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

Marc Khouzam
2009-06-15T15:06:59Z

> -----Original Message-----
> From: Hui Zhu [mailto:teawater@gmail.com]
> Sent: June-14-09 11:37 PM
> To: Michael Snyder; Marc Khouzam
> Cc: gdb-patches@sourceware.org
> Subject: Re: [RFA] Patch to fix reverse-debug recursion
> function tail bug
>
> On Mon, Jun 15, 2009 at 08:55, Michael
> Snyder<msnyder@vmware.com> wrote:
> > Hui Zhu wrote:
> >>
> >> PING
> >
> > Thanks for the reminder.
> >
> > I added some comment and changed the order of evaluation a bit,
> > hoping to reduce the performance impact on normal debugging.
> > And I ran the testsuites, before and after.
> >
> > Modified patch is attached -- is this OK with you guys?
> > Mark, can you confirm that it fixes your original bug?
> >
>
> This patch is OK with me.
> Marc, what do you think about it?

I tested before and after the patch and it does fix
the problem for me.

Thanks!

>
> Thanks,
> Hui
>
>
> >
> >
> >> On Mon, May 11, 2009 at 15:07, Hui Zhu<teawater@gmail.com> wrote:
> >>>
> >>> PING
> >>>
> >>> On Wed, May 6, 2009 at 15:23, Hui Zhu <teawater@gmail.com> wrote:
> >>>>
> >>>> Hi Michael,
> >>>>
> >>>> Like the prev patch I send to you, this issue still
> affect cvs-head
> >>>> and the patch can fix it.
> >>>> Please help me review it.
> >>>>
> >>>> The attachment is the new patch follow cvs-head.
> >>>>
> >>>> 2009-05-06  Hui Zhu  <teawater@gmail.com>
> >>>>
> >>>>      * infrun.c (handle_inferior_event): Check frame_id when
> >>>>      check range in reverse debug mode.
> >>>>
> >>>> Thanks,
> >>>> Hui
> >>>>
> >>>> On Sat, Mar 21, 2009 at 16:52, Hui Zhu
> <teawater@gmail.com> wrote:
> >>>>>
> >>>>> 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
> >>>>>
> >>
> >>
> >
> >
> > 2009-06-14  Hui Zhu  <teawater@gmail.com>
> >            Michael Snyder  <msnyder@vmware.com>
> >
> >        * infrun.c (handle_inferior_event): Improve reverse stepping
> >        through function epilogue.
> >
> > Index: infrun.c
> > ===================================================================
> > RCS file: /cvs/src/src/gdb/infrun.c,v
> > retrieving revision 1.387
> > diff -u -p -r1.387 infrun.c
> > --- infrun.c    11 Jun 2009 11:57:46 -0000      1.387
> > +++ infrun.c    15 Jun 2009 00:45:17 -0000
> > @@ -3623,9 +3623,17 @@ infrun: not switching back to stepped th
> >
> >      Note that step_range_end is the address of the first
> instruction
> >      beyond the step range, and NOT the address of the last
> instruction
> > -     within it! */
> > +     within it!
> > +
> > +     Note also that during reverse execution, we may be stepping
> > +     through a function epilogue and therefore must detect when
> > +     the current-frame changes in the middle of a line.  */
> > +
> >   if (stop_pc >= ecs->event_thread->step_range_start
> > -      && stop_pc < ecs->event_thread->step_range_end)
> > +      && stop_pc < ecs->event_thread->step_range_end
> > +      && (execution_direction != EXEC_REVERSE
> > +         || frame_id_eq (get_frame_id (get_current_frame ()),
> > +                         ecs->event_thread->step_frame_id)))
> >     {
> >       if (debug_infrun)
> >        fprintf_unfiltered (gdb_stdlog, "infrun: stepping
> inside range
> > [0x%s-0x%s]\n",
> >
> >
>