Fake VFORK_DONE events when following only the parent after a vfork.

FreeBSD does not currently report a ptrace event for a parent process
after it resumes due to the child exiting the shared memory region after
a vfork.  Take the same approach used in linux-nat.c in this case of
sleeping for a while and then reporting a fake VFORK_DONE event.

gdb/ChangeLog:

	* fbsd-nat.c (struct fbsd_fork_child_info): Rename to ...
	(struct fbsd_fork_info): ... this.
	(struct fbsd_fork_info) <child>: Rename to ...
	(struct fbsd_fork_info) <ptid>: ... this.
	(fbsd_pending_children): Update type.
	(fbsd_remember_child): Update type and field name.
	(fbsd_is_child_pending): Likewise.
	(fbsd_pending_vfork_done): New variable.
	(fbsd_is_vfork_done_pending): New function.
	(fbsd_next_vfork_done): New function.
	(fbsd_resume): Don't resume processes with a pending vfork done
	event.
	(fbsd_wait): Report pending vfork done events.
	(fbsd_follow_fork): Delay and record a pending vfork done event
	for a vfork parent when detaching the child.

2 files changed, 121 insertions, 9 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 1a51fb2..58c9c78 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,23 @@
 2016-07-01  John Baldwin  <jhb@FreeBSD.org>
 
+	* fbsd-nat.c (struct fbsd_fork_child_info): Rename to ...
+	(struct fbsd_fork_info): ... this.
+	(struct fbsd_fork_info) <child>: Rename to ...
+	(struct fbsd_fork_info) <ptid>: ... this.
+	(fbsd_pending_children): Update type.
+	(fbsd_remember_child): Update type and field name.
+	(fbsd_is_child_pending): Likewise.
+	(fbsd_pending_vfork_done): New variable.
+	(fbsd_is_vfork_done_pending): New function.
+	(fbsd_next_vfork_done): New function.
+	(fbsd_resume): Don't resume processes with a pending vfork done
+	event.
+	(fbsd_wait): Report pending vfork done events.
+	(fbsd_follow_fork): Delay and record a pending vfork done event
+	for a vfork parent when detaching the child.
+
+2016-07-01  John Baldwin  <jhb@FreeBSD.org>
+
 	* fbsd-nat.c (super_resume): Move earlier next to "super_wait".
 	(resume_one_thread_cb): Move below fork following helper code.
 	(resume_all_threads_cb): Likewise.
diff --git a/gdb/fbsd-nat.c b/gdb/fbsd-nat.c
index daf4580..fcb7ff5 100644
--- a/gdb/fbsd-nat.c
+++ b/gdb/fbsd-nat.c
@@ -530,13 +530,13 @@ fbsd_update_thread_list (struct target_ops *ops)
   sake.  FreeBSD versions newer than 9.1 contain both fixes.
 */
 
-struct fbsd_fork_child_info
+struct fbsd_fork_info
 {
-  struct fbsd_fork_child_info *next;
-  ptid_t child;			/* Pid of new child.  */
+  struct fbsd_fork_info *next;
+  ptid_t ptid;
 };
 
-static struct fbsd_fork_child_info *fbsd_pending_children;
+static struct fbsd_fork_info *fbsd_pending_children;
 
 /* Record a new child process event that is reported before the
    corresponding fork event in the parent.  */
@@ -544,9 +544,9 @@ static struct fbsd_fork_child_info *fbsd_pending_children;
 static void
 fbsd_remember_child (ptid_t pid)
 {
-  struct fbsd_fork_child_info *info = XCNEW (struct fbsd_fork_child_info);
+  struct fbsd_fork_info *info = XCNEW (struct fbsd_fork_info);
 
-  info->child = pid;
+  info->ptid = pid;
   info->next = fbsd_pending_children;
   fbsd_pending_children = info;
 }
@@ -557,25 +557,74 @@ fbsd_remember_child (ptid_t pid)
 static ptid_t
 fbsd_is_child_pending (pid_t pid)
 {
-  struct fbsd_fork_child_info *info, *prev;
+  struct fbsd_fork_info *info, *prev;
   ptid_t ptid;
 
   prev = NULL;
   for (info = fbsd_pending_children; info; prev = info, info = info->next)
     {
-      if (ptid_get_pid (info->child) == pid)
+      if (ptid_get_pid (info->ptid) == pid)
 	{
 	  if (prev == NULL)
 	    fbsd_pending_children = info->next;
 	  else
 	    prev->next = info->next;
-	  ptid = info->child;
+	  ptid = info->ptid;
 	  xfree (info);
 	  return ptid;
 	}
     }
   return null_ptid;
 }
+
+static struct fbsd_fork_info *fbsd_pending_vfork_done;
+
+/* Record a pending vfork done event.  */
+
+static void
+fbsd_add_vfork_done (ptid_t pid)
+{
+  struct fbsd_fork_info *info = XCNEW (struct fbsd_fork_info);
+
+  info->ptid = pid;
+  info->next = fbsd_pending_vfork_done;
+  fbsd_pending_vfork_done = info;
+}
+
+/* Check for a pending vfork done event for a specific PID.  */
+
+static int
+fbsd_is_vfork_done_pending (pid_t pid)
+{
+  struct fbsd_fork_info *info;
+
+  for (info = fbsd_pending_vfork_done; info != NULL; info = info->next)
+    {
+      if (ptid_get_pid (info->ptid) == pid)
+	return 1;
+    }
+  return 0;
+}
+
+/* Check for a pending vfork done event.  If one is found, remove it
+   from the list and return the PTID.  */
+
+static ptid
+fbsd_next_vfork_done (void)
+{
+  struct fbsd_fork_info *info;
+  ptid_t ptid;
+
+  if (fbsd_pending_vfork_done != NULL)
+    {
+      info = fbsd_pending_vfork_done;
+      fbsd_pending_vfork_done = info->next;
+      ptid = info->ptid;
+      xfree (info);
+      return ptid;
+    }
+  return null_ptid;
+}
 #endif
 
 static int
@@ -616,6 +665,17 @@ static void
 fbsd_resume (struct target_ops *ops,
 	     ptid_t ptid, int step, enum gdb_signal signo)
 {
+#ifdef TDP_RFPPWAIT
+  pid_t pid;
+
+  /* Don't PT_CONTINUE a process which has a pending vfork done event.  */
+  if (ptid_equal (minus_one_ptid, ptid))
+    pid = ptid_get_pid (inferior_ptid);
+  else
+    pid = ptid_get_pid (ptid);
+  if (fbsd_is_vfork_done_pending (pid))
+    return;
+#endif
 
   if (debug_fbsd_lwp)
     fprintf_unfiltered (gdb_stdlog,
@@ -650,6 +710,12 @@ fbsd_wait (struct target_ops *ops,
 
   while (1)
     {
+      wptid = fbsd_next_vfork_done ();
+      if (!ptid_equal (wptid, null_ptid))
+	{
+	  ourstatus->kind = TARGET_WAITKIND_VFORK_DONE;
+	  return wptid;
+	}
       wptid = super_wait (ops, ptid, ourstatus, target_options);
       if (ourstatus->kind == TARGET_WAITKIND_STOPPED)
 	{
@@ -828,6 +894,7 @@ fbsd_follow_fork (struct target_ops *ops, int follow_child,
   if (!follow_child && detach_fork)
     {
       struct thread_info *tp = inferior_thread ();
+      int has_vforked = tp->pending_follow.kind == TARGET_WAITKIND_VFORKED;
       pid_t child_pid = ptid_get_pid (tp->pending_follow.value.related_pid);
 
       /* Breakpoints have already been detached from the child by
@@ -835,6 +902,33 @@ fbsd_follow_fork (struct target_ops *ops, int follow_child,
 
       if (ptrace (PT_DETACH, child_pid, (PTRACE_TYPE_ARG3)1, 0) == -1)
 	perror_with_name (("ptrace"));
+
+      if (has_vforked)
+	{
+	  /* We can't insert breakpoints until the child process has
+	     finished with the shared memory region.  The parent
+	     process doesn't wait for the child process to exit or
+	     exec until after it has been resumed from the ptrace stop
+	     to report the fork.  Once it has been resumed it doesn't
+	     stop again before returning to userland, so there is no
+	     reliable way to wait on the parent.
+
+	     We can't stay attached to the child to wait for an exec
+	     or exit because it may invoke ptrace(PT_TRACE_ME)
+	     (e.g. if the parent process is a debugger forking a new
+	     child process).
+
+	     In the end, the best we can do is to make sure it runs
+	     for a little while.  Hopefully it will be out of range of
+	     any breakpoints we reinsert.  Usually this is only the
+	     single-step breakpoint at vfork's return point.  */
+
+	  usleep (10000);
+
+	  /* Schedule a fake VFORK_DONE event to report on the next
+	     wait.  */
+	  fbsd_add_vfork_done (inferior_ptid);
+	}
     }
 
   return 0;