[PATCH] Simplify gdb.threads/wp-replication.exp on counting HW watchpoints

[Yao Qi <qiyaoltc at gmail dot com>]

Nowadays, test gdb.threads/wp-replication.exp uses a while loop to
repeatedly insert HW watchpoint, resume and check no error message
coming out, in order to count HW watchpoints  There are some
drawbacks in this way,

 - the loop could be endless.  I think this is use to making trouble
   to S/390, since we had such comment

      # Some targets (like S/390) behave as though supporting
      # unlimited hardware watchpoints.  In this case we just take a
      # safe exit out of the loop.

   I hit this today too because a GDB internal error is triggered
   on "continue" in the loop, and $done is 0 invariantly, so the loop
   can't end.
 - the code counting hardware watchpoint is too complicated.  We can
   use "set breakpoint always-inserted on" to get the result of inserting
   HW watchpoint without resuming the inferior.  In this way,
   watch_count_done and empty_cycle in c file is no longer needed.

In this patch, I change to "set breakpoint always-inserted on" trick,
and only iterate $NR_THREADS times, to count the HW watchpoint.  In this
way, the loop can't be endless, and GDB doesn't need to resume the inferior.

gdb/testsuite:

2015-10-23  Yao Qi  <yao.qi@linaro.org>

	* gdb.threads/wp-replication.c (watch_count_done): Remove.
	(empty_cycle): Remove.
	(main): Don't call empty_cycle.  Don't use watch_count_done.
	* gdb.threads/wp-replication.exp: Don't set breakpoint on
	empty_cycle.  Rewrite the code counting HW watchpoints.
---
 gdb/testsuite/gdb.threads/wp-replication.c   | 24 ---------
 gdb/testsuite/gdb.threads/wp-replication.exp | 76 ++++++++++------------------
 2 files changed, 28 insertions(+), 72 deletions(-)

diff --git a/gdb/testsuite/gdb.threads/wp-replication.c b/gdb/testsuite/gdb.threads/wp-replication.c
index a7250b0..9fdc87a 100644
--- a/gdb/testsuite/gdb.threads/wp-replication.c
+++ b/gdb/testsuite/gdb.threads/wp-replication.c
@@ -47,11 +47,6 @@ int test_ready = 0;
    watchpoint triggers.  */
 int can_terminate = 0;
 
-/* Used to push the program out of the waiting loop after the
-   testcase is done counting the number of hardware watchpoints
-   available for our target.  */
-int watch_count_done = 0;
-
 /* Number of watchpoints GDB is capable of using (this is provided
    by GDB during the test run).  */
 int hw_watch_count = 0;
@@ -60,14 +55,6 @@ int hw_watch_count = 0;
 static int watched_data[NR_THREADS];
 pthread_mutex_t data_mutex;
 
-/* Wait function to keep threads busy while the testcase does
-   what it needs to do.  */
-void
-empty_cycle (void)
-{
-  usleep (1);
-}
-
 int
 main ()
 {
@@ -75,17 +62,6 @@ main ()
   pthread_t threads[NR_THREADS];
   int i;
 
-  /* Something to ensure that the breakpoint used to run to main
-     is only hit once.  */
-  empty_cycle ();
-
-  while (watch_count_done == 0)
-    {
-      /* GDB will modify the value of "watch_count_done" at runtime and we
-	 will get past this point.  */
-      empty_cycle ();
-    }
-
   pthread_mutex_init (&data_mutex, NULL);
 
   for (i = 0; i < NR_THREADS; i++)
diff --git a/gdb/testsuite/gdb.threads/wp-replication.exp b/gdb/testsuite/gdb.threads/wp-replication.exp
index ebfc332..9de27b2 100644
--- a/gdb/testsuite/gdb.threads/wp-replication.exp
+++ b/gdb/testsuite/gdb.threads/wp-replication.exp
@@ -47,56 +47,41 @@ if ![runto_main] then {
     return 0
 }
 
-# First, break at empty_cycle.
-gdb_test "break empty_cycle" \
-  "Breakpoint 2 at .*: file .*${srcfile}, line .*" \
-  "Breakpoint on empty_cycle"
-
 # Set some default values.
 set hwatch_count 0
-set done 0
+set count 0
 
 # Count the number of hardware watchpoints available on
 # this target.
-while { $done == 0 } {
-
-  gdb_test "continue" \
-    ".*Breakpoint 2, empty_cycle \\(\\) at .*${srcfile}.*" \
-    "Continue to empty_cycle to insert watchpoint $hwatch_count"
-
-  # Some targets do resource counting as we insert watchpoints.
-  # Such targets won't cause a watchpoint insertion failure, but
-  # will switch to software watchpoints silently.  We check for
-  # both cases here.
-  gdb_test_multiple "watch watched_data\[$hwatch_count\]" \
-       "watch watched_data\[$hwatch_count\]" {
-    -re "Hardware watchpoint .*$gdb_prompt $" {
-    }
-    -re "Watchpoint .*$gdb_prompt $" {
-      set done 1
-      break
-    }
-  }
-
-  gdb_test_multiple "continue" "watchpoint created successfully" {
-    -re ".*Breakpoint 2, empty_cycle \\(\\).*$gdb_prompt $" {
-      incr hwatch_count
-
-      # Some targets (like S/390) behave as though supporting
-      # unlimited hardware watchpoints.  In this case we just take a
-      # safe exit out of the loop.
-      if { $hwatch_count == $NR_THREADS } {
-	set done 1
-	break
-      }
-    }
-    -re ".*Could not insert hardware watchpoint.*$gdb_prompt $" {
-      set done 1
-      break
-    }
-  }
+
+# So we get an immediate warning/error if the target doesn't support a
+# hardware watchpoint or run out of hardware resource.
+gdb_test_no_output "set breakpoint always-inserted on"
+
+while { $count < $NR_THREADS } {
+    # Some targets do resource counting as we insert watchpoints.
+    # Such targets won't cause a watchpoint insertion failure, but
+    # will switch to software watchpoints silently.  We check for
+    # both cases here.
+    gdb_test_multiple "watch watched_data\[$hwatch_count\]" \
+	"watch watched_data\[$hwatch_count\]" {
+	    -re ".*Could not insert hardware watchpoint.*$gdb_prompt $" {
+		# End the loop.
+		set count $NR_THREADS
+	    }
+	    -re "Hardware watchpoint .*$gdb_prompt $" {
+		incr hwatch_count
+	    }
+	    -re "Watchpoint .*$gdb_prompt $" {
+		# End the loop.
+		set count $NR_THREADS
+	    }
+	}
+    incr count
 }
 
+gdb_test_no_output "set breakpoint always-inserted off"
+
 # Target cannot insert hardware watchpoints.  It should have reported
 # (through board settings) that it did not support them in the first place.
 # Just exit.
@@ -114,11 +99,6 @@ gdb_test_no_output "set var hw_watch_count=${hwatch_count}" \
 # the target supports.  Use that to do further testing.
 delete_breakpoints
 
-# Break out of the empty_cycle loop by changing the
-# controlling variable.
-gdb_test_no_output "set var watch_count_done=1" \
-		   "set var watch_count_done=1"
-
 # Prepare to create all the threads.
 gdb_test "break thread_started" \
 	 "Breakpoint \[0-9\]+ at .*: file .*${srcfile}, line .*" \
-- 
1.9.1