Re: Understanding GDB frames

Jim Blandy
2007-05-23T00:05:34Z

Maxim Grigoriev <maxim@tensilica.com> writes:
>> All those frames ought to be different, but GDB will treat
>> some of them as the same.
>
> I think distinguishing frames can be improved by using the third
> argument of frame_id, which is a "special address". Most of the
> implementations don't use it.

Yes --- that was meant for use by the IA-64, which has a separate
stack for saving registers. If you have a series of calls with frames
holding nothing but saved registers, then they may allocate no space
at all on the ordinary stack. So you need to use the register stack
pointer to distinguish frames, too.

After I'd sent my last post I realized that, of course, the "entry
point PC" approach fails in the (I'd guess) more common case that the
"return address PC" does not:

void foo (void) {}
main () { foo (); foo (); }

Perhaps the best approach is to use both the return address and the
entry point in the frame ID. If either have changed, it's certainly a
new frame.