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

Michael Snyder
2008-10-23T23:28:58Z

Hui, can you hold off on this change?

What I'm finding is that I can reproduce the bad behavior
that Pedro demonstrated on the 20080930 branch, but ONLY
if I omit Pedro's change in adjust_pc_after_break. If I
add Pedro's change, I can no longer reproduce any bad
behavior.

I've added Pedro's change to the branch now -- why don't
you temporarily take out all these changes, and then see
if you can make it manifest a problem.

teawater wrote:
> Sorry for understand your mean so later Pedro. I made a new patch that
> Set pc if forward execute and gdbarch_decr_pc_after_break is not 0 in
> replay mode. How do you think about it?
>
>
> And I think 20080930 branch is need your "adjust_pc_reverse.diff". Do
> you mind I check it in?
>
> On Tue, Oct 21, 2008 at 08:21, Pedro Alves <pedro@codesourcery.com> wrote:
>> On Tuesday 21 October 2008 00:36:12, teawater wrote:
>>> I think your mean is check breakpoint in address
>>> read_pc()+gdbarch_decr_pc_after_break (gdbarch) in record_wait, right?
>> Taking x86 as an example, when you're doing normal debugging and you
>> hit a breakpoint (SIGTRAP), the first read_pc GDB does to check where
>> what breakpoint was hit, will read back `breakpoint_PC + 1' --- GDB takes care
>> getting rid of that `+ 1' offset in infrun.c:adjust_pc_after_break. The
>> idea is for you to do the same as the kernel/hardware would --- still
>> check for breakpoints at read_pc, but increment PC by 1 before reporting the
>> breakpoint to GDB's core. E.g., see the `pc += gdbarch...' line from
>> the patch I posted previously, something like:
>>
>> record.c:record_wait ()
>> {
>> ...
>> + /* Check for breakpoint hits in forward execution. */
>> + pc = read_pc ();
>> + if (execution_direction == EXEC_FORWARD
>> + && regular_breakpoint_inserted_here_p (pc)
>> + /* && !single-stepping */)
>> + {
>> + status->kind = TARGET_WAITKIND_STOPPED;
>> + status->value.sig = TARGET_SIGNAL_TRAP;
>> + if (software_breakpoint_inserted_here_p (pc))
>> + {
>> + pc += gdbarch_decr_pc_after_break (gdbarch);
>> + write_pc (pc);
>> + }
>> +
>>
>> --
>> Pedro Alves
>>
>>
>> ------------------------------------------------------------------------
>>
>> --- a/record.c
>> +++ b/record.c
>> @@ -497,6 +497,30 @@ record_wait (ptid_t ptid, struct target_
>> int continue_flag = 1;
>> int first_record_end = 1;
>> struct cleanup *old_cleanups = make_cleanup (record_wait_cleanups, 0);
>> + CORE_ADDR tmp_pc;
>> +
>> + /* Check breakpoint when forward execute. */
>> + if (execution_direction == EXEC_FORWARD)
>> + {
>> + tmp_pc = regcache_read_pc (regcache);
>> + if (breakpoint_inserted_here_p (tmp_pc))
>> + {
>> + if (record_debug)
>> + {
>> + fprintf_unfiltered (gdb_stdlog,
>> + "Process record: break at 0x%s.\n",
>> + paddr_nz (tmp_pc));
>> + }
>> + if (gdbarch_decr_pc_after_break (get_regcache_arch (regcache)))
>> + {
>> + regcache_write_pc (regcache,
>> + tmp_pc +
>> + gdbarch_decr_pc_after_break
>> + (get_regcache_arch (regcache)));
>> + }
>> + goto replay_out;
>> + }
>> + }
>>
>> record_get_sig = 0;
>> act.sa_handler = record_sig_handler;
>> @@ -588,10 +612,6 @@ 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 +652,24 @@ record_wait (ptid_t ptid, struct target_
>> }
>>
>> /* check breakpoint */
>> - tmp_pc = read_pc ();
>> - for (bl = bp_location_chain; bl; bl = bl->global_next)
>> + tmp_pc = regcache_read_pc (regcache);
>> + if (breakpoint_inserted_here_p (tmp_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;
>> + fprintf_unfiltered (gdb_stdlog,
>> + "Process record: break at 0x%s.\n",
>> + paddr_nz (tmp_pc));
>> }
>> - if (bl->address == tmp_pc)
>> + if (gdbarch_decr_pc_after_break (get_regcache_arch (regcache))
>> + && execution_direction == EXEC_FORWARD)
>> {
>> - if (record_debug)
>> - {
>> - fprintf_unfiltered (gdb_stdlog,
>> - "Process record: break at 0x%s.\n",
>> - paddr_nz (tmp_pc));
>> - }
>> - continue_flag = 0;
>> - break;
>> + regcache_write_pc (regcache,
>> + tmp_pc +
>> + gdbarch_decr_pc_after_break
>> + (get_regcache_arch (regcache)));
>> }
>> + continue_flag = 0;
>> }
>> }
>> if (execution_direction == EXEC_REVERSE)
>> @@ -691,6 +700,7 @@ next:
>> perror_with_name (_("Process record: sigaction"));
>> }
>>
>> +replay_out:
>> if (record_get_sig)
>> {
>> status->value.sig = TARGET_SIGNAL_INT;