Introduce GDB_THREAD_OPTION_EXIT thread option, fix step-over-thread-exit

When stepping over a breakpoint with displaced stepping, GDB needs to
be informed if the stepped thread exits, otherwise the displaced
stepping buffer that was allocated to that thread leaks, and this can
result in deadlock, with other threads waiting for their turn to
displaced step, but their turn never comes.

Similarly, when stepping over a breakpoint in line, GDB also needs to
be informed if the stepped thread exits, so that is can clear the step
over state and re-resume threads.

This commit makes it possible for GDB to ask the target to report
thread exit events for a given thread, using the new "thread options"
mechanism introduced by a previous patch.

This only adds the core bits.  Following patches in the series will
teach the Linux backends (native & gdbserver) to handle the
GDB_THREAD_OPTION_EXIT option, and then a later patch will make use of
these thread exit events to clean up displaced stepping and inline
stepping state properly.

Reviewed-By: Andrew Burgess <aburgess@redhat.com>
Change-Id: I96b719fdf7fee94709e98bb3a90751d8134f3a38
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=27338

1 files changed, 10 insertions, 5 deletions

diff --git a/gdb/infrun.c b/gdb/infrun.c
index e1e761c..0a189d0 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -2516,24 +2516,29 @@ do_target_resume (ptid_t resume_ptid, bool step, enum gdb_signal sig)
   else
     target_pass_signals (signal_pass);
 
-  /* Request that the target report thread-{created,cloned} events in
-     the following situations:
+  /* Request that the target report thread-{created,cloned,exited}
+     events in the following situations:
 
      - If we are performing an in-line step-over-breakpoint, then we
        will remove a breakpoint from the target and only run the
        current thread.  We don't want any new thread (spawned by the
-       step) to start running, as it might miss the breakpoint.
+       step) to start running, as it might miss the breakpoint.  We
+       need to clear the step-over state if the stepped thread exits,
+       so we also enable thread-exit events.
 
      - If we are stepping over a breakpoint out of line (displaced
        stepping) then we won't remove a breakpoint from the target,
        but, if the step spawns a new clone thread, then we will need
        to fixup the $pc address in the clone child too, so we need it
-       to start stopped.
+       to start stopped.  We need to release the displaced stepping
+       buffer if the stepped thread exits, so we also enable
+       thread-exit events.
   */
   if (step_over_info_valid_p ()
       || displaced_step_in_progress_thread (tp))
     {
-      gdb_thread_options options = GDB_THREAD_OPTION_CLONE;
+      gdb_thread_options options
+	= GDB_THREAD_OPTION_CLONE | GDB_THREAD_OPTION_EXIT;
       if (target_supports_set_thread_options (options))
 	tp->set_thread_options (options);
       else