github.com/nicocha30/gvisor-ligolo@v0.0.0-20230726075806-989fa2c0a413/pkg/sentry/time/tsc_amd64.s (about)

     1  // Copyright 2018 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  #include "textflag.h"
    16  
    17  TEXT ·Rdtsc(SB),NOSPLIT|NOFRAME,$0-8
    18  	// N.B. We need LFENCE on Intel, AMD is more complicated.
    19  	// Modern AMD CPUs with modern kernels make LFENCE behave like it does
    20  	// on Intel with MSR_F10H_DECFG_LFENCE_SERIALIZE_BIT. MFENCE is
    21  	// otherwise needed on AMD.
    22  	LFENCE
    23  	RDTSC
    24  	SHLQ	$32, DX
    25  	ADDQ	DX, AX
    26  	MOVQ	AX, ret+0(FP)
    27  	RET