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