ndk: Fix <sys/atomics.h> declarations.
The atomic operations exported by the platform's C library do not
provide full memory barriers. This can result in incorrect results
when NDK machine code linked against them runs on multi-core devices.
While the bug has been fixed in the platform, this NDK header change
ensures that any source code that includes <sys/atomics.h> will end
up using a correct implementation of these functions, based on the
corresponding GCC builtins.
These builtins always provide a full barrier and have reasonable
performance. Application developers who depend on <sys/atomics.h>
should recompile their unmodified sources against this version
of the NDK as soon as possible.
diff --git a/ndk/platforms/android-3/include/sys/atomics.h b/ndk/platforms/android-3/include/sys/atomics.h
index d3fa145..3ada8de 100644
--- a/ndk/platforms/android-3/include/sys/atomics.h
+++ b/ndk/platforms/android-3/include/sys/atomics.h
@@ -33,10 +33,48 @@
__BEGIN_DECLS
-extern int __atomic_cmpxchg(int old, int _new, volatile int *ptr);
-extern int __atomic_swap(int _new, volatile int *ptr);
-extern int __atomic_dec(volatile int *ptr);
-extern int __atomic_inc(volatile int *ptr);
+/* Note: atomic operations that were exported by the C library didn't
+ * provide any memory barriers, which created potential issues on
+ * multi-core devices. We now define them as inlined calls to
+ * GCC sync builtins, which always provide a full barrier.
+ *
+ * NOTE: The C library still exports atomic functions by the same
+ * name to ensure ABI stability for existing NDK machine code.
+ *
+ * If you are an NDK developer, we encourage you to rebuild your
+ * unmodified sources against this header as soon as possible.
+ */
+#define __ATOMIC_INLINE__ static __inline__ __attribute__((always_inline))
+
+__ATOMIC_INLINE__ int
+__atomic_cmpxchg(int old, int _new, volatile int *ptr)
+{
+ /* We must return 0 on success */
+ return __sync_val_compare_and_swap(ptr, old, _new) != old;
+}
+
+__ATOMIC_INLINE__ int
+__atomic_swap(int _new, volatile int *ptr)
+{
+ int prev;
+ do {
+ prev = *ptr;
+ } while (__sync_val_compare_and_swap(ptr, prev, _new) != prev);
+ return prev;
+}
+
+__ATOMIC_INLINE__ int
+__atomic_dec(volatile int *ptr)
+{
+ return __sync_fetch_and_sub (ptr, 1);
+}
+
+__ATOMIC_INLINE__ int
+__atomic_inc(volatile int *ptr)
+{
+ return __sync_fetch_and_add (ptr, 1);
+}
+
int __futex_wait(volatile void *ftx, int val, const struct timespec *timeout);
int __futex_wake(volatile void *ftx, int count);
diff --git a/ndk/platforms/android-9/arch-x86/include/sys/atomics.h b/ndk/platforms/android-9/arch-x86/include/sys/atomics.h
deleted file mode 100644
index 7aed3ae..0000000
--- a/ndk/platforms/android-9/arch-x86/include/sys/atomics.h
+++ /dev/null
@@ -1,65 +0,0 @@
-/*
- * Copyright (C) 2011 The Android Open Source Project
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * * Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
- * * Redistributions in binary form must reproduce the above copyright
- * notice, this list of conditions and the following disclaimer in
- * the documentation and/or other materials provided with the
- * distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
- * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
- * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
- * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
- * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
- * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
- * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
- * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
- * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
-#ifndef _SYS_ATOMICS_H
-#define _SYS_ATOMICS_H
-
-#include <sys/cdefs.h>
-#include <sys/time.h>
-
-__BEGIN_DECLS
-
-static inline __attribute__((always_inline)) int
-__atomic_cmpxchg(int old, int _new, volatile int *ptr)
-{
- return !__sync_bool_compare_and_swap (ptr, old, _new);
-}
-
-static inline __attribute__((always_inline)) int
-__atomic_swap(int _new, volatile int *ptr)
-{
- return __sync_lock_test_and_set(ptr, _new);
-}
-
-static inline __attribute__((always_inline)) int
-__atomic_dec(volatile int *ptr)
-{
- return __sync_fetch_and_sub (ptr, 1);
-}
-
-static inline __attribute__((always_inline)) int
-__atomic_inc(volatile int *ptr)
-{
- return __sync_fetch_and_add (ptr, 1);
-}
-
-int __futex_wait(volatile void *ftx, int val, const struct timespec *timeout);
-int __futex_wake(volatile void *ftx, int count);
-
-__END_DECLS
-
-#endif /* _SYS_ATOMICS_H */
