Re: [PATCH 3/7] Force to insert software single step breakpoint

Yao Qi
2016-04-19T14:54:58Z

Pedro Alves <palves@redhat.com> writes:

> Another scenario occurred to me:
>
> - Thread A is software single-stepping.
> - Thread B hits single-step breakpoint of thread A.
> - We pause all threads and set thread B stepping past the
> single-step breakpoint of thread A.
>
> But if the single-step breakpoint is for another thread, then
> we won't actually manage to have thread B step past it, resulting
> in spurious re-hits and no-guaranteed forward progress. See
> e.g., non-stop-fair-events.exp:
>
> # On software single-step targets that don't support displaced
> # stepping, threads keep hitting each others' single-step
> # breakpoints, and then GDB needs to pause all threads to step
> # past those. The end result is that progress in the main
> # thread will be slower and it may take a bit longer for the
> # signal to be queued; bump the timeout.
>
> Sounds like we may need to look at the single-step breakpoint's thread
> id, and only insert it if it is for the thread that is going to be
> doing the step-over? We may need to record that in step_over_info and
> pass more info to stepping_past_instruction_at.

I think this is about any thread specific breakpoint, instead of
only single-step breakpoint (single-step breakpoint is thread specific
too). If we are doing step-over for thread A, do we need to insert any
breakpoints specific to other threads? (my answer is No).

--
Yao (齐尧)