Add atomic operations for ARM.

base/atomicops_internals_arm_gcc.h

Index: base/atomicops_internals_arm_gcc.h
===================================================================
--- base/atomicops_internals_arm_gcc.h	(revision 0)
+++ base/atomicops_internals_arm_gcc.h	(revision 0)
@@ -0,0 +1,124 @@
+// 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_
+
+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_