1// Copyright 2018 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//+build !amd64,!amd64p32,!386
6
7package cpu
8
9import (
10	"io/ioutil"
11)
12
13const (
14	_AT_HWCAP  = 16
15	_AT_HWCAP2 = 26
16
17	procAuxv = "/proc/self/auxv"
18
19	uintSize = int(32 << (^uint(0) >> 63))
20)
21
22// For those platforms don't have a 'cpuid' equivalent we use HWCAP/HWCAP2
23// These are initialized in cpu_$GOARCH.go
24// and should not be changed after they are initialized.
25var hwCap uint
26var hwCap2 uint
27
28func init() {
29	buf, err := ioutil.ReadFile(procAuxv)
30	if err != nil {
31		// e.g. on android /proc/self/auxv is not accessible, so silently
32		// ignore the error and leave Initialized = false
33		return
34	}
35
36	bo := hostByteOrder()
37	for len(buf) >= 2*(uintSize/8) {
38		var tag, val uint
39		switch uintSize {
40		case 32:
41			tag = uint(bo.Uint32(buf[0:]))
42			val = uint(bo.Uint32(buf[4:]))
43			buf = buf[8:]
44		case 64:
45			tag = uint(bo.Uint64(buf[0:]))
46			val = uint(bo.Uint64(buf[8:]))
47			buf = buf[16:]
48		}
49		switch tag {
50		case _AT_HWCAP:
51			hwCap = val
52		case _AT_HWCAP2:
53			hwCap2 = val
54		}
55	}
56	doinit()
57
58	Initialized = true
59}
60