c++ - Is there any way to set a breakpoint in gdb that is conditional on the call stack?

Question

I am debugging C++ in gdb 7.1 on Linux.

I have a function a() that is called in many places in the code. I want to set a breakpoint in it, but only if it was called from b(). Is there any way to do it?

Is there any way to do it only if b() was called from c(), and so on ad infinitum?

Answer 1

Update: There is now a better answer to this question: use GDB _is_caller convenience function.

The need you describe comes up quite often, usually in the context of some_utility_fn being called a lot, but you only are interested in the call which comes from some_other_fn.

You could probably script this entire interaction using the new embedded Python support in GDB from CVS trunk.

Without Python, you are limited in what you can do, but the usual technique is to have a disabled breakpoint on a(), and enable it from a command, attached to a breakpoint on b().

Here is an example:

int a(int x)
{
  return x + 1;
}

int b()
{
  return a(1);
}

int call_a_lots()
{
  int i, sum = 0;
  for (i = 0; i < 100; i++)
    sum += a(i);
}

int main()
{
  call_a_lots();
  return b();
}

gcc -g t.c
gdb -q ./a.out
Reading symbols from /tmp/a.out...done.
(gdb) break a
Breakpoint 1 at 0x4004cb: file t.c, line 3.
(gdb) disable 1
(gdb) break b
Breakpoint 2 at 0x4004d7: file t.c, line 8.
(gdb) command 2
>silent
>enable 1
>continue
>end
(gdb) run

Breakpoint 1, a (x=1) at t.c:3
3     return x + 1;
(gdb) bt
#0  a (x=1) at t.c:3
#1  0x00000000004004e1 in b () at t.c:8
#2  0x000000000040052c in main () at t.c:21
(gdb) q

Voila: we've stopped on a() called from b(), ignoring previous 100 calls to a().