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// 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_
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