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

Hui Zhu
2009-06-15T03:37:07Z

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?

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",
>
>