2004-12-07  Jeff Johnston  <jjohnstn@redhat.com>

	* linux-nat.c (find_singlestep_lwp_callback): New function.
	(linux-nat-wait): Before waiting on any pid, check if there
	is a stepping lwp and if so, wait on it specifically.

--- gdb-6.3/gdb/linux-nat.c.fix	Tue Dec  7 19:39:34 2004
+++ gdb-6.3/gdb/linux-nat.c	Tue Dec  7 19:39:46 2004
@@ -1489,9 +1489,21 @@ count_events_callback (struct lwp_info *
   return 0;
 }
 
-/* Select the LWP (if any) that is currently being single-stepped.  */
+/* Find an LWP (if any) that is currently being single-stepped.  */
 
 static int
+find_singlestep_lwp_callback (struct lwp_info *lp, void *data)
+{
+  if (lp->step)
+    return 1;
+  else
+    return 0;
+}
+
+/* Select the LWP with an event (if any) that is currently being 
+   single-stepped.  */
+		 
+static int
 select_singlestep_lwp_callback (struct lwp_info *lp, void *data)
 {
   if (lp->step && lp->status != 0)
@@ -1774,7 +1786,25 @@ retry:
      least if there are any LWPs at all.  */
   gdb_assert (num_lwps == 0 || iterate_over_lwps (resumed_callback, NULL));
 
-  /* First check if there is a LWP with a wait status pending.  */
+  /* Check if there is any LWP that is being single-stepped.  We need to
+     wait specifically on such an LWP because the higher-level code is
+     expecting a step operation to find an event on the stepped LWP.
+     It is possible for other events to occur before the step operation
+     gets the expected trap so we don't want to wait on any LWP.
+     This has ramifications when adjustment of the PC is required which can be
+     different after a breakpoint vs a step (e.g. x86).  */
+  lp = iterate_over_lwps (find_singlestep_lwp_callback, NULL);
+  if (lp) {
+    if (debug_linux_nat)
+      fprintf_unfiltered (gdb_stdlog,
+                         "LLW: Found step lwp %s.\n",
+                         target_pid_to_str (lp->ptid));
+    ptid = lp->ptid;
+    pid = PIDGET (ptid);
+  }
+
+  /* If any pid, check if there is a LWP with a wait status pending.  */
+
   if (pid == -1)
     {
       /* Any LWP that's been resumed will do.  */