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// Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package cpu implements processor feature detection
// used by the Go standard library.
package cpu
// debugOptions is set to true by the runtime if go was compiled with GOEXPERIMENT=debugcpu
// and GOOS is Linux or Darwin. This variable is linknamed in runtime/proc.go.
var debugOptions bool
var X86 x86
// The booleans in x86 contain the correspondingly named cpuid feature bit.
// HasAVX and HasAVX2 are only set if the OS does support XMM and YMM registers
// in addition to the cpuid feature bit being set.
// The struct is padded to avoid false sharing.
type x86 struct {
_ [CacheLineSize]byte
HasAES bool
HasADX bool
HasAVX bool
HasAVX2 bool
HasBMI1 bool
HasBMI2 bool
HasERMS bool
HasFMA bool
HasPOPCNT bool
HasSSE2 bool
HasSSE3 bool
HasSSSE3 bool
HasSSE41 bool
HasSSE42 bool
_ [CacheLineSize]byte
var PPC64 ppc64
// For ppc64x, it is safe to check only for ISA level starting on ISA v3.00,
// since there are no optional categories. There are some exceptions that also
// require kernel support to work (darn, scv), so there are feature bits for
// those as well. The minimum processor requirement is POWER8 (ISA 2.07), so we
// maintain some of the old feature checks for optional categories for
// safety.
// The struct is padded to avoid false sharing.
type ppc64 struct {
_ [CacheLineSize]byte
HasVMX bool // Vector unit (Altivec)
HasDFP bool // Decimal Floating Point unit
HasVSX bool // Vector-scalar unit
HasHTM bool // Hardware Transactional Memory
HasISEL bool // Integer select
HasVCRYPTO bool // Vector cryptography
HasHTMNOSC bool // HTM: kernel-aborted transaction in syscalls
HasDARN bool // Hardware random number generator (requires kernel enablement)
HasSCV bool // Syscall vectored (requires kernel enablement)
IsPOWER8 bool // ISA v2.07 (POWER8)
IsPOWER9 bool // ISA v3.00 (POWER9)
_ [CacheLineSize]byte
var ARM64 arm64
// The booleans in arm64 contain the correspondingly named cpu feature bit.
// The struct is padded to avoid false sharing.
type arm64 struct {
_ [CacheLineSize]byte
HasFP bool
HasASIMD bool
HasAES bool
HasPMULL bool
HasSHA1 bool
HasSHA2 bool
HasCRC32 bool
HasFPHP bool
HasCPUID bool
HasJSCVT bool
HasFCMA bool
HasLRCPC bool
HasDCPOP bool
HasSHA3 bool
HasSM3 bool
HasSM4 bool
HasSHA512 bool
HasSVE bool
_ [CacheLineSize]byte
var S390X s390x
type s390x struct {
_ [CacheLineSize]byte
HasZArch bool // z architecture mode is active [mandatory]
HasSTFLE bool // store facility list extended [mandatory]
HasLDisp bool // long (20-bit) displacements [mandatory]
HasEImm bool // 32-bit immediates [mandatory]
HasDFP bool // decimal floating point
HasETF3Enhanced bool // ETF-3 enhanced
HasMSA bool // message security assist (CPACF)
HasAES bool // KM-AES{128,192,256} functions
HasAESCBC bool // KMC-AES{128,192,256} functions
HasAESCTR bool // KMCTR-AES{128,192,256} functions
HasAESGCM bool // KMA-GCM-AES{128,192,256} functions
HasGHASH bool // KIMD-GHASH function
HasSHA1 bool // K{I,L}MD-SHA-1 functions
HasSHA256 bool // K{I,L}MD-SHA-256 functions
HasSHA512 bool // K{I,L}MD-SHA-512 functions
HasVX bool // vector facility. Note: the runtime sets this when it processes auxv records.
_ [CacheLineSize]byte
// initialize examines the processor and sets the relevant variables above.
// This is called by the runtime package early in program initialization,
// before normal init functions are run. env is set by runtime on Linux and Darwin
// if go was compiled with GOEXPERIMENT=debugcpu.
func initialize(env string) {
// options contains the cpu debug options that can be used in GODEBUGCPU.
// Options are arch dependent and are added by the arch specific doinit functions.
// Features that are mandatory for the specific GOARCH should not be added to options
// (e.g. SSE2 on amd64).
var options []option
// Option names should be lower case. e.g. avx instead of AVX.
type option struct {
Name string
Feature *bool
// processOptions disables CPU feature values based on the parsed env string.
// The env string is expected to be of the form feature1=0,feature2=0...
// where feature names is one of the architecture specifc list stored in the
// cpu packages options variable. If env contains all=0 then all capabilities
// referenced through the options variable are disabled. Other feature
// names and values other than 0 are silently ignored.
func processOptions(env string) {
for env != "" {
field := ""
i := indexByte(env, ',')
if i < 0 {
field, env = env, ""
} else {
field, env = env[:i], env[i+1:]
i = indexByte(field, '=')
if i < 0 {
key, value := field[:i], field[i+1:]
// Only allow turning off CPU features by specifying '0'.
if value == "0" {
if key == "all" {
for _, v := range options {
*v.Feature = false
} else {
for _, v := range options {
if v.Name == key {
*v.Feature = false
continue field
// indexByte returns the index of the first instance of c in s,
// or -1 if c is not present in s.
func indexByte(s string, c byte) int {
for i := 0; i < len(s); i++ {
if s[i] == c {
return i
return -1