From e31f85e6915d4bf6ed76c5da71c235525fa4ecc3 Mon Sep 17 00:00:00 2001
From: Koen Kooi <koen.kooi@linaro.org>
Date: Mon, 14 Apr 2014 10:29:42 +0200
Subject: [PATCH 5/5] GCC 4.7+ supports atomic ops for armv5 and up, but only
 exports the functions for armv6 and up. This patch works around the linker
 problems associated with that.

Forward ported from http://pkgs.fedoraproject.org/cgit/mongodb.git/tree/mongodb-2.4.5-atomics.patch

Upstream-status: pending
---
 src/mongo/bson/util/atomic_int.h                   | 26 ++++++++++++
 src/mongo/platform/atomic_intrinsics_gcc_generic.h | 47 ++++++++++++++++++++++
 2 files changed, 73 insertions(+)

diff --git a/src/mongo/bson/util/atomic_int.h b/src/mongo/bson/util/atomic_int.h
index 0b85363..ed02c23 100644
--- a/src/mongo/bson/util/atomic_int.h
+++ b/src/mongo/bson/util/atomic_int.h
@@ -24,6 +24,10 @@
 
 #include "mongo/platform/compiler.h"
 
+#define GCC_VERSION (__GNUC__ * 10000                 \
+                     + __GNUC_MINOR__ * 100           \
+                     + __GNUC_PATCHLEVEL__)
+
 namespace mongo {
 
     /**
@@ -72,6 +76,28 @@ namespace mongo {
         InterlockedAdd((volatile long *)&x,by);
     }
 # endif
+#elif defined(GCC_VERSION) && GCC_VERSION >= 40700
+// in GCC version >= 4.7.0 we can use the built-in atomic operations
+
+    inline void AtomicUInt::set(unsigned newX) {
+        __atomic_store_n (&x, newX, __ATOMIC_SEQ_CST);
+    }
+    AtomicUInt AtomicUInt::operator++() {    // ++prefix
+        return __atomic_add_fetch(&x, 1, __ATOMIC_SEQ_CST);
+    }
+    AtomicUInt AtomicUInt::operator++(int) { // postfix++
+        return __atomic_fetch_add(&x, 1, __ATOMIC_SEQ_CST);
+    }
+    AtomicUInt AtomicUInt::operator--() {    // --prefix
+        return __atomic_add_fetch(&x, -1, __ATOMIC_SEQ_CST);
+    }
+    AtomicUInt AtomicUInt::operator--(int) { // postfix--
+        return __atomic_fetch_add(&x, -1, __ATOMIC_SEQ_CST);
+    }
+    void AtomicUInt::signedAdd(int by) {
+        __atomic_fetch_add(&x, by, __ATOMIC_SEQ_CST);
+    }
+
 #elif defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4)
     // this is in GCC >= 4.1
     inline void AtomicUInt::set(unsigned newX) { __sync_synchronize(); x = newX; }
diff --git a/src/mongo/platform/atomic_intrinsics_gcc_generic.h b/src/mongo/platform/atomic_intrinsics_gcc_generic.h
index 64a2499..b7cc176 100644
--- a/src/mongo/platform/atomic_intrinsics_gcc_generic.h
+++ b/src/mongo/platform/atomic_intrinsics_gcc_generic.h
@@ -22,8 +22,53 @@
 
 #include <boost/utility.hpp>
 
+#define GCC_VERSION (__GNUC__ * 10000                 \
+                     + __GNUC_MINOR__ * 100           \
+                     + __GNUC_PATCHLEVEL__)
+
 namespace mongo {
 
+// If GCC version >= 4.7.0, we can use the built-in atomic operations
+#if defined(GCC_VERSION) && GCC_VERSION >= 40700
+
+    /**
+     * Instantiation of AtomicIntrinsics<>.
+     */
+    template <typename T>
+    class AtomicIntrinsics {
+    public:
+
+        static T compareAndSwap(volatile T* dest, T expected, T newValue) {
+            return __atomic_compare_exchange_n (dest, &expected, newValue, 0, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
+        }
+
+        static T swap(volatile T* dest, T newValue) {
+            return __atomic_exchange_n (dest, newValue, __ATOMIC_SEQ_CST);
+        }
+
+        static T load(volatile const T* value) {
+            return __atomic_load_n (value, __ATOMIC_SEQ_CST);
+        }
+
+        static T loadRelaxed(volatile const T* value) {
+            return *value;
+        }
+
+        static void store(volatile T* dest, T newValue) {
+            __atomic_store_n (dest, newValue, __ATOMIC_SEQ_CST);
+        }
+
+        static T fetchAndAdd(volatile T* dest, T increment) {
+            return __atomic_fetch_add (dest, increment, __ATOMIC_SEQ_CST);
+        }
+
+    private:
+        AtomicIntrinsics();
+        ~AtomicIntrinsics();
+    };
+
+#else // GCC version < 4.7, so we must use legacy (platform-specific) atomic operations
+
     /**
      * Instantiation of AtomicIntrinsics<> for all word types T.
      */
@@ -67,4 +112,6 @@ namespace mongo {
         ~AtomicIntrinsics();
     };
 
+#endif // GCC_VERSION >= 40700
+
 }  // namespace mongo
-- 
1.9.0