merge from open-source master
diff --git a/libcutils/atomic-android-arm.S b/libcutils/atomic-android-arm.S
index f4299fd..4da6195 100644
--- a/libcutils/atomic-android-arm.S
+++ b/libcutils/atomic-android-arm.S
@@ -17,8 +17,7 @@
#include <machine/cpu-features.h>
/*
- * NOTE: these atomic operations are SMP safe on all architectures,
- * except swap(), see below.
+ * NOTE: these atomic operations are SMP safe on all architectures.
*/
.text
@@ -213,11 +212,18 @@
* output: r0 = old value
*/
-/* FIXME: this is not safe on SMP systems
- * a general way to do it is to use kernel_cmpxchg */
-
+/* replaced swp instruction with ldrex/strex for ARMv6 & ARMv7 */
android_atomic_swap:
+#if defined (_ARM_HAVE_LDREX_STREX)
+1: ldrex r2, [r1]
+ strex r3, r0, [r1]
+ teq r3, #0
+ bne 1b
+ mov r0, r2
+ mcr p15, 0, r0, c7, c10, 5 /* or, use dmb */
+#else
swp r0, r0, [r1]
+#endif
bx lr
/*