[PATCH v2 2/2] gdb: retain thread-specific breakpoints in reverse execution targets

[Magne Hov <mhov@undo.io>]

Thread-specific breakpoints are currently ignored and removed (since
49fa26b0411d990d36f3f6c095d167f3d12afdf4) if the corresponding thread
has exited.  This makes sense for targets that only execute in the
forward direction because those breakpoints can never be hit again, but
for targets with reverse execution the same thread can be seen again.
---
 gdb/breakpoint.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index da6c8de9d14..9a25c5f663d 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -3157,10 +3157,12 @@ insert_breakpoint_locations (void)
 	continue;
 
       /* There is no point inserting thread-specific breakpoints if
-	 the thread no longer exists.  ALL_BP_LOCATIONS bp_location
-	 has BL->OWNER always non-NULL.  */
+	 the thread no longer exists, unless the target supports
+	 reverse execution.  ALL_BP_LOCATIONS bp_location has
+	 BL->OWNER always non-NULL.  */
       if (bl->owner->thread != -1
-	  && !valid_global_thread_id (bl->owner->thread))
+	  && !valid_global_thread_id (bl->owner->thread)
+	  && !target_can_execute_reverse ())
 	continue;
 
       switch_to_program_space_and_thread (bl->pspace);
@@ -3245,12 +3247,18 @@ remove_breakpoints (void)
   return val;
 }
 
-/* When a thread exits, remove breakpoints that are related to
-   that thread.  */
+/* When a thread exits, remove breakpoints that are related to that
+   thread and cannot be hit again.  */
 
 static void
 remove_threaded_breakpoints (struct thread_info *tp, int silent)
 {
+  /* Targets that support reverse execution may navigate to a point in
+     time where an exited thread reappears and where its breakpoints
+     are still relevant.  */
+  if (target_can_execute_reverse ())
+    return;
+
   for (breakpoint &b : all_breakpoints_safe ())
     {
       if (b.thread == tp->global_num && user_breakpoint_p (&b))
-- 
2.40.1