[PATCH v2 03/14] gdb: restore displaced step buffer bytes when another thread forks

[Simon Marchi]

In handle_inferior_event, where we handle forks, we make sure to restore
the bytes of the displaced stepping buffer in the child's address
space.  However, we only do it when the forking thread was the one
doing a displaced step.  It could happen that a thread forks while
another one is doing a displaced step.  In this case, we also need to
restore the bytes in the child.

Move the byte-restoring code outside of the condition that checks
whether the event thread was displaced stepping.

gdb/ChangeLog:

	* infrun.c (handle_inferior_event): Restore displaced step
	buffer bytes in child process when handling fork, even if fork
	happened in another thread than the displaced-stepping one.

Change-Id: Ibb0daaeb123aba03f4fb4b4d820754eb2436bc69
---
 gdb/infrun.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 0e0a7a691c43..5c383b4d8a12 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -5302,25 +5302,27 @@ handle_inferior_event (struct execution_control_state *ecs)
       {
 	struct regcache *regcache = get_thread_regcache (ecs->event_thread);
 	struct gdbarch *gdbarch = regcache->arch ();
+	inferior *parent_inf = find_inferior_ptid (ecs->target, ecs->ptid);
 
-	/* If checking displaced stepping is supported, and thread
-	   ecs->ptid is displaced stepping.  */
+	/* If this is a fork (child gets its own address space copy) and the
+	   displaced step buffer was in use at the time of the fork, restore
+	   displaced step buffer bytes in the child process.  */
+	if (ecs->ws.kind == TARGET_WAITKIND_FORKED)
+	  {
+	    displaced_step_inferior_state *displaced
+	      = get_displaced_stepping_state (parent_inf);
+
+	    if (displaced->step_thread != nullptr)
+	      displaced_step_restore (displaced, ecs->ws.value.related_pid);
+	  }
+
+	/* If displaced stepping is supported, and thread ecs->ptid is
+	   displaced stepping.  */
 	if (displaced_step_in_progress_thread (ecs->event_thread))
 	  {
-	    struct inferior *parent_inf
-	      = find_inferior_ptid (ecs->target, ecs->ptid);
 	    struct regcache *child_regcache;
 	    CORE_ADDR parent_pc;
 
-	    if (ecs->ws.kind == TARGET_WAITKIND_FORKED)
-	      {
-		struct displaced_step_inferior_state *displaced
-		  = get_displaced_stepping_state (parent_inf);
-
-		/* Restore scratch pad for child process.  */
-		displaced_step_restore (displaced, ecs->ws.value.related_pid);
-	      }
-
 	    /* GDB has got TARGET_WAITKIND_FORKED or TARGET_WAITKIND_VFORKED,
 	       indicating that the displaced stepping of syscall instruction
 	       has been done.  Perform cleanup for parent process here.  Note
-- 
2.29.2