[PATCH v8 8/8] perf tests: keep bp_signal memory accesses visible

[Himanshu Chauhan <himanshu.chauhan@oss.qualcomm.com>]

In the breakpoint signal handler test, a breakpoint is set on
__test_function. Keep that helper as a real call target so the breakpoint
has a stable address.

The test also relies on the watched variable being accessed as distinct
memory operations. Use READ_ONCE() and WRITE_ONCE() for those accesses
instead of making the object volatile, so the source marks the exact
operations that must be preserved.

Signed-off-by: Himanshu Chauhan <himanshu.chauhan@oss.qualcomm.com>
---
 tools/perf/tests/bp_signal.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/tools/perf/tests/bp_signal.c b/tools/perf/tests/bp_signal.c
index f580ba7486b1..2e4f7747d32f 100644
--- a/tools/perf/tests/bp_signal.c
+++ b/tools/perf/tests/bp_signal.c
@@ -36,15 +36,14 @@ static int fd3;
 static int overflows;
 static int overflows_2;
 
-static volatile long the_var;
-
+static long the_var;
 
 /*
  * Use ASM to ensure watchpoint and breakpoint can be triggered
  * at one instruction.
  */
 #if defined (__x86_64__)
-extern void __test_function(volatile long *ptr);
+extern void __test_function(long *ptr);
 asm (
 	".pushsection .text;"
 	".globl __test_function\n"
@@ -54,16 +53,19 @@ asm (
 	"ret\n"
 	".popsection\n");
 #else
-static void __test_function(volatile long *ptr)
+static noinline void __test_function(long *ptr)
 {
-	*ptr = 0x1234;
+	WRITE_ONCE(*ptr, 0x1234);
 }
 #endif
 
 static noinline int test_function(void)
 {
+	long value;
+
 	__test_function(&the_var);
-	the_var++;
+	value = READ_ONCE(the_var);
+	WRITE_ONCE(the_var, value + 1);
 	return time(NULL);
 }
 
-- 
2.43.0