Gdb

gdb allows you to debug Linux programs.

Notable functions

info functions
finish

Example

How to debug vlc

Here I try to find out where vlc exits because I am root:

gdb /usr/bin/vlc
(gdb) info functions
All defined functions:

Non-debugging symbols:
[...]
0x0000000000400f40  geteuid
[...]
(gdb) break geteuid
Breakpoint 1 at 0x400f40
(gdb) run
Starting program: /usr/bin/vlc 

Breakpoint 1, 0x00007ffff71cfc70 in geteuid () from /lib64/libc.so.6

ok, let's trace the program one command at a time:

(gdb) stepi
0x00007ffff71cfc75 in geteuid () from /lib64/libc.so.6
(gdb) stepi
0x00007ffff71cfc77 in geteuid () from /lib64/libc.so.6
(gdb) 
0x0000000000401103 in ?? ()
(gdb) 
0x0000000000401105 in ?? ()
(gdb) 
0x000000000040170f in ?? ()
[...]
(gdb) break *0x40170e
Breakpoint 3 at 0x40170e
(gdb) continue

See also

• objdump -- disassemble a program
• strace -- show syscalls from a running process
• hexeditors