c - How can I get GDB to tell me what address caused a segfault?

Question

I'd like to know if my program is accessing NULL pointers or stale memory.

The backtrace looks like this:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x2b0fa4c8 (LWP 1333)]
0x299a6ad4 in pthread_mutex_lock () from /lib/libpthread.so.0
(gdb) bt
#0  0x299a6ad4 in pthread_mutex_lock () from /lib/libpthread.so.0
#1  0x0058e900 in ?? ()

Answer 1

With GDB 7 and higher, you can examine the $_siginfo structure that is filled out when the signal occurs, and determine the faulting address:

(gdb) p $_siginfo._sifields._sigfault.si_addr

If it shows (void *) 0x0 (or a small number) then you have a NULL pointer dereference.