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

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().

I have tested this on gdb 7.6 that is already available but it does not work on gdb 7.2 and probably on gdb 7.1:

So this is main.cpp:

int a()
{
  int p = 0;
  p = p +1;
  return  p;
}

int b()
{
  return a();
}

int c()
{
  return a();
}

int main()
{
  c();
  b();
  a();
  return 0;
}

Then g++ -g main.cpp

This is my_check.py:

class MyBreakpoint (gdb.Breakpoint):
    def stop (self):
        if gdb.selected_frame().older().name()=="b":
          gdb.execute("bt")
          return True
        else:
          return False

MyBreakpoint("a")

And this is how it works:

4>gdb -q -x my_check.py ./a.out
Reading symbols from /home/a.out...done.
Breakpoint 1 at 0x400540: file main.cpp, line 3.
(gdb) r
Starting program: /home/a.out
#0  a () at main.cpp:3
#1  0x0000000000400559 in b () at main.cpp:10
#2  0x0000000000400574 in main () at main.cpp:21

Breakpoint 1, a () at main.cpp:3
3         int p = 0;
(gdb) c
Continuing.
[Inferior 1 (process 16739) exited normally]
(gdb) quit

gdb can handle this directly now without any need for Python. Just do this:

b a if $_caller_is("b")