modification time of your symbol file has changed since the
1501 last time @value{GDBN} read its symbols, @value{GDBN} will discard its symbol table and
1502 re-read it. When it does this, @value{GDBN} tries to retain your current
1507 @section Your program's arguments
1509 @cindex arguments (to your program)
1510 The arguments to your program can be specified by the arguments of the
1511 @code{run} command. They are passed to a shell, which expands wildcard
1512 characters and performs redirection of I/O, and thence to your program.
1513 Your @code{SHELL} environment variable (if it exists) specifies what
1514 shell @value{GDBN} if you do not define @code{SHELL}, @value{GDBN} uses
1517 @code{run} with no arguments uses the same arguments used by the previous
1518 @code{run}, or those set by the @code{set args} command.
1523 Specify the arguments to be used the next time your program is run. If
1524 @code{set args} has no arguments, @code{run} will execute your program
1525 with no arguments. Once you have run your program with arguments,
1526 using @code{set args} before the next @code{run} is the only way to run
1527 it again without arguments.
1531 Show the arguments to give your program when it is started.
1535 @section Your program's environment
1537 @cindex environment (of your program)
1538 The @dfn{environment} consists of a set of environment variables and
1539 their values. Environment variables conventionally record such things as
1540 your user name, your home directory, your terminal type, and your search
1541 path for programs to run. Usually you set up environment variables with
1542 the shell and they are inherited by all the other programs you run. When
1543 debugging, it can be useful to try running your program with a modified
1544 environment without having to start @value{GDBN} over again.
1547 @item path @var{directory}
1549 Add @var{directory} to the front of the @code{PATH} environment variable
1550 (the search path for executables), for both @value{GDBN} and your program.
1551 You may specify several directory names, separated by @samp{:} or
1552 whitespace. If @var{directory} is already in the path, it is moved to
1553 the front, so it will be searched sooner.
1555 You can use the string @samp{$cwd} to refer to whatever is the current
1556 working directory at the time @value{GDBN} searches the path. If you use
1557 @samp{.} instead, it refers to the directory where you executed the
1558 @code{path} command. @value{GDBN} fills in the current path where needed in
1559 the @var{directory} argument, before adding it to the search path.
1560 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1561 @c document that, since repeating it would be a no-op.
1565 Display the list of search paths for executables (the @code{PATH}
1566 environment variable).
1568 @item show environment @r{[}@var{varname}@r{]}
1569 @kindex show environment
1570 Print the value of environment variable @var{varname} to be given to
1571 your program when it starts. If you do not supply @var{varname},
1572 print the names and values of all environment variables to be given to
1573 your program. You can abbreviate @code{environment} as @code{env}.
1575 @item set environment @var{varname} @r{[}=@r{]} @var{value}
1576 @kindex set environment
1577 Set environment variable @var{varname} to @var{value}. The value
1578 changes for your program only, not for @value{GDBN} itself. @var{value} may
1579 be any string; the values of environment variables are just strings, and
1580 any interpretation is supplied by your program itself. The @var{value}
1581 parameter is optional; if it is eliminated, the variable is set to a
1583 @c "any string" here does not include leading, trailing
1584 @c blanks. Gnu asks: does anyone care?
1586 For example, this command:
1593 tells a Unix program, when subsequently run, that its user is named
1594 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1595 are not actually required.)
1597 @item unset environment @var{varname}
1598 @kindex unset environment
1599 Remove variable @var{varname} from the environment to be passed to your
1600 program. This is different from @samp{set env @var{varname} =};
1601 @code{unset environment} removes the variable from the environment,
1602 rather than assigning it an empty value.
1605 @emph{Warning:} @value{GDBN} runs your program using the shell indicated
1606 by your @code{SHELL} environment variable if it exists (or
1607 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1608 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1609 @file{.bashrc} for BASH---any variables you set in that file will affect
1610 your program. You may wish to move setting of environment variables to
1611 files that are only run when you sign on, such as @file{.login} or
1614 @node Working Directory
1615 @section Your program's working directory
1617 @cindex working directory (of your program)
1618 Each time you start your program with @code{run}, it inherits its
1619 working directory from the current working directory of @value{GDBN}.
1620 The @value{GDBN} working directory is initially whatever it inherited
1621 from its parent process (typically the shell), but you can specify a new
1622 working directory in @value{GDBN} with the @code{cd} command.
1624 The @value{GDBN} working directory also serves as a default for the commands
1625 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1629 @item cd @var{directory}
1631 Set the @value{GDBN} working directory to @var{directory}.
1635 Print the @value{GDBN} working directory.
1639 @section Your program's input and output
1644 By default, the program you run under @value{GDBN} does input and output to
1645 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal to
1646 its own terminal modes to interact with you, but it records the terminal
1647 modes your program was using and switches back to them when you continue
1648 running your program.
1652 @kindex info terminal
1653 Displays information recorded by @value{GDBN} about the terminal modes your
1657 You can redirect your program's input and/or output using shell
1658 redirection with the @code{run} command. For example,
1665 starts your program, diverting its output to the file @file{outfile}.
1668 @cindex controlling terminal
1669 Another way to specify where your program should do input and output is
1670 with the @code{tty} command. This command accepts a file name as
1671 argument, and causes this file to be the default for future @code{run}
1672 commands. It also resets the controlling terminal for the child
1673 process, for future @code{run} commands. For example,
1680 directs that processes started with subsequent @code{run} commands
1681 default to do input and output on the terminal @file{/dev/ttyb} and have
1682 that as their controlling terminal.
1684 An explicit redirection in @code{run} overrides the @code{tty} command's
1685 effect on the input/output device, but not its effect on the controlling
1688 When you use the @code{tty} command or redirect input in the @code{run}
1689 command, only the input @emph{for your program} is affected. The input
1690 for @value{GDBN} still comes from your terminal.
1693 @section Debugging an already-running process
1698 @item attach @var{process-id}
1699 This command attaches to a running process---one that was started
1700 outside @value{GDBN}. (@code{info files} will show your active
1701 targets.) The command takes as argument a process ID. The usual way to
1702 find out the process-id of a Unix process is with the @code{ps} utility,
1703 or with the @samp{jobs -l} shell command.
1705 @code{attach} will not repeat if you press @key{RET} a second time after
1706 executing the command.
1709 To use @code{attach}, you must be debugging in an environment which
1710 supports processes. You must also have permission to send the process a
1711 signal, and it must have the same effective user ID as the @value{GDBN}
1714 When using @code{attach}, you should first use the @code{file} command
1715 to specify the program running in the process and load its symbol table.
1716 @xref{Files, ,Commands to Specify Files}.
1718 The first thing @value{GDBN} does after arranging to debug the specified
1719 process is to stop it. You can examine and modify an attached process
1720 with all the @value{GDBN} commands that are ordinarily available when you start
1721 processes with @code{run}. You can insert breakpoints; you can step and
1722 continue; you can modify storage. If you would rather the process
1723 continue running, you may use the @code{continue} command after
1724 attaching @value{GDBN} to the process.
1729 When you have finished debugging the attached process, you can use the
1730 @code{detach} command to release it from @value{GDBN} control. Detaching
1731 the process continues its execution. After the @code{detach} command,
1732 that process and @value{GDBN} become completely independent once more, and you
1733 are ready to @code{attach} another process or start one with @code{run}.
1734 @code{detach} will not repeat if you press @key{RET} again after
1735 executing the command.
1738 If you exit @value{GDBN} or use the @code{run} command while you have an attached
1739 process, you kill that process. By default, you will be asked for
1740 confirmation if you try to do either of these things; you can control
1741 whether or not you need to confirm by using the @code{set confirm} command
1742 (@pxref{Messages/Warnings, ,Optional warnings and messages}).
1746 @section Killing the child process
1751 Kill the child process in which your program is running under @value{GDBN}.
1754 This command is useful if you wish to debug a core dump instead of a
1755 running process. @value{GDBN} ignores any core dump file while your program
1759 On some operating systems, a program cannot be executed outside @value{GDBN}
1760 while you have breakpoints set on it inside @value{GDBN}. You can use the
1761 @code{kill} command in this situation to permit running your program
1762 outside the debugger.
1764 The @code{kill} command is also useful if you wish to recompile and
1765 relink your program, since on many systems it is impossible to modify an
1766 executable file while it is running in a process. In this case, when you
1767 next type @code{run}, @value{GDBN} will notice that the file has changed, and
1768 will re-read the symbol table (while trying to preserve your current
1769 breakpoint settings).
1771 @node Process Information
1772 @section Additional process information
1775 @cindex process image
1776 Some operating systems provide a facility called @samp{/proc} that can
1777 be used to examine the image of a running process using file-system
1778 subroutines. If @value{GDBN} is configured for an operating system with this
1779 facility, the command @code{info proc} is available to report on several
1780 kinds of information about the process running your program.
1785 Summarize available information about the process.
1787 @item info proc mappings
1788 @kindex info proc mappings
1789 Report on the address ranges accessible in the program, with information
1790 on whether your program may read, write, or execute each range.
1792 @item info proc times
1793 @kindex info proc times
1794 Starting time, user CPU time, and system CPU time for your program and
1798 @kindex info proc id
1799 Report on the process IDs related to your program: its own process ID,
1800 the ID of its parent, the process group ID, and the session ID.
1802 @item info proc status
1803 @kindex info proc status
1804 General information on the state of the process. If the process is
1805 stopped, this report includes the reason for stopping, and any signal
1809 Show all the above information about the process.
1814 @chapter Stopping and Continuing
1816 The principal purposes of using a debugger are so that you can stop your
1817 program before it terminates; or so that, if your program runs into
1818 trouble, you can investigate and find out why.
1820 Inside @value{GDBN}, your program may stop for any of several reasons, such
1825 a breakpoint, or reaching a new line after a @value{GDBN}
1826 command such as @code{step}. You may then examine and change
1827 variables, set new breakpoints or remove old ones, and then continue
1828 execution. Usually, the messages shown by @value{GDBN} provide ample
1829 explanation of the status of your program---but you can also explicitly
1830 request this information at any time.
1834 @kindex info program
1835 Display information about the status of your program: whether it is
1845 * Breakpoints:: Breakpoints, watchpoints, and exceptions
1848 * Breakpoints:: Breakpoints and watchpoints
1850 @c Remnant makeinfo bug requires blank line after *successful* end-if in menu:
1852 * Continuing and Stepping:: Resuming execution
1858 @c makeinfo node-defaulting requires adjacency of @node and sectioning cmds
1859 @c ...hence distribute @node Breakpoints over two possible @if expansions.
1863 @section Breakpoints, watchpoints, and exceptions
1867 @section Breakpoints and watchpoints
1871 A @dfn{breakpoint} makes your program stop whenever a certain point in
1872 the program is reached. For each breakpoint, you can add various
1873 conditions to control in finer detail whether your program will stop.
1874 You can set breakpoints with the @code{break} command and its variants
1875 (@pxref{Set Breaks, ,Setting breakpoints}), to specify the place where
1876 your program should stop by line number, function name or exact address
1879 In languages with exception handling (such as GNU C++), you can also set
1880 breakpoints where an exception is raised (@pxref{Exception Handling,
1881 ,Breakpoints and exceptions}).
1885 @cindex memory tracing
1886 @cindex breakpoint on memory address
1887 @cindex breakpoint on variable modification
1888 A @dfn{watchpoint} is a special breakpoint that stops your program
1889 when the value of an expression changes. You must use a different
1890 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
1891 watchpoints}), but aside from that, you can manage a watchpoint like
1892 any other breakpoint: you enable, disable, and delete both breakpoints
1893 and watchpoints using the same commands.
1895 You can arrange to have values from your program displayed automatically
1896 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,
1897 ,Automatic display}.
1899 @cindex breakpoint numbers
1900 @cindex numbers for breakpoints
1901 @value{GDBN} assigns a number to each breakpoint or watchpoint when you
1902 create it; these numbers are successive integers starting with one. In
1903 many of the commands for controlling various features of breakpoints you
1904 use the breakpoint number to say which breakpoint you want to change.
1905 Each breakpoint may be @dfn{enabled} or @dfn{disabled}; if disabled, it has
1906 no effect on your program until you enable it again.
1909 * Set Breaks:: Setting breakpoints
1910 * Set Watchpoints:: Setting watchpoints
1912 * Exception Handling:: Breakpoints and exceptions
1915 * Delete Breaks:: Deleting breakpoints
1916 * Disabling:: Disabling breakpoints
1917 * Conditions:: Break conditions
1918 * Break Commands:: Breakpoint command lists
1920 * Breakpoint Menus:: Breakpoint menus
1923 * Error in Breakpoints:: ``Cannot insert breakpoints''
1928 @subsection Setting breakpoints
1930 @c FIXME LMB what does GDB do if no code on line of breakpt?
1931 @c consider in particular declaration with/without initialization.
1933 @c FIXME 2 is there stuff on this already? break at fun start, already init?
1938 @cindex latest breakpoint
1939 Breakpoints are set with the @code{break} command (abbreviated
1940 @code{b}). The debugger convenience variable @samp{$bpnum} records the
1941 number of the beakpoint you've set most recently; see @ref{Convenience
1942 Vars,, Convenience variables}, for a discussion of what you can do with
1943 convenience variables.
1945 You have several ways to say where the breakpoint should go.
1948 @item break @var{function}
1949 Set a breakpoint at entry to function @var{function}.
1951 When using source languages that permit overloading of symbols, such as
1952 C++, @var{function} may refer to more than one possible place to break.
1953 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
1956 @item break +@var{offset}
1957 @itemx break -@var{offset}
1958 Set a breakpoint some number of lines forward or back from the position
1959 at which execution stopped in the currently selected frame.
1961 @item break @var{linenum}
1962 Set a breakpoint at line @var{linenum} in the current source file.
1963 That file is the last file whose source text was printed. This
1964 breakpoint will stop your program just before it executes any of the
1967 @item break @var{filename}:@var{linenum}
1968 Set a breakpoint at line @var{linenum} in source file @var{filename}.
1970 @item break @var{filename}:@var{function}
1971 Set a breakpoint at entry to function @var{function} found in file
1972 @var{filename}. Specifying a file name as well as a function name is
1973 superfluous except when multiple files contain similarly named
1976 @item break *@var{address}
1977 Set a breakpoint at address @var{address}. You can use this to set
1978 breakpoints in parts of your program which do not have debugging
1979 information or source files.
1982 When called without any arguments, @code{break} sets a breakpoint at
1983 the next instruction to be executed in the selected stack frame
1984 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
1985 innermost, this will cause your program to stop as soon as control
1986 returns to that frame. This is similar to the effect of a
1987 @code{finish} command in the frame inside the selected frame---except
1988 that @code{finish} does not leave an active breakpoint. If you use
1989 @code{break} without an argument in the innermost frame, @value{GDBN} will stop
1990 the next time it reaches the current location; this may be useful
1993 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
1994 least one instruction has been executed. If it did not do this, you
1995 would be unable to proceed past a breakpoint without first disabling the
1996 breakpoint. This rule applies whether or not the breakpoint already
1997 existed when your program stopped.
1999 @item break @dots{} if @var{cond}
2000 Set a breakpoint with condition @var{cond}; evaluate the expression
2001 @var{cond} each time the breakpoint is reached, and stop only if the
2002 value is nonzero---that is, if @var{cond} evaluates as true.
2003 @samp{@dots{}} stands for one of the possible arguments described
2004 above (or no argument) specifying where to break. @xref{Conditions,
2005 ,Break conditions}, for more information on breakpoint conditions.
2007 @item tbreak @var{args}
2009 Set a breakpoint enabled only for one stop. @var{args} are the
2010 same as for the @code{break} command, and the breakpoint is set in the same
2011 way, but the breakpoint is automatically disabled after the first time your
2012 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2014 @item rbreak @var{regex}
2016 @cindex regular expression
2017 @c FIXME what kind of regexp?
2018 Set breakpoints on all functions matching the regular expression
2019 @var{regex}. This command
2020 sets an unconditional breakpoint on all matches, printing a list of all
2021 breakpoints it set. Once these breakpoints are set, they are treated
2022 just like the breakpoints set with the @code{break} command. They can
2023 be deleted, disabled, made conditional, etc., in the standard ways.
2026 When debugging C++ programs, @code{rbreak} is useful for setting
2027 breakpoints on overloaded functions that are not members of any special
2031 @kindex info breakpoints
2032 @cindex @code{$_} and @code{info breakpoints}
2033 @item info breakpoints @r{[}@var{n}@r{]}
2034 @itemx info break @r{[}@var{n}@r{]}
2035 @itemx info watchpoints @r{[}@var{n}@r{]}
2036 Print a table of all breakpoints and watchpoints set and not
2037 deleted, with the following columns for each breakpoint:
2040 @item Breakpoint Numbers
2042 Breakpoint or watchpoint.
2044 Whether the breakpoint is marked to be disabled or deleted when hit.
2045 @item Enabled or Disabled
2046 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2047 that are not enabled.
2049 Where the breakpoint is in your program, as a memory address
2051 Where the breakpoint is in the source for your program, as a file and
2056 Breakpoint commands, if any, are listed after the line for the
2057 corresponding breakpoint.
2060 @code{info break} with a breakpoint
2061 number @var{n} as argument lists only that breakpoint. The
2062 convenience variable @code{$_} and the default examining-address for
2063 the @code{x} command are set to the address of the last breakpoint
2064 listed (@pxref{Memory, ,Examining memory}).
2067 @value{GDBN} allows you to set any number of breakpoints at the same place in
2068 your program. There is nothing silly or meaningless about this. When
2069 the breakpoints are conditional, this is even useful
2070 (@pxref{Conditions, ,Break conditions}).
2072 @cindex negative breakpoint numbers
2073 @cindex internal @value{GDBN} breakpoints
2074 @value{GDBN} itself sometimes sets breakpoints in your program for special
2075 purposes, such as proper handling of @code{longjmp} (in C programs).
2076 These internal breakpoints are assigned negative numbers, starting with
2077 @code{-1}; @samp{info breakpoints} does not display them.
2079 You can see these breakpoints with the @value{GDBN} maintenance command
2080 @samp{maint info breakpoints}.
2083 @kindex maint info breakpoints
2084 @item maint info breakpoints
2085 Using the same format as @samp{info breakpoints}, display both the
2086 breakpoints you've set explicitly, and those @value{GDBN} is using for
2087 internal purposes. Internal breakpoints are shown with negative
2088 breakpoint numbers. The type column identifies what kind of breakpoint
2093 Normal, explicitly set breakpoint.
2096 Normal, explicitly set watchpoint.
2099 Internal breakpoint, used to handle correctly stepping through
2100 @code{longjmp} calls.
2102 @item longjmp resume
2103 Internal breakpoint at the target of a @code{longjmp}.
2106 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2109 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2115 @node Set Watchpoints
2116 @subsection Setting watchpoints
2117 @cindex setting watchpoints
2119 You can use a watchpoint to stop execution whenever the value of an
2120 expression changes, without having to predict a particular place
2121 where this may happen.
2123 Watchpoints currently execute two orders of magnitude more slowly than
2124 other breakpoints, but this can well be worth it to catch errors where
2125 you have no clue what part of your program is the culprit. Some
2126 processors provide special hardware to support watchpoint evaluation; future
2127 releases of @value{GDBN} will use such hardware if it is available.
2131 @item watch @var{expr}
2132 Set a watchpoint for an expression.
2134 @kindex info watchpoints
2135 @item info watchpoints
2136 This command prints a list of watchpoints and breakpoints; it is the
2137 same as @code{info break}.
2141 @node Exception Handling
2142 @subsection Breakpoints and exceptions
2143 @cindex exception handlers
2145 Some languages, such as GNU C++, implement exception handling. You can
2146 use @value{GDBN} to examine what caused your program to raise an exception,
2147 and to list the exceptions your program is prepared to handle at a
2148 given point in time.
2151 @item catch @var{exceptions}
2153 You can set breakpoints at active exception handlers by using the
2154 @code{catch} command. @var{exceptions} is a list of names of exceptions
2158 You can use @code{info catch} to list active exception handlers.
2159 @xref{Frame Info, ,Information about a frame}.
2161 There are currently some limitations to exception handling in @value{GDBN}.
2162 These will be corrected in a future release.
2166 If you call a function interactively, @value{GDBN} normally returns
2167 control to you when the function has finished executing. If the call
2168 raises an exception, however, the call may bypass the mechanism that
2169 returns control to you and cause your program to simply continue
2170 running until it hits a breakpoint, catches a signal that @value{GDBN} is
2171 listening for, or exits.
2173 You cannot raise an exception interactively.
2175 You cannot interactively install an exception handler.
2178 @cindex raise exceptions
2179 Sometimes @code{catch} is not the best way to debug exception handling:
2180 if you need to know exactly where an exception is raised, it is better to
2181 stop @emph{before} the exception handler is called, since that way you
2182 can see the stack before any unwinding takes place. If you set a
2183 breakpoint in an exception handler instead, it may not be easy to find
2184 out where the exception was raised.
2186 To stop just before an exception handler is called, you need some
2187 knowledge of the implementation. In the case of GNU C++, exceptions are
2188 raised by calling a library function named @code{__raise_exception}
2189 which has the following ANSI C interface:
2192 /* @var{addr} is where the exception identifier is stored.
2193 ID is the exception identifier. */
2194 void __raise_exception (void **@var{addr}, void *@var{id});
2198 To make the debugger catch all exceptions before any stack
2199 unwinding takes place, set a breakpoint on @code{__raise_exception}
2200 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2202 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2203 that depends on the value of @var{id}, you can stop your program when
2204 a specific exception is raised. You can use multiple conditional
2205 breakpoints to stop your program when any of a number of exceptions are
2210 @subsection Deleting breakpoints
2212 @cindex clearing breakpoints, watchpoints
2213 @cindex deleting breakpoints, watchpoints
2214 It is often necessary to eliminate a breakpoint or watchpoint once it
2215 has done its job and you no longer want your program to stop there. This
2216 is called @dfn{deleting} the breakpoint. A breakpoint that has been
2217 deleted no longer exists; it is forgotten.
2219 With the @code{clear} command you can delete breakpoints according to
2220 where they are in your program. With the @code{delete} command you can
2221 delete individual breakpoints or watchpoints by specifying their
2224 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2225 automatically ignores breakpoints on the first instruction to be executed
2226 when you continue execution without changing the execution address.
2231 Delete any breakpoints at the next instruction to be executed in the
2232 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2233 the innermost frame is selected, this is a good way to delete a
2234 breakpoint where your program just stopped.
2236 @item clear @var{function}
2237 @itemx clear @var{filename}:@var{function}
2238 Delete any breakpoints set at entry to the function @var{function}.
2240 @item clear @var{linenum}
2241 @itemx clear @var{filename}:@var{linenum}
2242 Delete any breakpoints set at or within the code of the specified line.
2244 @item delete @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2245 @cindex delete breakpoints
2248 Delete the breakpoints or watchpoints of the numbers specified as
2249 arguments. If no argument is specified, delete all breakpoints (@value{GDBN}
2250 asks confirmation, unless you have @code{set confirm off}). You
2251 can abbreviate this command as @code{d}.
2255 @subsection Disabling breakpoints
2257 @cindex disabled breakpoints
2258 @cindex enabled breakpoints
2259 Rather than deleting a breakpoint or watchpoint, you might prefer to
2260 @dfn{disable} it. This makes the breakpoint inoperative as if it had
2261 been deleted, but remembers the information on the breakpoint so that
2262 you can @dfn{enable} it again later.
2264 You disable and enable breakpoints and watchpoints with the
2265 @code{enable} and @code{disable} commands, optionally specifying one or
2266 more breakpoint numbers as arguments. Use @code{info break} or
2267 @code{info watch} to print a list of breakpoints or watchpoints if you
2268 do not know which numbers to use.
2270 A breakpoint or watchpoint can have any of four different states of
2275 Enabled. The breakpoint will stop your program. A breakpoint set
2276 with the @code{break} command starts out in this state.
2278 Disabled. The breakpoint has no effect on your program.
2280 Enabled once. The breakpoint will stop your program, but
2281 when it does so it will become disabled. A breakpoint set
2282 with the @code{tbreak} command starts out in this state.
2284 Enabled for deletion. The breakpoint will stop your program, but
2285 immediately after it does so it will be deleted permanently.
2288 You can use the following commands to enable or disable breakpoints and
2292 @item disable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2293 @kindex disable breakpoints
2296 Disable the specified breakpoints---or all breakpoints, if none are
2297 listed. A disabled breakpoint has no effect but is not forgotten. All
2298 options such as ignore-counts, conditions and commands are remembered in
2299 case the breakpoint is enabled again later. You may abbreviate
2300 @code{disable} as @code{dis}.
2302 @item enable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2303 @kindex enable breakpoints
2305 Enable the specified breakpoints (or all defined breakpoints). They
2306 become effective once again in stopping your program.
2308 @item enable @r{[}breakpoints@r{]} once @var{bnums}@dots{}
2309 Enable the specified breakpoints temporarily. Each will be disabled
2310 again the next time it stops your program.
2312 @item enable @r{[}breakpoints@r{]} delete @var{bnums}@dots{}
2313 Enable the specified breakpoints to work once and then die. Each of
2314 the breakpoints will be deleted the next time it stops your program.
2317 Save for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2318 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2319 subsequently, they become disabled or enabled only when you use one of
2320 the commands above. (The command @code{until} can set and delete a
2321 breakpoint of its own, but it will not change the state of your other
2322 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2326 @subsection Break conditions
2327 @cindex conditional breakpoints
2328 @cindex breakpoint conditions
2330 @c FIXME what is scope of break condition expr? Context where wanted?
2331 @c in particular for a watchpoint?
2332 The simplest sort of breakpoint breaks every time your program reaches a
2333 specified place. You can also specify a @dfn{condition} for a
2334 breakpoint. A condition is just a Boolean expression in your
2335 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2336 a condition evaluates the expression each time your program reaches it,
2337 and your program stops only if the condition is @emph{true}.
2339 This is the converse of using assertions for program validation; in that
2340 situation, you want to stop when the assertion is violated---that is,
2341 when the condition is false. In C, if you want to test an assertion expressed
2342 by the condition @var{assert}, you should set the condition
2343 @samp{! @var{assert}} on the appropriate breakpoint.
2345 Conditions are also accepted for watchpoints; you may not need them,
2346 since a watchpoint is inspecting the value of an expression anyhow---but
2347 it might be simpler, say, to just set a watchpoint on a variable name,
2348 and specify a condition that tests whether the new value is an interesting
2351 Break conditions can have side effects, and may even call functions in
2352 your program. This can be useful, for example, to activate functions
2353 that log program progress, or to use your own print functions to
2354 format special data structures. The effects are completely predictable
2355 unless there is another enabled breakpoint at the same address. (In
2356 that case, @value{GDBN} might see the other breakpoint first and stop your
2357 program without checking the condition of this one.) Note that
2358 breakpoint commands are usually more convenient and flexible for the
2359 purpose of performing side effects when a breakpoint is reached
2360 (@pxref{Break Commands, ,Breakpoint command lists}).
2362 Break conditions can be specified when a breakpoint is set, by using
2363 @samp{if} in the arguments to the @code{break} command. @xref{Set
2364 Breaks, ,Setting breakpoints}. They can also be changed at any time
2365 with the @code{condition} command. The @code{watch} command does not
2366 recognize the @code{if} keyword; @code{condition} is the only way to
2367 impose a further condition on a watchpoint.
2370 @item condition @var{bnum} @var{expression}
2372 Specify @var{expression} as the break condition for breakpoint or
2373 watchpoint number @var{bnum}. From now on, this breakpoint will stop
2374 your program only if the value of @var{expression} is true (nonzero, in
2375 C). When you use @code{condition}, @value{GDBN} checks @var{expression}
2376 immediately for syntactic correctness, and to determine whether symbols
2377 in it have referents in the context of your breakpoint.
2378 @c FIXME so what does GDB do if there is no referent? Moreover, what
2379 @c about watchpoints?
2381 not actually evaluate @var{expression} at the time the @code{condition}
2382 command is given, however. @xref{Expressions, ,Expressions}.
2384 @item condition @var{bnum}
2385 Remove the condition from breakpoint number @var{bnum}. It becomes
2386 an ordinary unconditional breakpoint.
2389 @cindex ignore count (of breakpoint)
2390 A special case of a breakpoint condition is to stop only when the
2391 breakpoint has been reached a certain number of times. This is so
2392 useful that there is a special way to do it, using the @dfn{ignore
2393 count} of the breakpoint. Every breakpoint has an ignore count, which
2394 is an integer. Most of the time, the ignore count is zero, and
2395 therefore has no effect. But if your program reaches a breakpoint whose
2396 ignore count is positive, then instead of stopping, it just decrements
2397 the ignore count by one and continues. As a result, if the ignore count
2398 value is @var{n}, the breakpoint will not stop the next @var{n} times it
2402 @item ignore @var{bnum} @var{count}
2404 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
2405 The next @var{count} times the breakpoint is reached, your program's
2406 execution will not stop; other than to decrement the ignore count, @value{GDBN}
2409 To make the breakpoint stop the next time it is reached, specify
2412 @item continue @var{count}
2413 @itemx c @var{count}
2414 @itemx fg @var{count}
2415 @kindex continue @var{count}
2416 Continue execution of your program, setting the ignore count of the
2417 breakpoint where your program stopped to @var{count} minus one.
2418 Thus, your program will not stop at this breakpoint until the
2419 @var{count}'th time it is reached.
2421 An argument to this command is meaningful only when your program stopped
2422 due to a breakpoint. At other times, the argument to @code{continue} is
2425 The synonym @code{fg} is provided purely for convenience, and has
2426 exactly the same behavior as other forms of the command.
2429 If a breakpoint has a positive ignore count and a condition, the condition
2430 is not checked. Once the ignore count reaches zero, the condition will
2433 You could achieve the effect of the ignore count with a condition such
2434 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
2435 is decremented each time. @xref{Convenience Vars, ,Convenience
2438 @node Break Commands
2439 @subsection Breakpoint command lists
2441 @cindex breakpoint commands
2442 You can give any breakpoint (or watchpoint) a series of commands to
2443 execute when your program stops due to that breakpoint. For example, you
2444 might want to print the values of certain expressions, or enable other
2448 @item commands @r{[}@var{bnum}@r{]}
2449 @itemx @dots{} @var{command-list} @dots{}
2453 Specify a list of commands for breakpoint number @var{bnum}. The commands
2454 themselves appear on the following lines. Type a line containing just
2455 @code{end} to terminate the commands.
2457 To remove all commands from a breakpoint, type @code{commands} and
2458 follow it immediately with @code{end}; that is, give no commands.
2460 With no @var{bnum} argument, @code{commands} refers to the last
2461 breakpoint or watchpoint set (not to the breakpoint most recently
2465 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
2466 disabled within a @var{command-list}.
2468 You can use breakpoint commands to start your program up again. Simply
2469 use the @code{continue} command, or @code{step}, or any other command
2470 that resumes execution.
2472 Any other commands in the command list, after a command that resumes
2473 execution, are ignored. This is because any time you resume execution
2474 (even with a simple @code{next} or @code{step}), you may encounter
2475 another breakpoint---which could have its own command list, leading to
2476 ambiguities about which list to execute.
2479 If the first command you specify in a command list is @code{silent}, the
2480 usual message about stopping at a breakpoint is not printed. This may
2481 be desirable for breakpoints that are to print a specific message and
2482 then continue. If none of the remaining commands print anything, you
2483 will see no sign that the breakpoint was reached. @code{silent} is
2484 meaningful only at the beginning of a breakpoint command list.
2486 The commands @code{echo} and @code{output} that allow you to print
2487 precisely controlled output are often useful in silent breakpoints.
2488 @xref{Output, ,Commands for controlled output}.
2490 For example, here is how you could use breakpoint commands to print the
2491 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
2504 One application for breakpoint commands is to compensate for one bug so
2505 you can test for another. Put a breakpoint just after the erroneous line
2506 of code, give it a condition to detect the case in which something
2507 erroneous has been done, and give it commands to assign correct values
2508 to any variables that need them. End with the @code{continue} command
2509 so that your program does not stop, and start with the @code{silent}
2510 command so that no output is produced. Here is an example:
2522 One deficiency in the operation of automatically continuing breakpoints
2523 under Unix appears when your program uses raw mode for the terminal.
2524 @value{GDBN} switches back to its own terminal modes (not raw) before executing
2525 commands, and then must switch back to raw mode when your program is
2526 continued. This causes any pending terminal input to be lost.
2527 @c FIXME: revisit below when GNU sys avail.
2528 @c In the GNU system, this will be fixed by changing the behavior of
2531 Under Unix, you can get around this problem by writing actions into
2532 the breakpoint condition rather than in commands. For example,
2535 condition 5 (x = y + 4), 0
2539 specifies a condition expression (@pxref{Expressions, ,Expressions}) that will
2540 change @code{x} as needed, then always have the value zero so your
2541 program will not stop. No input is lost here, because @value{GDBN} evaluates
2542 break conditions without changing the terminal modes. When you want
2543 to have nontrivial conditions for performing the side effects, the
2544 operators @samp{&&}, @samp{||} and @samp{?@dots{}:} may be useful.
2547 @node Breakpoint Menus
2548 @subsection Breakpoint menus
2550 @cindex symbol overloading
2552 Some programming languages (notably C++) permit a single function name
2553 to be defined several times, for application in different contexts.
2554 This is called @dfn{overloading}. When a function name is overloaded,
2555 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
2556 a breakpoint. If you realize this will be a problem, you can use
2557 something like @samp{break @var{function}(@var{types})} to specify which
2558 particular version of the function you want. Otherwise, @value{GDBN} offers
2559 you a menu of numbered choices for different possible breakpoints, and
2560 waits for your selection with the prompt @samp{>}. The first two
2561 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
2562 sets a breakpoint at each definition of @var{function}, and typing
2563 @kbd{0} aborts the @code{break} command without setting any new
2566 For example, the following session excerpt shows an attempt to set a
2567 breakpoint at the overloaded symbol @code{String::after}.
2568 We choose three particular definitions of that function name:
2570 @c FIXME! This is likely to change to show arg type lists, at least
2572 (@value{GDBP}) b String::after
2575 [2] file:String.cc; line number:867
2576 [3] file:String.cc; line number:860
2577 [4] file:String.cc; line number:875
2578 [5] file:String.cc; line number:853
2579 [6] file:String.cc; line number:846
2580 [7] file:String.cc; line number:735
2582 Breakpoint 1 at 0xb26c: file String.cc, line 867.
2583 Breakpoint 2 at 0xb344: file String.cc, line 875.
2584 Breakpoint 3 at 0xafcc: file String.cc, line 846.
2585 Multiple breakpoints were set.
2586 Use the "delete" command to delete unwanted breakpoints.
2592 @node Error in Breakpoints
2593 @subsection ``Cannot insert breakpoints''
2595 @c FIXME: "cannot insert breakpoints" error, v unclear.
2596 @c Q in pending mail to Gilmore. ---pesch@cygnus.com, 26mar91
2597 @c some light may be shed by looking at instances of
2598 @c ONE_PROCESS_WRITETEXT. But error message seems possible otherwise
2599 @c too. pesch, 20sep91
2600 Under some operating systems, breakpoints cannot be used in a program if
2601 any other process is running that program. In this situation,
2602 attempting to run or continue a program with a breakpoint causes @value{GDBN}
2603 to stop the other process.
2605 When this happens, you have three ways to proceed:
2609 Remove or disable the breakpoints, then continue.
2612 Suspend @value{GDBN}, and copy the file containing your program to a new name.
2613 Resume @value{GDBN} and use the @code{exec-file} command to specify that @value{GDBN}
2614 should run your program under that name. Then start your program again.
2616 @c FIXME: RMS commented here "Show example". Maybe when someone
2617 @c explains the first FIXME: in this section...
2620 Relink your program so that the text segment is nonsharable, using the
2621 linker option @samp{-N}. The operating system limitation may not apply
2622 to nonsharable executables.
2626 @node Continuing and Stepping
2627 @section Continuing and stepping
2631 @cindex resuming execution
2632 @dfn{Continuing} means resuming program execution until your program
2633 completes normally. In contrast, @dfn{stepping} means executing just
2634 one more ``step'' of your program, where ``step'' may mean either one
2635 line of source code, or one machine instruction (depending on what
2636 particular command you use). Either when continuing
2637 or when stepping, your program may stop even sooner, due to
2642 a breakpoint or to a signal. (If due to a signal, you may want to use
2643 @code{handle}, or use @samp{signal 0} to resume execution.
2644 @xref{Signals, ,Signals}.)
2648 @item continue @r{[}@var{ignore-count}@r{]}
2650 Resume program execution, at the address where your program last stopped;
2651 any breakpoints set at that address are bypassed. The optional argument
2652 @var{ignore-count} allows you to specify a further number of times to
2653 ignore a breakpoint at this location; its effect is like that of
2654 @code{ignore} (@pxref{Conditions, ,Break conditions}).
2656 To resume execution at a different place, you can use @code{return}
2657 (@pxref{Returning, ,Returning from a function}) to go back to the
2658 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
2659 different address}) to go to an arbitrary location in your program.
2662 A typical technique for using stepping is to set a breakpoint
2664 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions})
2667 (@pxref{Breakpoints, ,Breakpoints and watchpoints})
2670 beginning of the function or the section of your program where a
2671 problem is believed to lie, run your program until it stops at that
2672 breakpoint, and then step through the suspect area, examining the
2673 variables that are interesting, until you see the problem happen.
2679 Continue running your program until control reaches a different source
2680 line, then stop it and return control to @value{GDBN}. This command is
2681 abbreviated @code{s}.
2684 @emph{Warning:} If you use the @code{step} command while control is
2685 within a function that was compiled without debugging information,
2686 execution will proceed until control reaches another function.
2689 @item step @var{count}
2690 Continue running as in @code{step}, but do so @var{count} times. If a
2691 breakpoint is reached,
2693 or a signal not related to stepping occurs before @var{count} steps,
2695 stepping stops right away.
2697 @item next @r{[}@var{count}@r{]}
2700 Continue to the next source line in the current (innermost) stack frame.
2701 Similar to @code{step}, but any function calls appearing within the line
2702 of code are executed without stopping. Execution stops when control
2703 reaches a different line of code at the stack level which was executing
2704 when the @code{next} command was given. This command is abbreviated
2707 An argument @var{count} is a repeat count, as for @code{step}.
2709 @code{next} within a function that lacks debugging information acts like
2710 @code{step}, but any function calls appearing within the code of the
2711 function are executed without stopping.
2715 Continue running until just after function in the selected stack frame
2716 returns. Print the returned value (if any).
2718 Contrast this with the @code{return} command (@pxref{Returning,
2719 ,Returning from a function}).
2725 Continue running until a source line past the current line, in the
2726 current stack frame, is reached. This command is used to avoid single
2727 stepping through a loop more than once. It is like the @code{next}
2728 command, except that when @code{until} encounters a jump, it
2729 automatically continues execution until the program counter is greater
2730 than the address of the jump.
2732 This means that when you reach the end of a loop after single stepping
2733 though it, @code{until} will cause your program to continue execution
2734 until the loop is exited. In contrast, a @code{next} command at the end
2735 of a loop will simply step back to the beginning of the loop, which
2736 would force you to step through the next iteration.
2738 @code{until} always stops your program if it attempts to exit the current
2741 @code{until} may produce somewhat counterintuitive results if the order
2742 of machine code does not match the order of the source lines. For
2743 example, in the following excerpt from a debugging session, the @code{f}
2744 (@code{frame}) command shows that execution is stopped at line
2745 @code{206}; yet when we use @code{until}, we get to line @code{195}:
2749 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
2751 (@value{GDBP}) until
2752 195 for ( ; argc > 0; NEXTARG) @{
2755 This happened because, for execution efficiency, the compiler had
2756 generated code for the loop closure test at the end, rather than the
2757 start, of the loop---even though the test in a C @code{for}-loop is
2758 written before the body of the loop. The @code{until} command appeared
2759 to step back to the beginning of the loop when it advanced to this
2760 expression; however, it has not really gone to an earlier
2761 statement---not in terms of the actual machine code.
2763 @code{until} with no argument works by means of single
2764 instruction stepping, and hence is slower than @code{until} with an
2767 @item until @var{location}
2768 @item u @var{location}
2769 Continue running your program until either the specified location is
2770 reached, or the current stack frame returns. @var{location} is any of
2771 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
2772 ,Setting breakpoints}). This form of the command uses breakpoints,
2773 and hence is quicker than @code{until} without an argument.
2779 Execute one machine instruction, then stop and return to the debugger.
2781 It is often useful to do @samp{display/i $pc} when stepping by machine
2782 instructions. This will cause the next instruction to be executed to
2783 be displayed automatically at each stop. @xref{Auto Display,
2784 ,Automatic display}.
2786 An argument is a repeat count, as in @code{step}.
2793 Execute one machine instruction, but if it is a function call,
2794 proceed until the function returns.
2796 An argument is a repeat count, as in @code{next}.
2804 A signal is an asynchronous event that can happen in a program. The
2805 operating system defines the possible kinds of signals, and gives each
2806 kind a name and a number. For example, in Unix @code{SIGINT} is the
2807 signal a program gets when you type an interrupt (often @kbd{C-c});
2808 @code{SIGSEGV} is the signal a program gets from referencing a place in
2809 memory far away from all the areas in use; @code{SIGALRM} occurs when
2810 the alarm clock timer goes off (which happens only if your program has
2811 requested an alarm).
2813 @cindex fatal signals
2814 Some signals, including @code{SIGALRM}, are a normal part of the
2815 functioning of your program. Others, such as @code{SIGSEGV}, indicate
2816 errors; these signals are @dfn{fatal} (kill your program immediately) if the
2817 program has not specified in advance some other way to handle the signal.
2818 @code{SIGINT} does not indicate an error in your program, but it is normally
2819 fatal so it can carry out the purpose of the interrupt: to kill the program.
2821 @value{GDBN} has the ability to detect any occurrence of a signal in your
2822 program. You can tell @value{GDBN} in advance what to do for each kind of
2825 @cindex handling signals
2826 Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM}
2827 (so as not to interfere with their role in the functioning of your program)
2828 but to stop your program immediately whenever an error signal happens.
2829 You can change these settings with the @code{handle} command.
2833 @kindex info signals
2834 Print a table of all the kinds of signals and how @value{GDBN} has been told to
2835 handle each one. You can use this to see the signal numbers of all
2836 the defined types of signals.
2838 @item handle @var{signal} @var{keywords}@dots{}
2840 Change the way @value{GDBN} handles signal @var{signal}. @var{signal} can be the
2841 number of a signal or its name (with or without the @samp{SIG} at the
2842 beginning). The @var{keywords} say what change to make.
2846 The keywords allowed by the @code{handle} command can be abbreviated.
2847 Their full names are:
2851 @value{GDBN} should not stop your program when this signal happens. It may
2852 still print a message telling you that the signal has come in.
2855 @value{GDBN} should stop your program when this signal happens. This implies
2856 the @code{print} keyword as well.
2859 @value{GDBN} should print a message when this signal happens.
2862 @value{GDBN} should not mention the occurrence of the signal at all. This
2863 implies the @code{nostop} keyword as well.
2866 @value{GDBN} should allow your program to see this signal; your program will be
2867 able to handle the signal, or may be terminated if the signal is fatal
2871 @value{GDBN} should not allow your program to see this signal.
2875 When a signal stops your program, the signal is not visible until you
2876 continue. Your program will see the signal then, if @code{pass} is in
2877 effect for the signal in question @emph{at that time}. In other words,
2878 after @value{GDBN} reports a signal, you can use the @code{handle}
2879 command with @code{pass} or @code{nopass} to control whether that
2880 signal will be seen by your program when you later continue it.
2882 You can also use the @code{signal} command to prevent your program from
2883 seeing a signal, or cause it to see a signal it normally would not see,
2884 or to give it any signal at any time. For example, if your program stopped
2885 due to some sort of memory reference error, you might store correct
2886 values into the erroneous variables and continue, hoping to see more
2887 execution; but your program would probably terminate immediately as
2888 a result of the fatal signal once it saw the signal. To prevent this,
2889 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
2894 @chapter Examining the Stack
2896 When your program has stopped, the first thing you need to know is where it
2897 stopped and how it got there.
2900 Each time your program performs a function call, the information about
2901 where in your program the call was made from is saved in a block of data
2902 called a @dfn{stack frame}. The frame also contains the arguments of the
2903 call and the local variables of the function that was called. All the
2904 stack frames are allocated in a region of memory called the @dfn{call
2907 When your program stops, the @value{GDBN} commands for examining the
2908 stack allow you to see all of this information.
2910 @cindex selected frame
2911 One of the stack frames is @dfn{selected} by @value{GDBN} and many
2912 @value{GDBN} commands refer implicitly to the selected frame. In
2913 particular, whenever you ask @value{GDBN} for the value of a variable in
2914 your program, the value is found in the selected frame. There are
2915 special @value{GDBN} commands to select whichever frame you are
2918 When your program stops, @value{GDBN} automatically selects the
2919 currently executing frame and describes it briefly as the @code{frame}
2920 command does (@pxref{Frame Info, ,Information about a frame}).
2923 * Frames:: Stack frames
2924 * Backtrace:: Backtraces
2925 * Selection:: Selecting a frame
2926 * Frame Info:: Information on a frame
2928 * MIPS Stack:: MIPS machines and the function stack
2933 @section Stack frames
2937 The call stack is divided up into contiguous pieces called @dfn{stack
2938 frames}, or @dfn{frames} for short; each frame is the data associated
2939 with one call to one function. The frame contains the arguments given
2940 to the function, the function's local variables, and the address at
2941 which the function is executing.
2943 @cindex initial frame
2944 @cindex outermost frame
2945 @cindex innermost frame
2946 When your program is started, the stack has only one frame, that of the
2947 function @code{main}. This is called the @dfn{initial} frame or the
2948 @dfn{outermost} frame. Each time a function is called, a new frame is
2949 made. Each time a function returns, the frame for that function invocation
2950 is eliminated. If a function is recursive, there can be many frames for
2951 the same function. The frame for the function in which execution is
2952 actually occurring is called the @dfn{innermost} frame. This is the most
2953 recently created of all the stack frames that still exist.
2955 @cindex frame pointer
2956 Inside your program, stack frames are identified by their addresses. A
2957 stack frame consists of many bytes, each of which has its own address; each
2958 kind of computer has a convention for choosing one of those bytes whose
2959 address serves as the address of the frame. Usually this address is kept
2960 in a register called the @dfn{frame pointer register} while execution is
2961 going on in that frame.
2963 @cindex frame number
2964 @value{GDBN} assigns numbers to all existing stack frames, starting with
2965 zero for the innermost frame, one for the frame that called it,
2966 and so on upward. These numbers do not really exist in your program;
2967 they are assigned by @value{GDBN} to give you a way of designating stack
2968 frames in @value{GDBN} commands.
2970 @cindex frameless execution
2971 Some compilers provide a way to compile functions so that they operate
2972 without stack frames. (For example, the @code{@value{GCC}} option
2973 @samp{-fomit-frame-pointer} will generate functions without a frame.)
2974 This is occasionally done with heavily used library functions to save
2975 the frame setup time. @value{GDBN} has limited facilities for dealing
2976 with these function invocations. If the innermost function invocation
2977 has no stack frame, @value{GDBN} will nevertheless regard it as though
2978 it had a separate frame, which is numbered zero as usual, allowing
2979 correct tracing of the function call chain. However, @value{GDBN} has
2980 no provision for frameless functions elsewhere in the stack.
2985 A backtrace is a summary of how your program got where it is. It shows one
2986 line per frame, for many frames, starting with the currently executing
2987 frame (frame zero), followed by its caller (frame one), and on up the
2995 Print a backtrace of the entire stack: one line per frame for all
2996 frames in the stack.
2998 You can stop the backtrace at any time by typing the system interrupt
2999 character, normally @kbd{C-c}.
3001 @item backtrace @var{n}
3003 Similar, but print only the innermost @var{n} frames.
3005 @item backtrace -@var{n}
3007 Similar, but print only the outermost @var{n} frames.
3013 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3014 are additional aliases for @code{backtrace}.
3016 Each line in the backtrace shows the frame number and the function name.
3017 The program counter value is also shown---unless you use @code{set
3018 print address off}. The backtrace also shows the source file name and
3019 line number, as well as the arguments to the function. The program
3020 counter value is omitted if it is at the beginning of the code for that
3023 Here is an example of a backtrace. It was made with the command
3024 @samp{bt 3}, so it shows the innermost three frames.
3028 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3030 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3031 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3033 (More stack frames follow...)
3038 The display for frame zero does not begin with a program counter
3039 value, indicating that your program has stopped at the beginning of the
3040 code for line @code{993} of @code{builtin.c}.
3043 @section Selecting a frame
3045 Most commands for examining the stack and other data in your program work on
3046 whichever stack frame is selected at the moment. Here are the commands for
3047 selecting a stack frame; all of them finish by printing a brief description
3048 of the stack frame just selected.
3055 Select frame number @var{n}. Recall that frame zero is the innermost
3056 (currently executing) frame, frame one is the frame that called the
3057 innermost one, and so on. The highest-numbered frame is the one for
3060 @item frame @var{addr}
3062 Select the frame at address @var{addr}. This is useful mainly if the
3063 chaining of stack frames has been damaged by a bug, making it
3064 impossible for @value{GDBN} to assign numbers properly to all frames. In
3065 addition, this can be useful when your program has multiple stacks and
3066 switches between them.
3069 On the SPARC architecture, @code{frame} needs two addresses to
3070 select an arbitrary frame: a frame pointer and a stack pointer.
3071 @c note to future updaters: this is conditioned on a flag
3072 @c FRAME_SPECIFICATION_DYADIC in the tm-*.h files, currently only used
3073 @c by SPARC, hence the specific attribution. Generalize or list all
3074 @c possibilities if more supported machines start doing this.
3079 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3080 advances toward the outermost frame, to higher frame numbers, to frames
3081 that have existed longer. @var{n} defaults to one.
3086 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3087 advances toward the innermost frame, to lower frame numbers, to frames
3088 that were created more recently. @var{n} defaults to one. You may
3089 abbreviate @code{down} as @code{do}.
3092 All of these commands end by printing two lines of output describing the
3093 frame. The first line shows the frame number, the function name, the
3094 arguments, and the source file and line number of execution in that
3095 frame. The second line shows the text of that source line.
3101 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3103 10 read_input_file (argv[i]);
3107 After such a printout, the @code{list} command with no arguments will
3108 print ten lines centered on the point of execution in the frame.
3109 @xref{List, ,Printing source lines}.
3112 @item up-silently @var{n}
3113 @itemx down-silently @var{n}
3114 @kindex down-silently
3116 These two commands are variants of @code{up} and @code{down},
3117 respectively; they differ in that they do their work silently, without
3118 causing display of the new frame. They are intended primarily for use
3119 in @value{GDBN} command scripts, where the output might be unnecessary and
3124 @section Information about a frame
3126 There are several other commands to print information about the selected
3132 When used without any argument, this command does not change which
3133 frame is selected, but prints a brief description of the currently
3134 selected stack frame. It can be abbreviated @code{f}. With an
3135 argument, this command is used to select a stack frame.
3136 @xref{Selection, ,Selecting a frame}.
3142 This command prints a verbose description of the selected stack frame,
3143 including the address of the frame, the addresses of the next frame down
3144 (called by this frame) and the next frame up (caller of this frame), the
3145 language that the source code corresponding to this frame was written in,
3146 the address of the frame's arguments, the program counter saved in it
3147 (the address of execution in the caller frame), and which registers
3148 were saved in the frame. The verbose description is useful when
3149 something has gone wrong that has made the stack format fail to fit
3150 the usual conventions.
3152 @item info frame @var{addr}
3153 @itemx info f @var{addr}
3154 Print a verbose description of the frame at address @var{addr},
3155 without selecting that frame. The selected frame remains unchanged by
3160 Print the arguments of the selected frame, each on a separate line.
3164 Print the local variables of the selected frame, each on a separate
3165 line. These are all variables (declared either static or automatic)
3166 accessible at the point of execution of the selected frame.
3171 @cindex catch exceptions
3172 @cindex exception handlers
3173 Print a list of all the exception handlers that are active in the
3174 current stack frame at the current point of execution. To see other
3175 exception handlers, visit the associated frame (using the @code{up},
3176 @code{down}, or @code{frame} commands); then type @code{info catch}.
3177 @xref{Exception Handling, ,Breakpoints and exceptions}.
3183 @section MIPS machines and the function stack
3185 @cindex stack on MIPS
3187 MIPS based computers use an unusual stack frame, which sometimes
3188 requires @value{GDBN} to search backward in the object code to find the
3189 beginning of a function.
3191 @cindex response time, MIPS debugging
3192 To improve response time (especially for embedded applications, where
3193 @value{GDBN} may be restricted to a slow serial line for this search)
3194 you may want to limit the size of this search, using one of these
3196 @c FIXME! So what happens when GDB does *not* find the beginning of a
3199 @cindex @code{heuristic-fence-post} (MIPS)
3201 @item set heuristic-fence-post @var{limit}
3202 Restrict @var{GDBN} to examining at most @var{limit} bytes in its search
3203 for the beginning of a function. A value of @code{0} (the default)
3204 means there is no limit.
3206 @item show heuristic-fence-post
3207 Display the current limit.
3211 These commands are available @emph{only} when @value{GDBN} is configured
3212 for debugging programs on MIPS processors.
3216 @chapter Examining Source Files
3218 @value{GDBN} can print parts of your program's source, since the debugging
3219 information recorded in the program tells @value{GDBN} what source files were
3220 used to build it. When your program stops, @value{GDBN} spontaneously prints
3221 the line where it stopped. Likewise, when you select a stack frame
3222 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
3223 execution in that frame has stopped. You can print other portions of
3224 source files by explicit command.
3227 If you use @value{GDBN} through its GNU Emacs interface, you may prefer to use
3228 Emacs facilities to view source; @pxref{Emacs, ,Using @value{GDBN} under GNU
3233 * List:: Printing source lines
3235 * Search:: Searching source files
3238 * Source Path:: Specifying source directories
3239 * Machine Code:: Source and machine code
3243 @section Printing source lines
3247 To print lines from a source file, use the @code{list} command
3248 (abbreviated @code{l}). There are several ways to specify what part
3249 of the file you want to print.
3251 Here are the forms of the @code{list} command most commonly used:
3254 @item list @var{linenum}
3255 Print lines centered around line number @var{linenum} in the
3256 current source file.
3258 @item list @var{function}
3259 Print lines centered around the beginning of function
3263 Print more lines. If the last lines printed were printed with a
3264 @code{list} command, this prints lines following the last lines
3265 printed; however, if the last line printed was a solitary line printed
3266 as part of displaying a stack frame (@pxref{Stack, ,Examining the
3267 Stack}), this prints lines centered around that line.
3270 Print lines just before the lines last printed.
3273 By default, @value{GDBN} prints ten source lines with any of these forms of
3274 the @code{list} command. You can change this using @code{set listsize}:
3277 @item set listsize @var{count}
3278 @kindex set listsize
3279 Make the @code{list} command display @var{count} source lines (unless
3280 the @code{list} argument explicitly specifies some other number).
3283 @kindex show listsize
3284 Display the number of lines that @code{list} will currently display by
3288 Repeating a @code{list} command with @key{RET} discards the argument,
3289 so it is equivalent to typing just @code{list}. This is more useful
3290 than listing the same lines again. An exception is made for an
3291 argument of @samp{-}; that argument is preserved in repetition so that
3292 each repetition moves up in the source file.
3295 In general, the @code{list} command expects you to supply zero, one or two
3296 @dfn{linespecs}. Linespecs specify source lines; there are several ways
3297 of writing them but the effect is always to specify some source line.
3298 Here is a complete description of the possible arguments for @code{list}:
3301 @item list @var{linespec}
3302 Print lines centered around the line specified by @var{linespec}.
3304 @item list @var{first},@var{last}
3305 Print lines from @var{first} to @var{last}. Both arguments are
3308 @item list ,@var{last}
3309 Print lines ending with @var{last}.
3311 @item list @var{first},
3312 Print lines starting with @var{first}.
3315 Print lines just after the lines last printed.
3318 Print lines just before the lines last printed.
3321 As described in the preceding table.
3324 Here are the ways of specifying a single source line---all the
3329 Specifies line @var{number} of the current source file.
3330 When a @code{list} command has two linespecs, this refers to
3331 the same source file as the first linespec.
3334 Specifies the line @var{offset} lines after the last line printed.
3335 When used as the second linespec in a @code{list} command that has
3336 two, this specifies the line @var{offset} lines down from the
3340 Specifies the line @var{offset} lines before the last line printed.
3342 @item @var{filename}:@var{number}
3343 Specifies line @var{number} in the source file @var{filename}.
3345 @item @var{function}
3346 @c FIXME: "of the open-brace" is C-centric. When we add other langs...
3347 Specifies the line of the open-brace that begins the body of the
3348 function @var{function}.
3350 @item @var{filename}:@var{function}
3351 Specifies the line of the open-brace that begins the body of the
3352 function @var{function} in the file @var{filename}. You only need the
3353 file name with a function name to avoid ambiguity when there are
3354 identically named functions in different source files.
3356 @item *@var{address}
3357 Specifies the line containing the program address @var{address}.
3358 @var{address} may be any expression.
3363 @section Searching source files
3365 @kindex reverse-search
3367 There are two commands for searching through the current source file for a
3371 @item forward-search @var{regexp}
3372 @itemx search @var{regexp}
3374 @kindex forward-search
3375 The command @samp{forward-search @var{regexp}} checks each line,
3376 starting with the one following the last line listed, for a match for
3377 @var{regexp}. It lists the line that is found. You can use
3378 synonym @samp{search @var{regexp}} or abbreviate the command name as
3381 @item reverse-search @var{regexp}
3382 The command @samp{reverse-search @var{regexp}} checks each line, starting
3383 with the one before the last line listed and going backward, for a match
3384 for @var{regexp}. It lists the line that is found. You can abbreviate
3385 this command as @code{rev}.
3390 @section Specifying source directories
3393 @cindex directories for source files
3394 Executable programs sometimes do not record the directories of the source
3395 files from which they were compiled, just the names. Even when they do,
3396 the directories could be moved between the compilation and your debugging
3397 session. @value{GDBN} has a list of directories to search for source files;
3398 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
3399 it tries all the directories in the list, in the order they are present
3400 in the list, until it finds a file with the desired name. Note that
3401 the executable search path is @emph{not} used for this purpose. Neither is
3402 the current working directory, unless it happens to be in the source
3405 If @value{GDBN} cannot find a source file in the source path, and the object
3406 program records a directory, @value{GDBN} tries that directory too. If the
3407 source path is empty, and there is no record of the compilation
3408 directory, @value{GDBN} will, as a last resort, look in the current
3411 Whenever you reset or rearrange the source path, @value{GDBN} will clear out
3412 any information it has cached about where source files are found, where
3413 each line is in the file, etc.
3416 When you start @value{GDBN}, its source path is empty.
3417 To add other directories, use the @code{directory} command.
3420 @item directory @var{dirname} @dots{}
3421 Add directory @var{dirname} to the front of the source path. Several
3422 directory names may be given to this command, separated by @samp{:} or
3423 whitespace. You may specify a directory that is already in the source
3424 path; this moves it forward, so it will be searched sooner.
3426 You can use the string @samp{$cdir} to refer to the compilation
3427 directory (if one is recorded), and @samp{$cwd} to refer to the current
3428 working directory. @samp{$cwd} is not the same as @samp{.}---the former
3429 tracks the current working directory as it changes during your @value{GDBN}
3430 session, while the latter is immediately expanded to the current
3431 directory at the time you add an entry to the source path.
3434 Reset the source path to empty again. This requires confirmation.
3436 @c RET-repeat for @code{directory} is explicitly disabled, but since
3437 @c repeating it would be a no-op we do not say that. (thanks to RMS)
3439 @item show directories
3440 @kindex show directories
3441 Print the source path: show which directories it contains.
3444 If your source path is cluttered with directories that are no longer of
3445 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
3446 versions of source. You can correct the situation as follows:
3450 Use @code{directory} with no argument to reset the source path to empty.
3453 Use @code{directory} with suitable arguments to reinstall the
3454 directories you want in the source path. You can add all the
3455 directories in one command.
3459 @section Source and machine code
3461 You can use the command @code{info line} to map source lines to program
3462 addresses (and vice versa), and the command @code{disassemble} to display
3463 a range of addresses as machine instructions.
3466 @item info line @var{linespec}
3468 Print the starting and ending addresses of the compiled code for
3469 source line @var{linespec}. You can specify source lines in any of
3470 the ways understood by the @code{list} command (@pxref{List, ,Printing
3474 For example, we can use @code{info line} to discover the location of
3475 the object code for the first line of function
3476 @code{m4_changequote}:
3479 (@value{GDBP}) info line m4_changecom
3480 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
3484 We can also inquire (using @code{*@var{addr}} as the form for
3485 @var{linespec}) what source line covers a particular address:
3487 (@value{GDBP}) info line *0x63ff
3488 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
3491 @cindex @code{$_} and @code{info line}
3492 After @code{info line}, the default address for the @code{x} command
3493 is changed to the starting address of the line, so that @samp{x/i} is
3494 sufficient to begin examining the machine code (@pxref{Memory,
3495 ,Examining memory}). Also, this address is saved as the value of the
3496 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
3502 @cindex assembly instructions
3503 @cindex instructions, assembly
3504 @cindex machine instructions
3505 @cindex listing machine instructions
3506 This specialized command dumps a range of memory as machine
3507 instructions. The default memory range is the function surrounding the
3508 program counter of the selected frame. A single argument to this
3509 command is a program counter value; the function surrounding this value
3510 will be dumped. Two arguments specify a range of addresses (first
3511 inclusive, second exclusive) to dump.
3514 @ifclear H8EXCLUSIVE
3515 We can use @code{disassemble} to inspect the object code
3516 range shown in the last @code{info line} example (the example
3517 shows SPARC machine instructions):
3521 (@value{GDBP}) disas 0x63e4 0x6404
3522 Dump of assembler code from 0x63e4 to 0x6404:
3523 0x63e4 <builtin_init+5340>: ble 0x63f8 <builtin_init+5360>
3524 0x63e8 <builtin_init+5344>: sethi %hi(0x4c00), %o0
3525 0x63ec <builtin_init+5348>: ld [%i1+4], %o0
3526 0x63f0 <builtin_init+5352>: b 0x63fc <builtin_init+5364>
3527 0x63f4 <builtin_init+5356>: ld [%o0+4], %o0
3528 0x63f8 <builtin_init+5360>: or %o0, 0x1a4, %o0
3529 0x63fc <builtin_init+5364>: call 0x9288 <path_search>
3530 0x6400 <builtin_init+5368>: nop
3531 End of assembler dump.
3536 For example, here is the beginning of the output for the
3537 disassembly of a function @code{fact}:
3541 (@value{GDBP}) disas fact
3542 Dump of assembler code for function fact:
3544 0x802c <fact>: 6d f2 mov.w r2,@@-r7
3545 0x802e <fact+2>: 6d f3 mov.w r3,@@-r7
3546 0x8030 <fact+4>: 6d f6 mov.w r6,@@-r7
3547 0x8032 <fact+6>: 0d 76 mov.w r7,r6
3548 0x8034 <fact+8>: 6f 70 00 08 mov.w @@(0x8,r7),r0
3549 0x8038 <fact+12> 19 11 sub.w r1,r1
3557 @chapter Examining Data
3559 @cindex printing data
3560 @cindex examining data
3563 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
3564 @c document because it is nonstandard... Under Epoch it displays in a
3565 @c different window or something like that.
3566 The usual way to examine data in your program is with the @code{print}
3567 command (abbreviated @code{p}), or its synonym @code{inspect}.
3569 It evaluates and prints the value of an expression of the language your
3570 program is written in (@pxref{Languages, ,Using @value{GDBN} with Different
3575 @item print @var{exp}
3576 @itemx print /@var{f} @var{exp}
3577 @var{exp} is an expression (in the source language). By default the
3578 value of @var{exp} is printed in a format appropriate to its data type;
3579 you can choose a different format by specifying @samp{/@var{f}}, where
3580 @var{f} is a letter specifying the format; @pxref{Output Formats,,Output
3584 @itemx print /@var{f}
3585 If you omit @var{exp}, @value{GDBN} displays the last value again (from the
3586 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
3587 conveniently inspect the same value in an alternative format.
3590 A more low-level way of examining data is with the @code{x} command.
3591 It examines data in memory at a specified address and prints it in a
3592 specified format. @xref{Memory, ,Examining memory}.
3594 If you are interested in information about types, or about how the fields
3599 are declared, use the @code{ptype @var{exp}}
3600 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol Table}.
3603 * Expressions:: Expressions
3604 * Variables:: Program variables
3605 * Arrays:: Artificial arrays
3606 * Output Formats:: Output formats
3607 * Memory:: Examining memory
3608 * Auto Display:: Automatic display
3609 * Print Settings:: Print settings
3610 * Value History:: Value history
3611 * Convenience Vars:: Convenience variables
3612 * Registers:: Registers
3614 * Floating Point Hardware:: Floating point hardware
3619 @section Expressions
3622 @code{print} and many other @value{GDBN} commands accept an expression and
3623 compute its value. Any kind of constant, variable or operator defined
3624 by the programming language you are using is valid in an expression in
3625 @value{GDBN}. This includes conditional expressions, function calls, casts
3626 and string constants. It unfortunately does not include symbols defined
3627 by preprocessor @code{#define} commands.
3630 Because C is so widespread, most of the expressions shown in examples in
3631 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
3632 Languages}, for information on how to use expressions in other
3635 In this section, we discuss operators that you can use in @value{GDBN}
3636 expressions regardless of your programming language.
3638 Casts are supported in all languages, not just in C, because it is so
3639 useful to cast a number into a pointer so as to examine a structure
3640 at that address in memory.
3641 @c FIXME: casts supported---Mod2 true?
3644 @value{GDBN} supports these operators in addition to those of programming
3649 @samp{@@} is a binary operator for treating parts of memory as arrays.
3650 @xref{Arrays, ,Artificial arrays}, for more information.
3653 @samp{::} allows you to specify a variable in terms of the file or
3654 function where it is defined. @xref{Variables, ,Program variables}.
3656 @item @{@var{type}@} @var{addr}
3657 @cindex @{@var{type}@}
3658 @cindex type casting memory
3659 @cindex memory, viewing as typed object
3660 @cindex casts, to view memory
3661 Refers to an object of type @var{type} stored at address @var{addr} in
3662 memory. @var{addr} may be any expression whose value is an integer or
3663 pointer (but parentheses are required around binary operators, just as in
3664 a cast). This construct is allowed regardless of what kind of data is
3665 normally supposed to reside at @var{addr}.
3669 @section Program variables
3671 The most common kind of expression to use is the name of a variable
3674 Variables in expressions are understood in the selected stack frame
3675 (@pxref{Selection, ,Selecting a frame}); they must either be global
3676 (or static) or be visible according to the scope rules of the
3677 programming language from the point of execution in that frame. This
3678 means that in the function
3693 you can examine and use the variable @code{a} whenever your program is
3694 executing within the function @code{foo}, but you can only use or
3695 examine the variable @code{b} while your program is executing inside
3696 the block where @code{b} is declared.
3698 @cindex variable name conflict
3699 There is an exception: you can refer to a variable or function whose
3700 scope is a single source file even if the current execution point is not
3701 in this file. But it is possible to have more than one such variable or
3702 function with the same name (in different source files). If that
3703 happens, referring to that name has unpredictable effects. If you wish,
3704 you can specify a static variable in a particular function or file,
3705 using the colon-colon notation:
3709 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
3713 @var{file}::@var{variable}
3714 @var{function}::@var{variable}
3718 Here @var{file} or @var{function} is the name of the context for the
3719 static @var{variable}. In the case of file names, you can use quotes to
3720 make sure @value{GDBN} parses the file name as a single word---for example,
3721 to print a global value of @code{x} defined in @file{f2.c}:
3724 (@value{GDBP}) p 'f2.c'::x
3728 @cindex C++ scope resolution
3729 This use of @samp{::} is very rarely in conflict with the very similar
3730 use of the same notation in C++. @value{GDBN} also supports use of the C++
3731 scope resolution operator in @value{GDBN} expressions.
3732 @c FIXME: Um, so what happens in one of those rare cases where it's in
3736 @cindex wrong values
3737 @cindex variable values, wrong
3739 @emph{Warning:} Occasionally, a local variable may appear to have the
3740 wrong value at certain points in a function---just after entry to a new
3741 scope, and just before exit.
3743 You may see this problem when you are stepping by machine instructions.
3744 This is because on most machines, it takes more than one instruction to
3745 set up a stack frame (including local variable definitions); if you are
3746 stepping by machine instructions, variables may appear to have the wrong
3747 values until the stack frame is completely built. On exit, it usually
3748 also takes more than one machine instruction to destroy a stack frame;
3749 after you begin stepping through that group of instructions, local
3750 variable definitions may be gone.
3753 @section Artificial arrays
3755 @cindex artificial array
3757 It is often useful to print out several successive objects of the
3758 same type in memory; a section of an array, or an array of
3759 dynamically determined size for which only a pointer exists in the
3762 You can do this by referring to a contiguous span of memory as an
3763 @dfn{artificial array}, using the binary operator @samp{@@}. The left
3764 operand of @samp{@@} should be the first element of the desired array,
3765 as an individual object. The right operand should be the desired length
3766 of the array. The result is an array value whose elements are all of
3767 the type of the left argument. The first element is actually the left
3768 argument; the second element comes from bytes of memory immediately
3769 following those that hold the first element, and so on. Here is an
3770 example. If a program says
3773 int *array = (int *) malloc (len * sizeof (int));
3777 you can print the contents of @code{array} with
3783 The left operand of @samp{@@} must reside in memory. Array values made
3784 with @samp{@@} in this way behave just like other arrays in terms of
3785 subscripting, and are coerced to pointers when used in expressions.
3786 Artificial arrays most often appear in expressions via the value history
3787 (@pxref{Value History, ,Value history}), after printing one out.)
3789 Sometimes the artificial array mechanism is not quite enough; in
3790 moderately complex data structures, the elements of interest may not
3791 actually be adjacent---for example, if you are interested in the values
3792 of pointers in an array. One useful work-around in this situation is
3793 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
3794 variables}) as a counter in an expression that prints the first
3795 interesting value, and then repeat that expression via @key{RET}. For
3796 instance, suppose you have an array @code{dtab} of pointers to
3797 structures, and you are interested in the values of a field @code{fv}
3798 in each structure. Here is an example of what you might type:
3808 @node Output Formats
3809 @section Output formats
3811 @cindex formatted output
3812 @cindex output formats
3813 By default, @value{GDBN} prints a value according to its data type. Sometimes
3814 this is not what you want. For example, you might want to print a number
3815 in hex, or a pointer in decimal. Or you might want to view data in memory
3816 at a certain address as a character string or as an instruction. To do
3817 these things, specify an @dfn{output format} when you print a value.
3819 The simplest use of output formats is to say how to print a value
3820 already computed. This is done by starting the arguments of the
3821 @code{print} command with a slash and a format letter. The format
3822 letters supported are:
3826 Regard the bits of the value as an integer, and print the integer in
3830 Print as integer in signed decimal.
3833 Print as integer in unsigned decimal.
3836 Print as integer in octal.
3839 Print as integer in binary. The letter @samp{t} stands for ``two''.
3840 @footnote{@samp{b} cannot be used because these format letters are also
3841 used with the @code{x} command, where @samp{b} stands for ``byte'';
3842 @pxref{Memory,,Examining memory}.}
3845 Print as an address, both absolute in hex and as an offset from the
3846 nearest preceding symbol. This format can be used to discover where (in
3847 what function) an unknown address is located:
3850 (@value{GDBP}) p/a 0x54320
3851 $3 = 0x54320 <_initialize_vx+396>
3855 Regard as an integer and print it as a character constant.
3858 Regard the bits of the value as a floating point number and print
3859 using typical floating point syntax.
3862 For example, to print the program counter in hex (@pxref{Registers}), type
3869 Note that no space is required before the slash; this is because command
3870 names in @value{GDBN} cannot contain a slash.
3872 To reprint the last value in the value history with a different format,
3873 you can use the @code{print} command with just a format and no
3874 expression. For example, @samp{p/x} reprints the last value in hex.
3877 @section Examining memory
3879 You can use the command @code{x} (for ``examine'') to examine memory in
3880 any of several formats, independently of your program's data types.
3882 @cindex examining memory
3885 @item x/@var{nfu} @var{addr}
3888 Use the @code{x} command to examine memory.
3891 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
3892 much memory to display and how to format it; @var{addr} is an
3893 expression giving the address where you want to start displaying memory.
3894 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
3895 Several commands set convenient defaults for @var{addr}.
3898 @item @var{n}, the repeat count
3899 The repeat count is a decimal integer; the default is 1. It specifies
3900 how much memory (counting by units @var{u}) to display.
3901 @c This really is **decimal**; unaffected by 'set radix' as of GDB
3904 @item @var{f}, the display format
3905 The display format is one of the formats used by @code{print},
3906 or @samp{s} (null-terminated string) or @samp{i} (machine instruction).
3907 The default is @samp{x} (hexadecimal) initially, or the format from the
3908 last time you used either @code{x} or @code{print}.
3910 @item @var{u}, the unit size
3911 The unit size is any of
3917 Halfwords (two bytes).
3919 Words (four bytes). This is the initial default.
3921 Giant words (eight bytes).
3924 Each time you specify a unit size with @code{x}, that size becomes the
3925 default unit the next time you use @code{x}. (For the @samp{s} and
3926 @samp{i} formats, the unit size is ignored and is normally not written.)
3928 @item @var{addr}, starting display address
3929 @var{addr} is the address where you want @value{GDBN} to begin displaying
3930 memory. The expression need not have a pointer value (though it may);
3931 it is always interpreted as an integer address of a byte of memory.
3932 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
3933 @var{addr} is usually just after the last address examined---but several
3934 other commands also set the default address: @code{info breakpoints} (to
3935 the address of the last breakpoint listed), @code{info line} (to the
3936 starting address of a line), and @code{print} (if you use it to display
3937 a value from memory).
3940 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
3941 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
3942 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
3943 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
3944 @pxref{Registers}) in hexadecimal (@samp{x}).
3946 Since the letters indicating unit sizes are all distinct from the
3947 letters specifying output formats, you do not have to remember whether
3948 unit size or format comes first; either order will work. The output
3949 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
3950 (However, the count @var{n} must come first; @samp{wx4} will not work.)
3952 Even though the unit size @var{u} is ignored for the formats @samp{s}
3953 and @samp{i}, you might still want to use a count @var{n}; for example,
3954 @samp{3i} specifies that you want to see three machine instructions,
3955 including any operands. The command @code{disassemble} gives an
3956 alternative way of inspecting machine instructions; @pxref{Machine
3957 Code,,Source and machine code}.
3959 All the defaults for the arguments to @code{x} are designed to make it
3960 easy to continue scanning memory with minimal specifications each time
3961 you use @code{x}. For example, after you have inspected three machine
3962 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
3963 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
3964 the repeat count @var{n} is used again; the other arguments default as
3965 for successive uses of @code{x}.
3967 @cindex @code{$_}, @code{$__}, and value history
3968 The addresses and contents printed by the @code{x} command are not saved
3969 in the value history because there is often too much of them and they
3970 would get in the way. Instead, @value{GDBN} makes these values available for
3971 subsequent use in expressions as values of the convenience variables
3972 @code{$_} and @code{$__}. After an @code{x} command, the last address
3973 examined is available for use in expressions in the convenience variable
3974 @code{$_}. The contents of that address, as examined, are available in
3975 the convenience variable @code{$__}.
3977 If the @code{x} command has a repeat count, the address and contents saved
3978 are from the last memory unit printed; this is not the same as the last
3979 address printed if several units were printed on the last line of output.
3982 @section Automatic display
3983 @cindex automatic display
3984 @cindex display of expressions
3986 If you find that you want to print the value of an expression frequently
3987 (to see how it changes), you might want to add it to the @dfn{automatic
3988 display list} so that @value{GDBN} will print its value each time your program stops.
3989 Each expression added to the list is given a number to identify it;
3990 to remove an expression from the list, you specify that number.
3991 The automatic display looks like this:
3995 3: bar[5] = (struct hack *) 0x3804
3999 This display shows item numbers, expressions and their current values. As with
4000 displays you request manually using @code{x} or @code{print}, you can
4001 specify the output format you prefer; in fact, @code{display} decides
4002 whether to use @code{print} or @code{x} depending on how elaborate your
4003 format specification is---it uses @code{x} if you specify a unit size,
4004 or one of the two formats (@samp{i} and @samp{s}) that are only
4005 supported by @code{x}; otherwise it uses @code{print}.
4008 @item display @var{exp}
4010 Add the expression @var{exp} to the list of expressions to display
4011 each time your program stops. @xref{Expressions, ,Expressions}.
4013 @code{display} will not repeat if you press @key{RET} again after using it.
4015 @item display/@var{fmt} @var{exp}
4016 For @var{fmt} specifying only a display format and not a size or
4017 count, add the expression @var{exp} to the auto-display list but
4018 arranges to display it each time in the specified format @var{fmt}.
4019 @xref{Output Formats,,Output formats}.
4021 @item display/@var{fmt} @var{addr}
4022 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4023 number of units, add the expression @var{addr} as a memory address to
4024 be examined each time your program stops. Examining means in effect
4025 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4028 For example, @samp{display/i $pc} can be helpful, to see the machine
4029 instruction about to be executed each time execution stops (@samp{$pc}
4030 is a common name for the program counter; @pxref{Registers}).
4033 @item undisplay @var{dnums}@dots{}
4034 @itemx delete display @var{dnums}@dots{}
4035 @kindex delete display
4037 Remove item numbers @var{dnums} from the list of expressions to display.
4039 @code{undisplay} will not repeat if you press @key{RET} after using it.
4040 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4042 @item disable display @var{dnums}@dots{}
4043 @kindex disable display
4044 Disable the display of item numbers @var{dnums}. A disabled display
4045 item is not printed automatically, but is not forgotten. It may be
4046 enabled again later.
4048 @item enable display @var{dnums}@dots{}
4049 @kindex enable display
4050 Enable display of item numbers @var{dnums}. It becomes effective once
4051 again in auto display of its expression, until you specify otherwise.
4054 Display the current values of the expressions on the list, just as is
4055 done when your program stops.
4058 @kindex info display
4059 Print the list of expressions previously set up to display
4060 automatically, each one with its item number, but without showing the
4061 values. This includes disabled expressions, which are marked as such.
4062 It also includes expressions which would not be displayed right now
4063 because they refer to automatic variables not currently available.
4066 If a display expression refers to local variables, then it does not make
4067 sense outside the lexical context for which it was set up. Such an
4068 expression is disabled when execution enters a context where one of its
4069 variables is not defined. For example, if you give the command
4070 @code{display last_char} while inside a function with an argument
4071 @code{last_char}, then this argument will be displayed while your program
4072 continues to stop inside that function. When it stops elsewhere---where
4073 there is no variable @code{last_char}---display is disabled. The next time
4074 your program stops where @code{last_char} is meaningful, you can enable the
4075 display expression once again.
4077 @node Print Settings
4078 @section Print settings
4080 @cindex format options
4081 @cindex print settings
4082 @value{GDBN} provides the following ways to control how arrays, structures,
4083 and symbols are printed.
4086 These settings are useful for debugging programs in any language:
4089 @item set print address
4090 @item set print address on
4091 @kindex set print address
4092 @value{GDBN} will print memory addresses showing the location of stack
4093 traces, structure values, pointer values, breakpoints, and so forth,
4094 even when it also displays the contents of those addresses. The default
4095 is on. For example, this is what a stack frame display looks like, with
4096 @code{set print address on}:
4101 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4103 530 if (lquote != def_lquote)
4107 @item set print address off
4108 Do not print addresses when displaying their contents. For example,
4109 this is the same stack frame displayed with @code{set print address off}:
4113 (@value{GDBP}) set print addr off
4115 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4116 530 if (lquote != def_lquote)
4120 You can use @samp{set print address off} to eliminate all machine
4121 dependent displays from the @value{GDBN} interface. For example, with
4122 @code{print address off}, you should get the same text for backtraces on
4123 all machines---whether or not they involve pointer arguments.
4125 @item show print address
4126 @kindex show print address
4127 Show whether or not addresses are to be printed.
4130 When @value{GDBN} prints a symbolic address, it normally prints the
4131 closest earlier symbol plus an offset. If that symbol does not uniquely
4132 identify the address (for example, it is a name whose scope is a single
4133 source file), you may need to disambiguate. One way to do this is with
4134 @code{info line}, for example @code{info line *0x4537}. Alternately,
4135 you can set @value{GDBN} to print the source file and line number when
4136 it prints a symbolic address:
4139 @item set print symbol-filename on
4140 @kindex set print symbol-filename
4141 Tell @value{GDBN} to print the source file name and line number of a
4142 symbol in the symbolic form of an address.
4144 @item set print symbol-filename off
4145 Do not print source file name and line number of a symbol. This is the
4148 @item show print symbol-filename
4149 @kindex show print symbol-filename
4150 Show whether or not @value{GDBN} will print the source file name and
4151 line number of a symbol in the symbolic form of an address.
4154 Also, you may wish to see the symbolic form only if the address being
4155 printed is reasonably close to the closest earlier symbol:
4158 @item set print max-symbolic-offset @var{max-offset}
4159 @kindex set print max-symbolic-offset
4160 Tell @value{GDBN} to only display the symbolic form of an address if the
4161 offset between the closest earlier symbol and the address is less than
4162 @var{max-offset}. The default is 0, which means to always print the
4163 symbolic form of an address, if any symbol precedes it.
4165 @item show print max-symbolic-offset
4166 @kindex show print max-symbolic-offset
4167 Ask how large the maximum offset is that @value{GDBN} will print in a
4172 @item set print array
4173 @itemx set print array on
4174 @kindex set print array
4175 @value{GDBN} will pretty-print arrays. This format is more convenient to read,
4176 but uses more space. The default is off.
4178 @item set print array off
4179 Return to compressed format for arrays.
4181 @item show print array
4182 @kindex show print array
4183 Show whether compressed or pretty format is selected for displaying
4186 @item set print elements @var{number-of-elements}
4187 @kindex set print elements
4188 If @value{GDBN} is printing a large array, it will stop printing after it has
4189 printed the number of elements set by the @code{set print elements} command.
4190 This limit also applies to the display of strings.
4191 Setting the number of elements to zero means that the printing is unlimited.
4193 @item show print elements
4194 @kindex show print elements
4195 Display the number of elements of a large array that @value{GDBN} will print
4196 before losing patience.
4198 @item set print pretty on
4199 @kindex set print pretty
4200 Cause @value{GDBN} to print structures in an indented format with one member per
4216 @item set print pretty off
4217 Cause @value{GDBN} to print structures in a compact format, like this:
4221 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
4222 meat = 0x54 "Pork"@}
4227 This is the default format.
4229 @item show print pretty
4230 @kindex show print pretty
4231 Show which format @value{GDBN} will use to print structures.
4233 @item set print sevenbit-strings on
4234 @kindex set print sevenbit-strings
4235 Print using only seven-bit characters; if this option is set,
4236 @value{GDBN} will display any eight-bit characters (in strings or character
4237 values) using the notation @code{\}@var{nnn}. For example, @kbd{M-a} is
4238 displayed as @code{\341}.
4240 @item set print sevenbit-strings off
4241 Print using either seven-bit or eight-bit characters, as required. This
4244 @item show print sevenbit-strings
4245 @kindex show print sevenbit-strings
4246 Show whether or not @value{GDBN} will print only seven-bit characters.
4248 @item set print union on
4249 @kindex set print union
4250 Tell @value{GDBN} to print unions which are contained in structures. This is the
4253 @item set print union off
4254 Tell @value{GDBN} not to print unions which are contained in structures.
4256 @item show print union
4257 @kindex show print union
4258 Ask @value{GDBN} whether or not it will print unions which are contained in
4261 For example, given the declarations
4264 typedef enum @{Tree, Bug@} Species;
4265 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
4266 typedef enum @{Caterpillar, Cocoon, Butterfly@}
4277 struct thing foo = @{Tree, @{Acorn@}@};
4281 with @code{set print union on} in effect @samp{p foo} would print
4284 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
4288 and with @code{set print union off} in effect it would print
4291 $1 = @{it = Tree, form = @{...@}@}
4297 These settings are of interest when debugging C++ programs:
4300 @item set print demangle
4301 @itemx set print demangle on
4302 @kindex set print demangle
4303 Print C++ names in their source form rather than in the encoded
4304 (``mangled'') form passed to the assembler and linker for type-safe
4305 linkage. The default is @samp{on}.
4307 @item show print demangle
4308 @kindex show print demangle
4309 Show whether C++ names will be printed in mangled or demangled form.
4311 @item set print asm-demangle
4312 @itemx set print asm-demangle on
4313 @kindex set print asm-demangle
4314 Print C++ names in their source form rather than their mangled form, even
4315 in assembler code printouts such as instruction disassemblies.
4318 @item show print asm-demangle
4319 @kindex show print asm-demangle
4320 Show whether C++ names in assembly listings will be printed in mangled
4323 @item set demangle-style @var{style}
4324 @kindex set demangle-style
4325 @cindex C++ symbol decoding style
4326 @cindex symbol decoding style, C++
4327 Choose among several encoding schemes used by different compilers to
4328 represent C++ names. The choices for @var{style} are currently:
4332 Allow @value{GDBN} to choose a decoding style by inspecting your program.
4335 Decode based on the GNU C++ compiler (@code{g++}) encoding algorithm.
4338 Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm.
4341 Decode using the algorithm in the @cite{C++ Annotated Reference Manual}.
4342 @strong{Warning:} this setting alone is not sufficient to allow
4343 debugging @code{cfront}-generated executables. @value{GDBN} would
4344 require further enhancement to permit that.
4347 @item show demangle-style
4348 @kindex show demangle-style
4349 Display the encoding style currently in use for decoding C++ symbols.
4351 @item set print object
4352 @itemx set print object on
4353 @kindex set print object
4354 When displaying a pointer to an object, identify the @emph{actual}
4355 (derived) type of the object rather than the @emph{declared} type, using
4356 the virtual function table.
4358 @item set print object off
4359 Display only the declared type of objects, without reference to the
4360 virtual function table. This is the default setting.
4362 @item show print object
4363 @kindex show print object
4364 Show whether actual, or declared, object types will be displayed.
4366 @item set print vtbl
4367 @itemx set print vtbl on
4368 @kindex set print vtbl
4369 Pretty print C++ virtual function tables. The default is off.
4371 @item set print vtbl off
4372 Do not pretty print C++ virtual function tables.
4374 @item show print vtbl
4375 @kindex show print vtbl
4376 Show whether C++ virtual function tables are pretty printed, or not.
4381 @section Value history
4383 @cindex value history
4384 Values printed by the @code{print} command are saved in the @value{GDBN} @dfn{value
4385 history} so that you can refer to them in other expressions. Values are
4386 kept until the symbol table is re-read or discarded (for example with
4387 the @code{file} or @code{symbol-file} commands). When the symbol table
4388 changes, the value history is discarded, since the values may contain
4389 pointers back to the types defined in the symbol table.
4393 @cindex history number
4394 The values printed are given @dfn{history numbers} for you to refer to them
4395 by. These are successive integers starting with one. @code{print} shows you
4396 the history number assigned to a value by printing @samp{$@var{num} = }
4397 before the value; here @var{num} is the history number.
4399 To refer to any previous value, use @samp{$} followed by the value's
4400 history number. The way @code{print} labels its output is designed to
4401 remind you of this. Just @code{$} refers to the most recent value in
4402 the history, and @code{$$} refers to the value before that.
4403 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
4404 is the value just prior to @code{$$}, @code{$$1} is equivalent to
4405 @code{$$}, and @code{$$0} is equivalent to @code{$}.
4407 For example, suppose you have just printed a pointer to a structure and
4408 want to see the contents of the structure. It suffices to type
4414 If you have a chain of structures where the component @code{next} points
4415 to the next one, you can print the contents of the next one with this:
4422 You can print successive links in the chain by repeating this
4423 command---which you can do by just typing @key{RET}.
4425 Note that the history records values, not expressions. If the value of
4426 @code{x} is 4 and you type these commands:
4434 then the value recorded in the value history by the @code{print} command
4435 remains 4 even though the value of @code{x} has changed.
4440 Print the last ten values in the value history, with their item numbers.
4441 This is like @samp{p@ $$9} repeated ten times, except that @code{show
4442 values} does not change the history.
4444 @item show values @var{n}
4445 Print ten history values centered on history item number @var{n}.
4448 Print ten history values just after the values last printed. If no more
4449 values are available, produces no display.
4452 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
4453 same effect as @samp{show values +}.
4455 @node Convenience Vars
4456 @section Convenience variables
4458 @cindex convenience variables
4459 @value{GDBN} provides @dfn{convenience variables} that you can use within
4460 @value{GDBN} to hold on to a value and refer to it later. These variables
4461 exist entirely within @value{GDBN}; they are not part of your program, and
4462 setting a convenience variable has no direct effect on further execution
4463 of your program. That is why you can use them freely.
4465 Convenience variables are prefixed with @samp{$}. Any name preceded by
4466 @samp{$} can be used for a convenience variable, unless it is one of
4467 the predefined machine-specific register names (@pxref{Registers}).
4468 (Value history references, in contrast, are @emph{numbers} preceded
4469 by @samp{$}. @xref{Value History, ,Value history}.)
4471 You can save a value in a convenience variable with an assignment
4472 expression, just as you would set a variable in your program.
4476 set $foo = *object_ptr
4480 would save in @code{$foo} the value contained in the object pointed to by
4483 Using a convenience variable for the first time creates it; but its value
4484 is @code{void} until you assign a new value. You can alter the value with
4485 another assignment at any time.
4487 Convenience variables have no fixed types. You can assign a convenience
4488 variable any type of value, including structures and arrays, even if
4489 that variable already has a value of a different type. The convenience
4490 variable, when used as an expression, has the type of its current value.
4493 @item show convenience
4494 @kindex show convenience
4495 Print a list of convenience variables used so far, and their values.
4496 Abbreviated @code{show con}.
4499 One of the ways to use a convenience variable is as a counter to be
4500 incremented or a pointer to be advanced. For example, to print
4501 a field from successive elements of an array of structures:
4505 print bar[$i++]->contents
4506 @i{@dots{} repeat that command by typing @key{RET}.}
4509 Some convenience variables are created automatically by @value{GDBN} and given
4510 values likely to be useful.
4515 The variable @code{$_} is automatically set by the @code{x} command to
4516 the last address examined (@pxref{Memory, ,Examining memory}). Other
4517 commands which provide a default address for @code{x} to examine also
4518 set @code{$_} to that address; these commands include @code{info line}
4519 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
4520 except when set by the @code{x} command, in which case it is a pointer
4521 to the type of @code{$__}.
4525 The variable @code{$__} is automatically set by the @code{x} command
4526 to the value found in the last address examined. Its type is chosen
4527 to match the format in which the data was printed.
4534 You can refer to machine register contents, in expressions, as variables
4535 with names starting with @samp{$}. The names of registers are different
4536 for each machine; use @code{info registers} to see the names used on
4540 @item info registers
4541 @kindex info registers
4542 Print the names and values of all registers except floating-point
4543 registers (in the selected stack frame).
4545 @item info all-registers
4546 @kindex info all-registers
4547 @cindex floating point registers
4548 Print the names and values of all registers, including floating-point
4551 @item info registers @var{regname} @dots{}
4552 Print the relativized value of each specified register @var{regname}.
4553 @var{regname} may be any register name valid on the machine you are using, with
4554 or without the initial @samp{$}.
4557 @value{GDBN} has four ``standard'' register names that are available (in
4558 expressions) on most machines---whenever they do not conflict with an
4559 architecture's canonical mnemonics for registers. The register names
4560 @code{$pc} and @code{$sp} are used for the program counter register and
4561 the stack pointer. @code{$fp} is used for a register that contains a
4562 pointer to the current stack frame, and @code{$ps} is used for a
4563 register that contains the processor status. For example,
4564 you could print the program counter in hex with
4571 or print the instruction to be executed next with
4578 or add four to the stack pointer@footnote{This is a way of removing
4579 one word from the stack, on machines where stacks grow downward in
4580 memory (most machines, nowadays). This assumes that the innermost
4581 stack frame is selected; setting @code{$sp} is not allowed when other
4582 stack frames are selected. To pop entire frames off the stack,
4583 regardless of machine architecture, use @code{return};
4584 @pxref{Returning, ,Returning from a function}.} with
4590 Whenever possible, these four standard register names are available on
4591 your machine even though the machine has different canonical mnemonics,
4592 so long as there is no conflict. The @code{info registers} command
4593 shows the canonical names. For example, on the SPARC, @code{info
4594 registers} displays the processor status register as @code{$psr} but you
4595 can also refer to it as @code{$ps}.
4597 @value{GDBN} always considers the contents of an ordinary register as an
4598 integer when the register is examined in this way. Some machines have
4599 special registers which can hold nothing but floating point; these
4600 registers are considered to have floating point values. There is no way
4601 to refer to the contents of an ordinary register as floating point value
4602 (although you can @emph{print} it as a floating point value with
4603 @samp{print/f $@var{regname}}).
4605 Some registers have distinct ``raw'' and ``virtual'' data formats. This
4606 means that the data format in which the register contents are saved by
4607 the operating system is not the same one that your program normally
4608 sees. For example, the registers of the 68881 floating point
4609 coprocessor are always saved in ``extended'' (raw) format, but all C
4610 programs expect to work with ``double'' (virtual) format. In such
4611 cases, @value{GDBN} normally works with the virtual format only (the format that
4612 makes sense for your program), but the @code{info registers} command
4613 prints the data in both formats.
4615 Normally, register values are relative to the selected stack frame
4616 (@pxref{Selection, ,Selecting a frame}). This means that you get the
4617 value that the register would contain if all stack frames farther in
4618 were exited and their saved registers restored. In order to see the
4619 true contents of hardware registers, you must select the innermost
4620 frame (with @samp{frame 0}).
4622 However, @value{GDBN} must deduce where registers are saved, from the machine
4623 code generated by your compiler. If some registers are not saved, or if
4624 @value{GDBN} is unable to locate the saved registers, the selected stack
4625 frame will make no difference.
4629 @item set rstack_high_address @var{address}
4630 @kindex set rstack_high_address
4631 @cindex AMD 29K register stack
4632 @cindex register stack, AMD29K
4633 On AMD 29000 family processors, registers are saved in a separate
4634 ``register stack''. There is no way for @value{GDBN} to determine the extent
4635 of this stack. Normally, @value{GDBN} just assumes that the stack is ``large
4636 enough''. This may result in @value{GDBN} referencing memory locations that
4637 do not exist. If necessary, you can get around this problem by
4638 specifying the ending address of the register stack with the @code{set
4639 rstack_high_address} command. The argument should be an address, which
4640 you will probably want to precede with @samp{0x} to specify in
4643 @item show rstack_high_address
4644 @kindex show rstack_high_address
4645 Display the current limit of the register stack, on AMD 29000 family
4651 @node Floating Point Hardware
4652 @section Floating point hardware
4653 @cindex floating point
4655 @c FIXME! Really host, not target?
4656 Depending on the host machine architecture, @value{GDBN} may be able to give
4657 you more information about the status of the floating point hardware.
4662 Display hardware-dependent information about the floating
4663 point unit. The exact contents and layout vary depending on the
4664 floating point chip; on some platforms, @samp{info float} is not
4667 @c FIXME: this is a cop-out. Try to get examples, explanations. Only
4668 @c FIXME...supported currently on arm's and 386's. Mark properly with
4669 @c FIXME... m4 macros to isolate general statements from hardware-dep,
4670 @c FIXME... at that point.
4675 @chapter Using @value{GDBN} with Different Languages
4678 Although programming languages generally have common aspects, they are
4679 rarely expressed in the same manner. For instance, in ANSI C,
4680 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
4681 Modula-2, it is accomplished by @code{p^}. Values can also be
4682 represented (and displayed) differently. Hex numbers in C are written
4683 like @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
4685 @cindex working language
4686 Language-specific information is built into @value{GDBN} for some languages,
4687 allowing you to express operations like the above in your program's
4688 native language, and allowing @value{GDBN} to output values in a manner
4689 consistent with the syntax of your program's native language. The
4690 language you use to build expressions, called the @dfn{working
4691 language}, can be selected manually, or @value{GDBN} can set it
4695 * Setting:: Switching between source languages
4696 * Show:: Displaying the language
4697 * Checks:: Type and range checks
4698 * Support:: Supported languages
4702 @section Switching between source languages
4704 There are two ways to control the working language---either have @value{GDBN}
4705 set it automatically, or select it manually yourself. You can use the
4706 @code{set language} command for either purpose. On startup, @value{GDBN}
4707 defaults to setting the language automatically.
4710 * Manually:: Setting the working language manually
4711 * Automatically:: Having @value{GDBN} infer the source language
4715 @subsection Setting the working language
4717 If you allow @value{GDBN} to set the language automatically,
4718 expressions are interpreted the same way in your debugging session and
4721 @kindex set language
4722 If you wish, you may set the language manually. To do this, issue the
4723 command @samp{set language @var{lang}}, where @var{lang} is the name of
4724 a language, such as @code{c} or @code{modula-2}. For a list of the supported
4725 languages, type @samp{set language}.
4726 @c FIXME: rms: eventually this command should be "help set language".
4728 Setting the language manually prevents @value{GDBN} from updating the working
4729 language automatically. This can lead to confusion if you try
4730 to debug a program when the working language is not the same as the
4731 source language, when an expression is acceptable to both
4732 languages---but means different things. For instance, if the current
4733 source file were written in C, and @value{GDBN} was parsing Modula-2, a
4741 might not have the effect you intended. In C, this means to add
4742 @code{b} and @code{c} and place the result in @code{a}. The result
4743 printed would be the value of @code{a}. In Modula-2, this means to compare
4744 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
4747 @subsection Having @value{GDBN} infer the source language
4749 To have @value{GDBN} set the working language automatically, use @samp{set
4750 language local} or @samp{set language auto}. @value{GDBN} then infers the
4751 language that a program was written in by looking at the name of its
4752 source files, and examining their extensions:
4756 Modula-2 source file
4766 This information is recorded for each function or procedure in a source
4767 file. When your program stops in a frame (usually by encountering a
4768 breakpoint), @value{GDBN} sets the working language to the language recorded
4769 for the function in that frame. If the language for a frame is unknown
4770 (that is, if the function or block corresponding to the frame was
4771 defined in a source file that does not have a recognized extension), the
4772 current working language is not changed, and @value{GDBN} issues a warning.
4774 This may not seem necessary for most programs, which are written
4775 entirely in one source language. However, program modules and libraries
4776 written in one source language can be used by a main program written in
4777 a different source language. Using @samp{set language auto} in this
4778 case frees you from having to set the working language manually.
4781 @section Displaying the language
4783 The following commands will help you find out which language is the
4784 working language, and also what language source files were written in.
4786 @kindex show language
4791 Display the current working language. This is the
4792 language you can use with commands such as @code{print} to
4793 build and compute expressions that may involve variables in your program.
4796 Among the other information listed here (@pxref{Frame Info, ,Information
4797 about a frame}) is the source language for this frame. This is the
4798 language that will become the working language if you ever use an
4799 identifier that is in this frame.
4802 Among the other information listed here (@pxref{Symbols, ,Examining the
4803 Symbol Table}) is the source language of this source file.
4807 @section Type and range checking
4810 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
4811 checking are included, but they do not yet have any effect. This
4812 section documents the intended facilities.
4814 @c FIXME remove warning when type/range code added
4816 Some languages are designed to guard you against making seemingly common
4817 errors through a series of compile- and run-time checks. These include
4818 checking the type of arguments to functions and operators, and making
4819 sure mathematical overflows are caught at run time. Checks such as
4820 these help to ensure a program's correctness once it has been compiled
4821 by eliminating type mismatches, and providing active checks for range
4822 errors when your program is running.
4824 @value{GDBN} can check for conditions like the above if you wish.
4825 Although @value{GDBN} will not check the statements in your program, it
4826 can check expressions entered directly into @value{GDBN} for evaluation via
4827 the @code{print} command, for example. As with the working language,
4828 @value{GDBN} can also decide whether or not to check automatically based on
4829 your program's source language. @xref{Support, ,Supported languages},
4830 for the default settings of supported languages.
4833 * Type Checking:: An overview of type checking
4834 * Range Checking:: An overview of range checking
4837 @cindex type checking
4838 @cindex checks, type
4840 @subsection An overview of type checking
4842 Some languages, such as Modula-2, are strongly typed, meaning that the
4843 arguments to operators and functions have to be of the correct type,
4844 otherwise an error occurs. These checks prevent type mismatch
4845 errors from ever causing any run-time problems. For example,
4853 The second example fails because the @code{CARDINAL} 1 is not
4854 type-compatible with the @code{REAL} 2.3.
4856 For expressions you use in @value{GDBN} commands, you can tell the @value{GDBN}
4857 type checker to skip checking; to treat any mismatches as errors and
4858 abandon the expression; or only issue warnings when type mismatches
4859 occur, but evaluate the expression anyway. When you choose the last of
4860 these, @value{GDBN} evaluates expressions like the second example above, but
4861 also issues a warning.
4863 Even though you may turn type checking off, other type-based reasons may
4864 prevent @value{GDBN} from evaluating an expression. For instance, @value{GDBN} does not
4865 know how to add an @code{int} and a @code{struct foo}. These particular
4866 type errors have nothing to do with the language in use, and usually
4867 arise from expressions, such as the one described above, which make
4868 little sense to evaluate anyway.
4870 Each language defines to what degree it is strict about type. For
4871 instance, both Modula-2 and C require the arguments to arithmetical
4872 operators to be numbers. In C, enumerated types and pointers can be
4873 represented as numbers, so that they are valid arguments to mathematical
4874 operators. @xref{Support, ,Supported languages}, for further
4875 details on specific languages.
4877 @value{GDBN} provides some additional commands for controlling the type checker:
4880 @kindex set check type
4881 @kindex show check type
4883 @item set check type auto
4884 Set type checking on or off based on the current working language.
4885 @xref{Support, ,Supported languages}, for the default settings for
4888 @item set check type on
4889 @itemx set check type off
4890 Set type checking on or off, overriding the default setting for the
4891 current working language. Issue a warning if the setting does not
4892 match the language default. If any type mismatches occur in
4893 evaluating an expression while typechecking is on, @value{GDBN} prints a
4894 message and aborts evaluation of the expression.
4896 @item set check type warn
4897 Cause the type checker to issue warnings, but to always attempt to
4898 evaluate the expression. Evaluating the expression may still
4899 be impossible for other reasons. For example, @value{GDBN} cannot add
4900 numbers and structures.
4903 Show the current setting of the type checker, and whether or not @value{GDBN} is
4904 setting it automatically.
4907 @cindex range checking
4908 @cindex checks, range
4909 @node Range Checking
4910 @subsection An overview of range checking
4912 In some languages (such as Modula-2), it is an error to exceed the
4913 bounds of a type; this is enforced with run-time checks. Such range
4914 checking is meant to ensure program correctness by making sure
4915 computations do not overflow, or indices on an array element access do
4916 not exceed the bounds of the array.
4918 For expressions you use in @value{GDBN} commands, you can tell
4919 @value{GDBN} to treat range errors in one of three ways: ignore them,
4920 always treat them as errors and abandon the expression, or issue
4921 warnings but evaluate the expression anyway.
4923 A range error can result from numerical overflow, from exceeding an
4924 array index bound, or when you type a constant that is not a member
4925 of any type. Some languages, however, do not treat overflows as an
4926 error. In many implementations of C, mathematical overflow causes the
4927 result to ``wrap around'' to lower values---for example, if @var{m} is
4928 the largest integer value, and @var{s} is the smallest, then
4931 @var{m} + 1 @result{} @var{s}
4934 This, too, is specific to individual languages, and in some cases
4935 specific to individual compilers or machines. @xref{Support, ,
4936 Supported languages}, for further details on specific languages.
4938 @value{GDBN} provides some additional commands for controlling the range checker:
4941 @kindex set check range
4942 @kindex show check range
4944 @item set check range auto
4945 Set range checking on or off based on the current working language.
4946 @xref{Support, ,Supported languages}, for the default settings for
4949 @item set check range on
4950 @itemx set check range off
4951 Set range checking on or off, overriding the default setting for the
4952 current working language. A warning is issued if the setting does not
4953 match the language default. If a range error occurs, then a message
4954 is printed and evaluation of the expression is aborted.
4956 @item set check range warn
4957 Output messages when the @value{GDBN} range checker detects a range error,
4958 but attempt to evaluate the expression anyway. Evaluating the
4959 expression may still be impossible for other reasons, such as accessing
4960 memory that the process does not own (a typical example from many UNIX
4964 Show the current setting of the range checker, and whether or not it is
4965 being set automatically by @value{GDBN}.
4969 @section Supported languages
4971 @value{GDBN} 4 supports C, C++, and Modula-2. Some @value{GDBN}
4972 features may be used in expressions regardless of the language you
4973 use: the @value{GDBN} @code{@@} and @code{::} operators, and the
4974 @samp{@{type@}addr} construct (@pxref{Expressions, ,Expressions}) can be
4975 used with the constructs of any of the supported languages.
4977 The following sections detail to what degree each of these
4978 source languages is supported by @value{GDBN}. These sections are
4979 not meant to be language tutorials or references, but serve only as a
4980 reference guide to what the @value{GDBN} expression parser will accept, and
4981 what input and output formats should look like for different languages.
4982 There are many good books written on each of these languages; please
4983 look to these for a language reference or tutorial.
4987 * Modula-2:: Modula-2
4991 @subsection C and C++
4993 @cindex expressions in C or C++
4995 Since C and C++ are so closely related, many features of @value{GDBN} apply
4996 to both languages. Whenever this is the case, we discuss both languages
5002 The C++ debugging facilities are jointly implemented by the GNU C++
5003 compiler and @value{GDBN}. Therefore, to debug your C++ code effectively,
5004 you must compile your C++ programs with the GNU C++ compiler,
5009 @chapter C Language Support
5011 @cindex expressions in C
5013 Information specific to the C language is built into @value{GDBN} so that you
5014 can use C expressions while degugging. This also permits @value{GDBN} to
5015 output values in a manner consistent with C conventions.
5018 * C Operators:: C operators
5019 * C Constants:: C constants
5020 * Debugging C:: @value{GDBN} and C
5025 * C Operators:: C and C++ operators
5026 * C Constants:: C and C++ constants
5027 * Cplus expressions:: C++ expressions
5028 * C Defaults:: Default settings for C and C++
5029 * C Checks:: C and C++ type and range checks
5030 * Debugging C:: @value{GDBN} and C
5031 * Debugging C plus plus:: Special features for C++
5036 @cindex C and C++ operators
5038 @subsubsection C and C++ operators
5043 @section C operators
5046 Operators must be defined on values of specific types. For instance,
5047 @code{+} is defined on numbers, but not on structures. Operators are
5048 often defined on groups of types.
5051 For the purposes of C and C++, the following definitions hold:
5056 @emph{Integral types} include @code{int} with any of its storage-class
5057 specifiers; @code{char}; and @code{enum}.
5060 @emph{Floating-point types} include @code{float} and @code{double}.
5063 @emph{Pointer types} include all types defined as @code{(@var{type}
5067 @emph{Scalar types} include all of the above.
5071 The following operators are supported. They are listed here
5072 in order of increasing precedence:
5076 The comma or sequencing operator. Expressions in a comma-separated list
5077 are evaluated from left to right, with the result of the entire
5078 expression being the last expression evaluated.
5081 Assignment. The value of an assignment expression is the value
5082 assigned. Defined on scalar types.
5085 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
5086 and translated to @w{@code{@var{a} = @var{a op b}}}.
5087 @w{@code{@var{op}=}} and @code{=} have the same precendence.
5088 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
5089 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
5092 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
5093 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
5097 Logical @sc{or}. Defined on integral types.
5100 Logical @sc{and}. Defined on integral types.
5103 Bitwise @sc{or}. Defined on integral types.
5106 Bitwise exclusive-@sc{or}. Defined on integral types.
5109 Bitwise @sc{and}. Defined on integral types.
5112 Equality and inequality. Defined on scalar types. The value of these
5113 expressions is 0 for false and non-zero for true.
5115 @item <@r{, }>@r{, }<=@r{, }>=
5116 Less than, greater than, less than or equal, greater than or equal.
5117 Defined on scalar types. The value of these expressions is 0 for false
5118 and non-zero for true.
5121 left shift, and right shift. Defined on integral types.
5124 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
5127 Addition and subtraction. Defined on integral types, floating-point types and
5130 @item *@r{, }/@r{, }%
5131 Multiplication, division, and modulus. Multiplication and division are
5132 defined on integral and floating-point types. Modulus is defined on
5136 Increment and decrement. When appearing before a variable, the
5137 operation is performed before the variable is used in an expression;
5138 when appearing after it, the variable's value is used before the
5139 operation takes place.
5142 Pointer dereferencing. Defined on pointer types. Same precedence as
5146 Address operator. Defined on variables. Same precedence as @code{++}.
5149 For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is
5150 allowed in the C++ language itself: you can use @samp{&(&@var{ref})}
5151 (or, if you prefer, simply @samp{&&@var{ref}} to examine the address
5152 where a C++ reference variable (declared with @samp{&@var{ref}}) is
5157 Negative. Defined on integral and floating-point types. Same
5158 precedence as @code{++}.
5161 Logical negation. Defined on integral types. Same precedence as
5165 Bitwise complement operator. Defined on integral types. Same precedence as
5170 Structure member, and pointer-to-structure member. For convenience,
5171 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
5172 pointer based on the stored type information.
5173 Defined on @code{struct} and @code{union} data.
5176 Array indexing. @code{@var{a}[@var{i}]} is defined as
5177 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
5180 Function parameter list. Same precedence as @code{->}.
5184 C++ scope resolution operator. Defined on
5185 @code{struct}, @code{union}, and @code{class} types.
5193 represent the @value{GDBN} scope operator (@pxref{Expressions,
5196 Same precedence as @code{::}, above.
5201 @cindex C and C++ constants
5203 @subsubsection C and C++ constants
5205 @value{GDBN} allows you to express the constants of C and C++ in the
5211 @section C constants
5213 @value{GDBN} allows you to express the constants of C in the
5219 Integer constants are a sequence of digits. Octal constants are
5220 specified by a leading @samp{0} (ie. zero), and hexadecimal constants by
5221 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
5222 @samp{l}, specifying that the constant should be treated as a
5226 Floating point constants are a sequence of digits, followed by a decimal
5227 point, followed by a sequence of digits, and optionally followed by an
5228 exponent. An exponent is of the form:
5229 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
5230 sequence of digits. The @samp{+} is optional for positive exponents.
5233 Enumerated constants consist of enumerated identifiers, or their
5234 integral equivalents.
5237 Character constants are a single character surrounded by single quotes
5238 (@code{'}), or a number---the ordinal value of the corresponding character
5239 (usually its @sc{ASCII} value). Within quotes, the single character may
5240 be represented by a letter or by @dfn{escape sequences}, which are of
5241 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
5242 of the character's ordinal value; or of the form @samp{\@var{x}}, where
5243 @samp{@var{x}} is a predefined special character---for example,
5244 @samp{\n} for newline.
5247 String constants are a sequence of character constants surrounded
5248 by double quotes (@code{"}).
5251 Pointer constants are an integral value. You can also write pointers
5252 to constants using the C operator @samp{&}.
5255 Array constants are comma-separated lists surrounded by braces @samp{@{}
5256 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
5257 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
5258 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
5262 @node Cplus expressions
5263 @subsubsection C++ expressions
5265 @cindex expressions in C++
5266 @value{GDBN} expression handling has a number of extensions to
5267 interpret a significant subset of C++ expressions.
5269 @cindex C++ support, not in @sc{coff}
5270 @cindex @sc{coff} versus C++
5271 @cindex C++ and object formats
5272 @cindex object formats and C++
5273 @cindex a.out and C++
5274 @cindex @sc{ecoff} and C++
5275 @cindex @sc{xcoff} and C++
5276 @cindex @sc{elf}/stabs and C++
5277 @cindex @sc{elf}/@sc{dwarf} and C++
5279 @emph{Warning:} Most of these extensions depend on the use of additional
5280 debugging information in the symbol table, and thus require a rich,
5281 extendable object code format. In particular, if your system uses
5282 a.out, MIPS @sc{ecoff}, RS/6000 @sc{xcoff}, or Sun @sc{elf} with stabs
5283 extensions to the symbol table, these facilities are all available.
5284 Where the object code format is standard @sc{coff}, on the other hand,
5285 most of the C++ support in @value{GDBN} will @emph{not} work, nor can it.
5286 For the standard SVr4 debugging format, @sc{dwarf} in @sc{elf}, the
5287 standard is still evolving, so the C++ support in @value{GDBN} is still
5288 fragile; when this debugging format stabilizes, however, C++ support
5289 will also be available on systems that use it.
5294 @cindex member functions
5296 Member function calls are allowed; you can use expressions like
5299 count = aml->GetOriginal(x, y)
5303 @cindex namespace in C++
5305 While a member function is active (in the selected stack frame), your
5306 expressions have the same namespace available as the member function;
5307 that is, @value{GDBN} allows implicit references to the class instance
5308 pointer @code{this} following the same rules as C++.
5310 @cindex call overloaded functions
5311 @cindex type conversions in C++
5313 You can call overloaded functions; @value{GDBN} will resolve the function
5314 call to the right definition, with one restriction---you must use
5315 arguments of the type required by the function that you want to call.
5316 @value{GDBN} will not perform conversions requiring constructors or
5317 user-defined type operators.
5319 @cindex reference declarations
5321 @value{GDBN} understands variables declared as C++ references; you can use them in
5322 expressions just as you do in C++ source---they are automatically
5325 In the parameter list shown when @value{GDBN} displays a frame, the values of
5326 reference variables are not displayed (unlike other variables); this
5327 avoids clutter, since references are often used for large structures.
5328 The @emph{address} of a reference variable is always shown, unless
5329 you have specified @samp{set print address off}.
5332 @value{GDBN} supports the C++ name resolution operator @code{::}---your
5333 expressions can use it just as expressions in your program do. Since
5334 one scope may be defined in another, you can use @code{::} repeatedly if
5335 necessary, for example in an expression like
5336 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
5337 resolving name scope by reference to source files, in both C and C++
5338 debugging (@pxref{Variables, ,Program variables}).
5342 @subsubsection C and C++ defaults
5343 @cindex C and C++ defaults
5345 If you allow @value{GDBN} to set type and range checking automatically, they
5346 both default to @code{off} whenever the working language changes to
5347 C or C++. This happens regardless of whether you, or @value{GDBN},
5348 selected the working language.
5350 If you allow @value{GDBN} to set the language automatically, it sets the
5351 working language to C or C++ on entering code compiled from a source file
5352 whose name ends with @file{.c}, @file{.C}, or @file{.cc}.
5353 @xref{Automatically, ,Having @value{GDBN} infer the source language}, for
5357 @subsubsection C and C++ type and range checks
5358 @cindex C and C++ checks
5360 By default, when @value{GDBN} parses C or C++ expressions, type checking
5361 is not used. However, if you turn type checking on, @value{GDBN} will
5362 consider two variables type equivalent if:
5366 The two variables are structured and have the same structure, union, or
5370 Two two variables have the same type name, or types that have been
5371 declared equivalent through @code{typedef}.
5374 @c leaving this out because neither J Gilmore nor R Pesch understand it.
5377 The two @code{struct}, @code{union}, or @code{enum} variables are
5378 declared in the same declaration. (Note: this may not be true for all C
5383 Range checking, if turned on, is done on mathematical operations. Array
5384 indices are not checked, since they are often used to index a pointer
5385 that is not itself an array.
5390 @subsubsection @value{GDBN} and C
5394 @section @value{GDBN} and C
5397 The @code{set print union} and @code{show print union} commands apply to
5398 the @code{union} type. When set to @samp{on}, any @code{union} that is
5399 inside a @code{struct}
5403 will also be printed.
5404 Otherwise, it will appear as @samp{@{...@}}.
5406 The @code{@@} operator aids in the debugging of dynamic arrays, formed
5407 with pointers and a memory allocation function. @xref{Expressions,
5411 @node Debugging C plus plus
5412 @subsubsection @value{GDBN} features for C++
5414 @cindex commands for C++
5415 Some @value{GDBN} commands are particularly useful with C++, and some are
5416 designed specifically for use with C++. Here is a summary:
5419 @cindex break in overloaded functions
5420 @item @r{breakpoint menus}
5421 When you want a breakpoint in a function whose name is overloaded,
5422 @value{GDBN} breakpoint menus help you specify which function definition
5423 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
5425 @cindex overloading in C++
5426 @item rbreak @var{regex}
5427 Setting breakpoints using regular expressions is helpful for setting
5428 breakpoints on overloaded functions that are not members of any special
5430 @xref{Set Breaks, ,Setting breakpoints}.
5432 @cindex C++ exception handling
5433 @item catch @var{exceptions}
5435 Debug C++ exception handling using these commands. @xref{Exception
5436 Handling, ,Breakpoints and exceptions}.
5439 @item ptype @var{typename}
5440 Print inheritance relationships as well as other information for type
5442 @xref{Symbols, ,Examining the Symbol Table}.
5444 @cindex C++ symbol display
5445 @item set print demangle
5446 @itemx show print demangle
5447 @itemx set print asm-demangle
5448 @itemx show print asm-demangle
5449 Control whether C++ symbols display in their source form, both when
5450 displaying code as C++ source and when displaying disassemblies.
5451 @xref{Print Settings, ,Print settings}.
5453 @item set print object
5454 @itemx show print object
5455 Choose whether to print derived (actual) or declared types of objects.
5456 @xref{Print Settings, ,Print settings}.
5458 @item set print vtbl
5459 @itemx show print vtbl
5460 Control the format for printing virtual function tables.
5461 @xref{Print Settings, ,Print settings}.
5463 @item @r{Overloaded symbol names}
5464 You can specify a particular definition of an overloaded symbol, using
5465 the same notation that is used to declare such symbols in C++: type
5466 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
5467 also use the @value{GDBN} command-line word completion facilities to list the
5468 available choices, or to finish the type list for you.
5469 @xref{Completion,, Command completion}, for details on how to do this.
5473 @subsection Modula-2
5476 The extensions made to @value{GDBN} to support Modula-2 only support
5477 output from the GNU Modula-2 compiler (which is currently being
5478 developed). Other Modula-2 compilers are not currently supported, and
5479 attempting to debug executables produced by them will most likely
5480 result in an error as @value{GDBN} reads in the executable's symbol
5483 @cindex expressions in Modula-2
5485 * M2 Operators:: Built-in operators
5486 * Built-In Func/Proc:: Built-in functions and procedures
5487 * M2 Constants:: Modula-2 constants
5488 * M2 Defaults:: Default settings for Modula-2
5489 * Deviations:: Deviations from standard Modula-2
5490 * M2 Checks:: Modula-2 type and range checks
5491 * M2 Scope:: The scope operators @code{::} and @code{.}
5492 * GDB/M2:: @value{GDBN} and Modula-2
5496 @subsubsection Operators
5497 @cindex Modula-2 operators
5499 Operators must be defined on values of specific types. For instance,
5500 @code{+} is defined on numbers, but not on structures. Operators are
5501 often defined on groups of types. For the purposes of Modula-2, the
5502 following definitions hold:
5507 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
5511 @emph{Character types} consist of @code{CHAR} and its subranges.
5514 @emph{Floating-point types} consist of @code{REAL}.
5517 @emph{Pointer types} consist of anything declared as @code{POINTER TO
5521 @emph{Scalar types} consist of all of the above.
5524 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
5527 @emph{Boolean types} consist of @code{BOOLEAN}.
5531 The following operators are supported, and appear in order of
5532 increasing precedence:
5536 Function argument or array index separator.
5539 Assignment. The value of @var{var} @code{:=} @var{value} is
5543 Less than, greater than on integral, floating-point, or enumerated
5547 Less than, greater than, less than or equal to, greater than or equal to
5548 on integral, floating-point and enumerated types, or set inclusion on
5549 set types. Same precedence as @code{<}.
5551 @item =@r{, }<>@r{, }#
5552 Equality and two ways of expressing inequality, valid on scalar types.
5553 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
5554 available for inequality, since @code{#} conflicts with the script
5558 Set membership. Defined on set types and the types of their members.
5559 Same precedence as @code{<}.
5562 Boolean disjunction. Defined on boolean types.
5565 Boolean conjuction. Defined on boolean types.
5568 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
5571 Addition and subtraction on integral and floating-point types, or union
5572 and difference on set types.
5575 Multiplication on integral and floating-point types, or set intersection
5579 Division on floating-point types, or symmetric set difference on set
5580 types. Same precedence as @code{*}.
5583 Integer division and remainder. Defined on integral types. Same
5584 precedence as @code{*}.
5587 Negative. Defined on @code{INTEGER} and @code{REAL} data.
5590 Pointer dereferencing. Defined on pointer types.
5593 Boolean negation. Defined on boolean types. Same precedence as
5597 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
5598 precedence as @code{^}.
5601 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
5604 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
5608 @value{GDBN} and Modula-2 scope operators.
5612 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
5613 will treat the use of the operator @code{IN}, or the use of operators
5614 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
5615 @code{<=}, and @code{>=} on sets as an error.
5618 @cindex Modula-2 built-ins
5619 @node Built-In Func/Proc
5620 @subsubsection Built-in functions and procedures
5622 Modula-2 also makes available several built-in procedures and functions.
5623 In describing these, the following metavariables are used:
5628 represents an @code{ARRAY} variable.
5631 represents a @code{CHAR} constant or variable.
5634 represents a variable or constant of integral type.
5637 represents an identifier that belongs to a set. Generally used in the
5638 same function with the metavariable @var{s}. The type of @var{s} should
5639 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}.
5642 represents a variable or constant of integral or floating-point type.
5645 represents a variable or constant of floating-point type.
5651 represents a variable.
5654 represents a variable or constant of one of many types. See the
5655 explanation of the function for details.
5658 All Modula-2 built-in procedures also return a result, described below.
5662 Returns the absolute value of @var{n}.
5665 If @var{c} is a lower case letter, it returns its upper case
5666 equivalent, otherwise it returns its argument
5669 Returns the character whose ordinal value is @var{i}.
5672 Decrements the value in the variable @var{v}. Returns the new value.
5674 @item DEC(@var{v},@var{i})
5675 Decrements the value in the variable @var{v} by @var{i}. Returns the
5678 @item EXCL(@var{m},@var{s})
5679 Removes the element @var{m} from the set @var{s}. Returns the new
5682 @item FLOAT(@var{i})
5683 Returns the floating point equivalent of the integer @var{i}.
5686 Returns the index of the last member of @var{a}.
5689 Increments the value in the variable @var{v}. Returns the new value.
5691 @item INC(@var{v},@var{i})
5692 Increments the value in the variable @var{v} by @var{i}. Returns the
5695 @item INCL(@var{m},@var{s})
5696 Adds the element @var{m} to the set @var{s} if it is not already
5697 there. Returns the new set.
5700 Returns the maximum value of the type @var{t}.
5703 Returns the minimum value of the type @var{t}.
5706 Returns boolean TRUE if @var{i} is an odd number.
5709 Returns the ordinal value of its argument. For example, the ordinal
5710 value of a character is its ASCII value (on machines supporting the
5711 ASCII character set). @var{x} must be of an ordered type, which include
5712 integral, character and enumerated types.
5715 Returns the size of its argument. @var{x} can be a variable or a type.
5717 @item TRUNC(@var{r})
5718 Returns the integral part of @var{r}.
5720 @item VAL(@var{t},@var{i})
5721 Returns the member of the type @var{t} whose ordinal value is @var{i}.
5725 @emph{Warning:} Sets and their operations are not yet supported, so
5726 @value{GDBN} will treat the use of procedures @code{INCL} and @code{EXCL} as
5730 @cindex Modula-2 constants
5732 @subsubsection Constants
5734 @value{GDBN} allows you to express the constants of Modula-2 in the following
5740 Integer constants are simply a sequence of digits. When used in an
5741 expression, a constant is interpreted to be type-compatible with the
5742 rest of the expression. Hexadecimal integers are specified by a
5743 trailing @samp{H}, and octal integers by a trailing @samp{B}.
5746 Floating point constants appear as a sequence of digits, followed by a
5747 decimal point and another sequence of digits. An optional exponent can
5748 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
5749 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
5750 digits of the floating point constant must be valid decimal (base 10)
5754 Character constants consist of a single character enclosed by a pair of
5755 like quotes, either single (@code{'}) or double (@code{"}). They may
5756 also be expressed by their ordinal value (their ASCII value, usually)
5757 followed by a @samp{C}.
5760 String constants consist of a sequence of characters enclosed by a
5761 pair of like quotes, either single (@code{'}) or double (@code{"}).
5762 Escape sequences in the style of C are also allowed. @xref{C
5763 Constants, ,C and C++ constants}, for a brief explanation of escape
5767 Enumerated constants consist of an enumerated identifier.
5770 Boolean constants consist of the identifiers @code{TRUE} and
5774 Pointer constants consist of integral values only.
5777 Set constants are not yet supported.
5781 @subsubsection Modula-2 defaults
5782 @cindex Modula-2 defaults
5784 If type and range checking are set automatically by @value{GDBN}, they
5785 both default to @code{on} whenever the working language changes to
5786 Modula-2. This happens regardless of whether you, or @value{GDBN},
5787 selected the working language.
5789 If you allow @value{GDBN} to set the language automatically, then entering
5790 code compiled from a file whose name ends with @file{.mod} will set the
5791 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
5792 the language automatically}, for further details.
5795 @subsubsection Deviations from standard Modula-2
5796 @cindex Modula-2, deviations from
5798 A few changes have been made to make Modula-2 programs easier to debug.
5799 This is done primarily via loosening its type strictness:
5803 Unlike in standard Modula-2, pointer constants can be formed by
5804 integers. This allows you to modify pointer variables during
5805 debugging. (In standard Modula-2, the actual address contained in a
5806 pointer variable is hidden from you; it can only be modified
5807 through direct assignment to another pointer variable or expression that
5808 returned a pointer.)
5811 C escape sequences can be used in strings and characters to represent
5812 non-printable characters. @value{GDBN} will print out strings with these
5813 escape sequences embedded. Single non-printable characters are
5814 printed using the @samp{CHR(@var{nnn})} format.
5817 The assignment operator (@code{:=}) returns the value of its right-hand
5821 All built-in procedures both modify @emph{and} return their argument.
5825 @subsubsection Modula-2 type and range checks
5826 @cindex Modula-2 checks
5829 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
5832 @c FIXME remove warning when type/range checks added
5834 @value{GDBN} considers two Modula-2 variables type equivalent if:
5838 They are of types that have been declared equivalent via a @code{TYPE
5839 @var{t1} = @var{t2}} statement
5842 They have been declared on the same line. (Note: This is true of the
5843 GNU Modula-2 compiler, but it may not be true of other compilers.)
5846 As long as type checking is enabled, any attempt to combine variables
5847 whose types are not equivalent is an error.
5849 Range checking is done on all mathematical operations, assignment, array
5850 index bounds, and all built-in functions and procedures.
5853 @subsubsection The scope operators @code{::} and @code{.}
5856 @cindex colon, doubled as scope operator
5859 @c Info cannot handle :: but TeX can.
5865 There are a few subtle differences between the Modula-2 scope operator
5866 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
5871 @var{module} . @var{id}
5872 @var{scope} :: @var{id}
5876 where @var{scope} is the name of a module or a procedure,
5877 @var{module} the name of a module, and @var{id} is any declared
5878 identifier within your program, except another module.
5880 Using the @code{::} operator makes @value{GDBN} search the scope
5881 specified by @var{scope} for the identifier @var{id}. If it is not
5882 found in the specified scope, then @value{GDBN} will search all scopes
5883 enclosing the one specified by @var{scope}.
5885 Using the @code{.} operator makes @value{GDBN} search the current scope for
5886 the identifier specified by @var{id} that was imported from the
5887 definition module specified by @var{module}. With this operator, it is
5888 an error if the identifier @var{id} was not imported from definition
5889 module @var{module}, or if @var{id} is not an identifier in
5893 @subsubsection @value{GDBN} and Modula-2
5895 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
5896 Five subcommands of @code{set print} and @code{show print} apply
5897 specifically to C and C++: @samp{vtbl}, @samp{demangle},
5898 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
5899 apply to C++, and the last to the C @code{union} type, which has no direct
5900 analogue in Modula-2.
5902 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
5903 while using any language, is not useful with Modula-2. Its
5904 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
5905 created in Modula-2 as they can in C or C++. However, because an
5906 address can be specified by an integral constant, the construct
5907 @samp{@{@var{type}@}@var{adrexp}} is still useful. (@pxref{Expressions, ,Expressions})
5909 @cindex @code{#} in Modula-2
5910 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
5911 interpreted as the beginning of a comment. Use @code{<>} instead.
5916 @chapter Examining the Symbol Table
5918 The commands described in this section allow you to inquire about the
5919 symbols (names of variables, functions and types) defined in your
5920 program. This information is inherent in the text of your program and
5921 does not change as your program executes. @value{GDBN} finds it in your
5922 program's symbol table, in the file indicated when you started @value{GDBN}
5923 (@pxref{File Options, ,Choosing files}), or by one of the
5924 file-management commands (@pxref{Files, ,Commands to specify files}).
5926 @c FIXME! This might be intentionally specific to C and C++; if so, move
5927 @c to someplace in C section of lang chapter.
5928 @cindex symbol names
5929 @cindex names of symbols
5930 @cindex quoting names
5931 Occasionally, you may need to refer to symbols that contain unusual
5932 characters, which @value{GDBN} ordinarily treats as word delimiters. The
5933 most frequent case is in referring to static variables in other
5934 source files (@pxref{Variables,,Program variables}). File names
5935 are recorded in object files as debugging symbols, but @value{GDBN} would
5936 ordinarily parse a typical file name, like @file{foo.c}, as the three words
5937 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
5938 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
5945 looks up the value of @code{x} in the scope of the file @file{foo.c}.
5948 @item info address @var{symbol}
5949 @kindex info address
5950 Describe where the data for @var{symbol} is stored. For a register
5951 variable, this says which register it is kept in. For a non-register
5952 local variable, this prints the stack-frame offset at which the variable
5955 Note the contrast with @samp{print &@var{symbol}}, which does not work
5956 at all for a register variables, and for a stack local variable prints
5957 the exact address of the current instantiation of the variable.
5959 @item whatis @var{exp}
5961 Print the data type of expression @var{exp}. @var{exp} is not
5962 actually evaluated, and any side-effecting operations (such as
5963 assignments or function calls) inside it do not take place.
5964 @xref{Expressions, ,Expressions}.
5967 Print the data type of @code{$}, the last value in the value history.
5969 @item ptype @var{typename}
5971 Print a description of data type @var{typename}. @var{typename} may be
5972 the name of a type, or for C code it may have the form
5973 @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or
5974 @samp{enum @var{enum-tag}}.
5976 @item ptype @var{exp}
5978 Print a description of the type of expression @var{exp}. @code{ptype}
5979 differs from @code{whatis} by printing a detailed description, instead
5980 of just the name of the type.
5982 For example, for this variable declaration:
5985 struct complex @{double real; double imag;@} v;
5989 the two commands give this output:
5993 (@value{GDBP}) whatis v
5994 type = struct complex
5995 (@value{GDBP}) ptype v
5996 type = struct complex @{
6004 As with @code{whatis}, using @code{ptype} without an argument refers to
6005 the type of @code{$}, the last value in the value history.
6007 @item info types @var{regexp}
6010 Print a brief description of all types whose name matches @var{regexp}
6011 (or all types in your program, if you supply no argument). Each
6012 complete typename is matched as though it were a complete line; thus,
6013 @samp{i type value} gives information on all types in your program whose
6014 name includes the string @code{value}, but @samp{i type ^value$} gives
6015 information only on types whose complete name is @code{value}.
6017 This command differs from @code{ptype} in two ways: first, like
6018 @code{whatis}, it does not print a detailed description; second, it
6019 lists all source files where a type is defined.
6023 Show the name of the current source file---that is, the source file for
6024 the function containing the current point of execution---and the language
6028 @kindex info sources
6029 Print the names of all source files in your program for which there is
6030 debugging information, organized into two lists: files whose symbols
6031 have already been read, and files whose symbols will be read when needed.
6033 @item info functions
6034 @kindex info functions
6035 Print the names and data types of all defined functions.
6037 @item info functions @var{regexp}
6038 Print the names and data types of all defined functions
6039 whose names contain a match for regular expression @var{regexp}.
6040 Thus, @samp{info fun step} finds all functions whose names
6041 include @code{step}; @samp{info fun ^step} finds those whose names
6042 start with @code{step}.
6044 @item info variables
6045 @kindex info variables
6046 Print the names and data types of all variables that are declared
6047 outside of functions (i.e., excluding local variables).
6049 @item info variables @var{regexp}
6050 Print the names and data types of all variables (except for local
6051 variables) whose names contain a match for regular expression
6055 This was never implemented.
6057 @itemx info methods @var{regexp}
6058 @kindex info methods
6059 The @code{info methods} command permits the user to examine all defined
6060 methods within C++ program, or (with the @var{regexp} argument) a
6061 specific set of methods found in the various C++ classes. Many
6062 C++ classes provide a large number of methods. Thus, the output
6063 from the @code{ptype} command can be overwhelming and hard to use. The
6064 @code{info-methods} command filters the methods, printing only those
6065 which match the regular-expression @var{regexp}.
6068 @item maint print symbols @var{filename}
6069 @itemx maint print psymbols @var{filename}
6070 @itemx maint print msymbols @var{filename}
6071 @kindex maint print symbols
6073 @kindex maint print psymbols
6074 @cindex partial symbol dump
6075 Write a dump of debugging symbol data into the file @var{filename}.
6076 These commands are used to debug the @value{GDBN} symbol-reading code. Only
6077 symbols with debugging data are included. If you use @samp{maint print
6078 symbols}, @value{GDBN} includes all the symbols for which it has already
6079 collected full details: that is, @var{filename} reflects symbols for
6080 only those files whose symbols @value{GDBN} has read. You can use the
6081 command @code{info sources} to find out which files these are. If you
6082 use @samp{maint print psymbols} instead, the dump shows information about
6083 symbols that @value{GDBN} only knows partially---that is, symbols defined in
6084 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
6085 @samp{maint print msymbols} dumps just the minimal symbol information
6086 required for each object file from which @value{GDBN} has read some symbols.
6087 The description of @code{symbol-file} explains how @value{GDBN} reads
6088 symbols; both @code{info source} and @code{symbol-file} are described in
6089 @ref{Files, ,Commands to specify files}.
6093 @chapter Altering Execution
6095 Once you think you have found an error in your program, you might want to
6096 find out for certain whether correcting the apparent error would lead to
6097 correct results in the rest of the run. You can find the answer by
6098 experiment, using the @value{GDBN} features for altering execution of the
6101 For example, you can store new values into variables or memory
6104 give your program a signal, restart it
6107 restart your program
6109 at a different address, or even return prematurely from a function to
6113 * Assignment:: Assignment to variables
6114 * Jumping:: Continuing at a different address
6116 * Signaling:: Giving your program a signal
6119 * Returning:: Returning from a function
6120 * Calling:: Calling your program's functions
6121 * Patching:: Patching your program
6125 @section Assignment to variables
6128 @cindex setting variables
6129 To alter the value of a variable, evaluate an assignment expression.
6130 @xref{Expressions, ,Expressions}. For example,
6137 stores the value 4 into the variable @code{x}, and then prints the
6138 value of the assignment expression (which is 4).
6140 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
6141 information on operators in supported languages.
6144 @kindex set variable
6145 @cindex variables, setting
6146 If you are not interested in seeing the value of the assignment, use the
6147 @code{set} command instead of the @code{print} command. @code{set} is
6148 really the same as @code{print} except that the expression's value is
6149 not printed and is not put in the value history (@pxref{Value History,
6150 ,Value history}). The expression is evaluated only for its effects.
6152 If the beginning of the argument string of the @code{set} command
6153 appears identical to a @code{set} subcommand, use the @code{set
6154 variable} command instead of just @code{set}. This command is identical
6155 to @code{set} except for its lack of subcommands. For example, if
6156 your program has a variable @code{width}, you get
6157 an error if you try to set a new value with just @samp{set width=13},
6158 because @value{GDBN} has the command @code{set width}:
6161 (@value{GDBP}) whatis width
6163 (@value{GDBP}) p width
6165 (@value{GDBP}) set width=47
6166 Invalid syntax in expression.
6170 The invalid expression, of course, is @samp{=47}. In
6171 order to actually set the program's variable @code{width}, use
6174 (@value{GDBP}) set var width=47
6177 @value{GDBN} allows more implicit conversions in assignments than C; you can
6178 freely store an integer value into a pointer variable or vice versa,
6179 and you can convert any structure to any other structure that is the
6180 same length or shorter.
6181 @comment FIXME: how do structs align/pad in these conversions?
6182 @comment /pesch@cygnus.com 18dec1990
6184 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
6185 construct to generate a value of specified type at a specified address
6186 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
6187 to memory location @code{0x83040} as an integer (which implies a certain size
6188 and representation in memory), and
6191 set @{int@}0x83040 = 4
6195 stores the value 4 into that memory location.
6198 @section Continuing at a different address
6200 Ordinarily, when you continue your program, you do so at the place where
6201 it stopped, with the @code{continue} command. You can instead continue at
6202 an address of your own choosing, with the following commands:
6205 @item jump @var{linespec}
6207 Resume execution at line @var{linespec}. Execution will stop
6208 immediately if there is a breakpoint there. @xref{List, ,Printing
6209 source lines}, for a description of the different forms of
6212 The @code{jump} command does not change the current stack frame, or
6213 the stack pointer, or the contents of any memory location or any
6214 register other than the program counter. If line @var{linespec} is in
6215 a different function from the one currently executing, the results may
6216 be bizarre if the two functions expect different patterns of arguments or
6217 of local variables. For this reason, the @code{jump} command requests
6218 confirmation if the specified line is not in the function currently
6219 executing. However, even bizarre results are predictable if you are
6220 well acquainted with the machine-language code of your program.
6222 @item jump *@var{address}
6223 Resume execution at the instruction at address @var{address}.
6226 You can get much the same effect as the @code{jump} command by storing a
6227 new value into the register @code{$pc}. The difference is that this
6228 does not start your program running; it only changes the address where it
6229 @emph{will} run when it is continued. For example,
6236 causes the next @code{continue} command or stepping command to execute at
6237 address @code{0x485}, rather than at the address where your program stopped.
6238 @xref{Continuing and Stepping, ,Continuing and stepping}.
6240 The most common occasion to use the @code{jump} command is to back up,
6241 perhaps with more breakpoints set, over a portion of a program that has
6242 already executed, in order to examine its execution in more detail.
6247 @section Giving your program a signal
6250 @item signal @var{signalnum}
6252 Resume execution where your program stopped, but give it immediately the
6253 signal number @var{signalnum}.
6255 Alternatively, if @var{signalnum} is zero, continue execution without
6256 giving a signal. This is useful when your program stopped on account of
6257 a signal and would ordinary see the signal when resumed with the
6258 @code{continue} command; @samp{signal 0} causes it to resume without a
6261 @code{signal} does not repeat when you press @key{RET} a second time
6262 after executing the command.
6268 @section Returning from a function
6272 @itemx return @var{expression}
6273 @cindex returning from a function
6275 You can cancel execution of a function call with the @code{return}
6276 command. If you give an
6277 @var{expression} argument, its value is used as the function's return
6281 When you use @code{return}, @value{GDBN} discards the selected stack frame
6282 (and all frames within it). You can think of this as making the
6283 discarded frame return prematurely. If you wish to specify a value to
6284 be returned, give that value as the argument to @code{return}.
6286 This pops the selected stack frame (@pxref{Selection, ,Selecting a
6287 frame}), and any other frames inside of it, leaving its caller as the
6288 innermost remaining frame. That frame becomes selected. The
6289 specified value is stored in the registers used for returning values
6292 The @code{return} command does not resume execution; it leaves the
6293 program stopped in the state that would exist if the function had just
6294 returned. In contrast, the @code{finish} command (@pxref{Continuing
6295 and Stepping, ,Continuing and stepping}) resumes execution until the
6296 selected stack frame returns naturally.
6299 @section Calling program functions
6301 @cindex calling functions
6304 @item call @var{expr}
6305 Evaluate the expression @var{expr} without displaying @code{void}
6309 You can use this variant of the @code{print} command if you want to
6310 execute a function from your program, but without cluttering the output
6311 with @code{void} returned values. The result is printed and saved in
6312 the value history, if it is not void.
6315 @section Patching programs
6316 @cindex patching binaries
6317 @cindex writing into executables
6319 @cindex writing into corefiles
6322 By default, @value{GDBN} opens the file containing your program's executable
6327 read-only. This prevents accidental alterations
6328 to machine code; but it also prevents you from intentionally patching
6329 your program's binary.
6331 If you'd like to be able to patch the binary, you can specify that
6332 explicitly with the @code{set write} command. For example, you might
6333 want to turn on internal debugging flags, or even to make emergency
6338 @itemx set write off
6340 If you specify @samp{set write on}, @value{GDBN} will open executable
6344 files for both reading and writing; if you specify @samp{set write
6345 off} (the default), @value{GDBN} will open them read-only.
6347 If you have already loaded a file, you must load it again (using the
6352 command) after changing @code{set write}, for your new setting to take
6357 Display whether executable files
6361 will be opened for writing as well as reading.
6365 @chapter @value{GDBN} Files
6367 @value{GDBN} needs to know the file name of the program to be debugged, both in
6368 order to read its symbol table and in order to start your program.
6370 To debug a core dump of a previous run, you must also tell @value{GDBN}
6371 the name of the core dump file.
6375 * Files:: Commands to specify files
6376 * Symbol Errors:: Errors reading symbol files
6380 @section Commands to specify files
6381 @cindex symbol table
6384 @cindex core dump file
6385 The usual way to specify executable and core dump file names is with
6386 the command arguments given when you start @value{GDBN} (@pxref{Invocation,
6387 ,Getting In and Out of @value{GDBN}}.
6390 The usual way to specify an executable file name is with
6391 the command argument given when you start @value{GDBN}, (@pxref{Invocation,
6392 ,Getting In and Out of @value{GDBN}}.
6395 Occasionally it is necessary to change to a different file during a
6396 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
6397 a file you want to use. In these situations the @value{GDBN} commands
6398 to specify new files are useful.
6401 @item file @var{filename}
6402 @cindex executable file
6404 Use @var{filename} as the program to be debugged. It is read for its
6405 symbols and for the contents of pure memory. It is also the program
6406 executed when you use the @code{run} command. If you do not specify a
6407 directory and the file is not found in the @value{GDBN} working directory, @value{GDBN}
6408 uses the environment variable @code{PATH} as a list of directories to
6409 search, just as the shell does when looking for a program to run. You
6410 can change the value of this variable, for both @value{GDBN} and your program,
6411 using the @code{path} command.
6413 On systems with memory-mapped files, an auxiliary symbol table file
6414 @file{@var{filename}.syms} may be available for @var{filename}. If it
6415 is, @value{GDBN} will map in the symbol table from
6416 @file{@var{filename}.syms}, starting up more quickly. See the
6417 descriptions of the options @samp{-mapped} and @samp{-readnow} (available
6418 on the command line, and with the commands @code{file}, @code{symbol-file},
6419 or @code{add-symbol-file}), for more information.
6422 @code{file} with no argument makes @value{GDBN} discard any information it
6423 has on both executable file and the symbol table.
6425 @item exec-file @r{[} @var{filename} @r{]}
6427 Specify that the program to be run (but not the symbol table) is found
6428 in @var{filename}. @value{GDBN} will search the environment variable @code{PATH}
6429 if necessary to locate your program. Omitting @var{filename} means to
6430 discard information on the executable file.
6432 @item symbol-file @r{[} @var{filename} @r{]}
6434 Read symbol table information from file @var{filename}. @code{PATH} is
6435 searched when necessary. Use the @code{file} command to get both symbol
6436 table and program to run from the same file.
6438 @code{symbol-file} with no argument clears out @value{GDBN} information on your
6439 program's symbol table.
6441 The @code{symbol-file} command causes @value{GDBN} to forget the contents of its
6442 convenience variables, the value history, and all breakpoints and
6443 auto-display expressions. This is because they may contain pointers to
6444 the internal data recording symbols and data types, which are part of
6445 the old symbol table data being discarded inside @value{GDBN}.
6447 @code{symbol-file} will not repeat if you press @key{RET} again after
6450 When @value{GDBN} is configured for a particular environment, it will
6451 understand debugging information in whatever format is the standard
6452 generated for that environment; you may use either a GNU compiler, or
6453 other compilers that adhere to the local conventions. Best results are
6454 usually obtained from GNU compilers; for example, using @code{@value{GCC}}
6455 you can generate debugging information for optimized code.
6457 On some kinds of object files, the @code{symbol-file} command does not
6458 normally read the symbol table in full right away. Instead, it scans
6459 the symbol table quickly to find which source files and which symbols
6460 are present. The details are read later, one source file at a time,
6463 The purpose of this two-stage reading strategy is to make @value{GDBN} start up
6464 faster. For the most part, it is invisible except for occasional
6465 pauses while the symbol table details for a particular source file are
6466 being read. (The @code{set verbose} command can turn these pauses
6467 into messages if desired. @xref{Messages/Warnings, ,Optional warnings
6470 We have not implemented the two-stage strategy for COFF yet. When the
6471 symbol table is stored in COFF format, @code{symbol-file} reads the
6472 symbol table data in full right away.
6474 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6475 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6477 @cindex reading symbols immediately
6478 @cindex symbols, reading immediately
6480 @cindex memory-mapped symbol file
6481 @cindex saving symbol table
6482 You can override the @value{GDBN} two-stage strategy for reading symbol
6483 tables by using the @samp{-readnow} option with any of the commands that
6484 load symbol table information, if you want to be sure @value{GDBN} has the
6485 entire symbol table available.
6488 If memory-mapped files are available on your system through the
6489 @code{mmap} system call, you can use another option, @samp{-mapped}, to
6490 cause @value{GDBN} to write the symbols for your program into a reusable
6491 file. Future @value{GDBN} debugging sessions will map in symbol information
6492 from this auxiliary symbol file (if the program has not changed), rather
6493 than spending time reading the symbol table from the executable
6494 program. Using the @samp{-mapped} option has the same effect as
6495 starting @value{GDBN} with the @samp{-mapped} command-line option.
6497 You can use both options together, to make sure the auxiliary symbol
6498 file has all the symbol information for your program.
6500 The auxiliary symbol file for a program called @var{myprog} is called
6501 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
6502 than the corresponding executable), @value{GDBN} will always attempt to use
6503 it when you debug @var{myprog}; no special options or commands are
6506 The @file{.syms} file is specific to the host machine where you run
6507 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
6508 symbol table. It cannot be shared across multiple host platforms.
6510 @c FIXME: for now no mention of directories, since this seems to be in
6511 @c flux. 13mar1992 status is that in theory GDB would look either in
6512 @c current dir or in same dir as myprog; but issues like competing
6513 @c GDB's, or clutter in system dirs, mean that in practice right now
6514 @c only current dir is used. FFish says maybe a special GDB hierarchy
6515 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
6518 @item core-file @r{[} @var{filename} @r{]}
6521 Specify the whereabouts of a core dump file to be used as the ``contents
6522 of memory''. Traditionally, core files contain only some parts of the
6523 address space of the process that generated them; @value{GDBN} can access the
6524 executable file itself for other parts.
6526 @code{core-file} with no argument specifies that no core file is
6529 Note that the core file is ignored when your program is actually running
6530 under @value{GDBN}. So, if you have been running your program and you wish to
6531 debug a core file instead, you must kill the subprocess in which the
6532 program is running. To do this, use the @code{kill} command
6533 (@pxref{Kill Process, ,Killing the child process}).
6536 @item load @var{filename}
6539 Depending on what remote debugging facilities are configured into
6540 @value{GDBN}, the @code{load} command may be available. Where it exists, it
6541 is meant to make @var{filename} (an executable) available for debugging
6542 on the remote system---by downloading, or dynamic linking, for example.
6543 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
6544 the @code{add-symbol-file} command.
6546 If your @value{GDBN} does not have a @code{load} command, attempting to
6547 execute it gets the error message ``@code{You can't do that when your
6548 target is @dots{}}''
6552 On VxWorks, @code{load} will dynamically link @var{filename} on the
6553 current target system as well as adding its symbols in @value{GDBN}.
6557 @cindex download to Nindy-960
6558 With the Nindy interface to an Intel 960 board, @code{load} will
6559 download @var{filename} to the 960 as well as adding its symbols in
6564 @cindex download to H8/300 or H8/500
6565 @cindex H8/300 or H8/500 download
6566 @c start-sanitize-Hitachi-SH
6567 @cindex download to Hitachi SH
6568 @cindex Hitachi SH download
6569 @c end-sanitize-Hitachi-SH
6570 When you select remote debugging to a Hitachi
6571 @c start-sanitize-Hitachi-SH
6573 @c end-sanitize-Hitachi-SH
6574 H8/300, or H8/500 board
6575 (@pxref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}),
6576 the @code{load} command downloads your program to the Hitachi board and also
6577 opens it as the current executable target for @value{GDBN} on your host
6578 (like the @code{file} command).
6581 @code{load} will not repeat if you press @key{RET} again after using it.
6584 @item add-symbol-file @var{filename} @var{address}
6585 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6586 @kindex add-symbol-file
6587 @cindex dynamic linking
6588 The @code{add-symbol-file} command reads additional symbol table information
6589 from the file @var{filename}. You would use this command when @var{filename}
6590 has been dynamically loaded (by some other means) into the program that
6591 is running. @var{address} should be the memory address at which the
6592 file has been loaded; @value{GDBN} cannot figure this out for itself.
6594 The symbol table of the file @var{filename} is added to the symbol table
6595 originally read with the @code{symbol-file} command. You can use the
6596 @code{add-symbol-file} command any number of times; the new symbol data thus
6597 read keeps adding to the old. To discard all old symbol data instead,
6598 use the @code{symbol-file} command.
6600 @code{add-symbol-file} will not repeat if you press @key{RET} after using it.
6602 You can use the @samp{-mapped} and @samp{-readnow} options just as with
6603 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
6604 table information for @var{filename}.
6611 @code{info files} and @code{info target} are synonymous; both print
6612 the current target (@pxref{Targets, ,Specifying a Debugging Target}),
6615 names of the executable and core dump files
6618 name of the executable file
6620 currently in use by @value{GDBN}, and the files from which symbols were
6621 loaded. The command @code{help targets} lists all possible targets
6622 rather than current ones.
6625 All file-specifying commands allow both absolute and relative file names
6626 as arguments. @value{GDBN} always converts the file name to an absolute path
6627 name and remembers it that way.
6630 @cindex shared libraries
6631 @value{GDBN} supports SunOS, SVR4, and IBM RS/6000 shared libraries.
6632 @value{GDBN} automatically loads symbol definitions from shared libraries
6633 when you use the @code{run} command, or when you examine a core file.
6634 (Before you issue the @code{run} command, @value{GDBN} will not understand
6635 references to a function in a shared library, however---unless you are
6636 debugging a core file).
6637 @c FIXME: next @value{GDBN} release should permit some refs to undef
6638 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared lib
6642 @itemx info sharedlibrary
6643 @kindex info sharedlibrary
6645 Print the names of the shared libraries which are currently loaded.
6647 @item sharedlibrary @var{regex}
6648 @itemx share @var{regex}
6649 @kindex sharedlibrary
6651 This is an obsolescent command; you can use it to explicitly
6652 load shared object library symbols for files matching a UNIX regular
6653 expression, but as with files loaded automatically, it will only load
6654 shared libraries required by your program for a core file or after
6655 typing @code{run}. If @var{regex} is omitted all shared libraries
6656 required by your program are loaded.
6661 @section Errors reading symbol files
6663 While reading a symbol file, @value{GDBN} will occasionally encounter problems,
6664 such as symbol types it does not recognize, or known bugs in compiler
6665 output. By default, @value{GDBN} does not notify you of such problems, since
6666 they are relatively common and primarily of interest to people
6667 debugging compilers. If you are interested in seeing information
6668 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
6669 only one message about each such type of problem, no matter how many
6670 times the problem occurs; or you can ask @value{GDBN} to print more messages,
6671 to see how many times the problems occur, with the @code{set
6672 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
6675 The messages currently printed, and their meanings, are:
6678 @item inner block not inside outer block in @var{symbol}
6680 The symbol information shows where symbol scopes begin and end
6681 (such as at the start of a function or a block of statements). This
6682 error indicates that an inner scope block is not fully contained
6683 in its outer scope blocks.
6685 @value{GDBN} circumvents the problem by treating the inner block as if it had
6686 the same scope as the outer block. In the error message, @var{symbol}
6687 may be shown as ``@code{(don't know)}'' if the outer block is not a
6690 @item block at @var{address} out of order
6692 The symbol information for symbol scope blocks should occur in
6693 order of increasing addresses. This error indicates that it does not
6696 @value{GDBN} does not circumvent this problem, and will have trouble
6697 locating symbols in the source file whose symbols it is reading. (You
6698 can often determine what source file is affected by specifying
6699 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
6702 @item bad block start address patched
6704 The symbol information for a symbol scope block has a start address
6705 smaller than the address of the preceding source line. This is known
6706 to occur in the SunOS 4.1.1 (and earlier) C compiler.
6708 @value{GDBN} circumvents the problem by treating the symbol scope block as
6709 starting on the previous source line.
6711 @item bad string table offset in symbol @var{n}
6714 Symbol number @var{n} contains a pointer into the string table which is
6715 larger than the size of the string table.
6717 @value{GDBN} circumvents the problem by considering the symbol to have the
6718 name @code{foo}, which may cause other problems if many symbols end up
6721 @item unknown symbol type @code{0x@var{nn}}
6723 The symbol information contains new data types that @value{GDBN} does not yet
6724 know how to read. @code{0x@var{nn}} is the symbol type of the misunderstood
6725 information, in hexadecimal.
6727 @value{GDBN} circumvents the error by ignoring this symbol information. This
6728 will usually allow your program to be debugged, though certain symbols
6729 will not be accessible. If you encounter such a problem and feel like
6730 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint on
6731 @code{complain}, then go up to the function @code{read_dbx_symtab} and
6732 examine @code{*bufp} to see the symbol.
6734 @item stub type has NULL name
6735 @value{GDBN} could not find the full definition for
6744 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
6746 The symbol information for a C++ member function is missing some
6747 information that recent versions of the compiler should have output
6751 @item info mismatch between compiler and debugger
6753 @value{GDBN} could not parse a type specification output by the compiler.
6757 @chapter Specifying a Debugging Target
6758 @cindex debugging target
6761 A @dfn{target} is the execution environment occupied by your program.
6763 Often, @value{GDBN} runs in the same host environment as your program; in
6764 that case, the debugging target is specified as a side effect when you
6765 use the @code{file} or @code{core} commands. When you need more
6766 flexibility---for example, running @value{GDBN} on a physically separate
6767 host, or controlling a standalone system over a serial port or a
6768 realtime system over a TCP/IP connection---you
6773 can use the @code{target} command to specify one of the target types
6774 configured for @value{GDBN} (@pxref{Target Commands, ,Commands for managing
6778 * Active Targets:: Active targets
6779 * Target Commands:: Commands for managing targets
6780 * Remote:: Remote debugging
6783 @node Active Targets
6784 @section Active targets
6785 @cindex stacking targets
6786 @cindex active targets
6787 @cindex multiple targets
6790 There are three classes of targets: processes, core files, and
6791 executable files. @value{GDBN} can work concurrently on up to three active
6792 targets, one in each class. This allows you to (for example) start a
6793 process and inspect its activity without abandoning your work on a core
6796 For example, if you execute @samp{gdb a.out}, then the executable file
6797 @code{a.out} is the only active target. If you designate a core file as
6798 well---presumably from a prior run that crashed and coredumped---then
6799 @value{GDBN} has two active targets and will use them in tandem, looking
6800 first in the corefile target, then in the executable file, to satisfy
6801 requests for memory addresses. (Typically, these two classes of target
6802 are complementary, since core files contain only a program's
6803 read-write memory---variables and so on---plus machine status, while
6804 executable files contain only the program text and initialized data.)
6807 When you type @code{run}, your executable file becomes an active process
6808 target as well. When a process target is active, all @value{GDBN} commands
6809 requesting memory addresses refer to that target; addresses in an
6813 executable file target are obscured while the process
6817 Use the @code{exec-file} command to select a
6818 new executable target (@pxref{Files, ,Commands to specify
6822 Use the @code{core-file} and @code{exec-file} commands to select a
6823 new core file or executable target (@pxref{Files, ,Commands to specify
6824 files}). To specify as a target a process that is already running, use
6825 the @code{attach} command (@pxref{Attach, ,Debugging an
6826 already-running process}).
6829 @node Target Commands
6830 @section Commands for managing targets
6833 @item target @var{type} @var{parameters}
6834 Connects the @value{GDBN} host environment to a target
6839 machine or process. A target is typically a protocol for talking to
6840 debugging facilities. You use the argument @var{type} to specify the
6841 type or protocol of the target machine.
6843 Further @var{parameters} are interpreted by the target protocol, but
6844 typically include things like device names or host names to connect
6845 with, process numbers, and baud rates.
6848 The @code{target} command will not repeat if you press @key{RET} again
6849 after executing the command.
6853 Displays the names of all targets available. To display targets
6854 currently selected, use either @code{info target} or @code{info files}
6855 (@pxref{Files, ,Commands to specify files}).
6857 @item help target @var{name}
6858 Describe a particular target, including any parameters necessary to
6862 Here are some common targets (available, or not, depending on the GDB
6866 @item target exec @var{program}
6868 An executable file. @samp{target exec @var{program}} is the same as
6869 @samp{exec-file @var{program}}.
6872 @item target core @var{filename}
6874 A core dump file. @samp{target core @var{filename}} is the same as
6875 @samp{core-file @var{filename}}.
6879 @item target remote @var{dev}
6880 @kindex target remote
6881 Remote serial target in GDB-specific protocol. The argument @var{dev}
6882 specifies what serial device to use for the connection (e.g.
6883 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}.
6889 CPU simulator. @xref{Simulator,,Simulated CPU Target}.
6893 @item target udi @var{keyword}
6895 Remote AMD29K target, using the AMD UDI protocol. The @var{keyword}
6896 argument specifies which 29K board or simulator to use. @xref{UDI29K
6897 Remote,,@value{GDBN} and the UDI protocol for AMD29K}.
6899 @item target amd-eb @var{dev} @var{speed} @var{PROG}
6900 @kindex target amd-eb
6902 Remote PC-resident AMD EB29K board, attached over serial lines.
6903 @var{dev} is the serial device, as for @code{target remote};
6904 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
6905 name of the program to be debugged, as it appears to DOS on the PC.
6906 @xref{EB29K Remote, ,@value{GDBN} with a remote EB29K}.
6913 @c start-sanitize-Hitachi-SH
6915 @c end-sanitize-Hitachi-SH
6916 H8/300, or H8/500 board, attached via serial line to your host.
6917 @ifclear H8EXCLUSIVE
6918 @c Unix only, not currently of interest for H8-only manual
6919 Use special commands @code{device} and @code{speed} to control the serial
6920 line and the communications speed used.
6922 @xref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}.
6926 @item target nindy @var{devicename}
6927 @kindex target nindy
6928 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
6929 the name of the serial device to use for the connection, e.g.
6930 @file{/dev/ttya}. @xref{i960-Nindy Remote, ,@value{GDBN} with a remote i960 (Nindy)}.
6934 @item target st2000 @var{dev} @var{speed}
6935 @kindex target st2000
6936 A Tandem ST2000 phone switch, running Tandem's STDBUG protocol. @var{dev}
6937 is the name of the device attached to the ST2000 serial line;
6938 @var{speed} is the communication line speed. The arguments are not used
6939 if @value{GDBN} is configured to connect to the ST2000 using TCP or Telnet.
6940 @xref{ST2000 Remote,,@value{GDBN} with a Tandem ST2000}.
6944 @item target vxworks @var{machinename}
6945 @kindex target vxworks
6946 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
6947 is the target system's machine name or IP address.
6948 @xref{VxWorks Remote, ,@value{GDBN} and VxWorks}.
6953 Different targets are available on different configurations of @value{GDBN}; your
6954 configuration may have more or fewer targets.
6958 @section Remote debugging
6959 @cindex remote debugging
6961 If you are trying to debug a program running on a machine that cannot run
6962 GDB in the usual way, it is often useful to use remote debugging. For
6963 example, you might use remote debugging on an operating system kernel, or on
6964 a small system which does not have a general purpose operating system
6965 powerful enough to run a full-featured debugger.
6967 Some configurations of GDB have special serial or TCP/IP interfaces
6968 to make this work with particular debugging targets. In addition,
6969 GDB comes with a generic serial protocol (specific to GDB, but
6970 not specific to any particular target system) which you can use if you
6971 write the remote stubs---the code that will run on the remote system to
6972 communicate with GDB.
6974 Other remote targets may be available in your
6975 configuration of GDB; use @code{help targets} to list them.
6978 @c Text on starting up GDB in various specific cases; it goes up front
6979 @c in manuals configured for any of those particular situations, here
6983 * Remote Serial:: @value{GDBN} remote serial protocol
6986 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
6989 * UDI29K Remote:: @value{GDBN} and the UDI protocol for AMD29K
6990 * EB29K Remote:: @value{GDBN} with a remote EB29K
6993 * VxWorks Remote:: @value{GDBN} and VxWorks
6996 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
6999 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
7002 * MIPS Remote:: @value{GDBN} and MIPS boards
7005 * Simulator:: Simulated CPU target
7009 @include gdbinv-s.texi
7012 @node Controlling GDB
7013 @chapter Controlling @value{GDBN}
7015 You can alter the way @value{GDBN} interacts with you by using
7016 the @code{set} command. For commands controlling how @value{GDBN} displays
7017 data, @pxref{Print Settings, ,Print settings}; other settings are described here.
7021 * Editing:: Command editing
7022 * History:: Command history
7023 * Screen Size:: Screen size
7025 * Messages/Warnings:: Optional warnings and messages
7032 @value{GDBN} indicates its readiness to read a command by printing a string
7033 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
7034 can change the prompt string with the @code{set prompt} command. For
7035 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
7036 the prompt in one of the @value{GDBN} sessions so that you can always tell which
7037 one you are talking to.
7040 @item set prompt @var{newprompt}
7042 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
7045 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
7049 @section Command editing
7051 @cindex command line editing
7053 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
7054 GNU library provides consistent behavior for programs which provide a
7055 command line interface to the user. Advantages are @code{emacs}-style
7056 or @code{vi}-style inline editing of commands, @code{csh}-like history
7057 substitution, and a storage and recall of command history across
7060 You may control the behavior of command line editing in @value{GDBN} with the
7067 @itemx set editing on
7068 Enable command line editing (enabled by default).
7070 @item set editing off
7071 Disable command line editing.
7073 @kindex show editing
7075 Show whether command line editing is enabled.
7079 @section Command history
7081 @value{GDBN} can keep track of the commands you type during your
7082 debugging sessions, so that you can be certain of precisely what
7083 happened. Use these commands to manage the @value{GDBN} command
7087 @cindex history substitution
7088 @cindex history file
7089 @kindex set history filename
7090 @item set history filename @var{fname}
7091 Set the name of the @value{GDBN} command history file to @var{fname}. This is
7092 the file from which @value{GDBN} will read an initial command history
7093 list or to which it will write this list when it exits. This list is
7094 accessed through history expansion or through the history
7095 command editing characters listed below. This file defaults to the
7096 value of the environment variable @code{GDBHISTFILE}, or to
7097 @file{./.gdb_history} if this variable is not set.
7099 @cindex history save
7100 @kindex set history save
7101 @item set history save
7102 @itemx set history save on
7103 Record command history in a file, whose name may be specified with the
7104 @code{set history filename} command. By default, this option is disabled.
7106 @item set history save off
7107 Stop recording command history in a file.
7109 @cindex history size
7110 @kindex set history size
7111 @item set history size @var{size}
7112 Set the number of commands which @value{GDBN} will keep in its history list.
7113 This defaults to the value of the environment variable
7114 @code{HISTSIZE}, or to 256 if this variable is not set.
7117 @cindex history expansion
7118 History expansion assigns special meaning to the character @kbd{!}.
7119 @ifset have-readline-appendices
7120 @xref{Event Designators}.
7123 Since @kbd{!} is also the logical not operator in C, history expansion
7124 is off by default. If you decide to enable history expansion with the
7125 @code{set history expansion on} command, you may sometimes need to
7126 follow @kbd{!} (when it is used as logical not, in an expression) with
7127 a space or a tab to prevent it from being expanded. The readline
7128 history facilities will not attempt substitution on the strings
7129 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
7131 The commands to control history expansion are:
7135 @kindex set history expansion
7136 @item set history expansion on
7137 @itemx set history expansion
7138 Enable history expansion. History expansion is off by default.
7140 @item set history expansion off
7141 Disable history expansion.
7143 The readline code comes with more complete documentation of
7144 editing and history expansion features. Users unfamiliar with @code{emacs}
7145 or @code{vi} may wish to read it.
7146 @ifset have-readline-appendices
7147 @xref{Command Line Editing}.
7151 @kindex show history
7153 @itemx show history filename
7154 @itemx show history save
7155 @itemx show history size
7156 @itemx show history expansion
7157 These commands display the state of the @value{GDBN} history parameters.
7158 @code{show history} by itself displays all four states.
7163 @kindex show commands
7165 Display the last ten commands in the command history.
7167 @item show commands @var{n}
7168 Print ten commands centered on command number @var{n}.
7170 @item show commands +
7171 Print ten commands just after the commands last printed.
7175 @section Screen size
7176 @cindex size of screen
7177 @cindex pauses in output
7179 Certain commands to @value{GDBN} may produce large amounts of
7180 information output to the screen. To help you read all of it,
7181 @value{GDBN} pauses and asks you for input at the end of each page of
7182 output. Type @key{RET} when you want to continue the output, or @kbd{q}
7183 to discard the remaining output. Also, the screen width setting
7184 determines when to wrap lines of output. Depending on what is being
7185 printed, @value{GDBN} tries to break the line at a readable place,
7186 rather than simply letting it overflow onto the following line.
7188 Normally @value{GDBN} knows the size of the screen from the termcap data base
7189 together with the value of the @code{TERM} environment variable and the
7190 @code{stty rows} and @code{stty cols} settings. If this is not correct,
7191 you can override it with the @code{set height} and @code{set
7195 @item set height @var{lpp}
7197 @itemx set width @var{cpl}
7203 These @code{set} commands specify a screen height of @var{lpp} lines and
7204 a screen width of @var{cpl} characters. The associated @code{show}
7205 commands display the current settings.
7207 If you specify a height of zero lines, @value{GDBN} will not pause during output
7208 no matter how long the output is. This is useful if output is to a file
7209 or to an editor buffer.
7214 @cindex number representation
7215 @cindex entering numbers
7217 You can always enter numbers in octal, decimal, or hexadecimal in @value{GDBN} by
7218 the usual conventions: octal numbers begin with @samp{0}, decimal
7219 numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}.
7220 Numbers that begin with none of these are, by default, entered in base
7221 10; likewise, the default display for numbers---when no particular
7222 format is specified---is base 10. You can change the default base for
7223 both input and output with the @code{set radix} command.
7227 @item set radix @var{base}
7228 Set the default base for numeric input and display. Supported choices
7229 for @var{base} are decimal 2, 8, 10, 16. @var{base} must itself be
7230 specified either unambiguously or using the current default radix; for
7241 will set the base to decimal. On the other hand, @samp{set radix 10}
7242 will leave the radix unchanged no matter what it was.
7246 Display the current default base for numeric input and display.
7249 @node Messages/Warnings
7250 @section Optional warnings and messages
7252 By default, @value{GDBN} is silent about its inner workings. If you are running
7253 on a slow machine, you may want to use the @code{set verbose} command.
7254 It will make @value{GDBN} tell you when it does a lengthy internal operation, so
7255 you will not think it has crashed.
7257 Currently, the messages controlled by @code{set verbose} are those
7258 which announce that the symbol table for a source file is being read;
7259 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
7263 @item set verbose on
7264 Enables @value{GDBN} output of certain informational messages.
7266 @item set verbose off
7267 Disables @value{GDBN} output of certain informational messages.
7269 @kindex show verbose
7271 Displays whether @code{set verbose} is on or off.
7274 By default, if @value{GDBN} encounters bugs in the symbol table of an object
7275 file, it is silent; but if you are debugging a compiler, you may find
7276 this information useful (@pxref{Symbol Errors, ,Errors reading symbol files}).
7279 @kindex set complaints
7280 @item set complaints @var{limit}
7281 Permits @value{GDBN} to output @var{limit} complaints about each type of unusual
7282 symbols before becoming silent about the problem. Set @var{limit} to
7283 zero to suppress all complaints; set it to a large number to prevent
7284 complaints from being suppressed.
7286 @kindex show complaints
7287 @item show complaints
7288 Displays how many symbol complaints @value{GDBN} is permitted to produce.
7291 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
7292 lot of stupid questions to confirm certain commands. For example, if
7293 you try to run a program which is already running:
7297 The program being debugged has been started already.
7298 Start it from the beginning? (y or n)
7301 If you are willing to unflinchingly face the consequences of your own
7302 commands, you can disable this ``feature'':
7307 @cindex confirmation
7308 @cindex stupid questions
7309 @item set confirm off
7310 Disables confirmation requests.
7312 @item set confirm on
7313 Enables confirmation requests (the default).
7316 @kindex show confirm
7317 Displays state of confirmation requests.
7320 @c FIXME this does not really belong here. But where *does* it belong?
7321 @cindex reloading symbols
7322 Some systems allow individual object files that make up your program to
7323 be replaced without stopping and restarting your program.
7325 For example, in VxWorks you can simply recompile a defective object file
7326 and keep on running.
7328 If you are running on one of these systems, you can allow @value{GDBN} to
7329 reload the symbols for automatically relinked modules:
7332 @kindex set symbol-reloading
7333 @item set symbol-reloading on
7334 Replace symbol definitions for the corresponding source file when an
7335 object file with a particular name is seen again.
7337 @item set symbol-reloading off
7338 Do not replace symbol definitions when re-encountering object files of
7339 the same name. This is the default state; if you are not running on a
7340 system that permits automatically relinking modules, you should leave
7341 @code{symbol-reloading} off, since otherwise @value{GDBN} may discard symbols
7342 when linking large programs, that may contain several modules (from
7343 different directories or libraries) with the same name.
7345 @item show symbol-reloading
7346 Show the current @code{on} or @code{off} setting.
7350 @chapter Canned Sequences of Commands
7352 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
7353 command lists}), @value{GDBN} provides two ways to store sequences of commands
7354 for execution as a unit: user-defined commands and command files.
7357 * Define:: User-defined commands
7358 * Hooks:: User-defined command hooks
7359 * Command Files:: Command files
7360 * Output:: Commands for controlled output
7364 @section User-defined commands
7366 @cindex user-defined command
7367 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to which you
7368 assign a new name as a command. This is done with the @code{define}
7372 @item define @var{commandname}
7374 Define a command named @var{commandname}. If there is already a command
7375 by that name, you are asked to confirm that you want to redefine it.
7377 The definition of the command is made up of other @value{GDBN} command lines,
7378 which are given following the @code{define} command. The end of these
7379 commands is marked by a line containing @code{end}.
7381 @item document @var{commandname}
7383 Give documentation to the user-defined command @var{commandname}. The
7384 command @var{commandname} must already be defined. This command reads
7385 lines of documentation just as @code{define} reads the lines of the
7386 command definition, ending with @code{end}. After the @code{document}
7387 command is finished, @code{help} on command @var{commandname} will print
7388 the documentation you have specified.
7390 You may use the @code{document} command again to change the
7391 documentation of a command. Redefining the command with @code{define}
7392 does not change the documentation.
7394 @item help user-defined
7395 @kindex help user-defined
7396 List all user-defined commands, with the first line of the documentation
7400 @itemx show user @var{commandname}
7402 Display the @value{GDBN} commands used to define @var{commandname} (but not its
7403 documentation). If no @var{commandname} is given, display the
7404 definitions for all user-defined commands.
7407 User-defined commands do not take arguments. When they are executed, the
7408 commands of the definition are not printed. An error in any command
7409 stops execution of the user-defined command.
7411 Commands that would ask for confirmation if used interactively proceed
7412 without asking when used inside a user-defined command. Many @value{GDBN} commands
7413 that normally print messages to say what they are doing omit the messages
7414 when used in a user-defined command.
7417 @section User-defined command hooks
7418 @cindex command files
7420 You may define @emph{hooks}, which are a special kind of user-defined
7421 command. Whenever you run the command @samp{foo}, if the user-defined
7422 command @samp{hook-foo} exists, it is executed (with no arguments)
7423 before that command.
7425 In addition, a pseudo-command, @samp{stop} exists. Defining
7426 (@samp{hook-stop}) makes the associated commands execute every time
7427 execution stops in your program: before breakpoint commands are run,
7428 displays are printed, or the stack frame is printed.
7431 For example, to ignore @code{SIGALRM} signals while
7432 single-stepping, but treat them normally during normal execution,
7437 handle SIGALRM nopass
7444 define hook-continue
7450 You can define a hook for any single-word command in @value{GDBN}, but
7451 not for command aliases; you should define a hook for the basic command
7452 name, e.g. @code{backtrace} rather than @code{bt}.
7453 @c FIXME! So how does Joe User discover whether a command is an alias
7455 If an error occurs during the execution of your hook, execution of
7456 @value{GDBN} commands stops and @value{GDBN} issues a prompt
7457 (before the command that you actually typed had a chance to run).
7459 If you try to define a hook which does not match any known command, you
7460 will get a warning from the @code{define} command.
7463 @section Command files
7465 @cindex command files
7466 A command file for @value{GDBN} is a file of lines that are @value{GDBN} commands. Comments
7467 (lines starting with @kbd{#}) may also be included. An empty line in a
7468 command file does nothing; it does not mean to repeat the last command, as
7469 it would from the terminal.
7472 @cindex @file{@value{GDBINIT}}
7473 When you start @value{GDBN}, it automatically executes commands from its
7474 @dfn{init files}. These are files named @file{@value{GDBINIT}}. @value{GDBN} reads
7475 the init file (if any) in your home directory and then the init file
7476 (if any) in the current working directory. (The init files are not
7477 executed if you use the @samp{-nx} option; @pxref{Mode Options,
7481 @cindex init file name
7482 On some configurations of @value{GDBN}, the init file is known by a
7483 different name (these are typically environments where a specialized
7484 form of GDB may need to coexist with other forms, hence a different name
7485 for the specialized version's init file). These are the environments
7486 with special init file names:
7491 VxWorks (Wind River Systems real-time OS): @samp{.vxgdbinit}
7493 @kindex .os68gdbinit
7495 OS68K (Enea Data Systems real-time OS): @samp{.os68gdbinit}
7499 ES-1800 (Ericsson Telecom AB M68000 emulator): @samp{.esgdbinit}
7503 You can also request the execution of a command file with the
7504 @code{source} command:
7507 @item source @var{filename}
7509 Execute the command file @var{filename}.
7512 The lines in a command file are executed sequentially. They are not
7513 printed as they are executed. An error in any command terminates execution
7514 of the command file.
7516 Commands that would ask for confirmation if used interactively proceed
7517 without asking when used in a command file. Many @value{GDBN} commands that
7518 normally print messages to say what they are doing omit the messages
7519 when called from command files.
7522 @section Commands for controlled output
7524 During the execution of a command file or a user-defined command, normal
7525 @value{GDBN} output is suppressed; the only output that appears is what is
7526 explicitly printed by the commands in the definition. This section
7527 describes three commands useful for generating exactly the output you
7531 @item echo @var{text}
7533 @c I do not consider backslash-space a standard C escape sequence
7534 @c because it is not in ANSI.
7535 Print @var{text}. Nonprinting characters can be included in
7536 @var{text} using C escape sequences, such as @samp{\n} to print a
7537 newline. @strong{No newline will be printed unless you specify one.}
7538 In addition to the standard C escape sequences, a backslash followed
7539 by a space stands for a space. This is useful for displaying a
7540 string with spaces at the beginning or the end, since leading and
7541 trailing spaces are otherwise trimmed from all arguments.
7542 To print @samp{@w{ }and foo =@w{ }}, use the command
7543 @samp{echo \@w{ }and foo = \@w{ }}.
7545 A backslash at the end of @var{text} can be used, as in C, to continue
7546 the command onto subsequent lines. For example,
7549 echo This is some text\n\
7550 which is continued\n\
7551 onto several lines.\n
7554 produces the same output as
7557 echo This is some text\n
7558 echo which is continued\n
7559 echo onto several lines.\n
7562 @item output @var{expression}
7564 Print the value of @var{expression} and nothing but that value: no
7565 newlines, no @samp{$@var{nn} = }. The value is not entered in the
7566 value history either. @xref{Expressions, ,Expressions}, for more information on
7569 @item output/@var{fmt} @var{expression}
7570 Print the value of @var{expression} in format @var{fmt}. You can use
7571 the same formats as for @code{print}. @xref{Output Formats,,Output
7572 formats}, for more information.
7574 @item printf @var{string}, @var{expressions}@dots{}
7576 Print the values of the @var{expressions} under the control of
7577 @var{string}. The @var{expressions} are separated by commas and may
7578 be either numbers or pointers. Their values are printed as specified
7579 by @var{string}, exactly as if your program were to execute
7582 printf (@var{string}, @var{expressions}@dots{});
7585 For example, you can print two values in hex like this:
7588 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
7591 The only backslash-escape sequences that you can use in the format
7592 string are the simple ones that consist of backslash followed by a
7598 @chapter Using @value{GDBN} under GNU Emacs
7601 A special interface allows you to use GNU Emacs to view (and
7602 edit) the source files for the program you are debugging with
7605 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
7606 executable file you want to debug as an argument. This command starts
7607 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
7608 created Emacs buffer.
7610 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
7615 All ``terminal'' input and output goes through the Emacs buffer.
7618 This applies both to @value{GDBN} commands and their output, and to the input
7619 and output done by the program you are debugging.
7621 This is useful because it means that you can copy the text of previous
7622 commands and input them again; you can even use parts of the output
7625 All the facilities of Emacs' Shell mode are available for interacting
7626 with your program. In particular, you can send signals the usual
7627 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
7632 @value{GDBN} displays source code through Emacs.
7635 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
7636 source file for that frame and puts an arrow (@samp{=>}) at the
7637 left margin of the current line. Emacs uses a separate buffer for
7638 source display, and splits the screen to show both your @value{GDBN} session
7641 Explicit @value{GDBN} @code{list} or search commands still produce output as
7642 usual, but you probably will have no reason to use them.
7645 @emph{Warning:} If the directory where your program resides is not your
7646 current directory, it can be easy to confuse Emacs about the location of
7647 the source files, in which case the auxiliary display buffer will not
7648 appear to show your source. @value{GDBN} can find programs by searching your
7649 environment's @code{PATH} variable, so the @value{GDBN} input and output
7650 session will proceed normally; but Emacs does not get enough information
7651 back from @value{GDBN} to locate the source files in this situation. To
7652 avoid this problem, either start @value{GDBN} mode from the directory where
7653 your program resides, or specify a full path name when prompted for the
7654 @kbd{M-x gdb} argument.
7656 A similar confusion can result if you use the @value{GDBN} @code{file} command to
7657 switch to debugging a program in some other location, from an existing
7658 @value{GDBN} buffer in Emacs.
7661 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
7662 you need to call @value{GDBN} by a different name (for example, if you keep
7663 several configurations around, with different names) you can set the
7664 Emacs variable @code{gdb-command-name}; for example,
7667 (setq gdb-command-name "mygdb")
7671 (preceded by @kbd{ESC ESC}, or typed in the @code{*scratch*} buffer, or
7672 in your @file{.emacs} file) will make Emacs call the program named
7673 ``@code{mygdb}'' instead.
7675 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
7676 addition to the standard Shell mode commands:
7680 Describe the features of Emacs' @value{GDBN} Mode.
7683 Execute to another source line, like the @value{GDBN} @code{step} command; also
7684 update the display window to show the current file and location.
7687 Execute to next source line in this function, skipping all function
7688 calls, like the @value{GDBN} @code{next} command. Then update the display window
7689 to show the current file and location.
7692 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
7693 display window accordingly.
7696 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
7697 display window accordingly.
7700 Execute until exit from the selected stack frame, like the @value{GDBN}
7701 @code{finish} command.
7704 Continue execution of your program, like the @value{GDBN} @code{continue}
7707 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
7710 Go up the number of frames indicated by the numeric argument
7711 (@pxref{Arguments, , Numeric Arguments, emacs, The GNU Emacs Manual}),
7712 like the @value{GDBN} @code{up} command.
7714 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
7717 Go down the number of frames indicated by the numeric argument, like the
7718 @value{GDBN} @code{down} command.
7720 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
7723 Read the number where the cursor is positioned, and insert it at the end
7724 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
7725 around an address that was displayed earlier, type @kbd{disassemble};
7726 then move the cursor to the address display, and pick up the
7727 argument for @code{disassemble} by typing @kbd{C-x &}.
7729 You can customize this further by defining elements of the list
7730 @code{gdb-print-command}; once it is defined, you can format or
7731 otherwise process numbers picked up by @kbd{C-x &} before they are
7732 inserted. A numeric argument to @kbd{C-x &} will both indicate that you
7733 wish special formatting, and act as an index to pick an element of the
7734 list. If the list element is a string, the number to be inserted is
7735 formatted using the Emacs function @code{format}; otherwise the number
7736 is passed as an argument to the corresponding list element.
7739 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
7740 tells @value{GDBN} to set a breakpoint on the source line point is on.
7742 If you accidentally delete the source-display buffer, an easy way to get
7743 it back is to type the command @code{f} in the @value{GDBN} buffer, to
7744 request a frame display; when you run under Emacs, this will recreate
7745 the source buffer if necessary to show you the context of the current
7748 The source files displayed in Emacs are in ordinary Emacs buffers
7749 which are visiting the source files in the usual way. You can edit
7750 the files with these buffers if you wish; but keep in mind that @value{GDBN}
7751 communicates with Emacs in terms of line numbers. If you add or
7752 delete lines from the text, the line numbers that @value{GDBN} knows will cease
7753 to correspond properly with the code.
7755 @c The following dropped because Epoch is nonstandard. Reactivate
7756 @c if/when v19 does something similar. ---pesch@cygnus.com 19dec1990
7758 @kindex emacs epoch environment
7762 Version 18 of Emacs has a built-in window system called the @code{epoch}
7763 environment. Users of this environment can use a new command,
7764 @code{inspect} which performs identically to @code{print} except that
7765 each value is printed in its own window.
7771 @chapter Using @value{GDBN} with Energize
7774 The Energize Programming System is an integrated development environment
7775 that includes a point-and-click interface to many programming tools.
7776 When you use @value{GDBN} in this environment, you can use the standard
7777 Energize graphical interface to drive @value{GDBN}; you can also, if you
7778 choose, type @value{GDBN} commands as usual in a debugging window. Even if
7779 you use the graphical interface, the debugging window (which uses Emacs,
7780 and resembles the standard Emacs interface to @value{GDBN}) displays the
7781 equivalent commands, so that the history of your debugging session is
7784 When Energize starts up a @value{GDBN} session, it uses one of the
7785 command-line options @samp{-energize} or @samp{-cadillac} (``cadillac''
7786 is the name of the communications protocol used by the Energize system).
7787 This option makes @value{GDBN} run as one of the tools in the Energize Tool
7788 Set: it sends all output to the Energize kernel, and accept input from
7791 See the user manual for the Energize Programming System for
7792 information on how to use the Energize graphical interface and the other
7793 development tools that Energize integrates with @value{GDBN}.
7798 @chapter Reporting Bugs in @value{GDBN}
7799 @cindex bugs in @value{GDBN}
7800 @cindex reporting bugs in @value{GDBN}
7802 Your bug reports play an essential role in making @value{GDBN} reliable.
7804 Reporting a bug may help you by bringing a solution to your problem, or it
7805 may not. But in any case the principal function of a bug report is to help
7806 the entire community by making the next version of @value{GDBN} work better. Bug
7807 reports are your contribution to the maintenance of @value{GDBN}.
7809 In order for a bug report to serve its purpose, you must include the
7810 information that enables us to fix the bug.
7813 * Bug Criteria:: Have you found a bug?
7814 * Bug Reporting:: How to report bugs
7818 @section Have you found a bug?
7819 @cindex bug criteria
7821 If you are not sure whether you have found a bug, here are some guidelines:
7825 @cindex fatal signal
7826 @cindex debugger crash
7827 @cindex crash of debugger
7828 If the debugger gets a fatal signal, for any input whatever, that is a
7829 @value{GDBN} bug. Reliable debuggers never crash.
7832 @cindex error on valid input
7833 If @value{GDBN} produces an error message for valid input, that is a bug.
7836 @cindex invalid input
7837 If @value{GDBN} does not produce an error message for invalid input,
7838 that is a bug. However, you should note that your idea of
7839 ``invalid input'' might be our idea of ``an extension'' or ``support
7840 for traditional practice''.
7843 If you are an experienced user of debugging tools, your suggestions
7844 for improvement of @value{GDBN} are welcome in any case.
7848 @section How to report bugs
7850 @cindex @value{GDBN} bugs, reporting
7852 A number of companies and individuals offer support for GNU products.
7853 If you obtained @value{GDBN} from a support organization, we recommend you
7854 contact that organization first.
7856 You can find contact information for many support companies and
7857 individuals in the file @file{etc/SERVICE} in the GNU Emacs
7860 In any event, we also recommend that you send bug reports for @value{GDBN} to one
7864 bug-gdb@@prep.ai.mit.edu
7865 @{ucbvax|mit-eddie|uunet@}!prep.ai.mit.edu!bug-gdb
7868 @strong{Do not send bug reports to @samp{info-gdb}, or to
7869 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do not want to
7870 receive bug reports. Those that do, have arranged to receive @samp{bug-gdb}.
7872 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
7873 serves as a repeater. The mailing list and the newsgroup carry exactly
7874 the same messages. Often people think of posting bug reports to the
7875 newsgroup instead of mailing them. This appears to work, but it has one
7876 problem which can be crucial: a newsgroup posting often lacks a mail
7877 path back to the sender. Thus, if we need to ask for more information,
7878 we may be unable to reach you. For this reason, it is better to send
7879 bug reports to the mailing list.
7881 As a last resort, send bug reports on paper to:
7885 Free Software Foundation
7890 The fundamental principle of reporting bugs usefully is this:
7891 @strong{report all the facts}. If you are not sure whether to state a
7892 fact or leave it out, state it!
7894 Often people omit facts because they think they know what causes the
7895 problem and assume that some details do not matter. Thus, you might
7896 assume that the name of the variable you use in an example does not matter.
7897 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
7898 stray memory reference which happens to fetch from the location where that
7899 name is stored in memory; perhaps, if the name were different, the contents
7900 of that location would fool the debugger into doing the right thing despite
7901 the bug. Play it safe and give a specific, complete example. That is the
7902 easiest thing for you to do, and the most helpful.
7904 Keep in mind that the purpose of a bug report is to enable us to fix
7905 the bug if it is new to us. It is not as important as what happens if
7906 the bug is already known. Therefore, always write your bug reports on
7907 the assumption that the bug has not been reported previously.
7909 Sometimes people give a few sketchy facts and ask, ``Does this ring a
7910 bell?'' Those bug reports are useless, and we urge everyone to
7911 @emph{refuse to respond to them} except to chide the sender to report
7914 To enable us to fix the bug, you should include all these things:
7918 The version of @value{GDBN}. @value{GDBN} announces it if you start with no
7919 arguments; you can also print it at any time using @code{show version}.
7921 Without this, we will not know whether there is any point in looking for
7922 the bug in the current version of @value{GDBN}.
7925 The type of machine you are using, and the operating system name and
7929 What compiler (and its version) was used to compile @value{GDBN}---e.g.
7930 ``@value{GCC}--2.0''.
7933 What compiler (and its version) was used to compile the program you
7934 are debugging---e.g. ``@value{GCC}--2.0''.
7937 The command arguments you gave the compiler to compile your example and
7938 observe the bug. For example, did you use @samp{-O}? To guarantee
7939 you will not omit something important, list them all. A copy of the
7940 Makefile (or the output from make) is sufficient.
7942 If we were to try to guess the arguments, we would probably guess wrong
7943 and then we might not encounter the bug.
7946 A complete input script, and all necessary source files, that will
7950 A description of what behavior you observe that you believe is
7951 incorrect. For example, ``It gets a fatal signal.''
7953 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we will
7954 certainly notice it. But if the bug is incorrect output, we might not
7955 notice unless it is glaringly wrong. We are human, after all. You
7956 might as well not give us a chance to make a mistake.
7958 Even if the problem you experience is a fatal signal, you should still
7959 say so explicitly. Suppose something strange is going on, such as,
7960 your copy of @value{GDBN} is out of synch, or you have encountered a
7961 bug in the C library on your system. (This has happened!) Your copy
7962 might crash and ours would not. If you told us to expect a crash,
7963 then when ours fails to crash, we would know that the bug was not
7964 happening for us. If you had not told us to expect a crash, then we
7965 would not be able to draw any conclusion from our observations.
7968 If you wish to suggest changes to the @value{GDBN} source, send us context
7969 diffs. If you even discuss something in the @value{GDBN} source, refer to
7970 it by context, not by line number.
7972 The line numbers in our development sources will not match those in your
7973 sources. Your line numbers would convey no useful information to us.
7976 Here are some things that are not necessary:
7980 A description of the envelope of the bug.
7982 Often people who encounter a bug spend a lot of time investigating
7983 which changes to the input file will make the bug go away and which
7984 changes will not affect it.
7986 This is often time consuming and not very useful, because the way we
7987 will find the bug is by running a single example under the debugger
7988 with breakpoints, not by pure deduction from a series of examples.
7989 We recommend that you save your time for something else.
7991 Of course, if you can find a simpler example to report @emph{instead}
7992 of the original one, that is a convenience for us. Errors in the
7993 output will be easier to spot, running under the debugger will take
7996 However, simplification is not vital; if you do not want to do this,
7997 report the bug anyway and send us the entire test case you used.
8000 A patch for the bug.
8002 A patch for the bug does help us if it is a good one. But do not omit
8003 the necessary information, such as the test case, on the assumption that
8004 a patch is all we need. We might see problems with your patch and decide
8005 to fix the problem another way, or we might not understand it at all.
8007 Sometimes with a program as complicated as @value{GDBN} it is very hard to
8008 construct an example that will make the program follow a certain path
8009 through the code. If you do not send us the example, we will not be able
8010 to construct one, so we will not be able to verify that the bug is fixed.
8012 And if we cannot understand what bug you are trying to fix, or why your
8013 patch should be an improvement, we will not install it. A test case will
8014 help us to understand.
8017 A guess about what the bug is or what it depends on.
8019 Such guesses are usually wrong. Even we cannot guess right about such
8020 things without first using the debugger to find the facts.
8023 @c The readline documentation is distributed with the readline code
8024 @c and consists of the two following files:
8027 @c Use -I with makeinfo to point to the appropriate directory,
8028 @c environment var TEXINPUTS with TeX.
8029 @include rluser.texinfo
8030 @include inc-hist.texi
8033 @node Renamed Commands
8034 @appendix Renamed Commands
8036 The following commands were renamed in GDB 4, in order to make the
8037 command set as a whole more consistent and easier to use and remember:
8040 @kindex delete environment
8041 @kindex info copying
8042 @kindex info convenience
8043 @kindex info directories
8044 @kindex info editing
8045 @kindex info history
8046 @kindex info targets
8048 @kindex info version
8049 @kindex info warranty
8050 @kindex set addressprint
8051 @kindex set arrayprint
8052 @kindex set prettyprint
8053 @kindex set screen-height
8054 @kindex set screen-width
8055 @kindex set unionprint
8056 @kindex set vtblprint
8057 @kindex set demangle
8058 @kindex set asm-demangle
8059 @kindex set sevenbit-strings
8060 @kindex set array-max
8062 @kindex set history write
8063 @kindex show addressprint
8064 @kindex show arrayprint
8065 @kindex show prettyprint
8066 @kindex show screen-height
8067 @kindex show screen-width
8068 @kindex show unionprint
8069 @kindex show vtblprint
8070 @kindex show demangle
8071 @kindex show asm-demangle
8072 @kindex show sevenbit-strings
8073 @kindex show array-max
8074 @kindex show caution
8075 @kindex show history write
8080 @c END TEXI2ROFF-KILL
8082 OLD COMMAND NEW COMMAND
8084 --------------- -------------------------------
8085 @c END TEXI2ROFF-KILL
8086 add-syms add-symbol-file
8087 delete environment unset environment
8088 info convenience show convenience
8089 info copying show copying
8090 info directories show directories
8091 info editing show commands
8092 info history show values
8093 info targets help target
8094 info values show values
8095 info version show version
8096 info warranty show warranty
8097 set/show addressprint set/show print address
8098 set/show array-max set/show print elements
8099 set/show arrayprint set/show print array
8100 set/show asm-demangle set/show print asm-demangle
8101 set/show caution set/show confirm
8102 set/show demangle set/show print demangle
8103 set/show history write set/show history save
8104 set/show prettyprint set/show print pretty
8105 set/show screen-height set/show height
8106 set/show screen-width set/show width
8107 set/show sevenbit-strings set/show print sevenbit-strings
8108 set/show unionprint set/show print union
8109 set/show vtblprint set/show print vtbl
8111 unset [No longer an alias for delete]
8117 \vskip \parskip\vskip \baselineskip
8118 \halign{\tt #\hfil &\qquad#&\tt #\hfil\cr
8119 {\bf Old Command} &&{\bf New Command}\cr
8120 add-syms &&add-symbol-file\cr
8121 delete environment &&unset environment\cr
8122 info convenience &&show convenience\cr
8123 info copying &&show copying\cr
8124 info directories &&show directories \cr
8125 info editing &&show commands\cr
8126 info history &&show values\cr
8127 info targets &&help target\cr
8128 info values &&show values\cr
8129 info version &&show version\cr
8130 info warranty &&show warranty\cr
8131 set{\rm / }show addressprint &&set{\rm / }show print address\cr
8132 set{\rm / }show array-max &&set{\rm / }show print elements\cr
8133 set{\rm / }show arrayprint &&set{\rm / }show print array\cr
8134 set{\rm / }show asm-demangle &&set{\rm / }show print asm-demangle\cr
8135 set{\rm / }show caution &&set{\rm / }show confirm\cr
8136 set{\rm / }show demangle &&set{\rm / }show print demangle\cr
8137 set{\rm / }show history write &&set{\rm / }show history save\cr
8138 set{\rm / }show prettyprint &&set{\rm / }show print pretty\cr
8139 set{\rm / }show screen-height &&set{\rm / }show height\cr
8140 set{\rm / }show screen-width &&set{\rm / }show width\cr
8141 set{\rm / }show sevenbit-strings &&set{\rm / }show print sevenbit-strings\cr
8142 set{\rm / }show unionprint &&set{\rm / }show print union\cr
8143 set{\rm / }show vtblprint &&set{\rm / }show print vtbl\cr
8145 unset &&\rm(No longer an alias for delete)\cr
8148 @c END TEXI2ROFF-KILL
8151 @ifclear PRECONFIGURED
8152 @node Formatting Documentation
8153 @appendix Formatting Documentation
8155 @cindex GDB reference card
8156 @cindex reference card
8157 The GDB 4 release includes an already-formatted reference card, ready
8158 for printing with PostScript or GhostScript, in the @file{gdb}
8159 subdirectory of the main source directory@footnote{In
8160 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
8161 release.}. If you can use PostScript or GhostScript with your printer,
8162 you can print the reference card immediately with @file{refcard.ps}.
8164 The release also includes the source for the reference card. You
8165 can format it, using @TeX{}, by typing:
8171 The GDB reference card is designed to print in landscape mode on US
8172 ``letter'' size paper; that is, on a sheet 11 inches wide by 8.5 inches
8173 high. You will need to specify this form of printing as an option to
8174 your @sc{dvi} output program.
8176 @cindex documentation
8178 All the documentation for GDB comes as part of the machine-readable
8179 distribution. The documentation is written in Texinfo format, which is
8180 a documentation system that uses a single source file to produce both
8181 on-line information and a printed manual. You can use one of the Info
8182 formatting commands to create the on-line version of the documentation
8183 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
8185 GDB includes an already formatted copy of the on-line Info version of
8186 this manual in the @file{gdb} subdirectory. The main Info file is
8187 @file{gdb-@var{version-number}/gdb/gdb.info}, and it refers to
8188 subordinate files matching @samp{gdb.info*} in the same directory. If
8189 necessary, you can print out these files, or read them with any editor;
8190 but they are easier to read using the @code{info} subsystem in GNU Emacs
8191 or the standalone @code{info} program, available as part of the GNU
8192 Texinfo distribution.
8194 If you want to format these Info files yourself, you need one of the
8195 Info formatting programs, such as @code{texinfo-format-buffer} or
8198 If you have @code{makeinfo} installed, and are in the top level GDB
8199 source directory (@file{gdb-@value{GDBVN}}, in the case of version @value{GDBVN}), you can
8200 make the Info file by typing:
8207 If you want to typeset and print copies of this manual, you need @TeX{},
8208 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
8209 Texinfo definitions file.
8211 @TeX{} is a typesetting program; it does not print files directly, but
8212 produces output files called @sc{dvi} files. To print a typeset
8213 document, you need a program to print @sc{dvi} files. If your system
8214 has @TeX{} installed, chances are it has such a program. The precise
8215 command to use depends on your system; @kbd{lpr -d} is common; another
8216 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
8217 require a file name without any extension or a @samp{.dvi} extension.
8219 @TeX{} also requires a macro definitions file called
8220 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
8221 written in Texinfo format. On its own, @TeX{} cannot read, much less
8222 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
8223 and is located in the @file{gdb-@var{version-number}/texinfo}
8226 If you have @TeX{} and a @sc{dvi} printer program installed, you can
8227 typeset and print this manual. First switch to the the @file{gdb}
8228 subdirectory of the main source directory (for example, to
8229 @file{gdb-@value{GDBVN}/gdb}) and then type:
8235 @node Installing GDB
8236 @appendix Installing GDB
8237 @cindex configuring GDB
8238 @cindex installation
8240 GDB comes with a @code{configure} script that automates the process
8241 of preparing GDB for installation; you can then use @code{make} to
8242 build the @code{gdb} program.
8244 @c irrelevant in info file; it's as current as the code it lives with.
8245 @footnote{If you have a more recent version of GDB than @value{GDBVN},
8246 look at the @file{README} file in the sources; we may have improved the
8247 installation procedures since publishing this manual.}
8250 The GDB distribution includes all the source code you need for GDB in
8251 a single directory, whose name is usually composed by appending the
8252 version number to @samp{gdb}.
8254 For example, the GDB version @value{GDBVN} distribution is in the
8255 @file{gdb-@value{GDBVN}} directory. That directory contains:
8258 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
8259 script for configuring GDB and all its supporting libraries.
8261 @item gdb-@value{GDBVN}/gdb
8262 the source specific to GDB itself
8264 @item gdb-@value{GDBVN}/bfd
8265 source for the Binary File Descriptor library
8267 @item gdb-@value{GDBVN}/include
8270 @item gdb-@value{GDBVN}/libiberty
8271 source for the @samp{-liberty} free software library
8273 @item gdb-@value{GDBVN}/opcodes
8274 source for the library of opcode tables and disassemblers
8276 @item gdb-@value{GDBVN}/readline
8277 source for the GNU command-line interface
8279 @item gdb-@value{GDBVN}/glob
8280 source for the GNU filename pattern-matching subroutine
8282 @item gdb-@value{GDBVN}/mmalloc
8283 source for the GNU memory-mapped malloc package
8286 The simplest way to configure and build GDB is to run @code{configure}
8287 from the @file{gdb-@var{version-number}} source directory, which in
8288 this example is the @file{gdb-@value{GDBVN}} directory.
8290 First switch to the @file{gdb-@var{version-number}} source directory
8291 if you are not already in it; then run @code{configure}. Pass the
8292 identifier for the platform on which GDB will run as an
8298 cd gdb-@value{GDBVN}
8299 ./configure @var{host}
8304 where @var{host} is an identifier such as @samp{sun4} or
8305 @samp{decstation}, that identifies the platform where GDB will run.
8307 Running @samp{configure @var{host}} and then running @code{make} builds the
8308 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
8309 libraries, then @code{gdb} itself. The configured source files, and the
8310 binaries, are left in the corresponding source directories.
8312 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
8313 system does not recognize this automatically when you run a different
8314 shell, you may need to run @code{sh} on it explicitly:
8317 sh configure @var{host}
8320 If you run @code{configure} from a directory that contains source
8321 directories for multiple libraries or programs, such as the
8322 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
8323 creates configuration files for every directory level underneath (unless
8324 you tell it not to, with the @samp{--norecursion} option).
8326 You can run the @code{configure} script from any of the
8327 subordinate directories in the GDB distribution, if you only want to
8328 configure that subdirectory; but be sure to specify a path to it.
8330 For example, with version @value{GDBVN}, type the following to configure only
8331 the @code{bfd} subdirectory:
8335 cd gdb-@value{GDBVN}/bfd
8336 ../configure @var{host}
8340 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
8341 However, you should make sure that the shell on your path (named by
8342 the @samp{SHELL} environment variable) is publicly readable. Remember
8343 that GDB uses the shell to start your program---some systems refuse to
8344 let GDB debug child processes whose programs are not readable.
8347 * Separate Objdir:: Compiling GDB in another directory
8348 * Config Names:: Specifying names for hosts and targets
8349 * configure Options:: Summary of options for configure
8352 @node Separate Objdir
8353 @section Compiling GDB in another directory
8355 If you want to run GDB versions for several host or target machines,
8356 you need a different @code{gdb} compiled for each combination of
8357 host and target. @code{configure} is designed to make this easy by
8358 allowing you to generate each configuration in a separate subdirectory,
8359 rather than in the source directory. If your @code{make} program
8360 handles the @samp{VPATH} feature (GNU @code{make} does), running
8361 @code{make} in each of these directories builds the @code{gdb}
8362 program specified there.
8364 To build @code{gdb} in a separate directory, run @code{configure}
8365 with the @samp{--srcdir} option to specify where to find the source.
8366 (You also need to specify a path to find @code{configure}
8367 itself from your working directory. If the path to @code{configure}
8368 would be the same as the argument to @samp{--srcdir}, you can leave out
8369 the @samp{--srcdir} option; it will be assumed.)
8371 For example, with version @value{GDBVN}, you can build GDB in a separate
8372 directory for a Sun 4 like this:
8376 cd gdb-@value{GDBVN}
8379 ../gdb-@value{GDBVN}/configure sun4
8384 When @code{configure} builds a configuration using a remote source
8385 directory, it creates a tree for the binaries with the same structure
8386 (and using the same names) as the tree under the source directory. In
8387 the example, you'd find the Sun 4 library @file{libiberty.a} in the
8388 directory @file{gdb-sun4/libiberty}, and GDB itself in
8389 @file{gdb-sun4/gdb}.
8391 One popular reason to build several GDB configurations in separate
8392 directories is to configure GDB for cross-compiling (where GDB
8393 runs on one machine---the host---while debugging programs that run on
8394 another machine---the target). You specify a cross-debugging target by
8395 giving the @samp{--target=@var{target}} option to @code{configure}.
8397 When you run @code{make} to build a program or library, you must run
8398 it in a configured directory---whatever directory you were in when you
8399 called @code{configure} (or one of its subdirectories).
8401 The @code{Makefile} that @code{configure} generates in each source
8402 directory also runs recursively. If you type @code{make} in a source
8403 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
8404 directory configured with @samp{--srcdir=@var{path}/gdb-@value{GDBVN}}), you
8405 will build all the required libraries, and then build GDB.
8407 When you have multiple hosts or targets configured in separate
8408 directories, you can run @code{make} on them in parallel (for example,
8409 if they are NFS-mounted on each of the hosts); they will not interfere
8413 @section Specifying names for hosts and targets
8415 The specifications used for hosts and targets in the @code{configure}
8416 script are based on a three-part naming scheme, but some short predefined
8417 aliases are also supported. The full naming scheme encodes three pieces
8418 of information in the following pattern:
8421 @var{architecture}-@var{vendor}-@var{os}
8424 For example, you can use the alias @code{sun4} as a @var{host} argument,
8425 or as the value for @var{target} in a @code{--target=@var{target}}
8426 option. The equivalent full name is @samp{sparc-sun-sunos4}.
8428 The @code{configure} script accompanying GDB does not provide
8429 any query facility to list all supported host and target names or
8430 aliases. @code{configure} calls the Bourne shell script
8431 @code{config.sub} to map abbreviations to full names; you can read the
8432 script, if you wish, or you can use it to test your guesses on
8433 abbreviations---for example:
8436 % sh config.sub sun4
8438 % sh config.sub sun3
8440 % sh config.sub decstation
8442 % sh config.sub hp300bsd
8444 % sh config.sub i386v
8446 % sh config.sub i786v
8447 Invalid configuration `i786v': machine `i786v' not recognized
8451 @code{config.sub} is also distributed in the GDB source
8452 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
8454 @node configure Options
8455 @section @code{configure} options
8457 Here is a summary of the @code{configure} options and arguments that
8458 are most often useful for building @value{GDBN}. @code{configure} also has
8459 several other options not listed here. @inforef{What Configure
8460 Does,,configure.info}, for a full explanation of @code{configure}.
8461 @c FIXME: Would this be more, or less, useful as an xref (ref to printed
8462 @c manual in the printed manual, ref to info file only from the info file)?
8465 configure @r{[}--help@r{]}
8466 @r{[}--prefix=@var{dir}@r{]}
8467 @r{[}--srcdir=@var{path}@r{]}
8468 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
8469 @r{[}--target=@var{target}@r{]} @var{host}
8473 You may introduce options with a single @samp{-} rather than
8474 @samp{--} if you prefer; but you may abbreviate option names if you use
8479 Display a quick summary of how to invoke @code{configure}.
8481 @item -prefix=@var{dir}
8482 Configure the source to install programs and files under directory
8485 @item --srcdir=@var{path}
8486 @strong{Warning: using this option requires GNU @code{make}, or another
8487 @code{make} that implements the @code{VPATH} feature.}@*
8488 Use this option to make configurations in directories separate from the
8489 GDB source directories. Among other things, you can use this to
8490 build (or maintain) several configurations simultaneously, in separate
8491 directories. @code{configure} writes configuration specific files in
8492 the current directory, but arranges for them to use the source in the
8493 directory @var{path}. @code{configure} will create directories under
8494 the working directory in parallel to the source directories below
8498 Configure only the directory level where @code{configure} is executed; do not
8499 propagate configuration to subdirectories.
8502 Remove the configuration that the other arguments specify.
8504 @c This does not work (yet if ever). FIXME.
8505 @c @item --parse=@var{lang} @dots{}
8506 @c Configure the GDB expression parser to parse the listed languages.
8507 @c @samp{all} configures GDB for all supported languages. To get a
8508 @c list of all supported languages, omit the argument. Without this
8509 @c option, GDB is configured to parse all supported languages.
8511 @item --target=@var{target}
8512 Configure GDB for cross-debugging programs running on the specified
8513 @var{target}. Without this option, GDB is configured to debug
8514 programs that run on the same machine (@var{host}) as GDB itself.
8516 There is no convenient way to generate a list of all available targets.
8518 @item @var{host} @dots{}
8519 Configure GDB to run on the specified @var{host}.
8521 There is no convenient way to generate a list of all available hosts.
8525 @code{configure} accepts other options, for compatibility with
8526 configuring other GNU tools recursively; but these are the only
8527 options that affect GDB or its supporting libraries.
8530 @ifclear AGGLOMERATION
8532 @unnumbered GNU GENERAL PUBLIC LICENSE
8533 @center Version 2, June 1991
8536 Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc.
8537 675 Mass Ave, Cambridge, MA 02139, USA
8539 Everyone is permitted to copy and distribute verbatim copies
8540 of this license document, but changing it is not allowed.
8543 @unnumberedsec Preamble
8545 The licenses for most software are designed to take away your
8546 freedom to share and change it. By contrast, the GNU General Public
8547 License is intended to guarantee your freedom to share and change free
8548 software---to make sure the software is free for all its users. This
8549 General Public License applies to most of the Free Software
8550 Foundation's software and to any other program whose authors commit to
8551 using it. (Some other Free Software Foundation software is covered by
8552 the GNU Library General Public License instead.) You can apply it to
8555 When we speak of free software, we are referring to freedom, not
8556 price. Our General Public Licenses are designed to make sure that you
8557 have the freedom to distribute copies of free software (and charge for
8558 this service if you wish), that you receive source code or can get it
8559 if you want it, that you can change the software or use pieces of it
8560 in new free programs; and that you know you can do these things.
8562 To protect your rights, we need to make restrictions that forbid
8563 anyone to deny you these rights or to ask you to surrender the rights.
8564 These restrictions translate to certain responsibilities for you if you
8565 distribute copies of the software, or if you modify it.
8567 For example, if you distribute copies of such a program, whether
8568 gratis or for a fee, you must give the recipients all the rights that
8569 you have. You must make sure that they, too, receive or can get the
8570 source code. And you must show them these terms so they know their
8573 We protect your rights with two steps: (1) copyright the software, and
8574 (2) offer you this license which gives you legal permission to copy,
8575 distribute and/or modify the software.
8577 Also, for each author's protection and ours, we want to make certain
8578 that everyone understands that there is no warranty for this free
8579 software. If the software is modified by someone else and passed on, we
8580 want its recipients to know that what they have is not the original, so
8581 that any problems introduced by others will not reflect on the original
8582 authors' reputations.
8584 Finally, any free program is threatened constantly by software
8585 patents. We wish to avoid the danger that redistributors of a free
8586 program will individually obtain patent licenses, in effect making the
8587 program proprietary. To prevent this, we have made it clear that any
8588 patent must be licensed for everyone's free use or not licensed at all.
8590 The precise terms and conditions for copying, distribution and
8591 modification follow.
8594 @unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
8597 @center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
8602 This License applies to any program or other work which contains
8603 a notice placed by the copyright holder saying it may be distributed
8604 under the terms of this General Public License. The ``Program'', below,
8605 refers to any such program or work, and a ``work based on the Program''
8606 means either the Program or any derivative work under copyright law:
8607 that is to say, a work containing the Program or a portion of it,
8608 either verbatim or with modifications and/or translated into another
8609 language. (Hereinafter, translation is included without limitation in
8610 the term ``modification''.) Each licensee is addressed as ``you''.
8612 Activities other than copying, distribution and modification are not
8613 covered by this License; they are outside its scope. The act of
8614 running the Program is not restricted, and the output from the Program
8615 is covered only if its contents constitute a work based on the
8616 Program (independent of having been made by running the Program).
8617 Whether that is true depends on what the Program does.
8620 You may copy and distribute verbatim copies of the Program's
8621 source code as you receive it, in any medium, provided that you
8622 conspicuously and appropriately publish on each copy an appropriate
8623 copyright notice and disclaimer of warranty; keep intact all the
8624 notices that refer to this License and to the absence of any warranty;
8625 and give any other recipients of the Program a copy of this License
8626 along with the Program.
8628 You may charge a fee for the physical act of transferring a copy, and
8629 you may at your option offer warranty protection in exchange for a fee.
8632 You may modify your copy or copies of the Program or any portion
8633 of it, thus forming a work based on the Program, and copy and
8634 distribute such modifications or work under the terms of Section 1
8635 above, provided that you also meet all of these conditions:
8639 You must cause the modified files to carry prominent notices
8640 stating that you changed the files and the date of any change.
8643 You must cause any work that you distribute or publish, that in
8644 whole or in part contains or is derived from the Program or any
8645 part thereof, to be licensed as a whole at no charge to all third
8646 parties under the terms of this License.
8649 If the modified program normally reads commands interactively
8650 when run, you must cause it, when started running for such
8651 interactive use in the most ordinary way, to print or display an
8652 announcement including an appropriate copyright notice and a
8653 notice that there is no warranty (or else, saying that you provide
8654 a warranty) and that users may redistribute the program under
8655 these conditions, and telling the user how to view a copy of this
8656 License. (Exception: if the Program itself is interactive but
8657 does not normally print such an announcement, your work based on
8658 the Program is not required to print an announcement.)
8661 These requirements apply to the modified work as a whole. If
8662 identifiable sections of that work are not derived from the Program,
8663 and can be reasonably considered independent and separate works in
8664 themselves, then this License, and its terms, do not apply to those
8665 sections when you distribute them as separate works. But when you
8666 distribute the same sections as part of a whole which is a work based
8667 on the Program, the distribution of the whole must be on the terms of
8668 this License, whose permissions for other licensees extend to the
8669 entire whole, and thus to each and every part regardless of who wrote it.
8671 Thus, it is not the intent of this section to claim rights or contest
8672 your rights to work written entirely by you; rather, the intent is to
8673 exercise the right to control the distribution of derivative or
8674 collective works based on the Program.
8676 In addition, mere aggregation of another work not based on the Program
8677 with the Program (or with a work based on the Program) on a volume of
8678 a storage or distribution medium does not bring the other work under
8679 the scope of this License.
8682 You may copy and distribute the Program (or a work based on it,
8683 under Section 2) in object code or executable form under the terms of
8684 Sections 1 and 2 above provided that you also do one of the following:
8688 Accompany it with the complete corresponding machine-readable
8689 source code, which must be distributed under the terms of Sections
8690 1 and 2 above on a medium customarily used for software interchange; or,
8693 Accompany it with a written offer, valid for at least three
8694 years, to give any third party, for a charge no more than your
8695 cost of physically performing source distribution, a complete
8696 machine-readable copy of the corresponding source code, to be
8697 distributed under the terms of Sections 1 and 2 above on a medium
8698 customarily used for software interchange; or,
8701 Accompany it with the information you received as to the offer
8702 to distribute corresponding source code. (This alternative is
8703 allowed only for noncommercial distribution and only if you
8704 received the program in object code or executable form with such
8705 an offer, in accord with Subsection b above.)
8708 The source code for a work means the preferred form of the work for
8709 making modifications to it. For an executable work, complete source
8710 code means all the source code for all modules it contains, plus any
8711 associated interface definition files, plus the scripts used to
8712 control compilation and installation of the executable. However, as a
8713 special exception, the source code distributed need not include
8714 anything that is normally distributed (in either source or binary
8715 form) with the major components (compiler, kernel, and so on) of the
8716 operating system on which the executable runs, unless that component
8717 itself accompanies the executable.
8719 If distribution of executable or object code is made by offering
8720 access to copy from a designated place, then offering equivalent
8721 access to copy the source code from the same place counts as
8722 distribution of the source code, even though third parties are not
8723 compelled to copy the source along with the object code.
8726 You may not copy, modify, sublicense, or distribute the Program
8727 except as expressly provided under this License. Any attempt
8728 otherwise to copy, modify, sublicense or distribute the Program is
8729 void, and will automatically terminate your rights under this License.
8730 However, parties who have received copies, or rights, from you under
8731 this License will not have their licenses terminated so long as such
8732 parties remain in full compliance.
8735 You are not required to accept this License, since you have not
8736 signed it. However, nothing else grants you permission to modify or
8737 distribute the Program or its derivative works. These actions are
8738 prohibited by law if you do not accept this License. Therefore, by
8739 modifying or distributing the Program (or any work based on the
8740 Program), you indicate your acceptance of this License to do so, and
8741 all its terms and conditions for copying, distributing or modifying
8742 the Program or works based on it.
8745 Each time you redistribute the Program (or any work based on the
8746 Program), the recipient automatically receives a license from the
8747 original licensor to copy, distribute or modify the Program subject to
8748 these terms and conditions. You may not impose any further
8749 restrictions on the recipients' exercise of the rights granted herein.
8750 You are not responsible for enforcing compliance by third parties to
8754 If, as a consequence of a court judgment or allegation of patent
8755 infringement or for any other reason (not limited to patent issues),
8756 conditions are imposed on you (whether by court order, agreement or
8757 otherwise) that contradict the conditions of this License, they do not
8758 excuse you from the conditions of this License. If you cannot
8759 distribute so as to satisfy simultaneously your obligations under this
8760 License and any other pertinent obligations, then as a consequence you
8761 may not distribute the Program at all. For example, if a patent
8762 license would not permit royalty-free redistribution of the Program by
8763 all those who receive copies directly or indirectly through you, then
8764 the only way you could satisfy both it and this License would be to
8765 refrain entirely from distribution of the Program.
8767 If any portion of this section is held invalid or unenforceable under
8768 any particular circumstance, the balance of the section is intended to
8769 apply and the section as a whole is intended to apply in other
8772 It is not the purpose of this section to induce you to infringe any
8773 patents or other property right claims or to contest validity of any
8774 such claims; this section has the sole purpose of protecting the
8775 integrity of the free software distribution system, which is
8776 implemented by public license practices. Many people have made
8777 generous contributions to the wide range of software distributed
8778 through that system in reliance on consistent application of that
8779 system; it is up to the author/donor to decide if he or she is willing
8780 to distribute software through any other system and a licensee cannot
8783 This section is intended to make thoroughly clear what is believed to
8784 be a consequence of the rest of this License.
8787 If the distribution and/or use of the Program is restricted in
8788 certain countries either by patents or by copyrighted interfaces, the
8789 original copyright holder who places the Program under this License
8790 may add an explicit geographical distribution limitation excluding
8791 those countries, so that distribution is permitted only in or among
8792 countries not thus excluded. In such case, this License incorporates
8793 the limitation as if written in the body of this License.
8796 The Free Software Foundation may publish revised and/or new versions
8797 of the General Public License from time to time. Such new versions will
8798 be similar in spirit to the present version, but may differ in detail to
8799 address new problems or concerns.
8801 Each version is given a distinguishing version number. If the Program
8802 specifies a version number of this License which applies to it and ``any
8803 later version'', you have the option of following the terms and conditions
8804 either of that version or of any later version published by the Free
8805 Software Foundation. If the Program does not specify a version number of
8806 this License, you may choose any version ever published by the Free Software
8810 If you wish to incorporate parts of the Program into other free
8811 programs whose distribution conditions are different, write to the author
8812 to ask for permission. For software which is copyrighted by the Free
8813 Software Foundation, write to the Free Software Foundation; we sometimes
8814 make exceptions for this. Our decision will be guided by the two goals
8815 of preserving the free status of all derivatives of our free software and
8816 of promoting the sharing and reuse of software generally.
8819 @heading NO WARRANTY
8826 BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
8827 FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN
8828 OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
8829 PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
8830 OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
8831 MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS
8832 TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE
8833 PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
8834 REPAIR OR CORRECTION.
8837 IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
8838 WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
8839 REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
8840 INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
8841 OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
8842 TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
8843 YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
8844 PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
8845 POSSIBILITY OF SUCH DAMAGES.
8849 @heading END OF TERMS AND CONDITIONS
8852 @center END OF TERMS AND CONDITIONS
8856 @unnumberedsec Applying These Terms to Your New Programs
8858 If you develop a new program, and you want it to be of the greatest
8859 possible use to the public, the best way to achieve this is to make it
8860 free software which everyone can redistribute and change under these terms.
8862 To do so, attach the following notices to the program. It is safest
8863 to attach them to the start of each source file to most effectively
8864 convey the exclusion of warranty; and each file should have at least
8865 the ``copyright'' line and a pointer to where the full notice is found.
8868 @var{one line to give the program's name and an idea of what it does.}
8869 Copyright (C) 19@var{yy} @var{name of author}
8871 This program is free software; you can redistribute it and/or
8872 modify it under the terms of the GNU General Public License
8873 as published by the Free Software Foundation; either version 2
8874 of the License, or (at your option) any later version.
8876 This program is distributed in the hope that it will be useful,
8877 but WITHOUT ANY WARRANTY; without even the implied warranty of
8878 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
8879 GNU General Public License for more details.
8881 You should have received a copy of the GNU General Public License
8882 along with this program; if not, write to the
8883 Free Software Foundation, Inc., 675 Mass Ave,
8884 Cambridge, MA 02139, USA.
8887 Also add information on how to contact you by electronic and paper mail.
8889 If the program is interactive, make it output a short notice like this
8890 when it starts in an interactive mode:
8893 Gnomovision version 69, Copyright (C) 19@var{yy} @var{name of author}
8894 Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
8895 type `show w'. This is free software, and you are welcome
8896 to redistribute it under certain conditions; type `show c'
8900 The hypothetical commands @samp{show w} and @samp{show c} should show
8901 the appropriate parts of the General Public License. Of course, the
8902 commands you use may be called something other than @samp{show w} and
8903 @samp{show c}; they could even be mouse-clicks or menu items---whatever
8906 You should also get your employer (if you work as a programmer) or your
8907 school, if any, to sign a ``copyright disclaimer'' for the program, if
8908 necessary. Here is a sample; alter the names:
8911 Yoyodyne, Inc., hereby disclaims all copyright
8912 interest in the program `Gnomovision'
8913 (which makes passes at compilers) written
8916 @var{signature of Ty Coon}, 1 April 1989
8917 Ty Coon, President of Vice
8920 This General Public License does not permit incorporating your program into
8921 proprietary programs. If your program is a subroutine library, you may
8922 consider it more useful to permit linking proprietary applications with the
8923 library. If this is what you want to do, use the GNU Library General
8924 Public License instead of this License.
8933 % I think something like @colophon should be in texinfo. In the
8935 \long\def\colophon{\hbox to0pt{}\vfill
8936 \centerline{The body of this manual is set in}
8937 \centerline{\fontname\tenrm,}
8938 \centerline{with headings in {\bf\fontname\tenbf}}
8939 \centerline{and examples in {\tt\fontname\tentt}.}
8940 \centerline{{\it\fontname\tenit\/},}
8941 \centerline{{\bf\fontname\tenbf}, and}
8942 \centerline{{\sl\fontname\tensl\/}}
8943 \centerline{are used for emphasis.}\vfill}
8945 % Blame: pesch@cygnus.com, 1991.