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

teawater
2008-10-25T07:08:26Z

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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.

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
>>>
>>
>

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--- 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;