Re: [reverse/record] adjust_pc_after_break in reverse execution mode?

teawater
2008-10-20T15:50:32Z

[-- Attachment #1: Type: text/plain, Size: 3371 bytes --]

Thanks Pedro.

I make a patch too.

2008-10-20 Hui Zhu <teawater@gmail.com>

* record.c (record_wait): Check breakpint before forward
execute in replay mode.
Check breakpoint use function "breakpoint_inserted_here_p".

Thanks,
Hui

On Mon, Oct 20, 2008 at 20:09, Pedro Alves <pedro@codesourcery.com> wrote:
> A Monday 20 October 2008 01:39:30, Michael Snyder escreveu:
>> Pedro Alves wrote:
>> > On Sunday 19 October 2008 23:39:20, Michael Snyder wrote:
>> >> After codgitating for a bit (that's "thinking" when you're over 50),
>> >> I've decided that you're right.
>> >>
>> >> However, I have a new concern -- I'm worried about what it will do
>> >> when it's replaying but going forward.
>> >>
>> >> Could you possibly revisit your test and see what it does
>> >> if you record all the way to line 9 or 10, then back up
>> >> to line 6, then continue with breakpoints at 6 and 7?
>> >
>> > Eh, you're right. It's broken.
>>
>> Thought so.
>>
>> See, the problem is that "adjust_pc_after_break" is assuming
>> memory-breakpoint semantics, but Process Record/Replay actually
>> implements hardware-breakpoint semantics. It watches the
>> instruction-address "bus" and stops when the PC matches the
>> address of a breakpoint.
>>
>> I suspect this is probably a problem with other record/replay
>> back-ends too, but I haven't confirmed it yet.
>>
>> Still, I think that the patch you committed was correct
>> for the reverse case.
>
>> This is a corner case that reveals
>> that "reverse" and "replay" are not synonymous.
>
> They certainly aren't. When replaying, I believe it's just best to
> behave as close as possible to when it the inferior is really running.
> From the inferior control side, GDB be mostly as agnostic about
> "replay" vs normal run as possibly.
>
> IIUC from reading the code, I see two issues.
>
> 1) When going forward and in reply mode, breakpoint hits are being checked
> *after* a record item is replays. IIUC, we should check *before*,
> and report an adjusted PC.
>
> 2) Un-inserted breakpoints weren't accounted for AFAICT (GDB will
> un-inserted breakpoints temporarily when stepping over them).
> Maybe they are, I got lost. :-) There's a loop going through the
> bp_location_chain. Can you get rid of that and use
> regular_breakpoint_inserted_here_p or similars?
>
> Below is a 10 minutes hack at it, as a starting point. Replay stil
> isn't perfect, mainly because I got lost in the record_wait maze --- that,
> needs a bit of clean up. :-)
>
>>
>> > (gdb) record
>> > (gdb) b 6
>> > Breakpoint 2 at 0x8048352: file nop.c, line 6.
>> > (gdb) b 7
>> > Breakpoint 3 at 0x8048353: file nop.c, line 7.
>> > (gdb) n
>> >
>> > Breakpoint 3, main () at nop.c:7
>> > 7 asm ("nop");
>> > (gdb) n
>> > 8 asm ("nop");
>> > (gdb)
>> > 9 asm ("nop");
>> > (gdb) n
>> > 10 }
>> > (gdb) rc
>> > Continuing.
>> >
>> > Breakpoint 3, main () at nop.c:7
>> > 7 asm ("nop");
>> > (gdb) rn
>> >
>> > No more reverse-execution history.
>> > main () at nop.c:6
>> > 6 asm ("nop");
>> > (gdb) n
>> >
>> > Breakpoint 2, main () at nop.c:6
>> > 6 asm ("nop");
>> > (gdb)
>> > 8 asm ("nop");
>> > (gdb)
>> > 9 asm ("nop");
>> > (gdb)
>> >
>> >
>> >
>> > --
>> > Pedro Alves
>>
>>
>
>
>
> --
> Pedro Alves
>

[-- Attachment #2: record_wait_breakpoint.txt --]
[-- Type: text/plain, Size: 2708 bytes --]

--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2008-10-20 Hui Zhu <teawater@gmail.com>
+
+ * record.c (record_wait): Check breakpint before forward
+ execute in replay mode.
+ Check breakpoint use function "breakpoint_inserted_here_p".
+
2008-10-19 Hui Zhu <teawater@gmail.com>

* infrun.c (handle_inferior_event): Set "stop_pc" when
--- a/record.c
+++ b/record.c
@@ -498,6 +498,23 @@ record_wait (ptid_t ptid, struct target_
int first_record_end = 1;
struct cleanup *old_cleanups = make_cleanup (record_wait_cleanups, 0);

+ /* Check breakpoint when forward execute. */
+ if (execution_direction == EXEC_FORWARD)
+ {
+ if (breakpoint_inserted_here_p (read_pc ()))
+ {
+ if (record_debug)
+ {
+ fprintf_unfiltered (gdb_stdlog,
+ "Process record: break at 0x%s.\n",
+ paddr_nz (regcache_read_pc
+ (get_thread_regcache
+ (ptid))));
+ }
+ goto replay_out;
+ }
+ }
+
record_get_sig = 0;
act.sa_handler = record_sig_handler;
act.sa_mask = record_maskall;
@@ -588,10 +605,6 @@ record_wait (ptid_t ptid, struct target_
}
else
{
- CORE_ADDR tmp_pc;
- struct bp_location *bl;
- struct breakpoint *b;
-
if (record_debug > 1)
{
fprintf_unfiltered (gdb_stdlog,
@@ -632,35 +645,17 @@ record_wait (ptid_t ptid, struct target_
}

/* check breakpoint */
- tmp_pc = read_pc ();
- for (bl = bp_location_chain; bl; bl = bl->global_next)
+ if (breakpoint_inserted_here_p (read_pc ()))
{
- b = bl->owner;
- gdb_assert (b);
- if (b->enable_state != bp_enabled
- && b->enable_state != bp_permanent)
- continue;
-
- if (b->type == bp_watchpoint || b->type == bp_catch_fork
- || b->type == bp_catch_vfork
- || b->type == bp_catch_exec
- || b->type == bp_hardware_watchpoint
- || b->type == bp_read_watchpoint
- || b->type == bp_access_watchpoint)
+ if (record_debug)
{
- continue;
- }
- if (bl->address == tmp_pc)
- {
- if (record_debug)
- {
- fprintf_unfiltered (gdb_stdlog,
- "Process record: break at 0x%s.\n",
- paddr_nz (tmp_pc));
- }
- continue_flag = 0;
- break;
+ fprintf_unfiltered (gdb_stdlog,
+ "Process record: break at 0x%s.\n",
+ paddr_nz (regcache_read_pc
+ (get_thread_regcache
+ (ptid))));
}
+ continue_flag = 0;
}
}
if (execution_direction == EXEC_REVERSE)
@@ -691,6 +686,7 @@ next:
perror_with_name (_("Process record: sigaction"));
}

+replay_out:
if (record_get_sig)
{
status->value.sig = TARGET_SIGNAL_INT;