Re: [PATCH v3 05/17] Embed the pending step-over chain in thread_info objects

Doug Evans
2015-04-22T04:25:05Z

Pedro Alves writes:
> In order to teach non-stop mode to do in-line step-overs (pause all
> threads, remove breakpoint, single-step, reinsert breakpoint, restart
> threads), we'll need to be able to queue in-line step over requests,
> much like we queue displaced stepping (out-of-line) requests.
> Actually, the queue should be the same -- threads wait for their turn
> to step past something (breakpoint, watchpoint), doesn't matter what
> technique we end up using when the step over actually starts.
>
> I found that the queue management ends up simpler and more efficient
> if embedded in the thread objects themselves. This commit converts
> the existing displaced stepping queue to that. Later patches will
> make the in-line step-overs code paths use it too.
>
> gdb/ChangeLog:
> 2015-04-17 Pedro Alves <palves@redhat.com>
>
> * gdbthread.h (struct thread_info) <step_over_prev,
> step_over_next>: New fields.
> (thread_step_over_chain_enqueue, thread_step_over_chain_remove)
> (thread_step_over_chain_next, thread_is_in_step_over_chain): New
> declarations.
> * infrun.c (struct displaced_step_request): Delete.
> (struct displaced_step_inferior_state) <step_request_queue>:
> Delete field.
> (displaced_step_in_progress): New function.
> (displaced_step_prepare): Assert that trap_expected is set. Use
> thread_step_over_chain_enqueue. Split starting a new displaced
> step to ...
> (start_step_over): ... this new function.
> (resume): Assert the thread isn't waiting for a step over already.
> (proceed): Assert the thread isn't waiting for a step over
> already.
> (infrun_thread_stop_requested): Adjust to remove threads from the
> embedded step-over chain.
> (handle_inferior_event) <fork/vfork>: Call start_step_over after
> displaced_step_fixup.
> (handle_signal_stop): Call start_step_over after
> displaced_step_fixup.
> * infrun.h (step_over_queue_head): New declaration.
> * thread.c (step_over_chain_enqueue, step_over_chain_remove)
> (thread_step_over_chain_next, thread_is_in_step_over_chain)
> (thread_step_over_chain_enqueue)
> (thread_step_over_chain_remove): New functions.
> (delete_thread_1): Remove thread from the step-over chain.
>
> v3:
>
> More comments. The step-over chain is now a global instead of
> being per-inferior. Previous versions had actually broken
> multiple-processes displaced stepping at the same time. Added new
> thread_is_in_step_over_chain predicate, and new
> thread_step_over_chain_next helper function. Should make reading
> the code a bit easier (following patches adjusted too).
>...
>
> diff --git a/gdb/infrun.c b/gdb/infrun.c
> index 534ecef..f325a53 100644
> --- a/gdb/infrun.c
> +++ b/gdb/infrun.c
>...
> @@ -1855,24 +1842,44 @@ displaced_step_fixup (ptid_t event_ptid, enum gdb_signal signal)
> do_cleanups (old_cleanups);
>
> displaced->step_ptid = null_ptid;
> +}
>
> - /* Are there any pending displaced stepping requests? If so, run
> - one now. Leave the state object around, since we're likely to
> - need it again soon. */
> - while (displaced->step_request_queue)
> +/* Are there any pending step-over requests? If so, run one now. */

Hi.

Nit: IIUC "run one now" should read "run all we can now".

> +
> +static void
> +start_step_over (void)
> +{
>...