src/internal/cpu/cpu_x86.go

// 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.

//go:build 386 || amd64

package cpu

const CacheLinePadSize = 64

// cpuid is implemented in cpu_x86.s.
func cpuid(eaxArg, ecxArg uint32) (eax, ebx, ecx, edx uint32)

// xgetbv with ecx = 0 is implemented in cpu_x86.s.
func xgetbv() (eax, edx uint32)

// getGOAMD64level is implemented in cpu_x86.s. Returns number in [1,4].
func getGOAMD64level() int32

const (
	// edx bits
	cpuid_SSE2 = 1 << 26

	// ecx bits
	cpuid_SSE3      = 1 << 0
	cpuid_PCLMULQDQ = 1 << 1
	cpuid_SSSE3     = 1 << 9
	cpuid_FMA       = 1 << 12
	cpuid_SSE41     = 1 << 19
	cpuid_SSE42     = 1 << 20
	cpuid_POPCNT    = 1 << 23
	cpuid_AES       = 1 << 25
	cpuid_OSXSAVE   = 1 << 27
	cpuid_AVX       = 1 << 28

	// ebx bits
	cpuid_BMI1 = 1 << 3
	cpuid_AVX2 = 1 << 5
	cpuid_BMI2 = 1 << 8
	cpuid_ERMS = 1 << 9
	cpuid_ADX  = 1 << 19

	// edx bits for CPUID 0x80000001
	cpuid_RDTSCP = 1 << 27
)

var maxExtendedFunctionInformation uint32

func doinit() {
	options = []option{
		{Name: "adx", Feature: &X86.HasADX},
		{Name: "aes", Feature: &X86.HasAES},
		{Name: "erms", Feature: &X86.HasERMS},
		{Name: "pclmulqdq", Feature: &X86.HasPCLMULQDQ},
		{Name: "rdtscp", Feature: &X86.HasRDTSCP},
	}
	level := getGOAMD64level()
	if level < 2 {
		// These options are required at level 2. At lower levels
		// they can be turned off.
		options = append(options,
			option{Name: "popcnt", Feature: &X86.HasPOPCNT},
			option{Name: "sse3", Feature: &X86.HasSSE3},
			option{Name: "sse41", Feature: &X86.HasSSE41},
			option{Name: "sse42", Feature: &X86.HasSSE42},
			option{Name: "ssse3", Feature: &X86.HasSSSE3})
	}
	if level < 3 {
		// These options are required at level 3. At lower levels
		// they can be turned off.
		options = append(options,
			option{Name: "avx", Feature: &X86.HasAVX},
			option{Name: "avx2", Feature: &X86.HasAVX2},
			option{Name: "bmi1", Feature: &X86.HasBMI1},
			option{Name: "bmi2", Feature: &X86.HasBMI2},
			option{Name: "fma", Feature: &X86.HasFMA})
	}

	maxID, _, _, _ := cpuid(0, 0)

	if maxID < 1 {
		return
	}

	maxExtendedFunctionInformation, _, _, _ = cpuid(0x80000000, 0)

	_, _, ecx1, _ := cpuid(1, 0)

	X86.HasSSE3 = isSet(ecx1, cpuid_SSE3)
	X86.HasPCLMULQDQ = isSet(ecx1, cpuid_PCLMULQDQ)
	X86.HasSSSE3 = isSet(ecx1, cpuid_SSSE3)
	X86.HasSSE41 = isSet(ecx1, cpuid_SSE41)
	X86.HasSSE42 = isSet(ecx1, cpuid_SSE42)
	X86.HasPOPCNT = isSet(ecx1, cpuid_POPCNT)
	X86.HasAES = isSet(ecx1, cpuid_AES)

	// OSXSAVE can be false when using older Operating Systems
	// or when explicitly disabled on newer Operating Systems by
	// e.g. setting the xsavedisable boot option on Windows 10.
	X86.HasOSXSAVE = isSet(ecx1, cpuid_OSXSAVE)

	// The FMA instruction set extension only has VEX prefixed instructions.
	// VEX prefixed instructions require OSXSAVE to be enabled.
	// See Intel 64 and IA-32 Architecture Software Developer’s Manual Volume 2
	// Section 2.4 "AVX and SSE Instruction Exception Specification"
	X86.HasFMA = isSet(ecx1, cpuid_FMA) && X86.HasOSXSAVE

	osSupportsAVX := false
	// For XGETBV, OSXSAVE bit is required and sufficient.
	if X86.HasOSXSAVE {
		eax, _ := xgetbv()
		// Check if XMM and YMM registers have OS support.
		osSupportsAVX = isSet(eax, 1<<1) && isSet(eax, 1<<2)
	}

	X86.HasAVX = isSet(ecx1, cpuid_AVX) && osSupportsAVX

	if maxID < 7 {
		return
	}

	_, ebx7, _, _ := cpuid(7, 0)
	X86.HasBMI1 = isSet(ebx7, cpuid_BMI1)
	X86.HasAVX2 = isSet(ebx7, cpuid_AVX2) && osSupportsAVX
	X86.HasBMI2 = isSet(ebx7, cpuid_BMI2)
	X86.HasERMS = isSet(ebx7, cpuid_ERMS)
	X86.HasADX = isSet(ebx7, cpuid_ADX)

	var maxExtendedInformation uint32
	maxExtendedInformation, _, _, _ = cpuid(0x80000000, 0)

	if maxExtendedInformation < 0x80000001 {
		return
	}

	_, _, _, edxExt1 := cpuid(0x80000001, 0)
	X86.HasRDTSCP = isSet(edxExt1, cpuid_RDTSCP)
}

func isSet(hwc uint32, value uint32) bool {
	return hwc&value != 0
}

// Name returns the CPU name given by the vendor.
// If the CPU name can not be determined an
// empty string is returned.
func Name() string {
	if maxExtendedFunctionInformation < 0x80000004 {
		return ""
	}

	data := make([]byte, 0, 3*4*4)

	var eax, ebx, ecx, edx uint32
	eax, ebx, ecx, edx = cpuid(0x80000002, 0)
	data = appendBytes(data, eax, ebx, ecx, edx)
	eax, ebx, ecx, edx = cpuid(0x80000003, 0)
	data = appendBytes(data, eax, ebx, ecx, edx)
	eax, ebx, ecx, edx = cpuid(0x80000004, 0)
	data = appendBytes(data, eax, ebx, ecx, edx)

	// Trim leading spaces.
	for len(data) > 0 && data[0] == ' ' {
		data = data[1:]
	}

	// Trim tail after and including the first null byte.
	for i, c := range data {
		if c == '\x00' {
			data = data[:i]
			break
		}
	}

	return string(data)
}

func appendBytes(b []byte, args ...uint32) []byte {
	for _, arg := range args {
		b = append(b,
			byte((arg >> 0)),
			byte((arg >> 8)),
			byte((arg >> 16)),
			byte((arg >> 24)))
	}
	return b
}