Re: [PATCH 22/31] gdbserver: Queue no-resumed event after thread exit

Andrew Burgess via Gdb-patches
2023-06-08T18:17:06Z

Pedro Alves <pedro@palves.net> writes:

> Normally, if the last thread resumed thread on the target exits, the

"thread resumed thread" .... I think there's an extra 'thread' in there.

Otherwise, LGTM.

Reviewed-By: Andrew Burgess <aburgess@redhat.com>

Thanks,
Andrew

> server sends a no-resumed event to GDB. If however, GDB enables the
> GDB_THREAD_OPTION_EXIT option on a thread, and, that thread exits, the
> server sends a thread exit event for that thread instead.
>
> In all-stop RSP mode, since events can only be forwarded to GDB one at
> a time, and the whole target stops whenever an event is reported, GDB
> resumes the target again after getting a THREAD_EXITED event, and then
> the server finally reports back a no-resumed event if/when
> appropriate.
>
> For non-stop RSP though, events are asynchronous, and if the server
> sends a thread-exit event for the last resumed thread, the no-resumed
> event is never sent. This patch makes sure that in non-stop mode, the
> server queues a no-resumed event after the thread-exit event if it was
> the last resumed thread that exited.
>
> Without this, we'd see failures in step-over-thread-exit testcases
> added later in the series, like so:
>
> continue
> Continuing.
> - No unwaited-for children left.
> - (gdb) PASS: gdb.threads/step-over-thread-exit.exp: displaced-stepping=off: non-stop=on: target-non-stop=on: schedlock=off: ns_stop_all=1: continue stops when thread exits
> + FAIL: gdb.threads/step-over-thread-exit.exp: displaced-stepping=off: non-stop=on: target-non-stop=on: schedlock=off: ns_stop_all=1: continue stops when thread exits (timeout)
>
> (and other similar ones)
>
> Change-Id: I927d78b30f88236dbd5634b051a716f72420e7c7
> ---
> gdbserver/linux-low.cc | 47 +++++++++++++++++++++++++-----------------
> gdbserver/linux-low.h | 2 ++
> gdbserver/server.cc | 12 ++++++++++-
> gdbserver/target.cc | 6 ++++++
> gdbserver/target.h | 6 ++++++
> 5 files changed, 53 insertions(+), 20 deletions(-)
>
> diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
> index ebc3bf34127..bf6dc1d995a 100644
> --- a/gdbserver/linux-low.cc
> +++ b/gdbserver/linux-low.cc
> @@ -2963,7 +2963,6 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
> int report_to_gdb;
> int trace_event;
> int in_step_range;
> - int any_resumed;
>
> threads_debug_printf ("[%s]", target_pid_to_str (ptid).c_str ());
>
> @@ -2977,23 +2976,7 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
> in_step_range = 0;
> ourstatus->set_ignore ();
>
> - auto status_pending_p_any = [&] (thread_info *thread)
> - {
> - return status_pending_p_callback (thread, minus_one_ptid);
> - };
> -
> - auto not_stopped = [&] (thread_info *thread)
> - {
> - return not_stopped_callback (thread, minus_one_ptid);
> - };
> -
> - /* Find a resumed LWP, if any. */
> - if (find_thread (status_pending_p_any) != NULL)
> - any_resumed = 1;
> - else if (find_thread (not_stopped) != NULL)
> - any_resumed = 1;
> - else
> - any_resumed = 0;
> + bool was_any_resumed = any_resumed ();
>
> if (step_over_bkpt == null_ptid)
> pid = wait_for_event (ptid, &w, options);
> @@ -3004,7 +2987,7 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
> pid = wait_for_event (step_over_bkpt, &w, options & ~WNOHANG);
> }
>
> - if (pid == 0 || (pid == -1 && !any_resumed))
> + if (pid == 0 || (pid == -1 && !was_any_resumed))
> {
> gdb_assert (target_options & TARGET_WNOHANG);
>
> @@ -6166,6 +6149,32 @@ linux_process_target::thread_stopped (thread_info *thread)
> return get_thread_lwp (thread)->stopped;
> }
>
> +bool
> +linux_process_target::any_resumed ()
> +{
> + bool any_resumed;
> +
> + auto status_pending_p_any = [&] (thread_info *thread)
> + {
> + return status_pending_p_callback (thread, minus_one_ptid);
> + };
> +
> + auto not_stopped = [&] (thread_info *thread)
> + {
> + return not_stopped_callback (thread, minus_one_ptid);
> + };
> +
> + /* Find a resumed LWP, if any. */
> + if (find_thread (status_pending_p_any) != NULL)
> + any_resumed = 1;
> + else if (find_thread (not_stopped) != NULL)
> + any_resumed = 1;
> + else
> + any_resumed = 0;
> +
> + return any_resumed;
> +}
> +
> /* This exposes stop-all-threads functionality to other modules. */
>
> void
> diff --git a/gdbserver/linux-low.h b/gdbserver/linux-low.h
> index 1c1754d2b59..33a14e15173 100644
> --- a/gdbserver/linux-low.h
> +++ b/gdbserver/linux-low.h
> @@ -259,6 +259,8 @@ class linux_process_target : public process_stratum_target
>
> bool thread_stopped (thread_info *thread) override;
>
> + bool any_resumed () override;
> +
> void pause_all (bool freeze) override;
>
> void unpause_all (bool unfreeze) override;
> diff --git a/gdbserver/server.cc b/gdbserver/server.cc
> index 5099db1ee31..77b4b57466d 100644
> --- a/gdbserver/server.cc
> +++ b/gdbserver/server.cc
> @@ -4740,7 +4740,17 @@ handle_target_event (int err, gdb_client_data client_data)
> }
> }
> else
> - push_stop_notification (cs.last_ptid, cs.last_status);
> + {
> + push_stop_notification (cs.last_ptid, cs.last_status);
> +
> + if (cs.last_status.kind () == TARGET_WAITKIND_THREAD_EXITED
> + && !target_any_resumed ())
> + {
> + target_waitstatus ws;
> + ws.set_no_resumed ();
> + push_stop_notification (null_ptid, ws);
> + }
> + }
> }
>
> /* Be sure to not change the selected thread behind GDB's back.
> diff --git a/gdbserver/target.cc b/gdbserver/target.cc
> index 4584e9b3a8e..833e32a4830 100644
> --- a/gdbserver/target.cc
> +++ b/gdbserver/target.cc
> @@ -612,6 +612,12 @@ process_stratum_target::thread_stopped (thread_info *thread)
> gdb_assert_not_reached ("target op thread_stopped not supported");
> }
>
> +bool
> +process_stratum_target::any_resumed ()
> +{
> + return true;
> +}
> +
> bool
> process_stratum_target::supports_get_tib_address ()
> {
> diff --git a/gdbserver/target.h b/gdbserver/target.h
> index e2e818b130b..c3345fc67e8 100644
> --- a/gdbserver/target.h
> +++ b/gdbserver/target.h
> @@ -320,6 +320,9 @@ class process_stratum_target
> /* Return true if THREAD is known to be stopped now. */
> virtual bool thread_stopped (thread_info *thread);
>
> + /* Return true if any thread is known to be resumed. */
> + virtual bool any_resumed ();
> +
> /* Return true if the get_tib_address op is supported. */
> virtual bool supports_get_tib_address ();
>
> @@ -683,6 +686,9 @@ target_read_btrace_conf (struct btrace_target_info *tinfo,
> #define target_supports_software_single_step() \
> the_target->supports_software_single_step ()
>
> +#define target_any_resumed() \
> + the_target->any_resumed ()
> +
> ptid_t mywait (ptid_t ptid, struct target_waitstatus *ourstatus,
> target_wait_flags options, int connected_wait);
>
> --
> 2.36.0