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// Copyright 2018 Google LLC
//
// 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.
#include "textflag.h"
TEXT ·Rdtsc(SB),NOSPLIT,$0-8
// N.B. We need LFENCE on Intel, AMD is more complicated.
// Modern AMD CPUs with modern kernels make LFENCE behave like it does
// on Intel with MSR_F10H_DECFG_LFENCE_SERIALIZE_BIT. MFENCE is
// otherwise needed on AMD.
LFENCE
RDTSC
SHLQ $32, DX
ADDQ DX, AX
MOVQ AX, ret+0(FP)
RET
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