User guide

Chapter 5. Debugging

1 breakpoint keep y 0x080483f5 in main at iterations.c:8

stop only if i == 8936

breakpoint already hit 1 time

5.2.4. Forked Execution

Among the more challenging bugs that can confront programmers is where one program (the

parent) makes an independent copy of itself (a fork) that creates a child process which, in turn, fails.

Debugging the parent process may or may not be useful—the only way to get to the bug may be by

debugging the child process, but doing a gdb child isn't always possible.

To address this, GDB allows programmers to continue following the parent process after a fork, or to

follow a child process.

Note

This capability is not supported by all architectures for which GDB is built, but even under those

circumstances using GDB to follow a fork can still be possible. In such architectures, GDB can

attach itself to a process that is already running, allowing a second instance of GDB to attach to a

forked child process.

5.2.5. Threads

In most cases, a forked program immediately uses one of the variations of the exec function to start

a completely independent executable. In the same manner, threads use multiple paths of execution,

occurring simultaneously in the same executable. This can provide a whole new range of debugging

challenges, such as setting a breakpoint for a particular thread that won't interrupt the execution of any

other thread. GDB supports threaded debugging (but not in all architectures for which GDB can be

built).

5.2.6. GDB Variations and Environments

GDB normally uses a command-line interface, a CLI, but it also includes what's called a “machine

interface,” the MI. Internally, Eclipse invokes GDB using the MI but a number of other applications

similarly use MI to provide different user interfaces.

Emacs, oddly enough, also supports GDB. It offers a collection of major modes that provide an

interface to GDB. For more information on this, refer to info emacs; additional information on this is

also available from the following link:

http://www.gnu.org/software/emacs/manual/html_mono/emacs.html#GDB-Graphical-Interface

5.2.7. GDB Documentation

GDB is a very mature application, literally decades in the making, and is extremely well documented.

The most convenient way to access that documentation, and the way most likely to provide

documentation on the version of GDB actually installed, is through info gdb; this provides access

to the GDB info file included in the GDB installation. In addition, man gdb offers more concise GDB

information.

Red Hat also provides extensive GDB documentation on the following link:

http://sources.redhat.com/gdb/current/onlinedocs/gdb.html