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PiperOrigin-RevId: 194583126
Change-Id: Ica1d8821a90f74e7e745962d71801c598c652463

1 files changed, 42 insertions, 0 deletions

diff --git a/vdso/cycle_clock.h b/vdso/cycle_clock.h
new file mode 100644
index 000000000..93c5f2c0d
--- /dev/null
+++ b/vdso/cycle_clock.h
@@ -0,0 +1,42 @@
+// Copyright 2018 Google Inc.
+//
+// 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 VDSO_CYCLE_CLOCK_H_
+#define VDSO_CYCLE_CLOCK_H_
+
+#include <stdint.h>
+
+#include "vdso/barrier.h"
+
+namespace vdso {
+
+#if __x86_64__
+
+// TODO: The appropriate barrier instruction to use with rdtsc on
+// x86_64 depends on the vendor. Intel processors can use lfence but AMD may
+// need mfence, depending on MSR_F10H_DECFG_LFENCE_SERIALIZE_BIT.
+
+static inline uint64_t cycle_clock(void) {
+  uint32_t lo, hi;
+  asm volatile("lfence" : : : "memory");
+  asm volatile("rdtsc" : "=a"(lo), "=d"(hi));
+  return ((uint64_t)hi << 32) | lo;
+}
+#else
+#error "unsupported architecture"
+#endif
+
+}  // namespace vdso
+
+#endif  // VDSO_CYCLE_CLOCK_H_