libc/private/bionic_atomic_arm.h

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#ifndef BIONIC_ATOMIC_ARM_H
#define BIONIC_ATOMIC_ARM_H

__ATOMIC_INLINE__ void __bionic_memory_barrier(void) {
#if defined(ANDROID_SMP) && ANDROID_SMP == 1
  __asm__ __volatile__ ( "dmb" : : : "memory" );
#else
  /* A simple compiler barrier. */
  __asm__ __volatile__ ( "" : : : "memory" );
#endif
}

/* Compare-and-swap, without any explicit barriers. Note that this function
 * returns 0 on success, and 1 on failure. The opposite convention is typically
 * used on other platforms.
 */
__ATOMIC_INLINE__ int __bionic_cmpxchg(int32_t old_value, int32_t new_value, volatile int32_t* ptr) {
  int32_t prev, status;
  do {
    __asm__ __volatile__ (
          "ldrex %0, [%3]\n"
          "mov %1, #0\n"
          "teq %0, %4\n"
#ifdef __thumb2__
          "it eq\n"
#endif
          "strexeq %1, %5, [%3]"
          : "=&r" (prev), "=&r" (status), "+m"(*ptr)
          : "r" (ptr), "Ir" (old_value), "r" (new_value)
          : "cc");
  } while (__builtin_expect(status != 0, 0));
  return prev != old_value;
}

/* Swap, without any explicit barriers. */
__ATOMIC_INLINE__ int32_t __bionic_swap(int32_t new_value, volatile int32_t* ptr) {
  int32_t prev, status;
  do {
    __asm__ __volatile__ (
          "ldrex %0, [%3]\n"
          "strex %1, %4, [%3]"
          : "=&r" (prev), "=&r" (status), "+m" (*ptr)
          : "r" (ptr), "r" (new_value)
          : "cc");
  } while (__builtin_expect(status != 0, 0));
  return prev;
}

/* Atomic decrement, without explicit barriers. */
__ATOMIC_INLINE__ int32_t __bionic_atomic_dec(volatile int32_t* ptr) {
  int32_t prev, tmp, status;
  do {
    __asm__ __volatile__ (
          "ldrex %0, [%4]\n"
          "sub %1, %0, #1\n"
          "strex %2, %1, [%4]"
          : "=&r" (prev), "=&r" (tmp), "=&r" (status), "+m"(*ptr)
          : "r" (ptr)
          : "cc");
  } while (__builtin_expect(status != 0, 0));
  return prev;
}

#endif /* SYS_ATOMICS_ARM_H */