From 6c32dacf97eb6ecdc7a04d061cfe2bf317e18738 Mon Sep 17 00:00:00 2001 From: David 'Digit' Turner Date: Tue, 22 Nov 2011 11:18:44 +0100 Subject: [PATCH] ndk: Fix 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 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 should recompile their unmodified sources against this version of the NDK as soon as possible. --- ndk/platforms/android-3/include/sys/atomics.h | 46 +++++++++++-- .../android-9/arch-x86/include/sys/atomics.h | 65 ------------------- 2 files changed, 42 insertions(+), 69 deletions(-) delete mode 100644 ndk/platforms/android-9/arch-x86/include/sys/atomics.h diff --git a/ndk/platforms/android-3/include/sys/atomics.h b/ndk/platforms/android-3/include/sys/atomics.h index d3fa1454f..3ada8def8 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 7aed3ae0b..000000000 --- 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 -#include - -__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 */