Re: [PATCH 31/31] Cancel execution command on thread exit, when stepping, nexting, etc.

Andrew Burgess via Gdb-patches
2023-06-12T13:12:32Z

Pedro Alves <pedro@palves.net> writes:

> If your target has no support for TARGET_WAITKIND_NO_RESUMED events
> (and no way to support them, such as the yet-unsubmitted AMDGPU
> target), and you step over thread exit with scheduler-locking on, this
> is what you get:
>
> (gdb) n
> [Thread ... exited]
> *hang*
>
> Getting back the prompt by typing Ctrl-C may not even work, since no
> inferior thread is running to receive the SIGINT. Even if it works,
> it seems unnecessarily harsh. If you started an execution command for
> which there's a clear thread of interest (step, next, until, etc.),
> and that thread disappears, then I think it's more user friendly if
> GDB just detects the situation and aborts the command, giving back the
> prompt.
>
> That is what this commit implements. It does this by explicitly
> requesting the target to report thread exit events whenever the main
> resumed thread has a thread_fsm. Note that unlike stepping over a
> breakpoint, we don't need to enable clone events in this case.
>
> With this patch, we get:
>
> (gdb) n
> [Thread 0x7ffff7d89700 (LWP 3961883) exited]
> Command aborted, thread exited.
> (gdb)

LGTM.

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

Thanks,
Andrew

>
> Change-Id: I901ab64c91d10830590b2dac217b5264635a2b95
> ---
> gdb/infrun.c | 73 ++++++++++++++---
> .../gdb.threads/step-over-thread-exit.exp | 79 ++++++++++++-------
> 2 files changed, 115 insertions(+), 37 deletions(-)
>
> diff --git a/gdb/infrun.c b/gdb/infrun.c
> index 21e5aa0f50e..61d2a14c646 100644
> --- a/gdb/infrun.c
> +++ b/gdb/infrun.c
> @@ -1886,6 +1886,22 @@ displaced_step_prepare (thread_info *thread)
> return status;
> }
>
> +/* True if any thread of TARGET that matches RESUME_PTID requires
> + target_thread_events enabled. This assumes TARGET does not support
> + target thread options. */
> +
> +static bool
> +any_thread_needs_target_thread_events (process_stratum_target *target,
> + ptid_t resume_ptid)
> +{
> + for (thread_info *tp : all_non_exited_threads (target, resume_ptid))
> + if (displaced_step_in_progress_thread (tp)
> + || schedlock_applies (tp)
> + || tp->thread_fsm () != nullptr)
> + return true;
> + return false;
> +}
> +
> /* Maybe disable thread-{cloned,created,exited} event reporting after
> a step-over (either in-line or displaced) finishes. */
>
> @@ -1909,9 +1925,10 @@ update_thread_events_after_step_over (thread_info *event_thread,
> else
> {
> /* We can only control the target-wide target_thread_events
> - setting. Disable it, but only if other threads don't need it
> - enabled. */
> - if (!displaced_step_in_progress_any_thread ())
> + setting. Disable it, but only if other threads in the target
> + don't need it enabled. */
> + process_stratum_target *target = event_thread->inf->process_target ();
> + if (!any_thread_needs_target_thread_events (target, minus_one_ptid))
> target_thread_events (false);
> }
> }
> @@ -2488,12 +2505,25 @@ do_target_resume (ptid_t resume_ptid, bool step, enum gdb_signal sig)
> else
> target_thread_events (true);
> }
> + else if (tp->thread_fsm () != nullptr)
> + {
> + gdb_thread_options options = GDB_THREAD_OPTION_EXIT;
> + if (target_supports_set_thread_options (options))
> + tp->set_thread_options (options);
> + else
> + target_thread_events (true);
> + }
> else
> {
> if (target_supports_set_thread_options (0))
> tp->set_thread_options (0);
> - else if (!displaced_step_in_progress_any_thread ())
> - target_thread_events (false);
> + else
> + {
> + process_stratum_target *resume_target = tp->inf->process_target ();
> + if (!any_thread_needs_target_thread_events (resume_target,
> + resume_ptid))
> + target_thread_events (false);
> + }
> }
>
> /* If we're resuming more than one thread simultaneously, then any
> @@ -5671,6 +5701,13 @@ handle_thread_exited (execution_control_state *ecs)
> ecs->event_thread->stepping_over_breakpoint = 0;
> ecs->event_thread->stepping_over_watchpoint = 0;
>
> + /* If the thread had an FSM, then abort the command. But only after
> + finishing the step over, as in non-stop mode, aborting this
> + thread's command should not interfere with other threads. We
> + must check this before finish_step over, however, which may
> + update the thread list and delete the event thread. */
> + bool abort_cmd = (ecs->event_thread->thread_fsm () != nullptr);
> +
> /* Maybe the thread was doing a step-over, if so release
> resources and start any further pending step-overs.
>
> @@ -5684,6 +5721,13 @@ handle_thread_exited (execution_control_state *ecs)
> the event thread has exited. */
> gdb_assert (ret == 0);
>
> + if (abort_cmd)
> + {
> + delete_thread (ecs->event_thread);
> + ecs->event_thread = nullptr;
> + return false;
> + }
> +
> /* If finish_step_over started a new in-line step-over, don't
> try to restart anything else. */
> if (step_over_info_valid_p ())
> @@ -9062,7 +9106,8 @@ normal_stop (void)
> if (inferior_ptid != null_ptid)
> finish_ptid = ptid_t (inferior_ptid.pid ());
> }
> - else if (last.kind () != TARGET_WAITKIND_NO_RESUMED)
> + else if (last.kind () != TARGET_WAITKIND_NO_RESUMED
> + && last.kind () != TARGET_WAITKIND_THREAD_EXITED)
> finish_ptid = inferior_ptid;
>
> gdb::optional<scoped_finish_thread_state> maybe_finish_thread_state;
> @@ -9105,7 +9150,8 @@ normal_stop (void)
> {
> if ((last.kind () != TARGET_WAITKIND_SIGNALLED
> && last.kind () != TARGET_WAITKIND_EXITED
> - && last.kind () != TARGET_WAITKIND_NO_RESUMED)
> + && last.kind () != TARGET_WAITKIND_NO_RESUMED
> + && last.kind () != TARGET_WAITKIND_THREAD_EXITED)
> && target_has_execution ()
> && previous_thread != inferior_thread ())
> {
> @@ -9121,7 +9167,8 @@ normal_stop (void)
> update_previous_thread ();
> }
>
> - if (last.kind () == TARGET_WAITKIND_NO_RESUMED)
> + if (last.kind () == TARGET_WAITKIND_NO_RESUMED
> + || last.kind () == TARGET_WAITKIND_THREAD_EXITED)
> {
> stop_print_frame = false;
>
> @@ -9129,7 +9176,12 @@ normal_stop (void)
> if (current_ui->prompt_state == PROMPT_BLOCKED)
> {
> target_terminal::ours_for_output ();
> - gdb_printf (_("No unwaited-for children left.\n"));
> + if (last.kind () == TARGET_WAITKIND_NO_RESUMED)
> + gdb_printf (_("No unwaited-for children left.\n"));
> + else if (last.kind () == TARGET_WAITKIND_THREAD_EXITED)
> + gdb_printf (_("Command aborted, thread exited.\n"));
> + else
> + gdb_assert_not_reached ("unhandled");
> }
> }
>
> @@ -9214,7 +9266,8 @@ normal_stop (void)
> {
> if (last.kind () != TARGET_WAITKIND_SIGNALLED
> && last.kind () != TARGET_WAITKIND_EXITED
> - && last.kind () != TARGET_WAITKIND_NO_RESUMED)
> + && last.kind () != TARGET_WAITKIND_NO_RESUMED
> + && last.kind () != TARGET_WAITKIND_THREAD_EXITED)
> /* Delete the breakpoint we stopped at, if it wants to be deleted.
> Delete any breakpoint that is to be deleted at the next stop. */
> breakpoint_auto_delete (inferior_thread ()->control.stop_bpstat);
> diff --git a/gdb/testsuite/gdb.threads/step-over-thread-exit.exp b/gdb/testsuite/gdb.threads/step-over-thread-exit.exp
> index ed8534cf518..a0056740478 100644
> --- a/gdb/testsuite/gdb.threads/step-over-thread-exit.exp
> +++ b/gdb/testsuite/gdb.threads/step-over-thread-exit.exp
> @@ -29,7 +29,7 @@ if { [build_executable "failed to prepare" $testfile \
> # NS_STOP_ALL is only used if testing "set non-stop on", and indicates
> # whether to have GDB explicitly stop all threads before continuing to
> # thread exit.
> -proc test {displaced-stepping non-stop target-non-stop schedlock ns_stop_all} {
> +proc test {displaced-stepping non-stop target-non-stop schedlock cmd ns_stop_all} {
> if {${non-stop} == "off" && $ns_stop_all} {
> error "invalid arguments"
> }
> @@ -72,31 +72,54 @@ proc test {displaced-stepping non-stop target-non-stop schedlock ns_stop_all} {
>
> gdb_test_no_output "set scheduler-locking ${schedlock}"
>
> - gdb_test "continue" \
> - "No unwaited-for children left." \
> - "continue stops when thread exits"
> + if {$cmd == "continue"} {
> + gdb_test "continue" \
> + "No unwaited-for children left." \
> + "continue stops when thread exits"
> + } else {
> + gdb_test $cmd \
> + "Command aborted, thread exited\\." \
> + "command aborts when thread exits"
> + }
> } else {
> gdb_test_no_output "set scheduler-locking ${schedlock}"
>
> - for { set i 0 } { $i < 100 } { incr i } {
> - with_test_prefix "iter $i" {
> - set ok 0
> - set thread "<unknown>"
> - gdb_test_multiple "continue" "" {
> - -re -wrap "Thread ($::decimal) .*hit Breakpoint $::decimal.* my_exit_syscall .*" {
> - set thread $expect_out(1,string)
> - set ok 1
> - }
> - }
> - if {!${ok}} {
> - # Exit if there's a failure to avoid lengthy
> - # timeouts.
> - break
> + if {$cmd != "continue"} {
> + set thread "<unknown>"
> + gdb_test_multiple "continue" "" {
> + -re -wrap "Thread ($::decimal) .*hit Breakpoint $::decimal.* my_exit_syscall .*" {
> + set thread $expect_out(1,string)
> }
> + }
> + if {${non-stop}} {
> + gdb_test -nopass "thread $thread" "Switching to thread .*" \
> + "switch to event thread"
> + }
>
> - if {${non-stop}} {
> - gdb_test "thread $thread" "Switching to thread .*" \
> - "switch to event thread"
> + gdb_test $cmd \
> + "Command aborted, thread exited\\." \
> + "command aborts when thread exits"
> + } else {
> + for { set i 0 } { $i < 100 } { incr i } {
> + with_test_prefix "iter $i" {
> + set ok 0
> + set thread "<unknown>"
> + gdb_test_multiple "continue" "" {
> + -re -wrap "Thread ($::decimal) .*hit Breakpoint $::decimal.* my_exit_syscall .*" {
> + set thread $expect_out(1,string)
> + set ok 1
> + }
> + }
> + if {!${ok}} {
> + # Exit if there's a failure to avoid lengthy
> + # timeouts.
> + break
> + }
> +
> + if {${non-stop}} {
> + gdb_test -nopass "thread $thread" "Switching to thread .*" \
> + "switch to event thread"
> + }
> }
> }
> }
> @@ -112,13 +135,15 @@ foreach_with_prefix displaced-stepping {off auto} {
> }
>
> foreach_with_prefix schedlock {off on} {
> - if {${non-stop} == "on"} {
> - foreach_with_prefix ns_stop_all {0 1} {
> - test ${displaced-stepping} ${non-stop} ${target-non-stop} \
> - ${schedlock} ${ns_stop_all}
> + foreach_with_prefix cmd {"next" "continue"} {
> + if {${non-stop} == "on"} {
> + foreach_with_prefix ns_stop_all {0 1} {
> + test ${displaced-stepping} ${non-stop} ${target-non-stop} \
> + ${schedlock} ${cmd} ${ns_stop_all}
> + }
> + } else {
> + test ${displaced-stepping} ${non-stop} ${target-non-stop} ${schedlock} ${cmd} 0
> }
> - } else {
> - test ${displaced-stepping} ${non-stop} ${target-non-stop} ${schedlock} 0
> }
> }
> }
> --
> 2.36.0