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

Hui Zhu
2009-03-21T08:52:49Z

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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

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---
infrun.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

--- a/infrun.c
+++ b/infrun.c
@@ -3397,7 +3397,10 @@ infrun: BPSTAT_WHAT_SET_LONGJMP_RESUME (
beyond the step range, and NOT the address of the last instruction
within it! */
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
+ && (frame_id_eq (get_frame_id (get_current_frame ()),
+ ecs->event_thread->step_frame_id)
+ || execution_direction != EXEC_REVERSE))
{
if (debug_infrun)
fprintf_unfiltered (gdb_stdlog, "infrun: stepping inside range [0x%s-0x%s]\n",