On Aug 11, 2005, at 10:54 AM, Hollis Blanchard wrote:

GDB 6.3 contains this code in ppc-linux-tdep.c:

static const struct frame_unwind *
ppc_linux_sigtramp_sniffer (struct frame_info *next_frame)
{
  struct gdbarch_tdep *tdep = gdbarch_tdep (get_frame_arch 
(next_frame));

  if (frame_pc_unwind (next_frame)
      > frame_unwind_register_unsigned (next_frame, SP_REGNUM))
    /* Assume anything that is vaguely on the stack is a signal
       trampoline.  */
    return &ppc_linux_sigtramp_unwind;
  else
    return NULL;
}

Essentially it says that any time the program counter is above the 
stack pointer, we must be in a signal trampoline, and so GDB proceeds 
to grope about for a struct rt_sigframe on the stack.

This is not a good assumption. I'm using a GDB stub to debug Xen, and 
as it so happens, the Xen stack is below the Xen text. That means that 
the above test always triggers, but of course there is no rt_sigframe 
on the stack, and my backtrace runs away.

FYI: I looked at a GDB snapshot (gdb-6.3.50.20050818) and the problem 
had been resolved.

-Hollis