atomic.h: Fix build with clang

clang defines __ATOMIC_SEQ_CST but its implementation of the __atomic_exchange() builtin differs from that of gcc. Move the __clang__ branch of the ifdef ladder to the top and fix its implementation (there is no such builtin as __sync_exchange), so we can compile with clang again. Signed-off-by: Peter Maydell <[email protected]> Signed-off-by: Paolo Bonzini <[email protected]>
dannf · Nov 21, 2013 · 392a4d5 · 392a4d5
1 parent 7839ff5
commit 392a4d5
Showing 1 changed file with 3 additions and 3 deletions.
diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h
@@ -168,14 +168,14 @@
 #endif
 
 #ifndef atomic_xchg
-#ifdef __ATOMIC_SEQ_CST
+#if defined(__clang__)
+#define atomic_xchg(ptr, i)    __sync_swap(ptr, i)
+#elif defined(__ATOMIC_SEQ_CST)
 #define atomic_xchg(ptr, i)    ({                           \
     typeof(*ptr) _new = (i), _old;                          \
     __atomic_exchange(ptr, &_new, &_old, __ATOMIC_SEQ_CST); \
     _old;                                                   \
 })
-#elif defined __clang__
-#define atomic_xchg(ptr, i)    __sync_exchange(ptr, i)
 #else
 /* __sync_lock_test_and_set() is documented to be an acquire barrier only.  */
 #define atomic_xchg(ptr, i)    (smp_mb(), __sync_lock_test_and_set(ptr, i))