2 _dnl__ Copyright (c) 1988 1989 1990 1991 1992 Free Software Foundation, Inc.
4 \input texinfo @c -*-texinfo-*-
5 @c Copyright (c) 1988 1989 1990 1991 1992 Free Software Foundation, Inc.
7 @setfilename _GDBP__.info
9 @settitle Using _GDBN__ (v4)
12 @settitle Using _GDBN__ v4 (_HOST__)
14 @setchapternewpage odd
22 _0__@c ===> NOTE! <==_1__
23 @c Determine the edition number in *three* places by hand:
24 @c 1. First ifinfo section 2. title page 3. top node
25 @c To find the locations, search for !!set
27 @c The following is for Pesch for his RCS system.
28 @c This revision number *not* the same as the Edition number.
30 \def\$#1${{#1}} % Kluge: collect RCS revision info without $...$
31 \xdef\manvers{\$Revision$} % For use in headers, footers too
34 @c FOR UPDATES LEADING TO THIS DRAFT, GDB CHANGELOG CONSULTED BETWEEN:
35 @c Fri Oct 11 23:27:06 1991 John Gilmore (gnu at cygnus.com)
36 @c Sat Dec 22 02:51:40 1990 John Gilmore (gnu at cygint)
38 @c THIS MANUAL REQUIRES TEXINFO-2 macros and info-makers to format properly.
43 * Gdb: (gdb). The GNU debugger.
49 NOTE: this manual is marked up for preprocessing with a collection
50 of m4 macros called "pretex.m4".
52 THIS IS THE SOURCE PRIOR TO PREPROCESSING. The full source needs to
53 be run through m4 before either tex- or info- formatting: for example,
55 m4 pretex.m4 none.m4 all.m4 gdb.texinfo >gdb-all.texinfo
56 will produce (assuming your path finds either GNU m4 >= 0.84, or SysV
57 m4; Berkeley will not do) a file suitable for formatting. See the text in
58 "pretex.m4" for a fuller explanation (and the macro definitions).
64 This file documents the GNU debugger _GDBN__.
66 @c !!set edition, date, version
67 This is Edition 4.01, January 1992,
68 of @cite{Using GDB: A Guide to the GNU Source-Level Debugger}
69 for GDB Version _GDB_VN__.
71 Copyright (C) 1988, 1989, 1990, 1991 1992 Free Software Foundation, Inc.
73 Permission is granted to make and distribute verbatim copies of
74 this manual provided the copyright notice and this permission notice
75 are preserved on all copies.
78 Permission is granted to process this file through TeX and print the
79 results, provided the printed document carries copying permission
80 notice identical to this one except for the removal of this paragraph
81 (this paragraph not being relevant to the printed manual).
84 Permission is granted to copy and distribute modified versions of this
85 manual under the conditions for verbatim copying, provided also that the
86 section entitled ``GNU General Public License'' is included exactly as
87 in the original, and provided that the entire resulting derived work is
88 distributed under the terms of a permission notice identical to this
91 Permission is granted to copy and distribute translations of this manual
92 into another language, under the above conditions for modified versions,
93 except that the section entitled ``GNU General Public License'' may be
94 included in a translation approved by the Free Software Foundation
95 instead of in the original English.
100 @subtitle A Guide to the GNU Source-Level Debugger
102 @subtitle On _HOST__ Systems
105 @c !!set edition, date, version
106 @subtitle Edition 4.01, for _GDBN__ version _GDB_VN__
107 @subtitle January 1992
108 @author by Richard M. Stallman and Roland H. Pesch
112 \hfill rms\@ai.mit.edu, pesch\@cygnus.com\par
113 \hfill {\it Using _GDBN__}, \manvers\par
114 \hfill \TeX{}info \texinfoversion\par
118 @vskip 0pt plus 1filll
119 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992 Free Software Foundation, Inc.
121 Permission is granted to make and distribute verbatim copies of
122 this manual provided the copyright notice and this permission notice
123 are preserved on all copies.
125 Permission is granted to copy and distribute modified versions of this
126 manual under the conditions for verbatim copying, provided also that the
127 section entitled ``GNU General Public License'' is included exactly as
128 in the original, and provided that the entire resulting derived work is
129 distributed under the terms of a permission notice identical to this
132 Permission is granted to copy and distribute translations of this manual
133 into another language, under the above conditions for modified versions,
134 except that the section entitled ``GNU General Public License'' may be
135 included in a translation approved by the Free Software Foundation
136 instead of in the original English.
141 @node Top, Summary, (dir), (dir)
142 @top _GDBN__, the GNU symbolic debugger
144 This file describes _GDBN__, the GNU symbolic debugger.
146 @c !!set edition, date, version
147 This is Edition 4.01, January 1992, for GDB Version _GDB_VN__.
151 * Summary:: Summary of _GDBN__
152 * New Features:: New features since _GDBN__ version 3.5
153 * Sample Session:: A Sample _GDBN__ session
154 * Invocation:: Getting in and out of _GDBN__
155 * Commands:: _GDBN__ commands
156 * Running:: Running programs under _GDBN__
157 * Stopping:: Stopping and continuing
158 * Stack:: Examining the stack
159 * Source:: Examining source files
160 * Data:: Examining data
161 * Languages:: Using _GDBN__ with different languages
162 * Symbols:: Examining the symbol table
163 * Altering:: Altering execution
164 * _GDBN__ Files:: _GDBN__'s files
165 * Targets:: Specifying a debugging target
166 * Controlling _GDBN__:: Controlling _GDBN__
167 * Sequences:: Canned sequences of commands
168 * Emacs:: Using _GDBN__ under GNU Emacs
169 * _GDBN__ Bugs:: Reporting bugs in _GDBN__
171 * Installing _GDBN__:: Installing _GDBN__
172 * Copying:: GNU GENERAL PUBLIC LICENSE
175 --- The Detailed Node Listing ---
179 * Free Software:: Free Software
180 * Contributors:: Contributors to _GDBN__
182 Getting In and Out of _GDBN__
184 * Invoking _GDBN__:: Starting _GDBN__
185 * Leaving _GDBN__:: Leaving _GDBN__
186 * Shell Commands:: Shell Commands
190 * File Options:: Choosing Files
191 * Mode Options:: Choosing Modes
195 * Command Syntax:: Command Syntax
196 * Help:: Getting Help
198 Running Programs Under _GDBN__
200 * Compilation:: Compiling for Debugging
201 * Starting:: Starting your Program
202 * Arguments:: Your Program's Arguments
203 * Environment:: Your Program's Environment
204 * Working Directory:: Your Program's Working Directory
205 * Input/Output:: Your Program's Input and Output
206 * Attach:: Debugging an Already-Running Process
207 * Kill Process:: Killing the Child Process
209 Stopping and Continuing
211 * Breakpoints:: Breakpoints, Watchpoints, and Exceptions
212 * Continuing and Stepping:: Resuming Execution
215 Breakpoints, Watchpoints, and Exceptions
217 * Set Breaks:: Setting Breakpoints
218 * Set Watchpoints:: Setting Watchpoints
219 * Exception Handling:: Breakpoints and Exceptions
220 * Delete Breaks:: Deleting Breakpoints
221 * Disabling:: Disabling Breakpoints
222 * Conditions:: Break Conditions
223 * Break Commands:: Breakpoint Command Lists
224 * Breakpoint Menus:: Breakpoint Menus
225 * Error in Breakpoints:: ``Cannot insert breakpoints''
229 * Frames:: Stack Frames
230 * Backtrace:: Backtraces
231 * Selection:: Selecting a Frame
232 * Frame Info:: Information on a Frame
234 Examining Source Files
236 * List:: Printing Source Lines
237 * Search:: Searching Source Files
238 * Source Path:: Specifying Source Directories
239 * Machine Code:: Source and Machine Code
243 * Expressions:: Expressions
244 * Variables:: Program Variables
245 * Arrays:: Artificial Arrays
246 * Output formats:: Output formats
247 * Memory:: Examining Memory
248 * Auto Display:: Automatic Display
249 * Print Settings:: Print Settings
250 * Value History:: Value History
251 * Convenience Vars:: Convenience Variables
252 * Registers:: Registers
253 * Floating Point Hardware:: Floating Point Hardware
255 Using GDB with Different Languages
257 * Setting:: Switching between source languages
258 * Show:: Displaying the language
259 * Checks:: Type and Range checks
260 * Support:: Supported languages
262 Switching between source languages
264 * Manually:: Setting the working language manually
265 * Automatically:: Having GDB infer the source language
267 Type and range Checking
269 * Type Checking:: An overview of type checking
270 * Range Checking:: An overview of range checking
275 * Modula-2:: Modula-2
279 * C Operators:: C and C++ Operators
280 * C Constants:: C and C++ Constants
281 * Cplusplus expressions:: C++ Expressions
282 * C Defaults:: Default settings for C and C++
283 * C Checks:: C and C++ Type and Range Checks
284 * Debugging C:: _GDBN__ and C
285 * Debugging C plus plus:: Special features for C++
289 * M2 Operators:: Built-in operators
290 * Built-In Func/Proc:: Built-in Functions and Procedures
291 * M2 Constants:: Modula-2 Constants
292 * M2 Defaults:: Default settings for Modula-2
293 * Deviations:: Deviations from standard Modula-2
294 * M2 Checks:: Modula-2 Type and Range Checks
295 * M2 Scope:: The scope operators @code{::} and @code{.}
296 * GDB/M2:: GDB and Modula-2
300 * Assignment:: Assignment to Variables
301 * Jumping:: Continuing at a Different Address
302 * Signaling:: Giving your program a Signal
303 * Returning:: Returning from a Function
304 * Calling:: Calling your Program's Functions
305 * Patching:: Patching your Program
309 * Files:: Commands to Specify Files
310 * Symbol Errors:: Errors Reading Symbol Files
312 Specifying a Debugging Target
314 * Active Targets:: Active Targets
315 * Target Commands:: Commands for Managing Targets
316 * Remote:: Remote Debugging
320 * i960-Nindy Remote:: _GDBN__ with a Remote i960 (Nindy)
321 * EB29K Remote:: _GDBN__ with a Remote EB29K
322 * VxWorks Remote:: _GDBN__ and VxWorks
324 _GDBN__ with a Remote i960 (Nindy)
326 * Nindy Startup:: Startup with Nindy
327 * Nindy Options:: Options for Nindy
328 * Nindy reset:: Nindy Reset Command
330 _GDBN__ with a Remote EB29K
332 * Comms (EB29K):: Communications Setup
333 * gdb-EB29K:: EB29K cross-debugging
334 * Remote Log:: Remote Log
338 * VxWorks connection:: Connecting to VxWorks
339 * VxWorks download:: VxWorks Download
340 * VxWorks attach:: Running Tasks
345 * Editing:: Command Editing
346 * History:: Command History
347 * Screen Size:: Screen Size
349 * Messages/Warnings:: Optional Warnings and Messages
351 Canned Sequences of Commands
353 * Define:: User-Defined Commands
354 * Command Files:: Command Files
355 * Output:: Commands for Controlled Output
357 Reporting Bugs in _GDBN__
359 * Bug Criteria:: Have You Found a Bug?
360 * Bug Reporting:: How to Report Bugs
364 * Separate Objdir:: Compiling _GDBN__ in another directory
365 * Config Names:: Specifying names for hosts and targets
366 * configure Options:: Summary of options for configure
367 * Formatting Documentation:: How to format and print GDB documentation
370 @node Summary, New Features, Top, Top
371 @unnumbered Summary of _GDBN__
373 The purpose of a debugger such as _GDBN__ is to allow you to see what is
374 going on ``inside'' another program while it executes---or what another
375 program was doing at the moment it crashed.
377 _GDBN__ can do four main kinds of things (plus other things in support of
378 these) to help you catch bugs in the act:
382 Start your program, specifying anything that might affect its behavior.
385 Make your program stop on specified conditions.
388 Examine what has happened, when your program has stopped.
391 Change things in your program, so you can experiment with correcting the
392 effects of one bug and go on to learn about another.
395 You can use _GDBN__ to debug programs written in C, C++, and Modula-2.
396 Fortran support will be added when a GNU Fortran compiler is ready.
399 * Free Software:: Free Software
400 * Contributors:: Contributors to GDB
403 @node Free Software, Contributors, Summary, Summary
404 @unnumberedsec Free Software
406 _GDBN__ is @dfn{free software}, protected by the GNU General Public License
407 (GPL). The GPL gives you the freedom to copy or adapt a licensed
408 program---but every person getting a copy also gets with it the
409 freedom to modify that copy (which means that they must get access to
410 the source code), and the freedom to distribute further copies.
411 Typical software companies use copyrights to limit your freedoms; the
412 Free Software Foundation uses the GPL to preserve these freedoms.
414 Fundamentally, the General Public License is a license which says that
415 you have these freedoms and that you cannot take these freedoms away
418 For full details, @pxref{Copying, ,GNU GENERAL PUBLIC LICENSE}.
420 @node Contributors, , Free Software, Summary
421 @unnumberedsec Contributors to GDB
423 Richard Stallman was the original author of GDB, and of many other GNU
424 programs. Many others have contributed to its development. This
425 section attempts to credit major contributors. One of the virtues of
426 free software is that everyone is free to contribute to it; with
427 regret, we cannot actually acknowledge everyone here. The file
428 @file{ChangeLog} in the GDB distribution approximates a blow-by-blow
431 Changes much prior to version 2.0 are lost in the mists of time.
434 @emph{Plea:} Additions to this section are particularly welcome. If you
435 or your friends (or enemies; let's be evenhanded) have been unfairly
436 omitted from this list, we would like to add your names!
439 So that they may not regard their long labor as thankless, we
440 particularly thank those who shepherded GDB through major releases: Stu
441 Grossman and John Gilmore (release 4.4), John Gilmore (releases 4.3, 4.2,
442 4.1, 4.0, and 3.9); Jim Kingdon (releases 3.5, 3.4, 3.3); and Randy
443 Smith (releases 3.2, 3.1, 3.0). As major maintainer of GDB for some
444 period, each contributed significantly to the structure, stability, and
445 capabilities of the entire debugger.
447 Richard Stallman, assisted at various times by Pete TerMaat, Chris
448 Hanson, and Richard Mlynarik, handled releases through 2.8.
450 Michael Tiemann is the author of most of the GNU C++ support in GDB,
451 with significant additional contributions from Per Bothner. James
452 Clark wrote the GNU C++ demangler. Early work on C++ was by Peter
453 TerMaat (who also did much general update work leading to release 3.0).
455 GDB 4 uses the BFD subroutine library to examine multiple
456 object-file formats; BFD was a joint project of David V.
457 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
459 David Johnson wrote the original COFF support; Pace Willison did
460 the original support for encapsulated COFF.
462 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
463 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
464 support. Jean-Daniel Fekete contributed Sun 386i support. Chris
465 Hanson improved the HP9000 support. Noboyuki Hikichi and Tomoyuki
466 Hasei contributed Sony/News OS 3 support. David Johnson contributed
467 Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support.
468 Keith Packard contributed NS32K support. Doug Rabson contributed
469 Acorn Risc Machine support. Chris Smith contributed Convex support
470 (and Fortran debugging). Jonathan Stone contributed Pyramid support.
471 Michael Tiemann contributed SPARC support. Tim Tucker contributed
472 support for the Gould NP1 and Gould Powernode. Pace Willison
473 contributed Intel 386 support. Jay Vosburgh contributed Symmetry
476 Rich Schaefer and Peter Schauer helped with support of SunOS shared
479 Jay Fenlason and Roland McGrath ensured that GDB and GAS agree about
480 several machine instruction sets.
482 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped
483 develop remote debugging. Intel Corporation and Wind River Systems
484 contributed remote debugging modules for their products.
486 Brian Fox is the author of the readline libraries providing
487 command-line editing and command history.
489 Andrew Beers of SUNY Buffalo wrote the language-switching code and
490 the Modula-2 support, and contributed the Languages chapter of this
493 @node New Features, Sample Session, Summary, Top
494 @unnumbered New Features since _GDBN__ version 3.5
498 Using the new command @code{target}, you can select at runtime whether
499 you are debugging local files, local processes, standalone systems over
500 a serial port, realtime systems over a TCP/IP connection, etc. The
501 command @code{load} can download programs into a remote system. Serial
502 stubs are available for Motorola 680x0 and Intel 80386 remote systems;
503 _GDBN__ also supports debugging realtime processes running under
504 VxWorks, using SunRPC Remote Procedure Calls over TCP/IP to talk to a
505 debugger stub on the target system. Internally, _GDBN__ now uses a
506 function vector to mediate access to different targets; if you need to
507 add your own support for a remote protocol, this makes it much easier.
510 _GDBN__ now sports watchpoints as well as breakpoints. You can use a
511 watchpoint to stop execution whenever the value of an expression
512 changes, without having to predict a particular place in your program
513 where this may happen.
516 Commands that issue wide output now insert newlines at places designed
517 to make the output more readable.
519 @item Object Code Formats
520 _GDBN__ uses a new library called the Binary File Descriptor (BFD)
521 Library to permit it to switch dynamically, without reconfiguration or
522 recompilation, between different object-file formats. Formats currently
523 supported are COFF, a.out, and the Intel 960 b.out; files may be read as
524 .o's, archive libraries, or core dumps. BFD is available as a
525 subroutine library so that other programs may take advantage of it, and
526 the other GNU binary utilities are being converted to use it.
528 @item Configuration and Ports
529 Compile-time configuration (to select a particular architecture and
530 operating system) is much easier. The script @code{configure} now
531 allows you to configure _GDBN__ as either a native debugger or a
532 cross-debugger. @xref{Installing _GDBN__}, for details on how to
533 configure and on what architectures are now available.
536 The user interface to _GDBN__'s control variables has been simplified
537 and consolidated in two commands, @code{set} and @code{show}. Output
538 lines are now broken at readable places, rather than overflowing onto
539 the next line. You can suppress output of machine-level addresses,
540 displaying only source language information.
543 _GDBN__ now supports C++ multiple inheritance (if used with a GCC
544 version 2 compiler), and also has limited support for C++ exception
545 handling, with the commands @code{catch} and @code{info catch}: _GDBN__
546 can break when an exception is raised, before the stack is peeled back
547 to the exception handler's context.
550 _GDBN__ now has preliminary support for the GNU Modula-2 compiler,
551 currently under development at the State University of New York at
552 Buffalo. Coordinated development of both _GDBN__ and the GNU Modula-2
553 compiler will continue into 1992. Other Modula-2 compilers are
554 currently not supported, and attempting to debug programs compiled with
555 them will likely result in an error as the symbol table of the
556 executable is read in.
558 @item Command Rationalization
559 Many _GDBN__ commands have been renamed to make them easier to remember
560 and use. In particular, the subcommands of @code{info} and
561 @code{show}/@code{set} are grouped to make the former refer to the state
562 of your program, and the latter refer to the state of _GDBN__ itself.
563 @xref{Renamed Commands}, for details on what commands were renamed.
565 @item Shared Libraries
566 _GDBN__ 4 can debug programs and core files that use SunOS shared
570 _GDBN__ 4 has a reference card. @xref{Formatting Documentation} for
571 instructions on printing it.
573 @item Work in Progress
574 Kernel debugging for BSD and Mach systems; Tahoe and HPPA architecture
578 @node Sample Session, Invocation, New Features, Top
579 @chapter A Sample _GDBN__ Session
581 You can use this manual at your leisure to read all about _GDBN__.
582 However, a handful of commands are enough to get started using the
583 debugger. This chapter illustrates these commands.
586 In this sample session, we emphasize user input like this: @i{input},
587 to make it easier to pick out from the surrounding output.
590 @c FIXME: this example may not be appropriate for some configs, where
591 @c FIXME...primary interest is in remote use.
593 One of the preliminary versions of GNU @code{m4} (a generic macro
594 processor) exhibits the following bug: sometimes, when we change its
595 quote strings from the default, the commands used to capture one macro's
596 definition in another stop working. In the following short @code{m4}
597 session, we define a macro @code{foo} which expands to @code{0000}; we
598 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
599 same thing. However, when we change the open quote string to
600 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
601 procedure fails to define a new synonym @code{baz}:
610 @i{define(bar,defn(`foo'))}
614 @i{changequote(<QUOTE>,<UNQUOTE>)}
616 @i{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
619 m4: End of input: 0: fatal error: EOF in string
623 Let's use _GDBN__ to try to see what's going on.
627 @c FIXME: this falsifies the exact text played out, to permit smallbook
628 @c FIXME... format to come out better.
629 GDB is free software and you are welcome to distribute copies
630 of it under certain conditions; type "show copying" to see
632 There is absolutely no warranty for GDB; type "show warranty"
634 GDB _GDB_VN__, Copyright 1992 Free Software Foundation, Inc...
639 _GDBN__ reads only enough symbol data to know where to find the rest when
640 needed; as a result, the first prompt comes up very quickly. We now
641 tell _GDBN__ to use a narrower display width than usual, so that examples
642 will fit in this manual.
645 (_GDBP__) @i{set width 70}
649 Let's see how the @code{m4} built-in @code{changequote} works.
650 Having looked at the source, we know the relevant subroutine is
651 @code{m4_changequote}, so we set a breakpoint there with _GDBN__'s
652 @code{break} command.
655 (_GDBP__) @i{break m4_changequote}
656 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
660 Using the @code{run} command, we start @code{m4} running under _GDBN__
661 control; as long as control does not reach the @code{m4_changequote}
662 subroutine, the program runs as usual:
666 Starting program: /work/Editorial/gdb/gnu/m4/m4
674 To trigger the breakpoint, we call @code{changequote}. _GDBN__
675 suspends execution of @code{m4}, displaying information about the
676 context where it stops.
679 @i{changequote(<QUOTE>,<UNQUOTE>)}
681 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
683 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]), argc, 1, 3))
687 Now we use the command @code{n} (@code{next}) to advance execution to
688 the next line of the current function.
692 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
697 @code{set_quotes} looks like a promising subroutine. We can go into it
698 by using the command @code{s} (@code{step}) instead of @code{next}.
699 @code{step} goes to the next line to be executed in @emph{any}
700 subroutine, so it steps into @code{set_quotes}.
704 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
706 530 if (lquote != def_lquote)
710 The display that shows the subroutine where @code{m4} is now
711 suspended (and its arguments) is called a stack frame display. It
712 shows a summary of the stack. We can use the @code{backtrace}
713 command (which can also be spelled @code{bt}), to see where we are
714 in the stack as a whole: the @code{backtrace} command displays a
715 stack frame for each active subroutine.
719 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
721 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
723 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
724 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
726 #4 0x79dc in expand_input () at macro.c:40
727 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
731 Let's step through a few more lines to see what happens. The first two
732 times, we can use @samp{s}; the next two times we use @code{n} to avoid
733 falling into the @code{xstrdup} subroutine.
737 0x3b5c 532 if (rquote != def_rquote)
739 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
740 def_lquote : xstrdup(lq);
742 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
745 538 len_lquote = strlen(rquote);
749 The last line displayed looks a little odd; let's examine the variables
750 @code{lquote} and @code{rquote} to see if they are in fact the new left
751 and right quotes we specified. We can use the command @code{p}
752 (@code{print}) to see their values.
755 (_GDBP__) @i{p lquote}
756 $1 = 0x35d40 "<QUOTE>"
757 (_GDBP__) @i{p rquote}
758 $2 = 0x35d50 "<UNQUOTE>"
762 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
763 Let's look at some context; we can display ten lines of source
764 surrounding the current line, with the @code{l} (@code{list}) command.
770 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
772 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
775 538 len_lquote = strlen(rquote);
776 539 len_rquote = strlen(lquote);
783 Let's step past the two lines that set @code{len_lquote} and
784 @code{len_rquote}, and then examine the values of those variables.
788 539 len_rquote = strlen(lquote);
791 (_GDBP__) @i{p len_lquote}
793 (_GDBP__) @i{p len_rquote}
798 That certainly looks wrong, assuming @code{len_lquote} and
799 @code{len_rquote} are meant to be the lengths of @code{lquote} and
800 @code{rquote} respectively. Let's try setting them to better values.
801 We can use the @code{p} command for this, since it'll print the value of
802 any expression---and that expression can include subroutine calls and
806 (_GDBP__) p len_lquote=strlen(lquote)
808 (_GDBP__) p len_rquote=strlen(rquote)
813 Let's see if that fixes the problem of using the new quotes with the
814 @code{m4} built-in @code{defn}. We can allow @code{m4} to continue
815 executing with the @code{c} (@code{continue}) command, and then try the
816 example that caused trouble initially:
822 @i{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
829 Success! The new quotes now work just as well as the default ones. The
830 problem seems to have been just the two typos defining the wrong
831 lengths. We'll let @code{m4} exit by giving it an EOF as input.
835 Program exited normally.
839 The message @samp{Program exited normally.} is from _GDBN__; it
840 indicates @code{m4} has finished executing. We can end our _GDBN__
841 session with the _GDBN__ @code{quit} command.
845 _1__@end smallexample
847 @node Invocation, Commands, Sample Session, Top
848 @chapter Getting In and Out of _GDBN__
850 Type @kbd{gdb} or @kbd{gdb @var{program} @var{core}} to start GDB
851 and type @kbd{quit} or @kbd{C-d} to exit.
854 * Invoking _GDBN__:: Starting _GDBN__
855 * Leaving _GDBN__:: Leaving _GDBN__
856 * Shell Commands:: Shell Commands
859 @node Invoking _GDBN__, Leaving _GDBN__, Invocation, Invocation
860 @section Starting _GDBN__
862 Start _GDBN__ with the shell command @code{_GDBP__}. Once it's running,
863 _GDBN__ reads commands from the terminal until you tell it to exit.
865 You can run @code{_GDBP__} with no arguments or options; but the most
866 usual way to start _GDBN__ is with one argument or two, specifying an
867 executable program as the argument:
870 _GDBP__ @var{program}
874 You can also start with both an executable program and a core file
878 _GDBP__ @var{program} @var{core}
881 You can, instead, specify a process ID as a second argument, if you want
882 to debug a running process:
885 _GDBP__ @var{program} 1234
889 would attach _GDBN__ to process @code{1234} (unless you also have a file
890 named @file{1234}; _GDBN__ does check for a core file first).
893 You can further control how _GDBN__ starts up by using command-line
894 options. _GDBN__ itself can remind you of the options available.
904 to display all available options and briefly describe their use
905 (@samp{_GDBP__ -h} is a shorter equivalent).
907 All options and command line arguments you give are processed
908 in sequential order. The order makes a difference when the
909 @samp{-x} option is used.
912 * File Options:: Choosing Files
913 * Mode Options:: Choosing Modes
915 _include__(gdbinv-m.m4)_dnl__
919 @node File Options, Mode Options, Invoking _GDBN__, Invoking _GDBN__
920 @subsection Choosing Files
922 When _GDBN__ starts, it reads any arguments other than options as
923 specifying an executable file and core file (or process ID). This is
924 the same as if the arguments were specified by the @samp{-se} and
925 @samp{-c} options respectively. (_GDBN__ reads the first argument
926 that does not have an associated option flag as equivalent to the
927 @samp{-se} option followed by that argument; and the second argument
928 that does not have an associated option flag, if any, as equivalent to
929 the @samp{-c} option followed by that argument.)
931 Many options have both long and short forms; both are shown in the
932 following list. _GDBN__ also recognizes the long forms if you truncate
933 them, so long as enough of the option is present to be unambiguous.
934 (If you prefer, you can flag option arguments with @samp{--} rather
935 than @samp{-}, though we illustrate the more usual convention.)
938 @item -symbols=@var{file}
940 Read symbol table from file @var{file}.
942 @item -exec=@var{file}
944 Use file @var{file} as the executable file to execute when
945 appropriate, and for examining pure data in conjunction with a core
949 Read symbol table from file @var{file} and use it as the executable
952 @item -core=@var{file}
954 Use file @var{file} as a core dump to examine.
956 @item -command=@var{file}
958 Execute _GDBN__ commands from file @var{file}. @xref{Command Files}.
960 @item -directory=@var{directory}
961 @itemx -d @var{directory}
962 Add @var{directory} to the path to search for source files.
966 @node Mode Options, Mode Options, File Options, Invoking _GDBN__
969 @node Mode Options, , File Options, Invoking _GDBN__
971 @subsection Choosing Modes
973 You can run _GDBN__ in various alternative modes---for example, in
974 batch mode or quiet mode.
979 Do not execute commands from any @file{_GDBINIT__} initialization files.
980 Normally, the commands in these files are executed after all the
981 command options and arguments have been processed.
982 @xref{Command Files}.
986 ``Quiet''. Do not print the introductory and copyright messages. These
987 messages are also suppressed in batch mode.
990 Run in batch mode. Exit with status @code{0} after processing all the command
991 files specified with @samp{-x} (and @file{_GDBINIT__}, if not inhibited).
992 Exit with nonzero status if an error occurs in executing the _GDBN__
993 commands in the command files.
995 Batch mode may be useful for running _GDBN__ as a filter, for example to
996 download and run a program on another computer; in order to make this
997 more useful, the message
1000 Program exited normally.
1004 (which is ordinarily issued whenever a program running under _GDBN__ control
1005 terminates) is not issued when running in batch mode.
1007 @item -cd=@var{directory}
1008 Run _GDBN__ using @var{directory} as its working directory,
1009 instead of the current directory.
1013 Emacs sets this option when it runs _GDBN__ as a subprocess. It tells _GDBN__
1014 to output the full file name and line number in a standard,
1015 recognizable fashion each time a stack frame is displayed (which
1016 includes each time your program stops). This recognizable format looks
1017 like two @samp{\032} characters, followed by the file name, line number
1018 and character position separated by colons, and a newline. The
1019 Emacs-to-_GDBN__ interface program uses the two @samp{\032} characters as
1020 a signal to display the source code for the frame.
1023 Set the line speed (baud rate or bits per second) of any serial
1024 interface used by _GDBN__ for remote debugging.
1026 @item -tty=@var{device}
1027 Run using @var{device} for your program's standard input and output.
1028 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1032 _include__(gdbinv-s.m4)
1034 @node Leaving _GDBN__, Shell Commands, Invoking _GDBN__, Invocation
1035 @section Leaving _GDBN__
1036 @cindex exiting _GDBN__
1042 To exit _GDBN__, use the @code{quit} command (abbreviated @code{q}), or type
1043 an end-of-file character (usually @kbd{C-d}).
1047 An interrupt (often @kbd{C-c}) will not exit from _GDBN__, but rather
1048 will terminate the action of any _GDBN__ command that is in progress and
1049 return to _GDBN__ command level. It is safe to type the interrupt
1050 character at any time because _GDBN__ does not allow it to take effect
1051 until a time when it is safe.
1053 If you have been using _GDBN__ to control an attached process or device, you
1054 can release it with the @code{detach} command; @pxref{Attach,
1055 ,Debugging an Already-Running Process}..
1057 @node Shell Commands, , Leaving _GDBN__, Invocation
1058 @section Shell Commands
1060 If you need to execute occasional shell commands during your
1061 debugging session, there is no need to leave or suspend _GDBN__; you can
1062 just use the @code{shell} command.
1065 @item shell @var{command string}
1067 @cindex shell escape
1068 Directs _GDBN__ to invoke an inferior shell to execute @var{command
1069 string}. If it exists, the environment variable @code{SHELL} is used
1070 for the name of the shell to run. Otherwise _GDBN__ uses
1074 The utility @code{make} is often needed in development environments.
1075 You do not have to use the @code{shell} command for this purpose in _GDBN__:
1078 @item make @var{make-args}
1080 @cindex calling make
1081 Causes _GDBN__ to execute an inferior @code{make} program with the specified
1082 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1085 @node Commands, Running, Invocation, Top
1086 @chapter _GDBN__ Commands
1088 You can abbreviate GDB command if that abbreviation is unambiguous;
1089 and you can repeat certain GDB commands by typing just @key{RET}.
1092 * Command Syntax:: Command Syntax
1093 * Help:: Getting Help
1096 @node Command Syntax, Help, Commands, Commands
1097 @section Command Syntax
1099 A _GDBN__ command is a single line of input. There is no limit on how long
1100 it can be. It starts with a command name, which is followed by arguments
1101 whose meaning depends on the command name. For example, the command
1102 @code{step} accepts an argument which is the number of times to step,
1103 as in @samp{step 5}. You can also use the @code{step} command with
1104 no arguments. Some command names do not allow any arguments.
1106 @cindex abbreviation
1107 _GDBN__ command names may always be truncated if that abbreviation is
1108 unambiguous. Other possible command abbreviations are listed in the
1109 documentation for individual commands. In some cases, even ambiguous
1110 abbreviations are allowed; for example, @code{s} is specially defined as
1111 equivalent to @code{step} even though there are other commands whose
1112 names start with @code{s}. You can test abbreviations by using them as
1113 arguments to the @code{help} command.
1115 @cindex repeating commands
1117 A blank line as input to _GDBN__ (typing just @key{RET}) means to
1118 repeat the previous command. Certain commands (for example, @code{run})
1119 will not repeat this way; these are commands for which unintentional
1120 repetition might cause trouble and which you are unlikely to want to
1123 The @code{list} and @code{x} commands, when you repeat them with
1124 @key{RET}, construct new arguments rather than repeating
1125 exactly as typed. This permits easy scanning of source or memory.
1127 _GDBN__ can also use @key{RET} in another way: to partition lengthy
1128 output, in a way similar to the common utility @code{more}
1129 (@pxref{Screen Size}). Since it is easy to press one @key{RET} too many
1130 in this situation, _GDBN__ disables command repetition after any command
1131 that generates this sort of display.
1135 A line of input starting with @kbd{#} is a comment; it does nothing.
1136 This is useful mainly in command files (@pxref{Command Files}).
1138 @node Help, , Command Syntax, Commands
1139 @section Getting Help
1140 @cindex online documentation
1143 You can always ask _GDBN__ itself for information on its commands, using the
1144 command @code{help}.
1150 You can use @code{help} (abbreviated @code{h}) with no arguments to
1151 display a short list of named classes of commands:
1155 List of classes of commands:
1157 running -- Running the program
1158 stack -- Examining the stack
1159 data -- Examining data
1160 breakpoints -- Making program stop at certain points
1161 files -- Specifying and examining files
1162 status -- Status inquiries
1163 support -- Support facilities
1164 user-defined -- User-defined commands
1165 aliases -- Aliases of other commands
1166 obscure -- Obscure features
1168 Type "help" followed by a class name for a list of
1169 commands in that class.
1170 Type "help" followed by command name for full
1172 Command name abbreviations are allowed if unambiguous.
1176 @item help @var{class}
1177 Using one of the general help classes as an argument, you can get a
1178 list of the individual commands in that class. For example, here is the
1179 help display for the class @code{status}:
1182 (_GDBP__) help status
1187 show -- Generic command for showing things set with "set"
1188 info -- Generic command for printing status
1190 Type "help" followed by command name for full
1192 Command name abbreviations are allowed if unambiguous.
1196 @item help @var{command}
1197 With a command name as @code{help} argument, _GDBN__ will display a
1198 short paragraph on how to use that command.
1201 In addition to @code{help}, you can use the _GDBN__ commands @code{info}
1202 and @code{show} to inquire about the state of your program, or the state
1203 of _GDBN__ itself. Each command supports many topics of inquiry; this
1204 manual introduces each of them in the appropriate context. The listings
1205 under @code{info} and under @code{show} in the Index point to
1206 all the sub-commands. @xref{Index}.
1213 This command (abbreviated @code{i}) is for describing the state of your
1214 program; for example, it can list the arguments given to your program
1215 (@code{info args}), the registers currently in use (@code{info
1216 registers}), or the breakpoints you have set (@code{info breakpoints}).
1217 You can get a complete list of the @code{info} sub-commands with
1218 @w{@code{help info}}.
1222 In contrast, @code{show} is for describing the state of _GDBN__ itself.
1223 You can change most of the things you can @code{show}, by using the
1224 related command @code{set}; for example, you can control what number
1225 system is used for displays with @code{set radix}, or simply inquire
1226 which is currently in use with @code{show radix}.
1229 To display all the settable parameters and their current
1230 values, you can use @code{show} with no arguments; you may also use
1231 @code{info set}. Both commands produce the same display.
1232 @c FIXME: "info set" violates the rule that "info" is for state of
1233 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1234 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1238 Here are three miscellaneous @code{show} subcommands, all of which are
1239 exceptional in lacking corresponding @code{set} commands:
1242 @kindex show version
1243 @cindex version number
1245 Show what version of _GDBN__ is running. You should include this
1246 information in _GDBN__ bug-reports. If multiple versions of _GDBN__ are in
1247 use at your site, you may occasionally want to make sure what version
1248 of _GDBN__ you are running; as _GDBN__ evolves, new commands are introduced,
1249 and old ones may wither away. The version number is also announced
1250 when you start _GDBN__ with no arguments.
1252 @kindex show copying
1254 Display information about permission for copying _GDBN__.
1256 @kindex show warranty
1258 Display the GNU ``NO WARRANTY'' statement.
1261 @node Running, Stopping, Commands, Top
1262 @chapter Running Programs Under _GDBN__
1264 To debug a program, you must run it under _GDBN__.
1267 * Compilation:: Compiling for Debugging
1268 * Starting:: Starting your Program
1269 * Arguments:: Your Program's Arguments
1270 * Environment:: Your Program's Environment
1271 * Working Directory:: Your Program's Working Directory
1272 * Input/Output:: Your Program's Input and Output
1273 * Attach:: Debugging an Already-Running Process
1274 * Kill Process:: Killing the Child Process
1277 @node Compilation, Starting, Running, Running
1278 @section Compiling for Debugging
1280 In order to debug a program effectively, you need to generate
1281 debugging information when you compile it. This debugging information
1282 is stored in the object file; it describes the data type of each
1283 variable or function and the correspondence between source line numbers
1284 and addresses in the executable code.
1286 To request debugging information, specify the @samp{-g} option when you run
1289 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1290 options together. Using those compilers, you cannot generate optimized
1291 executables containing debugging information.
1293 The GNU C compiler supports @samp{-g} with or without @samp{-O}, making it
1294 possible to debug optimized code. We recommend that you @emph{always} use
1295 @samp{-g} whenever you compile a program. You may think your program is
1296 correct, but there is no sense in pushing your luck.
1298 Some things do not work as well with @samp{-g -O} as with just
1299 @samp{-g}, particularly on machines with instruction scheduling. If in
1300 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1301 please report it as a bug (including a test case!).
1303 Older versions of the GNU C compiler permitted a variant option
1304 @samp{-gg} for debugging information. _GDBN__ no longer supports this
1305 format; if your GNU C compiler has this option, do not use it.
1308 @comment As far as I know, there are no cases in which _GDBN__ will
1309 @comment produce strange output in this case. (but no promises).
1310 If your program includes archives made with the @code{ar} program, and
1311 if the object files used as input to @code{ar} were compiled without the
1312 @samp{-g} option and have names longer than 15 characters, _GDBN__ will get
1313 confused reading your program's symbol table. No error message will be
1314 given, but _GDBN__ may behave strangely. The reason for this problem is a
1315 deficiency in the Unix archive file format, which cannot represent file
1316 names longer than 15 characters.
1318 To avoid this problem, compile the archive members with the @samp{-g}
1319 option or use shorter file names. Alternatively, use a version of GNU
1320 @code{ar} dated more recently than August 1989.
1323 @node Starting, Arguments, Compilation, Running
1324 @section Starting your Program
1332 Use the @code{run} command to start your program under _GDBN__. You must
1333 first specify the program name
1338 _GDBN__ (@pxref{Invocation, ,Getting In and Out of _GDBN__}), or by using the
1339 @code{file} or @code{exec-file} command (@pxref{Files, ,Commands to
1344 If you are running your program in an execution environment that
1345 supports processes, @code{run} creates an inferior process and makes
1346 that process run your program. (In environments without processes,
1347 @code{run} jumps to the start of your program.)
1349 The execution of a program is affected by certain information it
1350 receives from its superior. _GDBN__ provides ways to specify this
1351 information, which you must do @i{before} starting your program. (You
1352 can change it after starting your program, but such changes will only affect
1353 your program the next time you start it.) This information may be
1354 divided into four categories:
1357 @item The @i{arguments.}
1358 Specify the arguments to give your program as the arguments of the
1359 @code{run} command. If a shell is available on your target, the shell
1360 is used to pass the arguments, so that you may use normal conventions
1361 (such as wildcard expansion or variable substitution) in describing
1362 the arguments. In Unix systems, you can control which shell is used
1363 with the @code{SHELL} environment variable. @xref{Arguments, ,Your
1364 Program's Arguments}.
1366 @item The @i{environment.}
1367 Your program normally inherits its environment from _GDBN__, but you can
1368 use the _GDBN__ commands @code{set environment} and @code{unset
1369 environment} to change parts of the environment that will be given to
1370 your program. @xref{Environment, ,Your Program's Environment}.
1372 @item The @i{working directory.}
1373 Your program inherits its working directory from _GDBN__. You can set
1374 _GDBN__'s working directory with the @code{cd} command in _GDBN__.
1375 @xref{Working Directory, ,Your Program's Working Directory}.
1377 @item The @i{standard input and output.}
1378 Your program normally uses the same device for standard input and
1379 standard output as _GDBN__ is using. You can redirect input and output
1380 in the @code{run} command line, or you can use the @code{tty} command to
1381 set a different device for your program.
1382 @xref{Input/Output, ,Your Program's Input and Output}.
1385 @emph{Warning:} While input and output redirection work, you cannot use
1386 pipes to pass the output of the program you are debugging to another
1387 program; if you attempt this, _GDBN__ is likely to wind up debugging the
1391 @c FIXME: Rewrite following paragraph, especially its third sentence.
1392 When you issue the @code{run} command, your program begins to execute
1393 immediately. @xref{Stopping, ,Stopping and Continuing}, for
1394 discussion of how to arrange for your program to stop. Once your
1395 program has been started by the @code{run} command (and then stopped),
1396 you may evaluate expressions that involve calls to functions in your
1397 program, using the @code{print} or @code{call} commands. @xref{Data,
1400 If the modification time of your symbol file has changed since the
1401 last time _GDBN__ read its symbols, _GDBN__ will discard its symbol table and
1402 re-read it. When it does this, _GDBN__ tries to retain your current
1405 @node Arguments, Environment, Starting, Running
1406 @section Your Program's Arguments
1408 @cindex arguments (to your program)
1409 The arguments to your program can be specified by the arguments of the
1410 @code{run} command. They are passed to a shell, which expands wildcard
1411 characters and performs redirection of I/O, and thence to your program.
1412 _GDBN__ uses the shell indicated by your environment variable
1413 @code{SHELL} if it exists; otherwise, _GDBN__ uses @code{/bin/sh}.
1415 @code{run} with no arguments uses the same arguments used by the previous
1416 @code{run}, or those set by the @code{set args} command.
1421 Specify the arguments to be used the next time your program is run. If
1422 @code{set args} has no arguments, @code{run} will execute your program
1423 with no arguments. Once you have run your program with arguments,
1424 using @code{set args} before the next @code{run} is the only way to run
1425 it again without arguments.
1429 Show the arguments to give your program when it is started.
1432 @node Environment, Working Directory, Arguments, Running
1433 @section Your Program's Environment
1435 @cindex environment (of your program)
1436 The @dfn{environment} consists of a set of environment variables and
1437 their values. Environment variables conventionally record such things as
1438 your user name, your home directory, your terminal type, and your search
1439 path for programs to run. Usually you set up environment variables with
1440 the shell and they are inherited by all the other programs you run. When
1441 debugging, it can be useful to try running your program with a modified
1442 environment without having to start _GDBN__ over again.
1445 @item path @var{directory}
1447 Add @var{directory} to the front of the @code{PATH} environment variable
1448 (the search path for executables), for both _GDBN__ and your program.
1449 You may specify several directory names, separated by @samp{:} or
1450 whitespace. If @var{directory} is already in the path, it is moved to
1451 the front, so it will be searched sooner.
1453 You can use the string @samp{$cwd} to refer to whatever is the current
1454 working directory at the time _GDBN__ searches the path. If you use
1455 @samp{.} instead, it refers to the directory where you executed the
1456 @code{path} command. _GDBN__ fills in the current path where needed in
1457 the @var{directory} argument, before adding it to the search path.
1458 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1459 @c document that, since repeating it would be a no-op.
1463 Display the list of search paths for executables (the @code{PATH}
1464 environment variable).
1466 @item show environment @r{[}@var{varname}@r{]}
1467 @kindex show environment
1468 Print the value of environment variable @var{varname} to be given to
1469 your program when it starts. If you do not supply @var{varname},
1470 print the names and values of all environment variables to be given to
1471 your program. You can abbreviate @code{environment} as @code{env}.
1473 @item set environment @var{varname} @r{[}=@r{]} @var{value}
1474 @kindex set environment
1475 Sets environment variable @var{varname} to @var{value}. The value
1476 changes for your program only, not for _GDBN__ itself. @var{value} may
1477 be any string; the values of environment variables are just strings, and
1478 any interpretation is supplied by your program itself. The @var{value}
1479 parameter is optional; if it is eliminated, the variable is set to a
1481 @c "any string" here does not include leading, trailing
1482 @c blanks. Gnu asks: does anyone care?
1484 For example, this command:
1491 tells a Unix program, when subsequently run, that its user is named
1492 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1493 are not actually required.)
1495 @item unset environment @var{varname}
1496 @kindex unset environment
1497 Remove variable @var{varname} from the environment to be passed to your
1498 program. This is different from @samp{set env @var{varname} =};
1499 @code{unset environment} removes the variable from the environment,
1500 rather than assigning it an empty value.
1503 @node Working Directory, Input/Output, Environment, Running
1504 @section Your Program's Working Directory
1506 @cindex working directory (of your program)
1507 Each time you start your program with @code{run}, it inherits its
1508 working directory from the current working directory of _GDBN__. _GDBN__'s
1509 working directory is initially whatever it inherited from its parent
1510 process (typically the shell), but you can specify a new working
1511 directory in _GDBN__ with the @code{cd} command.
1513 The _GDBN__ working directory also serves as a default for the commands
1514 that specify files for _GDBN__ to operate on. @xref{Files, ,Commands to
1518 @item cd @var{directory}
1520 Set _GDBN__'s working directory to @var{directory}.
1524 Print _GDBN__'s working directory.
1527 @node Input/Output, Attach, Working Directory, Running
1528 @section Your Program's Input and Output
1533 By default, the program you run under _GDBN__ does input and output to
1534 the same terminal that _GDBN__ uses. _GDBN__ switches the terminal to
1535 its own terminal modes to interact with you, but it records the terminal
1536 modes your program was using and switches back to them when you continue
1537 running your program.
1541 @kindex info terminal
1542 Displays _GDBN__'s recorded information about the terminal modes your
1546 You can redirect your program's input and/or output using shell
1547 redirection with the @code{run} command. For example,
1554 starts your program, diverting its output to the file @file{outfile}.
1557 @cindex controlling terminal
1558 Another way to specify where your program should do input and output is
1559 with the @code{tty} command. This command accepts a file name as
1560 argument, and causes this file to be the default for future @code{run}
1561 commands. It also resets the controlling terminal for the child
1562 process, for future @code{run} commands. For example,
1569 directs that processes started with subsequent @code{run} commands
1570 default to do input and output on the terminal @file{/dev/ttyb} and have
1571 that as their controlling terminal.
1573 An explicit redirection in @code{run} overrides the @code{tty} command's
1574 effect on the input/output device, but not its effect on the controlling
1577 When you use the @code{tty} command or redirect input in the @code{run}
1578 command, only the input @emph{for your program} is affected. The input
1579 for _GDBN__ still comes from your terminal.
1581 @node Attach, Kill Process, Input/Output, Running
1582 @section Debugging an Already-Running Process
1587 @item attach @var{process-id}
1589 attaches to a running process---one that was started outside _GDBN__.
1590 (@code{info files} will show your active targets.) The command takes as
1591 argument a process ID. The usual way to find out the process-id of
1592 a Unix process is with the @code{ps} utility, or with the @samp{jobs -l}
1595 @code{attach} will not repeat if you press @key{RET} a second time after
1596 executing the command.
1599 To use @code{attach}, you must be debugging in an environment which
1600 supports processes. You must also have permission to send the process a
1601 signal, and it must have the same effective user ID as the _GDBN__
1604 When using @code{attach}, you should first use the @code{file} command
1605 to specify the program running in the process and load its symbol table.
1606 @xref{Files, ,Commands to Specify Files}.
1608 The first thing _GDBN__ does after arranging to debug the specified
1609 process is to stop it. You can examine and modify an attached process
1610 with all the _GDBN__ commands that are ordinarily available when you start
1611 processes with @code{run}. You can insert breakpoints; you can step and
1612 continue; you can modify storage. If you would rather the process
1613 continue running, you may use the @code{continue} command after
1614 attaching _GDBN__ to the process.
1619 When you have finished debugging the attached process, you can use the
1620 @code{detach} command to release it from _GDBN__'s control. Detaching
1621 the process continues its execution. After the @code{detach} command,
1622 that process and _GDBN__ become completely independent once more, and you
1623 are ready to @code{attach} another process or start one with @code{run}.
1624 @code{detach} will not repeat if you press @key{RET} again after
1625 executing the command.
1628 If you exit _GDBN__ or use the @code{run} command while you have an attached
1629 process, you kill that process. By default, you will be asked for
1630 confirmation if you try to do either of these things; you can control
1631 whether or not you need to confirm by using the @code{set confirm} command
1632 (@pxref{Messages/Warnings, ,Optional Warnings and Messages}).
1634 @node Kill Process, , Attach, Running
1636 @section Killing the Child Process
1641 Kill the child process in which your program is running under _GDBN__.
1644 This command is useful if you wish to debug a core dump instead of a
1645 running process. _GDBN__ ignores any core dump file while your program
1649 On some operating systems, a program cannot be executed outside _GDBN__
1650 while you have breakpoints set on it inside _GDBN__. You can use the
1651 @code{kill} command in this situation to permit running your program
1652 outside the debugger.
1654 The @code{kill} command is also useful if you wish to recompile and
1655 relink your program, since on many systems it is impossible to modify an
1656 executable file while it is running in a process. In this case, when you
1657 next type @code{run}, _GDBN__ will notice that the file has changed, and
1658 will re-read the symbol table (while trying to preserve your current
1659 breakpoint settings).
1661 @node Stopping, Stack, Running, Top
1662 @chapter Stopping and Continuing
1664 The principal purpose of using a debugger is so that you can stop your
1665 program before it terminates; or so that, if your program runs into
1666 trouble, you can investigate and find out why.
1668 Inside _GDBN__, your program may stop for any of several reasons, such
1669 as a signal, a breakpoint, or reaching a new line after a _GDBN__
1670 command such as @code{step}. You may then examine and change
1671 variables, set new breakpoints or remove old ones, and then continue
1672 execution. Usually, the messages shown by _GDBN__ provide ample
1673 explanation of the status of your program---but you can also explicitly
1674 request this information at any time.
1678 @kindex info program
1679 Display information about the status of your program: whether it is
1680 running or not, what process it is, and why it stopped.
1684 * Breakpoints:: Breakpoints, Watchpoints, and Exceptions
1685 * Continuing and Stepping:: Resuming Execution
1689 @node Breakpoints, Continuing and Stepping, Stopping, Stopping
1690 @section Breakpoints, Watchpoints, and Exceptions
1693 A @dfn{breakpoint} makes your program stop whenever a certain point in
1694 the program is reached. For each breakpoint, you can add various
1695 conditions to control in finer detail whether your program will stop.
1696 You can set breakpoints with the @code{break} command and its variants
1697 (@pxref{Set Breaks, ,Setting Breakpoints}), to specify the place where
1698 your program should stop by line number, function name or exact address
1699 in the program. In languages with exception handling (such as GNU
1700 C++), you can also set breakpoints where an exception is raised
1701 (@pxref{Exception Handling, ,Breakpoints and Exceptions}).
1704 A @dfn{watchpoint} is a special breakpoint that stops your program
1705 when the value of an expression changes. You must use a different
1706 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
1707 Watchpoints}), but aside from that, you can manage a watchpoint like
1708 any other breakpoint: you enable, disable, and delete both breakpoints
1709 and watchpoints using the same commands.
1711 Each breakpoint or watchpoint is assigned a number when it is created;
1712 these numbers are successive integers starting with one. In many of the
1713 commands for controlling various features of breakpoints you use the
1714 breakpoint number to say which breakpoint you want to change. Each
1715 breakpoint may be @dfn{enabled} or @dfn{disabled}; if disabled, it has
1716 no effect on your program until you enable it again.
1719 * Set Breaks:: Setting Breakpoints
1720 * Set Watchpoints:: Setting Watchpoints
1721 * Exception Handling:: Breakpoints and Exceptions
1722 * Delete Breaks:: Deleting Breakpoints
1723 * Disabling:: Disabling Breakpoints
1724 * Conditions:: Break Conditions
1725 * Break Commands:: Breakpoint Command Lists
1726 * Breakpoint Menus:: Breakpoint Menus
1727 * Error in Breakpoints::
1730 @node Set Breaks, Set Watchpoints, Breakpoints, Breakpoints
1731 @subsection Setting Breakpoints
1733 @c FIXME LMB what does GDB do if no code on line of breakpt?
1734 @c consider in particular declaration with/without initialization.
1736 @c FIXME 2 is there stuff on this already? break at fun start, already init?
1740 Breakpoints are set with the @code{break} command (abbreviated @code{b}).
1742 You have several ways to say where the breakpoint should go.
1745 @item break @var{function}
1746 Set a breakpoint at entry to function @var{function}. When using source
1747 languages that permit overloading of symbols, such as C++,
1748 @var{function} may refer to more than one possible place to break.
1749 @xref{Breakpoint Menus}, for a discussion of that situation.
1751 @item break +@var{offset}
1752 @itemx break -@var{offset}
1753 Set a breakpoint some number of lines forward or back from the position
1754 at which execution stopped in the currently selected frame.
1756 @item break @var{linenum}
1757 Set a breakpoint at line @var{linenum} in the current source file.
1758 That file is the last file whose source text was printed. This
1759 breakpoint will stop your program just before it executes any of the
1762 @item break @var{filename}:@var{linenum}
1763 Set a breakpoint at line @var{linenum} in source file @var{filename}.
1765 @item break @var{filename}:@var{function}
1766 Set a breakpoint at entry to function @var{function} found in file
1767 @var{filename}. Specifying a file name as well as a function name is
1768 superfluous except when multiple files contain similarly named
1771 @item break *@var{address}
1772 Set a breakpoint at address @var{address}. You can use this to set
1773 breakpoints in parts of your program which do not have debugging
1774 information or source files.
1777 When called without any arguments, @code{break} sets a breakpoint at
1778 the next instruction to be executed in the selected stack frame
1779 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
1780 innermost, this will cause your program to stop as soon as control
1781 returns to that frame. This is similar to the effect of a
1782 @code{finish} command in the frame inside the selected frame---except
1783 that @code{finish} does not leave an active breakpoint. If you use
1784 @code{break} without an argument in the innermost frame, _GDBN__ will stop
1785 the next time it reaches the current location; this may be useful
1788 _GDBN__ normally ignores breakpoints when it resumes execution, until at
1789 least one instruction has been executed. If it did not do this, you
1790 would be unable to proceed past a breakpoint without first disabling the
1791 breakpoint. This rule applies whether or not the breakpoint already
1792 existed when your program stopped.
1794 @item break @dots{} if @var{cond}
1795 Set a breakpoint with condition @var{cond}; evaluate the expression
1796 @var{cond} each time the breakpoint is reached, and stop only if the
1797 value is nonzero---that is, if @var{cond} evaluates as true.
1798 @samp{@dots{}} stands for one of the possible arguments described
1799 above (or no argument) specifying where to break. @xref{Conditions,
1800 ,Break Conditions}, for more information on breakpoint conditions.
1802 @item tbreak @var{args}
1804 Set a breakpoint enabled only for one stop. @var{args} are the
1805 same as for the @code{break} command, and the breakpoint is set in the same
1806 way, but the breakpoint is automatically disabled after the first time your
1807 program stops there. @xref{Disabling, ,Disabling Breakpoints}.
1809 @item rbreak @var{regex}
1811 @cindex regular expression
1812 @c FIXME what kind of regexp?
1813 Set breakpoints on all functions matching the regular expression
1814 @var{regex}. This command
1815 sets an unconditional breakpoint on all matches, printing a list of all
1816 breakpoints it set. Once these breakpoints are set, they are treated
1817 just like the breakpoints set with the @code{break} command. They can
1818 be deleted, disabled, made conditional, etc., in the standard ways.
1820 When debugging C++ programs, @code{rbreak} is useful for setting
1821 breakpoints on overloaded functions that are not members of any special
1824 @kindex info breakpoints
1825 @cindex @code{$_} and @code{info breakpoints}
1826 @item info breakpoints @r{[}@var{n}@r{]}
1827 @item info break @r{[}@var{n}@r{]}
1828 Print a list of all breakpoints (but not watchpoints) set and not
1829 deleted, showing their numbers, where in your program they are, and any
1830 special features in use for them. Disabled breakpoints are included in
1831 the list, but marked as disabled. @code{info break} with a breakpoint
1832 number @var{n} as argument lists only that breakpoint. The
1833 convenience variable @code{$_} and the default examining-address for
1834 the @code{x} command are set to the address of the last breakpoint
1835 listed (@pxref{Memory, ,Examining Memory}). The equivalent command
1836 for watchpoints is @code{info watch}.
1839 _GDBN__ allows you to set any number of breakpoints at the same place in
1840 your program. There is nothing silly or meaningless about this. When
1841 the breakpoints are conditional, this is even useful
1842 (@pxref{Conditions, ,Break Conditions}).
1844 @node Set Watchpoints, Exception Handling, Set Breaks, Breakpoints
1845 @subsection Setting Watchpoints
1846 @cindex setting watchpoints
1848 You can use a watchpoint to stop execution whenever the value of an
1849 expression changes, without having to predict a particular place
1850 where this may happen.
1852 Watchpoints currently execute two orders of magnitude more slowly than
1853 other breakpoints, but this can well be worth it to catch errors where
1854 you have no clue what part of your program is the culprit. Some
1855 processors provide special hardware to support watchpoint evaluation; future
1856 releases of _GDBN__ will use such hardware if it is available.
1860 @item watch @var{expr}
1861 Set a watchpoint for an expression.
1863 @kindex info watchpoints
1864 @item info watchpoints
1865 This command prints a list of watchpoints; it is otherwise similar to
1869 @node Exception Handling, Delete Breaks, Set Watchpoints, Breakpoints
1870 @subsection Breakpoints and Exceptions
1871 @cindex exception handlers
1873 Some languages, such as GNU C++, implement exception handling. You can
1874 use _GDBN__ to examine what caused your program to raise an exception,
1875 and to list the exceptions your program is prepared to handle at a
1876 given point in time.
1879 @item catch @var{exceptions}
1881 You can set breakpoints at active exception handlers by using the
1882 @code{catch} command. @var{exceptions} is a list of names of exceptions
1886 You can use @code{info catch} to list active exception handlers.
1887 @xref{Frame Info, ,Information About a Frame}.
1889 There are currently some limitations to exception handling in _GDBN__.
1890 These will be corrected in a future release.
1894 If you call a function interactively, _GDBN__ normally returns
1895 control to you when the function has finished executing. If the call
1896 raises an exception, however, the call may bypass the mechanism that
1897 returns control to you and cause your program to simply continue
1898 running until it hits a breakpoint, catches a signal that _GDBN__ is
1899 listening for, or exits.
1901 You cannot raise an exception interactively.
1903 You cannot interactively install an exception handler.
1906 @cindex raise exceptions
1907 Sometimes @code{catch} is not the best way to debug exception handling:
1908 if you need to know exactly where an exception is raised, it is better to
1909 stop @emph{before} the exception handler is called, since that way you
1910 can see the stack before any unwinding takes place. If you set a
1911 breakpoint in an exception handler instead, it may not be easy to find
1912 out where the exception was raised.
1914 To stop just before an exception handler is called, you need some
1915 knowledge of the implementation. In the case of GNU C++, exceptions are
1916 raised by calling a library function named @code{__raise_exception}
1917 which has the following ANSI C interface:
1920 /* @var{addr} is where the exception identifier is stored.
1921 ID is the exception identifier. */
1922 void __raise_exception (void **@var{addr}, void *@var{id});
1926 To make the debugger catch all exceptions before any stack
1927 unwinding takes place, set a breakpoint on @code{__raise_exception}
1928 (@pxref{Breakpoints, ,Breakpoints Watchpoints and Exceptions}).
1930 With a conditional breakpoint (@pxref{Conditions, ,Break Conditions})
1931 that depends on the value of @var{id}, you can stop your program when
1932 a specific exception is raised. You can use multiple conditional
1933 breakpoints to stop your program when any of a number of exceptions are
1936 @node Delete Breaks, Disabling, Exception Handling, Breakpoints
1937 @subsection Deleting Breakpoints
1939 @cindex clearing breakpoints, watchpoints
1940 @cindex deleting breakpoints, watchpoints
1941 It is often necessary to eliminate a breakpoint or watchpoint once it
1942 has done its job and you no longer want your program to stop there. This
1943 is called @dfn{deleting} the breakpoint. A breakpoint that has been
1944 deleted no longer exists; it is forgotten.
1946 With the @code{clear} command you can delete breakpoints according to
1947 where they are in your program. With the @code{delete} command you can
1948 delete individual breakpoints or watchpoints by specifying their
1951 It is not necessary to delete a breakpoint to proceed past it. _GDBN__
1952 automatically ignores breakpoints on the first instruction to be executed
1953 when you continue execution without changing the execution address.
1958 Delete any breakpoints at the next instruction to be executed in the
1959 selected stack frame (@pxref{Selection, ,Selecting a Frame}). When
1960 the innermost frame is selected, this is a good way to delete a
1961 breakpoint where your program just stopped.
1963 @item clear @var{function}
1964 @itemx clear @var{filename}:@var{function}
1965 Delete any breakpoints set at entry to the function @var{function}.
1967 @item clear @var{linenum}
1968 @itemx clear @var{filename}:@var{linenum}
1969 Delete any breakpoints set at or within the code of the specified line.
1971 @item delete @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
1972 @cindex delete breakpoints
1975 Delete the breakpoints or watchpoints of the numbers specified as
1976 arguments. If no argument is specified, delete all breakpoints (_GDBN__
1977 asks confirmation, unless you have @code{set confirm off}). You
1978 can abbreviate this command as @code{d}.
1981 @node Disabling, Conditions, Delete Breaks, Breakpoints
1982 @subsection Disabling Breakpoints
1984 @cindex disabled breakpoints
1985 @cindex enabled breakpoints
1986 Rather than deleting a breakpoint or watchpoint, you might prefer to
1987 @dfn{disable} it. This makes the breakpoint inoperative as if it had
1988 been deleted, but remembers the information on the breakpoint so that
1989 you can @dfn{enable} it again later.
1991 You disable and enable breakpoints and watchpoints with the
1992 @code{enable} and @code{disable} commands, optionally specifying one or
1993 more breakpoint numbers as arguments. Use @code{info break} or
1994 @code{info watch} to print a list of breakpoints or watchpoints if you
1995 do not know which numbers to use.
1997 A breakpoint or watchpoint can have any of four different states of
2002 Enabled. The breakpoint will stop your program. A breakpoint set
2003 with the @code{break} command starts out in this state.
2005 Disabled. The breakpoint has no effect on your program.
2007 Enabled once. The breakpoint will stop your program, but
2008 when it does so it will become disabled. A breakpoint set
2009 with the @code{tbreak} command starts out in this state.
2011 Enabled for deletion. The breakpoint will stop your program, but
2012 immediately after it does so it will be deleted permanently.
2015 You can use the following commands to enable or disable breakpoints and
2019 @item disable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2020 @kindex disable breakpoints
2023 Disable the specified breakpoints---or all breakpoints, if none are
2024 listed. A disabled breakpoint has no effect but is not forgotten. All
2025 options such as ignore-counts, conditions and commands are remembered in
2026 case the breakpoint is enabled again later. You may abbreviate
2027 @code{disable} as @code{dis}.
2029 @item enable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2030 @kindex enable breakpoints
2032 Enable the specified breakpoints (or all defined breakpoints). They
2033 become effective once again in stopping your program.
2035 @item enable @r{[}breakpoints@r{]} once @var{bnums}@dots{}
2036 Enable the specified breakpoints temporarily. Each will be disabled
2037 again the next time it stops your program.
2039 @item enable @r{[}breakpoints@r{]} delete @var{bnums}@dots{}
2040 Enable the specified breakpoints to work once and then die. Each of
2041 the breakpoints will be deleted the next time it stops your program.
2044 Save for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2045 ,Setting Breakpoints}), breakpoints that you set are initially
2046 enabled; subsequently, they become disabled or enabled only when you
2047 use one of the commands above. (The command @code{until} can set and
2048 delete a breakpoint of its own, but it will not change the state of
2049 your other breakpoints; @pxref{Continuing and Stepping, ,Continuing and Stepping}.)
2051 @node Conditions, Break Commands, Disabling, Breakpoints
2052 @subsection Break Conditions
2053 @cindex conditional breakpoints
2054 @cindex breakpoint conditions
2056 @c FIXME what is scope of break condition expr? Context where wanted?
2057 @c in particular for a watchpoint?
2058 The simplest sort of breakpoint breaks every time your program reaches a
2059 specified place. You can also specify a @dfn{condition} for a
2060 breakpoint. A condition is just a Boolean expression in your
2061 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2062 a condition evaluates the expression each time your program reaches it,
2063 and your program stops only if the condition is @emph{true}.
2065 This is the converse of using assertions for program validation; in that
2066 situation, you want to stop when the assertion is violated---that is,
2067 when the condition is false. In C, if you want to test an assertion expressed
2068 by the condition @var{assert}, you should set the condition
2069 @samp{! @var{assert}} on the appropriate breakpoint.
2071 Conditions are also accepted for watchpoints; you may not need them,
2072 since a watchpoint is inspecting the value of an expression anyhow---but
2073 it might be simpler, say, to just set a watchpoint on a variable name,
2074 and specify a condition that tests whether the new value is an interesting
2077 Break conditions can have side effects, and may even call functions in
2078 your program. This can be useful, for example, to activate functions
2079 that log program progress, or to use your own print functions to
2080 format special data structures. The effects are completely predictable
2081 unless there is another enabled breakpoint at the same address. (In
2082 that case, _GDBN__ might see the other breakpoint first and stop your
2083 program without checking the condition of this one.) Note that
2084 breakpoint commands are usually more convenient and flexible for the
2085 purpose of performing side effects when a breakpoint is reached
2086 (@pxref{Break Commands, ,Breakpoint Command Lists}).
2088 Break conditions can be specified when a breakpoint is set, by using
2089 @samp{if} in the arguments to the @code{break} command. @xref{Set
2090 Breaks, ,Setting Breakpoints}. They can also be changed at any time
2091 with the @code{condition} command. The @code{watch} command does not
2092 recognize the @code{if} keyword; @code{condition} is the only way to
2093 impose a further condition on a watchpoint.
2096 @item condition @var{bnum} @var{expression}
2098 Specify @var{expression} as the break condition for breakpoint or
2099 watchpoint number @var{bnum}. From now on, this breakpoint will stop
2100 your program only if the value of @var{expression} is true (nonzero, in
2101 C). When you use @code{condition}, _GDBN__ checks @var{expression}
2102 immediately for syntactic correctness, and to determine whether symbols
2103 in it have referents in the context of your breakpoint.
2104 @c FIXME so what does GDB do if there is no referent? Moreover, what
2105 @c about watchpoints?
2107 not actually evaluate @var{expression} at the time the @code{condition}
2108 command is given, however. @xref{Expressions, ,Expressions}.
2110 @item condition @var{bnum}
2111 Remove the condition from breakpoint number @var{bnum}. It becomes
2112 an ordinary unconditional breakpoint.
2115 @cindex ignore count (of breakpoint)
2116 A special case of a breakpoint condition is to stop only when the
2117 breakpoint has been reached a certain number of times. This is so
2118 useful that there is a special way to do it, using the @dfn{ignore
2119 count} of the breakpoint. Every breakpoint has an ignore count, which
2120 is an integer. Most of the time, the ignore count is zero, and
2121 therefore has no effect. But if your program reaches a breakpoint whose
2122 ignore count is positive, then instead of stopping, it just decrements
2123 the ignore count by one and continues. As a result, if the ignore count
2124 value is @var{n}, the breakpoint will not stop the next @var{n} times it
2128 @item ignore @var{bnum} @var{count}
2130 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
2131 The next @var{count} times the breakpoint is reached, your program's
2132 execution will not stop; other than to decrement the ignore count, _GDBN__
2135 To make the breakpoint stop the next time it is reached, specify
2138 @item continue @var{count}
2139 @itemx c @var{count}
2140 @itemx fg @var{count}
2141 @kindex continue @var{count}
2142 Continue execution of your program, setting the ignore count of the
2143 breakpoint where your program stopped to @var{count} minus one.
2144 Thus, your program will not stop at this breakpoint until the
2145 @var{count}'th time it is reached.
2147 An argument to this command is meaningful only when your program stopped
2148 due to a breakpoint. At other times, the argument to @code{continue} is
2151 The synonym @code{fg} is provided purely for convenience, and has
2152 exactly the same behavior as other forms of the command.
2155 If a breakpoint has a positive ignore count and a condition, the condition
2156 is not checked. Once the ignore count reaches zero, the condition will
2159 You could achieve the effect of the ignore count with a condition such
2160 as _0__@w{@samp{$foo-- <= 0}}_1__ using a debugger convenience variable that
2161 is decremented each time. @xref{Convenience Vars, ,Convenience
2164 @node Break Commands, Breakpoint Menus, Conditions, Breakpoints
2165 @subsection Breakpoint Command Lists
2167 @cindex breakpoint commands
2168 You can give any breakpoint (or watchpoint) a series of commands to
2169 execute when your program stops due to that breakpoint. For example, you
2170 might want to print the values of certain expressions, or enable other
2174 @item commands @r{[}@var{bnum}@r{]}
2175 @itemx @dots{} @var{command-list} @dots{}
2179 Specify a list of commands for breakpoint number @var{bnum}. The commands
2180 themselves appear on the following lines. Type a line containing just
2181 @code{end} to terminate the commands.
2183 To remove all commands from a breakpoint, type @code{commands} and
2184 follow it immediately with @code{end}; that is, give no commands.
2186 With no @var{bnum} argument, @code{commands} refers to the last
2187 breakpoint or watchpoint set (not to the breakpoint most recently
2191 Pressing @key{RET} as a means of repeating the last _GDBN__ command is
2192 disabled within a @var{command-list}.
2194 You can use breakpoint commands to start your program up again. Simply
2195 use the @code{continue} command, or @code{step}, or any other command
2196 that resumes execution. Subsequent commands in the command list are
2200 If the first command specified is @code{silent}, the usual message about
2201 stopping at a breakpoint is not printed. This may be desirable for
2202 breakpoints that are to print a specific message and then continue.
2203 If the remaining commands too print nothing, you will see no sign that
2204 the breakpoint was reached at all. @code{silent} is meaningful only
2205 at the beginning of a breakpoint command list.
2207 The commands @code{echo} and @code{output} that allow you to print
2208 precisely controlled output are often useful in silent breakpoints.
2209 @xref{Output, ,Commands for Controlled Output}.
2211 For example, here is how you could use breakpoint commands to print the
2212 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
2225 One application for breakpoint commands is to compensate for one bug so
2226 you can test for another. Put a breakpoint just after the erroneous line
2227 of code, give it a condition to detect the case in which something
2228 erroneous has been done, and give it commands to assign correct values
2229 to any variables that need them. End with the @code{continue} command
2230 so that your program does not stop, and start with the @code{silent}
2231 command so that no output is produced. Here is an example:
2243 One deficiency in the operation of automatically continuing breakpoints
2244 under Unix appears when your program uses raw mode for the terminal.
2245 _GDBN__ switches back to its own terminal modes (not raw) before executing
2246 commands, and then must switch back to raw mode when your program is
2247 continued. This causes any pending terminal input to be lost.
2248 @c FIXME: revisit below when GNU sys avail.
2249 @c In the GNU system, this will be fixed by changing the behavior of
2252 Under Unix, you can get around this problem by writing actions into
2253 the breakpoint condition rather than in commands. For example
2256 condition 5 (x = y + 4), 0
2260 specifies a condition expression (@pxref{Expressions, ,Expressions}) that will
2261 change @code{x} as needed, then always have the value zero so your
2262 program will not stop. No input is lost here, because _GDBN__ evaluates
2263 break conditions without changing the terminal modes. When you want
2264 to have nontrivial conditions for performing the side effects, the
2265 operators @samp{&&}, @samp{||} and @samp{?@dots{}:} may be useful.
2267 @node Breakpoint Menus, Error in Breakpoints, Break Commands, Breakpoints
2268 @subsection Breakpoint Menus
2270 @cindex symbol overloading
2272 Some programming languages (notably C++) permit a single function name
2273 to be defined several times, for application in different contexts.
2274 This is called @dfn{overloading}. When a function name is overloaded,
2275 @samp{break @var{function}} is not enough to tell _GDBN__ where you
2276 want a breakpoint. _GDBN__ offers you a menu of numbered choices for
2277 different possible breakpoints, and waits for your selection with the
2278 prompt @samp{>}. The first two options are always @samp{[0] cancel}
2279 and @samp{[1] all}. Typing @kbd{1} sets a breakpoint at each
2280 definition of @var{function}, and typing @kbd{0} aborts the
2281 @code{break} command without setting any new breakpoints.
2283 For example, the following session excerpt shows an attempt to set a
2284 breakpoint at the overloaded symbol @code{String::after}.
2285 We choose three particular definitions of that function name:
2288 (_GDBP__) b String::after
2291 [2] file:String.cc; line number:867
2292 [3] file:String.cc; line number:860
2293 [4] file:String.cc; line number:875
2294 [5] file:String.cc; line number:853
2295 [6] file:String.cc; line number:846
2296 [7] file:String.cc; line number:735
2298 Breakpoint 1 at 0xb26c: file String.cc, line 867.
2299 Breakpoint 2 at 0xb344: file String.cc, line 875.
2300 Breakpoint 3 at 0xafcc: file String.cc, line 846.
2301 Multiple breakpoints were set.
2302 Use the "delete" command to delete unwanted breakpoints.
2306 @node Error in Breakpoints, , Breakpoint Menus, Breakpoints
2307 @subsection ``Cannot Insert Breakpoints''
2309 @c FIXME: "cannot insert breakpoints" error, v unclear.
2310 @c Q in pending mail to Gilmore. ---pesch@cygnus.com, 26mar91
2311 @c some light may be shed by looking at instances of
2312 @c ONE_PROCESS_WRITETEXT. But error seems possible otherwise
2313 @c too. pesch, 20sep91
2314 Under some operating systems, breakpoints cannot be used in a program if
2315 any other process is running that program. In this situation,
2316 attempting to run or continue a program with a breakpoint causes _GDBN__
2317 to stop the other process.
2319 When this happens, you have three ways to proceed:
2323 Remove or disable the breakpoints, then continue.
2326 Suspend _GDBN__, and copy the file containing your program to a new name.
2327 Resume _GDBN__ and use the @code{exec-file} command to specify that _GDBN__
2328 should run your program under that name. Then start your program again.
2330 @c FIXME: RMS commented here "Show example". Maybe when someone
2331 @c explains the first FIXME: in this section...
2334 Relink your program so that the text segment is nonsharable, using the
2335 linker option @samp{-N}. The operating system limitation may not apply
2336 to nonsharable executables.
2339 @node Continuing and Stepping, Signals, Breakpoints, Stopping
2340 @section Continuing and Stepping
2344 @cindex resuming execution
2345 @dfn{Continuing} means resuming program execution until your program
2346 completes normally. In contrast, @dfn{stepping} means executing just
2347 one more ``step'' of your program, where ``step'' may mean either one
2348 line of source code, or one machine instruction (depending on what
2349 particular command you use). Either when continuing
2350 or when stepping, your program may stop even sooner, due to a breakpoint
2351 or to a signal. (If due to a signal, you may want to use @code{handle},
2352 or use @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
2355 @item continue @r{[}@var{ignore-count}@r{]}
2357 Resume program execution, at the address where your program last stopped;
2358 any breakpoints set at that address are bypassed. The optional argument
2359 @var{ignore-count} allows you to specify a further number of times to
2360 ignore a breakpoint at this location; its effect is like that of
2361 @code{ignore} (@pxref{Conditions, ,Break Conditions}).
2363 To resume execution at a different place, you can use @code{return}
2364 (@pxref{Returning, ,Returning from a Function}) to go back to the
2365 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
2366 Different Address}) to go to an arbitrary location in your program.
2369 A typical technique for using stepping is to set a breakpoint
2370 (@pxref{Breakpoints, ,Breakpoints Watchpoints and Exceptions}) at the
2371 beginning of the function or the section of your program where a
2372 problem is believed to lie, run your program until it stops at that
2373 breakpoint, and then step through the suspect area, examining the
2374 variables that are interesting, until you see the problem happen.
2380 Continue running your program until control reaches a different source
2381 line, then stop it and return control to _GDBN__. This command is
2382 abbreviated @code{s}.
2385 @emph{Warning:} If you use the @code{step} command while control is
2386 within a function that was compiled without debugging information,
2387 execution will proceed until control reaches another function.
2390 @item step @var{count}
2391 Continue running as in @code{step}, but do so @var{count} times. If a
2392 breakpoint is reached or a signal not related to stepping occurs before
2393 @var{count} steps, stepping stops right away.
2395 @item next @r{[}@var{count}@r{]}
2398 Continue to the next source line in the current (innermost) stack frame.
2399 Similar to @code{step}, but any function calls appearing within the line
2400 of code are executed without stopping. Execution stops when control
2401 reaches a different line of code at the stack level which was executing
2402 when the @code{next} command was given. This command is abbreviated
2405 An argument @var{count} is a repeat count, as for @code{step}.
2407 @code{next} within a function that lacks debugging information acts like
2408 @code{step}, but any function calls appearing within the code of the
2409 function are executed without stopping.
2413 Continue running until just after function in the selected stack frame
2414 returns. Print the returned value (if any).
2416 Contrast this with the @code{return} command (@pxref{Returning,
2417 ,Returning from a Function}).
2423 Continue running until a source line past the current line, in the
2424 current stack frame, is reached. This command is used to avoid single
2425 stepping through a loop more than once. It is like the @code{next}
2426 command, except that when @code{until} encounters a jump, it
2427 automatically continues execution until the program counter is greater
2428 than the address of the jump.
2430 This means that when you reach the end of a loop after single stepping
2431 though it, @code{until} will cause your program to continue execution
2432 until the loop is exited. In contrast, a @code{next} command at the end
2433 of a loop will simply step back to the beginning of the loop, which
2434 would force you to step through the next iteration.
2436 @code{until} always stops your program if it attempts to exit the current
2439 @code{until} may produce somewhat counterintuitive results if the order
2440 of machine code does not match the order of the source lines. For
2441 example, in the following excerpt from a debugging session, the @code{f}
2442 (@code{frame}) command shows that execution is stopped at line
2443 @code{206}; yet when we use @code{until}, we get to line @code{195}:
2447 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
2450 195 for ( ; argc > 0; NEXTARG) @{
2453 This happened because, for execution efficiency, the compiler had
2454 generated code for the loop closure test at the end, rather than the
2455 start, of the loop---even though the test in a C @code{for}-loop is
2456 written before the body of the loop. The @code{until} command appeared
2457 to step back to the beginning of the loop when it advanced to this
2458 expression; however, it has not really gone to an earlier
2459 statement---not in terms of the actual machine code.
2461 @code{until} with no argument works by means of single
2462 instruction stepping, and hence is slower than @code{until} with an
2465 @item until @var{location}
2466 @item u @var{location}
2467 Continue running your program until either the specified location is
2468 reached, or the current stack frame returns. @var{location} is any of
2469 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
2470 ,Setting Breakpoints}). This form of the command uses breakpoints,
2471 and hence is quicker than @code{until} without an argument.
2477 Execute one machine instruction, then stop and return to the debugger.
2479 It is often useful to do @samp{display/i $pc} when stepping by machine
2480 instructions. This will cause the next instruction to be executed to
2481 be displayed automatically at each stop. @xref{Auto Display,
2482 ,Automatic Display}.
2484 An argument is a repeat count, as in @code{step}.
2490 Execute one machine instruction, but if it is a function call,
2491 proceed until the function returns.
2493 An argument is a repeat count, as in @code{next}.
2496 @node Signals, , Continuing and Stepping, Stopping
2500 A signal is an asynchronous event that can happen in a program. The
2501 operating system defines the possible kinds of signals, and gives each
2502 kind a name and a number. For example, in Unix @code{SIGINT} is the
2503 signal a program gets when you type an interrupt (often @kbd{C-c});
2504 @code{SIGSEGV} is the signal a program gets from referencing a place in
2505 memory far away from all the areas in use; @code{SIGALRM} occurs when
2506 the alarm clock timer goes off (which happens only if your program has
2507 requested an alarm).
2509 @cindex fatal signals
2510 Some signals, including @code{SIGALRM}, are a normal part of the
2511 functioning of your program. Others, such as @code{SIGSEGV}, indicate
2512 errors; these signals are @dfn{fatal} (kill your program immediately) if the
2513 program has not specified in advance some other way to handle the signal.
2514 @code{SIGINT} does not indicate an error in your program, but it is normally
2515 fatal so it can carry out the purpose of the interrupt: to kill the program.
2517 _GDBN__ has the ability to detect any occurrence of a signal in your
2518 program. You can tell _GDBN__ in advance what to do for each kind of
2521 @cindex handling signals
2522 Normally, _GDBN__ is set up to ignore non-erroneous signals like @code{SIGALRM}
2523 (so as not to interfere with their role in the functioning of your program)
2524 but to stop your program immediately whenever an error signal happens.
2525 You can change these settings with the @code{handle} command.
2529 @kindex info signals
2530 Print a table of all the kinds of signals and how _GDBN__ has been told to
2531 handle each one. You can use this to see the signal numbers of all
2532 the defined types of signals.
2534 @item handle @var{signal} @var{keywords}@dots{}
2536 Change the way _GDBN__ handles signal @var{signal}. @var{signal} can be the
2537 number of a signal or its name (with or without the @samp{SIG} at the
2538 beginning). The @var{keywords} say what change to make.
2542 The keywords allowed by the @code{handle} command can be abbreviated.
2543 Their full names are:
2547 _GDBN__ should not stop your program when this signal happens. It may
2548 still print a message telling you that the signal has come in.
2551 _GDBN__ should stop your program when this signal happens. This implies
2552 the @code{print} keyword as well.
2555 _GDBN__ should print a message when this signal happens.
2558 _GDBN__ should not mention the occurrence of the signal at all. This
2559 implies the @code{nostop} keyword as well.
2562 _GDBN__ should allow your program to see this signal; your program will be
2563 able to handle the signal, or may be terminated if the signal is fatal
2567 _GDBN__ should not allow your program to see this signal.
2571 When a signal has been set to stop your program, your program cannot see the
2572 signal until you continue. It will see the signal then, if @code{pass} is
2573 in effect for the signal in question @i{at that time}. In other words,
2574 after _GDBN__ reports a signal, you can use the @code{handle} command with
2575 @code{pass} or @code{nopass} to control whether that signal will be seen by
2576 your program when you later continue it.
2578 You can also use the @code{signal} command to prevent your program from
2579 seeing a signal, or cause it to see a signal it normally would not see,
2580 or to give it any signal at any time. For example, if your program stopped
2581 due to some sort of memory reference error, you might store correct
2582 values into the erroneous variables and continue, hoping to see more
2583 execution; but your program would probably terminate immediately as
2584 a result of the fatal signal once it saw the signal. To prevent this,
2585 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
2588 @node Stack, Source, Stopping, Top
2589 @chapter Examining the Stack
2591 When your program has stopped, the first thing you need to know is where it
2592 stopped and how it got there.
2595 Each time your program performs a function call, the information about
2596 where in your program the call was made from is saved in a block of data
2597 called a @dfn{stack frame}. The frame also contains the arguments of the
2598 call and the local variables of the function that was called. All the
2599 stack frames are allocated in a region of memory called the @dfn{call
2602 When your program stops, the _GDBN__ commands for examining the stack allow you
2603 to see all of this information.
2605 @cindex selected frame
2606 One of the stack frames is @dfn{selected} by _GDBN__ and many _GDBN__ commands
2607 refer implicitly to the selected frame. In particular, whenever you ask
2608 _GDBN__ for the value of a variable in your program, the value is found in the
2609 selected frame. There are special _GDBN__ commands to select whichever frame
2610 you are interested in.
2612 When your program stops, _GDBN__ automatically selects the currently executing
2613 frame and describes it briefly as the @code{frame} command does
2614 (@pxref{Frame Info, ,Information About a Frame}).
2617 * Frames:: Stack Frames
2618 * Backtrace:: Backtraces
2619 * Selection:: Selecting a Frame
2620 * Frame Info:: Information on a Frame
2623 @node Frames, Backtrace, Stack, Stack
2624 @section Stack Frames
2628 The call stack is divided up into contiguous pieces called @dfn{stack
2629 frames}, or @dfn{frames} for short; each frame is the data associated
2630 with one call to one function. The frame contains the arguments given
2631 to the function, the function's local variables, and the address at
2632 which the function is executing.
2634 @cindex initial frame
2635 @cindex outermost frame
2636 @cindex innermost frame
2637 When your program is started, the stack has only one frame, that of the
2638 function @code{main}. This is called the @dfn{initial} frame or the
2639 @dfn{outermost} frame. Each time a function is called, a new frame is
2640 made. Each time a function returns, the frame for that function invocation
2641 is eliminated. If a function is recursive, there can be many frames for
2642 the same function. The frame for the function in which execution is
2643 actually occurring is called the @dfn{innermost} frame. This is the most
2644 recently created of all the stack frames that still exist.
2646 @cindex frame pointer
2647 Inside your program, stack frames are identified by their addresses. A
2648 stack frame consists of many bytes, each of which has its own address; each
2649 kind of computer has a convention for choosing one of those bytes whose
2650 address serves as the address of the frame. Usually this address is kept
2651 in a register called the @dfn{frame pointer register} while execution is
2652 going on in that frame.
2654 @cindex frame number
2655 _GDBN__ assigns numbers to all existing stack frames, starting with
2656 zero for the innermost frame, one for the frame that called it,
2657 and so on upward. These numbers do not really exist in your program;
2658 they are assigned by _GDBN__ to give you a way of designating stack
2659 frames in _GDBN__ commands.
2661 @cindex frameless execution
2662 Some compilers allow functions to be compiled so that they operate
2663 without stack frames. (For example, the @code{_GCC__} option
2664 @samp{-fomit-frame-pointer} will generate functions without a frame.)
2665 This is occasionally done with heavily used library functions to save
2666 the frame setup time. _GDBN__ has limited facilities for dealing with
2667 these function invocations. If the innermost function invocation has no
2668 stack frame, _GDBN__ will nevertheless regard it as though it had a
2669 separate frame, which is numbered zero as usual, allowing correct
2670 tracing of the function call chain. However, _GDBN__ has no provision
2671 for frameless functions elsewhere in the stack.
2673 @node Backtrace, Selection, Frames, Stack
2676 A backtrace is a summary of how your program got where it is. It shows one
2677 line per frame, for many frames, starting with the currently executing
2678 frame (frame zero), followed by its caller (frame one), and on up the
2686 Print a backtrace of the entire stack: one line per frame for all
2687 frames in the stack.
2689 You can stop the backtrace at any time by typing the system interrupt
2690 character, normally @kbd{C-c}.
2692 @item backtrace @var{n}
2694 Similar, but print only the innermost @var{n} frames.
2696 @item backtrace -@var{n}
2698 Similar, but print only the outermost @var{n} frames.
2704 The names @code{where} and @code{info stack} (abbreviated @code{info s})
2705 are additional aliases for @code{backtrace}.
2707 Each line in the backtrace shows the frame number and the function name.
2708 The program counter value is also shown---unless you use @code{set
2709 print address off}. The backtrace also shows the source file name and
2710 line number, as well as the arguments to the function. The program
2711 counter value is omitted if it is at the beginning of the code for that
2714 Here is an example of a backtrace. It was made with the command
2715 @samp{bt 3}, so it shows the innermost three frames.
2719 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
2721 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
2722 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
2724 (More stack frames follow...)
2729 The display for frame zero does not begin with a program counter
2730 value, indicating that your program has stopped at the beginning of the
2731 code for line @code{993} of @code{builtin.c}.
2733 @node Selection, Frame Info, Backtrace, Stack
2734 @section Selecting a Frame
2736 Most commands for examining the stack and other data in your program work on
2737 whichever stack frame is selected at the moment. Here are the commands for
2738 selecting a stack frame; all of them finish by printing a brief description
2739 of the stack frame just selected.
2746 Select frame number @var{n}. Recall that frame zero is the innermost
2747 (currently executing) frame, frame one is the frame that called the
2748 innermost one, and so on. The highest-numbered frame is @code{main}'s
2751 @item frame @var{addr}
2753 Select the frame at address @var{addr}. This is useful mainly if the
2754 chaining of stack frames has been damaged by a bug, making it
2755 impossible for _GDBN__ to assign numbers properly to all frames. In
2756 addition, this can be useful when your program has multiple stacks and
2757 switches between them.
2760 On the SPARC architecture, @code{frame} needs two addresses to
2761 select an arbitrary frame: a frame pointer and a stack pointer.
2762 @c note to future updaters: this is conditioned on a flag
2763 @c FRAME_SPECIFICATION_DYADIC in the tm-*.h files, currently only used
2764 @c by SPARC, hence the specific attribution. Generalize or list all
2765 @c possibilities if more supported machines start doing this.
2770 Move @var{n} frames up the stack. For positive numbers @var{n}, this
2771 advances toward the outermost frame, to higher frame numbers, to frames
2772 that have existed longer. @var{n} defaults to one.
2777 Move @var{n} frames down the stack. For positive numbers @var{n}, this
2778 advances toward the innermost frame, to lower frame numbers, to frames
2779 that were created more recently. @var{n} defaults to one. You may
2780 abbreviate @code{down} as @code{do}.
2783 All of these commands end by printing two lines of output describing the
2784 frame. The first line shows the frame number, the function name, the
2785 arguments, and the source file and line number of execution in that
2786 frame. The second line shows the text of that source line. For
2792 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
2794 10 read_input_file (argv[i]);
2798 After such a printout, the @code{list} command with no arguments will
2799 print ten lines centered on the point of execution in the frame.
2800 @xref{List, ,Printing Source Lines}.
2803 @item up-silently @var{n}
2804 @itemx down-silently @var{n}
2805 @kindex down-silently
2807 These two commands are variants of @code{up} and @code{down},
2808 respectively; they differ in that they do their work silently, without
2809 causing display of the new frame. They are intended primarily for use
2810 in _GDBN__ command scripts, where the output might be unnecessary and
2814 @node Frame Info, , Selection, Stack
2815 @section Information About a Frame
2817 There are several other commands to print information about the selected
2823 When used without any argument, this command does not change which
2824 frame is selected, but prints a brief description of the currently
2825 selected stack frame. It can be abbreviated @code{f}. With an
2826 argument, this command is used to select a stack frame
2827 (@pxref{Selection, ,Selecting a Frame}).
2833 This command prints a verbose description of the selected stack frame,
2834 including the address of the frame, the addresses of the next frame down
2835 (called by this frame) and the next frame up (caller of this frame), the
2836 language that the source code corresponding to this frame was written in,
2837 the address of the frame's arguments, the program counter saved in it
2838 (the address of execution in the caller frame), and which registers
2839 were saved in the frame. The verbose description is useful when
2840 something has gone wrong that has made the stack format fail to fit
2841 the usual conventions.
2843 @item info frame @var{addr}
2844 @itemx info f @var{addr}
2845 Print a verbose description of the frame at address @var{addr},
2846 without selecting that frame. The selected frame remains unchanged by
2851 Print the arguments of the selected frame, each on a separate line.
2855 Print the local variables of the selected frame, each on a separate
2856 line. These are all variables declared static or automatic within all
2857 program blocks that execution in this frame is currently inside of.
2861 @cindex catch exceptions
2862 @cindex exception handlers
2863 Print a list of all the exception handlers that are active in the
2864 current stack frame at the current point of execution. To see other
2865 exception handlers, visit the associated frame (using the @code{up},
2866 @code{down}, or @code{frame} commands); then type @code{info catch}.
2867 @xref{Exception Handling, ,Breakpoints and Exceptions}.
2870 @node Source, Data, Stack, Top
2871 @chapter Examining Source Files
2873 _GDBN__ can print parts of your program's source, since the debugging
2874 information recorded in your program tells _GDBN__ what source files were
2875 used to build it. When your program stops, _GDBN__ spontaneously prints
2876 the line where it stopped. Likewise, when you select a stack frame
2877 (@pxref{Selection, ,Selecting a Frame}), _GDBN__ prints the line where
2878 execution in that frame has stopped. You can print other portions of
2879 source files by explicit command.
2881 If you use _GDBN__ through its GNU Emacs interface, you may prefer to use
2882 Emacs facilities to view source; @pxref{Emacs, ,Using _GDBN__ under GNU
2886 * List:: Printing Source Lines
2887 * Search:: Searching Source Files
2888 * Source Path:: Specifying Source Directories
2889 * Machine Code:: Source and Machine Code
2892 @node List, Search, Source, Source
2893 @section Printing Source Lines
2897 To print lines from a source file, use the @code{list} command
2898 (abbreviated @code{l}). There are several ways to specify what part
2899 of the file you want to print.
2901 Here are the forms of the @code{list} command most commonly used:
2904 @item list @var{linenum}
2905 Print lines centered around line number @var{linenum} in the
2906 current source file.
2908 @item list @var{function}
2909 Print lines centered around the beginning of function
2913 Print more lines. If the last lines printed were printed with a
2914 @code{list} command, this prints lines following the last lines
2915 printed; however, if the last line printed was a solitary line printed
2916 as part of displaying a stack frame (@pxref{Stack, ,Examining the
2917 Stack}), this prints lines centered around that line.
2920 Print lines just before the lines last printed.
2923 By default, _GDBN__ prints ten source lines with any of these forms of
2924 the @code{list} command. You can change this using @code{set listsize}:
2927 @item set listsize @var{count}
2928 @kindex set listsize
2929 Make the @code{list} command display @var{count} source lines (unless
2930 the @code{list} argument explicitly specifies some other number).
2933 @kindex show listsize
2934 Display the number of lines that @code{list} will currently display by
2938 Repeating a @code{list} command with @key{RET} discards the argument,
2939 so it is equivalent to typing just @code{list}. This is more useful
2940 than listing the same lines again. An exception is made for an
2941 argument of @samp{-}; that argument is preserved in repetition so that
2942 each repetition moves up in the source file.
2945 In general, the @code{list} command expects you to supply zero, one or two
2946 @dfn{linespecs}. Linespecs specify source lines; there are several ways
2947 of writing them but the effect is always to specify some source line.
2948 Here is a complete description of the possible arguments for @code{list}:
2951 @item list @var{linespec}
2952 Print lines centered around the line specified by @var{linespec}.
2954 @item list @var{first},@var{last}
2955 Print lines from @var{first} to @var{last}. Both arguments are
2958 @item list ,@var{last}
2959 Print lines ending with @var{last}.
2961 @item list @var{first},
2962 Print lines starting with @var{first}.
2965 Print lines just after the lines last printed.
2968 Print lines just before the lines last printed.
2971 As described in the preceding table.
2974 Here are the ways of specifying a single source line---all the
2979 Specifies line @var{number} of the current source file.
2980 When a @code{list} command has two linespecs, this refers to
2981 the same source file as the first linespec.
2984 Specifies the line @var{offset} lines after the last line printed.
2985 When used as the second linespec in a @code{list} command that has
2986 two, this specifies the line @var{offset} lines down from the
2990 Specifies the line @var{offset} lines before the last line printed.
2992 @item @var{filename}:@var{number}
2993 Specifies line @var{number} in the source file @var{filename}.
2995 @item @var{function}
2996 @c FIXME: "of the open-brace" is C-centric. When we add other langs...
2997 Specifies the line of the open-brace that begins the body of the
2998 function @var{function}.
3000 @item @var{filename}:@var{function}
3001 Specifies the line of the open-brace that begins the body of the
3002 function @var{function} in the file @var{filename}. You only need the
3003 file name with a function name to avoid ambiguity when there are
3004 identically named functions in different source files.
3006 @item *@var{address}
3007 Specifies the line containing the program address @var{address}.
3008 @var{address} may be any expression.
3011 @node Search, Source Path, List, Source
3012 @section Searching Source Files
3014 @kindex reverse-search
3016 There are two commands for searching through the current source file for a
3020 @item forward-search @var{regexp}
3021 @itemx search @var{regexp}
3023 @kindex forward-search
3024 The command @samp{forward-search @var{regexp}} checks each line,
3025 starting with the one following the last line listed, for a match for
3026 @var{regexp}. It lists the line that is found. You can use
3027 synonym @samp{search @var{regexp}} or abbreviate the command name as
3030 @item reverse-search @var{regexp}
3031 The command @samp{reverse-search @var{regexp}} checks each line, starting
3032 with the one before the last line listed and going backward, for a match
3033 for @var{regexp}. It lists the line that is found. You can abbreviate
3034 this command as @code{rev}.
3037 @node Source Path, Machine Code, Search, Source
3038 @section Specifying Source Directories
3041 @cindex directories for source files
3042 Executable programs sometimes do not record the directories of the source
3043 files from which they were compiled, just the names. Even when they do,
3044 the directories could be moved between the compilation and your debugging
3045 session. _GDBN__ has a list of directories to search for source files;
3046 this is called the @dfn{source path}. Each time _GDBN__ wants a source file,
3047 it tries all the directories in the list, in the order they are present
3048 in the list, until it finds a file with the desired name. Note that
3049 the executable search path is @emph{not} used for this purpose. Neither is
3050 the current working directory, unless it happens to be in the source
3053 If _GDBN__ cannot find a source file in the source path, and the object
3054 program records a directory, _GDBN__ tries that directory too. If the
3055 source path is empty, and there is no record of the compilation
3056 directory, _GDBN__ will, as a last resort, look in the current
3059 Whenever you reset or rearrange the source path, _GDBN__ will clear out
3060 any information it has cached about where source files are found, where
3061 each line is in the file, etc.
3064 When you start _GDBN__, its source path is empty.
3065 To add other directories, use the @code{directory} command.
3068 @item directory @var{dirname} @dots{}
3069 Add directory @var{dirname} to the front of the source path. Several
3070 directory names may be given to this command, separated by @samp{:} or
3071 whitespace. You may specify a directory that is already in the source
3072 path; this moves it forward, so it will be searched sooner.
3074 You can use the string @samp{$cdir} to refer to the compilation
3075 directory (if one is recorded), and @samp{$cwd} to refer to the current
3076 working directory. @samp{$cwd} is not the same as @samp{.}---the former
3077 tracks the current working directory as it changes during your _GDBN__
3078 session, while the latter is immediately expanded to the current
3079 directory at the time you add an entry to the source path.
3082 Reset the source path to empty again. This requires confirmation.
3084 @c RET-repeat for @code{directory} is explicitly disabled, but since
3085 @c repeating it would be a no-op we do not say that. (thanks to RMS)
3087 @item show directories
3088 @kindex show directories
3089 Print the source path: show which directories it contains.
3092 If your source path is cluttered with directories that are no longer of
3093 interest, _GDBN__ may sometimes cause confusion by finding the wrong
3094 versions of source. You can correct the situation as follows:
3098 Use @code{directory} with no argument to reset the source path to empty.
3101 Use @code{directory} with suitable arguments to reinstall the
3102 directories you want in the source path. You can add all the
3103 directories in one command.
3106 @node Machine Code, , Source Path, Source
3107 @section Source and Machine Code
3109 You can use the command @code{info line} to map source lines to program
3110 addresses (and viceversa), and the command @code{disassemble} to display
3111 a range of addresses as machine instructions.
3114 @item info line @var{linespec}
3116 Print the starting and ending addresses of the compiled code for
3117 source line @var{linespec}. You can specify source lines in any of
3118 the ways understood by the @code{list} command (@pxref{List, ,Printing
3122 For example, we can use @code{info line} to discover the location of
3123 the object code for the first line of function
3124 @code{m4_changequote}:
3127 (_GDBP__) info line m4_changecom
3128 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
3132 We can also inquire (using @code{*@var{addr}} as the form for
3133 @var{linespec}) what source line covers a particular address:
3135 (_GDBP__) info line *0x63ff
3136 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
3139 @cindex @code{$_} and @code{info line}
3140 After @code{info line}, the default address for the @code{x} command
3141 is changed to the starting address of the line, so that @samp{x/i} is
3142 sufficient to begin examining the machine code (@pxref{Memory,
3143 ,Examining Memory}). Also, this address is saved as the value of the
3144 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
3150 This specialized command is provided to dump a range of memory as
3151 machine instructions. The default memory range is the function
3152 surrounding the program counter of the selected frame. A single
3153 argument to this command is a program counter value; the function
3154 surrounding this value will be dumped. Two arguments (separated by one
3155 or more spaces) specify a range of addresses (first inclusive, second
3156 exclusive) to be dumped.
3159 We can use @code{disassemble} to inspect the object code
3160 range shown in the last @code{info line} example:
3163 (_GDBP__) disas 0x63e4 0x6404
3164 Dump of assembler code from 0x63e4 to 0x6404:
3165 0x63e4 <builtin_init+5340>: ble 0x63f8 <builtin_init+5360>
3166 0x63e8 <builtin_init+5344>: sethi %hi(0x4c00), %o0
3167 0x63ec <builtin_init+5348>: ld [%i1+4], %o0
3168 0x63f0 <builtin_init+5352>: b 0x63fc <builtin_init+5364>
3169 0x63f4 <builtin_init+5356>: ld [%o0+4], %o0
3170 0x63f8 <builtin_init+5360>: or %o0, 0x1a4, %o0
3171 0x63fc <builtin_init+5364>: call 0x9288 <path_search>
3172 0x6400 <builtin_init+5368>: nop
3173 End of assembler dump.
3177 @node Data, Languages, Source, Top
3178 @chapter Examining Data
3180 @cindex printing data
3181 @cindex examining data
3184 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
3185 @c document because it is nonstandard... Under Epoch it displays in a
3186 @c different window or something like that.
3187 The usual way to examine data in your program is with the @code{print}
3188 command (abbreviated @code{p}), or its synonym @code{inspect}. It
3189 evaluates and prints the value of an expression of the language your
3190 program is written in (@pxref{Languages, ,Using _GDBN__ with Different
3194 @item print @var{exp}
3195 @itemx print /@var{f} @var{exp}
3196 @var{exp} is an expression (in the source language). By default
3197 the value of @var{exp} is printed in a format appropriate to its data
3198 type; you can choose a different format by specifying @samp{/@var{f}},
3199 where @var{f} is a letter specifying the format; @pxref{Output formats}.
3202 @itemx print /@var{f}
3203 If you omit @var{exp}, _GDBN__ displays the last value again (from the
3204 @dfn{value history}; @pxref{Value History, ,Value History}). This allows you to
3205 conveniently inspect the same value in an alternative format.
3208 A more low-level way of examining data is with the @code{x} command.
3209 It examines data in memory at a specified address and prints it in a
3210 specified format. @xref{Memory, ,Examining Memory}.
3212 If you are interested in information about types, or about how the fields
3213 of a struct or class are declared, use the @code{ptype @var{exp}}
3214 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol Table}.
3217 * Expressions:: Expressions
3218 * Variables:: Program Variables
3219 * Arrays:: Artificial Arrays
3220 * Output formats:: Output formats
3221 * Memory:: Examining Memory
3222 * Auto Display:: Automatic Display
3223 * Print Settings:: Print Settings
3224 * Value History:: Value History
3225 * Convenience Vars:: Convenience Variables
3226 * Registers:: Registers
3227 * Floating Point Hardware:: Floating Point Hardware
3230 @node Expressions, Variables, Data, Data
3231 @section Expressions
3234 @code{print} and many other _GDBN__ commands accept an expression and
3235 compute its value. Any kind of constant, variable or operator defined
3236 by the programming language you are using is legal in an expression in
3237 _GDBN__. This includes conditional expressions, function calls, casts
3238 and string constants. It unfortunately does not include symbols defined
3239 by preprocessor @code{#define} commands.
3241 Because C is so widespread, most of the expressions shown in examples in
3242 this manual are in C. @xref{Languages, , Using _GDBN__ with Different
3243 Languages}, for information on how to use expressions in other
3246 In this section, we discuss operators that you can use in _GDBN__
3247 expressions regardless of your programming language.
3249 Casts are supported in all languages, not just in C, because it is so
3250 useful to cast a number into a pointer so as to examine a structure
3251 at that address in memory.
3252 @c FIXME: casts supported---Mod2 true?
3254 _GDBN__ supports these operators in addition to those of programming
3259 @samp{@@} is a binary operator for treating parts of memory as arrays.
3260 @xref{Arrays, ,Artificial Arrays}, for more information.
3263 @samp{::} allows you to specify a variable in terms of the file or
3264 function where it is defined. @xref{Variables, ,Program Variables}.
3266 @item @{@var{type}@} @var{addr}
3267 Refers to an object of type @var{type} stored at address @var{addr} in
3268 memory. @var{addr} may be any expression whose value is an integer or
3269 pointer (but parentheses are required around binary operators, just as in
3270 a cast). This construct is allowed regardless of what kind of data is
3271 normally supposed to reside at @var{addr}.
3274 @node Variables, Arrays, Expressions, Data
3275 @section Program Variables
3277 The most common kind of expression to use is the name of a variable
3280 Variables in expressions are understood in the selected stack frame
3281 (@pxref{Selection, ,Selecting a Frame}); they must either be global
3282 (or static) or be visible according to the scope rules of the
3283 programming language from the point of execution in that frame. This
3284 means that in the function
3299 the variable @code{a} is usable whenever your program is executing
3300 within the function @code{foo}, but the variable @code{b} is visible
3301 only while your program is executing inside the block in which @code{b}
3304 @cindex variable name conflict
3305 There is an exception: you can refer to a variable or function whose
3306 scope is a single source file even if the current execution point is not
3307 in this file. But it is possible to have more than one such variable or
3308 function with the same name (in different source files). If that happens,
3309 referring to that name has unpredictable effects. If you wish, you can
3310 specify a variable in a particular file, using the colon-colon notation:
3314 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
3318 @var{file}::@var{variable}
3322 Here @var{file} is the name of the source file whose variable you want.
3324 @cindex C++ scope resolution
3325 This use of @samp{::} is very rarely in conflict with the very similar
3326 use of the same notation in C++. _GDBN__ also supports use of the C++
3327 scope resolution operator in _GDBN__ expressions.
3329 @cindex wrong values
3330 @cindex variable values, wrong
3332 @emph{Warning:} Occasionally, a local variable may appear to have the
3333 wrong value at certain points in a function---just after entry to the
3334 function, and just before exit. You may see this problem when you are
3335 stepping by machine instructions. This is because on most machines, it
3336 takes more than one instruction to set up a stack frame (including local
3337 variable definitions); if you are stepping by machine instructions,
3338 variables may appear to have the wrong values until the stack frame is
3339 completely built. On function exit, it usually also takes more than one
3340 machine instruction to destroy a stack frame; after you begin stepping
3341 through that group of instructions, local variable definitions may be
3345 @node Arrays, Output formats, Variables, Data
3346 @section Artificial Arrays
3348 @cindex artificial array
3350 It is often useful to print out several successive objects of the
3351 same type in memory; a section of an array, or an array of
3352 dynamically determined size for which only a pointer exists in the
3355 This can be done by constructing an @dfn{artificial array} with the
3356 binary operator @samp{@@}. The left operand of @samp{@@} should be
3357 the first element of the desired array, as an individual object.
3358 The right operand should be the desired length of the array. The result is
3359 an array value whose elements are all of the type of the left argument.
3360 The first element is actually the left argument; the second element
3361 comes from bytes of memory immediately following those that hold the
3362 first element, and so on. Here is an example. If a program says
3365 int *array = (int *) malloc (len * sizeof (int));
3369 you can print the contents of @code{array} with
3375 The left operand of @samp{@@} must reside in memory. Array values made
3376 with @samp{@@} in this way behave just like other arrays in terms of
3377 subscripting, and are coerced to pointers when used in expressions.
3378 Artificial arrays most often appear in expressions via the value history
3379 (@pxref{Value History, ,Value History}), after printing one out.)
3381 Sometimes the artificial array mechanism is not quite enough; in
3382 moderately complex data structures, the elements of interest may not
3383 actually be adjacent---for example, if you are interested in the values
3384 of pointers in an array. One useful work-around in this situation is
3385 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
3386 Variables}) as a counter in an expression that prints the first
3387 interesting value, and then repeat that expression via @key{RET}. For
3388 instance, suppose you have an array @code{dtab} of pointers to
3389 structures, and you are interested in the values of a field @code{fv}
3390 in each structure. Here is an example of what you might type:
3400 @node Output formats, Memory, Arrays, Data
3401 @section Output formats
3403 @cindex formatted output
3404 @cindex output formats
3405 By default, _GDBN__ prints a value according to its data type. Sometimes
3406 this is not what you want. For example, you might want to print a number
3407 in hex, or a pointer in decimal. Or you might want to view data in memory
3408 at a certain address as a character string or as an instruction. To do
3409 these things, specify an @dfn{output format} when you print a value.
3411 The simplest use of output formats is to say how to print a value
3412 already computed. This is done by starting the arguments of the
3413 @code{print} command with a slash and a format letter. The format
3414 letters supported are:
3418 Regard the bits of the value as an integer, and print the integer in
3422 Print as integer in signed decimal.
3425 Print as integer in unsigned decimal.
3428 Print as integer in octal.
3431 Print as integer in binary. The letter @samp{t} stands for ``two''.
3434 Print as an address, both absolute in hex and as an offset from the
3435 nearest preceding symbol. This format can be used to discover where (in
3436 what function) an unknown address is located:
3439 (_GDBP__) p/a 0x54320
3440 _0__$3 = 0x54320 <_initialize_vx+396>_1__
3444 Regard as an integer and print it as a character constant.
3447 Regard the bits of the value as a floating point number and print
3448 using typical floating point syntax.
3451 For example, to print the program counter in hex (@pxref{Registers}), type
3458 Note that no space is required before the slash; this is because command
3459 names in _GDBN__ cannot contain a slash.
3461 To reprint the last value in the value history with a different format,
3462 you can use the @code{print} command with just a format and no
3463 expression. For example, @samp{p/x} reprints the last value in hex.
3465 @node Memory, Auto Display, Output formats, Data
3466 @section Examining Memory
3468 You can use the command @code{x} (for ``examine'') to examine memory in
3469 any of several formats, independently of your program's data types.
3471 @cindex examining memory
3474 @item x/@var{nfu} @var{addr}
3477 Use the command @code{x} to examine memory.
3480 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
3481 much memory to display and how to format it; @var{addr} is an
3482 expression giving the address where you want to start displaying memory.
3483 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
3484 Several commands set convenient defaults for @var{addr}.
3487 @item @var{n}, the repeat count
3488 The repeat count is a decimal integer; the default is 1. It specifies
3489 how much memory (counting by units @var{u}) to display.
3490 @c This really is **decimal**; unaffected by 'set radix' as of GDB
3493 @item @var{f}, the display format
3494 The display format is one of the formats used by @code{print},
3495 or @samp{s} (null-terminated string) or @samp{i} (machine instruction).
3496 The default is @samp{x} (hexadecimal) initially, or the format from the
3497 last time you used either @code{x} or @code{print}.
3499 @item @var{u}, the unit size
3500 The unit size is any of
3505 Halfwords (two bytes).
3507 Words (four bytes). This is the initial default.
3509 Giant words (eight bytes).
3512 Each time you specify a unit size with @code{x}, that size becomes the
3513 default unit the next time you use @code{x}. (For the @samp{s} and
3514 @samp{i} formats, the unit size is ignored and is normally not written.)
3516 @item @var{addr}, starting display address
3517 @var{addr} is the address where you want _GDBN__ to begin displaying
3518 memory. The expression need not have a pointer value (though it may);
3519 it is always interpreted as an integer address of a byte of memory.
3520 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
3521 @var{addr} is usually just after the last address examined---but several
3522 other commands also set the default address: @code{info breakpoints} (to
3523 the address of the last breakpoint listed), @code{info line} (to the
3524 starting address of a line), and @code{print} (if you use it to display
3525 a value from memory).
3528 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
3529 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
3530 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
3531 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
3532 @pxref{Registers}) in hexadecimal (@samp{x}).
3534 Since the letters indicating unit sizes are all distinct from the
3535 letters specifying output formats, you do not have to remember whether
3536 unit size or format comes first; either order will work. The output
3537 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
3538 (However, the count @var{n} must come first; @samp{wx4} will not work.)
3540 Even though the unit size @var{u} is ignored for the formats @samp{s}
3541 and @samp{i}, you might still want to use a count @var{n}; for example,
3542 @samp{3i} specifies that you want to see three machine instructions,
3543 including any operands. The command @code{disassemble} gives an
3544 alternative way of inspecting machine instructions; @pxref{Machine
3547 All the defaults for the arguments to @code{x} are designed to make it
3548 easy to continue scanning memory with minimal specifications each time
3549 you use @code{x}. For example, after you have inspected three machine
3550 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
3551 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
3552 the repeat count @var{n} is used again; the other arguments default as
3553 for successive uses of @code{x}.
3555 @cindex @code{$_}, @code{$__}, and value history
3556 The addresses and contents printed by the @code{x} command are not saved
3557 in the value history because there is often too much of them and they
3558 would get in the way. Instead, _GDBN__ makes these values available for
3559 subsequent use in expressions as values of the convenience variables
3560 @code{$_} and @code{$__}. After an @code{x} command, the last address
3561 examined is available for use in expressions in the convenience variable
3562 @code{$_}. The contents of that address, as examined, are available in
3563 the convenience variable @code{$__}.
3565 If the @code{x} command has a repeat count, the address and contents saved
3566 are from the last memory unit printed; this is not the same as the last
3567 address printed if several units were printed on the last line of output.
3569 @node Auto Display, Print Settings, Memory, Data
3570 @section Automatic Display
3571 @cindex automatic display
3572 @cindex display of expressions
3574 If you find that you want to print the value of an expression frequently
3575 (to see how it changes), you might want to add it to the @dfn{automatic
3576 display list} so that _GDBN__ will print its value each time your program stops.
3577 Each expression added to the list is given a number to identify it;
3578 to remove an expression from the list, you specify that number.
3579 The automatic display looks like this:
3583 3: bar[5] = (struct hack *) 0x3804
3587 showing item numbers, expressions and their current values. As with
3588 displays you request manually using @code{x} or @code{print}, you can
3589 specify the output format you prefer; in fact, @code{display} decides
3590 whether to use @code{print} or @code{x} depending on how elaborate your
3591 format specification is---it uses @code{x} if you specify a unit size,
3592 or one of the two formats (@samp{i} and @samp{s}) that are only
3593 supported by @code{x}; otherwise it uses @code{print}.
3596 @item display @var{exp}
3598 Add the expression @var{exp} to the list of expressions to display
3599 each time your program stops. @xref{Expressions, ,Expressions}.
3601 @code{display} will not repeat if you press @key{RET} again after using it.
3603 @item display/@var{fmt} @var{exp}
3604 For @var{fmt} specifying only a display format and not a size or
3605 count, add the expression @var{exp} to the auto-display list but
3606 arranges to display it each time in the specified format @var{fmt}.
3607 @xref{Output formats}.
3609 @item display/@var{fmt} @var{addr}
3610 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
3611 number of units, add the expression @var{addr} as a memory address to
3612 be examined each time your program stops. Examining means in effect
3613 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining Memory}.
3616 For example, @samp{display/i $pc} can be helpful, to see the machine
3617 instruction about to be executed each time execution stops (@samp{$pc}
3618 is a common name for the program counter; @pxref{Registers}).
3621 @item undisplay @var{dnums}@dots{}
3622 @itemx delete display @var{dnums}@dots{}
3623 @kindex delete display
3625 Remove item numbers @var{dnums} from the list of expressions to display.
3627 @code{undisplay} will not repeat if you press @key{RET} after using it.
3628 (Otherwise you would just get the error @samp{No display number @dots{}}.)
3630 @item disable display @var{dnums}@dots{}
3631 @kindex disable display
3632 Disable the display of item numbers @var{dnums}. A disabled display
3633 item is not printed automatically, but is not forgotten. It may be
3634 enabled again later.
3636 @item enable display @var{dnums}@dots{}
3637 @kindex enable display
3638 Enable display of item numbers @var{dnums}. It becomes effective once
3639 again in auto display of its expression, until you specify otherwise.
3642 Display the current values of the expressions on the list, just as is
3643 done when your program stops.
3646 @kindex info display
3647 Print the list of expressions previously set up to display
3648 automatically, each one with its item number, but without showing the
3649 values. This includes disabled expressions, which are marked as such.
3650 It also includes expressions which would not be displayed right now
3651 because they refer to automatic variables not currently available.
3654 If a display expression refers to local variables, then it does not make
3655 sense outside the lexical context for which it was set up. Such an
3656 expression is disabled when execution enters a context where one of its
3657 variables is not defined. For example, if you give the command
3658 @code{display last_char} while inside a function with an argument
3659 @code{last_char}, then this argument will be displayed while your program
3660 continues to stop inside that function. When it stops elsewhere---where
3661 there is no variable @code{last_char}---display is disabled. The next time
3662 your program stops where @code{last_char} is meaningful, you can enable the
3663 display expression once again.
3665 @node Print Settings, Value History, Auto Display, Data
3666 @section Print Settings
3668 @cindex format options
3669 @cindex print settings
3670 _GDBN__ provides the following ways to control how arrays, structures,
3671 and symbols are printed.
3674 These settings are useful for debugging programs in any language:
3677 @item set print address
3678 @item set print address on
3679 @kindex set print address
3680 _GDBN__ will print memory addresses showing the location of stack
3681 traces, structure values, pointer values, breakpoints, and so forth,
3682 even when it also displays the contents of those addresses. The default
3683 is on. For example, this is what a stack frame display looks like, with
3684 @code{set print address on}:
3689 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
3691 530 if (lquote != def_lquote)
3695 @item set print address off
3696 Do not print addresses when displaying their contents. For example,
3697 this is the same stack frame displayed with @code{set print address off}:
3701 (_GDBP__) set print addr off
3703 #0 set_quotes (lq="<<", rq=">>") at input.c:530
3704 530 if (lquote != def_lquote)
3708 @item show print address
3709 @kindex show print address
3710 Show whether or not addresses are to be printed.
3712 @item set print array
3713 @itemx set print array on
3714 @kindex set print array
3715 _GDBN__ will pretty print arrays. This format is more convenient to read,
3716 but uses more space. The default is off.
3718 @item set print array off.
3719 Return to compressed format for arrays.
3721 @item show print array
3722 @kindex show print array
3723 Show whether compressed or pretty format is selected for displaying
3726 @item set print elements @var{number-of-elements}
3727 @kindex set print elements
3728 If _GDBN__ is printing a large array, it will stop printing after it has
3729 printed the number of elements set by the @code{set print elements} command.
3730 This limit also applies to the display of strings.
3732 @item show print elements
3733 @kindex show print elements
3734 Display the number of elements of a large array that _GDBN__ will print
3735 before losing patience.
3737 @item set print pretty on
3738 @kindex set print pretty
3739 Cause _GDBN__ to print structures in an indented format with one member per
3755 @item set print pretty off
3756 Cause _GDBN__ to print structures in a compact format, like this:
3760 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, meat \
3766 This is the default format.
3768 @item show print pretty
3769 @kindex show print pretty
3770 Show which format _GDBN__ will use to print structures.
3772 @item set print sevenbit-strings on
3773 @kindex set print sevenbit-strings
3774 Print using only seven-bit characters; if this option is set,
3775 _GDBN__ will display any eight-bit characters (in strings or character
3776 values) using the notation @code{\}@var{nnn}. For example, @kbd{M-a} is
3777 displayed as @code{\341}.
3779 @item set print sevenbit-strings off
3780 Print using either seven-bit or eight-bit characters, as required. This
3783 @item show print sevenbit-strings
3784 @kindex show print sevenbit-strings
3785 Show whether or not _GDBN__ will print only seven-bit characters.
3787 @item set print union on
3788 @kindex set print union
3789 Tell _GDBN__ to print unions which are contained in structures. This is the
3792 @item set print union off
3793 Tell _GDBN__ not to print unions which are contained in structures.
3795 @item show print union
3796 @kindex show print union
3797 Ask _GDBN__ whether or not it will print unions which are contained in
3800 For example, given the declarations
3803 typedef enum @{Tree, Bug@} Species;
3804 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
3805 typedef enum @{Caterpillar, Cocoon, Butterfly@}
3816 struct thing foo = @{Tree, @{Acorn@}@};
3820 with @code{set print union on} in effect @samp{p foo} would print
3823 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
3827 and with @code{set print union off} in effect it would print
3830 $1 = @{it = Tree, form = @{...@}@}
3835 These settings are of interest when debugging C++ programs:
3838 @item set print demangle
3839 @itemx set print demangle on
3840 @kindex set print demangle
3841 Print C++ names in their source form rather than in the mangled form
3842 in which they are passed to the assembler and linker for type-safe linkage.
3845 @item show print demangle
3846 @kindex show print demangle
3847 Show whether C++ names will be printed in mangled or demangled form.
3849 @item set print asm-demangle
3850 @itemx set print asm-demangle on
3851 @kindex set print asm-demangle
3852 Print C++ names in their source form rather than their mangled form, even
3853 in assembler code printouts such as instruction disassemblies.
3856 @item show print asm-demangle
3857 @kindex show print asm-demangle
3858 Show whether C++ names in assembly listings will be printed in mangled
3861 @item set print object
3862 @itemx set print object on
3863 @kindex set print object
3864 When displaying a pointer to an object, identify the @emph{actual}
3865 (derived) type of the object rather than the @emph{declared} type, using
3866 the virtual function table.
3868 @item set print object off
3869 Display only the declared type of objects, without reference to the
3870 virtual function table. This is the default setting.
3872 @item show print object
3873 @kindex show print object
3874 Show whether actual, or declared, object types will be displayed.
3876 @item set print vtbl
3877 @itemx set print vtbl on
3878 @kindex set print vtbl
3879 Pretty print C++ virtual function tables. The default is off.
3881 @item set print vtbl off
3882 Do not pretty print C++ virtual function tables.
3884 @item show print vtbl
3885 @kindex show print vtbl
3886 Show whether C++ virtual function tables are pretty printed, or not.
3889 @node Value History, Convenience Vars, Print Settings, Data
3890 @section Value History
3892 @cindex value history
3893 Values printed by the @code{print} command are saved in _GDBN__'s @dfn{value
3894 history} so that you can refer to them in other expressions. Values are
3895 kept until the symbol table is re-read or discarded (for example with
3896 the @code{file} or @code{symbol-file} commands). When the symbol table
3897 changes, the value history is discarded, since the values may contain
3898 pointers back to the types defined in the symbol table.
3902 @cindex history number
3903 The values printed are given @dfn{history numbers} for you to refer to them
3904 by. These are successive integers starting with one. @code{print} shows you
3905 the history number assigned to a value by printing @samp{$@var{num} = }
3906 before the value; here @var{num} is the history number.
3908 To refer to any previous value, use @samp{$} followed by the value's
3909 history number. The way @code{print} labels its output is designed to
3910 remind you of this. Just @code{$} refers to the most recent value in
3911 the history, and @code{$$} refers to the value before that.
3912 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
3913 is the value just prior to @code{$$}, @code{$$1} is equivalent to
3914 @code{$$}, and @code{$$0} is equivalent to @code{$}.
3916 For example, suppose you have just printed a pointer to a structure and
3917 want to see the contents of the structure. It suffices to type
3923 If you have a chain of structures where the component @code{next} points
3924 to the next one, you can print the contents of the next one with this:
3931 You can print successive links in the chain by repeating this
3932 command---which you can do by just typing @key{RET}.
3934 Note that the history records values, not expressions. If the value of
3935 @code{x} is 4 and you type these commands:
3943 then the value recorded in the value history by the @code{print} command
3944 remains 4 even though the value of @code{x} has changed.
3949 Print the last ten values in the value history, with their item numbers.
3950 This is like @samp{p@ $$9} repeated ten times, except that @code{show
3951 values} does not change the history.
3953 @item show values @var{n}
3954 Print ten history values centered on history item number @var{n}.
3957 Print ten history values just after the values last printed. If no more
3958 values are available, produces no display.
3961 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
3962 same effect as @samp{show values +}.
3964 @node Convenience Vars, Registers, Value History, Data
3965 @section Convenience Variables
3967 @cindex convenience variables
3968 _GDBN__ provides @dfn{convenience variables} that you can use within
3969 _GDBN__ to hold on to a value and refer to it later. These variables
3970 exist entirely within _GDBN__; they are not part of your program, and
3971 setting a convenience variable has no direct effect on further execution
3972 of your program. That is why you can use them freely.
3974 Convenience variables are prefixed with @samp{$}. Any name preceded by
3975 @samp{$} can be used for a convenience variable, unless it is one of
3976 the predefined machine-specific register names (@pxref{Registers}).
3977 (Value history references, in contrast, are @emph{numbers} preceded
3978 by @samp{$}. @xref{Value History, ,Value History}.)
3980 You can save a value in a convenience variable with an assignment
3981 expression, just as you would set a variable in your program. Example:
3984 set $foo = *object_ptr
3988 would save in @code{$foo} the value contained in the object pointed to by
3991 Using a convenience variable for the first time creates it; but its value
3992 is @code{void} until you assign a new value. You can alter the value with
3993 another assignment at any time.
3995 Convenience variables have no fixed types. You can assign a convenience
3996 variable any type of value, including structures and arrays, even if
3997 that variable already has a value of a different type. The convenience
3998 variable, when used as an expression, has the type of its current value.
4001 @item show convenience
4002 @kindex show convenience
4003 Print a list of convenience variables used so far, and their values.
4004 Abbreviated @code{show con}.
4007 One of the ways to use a convenience variable is as a counter to be
4008 incremented or a pointer to be advanced. For example, to print
4009 a field from successive elements of an array of structures:
4013 print bar[$i++]->contents
4014 @i{@dots{} repeat that command by typing @key{RET}.}
4017 Some convenience variables are created automatically by _GDBN__ and given
4018 values likely to be useful.
4023 The variable @code{$_} is automatically set by the @code{x} command to
4024 the last address examined (@pxref{Memory, ,Examining Memory}). Other
4025 commands which provide a default address for @code{x} to examine also
4026 set @code{$_} to that address; these commands include @code{info line}
4027 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
4028 except when set by the @code{x} command, in which case it is a pointer
4029 to the type of @code{$__}.
4033 The variable @code{$__} is automatically set by the @code{x} command
4034 to the value found in the last address examined. Its type is chosen
4035 to match the format in which the data was printed.
4038 @node Registers, Floating Point Hardware, Convenience Vars, Data
4042 You can refer to machine register contents, in expressions, as variables
4043 with names starting with @samp{$}. The names of registers are different
4044 for each machine; use @code{info registers} to see the names used on
4048 @item info registers
4049 @kindex info registers
4050 Print the names and values of all registers except floating-point
4051 registers (in the selected stack frame).
4053 @item info all-registers
4054 @kindex info all-registers
4055 @cindex floating point registers
4056 Print the names and values of all registers, including floating-point
4059 @item info registers @var{regname}
4060 Print the relativized value of register @var{regname}. @var{regname}
4061 may be any register name valid on the machine you are using, with
4062 or without the initial @samp{$}.
4065 _GDBN__ has four ``standard'' register names that are available (in
4066 expressions) on most machines---whenever they do not conflict with an
4067 architecture's canonical mnemonics for registers. The register names
4068 @code{$pc} and @code{$sp} are used for the program counter register and
4069 the stack pointer. @code{$fp} is used for a register that contains a
4070 pointer to the current stack frame, and @code{$ps} is used for a
4071 register that contains the processor status. For example,
4072 you could print the program counter in hex with
4079 or print the instruction to be executed next with
4086 or add four to the stack pointer @footnote{This is a way of removing
4087 one word from the stack, on machines where stacks grow downward in
4088 memory (most machines, nowadays). This assumes that the innermost
4089 stack frame is selected; setting @code{$sp} is not allowed when other
4090 stack frames are selected. To pop entire frames off the stack,
4091 regardless of machine architecture, use @code{return};
4092 @pxref{Returning, ,Returning from a Function}.} with
4098 Whenever possible, these four standard register names are available on
4099 your machine even though the machine has different canonical mnemonics,
4100 so long as there is no conflict. The @code{info registers} command
4101 shows the canonical names. For example, on the SPARC, @code{info
4102 registers} displays the processor status register as @code{$psr} but you
4103 can also refer to it as @code{$ps}.
4105 _GDBN__ always considers the contents of an ordinary register as an
4106 integer when the register is examined in this way. Some machines have
4107 special registers which can hold nothing but floating point; these
4108 registers are considered to have floating point values. There is no way
4109 to refer to the contents of an ordinary register as floating point value
4110 (although you can @emph{print} it as a floating point value with
4111 @samp{print/f $@var{regname}}).
4113 Some registers have distinct ``raw'' and ``virtual'' data formats. This
4114 means that the data format in which the register contents are saved by
4115 the operating system is not the same one that your program normally
4116 sees. For example, the registers of the 68881 floating point
4117 coprocessor are always saved in ``extended'' (raw) format, but all C
4118 programs expect to work with ``double'' (virtual) format. In such
4119 cases, _GDBN__ normally works with the virtual format only (the format that
4120 makes sense for your program), but the @code{info registers} command
4121 prints the data in both formats.
4123 Normally, register values are relative to the selected stack frame
4124 (@pxref{Selection, ,Selecting a Frame}). This means that you get the
4125 value that the register would contain if all stack frames farther in
4126 were exited and their saved registers restored. In order to see the
4127 true contents of hardware registers, you must select the innermost
4128 frame (with @samp{frame 0}).
4130 However, _GDBN__ must deduce where registers are saved, from the machine
4131 code generated by your compiler. If some registers are not saved, or if
4132 _GDBN__ is unable to locate the saved registers, the selected stack
4133 frame will make no difference.
4135 @node Floating Point Hardware, , Registers, Data
4136 @section Floating Point Hardware
4137 @cindex floating point
4139 Depending on the host machine architecture, _GDBN__ may be able to give
4140 you more information about the status of the floating point hardware.
4145 If available, provides hardware-dependent information about the floating
4146 point unit. The exact contents and layout vary depending on the
4147 floating point chip.
4149 @c FIXME: this is a cop-out. Try to get examples, explanations. Only
4150 @c FIXME...supported currently on arm's and 386's. Mark properly with
4151 @c FIXME... m4 macros to isolate general statements from hardware-dep,
4152 @c FIXME... at that point.
4154 @node Languages, Symbols, Data, Top
4155 @chapter Using _GDBN__ with Different Languages
4158 Although programming languages generally have common aspects, they are
4159 rarely expressed in the same manner. For instance, in ANSI C,
4160 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
4161 Modula-2, it is accomplished by @code{p^}. Values can also be
4162 represented (and displayed) differently. Hex numbers in C are written
4163 like @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
4165 @cindex working language
4166 Language-specific information is built into _GDBN__ for some languages,
4167 allowing you to express operations like the above in your program's
4168 native language, and allowing _GDBN__ to output values in a manner
4169 consistent with the syntax of your program's native language. The
4170 language you use to build expressions, called the @dfn{working
4171 language}, can be selected manually, or _GDBN__ can set it
4175 * Setting:: Switching between source languages
4176 * Show:: Displaying the language
4177 * Checks:: Type and Range checks
4178 * Support:: Supported languages
4181 @node Setting, Show, Languages, Languages
4182 @section Switching between source languages
4184 There are two ways to control the working language---either have _GDBN__
4185 set it automatically, or select it manually yourself. You can use the
4186 @code{set language} command for either purpose. On startup, _GDBN__
4187 defaults to setting the language automatically.
4190 * Manually:: Setting the working language manually
4191 * Automatically:: Having _GDBN__ infer the source language
4194 @node Manually, Automatically, Setting, Setting
4195 @subsection Setting the working language
4197 @kindex set language
4198 To set the language, issue the command @samp{set language @var{lang}},
4199 where @var{lang} is the name of a language: @code{c} or @code{modula-2}.
4200 For a list of the supported languages, type @samp{set language}.
4202 Setting the language manually prevents _GDBN__ from updating the working
4203 language automatically. This can lead to confusion if you try
4204 to debug a program when the working language is not the same as the
4205 source language, when an expression is acceptable to both
4206 languages---but means different things. For instance, if the current
4207 source file were written in C, and _GDBN__ was parsing Modula-2, a
4215 might not have the effect you intended. In C, this means to add
4216 @code{b} and @code{c} and place the result in @code{a}. The result
4217 printed would be the value of @code{a}. In Modula-2, this means to compare
4218 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
4220 If you allow _GDBN__ to set the language automatically, then
4221 you can count on expressions evaluating the same way in your debugging
4222 session and in your program.
4224 @node Automatically, , Manually, Setting
4225 @subsection Having _GDBN__ infer the source language
4227 To have _GDBN__ set the working language automatically, use @samp{set
4228 language local} or @samp{set language auto}. _GDBN__ then infers the
4229 language that a program was written in by looking at the name of its
4230 source files, and examining their extensions:
4234 Modula-2 source file
4238 C or C++ source file.
4241 This information is recorded for each function or procedure in a source
4242 file. When your program stops in a frame (usually by encountering a
4243 breakpoint), _GDBN__ sets the working language to the language recorded
4244 for the function in that frame. If the language for a frame is unknown
4245 (that is, if the function or block corresponding to the frame was
4246 defined in a source file that does not have a recognized extension), the
4247 current working language is not changed, and _GDBN__ issues a warning.
4249 This may not seem necessary for most programs, which are written
4250 entirely in one source language. However, program modules and libraries
4251 written in one source language can be used by a main program written in
4252 a different source language. Using @samp{set language auto} in this
4253 case frees you from having to set the working language manually.
4255 @node Show, Checks, Setting, Languages
4256 @section Displaying the language
4258 The following commands will help you find out which language is the
4259 working language, and also what language source files were written in.
4261 @kindex show language
4266 Display the current working language. This is the
4267 language you can use with commands such as @code{print} to
4268 build and compute expressions that may involve variables in your program.
4271 Among the other information listed here (@pxref{Frame Info, ,Information
4272 about a Frame}) is the source language for this frame. This is the
4273 language that will become the working language if you ever use an
4274 identifier that is in this frame.
4277 Among the other information listed here (@pxref{Symbols, ,Examining the
4278 Symbol Table}) is the source language of this source file.
4281 @node Checks, Support, Show, Languages
4282 @section Type and range Checking
4285 @emph{Warning:} In this release, the _GDBN__ commands for type and range
4286 checking are included, but they do not yet have any effect. This
4287 section documents the intended facilities.
4289 @c FIXME remove warning when type/range code added
4291 Some languages are designed to guard you against making seemingly common
4292 errors through a series of compile- and run-time checks. These include
4293 checking the type of arguments to functions and operators, and making
4294 sure mathematical overflows are caught at run time. Checks such as
4295 these help to ensure a program's correctness once it has been compiled
4296 by eliminating type mismatches, and providing active checks for range
4297 errors when your program is running.
4299 _GDBN__ can check for conditions like the above if you wish.
4300 Although _GDBN__ will not check the statements in your program, it
4301 can check expressions entered directly into _GDBN__ for evaluation via
4302 the @code{print} command, for example. As with the working language,
4303 _GDBN__ can also decide whether or not to check automatically based on
4304 your program's source language. @xref{Support, ,Supported Languages},
4305 for the default settings of supported languages.
4308 * Type Checking:: An overview of type checking
4309 * Range Checking:: An overview of range checking
4312 @cindex type checking
4313 @cindex checks, type
4314 @node Type Checking, Range Checking, Checks, Checks
4315 @subsection An overview of type checking
4317 Some languages, such as Modula-2, are strongly typed, meaning that the
4318 arguments to operators and functions have to be of the correct type,
4319 otherwise an error occurs. These checks prevent type mismatch
4320 errors from ever causing any run-time problems. For example,
4328 The second example fails because the @code{CARDINAL} 1 is not
4329 type-compatible with the @code{REAL} 2.3.
4331 For expressions you use in _GDBN__ commands, you can tell the _GDBN__
4332 type checker to skip checking; to treat any mismatches as errors and
4333 abandon the expression; or only issue warnings when type mismatches
4334 occur, but evaluate the expression anyway. When you choose the last of
4335 these, _GDBN__ evaluates expressions like the second example above, but
4336 also issues a warning.
4338 Even though you may turn type checking off, other type-based reasons may
4339 prevent _GDBN__ from evaluating an expression. For instance, _GDBN__ does not
4340 know how to add an @code{int} and a @code{struct foo}. These particular
4341 type errors have nothing to do with the language in use, and usually
4342 arise from expressions, such as the one described above, which make
4343 little sense to evaluate anyway.
4345 Each language defines to what degree it is strict about type. For
4346 instance, both Modula-2 and C require the arguments to arithmetical
4347 operators to be numbers. In C, enumerated types and pointers can be
4348 represented as numbers, so that they are valid arguments to mathematical
4349 operators. @xref{Support, ,Supported Languages}, for further
4350 details on specific languages.
4352 _GDBN__ provides some additional commands for controlling the type checker:
4355 @kindex set check type
4356 @kindex show check type
4358 @item set check type auto
4359 Set type checking on or off based on the current working language.
4360 @xref{Support, ,Supported Languages}, for the default settings for
4363 @item set check type on
4364 @itemx set check type off
4365 Set type checking on or off, overriding the default setting for the
4366 current working language. Issue a warning if the setting does not
4367 match the language's default. If any type mismatches occur in
4368 evaluating an expression while typechecking is on, _GDBN__ prints a
4369 message and aborts evaluation of the expression.
4371 @item set check type warn
4372 Cause the type checker to issue warnings, but to always attempt to
4373 evaluate the expression. Evaluating the expression may still
4374 be impossible for other reasons. For example, _GDBN__ cannot add
4375 numbers and structures.
4378 Show the current setting of the type checker, and whether or not _GDBN__ is
4379 setting it automatically.
4382 @cindex range checking
4383 @cindex checks, range
4384 @node Range Checking, , Type Checking, Checks
4385 @subsection An overview of Range Checking
4387 In some languages (such as Modula-2), it is an error to exceed the
4388 bounds of a type; this is enforced with run-time checks. Such range
4389 checking is meant to ensure program correctness by making sure
4390 computations do not overflow, or indices on an array element access do
4391 not exceed the bounds of the array.
4393 For expressions you use in _GDBN__ commands, you can tell _GDBN__ to
4394 ignore range errors; to always treat them as errors and abandon the
4395 expression; or to issue warnings when a range error occurs but evaluate
4396 the expression anyway.
4398 A range error can result from numerical overflow, from exceeding an
4399 array index bound, or when you type in a constant that is not a member
4400 of any type. Some languages, however, do not treat overflows as an
4401 error. In many implementations of C, mathematical overflow causes the
4402 result to ``wrap around'' to lower values---for example, if @var{m} is
4403 the largest integer value, and @var{s} is the smallest, then
4406 @var{m} + 1 @result{} @var{s}
4409 This, too, is specific to individual languages, and in some cases
4410 specific to individual compilers or machines. @xref{Support, ,
4411 Supported Languages}, for further details on specific languages.
4413 _GDBN__ provides some additional commands for controlling the range checker:
4416 @kindex set check range
4417 @kindex show check range
4419 @item set check range auto
4420 Set range checking on or off based on the current working language.
4421 @xref{Support, ,Supported Languages}, for the default settings for
4424 @item set check range on
4425 @itemx set check range off
4426 Set range checking on or off, overriding the default setting for the
4427 current working language. A warning is issued if the setting does not
4428 match the language's default. If a range error occurs, then a message
4429 is printed and evaluation of the expression is aborted.
4431 @item set check range warn
4432 Output messages when the _GDBN__ range checker detects a range error,
4433 but attempt to evaluate the expression anyway. Evaluating the
4434 expression may still be impossible for other reasons, such as accessing
4435 memory that the process does not own (a typical example from many UNIX
4439 Show the current setting of the range checker, and whether or not it is
4440 being set automatically by _GDBN__.
4443 @node Support, , Checks, Languages
4444 @section Supported Languages
4446 _GDBN__ 4 supports C, C++, and Modula-2. The syntax for C and C++ is so
4447 closely related that _GDBN__ does not distinguish the two. Some _GDBN__
4448 features may be used in expressions regardless of the language you
4449 use: the _GDBN__ @code{@@} and @code{::} operators, and the
4450 @samp{@{type@}addr} construct (@pxref{Expressions, ,Expressions}) can be
4451 used with the constructs of any of the supported languages.
4453 The following sections detail to what degree each of these
4454 source languages is supported by _GDBN__. These sections are
4455 not meant to be language tutorials or references, but serve only as a
4456 reference guide to what the _GDBN__ expression parser will accept, and
4457 what input and output formats should look like for different languages.
4458 There are many good books written on each of these languages; please
4459 look to these for a language reference or tutorial.
4463 * Modula-2:: Modula-2
4466 @node C, Modula-2, Support, Support
4467 @subsection C and C++
4470 @cindex expressions in C or C++
4471 Since C and C++ are so closely related, _GDBN__ does not distinguish
4472 between them when interpreting the expressions recognized in _GDBN__
4478 The C++ debugging facilities are jointly implemented by the GNU C++
4479 compiler and _GDBN__. Therefore, to debug your C++ code effectively,
4480 you must compile your C++ programs with the GNU C++ compiler,
4484 * C Operators:: C and C++ Operators
4485 * C Constants:: C and C++ Constants
4486 * Cplusplus expressions:: C++ Expressions
4487 * C Defaults:: Default settings for C and C++
4488 * C Checks:: C and C++ Type and Range Checks
4489 * Debugging C:: _GDBN__ and C
4490 * Debugging C plus plus:: Special features for C++
4493 @cindex C and C++ operators
4494 @node C Operators, C Constants, C, C
4495 @subsubsection C and C++ Operators
4497 Operators must be defined on values of specific types. For instance,
4498 @code{+} is defined on numbers, but not on structures. Operators are
4499 often defined on groups of types. For the purposes of C and C++, the
4500 following definitions hold:
4504 @emph{Integral types} include @code{int} with any of its storage-class
4505 specifiers, @code{char}, and @code{enum}s.
4508 @emph{Floating-point types} include @code{float} and @code{double}.
4511 @emph{Pointer types} include all types defined as @code{(@var{type}
4515 @emph{Scalar types} include all of the above.
4519 The following operators are supported. They are listed here
4520 in order of increasing precedence:
4524 The comma or sequencing operator. Expressions in a comma-separated list
4525 are evaluated from left to right, with the result of the entire
4526 expression being the last expression evaluated.
4529 Assignment. The value of an assignment expression is the value
4530 assigned. Defined on scalar types.
4533 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
4534 and translated to @w{@code{@var{a} = @var{a op b}}}.
4535 @w{@code{@var{op}=}} and @code{=} have the same precendence.
4536 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
4537 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
4540 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
4541 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
4545 Logical @sc{or}. Defined on integral types.
4548 Logical @sc{and}. Defined on integral types.
4551 Bitwise @sc{or}. Defined on integral types.
4554 Bitwise exclusive-@sc{or}. Defined on integral types.
4557 Bitwise @sc{and}. Defined on integral types.
4560 Equality and inequality. Defined on scalar types. The value of these
4561 expressions is 0 for false and non-zero for true.
4563 @item <@r{, }>@r{, }<=@r{, }>=
4564 Less than, greater than, less than or equal, greater than or equal.
4565 Defined on scalar types. The value of these expressions is 0 for false
4566 and non-zero for true.
4569 left shift, and right shift. Defined on integral types.
4572 The _GDBN__ ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
4575 Addition and subtraction. Defined on integral types, floating-point types and
4578 @item *@r{, }/@r{, }%
4579 Multiplication, division, and modulus. Multiplication and division are
4580 defined on integral and floating-point types. Modulus is defined on
4584 Increment and decrement. When appearing before a variable, the
4585 operation is performed before the variable is used in an expression;
4586 when appearing after it, the variable's value is used before the
4587 operation takes place.
4590 Pointer dereferencing. Defined on pointer types. Same precedence as
4594 Address operator. Defined on variables. Same precedence as @code{++}.
4597 Negative. Defined on integral and floating-point types. Same
4598 precedence as @code{++}.
4601 Logical negation. Defined on integral types. Same precedence as
4605 Bitwise complement operator. Defined on integral types. Same precedence as
4609 Structure member, and pointer-to-structure member. For convenience,
4610 _GDBN__ regards the two as equivalent, choosing whether to dereference a
4611 pointer based on the stored type information.
4612 Defined on @code{struct}s and @code{union}s.
4615 Array indexing. @code{@var{a}[@var{i}]} is defined as
4616 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
4619 Function parameter list. Same precedence as @code{->}.
4622 C++ scope resolution operator. Defined on
4623 @code{struct}, @code{union}, and @code{class} types.
4626 The _GDBN__ scope operator (@pxref{Expressions, ,Expressions}). Same precedence as
4627 @code{::}, above._1__
4630 @cindex C and C++ constants
4631 @node C Constants, Cplusplus expressions, C Operators, C
4632 @subsubsection C and C++ Constants
4634 _GDBN__ allows you to express the constants of C and C++ in the
4639 Integer constants are a sequence of digits. Octal constants are
4640 specified by a leading @samp{0} (ie. zero), and hexadecimal constants by
4641 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
4642 @samp{l}, specifying that the constant should be treated as a
4646 Floating point constants are a sequence of digits, followed by a decimal
4647 point, followed by a sequence of digits, and optionally followed by an
4648 exponent. An exponent is of the form:
4649 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
4650 sequence of digits. The @samp{+} is optional for positive exponents.
4653 Enumerated constants consist of enumerated identifiers, or their
4654 integral equivalents.
4657 Character constants are a single character surrounded by single quotes
4658 (@code{'}), or a number---the ordinal value of the corresponding character
4659 (usually its @sc{ASCII} value). Within quotes, the single character may
4660 be represented by a letter or by @dfn{escape sequences}, which are of
4661 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
4662 of the character's ordinal value; or of the form @samp{\@var{x}}, where
4663 @samp{@var{x}} is a predefined special character---for example,
4664 @samp{\n} for newline.
4667 String constants are a sequence of character constants surrounded
4668 by double quotes (@code{"}).
4671 Pointer constants are an integral value.
4674 @node Cplusplus expressions, C Defaults, C Constants, C
4675 @subsubsection C++ Expressions
4677 @cindex expressions in C++
4678 _GDBN__'s expression handling has the following extensions to
4679 interpret a significant subset of C++ expressions:
4683 @cindex member functions
4685 Member function calls are allowed; you can use expressions like
4688 count = aml->GetOriginal(x, y)
4692 @cindex namespace in C++
4694 While a member function is active (in the selected stack frame), your
4695 expressions have the same namespace available as the member function;
4696 that is, _GDBN__ allows implicit references to the class instance
4697 pointer @code{this} following the same rules as C++.
4699 @cindex call overloaded functions
4700 @cindex type conversions in C++
4702 You can call overloaded functions; _GDBN__ will resolve the function
4703 call to the right definition, with one restriction---you must use
4704 arguments of the type required by the function that you want to call.
4705 _GDBN__ will not perform conversions requiring constructors or
4706 user-defined type operators.
4708 @cindex reference declarations
4710 _GDBN__ understands variables declared as C++ references; you can use them in
4711 expressions just as you do in C++ source---they are automatically
4714 In the parameter list shown when _GDBN__ displays a frame, the values of
4715 reference variables are not displayed (unlike other variables); this
4716 avoids clutter, since references are often used for large structures.
4717 The @emph{address} of a reference variable is always shown, unless
4718 you have specified @samp{set print address off}.
4721 _GDBN__ supports the C++ name resolution operator @code{::}---your
4722 expressions can use it just as expressions in your program do. Since
4723 one scope may be defined in another, you can use @code{::} repeatedly if
4724 necessary, for example in an expression like
4725 @samp{@var{scope1}::@var{scope2}::@var{name}}. _GDBN__ also allows
4726 resolving name scope by reference to source files, in both C and C++
4727 debugging (@pxref{Variables, ,Program Variables}).
4730 @node C Defaults, C Checks, Cplusplus expressions, C
4731 @subsubsection C and C++ Defaults
4732 @cindex C and C++ defaults
4734 If you allow _GDBN__ to set type and range checking automatically, they
4735 both default to @code{off} whenever the working language changes to
4736 C/C++. This happens regardless of whether you, or _GDBN__,
4737 selected the working language.
4739 If you allow _GDBN__ to set the language automatically, it sets the
4740 working language to C/C++ on entering code compiled from a source file
4741 whose name ends with @file{.c} or @file{.cc}.
4742 @xref{Automatically, ,Having _GDBN__ infer the source language}, for
4745 @node C Checks, Debugging C, C Defaults, C
4746 @subsubsection C and C++ Type and Range Checks
4747 @cindex C and C++ checks
4750 @emph{Warning:} in this release, _GDBN__ does not yet perform type or
4753 @c FIXME remove warning when type/range checks added
4755 By default, when _GDBN__ parses C or C++ expressions, type checking
4756 is not used. However, if you turn type checking on, _GDBN__ will
4757 consider two variables type equivalent if:
4761 The two variables are structured and have the same structure, union, or
4765 Two two variables have the same type name, or types that have been
4766 declared equivalent through @code{typedef}.
4769 @c leaving this out because neither J Gilmore nor R Pesch understand it.
4772 The two @code{struct}, @code{union}, or @code{enum} variables are
4773 declared in the same declaration. (Note: this may not be true for all C
4778 Range checking, if turned on, is done on mathematical operations. Array
4779 indices are not checked, since they are often used to index a pointer
4780 that is not itself an array.
4782 @node Debugging C, Debugging C plus plus, C Checks, C
4783 @subsubsection _GDBN__ and C
4785 The @code{set print union} and @code{show print union} commands apply to
4786 the @code{union} type. When set to @samp{on}, any @code{union} that is
4787 inside a @code{struct} or @code{class} will also be printed.
4788 Otherwise, it will appear as @samp{@{...@}}.
4790 The @code{@@} operator aids in the debugging of dynamic arrays, formed
4791 with pointers and a memory allocation function. (@pxref{Expressions, ,Expressions})
4793 @node Debugging C plus plus, , Debugging C, C
4794 @subsubsection _GDBN__ Commands for C++
4796 @cindex commands for C++
4797 Some _GDBN__ commands are particularly useful with C++, and some are
4798 designed specifically for use with C++. Here is a summary:
4801 @cindex break in overloaded functions
4802 @item @r{breakpoint menus}
4803 When you want a breakpoint in a function whose name is overloaded,
4804 _GDBN__'s breakpoint menus help you specify which function definition
4805 you want. @xref{Breakpoint Menus}.
4807 @cindex overloading in C++
4808 @item rbreak @var{regex}
4809 Setting breakpoints using regular expressions is helpful for setting
4810 breakpoints on overloaded functions that are not members of any special
4812 @xref{Set Breaks, ,Setting Breakpoints}.
4814 @cindex C++ exception handling
4815 @item catch @var{exceptions}
4817 Debug C++ exception handling using these commands. @xref{Exception
4818 Handling, ,Breakpoints and Exceptions}.
4821 @item ptype @var{typename}
4822 Print inheritance relationships as well as other information for type
4824 @xref{Symbols, ,Examining the Symbol Table}.
4826 @cindex C++ symbol display
4827 @item set print demangle
4828 @itemx show print demangle
4829 @itemx set print asm-demangle
4830 @itemx show print asm-demangle
4831 Control whether C++ symbols display in their source form, both when
4832 displaying code as C++ source and when displaying disassemblies.
4833 @xref{Print Settings, ,Print Settings}.
4835 @item set print object
4836 @itemx show print object
4837 Choose whether to print derived (actual) or declared types of objects.
4838 @xref{Print Settings, ,Print Settings}.
4840 @item set print vtbl
4841 @itemx show print vtbl
4842 Control the format for printing virtual function tables.
4843 @xref{Print Settings, ,Print Settings}.
4846 @node Modula-2, , C, Support
4847 @subsection Modula-2
4850 The extensions made to _GDBN__ to support Modula-2 support output
4851 from the GNU Modula-2 compiler (which is currently being developed).
4852 Other Modula-2 compilers are not currently supported, and attempting to
4853 debug executables produced by them will most likely result in an error
4854 as _GDBN__ reads in the executable's symbol table.
4856 @cindex expressions in Modula-2
4858 * M2 Operators:: Built-in operators
4859 * Built-In Func/Proc:: Built-in Functions and Procedures
4860 * M2 Constants:: Modula-2 Constants
4861 * M2 Defaults:: Default settings for Modula-2
4862 * Deviations:: Deviations from standard Modula-2
4863 * M2 Checks:: Modula-2 Type and Range Checks
4864 * M2 Scope:: The scope operators @code{::} and @code{.}
4865 * GDB/M2:: _GDBN__ and Modula-2
4868 @node M2 Operators, Built-In Func/Proc, Modula-2, Modula-2
4869 @subsubsection Operators
4870 @cindex Modula-2 operators
4872 Operators must be defined on values of specific types. For instance,
4873 @code{+} is defined on numbers, but not on structures. Operators are
4874 often defined on groups of types. For the purposes of Modula-2, the
4875 following definitions hold:
4880 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
4884 @emph{Character types} consist of @code{CHAR} and its subranges.
4887 @emph{Floating-point types} consist of @code{REAL}.
4890 @emph{Pointer types} consist of anything declared as @code{POINTER TO
4894 @emph{Scalar types} consist of all of the above.
4897 @emph{Set types} consist of @code{SET}s and @code{BITSET}s.
4900 @emph{Boolean types} consist of @code{BOOLEAN}.
4904 The following operators are supported, and appear in order of
4905 increasing precedence:
4909 Function argument or array index separator.
4912 Assignment. The value of @var{var} @code{:=} @var{value} is
4916 Less than, greater than on integral, floating-point, or enumerated
4920 Less than, greater than, less than or equal to, greater than or equal to
4921 on integral, floating-point and enumerated types, or set inclusion on
4922 set types. Same precedence as @code{<}.
4924 @item =@r{, }<>@r{, }#
4925 Equality and two ways of expressing inequality, valid on scalar types.
4926 Same precedence as @code{<}. In _GDBN__ scripts, only @code{<>} is
4927 available for inequality, since @code{#} conflicts with the script
4931 Set membership. Defined on set types and the types of their members.
4932 Same precedence as @code{<}.
4935 Boolean disjunction. Defined on boolean types.
4938 Boolean conjuction. Defined on boolean types.
4941 The _GDBN__ ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
4944 Addition and subtraction on integral and floating-point types, or union
4945 and difference on set types.
4948 Multiplication on integral and floating-point types, or set intersection
4952 Division on floating-point types, or symmetric set difference on set
4953 types. Same precedence as @code{*}.
4956 Integer division and remainder. Defined on integral types. Same
4957 precedence as @code{*}.
4960 Negative. Defined on @code{INTEGER}s and @code{REAL}s.
4963 Pointer dereferencing. Defined on pointer types.
4966 Boolean negation. Defined on boolean types. Same precedence as
4970 @code{RECORD} field selector. Defined on @code{RECORD}s. Same
4971 precedence as @code{^}.
4974 Array indexing. Defined on @code{ARRAY}s. Same precedence as @code{^}.
4977 Procedure argument list. Defined on @code{PROCEDURE}s. Same precedence
4981 _GDBN__ and Modula-2 scope operators.
4985 @emph{Warning:} Sets and their operations are not yet supported, so _GDBN__
4986 will treat the use of the operator @code{IN}, or the use of operators
4987 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
4988 @code{<=}, and @code{>=} on sets as an error.
4991 @cindex Modula-2 built-ins
4992 @node Built-In Func/Proc, M2 Constants, M2 Operators, Modula-2
4993 @subsubsection Built-in Functions and Procedures
4995 Modula-2 also makes available several built-in procedures and functions.
4996 In describing these, the following metavariables are used:
5001 represents an @code{ARRAY} variable.
5004 represents a @code{CHAR} constant or variable.
5007 represents a variable or constant of integral type.
5010 represents an identifier that belongs to a set. Generally used in the
5011 same function with the metavariable @var{s}. The type of @var{s} should
5012 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}.
5015 represents a variable or constant of integral or floating-point type.
5018 represents a variable or constant of floating-point type.
5024 represents a variable.
5027 represents a variable or constant of one of many types. See the
5028 explanation of the function for details.
5031 All Modula-2 built-in procedures also return a result, described below.
5035 Returns the absolute value of @var{n}.
5038 If @var{c} is a lower case letter, it returns its upper case
5039 equivalent, otherwise it returns its argument
5042 Returns the character whose ordinal value is @var{i}.
5045 Decrements the value in the variable @var{v}. Returns the new value.
5047 @item DEC(@var{v},@var{i})
5048 Decrements the value in the variable @var{v} by @var{i}. Returns the
5051 @item EXCL(@var{m},@var{s})
5052 Removes the element @var{m} from the set @var{s}. Returns the new
5055 @item FLOAT(@var{i})
5056 Returns the floating point equivalent of the integer @var{i}.
5059 Returns the index of the last member of @var{a}.
5062 Increments the value in the variable @var{v}. Returns the new value.
5064 @item INC(@var{v},@var{i})
5065 Increments the value in the variable @var{v} by @var{i}. Returns the
5068 @item INCL(@var{m},@var{s})
5069 Adds the element @var{m} to the set @var{s} if it is not already
5070 there. Returns the new set.
5073 Returns the maximum value of the type @var{t}.
5076 Returns the minimum value of the type @var{t}.
5079 Returns boolean TRUE if @var{i} is an odd number.
5082 Returns the ordinal value of its argument. For example, the ordinal
5083 value of a character is its ASCII value (on machines supporting the
5084 ASCII character set). @var{x} must be of an ordered type, which include
5085 integral, character and enumerated types.
5088 Returns the size of its argument. @var{x} can be a variable or a type.
5090 @item TRUNC(@var{r})
5091 Returns the integral part of @var{r}.
5093 @item VAL(@var{t},@var{i})
5094 Returns the member of the type @var{t} whose ordinal value is @var{i}.
5098 @emph{Warning:} Sets and their operations are not yet supported, so
5099 _GDBN__ will treat the use of procedures @code{INCL} and @code{EXCL} as
5103 @cindex Modula-2 constants
5104 @node M2 Constants, M2 Defaults, Built-In Func/Proc, Modula-2
5105 @subsubsection Constants
5107 _GDBN__ allows you to express the constants of Modula-2 in the following
5113 Integer constants are simply a sequence of digits. When used in an
5114 expression, a constant is interpreted to be type-compatible with the
5115 rest of the expression. Hexadecimal integers are specified by a
5116 trailing @samp{H}, and octal integers by a trailing @samp{B}.
5119 Floating point constants appear as a sequence of digits, followed by a
5120 decimal point and another sequence of digits. An optional exponent can
5121 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
5122 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
5123 digits of the floating point constant must be valid decimal (base 10)
5127 Character constants consist of a single character enclosed by a pair of
5128 like quotes, either single (@code{'}) or double (@code{"}). They may
5129 also be expressed by their ordinal value (their ASCII value, usually)
5130 followed by a @samp{C}.
5133 String constants consist of a sequence of characters enclosed by a
5134 pair of like quotes, either single (@code{'}) or double (@code{"}).
5135 Escape sequences in the style of C are also allowed. @xref{C
5136 Constants, ,C and C++ Constants}, for a brief explanation of escape
5140 Enumerated constants consist of an enumerated identifier.
5143 Boolean constants consist of the identifiers @code{TRUE} and
5147 Pointer constants consist of integral values only.
5150 Set constants are not yet supported.
5153 @node M2 Defaults, Deviations, M2 Constants, Modula-2
5154 @subsubsection Modula-2 Defaults
5155 @cindex Modula-2 defaults
5157 If type and range checking are set automatically by _GDBN__, they
5158 both default to @code{on} whenever the working language changes to
5159 Modula-2. This happens regardless of whether you, or _GDBN__,
5160 selected the working language.
5162 If you allow _GDBN__ to set the language automatically, then entering
5163 code compiled from a file whose name ends with @file{.mod} will set the
5164 working language to Modula-2. @xref{Automatically, ,Having _GDBN__ set
5165 the language automatically}, for further details.
5167 @node Deviations, M2 Checks, M2 Defaults, Modula-2
5168 @subsubsection Deviations from Standard Modula-2
5169 @cindex Modula-2, deviations from
5171 A few changes have been made to make Modula-2 programs easier to debug.
5172 This is done primarily via loosening its type strictness:
5176 Unlike in standard Modula-2, pointer constants can be formed by
5177 integers. This allows you to modify pointer variables during
5178 debugging. (In standard Modula-2, the actual address contained in a
5179 pointer variable is hidden from you; it can only be modified
5180 through direct assignment to another pointer variable or expression that
5181 returned a pointer.)
5184 C escape sequences can be used in strings and characters to represent
5185 non-printable characters. _GDBN__ will print out strings with these
5186 escape sequences embedded. Single non-printable characters are
5187 printed using the @samp{CHR(@var{nnn})} format.
5190 The assignment operator (@code{:=}) returns the value of its right-hand
5194 All built-in procedures both modify @emph{and} return their argument.
5197 @node M2 Checks, M2 Scope, Deviations, Modula-2
5198 @subsubsection Modula-2 Type and Range Checks
5199 @cindex Modula-2 checks
5202 @emph{Warning:} in this release, _GDBN__ does not yet perform type or
5205 @c FIXME remove warning when type/range checks added
5207 _GDBN__ considers two Modula-2 variables type equivalent if:
5211 They are of types that have been declared equivalent via a @code{TYPE
5212 @var{t1} = @var{t2}} statement
5215 They have been declared on the same line. (Note: This is true of the
5216 GNU Modula-2 compiler, but it may not be true of other compilers.)
5219 As long as type checking is enabled, any attempt to combine variables
5220 whose types are not equivalent is an error.
5222 Range checking is done on all mathematical operations, assignment, array
5223 index bounds, and all built-in functions and procedures.
5225 @node M2 Scope, GDB/M2, M2 Checks, Modula-2
5226 @subsubsection The scope operators @code{::} and @code{.}
5229 @kindex colon, doubled as scope operator
5232 @c Info cannot handoe :: but TeX can.
5238 There are a few subtle differences between the Modula-2 scope operator
5239 (@code{.}) and the _GDBN__ scope operator (@code{::}). The two have
5244 @var{module} . @var{id}
5245 @var{scope} :: @var{id}
5249 where @var{scope} is the name of a module or a procedure,
5250 @var{module} the name of a module, and @var{id} is any declared
5251 identifier within your program, except another module.
5253 Using the @code{::} operator makes _GDBN__ search the scope
5254 specified by @var{scope} for the identifier @var{id}. If it is not
5255 found in the specified scope, then _GDBN__ will search all scopes
5256 enclosing the one specified by @var{scope}.
5258 Using the @code{.} operator makes _GDBN__ search the current scope for
5259 the identifier specified by @var{id} that was imported from the
5260 definition module specified by @var{module}. With this operator, it is
5261 an error if the identifier @var{id} was not imported from definition
5262 module @var{module}, or if @var{id} is not an identifier in
5265 @node GDB/M2, , M2 Scope, Modula-2
5266 @subsubsection _GDBN__ and Modula-2
5268 Some _GDBN__ commands have little use when debugging Modula-2 programs.
5269 Five subcommands of @code{set print} and @code{show print} apply
5270 specifically to C and C++: @samp{vtbl}, @samp{demangle},
5271 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
5272 apply to C++, and the last to C's @code{union} type, which has no direct
5273 analogue in Modula-2.
5275 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
5276 while using any language, is not useful with Modula-2. Its
5277 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
5278 created in Modula-2 as they can in C or C++. However, because an
5279 address can be specified by an integral constant, the construct
5280 @samp{@{@var{type}@}@var{adrexp}} is still useful. (@pxref{Expressions, ,Expressions})
5282 @cindex @code{#} in Modula-2
5283 In _GDBN__ scripts, the Modula-2 inequality operator @code{#} is
5284 interpreted as the beginning of a comment. Use @code{<>} instead.
5286 @node Symbols, Altering, Languages, Top
5287 @chapter Examining the Symbol Table
5289 The commands described in this section allow you to inquire about the
5290 symbols (names of variables, functions and types) defined in your
5291 program. This information is inherent in the text of your program and
5292 does not change as your program executes. _GDBN__ finds it in your
5293 program's symbol table, in the file indicated when you started _GDBN__
5294 (@pxref{File Options, ,Choosing Files}), or by one of the
5295 file-management commands (@pxref{Files, ,Commands to Specify Files}).
5298 @item info address @var{symbol}
5299 @kindex info address
5300 Describe where the data for @var{symbol} is stored. For a register
5301 variable, this says which register it is kept in. For a non-register
5302 local variable, this prints the stack-frame offset at which the variable
5305 Note the contrast with @samp{print &@var{symbol}}, which does not work
5306 at all for a register variables, and for a stack local variable prints
5307 the exact address of the current instantiation of the variable.
5309 @item whatis @var{exp}
5311 Print the data type of expression @var{exp}. @var{exp} is not
5312 actually evaluated, and any side-effecting operations (such as
5313 assignments or function calls) inside it do not take place.
5314 @xref{Expressions, ,Expressions}.
5317 Print the data type of @code{$}, the last value in the value history.
5319 @item ptype @var{typename}
5321 Print a description of data type @var{typename}. @var{typename} may be
5322 the name of a type, or for C code it may have the form
5323 @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or
5324 @samp{enum @var{enum-tag}}.
5326 @item ptype @var{exp}
5328 Print a description of the type of expression @var{exp}. @code{ptype}
5329 differs from @code{whatis} by printing a detailed description, instead
5330 of just the name of the type. For example, if your program declares a
5334 struct complex @{double real; double imag;@} v;
5338 compare the output of the two commands:
5343 type = struct complex
5345 type = struct complex @{
5353 As with @code{whatis}, using @code{ptype} without an argument refers to
5354 the type of @code{$}, the last value in the value history.
5356 @item info types @var{regexp}
5359 Print a brief description of all types whose name matches @var{regexp}
5360 (or all types in your program, if you supply no argument). Each
5361 complete typename is matched as though it were a complete line; thus,
5362 @samp{i type value} gives information on all types in your program whose
5363 name includes the string @code{value}, but @samp{i type ^value$} gives
5364 information only on types whose complete name is @code{value}.
5366 This command differs from @code{ptype} in two ways: first, like
5367 @code{whatis}, it does not print a detailed description; second, it
5368 lists all source files where a type is defined.
5372 Show the name of the current source file---that is, the source file for
5373 the function containing the current point of execution---and the language
5377 @kindex info sources
5378 Print the names of all source files in your program for which there is
5379 debugging information, organized into two lists: files whose symbols
5380 have already been read, and files whose symbols will be read when needed.
5382 @item info functions
5383 @kindex info functions
5384 Print the names and data types of all defined functions.
5386 @item info functions @var{regexp}
5387 Print the names and data types of all defined functions
5388 whose names contain a match for regular expression @var{regexp}.
5389 Thus, @samp{info fun step} finds all functions whose names
5390 include @code{step}; @samp{info fun ^step} finds those whose names
5391 start with @code{step}.
5393 @item info variables
5394 @kindex info variables
5395 Print the names and data types of all variables that are declared
5396 outside of functions (i.e., excluding local variables).
5398 @item info variables @var{regexp}
5399 Print the names and data types of all variables (except for local
5400 variables) whose names contain a match for regular expression
5404 This was never implemented.
5406 @itemx info methods @var{regexp}
5407 @kindex info methods
5408 The @code{info methods} command permits the user to examine all defined
5409 methods within C++ program, or (with the @var{regexp} argument) a
5410 specific set of methods found in the various C++ classes. Many
5411 C++ classes provide a large number of methods. Thus, the output
5412 from the @code{ptype} command can be overwhelming and hard to use. The
5413 @code{info-methods} command filters the methods, printing only those
5414 which match the regular-expression @var{regexp}.
5417 @item printsyms @var{filename}
5418 @itemx printpsyms @var{filename}
5422 @cindex partial symbol dump
5423 Write a dump of debugging symbol data into the file @var{filename}.
5424 These commands are used to debug the _GDBN__ symbol-reading code. Only
5425 symbols with debugging data are included. If you use @code{printsyms},
5426 _GDBN__ includes all the symbols for which it has already collected full
5427 details: that is, @var{filename} reflects symbols for only those files
5428 whose symbols _GDBN__ has read. You can use the command @code{info
5429 sources} to find out which files these are. If you use
5430 @code{printpsyms}, the dump also shows information about symbols that
5431 _GDBN__ only knows partially---that is, symbols defined in files that
5432 _GDBN__ has skimmed, but not yet read completely. The description of
5433 @code{symbol-file} describes how _GDBN__ reads symbols; both commands
5434 are described under @ref{Files, ,Commands to Specify Files}.
5437 @node Altering, _GDBN__ Files, Symbols, Top
5438 @chapter Altering Execution
5440 Once you think you have found an error in your program, you might want to
5441 find out for certain whether correcting the apparent error would lead to
5442 correct results in the rest of the run. You can find the answer by
5443 experiment, using the _GDBN__ features for altering execution of the
5446 For example, you can store new values into variables or memory
5447 locations, give your program a signal, restart it at a different address,
5448 or even return prematurely from a function to its caller.
5451 * Assignment:: Assignment to Variables
5452 * Jumping:: Continuing at a Different Address
5453 * Signaling:: Giving your program a Signal
5454 * Returning:: Returning from a Function
5455 * Calling:: Calling your Program's Functions
5456 * Patching:: Patching your Program
5459 @node Assignment, Jumping, Altering, Altering
5460 @section Assignment to Variables
5463 @cindex setting variables
5464 To alter the value of a variable, evaluate an assignment expression.
5465 @xref{Expressions, ,Expressions}. For example,
5472 stores the value 4 into the variable @code{x}, and then prints the
5473 value of the assignment expression (which is 4). @xref{Languages,
5474 ,Using _GDBN__ with Different Languages}, for more information on
5475 operators in supported languages.
5477 @kindex set variable
5478 @cindex variables, setting
5479 If you are not interested in seeing the value of the assignment, use the
5480 @code{set} command instead of the @code{print} command. @code{set} is
5481 really the same as @code{print} except that the expression's value is not
5482 printed and is not put in the value history (@pxref{Value History, ,Value History}). The
5483 expression is evaluated only for its effects.
5485 If the beginning of the argument string of the @code{set} command
5486 appears identical to a @code{set} subcommand, use the @code{set
5487 variable} command instead of just @code{set}. This command is identical
5488 to @code{set} except for its lack of subcommands. For example, a
5489 program might well have a variable @code{width}---which leads to
5490 an error if we try to set a new value with just @samp{set width=13}, as
5491 we might if @code{set width} did not happen to be a _GDBN__ command:
5494 (_GDBP__) whatis width
5498 (_GDBP__) set width=47
5499 Invalid syntax in expression.
5503 The invalid expression, of course, is @samp{=47}. What we can do in
5504 order to actually set our program's variable @code{width} is
5507 (_GDBP__) set var width=47
5510 _GDBN__ allows more implicit conversions in assignments than C; you can
5511 freely store an integer value into a pointer variable or vice versa,
5512 and any structure can be converted to any other structure that is the
5513 same length or shorter.
5514 @comment FIXME: how do structs align/pad in these conversions?
5515 @comment /pesch@cygnus.com 18dec1990
5517 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
5518 construct to generate a value of specified type at a specified address
5519 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
5520 to memory location @code{0x83040} as an integer (which implies a certain size
5521 and representation in memory), and
5524 set @{int@}0x83040 = 4
5528 stores the value 4 into that memory location.
5530 @node Jumping, Signaling, Assignment, Altering
5531 @section Continuing at a Different Address
5533 Ordinarily, when you continue your program, you do so at the place where
5534 it stopped, with the @code{continue} command. You can instead continue at
5535 an address of your own choosing, with the following commands:
5538 @item jump @var{linespec}
5540 Resume execution at line @var{linespec}. Execution will stop
5541 immediately if there is a breakpoint there. @xref{List, ,Printing
5542 Source Lines}, for a description of the different forms of
5545 The @code{jump} command does not change the current stack frame, or
5546 the stack pointer, or the contents of any memory location or any
5547 register other than the program counter. If line @var{linespec} is in
5548 a different function from the one currently executing, the results may
5549 be bizarre if the two functions expect different patterns of arguments or
5550 of local variables. For this reason, the @code{jump} command requests
5551 confirmation if the specified line is not in the function currently
5552 executing. However, even bizarre results are predictable if you are
5553 well acquainted with the machine-language code of your program.
5555 @item jump *@var{address}
5556 Resume execution at the instruction at address @var{address}.
5559 You can get much the same effect as the @code{jump} command by storing a
5560 new value into the register @code{$pc}. The difference is that this
5561 does not start your program running; it only changes the address where it
5562 @emph{will} run when it is continued. For example,
5569 causes the next @code{continue} command or stepping command to execute at
5570 address @code{0x485}, rather than at the address where your program stopped.
5571 @xref{Continuing and Stepping, ,Continuing and Stepping}.
5573 The most common occasion to use the @code{jump} command is to back up,
5574 perhaps with more breakpoints set, over a portion of a program that has
5575 already executed, in order to examine its execution in more detail.
5577 @node Signaling, Returning, Jumping, Altering
5579 @section Giving your program a Signal
5582 @item signal @var{signalnum}
5584 Resume execution where your program stopped, but give it immediately the
5585 signal number @var{signalnum}.
5587 Alternatively, if @var{signalnum} is zero, continue execution without
5588 giving a signal. This is useful when your program stopped on account of
5589 a signal and would ordinary see the signal when resumed with the
5590 @code{continue} command; @samp{signal 0} causes it to resume without a
5593 @code{signal} does not repeat when you press @key{RET} a second time
5594 after executing the command.
5598 @node Returning, Calling, Signaling, Altering
5599 @section Returning from a Function
5603 @itemx return @var{expression}
5604 @cindex returning from a function
5606 You can cancel execution of a function call with the @code{return}
5607 command. If you give an
5608 @var{expression} argument, its value is used as the function's return
5612 When you use @code{return}, _GDBN__ discards the selected stack frame
5613 (and all frames within it). You can think of this as making the
5614 discarded frame return prematurely. If you wish to specify a value to
5615 be returned, give that value as the argument to @code{return}.
5617 This pops the selected stack frame (@pxref{Selection, ,Selecting a
5618 Frame}), and any other frames inside of it, leaving its caller as the
5619 innermost remaining frame. That frame becomes selected. The
5620 specified value is stored in the registers used for returning values
5623 The @code{return} command does not resume execution; it leaves the
5624 program stopped in the state that would exist if the function had just
5625 returned. In contrast, the @code{finish} command (@pxref{Continuing
5626 and Stepping, ,Continuing and Stepping}) resumes execution until the
5627 selected stack frame returns naturally.
5629 @node Calling, Patching, Returning, Altering
5630 @section Calling your Program's Functions
5632 @cindex calling functions
5635 @item call @var{expr}
5636 Evaluate the expression @var{expr} without displaying @code{void}
5640 You can use this variant of the @code{print} command if you want to
5641 execute a function from your program, but without cluttering the output
5642 with @code{void} returned values. The result is printed and saved in
5643 the value history, if it is not void.
5645 @node Patching, , Calling, Altering
5646 @section Patching your Program
5647 @cindex patching binaries
5648 @cindex writing into executables
5649 @cindex writing into corefiles
5651 By default, _GDBN__ opens the file containing your program's executable
5652 code (or the corefile) read-only. This prevents accidental alterations
5653 to machine code; but it also prevents you from intentionally patching
5654 your program's binary.
5656 If you'd like to be able to patch the binary, you can specify that
5657 explicitly with the @code{set write} command. For example, you might
5658 want to turn on internal debugging flags, or even to make emergency
5663 @itemx set write off
5665 If you specify @samp{set write on}, _GDBN__ will open executable and
5666 core files for both reading and writing; if you specify @samp{set write
5667 off} (the default), _GDBN__ will open them read-only.
5669 If you have already loaded a file, you must load it
5670 again (using the @code{exec-file} or @code{core-file} command) after
5671 changing @code{set write}, for your new setting to take effect.
5675 Display whether executable files and core files will be opened for
5676 writing as well as reading.
5679 @node _GDBN__ Files, Targets, Altering, Top
5680 @chapter _GDBN__'s Files
5682 _GDBN__ needs to know the file name of the program to be debugged, both in
5683 order to read its symbol table and in order to start your program. To
5684 debug a core dump of a previous run, _GDBN__ must be told the file name of
5688 * Files:: Commands to Specify Files
5689 * Symbol Errors:: Errors Reading Symbol Files
5692 @node Files, Symbol Errors, _GDBN__ Files, _GDBN__ Files
5693 @section Commands to Specify Files
5694 @cindex core dump file
5695 @cindex symbol table
5697 The usual way to specify executable and core dump file names is with
5698 the command arguments given when you start _GDBN__, (@pxref{Invocation,
5699 ,Getting In and Out of _GDBN__}.
5701 Occasionally it is necessary to change to a different file during a
5702 _GDBN__ session. Or you may run _GDBN__ and forget to specify the files you
5703 want to use. In these situations the _GDBN__ commands to specify new files
5707 @item file @var{filename}
5708 @cindex executable file
5710 Use @var{filename} as the program to be debugged. It is read for its
5711 symbols and for the contents of pure memory. It is also the program
5712 executed when you use the @code{run} command. If you do not specify a
5713 directory and the file is not found in _GDBN__'s working directory, _GDBN__
5714 uses the environment variable @code{PATH} as a list of directories to
5715 search, just as the shell does when looking for a program to run. You
5716 can change the value of this variable, for both _GDBN__ and your program,
5717 using the @code{path} command.
5720 @code{file} with no argument makes _GDBN__ discard any information it
5721 has on both executable file and the symbol table.
5723 @item exec-file @r{[} @var{filename} @r{]}
5725 Specify that the program to be run (but not the symbol table) is found
5726 in @var{filename}. _GDBN__ will search the environment variable @code{PATH}
5727 if necessary to locate your program. Omitting @var{filename} means to
5728 discard information on the executable file.
5730 @item symbol-file @r{[} @var{filename} @r{]}
5732 Read symbol table information from file @var{filename}. @code{PATH} is
5733 searched when necessary. Use the @code{file} command to get both symbol
5734 table and program to run from the same file.
5736 @code{symbol-file} with no argument clears out _GDBN__'s information on your
5737 program's symbol table.
5739 The @code{symbol-file} command causes _GDBN__ to forget the contents of its
5740 convenience variables, the value history, and all breakpoints and
5741 auto-display expressions. This is because they may contain pointers to
5742 the internal data recording symbols and data types, which are part of
5743 the old symbol table data being discarded inside _GDBN__.
5745 @code{symbol-file} will not repeat if you press @key{RET} again after
5748 On some kinds of object files, the @code{symbol-file} command does not
5749 actually read the symbol table in full right away. Instead, it scans
5750 the symbol table quickly to find which source files and which symbols
5751 are present. The details are read later, one source file at a time,
5754 The purpose of this two-stage reading strategy is to make _GDBN__ start up
5755 faster. For the most part, it is invisible except for occasional
5756 pauses while the symbol table details for a particular source file are
5757 being read. (The @code{set verbose} command can turn these pauses
5758 into messages if desired. @xref{Messages/Warnings, ,Optional Warnings
5761 When the symbol table is stored in COFF format, @code{symbol-file} does
5762 read the symbol table data in full right away. We have not implemented
5763 the two-stage strategy for COFF yet.
5765 When _GDBN__ is configured for a particular environment, it will
5766 understand debugging information in whatever format is the standard
5767 generated for that environment; you may use either a GNU compiler, or
5768 other compilers that adhere to the local conventions. Best results are
5769 usually obtained from GNU compilers; for example, using @code{_GCC__}
5770 you can generate debugging information for optimized code.
5772 @item core-file @r{[} @var{filename} @r{]}
5775 Specify the whereabouts of a core dump file to be used as the ``contents
5776 of memory''. Traditionally, core files contain only some parts of the
5777 address space of the process that generated them; _GDBN__ can access the
5778 executable file itself for other parts.
5780 @code{core-file} with no argument specifies that no core file is
5783 Note that the core file is ignored when your program is actually running
5784 under _GDBN__. So, if you have been running your program and you wish to
5785 debug a core file instead, you must kill the subprocess in which the
5786 program is running. To do this, use the @code{kill} command
5787 (@pxref{Kill Process, ,Killing the Child Process}).
5789 @item load @var{filename}
5792 Depending on what remote debugging facilities are configured into
5793 _GDBN__, the @code{load} command may be available. Where it exists, it
5794 is meant to make @var{filename} (an executable) available for debugging
5795 on the remote system---by downloading, or dynamic linking, for example.
5796 @code{load} also records @var{filename}'s symbol table in _GDBN__, like
5797 the @code{add-symbol-file} command.
5799 If @code{load} is not available on your _GDBN__, attempting to execute
5800 it gets the error message ``@code{You can't do that when your target is
5805 On VxWorks, @code{load} will dynamically link @var{filename} on the
5806 current target system as well as adding its symbols in _GDBN__.
5810 @cindex download to Nindy-960
5811 With the Nindy interface to an Intel 960 board, @code{load} will
5812 download @var{filename} to the 960 as well as adding its symbols in
5816 @code{load} will not repeat if you press @key{RET} again after using it.
5818 @item add-symbol-file @var{filename} @var{address}
5819 @kindex add-symbol-file
5820 @cindex dynamic linking
5821 The @code{add-symbol-file} command reads additional symbol table information
5822 from the file @var{filename}. You would use this command when @var{filename}
5823 has been dynamically loaded (by some other means) into the program that
5824 is running. @var{address} should be the memory address at which the
5825 file has been loaded; _GDBN__ cannot figure this out for itself.
5827 The symbol table of the file @var{filename} is added to the symbol table
5828 originally read with the @code{symbol-file} command. You can use the
5829 @code{add-symbol-file} command any number of times; the new symbol data thus
5830 read keeps adding to the old. To discard all old symbol data instead,
5831 use the @code{symbol-file} command.
5833 @code{add-symbol-file} will not repeat if you press @key{RET} after using it.
5839 @code{info files} and @code{info target} are synonymous; both print
5840 the current targets (@pxref{Targets, ,Specifying a Debugging Target}),
5841 including the names of the executable and core dump files currently in
5842 use by _GDBN__, and the files from which symbols were loaded. The command
5843 @code{help targets} lists all possible targets rather than current
5848 All file-specifying commands allow both absolute and relative file names
5849 as arguments. _GDBN__ always converts the file name to an absolute path
5850 name and remembers it that way.
5852 @cindex shared libraries
5854 _GDBN__ supports the SunOS shared library format. _GDBN__ automatically
5855 loads symbol definitions from shared libraries when you use the
5856 @code{run} command, or when you examine a core file. (Before you issue
5857 the @code{run} command, _GDBN__ will not understand references to a
5858 function in a shared library, however---unless you are debugging a core
5860 @c FIXME: next _GDBN__ release should permit some refs to undef
5861 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared lib
5865 @itemx info sharedlibrary
5866 @kindex info sharedlibrary
5868 Print the names of the shared libraries which are currently loaded.
5870 @item sharedlibrary @var{regex}
5871 @itemx share @var{regex}
5872 @kindex sharedlibrary
5874 This is an obsolescent command; you can use it to explicitly
5875 load shared object library symbols for files matching a UNIX regular
5876 expression, but as with files loaded automatically, it will only load
5877 shared libraries required by your program for a core file or after
5878 typing @code{run}. If @var{regex} is omitted all shared libraries
5879 required by your program are loaded.
5882 @node Symbol Errors, , Files, _GDBN__ Files
5883 @section Errors Reading Symbol Files
5885 While reading a symbol file, _GDBN__ will occasionally encounter problems,
5886 such as symbol types it does not recognize, or known bugs in compiler
5887 output. By default, _GDBN__ does not notify you of such problems, since
5888 they are relatively common and primarily of interest to people
5889 debugging compilers. If you are interested in seeing information
5890 about ill-constructed symbol tables, you can either ask _GDBN__ to print
5891 only one message about each such type of problem, no matter how many
5892 times the problem occurs; or you can ask _GDBN__ to print more messages,
5893 to see how many times the problems occur, with the @code{set
5894 complaints} command (@pxref{Messages/Warnings, ,Optional Warnings and
5897 The messages currently printed, and their meanings, are:
5900 @item inner block not inside outer block in @var{symbol}
5902 The symbol information shows where symbol scopes begin and end
5903 (such as at the start of a function or a block of statements). This
5904 error indicates that an inner scope block is not fully contained
5905 in its outer scope blocks.
5907 _GDBN__ circumvents the problem by treating the inner block as if it had
5908 the same scope as the outer block. In the error message, @var{symbol}
5909 may be shown as ``@code{(don't know)}'' if the outer block is not a
5912 @item block at @var{address} out of order
5914 The symbol information for symbol scope blocks should occur in
5915 order of increasing addresses. This error indicates that it does not
5918 _GDBN__ does not circumvent this problem, and will have trouble locating
5919 symbols in the source file whose symbols being read. (You can often
5920 determine what source file is affected by specifying @code{set verbose
5921 on}. @xref{Messages/Warnings, ,Optional Warnings and Messages}.)
5923 @item bad block start address patched
5925 The symbol information for a symbol scope block has a start address
5926 smaller than the address of the preceding source line. This is known
5927 to occur in the SunOS 4.1.1 (and earlier) C compiler.
5929 _GDBN__ circumvents the problem by treating the symbol scope block as
5930 starting on the previous source line.
5932 @item bad string table offset in symbol @var{n}
5935 Symbol number @var{n} contains a pointer into the string table which is
5936 larger than the size of the string table.
5938 _GDBN__ circumvents the problem by considering the symbol to have the
5939 name @code{foo}, which may cause other problems if many symbols end up
5942 @item unknown symbol type @code{0x@var{nn}}
5944 The symbol information contains new data types that _GDBN__ does not yet
5945 know how to read. @code{0x@var{nn}} is the symbol type of the misunderstood
5946 information, in hexadecimal.
5948 _GDBN__ circumvents the error by ignoring this symbol information. This
5949 will usually allow your program to be debugged, though certain symbols
5950 will not be accessible. If you encounter such a problem and feel like
5951 debugging it, you can debug @code{_GDBP__} with itself, breakpoint on
5952 @code{complain}, then go up to the function @code{read_dbx_symtab} and
5953 examine @code{*bufp} to see the symbol.
5955 @item stub type has NULL name
5956 _GDBN__ could not find the full definition for a struct or class.
5958 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
5960 The symbol information for a C++ member function is missing some
5961 information that recent versions of the compiler should have output
5964 @item info mismatch between compiler and debugger
5966 _GDBN__ could not parse a type specification output by the compiler.
5969 @node Targets, Controlling _GDBN__, _GDBN__ Files, Top
5970 @chapter Specifying a Debugging Target
5971 @cindex debugging target
5974 A @dfn{target} is the execution environment occupied by your program.
5975 Often, _GDBN__ runs in the same host environment as your program; in
5976 that case, the debugging target is specified as a side effect when you
5977 use the @code{file} or @code{core} commands. When you need more
5978 flexibility---for example, running _GDBN__ on a physically separate
5979 host, or controlling a standalone system over a serial port or a
5980 realtime system over a TCP/IP connection---you can use the @code{target}
5981 command to specify one of the target types configured for _GDBN__
5982 (@pxref{Target Commands, ,Commands for Managing Targets}).
5985 * Active Targets:: Active Targets
5986 * Target Commands:: Commands for Managing Targets
5987 * Remote:: Remote Debugging
5990 @node Active Targets, Target Commands, Targets, Targets
5991 @section Active Targets
5992 @cindex stacking targets
5993 @cindex active targets
5994 @cindex multiple targets
5996 There are three classes of targets: processes, core files, and
5997 executable files. _GDBN__ can work concurrently on up to three active
5998 targets, one in each class. This allows you to (for example) start a
5999 process and inspect its activity without abandoning your work on a core
6002 If, for example, you execute @samp{gdb a.out}, then the executable file
6003 @code{a.out} is the only active target. If you designate a core file as
6004 well---presumably from a prior run that crashed and coredumped---then
6005 _GDBN__ has two active targets and will use them in tandem, looking
6006 first in the corefile target, then in the executable file, to satisfy
6007 requests for memory addresses. (Typically, these two classes of target
6008 are complementary, since core files contain only a program's
6009 read-write memory---variables and so on---plus machine status, while
6010 executable files contain only the program text and initialized data.)
6012 When you type @code{run}, your executable file becomes an active process
6013 target as well. When a process target is active, all _GDBN__ commands
6014 requesting memory addresses refer to that target; addresses in an active
6015 core file or executable file target are obscured while the process
6018 Use the @code{core-file} and @code{exec-file} commands to select a
6019 new core file or executable target (@pxref{Files, ,Commands to Specify
6020 Files}). To specify as a target a process that is already running, use
6021 the @code{attach} command (@pxref{Attach, ,Debugging an
6022 Already-Running Process}.).
6024 @node Target Commands, Remote, Active Targets, Targets
6025 @section Commands for Managing Targets
6028 @item target @var{type} @var{parameters}
6029 Connects the _GDBN__ host environment to a target machine or process. A
6030 target is typically a protocol for talking to debugging facilities. You
6031 use the argument @var{type} to specify the type or protocol of the
6034 Further @var{parameters} are interpreted by the target protocol, but
6035 typically include things like device names or host names to connect
6036 with, process numbers, and baud rates.
6038 The @code{target} command will not repeat if you press @key{RET} again
6039 after executing the command.
6043 Displays the names of all targets available. To display targets
6044 currently selected, use either @code{info target} or @code{info files}
6045 (@pxref{Files, ,Commands to Specify Files}).
6047 @item help target @var{name}
6048 Describe a particular target, including any parameters necessary to
6052 Here are some common targets (available, or not, depending on the _GDBN__
6056 @item target exec @var{prog}
6058 An executable file. @samp{target exec @var{prog}} is the same as
6059 @samp{exec-file @var{prog}}.
6061 @item target core @var{filename}
6063 A core dump file. @samp{target core @var{filename}} is the same as
6064 @samp{core-file @var{filename}}.
6066 @item target remote @var{dev}
6067 @kindex target remote
6068 Remote serial target in _GDBN__-specific protocol. The argument @var{dev}
6069 specifies what serial device to use for the connection (e.g.
6070 @file{/dev/ttya}). @xref{Remote, ,Remote Debugging}.
6073 @item target amd-eb @var{dev} @var{speed} @var{PROG}
6074 @kindex target amd-eb
6076 Remote PC-resident AMD EB29K board, attached over serial lines.
6077 @var{dev} is the serial device, as for @code{target remote};
6078 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
6079 name of the program to be debugged, as it appears to DOS on the PC.
6080 @xref{EB29K Remote, ,GDB with a Remote EB29K}.
6084 @item target nindy @var{devicename}
6085 @kindex target nindy
6086 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
6087 the name of the serial device to use for the connection, e.g.
6088 @file{/dev/ttya}. @xref{i960-Nindy Remote, ,_GDBN__ with a Remote i960 (Nindy)}.
6092 @item target vxworks @var{machinename}
6093 @kindex target vxworks
6094 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
6095 is the target system's machine name or IP address.
6096 @xref{VxWorks Remote, ,_GDBN__ and VxWorks}.
6101 Different targets are available on different configurations of _GDBN__; your
6102 configuration may have more or fewer targets.
6105 @node Remote, , Target Commands, Targets
6106 @section Remote Debugging
6107 @cindex remote debugging
6109 If you are trying to debug a program running on a machine that cannot run
6110 _GDBN__ in the usual way, it is often useful to use remote debugging. For
6111 example, you might use remote debugging on an operating system kernel, or on
6112 a small system which does not have a general purpose operating system
6113 powerful enough to run a full-featured debugger.
6115 Some configurations of _GDBN__ have special serial or TCP/IP interfaces
6116 to make this work with particular debugging targets. In addition,
6117 _GDBN__ comes with a generic serial protocol (specific to _GDBN__, but
6118 not specific to any particular target system) which you can use if you
6119 write the remote stubs---the code that will run on the remote system to
6120 communicate with _GDBN__.
6122 To use the _GDBN__ remote serial protocol, the program to be debugged on
6123 the remote machine needs to contain a debugging stub which talks to
6124 _GDBN__ over the serial line. Several working remote stubs are
6125 distributed with _GDBN__; see the @file{README} file in the _GDBN__
6126 distribution for more information.
6128 For details of this communication protocol, see the comments in the
6129 _GDBN__ source file @file{remote.c}.
6131 To start remote debugging, first run _GDBN__ and specify as an executable file
6132 the program that is running in the remote machine. This tells _GDBN__ how
6133 to find your program's symbols and the contents of its pure text. Then
6134 establish communication using the @code{target remote} command with a device
6135 name as an argument. For example:
6138 target remote /dev/ttyb
6142 if the serial line is connected to the device named @file{/dev/ttyb}. This
6143 will stop the remote machine if it is not already stopped.
6145 Now you can use all the usual commands to examine and change data and to
6146 step and continue the remote program.
6148 To resume the remote program and stop debugging it, use the @code{detach}
6151 Other remote targets may be available in your
6152 configuration of _GDBN__; use @code{help targets} to list them.
6155 _dnl__ Text on starting up GDB in various specific cases; it goes up front
6156 _dnl__ in manuals configured for any of those particular situations, here
6159 _include__(gdbinv-m.m4)<>_dnl__
6161 _include__(gdbinv-s.m4)
6164 @node Controlling _GDBN__, Sequences, Targets, Top
6165 @chapter Controlling _GDBN__
6167 You can alter many aspects of _GDBN__'s interaction with you by using
6168 the @code{set} command. For commands controlling how _GDBN__ displays
6169 data, @pxref{Print Settings, ,Print Settings}; other settings are described here.
6173 * Editing:: Command Editing
6174 * History:: Command History
6175 * Screen Size:: Screen Size
6177 * Messages/Warnings:: Optional Warnings and Messages
6180 @node Prompt, Editing, Controlling _GDBN__, Controlling _GDBN__
6184 _GDBN__ indicates its readiness to read a command by printing a string
6185 called the @dfn{prompt}. This string is normally @samp{(_GDBP__)}. You
6186 can change the prompt string with the @code{set prompt} command. For
6187 instance, when debugging _GDBN__ with _GDBN__, it is useful to change
6188 the prompt in one of the _GDBN__<>s so that you can always tell which
6189 one you are talking to.
6192 @item set prompt @var{newprompt}
6194 Directs _GDBN__ to use @var{newprompt} as its prompt string henceforth.
6197 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
6200 @node Editing, History, Prompt, Controlling _GDBN__
6201 @section Command Editing
6203 @cindex command line editing
6205 _GDBN__ reads its input commands via the @dfn{readline} interface. This
6206 GNU library provides consistent behavior for programs which provide a
6207 command line interface to the user. Advantages are @code{emacs}-style
6208 or @code{vi}-style inline editing of commands, @code{csh}-like history
6209 substitution, and a storage and recall of command history across
6212 You may control the behavior of command line editing in _GDBN__ with the
6219 @itemx set editing on
6220 Enable command line editing (enabled by default).
6222 @item set editing off
6223 Disable command line editing.
6225 @kindex show editing
6227 Show whether command line editing is enabled.
6230 @node History, Screen Size, Editing, Controlling _GDBN__
6231 @section Command History
6234 @cindex history substitution
6235 @cindex history file
6236 @kindex set history filename
6237 @item set history filename @var{fname}
6238 Set the name of the _GDBN__ command history file to @var{fname}. This is
6239 the file from which _GDBN__ will read an initial command history
6240 list or to which it will write this list when it exits. This list is
6241 accessed through history expansion or through the history
6242 command editing characters listed below. This file defaults to the
6243 value of the environment variable @code{GDBHISTFILE}, or to
6244 @file{./.gdb_history} if this variable is not set.
6246 @cindex history save
6247 @kindex set history save
6248 @item set history save
6249 @itemx set history save on
6250 Record command history in a file, whose name may be specified with the
6251 @code{set history filename} command. By default, this option is disabled.
6253 @item set history save off
6254 Stop recording command history in a file.
6256 @cindex history size
6257 @kindex set history size
6258 @item set history size @var{size}
6259 Set the number of commands which _GDBN__ will keep in its history list.
6260 This defaults to the value of the environment variable
6261 @code{HISTSIZE}, or to 256 if this variable is not set.
6264 @cindex history expansion
6265 History expansion assigns special meaning to the character @kbd{!}.
6267 @xref{Event Designators}.
6269 Since @kbd{!} is also the logical not operator in C, history expansion
6270 is off by default. If you decide to enable history expansion with the
6271 @code{set history expansion on} command, you may sometimes need to
6272 follow @kbd{!} (when it is used as logical not, in an expression) with
6273 a space or a tab to prevent it from being expanded. The readline
6274 history facilities will not attempt substitution on the strings
6275 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
6277 The commands to control history expansion are:
6281 @kindex set history expansion
6282 @item set history expansion on
6283 @itemx set history expansion
6284 Enable history expansion. History expansion is off by default.
6286 @item set history expansion off
6287 Disable history expansion.
6289 The readline code comes with more complete documentation of
6290 editing and history expansion features. Users unfamiliar with @code{emacs}
6291 or @code{vi} may wish to read it.
6293 @xref{Command Line Editing}.
6297 @kindex show history
6299 @itemx show history filename
6300 @itemx show history save
6301 @itemx show history size
6302 @itemx show history expansion
6303 These commands display the state of the _GDBN__ history parameters.
6304 @code{show history} by itself displays all four states.
6309 @kindex show commands
6311 Display the last ten commands in the command history.
6313 @item show commands @var{n}
6314 Print ten commands centered on command number @var{n}.
6316 @item show commands +
6317 Print ten commands just after the commands last printed.
6320 @node Screen Size, Numbers, History, Controlling _GDBN__
6321 @section Screen Size
6322 @cindex size of screen
6323 @cindex pauses in output
6325 Certain commands to _GDBN__ may produce large amounts of information
6326 output to the screen. To help you read all of it, _GDBN__ pauses and
6327 asks you for input at the end of each page of output. Type @key{RET}
6328 when you want to continue the output. _GDBN__ also uses the screen
6329 width setting to determine when to wrap lines of output. Depending on
6330 what is being printed, it tries to break the line at a readable place,
6331 rather than simply letting it overflow onto the following line.
6333 Normally _GDBN__ knows the size of the screen from the termcap data base
6334 together with the value of the @code{TERM} environment variable and the
6335 @code{stty rows} and @code{stty cols} settings. If this is not correct,
6336 you can override it with the @code{set height} and @code{set
6340 @item set height @var{lpp}
6342 @itemx set width @var{cpl}
6348 These @code{set} commands specify a screen height of @var{lpp} lines and
6349 a screen width of @var{cpl} characters. The associated @code{show}
6350 commands display the current settings.
6352 If you specify a height of zero lines, _GDBN__ will not pause during output
6353 no matter how long the output is. This is useful if output is to a file
6354 or to an editor buffer.
6357 @node Numbers, Messages/Warnings, Screen Size, Controlling _GDBN__
6359 @cindex number representation
6360 @cindex entering numbers
6362 You can always enter numbers in octal, decimal, or hexadecimal in _GDBN__ by
6363 the usual conventions: octal numbers begin with @samp{0}, decimal
6364 numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}.
6365 Numbers that begin with none of these are, by default, entered in base
6366 10; likewise, the default display for numbers---when no particular
6367 format is specified---is base 10. You can change the default base for
6368 both input and output with the @code{set radix} command.
6372 @item set radix @var{base}
6373 Set the default base for numeric input and display. Supported choices
6374 for @var{base} are decimal 2, 8, 10, 16. @var{base} must itself be
6375 specified either unambiguously or using the current default radix; for
6386 will set the base to decimal. On the other hand, @samp{set radix 10}
6387 will leave the radix unchanged no matter what it was.
6391 Display the current default base for numeric input and display.
6394 @node Messages/Warnings, , Numbers, Controlling _GDBN__
6395 @section Optional Warnings and Messages
6397 By default, _GDBN__ is silent about its inner workings. If you are running
6398 on a slow machine, you may want to use the @code{set verbose} command.
6399 It will make _GDBN__ tell you when it does a lengthy internal operation, so
6400 you will not think it has crashed.
6402 Currently, the messages controlled by @code{set verbose} are those
6403 which announce that the symbol table for a source file is being read
6404 (@pxref{Files, ,Commands to Specify Files}, in the description of the
6405 command @code{symbol-file}).
6406 @c The following is the right way to do it, but emacs 18.55 does not support
6407 @c @ref, and neither the emacs lisp manual version of texinfmt or makeinfo
6410 see @code{symbol-file} in @ref{Files, ,Commands to Specify Files}).
6415 @item set verbose on
6416 Enables _GDBN__'s output of certain informational messages.
6418 @item set verbose off
6419 Disables _GDBN__'s output of certain informational messages.
6421 @kindex show verbose
6423 Displays whether @code{set verbose} is on or off.
6426 By default, if _GDBN__ encounters bugs in the symbol table of an object
6427 file, it is silent; but if you are debugging a compiler, you may find
6428 this information useful (@pxref{Symbol Errors, ,Errors Reading Symbol Files}).
6431 @kindex set complaints
6432 @item set complaints @var{limit}
6433 Permits _GDBN__ to output @var{limit} complaints about each type of unusual
6434 symbols before becoming silent about the problem. Set @var{limit} to
6435 zero to suppress all complaints; set it to a large number to prevent
6436 complaints from being suppressed.
6438 @kindex show complaints
6439 @item show complaints
6440 Displays how many symbol complaints _GDBN__ is permitted to produce.
6443 By default, _GDBN__ is cautious, and asks what sometimes seem to be a
6444 lot of stupid questions to confirm certain commands. For example, if
6445 you try to run a program which is already running:
6449 The program being debugged has been started already.
6450 Start it from the beginning? (y or n)
6453 If you are willing to unflinchingly face the consequences of your own
6454 commands, you can disable this ``feature'':
6459 @cindex confirmation
6460 @cindex stupid questions
6461 @item set confirm off
6462 Disables confirmation requests.
6464 @item set confirm on
6465 Enables confirmation requests (the default).
6468 @kindex show confirm
6469 Displays state of confirmation requests.
6472 @c FIXME this does not really belong here. But where *does* it belong?
6473 @cindex reloading symbols
6474 Some systems allow individual object files that make up your program to
6475 be replaced without stopping and restarting your program.
6477 For example, in VxWorks you can simply recompile a defective object file
6478 and keep on running.
6480 If you are running on one of these systems, you can allow _GDBN__ to
6481 reload the symbols for automatically relinked modules:
6484 @kindex set symbol-reloading
6485 @item set symbol-reloading on
6486 Replace symbol definitions for the corresponding source file when an
6487 object file with a particular name is seen again.
6489 @item set symbol-reloading off
6490 Do not replace symbol definitions when re-encountering object files of
6491 the same name. This is the default state; if you are not running on a
6492 system that permits automatically relinking modules, you should leave
6493 @code{symbol-reloading} off, since otherwise _GDBN__ may discard symbols
6494 when linking large programs, that may contain several modules (from
6495 different directories or libraries) with the same name.
6497 @item show symbol-reloading
6498 Show the current @code{on} or @code{off} setting.
6501 @node Sequences, Emacs, Controlling _GDBN__, Top
6502 @chapter Canned Sequences of Commands
6504 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
6505 Command Lists}), _GDBN__ provides two ways to store sequences of commands
6506 for execution as a unit: user-defined commands and command files.
6509 * Define:: User-Defined Commands
6510 * Command Files:: Command Files
6511 * Output:: Commands for Controlled Output
6514 @node Define, Command Files, Sequences, Sequences
6515 @section User-Defined Commands
6517 @cindex user-defined command
6518 A @dfn{user-defined command} is a sequence of _GDBN__ commands to which you
6519 assign a new name as a command. This is done with the @code{define}
6523 @item define @var{commandname}
6525 Define a command named @var{commandname}. If there is already a command
6526 by that name, you are asked to confirm that you want to redefine it.
6528 The definition of the command is made up of other _GDBN__ command lines,
6529 which are given following the @code{define} command. The end of these
6530 commands is marked by a line containing @code{end}.
6532 @item document @var{commandname}
6534 Give documentation to the user-defined command @var{commandname}. The
6535 command @var{commandname} must already be defined. This command reads
6536 lines of documentation just as @code{define} reads the lines of the
6537 command definition, ending with @code{end}. After the @code{document}
6538 command is finished, @code{help} on command @var{commandname} will print
6539 the documentation you have specified.
6541 You may use the @code{document} command again to change the
6542 documentation of a command. Redefining the command with @code{define}
6543 does not change the documentation.
6545 @item help user-defined
6546 @kindex help user-defined
6547 List all user-defined commands, with the first line of the documentation
6551 @itemx info user @var{commandname}
6553 Display the _GDBN__ commands used to define @var{commandname} (but not its
6554 documentation). If no @var{commandname} is given, display the
6555 definitions for all user-defined commands.
6558 User-defined commands do not take arguments. When they are executed, the
6559 commands of the definition are not printed. An error in any command
6560 stops execution of the user-defined command.
6562 Commands that would ask for confirmation if used interactively proceed
6563 without asking when used inside a user-defined command. Many _GDBN__ commands
6564 that normally print messages to say what they are doing omit the messages
6565 when used in a user-defined command.
6567 @node Command Files, Output, Define, Sequences
6568 @section Command Files
6570 @cindex command files
6571 A command file for _GDBN__ is a file of lines that are _GDBN__ commands. Comments
6572 (lines starting with @kbd{#}) may also be included. An empty line in a
6573 command file does nothing; it does not mean to repeat the last command, as
6574 it would from the terminal.
6577 @cindex @file{_GDBINIT__}
6578 When you start _GDBN__, it automatically executes commands from its
6579 @dfn{init files}. These are files named @file{_GDBINIT__}. _GDBN__ reads
6580 the init file (if any) in your home directory and then the init file
6581 (if any) in the current working directory. (The init files are not
6582 executed if you use the @samp{-nx} option; @pxref{Mode Options,
6583 ,Choosing Modes}.) You can also request the execution of a command
6584 file with the @code{source} command:
6587 @item source @var{filename}
6589 Execute the command file @var{filename}.
6592 The lines in a command file are executed sequentially. They are not
6593 printed as they are executed. An error in any command terminates execution
6594 of the command file.
6596 Commands that would ask for confirmation if used interactively proceed
6597 without asking when used in a command file. Many _GDBN__ commands that
6598 normally print messages to say what they are doing omit the messages
6599 when called from command files.
6601 @node Output, , Command Files, Sequences
6602 @section Commands for Controlled Output
6604 During the execution of a command file or a user-defined command, normal
6605 _GDBN__ output is suppressed; the only output that appears is what is
6606 explicitly printed by the commands in the definition. This section
6607 describes three commands useful for generating exactly the output you
6611 @item echo @var{text}
6613 @c I do not consider backslash-space a standard C escape sequence
6614 @c because it is not in ANSI.
6615 Print @var{text}. Nonprinting characters can be included in
6616 @var{text} using C escape sequences, such as @samp{\n} to print a
6617 newline. @strong{No newline will be printed unless you specify one.}
6618 In addition to the standard C escape sequences, a backslash followed
6619 by a space stands for a space. This is useful for outputting a
6620 string with spaces at the beginning or the end, since leading and
6621 trailing spaces are otherwise trimmed from all arguments.
6622 To print @samp{@w{ }and foo =@w{ }}, use the command
6623 @samp{echo \@w{ }and foo = \@w{ }}.
6625 A backslash at the end of @var{text} can be used, as in C, to continue
6626 the command onto subsequent lines. For example,
6629 echo This is some text\n\
6630 which is continued\n\
6631 onto several lines.\n
6634 produces the same output as
6637 echo This is some text\n
6638 echo which is continued\n
6639 echo onto several lines.\n
6642 @item output @var{expression}
6644 Print the value of @var{expression} and nothing but that value: no
6645 newlines, no @samp{$@var{nn} = }. The value is not entered in the
6646 value history either. @xref{Expressions, ,Expressions}, for more information on
6649 @item output/@var{fmt} @var{expression}
6650 Print the value of @var{expression} in format @var{fmt}. You can use
6651 the same formats as for @code{print}; @pxref{Output formats}, for more
6654 @item printf @var{string}, @var{expressions}@dots{}
6656 Print the values of the @var{expressions} under the control of
6657 @var{string}. The @var{expressions} are separated by commas and may
6658 be either numbers or pointers. Their values are printed as specified
6659 by @var{string}, exactly as if your program were to execute
6662 printf (@var{string}, @var{expressions}@dots{});
6665 For example, you can print two values in hex like this:
6668 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
6671 The only backslash-escape sequences that you can use in the format
6672 string are the simple ones that consist of backslash followed by a
6676 @node Emacs, _GDBN__ Bugs, Sequences, Top
6677 @chapter Using _GDBN__ under GNU Emacs
6680 A special interface allows you to use GNU Emacs to view (and
6681 edit) the source files for the program you are debugging with
6684 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
6685 executable file you want to debug as an argument. This command starts
6686 _GDBN__ as a subprocess of Emacs, with input and output through a newly
6687 created Emacs buffer.
6689 Using _GDBN__ under Emacs is just like using _GDBN__ normally except for two
6694 All ``terminal'' input and output goes through the Emacs buffer.
6697 This applies both to _GDBN__ commands and their output, and to the input
6698 and output done by the program you are debugging.
6700 This is useful because it means that you can copy the text of previous
6701 commands and input them again; you can even use parts of the output
6704 All the facilities of Emacs' Shell mode are available for interacting
6705 with your program. In particular, you can send signals the usual
6706 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
6711 _GDBN__ displays source code through Emacs.
6714 Each time _GDBN__ displays a stack frame, Emacs automatically finds the
6715 source file for that frame and puts an arrow (_0__@samp{=>}_1__) at the
6716 left margin of the current line. Emacs uses a separate buffer for
6717 source display, and splits the window to show both your _GDBN__ session
6720 Explicit _GDBN__ @code{list} or search commands still produce output as
6721 usual, but you probably will have no reason to use them.
6724 @emph{Warning:} If the directory where your program resides is not your
6725 current directory, it can be easy to confuse Emacs about the location of
6726 the source files, in which case the auxiliary display buffer will not
6727 appear to show your source. _GDBN__ can find programs by searching your
6728 environment's @code{PATH} variable, so the _GDBN__ input and output
6729 session will proceed normally; but Emacs does not get enough information
6730 back from _GDBN__ to locate the source files in this situation. To
6731 avoid this problem, either start _GDBN__ mode from the directory where
6732 your program resides, or specify a full path name when prompted for the
6733 @kbd{M-x gdb} argument.
6735 A similar confusion can result if you use the _GDBN__ @code{file} command to
6736 switch to debugging a program in some other location, from an existing
6737 _GDBN__ buffer in Emacs.
6740 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
6741 you need to call _GDBN__ by a different name (for example, if you keep
6742 several configurations around, with different names) you can set the
6743 Emacs variable @code{gdb-command-name}; for example,
6746 (setq gdb-command-name "mygdb")
6750 (preceded by @kbd{ESC ESC}, or typed in the @code{*scratch*} buffer, or
6751 in your @file{.emacs} file) will make Emacs call the program named
6752 ``@code{mygdb}'' instead.
6754 In the _GDBN__ I/O buffer, you can use these special Emacs commands in
6755 addition to the standard Shell mode commands:
6759 Describe the features of Emacs' _GDBN__ Mode.
6762 Execute to another source line, like the _GDBN__ @code{step} command; also
6763 update the display window to show the current file and location.
6766 Execute to next source line in this function, skipping all function
6767 calls, like the _GDBN__ @code{next} command. Then update the display window
6768 to show the current file and location.
6771 Execute one instruction, like the _GDBN__ @code{stepi} command; update
6772 display window accordingly.
6775 Execute to next instruction, using the _GDBN__ @code{nexti} command; update
6776 display window accordingly.
6779 Execute until exit from the selected stack frame, like the _GDBN__
6780 @code{finish} command.
6783 Continue execution of your program, like the _GDBN__ @code{continue}
6786 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
6789 Go up the number of frames indicated by the numeric argument
6790 (@pxref{Arguments, , Numeric Arguments, emacs, The GNU Emacs Manual}),
6791 like the _GDBN__ @code{up} command.
6793 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
6796 Go down the number of frames indicated by the numeric argument, like the
6797 _GDBN__ @code{down} command.
6799 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
6802 Read the number where the cursor is positioned, and insert it at the end
6803 of the _GDBN__ I/O buffer. For example, if you wish to disassemble code
6804 around an address that was displayed earlier, type @kbd{disassemble};
6805 then move the cursor to the address display, and pick up the
6806 argument for @code{disassemble} by typing @kbd{C-x &}.
6808 You can customize this further on the fly by defining elements of the list
6809 @code{gdb-print-command}; once it is defined, you can format or
6810 otherwise process numbers picked up by @kbd{C-x &} before they are
6811 inserted. A numeric argument to @kbd{C-x &} will both indicate that you
6812 wish special formatting, and act as an index to pick an element of the
6813 list. If the list element is a string, the number to be inserted is
6814 formatted using the Emacs function @code{format}; otherwise the number
6815 is passed as an argument to the corresponding list element.
6818 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
6819 tells _GDBN__ to set a breakpoint on the source line point is on.
6821 If you accidentally delete the source-display buffer, an easy way to get
6822 it back is to type the command @code{f} in the _GDBN__ buffer, to
6823 request a frame display; when you run under Emacs, this will recreate
6824 the source buffer if necessary to show you the context of the current
6827 The source files displayed in Emacs are in ordinary Emacs buffers
6828 which are visiting the source files in the usual way. You can edit
6829 the files with these buffers if you wish; but keep in mind that _GDBN__
6830 communicates with Emacs in terms of line numbers. If you add or
6831 delete lines from the text, the line numbers that _GDBN__ knows will cease
6832 to correspond properly to the code.
6834 @c The following dropped because Epoch is nonstandard. Reactivate
6835 @c if/when v19 does something similar. ---pesch@cygnus.com 19dec1990
6837 @kindex emacs epoch environment
6841 Version 18 of Emacs has a built-in window system called the @code{epoch}
6842 environment. Users of this environment can use a new command,
6843 @code{inspect} which performs identically to @code{print} except that
6844 each value is printed in its own window.
6847 @node _GDBN__ Bugs, Renamed Commands, Emacs, Top
6848 @chapter Reporting Bugs in _GDBN__
6849 @cindex Bugs in _GDBN__
6850 @cindex Reporting Bugs in _GDBN__
6852 Your bug reports play an essential role in making _GDBN__ reliable.
6854 Reporting a bug may help you by bringing a solution to your problem, or it
6855 may not. But in any case the principal function of a bug report is to help
6856 the entire community by making the next version of _GDBN__ work better. Bug
6857 reports are your contribution to the maintenance of _GDBN__.
6859 In order for a bug report to serve its purpose, you must include the
6860 information that enables us to fix the bug.
6863 * Bug Criteria:: Have You Found a Bug?
6864 * Bug Reporting:: How to Report Bugs
6867 @node Bug Criteria, Bug Reporting, _GDBN__ Bugs, _GDBN__ Bugs
6868 @section Have You Found a Bug?
6869 @cindex Bug Criteria
6871 If you are not sure whether you have found a bug, here are some guidelines:
6875 @cindex Fatal Signal
6877 If the debugger gets a fatal signal, for any input whatever, that is a
6878 _GDBN__ bug. Reliable debuggers never crash.
6881 @cindex error on Valid Input
6882 If _GDBN__ produces an error message for valid input, that is a bug.
6885 @cindex Invalid Input
6886 If _GDBN__ does not produce an error message for invalid input,
6887 that is a bug. However, you should note that your idea of
6888 ``invalid input'' might be our idea of ``an extension'' or ``support
6889 for traditional practice''.
6892 If you are an experienced user of debugging tools, your suggestions
6893 for improvement of _GDBN__ are welcome in any case.
6896 @node Bug Reporting, , Bug Criteria, _GDBN__ Bugs
6897 @section How to Report Bugs
6899 @cindex _GDBN__ Bugs, Reporting
6901 A number of companies and individuals offer support for GNU products.
6902 If you obtained _GDBN__ from a support organization, we recommend you
6903 contact that organization first.
6905 Contact information for many support companies and individuals is
6906 available in the file @file{etc/SERVICE} in the GNU Emacs distribution.
6908 In any event, we also recommend that you send bug reports for _GDBN__ to one
6912 bug-gdb@@prep.ai.mit.edu
6913 @{ucbvax|mit-eddie|uunet@}!prep.ai.mit.edu!bug-gdb
6916 @strong{Do not send bug reports to @samp{info-gdb}, or to
6917 @samp{help-gdb}, or to any newsgroups.} Most users of _GDBN__ do not want to
6918 receive bug reports. Those that do, have arranged to receive @samp{bug-gdb}.
6920 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
6921 serves as a repeater. The mailing list and the newsgroup carry exactly
6922 the same messages. Often people think of posting bug reports to the
6923 newsgroup instead of mailing them. This appears to work, but it has one
6924 problem which can be crucial: a newsgroup posting often lacks a mail
6925 path back to the sender. Thus, if we need to ask for more information,
6926 we may be unable to reach you. For this reason, it is better to send
6927 bug reports to the mailing list.
6929 As a last resort, send bug reports on paper to:
6933 Free Software Foundation
6938 The fundamental principle of reporting bugs usefully is this:
6939 @strong{report all the facts}. If you are not sure whether to state a
6940 fact or leave it out, state it!
6942 Often people omit facts because they think they know what causes the
6943 problem and assume that some details do not matter. Thus, you might
6944 assume that the name of the variable you use in an example does not matter.
6945 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
6946 stray memory reference which happens to fetch from the location where that
6947 name is stored in memory; perhaps, if the name were different, the contents
6948 of that location would fool the debugger into doing the right thing despite
6949 the bug. Play it safe and give a specific, complete example. That is the
6950 easiest thing for you to do, and the most helpful.
6952 Keep in mind that the purpose of a bug report is to enable us to fix
6953 the bug if it is new to us. It is not as important as what happens if
6954 the bug is already known. Therefore, always write your bug reports on
6955 the assumption that the bug has not been reported previously.
6957 Sometimes people give a few sketchy facts and ask, ``Does this ring a
6958 bell?'' Those bug reports are useless, and we urge everyone to
6959 @emph{refuse to respond to them} except to chide the sender to report
6962 To enable us to fix the bug, you should include all these things:
6966 The version of _GDBN__. _GDBN__ announces it if you start with no
6967 arguments; you can also print it at any time using @code{show version}.
6969 Without this, we will not know whether there is any point in looking for
6970 the bug in the current version of _GDBN__.
6973 The type of machine you are using, and the operating system name and
6977 What compiler (and its version) was used to compile _GDBN__---e.g.
6981 What compiler (and its version) was used to compile the program you
6982 are debugging---e.g. ``_GCC__-1.37.1''.
6985 The command arguments you gave the compiler to compile your example and
6986 observe the bug. For example, did you use @samp{-O}? To guarantee
6987 you will not omit something important, list them all. A copy of the
6988 Makefile (or the output from make) is sufficient.
6990 If we were to try to guess the arguments, we would probably guess wrong
6991 and then we might not encounter the bug.
6994 A complete input script, and all necessary source files, that will
6998 A description of what behavior you observe that you believe is
6999 incorrect. For example, ``It gets a fatal signal.''
7001 Of course, if the bug is that _GDBN__ gets a fatal signal, then we will
7002 certainly notice it. But if the bug is incorrect output, we might not
7003 notice unless it is glaringly wrong. We are human, after all. You
7004 might as well not give us a chance to make a mistake.
7006 Even if the problem you experience is a fatal signal, you should still
7007 say so explicitly. Suppose something strange is going on, such as,
7008 your copy of _GDBN__ is out of synch, or you have encountered a
7009 bug in the C library on your system. (This has happened!) Your copy
7010 might crash and ours would not. If you told us to expect a crash,
7011 then when ours fails to crash, we would know that the bug was not
7012 happening for us. If you had not told us to expect a crash, then we
7013 would not be able to draw any conclusion from our observations.
7016 If you wish to suggest changes to the _GDBN__ source, send us context
7017 diffs. If you even discuss something in the _GDBN__ source, refer to
7018 it by context, not by line number.
7020 The line numbers in our development sources will not match those in your
7021 sources. Your line numbers would convey no useful information to us.
7024 Here are some things that are not necessary:
7028 A description of the envelope of the bug.
7030 Often people who encounter a bug spend a lot of time investigating
7031 which changes to the input file will make the bug go away and which
7032 changes will not affect it.
7034 This is often time consuming and not very useful, because the way we
7035 will find the bug is by running a single example under the debugger
7036 with breakpoints, not by pure deduction from a series of examples.
7037 We recommend that you save your time for something else.
7039 Of course, if you can find a simpler example to report @emph{instead}
7040 of the original one, that is a convenience for us. Errors in the
7041 output will be easier to spot, running under the debugger will take
7044 However, simplification is not vital; if you do not want to do this,
7045 report the bug anyway and send us the entire test case you used.
7048 A patch for the bug.
7050 A patch for the bug does help us if it is a good one. But do not omit
7051 the necessary information, such as the test case, on the assumption that
7052 a patch is all we need. We might see problems with your patch and decide
7053 to fix the problem another way, or we might not understand it at all.
7055 Sometimes with a program as complicated as _GDBN__ it is very hard to
7056 construct an example that will make the program follow a certain path
7057 through the code. If you do not send us the example, we will not be able
7058 to construct one, so we will not be able to verify that the bug is fixed.
7060 And if we cannot understand what bug you are trying to fix, or why your
7061 patch should be an improvement, we will not install it. A test case will
7062 help us to understand.
7065 A guess about what the bug is or what it depends on.
7067 Such guesses are usually wrong. Even we cannot guess right about such
7068 things without first using the debugger to find the facts.
7071 @c Note: no need to update nodes for rdl-apps.texi since it appears
7072 @c *only* in the TeX version of the manual.
7073 @c Note: eventually, make a cross reference to the readline Info nodes.
7075 @c appendices describing GNU readline. Distributed with readline code.
7076 @include rluser.texinfo
7077 @include inc-hist.texi
7080 @node Renamed Commands, Installing _GDBN__, _GDBN__ Bugs, Top
7081 @appendix Renamed Commands
7083 The following commands were renamed in _GDBN__ 4, in order to make the
7084 command set as a whole more consistent and easier to use and remember:
7087 @kindex delete environment
7088 @kindex info copying
7089 @kindex info convenience
7090 @kindex info directories
7091 @kindex info editing
7092 @kindex info history
7093 @kindex info targets
7095 @kindex info version
7096 @kindex info warranty
7097 @kindex set addressprint
7098 @kindex set arrayprint
7099 @kindex set prettyprint
7100 @kindex set screen-height
7101 @kindex set screen-width
7102 @kindex set unionprint
7103 @kindex set vtblprint
7104 @kindex set demangle
7105 @kindex set asm-demangle
7106 @kindex set sevenbit-strings
7107 @kindex set array-max
7109 @kindex set history write
7110 @kindex show addressprint
7111 @kindex show arrayprint
7112 @kindex show prettyprint
7113 @kindex show screen-height
7114 @kindex show screen-width
7115 @kindex show unionprint
7116 @kindex show vtblprint
7117 @kindex show demangle
7118 @kindex show asm-demangle
7119 @kindex show sevenbit-strings
7120 @kindex show array-max
7121 @kindex show caution
7122 @kindex show history write
7127 @c END TEXI2ROFF-KILL
7129 OLD COMMAND NEW COMMAND
7131 --------------- -------------------------------
7132 @c END TEXI2ROFF-KILL
7133 add-syms add-symbol-file
7134 delete environment unset environment
7135 info convenience show convenience
7136 info copying show copying
7137 info directories show directories
7138 info editing show commands
7139 info history show values
7140 info targets help target
7141 info values show values
7142 info version show version
7143 info warranty show warranty
7144 set/show addressprint set/show print address
7145 set/show array-max set/show print elements
7146 set/show arrayprint set/show print array
7147 set/show asm-demangle set/show print asm-demangle
7148 set/show caution set/show confirm
7149 set/show demangle set/show print demangle
7150 set/show history write set/show history save
7151 set/show prettyprint set/show print pretty
7152 set/show screen-height set/show height
7153 set/show screen-width set/show width
7154 set/show sevenbit-strings set/show print sevenbit-strings
7155 set/show unionprint set/show print union
7156 set/show vtblprint set/show print vtbl
7158 unset [No longer an alias for delete]
7164 \vskip \parskip\vskip \baselineskip
7165 \halign{\tt #\hfil &\qquad#&\tt #\hfil\cr
7166 {\bf Old Command} &&{\bf New Command}\cr
7167 add-syms &&add-symbol-file\cr
7168 delete environment &&unset environment\cr
7169 info convenience &&show convenience\cr
7170 info copying &&show copying\cr
7171 info directories &&show directories \cr
7172 info editing &&show commands\cr
7173 info history &&show values\cr
7174 info targets &&help target\cr
7175 info values &&show values\cr
7176 info version &&show version\cr
7177 info warranty &&show warranty\cr
7178 set{\rm / }show addressprint &&set{\rm / }show print address\cr
7179 set{\rm / }show array-max &&set{\rm / }show print elements\cr
7180 set{\rm / }show arrayprint &&set{\rm / }show print array\cr
7181 set{\rm / }show asm-demangle &&set{\rm / }show print asm-demangle\cr
7182 set{\rm / }show caution &&set{\rm / }show confirm\cr
7183 set{\rm / }show demangle &&set{\rm / }show print demangle\cr
7184 set{\rm / }show history write &&set{\rm / }show history save\cr
7185 set{\rm / }show prettyprint &&set{\rm / }show print pretty\cr
7186 set{\rm / }show screen-height &&set{\rm / }show height\cr
7187 set{\rm / }show screen-width &&set{\rm / }show width\cr
7188 set{\rm / }show sevenbit-strings &&set{\rm / }show print sevenbit-strings\cr
7189 set{\rm / }show unionprint &&set{\rm / }show print union\cr
7190 set{\rm / }show vtblprint &&set{\rm / }show print vtbl\cr
7192 unset &&\rm(No longer an alias for delete)\cr
7195 @c END TEXI2ROFF-KILL
7197 @node Installing _GDBN__, Copying, Renamed Commands, Top
7198 @appendix Installing _GDBN__
7199 @cindex configuring _GDBN__
7200 @cindex installation
7203 @c irrelevant in info file; it's as current as the code it lives with.
7205 @emph{Warning:} These installation instructions are current as of
7206 _GDBN__ version _GDB_VN__. If you're installing a more recent release
7207 of _GDBN__, we may have improved the installation procedures since
7208 printing this manual; see the @file{README} file included in your
7209 release for the most recent instructions.
7213 _GDBN__ comes with a @code{configure} script that automates the process
7214 of preparing _GDBN__ for installation; you can then use @code{make} to
7215 build the @code{_GDBP__} program.
7217 The _GDBN__ distribution includes all the source code you need for _GDBN__ in
7218 a single directory, whose name is usually composed by appending the
7219 version number to @samp{gdb}.
7221 For example, the _GDBN__ version _GDB_VN__ distribution is in the @file{gdb-_GDB_VN__}
7222 directory. That directory contains:
7225 @item gdb-_GDB_VN__/configure @r{(and supporting files)}
7226 script for configuring _GDBN__ and all its supporting libraries.
7228 @item gdb-_GDB_VN__/gdb
7229 the source specific to _GDBN__ itself
7231 @item gdb-_GDB_VN__/bfd
7232 source for the Binary File Descriptor Library
7234 @item gdb-_GDB_VN__/include
7237 @item gdb-_GDB_VN__/libiberty
7238 source for the @samp{-liberty} free software library
7240 @item gdb-_GDB_VN__/readline
7241 source for the GNU command-line interface
7244 The simplest way to configure and build _GDBN__ is to run @code{configure}
7245 from the @file{gdb-@var{version-number}} source directory, which in
7246 this example is the @file{gdb-_GDB_VN__} directory.
7248 First switch to the @file{gdb-@var{version-number}} source directory
7249 if you are not already in it; then run @code{configure}. Pass the
7250 identifier for the platform on which _GDBN__ will run as an
7257 ./configure @var{host}
7262 where @var{host} is an identifier such as @samp{sun4} or
7263 @samp{decstation}, that identifies the platform where _GDBN__ will run.
7265 This @code{configure} command builds the three libraries @file{bfd},
7266 @file{readline}, and @file{libiberty}, then @code{gdb} itself. The
7267 configured source files, and the binaries, are left in the
7268 corresponding source directories.
7270 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
7271 system does not recognize this automatically when you run a different
7272 shell, you may need to run @code{sh} on it explicitly:
7275 sh configure @var{host}
7278 If you run @code{configure} from a directory that contains source
7279 directories for multiple libraries or programs, such as the
7280 @file{gdb-_GDB_VN__} source directory for version _GDB_VN__, @code{configure}
7281 creates configuration files for every directory level underneath (unless
7282 you tell it not to, with th @samp{--norecursion} option).
7284 You can run the @code{configure} script from any of the
7285 subordinate directories in the _GDBN__ distribution, if you only want to
7286 configure that subdirectory; but be sure to specify a path to it.
7288 For example, with version _GDB_VN__, type the following to configure only
7289 the @code{bfd} subdirectory:
7293 cd gdb-_GDB_VN__/bfd
7294 ../configure @var{host}
7298 You can install @code{_GDBP__} anywhere; it has no hardwired paths.
7299 However, you should make sure that the shell on your path (named by
7300 the @samp{SHELL} environment variable) is publicly readable. Remember
7301 that _GDBN__ uses the shell to start your program---some systems refuse to
7302 let _GDBN__ debug child processes whose programs are not readable.
7305 * Separate Objdir:: Compiling _GDBN__ in another directory
7306 * Config Names:: Specifying names for hosts and targets
7307 * configure Options:: Summary of options for configure
7308 * Formatting Documentation:: How to format and print _GDBN__ documentation
7311 @node Separate Objdir, Config Names, Installing _GDBN__, Installing _GDBN__
7312 @section Compiling _GDBN__ in Another Directory
7314 If you want to run _GDBN__ versions for several host or target machines,
7315 you'll need a different @code{_GDBP__} compiled for each combination of
7316 host and target. @code{configure} is designed to make this easy by
7317 allowing you to generate each configuration in a separate subdirectory,
7318 rather than in the source directory. If your @code{make} program
7319 handles the @samp{VPATH} feature (GNU @code{make} does), running
7320 @code{make} in each of these directories then builds the @code{_GDBP__}
7321 program specified there.
7323 To build @code{_GDBP__} in a separate directory, run @code{configure}
7324 with the @samp{--srcdir} option to specify where to find the source.
7325 (Remember, you'll also need to specify a path to find @code{configure}
7326 itself from your working directory.)
7328 For example, with version _GDB_VN__, you can build _GDBN__ in a separate
7329 directory for a Sun 4 like this:
7336 ../gdb-_GDB_VN__/configure --srcdir=../gdb-_GDB_VN__ sun4
7341 When @code{configure} builds a configuration using a remote source
7342 directory, it creates a tree for the binaries with the same structure
7343 (and using the same names) as the tree under the source directory. In
7344 the example, you'd find the Sun 4 library @file{libiberty.a} in the
7345 directory @file{gdb-sun4/libiberty}, and _GDBN__ itself in
7346 @file{gdb-sun4/gdb}.
7348 One popular use for building several _GDBN__ configurations in separate
7349 directories is to configure _GDBN__ for cross-compiling (where _GDBN__
7350 runs on one machine---the host---while debugging programs that run on
7351 another machine---the target). You specify a cross-debugging target by
7352 giving the @samp{--target=@var{target}} option to @code{configure}.
7354 When you run @code{make} to build a program or library, you must run
7355 it in a configured directory---whatever directory you were in when you
7356 called @code{configure} (or one of its subdirectories).
7358 The @code{Makefile} generated by @code{configure} for each source
7359 directory also runs recursively. If you type @code{make} in a source
7360 directory such as @file{gdb-_GDB_VN__} (or in a separate configured
7361 directory configured with @samp{--srcdir=@var{path}/gdb-_GDB_VN__}), you
7362 will build all the required libraries, then build _GDBN__.
7364 When you have multiple hosts or targets configured in separate
7365 directories, you can run @code{make} on them in parallel (for example,
7366 if they are NFS-mounted on each of the hosts); they will not interfere
7369 @node Config Names, configure Options, Separate Objdir, Installing _GDBN__
7370 @section Specifying Names for Hosts and Targets
7372 The specifications used for hosts and targets in the @code{configure}
7373 script are based on a three-part naming scheme, but some short predefined
7374 aliases are also supported. The full naming scheme encodes three pieces
7375 of information in the following pattern:
7378 @var{architecture}-@var{vendor}-@var{os}
7381 For example, you can use the alias @code{sun4} as a @var{host} argument
7382 or in a @code{+target=@var{target}} option, but the equivalent full name
7383 is @samp{sparc-sun-sunos4}.
7385 The following table shows all the architectures, hosts, and OS
7386 prefixes that @code{configure} recognizes in _GDBN__ version _GDB_VN__. Entries
7387 in the ``OS prefix'' column ending in a @samp{*} may be followed by a
7390 @c FIXME! Update for gdb 4.4
7393 @c END TEXI2ROFF-KILL
7396 ARCHITECTURE VENDOR OS prefix
7398 ------------+--------------------------+---------------------------
7399 @c END TEXI2ROFF-KILL
7401 580 | altos hp | aix* msdos*
7402 a29k | amd ibm | amigados newsos*
7403 alliant | amdahl intel | aout nindy*
7404 arm | aout isi | bout osf*
7405 c1 | apollo little | bsd* sco*
7406 c2 | att mips | coff sunos*
7407 cray2 | bcs motorola | ctix* svr4
7408 h8300 | bout ncr | dgux* sym*
7409 i386 | bull next | dynix* sysv*
7410 i860 | cbm nyu | ebmon ultrix*
7411 i960 | coff sco | esix* unicos*
7412 m68000 | convergent sequent | hds unos*
7413 m68k | convex sgi | hpux* uts
7414 m88k | cray sony | irix* v88r*
7415 mips | dec sun | isc* vms*
7416 ns32k | encore unicom | kern vxworks*
7417 pyramid | gould utek | mach*
7418 romp | hitachi wrs |
7432 \vskip \baselineskip
7433 \hfil\vbox{\offinterlineskip
7434 \halign{\strut\tt #\hfil\ &\vrule#&\strut\ \tt #\hfil\ &\strut\ \tt #\hfil
7435 \ &\vrule#&\strut\ \tt #\hfil\ &\strut\ \tt #\hfil \cr
7436 {\bf Architecture} &&{\bf Vendor} &&&{\bf OS prefix}\cr
7437 \multispan7\hrulefill\cr
7438 580 && altos & hp && aix* & msdos* \cr
7439 a29k && amd & ibm && amigados & newsos* \cr
7440 alliant && amdahl & intel && aout & nindy* \cr
7441 arm && aout & isi && bout & osf* \cr
7442 c1 && apollo & little && bsd* & sco* \cr
7443 c2 && att & mips && coff & sunos* \cr
7444 cray2 && bcs & motorola && ctix* & svr4 \cr
7445 h8300 && bout & ncr && dgux* & sym* \cr
7446 i386 && bull & next && dynix* & sysv* \cr
7447 i860 && cbm & nyu && ebmon & ultrix* \cr
7448 i960 && coff & sco && esix* & unicos* \cr
7449 m68000 && convergent& sequent && hds & unos* \cr
7450 m68k && convex & sgi && hpux* & uts \cr
7451 m88k && cray & sony && irix* & v88r* \cr
7452 mips && dec & sun && isc* & vms* \cr
7453 ns32k && encore & unicom && kern & vxworks* \cr
7454 pyramid && gould & utek && mach* & \cr
7455 romp && hitachi & wrs && & \cr
7456 rs6000 && & && & \cr
7465 @c END TEXI2ROFF-KILL
7468 @emph{Warning:} @code{configure} can represent a very large number of
7469 combinations of architecture, vendor, and OS. There is by no means
7470 support available for all possible combinations!
7473 The @code{configure} script accompanying _GDBN__ does not provide
7474 any query facility to list all supported host and target names or
7475 aliases. @code{configure} calls the Bourne shell script
7476 @code{config.sub} to map abbreviations to full names; you can read the
7477 script, if you wish, or you can use it to test your guesses on
7478 abbreviations---for example:
7481 % sh config.sub sun4
7483 % sh config.sub sun3
7485 % sh config.sub decstation
7487 % sh config.sub hp300bsd
7489 % sh config.sub i386v
7491 % sh config.sub i486v
7492 *** Configuration "i486v" not recognized
7496 @code{config.sub} is also distributed in the GDB source
7497 directory (@file{gdb-_GDB_VN__}, for version _GDB_VN__).
7499 @node configure Options, Formatting Documentation, Config Names, Installing _GDBN__
7500 @section @code{configure} Options
7502 Here is a summary of all the @code{configure} options and arguments that
7503 you might use for building _GDBN__:
7506 configure @r{[}--destdir=@var{dir}@r{]} @r{[}--srcdir=@var{path}@r{]}
7507 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
7508 @r{[}--target=@var{target}@r{]} @var{host}
7512 You may introduce options with a single @samp{-} rather than
7513 @samp{--} if you prefer; but you may abbreviate option names if you use
7517 @item --destdir=@var{dir}
7518 @var{dir} is an installation directory @emph{path prefix}. After you
7519 configure with this option, @code{make install} will install _GDBN__ as
7520 @file{@var{dir}/bin/_GDBP__}, and the libraries in @file{@var{dir}/lib}.
7521 If you specify @samp{--destdir=/usr/local}, for example, @code{make
7522 install} creates @file{/usr/local/bin/gdb}.
7524 @item --srcdir=@var{path}
7525 Use this option to make configurations in directories separate from the
7526 _GDBN__ source directories. Among other things, you can use this to
7527 build (or maintain) several configurations simultaneously, in separate
7528 directories. @code{configure} writes configuration specific files in
7529 the current directory, but arranges for them to use the source in the
7530 directory @var{path}. @code{configure} will create directories under
7531 the working directory in parallel to the source directories below
7535 Configure only the directory level where @code{configure} is executed; do not
7536 propagate configuration to subdirectories.
7539 Remove the configuration that the other arguments specify.
7541 @c This does not work (yet if ever). FIXME.
7542 @c @item --parse=@var{lang} @dots{}
7543 @c Configure the _GDBN__ expression parser to parse the listed languages.
7544 @c @samp{all} configures _GDBN__ for all supported languages. To get a
7545 @c list of all supported languages, omit the argument. Without this
7546 @c option, _GDBN__ is configured to parse all supported languages.
7548 @item --target=@var{target}
7549 Configure _GDBN__ for cross-debugging programs running on the specified
7550 @var{target}. Without this option, _GDBN__ is configured to debug
7551 programs that run on the same machine (@var{host}) as _GDBN__ itself.
7553 There is no convenient way to generate a list of all available targets.
7555 @item @var{host} @dots{}
7556 Configure _GDBN__ to run on the specified @var{host}.
7558 There is no convenient way to generate a list of all available hosts.
7562 @code{configure} accepts other options, for compatibility with
7563 configuring other GNU tools recursively; but these are the only
7564 options that affect _GDBN__ or its supporting libraries.
7566 @node Formatting Documentation, , configure Options, Installing _GDBN__
7567 @section Formatting the Documentation
7569 All the documentation for _GDBN__, including this manual, comes as part of
7570 the distribution. The documentation is written in Texinfo format,
7571 which is a documentation system that uses a single source file to
7572 produce both on-line information and a printed manual. You can use
7573 one of the Info formatting commands to create the on-line version of
7574 the documentation and @TeX{} (or @code{texi2roff}) to typeset the
7577 _GDBN__ includes an already formatted copy of the on-line Info version of
7578 this manual in the @file{gdb} subdirectory. The main Info file is
7579 @file{gdb-@var{version-number}/gdb/gdb.info}, and it refers to
7580 subordinate files matching @samp{gdb.info*} in the same directory.
7582 If you want to format these Info files yourself, you need one of the
7583 Info formatting programs, such as @code{texinfo-format-buffer} or
7586 If you have @code{makeinfo} installed, and are in the top level _GDBN__
7587 source directory (@file{gdb-_GDB_VN__}, in the case of version _GDB_VN__), you can
7588 make the Info file by typing:
7595 If you want to typeset and print copies of this manual, you need
7596 @TeX{}, a printing program such as @code{lpr}, and @file{texinfo.tex},
7597 the Texinfo definitions file.
7599 @TeX{} is typesetting program; it does not print files directly, but
7600 produces output files called @sc{dvi} files. To print a typeset
7601 document, you need a program to print @sc{dvi} files. If your system
7602 has @TeX{} installed, chances are it has such a program. The precise
7603 command to use depends on your system; @kbd{lpr -d} is common; another
7604 is @kbd{dvips}. The @sc{dvi} print command may require a file name
7605 without any extension or a @samp{.dvi} extension.
7607 @TeX{} also requires a macro definitions file called
7608 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
7609 written in Texinfo format. On its own, @TeX{} cannot read, much less
7610 typeset a Texinfo file. @file{texinfo.tex} is distributed with _GDBN__
7611 and is located in the @file{gdb-@var{version-number}/texinfo}
7614 If you have @TeX{} and a @sc{dvi} printer program installed, you can
7615 typeset and print this manual. First switch to the the @file{gdb}
7616 subdirectory of the main source directory (for example, to
7617 @file{gdb-_GDB_VN__/gdb}) and then type:
7623 @cindex _GDBN__ reference card
7624 @cindex reference card
7625 In addition to the manual, the _GDBN__ 4 release includes a three-column
7626 reference card. Format the _GDBN__ reference card by typing:
7632 The _GDBN__ reference card is designed to print in landscape mode on US
7633 ``letter'' size paper; that is, on a sheet 11 inches wide by 8.5 inches
7634 high. You will need to specify this form of printing as an option to
7635 your @sc{dvi} output program.
7637 The GDB 4 release includes an already-formatted reference card, ready
7638 for printing on a PostScript or GhostScript printer, in the @file{gdb}
7639 subdirectory of the main source directory---in
7640 @file{gdb-4.2/gdb/refcard.ps} of the version 4.2 release. If you have
7641 a PostScript or GhostScript printer, you can print the reference card
7642 by just sending @file{refcard.ps} to the printer.
7644 @node Copying, Index, Installing _GDBN__, Top
7645 @unnumbered GNU GENERAL PUBLIC LICENSE
7646 @center Version 2, June 1991
7649 Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc.
7650 675 Mass Ave, Cambridge, MA 02139, USA
7652 Everyone is permitted to copy and distribute verbatim copies
7653 of this license document, but changing it is not allowed.
7656 @unnumberedsec Preamble
7658 The licenses for most software are designed to take away your
7659 freedom to share and change it. By contrast, the GNU General Public
7660 License is intended to guarantee your freedom to share and change free
7661 software---to make sure the software is free for all its users. This
7662 General Public License applies to most of the Free Software
7663 Foundation's software and to any other program whose authors commit to
7664 using it. (Some other Free Software Foundation software is covered by
7665 the GNU Library General Public License instead.) You can apply it to
7668 When we speak of free software, we are referring to freedom, not
7669 price. Our General Public Licenses are designed to make sure that you
7670 have the freedom to distribute copies of free software (and charge for
7671 this service if you wish), that you receive source code or can get it
7672 if you want it, that you can change the software or use pieces of it
7673 in new free programs; and that you know you can do these things.
7675 To protect your rights, we need to make restrictions that forbid
7676 anyone to deny you these rights or to ask you to surrender the rights.
7677 These restrictions translate to certain responsibilities for you if you
7678 distribute copies of the software, or if you modify it.
7680 For example, if you distribute copies of such a program, whether
7681 gratis or for a fee, you must give the recipients all the rights that
7682 you have. You must make sure that they, too, receive or can get the
7683 source code. And you must show them these terms so they know their
7686 We protect your rights with two steps: (1) copyright the software, and
7687 (2) offer you this license which gives you legal permission to copy,
7688 distribute and/or modify the software.
7690 Also, for each author's protection and ours, we want to make certain
7691 that everyone understands that there is no warranty for this free
7692 software. If the software is modified by someone else and passed on, we
7693 want its recipients to know that what they have is not the original, so
7694 that any problems introduced by others will not reflect on the original
7695 authors' reputations.
7697 Finally, any free program is threatened constantly by software
7698 patents. We wish to avoid the danger that redistributors of a free
7699 program will individually obtain patent licenses, in effect making the
7700 program proprietary. To prevent this, we have made it clear that any
7701 patent must be licensed for everyone's free use or not licensed at all.
7703 The precise terms and conditions for copying, distribution and
7704 modification follow.
7707 @unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
7710 @center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
7715 This License applies to any program or other work which contains
7716 a notice placed by the copyright holder saying it may be distributed
7717 under the terms of this General Public License. The ``Program'', below,
7718 refers to any such program or work, and a ``work based on the Program''
7719 means either the Program or any derivative work under copyright law:
7720 that is to say, a work containing the Program or a portion of it,
7721 either verbatim or with modifications and/or translated into another
7722 language. (Hereinafter, translation is included without limitation in
7723 the term ``modification''.) Each licensee is addressed as ``you''.
7725 Activities other than copying, distribution and modification are not
7726 covered by this License; they are outside its scope. The act of
7727 running the Program is not restricted, and the output from the Program
7728 is covered only if its contents constitute a work based on the
7729 Program (independent of having been made by running the Program).
7730 Whether that is true depends on what the Program does.
7733 You may copy and distribute verbatim copies of the Program's
7734 source code as you receive it, in any medium, provided that you
7735 conspicuously and appropriately publish on each copy an appropriate
7736 copyright notice and disclaimer of warranty; keep intact all the
7737 notices that refer to this License and to the absence of any warranty;
7738 and give any other recipients of the Program a copy of this License
7739 along with the Program.
7741 You may charge a fee for the physical act of transferring a copy, and
7742 you may at your option offer warranty protection in exchange for a fee.
7745 You may modify your copy or copies of the Program or any portion
7746 of it, thus forming a work based on the Program, and copy and
7747 distribute such modifications or work under the terms of Section 1
7748 above, provided that you also meet all of these conditions:
7752 You must cause the modified files to carry prominent notices
7753 stating that you changed the files and the date of any change.
7756 You must cause any work that you distribute or publish, that in
7757 whole or in part contains or is derived from the Program or any
7758 part thereof, to be licensed as a whole at no charge to all third
7759 parties under the terms of this License.
7762 If the modified program normally reads commands interactively
7763 when run, you must cause it, when started running for such
7764 interactive use in the most ordinary way, to print or display an
7765 announcement including an appropriate copyright notice and a
7766 notice that there is no warranty (or else, saying that you provide
7767 a warranty) and that users may redistribute the program under
7768 these conditions, and telling the user how to view a copy of this
7769 License. (Exception: if the Program itself is interactive but
7770 does not normally print such an announcement, your work based on
7771 the Program is not required to print an announcement.)
7774 These requirements apply to the modified work as a whole. If
7775 identifiable sections of that work are not derived from the Program,
7776 and can be reasonably considered independent and separate works in
7777 themselves, then this License, and its terms, do not apply to those
7778 sections when you distribute them as separate works. But when you
7779 distribute the same sections as part of a whole which is a work based
7780 on the Program, the distribution of the whole must be on the terms of
7781 this License, whose permissions for other licensees extend to the
7782 entire whole, and thus to each and every part regardless of who wrote it.
7784 Thus, it is not the intent of this section to claim rights or contest
7785 your rights to work written entirely by you; rather, the intent is to
7786 exercise the right to control the distribution of derivative or
7787 collective works based on the Program.
7789 In addition, mere aggregation of another work not based on the Program
7790 with the Program (or with a work based on the Program) on a volume of
7791 a storage or distribution medium does not bring the other work under
7792 the scope of this License.
7795 You may copy and distribute the Program (or a work based on it,
7796 under Section 2) in object code or executable form under the terms of
7797 Sections 1 and 2 above provided that you also do one of the following:
7801 Accompany it with the complete corresponding machine-readable
7802 source code, which must be distributed under the terms of Sections
7803 1 and 2 above on a medium customarily used for software interchange; or,
7806 Accompany it with a written offer, valid for at least three
7807 years, to give any third party, for a charge no more than your
7808 cost of physically performing source distribution, a complete
7809 machine-readable copy of the corresponding source code, to be
7810 distributed under the terms of Sections 1 and 2 above on a medium
7811 customarily used for software interchange; or,
7814 Accompany it with the information you received as to the offer
7815 to distribute corresponding source code. (This alternative is
7816 allowed only for noncommercial distribution and only if you
7817 received the program in object code or executable form with such
7818 an offer, in accord with Subsection b above.)
7821 The source code for a work means the preferred form of the work for
7822 making modifications to it. For an executable work, complete source
7823 code means all the source code for all modules it contains, plus any
7824 associated interface definition files, plus the scripts used to
7825 control compilation and installation of the executable. However, as a
7826 special exception, the source code distributed need not include
7827 anything that is normally distributed (in either source or binary
7828 form) with the major components (compiler, kernel, and so on) of the
7829 operating system on which the executable runs, unless that component
7830 itself accompanies the executable.
7832 If distribution of executable or object code is made by offering
7833 access to copy from a designated place, then offering equivalent
7834 access to copy the source code from the same place counts as
7835 distribution of the source code, even though third parties are not
7836 compelled to copy the source along with the object code.
7839 You may not copy, modify, sublicense, or distribute the Program
7840 except as expressly provided under this License. Any attempt
7841 otherwise to copy, modify, sublicense or distribute the Program is
7842 void, and will automatically terminate your rights under this License.
7843 However, parties who have received copies, or rights, from you under
7844 this License will not have their licenses terminated so long as such
7845 parties remain in full compliance.
7848 You are not required to accept this License, since you have not
7849 signed it. However, nothing else grants you permission to modify or
7850 distribute the Program or its derivative works. These actions are
7851 prohibited by law if you do not accept this License. Therefore, by
7852 modifying or distributing the Program (or any work based on the
7853 Program), you indicate your acceptance of this License to do so, and
7854 all its terms and conditions for copying, distributing or modifying
7855 the Program or works based on it.
7858 Each time you redistribute the Program (or any work based on the
7859 Program), the recipient automatically receives a license from the
7860 original licensor to copy, distribute or modify the Program subject to
7861 these terms and conditions. You may not impose any further
7862 restrictions on the recipients' exercise of the rights granted herein.
7863 You are not responsible for enforcing compliance by third parties to
7867 If, as a consequence of a court judgment or allegation of patent
7868 infringement or for any other reason (not limited to patent issues),
7869 conditions are imposed on you (whether by court order, agreement or
7870 otherwise) that contradict the conditions of this License, they do not
7871 excuse you from the conditions of this License. If you cannot
7872 distribute so as to satisfy simultaneously your obligations under this
7873 License and any other pertinent obligations, then as a consequence you
7874 may not distribute the Program at all. For example, if a patent
7875 license would not permit royalty-free redistribution of the Program by
7876 all those who receive copies directly or indirectly through you, then
7877 the only way you could satisfy both it and this License would be to
7878 refrain entirely from distribution of the Program.
7880 If any portion of this section is held invalid or unenforceable under
7881 any particular circumstance, the balance of the section is intended to
7882 apply and the section as a whole is intended to apply in other
7885 It is not the purpose of this section to induce you to infringe any
7886 patents or other property right claims or to contest validity of any
7887 such claims; this section has the sole purpose of protecting the
7888 integrity of the free software distribution system, which is
7889 implemented by public license practices. Many people have made
7890 generous contributions to the wide range of software distributed
7891 through that system in reliance on consistent application of that
7892 system; it is up to the author/donor to decide if he or she is willing
7893 to distribute software through any other system and a licensee cannot
7896 This section is intended to make thoroughly clear what is believed to
7897 be a consequence of the rest of this License.
7900 If the distribution and/or use of the Program is restricted in
7901 certain countries either by patents or by copyrighted interfaces, the
7902 original copyright holder who places the Program under this License
7903 may add an explicit geographical distribution limitation excluding
7904 those countries, so that distribution is permitted only in or among
7905 countries not thus excluded. In such case, this License incorporates
7906 the limitation as if written in the body of this License.
7909 The Free Software Foundation may publish revised and/or new versions
7910 of the General Public License from time to time. Such new versions will
7911 be similar in spirit to the present version, but may differ in detail to
7912 address new problems or concerns.
7914 Each version is given a distinguishing version number. If the Program
7915 specifies a version number of this License which applies to it and ``any
7916 later version'', you have the option of following the terms and conditions
7917 either of that version or of any later version published by the Free
7918 Software Foundation. If the Program does not specify a version number of
7919 this License, you may choose any version ever published by the Free Software
7923 If you wish to incorporate parts of the Program into other free
7924 programs whose distribution conditions are different, write to the author
7925 to ask for permission. For software which is copyrighted by the Free
7926 Software Foundation, write to the Free Software Foundation; we sometimes
7927 make exceptions for this. Our decision will be guided by the two goals
7928 of preserving the free status of all derivatives of our free software and
7929 of promoting the sharing and reuse of software generally.
7932 @heading NO WARRANTY
7939 BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
7940 FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN
7941 OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
7942 PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
7943 OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
7944 MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS
7945 TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE
7946 PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
7947 REPAIR OR CORRECTION.
7950 IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
7951 WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
7952 REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
7953 INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
7954 OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
7955 TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
7956 YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
7957 PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
7958 POSSIBILITY OF SUCH DAMAGES.
7962 @heading END OF TERMS AND CONDITIONS
7965 @center END OF TERMS AND CONDITIONS
7969 @unnumberedsec Applying These Terms to Your New Programs
7971 If you develop a new program, and you want it to be of the greatest
7972 possible use to the public, the best way to achieve this is to make it
7973 free software which everyone can redistribute and change under these terms.
7975 To do so, attach the following notices to the program. It is safest
7976 to attach them to the start of each source file to most effectively
7977 convey the exclusion of warranty; and each file should have at least
7978 the ``copyright'' line and a pointer to where the full notice is found.
7981 @var{one line to give the program's name and an idea of what it does.}
7982 Copyright (C) 19@var{yy} @var{name of author}
7984 This program is free software; you can redistribute it and/or
7985 modify it under the terms of the GNU General Public License
7986 as published by the Free Software Foundation; either version 2
7987 of the License, or (at your option) any later version.
7989 This program is distributed in the hope that it will be useful,
7990 but WITHOUT ANY WARRANTY; without even the implied warranty of
7991 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
7992 GNU General Public License for more details.
7994 You should have received a copy of the GNU General Public License
7995 along with this program; if not, write to the
7996 Free Software Foundation, Inc., 675 Mass Ave,
7997 Cambridge, MA 02139, USA.
8000 Also add information on how to contact you by electronic and paper mail.
8002 If the program is interactive, make it output a short notice like this
8003 when it starts in an interactive mode:
8006 Gnomovision version 69, Copyright (C) 19@var{yy} @var{name of author}
8007 Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
8008 type `show w'. This is free software, and you are welcome
8009 to redistribute it under certain conditions; type `show c'
8013 The hypothetical commands @samp{show w} and @samp{show c} should show
8014 the appropriate parts of the General Public License. Of course, the
8015 commands you use may be called something other than @samp{show w} and
8016 @samp{show c}; they could even be mouse-clicks or menu items---whatever
8019 You should also get your employer (if you work as a programmer) or your
8020 school, if any, to sign a ``copyright disclaimer'' for the program, if
8021 necessary. Here is a sample; alter the names:
8024 Yoyodyne, Inc., hereby disclaims all copyright
8025 interest in the program `Gnomovision'
8026 (which makes passes at compilers) written
8029 @var{signature of Ty Coon}, 1 April 1989
8030 Ty Coon, President of Vice
8033 This General Public License does not permit incorporating your program into
8034 proprietary programs. If your program is a subroutine library, you may
8035 consider it more useful to permit linking proprietary applications with the
8036 library. If this is what you want to do, use the GNU Library General
8037 Public License instead of this License.
8039 @node Index, , Copying, Top
8045 % I think something like @colophon should be in texinfo. In the
8047 \long\def\colophon{\hbox to0pt{}\vfill
8048 \centerline{The body of this manual is set in}
8049 \centerline{\fontname\tenrm,}
8050 \centerline{with headings in {\bf\fontname\tenbf}}
8051 \centerline{and examples in {\tt\fontname\tentt}.}
8052 \centerline{{\it\fontname\tenit\/},}
8053 \centerline{{\bf\fontname\tenbf}, and}
8054 \centerline{{\sl\fontname\tensl\/}}
8055 \centerline{are used for emphasis.}\vfill}
8057 % Blame: pesch@cygnus.com, 1991.