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

teawater
2008-10-30T01:51:21Z

Maybe I can checked it in first. :)

On Wed, Oct 29, 2008 at 06:51, Michael Snyder <msnyder@vmware.com> wrote:
> 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;
>
>