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// Copyright 2019 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
import (
"os"
)
const (
_AT_HWCAP = 16
_AT_HWCAP2 = 26
procAuxv = "/proc/self/auxv"
uintSize = int(32 << (^uint(0) >> 63))
)
// For those platforms don't have a 'cpuid' equivalent we use HWCAP/HWCAP2
// These are initialized in cpu_$GOARCH.go
// and should not be changed after they are initialized.
var hwCap uint
var hwCap2 uint
func readHWCAP() error {
// For Go 1.21+, get auxv from the Go runtime.
if a := getAuxv(); len(a) > 0 {
for len(a) >= 2 {
tag, val := a[0], uint(a[1])
a = a[2:]
switch tag {
case _AT_HWCAP:
hwCap = val
case _AT_HWCAP2:
hwCap2 = val
}
}
return nil
}
buf, err := os.ReadFile(procAuxv)
if err != nil {
// e.g. on android /proc/self/auxv is not accessible, so silently
// ignore the error and leave Initialized = false. On some
// architectures (e.g. arm64) doinit() implements a fallback
// readout and will set Initialized = true again.
return err
}
bo := hostByteOrder()
for len(buf) >= 2*(uintSize/8) {
var tag, val uint
switch uintSize {
case 32:
tag = uint(bo.Uint32(buf[0:]))
val = uint(bo.Uint32(buf[4:]))
buf = buf[8:]
case 64:
tag = uint(bo.Uint64(buf[0:]))
val = uint(bo.Uint64(buf[8:]))
buf = buf[16:]
}
switch tag {
case _AT_HWCAP:
hwCap = val
case _AT_HWCAP2:
hwCap2 = val
}
}
return nil
}
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