Implement GDB_THREAD_OPTION_EXIT support for native Linux

This implements support for the new GDB_THREAD_OPTION_EXIT thread
option for native Linux.

Reviewed-By: Andrew Burgess <aburgess@redhat.com>
Change-Id: Ia69fc0b9b96f9af7de7cefc1ddb1fba9bbb0bb90
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=27338

gdb/linux-nat.c

@@ -268,6 +268,18 @@ pending_status_str (lwp_info *lp)
     return status_to_str (lp->status);
 }
 
+/* Return true if we should report exit events for LP.  */
+
+static bool
+report_exit_events_for (lwp_info *lp)
+{
+  thread_info *thr = linux_target->find_thread (lp->ptid);
+  gdb_assert (thr != nullptr);
+
+  return (report_thread_events
+	  || (thr->thread_options () & GDB_THREAD_OPTION_EXIT) != 0);
+}
+
 
 /* LWP accessors.  */
 
@@ -2148,8 +2160,7 @@ wait_lwp (struct lwp_info *lp)
       /* Check if the thread has exited.  */
       if (WIFEXITED (status) || WIFSIGNALED (status))
 	{
-	  if (report_thread_events
+	  if (report_exit_events_for (lp) || is_leader (lp))
-	      || lp->ptid.pid () == lp->ptid.lwp ())
 	    {
 	      linux_nat_debug_printf ("LWP %d exited.", lp->ptid.pid ());
 
@@ -2932,7 +2943,7 @@ linux_nat_filter_event (int lwpid, int status)
   /* Check if the thread has exited.  */
   if (WIFEXITED (status) || WIFSIGNALED (status))
     {
-      if (!report_thread_events && !is_leader (lp))
+      if (!report_exit_events_for (lp) && !is_leader (lp))
 	{
 	  linux_nat_debug_printf ("%s exited.",
 				  lp->ptid.to_string ().c_str ());
@@ -3142,10 +3153,11 @@ check_zombie_leaders (void)
     }
 }
 
-/* Convenience function that is called when the kernel reports an exit
+/* Convenience function that is called when we're about to return an
-   event.  This decides whether to report the event to GDB as a
+   event to the core.  If the event is an exit or signalled event,
-   process exit event, a thread exit event, or to suppress the
+   then this decides whether to report it as process-wide event, as a
-   event.  */
+   thread exit event, or to suppress it.  All other event kinds are
+   passed through unmodified.  */
 
 static ptid_t
 filter_exit_event (struct lwp_info *event_child,
@@ -3153,9 +3165,17 @@ filter_exit_event (struct lwp_info *event_child,
 {
   ptid_t ptid = event_child->ptid;
 
+  /* Note we must filter TARGET_WAITKIND_SIGNALLED as well, otherwise
+     if a non-leader thread exits with a signal, we'd report it to the
+     core which would interpret it as the whole-process exiting.
+     There is no TARGET_WAITKIND_THREAD_SIGNALLED event kind.  */
+  if (ourstatus->kind () != TARGET_WAITKIND_EXITED
+      && ourstatus->kind () != TARGET_WAITKIND_SIGNALLED)
+    return ptid;
+
   if (!is_leader (event_child))
     {
-      if (report_thread_events)
+      if (report_exit_events_for (event_child))
 	{
 	  ourstatus->set_thread_exited (0);
 	  /* Delete lwp, but not thread_info, infrun will need it to
@@ -3388,10 +3408,7 @@ linux_nat_wait_1 (ptid_t ptid, struct target_waitstatus *ourstatus,
   else
     lp->core = linux_common_core_of_thread (lp->ptid);
 
-  if (ourstatus->kind () == TARGET_WAITKIND_EXITED)
   return filter_exit_event (lp, ourstatus);
-
-  return lp->ptid;
 }
 
 /* Resume LWPs that are currently stopped without any pending status
@@ -4513,7 +4530,8 @@ linux_nat_target::thread_events (int enable)
 bool
 linux_nat_target::supports_set_thread_options (gdb_thread_options options)
 {
-  constexpr gdb_thread_options supported_options = GDB_THREAD_OPTION_CLONE;
+  constexpr gdb_thread_options supported_options
+    = GDB_THREAD_OPTION_CLONE | GDB_THREAD_OPTION_EXIT;
   return ((options & supported_options) == options);
 }