0fec6b9d88
__atomic_cmpxchg and other related atomic operations did not provide memory barriers, which can be a problem for non-platform code that links against them when it runs on multi-core devices. This patch does two things to fix this: - It modifies the existing implementation of the functions that are exported by the C library to always provide full memory barriers. We need to keep them exported by the C library to prevent breaking existing application machine code. - It also modifies <sys/atomics.h> to only export always-inlined versions of the functions, to ensure that any application code compiled against the new header will not rely on the platform version of the functions. This ensure that said machine code will run properly on all multi-core devices. This is based on the GCC built-in sync primitives. The end result should be only slightly slower than the previous implementation. Note that the platform code does not use these functions at all. A previous patch completely removed their usage in the pthread and libstdc++ code. + rename arch-arm/bionic/atomics_arm.S to futex_arm.S + rename arch-x86/bionic/atomics_x86.S to futex_x86.S + remove arch-x86/include/sys/atomics.h which already provided inlined functions to the x86 platform. Change-Id: I752a594475090cf37fa926bb38209c2175dda539
85 lines
2.8 KiB
C
85 lines
2.8 KiB
C
/*
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* Copyright (C) 2008 The Android Open Source Project
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#ifndef _SYS_ATOMICS_H
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#define _SYS_ATOMICS_H
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#include <sys/cdefs.h>
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#include <sys/time.h>
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__BEGIN_DECLS
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/* Note: atomic operations that were exported by the C library didn't
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* provide any memory barriers, which created potential issues on
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* multi-core devices. We now define them as inlined calls to
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* GCC sync builtins, which always provide a full barrier.
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*
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* NOTE: The C library still exports atomic functions by the same
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* name to ensure ABI stability for existing NDK machine code.
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*
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* If you are an NDK developer, we encourage you to rebuild your
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* unmodified sources against this header as soon as possible.
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*/
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#define __ATOMIC_INLINE__ static __inline__ __attribute__((always_inline))
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__ATOMIC_INLINE__ int
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__atomic_cmpxchg(int old, int _new, volatile int *ptr)
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{
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/* We must return 0 on success */
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return __sync_val_compare_and_swap(ptr, old, _new) != old;
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}
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__ATOMIC_INLINE__ int
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__atomic_swap(int _new, volatile int *ptr)
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{
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int prev;
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do {
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prev = *ptr;
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} while (__sync_val_compare_and_swap(ptr, prev, _new) != prev);
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return prev;
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}
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__ATOMIC_INLINE__ int
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__atomic_dec(volatile int *ptr)
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{
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return __sync_fetch_and_sub (ptr, 1);
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}
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__ATOMIC_INLINE__ int
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__atomic_inc(volatile int *ptr)
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{
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return __sync_fetch_and_add (ptr, 1);
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}
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int __futex_wait(volatile void *ftx, int val, const struct timespec *timeout);
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int __futex_wake(volatile void *ftx, int count);
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__END_DECLS
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#endif /* _SYS_ATOMICS_H */
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