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cpu: support darwin/arm64 CPU feature detection
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Support ARM64 features detection. The CPU features which are supported by
Apple Silicon M1 are assumed as the minimal set of features for Go programs
running on darwin/arm64.

The ARM64 supporting features are referred to
https://en.wikichip.org/wiki/arm/armv8#ARMv8_Extensions_and_Processor_Features
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howjmay committed Jul 3, 2021
1 parent 59db8d7 commit 1ba4687
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Showing 8 changed files with 271 additions and 26 deletions.
98 changes: 98 additions & 0 deletions cpu/cpu_android_arm64.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,98 @@
// Copyright 2021 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.

// +build arm64
// +build android

package cpu

// HWCAP/HWCAP2 bits. These are exposed by Linux.
const (
hwcap_FP = 1 << 0
hwcap_ASIMD = 1 << 1
hwcap_EVTSTRM = 1 << 2
hwcap_AES = 1 << 3
hwcap_PMULL = 1 << 4
hwcap_SHA1 = 1 << 5
hwcap_SHA2 = 1 << 6
hwcap_CRC32 = 1 << 7
hwcap_ATOMICS = 1 << 8
hwcap_FPHP = 1 << 9
hwcap_ASIMDHP = 1 << 10
hwcap_CPUID = 1 << 11
hwcap_ASIMDRDM = 1 << 12
hwcap_JSCVT = 1 << 13
hwcap_FCMA = 1 << 14
hwcap_LRCPC = 1 << 15
hwcap_DCPOP = 1 << 16
hwcap_SHA3 = 1 << 17
hwcap_SM3 = 1 << 18
hwcap_SM4 = 1 << 19
hwcap_ASIMDDP = 1 << 20
hwcap_SHA512 = 1 << 21
hwcap_SVE = 1 << 22
hwcap_ASIMDFHM = 1 << 23
)

func osInit() {
if err := readHWCAP(); err != nil {
// failed to read /proc/self/auxv, try reading registers directly
readARM64Registers()
return
}

// HWCap was populated by the runtime from the auxiliary vector.
// Use HWCap information since reading aarch64 system registers
// is not supported in user space on older linux kernels.
ARM64.HasFP = isSet(hwCap, hwcap_FP)
ARM64.HasASIMD = isSet(hwCap, hwcap_ASIMD)
ARM64.HasEVTSTRM = isSet(hwCap, hwcap_EVTSTRM)
ARM64.HasAES = isSet(hwCap, hwcap_AES)
ARM64.HasPMULL = isSet(hwCap, hwcap_PMULL)
ARM64.HasSHA1 = isSet(hwCap, hwcap_SHA1)
ARM64.HasSHA2 = isSet(hwCap, hwcap_SHA2)
ARM64.HasCRC32 = isSet(hwCap, hwcap_CRC32)
ARM64.HasFPHP = isSet(hwCap, hwcap_FPHP)
ARM64.HasASIMDHP = isSet(hwCap, hwcap_ASIMDHP)
ARM64.HasASIMDRDM = isSet(hwCap, hwcap_ASIMDRDM)
ARM64.HasJSCVT = isSet(hwCap, hwcap_JSCVT)
ARM64.HasFCMA = isSet(hwCap, hwcap_FCMA)
ARM64.HasLRCPC = isSet(hwCap, hwcap_LRCPC)
ARM64.HasDCPOP = isSet(hwCap, hwcap_DCPOP)
ARM64.HasSHA3 = isSet(hwCap, hwcap_SHA3)
ARM64.HasSM3 = isSet(hwCap, hwcap_SM3)
ARM64.HasSM4 = isSet(hwCap, hwcap_SM4)
ARM64.HasASIMDDP = isSet(hwCap, hwcap_ASIMDDP)
ARM64.HasSHA512 = isSet(hwCap, hwcap_SHA512)
ARM64.HasSVE = isSet(hwCap, hwcap_SVE)
ARM64.HasASIMDFHM = isSet(hwCap, hwcap_ASIMDFHM)

// The Samsung S9+ kernel reports support for atomics, but not all cores
// actually support them, resulting in SIGILL. See issue #28431.
// TODO(elias.naur): Only disable the optimization on bad chipsets on android.
ARM64.HasATOMICS = false

// Check to see if executing on a NeoverseN1 and in order to do that,
// check the AUXV for the CPUID bit. The getMIDR function executes an
// instruction which would normally be an illegal instruction, but it's
// trapped by the kernel, the value sanitized and then returned. Without
// the CPUID bit the kernel will not trap the instruction and the process
// will be terminated with SIGILL.
if ARM64.HasCPUID {
midr := getMIDR()
part_num := uint16((midr >> 4) & 0xfff)
implementor := byte((midr >> 24) & 0xff)

if implementor == 'A' && part_num == 0xd0c {
ARM64.IsNeoverseN1 = true
}
if implementor == 'A' && part_num == 0xd40 {
ARM64.IsZeus = true
}
}
}

func isSet(hwc uint, value uint) bool {
return hwc&value != 0
}
32 changes: 11 additions & 21 deletions cpu/cpu_arm64.go
Original file line number Diff line number Diff line change
Expand Up @@ -4,8 +4,6 @@

package cpu

import "runtime"

const cacheLineSize = 64

func initOptions() {
Expand Down Expand Up @@ -38,25 +36,8 @@ func initOptions() {
}

func archInit() {
switch runtime.GOOS {
case "freebsd":
readARM64Registers()
case "linux", "netbsd":
doinit()
default:
// Most platforms don't seem to allow reading these registers.
//
// OpenBSD:
// See https://golang.org/issue/31746
setMinimalFeatures()
}
}

// setMinimalFeatures fakes the minimal ARM64 features expected by
// TestARM64minimalFeatures.
func setMinimalFeatures() {
ARM64.HasASIMD = true
ARM64.HasFP = true
setMinimalFeatures()
osInit()
}

func readARM64Registers() {
Expand Down Expand Up @@ -170,3 +151,12 @@ func parseARM64SystemRegisters(isar0, isar1, pfr0 uint64) {
func extractBits(data uint64, start, end uint) uint {
return (uint)(data>>start) & ((1 << (end - start + 1)) - 1)
}

// setMinimalFeatures fakes the minimal ARM64 features expected by
// TestARM64minimalFeatures.
func setMinimalFeatures() {
ARM64.HasASIMD = true
ARM64.HasFP = true
}

func getMIDR() uint64
6 changes: 6 additions & 0 deletions cpu/cpu_arm64.s
Original file line number Diff line number Diff line change
Expand Up @@ -30,3 +30,9 @@ TEXT ·getpfr0(SB),NOSPLIT,$0-8
WORD $0xd5380400
MOVD R0, ret+0(FP)
RET

// func getMIDR() uint64
TEXT ·getMIDR(SB), NOSPLIT, $0-8
MRS MIDR_EL1, R0
MOVD R0, ret+0(FP)
RET
133 changes: 133 additions & 0 deletions cpu/cpu_darwin_arm64.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,133 @@
// Copyright 2021 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.

// +build arm64
// +build darwin
// +build !ios

package cpu

import (
"fmt"
"strings"
"syscall"
"unsafe"
)

func osInit() {
ARM64.HasFP = sysctlEnabled("hw.optional.floatingpoint")
ARM64.HasASIMD = sysctlEnabled("hw.optional.neon")
ARM64.HasCRC32 = sysctlEnabled("hw.optional.armv8_crc32")
ARM64.HasATOMICS = sysctlEnabled("hw.optional.armv8_1_atomics")
ARM64.HasFPHP = sysctlEnabled("hw.optional.neon_hpfp")
ARM64.HasASIMDHP = sysctlEnabled("hw.optional.floatingpoint")
ARM64.HasSHA3 = sysctlEnabled("hw.optional.armv8_2_sha3")
ARM64.HasSHA512 = sysctlEnabled("hw.optional.armv8_2_sha512")
ARM64.HasASIMDFHM = sysctlEnabled("hw.optional.armv8_2_fhm")

// There are no hw.optional sysctl values for the below features on Mac OS 11.0
// to detect their supported state dynamically. Assume the CPU features that
// Apple Silicon M1 supports to be available as a minimal set of features
// to all Go programs running on darwin/arm64.
ARM64.HasEVTSTRM = true
ARM64.HasAES = true
ARM64.HasPMULL = true
ARM64.HasSHA1 = true
ARM64.HasSHA2 = true
ARM64.HasCPUID = true
ARM64.HasASIMDRDM = true
ARM64.HasJSCVT = true
ARM64.HasFCMA = true
ARM64.HasLRCPC = true
ARM64.HasDCPOP = true
ARM64.HasSM3 = true
ARM64.HasSM4 = true
ARM64.HasASIMDDP = true
ARM64.HasSVE = true
}

// The following is minimal copy of functionality from x/sys/unix so the cpu package can call
// sysctl without depending on x/sys/unix.

func sysctlEnabled(name string, args ...int) bool {
mib, err := nametomib(name)
if err != nil {
return false
}

for _, a := range args {
mib = append(mib, _C_int(a))
}

// Find size.
n := uintptr(0)
if err := sysctl(mib, nil, &n, nil, 0); err != nil {
return false
}

return true
}

type _C_int int32

func sysctl(mib []_C_int, old *byte, oldlen *uintptr, new *byte, newlen uintptr) (err error) {
var _zero uintptr
var _p0 unsafe.Pointer
if len(mib) > 0 {
_p0 = unsafe.Pointer(&mib[0])
} else {
_p0 = unsafe.Pointer(&_zero)
}
_, _, errno := syscall.Syscall6(
syscall.SYS___SYSCTL,
uintptr(_p0),
uintptr(len(mib)),
uintptr(unsafe.Pointer(old)),
uintptr(unsafe.Pointer(oldlen)),
uintptr(unsafe.Pointer(new)),
uintptr(newlen))
if errno != 0 {
return errno
}
return nil
}

// nametomib is a copy from "unix.nametomib()" in "unix/syscall_darwin.go".
func nametomib(name string) (mib []_C_int, err error) {
const CTL_MAXNAME = 0xc
const siz = unsafe.Sizeof(mib[0])

// NOTE(rsc): It seems strange to set the buffer to have
// size CTL_MAXNAME+2 but use only CTL_MAXNAME
// as the size. I don't know why the +2 is here, but the
// kernel uses +2 for its own implementation of this function.
// I am scared that if we don't include the +2 here, the kernel
// will silently write 2 words farther than we specify
// and we'll get memory corruption.
var buf [CTL_MAXNAME + 2]_C_int
n := uintptr(CTL_MAXNAME) * siz

p := (*byte)(unsafe.Pointer(&buf[0]))
bytes, err := byteSliceFromString(name)
if err != nil {
return nil, err
}

// Magic sysctl: "setting" 0.3 to a string name
// lets you read back the array of integers form.
if err = sysctl([]_C_int{0, 3}, p, &n, &bytes[0], uintptr(len(name))); err != nil {
return nil, err
}
return buf[0 : n/siz], nil
}

// byteSliceFromString is a simple copy of "unix.ByteSliceFromString()"
func byteSliceFromString(s string) ([]byte, error) {
if strings.IndexByte(s, 0) != -1 {
return nil, fmt.Errorf("invalid argument in cpu.byteSliceFromString()")
}
a := make([]byte, len(s)+1)
copy(a, s)
return a, nil
}
12 changes: 12 additions & 0 deletions cpu/cpu_freebsd_arm64.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,12 @@
// Copyright 2021 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.

// +build arm64
// +build freebsd

package cpu

func osInit() {
readARM64Registers()
}
6 changes: 5 additions & 1 deletion cpu/cpu_linux_arm64.go
Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,10 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// +build arm64
// +build linux
// +build !android

package cpu

// HWCAP/HWCAP2 bits. These are exposed by Linux.
Expand Down Expand Up @@ -32,7 +36,7 @@ const (
hwcap_ASIMDFHM = 1 << 23
)

func doinit() {
func osInit() {
if err := readHWCAP(); err != nil {
// failed to read /proc/self/auxv, try reading registers directly
readARM64Registers()
Expand Down
8 changes: 5 additions & 3 deletions cpu/cpu_other_arm64.go
Original file line number Diff line number Diff line change
Expand Up @@ -2,9 +2,11 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

//go:build !linux && !netbsd && arm64
// +build !linux,!netbsd,arm64
//go:build !linux && !netbsd && !darwin && arm64
// +build !linux,!netbsd,!darwin,arm64

package cpu

func doinit() {}
func osInit() {
setMinimalFeatures()
}
2 changes: 1 addition & 1 deletion cpu/cpu_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -42,7 +42,7 @@ func TestAVX512HasAVX2AndAVX(t *testing.T) {
}

func TestARM64minimalFeatures(t *testing.T) {
if runtime.GOARCH != "arm64" || (runtime.GOOS == "darwin" || runtime.GOOS == "ios") {
if runtime.GOARCH != "arm64" || runtime.GOOS == "ios" {
return
}
if !cpu.ARM64.HasASIMD {
Expand Down

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