Add arm64 support to leveldb.

Author: cmumford

port/atomic_pointer.h

@@ -35,6 +35,8 @@
 #define ARCH_CPU_X86_FAMILY 1
 #elif defined(__ARMEL__)
 #define ARCH_CPU_ARM_FAMILY 1
+#elif defined(__aarch64__)
+#define ARCH_CPU_ARM64_FAMILY 1
 #elif defined(__ppc__) || defined(__powerpc__) || defined(__powerpc64__)
 #define ARCH_CPU_PPC_FAMILY 1
 #endif
@@ -92,6 +94,13 @@ inline void MemoryBarrier() {
 }
 #define LEVELDB_HAVE_MEMORY_BARRIER
 
+// ARM64
+#elif defined(ARCH_CPU_ARM64_FAMILY)
+inline void MemoryBarrier() {
+  asm volatile("dmb sy" : : : "memory");
+}
+#define LEVELDB_HAVE_MEMORY_BARRIER
+
 // PPC
 #elif defined(ARCH_CPU_PPC_FAMILY) && defined(__GNUC__)
 inline void MemoryBarrier() {
@@ -215,6 +224,7 @@ class AtomicPointer {
 #undef LEVELDB_HAVE_MEMORY_BARRIER
 #undef ARCH_CPU_X86_FAMILY
 #undef ARCH_CPU_ARM_FAMILY
+#undef ARCH_CPU_ARM64_FAMILY
 #undef ARCH_CPU_PPC_FAMILY
 
 }  // namespace port