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