hwcap_linux.go

     1  // Copyright 2019 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package cpu
     6  
     7  import (
     8  	"io/ioutil"
     9  )
    10  
    11  const (
    12  	_AT_HWCAP  = 16
    13  	_AT_HWCAP2 = 26
    14  
    15  	procAuxv = "/proc/self/auxv"
    16  
    17  	uintSize = int(32 << (^uint(0) >> 63))
    18  )
    19  
    20  // For those platforms don't have a 'cpuid' equivalent we use HWCAP/HWCAP2
    21  // These are initialized in cpu_$GOARCH.go
    22  // and should not be changed after they are initialized.
    23  var hwCap uint
    24  var hwCap2 uint
    25  
    26  func readHWCAP() error {
    27  	buf, err := ioutil.ReadFile(procAuxv)
    28  	if err != nil {
    29  		// e.g. on android /proc/self/auxv is not accessible, so silently
    30  		// ignore the error and leave Initialized = false. On some
    31  		// architectures (e.g. arm64) doinit() implements a fallback
    32  		// readout and will set Initialized = true again.
    33  		return err
    34  	}
    35  	bo := hostByteOrder()
    36  	for len(buf) >= 2*(uintSize/8) {
    37  		var tag, val uint
    38  		switch uintSize {
    39  		case 32:
    40  			tag = uint(bo.Uint32(buf[0:]))
    41  			val = uint(bo.Uint32(buf[4:]))
    42  			buf = buf[8:]
    43  		case 64:
    44  			tag = uint(bo.Uint64(buf[0:]))
    45  			val = uint(bo.Uint64(buf[8:]))
    46  			buf = buf[16:]
    47  		}
    48  		switch tag {
    49  		case _AT_HWCAP:
    50  			hwCap = val
    51  		case _AT_HWCAP2:
    52  			hwCap2 = val
    53  		}
    54  	}
    55  	return nil
    56  }
    57
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