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

Michael Snyder
2008-10-28T22:58:30Z

teawater wrote:
> The old patch make my_waitpid_record set pc even if this is not a breakpoint.
> So I make a new patch that my_waitpid_record just set pc when this is
> a breakpoint.

Well, before I can evaluate the patch, I need a test case
to see what behavior it is fixing. Doesn't have to be a
formal DEJAGNU script, just something like the printf example
that you posted for the other bug.

Right now, I am unable to get the reverse-20080930-branch
to exhibit any bad behavior that I could attribute to this
issue. It seems to work just fine...

> 2008-10-24 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"
> in replay mode.
> Set pc if forward execute, gdbarch_decr_pc_after_break is not
> 0 and this is not single step in replay mode.
>
> * linux-nat.c (my_waitpid_record): Add
> gdbarch_decr_pc_after_break to pc if need.
>
>
>
> On Fri, Oct 24, 2008 at 17:57, teawater <teawater@gmail.com> wrote:
>> Hi buddies,
>>
>> This is the new patch that fix the break bug.
>>
>> But I think I still need to add some code to deal with signal.
>>
>> 2008-10-24 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"
>> in replay mode.
>> Set pc if forward execute, gdbarch_decr_pc_after_break is not
>> 0 and this is not single step in replay mode.
>>
>> * linux-nat.c (my_waitpid_record): Add
>> gdbarch_decr_pc_after_break to pc if need.
>>
>> Thanks,
>> Hui
>>
>> On Fri, Oct 24, 2008 at 16:10, teawater <teawater@gmail.com> wrote:
>>> Thanks Pedro and Michael,
>>>
>>> I think the reason is P record let inferior step recycle in the
>>> linux-nat target.
>>> So when it break by breakpint, it will not let
>>> (pc+gdbarch_decr_pc_after_break (gdbarch)). Then after
>>> adjust_pc_after_break, The PC is error.
>>>
>>> I will try to deal with it.
>>>
>>> Hui
>>>
>>> On Fri, Oct 24, 2008 at 09:50, Pedro Alves <pedro@codesourcery.com> wrote:
>>>> On Friday 24 October 2008 01:37:31, Michael Snyder wrote:
>>>>>> In sum, it appears that decr_pc_after_break doesn't matter when you have
>>>>>> continguous breakpoints, as long as you get from from B1's address to B2's
>>>>>> address by single-stepping. All is good then, it appears!
>>>>> I agree, at least that is the conclusion I am leaning toward.
>>>>>
>>>> Not so fast! I knew I had to spend a little extra thinking about
>>>> it, 'cause I knew something was broken, just couldn't find what. :-)
>>>> *as long as you get from from B1's address to B2's address
>>>> by single-stepping* was a restriction that doesn't always apply.
>>>>
>>>> Here's a test that will fail in forward record/replay mode, but not
>>>> in normal "play" mode.
>>>>
>>>> volatile int global_foo = 0;
>>>>
>>>> int
>>>> main (int argc, char **argv)
>>>> {
>>>> asm ("nop"); /* 1st insn */
>>>> asm ("nop"); /* 2nd insn */
>>>> asm ("nop"); /* 3rd insn */
>>>> asm ("nop"); /* 4th insn */
>>>> if (!global_foo)
>>>> goto ahead;
>>>> asm ("nop"); /* 5th insn */
>>>> asm ("nop"); /* 6th insn */
>>>> asm ("nop"); /* 7th insn */
>>>> asm ("nop"); /* 8th insn */ <<< break 1 here
>>>> ahead:
>>>> asm ("nop"); /* 9th insn */ <<< break 2 here
>>>> end:
>>>> return 0;
>>>> }
>>>>
>>>> If you let the program reply until break 2 is hit, and assuming insn
>>>> 8th and 9th are assembled as contiguous (they do on x86 -O0 for me), you'll
>>>> see that adjust_pc_after_break will indeed make it appear that breakpoint
>>>> 1 was hit. Now, nops are nops, but real code could have something
>>>> else there...
>>>>
>>>> /me goes back to bed.
>>>>
>>>> --
>>>> Pedro Alves
>>>>
>>
>> ------------------------------------------------------------------------
>>
>> --- a/linux-nat.c
>> +++ b/linux-nat.c
>> @@ -514,7 +514,9 @@ my_waitpid_record (int pid, int *status,
>> struct bp_location *bl;
>> struct breakpoint *b;
>> CORE_ADDR pc;
>> + CORE_ADDR decr_pc_after_break;
>> struct lwp_info *lp;
>> + int is_breakpoint = 1;
>>
>> wait_begin:
>> ret = my_waitpid (pid, status, flags);
>> @@ -530,7 +532,7 @@ wait_begin:
>>
>> if (WIFSTOPPED (*status) && WSTOPSIG (*status) == SIGTRAP)
>> {
>> - /* Check if there is a breakpoint */
>> + /* Check if there is a breakpoint. */
>> pc = 0;
>> registers_changed ();
>> for (bl = bp_location_chain; bl; bl = bl->global_next)
>> @@ -602,7 +604,26 @@ wait_begin:
>> goto wait_begin;
>> }
>>
>> + is_breakpoint = 0;
>> +
>> out:
>> + /* Add gdbarch_decr_pc_after_break to pc because pc will be break at address
>> + add gdbarch_decr_pc_after_break when inferior non-step execute. */
>> + if (is_breakpoint)
>> + {
>> + decr_pc_after_break = gdbarch_decr_pc_after_break
>> + (get_regcache_arch (get_thread_regcache (pid_to_ptid (ret))));
>> + if (decr_pc_after_break)
>> + {
>> + if (!pc)
>> + {
>> + pc = regcache_read_pc (get_thread_regcache (pid_to_ptid (ret)));
>> + }
>> + regcache_write_pc (get_thread_regcache (pid_to_ptid (ret)),
>> + pc + decr_pc_after_break);
>> + }
>> + }
>> +
>> return ret;
>> }
>>
>> --- a/record.c
>> +++ b/record.c
>> @@ -497,6 +497,33 @@ 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;
>> +
>> + status->kind = TARGET_WAITKIND_STOPPED;
>> +
>> + /* 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))
>> + && !record_resume_step)
>> + {
>> + 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;
>> @@ -521,7 +548,6 @@ record_wait (ptid_t ptid, struct target_
>>
>> /* Loop over the record_list, looking for the next place to
>> stop. */
>> - status->kind = TARGET_WAITKIND_STOPPED;
>> do
>> {
>> /* Check for beginning and end of log. */
>> @@ -588,10 +614,6 @@ 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 +654,25 @@ 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
>> + && !record_resume_step)
>> {
>> - 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 +703,7 @@ next:
>> perror_with_name (_("Process record: sigaction"));
>> }
>>
>> +replay_out:
>> if (record_get_sig)
>> {
>> status->value.sig = TARGET_SIGNAL_INT;