[RFA] Patch to fix reverse-debug recursion function tail bug

[Hui Zhu <teawater at gmail dot com>]

Hi,

This patch is for bug report by Marc in
http://sourceware.org/ml/gdb/2009-03/msg00127.html.

This bug in "handle_inferior_event" deal with recursion function tail
in reverse debug.
infrun: infwait_normal_state
infrun: TARGET_WAITKIND_STOPPED
infrun: stop_pc = 0x8048457
infrun: stepping inside range [0x8048457-0x804845a]
infrun: stop_stepping
factorial (x=4) at b.cc:5

Inferior already step into another frame. But because this is a
recursion function call, And 0x8048457 is in
ecs->event_thread->step_range_start and
ecs->event_thread->step_range_start.

So gdb run in:

if (stop_pc >= ecs->event_thread->step_range_start
      && stop_pc < ecs->event_thread->step_range_end)
    {

This code is in front of:
  if (!frame_id_eq (get_frame_id (get_current_frame ()),
		    ecs->event_thread->step_frame_id)
      && (frame_id_eq (frame_unwind_id (get_current_frame ()),
		       ecs->event_thread->step_frame_id)
	  || execution_direction == EXEC_REVERSE))

So gdb check range without check frame_id.

So I make a patch to check frame_id when check range in reverse debug mode.

2008-03-21  Hui Zhu  <teawater@gmail.com>

	* infrun.c (handle_inferior_event): Check frame_id when
	check range in reverse debug mode.





Actually, there is another thing, when gdb begin reverse-debug, it's range is:
 8048439:	8b 45 08             	mov    0x8(%ebp),%eax
 804843c:	83 e8 01             	sub    $0x1,%eax
 804843f:	89 04 24             	mov    %eax,(%esp)
 8048442:	e8 dd ff ff ff       	call   8048424 <_Z9factoriali>
 8048447:	0f af 45 08          	imul   0x8(%ebp),%eax
 804844b:	89 45 fc             	mov    %eax,-0x4(%ebp)
Why is changed to infrun: stepping inside range [0x8048457-0x804845a]?
That is because when inferior step at:
 8048458:	c3                   	ret
In this address, $ebp is same with high level function and this
function is factorial too.
So the gdb can't found inferior step into another frame.  It will run to:
  ecs->event_thread->step_range_start = stop_pc_sal.pc;
  ecs->event_thread->step_range_end = stop_pc_sal.end;
  ecs->event_thread->step_frame_id = get_frame_id (get_current_frame ());
  ecs->event_thread->current_line = stop_pc_sal.line;
  ecs->event_thread->current_symtab = stop_pc_sal.symtab;

  if (debug_infrun)
     fprintf_unfiltered (gdb_stdlog, "infrun: keep going\n");
  keep_going (ecs);
}
So ecs->event_thread->step_range_start and ecs->event_thread->step_range_end.

I don't find that it affect the reverse debug or something.  So I didn't fix it.




Thanks,
Hui

Attachment: fix-function-tail-stack-same.txt
Description: Text document