gdb (1)

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NAME

gdb - The GNU Debugger

SYNOPSIS

gdb [-help] [-nh] [-nx] [-q] [-batch] [-cd=dir] [-f] [-b bps]
    [-tty=dev] [-s symfile] [-e prog] [-se prog] [-c core] [-p procID]
    [-x cmds] [-d dir] [prog|prog procID|prog core]

DESCRIPTION

The purpose of a debugger such as 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.

can do four main kinds of things (plus other things in support of these) 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 the effects of one bug and go on to learn about another.

You can use

to debug programs written in C, C@t{++}, Fortran and Modula-2.

is invoked with the shell command "gdb". Once started, it reads commands from the terminal until you tell it to exit with the command "quit". You can get online help from itself by using the command "help".

You can run "gdb" with no arguments or options; but the most usual way to start

is with one argument or two, specifying an executable program as the argument:

        gdb program

You can also start with both an executable program and a core file specified:

        gdb program core

You can, instead, specify a process

as a second argument, if you want to debug a running process:

        gdb program 1234
        gdb -p 1234

would attach

to process 1234 (unless you also have a file named 1234; does check for a core file first). With option -p you can omit the program filename.

Here are some of the most frequently needed

commands:

break [file:]functiop

Set a breakpoint at function (in file).

run [arglist]

Start your program (with arglist, if specified).

bt

Backtrace: display the program stack.

print expr

Display the value of an expression.

c

Continue running your program (after stopping, e.g. at a breakpoint).

next

Execute next program line (after stopping); step over any function 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.

step

Execute next program line (after stopping); step into any function calls in the line.

help [name]

Show information about

GDB

command name, or general information about using

GDB.

quit

Exit from

GDB.

For full details on

see Using Guide to the Source-Level Debugger, by Richard M. Stallman and Roland H. Pesch. The same text is available online as the "gdb" entry in the "info" program.

OPTIONS

Any arguments other than options specify an executable file and core file (or process ); that is, the first argument encountered with no associated option flag is equivalent to a -se option, and the second, if any, is equivalent to a -c option if it's the name of a file. 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 + rather than -, though we illustrate the more usual convention.)

All the options and command line arguments you give are processed in sequential order. The order makes a difference when the -x option is used.

-help

-h

List all options, with brief explanations.

-symbols=file

-s file

Read symbol table from file file.

-write

Enable writing into executable and core files.

-exec=file

-e file

Use file file as the executable file to execute when appropriate, and for examining pure data in conjunction with a core dump.

-se=file

Read symbol table from file file and use it as the executable file.

-core=file

-c file

Use file file as a core dump to examine.

-command=file

-x file

Execute

GDB

commands from file file.

-ex command

Execute given

GDB

command.

-directory=directory

-d directory

Add directory to the path to search for source files.

-nh

Do not execute commands from ~/.gdbinit.

-nx

-n

Do not execute commands from any .gdbinit initialization files.

-quiet

-q

``Quiet''. Do not print the introductory and copyright messages. These messages are also suppressed in batch mode.

-batch

Run in batch mode. Exit with status 0 after processing all the command files specified with -x (and .gdbinit, if not inhibited). Exit with nonzero status if an error occurs in executing the

GDB

commands in the command files.

Batch mode may be useful for running

GDB

as a filter, for example to download and run a program on another computer; in order to make this more useful, the message

        Program exited normally.

(which is ordinarily issued whenever a program running under

GDB

control terminates) is not issued when running in batch mode.

-cd=directory

Run

GDB

using directory as its working directory, instead of the current directory.

-fullname

-f

Emacs sets this option when it runs

GDB

as a subprocess. It tells

GDB

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 \032 characters, followed by the file name, line number and character position separated by colons, and a newline. The Emacs-to-GDB interface program uses the two \032 characters as a signal to display the source code for the frame.

-b bps

Set the line speed (baud rate or bits per second) of any serial interface used by

GDB

for remote debugging.

-tty=device

Run using device for your program's standard input and output.

SEE ALSO

The full documentation for is maintained as a Texinfo manual. If the "info" and "gdb" programs and 's Texinfo documentation are properly installed at your site, the command

        info gdb

should give you access to the complete manual.

Using

Guide to the Source-Level Debugger, Richard M. Stallman and Roland H. Pesch, July 1991.

COPYRIGHT

Copyright (c) 1988-2016 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document under the terms of the

Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being ``Free Software'' and ``Free Software Needs Free Documentation'', with the Front-Cover Texts being ``A Manual,'' and with the Back-Cover Texts as in (a) below.

(a) The

's Back-Cover Text is: ``You are free to copy and modify this Manual. Buying copies from Press supports the in developing and promoting software freedom.''