Re: [RFC 2/3] use reinsert breakpoint for vCont;s

Antoine Tremblay
2016-05-12T13:25:47Z

Yao Qi writes:

> Yao Qi <qiyaoltc@gmail.com> writes:
>
>> +
>> + if (!step_over_finished && !can_hardware_single_step ())
>> + {
>> + /* If the thread resumed by resume_step hits the reinsert
>> + breakpoint, delete the reinsert breakpoint for it. */
>> + if (current_thread->last_resume_kind == resume_step)
>> + delete_reinsert_breakpoints (current_thread);
>> + else
>> + {
>> + /* If the thread resumed by other kind, like
>> + resume_continue, hits the breakpoint (either
>> + reinsert breakpoint or GDB breakpoint), delete
>> + all reinsert breakpoints if it hits non-reinsert
>> + breakpoints, otherwise, leave reinsert breakpoint there
>> + and step over it. */
>> + if (non_reinsert_breakpoint_inserted_here (event_child->stop_pc))
>> + delete_reinsert_breakpoints (NULL);
>> + }
>> + }
>> }
>> else
>> {
>> /* We have some other signal, possibly a step-over dance was in
>> progress, and it should be cancelled too. */
>> step_over_finished = finish_step_over (event_child);
>> +
>> + if (!step_over_finished && !can_hardware_single_step ())
>> + delete_reinsert_breakpoints (NULL);
>> }
>>
>> /* We have all the data we need. Either report the event to GDB, or
>> @@ -3568,6 +3590,8 @@ linux_wait_1 (ptid_t ptid,
>>
>> /* Alright, we're going to report a stop. */
>>
>> + delete_reinsert_breakpoints (NULL);
>> +
>
> The SIGILL is caused by removing these reinsert breakpoints when threads
> are still running. I adjust the code removing reinsert breakpoints when
> threads stop, the SIGILL goes away.

I think the insertion of the breakpoints may also be unsafe in non-stop
mode, since correct me if am wrong but in linux_resume we can't assume
that all threads are stopped and thus when we call single_step from:
linux_resume->linux_resume_one_lwp->single_step another thread could
hit the memory we're writing to.

We should stop all threads before the breakpoint insertion like done in
start_step_over.

Actually I think we should have a function like
start_software_vCont that does stops all threads, insert the
breakpoints, resume all threads...

I have not pinpointed the design of this however as I'd rather not call
it from the linux_resume_one_lwp callback. It would be weird to mess
with the thread running state there.

I'm thinking, maybe again close to what step over is doing having a:

if (software_single_step && !hardware_single_step)
find_inferior (&all_threads, need_software_vCont..)

if (need_software_vCont)
start_software_vCont
- stop all threads
- call single_step to insert the breakpoints
- resume all threads

And I guess we can have a stop_software_vCont to match it.

I have not gone through the stop scenarios enough yet to tell where however...