From 601976dede1271acbcae9e43c6f3a287d6c71571 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Markus=20M=C3=A4kel=C3=A4?= <markus456@gmail.com>
Date: Fri, 28 Apr 2017 11:47:46 +0300
Subject: [PATCH] Use __atomic builtins only where they are supported

Use the newer __atomic builtins only with GCC >= 4.7. The older __sync
builtins are used elsewhere.
---
 include/maxscale/atomic.h | 17 ++++++++++++++++
 server/core/atomic.cc     | 42 ++++++++++++++++++++++++++++++++++++---
 2 files changed, 56 insertions(+), 3 deletions(-)

diff --git a/include/maxscale/atomic.h b/include/maxscale/atomic.h
index c5d8c8cc4..bfcd1067d 100644
--- a/include/maxscale/atomic.h
+++ b/include/maxscale/atomic.h
@@ -20,6 +20,17 @@
 
 MXS_BEGIN_DECLS
 
+/**
+ * Pre 4.7 GCC doesn't support the __atomic builtin functions. The older __sync
+ * builtins don't have proper store/load functionality so we use a somewhat ugly
+ * hack to emulate the store/load.
+ */
+#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 7)
+#ifndef MXS_USE_ATOMIC_BUILTINS
+#define MXS_USE_ATOMIC_BUILTINS 1
+#endif
+#endif
+
 /**
  * Implementation of an atomic add operations for the GCC environment.
  *
@@ -76,7 +87,13 @@ void atomic_store_uint64(uint64_t *variable, uint64_t value);
 static inline void atomic_synchronize()
 {
 #ifdef __GNUC__
+
+#ifdef MXS_USE_ATOMIC_BUILTINS
+    __atomic_thread_fence(__ATOMIC_SEQ_CST);
+#else
     __sync_synchronize(); /* Memory barrier. */
+#endif
+
 #else
 #error "No GNUC atomics available."
 #endif
diff --git a/server/core/atomic.cc b/server/core/atomic.cc
index 549431724..ea9afc819 100644
--- a/server/core/atomic.cc
+++ b/server/core/atomic.cc
@@ -19,45 +19,81 @@
 
 int atomic_add(int *variable, int value)
 {
+#ifdef MXS_USE_ATOMIC_BUILTINS
+    return __atomic_add_fetch(variable, value, __ATOMIC_SEQ_CST);
+#else
     return __sync_fetch_and_add(variable, value);
+#endif
 }
 
 int64_t atomic_add_int64(int64_t *variable, int64_t value)
 {
+#ifdef MXS_USE_ATOMIC_BUILTINS
+    return __atomic_add_fetch(variable, value, __ATOMIC_SEQ_CST);
+#else
     return __sync_fetch_and_add(variable, value);
+#endif
 }
 
 uint64_t atomic_add_uint64(uint64_t *variable, int64_t value)
 {
+#ifdef MXS_USE_ATOMIC_BUILTINS
+    return __atomic_add_fetch(variable, value, __ATOMIC_SEQ_CST);
+#else
     return __sync_fetch_and_add(variable, value);
+#endif
 }
 
 int atomic_load_int32(int *variable)
 {
+#ifdef MXS_USE_ATOMIC_BUILTINS
     return __atomic_load_n(variable, __ATOMIC_SEQ_CST);
+#else
+    return __sync_fetch_and_or(variable, 0);
+#endif
 }
 
 int64_t atomic_load_int64(int64_t *variable)
 {
+#ifdef MXS_USE_ATOMIC_BUILTINS
     return __atomic_load_n(variable, __ATOMIC_SEQ_CST);
+#else
+    return __sync_fetch_and_or(variable, 0);
+#endif
 }
 
 uint64_t atomic_load_uint64(uint64_t *variable)
 {
+#ifdef MXS_USE_ATOMIC_BUILTINS
     return __atomic_load_n(variable, __ATOMIC_SEQ_CST);
+#else
+    return __sync_fetch_and_or(variable, 0);
+#endif
 }
 
 void atomic_store_int32(int *variable, int value)
 {
-    return __atomic_store_n(variable, value, __ATOMIC_SEQ_CST);
+#ifdef MXS_USE_ATOMIC_BUILTINS
+    __atomic_store_n(variable, value, __ATOMIC_SEQ_CST);
+#else
+    __sync_lock_test_and_set(variable, value);
+#endif
 }
 
 void atomic_store_int64(int64_t *variable, int64_t value)
 {
-    return __atomic_store_n(variable, value, __ATOMIC_SEQ_CST);
+#ifdef MXS_USE_ATOMIC_BUILTINS
+    __atomic_store_n(variable, value, __ATOMIC_SEQ_CST);
+#else
+    __sync_lock_test_and_set(variable, value);
+#endif
 }
 
 void atomic_store_uint64(uint64_t *variable, uint64_t value)
 {
-    return __atomic_store_n(variable, value, __ATOMIC_SEQ_CST);
+#ifdef MXS_USE_ATOMIC_BUILTINS
+    __atomic_store_n(variable, value, __ATOMIC_SEQ_CST);
+#else
+    __sync_lock_test_and_set(variable, value);
+#endif
 }