_dnl__ -*-Texinfo-*- _dnl__ Copyright (c) 1988 1989 1990 1991 Free Software Foundation, Inc. \input texinfo @setfilename _GDBP__.info @c $Id$ @c THIS MANUAL REQUIRES TEXINFO-2 macros and info-makers to format properly. @c @c NOTE: this manual is marked up for preprocessing with a collection @c of m4 macros called "pretex.m4". If you see <_if__> and <_fi__> @c scattered around the source, you have the full source before @c preprocessing; if you don't, you have the source configured for @c _HOST__ architectures (and you can of course get the full source, @c with all configurations, from wherever you got this). _if__(0) THIS IS THE SOURCE PRIOR TO PREPROCESSING. The full source needs to be run through m4 before either tex- or info- formatting: for example, _0__ m4 pretex.m4 none.m4 all.m4 gdb.texinfo >gdb-all.texinfo _1__ will produce (assuming your path finds either GNU m4 >= 0.84, or SysV m4; Berkeley won't do) a file suitable for formatting. See the text in "pretex.m4" for a fuller explanation (and the macro definitions). _fi__(0) _include__(gdbVN.m4) @tex \def\$#1${{#1}} % Kluge: collect RCS revision info without $...$ \xdef\manvers{\$Revision$} % For use in headers, footers too @end tex @c @syncodeindex ky cp @c FOR UPDATES LEADING TO THIS DRAFT, GDB CHANGELOG CONSULTED BETWEEN: @c Fri Sep 20 16:10:52 1991 John Gilmore (gnu at cygnus.com) @c Sat Dec 22 02:51:40 1990 John Gilmore (gnu at cygint) @ifinfo This file documents the GNU debugger _GDBN__. Copyright (C) 1988, 1989, 1990, 1991 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. @ignore Permission is granted to process this file through TeX and print the results, provided the printed document carries copying permission notice identical to this one except for the removal of this paragraph (this paragraph not being relevant to the printed manual). @end ignore Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled ``GNU General Public License'' is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled ``GNU General Public License'' may be included in a translation approved by the Free Software Foundation instead of in the original English. @end ifinfo @c @smallbook @setchapternewpage odd _if__(_GENERIC__) @settitle Using _GDBN__ (_GDB_VN__) _fi__(_GENERIC__) _if__(!_GENERIC__) @settitle Using _GDBN__ _GDB_VN__ (_HOST__) _fi__(!_GENERIC__) @iftex @finalout @end iftex @titlepage @title{Using _GDBN__} @subtitle{A Guide to the GNU Source-Level Debugger} _if__(!_GENERIC__) @subtitle{On _HOST__ Systems} _fi__(!_GENERIC__) @sp 1 @c Maybe crank this up to "Fourth Edition" when released at FSF @c @subtitle Third Edition---_GDBN__ version _GDB_VN__ @subtitle _GDBN__ version _GDB_VN__ @subtitle July 1991 @author{Richard M. Stallman@qquad @hfill Free Software Foundation} @author{Roland H. Pesch@qquad @hfill Cygnus Support} @page @tex {\parskip=0pt \hfill rms\@ai.mit.edu, pesch\@cygnus.com\par \hfill {\it Using _GDBN__}, \manvers\par \hfill \TeX{}info \texinfoversion\par } @end tex @vskip 0pt plus 1filll Copyright @copyright{} 1988, 1989, 1990, 1991 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled ``GNU General Public License'' is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled ``GNU General Public License'' may be included in a translation approved by the Free Software Foundation instead of in the original English. @end titlepage @page @node Top, Summary, (dir), (dir) @ifinfo This file describes version _GDB_VN__ of GDB, the GNU symbolic debugger. @end ifinfo @menu * Summary:: Summary of _GDBN__ * New Features:: New Features in _GDBN__ version _GDB_VN__ * Sample Session:: A Sample _GDBN__ Session * Invocation:: Getting In and Out of _GDBN__ * Commands:: _GDBN__ Commands * Running:: Running Programs Under _GDBN__ * Stopping:: Stopping and Continuing * Stack:: Examining the Stack * Source:: Examining Source Files * Data:: Examining Data * Languages:: Using _GDBN__ with Different Languages * Symbols:: Examining the Symbol Table * Altering:: Altering Execution * _GDBN__ Files:: _GDBN__'s Files * Targets:: Specifying a Debugging Target * Controlling _GDBN__:: Controlling _GDBN__ * Sequences:: Canned Sequences of Commands * Emacs:: Using _GDBN__ under GNU Emacs * _GDBN__ Bugs:: Reporting Bugs in _GDBN__ * Renamed Commands:: * Installing _GDBN__:: Installing _GDBN__ * Copying:: GNU GENERAL PUBLIC LICENSE * Index:: Index --- The Detailed Node Listing --- Summary of _GDBN__ * Free Software:: Free Software * Contributors:: Contributors to _GDBN__ Getting In and Out of _GDBN__ * Starting _GDBN__:: Starting _GDBN__ * Leaving _GDBN__:: Leaving _GDBN__ * Shell Commands:: Shell Commands Starting _GDBN__ * File Options:: Choosing Files * Mode Options:: Choosing Modes _GDBN__ Commands * Command Syntax:: Command Syntax * Help:: Getting Help Running Programs Under _GDBN__ * Compilation:: Compiling for Debugging * Starting:: Starting your Program * Arguments:: Your Program's Arguments * Environment:: Your Program's Environment * Working Directory:: Your Program's Working Directory * Input/Output:: Your Program's Input and Output * Attach:: Debugging an Already-Running Process * Kill Process:: Killing the Child Process Stopping and Continuing * Breakpoints:: Breakpoints, Watchpoints, and Exceptions * Continuing and Stepping:: Resuming Execution * Signals:: Signals Breakpoints, Watchpoints, and Exceptions * Set Breaks:: Setting Breakpoints * Set Watchpoints:: Setting Watchpoints * Exception Handling:: Breakpoints and Exceptions * Delete Breaks:: Deleting Breakpoints * Disabling:: Disabling Breakpoints * Conditions:: Break Conditions * Break Commands:: Breakpoint Command Lists * Breakpoint Menus:: Breakpoint Menus * Error in Breakpoints:: ``Cannot insert breakpoints'' Examining the Stack * Frames:: Stack Frames * Backtrace:: Backtraces * Selection:: Selecting a Frame * Frame Info:: Information on a Frame Examining Source Files * List:: Printing Source Lines * Search:: Searching Source Files * Source Path:: Specifying Source Directories * Machine Code:: Source and Machine Code Examining Data * Expressions:: Expressions * Variables:: Program Variables * Arrays:: Artificial Arrays * Output formats:: Output formats * Memory:: Examining Memory * Auto Display:: Automatic Display * Print Settings:: Print Settings * Value History:: Value History * Convenience Vars:: Convenience Variables * Registers:: Registers * Floating Point Hardware:: Floating Point Hardware Using GDB with Different Languages * Setting:: Switching between source languages * Show:: Displaying the language * Checks:: Type and Range checks * Support:: Supported languages Switching between source languages * Manually:: Setting the working language manually * Automatically:: Having GDB infer the source language Type and range Checking * Type Checking:: An overview of type checking * Range Checking:: An overview of range checking Supported Languages * C:: C and C++ * Modula-2:: Modula-2 C and C++ * C Operators:: C and C++ Operators * C Constants:: C and C++ Constants * Cplusplus expressions:: C++ Expressions * C Defaults:: Default settings for C and C++ * C Checks:: C and C++ Type and Range Checks * Debugging C:: _GDBN__ and C * Debugging C plus plus:: Special features for C++ Modula-2 * M2 Operators:: Built-in operators * Builtin Func/Proc:: Built-in Functions and Procedures * M2 Constants:: Modula-2 Constants * M2 Defaults:: Default settings for Modula-2 * Deviations:: Deviations from standard Modula-2 * M2 Checks:: Modula-2 Type and Range Checks * M2 Scope:: The scope operators @code{::} and @code{.} * GDB/M2:: GDB and Modula-2 Altering Execution * Assignment:: Assignment to Variables * Jumping:: Continuing at a Different Address * Signaling:: Giving the Program a Signal * Returning:: Returning from a Function * Calling:: Calling your Program's Functions * Patching:: Patching your Program _GDBN__'s Files * Files:: Commands to Specify Files * Symbol Errors:: Errors Reading Symbol Files Specifying a Debugging Target * Active Targets:: Active Targets * Target Commands:: Commands for Managing Targets * Remote:: Remote Debugging Remote Debugging * i960-Nindy Remote:: _GDBN__ with a Remote i960 (Nindy) * EB29K Remote:: _GDBN__ with a Remote EB29K * VxWorks Remote:: _GDBN__ and VxWorks _GDBN__ with a Remote i960 (Nindy) * Nindy Startup:: Startup with Nindy * Nindy Options:: Options for Nindy * Nindy reset:: Nindy Reset Command _GDBN__ with a Remote EB29K * Comms (EB29K):: Communications Setup * gdb-EB29K:: EB29K cross-debugging * Remote Log:: Remote Log _GDBN__ and VxWorks * VxWorks connection:: Connecting to VxWorks * VxWorks download:: VxWorks Download * VxWorks attach:: Running Tasks Controlling _GDBN__ * Prompt:: Prompt * Editing:: Command Editing * History:: Command History * Screen Size:: Screen Size * Numbers:: Numbers * Messages/Warnings:: Optional Warnings and Messages Canned Sequences of Commands * Define:: User-Defined Commands * Command Files:: Command Files * Output:: Commands for Controlled Output Reporting Bugs in _GDBN__ * Bug Criteria:: Have You Found a Bug? * Bug Reporting:: How to Report Bugs Installing GDB * Subdirectories:: Configuration subdirectories * Config Names:: Specifying names for hosts and targets * configure Options:: Summary of options for configure * Formatting Documentation:: How to format and print GDB documentation @end menu @node Summary, New Features, Top, Top @unnumbered Summary of _GDBN__ The purpose of a debugger such as _GDBN__ is to allow you to see what is going on ``inside'' another program while it executes---or what another program was doing at the moment it crashed. _GDBN__ can do four main kinds of things (plus other things in support of these) to help you catch bugs in the act: @itemize @bullet @item Start your program, specifying anything that might affect its behavior. @item Make your program stop on specified conditions. @item Examine what has happened, when your program has stopped. @item Change things in your program, so you can experiment with correcting the effects of one bug and go on to learn about another. @end itemize You can use _GDBN__ to debug programs written in C, C++, and Modula-2. Fortran support will be added when a GNU Fortran compiler is ready. @menu * Free Software:: Free Software * Contributors:: Contributors to GDB @end menu @node Free Software, Contributors, Summary, Summary @unnumberedsec Free Software _GDBN__ is @dfn{free software}, protected by the GNU General Public License (GPL). The GPL gives you the freedom to copy or adapt a licensed program---but every person getting a copy also gets with it the freedom to modify that copy (which means that they must get access to the source code), and the freedom to distribute further copies. Typical software companies use copyrights to limit your freedoms; the Free Software Foundation uses the GPL to preserve these freedoms. Fundamentally, the General Public License is a license which says that you have these freedoms and that you can't take these freedoms away from anyone else. @c FIXME: (passim) go through all xrefs, expanding to use text headings For full details, @pxref{Copying}. @node Contributors, , Free Software, Summary @unnumberedsec Contributors to GDB Richard Stallman was the original author of GDB, and of many other GNU programs. Many others have contributed to its development. This section attempts to credit major contributors. One of the virtues of free software is that everyone is free to contribute to it; with regret, we cannot actually acknowledge everyone here. The file @file{ChangeLog} in the GDB distribution approximates a blow-by-blow account. Changes much prior to version 2.0 are lost in the mists of time. @quotation @emph{Plea:} Additions to this section are particularly welcome. If you or your friends (or enemies; let's be evenhanded) have been unfairly omitted from this list, we would like to add your names! @end quotation So that they may not regard their long labor as thankless, we particularly thank those who shepherded GDB through major releases: John Gilmore (releases _GDB_VN__, 4.0); Jim Kingdon (releases 3.9, 3.5, 3.4, 3.3); and Randy Smith (releases 3.2, 3.1, 3.0). As major maintainer of GDB for some period, each contributed significantly to the structure, stability, and capabilities of the entire debugger. Richard Stallman, assisted at various times by Pete TerMaat, Chris Hanson, and Richard Mlynarik, handled releases through 2.8. Michael Tiemann is the author of most of the GNU C++ support in GDB, with significant additional contributions from Per Bothner. James Clark wrote the GNU C++ demangler. Early work on C++ was by Peter TerMaat (who also did much general update work leading to release 3.0). GDB _GDB_VN__ uses the BFD subroutine library to examine multiple object-file formats; BFD was a joint project of V. Gumby Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore. David Johnson wrote the original COFF support; Pace Willison did the original support for encapsulated COFF. Adam de Boor and Bradley Davis contributed the ISI Optimum V support. Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS support. Jean-Daniel Fekete contributed Sun 386i support. Chris Hanson improved the HP9000 support. Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support. David Johnson contributed Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support. Keith Packard contributed NS32K support. Doug Rabson contributed Acorn Risc Machine support. Chris Smith contributed Convex support (and Fortran debugging). Jonathan Stone contributed Pyramid support. Michael Tiemann contributed SPARC support. Tim Tucker contributed support for the Gould NP1 and Gould Powernode. Pace Willison contributed Intel 386 support. Jay Vosburgh contributed Symmetry support. Rich Schaefer and Peter Schauer helped with support of SunOS shared libraries. Jay Fenlason and Roland McGrath ensured that GDB and GAS agree about several machine instruction sets. Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop remote debugging. Intel Corporation and Wind River Systems contributed remote debugging modules for their products. Brian Fox is the author of the readline libraries providing command-line editing and command history. Andrew Beers of SUNY Buffalo wrote the language-switching code and the Modula-2 support, and contributed the Languages chapter of this manual. @node New Features, Sample Session, Summary, Top @unnumbered New Features since _GDBN__ version 3.5 @table @emph @item Targets Using the new command @code{target}, you can select at runtime whether you are debugging local files, local processes, standalone systems over a serial port, realtime systems over a TCP/IP connection, etc. The command @code{load} can download programs into a remote system. Serial stubs are available for Motorola 680x0 and Intel 80386 remote systems; _GDBN__ also supports debugging realtime processes running under VxWorks, using SunRPC Remote Procedure Calls over TCP/IP to talk to a debugger stub on the target system. Internally, _GDBN__ now uses a function vector to mediate access to different targets; if you need to add your own support for a remote protocol, this makes it much easier. @item Watchpoints _GDBN__ now sports watchpoints as well as breakpoints. You can use a watchpoint to stop execution whenever the value of an expression changes, without having to predict a particular place in your program where this may happen. @item Wide Output Commands that issue wide output now insert newlines at places designed to make the output more readable. @item Object Code Formats _GDBN__ uses a new library called the Binary File Descriptor (BFD) Library to permit it to switch dynamically, without reconfiguration or recompilation, between different object-file formats. Formats currently supported are COFF, a.out, and the Intel 960 b.out; files may be read as .o's, archive libraries, or core dumps. BFD is available as a subroutine library so that other programs may take advantage of it, and the other GNU binary utilities are being converted to use it. @item Configuration and Ports Compile-time configuration (to select a particular architecture and operating system) is much easier. The script @code{configure} now allows you to configure _GDBN__ as either a native debugger or a cross-debugger. @xref{Installing _GDBN__} for details on how to configure and on what architectures are now available. @item Interaction The user interface to _GDBN__'s control variables has been simplified and consolidated in two commands, @code{set} and @code{show}. Output lines are now broken at readable places, rather than overflowing onto the next line. You can suppress output of machine-level addresses, displaying only source language information. @item C++ _GDBN__ now supports C++ multiple inheritance (if used with a GCC version 2 compiler), and also has limited support for C++ exception handling, with the commands @code{catch} and @code{info catch}: _GDBN__ can break when an exception is raised, before the stack is peeled back to the exception handler's context. @item Modula-2 _GDBN__ now has preliminary support for the GNU Modula-2 compiler, currently under development at the State University of New York at Buffalo. Coordinated development of both _GDBN__ and the GNU Modula-2 compiler will continue through the fall of 1991 and into 1992. Other Modula-2 compilers are currently not supported, and attempting to debug programs compiled with them will likely result in an error as the symbol table of the executable is read in. @item Command Rationalization Many _GDBN__ commands have been renamed to make them easier to remember and use. In particular, the subcommands of @code{info} and @code{show}/@code{set} are grouped to make the former refer to the state of your program, and the latter refer to the state of _GDBN__ itself. @xref{Renamed Commands}, for details on what commands were renamed. @item Shared Libraries _GDBN__ _GDB_VN__ can debug programs and core files that use SunOS shared libraries. You can load symbols from a shared library with the command @code{sharedlibrary} (@pxref{Files}). @item Reference Card _GDBN__ _GDB_VN__ has a reference card; @xref{Formatting Documentation} for instructions on printing it. @item Work in Progress Kernel debugging for BSD and Mach systems; Tahoe and HPPA architecture support. @end table @node Sample Session, Invocation, New Features, Top @chapter A Sample _GDBN__ Session You can use this manual at your leisure to read all about _GDBN__. However, a handful of commands are enough to get started using the debugger. This chapter illustrates these commands. @iftex In this sample session, we emphasize user input like this: @i{input}, to make it easier to pick out from the surrounding output. @end iftex @c FIXME: this example may not be appropriate for some configs, where @c FIXME...primary interest is in remote use. _0__ One of the preliminary versions of GNU @code{m4} (a generic macro processor) exhibits the following bug: sometimes, when we change its quote strings from the default, the commands used to capture one macro's definition in another stop working. In the following short @code{m4} session, we define a macro @code{foo} which expands to @code{0000}; we then use the @code{m4} builtin @code{defn} to define @code{bar} as the same thing. However, when we change the open quote string to @code{} and the close quote string to @code{}, the same procedure fails to define a new synonym @code{baz}: @smallexample $ @i{cd gnu/m4} $ @i{./m4} @i{define(foo,0000)} @i{foo} 0000 @i{define(bar,defn(`foo'))} @i{bar} 0000 @i{changequote(,)} @i{define(baz,defn(foo))} @i{baz} @i{C-d} m4: End of input: 0: fatal error: EOF in string @end smallexample @noindent Let's use _GDBN__ to try to see what's going on. @smallexample $ @i{_GDBP__ m4} GDB is free software and you are welcome to distribute copies of it under certain conditions; type "info copying" to see the conditions. There is absolutely no warranty for GDB; type "info warranty" for details. GDB _GDB_VN__, Copyright 1991 Free Software Foundation, Inc... (_GDBP__) @end smallexample @noindent _GDBN__ reads only enough symbol data to know where to find the rest when needed; as a result, the first prompt comes up very quickly. We then tell _GDBN__ to use a narrower display width than usual, so that examples will fit in this manual. @smallexample (_GDBP__) @i{set width 70} @end smallexample @noindent Let's see how the @code{m4} builtin @code{changequote} works. Having looked at the source, we know the relevant subroutine is @code{m4_changequote}, so we set a breakpoint there with _GDBN__'s @code{break} command. @smallexample (_GDBP__) @i{break m4_changequote} Breakpoint 1 at 0x62f4: file builtin.c, line 879. @end smallexample @noindent Using the @code{run} command, we start @code{m4} running under _GDBN__ control; as long as control does not reach the @code{m4_changequote} subroutine, the program runs as usual: @smallexample (_GDBP__) @i{run} Starting program: /work/Editorial/gdb/gnu/m4/m4 @i{define(foo,0000)} @i{foo} 0000 @end smallexample @noindent To trigger the breakpoint, we call @code{changequote}. _GDBN__ suspends execution of @code{m4}, displaying information about the context where it stops. @smallexample @i{changequote(,)} Breakpoint 1, m4_changequote (argc=3, argv=0x33c70) at builtin.c:879 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]), argc, 1, 3)) @end smallexample @noindent Now we use the command @code{n} (@code{next}) to advance execution to the next line of the current function. @smallexample (_GDBP__) @i{n} 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1]) : nil, @end smallexample @noindent @code{set_quotes} looks like a promising subroutine. We can go into it by using the command @code{s} (@code{step}) instead of @code{next}. @code{step} goes to the next line to be executed in @emph{any} subroutine, so it steps into @code{set_quotes}. @smallexample (_GDBP__) @i{s} set_quotes (lq=0x34c78 "", rq=0x34c88 "") at input.c:530 530 if (lquote != def_lquote) @end smallexample @noindent The summary display showing the subroutine where @code{m4} is now suspended (and its arguments) is called a stack frame display. We can use the @code{backtrace} command (which can also be spelled @code{bt}), to see where we are in the stack: it displays a stack frame for each active subroutine. @smallexample (_GDBP__) @i{bt} #0 set_quotes (lq=0x34c78 "", rq=0x34c88 "") at input.c:530 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70) at builtin.c:882 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30) at macro.c:71 #4 0x79dc in expand_input () at macro.c:40 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195 @end smallexample @noindent Let's step through a few more lines to see what happens. The first two times, we can use @samp{s}; the next two times we use @code{n} to avoid falling into the @code{xstrdup} subroutine. @smallexample (_GDBP__) @i{s} 0x3b5c 532 if (rquote != def_rquote) (_GDBP__) @i{s} 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? def_lquote :\ xstrdup(lq); (_GDBP__) @i{n} 536 rquote = (rq == nil || *rq == '\0') ? def_rquote : xstrdup\ (rq); (_GDBP__) @i{n} 538 len_lquote = strlen(rquote); @end smallexample @noindent The last line displayed looks a little odd; let's examine the variables @code{lquote} and @code{rquote} to see if they are in fact the new left and right quotes we specified. We can use the command @code{p} (@code{print}) to see their values. @smallexample (_GDBP__) @i{p lquote} $1 = 0x35d40 "" (_GDBP__) @i{p rquote} $2 = 0x35d50 "" @end smallexample @noindent @code{lquote} and @code{rquote} are indeed the new left and right quotes. Let's look at some context; we can display ten lines of source surrounding the current line, with the @code{l} (@code{list}) command. @smallexample (_GDBP__) @i{l} 533 xfree(rquote); 534 535 lquote = (lq == nil || *lq == '\0') ? def_lquote : xstrdup\ (lq); 536 rquote = (rq == nil || *rq == '\0') ? def_rquote : xstrdup\ (rq); 537 538 len_lquote = strlen(rquote); 539 len_rquote = strlen(lquote); 540 @} 541 542 void @end smallexample @noindent Let's step past the two lines that set @code{len_lquote} and @code{len_rquote}, and then examine the values of those variables. @smallexample (_GDBP__) @i{n} 539 len_rquote = strlen(lquote); (_GDBP__) @i{n} 540 @} (_GDBP__) @i{p len_lquote} $3 = 9 (_GDBP__) @i{p len_rquote} $4 = 7 @end smallexample @noindent That certainly looks wrong, assuming @code{len_lquote} and @code{len_rquote} are meant to be the lengths of @code{lquote} and @code{rquote} respectively. Let's try setting them to better values. We can use the @code{p} command for this, since it'll print the value of any expression---and that expression can include subroutine calls and assignments. @smallexample (_GDBP__) p len_lquote=strlen(lquote) $5 = 7 (_GDBP__) p len_rquote=strlen(rquote) $6 = 9 @end smallexample @noindent Let's see if that fixes the problem of using the new quotes with the @code{m4} built-in @code{defn}. We can allow @code{m4} to continue executing with the @code{c} (@code{continue}) command, and then try the example that caused trouble initially: @smallexample (_GDBP__) @i{c} Continuing. @i{define(baz,defn(foo))} baz 0000 @end smallexample @noindent Success! The new quotes now work just as well as the default ones. The problem seems to have been just the two typos defining the wrong lengths. We'll let @code{m4} exit by giving it an EOF as input. @smallexample @i{C-d} Program exited normally. @end smallexample @noindent The message @samp{Program exited normally.} is from _GDBN__; it indicates @code{m4} has finished executing. We can end our _GDBN__ session with the _GDBN__ @code{quit} command. @smallexample (_GDBP__) @i{quit} _1__@end smallexample @node Invocation, Commands, Sample Session, Top @chapter Getting In and Out of _GDBN__ @menu * Starting _GDBN__:: Starting _GDBN__ * Leaving _GDBN__:: Leaving _GDBN__ * Shell Commands:: Shell Commands @end menu @node Starting _GDBN__, Leaving _GDBN__, Invocation, Invocation @section Starting _GDBN__ _GDBN__ is invoked with the shell command @code{_GDBP__}. Once started, it reads commands from the terminal until you tell it to exit. You can run @code{_GDBP__} with no arguments or options; but the most usual way to start _GDBN__ is with one argument or two, specifying an executable program as the argument: @example _GDBP__ program @end example @noindent You can also start with both an executable program and a core file specified: @example _GDBP__ program core @end example You can, instead, specify a process ID as a second argument, if you want to debug a running process: @example _GDBP__ program 1234 @end example @noindent would attach _GDBN__ to process @code{1234} (unless you also have a file named @file{1234}; _GDBN__ does check for a core file first). @noindent You can further control how _GDBN__ starts up by using command-line options. _GDBN__ itself can remind you of the options available: @example _GDBP__ -help @end example @noindent will display all available options and briefly describe their use (@samp{_GDBP__ -h} is a shorter equivalent). All options and command line arguments you give are processed in sequential order. The order makes a difference when the @samp{-x} option is used. @menu * File Options:: Choosing Files * Mode Options:: Choosing Modes _if__(!_GENERIC__) _include__(gdbinv-m.m4)_dnl__ _fi__(!_GENERIC__) @end menu @node File Options, Mode Options, Starting _GDBN__, Starting _GDBN__ @subsection Choosing Files As shown above, any arguments other than options specify an executable file and core file; that is, the first argument encountered with no associated option flag is equivalent to a @samp{-se} option, and the second, if any, is equivalent to a @samp{-c} option. Many options have both long and short forms; both are shown here. The long forms are also recognized if you truncate them, so long as enough of the option is present to be unambiguous. (If you prefer, you can flag option arguments with @samp{+} rather than @samp{-}, though we illustrate the more usual convention.) @table @code @item -symbols=@var{file} @itemx -s @var{file} Read symbol table from file @var{file}. @item -exec=@var{file} @itemx -e @var{file} Use file @var{file} as the executable file to execute when appropriate, and for examining pure data in conjunction with a core dump. @item -se=@var{file} Read symbol table from file @var{file} and use it as the executable file. @item -core=@var{file} @itemx -c @var{file} Use file @var{file} as a core dump to examine. @item -command=@var{file} @itemx -x @var{file} Execute _GDBN__ commands from file @var{file}. @xref{Command Files}. @item -directory=@var{directory} @itemx -d @var{directory} Add @var{directory} to the path to search for source files. @end table _if__(!_GENERIC__) @node Mode Options, Mode Options, File Options, Starting _GDBN__ _fi__(!_GENERIC__) _if__(_GENERIC__) @node Mode Options, , File Options, Starting _GDBN__ _fi__(_GENERIC__) @subsection Choosing Modes @table @code @item -nx @itemx -n Do not execute commands from any @file{_GDBINIT__} initialization files. Normally, the commands in these files are executed after all the command options and arguments have been processed. @xref{Command Files}. @item -quiet @itemx -q ``Quiet''. Do not print the introductory and copyright messages. These messages are also suppressed in batch mode. @item -batch Run in batch mode. Exit with status @code{0} after processing all the command files specified with @samp{-x} (and @file{_GDBINIT__}, if not inhibited). Exit with nonzero status if an error occurs in executing the _GDBN__ commands in the command files. Batch mode may be useful for running _GDBN__ as a filter, for example to download and run a program on another computer; in order to make this more useful, the message @example Program exited normally. @end example @noindent (which is ordinarily issued whenever a program running under _GDBN__ control terminates) is not issued when running in batch mode. @item -cd=@var{directory} Run _GDBN__ using @var{directory} as its working directory, instead of the current directory. @item -fullname @itemx -f Emacs sets this option when it runs _GDBN__ as a subprocess. It tells _GDBN__ to output the full file name and line number in a standard, recognizable fashion each time a stack frame is displayed (which includes each time the program stops). This recognizable format looks like two @samp{\032} characters, followed by the file name, line number and character position separated by colons, and a newline. The Emacs-to-_GDBN__ interface program uses the two @samp{\032} characters as a signal to display the source code for the frame. @item -b @var{bps} Set the line speed (baud rate or bits per second) of any serial interface used by _GDBN__ for remote debugging. @item -tty=@var{device} Run using @var{device} for your program's standard input and output. @c FIXME: kingdon thinks there's more to -tty. Investigate. @end table _if__(!_GENERIC__) _include__(gdbinv-s.m4) _fi__(!_GENERIC__) @node Leaving _GDBN__, Shell Commands, Starting _GDBN__, Invocation @section Leaving _GDBN__ @cindex exiting _GDBN__ @table @code @item quit @kindex quit @kindex q To exit _GDBN__, use the @code{quit} command (abbreviated @code{q}), or type an end-of-file character (usually @kbd{C-d}). @end table @cindex interrupt An interrupt (often @kbd{C-c}) will not exit from _GDBN__, but rather will terminate the action of any _GDBN__ command that is in progress and return to _GDBN__ command level. It is safe to type the interrupt character at any time because _GDBN__ does not allow it to take effect until a time when it is safe. If you've been using _GDBN__ to control an attached process or device, you can release it with the @code{detach} command; @pxref{Attach}. @node Shell Commands, , Leaving _GDBN__, Invocation @section Shell Commands If you need to execute occasional shell commands during your debugging session, there's no need to leave or suspend _GDBN__; you can just use the @code{shell} command. @table @code @item shell @var{command string} @kindex shell @cindex shell escape Directs _GDBN__ to invoke an inferior shell to execute @var{command string}. If it exists, the environment variable @code{SHELL} is used for the name of the shell to run. Otherwise _GDBN__ uses @code{/bin/sh}. @end table The utility @code{make} is often needed in development environments. You don't have to use the @code{shell} command for this purpose in _GDBN__: @table @code @item make @var{make-args} @kindex make @cindex calling make Causes _GDBN__ to execute an inferior @code{make} program with the specified arguments. This is equivalent to @samp{shell make @var{make-args}}. @end table @node Commands, Running, Invocation, Top @chapter _GDBN__ Commands @menu * Command Syntax:: Command Syntax * Help:: Getting Help @end menu @node Command Syntax, Help, Commands, Commands @section Command Syntax A _GDBN__ command is a single line of input. There is no limit on how long it can be. It starts with a command name, which is followed by arguments whose meaning depends on the command name. For example, the command @code{step} accepts an argument which is the number of times to step, as in @samp{step 5}. You can also use the @code{step} command with no arguments. Some command names do not allow any arguments. @cindex abbreviation _GDBN__ command names may always be truncated if that abbreviation is unambiguous. Other possible command abbreviations are listed in the documentation for individual commands. In some cases, even ambiguous abbreviations are allowed; for example, @code{s} is specially defined as equivalent to @code{step} even though there are other commands whose names start with @code{s}. You can test abbreviations by using them as arguments to the @code{help} command. @cindex repeating commands @kindex RET A blank line as input to _GDBN__ (typing just @key{RET}) means to repeat the previous command. Certain commands (for example, @code{run}) will not repeat this way; these are commands for which unintentional repetition might cause trouble and which you are unlikely to want to repeat. The @code{list} and @code{x} commands, when you repeat them with @key{RET}, construct new arguments rather than repeating exactly as typed. This permits easy scanning of source or memory. _GDBN__ can also use @key{RET} in another way: to partition lengthy output, in a way similar to the common utility @code{more} (@pxref{Screen Size}). Since it's easy to press one @key{RET} too many in this situation, _GDBN__ disables command repetition after any command that generates this sort of display. @kindex # @cindex comment A line of input starting with @kbd{#} is a comment; it does nothing. This is useful mainly in command files (@xref{Command Files}). @node Help, , Command Syntax, Commands @section Getting Help @cindex online documentation @kindex help You can always ask _GDBN__ itself for information on its commands, using the command @code{help}. @table @code @item help @itemx h @kindex h You can use @code{help} (abbreviated @code{h}) with no arguments to display a short list of named classes of commands: @smallexample (_GDBP__) help List of classes of commands: running -- Running the program stack -- Examining the stack data -- Examining data breakpoints -- Making program stop at certain points files -- Specifying and examining files status -- Status inquiries support -- Support facilities user-defined -- User-defined commands aliases -- Aliases of other commands obscure -- Obscure features Type "help" followed by a class name for a list of commands in that class. Type "help" followed by command name for full documentation. Command name abbreviations are allowed if unambiguous. (_GDBP__) @end smallexample @item help @var{class} Using one of the general help classes as an argument, you can get a list of the individual commands in that class. For example, here is the help display for the class @code{status}: @smallexample (_GDBP__) help status Status inquiries. List of commands: show -- Generic command for showing things set with "set" info -- Generic command for printing status Type "help" followed by command name for full documentation. Command name abbreviations are allowed if unambiguous. (_GDBP__) @end smallexample @item help @var{command} With a command name as @code{help} argument, _GDBN__ will display a short paragraph on how to use that command. @end table In addition to @code{help}, you can use the _GDBN__ commands @code{info} and @code{show} to inquire about the state of your program, or the state of _GDBN__ itself. Each command supports many topics of inquiry; this manual introduces each of them in the appropriate context. The listings under @code{info} and under @code{show} in the Index point to all the sub-commands. @c FIXME: @pxref{Index} used to be here, but even though it shows up in @c FIXME...the 'aux' file with a pageno the xref can't find it. @c @group @table @code @item info @kindex info @kindex i This command (abbreviated @code{i}) is for describing the state of your program; for example, it can list the arguments given to your program (@code{info args}), the registers currently in use (@code{info registers}), or the breakpoints you've set (@code{info breakpoints}). You can get a complete list of the @code{info} sub-commands with @w{@code{help info}}. @kindex show @item show In contrast, @code{show} is for describing the state of _GDBN__ itself. You can change most of the things you can @code{show}, by using the related command @code{set}; for example, you can control what number system is used for displays with @code{set radix}, or simply inquire which is currently in use with @code{show radix}. @kindex info set To display all the settable parameters and their current values, you can use @code{show} with no arguments; you may also use @code{info set}. Both commands produce the same display. @c FIXME: "info set" violates the rule that "info" is for state of @c FIXME...program. Ck w/ GNU: "info set" to be called something else, @c FIXME...or change desc of rule---eg "state of prog and debugging session"? @end table @c @end group Here are three miscellaneous @code{show} subcommands, all of which are exceptional in lacking corresponding @code{set} commands: @table @code @kindex show version @cindex version number @item show version Show what version of _GDBN__ is running. You should include this information in _GDBN__ bug-reports. If multiple versions of _GDBN__ are in use at your site, you may occasionally want to make sure what version of _GDBN__ you're running; as _GDBN__ evolves, new commands are introduced, and old ones may wither away. The version number is also announced when you start _GDBN__ with no arguments. @kindex show copying @item show copying Display information about permission for copying _GDBN__. @kindex show warranty @item show warranty Display the GNU ``NO WARRANTY'' statement. @end table @node Running, Stopping, Commands, Top @chapter Running Programs Under _GDBN__ @menu * Compilation:: Compiling for Debugging * Starting:: Starting your Program * Arguments:: Your Program's Arguments * Environment:: Your Program's Environment * Working Directory:: Your Program's Working Directory * Input/Output:: Your Program's Input and Output * Attach:: Debugging an Already-Running Process * Kill Process:: Killing the Child Process @end menu @node Compilation, Starting, Running, Running @section Compiling for Debugging In order to debug a program effectively, you need to generate debugging information when you compile it. This debugging information is stored in the object file; it describes the data type of each variable or function and the correspondence between source line numbers and addresses in the executable code. To request debugging information, specify the @samp{-g} option when you run the compiler. Many C compilers are unable to handle the @samp{-g} and @samp{-O} options together. Using those compilers, you cannot generate optimized executables containing debugging information. The GNU C compiler supports @samp{-g} with or without @samp{-O}, making it possible to debug optimized code. We recommend that you @emph{always} use @samp{-g} whenever you compile a program. You may think the program is correct, but there's no sense in pushing your luck. Some things do not work as well with @samp{-g -O} as with just @samp{-g}, particularly on machines with instruction scheduling. If in doubt, recompile with @samp{-g} alone, and if this fixes the problem, please report it as a bug (including a test case!). Older versions of the GNU C compiler permitted a variant option @samp{-gg} for debugging information. _GDBN__ no longer supports this format; if your GNU C compiler has this option, do not use it. @ignore @comment As far as I know, there are no cases in which _GDBN__ will @comment produce strange output in this case. (but no promises). If your program includes archives made with the @code{ar} program, and if the object files used as input to @code{ar} were compiled without the @samp{-g} option and have names longer than 15 characters, _GDBN__ will get confused reading the program's symbol table. No error message will be given, but _GDBN__ may behave strangely. The reason for this problem is a deficiency in the Unix archive file format, which cannot represent file names longer than 15 characters. To avoid this problem, compile the archive members with the @samp{-g} option or use shorter file names. Alternatively, use a version of GNU @code{ar} dated more recently than August 1989. @end ignore @node Starting, Arguments, Compilation, Running @section Starting your Program @cindex starting @cindex running @table @code @item run @itemx r @kindex run Use the @code{run} command to start your program under _GDBN__. You must first specify the program name _if__(_VXWORKS__) (except on VxWorks) _fi__(_VXWORKS__) with an argument to _GDBN__ (@pxref{Invocation}), or using the @code{file} or @code{exec-file} command (@pxref{Files}). @refill @end table On targets that support processes, @code{run} creates an inferior process and makes that process run your program. On other targets, @code{run} jumps to the start of the program. The execution of a program is affected by certain information it receives from its superior. _GDBN__ provides ways to specify this information, which you must do @i{before} starting the program. (You can change it after starting the program, but such changes will only affect the program the next time you start it.) This information may be divided into four categories: @table @asis @item The @i{arguments.} You specify the arguments to give your program as the arguments of the @code{run} command. If a shell is available on your target, the shell is used to pass the arguments, so that you may use normal conventions (such as wildcard expansion or variable substitution) in describing the arguments. In Unix systems, you can control which shell is used with the @code{SHELL} environment variable. @xref{Arguments}.@refill @item The @i{environment.} Your program normally inherits its environment from _GDBN__, but you can use the _GDBN__ commands @code{set environment} and @code{unset environment} to change parts of the environment that will be given to the program. @xref{Environment}.@refill @item The @i{working directory.} Your program inherits its working directory from _GDBN__. You can set _GDBN__'s working directory with the @code{cd} command in _GDBN__. @xref{Working Directory}. @item The @i{standard input and output.} Your program normally uses the same device for standard input and standard output as _GDBN__ is using. You can redirect input and output in the @code{run} command line, or you can use the @code{tty} command to set a different device for your program. @xref{Input/Output}. @cindex pipes @emph{Warning:} While input and output redirection work, you can't use pipes to pass the output of the program you're debugging to another program; if you attempt this, _GDBN__ is likely to wind up debugging the wrong program. @end table When you issue the @code{run} command, your program begins to execute immediately. @xref{Stopping}, for discussion of how to arrange for your program to stop. Once your program has been started by the @code{run} command (and then stopped), you may evaluate expressions that involve calls to functions in the inferior, using the @code{print} or @code{call} commands. @xref{Data}. If the modification time of your symbol file has changed since the last time _GDBN__ read its symbols, _GDBN__ will discard its symbol table and re-read it. In this process, it tries to retain your current breakpoints. @node Arguments, Environment, Starting, Running @section Your Program's Arguments @cindex arguments (to your program) The arguments to your program can be specified by the arguments of the @code{run} command. They are passed to a shell, which expands wildcard characters and performs redirection of I/O, and thence to the program. _GDBN__ uses the shell indicated by your environment variable @code{SHELL} if it exists; otherwise, _GDBN__ uses @code{/bin/sh}. @code{run} with no arguments uses the same arguments used by the previous @code{run}, or those set by the @code{set args} command. @kindex set args @table @code @item set args Specify the arguments to be used the next time your program is run. If @code{set args} has no arguments, @code{run} will execute your program with no arguments. Once you have run your program with arguments, using @code{set args} before the next @code{run} is the only way to run it again without arguments. @item show args @kindex show args Show the arguments to give your program when it is started. @end table @node Environment, Working Directory, Arguments, Running @section Your Program's Environment @cindex environment (of your program) The @dfn{environment} consists of a set of environment variables and their values. Environment variables conventionally record such things as your user name, your home directory, your terminal type, and your search path for programs to run. Usually you set up environment variables with the shell and they are inherited by all the other programs you run. When debugging, it can be useful to try running the program with a modified environment without having to start _GDBN__ over again. @table @code @item path @var{directory} @kindex path Add @var{directory} to the front of the @code{PATH} environment variable (the search path for executables), for both _GDBN__ and your program. You may specify several directory names, separated by @samp{:} or whitespace. If @var{directory} is already in the path, it is moved to the front, so it will be searched sooner. You can use the string @samp{$cwd} to refer to whatever is the current working directory at the time _GDBN__ searches the path. If you use @samp{.} instead, it refers to the directory where you executed the @code{path} command. _GDBN__ fills in the current path where needed in the @var{directory} argument, before adding it to the search path. @c 'path' is explicitly nonrepeatable, but RMS points out it's silly to @c document that, since repeating it would be a no-op. @item show paths @kindex show paths Display the list of search paths for executables (the @code{PATH} environment variable). @item show environment @r{[}@var{varname}@r{]} @kindex show environment Print the value of environment variable @var{varname} to be given to your program when it starts. If you don't supply @var{varname}, print the names and values of all environment variables to be given to your program. You can abbreviate @code{environment} as @code{env}. @item set environment @var{varname} @r{[}=@r{]} @var{value} @kindex set environment Sets environment variable @var{varname} to @var{value}. The value changes for your program only, not for _GDBN__ itself. @var{value} may be any string; the values of environment variables are just strings, and any interpretation is supplied by your program itself. The @var{value} parameter is optional; if it is eliminated, the variable is set to a null value. @c "any string" here doesn't include leading, trailing @c blanks. Gnu asks: does anyone care? For example, this command: @example set env USER = foo @end example @noindent tells a Unix program, when subsequently run, that its user is named @samp{foo}. (The spaces around @samp{=} are used for clarity here; they are not actually required.) @item unset environment @var{varname} @kindex unset environment Remove variable @var{varname} from the environment to be passed to your program. This is different from @samp{set env @var{varname} =}; @code{unset environment} removes the variable from the environment, rather than assigning it an empty value. @end table @node Working Directory, Input/Output, Environment, Running @section Your Program's Working Directory @cindex working directory (of your program) Each time you start your program with @code{run}, it inherits its working directory from the current working directory of _GDBN__. _GDBN__'s working directory is initially whatever it inherited from its parent process (typically the shell), but you can specify a new working directory in _GDBN__ with the @code{cd} command. The _GDBN__ working directory also serves as a default for the commands that specify files for _GDBN__ to operate on. @xref{Files}. @table @code @item cd @var{directory} @kindex cd Set _GDBN__'s working directory to @var{directory}. @item pwd @kindex pwd Print _GDBN__'s working directory. @end table @node Input/Output, Attach, Working Directory, Running @section Your Program's Input and Output @cindex redirection @cindex i/o @cindex terminal By default, the program you run under _GDBN__ does input and output to the same terminal that _GDBN__ uses. _GDBN__ switches the terminal to its own terminal modes to interact with you, but it records the terminal modes your program was using and switches back to them when you continue running your program. @table @code @item info terminal @kindex info terminal Displays _GDBN__'s recorded information about the terminal modes your program is using. @end table You can redirect the program's input and/or output using shell redirection with the @code{run} command. For example, _0__@example run > outfile _1__@end example @noindent starts the program, diverting its output to the file @file{outfile}. @kindex tty @cindex controlling terminal Another way to specify where the program should do input and output is with the @code{tty} command. This command accepts a file name as argument, and causes this file to be the default for future @code{run} commands. It also resets the controlling terminal for the child process, for future @code{run} commands. For example, @example tty /dev/ttyb @end example @noindent directs that processes started with subsequent @code{run} commands default to do input and output on the terminal @file{/dev/ttyb} and have that as their controlling terminal. An explicit redirection in @code{run} overrides the @code{tty} command's effect on the input/output device, but not its effect on the controlling terminal. When you use the @code{tty} command or redirect input in the @code{run} command, only the input @emph{for your program} is affected. The input for _GDBN__ still comes from your terminal. @node Attach, Kill Process, Input/Output, Running @section Debugging an Already-Running Process @kindex attach @cindex attach @table @code @item attach @var{process-id} This command attaches to a running process---one that was started outside _GDBN__. (@code{info files} will show your active targets.) The command takes as argument a process ID. The usual way to find out the process-id of a Unix process is with the @code{ps} utility, or with the @samp{jobs -l} shell command. @code{attach} will not repeat if you press @key{RET} a second time after executing the command. @end table To use @code{attach}, you must be debugging in an environment which supports processes. You must also have permission to send the process a signal, and it must have the same effective user ID as the _GDBN__ process. When using @code{attach}, you should first use the @code{file} command to specify the program running in the process and load its symbol table. @xref{Files}. The first thing _GDBN__ does after arranging to debug the specified process is to stop it. You can examine and modify an attached process with all the _GDBN__ commands that are ordinarily available when you start processes with @code{run}. You can insert breakpoints; you can step and continue; you can modify storage. If you would rather the process continue running, you may use the @code{continue} command after attaching _GDBN__ to the process. @table @code @item detach @kindex detach When you have finished debugging the attached process, you can use the @code{detach} command to release it from _GDBN__'s control. Detaching the process continues its execution. After the @code{detach} command, that process and _GDBN__ become completely independent once more, and you are ready to @code{attach} another process or start one with @code{run}. @code{detach} will not repeat if you press @key{RET} again after executing the command. @end table If you exit _GDBN__ or use the @code{run} command while you have an attached process, you kill that process. By default, you will be asked for confirmation if you try to do either of these things; you can control whether or not you need to confirm by using the @code{set confirm} command (@pxref{Messages/Warnings}). @node Kill Process, , Attach, Running @c @group @section Killing the Child Process @table @code @item kill @kindex kill Kill the child process in which your program is running under _GDBN__. @end table This command is useful if you wish to debug a core dump instead of a running process. _GDBN__ ignores any core dump file while your program is running. @c @end group On some operating systems, a program can't be executed outside _GDBN__ while you have breakpoints set on it inside _GDBN__. You can use the @code{kill} command in this situation to permit running the program outside the debugger. The @code{kill} command is also useful if you wish to recompile and relink the program, since on many systems it is impossible to modify an executable file while it is running in a process. In this case, when you next type @code{run}, _GDBN__ will notice that the file has changed, and will re-read the symbol table (while trying to preserve your current breakpoint settings). @node Stopping, Stack, Running, Top @chapter Stopping and Continuing The principal purpose of using a debugger is so that you can stop your program before it terminates; or so that, if the program runs into trouble, you can investigate and find out why. Inside _GDBN__, your program may stop for any of several reasons, such as a signal, a breakpoint, or reaching a new line after a _GDBN__ command such as @code{step}. You may then examine and change variables, set new breakpoints or remove old ones, and then continue execution. Usually, the messages shown by _GDBN__ provide ample explanation of the status of your program---but you can also explicitly request this information at any time. @table @code @item info program @kindex info program Display information about the status of your program: whether it is running or not, what process it is, and why it stopped. @end table @menu * Breakpoints:: Breakpoints, Watchpoints, and Exceptions * Continuing and Stepping:: Resuming Execution * Signals:: Signals @end menu @node Breakpoints, Continuing and Stepping, Stopping, Stopping @section Breakpoints, Watchpoints, and Exceptions @cindex breakpoints A @dfn{breakpoint} makes your program stop whenever a certain point in the program is reached. For each breakpoint, you can add various conditions to control in finer detail whether the program will stop. You can set breakpoints with the @code{break} command and its variants (@pxref{Set Breaks}), to specify the place where the program should stop by line number, function name or exact address in the program. In languages with exception handling (such as GNU C++), you can also set breakpoints where an exception is raised (@pxref{Exception Handling}). @cindex watchpoints A @dfn{watchpoint} is a special breakpoint that stops your program when the value of an expression changes. You must use a different command to set watchpoints (@pxref{Set Watchpoints}), but aside from that, you can manage a watchpoint like any other breakpoint: you enable, disable, and delete both breakpoints and watchpoints using the same commands. Each breakpoint or watchpoint is assigned a number when it is created; these numbers are successive integers starting with one. In many of the commands for controlling various features of breakpoints you use the breakpoint number to say which breakpoint you want to change. Each breakpoint may be @dfn{enabled} or @dfn{disabled}; if disabled, it has no effect on the program until you enable it again. @menu * Set Breaks:: Setting Breakpoints * Set Watchpoints:: Setting Watchpoints * Exception Handling:: Breakpoints and Exceptions * Delete Breaks:: Deleting Breakpoints * Disabling:: Disabling Breakpoints * Conditions:: Break Conditions * Break Commands:: Breakpoint Command Lists * Breakpoint Menus:: Breakpoint Menus * Error in Breakpoints:: @end menu @node Set Breaks, Set Watchpoints, Breakpoints, Breakpoints @subsection Setting Breakpoints @kindex break @kindex b Breakpoints are set with the @code{break} command (abbreviated @code{b}). You have several ways to say where the breakpoint should go. @table @code @item break @var{function} Set a breakpoint at entry to function @var{function}. When using source languages that permit overloading of symbols, such as C++, @var{function} may refer to more than one possible place to break. @xref{Breakpoint Menus}, for a discussion of that situation. @item break +@var{offset} @itemx break -@var{offset} Set a breakpoint some number of lines forward or back from the position at which execution stopped in the currently selected frame. @item break @var{linenum} Set a breakpoint at line @var{linenum} in the current source file. That file is the last file whose source text was printed. This breakpoint will stop the program just before it executes any of the code on that line. @item break @var{filename}:@var{linenum} Set a breakpoint at line @var{linenum} in source file @var{filename}. @item break @var{filename}:@var{function} Set a breakpoint at entry to function @var{function} found in file @var{filename}. Specifying a file name as well as a function name is superfluous except when multiple files contain similarly named functions. @item break *@var{address} Set a breakpoint at address @var{address}. You can use this to set breakpoints in parts of the program which do not have debugging information or source files. @item break When called without any arguments, @code{break} sets a breakpoint at the next instruction to be executed in the selected stack frame (@pxref{Stack}). In any selected frame but the innermost, this will cause the program to stop as soon as control returns to that frame. This is similar to the effect of a @code{finish} command in the frame inside the selected frame---except that @code{finish} doesn't leave an active breakpoint. If you use @code{break} without an argument in the innermost frame, _GDBN__ will stop the next time it reaches the current location; this may be useful inside loops. _GDBN__ normally ignores breakpoints when it resumes execution, until at least one instruction has been executed. If it did not do this, you would be unable to proceed past a breakpoint without first disabling the breakpoint. This rule applies whether or not the breakpoint already existed when the program stopped. @item break @dots{} if @var{cond} Set a breakpoint with condition @var{cond}; evaluate the expression @var{cond} each time the breakpoint is reached, and stop only if the value is nonzero---that is, if @var{cond} evaluates as true. @samp{@dots{}} stands for one of the possible arguments described above (or no argument) specifying where to break. @xref{Conditions}, for more information on breakpoint conditions. @item tbreak @var{args} @kindex tbreak Set a breakpoint enabled only for one stop. @var{args} are the same as for the @code{break} command, and the breakpoint is set in the same way, but the breakpoint is automatically disabled the first time it is hit. @xref{Disabling}. @item rbreak @var{regex} @kindex rbreak @cindex regular expression Set breakpoints on all functions matching the regular expression @var{regex}. This command sets an unconditional breakpoint on all matches, printing a list of all breakpoints it set. Once these breakpoints are set, they are treated just like the breakpoints set with the @code{break} command. They can be deleted, disabled, made conditional, etc., in the standard ways. When debugging C++ programs, @code{rbreak} is useful for setting breakpoints on overloaded functions that are not members of any special classes. @kindex info breakpoints @cindex @code{$_} and @code{info breakpoints} @item info breakpoints @r{[}@var{n}@r{]} @item info break @r{[}@var{n}@r{]} Print a list of all breakpoints (but not watchpoints) set and not deleted, showing their numbers, where in the program they are, and any special features in use for them. Disabled breakpoints are included in the list, but marked as disabled. @code{info break} with a breakpoint number @var{n} as argument lists only that breakpoint. The convenience variable @code{$_} and the default examining-address for the @code{x} command are set to the address of the last breakpoint listed (@pxref{Memory}). The equivalent command for watchpoints is @code{info watch}. @end table _GDBN__ allows you to set any number of breakpoints at the same place in the program. There is nothing silly or meaningless about this. When the breakpoints are conditional, this is even useful (@pxref{Conditions}). @node Set Watchpoints, Exception Handling, Set Breaks, Breakpoints @subsection Setting Watchpoints @cindex setting watchpoints You can use a watchpoint to stop execution whenever the value of an expression changes, without having to predict a particular place where this may happen. Watchpoints currently execute two orders of magnitude more slowly than other breakpoints, but this can well be worth it to catch errors where you have no clue what part of your program is the culprit. Some processors provide special hardware to support watchpoint evaluation; future releases of _GDBN__ will use such hardware if it is available. @table @code @kindex watch @item watch @var{expr} Set a watchpoint for an expression. @kindex info watchpoints @item info watchpoints This command prints a list of watchpoints; it is otherwise similar to @code{info break}. @end table @node Exception Handling, Delete Breaks, Set Watchpoints, Breakpoints @subsection Breakpoints and Exceptions @cindex exception handlers Some languages, such as GNU C++, implement exception handling. You can use _GDBN__ to examine what caused the program to raise an exception, and to list the exceptions the program is prepared to handle at a given point in time. @table @code @item catch @var{exceptions} @kindex catch You can set breakpoints at active exception handlers by using the @code{catch} command. @var{exceptions} is a list of names of exceptions to catch. @end table You can use @code{info catch} to list active exception handlers; @pxref{Frame Info}. There are currently some limitations to exception handling in _GDBN__. These will be corrected in a future release. @itemize @bullet @item If you call a function interactively, _GDBN__ normally returns control to you when the function has finished executing. If the call raises an exception, however, the call may bypass the mechanism that returns control to the user and cause the program to simply continue running until it hits a breakpoint, catches a signal that _GDBN__ is listening for, or exits. @item You cannot raise an exception interactively. @item You cannot interactively install an exception handler. @end itemize @cindex raise exceptions Sometimes @code{catch} is not the best way to debug exception handling: if you need to know exactly where an exception is raised, it's better to stop @emph{before} the exception handler is called, since that way you can see the stack before any unwinding takes place. If you set a breakpoint in an exception handler instead, it may not be easy to find out where the exception was raised. To stop just before an exception handler is called, you need some knowledge of the implementation. In the case of GNU C++, exceptions are raised by calling a library function named @code{__raise_exception} which has the following ANSI C interface: @example /* @var{addr} is where the exception identifier is stored. ID is the exception identifier. */ void __raise_exception (void **@var{addr}, void *@var{id}); @end example @noindent To make the debugger catch all exceptions before any stack unwinding takes place, set a breakpoint on @code{__raise_exception} (@pxref{Breakpoints}). With a conditional breakpoint (@xref{Conditions}) that depends on the value of @var{id}, you can stop your program when a specific exception is raised. You can use multiple conditional breakpoints to stop the program when any of a number of exceptions are raised. @node Delete Breaks, Disabling, Exception Handling, Breakpoints @subsection Deleting Breakpoints @cindex clearing breakpoints, watchpoints @cindex deleting breakpoints, watchpoints It is often necessary to eliminate a breakpoint or watchpoint once it has done its job and you no longer want the program to stop there. This is called @dfn{deleting} the breakpoint. A breakpoint that has been deleted no longer exists; it is forgotten. With the @code{clear} command you can delete breakpoints according to where they are in the program. With the @code{delete} command you can delete individual breakpoints or watchpoints by specifying their breakpoint numbers. It is not necessary to delete a breakpoint to proceed past it. _GDBN__ automatically ignores breakpoints on the first instruction to be executed when you continue execution without changing the execution address. @table @code @item clear @kindex clear Delete any breakpoints at the next instruction to be executed in the selected stack frame (@pxref{Selection}). When the innermost frame is selected, this is a good way to delete a breakpoint that the program just stopped at. @item clear @var{function} @itemx clear @var{filename}:@var{function} Delete any breakpoints set at entry to the function @var{function}. @item clear @var{linenum} @itemx clear @var{filename}:@var{linenum} Delete any breakpoints set at or within the code of the specified line. @item delete @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]} @cindex delete breakpoints @kindex delete @kindex d Delete the breakpoints or watchpoints of the numbers specified as arguments. If no argument is specified, delete all breakpoints (_GDBN__ asks confirmation, unless you've @code{set confirm off}). You can abbreviate this command as @code{d}. @end table @node Disabling, Conditions, Delete Breaks, Breakpoints @subsection Disabling Breakpoints @cindex disabled breakpoints @cindex enabled breakpoints Rather than deleting a breakpoint or watchpoint, you might prefer to @dfn{disable} it. This makes the breakpoint inoperative as if it had been deleted, but remembers the information on the breakpoint so that you can @dfn{enable} it again later. You disable and enable breakpoints and watchpoints with the @code{enable} and @code{disable} commands, optionally specifying one or more breakpoint numbers as arguments. Use @code{info break} or @code{info watch} to print a list of breakpoints or watchpoints if you don't know which numbers to use. A breakpoint or watchpoint can have any of four different states of enablement: @itemize @bullet @item Enabled. The breakpoint will stop the program. A breakpoint set with the @code{break} command starts out in this state. @item Disabled. The breakpoint has no effect on the program. @item Enabled once. The breakpoint will stop the program, but when it does so it will become disabled. A breakpoint set with the @code{tbreak} command starts out in this state. @item Enabled for deletion. The breakpoint will stop the program, but immediately after it does so it will be deleted permanently. @end itemize You can use the following commands to enable or disable breakpoints and watchpoints: @table @code @item disable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]} @kindex disable breakpoints @kindex disable @kindex dis Disable the specified breakpoints---or all breakpoints, if none are listed. A disabled breakpoint has no effect but is not forgotten. All options such as ignore-counts, conditions and commands are remembered in case the breakpoint is enabled again later. You may abbreviate @code{disable} as @code{dis}. @item enable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]} @kindex enable breakpoints @kindex enable Enable the specified breakpoints (or all defined breakpoints). They become effective once again in stopping the program. @item enable @r{[}breakpoints@r{]} once @var{bnums}@dots{} Enable the specified breakpoints temporarily. Each will be disabled again the next time it stops the program. @item enable @r{[}breakpoints@r{]} delete @var{bnums}@dots{} Enable the specified breakpoints to work once and then die. Each of the breakpoints will be deleted the next time it stops the program. @end table Save for a breakpoint set with @code{tbreak} (@pxref{Set Breaks}), breakpoints that you set are initially enabled; subsequently, they become disabled or enabled only when you use one of the commands above. (The command @code{until} can set and delete a breakpoint of its own, but it will not change the state of your other breakpoints; @pxref{Continuing and Stepping}.) @node Conditions, Break Commands, Disabling, Breakpoints @subsection Break Conditions @cindex conditional breakpoints @cindex breakpoint conditions The simplest sort of breakpoint breaks every time the program reaches a specified place. You can also specify a @dfn{condition} for a breakpoint. A condition is just a Boolean expression in your programming language. (@xref{Expressions}). A breakpoint with a condition evaluates the expression each time the program reaches it, and the program stops only if the condition is @emph{true}. This is the converse of using assertions for program validation; in that situation, you want to stop when the assertion is violated---that is, when the condition is false. In C, if you want to test an assertion expressed by the condition @var{assert}, you should set the condition @samp{! @var{assert}} on the appropriate breakpoint. Conditions are also accepted for watchpoints; you may not need them, since a watchpoint is inspecting the value of an expression anyhow---but it might be simpler, say, to just set a watchpoint on a variable name, and specify a condition that tests whether the new value is an interesting one. Break conditions ca have side effects, and may even call functions in your program. This can be useful, for example, to activate functions that log program progress, or to use your own print functions to format special data structures. The effects are completely predictable unless there is another enabled breakpoint at the same address. (In that case, _GDBN__ might see the other breakpoint first and stop the program without checking the condition of this one.) Note that breakpoint commands are usually more convenient and flexible for the purpose of performing side effects when a breakpoint is reached (@pxref{Break Commands}). Break conditions can be specified when a breakpoint is set, by using @samp{if} in the arguments to the @code{break} command. @xref{Set Breaks}. They can also be changed at any time with the @code{condition} command. The @code{watch} command doesn't recognize the @code{if} keyword; @code{condition} is the only way to impose a further condition on a watchpoint. @table @code @item condition @var{bnum} @var{expression} @kindex condition Specify @var{expression} as the break condition for breakpoint or watchpoint number @var{bnum}. From now on, this breakpoint will stop the program only if the value of @var{expression} is true (nonzero, in C). When you use @code{condition}, _GDBN__ checks @var{expression} immediately for syntactic correctness, and to determine whether symbols in it have referents in the context of your breakpoint. _GDBN__ does not actually evaluate @var{expression} at the time the @code{condition} command is given, however. @xref{Expressions}. @item condition @var{bnum} Remove the condition from breakpoint number @var{bnum}. It becomes an ordinary unconditional breakpoint. @end table @cindex ignore count (of breakpoint) A special case of a breakpoint condition is to stop only when the breakpoint has been reached a certain number of times. This is so useful that there is a special way to do it, using the @dfn{ignore count} of the breakpoint. Every breakpoint has an ignore count, which is an integer. Most of the time, the ignore count is zero, and therefore has no effect. But if the program reaches a breakpoint whose ignore count is positive, then instead of stopping, it just decrements the ignore count by one and continues. As a result, if the ignore count value is @var{n}, the breakpoint will not stop the next @var{n} times it is reached. @table @code @item ignore @var{bnum} @var{count} @kindex ignore Set the ignore count of breakpoint number @var{bnum} to @var{count}. The next @var{count} times the breakpoint is reached, your program's execution will not stop; other than to decrement the ignore count, _GDBN__ takes no action. To make the breakpoint stop the next time it is reached, specify a count of zero. @item continue @var{count} @itemx c @var{count} @itemx fg @var{count} @kindex continue @var{count} Continue execution of the program, setting the ignore count of the breakpoint that the program stopped at to @var{count} minus one. Thus, the program will not stop at this breakpoint until the @var{count}'th time it is reached. An argument to this command is meaningful only when the program stopped due to a breakpoint. At other times, the argument to @code{continue} is ignored. The synonym @code{fg} is provided purely for convenience, and has exactly the same behavior as other forms of the command. @end table If a breakpoint has a positive ignore count and a condition, the condition is not checked. Once the ignore count reaches zero, the condition will be checked. You could achieve the effect of the ignore count with a condition such as _0__@w{@samp{$foo-- <= 0}}_1__ using a debugger convenience variable that is decremented each time. @xref{Convenience Vars}. @node Break Commands, Breakpoint Menus, Conditions, Breakpoints @subsection Breakpoint Command Lists @cindex breakpoint commands You can give any breakpoint (or watchpoint) a series of commands to execute when the program stops due to that breakpoint. For example, you might want to print the values of certain expressions, or enable other breakpoints. @table @code @item commands @r{[}@var{bnum}@r{]} @itemx @dots{} @var{command-list} @dots{} @itemx end @kindex commands @kindex end Specify a list of commands for breakpoint number @var{bnum}. The commands themselves appear on the following lines. Type a line containing just @code{end} to terminate the commands. To remove all commands from a breakpoint, type @code{commands} followed immediately by @code{end}; that is, give no commands. With no @var{bnum} argument, @code{commands} refers to the last breakpoint or watchpoint set (not to the breakpoint most recently encountered). @end table Pressing @key{RET} as a means of repeating the last _GDBN__ command is disabled within a @var{command-list}. You can use breakpoint commands to start the program up again. Simply use the @code{continue} command, or @code{step}, or any other command that resumes execution. Subsequent commands in the command list are ignored. @kindex silent If the first command specified is @code{silent}, the usual message about stopping at a breakpoint is not printed. This may be desirable for breakpoints that are to print a specific message and then continue. If the remaining commands too print nothing, you will see no sign that the breakpoint was reached at all. @code{silent} is meaningful only at the beginning of a breakpoint command list. The commands @code{echo} and @code{output} that allow you to print precisely controlled output are often useful in silent breakpoints. @xref{Output}. For example, here is how you could use breakpoint commands to print the value of @code{x} at entry to @code{foo} whenever @code{x} is positive. _0__@example break foo if x>0 commands silent echo x is\040 output x echo \n cont end _1__@end example One application for breakpoint commands is to compensate for one bug so you can test for another. Put a breakpoint just after the erroneous line of code, give it a condition to detect the case in which something erroneous has been done, and give it commands to assign correct values to any variables that need them. End with the @code{continue} command so that the program does not stop, and start with the @code{silent} command so that no output is produced. Here is an example: @example break 403 commands silent set x = y + 4 cont end @end example @cindex lost output One deficiency in the operation of automatically continuing breakpoints under Unix appears when your program uses raw mode for the terminal. _GDBN__ switches back to its own terminal modes (not raw) before executing commands, and then must switch back to raw mode when your program is continued. This causes any pending terminal input to be lost. @c FIXME: revisit below when GNU sys avail. @c In the GNU system, this will be fixed by changing the behavior of @c terminal modes. Under Unix, you can get around this problem by writing actions into the breakpoint condition rather than in commands. For example @example condition 5 (x = y + 4), 0 @end example @noindent specifies a condition expression (@xref{Expressions}) that will change @code{x} as needed, then always have the value zero so the program will not stop. No input is lost here, because _GDBN__ evaluates break conditions without changing the terminal modes. When you want to have nontrivial conditions for performing the side effects, the operators @samp{&&}, @samp{||} and @samp{?@dots{}:} may be useful. @node Breakpoint Menus, Error in Breakpoints, Break Commands, Breakpoints @subsection Breakpoint Menus @cindex overloading @cindex symbol overloading Some programming languages (notably C++) permit a single function name to be defined several times, for application in different contexts. This is called @dfn{overloading}. When a function name is overloaded, @samp{break @var{function}} is not enough to tell _GDBN__ where you want a breakpoint. _GDBN__ offers you a menu of numbered choices for different possible breakpoints, and waits for your selection with the prompt @samp{>}. The first two options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1} sets a breakpoint at each definition of @var{function}, and typing @kbd{0} aborts the @code{break} command without setting any new breakpoints. For example, the following session excerpt shows an attempt to set a breakpoint at the overloaded symbol @code{String::after}. We choose three particular definitions of that function name: @example (_GDBP__) b String::after [0] cancel [1] all [2] file:String.cc; line number:867 [3] file:String.cc; line number:860 [4] file:String.cc; line number:875 [5] file:String.cc; line number:853 [6] file:String.cc; line number:846 [7] file:String.cc; line number:735 > 2 4 6 Breakpoint 1 at 0xb26c: file String.cc, line 867. Breakpoint 2 at 0xb344: file String.cc, line 875. Breakpoint 3 at 0xafcc: file String.cc, line 846. Multiple breakpoints were set. Use the "delete" command to delete unwanted breakpoints. (_GDBP__) @end example @node Error in Breakpoints, , Breakpoint Menus, Breakpoints @subsection ``Cannot Insert Breakpoints'' @c FIXME: "cannot insert breakpoints" error, v unclear. @c Q in pending mail to Gilmore. ---pesch@cygnus.com, 26mar91 @c some light may be shed by looking at instances of @c ONE_PROCESS_WRITETEXT. But error seems possible otherwise @c too. pesch, 20sep91 Under some operating systems, breakpoints cannot be used in a program if any other process is running that program. In this situation, attempting to run or continue a program with a breakpoint causes _GDBN__ to stop the other process. When this happens, you have three ways to proceed: @enumerate @item Remove or disable the breakpoints, then continue. @item Suspend _GDBN__, and copy the file containing the program to a new name. Resume _GDBN__ and use the @code{exec-file} command to specify that _GDBN__ should run the program under that name. Then start the program again. @c FIXME: RMS commented here "Show example". Maybe when someone @c explains the first FIXME: in this section... @item Relink the program so that the text segment is nonsharable, using the linker option @samp{-N}. The operating system limitation may not apply to nonsharable executables. @end enumerate @node Continuing and Stepping, Signals, Breakpoints, Stopping @section Continuing and Stepping @cindex stepping @cindex continuing @cindex resuming execution @dfn{Continuing} means resuming program execution until your program completes normally. In contrast, @dfn{stepping} means resuming program execution for a very limited time: one line of source code, or one machine instruction. Either when continuing or when stepping, the program may stop even sooner, due to a breakpoint or to a signal. (If due to a signal, you may want to use @code{handle}, or use @samp{signal 0} to resume execution; @pxref{Signals}.) @table @code @item continue @r{[}@var{ignore-count}@r{]} @kindex continue Resume program execution, at the address where the program last stopped; any breakpoints set at that address are bypassed. The optional argument @var{ignore-count} allows you to specify a further number of times to ignore a breakpoint at this location; its effect is like that of @code{ignore} (@pxref{Conditions}). To resume execution at a different place, you can use @code{return} (@pxref{Returning}) to go back to the calling function; or @code{jump} (@pxref{Jumping}) to go to an arbitrary location in your program. @end table A typical technique for using stepping is to set a breakpoint (@pxref{Breakpoints}) at the beginning of the function or the section of the program in which a problem is believed to lie, run the program until it stops at that breakpoint, and then step through the suspect area, examining the variables that are interesting, until you see the problem happen. @table @code @item step @kindex step @kindex s Continue running the program until control reaches a different source line, then stop it and return control to _GDBN__. This command is abbreviated @code{s}. @quotation @emph{Warning:} If you use the @code{step} command while control is within a function that was compiled without debugging information, execution will proceed until control reaches another function. @end quotation @item step @var{count} Continue running as in @code{step}, but do so @var{count} times. If a breakpoint is reached or a signal not related to stepping occurs before @var{count} steps, stepping stops right away. @item next @r{[}@var{count}@r{]} @kindex next @kindex n Continue to the next source line in the current (innermost) stack frame. Similar to @code{step}, but any function calls appearing within the line of code are executed without stopping. Execution stops when control reaches a different line of code at the stack level which was executing when the @code{next} command was given. This command is abbreviated @code{n}. An argument @var{count} is a repeat count, as for @code{step}. @code{next} within a function that lacks debugging information acts like @code{step}, but any function calls appearing within the code of the function are executed without stopping. @item finish @kindex finish Continue running until just after function in the selected stack frame returns. Print the returned value (if any). Contrast this with the @code{return} command (@pxref{Returning}). @item until @kindex until @item u @kindex u Continue running until a source line past the current line, in the current stack frame, is reached. This command is used to avoid single stepping through a loop more than once. It is like the @code{next} command, except that when @code{until} encounters a jump, it automatically continues execution until the program counter is greater than the address of the jump. This means that when you reach the end of a loop after single stepping though it, @code{until} will cause the program to continue execution until the loop is exited. In contrast, a @code{next} command at the end of a loop will simply step back to the beginning of the loop, which would force you to step through the next iteration. @code{until} always stops the program if it attempts to exit the current stack frame. @code{until} may produce somewhat counterintuitive results if the order of machine code does not match the order of the source lines. For example, in the following excerpt from a debugging session, the @code{f} (@code{frame}) command shows that execution is stopped at line @code{206}; yet when we use @code{until}, we get to line @code{195}: @example (_GDBP__) f #0 main (argc=4, argv=0xf7fffae8) at m4.c:206 206 expand_input(); (_GDBP__) until 195 for ( ; argc > 0; NEXTARG) @{ @end example This happened because, for execution efficiency, the compiler had generated code for the loop closure test at the end, rather than the start, of the loop---even though the test in a C @code{for}-loop is written before the body of the loop. The @code{until} command appeared to step back to the beginning of the loop when it advanced to this expression; however, it has not really gone to an earlier statement---not in terms of the actual machine code. @code{until} with no argument works by means of single instruction stepping, and hence is slower than @code{until} with an argument. @item until @var{location} @item u @var{location} Continue running the program until either the specified location is reached, or the current stack frame returns. @var{location} is any of the forms of argument acceptable to @code{break} (@pxref{Set Breaks}). This form of the command uses breakpoints, and hence is quicker than @code{until} without an argument. @item stepi @itemx si @kindex stepi @kindex si Execute one machine instruction, then stop and return to the debugger. It is often useful to do @samp{display/i $pc} when stepping by machine instructions. This will cause the next instruction to be executed to be displayed automatically at each stop. @xref{Auto Display}. An argument is a repeat count, as in @code{step}. @item nexti @itemx ni @kindex nexti @kindex ni Execute one machine instruction, but if it is a function call, proceed until the function returns. An argument is a repeat count, as in @code{next}. @end table @node Signals, , Continuing and Stepping, Stopping @section Signals @cindex signals A signal is an asynchronous event that can happen in a program. The operating system defines the possible kinds of signals, and gives each kind a name and a number. For example, in Unix @code{SIGINT} is the signal a program gets when you type an interrupt (often @kbd{C-c}); @code{SIGSEGV} is the signal a program gets from referencing a place in memory far away from all the areas in use; @code{SIGALRM} occurs when the alarm clock timer goes off (which happens only if the program has requested an alarm). @cindex fatal signals Some signals, including @code{SIGALRM}, are a normal part of the functioning of the program. Others, such as @code{SIGSEGV}, indicate errors; these signals are @dfn{fatal} (kill the program immediately) if the program has not specified in advance some other way to handle the signal. @code{SIGINT} does not indicate an error in the program, but it is normally fatal so it can carry out the purpose of the interrupt: to kill the program. _GDBN__ has the ability to detect any occurrence of a signal in the program running under _GDBN__'s control. You can tell _GDBN__ in advance what to do for each kind of signal. @cindex handling signals Normally, _GDBN__ is set up to ignore non-erroneous signals like @code{SIGALRM} (so as not to interfere with their role in the functioning of the program) but to stop the program immediately whenever an error signal happens. You can change these settings with the @code{handle} command. @table @code @item info signals @kindex info signals Print a table of all the kinds of signals and how _GDBN__ has been told to handle each one. You can use this to see the signal numbers of all the defined types of signals. @item handle @var{signal} @var{keywords}@dots{} @kindex handle Change the way _GDBN__ handles signal @var{signal}. @var{signal} can be the number of a signal or its name (with or without the @samp{SIG} at the beginning). The @var{keywords} say what change to make. @end table @c @group The keywords allowed by the @code{handle} command can be abbreviated. Their full names are: @table @code @item nostop _GDBN__ should not stop the program when this signal happens. It may still print a message telling you that the signal has come in. @item stop _GDBN__ should stop the program when this signal happens. This implies the @code{print} keyword as well. @item print _GDBN__ should print a message when this signal happens. @item noprint _GDBN__ should not mention the occurrence of the signal at all. This implies the @code{nostop} keyword as well. @item pass _GDBN__ should allow the program to see this signal; the program will be able to handle the signal, or may be terminated if the signal is fatal and not handled. @item nopass _GDBN__ should not allow the program to see this signal. @end table @c @end group When a signal has been set to stop the program, the program cannot see the signal until you continue. It will see the signal then, if @code{pass} is in effect for the signal in question @i{at that time}. In other words, after _GDBN__ reports a signal, you can use the @code{handle} command with @code{pass} or @code{nopass} to control whether that signal will be seen by the program when you later continue it. You can also use the @code{signal} command to prevent the program from seeing a signal, or cause it to see a signal it normally would not see, or to give it any signal at any time. For example, if the program stopped due to some sort of memory reference error, you might store correct values into the erroneous variables and continue, hoping to see more execution; but the program would probably terminate immediately as a result of the fatal signal once it sees the signal. To prevent this, you can continue with @samp{signal 0}. @xref{Signaling}. @node Stack, Source, Stopping, Top @chapter Examining the Stack When your program has stopped, the first thing you need to know is where it stopped and how it got there. @cindex call stack Each time your program performs a function call, the information about where in the program the call was made from is saved in a block of data called a @dfn{stack frame}. The frame also contains the arguments of the call and the local variables of the function that was called. All the stack frames are allocated in a region of memory called the @dfn{call stack}. When your program stops, the _GDBN__ commands for examining the stack allow you to see all of this information. @cindex selected frame One of the stack frames is @dfn{selected} by _GDBN__ and many _GDBN__ commands refer implicitly to the selected frame. In particular, whenever you ask _GDBN__ for the value of a variable in the program, the value is found in the selected frame. There are special _GDBN__ commands to select whichever frame you are interested in. When the program stops, _GDBN__ automatically selects the currently executing frame and describes it briefly as the @code{frame} command does (@pxref{Frame Info, Info}). @menu * Frames:: Stack Frames * Backtrace:: Backtraces * Selection:: Selecting a Frame * Frame Info:: Information on a Frame @end menu @node Frames, Backtrace, Stack, Stack @section Stack Frames @cindex frame @cindex stack frame The call stack is divided up into contiguous pieces called @dfn{stack frames}, or @dfn{frames} for short; each frame is the data associated with one call to one function. The frame contains the arguments given to the function, the function's local variables, and the address at which the function is executing. @cindex initial frame @cindex outermost frame @cindex innermost frame When your program is started, the stack has only one frame, that of the function @code{main}. This is called the @dfn{initial} frame or the @dfn{outermost} frame. Each time a function is called, a new frame is made. Each time a function returns, the frame for that function invocation is eliminated. If a function is recursive, there can be many frames for the same function. The frame for the function in which execution is actually occurring is called the @dfn{innermost} frame. This is the most recently created of all the stack frames that still exist. @cindex frame pointer Inside your program, stack frames are identified by their addresses. A stack frame consists of many bytes, each of which has its own address; each kind of computer has a convention for choosing one of those bytes whose address serves as the address of the frame. Usually this address is kept in a register called the @dfn{frame pointer register} while execution is going on in that frame. @cindex frame number _GDBN__ assigns numbers to all existing stack frames, starting with zero for the innermost frame, one for the frame that called it, and so on upward. These numbers do not really exist in your program; they are assigned by _GDBN__ to give you a way of designating stack frames in _GDBN__ commands. @cindex frameless execution Some compilers allow functions to be compiled so that they operate without stack frames. (For example, the @code{_GCC__} option @samp{-fomit-frame-pointer} will generate functions without a frame.) This is occasionally done with heavily used library functions to save the frame setup time. _GDBN__ has limited facilities for dealing with these function invocations. If the innermost function invocation has no stack frame, _GDBN__ will nevertheless regard it as though it had a separate frame, which is numbered zero as usual, allowing correct tracing of the function call chain. However, _GDBN__ has no provision for frameless functions elsewhere in the stack. @node Backtrace, Selection, Frames, Stack @section Backtraces A backtrace is a summary of how the program got where it is. It shows one line per frame, for many frames, starting with the currently executing frame (frame zero), followed by its caller (frame one), and on up the stack. @table @code @item backtrace @itemx bt @kindex backtrace @kindex bt Print a backtrace of the entire stack: one line per frame for all frames in the stack. You can stop the backtrace at any time by typing the system interrupt character, normally @kbd{C-c}. @item backtrace @var{n} @itemx bt @var{n} Similar, but print only the innermost @var{n} frames. @item backtrace -@var{n} @itemx bt -@var{n} Similar, but print only the outermost @var{n} frames. @end table @kindex where @kindex info stack @kindex info s The names @code{where} and @code{info stack} (abbreviated @code{info s}) are additional aliases for @code{backtrace}. Each line in the backtrace shows the frame number and the function name. The program counter value is also shown---unless you use @code{set print address off}. The backtrace also shows the source file name and line number, as well as the arguments to the function. The program counter value is omitted if it is at the beginning of the code for that line number. Here is an example of a backtrace. It was made with the command @samp{bt 3}, so it shows the innermost three frames. @smallexample @group #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8) at builtin.c:993 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08) at macro.c:71 (More stack frames follow...) @end group @end smallexample @noindent The display for frame zero doesn't begin with a program counter value, indicating that the program has stopped at the beginning of the code for line @code{993} of @code{builtin.c}. @node Selection, Frame Info, Backtrace, Stack @section Selecting a Frame Most commands for examining the stack and other data in the program work on whichever stack frame is selected at the moment. Here are the commands for selecting a stack frame; all of them finish by printing a brief description of the stack frame just selected. @table @code @item frame @var{n} @itemx f @var{n} @kindex frame @kindex f Select frame number @var{n}. Recall that frame zero is the innermost (currently executing) frame, frame one is the frame that called the innermost one, and so on. The highest-numbered frame is @code{main}'s frame. @item frame @var{addr} @itemx f @var{addr} Select the frame at address @var{addr}. This is useful mainly if the chaining of stack frames has been damaged by a bug, making it impossible for _GDBN__ to assign numbers properly to all frames. In addition, this can be useful when the program has multiple stacks and switches between them. _if_(_SPARC__) On the SPARC architecture, @code{frame} needs two addresses to select an arbitrary frame: a frame pointer and a stack pointer. @c note to future updaters: this is conditioned on a flag @c FRAME_SPECIFICATION_DYADIC in the tm-*.h files, currently only used @c by SPARC, hence the specific attribution. Generalize or list all @c possibilities if more supported machines start doing this. _fi_(_SPARC__) @item up @var{n} @kindex up Move @var{n} frames up the stack. For positive numbers @var{n}, this advances toward the outermost frame, to higher frame numbers, to frames that have existed longer. @var{n} defaults to one. @item down @var{n} @kindex down @kindex do Move @var{n} frames down the stack. For positive numbers @var{n}, this advances toward the innermost frame, to lower frame numbers, to frames that were created more recently. @var{n} defaults to one. You may abbreviate @code{down} as @code{do}. @end table All of these commands end by printing two lines of output describing the frame. The first line shows the frame number, the function name, the arguments, and the source file and line number of execution in that frame. The second line shows the text of that source line. For example: @smallexample (_GDBP__) up #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc) at env.c:10 10 read_input_file (argv[i]); @end smallexample After such a printout, the @code{list} command with no arguments will print ten lines centered on the point of execution in the frame. @xref{List}. @table @code @item up-silently @var{n} @itemx down-silently @var{n} @kindex down-silently @kindex up-silently These two commands are variants of @code{up} and @code{down}, respectively; they differ in that they do their work silently, without causing display of the new frame. They are intended primarily for use in _GDBN__ command scripts, where the output might be unnecessary and distracting. @end table @node Frame Info, , Selection, Stack @section Information About a Frame There are several other commands to print information about the selected stack frame. @table @code @item frame @itemx f When used without any argument, this command does not change which frame is selected, but prints a brief description of the currently selected stack frame. It can be abbreviated @code{f}. With an argument, this command is used to select a stack frame (@pxref{Selection}). @item info frame @kindex info frame @itemx info f @kindex info f This command prints a verbose description of the selected stack frame, including the address of the frame, the addresses of the next frame down (called by this frame) and the next frame up (caller of this frame), the language that the source code corresponding to this frame was written in, the address of the frame's arguments, the program counter saved in it (the address of execution in the caller frame), and which registers were saved in the frame. The verbose description is useful when something has gone wrong that has made the stack format fail to fit the usual conventions. @item info frame @var{addr} @itemx info f @var{addr} Print a verbose description of the frame at address @var{addr}, without selecting that frame. The selected frame remains unchanged by this command. @item info args @kindex info args Print the arguments of the selected frame, each on a separate line. @item info locals @kindex info locals Print the local variables of the selected frame, each on a separate line. These are all variables declared static or automatic within all program blocks that execution in this frame is currently inside of. @item info catch @kindex info catch @cindex catch exceptions @cindex exception handlers Print a list of all the exception handlers that are active in the current stack frame at the current point of execution. To see other exception handlers, visit the associated frame (using the @code{up}, @code{down}, or @code{frame} commands); then type @code{info catch}. @xref{Exception Handling}. @end table @node Source, Data, Stack, Top @chapter Examining Source Files _GDBN__ can print parts of your program's source, since the debugging information recorded in your program tells _GDBN__ what source files were used to built it. When your program stops, _GDBN__ spontaneously prints the line where it stopped. Likewise, when you select a stack frame (@pxref{Selection}), _GDBN__ prints the line where execution in that frame has stopped. You can print other portions of source files by explicit command. If you use _GDBN__ through its GNU Emacs interface, you may prefer to use Emacs facilities to view source; @pxref{Emacs}. @menu * List:: Printing Source Lines * Search:: Searching Source Files * Source Path:: Specifying Source Directories * Machine Code:: Source and Machine Code @end menu @node List, Search, Source, Source @section Printing Source Lines @kindex list @kindex l To print lines from a source file, use the @code{list} command (abbreviated @code{l}). There are several ways to specify what part of the file you want to print. Here are the forms of the @code{list} command most commonly used: @table @code @item list @var{linenum} Print lines centered around line number @var{linenum} in the current source file. @item list @var{function} Print lines centered around the beginning of function @var{function}. @item list Print more lines. If the last lines printed were printed with a @code{list} command, this prints lines following the last lines printed; however, if the last line printed was a solitary line printed as part of displaying a stack frame (@pxref{Stack}), this prints lines centered around that line. @item list - Print lines just before the lines last printed. @end table By default, _GDBN__ prints ten source lines with any of these forms of the @code{list} command. You can change this using @code{set listsize}: @table @code @item set listsize @var{count} @kindex set listsize Make the @code{list} command display @var{count} source lines (unless the @code{list} argument explicitly specifies some other number). @item show listsize @kindex show listsize Display the number of lines that @code{list} will currently display by default. @end table Repeating a @code{list} command with @key{RET} discards the argument, so it is equivalent to typing just @code{list}. This is more useful than listing the same lines again. An exception is made for an argument of @samp{-}; that argument is preserved in repetition so that each repetition moves up in the source file. @cindex linespec In general, the @code{list} command expects you to supply zero, one or two @dfn{linespecs}. Linespecs specify source lines; there are several ways of writing them but the effect is always to specify some source line. Here is a complete description of the possible arguments for @code{list}: @table @code @item list @var{linespec} Print lines centered around the line specified by @var{linespec}. @item list @var{first},@var{last} Print lines from @var{first} to @var{last}. Both arguments are linespecs. @item list ,@var{last} Print lines ending with @var{last}. @item list @var{first}, Print lines starting with @var{first}. @item list + Print lines just after the lines last printed. @item list - Print lines just before the lines last printed. @item list As described in the preceding table. @end table Here are the ways of specifying a single source line---all the kinds of linespec. @table @code @item @var{number} Specifies line @var{number} of the current source file. When a @code{list} command has two linespecs, this refers to the same source file as the first linespec. @item +@var{offset} Specifies the line @var{offset} lines after the last line printed. When used as the second linespec in a @code{list} command that has two, this specifies the line @var{offset} lines down from the first linespec. @item -@var{offset} Specifies the line @var{offset} lines before the last line printed. @item @var{filename}:@var{number} Specifies line @var{number} in the source file @var{filename}. @item @var{function} @c FIXME: "of the open-brace" is C-centric. When we add other langs... Specifies the line of the open-brace that begins the body of the function @var{function}. @item @var{filename}:@var{function} Specifies the line of the open-brace that begins the body of the function @var{function} in the file @var{filename}. You only need the file name with a function name to avoid ambiguity when there are identically named functions in different source files. @item *@var{address} Specifies the line containing the program address @var{address}. @var{address} may be any expression. @end table @node Search, Source Path, List, Source @section Searching Source Files @cindex searching @kindex reverse-search There are two commands for searching through the current source file for a regular expression. @table @code @item forward-search @var{regexp} @itemx search @var{regexp} @kindex search @kindex forward-search The command @samp{forward-search @var{regexp}} checks each line, starting with the one following the last line listed, for a match for @var{regexp}. It lists the line that is found. You can abbreviate the command name as @code{fo}. The synonym @samp{search @var{regexp}} is also supported. @item reverse-search @var{regexp} The command @samp{reverse-search @var{regexp}} checks each line, starting with the one before the last line listed and going backward, for a match for @var{regexp}. It lists the line that is found. You can abbreviate this command as @code{rev}. @end table @node Source Path, Machine Code, Search, Source @section Specifying Source Directories @cindex source path @cindex directories for source files Executable programs sometimes do not record the directories of the source files from which they were compiled, just the names. Even when they do, the directories could be moved between the compilation and your debugging session. _GDBN__ has a list of directories to search for source files; this is called the @dfn{source path}. Each time _GDBN__ wants a source file, it tries all the directories in the list, in the order they are present in the list, until it finds a file with the desired name. Note that the executable search path is @emph{not} used for this purpose. Neither is the current working directory, unless it happens to be in the source path. If _GDBN__ can't find a source file in the source path, and the object program records a directory, _GDBN__ tries that directory too. If the source path is empty, and there is no record of the compilation directory, _GDBN__ will, as a last resort, look in the current directory. Whenever you reset or rearrange the source path, _GDBN__ will clear out any information it has cached about where source files are found, where each line is in the file, etc. @kindex directory When you start _GDBN__, its source path is empty. To add other directories, use the @code{directory} command. @table @code @item directory @var{dirname} @dots{} Add directory @var{dirname} to the front of the source path. Several directory names may be given to this command, separated by @samp{:} or whitespace. You may specify a directory that is already in the source path; this moves it forward, so it will be searched sooner. You can use the string @samp{$cdir} to refer to the compilation directory (if one is recorded), and @samp{$cwd} to refer to the current working directory. @samp{$cwd} is not the same as @samp{.}---the former tracks the current working directory as it changes during your _GDBN__ session, while the latter is immediately expanded to the current directory at the time you add an entry to the source path. @item directory Reset the source path to empty again. This requires confirmation. @c RET-repeat for @code{directory} is explicitly disabled, but since @c repeating it would be a no-op we don't say that. (thanks to RMS) @item show directories @kindex show directories Print the source path: show which directories it contains. @end table If your source path is cluttered with directories that are no longer of interest, _GDBN__ may sometimes cause confusion by finding the wrong versions of source. You can correct the situation as follows: @enumerate @item Use @code{directory} with no argument to reset the source path to empty. @item Use @code{directory} with suitable arguments to reinstall the directories you want in the source path. You can add all the directories in one command. @end enumerate @node Machine Code, , Source Path, Source @section Source and Machine Code You can use the command @code{info line} to map source lines to program addresses (and viceversa), and the command @code{disassemble} to display a range of addresses as machine instructions. @table @code @item info line @var{linespec} @kindex info line Print the starting and ending addresses of the compiled code for source line @var{linespec}. You can specify source lines in any of the ways understood by the @code{list} command (@pxref{List}). @end table For example, we can use @code{info line} to inquire on where the object code for the first line of function @code{m4_changequote} lies: @smallexample (_GDBP__) info line m4_changecom Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350. @end smallexample @noindent We can also inquire (using @code{*@var{addr}} as the form for @var{linespec}) what source line covers a particular address: @smallexample (_GDBP__) info line *0x63ff Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404. @end smallexample @cindex @code{$_} and @code{info line} After @code{info line}, the default address for the @code{x} command is changed to the starting address of the line, so that @samp{x/i} is sufficient to begin examining the machine code (@pxref{Memory}). Also, this address is saved as the value of the convenience variable @code{$_} (@pxref{Convenience Vars}). @table @code @kindex disassemble @item disassemble This specialized command is provided to dump a range of memory as machine instructions. The default memory range is the function surrounding the program counter of the selected frame. A single argument to this command is a program counter value; the function surrounding this value will be dumped. Two arguments (separated by one or more spaces) specify a range of addresses (first inclusive, second exclusive) to be dumped. @end table We can use @code{disassemble} to inspect the object code range shown in the last @code{info line} example: @smallexample (_GDBP__) disas 0x63e4 0x6404 Dump of assembler code from 0x63e4 to 0x6404: 0x63e4 : ble 0x63f8 0x63e8 : sethi %hi(0x4c00), %o0 0x63ec : ld [%i1+4], %o0 0x63f0 : b 0x63fc 0x63f4 : ld [%o0+4], %o0 0x63f8 : or %o0, 0x1a4, %o0 0x63fc : call 0x9288 0x6400 : nop End of assembler dump. (_GDBP__) @end smallexample @node Data, Languages, Source, Top @chapter Examining Data @cindex printing data @cindex examining data @kindex print @kindex inspect @c "inspect" isn't quite a synonym if you're using Epoch, which we don't @c document because it's nonstandard... Under Epoch it displays in a @c different window or something like that. The usual way to examine data in your program is with the @code{print} command (abbreviated @code{p}), or its synonym @code{inspect}. It evaluates and prints the value of an expression of the language your program is written in (@pxref{Languages}). You type @example print @var{exp} @end example @noindent where @var{exp} is an expression (in the source language), and the value of @var{exp} is printed in a format appropriate to its data type. A more low-level way of examining data is with the @code{x} command. It examines data in memory at a specified address and prints it in a specified format. @xref{Memory}. If you're interested in information about types, or about how the fields of a struct or class are declared, use the @code{ptype @var{exp}} command rather than @code{print}. @xref{Symbols}. @menu * Expressions:: Expressions * Variables:: Program Variables * Arrays:: Artificial Arrays * Output formats:: Output formats * Memory:: Examining Memory * Auto Display:: Automatic Display * Print Settings:: Print Settings * Value History:: Value History * Convenience Vars:: Convenience Variables * Registers:: Registers * Floating Point Hardware:: Floating Point Hardware @end menu @node Expressions, Variables, Data, Data @section Expressions @cindex expressions @code{print} and many other _GDBN__ commands accept an expression and compute its value. Any kind of constant, variable or operator defined by the programming language you are using is legal in an expression in _GDBN__. This includes conditional expressions, function calls, casts and string constants. It unfortunately does not include symbols defined by preprocessor @code{#define} commands. Because C is so widespread, most of the expressions shown in examples in this manual are in C. @xref{Languages,, Using _GDBN__ with Different Languages}, for information on how to use expressions in other languages. In this section, we discuss operators that you can use in _GDBN__ expressions regardless of your programming language. Casts are supported in all languages, not just in C, because it is so useful to cast a number into a pointer so as to examine a structure at that address in memory. @c FIXME: casts supported---Mod2 true? _GDBN__ supports these operators in addition to those of programming languages: @table @code @item @@ @samp{@@} is a binary operator for treating parts of memory as arrays. @xref{Arrays}, for more information. @item :: @samp{::} allows you to specify a variable in terms of the file or function where it is defined. @xref{Variables}. @item @{@var{type}@} @var{addr} Refers to an object of type @var{type} stored at address @var{addr} in memory. @var{addr} may be any expression whose value is an integer or pointer (but parentheses are required around binary operators, just as in a cast). This construct is allowed regardless of what kind of data is normally supposed to reside at @var{addr}.@refill @end table @node Variables, Arrays, Expressions, Data @section Program Variables The most common kind of expression to use is the name of a variable in your program. Variables in expressions are understood in the selected stack frame (@pxref{Selection}); they must either be global (or static) or be visible according to the scope rules of the programming language from the point of execution in that frame. This means that in the function @example foo (a) int a; @{ bar (a); @{ int b = test (); bar (b); @} @} @end example @noindent the variable @code{a} is usable whenever the program is executing within the function @code{foo}, but the variable @code{b} is visible only while the program is executing inside the block in which @code{b} is declared. @cindex variable name conflict There is an exception: you can refer to a variable or function whose scope is a single source file even if the current execution point is not in this file. But it is possible to have more than one such variable or function with the same name (in different source files). If that happens, referring to that name has unpredictable effects. If you wish, you can specify a variable in a particular file, using the colon-colon notation: @cindex colon-colon @kindex :: @example @var{file}::@var{variable} @end example @noindent Here @var{file} is the name of the source file whose variable you want. @cindex C++ scope resolution This use of @samp{::} is very rarely in conflict with the very similar use of the same notation in C++. _GDBN__ also supports use of the C++ scope resolution operator in _GDBN__ expressions. @cindex wrong values @cindex variable values, wrong @quotation @emph{Warning:} Occasionally, a local variable may appear to have the wrong value at certain points in a function---just after entry to the function, and just before exit. You may see this problem when you're stepping by machine instructions. This is because on most machines, it takes more than one instruction to set up a stack frame (including local variable definitions); if you're stepping by machine instructions, variables may appear to have the wrong values until the stack frame is completely built. On function exit, it usually also takes more than one machine instruction to destroy a stack frame; after you begin stepping through that group of instructions, local variable definitions may be gone. @end quotation @node Arrays, Output formats, Variables, Data @section Artificial Arrays @cindex artificial array @kindex @@ It is often useful to print out several successive objects of the same type in memory; a section of an array, or an array of dynamically determined size for which only a pointer exists in the program. This can be done by constructing an @dfn{artificial array} with the binary operator @samp{@@}. The left operand of @samp{@@} should be the first element of the desired array, as an individual object. The right operand should be the desired length of the array. The result is an array value whose elements are all of the type of the left argument. The first element is actually the left argument; the second element comes from bytes of memory immediately following those that hold the first element, and so on. Here is an example. If a program says @example int *array = (int *) malloc (len * sizeof (int)); @end example @noindent you can print the contents of @code{array} with @example p *array@@len @end example The left operand of @samp{@@} must reside in memory. Array values made with @samp{@@} in this way behave just like other arrays in terms of subscripting, and are coerced to pointers when used in expressions. Artificial arrays most often appear in expressions via the value history (@pxref{Value History}), after printing one out.) Sometimes the artificial array mechanism isn't quite enough; in moderately complex data structures, the elements of interest may not actually be adjacent---for example, if you're interested in the values of pointers in an array. One useful work-around in this situation is to use a convenience variable (@pxref{Convenience Vars}) as a counter in an expression that prints the first interesting value, and then repeat that expression via @key{RET}. For instance, suppose you have an array @code{dtab} of pointers to structures, and you're interested in the values of a field @code{fv} in each structure. Here's an example of what you might type: @example set $i = 0 p dtab[$i++]->fv @key{RET} @key{RET} @dots{} @end example @node Output formats, Memory, Arrays, Data @section Output formats @cindex formatted output @cindex output formats By default, _GDBN__ prints a value according to its data type. Sometimes this is not what you want. For example, you might want to print a number in hex, or a pointer in decimal. Or you might want to view data in memory at a certain address as a character string or as an instruction. To do these things, specify an @dfn{output format} when you print a value. The simplest use of output formats is to say how to print a value already computed. This is done by starting the arguments of the @code{print} command with a slash and a format letter. The format letters supported are: @table @code @item x Regard the bits of the value as an integer, and print the integer in hexadecimal. @item d Print as integer in signed decimal. @item u Print as integer in unsigned decimal. @item o Print as integer in octal. @item t Print as integer in binary. The letter @samp{t} stands for ``two''. @item a Print as an address, both absolute in hex and as an offset from the nearest preceding symbol. This format can be used to discover where (in what function) an unknown address is located: @example (_GDBP__) p/a 0x54320 _0__$3 = 0x54320 <_initialize_vx+396>_1__ @end example @item c Regard as an integer and print it as a character constant. @item f Regard the bits of the value as a floating point number and print using typical floating point syntax. @end table For example, to print the program counter in hex (@pxref{Registers}), type @example p/x $pc @end example @noindent Note that no space is required before the slash; this is because command names in _GDBN__ cannot contain a slash. To reprint the last value in the value history with a different format, you can use the @code{print} command with just a format and no expression. For example, @samp{p/x} reprints the last value in hex. @node Memory, Auto Display, Output formats, Data @section Examining Memory @cindex examining memory @table @code @kindex x @item x/@var{nfu} @var{expr} The command @code{x} (for `examine') can be used to examine memory without being constrained by your program's data types. You can specify the unit size @var{u} of memory to inspect, and a repeat count @var{n} of how many of those units to display. @code{x} understands the formats @var{f} used by @code{print}; two additional formats, @samp{s} (string) and @samp{i} (machine instruction) can be used without specifying a unit size. @end table For example, @samp{x/3uh 0x54320} is a request to display three halfwords (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}), starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four words (@samp{w}) of memory above the stack pointer (here, @samp{$sp}; @pxref{Registers}) in hexadecimal (@samp{x}). Since the letters indicating unit sizes are all distinct from the letters specifying output formats, you don't have to remember whether unit size or format comes first; either order will work. The output specifications @samp{4xw} and @samp{4wx} mean exactly the same thing. After the format specification, you supply an expression for the address where _GDBN__ is to begin reading from memory. The expression need not have a pointer value (though it may); it is always interpreted as an integer address of a byte of memory. @xref{Expressions} for more information on expressions. These are the memory units @var{u} you can specify with the @code{x} command: @table @code @item b Examine individual bytes. @item h Examine halfwords (two bytes each). @item w Examine words (four bytes each). @cindex word Many assemblers and cpu designers still use `word' for a 16-bit quantity, as a holdover from specific predecessor machines of the 1970's that really did use two-byte words. But more generally the term `word' has always referred to the size of quantity that a machine normally operates on and stores in its registers. This is 32 bits for all the machines that _GDBN__ runs on. @item g Examine giant words (8 bytes). @end table You can combine these unit specifications with any of the formats described for @code{print}. @xref{Output formats}. @code{x} has two additional output specifications which derive the unit size from the data inspected: @table @code @item s Print a null-terminated string of characters. Any explicitly specified unit size is ignored; instead, the unit is however many bytes it takes to reach a null character (including the null character). @item i Print a machine instruction in assembler syntax (or nearly). Any specified unit size is ignored; the number of bytes in an instruction varies depending on the type of machine, the opcode and the addressing modes used. The command @code{disassemble} gives an alternative way of inspecting machine instructions. @xref{Machine Code}. @end table If you omit either the format @var{f} or the unit size @var{u}, @code{x} will use the same one that was used last. If you don't use any letters or digits after the slash, you can omit the slash as well. You can also omit the address to examine. Then the address used is just after the last unit examined. This is why string and instruction formats actually compute a unit-size based on the data: so that the next string or instruction examined will start in the right place. When the @code{print} command shows a value that resides in memory, @code{print} also sets the default address for the @code{x} command. @code{info line} also sets the default for @code{x}, to the address of the start of the machine code for the specified line (@pxref{Machine Code}), and @code{info breakpoints} sets it to the address of the last breakpoint listed (@pxref{Set Breaks}). When you use @key{RET} to repeat an @code{x} command, the address specified previously (if any) is ignored, so that the repeated command examines the successive locations in memory rather than the same ones. You can examine several consecutive units of memory with one command by writing a repeat-count after the slash (before the format letters, if any). Omitting the repeat count @var{n} displays one unit of the appropriate size. The repeat count must be a decimal integer. It has the same effect as repeating the @code{x} command @var{n} times except that the output may be more compact, with several units per line. For example, @example x/10i $pc @end example @noindent prints ten instructions starting with the one to be executed next in the selected frame. After doing this, you could print a further seven instructions with @example x/7 @end example @noindent ---where the format and address are allowed to default. @cindex @code{$_}, @code{$__}, and value history The addresses and contents printed by the @code{x} command are not put in the value history because there is often too much of them and they would get in the way. Instead, _GDBN__ makes these values available for subsequent use in expressions as values of the convenience variables @code{$_} and @code{$__}. After an @code{x} command, the last address examined is available for use in expressions in the convenience variable @code{$_}. The contents of that address, as examined, are available in the convenience variable @code{$__}. If the @code{x} command has a repeat count, the address and contents saved are from the last memory unit printed; this is not the same as the last address printed if several units were printed on the last line of output. @node Auto Display, Print Settings, Memory, Data @section Automatic Display @cindex automatic display @cindex display of expressions If you find that you want to print the value of an expression frequently (to see how it changes), you might want to add it to the @dfn{automatic display list} so that _GDBN__ will print its value each time the program stops. Each expression added to the list is given a number to identify it; to remove an expression from the list, you specify that number. The automatic display looks like this: @example 2: foo = 38 3: bar[5] = (struct hack *) 0x3804 @end example @noindent showing item numbers, expressions and their current values. As with displays you request manually using @code{x} or @code{print}, you can specify the output format you prefer; in fact, @code{display} decides whether to use @code{print} or @code{x} depending on how elaborate your format specification is---it uses @code{x} if you specify a unit size, or one of the two formats (@samp{i} and @samp{s}) that are only supported by @code{x}; otherwise it uses @code{print}. @table @code @item display @var{exp} @kindex display Add the expression @var{exp} to the list of expressions to display each time the program stops. @xref{Expressions}. @code{display} will not repeat if you press @key{RET} again after using it. @item display/@var{fmt} @var{exp} For @var{fmt} specifying only a display format and not a size or count, add the expression @var{exp} to the auto-display list but arranges to display it each time in the specified format @var{fmt}. @xref{Output formats}. @item display/@var{fmt} @var{addr} For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a number of units, add the expression @var{addr} as a memory address to be examined each time the program stops. Examining means in effect doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory}. @end table For example, @samp{display/i $pc} can be helpful, to see the machine instruction about to be executed each time execution stops (@samp{$pc} is a common name for the program counter; @pxref{Registers}). @table @code @item undisplay @var{dnums}@dots{} @itemx delete display @var{dnums}@dots{} @kindex delete display @kindex undisplay Remove item numbers @var{dnums} from the list of expressions to display. @code{undisplay} will not repeat if you press @key{RET} after using it. (Otherwise you would just get the error @samp{No display number @dots{}}.) @item disable display @var{dnums}@dots{} @kindex disable display Disable the display of item numbers @var{dnums}. A disabled display item is not printed automatically, but is not forgotten. It may be enabled again later. @item enable display @var{dnums}@dots{} @kindex enable display Enable display of item numbers @var{dnums}. It becomes effective once again in auto display of its expression, until you specify otherwise. @item display Display the current values of the expressions on the list, just as is done when the program stops. @item info display @kindex info display Print the list of expressions previously set up to display automatically, each one with its item number, but without showing the values. This includes disabled expressions, which are marked as such. It also includes expressions which would not be displayed right now because they refer to automatic variables not currently available. @end table If a display expression refers to local variables, then it does not make sense outside the lexical context for which it was set up. Such an expression is disabled when execution enters a context where one of its variables is not defined. For example, if you give the command @code{display last_char} while inside a function with an argument @code{last_char}, then this argument will be displayed while the program continues to stop inside that function. When it stops elsewhere---where there is no variable @code{last_char}---display is disabled. The next time your program stops where @code{last_char} is meaningful, you can enable the display expression once again. @node Print Settings, Value History, Auto Display, Data @section Print Settings @cindex format options @cindex print settings _GDBN__ provides the following ways to control how arrays, structures, and symbols are printed. @noindent These settings are useful for debugging programs in any language: @table @code @item set print address @item set print address on @kindex set print address _GDBN__ will print memory addresses showing the location of stack traces, structure values, pointer values, breakpoints, and so forth, even when it also displays the contents of those addresses. The default is on. For example, this is what a stack frame display looks like, with @code{set print address on}: @smallexample (_GDBP__) f #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>") at input.c:530 530 if (lquote != def_lquote) @end smallexample @item set print address off Do not print addresses when displaying their contents. For example, this is the same stack frame displayed with @code{set print address off}: @example (_GDBP__) set print addr off (_GDBP__) f #0 set_quotes (lq="<<", rq=">>") at input.c:530 530 if (lquote != def_lquote) @end example @item show print address @kindex show print address Show whether or not addresses are to be printed. @item set print array @itemx set print array on @kindex set print array _GDBN__ will pretty print arrays. This format is more convenient to read, but uses more space. The default is off. @item set print array off. Return to compressed format for arrays. @item show print array @kindex show print array Show whether compressed or pretty format is selected for displaying arrays. @item set print elements @var{number-of-elements} @kindex set print elements If _GDBN__ is printing a large array, it will stop printing after it has printed the number of elements set by the @code{set print elements} command. This limit also applies to the display of strings. @item show print elements @kindex show print elements Display the number of elements of a large array that _GDBN__ will print before losing patience. @item set print pretty on @kindex set print pretty Cause _GDBN__ to print structures in an indented format with one member per line, like this: @example $1 = @{ next = 0x0, flags = @{ sweet = 1, sour = 1 @}, meat = 0x54 "Pork" @} @end example @item set print pretty off Cause _GDBN__ to print structures in a compact format, like this: @smallexample $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, meat \ = 0x54 "Pork"@} @end smallexample @noindent This is the default format. @item show print pretty @kindex show print pretty Show which format _GDBN__ will use to print structures. @item set print sevenbit-strings on @kindex set print sevenbit-strings Print using only seven-bit characters; if this option is set, _GDBN__ will display any eight-bit characters (in strings or character values) using the notation @code{\}@var{nnn}. For example, @kbd{M-a} is displayed as @code{\341}. @item set print sevenbit-strings off Print using either seven-bit or eight-bit characters, as required. This is the default. @item show print sevenbit-strings @kindex show print sevenbit-strings Show whether or not _GDBN__ will print only seven-bit characters. @item set print union on @kindex set print union Tell _GDBN__ to print unions which are contained in structures. This is the default setting. @item set print union off Tell _GDBN__ not to print unions which are contained in structures. @item show print union @kindex show print union Ask _GDBN__ whether or not it will print unions which are contained in structures. For example, given the declarations @smallexample typedef enum @{Tree, Bug@} Species; typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms; typedef enum @{Caterpillar, Cocoon, Butterfly@} Bug_forms; struct thing @{ Species it; union @{ Tree_forms tree; Bug_forms bug; @} form; @}; struct thing foo = @{Tree, @{Acorn@}@}; @end smallexample @noindent with @code{set print union on} in effect @samp{p foo} would print @smallexample $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@} @end smallexample @noindent and with @code{set print union off} in effect it would print @smallexample $1 = @{it = Tree, form = @{...@}@} @end smallexample @end table @noindent These settings are of interest when debugging C++ programs: @table @code @item set print demangle @itemx set print demangle on @kindex set print demangle Print C++ names in their source form rather than in the mangled form in which they are passed to the assembler and linker for type-safe linkage. The default is on. @item show print demangle @kindex show print demangle Show whether C++ names will be printed in mangled or demangled form. @item set print asm-demangle @itemx set print asm-demangle on @kindex set print asm-demangle Print C++ names in their source form rather than their mangled form, even in assembler code printouts such as instruction disassemblies. The default is off. @item show print asm-demangle @kindex show print asm-demangle Show whether C++ names in assembly listings will be printed in mangled or demangled form. @item set print object @itemx set print object on @kindex set print object When displaying a pointer to an object, identify the @emph{actual} (derived) type of the object rather than the @emph{declared} type, using the virtual function table. @item set print object off Display only the declared type of objects, without reference to the virtual function table. This is the default setting. @item show print object @kindex show print object Show whether actual, or declared, object types will be displayed. @item set print vtbl @itemx set print vtbl on @kindex set print vtbl Pretty print C++ virtual function tables. The default is off. @item set print vtbl off Do not pretty print C++ virtual function tables. @item show print vtbl @kindex show print vtbl Show whether C++ virtual function tables are pretty printed, or not. @end table @node Value History, Convenience Vars, Print Settings, Data @section Value History @cindex value history Values printed by the @code{print} command are saved in _GDBN__'s @dfn{value history} so that you can refer to them in other expressions. Values are kept until the symbol table is re-read or discarded (for example with the @code{file} or @code{symbol-file} commands). When the symbol table changes, the value history is discarded, since the values may contain pointers back to the types defined in the symbol table. @cindex @code{$} @cindex @code{$$} @cindex history number The values printed are given @dfn{history numbers} for you to refer to them by. These are successive integers starting with one. @code{print} shows you the history number assigned to a value by printing @samp{$@var{num} = } before the value; here @var{num} is the history number. To refer to any previous value, use @samp{$} followed by the value's history number. The way @code{print} labels its output is designed to remind you of this. Just @code{$} refers to the most recent value in the history, and @code{$$} refers to the value before that. @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2} is the value just prior to @code{$$}, @code{$$1} is equivalent to @code{$$}, and @code{$$0} is equivalent to @code{$}. For example, suppose you have just printed a pointer to a structure and want to see the contents of the structure. It suffices to type @example p *$ @end example If you have a chain of structures where the component @code{next} points to the next one, you can print the contents of the next one with this: @example p *$.next @end example @noindent You can print successive links in the chain by repeating this command---which you can do by just typing @key{RET}. Note that the history records values, not expressions. If the value of @code{x} is 4 and you type these commands: @example print x set x=5 @end example @noindent then the value recorded in the value history by the @code{print} command remains 4 even though the value of @code{x} has changed. @table @code @kindex show values @item show values Print the last ten values in the value history, with their item numbers. This is like @samp{p@ $$9} repeated ten times, except that @code{show values} does not change the history. @item show values @var{n} Print ten history values centered on history item number @var{n}. @item show values + Print ten history values just after the values last printed. If no more values are available, produces no display. @end table Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the same effect as @samp{show values +}. @node Convenience Vars, Registers, Value History, Data @section Convenience Variables @cindex convenience variables _GDBN__ provides @dfn{convenience variables} that you can use within _GDBN__ to hold on to a value and refer to it later. These variables exist entirely within _GDBN__; they are not part of your program, and setting a convenience variable has no direct effect on further execution of your program. That's why you can use them freely. Convenience variables are prefixed with @samp{$}. Any name preceded by @samp{$} can be used for a convenience variable, unless it is one of the predefined machine-specific register names (@pxref{Registers}). (Value history references, in contrast, are @emph{numbers} preceded by @samp{$}. @xref{Value History}.) You can save a value in a convenience variable with an assignment expression, just as you would set a variable in your program. Example: @example set $foo = *object_ptr @end example @noindent would save in @code{$foo} the value contained in the object pointed to by @code{object_ptr}. Using a convenience variable for the first time creates it; but its value is @code{void} until you assign a new value. You can alter the value with another assignment at any time. Convenience variables have no fixed types. You can assign a convenience variable any type of value, including structures and arrays, even if that variable already has a value of a different type. The convenience variable, when used as an expression, has the type of its current value. @table @code @item show convenience @kindex show convenience Print a list of convenience variables used so far, and their values. Abbreviated @code{show con}. @end table One of the ways to use a convenience variable is as a counter to be incremented or a pointer to be advanced. For example, to print a field from successive elements of an array of structures: _0__@example set $i = 0 print bar[$i++]->contents @i{@dots{} repeat that command by typing @key{RET}.} _1__@end example Some convenience variables are created automatically by _GDBN__ and given values likely to be useful. @table @code @item $_ @kindex $_ The variable @code{$_} is automatically set by the @code{x} command to the last address examined (@pxref{Memory}). Other commands which provide a default address for @code{x} to examine also set @code{$_} to that address; these commands include @code{info line} and @code{info breakpoint}. The type of @code{$_} is @code{void *} except when set by the @code{x} command, in which case it is a pointer to the type of @code{$__}. @item $__ @kindex $__ The variable @code{$__} is automatically set by the @code{x} command to the value found in the last address examined. Its type is chosen to match the format in which the data was printed. @end table @node Registers, Floating Point Hardware, Convenience Vars, Data @section Registers @cindex registers You can refer to machine register contents, in expressions, as variables with names starting with @samp{$}. The names of registers are different for each machine; use @code{info registers} to see the names used on your machine. @table @code @item info registers @kindex info registers Print the names and values of all registers except floating-point registers (in the selected stack frame). @item info all-registers @kindex info all-registers @cindex floating point registers Print the names and values of all registers, including floating-point registers. @item info registers @var{regname} Print the relativized value of register @var{regname}. @var{regname} may be any register name valid on the machine you are using, with or without the initial @samp{$}. @end table The register names @code{$pc} and @code{$sp} are used on most machines for the program counter register and the stack pointer. For example, you could print the program counter in hex with @example p/x $pc @end example @noindent or print the instruction to be executed next with @example x/i $pc @end example @noindent or add four to the stack pointer with @example set $sp += 4 @end example @noindent The last is a way of removing one word from the stack, on machines where stacks grow downward in memory (most machines, nowadays). This assumes that the innermost stack frame is selected; setting @code{$sp} is not allowed when other stack frames are selected. (To pop entire frames off the stack, regardless of machine architecture, use @code{return}; @pxref{Returning}.) Often @code{$fp} is used for a register that contains a pointer to the current stack frame, and @code{$ps} is sometimes used for a register that contains the processor status. These standard register names may be available on your machine even though the @code{info registers} command shows other names. For example, on the SPARC, @code{info registers} displays the processor status register as @code{$psr} but you can also refer to it as @code{$ps}. _GDBN__ always considers the contents of an ordinary register as an integer when the register is examined in this way. Some machines have special registers which can hold nothing but floating point; these registers are considered to have floating point values. There is no way to refer to the contents of an ordinary register as floating point value (although you can @emph{print} it as a floating point value with @samp{print/f $@var{regname}}). Some registers have distinct ``raw'' and ``virtual'' data formats. This means that the data format in which the register contents are saved by the operating system is not the same one that your program normally sees. For example, the registers of the 68881 floating point coprocessor are always saved in ``extended'' (raw) format, but all C programs expect to work with ``double'' (virtual) format. In such cases, _GDBN__ normally works with the virtual format only (the format that makes sense for your program), but the @code{info registers} command prints the data in both formats. Normally, register values are relative to the selected stack frame (@pxref{Selection}). This means that you get the value that the register would contain if all stack frames farther in were exited and their saved registers restored. In order to see the true contents of hardware registers, you must select the innermost frame (with @samp{frame 0}). However, _GDBN__ must deduce where registers are saved, from the machine code generated by your compiler. If some registers are not saved, or if _GDBN__ is unable to locate the saved registers, the selected stack frame will make no difference. @node Floating Point Hardware, , Registers, Data @section Floating Point Hardware @cindex floating point Depending on the host machine architecture, _GDBN__ may be able to give you more information about the status of the floating point hardware. @table @code @item info float @kindex info float If available, provides hardware-dependent information about the floating point unit. The exact contents and layout vary depending on the floating point chip. @end table @c FIXME: this is a cop-out. Try to get examples, explanations. Only @c FIXME...supported currently on arm's and 386's. Mark properly with @c FIXME... m4 macros to isolate general statements from hardware-dep, @c FIXME... at that point. @node Languages, Symbols, Data, Top @chapter Using _GDBN__ with Different Languages @cindex languages Although programming languages generally have common aspects, they are rarely expressed in the same manner. For instance, in ANSI C, dereferencing a pointer @code{p} is accomplished by @code{*p}, but in Modula-2, it is accomplished by @code{p^}. Values can also be represented (and displayed) differently. Hex numbers in C are written like @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}. @cindex working language Language-specific information is built into _GDBN__ for some languages, allowing you to express operations like the above in the program's native language, and allowing _GDBN__ to output values in a manner consistent with the syntax of the program's native language. The language you use to build expressions, called the @dfn{working language}, can be selected manually, or _GDBN__ can set it automatically. @menu * Setting:: Switching between source languages * Show:: Displaying the language * Checks:: Type and Range checks * Support:: Supported languages @end menu @node Setting, Show, Languages, Languages @section Switching between source languages There are two ways to control the working language---either have _GDBN__ set it automatically, or select it manually yourself. You can use the @code{set language} command for either purpose. On startup, _GDBN__ defaults to setting the language automatically. @menu * Manually:: Setting the working language manually * Automatically:: Having _GDBN__ infer the source language @end menu @node Manually, Automatically, Setting, Setting @subsection Setting the working language @kindex set language To set the language, issue the command @samp{set language @var{lang}}, where @var{lang} is the name of a language: @code{c} or @code{modula-2}. For a list of the supported languages, type @samp{set language}. Setting the language manually prevents _GDBN__ from updating the working language automatically. This can lead to confusion if you try to debug a program when the working language is not the same as the source language, when an expression is acceptable to both languages---but means different things. For instance, if the current source file were written in C, and _GDBN__ was parsing Modula-2, a command such as: @example print a = b + c @end example @noindent might not have the effect you intended. In C, this means to add @code{b} and @code{c} and place the result in @code{a}. The result printed would be the value of @code{a}. In Modula-2, this means to compare @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value. If you allow _GDBN__ to set the language automatically, then you can count on expressions evaluating the same way in your debugging session and in your program. @node Automatically, , Manually, Setting @subsection Having _GDBN__ infer the source language To have _GDBN__ set the working language automatically, use @samp{set language local} or @samp{set language auto}. _GDBN__ then infers the language that a program was written in by looking at the name of its source files, and examining their extensions: @table @file @item *.mod Modula-2 source file @item *.c @itemx *.cc C or C++ source file. @end table This information is recorded for each function or procedure in a source file. When your program stops in a frame (usually by encountering a breakpoint), _GDBN__ sets the working language to the language recorded for the function in that frame. If the language for a frame is unknown (that is, if the function or block corresponding to the frame was defined in a source file that does not have a recognized extension), the current working language is not changed, and _GDBN__ issues a warning. This may not seem necessary for most programs, which are written entirely in one source language. However, program modules and libraries written in one source language can be used by a main program written in a different source language. Using @samp{set language auto} in this case frees you from having to set the working language manually. @node Show, Checks, Setting, Languages @section Displaying the language The following commands will help you find out which language is the working language, and also what language source files were written in. @kindex show language @kindex info frame @kindex info source @table @code @item show language Display the current working language. This is the language you can use with commands such as @code{print} to build and compute expressions that may involve variables in the program. @item info frame Among the other information listed here (@pxref{Frame Info,,Information about a Frame}) is the source language for this frame. This is the language that will become the working language if you ever use an identifier that is in this frame. @item info source Among the other information listed here (@pxref{Symbols,,Examining the Symbol Table}) is the source language of this source file. @end table @node Checks, Support, Show, Languages @section Type and range Checking @quotation @emph{Warning:} In this release, the _GDBN__ commands for type and range checking are included, but they do not yet have any effect. This section documents the intended facilities. @end quotation @c FIXME remove warning when type/range code added Some languages are designed to guard you against making seemingly common errors through a series of compile- and run-time checks. These include checking the type of arguments to functions and operators, and making sure mathematical overflows are caught at run time. Checks such as these help to ensure a program's correctness once it has been compiled by eliminating type mismatches, and providing active checks for range errors when the program is running. _GDBN__ can check for conditions like the above if you wish. Although _GDBN__ will not check the statements in your program, it can check expressions entered directly into _GDBN__ for evaluation via the @code{print} command, for example. As with the working language, _GDBN__ can also decide whether or not to check automatically based on the source language of the program being debugged. @xref{Support,,Supported Languages}, for the default settings of supported languages. @menu * Type Checking:: An overview of type checking * Range Checking:: An overview of range checking @end menu @cindex type checking @cindex checks, type @node Type Checking, Range Checking, Checks, Checks @subsection An overview of type checking Some languages, such as Modula-2, are strongly typed, meaning that the arguments to operators and functions have to be of the correct type, otherwise an error occurs. These checks prevent type mismatch errors from ever causing any run-time problems. For example, @example 1 + 2 @result{} 3 @error{} 1 + 2.3 @end example The second example fails because the @code{CARDINAL} 1 is not type-compatible with the @code{REAL} 2.3. For expressions you use in _GDBN__ commands, you can tell the _GDBN__ type checker to skip checking; to treat any mismatches as errors and abandon the expression; or only issue warnings when type mismatches occur, but evaluate the expression anyway. When you choose the last of these, _GDBN__ evaluates expressions like the second example above, but also issues a warning. Even though you may turn type checking off, other type-based reasons may prevent _GDBN__ from evaluating an expression. For instance, _GDBN__ does not know how to add an @code{int} and a @code{struct foo}. These particular type errors have nothing to do with the language in use, and usually arise from expressions, such as the one described above, which make little sense to evaluate anyway. Each language defines to what degree it is strict about type. For instance, both Modula-2 and C require the arguments to arithmetical operators to be numbers. In C, enumerated types and pointers can be represented as numbers, so that they are valid arguments to mathematical operators. @xref{Support,,Supported Languages}, for futher details on specific languages. _GDBN__ provides some additional commands for controlling the type checker: @kindex set check @kindex set check type @kindex show check type @table @code @item set check type auto Set type checking on or off based on the current working language. @xref{Support,,Supported Languages}, for the default settings for each language. @item set check type on @itemx set check type off Set type checking on or off, overriding the default setting for the current working language. Issue a warning if the setting does not match the language's default. If any type mismatches occur in evaluating an expression while typechecking is on, _GDBN__ prints a message and aborts evaluation of the expression. @item set check type warn Cause the type checker to issue warnings, but to always attempt to evaluate the expression. Evaluating the expression may still be impossible for other reasons. For example, _GDBN__ cannot add numbers and structures. @item show type Show the current setting of the type checker, and whether or not _GDBN__ is setting it automatically. @end table @cindex range checking @cindex checks, range @node Range Checking, , Type Checking, Checks @subsection An overview of Range Checking In some languages (such as Modula-2), it is an error to exceed the bounds of a type; this is enforced with run-time checks. Such range checking is meant to ensure program correctness by making sure computations do not overflow, or indices on an array element access do not exceed the bounds of the array. For expressions you use in _GDBN__ commands, you can tell _GDBN__ to ignore range errors; to always treat them as errors and abandon the expression; or to issue warnings when a range error occurs but evaluate the expression anyway. A range error can result from numerical overflow, from exceeding an array index bound, or when you type in a constant that is not a member of any type. Some languages, however, do not treat overflows as an error. In many implementations of C, mathematical overflow causes the result to ``wrap around'' to lower values---for example, if @var{m} is the largest integer value, and @var{s} is the smallest, then @example @var{m} + 1 @result{} @var{s} @end example This, too, is specific to individual languages, and in some cases specific to individual compilers or machines. @xref{Support,, Supported Languages}, for further details on specific languages. _GDBN__ provides some additional commands for controlling the range checker: @kindex set check @kindex set check range @kindex show check range @table @code @item set check range auto Set range checking on or off based on the current working language. @xref{Support,,Supported Languages}, for the default settings for each language. @item set check range on @itemx set check range off Set range checking on or off, overriding the default setting for the current working language. A warning is issued if the setting does not match the language's default. If a range error occurs, then a message is printed and evaluation of the expression is aborted. @item set check range warn Output messages when the _GDBN__ range checker detects a range error, but attempt to evaluate the expression anyway. Evaluating the expression may still be impossible for other reasons, such as accessing memory that the process does not own (a typical example from many UNIX systems). @item show range Show the current setting of the range checker, and whether or not it is being set automatically by _GDBN__. @end table @node Support, , Checks, Languages @section Supported Languages _GDBN__ _GDB_VN__ supports C, C++, and Modula-2. The syntax for C and C++ is so closely related that _GDBN__ does not distinguish the two. Some _GDBN__ features may be used in expressions regardless of the language you use: the _GDBN__ @code{@@} and @code{::} operators, and the @samp{@{type@}addr} construct (@pxref{Expressions}) can be used with the constructs of any of the supported languages. The following sections detail to what degree each of these source languages is supported by _GDBN__. These sections are not meant to be language tutorials or references, but serve only as a reference guide to what the _GDBN__ expression parser will accept, and what input and output formats should look like for different languages. There are many good books written on each of these languages; please look to these for a language reference or tutorial. @menu * C:: C and C++ * Modula-2:: Modula-2 @end menu @node C, Modula-2, Support, Support @subsection C and C++ @cindex C and C++ @cindex expressions in C or C++ Since C and C++ are so closely related, _GDBN__ does not distinguish between them when interpreting the expressions recognized in _GDBN__ commands. @cindex C++ @kindex g++ @cindex GNU C++ The C++ debugging facilities are jointly implemented by the GNU C++ compiler and _GDBN__. Therefore, to debug your C++ code effectively, you must compile your C++ programs with the GNU C++ compiler, @code{g++}. @menu * C Operators:: C and C++ Operators * C Constants:: C and C++ Constants * Cplusplus expressions:: C++ Expressions * C Defaults:: Default settings for C and C++ * C Checks:: C and C++ Type and Range Checks * Debugging C:: _GDBN__ and C * Debugging C plus plus:: Special features for C++ @end menu @cindex C and C++ operators @node C Operators, C Constants, C, C @subsubsection C and C++ Operators Operators must be defined on values of specific types. For instance, @code{+} is defined on numbers, but not on structures. Operators are often defined on groups of types. For the purposes of C and C++, the following definitions hold: @itemize @bullet @item @emph{Integral types} include @code{int} with any of its storage-class specifiers, @code{char}, and @code{enum}s. @item @emph{Floating-point types} include @code{float} and @code{double}. @item @emph{Pointer types} include all types defined as @code{(@var{type} *)}. @item @emph{Scalar types} include all of the above. @end itemize @noindent The following operators are supported. They are listed here in order of increasing precedence: @table @code _0__ @item , The comma or sequencing operator. Expressions in a comma-separated list are evaluated from left to right, with the result of the entire expression being the last expression evaluated. @item = Assignment. The value of an assignment expression is the value assigned. Defined on scalar types. @item @var{op}= Used in an expression of the form @var{a} @var{op}@code{=} @var{b}, and translated to @var{a} @code{=} @var{a op b}. @var{op}@code{=} and @code{=} have the same precendence. @var{op} is any one of the operators @code{|}, @code{^}, @code{&}, @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}. @item ?: The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an integral type. @item || Logical OR. Defined on integral types. @item && Logical AND. Defined on integral types. @item | Bitwise OR. Defined on integral types. @item ^ Bitwise exclusive-OR. Defined on integral types. @item & Bitwise AND. Defined on integral types. @item ==@r{, }!= Equality and inequality. Defined on scalar types. The value of these expressions is 0 for false and non-zero for true. @item <@r{, }>@r{, }<=@r{, }>= Less than, greater than, less than or equal, greater than or equal. Defined on scalar types. The value of these expressions is 0 for false and non-zero for true. @item <<@r{, }>> left shift, and right shift. Defined on integral types. @item @@ The _GDBN__ ``artificial array'' operator (@pxref{Expressions}). @item +@r{, }- Addition and subtraction. Defined on integral types, floating-point types and pointer types. @item *@r{, }/@r{, }% Multiplication, division, and modulus. Multiplication and division are defined on integral and floating-point types. Modulus is defined on integral types. @item ++@r{, }-- Increment and decrement. When appearing before a variable, the operation is performed before the variable is used in an expression; when appearing after it, the variable's value is used before the operation takes place. @item * Pointer dereferencing. Defined on pointer types. Same precedence as @code{++}. @item & Address operator. Defined on variables. Same precedence as @code{++}. @item - Negative. Defined on integral and floating-point types. Same precedence as @code{++}. @item ! Logical negation. Defined on integral types. Same precedence as @code{++}. @item ~ Bitwise complement operator. Defined on integral types. Same precedence as @code{++}. @item .@r{, }-> Structure member, and pointer-to-structure member. For convenience, _GDBN__ regards the two as equivalent, choosing whether to dereference a pointer based on the stored type information. Defined on @code{struct}s and @code{union}s. @item [] Array indexing. @code{@var{a}[@var{i}]} is defined as @code{*(@var{a}+@var{i})}. Same precedence as @code{->}. @item () Function parameter list. Same precedence as @code{->}. @item :: C++ scope resolution operator. Defined on @code{struct}, @code{union}, and @code{class} types. @item :: The _GDBN__ scope operator (@pxref{Expressions}). Same precedence as @code{::}, above. _1__ @end table @cindex C and C++ constants @node C Constants, Cplusplus expressions, C Operators, C @subsubsection C and C++ Constants _GDBN__ allows you to express the constants of C and C++ in the following ways: @itemize @bullet @item Integer constants are a sequence of digits. Octal constants are specified by a leading @samp{0} (ie. zero), and hexadecimal constants by a leading @samp{0x} or @samp{0X}. Constants may also end with an @samp{l}, specifying that the constant should be treated as a @code{long} value. @item Floating point constants are a sequence of digits, followed by a decimal point, followed by a sequence of digits, and optionally followed by an exponent. An exponent is of the form: @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another sequence of digits. The @samp{+} is optional for positive exponents. @item Enumerated constants consist of enumerated identifiers, or their integral equivalents. @item Character constants are a single character surrounded by single quotes (@code{'}), or a number---the ordinal value of the corresponding character (usually its @sc{ASCII} value). Within quotes, the single character may be represented by a letter or by @dfn{escape sequences}, which are of the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation of the character's ordinal value; or of the form @samp{\@var{x}}, where @samp{@var{x}} is a predefined special character---for example, @samp{\n} for newline. @item String constants are a sequence of character constants surrounded by double quotes (@code{"}). @item Pointer constants are an integral value. @end itemize @node Cplusplus expressions, C Defaults, C Constants, C @subsubsection C++ Expressions @cindex expressions in C++ _GDBN__'s expression handling has the following extensions to interpret a significant subset of C++ expressions: @enumerate @cindex member functions @item Member function calls are allowed; you can use expressions like @example count = aml->GetOriginal(x, y) @end example @kindex this @cindex namespace in C++ @item While a member function is active (in the selected stack frame), your expressions have the same namespace available as the member function; that is, _GDBN__ allows implicit references to the class instance pointer @code{this} following the same rules as C++. @cindex call overloaded functions @cindex type conversions in C++ @item You can call overloaded functions; _GDBN__ will resolve the function call to the right definition, with one restriction---you must use arguments of the type required by the function that you want to call. _GDBN__ will not perform conversions requiring constructors or user-defined type operators. @cindex reference declarations @item _GDBN__ understands variables declared as C++ references; you can use them in expressions just as you do in C++ source---they are automatically dereferenced. In the parameter list shown when _GDBN__ displays a frame, the values of reference variables are not displayed (unlike other variables); this avoids clutter, since references are often used for large structures. The @emph{address} of a reference variable is always shown, unless you've specified @samp{set print address off}. @item _GDBN__ supports the C++ name resolution operator @code{::}---your expressions can use it just as expressions in your program do. Since one scope may be defined in another, you can use @code{::} repeatedly if necessary, for example in an expression like @samp{@var{scope1}::@var{scope2}::@var{name}}. _GDBN__ also allows resolving name scope by reference to source files, in both C and C++ debugging; @pxref{Variables}. @end enumerate @node C Defaults, C Checks, Cplusplus expressions, C @subsubsection C and C++ Defaults @cindex C and C++ defaults If you allow _GDBN__ to set type and range checking automatically, they both default to @code{off} whenever the working language changes to C/C++. This happens regardless of whether you, or _GDBN__, selected the working language. If you allow _GDBN__ to set the language automatically, it sets the working language to C/C++ on entering code compiled from a source file whose name ends with @file{.c} or @file{.cc}. @xref{Automatically,,Having _GDBN__ infer the source language}, for further details. @node C Checks, Debugging C, C Defaults, C @subsubsection C and C++ Type and Range Checks @cindex C and C++ checks @quotation @emph{Warning:} in this release, _GDBN__ does not yet perform type or range checking. @end quotation @c FIXME remove warning when type/range checks added By default, when _GDBN__ parses C or C++ expressions, type checking is not used. However, if you turn type checking on, _GDBN__ will consider two variables type equivalent if: @itemize @bullet @item The two variables are structured and have the same structure, union, or enumerated tag. @item Two two variables have the same type name, or types that have been declared equivalent through @code{typedef}. @ignore @c leaving this out because neither J Gilmore nor R Pesch understand it. @c FIXME--beers? @item The two @code{struct}, @code{union}, or @code{enum} variables are declared in the same declaration. (Note: this may not be true for all C compilers.) @end ignore @end itemize Range checking, if turned on, is done on mathematical operations. Array indices are not checked, since they are often used to index a pointer that is not itself an array. @node Debugging C, Debugging C plus plus, C Checks, C @subsubsection _GDBN__ and C The @code{set print union} and @code{show print union} commands apply to the @code{union} type. When set to @samp{on}, any @code{union} that is inside a @code{struct} or @code{class} will also be printed. Otherwise, it will appear as @samp{@{...@}}. The @code{@@} operator aids in the debugging of dynamic arrays, formed with pointers and a memory allocation function. (@pxref{Expressions}) @node Debugging C plus plus, , Debugging C, C @subsubsection _GDBN__ Commands for C++ @cindex commands for C++ Some _GDBN__ commands are particularly useful with C++, and some are designed specifically for use with C++. Here is a summary: @table @code @cindex break in overloaded functions @item @r{breakpoint menus} When you want a breakpoint in a function whose name is overloaded, _GDBN__'s breakpoint menus help you specify which function definition you want. @xref{Breakpoint Menus}. @cindex overloading in C++ @item rbreak @var{regex} Setting breakpoints using regular expressions is helpful for setting breakpoints on overloaded functions that are not members of any special classes. @xref{Set Breaks}. @cindex C++ exception handling @item catch @var{exceptions} @itemx info catch Debug C++ exception handling using these commands. @xref{Exception Handling}. @cindex inheritance @item ptype @var{typename} Print inheritance relationships as well as other information for type @var{typename}. @xref{Symbols}. @cindex C++ symbol display @item set print demangle @itemx show print demangle @itemx set print asm-demangle @itemx show print asm-demangle Control whether C++ symbols display in their source form, both when displaying code as C++ source and when displaying disassemblies. @xref{Print Settings}. @item set print object @itemx show print object Choose whether to print derived (actual) or declared types of objects. @xref{Print Settings}. @item set print vtbl @itemx show print vtbl Control the format for printing virtual function tables. @xref{Print Settings}. @end table @node Modula-2, , C, Support @subsection Modula-2 @cindex Modula-2 The extensions made to _GDBN__ to support Modula-2 support output from the GNU Modula-2 compiler (which is currently being developed). Other Modula-2 compilers are not currently supported, and attempting to debug executables produced by them will most likely result in an error as _GDBN__ reads in the executable's symbol table. @cindex expressions in Modula-2 @menu * M2 Operators:: Built-in operators * Builtin Func/Proc:: Built-in Functions and Procedures * M2 Constants:: Modula-2 Constants * M2 Defaults:: Default settings for Modula-2 * Deviations:: Deviations from standard Modula-2 * M2 Checks:: Modula-2 Type and Range Checks * M2 Scope:: The scope operators @code{::} and @code{.} * GDB/M2:: _GDBN__ and Modula-2 @end menu @node M2 Operators, Builtin Func/Proc, Modula-2, Modula-2 @subsubsection Operators @cindex Modula-2 operators Operators must be defined on values of specific types. For instance, @code{+} is defined on numbers, but not on structures. Operators are often defined on groups of types. For the purposes of Modula-2, the following definitions hold: @itemize @bullet @item @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and their subranges. @item @emph{Character types} consist of @code{CHAR} and its subranges. @item @emph{Floating-point types} consist of @code{REAL}. @item @emph{Pointer types} consist of anything declared as @code{POINTER TO @var{type}}. @item @emph{Scalar types} consist of all of the above. @item @emph{Set types} consist of @code{SET}s and @code{BITSET}s. @item @emph{Boolean types} consist of @code{BOOLEAN}. @end itemize @noindent The following operators are supported, and appear in order of increasing precedence: @table @code _0__ @item , Function argument or array index separator. @item := Assignment. The value of @var{var} @code{:=} @var{value} is @var{value}. @item <@r{, }> Less than, greater than on integral, floating-point, or enumerated types. @item <=@r{, }>= Less than, greater than, less than or equal to, greater than or equal to on integral, floating-point and enumerated types, or set inclusion on set types. Same precedence as @code{<}. @item =@r{, }<>@r{, }# Equality and two ways of expressing inequality, valid on scalar types. Same precedence as @code{<}. In _GDBN__ scripts, only @code{<>} is available for inequality, since @code{#} conflicts with the script comment character. @item IN Set membership. Defined on set types and the types of their members. Same precedence as @code{<}. @item OR Boolean disjunction. Defined on boolean types. @item AND@r{, }& Boolean conjuction. Defined on boolean types. @item @@ The _GDBN__ ``artificial array'' operator (@pxref{Expressions}). @item +@r{, }- Addition and subtraction on integral and floating-point types, or union and difference on set types. @item * Multiplication on integral and floating-point types, or set intersection on set types. @item / Division on floating-point types, or symmetric set difference on set types. Same precedence as @code{*}. @item DIV@r{, }MOD Integer division and remainder. Defined on integral types. Same precedence as @code{*}. @item - Negative. Defined on @code{INTEGER}s and @code{REAL}s. @item ^ Pointer dereferencing. Defined on pointer types. @item NOT Boolean negation. Defined on boolean types. Same precedence as @code{^}. @item . @code{RECORD} field selector. Defined on @code{RECORD}s. Same precedence as @code{^}. @item [] Array indexing. Defined on @code{ARRAY}s. Same precedence as @code{^}. @item () Procedure argument list. Defined on @code{PROCEDURE}s. Same precedence as @code{^}. @item ::@r{, }. _GDBN__ and Modula-2 scope operators. @end table @quotation @emph{Warning:} Sets and their operations are not yet supported, so _GDBN__ will treat the use of the operator @code{IN}, or the use of operators @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#}, @code{<=}, and @code{>=} on sets as an error. @end quotation _1__ @cindex Modula-2 builtins @node Builtin Func/Proc, M2 Constants, M2 Operators, Modula-2 @subsubsection Built-in Functions and Procedures Modula-2 also makes available several built-in procedures and functions. In describing these, the following metavariables are used: @table @var @item a represents an @code{ARRAY} variable. @item c represents a @code{CHAR} constant or variable. @item i represents a variable or constant of integral type. @item m represents an identifier that belongs to a set. Generally used in the same function with the metavariable @var{s}. The type of @var{s} should be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}. @item n represents a variable or constant of integral or floating-point type. @item r represents a variable or constant of floating-point type. @item t represents a type. @item v represents a variable. @item x represents a variable or constant of one of many types. See the explanation of the function for details. @end table All Modula-2 built-in procedures also return a result, described below. @table @code @item ABS(@var{n}) Returns the absolute value of @var{n}. @item CAP(@var{c}) If @var{c} is a lower case letter, it returns its upper case equivalent, otherwise it returns its argument @item CHR(@var{i}) Returns the character whose ordinal value is @var{i}. @item DEC(@var{v}) Decrements the value in the variable @var{v}. Returns the new value. @item DEC(@var{v},@var{i}) Decrements the value in the variable @var{v} by @var{i}. Returns the new value. @item EXCL(@var{m},@var{s}) Removes the element @var{m} from the set @var{s}. Returns the new set. @item FLOAT(@var{i}) Returns the floating point equivalent of the integer @var{i}. @item HIGH(@var{a}) Returns the index of the last member of @var{a}. @item INC(@var{v}) Increments the value in the variable @var{v}. Returns the new value. @item INC(@var{v},@var{i}) Increments the value in the variable @var{v} by @var{i}. Returns the new value. @item INCL(@var{m},@var{s}) Adds the element @var{m} to the set @var{s} if it is not already there. Returns the new set. @item MAX(@var{t}) Returns the maximum value of the type @var{t}. @item MIN(@var{t}) Returns the minimum value of the type @var{t}. @item ODD(@var{i}) Returns boolean TRUE if @var{i} is an odd number. @item ORD(@var{x}) Returns the ordinal value of its argument. For example, the ordinal value of a character is its ASCII value (on machines supporting the ASCII character set). @var{x} must be of an ordered type, which include integral, character and enumerated types. @item SIZE(@var{x}) Returns the size of its argument. @var{x} can be a variable or a type. @item TRUNC(@var{r}) Returns the integral part of @var{r}. @item VAL(@var{t},@var{i}) Returns the member of the type @var{t} whose ordinal value is @var{i}. @end table @quotation @emph{Warning:} Sets and their operations are not yet supported, so _GDBN__ will treat the use of procedures @code{INCL} and @code{EXCL} as an error. @end quotation @cindex Modula-2 constants @node M2 Constants, M2 Defaults, Builtin Func/Proc, Modula-2 @subsubsection Constants _GDBN__ allows you to express the constants of Modula-2 in the following ways: @itemize @bullet @item Integer constants are simply a sequence of digits. When used in an expression, a constant is interpreted to be type-compatible with the rest of the expression. Hexadecimal integers are specified by a trailing @samp{H}, and octal integers by a trailing @samp{B}. @item Floating point constants appear as a sequence of digits, followed by a decimal point and another sequence of digits. An optional exponent can then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the digits of the floating point constant must be valid decimal (base 10) digits. @item Character constants consist of a single character enclosed by a pair of like quotes, either single (@code{'}) or double (@code{"}). They may also be expressed by their ordinal value (their ASCII value, usually) followed by a @samp{C}. @item String constants consist of a sequence of characters enclosed by a pair of like quotes, either single (@code{'}) or double (@code{"}). Escape sequences in the style of C are also allowed. @xref{C Constants}, for a brief explanation of escape sequences. @item Enumerated constants consist of an enumerated identifier. @item Boolean constants consist of the identifiers @code{TRUE} and @code{FALSE}. @item Pointer constants consist of integral values only. @item Set constants are not yet supported. @end itemize @node M2 Defaults, Deviations, M2 Constants, Modula-2 @subsubsection Modula-2 Defaults @cindex Modula-2 defaults If type and range checking are set automatically by _GDBN__, they both default to @code{on} whenever the working language changes to Modula-2. This happens regardless of whether you, or _GDBN__, selected the working language. If you allow _GDBN__ to set the language automatically, then entering code compiled from a file whose name ends with @file{.mod} will set the working language to Modula-2. @xref{Automatically,,Having _GDBN__ set the language automatically}, for further details. @node Deviations, M2 Checks, M2 Defaults, Modula-2 @subsubsection Deviations from Standard Modula-2 @cindex Modula-2, deviations from A few changes have been made to make Modula-2 programs easier to debug. This is done primarily via loosening its type strictness: @itemize @bullet @item Unlike in standard Modula-2, pointer constants can be formed by integers. This allows you to modify pointer variables during debugging. (In standard Modula-2, the actual address contained in a pointer variable is hidden from you; it can only be modified through direct assignment to another pointer variable or expression that returned a pointer.) @item C escape sequences can be used in strings and characters to represent non-printable characters. _GDBN__ will print out strings with these escape sequences embedded. Single non-printable characters are printed using the @samp{CHR(@var{nnn})} format. @item The assignment operator (@code{:=}) returns the value of its right-hand argument. @item All builtin procedures both modify @emph{and} return their argument. @end itemize @node M2 Checks, M2 Scope, Deviations, Modula-2 @subsubsection Modula-2 Type and Range Checks @cindex Modula-2 checks @quotation @emph{Warning:} in this release, _GDBN__ does not yet perform type or range checking. @end quotation @c FIXME remove warning when type/range checks added _GDBN__ considers two Modula-2 variables type equivalent if: @itemize @bullet @item They are of types that have been declared equivalent via a @code{TYPE @var{t1} = @var{t2}} statement @item They have been declared on the same line. (Note: This is true of the GNU Modula-2 compiler, but it may not be true of other compilers.) @end itemize As long as type checking is enabled, any attempt to combine variables whose types are not equivalent is an error. Range checking is done on all mathematical operations, assignment, array index bounds, and all builtin functions and procedures. @node M2 Scope, GDB/M2, M2 Checks, Modula-2 @subsubsection The scope operators @code{::} and @code{.} @cindex scope @kindex . @kindex :: There are a few subtle differences between the Modula-2 scope operator (@code{.}) and the _GDBN__ scope operator (@code{::}). The two have similar syntax: @example @var{module} . @var{id} @var{scope} :: @var{id} @end example @noindent where @var{scope} is the name of a module or a procedure, @var{module} the name of a module, and @var{id} is any delcared identifier within the program, except another module. Using the @code{::} operator makes _GDBN__ search the scope specified by @var{scope} for the identifier @var{id}. If it is not found in the specified scope, then _GDBN__ will search all scopes enclosing the one specified by @var{scope}. Using the @code{.} operator makes _GDBN__ search the current scope for the identifier specified by @var{id} that was imported from the definition module specified by @var{module}. With this operator, it is an error if the identifier @var{id} was not imported from definition module @var{module}, or if @var{id} is not an identifier in @var{module}. @node GDB/M2, , M2 Scope, Modula-2 @subsubsection _GDBN__ and Modula-2 Some _GDBN__ commands have little use when debugging Modula-2 programs. Five subcommands of @code{set print} and @code{show print} apply specifically to C and C++: @samp{vtbl}, @samp{demangle}, @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four apply to C++, and the last to C's @code{union} type, which has no direct analogue in Modula-2. The @code{@@} operator (@pxref{Expressions}), while available while using any language, is not useful with Modula-2. Its intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be created in Modula-2 as they can in C or C++. However, because an address can be specified by an integral constant, the construct @samp{@{@var{type}@}@var{adrexp}} is still useful. (@pxref{Expressions}) _0__ @cindex @code{#} in Modula-2 In _GDBN__ scripts, the Modula-2 inequality operator @code{#} is interpreted as the beginning of a comment. Use @code{<>} instead. _1__ @node Symbols, Altering, Languages, Top @chapter Examining the Symbol Table The commands described in this section allow you to inquire about the symbols (names of variables, functions and types) defined in your program. This information is inherent in the text of your program and does not change as the program executes. _GDBN__ finds it in your program's symbol table, in the file indicated when you started _GDBN__ (@pxref{File Options}), or by one of the file-management commands (@pxref{Files}). @table @code @item info address @var{symbol} @kindex info address Describe where the data for @var{symbol} is stored. For a register variable, this says which register it is kept in. For a non-register local variable, this prints the stack-frame offset at which the variable is always stored. Note the contrast with @samp{print &@var{symbol}}, which does not work at all for a register variables, and for a stack local variable prints the exact address of the current instantiation of the variable. @item whatis @var{exp} @kindex whatis Print the data type of expression @var{exp}. @var{exp} is not actually evaluated, and any side-effecting operations (such as assignments or function calls) inside it do not take place. @xref{Expressions}. @item whatis Print the data type of @code{$}, the last value in the value history. @item ptype @var{typename} @kindex ptype Print a description of data type @var{typename}. @var{typename} may be the name of a type, or for C code it may have the form @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or @samp{enum @var{enum-tag}}.@refill @item ptype @var{exp} Print a description of the type of expression @var{exp}. @code{ptype} differs from @code{whatis} by printing a detailed description, instead of just the name of the type. For example, if your program declares a variable as @example struct complex @{double real; double imag;@} v; @end example @noindent compare the output of the two commands: @example (_GDBP__) whatis v type = struct complex (_GDBP__) ptype v type = struct complex @{ double real; double imag; @} @end example @item info types @var{regexp} @itemx info types @kindex info types Print a brief description of all types whose name matches @var{regexp} (or all types in your program, if you supply no argument). Each complete typename is matched as though it were a complete line; thus, @samp{i type value} gives information on all types in your program whose name includes the string @code{value}, but @samp{i type ^value$} gives information only on types whose complete name is @code{value}. This command differs from @code{ptype} in two ways: first, like @code{whatis}, it does not print a detailed description; second, it lists all source files where a type is defined. @item info source @kindex info source Show the name of the current source file---that is, the source file for the function containing the current point of execution---and the language it was written in. @item info sources @kindex info sources Print the names of all source files in the program for which there is debugging information, organized into two lists: files whose symbols have already been read, and files whose symbols will be read when needed. @item info functions @kindex info functions Print the names and data types of all defined functions. @item info functions @var{regexp} Print the names and data types of all defined functions whose names contain a match for regular expression @var{regexp}. Thus, @samp{info fun step} finds all functions whose names include @code{step}; @samp{info fun ^step} finds those whose names start with @code{step}. @item info variables @kindex info variables Print the names and data types of all variables that are declared outside of functions (i.e., excluding local variables). @item info variables @var{regexp} Print the names and data types of all variables (except for local variables) whose names contain a match for regular expression @var{regexp}. @ignore This was never implemented. @item info methods @itemx info methods @var{regexp} @kindex info methods The @code{info methods} command permits the user to examine all defined methods within C++ program, or (with the @var{regexp} argument) a specific set of methods found in the various C++ classes. Many C++ classes provide a large number of methods. Thus, the output from the @code{ptype} command can be overwhelming and hard to use. The @code{info-methods} command filters the methods, printing only those which match the regular-expression @var{regexp}. @end ignore @item printsyms @var{filename} @kindex printsyms Write a dump of debugging symbol data into the file @var{filename}. Only symbols with debugging data are included. _GDBN__ includes all the symbols it already knows about: that is, @var{filename} reflects symbols for only those files whose symbols _GDBN__ has read. You can find out which files these are using the command @code{info files}. The description of @code{symbol-file} describes how _GDBN__ reads symbols; both commands are described under @ref{Files}. @end table @node Altering, _GDBN__ Files, Symbols, Top @chapter Altering Execution Once you think you have found an error in the program, you might want to find out for certain whether correcting the apparent error would lead to correct results in the rest of the run. You can find the answer by experiment, using the _GDBN__ features for altering execution of the program. For example, you can store new values into variables or memory locations, give the program a signal, restart it at a different address, or even return prematurely from a function to its caller. @menu * Assignment:: Assignment to Variables * Jumping:: Continuing at a Different Address * Signaling:: Giving the Program a Signal * Returning:: Returning from a Function * Calling:: Calling your Program's Functions * Patching:: Patching your Program @end menu @node Assignment, Jumping, Altering, Altering @section Assignment to Variables @cindex assignment @cindex setting variables To alter the value of a variable, evaluate an assignment expression. @xref{Expressions}. For example, @example print x=4 @end example @noindent would store the value 4 into the variable @code{x}, and then print the value of the assignment expression (which is 4). @xref{Languages}, for more information on operators in supported languages. @kindex set variable @cindex variables, setting If you are not interested in seeing the value of the assignment, use the @code{set} command instead of the @code{print} command. @code{set} is really the same as @code{print} except that the expression's value is not printed and is not put in the value history (@pxref{Value History}). The expression is evaluated only for its effects. If the beginning of the argument string of the @code{set} command appears identical to a @code{set} subcommand, use the @code{set variable} command instead of just @code{set}. This command is identical to @code{set} except for its lack of subcommands. For example, a program might well have a variable @code{width}---which leads to an error if we try to set a new value with just @samp{set width=13}, as we might if @code{set width} didn't happen to be a _GDBN__ command: @example (_GDBP__) whatis width type = double (_GDBP__) p width $4 = 13 (_GDBP__) set width=47 Invalid syntax in expression. @end example @noindent The invalid expression, of course, is @samp{=47}. What we can do in order to actually set our program's variable @code{width} is @example (_GDBP__) set var width=47 @end example _GDBN__ allows more implicit conversions in assignments than C does; you can freely store an integer value into a pointer variable or vice versa, and any structure can be converted to any other structure that is the same length or shorter. @comment FIXME: how do structs align/pad in these conversions? @comment /pesch@cygnus.com 18dec1990 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}} construct to generate a value of specified type at a specified address (@pxref{Expressions}). For example, @code{@{int@}0x83040} refers to memory location @code{0x83040} as an integer (which implies a certain size and representation in memory), and @example set @{int@}0x83040 = 4 @end example @noindent stores the value 4 into that memory location. @node Jumping, Signaling, Assignment, Altering @section Continuing at a Different Address Ordinarily, when you continue the program, you do so at the place where it stopped, with the @code{continue} command. You can instead continue at an address of your own choosing, with the following commands: @table @code @item jump @var{linespec} @kindex jump Resume execution at line @var{linespec}. Execution will stop immediately if there is a breakpoint there. @xref{List} for a description of the different forms of @var{linespec}. The @code{jump} command does not change the current stack frame, or the stack pointer, or the contents of any memory location or any register other than the program counter. If line @var{linespec} is in a different function from the one currently executing, the results may be bizarre if the two functions expect different patterns of arguments or of local variables. For this reason, the @code{jump} command requests confirmation if the specified line is not in the function currently executing. However, even bizarre results are predictable if you are well acquainted with the machine-language code of the program. @item jump *@var{address} Resume execution at the instruction at address @var{address}. @end table You can get much the same effect as the @code{jump} command by storing a new value into the register @code{$pc}. The difference is that this does not start the program running; it only changes the address where it @emph{will} run when it is continued. For example, @example set $pc = 0x485 @end example @noindent causes the next @code{continue} command or stepping command to execute at address 0x485, rather than at the address where the program stopped. @xref{Continuing and Stepping}. The most common occasion to use the @code{jump} command is to back up, perhaps with more breakpoints set, over a portion of a program that has already executed, in order to examine its execution in more detail. @node Signaling, Returning, Jumping, Altering @c @group @section Giving the Program a Signal @table @code @item signal @var{signalnum} @kindex signal Resume execution where the program stopped, but give it immediately the signal number @var{signalnum}. Alternatively, if @var{signalnum} is zero, continue execution without giving a signal. This is useful when the program stopped on account of a signal and would ordinary see the signal when resumed with the @code{continue} command; @samp{signal 0} causes it to resume without a signal. @code{signal} does not repeat when you press @key{RET} a second time after executing the command. @end table @c @end group @node Returning, Calling, Signaling, Altering @section Returning from a Function @table @code @item return @itemx return @var{expression} @cindex returning from a function @kindex return You can cancel execution of a function call with the @code{return} command. If you give an @var{expression} argument, its value is used as the function's return value. @end table When you use @code{return}, _GDBN__ discards the selected stack frame (and all frames within it). You can think of this as making the discarded frame return prematurely. If you wish to specify a value to be returned, give that value as the argument to @code{return}. This pops the selected stack frame (@pxref{Selection}), and any other frames inside of it, leaving its caller as the innermost remaining frame. That frame becomes selected. The specified value is stored in the registers used for returning values of functions. The @code{return} command does not resume execution; it leaves the program stopped in the state that would exist if the function had just returned. In contrast, the @code{finish} command (@pxref{Continuing and Stepping}) resumes execution until the selected stack frame returns naturally.@refill @node Calling, Patching, Returning, Altering @section Calling your Program's Functions @cindex calling functions @kindex call @table @code @item call @var{expr} Evaluate the expression @var{expr} without displaying @code{void} returned values. @end table You can use this variant of the @code{print} command if you want to execute a function from your program, but without cluttering the output with @code{void} returned values. The result is printed and saved in the value history, if it is not void. @node Patching, , Calling, Altering @section Patching your Program @cindex patching binaries @cindex writing into executables @cindex writing into corefiles By default, _GDBN__ opens the file containing your program's executable code (or the corefile) read-only. This prevents accidental alterations to machine code; but it also prevents you from intentionally patching your program's binary. If you'd like to be able to patch the binary, you can specify that explicitly with the @code{set write} command. For example, you might want to turn on internal debugging flags, or even to make emergency repairs. @table @code @item set write on @itemx set write off @kindex set write If you specify @samp{set write on}, _GDBN__ will open executable and core files for both reading and writing; if you specify @samp{set write off} (the default), _GDBN__ will open them read-only. If you've already loaded a file, you must load it again (using the @code{exec-file} or @code{core-file} command) after changing @code{set write}, for your new setting to take effect. @item show write Display whether executable files and core files will be opened for writing as well as reading. @end table @node _GDBN__ Files, Targets, Altering, Top @chapter _GDBN__'s Files @menu * Files:: Commands to Specify Files * Symbol Errors:: Errors Reading Symbol Files @end menu @node Files, Symbol Errors, _GDBN__ Files, _GDBN__ Files @section Commands to Specify Files @cindex core dump file @cindex symbol table _GDBN__ needs to know the file name of the program to be debugged, both in order to read its symbol table and in order to start the program. To debug a core dump of a previous run, _GDBN__ must be told the file name of the core dump. The usual way to specify the executable and core dump file names is with the command arguments given when you start _GDBN__, as discussed in @pxref{Invocation}. Occasionally it is necessary to change to a different file during a _GDBN__ session. Or you may run _GDBN__ and forget to specify the files you want to use. In these situations the _GDBN__ commands to specify new files are useful. @table @code @item file @var{filename} @cindex executable file @kindex file Use @var{filename} as the program to be debugged. It is read for its symbols and for the contents of pure memory. It is also the program executed when you use the @code{run} command. If you do not specify a directory and the file is not found in _GDBN__'s working directory, _GDBN__ uses the environment variable @code{PATH} as a list of directories to search, just as the shell does when looking for a program to run. You can change the value of this variable, for both _GDBN__ and your program, using the @code{path} command. @code{file} with no argument makes _GDBN__ discard any information it has on both executable file and the symbol table. @item exec-file @var{filename} @kindex exec-file Specify that the program to be run (but not the symbol table) is found in @var{filename}. _GDBN__ will search the environment variable @code{PATH} if necessary to locate the program. @item symbol-file @var{filename} @kindex symbol-file Read symbol table information from file @var{filename}. @code{PATH} is searched when necessary. Use the @code{file} command to get both symbol table and program to run from the same file. @code{symbol-file} with no argument clears out _GDBN__'s information on your program's symbol table. The @code{symbol-file} command causes _GDBN__ to forget the contents of its convenience variables, the value history, and all breakpoints and auto-display expressions. This is because they may contain pointers to the internal data recording symbols and data types, which are part of the old symbol table data being discarded inside _GDBN__. @code{symbol-file} will not repeat if you press @key{RET} again after executing it once. On some kinds of object files, the @code{symbol-file} command does not actually read the symbol table in full right away. Instead, it scans the symbol table quickly to find which source files and which symbols are present. The details are read later, one source file at a time, when they are needed. The purpose of this two-stage reading strategy is to make _GDBN__ start up faster. For the most part, it is invisible except for occasional pauses while the symbol table details for a particular source file are being read. (The @code{set verbose} command can turn these pauses into messages if desired. @xref{Messages/Warnings}). When the symbol table is stored in COFF format, @code{symbol-file} does read the symbol table data in full right away. We haven't implemented the two-stage strategy for COFF yet. When _GDBN__ is configured for a particular environment, it will understand debugging information in whatever format is the standard generated for that environment; you may use either a GNU compiler, or other compilers that adhere to the local conventions. Best results are usually obtained from GNU compilers; for example, using @code{_GCC__} you can generate debugging information for optimized code. @item core-file @var{filename} @itemx core @var{filename} @kindex core @kindex core-file Specify the whereabouts of a core dump file to be used as the ``contents of memory''. Traditionally, core files contain only some parts of the address space of the process that generated them; _GDBN__ can access the executable file itself for other parts. @code{core-file} with no argument specifies that no core file is to be used. Note that the core file is ignored when your program is actually running under _GDBN__. So, if you have been running the program and you wish to debug a core file instead, you must kill the subprocess in which the program is running. To do this, use the @code{kill} command (@pxref{Kill Process}). @item load @var{filename} @kindex load _if__(_GENERIC__) Depending on what remote debugging facilities are configured into _GDBN__, the @code{load} command may be available. Where it exists, it is meant to make @var{filename} (an executable) available for debugging on the remote system---by downloading, or dynamic linking, for example. @code{load} also records @var{filename}'s symbol table in _GDBN__, like the @code{add-symbol-file} command. If @code{load} is not available on your _GDBN__, attempting to execute it gets the error message ``@code{You can't do that when your target is @dots{}}'' _fi__(_GENERIC__) _if__(_VXWORKS__) On VxWorks, @code{load} will dynamically link @var{filename} on the current target system as well as adding its symbols in _GDBN__. _fi__(_VXWORKS__) _if__(_I960__) @cindex download to Nindy-960 With the Nindy interface to an Intel 960 board, @code{load} will download @var{filename} to the 960 as well as adding its symbols in _GDBN__. _fi__(_I960__) @code{load} will not repeat if you press @key{RET} again after using it. @item add-symbol-file @var{filename} @var{address} @kindex add-symbol-file @cindex dynamic linking The @code{add-symbol-file} command reads additional symbol table information from the file @var{filename}. You would use this command when @var{filename} has been dynamically loaded (by some other means) into the program that is running. @var{address} should be the memory address at which the file has been loaded; _GDBN__ cannot figure this out for itself. The symbol table of the file @var{filename} is added to the symbol table originally read with the @code{symbol-file} command. You can use the @code{add-symbol-file} command any number of times; the new symbol data thus read keeps adding to the old. To discard all old symbol data instead, use the @code{symbol-file} command. @code{add-symbol-file} will not repeat if you press @key{RET} after using it. @item info files @itemx info target @kindex info files @kindex info target @code{info files} and @code{info target} are synonymous; both print the current targets (@pxref{Targets}), including the names of the executable and core dump files currently in use by _GDBN__, and the files from which symbols were loaded. The command @code{help targets} lists all possible targets rather than current ones. @end table All file-specifying commands allow both absolute and relative file names as arguments. _GDBN__ always converts the file name to an absolute path name and remembers it that way. @cindex shared libraries _GDBN__ supports the SunOS shared library format. _GDBN__ automatically loads symbol definitions from shared libraries when you use the @code{run} command, or when you examine a core file. (Before you issue the @code{run} command, _GDBN__ won't understand references to a function in a shared library, however---unless you're debugging a core file). @c FIXME: next _GDBN__ release should permit some refs to undef @c FIXME...symbols---eg in a break cmd---assuming they're from a shared lib @table @code @item info share @itemx info sharedlibrary @kindex info sharedlibrary @kindex info share Print the names of the shared libraries which are currently loaded. @item sharedlibrary @var{regex} @itemx share @var{regex} @kindex sharedlibrary @kindex share This is an obsolescent command; you can use it to explicitly load shared object library symbols for files matching a UNIX regular expression, but as with files loaded automatically, it will only load shared libraries required by your program for a core file or after typing @code{run}. If @var{regex} is omitted all shared libraries required by your program are loaded. @end table @node Symbol Errors, , Files, _GDBN__ Files @section Errors Reading Symbol Files While reading a symbol file, _GDBN__ will occasionally encounter problems, such as symbol types it does not recognize, or known bugs in compiler output. By default, _GDBN__ does not notify you of such problems, since they're relatively common and primarily of interest to people debugging compilers. If you are interested in seeing information about ill-constructed symbol tables, you can either ask _GDBN__ to print only one message about each such type of problem, no matter how many times the problem occurs; or you can ask _GDBN__ to print more messages, to see how many times the problems occur, with the @code{set complaints} command (@xref{Messages/Warnings}). The messages currently printed, and their meanings, are: @table @code @item inner block not inside outer block in @var{symbol} The symbol information shows where symbol scopes begin and end (such as at the start of a function or a block of statements). This error indicates that an inner scope block is not fully contained in its outer scope blocks. _GDBN__ circumvents the problem by treating the inner block as if it had the same scope as the outer block. In the error message, @var{symbol} may be shown as ``@code{(don't know)}'' if the outer block is not a function. @item block at @var{address} out of order The symbol information for symbol scope blocks should occur in order of increasing addresses. This error indicates that it does not do so. _GDBN__ does not circumvent this problem, and will have trouble locating symbols in the source file whose symbols being read. (You can often determine what source file is affected by specifying @code{set verbose on}. @xref{Messages/Warnings}.) @item bad block start address patched The symbol information for a symbol scope block has a start address smaller than the address of the preceding source line. This is known to occur in the SunOS 4.1.1 (and earlier) C compiler. _GDBN__ circumvents the problem by treating the symbol scope block as starting on the previous source line. @item bad string table offset in symbol @var{n} @cindex foo Symbol number @var{n} contains a pointer into the string table which is larger than the size of the string table. _GDBN__ circumvents the problem by considering the symbol to have the name @code{foo}, which may cause other problems if many symbols end up with this name. @item unknown symbol type @code{0x@var{nn}} The symbol information contains new data types that _GDBN__ does not yet know how to read. @code{0x@var{nn}} is the symbol type of the misunderstood information, in hexadecimal. _GDBN__ circumvents the error by ignoring this symbol information. This will usually allow the program to be debugged, though certain symbols will not be accessible. If you encounter such a problem and feel like debugging it, you can debug @code{_GDBP__} with itself, breakpoint on @code{complain}, then go up to the function @code{read_dbx_symtab} and examine @code{*bufp} to see the symbol. @item stub type has NULL name _GDBN__ could not find the full definition for a struct or class. @ignore @c this is #if 0'd in dbxread.c as of (at least!) 17 may 1991 @item const/volatile indicator missing, got '@var{X}' The symbol information for a C++ member function is missing some information that the compiler should have output for it. @end ignore @item C++ type mismatch between compiler and debugger _GDBN__ could not parse a type specification output by the compiler for some C++ object. @end table @node Targets, Controlling _GDBN__, _GDBN__ Files, Top @chapter Specifying a Debugging Target @cindex debugging target @kindex target A @dfn{target} is an interface between the debugger and a particular kind of file or process. Often, you will be able to run _GDBN__ in the same host environment as the program you are debugging; in that case, the debugging target can just be specified as a side effect of the @code{file} or @code{core} commands. When you need more flexibility---for example, running _GDBN__ on a physically separate host, controlling standalone systems over a serial port, or realtime systems over a TCP/IP connection---you can use the @code{target} command. @menu * Active Targets:: Active Targets * Target Commands:: Commands for Managing Targets * Remote:: Remote Debugging @end menu @node Active Targets, Target Commands, Targets, Targets @section Active Targets @cindex stacking targets @cindex active targets @cindex multiple targets Targets are managed in three @dfn{strata} that correspond to different classes of target: processes, core files, and executable files. This allows you to (for example) start a process and inspect its activity without abandoning your work on a core file. More than one target can potentially respond to a request. In particular, when you access memory _GDBN__ will examine the three strata of targets until it finds a target that can handle that particular address. Strata are always examined in a fixed order: first a process if there is one, then a core file if there is one, and finally an executable file if there is one of those. When you specify a new target in a given stratum, it replaces any target previously in that stratum. To get rid of a target without replacing it, use the @code{detach} command. The related command @code{attach} provides you with a way of choosing a particular running process as a new target. @xref{Attach}. @node Target Commands, Remote, Active Targets, Targets @section Commands for Managing Targets @table @code @item target @var{type} @var{parameters} Connects the _GDBN__ host environment to a target machine or process. A target is typically a protocol for talking to debugging facilities. You use the argument @var{type} to specify the type or protocol of the target machine. Further @var{parameters} are interpreted by the target protocol, but typically include things like device names or host names to connect with, process numbers, and baud rates. The @code{target} command will not repeat if you press @key{RET} again after executing the command. @item help target @kindex help target Displays the names of all targets available. To display targets currently selected, use either @code{info target} or @code{info files} (@pxref{Files}). @item help target @var{name} Describe a particular target, including any parameters necessary to select it. @end table Here are some common targets (available, or not, depending on the _GDBN__ configuration): @table @code @item target exec @var{prog} @kindex target exec An executable file. @samp{target exec @var{prog}} is the same as @samp{exec-file @var{prog}}. @item target core @var{filename} @kindex target core A core dump file. @samp{target core @var{filename}} is the same as @samp{core-file @var{filename}}. @item target remote @var{dev} @kindex target remote Remote serial target in _GDBN__-specific protocol. The argument @var{dev} specifies what serial device to use for the connection (e.g. @file{/dev/ttya}). @xref{Remote}. _if__(_AMD29K__) @item target amd-eb @var{dev} @var{speed} @var{PROG} @kindex target amd-eb @cindex AMD EB29K Remote PC-resident AMD EB29K board, attached over serial lines. @var{dev} is the serial device, as for @code{target remote}; @var{speed} allows you to specify the linespeed; and @var{PROG} is the name of the program to be debugged, as it appears to DOS on the PC. @xref{EB29K Remote}. _fi__(_AMD29K__) _if__(_I960__) @item target nindy @var{devicename} @kindex target nindy An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is the name of the serial device to use for the connection, e.g. @file{/dev/ttya}. @xref{i960-Nindy Remote}. _fi__(_I960__) _if__(_VXWORKS__) @item target vxworks @var{machinename} @kindex target vxworks A VxWorks system, attached via TCP/IP. The argument @var{machinename} is the target system's machine name or IP address. @xref{VxWorks Remote}. _fi__(_VXWORKS__) @end table _if__(_GENERIC__) Different targets are available on different configurations of _GDBN__; your configuration may have more or fewer targets. _fi__(_GENERIC__) @node Remote, , Target Commands, Targets @section Remote Debugging @cindex remote debugging _if__(_GENERIC__) @menu _include__(gdbinv-m.m4)<>_dnl__ @end menu _fi__(_GENERIC__) If you are trying to debug a program running on a machine that can't run _GDBN__ in the usual way, it is often useful to use remote debugging. For example, you might use remote debugging on an operating system kernel, or on a small system which does not have a general purpose operating system powerful enough to run a full-featured debugger. Some configurations of _GDBN__ have special serial or TCP/IP interfaces to make this work with particular debugging targets. In addition, _GDBN__ comes with a generic serial protocol (specific to _GDBN__, but not specific to any particular target system) which you can use if you write the remote stubs---the code that will run on the remote system to communicate with _GDBN__. To use the _GDBN__ remote serial protocol, the program to be debugged on the remote machine needs to contain a debugging stub which talks to _GDBN__ over the serial line. Several working remote stubs are distributed with _GDBN__; see the @file{README} file in the _GDBN__ distribution for more information. For details of this communication protocol, see the comments in the _GDBN__ source file @file{remote.c}. To start remote debugging, first run _GDBN__ and specify as an executable file the program that is running in the remote machine. This tells _GDBN__ how to find the program's symbols and the contents of its pure text. Then establish communication using the @code{target remote} command with a device name as an argument. For example: @example target remote /dev/ttyb @end example @noindent if the serial line is connected to the device named @file{/dev/ttyb}. This will stop the remote machine if it is not already stopped. Now you can use all the usual commands to examine and change data and to step and continue the remote program. To resume the remote program and stop debugging it, use the @code{detach} command. Other remote targets may be available in your configuration of _GDBN__; use @code{help targets} to list them. _if__(_GENERIC__) @c Text on starting up GDB in various specific cases; it goes up front @c in manuals configured for any of those particular situations, here @c otherwise. _include__(gdbinv-s.m4) _fi__(_GENERIC__) @node Controlling _GDBN__, Sequences, Targets, Top @chapter Controlling _GDBN__ You can alter many aspects of _GDBN__'s interaction with you by using the @code{set} command. For commands controlling how _GDBN__ displays data, @pxref{Print Settings}; other settings are described here. @menu * Prompt:: Prompt * Editing:: Command Editing * History:: Command History * Screen Size:: Screen Size * Numbers:: Numbers * Messages/Warnings:: Optional Warnings and Messages @end menu @node Prompt, Editing, Controlling _GDBN__, Controlling _GDBN__ @section Prompt @cindex prompt _GDBN__ indicates its readiness to read a command by printing a string called the @dfn{prompt}. This string is normally @samp{(_GDBP__)}. You can change the prompt string with the @code{set prompt} command. For instance, when debugging _GDBN__ with _GDBN__, it is useful to change the prompt in one of the _GDBN__<>s so that you can always tell which one you are talking to. @table @code @item set prompt @var{newprompt} @kindex set prompt Directs _GDBN__ to use @var{newprompt} as its prompt string henceforth. @kindex show prompt @item show prompt Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}} @end table @node Editing, History, Prompt, Controlling _GDBN__ @section Command Editing @cindex readline @cindex command line editing _GDBN__ reads its input commands via the @dfn{readline} interface. This GNU library provides consistent behavior for programs which provide a command line interface to the user. Advantages are @code{emacs}-style or @code{vi}-style inline editing of commands, @code{csh}-like history substitution, and a storage and recall of command history across debugging sessions. You may control the behavior of command line editing in _GDBN__ with the command @code{set}. @table @code @kindex set editing @cindex editing @item set editing @itemx set editing on Enable command line editing (enabled by default). @item set editing off Disable command line editing. @kindex show editing @item show editing Show whether command line editing is enabled. @end table @node History, Screen Size, Editing, Controlling _GDBN__ @section Command History @table @code @cindex history substitution @cindex history file @kindex set history filename @item set history filename @var{fname} Set the name of the _GDBN__ command history file to @var{fname}. This is the file from which _GDBN__ will read an initial command history list or to which it will write this list when it exits. This list is accessed through history expansion or through the history command editing characters listed below. This file defaults to the value of the environment variable @code{GDBHISTFILE}, or to @file{./.gdb_history} if this variable is not set. @cindex history save @kindex set history save @item set history save @itemx set history save on Record command history in a file, whose name may be specified with the @code{set history filename} command. By default, this option is disabled. @item set history save off Stop recording command history in a file. @cindex history size @kindex set history size @item set history size @var{size} Set the number of commands which _GDBN__ will keep in its history list. This defaults to the value of the environment variable @code{HISTSIZE}, or to 256 if this variable is not set. @end table @cindex history expansion History expansion assigns special meaning to the character @kbd{!}. @iftex (@xref{Event Designators}.) @end iftex Since @kbd{!} is also the logical not operator in C, history expansion is off by default. If you decide to enable history expansion with the @code{set history expansion on} command, you may sometimes need to follow @kbd{!} (when it is used as logical not, in an expression) with a space or a tab to prevent it from being expanded. The readline history facilities will not attempt substitution on the strings @kbd{!=} and @kbd{!(}, even when history expansion is enabled. The commands to control history expansion are: @table @code @kindex set history expansion @item set history expansion on @itemx set history expansion Enable history expansion. History expansion is off by default. @item set history expansion off Disable history expansion. The readline code comes with more complete documentation of editing and history expansion features. Users unfamiliar with @code{emacs} or @code{vi} may wish to read it. @iftex @xref{Command Line Editing}. @end iftex @c @group @kindex show history @item show history @itemx show history filename @itemx show history save @itemx show history size @itemx show history expansion These commands display the state of the _GDBN__ history parameters. @code{show history} by itself displays all four states. @c @end group @end table @table @code @kindex show commands @item show commands Display the last ten commands in the command history. @item show commands @var{n} Print ten commands centered on command number @var{n}. @item show commands + Print ten commands just after the commands last printed. @end table @node Screen Size, Numbers, History, Controlling _GDBN__ @section Screen Size @cindex size of screen @cindex pauses in output Certain commands to _GDBN__ may produce large amounts of information output to the screen. To help you read all of it, _GDBN__ pauses and asks you for input at the end of each page of output. Type @key{RET} when you want to continue the output. _GDBN__ also uses the screen width setting to determine when to wrap lines of output. Depending on what is being printed, it tries to break the line at a readable place, rather than simply letting it overflow onto the following line. Normally _GDBN__ knows the size of the screen from the termcap data base together with the value of the @code{TERM} environment variable and the @code{stty rows} and @code{stty cols} settings. If this is not correct, you can override it with the @code{set height} and @code{set width} commands: @table @code @item set height @var{lpp} @itemx show height @itemx set width @var{cpl} @itemx show width @kindex set height @kindex set width @kindex show width @kindex show height These @code{set} commands specify a screen height of @var{lpp} lines and a screen width of @var{cpl} characters. The associated @code{show} commands display the current settings. If you specify a height of zero lines, _GDBN__ will not pause during output no matter how long the output is. This is useful if output is to a file or to an editor buffer. @end table @node Numbers, Messages/Warnings, Screen Size, Controlling _GDBN__ @section Numbers @cindex number representation @cindex entering numbers You can always enter numbers in octal, decimal, or hexadecimal in _GDBN__ by the usual conventions: octal numbers begin with @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}. Numbers that begin with none of these are, by default, entered in base 10; likewise, the default display for numbers---when no particular format is specified---is base 10. You can change the default base for both input and output with the @code{set radix} command. @table @code @kindex set radix @item set radix @var{base} Set the default base for numeric input and display. Supported choices for @var{base} are decimal 2, 8, 10, 16. @var{base} must itself be specified either unambiguously or using the current default radix; for example, any of @example set radix 1010 set radix 012 set radix 10. set radix 0xa @end example @noindent will set the base to decimal. On the other hand, @samp{set radix 10} will leave the radix unchanged no matter what it was. @kindex show radix @item show radix Display the current default base for numeric input and display. @end table @node Messages/Warnings, , Numbers, Controlling _GDBN__ @section Optional Warnings and Messages By default, _GDBN__ is silent about its inner workings. If you are running on a slow machine, you may want to use the @code{set verbose} command. It will make _GDBN__ tell you when it does a lengthy internal operation, so you won't think it has crashed. Currently, the messages controlled by @code{set verbose} are those which announce that the symbol table for a source file is being read (@pxref{Files}, in the description of the command @code{symbol-file}). @c The following is the right way to do it, but emacs 18.55 doesn't support @c @ref, and neither the emacs lisp manual version of texinfmt or makeinfo @c is released. @ignore see @code{symbol-file} in @ref{Files}). @end ignore @table @code @kindex set verbose @item set verbose on Enables _GDBN__'s output of certain informational messages. @item set verbose off Disables _GDBN__'s output of certain informational messages. @kindex show verbose @item show verbose Displays whether @code{set verbose} is on or off. @end table By default, if _GDBN__ encounters bugs in the symbol table of an object file, it is silent; but if you are debugging a compiler, you may find this information useful (@pxref{Symbol Errors}). @table @code @kindex set complaints @item set complaints @var{limit} Permits _GDBN__ to output @var{limit} complaints about each type of unusual symbols before becoming silent about the problem. Set @var{limit} to zero to suppress all complaints; set it to a large number to prevent complaints from being suppressed. @kindex show complaints @item show complaints Displays how many symbol complaints _GDBN__ is permitted to produce. @end table By default, _GDBN__ is cautious, and asks what sometimes seem to be a lot of stupid questions to confirm certain commands. For example, if you try to run a program which is already running: @example (_GDBP__) run The program being debugged has been started already. Start it from the beginning? (y or n) @end example If you're willing to unflinchingly face the consequences of your own commands, you can disable this ``feature'': @table @code @kindex set confirm @cindex flinching @cindex confirmation @cindex stupid questions @item set confirm off Disables confirmation requests. @item set confirm on Enables confirmation requests (the default). @item show confirm @kindex show confirm Displays state of confirmation requests. @end table @c FIXME this doesn't really belong here. But where *does* it belong? @cindex reloading symbols Some systems allow individual object files that make up your program to be replaced without stopping and restarting your program. _if__(_VXWORKS__) For example, in VxWorks you can simply recompile a defective object file and keep on running. _fi__(_VXWORKS__) If you're running on one of these systems, you can allow _GDBN__ to reload the symbols for automatically relinked modules:@refill @table @code @kindex set symbol-reloading @item set symbol-reloading on Replace symbol definitions for the corresponding source file when an object file with a particular name is seen again. @item set symbol-reloading off Don't replace symbol definitions when re-encountering object files of the same name. This is the default state; if you're not running on a system that permits automatically relinking modules, you should leave @code{symbol-reloading} off, since otherwise _GDBN__ may discard symbols when linking large programs, that may contain several modules (from different directories or libraries) with the same name. @item show symbol-reloading Show the current @code{on} or @code{off} setting. @end table @node Sequences, Emacs, Controlling _GDBN__, Top @chapter Canned Sequences of Commands Aside from breakpoint commands (@pxref{Break Commands}), _GDBN__ provides two ways to store sequences of commands for execution as a unit: user-defined commands and command files. @menu * Define:: User-Defined Commands * Command Files:: Command Files * Output:: Commands for Controlled Output @end menu @node Define, Command Files, Sequences, Sequences @section User-Defined Commands @cindex user-defined command A @dfn{user-defined command} is a sequence of _GDBN__ commands to which you assign a new name as a command. This is done with the @code{define} command. @table @code @item define @var{commandname} @kindex define Define a command named @var{commandname}. If there is already a command by that name, you are asked to confirm that you want to redefine it. The definition of the command is made up of other _GDBN__ command lines, which are given following the @code{define} command. The end of these commands is marked by a line containing @code{end}. @item document @var{commandname} @kindex document Give documentation to the user-defined command @var{commandname}. The command @var{commandname} must already be defined. This command reads lines of documentation just as @code{define} reads the lines of the command definition, ending with @code{end}. After the @code{document} command is finished, @code{help} on command @var{commandname} will print the documentation you have specified. You may use the @code{document} command again to change the documentation of a command. Redefining the command with @code{define} does not change the documentation. @item help user-defined @kindex help user-defined List all user-defined commands, with the first line of the documentation (if any) for each. @item info user @itemx info user @var{commandname} @kindex info user Display the _GDBN__ commands used to define @var{commandname} (but not its documentation). If no @var{commandname} is given, display the definitions for all user-defined commands. @end table User-defined commands do not take arguments. When they are executed, the commands of the definition are not printed. An error in any command stops execution of the user-defined command. Commands that would ask for confirmation if used interactively proceed without asking when used inside a user-defined command. Many _GDBN__ commands that normally print messages to say what they are doing omit the messages when used in a user-defined command. @node Command Files, Output, Define, Sequences @section Command Files @cindex command files A command file for _GDBN__ is a file of lines that are _GDBN__ commands. Comments (lines starting with @kbd{#}) may also be included. An empty line in a command file does nothing; it does not mean to repeat the last command, as it would from the terminal. @cindex init file @cindex @file{_GDBINIT__} When you start _GDBN__, it automatically executes commands from its @dfn{init files}. These are files named @file{_GDBINIT__}. _GDBN__ reads the init file (if any) in your home directory and then the init file (if any) in the current working directory. (The init files are not executed if you use the @samp{-nx} option; @pxref{Mode Options}.) You can also request the execution of a command file with the @code{source} command: @table @code @item source @var{filename} @kindex source Execute the command file @var{filename}. @end table The lines in a command file are executed sequentially. They are not printed as they are executed. An error in any command terminates execution of the command file. Commands that would ask for confirmation if used interactively proceed without asking when used in a command file. Many _GDBN__ commands that normally print messages to say what they are doing omit the messages when called from command files. @node Output, , Command Files, Sequences @section Commands for Controlled Output During the execution of a command file or a user-defined command, normal _GDBN__ output is suppressed; the only output that appears is what is explicitly printed by the commands in the definition. This section describes three commands useful for generating exactly the output you want. @table @code @item echo @var{text} @kindex echo @c I don't consider backslash-space a standard C escape sequence @c because it's not in ANSI. Print @var{text}. Nonprinting characters can be included in @var{text} using C escape sequences, such as @samp{\n} to print a newline. @b{No newline will be printed unless you specify one.} In addition to the standard C escape sequences, a backslash followed by a space stands for a space. This is useful for outputting a string with spaces at the beginning or the end, since leading and trailing spaces are otherwise trimmed from all arguments. Thus, to print @samp{@ and foo =@ }, use the command @samp{echo \@ and foo = \@ }. @c FIXME: verify hard copy actually issues enspaces for '@ '! Will this @c confuse texinfo? A backslash at the end of @var{text} can be used, as in C, to continue the command onto subsequent lines. For example, @example echo This is some text\n\ which is continued\n\ onto several lines.\n @end example produces the same output as @example echo This is some text\n echo which is continued\n echo onto several lines.\n @end example @item output @var{expression} @kindex output Print the value of @var{expression} and nothing but that value: no newlines, no @samp{$@var{nn} = }. The value is not entered in the value history either. @xref{Expressions} for more information on expressions. @item output/@var{fmt} @var{expression} Print the value of @var{expression} in format @var{fmt}. You can use the same formats as for @code{print}; @pxref{Output formats}, for more information. @item printf @var{string}, @var{expressions}@dots{} @kindex printf Print the values of the @var{expressions} under the control of @var{string}. The @var{expressions} are separated by commas and may be either numbers or pointers. Their values are printed as specified by @var{string}, exactly as if the program were to execute @example printf (@var{string}, @var{expressions}@dots{}); @end example For example, you can print two values in hex like this: @example printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo @end example The only backslash-escape sequences that you can use in the format string are the simple ones that consist of backslash followed by a letter. @end table @node Emacs, _GDBN__ Bugs, Sequences, Top @chapter Using _GDBN__ under GNU Emacs @cindex emacs A special interface allows you to use GNU Emacs to view (and edit) the source files for the program you are debugging with _GDBN__. To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the executable file you want to debug as an argument. This command starts _GDBN__ as a subprocess of Emacs, with input and output through a newly created Emacs buffer. Using _GDBN__ under Emacs is just like using _GDBN__ normally except for two things: @itemize @bullet @item All ``terminal'' input and output goes through the Emacs buffer. @end itemize This applies both to _GDBN__ commands and their output, and to the input and output done by the program you are debugging. This is useful because it means that you can copy the text of previous commands and input them again; you can even use parts of the output in this way. All the facilities of Emacs' Shell mode are available for interacting with your program. In particular, you can send signals the usual way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a stop. @itemize @bullet @item _GDBN__ displays source code through Emacs. @end itemize Each time _GDBN__ displays a stack frame, Emacs automatically finds the source file for that frame and puts an arrow (_0__@samp{=>}_1__) at the left margin of the current line. Emacs uses a separate buffer for source display, and splits the window to show both your _GDBN__ session and the source. Explicit _GDBN__ @code{list} or search commands still produce output as usual, but you probably will have no reason to use them. @quotation @emph{Warning:} If the directory where your program resides is not your current directory, it can be easy to confuse Emacs about the location of the source files, in which case the auxiliary display buffer will not appear to show your source. _GDBN__ can find programs by searching your environment's @code{PATH} variable, so the _GDBN__ input and output session will proceed normally; but Emacs doesn't get enough information back from _GDBN__ to locate the source files in this situation. To avoid this problem, either start _GDBN__ mode from the directory where your program resides, or specify a full path name when prompted for the @kbd{M-x gdb} argument. A similar confusion can result if you use the _GDBN__ @code{file} command to switch to debugging a program in some other location, from an existing _GDBN__ buffer in Emacs. @end quotation By default, @kbd{M-x gdb} calls the program called @file{gdb}. If you need to call _GDBN__ by a different name (for example, if you keep several configurations around, with different names) you can set the Emacs variable @code{gdb-command-name}; for example, @example (setq gdb-command-name "mygdb") @end example @noindent (preceded by @kbd{ESC ESC}, or typed in the @code{*scratch*} buffer, or in your @file{.emacs} file) will make Emacs call the program named ``@code{mygdb}'' instead. In the _GDBN__ I/O buffer, you can use these special Emacs commands in addition to the standard Shell mode commands: @table @kbd @item C-h m Describe the features of Emacs' _GDBN__ Mode. @item M-s Execute to another source line, like the _GDBN__ @code{step} command; also update the display window to show the current file and location. @item M-n Execute to next source line in this function, skipping all function calls, like the _GDBN__ @code{next} command. Then update the display window to show the current file and location. @item M-i Execute one instruction, like the _GDBN__ @code{stepi} command; update display window accordingly. @item M-x gdb-nexti Execute to next instruction, using the _GDBN__ @code{nexti} command; update display window accordingly. @item C-c C-f Execute until exit from the selected stack frame, like the _GDBN__ @code{finish} command. @item M-c Continue execution of the program, like the _GDBN__ @code{continue} command. @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}. @item M-u Go up the number of frames indicated by the numeric argument (@pxref{Arguments, , Numeric Arguments, emacs, The GNU Emacs Manual}), like the _GDBN__ @code{up} command. @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.@refill @item M-d Go down the number of frames indicated by the numeric argument, like the _GDBN__ @code{down} command. @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}. @item C-x & Read the number where the cursor is positioned, and insert it at the end of the _GDBN__ I/O buffer. For example, if you wish to disassemble code around an address that was displayed earlier, type @kbd{disassemble}; then move the cursor to the address display, and pick up the argument for @code{disassemble} by typing @kbd{C-x &}. You can customize this further on the fly by defining elements of the list @code{gdb-print-command}; once it is defined, you can format or otherwise process numbers picked up by @kbd{C-x &} before they are inserted. A numeric argument to @kbd{C-x &} will both indicate that you wish special formatting, and act as an index to pick an element of the list. If the list element is a string, the number to be inserted is formatted using the Emacs function @code{format}; otherwise the number is passed as an argument to the corresponding list element. @end table In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break}) tells _GDBN__ to set a breakpoint on the source line point is on. If you accidentally delete the source-display buffer, an easy way to get it back is to type the command @code{f} in the _GDBN__ buffer, to request a frame display; when you run under Emacs, this will recreate the source buffer if necessary to show you the context of the current frame. The source files displayed in Emacs are in ordinary Emacs buffers which are visiting the source files in the usual way. You can edit the files with these buffers if you wish; but keep in mind that _GDBN__ communicates with Emacs in terms of line numbers. If you add or delete lines from the text, the line numbers that _GDBN__ knows will cease to correspond properly to the code. @c The following dropped because Epoch is nonstandard. Reactivate @c if/when v19 does something similar. ---pesch@cygnus.com 19dec1990 @ignore @kindex emacs epoch environment @kindex epoch @kindex inspect Version 18 of Emacs has a built-in window system called the @code{epoch} environment. Users of this environment can use a new command, @code{inspect} which performs identically to @code{print} except that each value is printed in its own window. @end ignore @node _GDBN__ Bugs, Renamed Commands, Emacs, Top @chapter Reporting Bugs in _GDBN__ @cindex Bugs in _GDBN__ @cindex Reporting Bugs in _GDBN__ Your bug reports play an essential role in making _GDBN__ reliable. Reporting a bug may help you by bringing a solution to your problem, or it may not. But in any case the principal function of a bug report is to help the entire community by making the next version of _GDBN__ work better. Bug reports are your contribution to the maintenance of _GDBN__. In order for a bug report to serve its purpose, you must include the information that enables us to fix the bug. @menu * Bug Criteria:: Have You Found a Bug? * Bug Reporting:: How to Report Bugs @end menu @node Bug Criteria, Bug Reporting, _GDBN__ Bugs, _GDBN__ Bugs @section Have You Found a Bug? @cindex Bug Criteria If you are not sure whether you have found a bug, here are some guidelines: @itemize @bullet @item @cindex Fatal Signal @cindex Core Dump If the debugger gets a fatal signal, for any input whatever, that is a _GDBN__ bug. Reliable debuggers never crash. @item @cindex error on Valid Input If _GDBN__ produces an error message for valid input, that is a bug. @item @cindex Invalid Input If _GDBN__ does not produce an error message for invalid input, that is a bug. However, you should note that your idea of ``invalid input'' might be our idea of ``an extension'' or ``support for traditional practice''. @item If you are an experienced user of debugging tools, your suggestions for improvement of _GDBN__ are welcome in any case. @end itemize @node Bug Reporting, , Bug Criteria, _GDBN__ Bugs @section How to Report Bugs @cindex Bug Reports @cindex _GDBN__ Bugs, Reporting A number of companies and individuals offer support for GNU products. If you obtained _GDBN__ from a support organization, we recommend you contact that organization first. Contact information for many support companies and individuals is available in the file @file{etc/SERVICE} in the GNU Emacs distribution. In any event, we also recommend that you send bug reports for _GDBN__ to one of these addresses: @example bug-gdb@@prep.ai.mit.edu @{ucbvax|mit-eddie|uunet@}!prep.ai.mit.edu!bug-gdb @end example @strong{Do not send bug reports to @samp{info-gdb}, or to @samp{help-gdb}, or to any newsgroups.} Most users of _GDBN__ do not want to receive bug reports. Those that do, have arranged to receive @samp{bug-gdb}. The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which serves as a repeater. The mailing list and the newsgroup carry exactly the same messages. Often people think of posting bug reports to the newsgroup instead of mailing them. This appears to work, but it has one problem which can be crucial: a newsgroup posting often lacks a mail path back to the sender. Thus, if we need to ask for more information, we may be unable to reach you. For this reason, it is better to send bug reports to the mailing list. As a last resort, send bug reports on paper to: @example GNU Debugger Bugs Free Software Foundation 545 Tech Square Cambridge, MA 02139 @end example The fundamental principle of reporting bugs usefully is this: @strong{report all the facts}. If you are not sure whether to state a fact or leave it out, state it! Often people omit facts because they think they know what causes the problem and assume that some details don't matter. Thus, you might assume that the name of the variable you use in an example does not matter. Well, probably it doesn't, but one cannot be sure. Perhaps the bug is a stray memory reference which happens to fetch from the location where that name is stored in memory; perhaps, if the name were different, the contents of that location would fool the debugger into doing the right thing despite the bug. Play it safe and give a specific, complete example. That is the easiest thing for you to do, and the most helpful. Keep in mind that the purpose of a bug report is to enable us to fix the bug if it is new to us. It isn't as important what happens if the bug is already known. Therefore, always write your bug reports on the assumption that the bug has not been reported previously. Sometimes people give a few sketchy facts and ask, ``Does this ring a bell?'' Those bug reports are useless, and we urge everyone to @emph{refuse to respond to them} except to chide the sender to report bugs properly. To enable us to fix the bug, you should include all these things: @itemize @bullet @item The version of _GDBN__. _GDBN__ announces it if you start with no arguments; you can also print it at any time using @code{show version}. Without this, we won't know whether there is any point in looking for the bug in the current version of _GDBN__. @item A complete input script, and all necessary source files, that will reproduce the bug. @item What compiler (and its version) was used to compile _GDBN__---e.g. ``_GCC__-1.37.1''. @item The command arguments you gave the compiler to compile your example and observe the bug. For example, did you use @samp{-O}? To guarantee you won't omit something important, list them all. If we were to try to guess the arguments, we would probably guess wrong and then we might not encounter the bug. @item The type of machine you are using, and the operating system name and version number. @item A description of what behavior you observe that you believe is incorrect. For example, ``It gets a fatal signal.'' Of course, if the bug is that _GDBN__ gets a fatal signal, then we will certainly notice it. But if the bug is incorrect output, we might not notice unless it is glaringly wrong. We are human, after all. You might as well not give us a chance to make a mistake. Even if the problem you experience is a fatal signal, you should still say so explicitly. Suppose something strange is going on, such as, your copy of _GDBN__ is out of synch, or you have encountered a bug in the C library on your system. (This has happened!) Your copy might crash and ours would not. If you told us to expect a crash, then when ours fails to crash, we would know that the bug was not happening for us. If you had not told us to expect a crash, then we would not be able to draw any conclusion from our observations. @item If you wish to suggest changes to the _GDBN__ source, send us context diffs. If you even discuss something in the _GDBN__ source, refer to it by context, not by line number. The line numbers in our development sources won't match those in your sources. Your line numbers would convey no useful information to us. @end itemize Here are some things that are not necessary: @itemize @bullet @item A description of the envelope of the bug. Often people who encounter a bug spend a lot of time investigating which changes to the input file will make the bug go away and which changes will not affect it. This is often time consuming and not very useful, because the way we will find the bug is by running a single example under the debugger with breakpoints, not by pure deduction from a series of examples. We recommend that you save your time for something else. Of course, if you can find a simpler example to report @emph{instead} of the original one, that is a convenience for us. Errors in the output will be easier to spot, running under the debugger will take less time, etc. However, simplification is not vital; if you don't want to do this, report the bug anyway and send us the entire test case you used. @item A patch for the bug. A patch for the bug does help us if it is a good one. But don't omit the necessary information, such as the test case, on the assumption that a patch is all we need. We might see problems with your patch and decide to fix the problem another way, or we might not understand it at all. Sometimes with a program as complicated as _GDBN__ it is very hard to construct an example that will make the program follow a certain path through the code. If you don't send us the example, we won't be able to construct one, so we won't be able to verify that the bug is fixed. And if we can't understand what bug you are trying to fix, or why your patch should be an improvement, we won't install it. A test case will help us to understand. @item A guess about what the bug is or what it depends on. Such guesses are usually wrong. Even we can't guess right about such things without first using the debugger to find the facts. @end itemize @iftex @include rdl-apps.texi @end iftex @node Renamed Commands, Installing _GDBN__, _GDBN__ Bugs, Top @appendix Renamed Commands The following commands were renamed in _GDBN__ 4.0, in order to make the command set as a whole more consistent and easier to use and remember: @kindex add-syms @kindex delete environment @kindex info copying @kindex info convenience @kindex info directories @kindex info editing @kindex info history @kindex info targets @kindex info values @kindex info version @kindex info warranty @kindex set addressprint @kindex set arrayprint @kindex set prettyprint @kindex set screen-height @kindex set screen-width @kindex set unionprint @kindex set vtblprint @kindex set demangle @kindex set asm-demangle @kindex set sevenbit-strings @kindex set array-max @kindex set caution @kindex set history write @kindex show addressprint @kindex show arrayprint @kindex show prettyprint @kindex show screen-height @kindex show screen-width @kindex show unionprint @kindex show vtblprint @kindex show demangle @kindex show asm-demangle @kindex show sevenbit-strings @kindex show array-max @kindex show caution @kindex show history write @kindex unset @ifinfo @example OLD COMMAND NEW COMMAND --------------- ------------------------------- add-syms add-symbol-file delete environment unset environment info convenience show convenience info copying show copying info directories show directories info editing show commands info history show values info targets help target info values show values info version show version info warranty show warranty set/show addressprint set/show print address set/show array-max set/show print elements set/show arrayprint set/show print array set/show asm-demangle set/show print asm-demangle set/show caution set/show confirm set/show demangle set/show print demangle set/show history write set/show history save set/show prettyprint set/show print pretty set/show screen-height set/show height set/show screen-width set/show width set/show sevenbit-strings set/show print sevenbit-strings set/show unionprint set/show print union set/show vtblprint set/show print vtbl unset [No longer an alias for delete] @end example @end ifinfo @tex \vskip \parskip\vskip \baselineskip \halign{\tt #\hfil &\qquad#&\tt #\hfil\cr {\bf Old Command} &&{\bf New Command}\cr add-syms &&add-symbol-file\cr delete environment &&unset environment\cr info convenience &&show convenience\cr info copying &&show copying\cr info directories &&show directories \cr info editing &&show commands\cr info history &&show values\cr info targets &&help target\cr info values &&show values\cr info version &&show version\cr info warranty &&show warranty\cr set{\rm / }show addressprint &&set{\rm / }show print address\cr set{\rm / }show array-max &&set{\rm / }show print elements\cr set{\rm / }show arrayprint &&set{\rm / }show print array\cr set{\rm / }show asm-demangle &&set{\rm / }show print asm-demangle\cr set{\rm / }show caution &&set{\rm / }show confirm\cr set{\rm / }show demangle &&set{\rm / }show print demangle\cr set{\rm / }show history write &&set{\rm / }show history save\cr set{\rm / }show prettyprint &&set{\rm / }show print pretty\cr set{\rm / }show screen-height &&set{\rm / }show height\cr set{\rm / }show screen-width &&set{\rm / }show width\cr set{\rm / }show sevenbit-strings &&set{\rm / }show print sevenbit-strings\cr set{\rm / }show unionprint &&set{\rm / }show print union\cr set{\rm / }show vtblprint &&set{\rm / }show print vtbl\cr \cr unset &&\rm(No longer an alias for delete)\cr } @end tex @node Installing _GDBN__, Copying, Renamed Commands, Top @appendix Installing _GDBN__ @cindex configuring _GDBN__ @cindex installation _GDBN__ comes with a @code{configure} script that automates the process of preparing _GDBN__ for installation; you can then use @code{make} to build the @code{_GDBP__} program. The _GDBP__ distribution includes all the source code you need for _GDBP__ in a single directory @file{gdb-_GDB_VN__}. That directory in turn contains: @table @code @item gdb-_GDB_VN__/configure Overall script for configuring _GDBN__ and all its supporting libraries. @item gdb-_GDB_VN__/gdb the source specific to _GDBN__ itself @item gdb-_GDB_VN__/bfd source for the Binary File Descriptor Library @item gdb-_GDB_VN__/include GNU include files @item gdb-_GDB_VN__/libiberty source for the @samp{-liberty} free software library @item gdb-_GDB_VN__/readline source for the GNU command-line interface @end table @noindent Each of these directories has its own @code{configure} script, which are used by the overall @code{configure} script in @file{gdb-_GDB_VN__}. It is most convenient to run @code{configure} from the @file{gdb-_GDB_VN__} directory. The simplest way to configure and build _GDBN__ is the following: @example cd gdb-_GDB_VN__ ./configure @var{host} make @end example @noindent where @var{host} is something like @samp{sun4} or @samp{decstation}, that identifies the platform where _GDBN__ will run. This builds the three libraries @file{bfd}, @file{readline}, and @file{libiberty}, then @code{gdb} itself. The configured source files, and the binaries, are left in the corresponding source directories. You can install @code{_GDBP__} anywhere; it has no hardwired paths. However, you should make sure that the shell on your path (named by the @samp{SHELL} environment variable) is publicly readable; some systems refuse to let _GDBN__ debug child processes whose programs are not readable, and _GDBN__ uses the shell to start your program. @menu * Subdirectories:: Configuration subdirectories * Config Names:: Specifying names for hosts and targets * configure Options:: Summary of options for configure * Formatting Documentation:: How to format and print _GDBN__ documentation @end menu @node Subdirectories, Config Names, Installing _GDBN__, Installing _GDBN__ @section Configuration Subdirectories If you want to run _GDBN__ versions for several host or target machines, you'll need a different _GDBP__ compiled for each combination of host and target. @code{configure} is designed to make this easy by allowing you to generate each configuration in a separate subdirectory. If your @code{make} program handles the @samp{VPATH} feature (GNU @code{make} does), running @code{make} in each of these directories then builds the _GDBP__ program specified there. @code{configure} creates these subdirectories for you when you simultaneously specify several configurations; but it's a good habit even for a single configuration. You can specify the use of subdirectories using the @samp{+subdirs} option (abbreviated @samp{+sub}). For example, you can build _GDBN__ on a Sun 4 as follows: @example @group cd gdb-_GDB_VN__ ./configure +sub sun4 cd Host-sparc-sun-sunos4/Target-sparc-sun-sunos4 make @end group @end example When @code{configure} uses subdirectories to build programs or libraries, it creates nested directories @file{Host-@var{host}/Target-@var{target}}. (As you see in the example, the names used for @var{host} and @var{target} may be expanded from your @code{configure} argument; @pxref{Config Names}). @code{configure} uses these two directory levels because _GDBN__ can be configured for cross-compiling: _GDBN__ can run on one machine (the host) while debugging programs that run on another machine (the target). You specify cross-debugging targets by giving the @samp{+target=@var{target}} option to @code{configure}. Specifying only hosts still gives you two levels of subdirectory for each host, with the same configuration suffix on both; that is, if you give any number of hosts but no targets, _GDBN__ will be configured for native debugging on each host. On the other hand, whenever you specify both hosts and targets on the same command line, @code{configure} creates all combinations of the hosts and targets you list.@refill When you run @code{make} to build a program or library, you must run it in a configured directory. If you made a single configuration, without subdirectories, run @code{make} in the source directory. If you have @file{Host-@var{host}/Target-@var{target}} subdirectories, run @code{make} in those subdirectories. Each @code{configure} and @code{Makefile} under each source directory runs recursively, so that typing @code{make} in @file{gdb-_GDB_VN__} (or in a @file{gdb-_GDB_VN__/Host-@var{host}/Target-@var{target}} subdirectory) builds all the required libraries, then _GDBN__.@refill If you run @code{configure} from a directory (such as @file{gdb-_GDB_VN__}) that contains source directories for multiple libraries or programs, @code{configure} creates the @file{Host-@var{host}/Target-@var{target}} subdirectories in each library or program's source directory. For example, typing: @example cd gdb-_GDB_VN__ configure sun4 +target=vxworks960 @end example @noindent creates the following directories: @smallexample gdb-_GDB_VN__/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks gdb-_GDB_VN__/bfd/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks gdb-_GDB_VN__/gdb/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks gdb-_GDB_VN__/libiberty/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks gdb-_GDB_VN__/readline/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks @end smallexample @noindent The @code{Makefile} in @smallexample gdb-_GDB_VN__/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks @end smallexample @noindent will @code{cd} to the appropriate lower-level directories, for example: @smallexample gdb-_GDB_VN__/bfd/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks @end smallexample @noindent building each in turn. When you have multiple hosts or targets configured, you can run @code{make} on them in parallel (for example, if they are NFS-mounted on each of the hosts); they will not interfere with each other. @node Config Names, configure Options, Subdirectories, Installing _GDBN__ @section Specifying Names for Hosts and Targets The specifications used for hosts and targets in the @code{configure} script are based on a three-part naming scheme, but some short predefined aliases are also supported. The full naming scheme encodes three pieces of information in the following pattern: @example @var{architecture}-@var{vendor}-@var{os} @end example For example, you can use the alias @code{sun4} as a @var{host} argument or in a @code{+target=@var{target}} option, but the full name of that configuration specifies that the architecture is @samp{sparc}, the vendor is @samp{sun}, and the operating system is @samp{sunos4}. @iftex @c I know this is ugly, but @group is useless except in examples now... @c (using texinfo 2.52 or so) @page @end iftex The following table shows all the architectures, hosts, and OS prefixes that @code{configure} recognizes in _GDBN__ _GDB_VN__. Entries in the ``OS prefix'' column ending in a @samp{*} may be followed by a release number. @ifinfo @example ARCHITECTURE VENDOR OS prefix ------------+-------------+------------- | | 580 | altos | aix* a29k | amdahl | amigados alliant | aout | aout arm | apollo | bout c1 | att | bsd* c2 | bull | coff cray2 | bcs | ctix* h8300 | bout | dynix* i386 | cbm | esix* i860 | coff | hpux* i960 | convergent | irix* m68000 | convex | isc* m68k | cray | kern m88k | dec | mach* mips | encore | newsos* ns32k | gould | nindy* pyramid | hp | none romp | ibm | osf* rs6000 | intel | sco* rtpc | isi | sunos* sparc | little | svr4 tahoe | mips | sym* tron | motorola | sysv* vax | ncr | ultrix* xmp | next | unicos ymp | none | unos* | nyu | uts | sco | v88r* | sequent | vms* | sgi | vxworks* | sony | | sun | | unicom | | utek | | wrs | @end example @quotation @emph{Warning:} Many combinations of architecture, vendor, and OS are untested. @end quotation @end ifinfo @c FIXME: this table is probably screwed in @smallbook. Try setting @c FIXME...smallbook fonts? @tex %\vskip\parskip \vskip \baselineskip \halign{\hskip\parindent\tt #\hfil &\qquad#&\tt #\hfil &\qquad#&\tt #\hfil &\qquad\qquad\it #\hfil\cr {\bf Architecture} &&{\bf Vendor} &&{\bf OS prefix}\cr \multispan5\hrulefill\cr \cr 580 && altos && aix* \cr a29k && amdahl && amigados\cr alliant && aout && aout \cr arm && apollo && bout \cr c1 && att && bsd* \cr c2 && bull && coff \cr cray2 && bcs && ctix* \cr h8300 && bout && dynix* \cr i386 && cbm && esix* \cr i860 && coff && hpux* &Warning: Many combinations \cr i960 && convergent && irix* &of architecture, vendor \cr m68000 && convex && isc* &and OS are untested. \cr m68k && cray && kern \cr m88k && dec && mach* \cr mips && encore && newsos* \cr ns32k && gould && nindy* \cr pyramid && hp && none \cr romp && ibm && osf* \cr rs6000 && intel && sco* \cr rtpc && isi && sunos* \cr sparc && little && svr4 \cr tahoe && mips && sym* \cr tron && motorola && sysv* \cr vax && ncr && ultrix* \cr xmp && next && unicos \cr ymp && none && unos* \cr && nyu && uts \cr && sco && v88r* \cr && sequent && vms* \cr && sgi && vxworks*\cr && sony &&\cr && sun &&\cr && unicom &&\cr && utek &&\cr && wrs &&\cr } @end tex The @code{configure} script accompanying _GDBN__ _GDB_VN__ does not provide any query facility to list all supported host and target names or aliases. @code{configure} calls the Bourne shell script @code{config.sub} to map abbreviations to full names; you can read the script, if you wish, or you can use it to test your guesses on abbreviations---for example: @example % sh config.sub sun4 sparc-sun-sunos4 % sh config.sub sun3 m68k-sun-sunos4 % sh config.sub decstation mips-dec-ultrix % sh config.sub hp300bsd m68k-hp-bsd % sh config.sub i386v i386-none-sysv % sh config.sub i486v *** No vendor: configuration `i486v' not recognized @end example @node configure Options, Formatting Documentation, Config Names, Installing _GDBN__ @section @code{configure} Options Here is a summary of all the @code{configure} options and arguments that you might use for building _GDBN__: @example configure @r{[}+destdir=@var{dir}@r{]} @r{[}+subdirs@r{]} @r{[}+norecur@r{]} @r{[}+rm@r{]} @r{[}+target=@var{target}@dots{}@r{]} @var{host}@dots{} @end example @noindent You may introduce options with the character @samp{-} rather than @samp{+} if you prefer; but you may abbreviate option names if you use @samp{+}. @table @code @item +destdir=@var{dir} @var{dir} is an installation directory @emph{path prefix}. After you configure with this option, @code{make install} will install _GDBN__ as @file{@var{dir}/bin/_GDBP__}, and the libraries in @file{@var{dir}/lib}. If you specify @samp{+destdir=/usr/local}, for example, @code{make install} creates @file{/usr/local/bin/gdb}.@refill @item +subdirs Write configuration specific files in subdirectories of the form @example Host-@var{host}/Target-@var{target} @end example @noindent (and configure the @code{Makefile} to write binaries there too). Without this option, if you specify only one configuration for _GDBN__, @code{configure} will use the same directory for source, configured files, and binaries. This option is used automatically if you specify more than one @var{host} or more than one @samp{+target=@var{target}} option on the @code{configure} command line. @item +norecur Configure only the directory where @code{configure} is executed; do not propagate configuration to subdirectories. @item +rm Remove the configuration that the other arguments specify. @c This doesn't work (yet if ever). FIXME. @c @item +parse=@var{lang} @dots{} @c Configure the _GDBN__ expression parser to parse the listed languages. @c @samp{all} configures _GDBN__ for all supported languages. To get a @c list of all supported languages, omit the argument. Without this @c option, _GDBN__ is configured to parse all supported languages. @item +target=@var{target} @dots{} Configure _GDBN__ for cross-debugging programs running on each specified @var{target}. You may specify as many @samp{+target} options as you wish. Without this option, _GDBN__ is configured to debug programs that run on the same machine (@var{host}) as _GDBN__ itself. There is no convenient way to generate a list of all available targets. @item @var{host} @dots{} Configure _GDBN__ to run on each specified @var{host}. You may specify as many host names as you wish. There is no convenient way to generate a list of all available hosts. @end table @noindent @code{configure} accepts other options, for compatibility with configuring other GNU tools recursively; but these are the only options that affect _GDBN__ or its supporting libraries. @node Formatting Documentation, , configure Options, Installing _GDBN__ @section Formatting the Documentation @cindex _GDBN__ reference card @cindex reference card The _GDBN__ _GDB_VN__ release includes an already-formatted reference card, ready for printing on a PostScript printer, as @file{gdb-_GDB_VN__/gdb/refcard.ps}. It uses the most common PostScript fonts: the Times family, Courier, and Symbol. If you have a PostScript printer, you can print the reference card by just sending @file{refcard.ps} to the printer. The release also includes the online Info version of this manual already formatted: the main Info file is @file{gdb-_GDB_VN__/gdb/gdb.info}, and it refers to subordinate files matching @samp{gdb.info*} in the same directory. If you want to make these Info files yourself from the _GDBN__ manual's source, you need the GNU @code{makeinfo} program. Once you have it, you can type @example cd gdb-_GDB_VN__/gdb make gdb.info @end example @noindent to make the Info file. If you want to format and print copies of the manual, you need several things: @itemize @bullet @item @TeX{}, the public domain typesetting program written by Donald Knuth, must be installed on your system and available through your execution path. @item @file{gdb-_GDB_VN__/texinfo}: @TeX{} macros defining the GNU Documentation Format. @item @emph{A @sc{dvi} output program.} @TeX{} doesn't actually make marks on paper; it produces output files called @sc{dvi} files. If your system has @TeX{} installed, chances are it has a program for printing out these files; one popular example is @code{dvips}, which can print @sc{dvi} files on PostScript printers. @end itemize @noindent Once you have these things, you can type @example cd gdb-_GDB_VN__/gdb make gdb.dvi @end example @noindent to format the text of this manual, and print it with the usual output method for @TeX{} @sc{dvi} files at your site. If you want to print the reference card, but don't have a PostScript printer, or you want to use Computer Modern fonts instead, you can still print it if you have @TeX{}. Format the reference card by typing @example cd gdb-_GDB_VN__/gdb make refcard.dvi @end example @noindent The _GDBN__ reference card is designed to print in landscape mode on US ``letter'' size paper; that is, on a sheet 11 inches wide by 8.5 inches high. You will need to specify this form of printing as an option to your @sc{dvi} output program. @node Copying, Index, Installing _GDBN__, Top @unnumbered GNU GENERAL PUBLIC LICENSE @center Version 2, June 1991 @display Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc. 675 Mass Ave, Cambridge, MA 02139, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. @end display @unnumberedsec Preamble The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software---to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too. When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things. To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it. For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights. We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software. Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations. Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all. The precise terms and conditions for copying, distribution and modification follow. @iftex @unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION @end iftex @ifinfo @center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION @end ifinfo @enumerate @item This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this General Public License. The ``Program'', below, refers to any such program or work, and a ``work based on the Program'' means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language. (Hereinafter, translation is included without limitation in the term ``modification''.) Each licensee is addressed as ``you''. Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does. @item You may copy and distribute verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any warranty; and give any other recipients of the Program a copy of this License along with the Program. You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee. @item You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions: @alphaenumerate @item You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change. @item You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License. @item If the modified program normally reads commands interactively when run, you must cause it, when started running for such interactive use in the most ordinary way, to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide a warranty) and that users may redistribute the program under these conditions, and telling the user how to view a copy of this License. (Exception: if the Program itself is interactive but does not normally print such an announcement, your work based on the Program is not required to print an announcement.) @end alphaenumerate These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it. Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program. In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License. @item You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following: @alphaenumerate @item Accompany it with the complete corresponding machine-readable source code, which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or, @item Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or, @item Accompany it with the information you received as to the offer to distribute corresponding source code. (This alternative is allowed only for noncommercial distribution and only if you received the program in object code or executable form with such an offer, in accord with Subsection b above.) @end alphaenumerate The source code for a work means the preferred form of the work for making modifications to it. For an executable work, complete source code means all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable. However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable. If distribution of executable or object code is made by offering access to copy from a designated place, then offering equivalent access to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source along with the object code. @item You may not copy, modify, sublicense, or distribute the Program except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance. @item You are not required to accept this License, since you have not signed it. However, nothing else grants you permission to modify or distribute the Program or its derivative works. These actions are prohibited by law if you do not accept this License. Therefore, by modifying or distributing the Program (or any work based on the Program), you indicate your acceptance of this License to do so, and all its terms and conditions for copying, distributing or modifying the Program or works based on it. @item Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions. You may not impose any further restrictions on the recipients' exercise of the rights granted herein. You are not responsible for enforcing compliance by third parties to this License. @item If, as a consequence of a court judgment or allegation of patent infringement or for any other reason (not limited to patent issues), conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not distribute the Program at all. For example, if a patent license would not permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly through you, then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program. If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances. It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the free software distribution system, which is implemented by public license practices. Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system; it is up to the author/donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice. This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License. @item If the distribution and/or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces, the original copyright holder who places the Program under this License may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only in or among countries not thus excluded. In such case, this License incorporates the limitation as if written in the body of this License. @item The Free Software Foundation may publish revised and/or new versions of the General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. Each version is given a distinguishing version number. If the Program specifies a version number of this License which applies to it and ``any later version'', you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation. @item If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different, write to the author to ask for permission. For software which is copyrighted by the Free Software Foundation, write to the Free Software Foundation; we sometimes make exceptions for this. Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally. @iftex @heading NO WARRANTY @end iftex @ifinfo @center NO WARRANTY @end ifinfo @item BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION. @item IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. @end enumerate @iftex @heading END OF TERMS AND CONDITIONS @end iftex @ifinfo @center END OF TERMS AND CONDITIONS @end ifinfo @page @unnumberedsec Applying These Terms to Your New Programs If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms. To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the ``copyright'' line and a pointer to where the full notice is found. @smallexample @var{one line to give the program's name and a brief idea of what it does.} Copyright (C) 19@var{yy} @var{name of author} This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. @end smallexample Also add information on how to contact you by electronic and paper mail. If the program is interactive, make it output a short notice like this when it starts in an interactive mode: @smallexample Gnomovision version 69, Copyright (C) 19@var{yy} @var{name of author} Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details. @end smallexample The hypothetical commands @samp{show w} and @samp{show c} should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than @samp{show w} and @samp{show c}; they could even be mouse-clicks or menu items---whatever suits your program. You should also get your employer (if you work as a programmer) or your school, if any, to sign a ``copyright disclaimer'' for the program, if necessary. Here is a sample; alter the names: @example Yoyodyne, Inc., hereby disclaims all copyright interest in the program `Gnomovision' (which makes passes at compilers) written by James Hacker. @var{signature of Ty Coon}, 1 April 1989 Ty Coon, President of Vice @end example This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License. @node Index, , Copying, Top @unnumbered Index @printindex cp @tex % I think something like @colophon should be in texinfo. In the % meantime: \long\def\colophon{\hbox to0pt{}\vfill \centerline{The body of this manual is set in} \centerline{\fontname\tenrm,} \centerline{with headings in {\bf\fontname\tenbf}} \centerline{and examples in {\tt\fontname\tentt}.} \centerline{{\it\fontname\tenit\/} and} \centerline{{\sl\fontname\tensl\/}} \centerline{are used for emphasis.}\vfill} \page\colophon % Blame: pesch@cygnus.com, 28mar91. @end tex @contents @bye