[lttng-dev] [PATCH 5/7] Use __atomic builtins to implement CMM_{LOAD, STORE}_SHARED

[Ondřej Surý]

Instead of using CMM_ACCESS_ONCE() with memory barriers, use __atomic
builtins with relaxed memory ordering to implement CMM_LOAD_SHARED() and
CMM_STORE_SHARED().

Signed-off-by: Ondřej Surý <ondrej at sury.org>
---
 include/urcu/system.h | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/include/urcu/system.h b/include/urcu/system.h
index faae390..99e7443 100644
--- a/include/urcu/system.h
+++ b/include/urcu/system.h
@@ -26,7 +26,7 @@
  * Identify a shared load. A cmm_smp_rmc() or cmm_smp_mc() should come
  * before the load.
  */
-#define _CMM_LOAD_SHARED(p)	       CMM_ACCESS_ONCE(p)
+#define _CMM_LOAD_SHARED(p)	       __atomic_load_n(&(p), __ATOMIC_RELAXED)
 
 /*
  * Load a data from shared memory, doing a cache flush if required.
@@ -42,7 +42,7 @@
  * Identify a shared store. A cmm_smp_wmc() or cmm_smp_mc() should
  * follow the store.
  */
-#define _CMM_STORE_SHARED(x, v)	__extension__ ({ CMM_ACCESS_ONCE(x) = (v); })
+#define _CMM_STORE_SHARED(x, v)	__atomic_store_n(&(x), (v), __ATOMIC_RELAXED)
 
 /*
  * Store v into x, where x is located in shared memory. Performs the
@@ -51,9 +51,8 @@
 #define CMM_STORE_SHARED(x, v)						\
 	__extension__							\
 	({								\
-		__typeof__(x) _v = _CMM_STORE_SHARED(x, v);		\
+		_CMM_STORE_SHARED(x, v);				\
 		cmm_smp_wmc();						\
-		_v = _v;	/* Work around clang "unused result" */	\
 	})
 
 #endif /* _URCU_SYSTEM_H */
-- 
2.39.2