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Section: GNU Tools (1)
gdb - The GNU Debugger
- [-help][-nx][-q][-batch][-cd=dir][-f][-b bps][-tty=dev][-s symfile][-e prog] [-se prog][-c core][-x file][-ex cmd][-d dir][prog[core|procID]]
The purpose of a debugger such as GDB is to allow you to see what isgoing on ``inside'' another program while it executes---or what anotherprogram was doing at the moment it crashed.
GDB can do four main kinds of things (plus other things in support ofthese) to help you catch bugs in the act:
- Start your program, specifying anything that might affect its behavior.
- Make your program stop on specified conditions.
- Examine what has happened, when your program has stopped.
- Change things in your program, so you can experiment with correcting theeffects of one bug and go on to learn about another.
You can use GDB to debug programs written in C, C++, and Modula-2.Fortran support will be added when a GNU Fortran compiler is ready.
GDB is invoked with the shell command gdb. Once started, it readscommands from the terminal until you tell it to exit with the GDBcommand quit. You can get online help from gdb itselfby using the command help.
You can run gdb with no arguments or options; but the mostusual way to start GDB is with one argument or two, specifying anexecutable program as the argument:
You can also start with both an executable program and a core file specified:
gdb program core
You can, instead, specify a process ID as a second argument, if you wantto debug a running process:
gdb program 1234
would attach GDB to process 1234 (unless you also have a filenamed `1234'; GDB does check for a core file first).
Here are some of the most frequently needed GDB commands:
- break [file:]function
- Set a breakpoint at function (in file).
- run [arglist]
- Start your program (with arglist, if specified).
- Backtrace: display the program stack.
- print expr
- Display the value of an expression.
- Continue running your program (after stopping, e.g. at a breakpoint).
- Execute next program line (after stopping); step over anyfunction calls in the line.
- edit [file:]function
- look at the program line where it is presently stopped.
- list [file:]function
- type the text of the program in the vicinity of where it is presently stopped.
- Execute next program line (after stopping); step into anyfunction calls in the line.
- help [name]
- Show information about GDB command name, or general informationabout using GDB.
- Exit from GDB.
For full details on GDB, see Using GDB: A Guide to the GNU Source-Level Debugger, by Richard M. Stallman and Roland H. Pesch. The same text is available onlineas the gdb entry in the info program.
Any arguments other than options specify an executablefile and core file (or process ID); that is, the first argumentencountered with no associated option flag is equivalent to a `-se
' option, and thesecond, if any, is equivalent to a `-c
' option if it's the name of a file. Many options haveboth long and short forms; both are shown here. The long forms are alsorecognized if you truncate them, so long as enough of the option ispresent to be unambiguous. (If you prefer, you can flag optionarguments with `+
' rather than `-
', though we illustrate themore usual convention.)
All the options and command line arguments you give are processedin sequential order. The order makes a difference when the`-x' option is used.
- List all options, with brief explanations.
- -s file
- Read symbol table from file file.
- Enable writing into executable and core files.
- -e file
- Use file file as the executable file to execute whenappropriate, and for examining pure data in conjunction with a coredump.
- Read symbol table from file file and use it as the executablefile.
- -c file
- Use file file as a core dump to examine.
- -x file
- Execute GDB commands from file file.
- -ex command
- Execute given GDB command.
- -d directory
- Add directory to the path to search for source files.
- Do not execute commands from any `.gdbinit' initialization files.Normally, the commands in these files are executed after all thecommand options and arguments have been processed.
- ``Quiet''. Do not print the introductory and copyright messages. Thesemessages are also suppressed in batch mode.
- Run in batch mode. Exit with status 0 after processing all the commandfiles specified with `-x' (and `.gdbinit', if not inhibited).Exit with nonzero status if an error occurs in executing the GDBcommands in the command files.
Batch mode may be useful for running GDB as a filter, for example todownload and run a program on another computer; in order to make thismore useful, the message
Program exited normally.
(which is ordinarily issued whenever a program running under GDB controlterminates) is not issued when running in batch mode.
- Run GDB using directory as its working directory,instead of the current directory.
- Emacs sets this option when it runs GDB as a subprocess. It tells GDBto output the full file name and line number in a standard,recognizable fashion each time a stack frame is displayed (whichincludes each time the program stops). This recognizable format lookslike two ` 32' characters, followed by the file name, line numberand character position separated by colons, and a newline. TheEmacs-to-GDB interface program uses the two ` 32' characters asa signal to display the source code for the frame.
- -b bps
- Set the line speed (baud rate or bits per second) of any serialinterface used by GDB for remote debugging.
- Run using device for your program's standard input and output.
;Using GDB: A Guide to the GNU Source-Level Debugger
, Richard M. Stallman and Roland H. Pesch, July 1991.
Copyright (c) 1991, 2010 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies ofthis manual provided the copyright notice and this permission noticeare preserved on all copies.
Permission is granted to copy and distribute modified versions of thismanual under the conditions for verbatim copying, provided that theentire resulting derived work is distributed under the terms of apermission notice identical to this one.
Permission is granted to copy and distribute translations of thismanual into another language, under the above conditions for modifiedversions, except that this permission notice may be included intranslations approved by the Free Software Foundation instead of inthe original English.
- SEE ALSO
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