bionic: Do not use <sys/atomics.h> for platform code.

We're going to modify the __atomic_xxx implementation to provide
full memory barriers, to avoid problems for NDK machine code that
link to these functions.

First step is to remove their usage from our platform code.
We now use inlined versions of the same functions for a slight
performance boost.

+ remove obsolete atomics_x86.c (was never compiled)

NOTE: This improvement was benchmarked on various devices.
      Comparing a pthread mutex lock + atomic increment + unlock
      we get:

  - ARMv7 emulator, running on a 2.4 GHz Xeon:
       before: 396 ns    after: 288 ns

  - x86 emulator in KVM mode on same machine:
       before: 27 ns     after: 27 ns

  - Google Nexus S, in ARMv7 mode (single-core):
       before: 82 ns     after: 76 ns

  - Motorola Xoom, in ARMv7 mode (multi-core):
       before: 121 ns    after: 120 ns

The code has also been rebuilt in ARMv5TE mode for correctness.

Change-Id: Ic1dc72b173d59b2e7af901dd70d6a72fb2f64b17

1 files changed, 62 insertions, 0 deletions

diff --git a/libc/private/bionic_atomic_gcc_builtin.h b/libc/private/bionic_atomic_gcc_builtin.h
new file mode 100644
index 0000000..e7c5761
--- /dev/null
+++ b/libc/private/bionic_atomic_gcc_builtin.h
@@ -0,0 +1,62 @@
+/*
+ * 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_GCC_BUILTIN_H
+#define BIONIC_ATOMIC_GCC_BUILTIN_H
+
+/* This header file is used by default if we don't have optimized atomic
+ * routines for a given platform. See bionic_atomic_arm.h and
+ * bionic_atomic_x86.h for examples.
+ */
+
+__ATOMIC_INLINE__ void
+__bionic_memory_barrier(void)
+{
+    __sync_synchronize();
+}
+
+__ATOMIC_INLINE__ int
+__bionic_cmpxchg(int32_t old_value, int32_t new_value, volatile int32_t* ptr)
+{
+    /* We must return 0 on success */
+    return __sync_bool_compare_and_swap(ptr, old_value, new_value) == 0;
+}
+
+__ATOMIC_INLINE__ int32_t
+__bionic_swap(int32_t new_value, volatile int32_t* ptr)
+{
+    int32_t prev;
+    do {
+        prev = *ptr;
+        status = __sync_val_compare_and_swap(ptr, prev, new_value);
+    } while (status == 0);
+    return prev;
+}
+
+__ATOMIC_INLINE__ int32_t
+__bionic_atomic_inc(volatile int32_t* ptr)
+{
+    /* We must return the old value */
+    return __sync_fetch_and_add(ptr, 1);
+}
+
+__ATOMIC_INLINE__ int32_t
+__bionic_atomic_dec(volatile int32_t* ptr)
+{
+    /* We must return the old value */
+    return __sync_fetch_and_add(ptr, -1);
+}
+
+#endif /* BIONIC_ATOMIC_GCC_BUILTIN_H */