[PATCH v2 18/23] Fix step-over-{trips-on-watchpoint|lands-on-breakpoint}.exp race

[Pedro Alves <palves@redhat.com>]

On a target that is both always in non-stop mode and can do displaced
stepping (such as native x86_64 GNU/Linux, with "maint set
target-non-stop on"), the step-over-trips-on-watchpoint.exp test
sometimes fails like this:

   (gdb) PASS: gdb.threads/step-over-trips-on-watchpoint.exp: no thread-specific bp: step: thread 1
   set scheduler-locking off
   (gdb) PASS: gdb.threads/step-over-trips-on-watchpoint.exp: no thread-specific bp: step: set scheduler-locking off
   step
  -[Switching to Thread 0x7ffff7fc0700 (LWP 11782)]
  -Hardware watchpoint 4: watch_me
  -
  -Old value = 0
  -New value = 1
  -child_function (arg=0x0) at /home/pedro/gdb/mygit/src/gdb/testsuite/gdb.threads/step-over-trips-on-watchpoint.c:39
  -39           other = 1; /* set thread-specific breakpoint here */
  -(gdb) PASS: gdb.threads/step-over-trips-on-watchpoint.exp: no thread-specific bp: step: step
  +wait_threads () at /home/pedro/gdb/mygit/src/gdb/testsuite/gdb.threads/step-over-trips-on-watchpoint.c:49
  +49       return 1; /* in wait_threads */
  +(gdb) FAIL: gdb.threads/step-over-trips-on-watchpoint.exp: no thread-specific bp: step: step

Note "scheduler-locking" was set off.  The problem is that on such
targets, the step-over of thread 2 and the "step" of thread 1 can be
set to run simultaneously (since with displaced stepping the
breakpoint isn't ever removed from the target), and sometimes, the
"step" of thread 1 finishes first, so it'd take another resume to see
the watchpoint trigger.  Fix this by replacing the wait_threads
function with a one-line infinite loop that doesn't call any function,
so that the "step" of thread 1 never finishes.

gdb/testsuite/ChangeLog:
2015-04-07  Pedro Alves  <palves@redhat.com>

	* gdb.threads/step-over-lands-on-breakpoint.c (wait_threads):
	Delete function.
	(main): Add alarm.  Run an infinite loop instead of calling
	wait_threads.
	* gdb.threads/step-over-lands-on-breakpoint.exp (do_test): Change
	comment.
	* gdb.threads/step-over-trips-on-watchpoint.c (wait_threads):
	Delete function.
	(main): Add alarm.  Run an infinite loop instead of calling
	wait_threads.
	* gdb.threads/step-over-trips-on-watchpoint.exp (do_test): Change
	comment.
---
 .../gdb.threads/step-over-lands-on-breakpoint.c         | 17 ++++++++++-------
 .../gdb.threads/step-over-lands-on-breakpoint.exp       |  6 +++---
 .../gdb.threads/step-over-trips-on-watchpoint.c         | 17 ++++++++++-------
 .../gdb.threads/step-over-trips-on-watchpoint.exp       |  9 ++++-----
 4 files changed, 27 insertions(+), 22 deletions(-)

diff --git a/gdb/testsuite/gdb.threads/step-over-lands-on-breakpoint.c b/gdb/testsuite/gdb.threads/step-over-lands-on-breakpoint.c
index 0a6ed8f..2480164 100644
--- a/gdb/testsuite/gdb.threads/step-over-lands-on-breakpoint.c
+++ b/gdb/testsuite/gdb.threads/step-over-lands-on-breakpoint.c
@@ -41,23 +41,26 @@ child_function (void *arg)
   pthread_exit (NULL);
 }
 
-static int
-wait_threads (void)
-{
-  return 1; /* in wait_threads */
-}
-
 int
 main ()
 {
   int res;
   long i;
 
+  alarm (300);
+
   pthread_barrier_init (&barrier, NULL, 2);
 
   res = pthread_create (&child_thread, NULL, child_function, NULL);
   pthread_barrier_wait (&barrier);
-  wait_threads (); /* set wait-thread breakpoint here */
+
+  /* Use an infinite loop with no function calls so that "step" over
+     this line never finishes before the breakpoint in the other
+     thread triggers.  That can happen if the step-over of thread 2 is
+     done with displaced stepping on a target that is always in
+     non-stop mode, as in that case GDB runs both threads
+     simultaneously.  */
+  while (1); /* set wait-thread breakpoint here */
 
   pthread_join (child_thread, NULL);
 
diff --git a/gdb/testsuite/gdb.threads/step-over-lands-on-breakpoint.exp b/gdb/testsuite/gdb.threads/step-over-lands-on-breakpoint.exp
index 4d27059..239aa96 100644
--- a/gdb/testsuite/gdb.threads/step-over-lands-on-breakpoint.exp
+++ b/gdb/testsuite/gdb.threads/step-over-lands-on-breakpoint.exp
@@ -59,9 +59,9 @@ proc do_test {displaced command} {
 	gdb_test_no_output "set scheduler-locking off"
 
 	# Thread 2 is still stopped at a breakpoint that needs to be
-	# stepped over before proceeding thread 1.  However, right
-	# where the step-over lands there's another breakpoint
-	# installed, which should trap and be reported to the user.
+	# stepped over.  However, right where the step-over lands
+	# there's another breakpoint installed, which should trap and
+	# be reported to the user.
 	gdb_test "$command" "step-over here.*"
     }
 }
diff --git a/gdb/testsuite/gdb.threads/step-over-trips-on-watchpoint.c b/gdb/testsuite/gdb.threads/step-over-trips-on-watchpoint.c
index 6cf97fb..34ba079 100644
--- a/gdb/testsuite/gdb.threads/step-over-trips-on-watchpoint.c
+++ b/gdb/testsuite/gdb.threads/step-over-trips-on-watchpoint.c
@@ -43,23 +43,26 @@ child_function (void *arg)
   pthread_exit (NULL);
 }
 
-static int
-wait_threads (void)
-{
-  return 1; /* in wait_threads */
-}
-
 int
 main ()
 {
   int res;
   long i;
 
+  alarm (300);
+
   pthread_barrier_init (&barrier, NULL, 2);
 
   res = pthread_create (&child_thread, NULL, child_function, NULL);
   pthread_barrier_wait (&barrier);
-  wait_threads (); /* set wait-thread breakpoint here */
+
+  /* Use an infinite loop with no function calls so that "step" over
+     this line never finishes before the watchpoint in the other
+     thread triggers.  That can happen if the step-over of thread 2 is
+     done with displaced stepping on a target that is always in
+     non-stop mode, as in that case GDB runs both threads
+     simultaneously.  */
+  while (1); /* set wait-thread breakpoint here */
 
   pthread_join (child_thread, NULL);
 
diff --git a/gdb/testsuite/gdb.threads/step-over-trips-on-watchpoint.exp b/gdb/testsuite/gdb.threads/step-over-trips-on-watchpoint.exp
index 3ccceae..a2dc1b9 100644
--- a/gdb/testsuite/gdb.threads/step-over-trips-on-watchpoint.exp
+++ b/gdb/testsuite/gdb.threads/step-over-trips-on-watchpoint.exp
@@ -112,11 +112,10 @@ proc do_test { displaced with_bp } {
 		gdb_test "thread 1" "Switching to .*"
 		gdb_test_no_output "set scheduler-locking off"
 
-		# Thread 2 is still stopped at a breakpoint that needs to be
-		# stepped over before proceeding thread 1.  However, the
-		# instruction that is under the breakpoint triggers a
-		# watchpoint, which should trap and be reported to the
-		# user.
+		# Thread 2 is still stopped at a breakpoint that needs
+		# to be stepped over.  However, the instruction that
+		# is under the breakpoint triggers a watchpoint, which
+		# should trap and be reported to the user.
 		gdb_test "$command" "Hardware watchpoint.*: watch_me.*New value = 1.*"
 	    }
 	}
-- 
1.9.3