| // 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 ( |
| "io/ioutil" |
| ) |
| |
| 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 := ioutil.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 |
| } |