131 lines
4.0 KiB
C++
131 lines
4.0 KiB
C++
// Copyright (c) 2009 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// This file is an internal atomic implementation, use base/atomicops.h instead.
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//
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// LinuxKernelCmpxchg and Barrier_AtomicIncrement are from Google Gears.
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#ifndef BASE_ATOMICOPS_INTERNALS_ARM_GCC_H_
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#define BASE_ATOMICOPS_INTERNALS_ARM_GCC_H_
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#include "build_config.h"
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namespace base {
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namespace subtle {
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// 0xffff0fc0 is the hard coded address of a function provided by
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// the kernel which implements an atomic compare-exchange. On older
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// ARM architecture revisions (pre-v6) this may be implemented using
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// a syscall. This address is stable, and in active use (hard coded)
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// by at least glibc-2.7 and the Android C library.
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typedef Atomic32 (*LinuxKernelCmpxchgFunc)(Atomic32 old_value,
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Atomic32 new_value,
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volatile Atomic32* ptr);
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LinuxKernelCmpxchgFunc pLinuxKernelCmpxchg __attribute__((weak)) =
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(LinuxKernelCmpxchgFunc) 0xffff0fc0;
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typedef void (*LinuxKernelMemoryBarrierFunc)(void);
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LinuxKernelMemoryBarrierFunc pLinuxKernelMemoryBarrier __attribute__((weak)) =
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(LinuxKernelMemoryBarrierFunc) 0xffff0fa0;
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inline Atomic32 NoBarrier_CompareAndSwap(volatile Atomic32* ptr,
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Atomic32 old_value,
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Atomic32 new_value) {
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Atomic32 prev_value = *ptr;
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do {
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if (!pLinuxKernelCmpxchg(old_value, new_value,
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const_cast<Atomic32*>(ptr))) {
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return old_value;
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}
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prev_value = *ptr;
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} while (prev_value == old_value);
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return prev_value;
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}
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inline Atomic32 NoBarrier_AtomicExchange(volatile Atomic32* ptr,
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Atomic32 new_value) {
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Atomic32 old_value;
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do {
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old_value = *ptr;
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} while (pLinuxKernelCmpxchg(old_value, new_value,
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const_cast<Atomic32*>(ptr)));
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return old_value;
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}
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inline Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr,
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Atomic32 increment) {
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return Barrier_AtomicIncrement(ptr, increment);
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}
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inline Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr,
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Atomic32 increment) {
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for (;;) {
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// Atomic exchange the old value with an incremented one.
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Atomic32 old_value = *ptr;
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Atomic32 new_value = old_value + increment;
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if (pLinuxKernelCmpxchg(old_value, new_value,
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const_cast<Atomic32*>(ptr)) == 0) {
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// The exchange took place as expected.
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return new_value;
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}
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// Otherwise, *ptr changed mid-loop and we need to retry.
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}
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}
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inline Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr,
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Atomic32 old_value,
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Atomic32 new_value) {
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return NoBarrier_CompareAndSwap(ptr, old_value, new_value);
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}
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inline Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr,
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Atomic32 old_value,
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Atomic32 new_value) {
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return NoBarrier_CompareAndSwap(ptr, old_value, new_value);
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}
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inline void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value) {
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*ptr = value;
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}
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inline void MemoryBarrier() {
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#if defined (ARMV6_OR_7)
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__asm__ __volatile__("dmb" : : : "memory");
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#else
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pLinuxKernelMemoryBarrier();
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#endif
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}
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inline void Acquire_Store(volatile Atomic32* ptr, Atomic32 value) {
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*ptr = value;
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MemoryBarrier();
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}
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inline void Release_Store(volatile Atomic32* ptr, Atomic32 value) {
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MemoryBarrier();
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*ptr = value;
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}
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inline Atomic32 NoBarrier_Load(volatile const Atomic32* ptr) {
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return *ptr;
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}
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inline Atomic32 Acquire_Load(volatile const Atomic32* ptr) {
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Atomic32 value = *ptr;
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MemoryBarrier();
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return value;
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}
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inline Atomic32 Release_Load(volatile const Atomic32* ptr) {
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MemoryBarrier();
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return *ptr;
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}
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} // namespace base::subtle
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} // namespace base
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#endif // BASE_ATOMICOPS_INTERNALS_ARM_GCC_H_
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