1 // Copyright 2015 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 arm64 6 7 package runtime 8 9 import "internal/cpu" 10 11 var randomNumber uint32 12 13 func archauxv(tag, val uintptr) { 14 switch tag { 15 case _AT_RANDOM: 16 // sysargs filled in startupRandomData, but that 17 // pointer may not be word aligned, so we must treat 18 // it as a byte array. 19 randomNumber = uint32(startupRandomData[4]) | uint32(startupRandomData[5])<<8 | 20 uint32(startupRandomData[6])<<16 | uint32(startupRandomData[7])<<24 21 22 case _AT_HWCAP: 23 // arm64 doesn't have a 'cpuid' instruction equivalent and relies on 24 // HWCAP/HWCAP2 bits for hardware capabilities. 25 hwcap := uint(val) 26 if GOOS == "android" { 27 // The Samsung S9+ kernel reports support for atomics, but not all cores 28 // actually support them, resulting in SIGILL. See issue #28431. 29 // TODO(elias.naur): Only disable the optimization on bad chipsets. 30 const hwcap_ATOMICS = 1 << 8 31 hwcap &= ^uint(hwcap_ATOMICS) 32 } 33 cpu.HWCap = hwcap 34 case _AT_HWCAP2: 35 cpu.HWCap2 = uint(val) 36 } 37 } 38 39 //go:nosplit 40 func cputicks() int64 { 41 // Currently cputicks() is used in blocking profiler and to seed fastrand(). 42 // nanotime() is a poor approximation of CPU ticks that is enough for the profiler. 43 // randomNumber provides better seeding of fastrand. 44 return nanotime() + int64(randomNumber) 45 } 46