Question

I have a program that I hope to debug in gdb for a segmentation fault, but I’m not sure how I can generate a core file from it.

I tried $ ulimit -c unlimited, but when I ran the program and then navigated into /cores/, there was no core file generated there when I typed ls.

Am I missing anything here?

Answer 1

The way you enable core file generation is dependent on your shell. The syntax you’re showing is for someone using sh or bash as their shell, and it should work fine. e.g.

% sh
sh-3.2$ cat>/tmp/a.c
int main ()
{
  void (*f)() = 0;
  f();
}
sh-3.2$ clang -g /tmp/a.c -o /tmp/a.out
sh-3.2$ ulimit -c unlimited
sh-3.2$ /tmp/a.out
Segmentation fault: 11 (core dumped)
sh-3.2$ ls -l /cores/core.10893 
-r--------  1 jason  admin  367714304 Nov 16 13:13 /cores/core.10893

sh-3.2$ gdb -q /tmp/a.out /cores/core.10893 
Reading symbols for shared libraries .. done
Reading symbols for shared libraries . done
Reading symbols for shared libraries 
warning: Could not find object file "/var/folders/5h/nlzqfv116jnc68g495d_3j4m0000gn/T/a-pUbMeU.o" - no debug information available for "/tmp/a.c".

.......................... done
#0  0x0000000000000000 in ?? ()
(gdb) add-dsym /tmp/a.out.dSYM 
Added dsym "/tmp/a.out.dSYM" to "[memory object "/private/tmp/a.out" at 0x10f5d7000]".
(gdb) bt
#0  0x0000000000000000 in ?? ()
#1  0x000000010f5d7f3d in main () at /tmp/a.c:4
(gdb)