[binutils-gdb] Implement GDB_THREAD_OPTION_EXIT support for Linux GDBserver

[binutils-gdb] Implement GDB_THREAD_OPTION_EXIT support for Linux GDBserver

[Pedro Alves]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=4898949800206894305b954e10a9a8c36e2d08c7

commit 4898949800206894305b954e10a9a8c36e2d08c7
Author: Pedro Alves <pedro@palves.net>
Date:   Thu Mar 17 19:25:03 2022 +0000

    Implement GDB_THREAD_OPTION_EXIT support for Linux GDBserver
    
    This implements support for the new GDB_THREAD_OPTION_EXIT thread
    option for Linux GDBserver.
    
    Reviewed-By: Andrew Burgess <aburgess@redhat.com>
    Change-Id: I96b719fdf7fee94709e98bb3a90751d8134f3a38
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=27338

Diff:
---
 gdbserver/linux-low.cc | 38 +++++++++++++++++++++++++-------------
 gdbserver/linux-low.h  |  9 +++++----
 2 files changed, 30 insertions(+), 17 deletions(-)

diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
index ca2b7aa1e1b..b4a1191b5b4 100644
--- a/gdbserver/linux-low.cc
+++ b/gdbserver/linux-low.cc
@@ -144,6 +144,18 @@ is_leader (thread_info *thread)
   return ptid.pid () == ptid.lwp ();
 }
 
+/* Return true if we should report thread exit events to GDB, for
+   THR.  */
+
+static bool
+report_exit_events_for (thread_info *thr)
+{
+  client_state &cs = get_client_state ();
+
+  return (cs.report_thread_events
+	  || (thr->thread_options & GDB_THREAD_OPTION_EXIT) != 0);
+}
+
 /* LWP accessors.  */
 
 /* See nat/linux-nat.h.  */
@@ -2233,7 +2245,6 @@ linux_low_ptrace_options (int attached)
 void
 linux_process_target::filter_event (int lwpid, int wstat)
 {
-  client_state &cs = get_client_state ();
   struct lwp_info *child;
   struct thread_info *thread;
   int have_stop_pc = 0;
@@ -2320,7 +2331,7 @@ linux_process_target::filter_event (int lwpid, int wstat)
       /* If this is not the leader LWP, then the exit signal was not
 	 the end of the debugged application and should be ignored,
 	 unless GDB wants to hear about thread exits.  */
-      if (cs.report_thread_events || is_leader (thread))
+      if (report_exit_events_for (thread) || is_leader (thread))
 	{
 	  /* Since events are serialized to GDB core, and we can't
 	     report this one right now.  Leave the status pending for
@@ -2888,13 +2899,20 @@ ptid_t
 linux_process_target::filter_exit_event (lwp_info *event_child,
 					 target_waitstatus *ourstatus)
 {
-  client_state &cs = get_client_state ();
   struct thread_info *thread = get_lwp_thread (event_child);
   ptid_t ptid = ptid_of (thread);
 
+  /* 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 (thread))
     {
-      if (cs.report_thread_events)
+      if (report_exit_events_for (thread))
 	ourstatus->set_thread_exited (0);
       else
 	ourstatus->set_ignore ();
@@ -3037,10 +3055,7 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
 	     WTERMSIG (w));
 	}
 
-      if (ourstatus->kind () == TARGET_WAITKIND_EXITED)
-	return filter_exit_event (event_child, ourstatus);
-
-      return ptid_of (current_thread);
+      return filter_exit_event (event_child, ourstatus);
     }
 
   /* If step-over executes a breakpoint instruction, in the case of a
@@ -3607,10 +3622,7 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
 			target_pid_to_str (ptid_of (current_thread)).c_str (),
 			ourstatus->to_string ().c_str ());
 
-  if (ourstatus->kind () == TARGET_WAITKIND_EXITED)
-    return filter_exit_event (event_child, ourstatus);
-
-  return ptid_of (current_thread);
+  return filter_exit_event (event_child, ourstatus);
 }
 
 /* Get rid of any pending event in the pipe.  */
@@ -5920,7 +5932,7 @@ linux_process_target::supports_vfork_events ()
 gdb_thread_options
 linux_process_target::supported_thread_options ()
 {
-  return GDB_THREAD_OPTION_CLONE;
+  return GDB_THREAD_OPTION_CLONE | GDB_THREAD_OPTION_EXIT;
 }
 
 /* Check if exec events are supported.  */
diff --git a/gdbserver/linux-low.h b/gdbserver/linux-low.h
index b5ff9391198..3597e33289c 100644
--- a/gdbserver/linux-low.h
+++ b/gdbserver/linux-low.h
@@ -575,10 +575,11 @@ private: /* Back to private.  */
      exited.  */
   void check_zombie_leaders ();
 
-  /* Convenience function that is called when the kernel reports an exit
-     event.  This decides whether to report the event to GDB as a
-     process exit event, a thread exit event, or to suppress the
-     event.  */
+  /* Convenience function that is called when we're about to return an
+     event to the core.  If the event is an exit or signalled event,
+     then this decides whether to report it as process-wide event, as
+     a thread exit event, or to suppress it.  All other event kinds
+     are passed through unmodified.  */
   ptid_t filter_exit_event (lwp_info *event_child,
 			    target_waitstatus *ourstatus);