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 // For go:linkname 10 import _ "unsafe" 11 12 var randomNumber uint32 13 14 // arm64 doesn't have a 'cpuid' instruction equivalent and relies on 15 // HWCAP/HWCAP2 bits for hardware capabilities. 16 17 //go:linkname cpu_hwcap internal/cpu.arm64_hwcap 18 //go:linkname cpu_hwcap2 internal/cpu.arm64_hwcap2 19 var cpu_hwcap uint 20 var cpu_hwcap2 uint 21 22 func archauxv(tag, val uintptr) { 23 switch tag { 24 case _AT_RANDOM: 25 // sysargs filled in startupRandomData, but that 26 // pointer may not be word aligned, so we must treat 27 // it as a byte array. 28 randomNumber = uint32(startupRandomData[4]) | uint32(startupRandomData[5])<<8 | 29 uint32(startupRandomData[6])<<16 | uint32(startupRandomData[7])<<24 30 case _AT_HWCAP: 31 cpu_hwcap = uint(val) 32 case _AT_HWCAP2: 33 cpu_hwcap2 = uint(val) 34 } 35 } 36 37 //go:nosplit 38 func cputicks() int64 { 39 // Currently cputicks() is used in blocking profiler and to seed fastrand(). 40 // nanotime() is a poor approximation of CPU ticks that is enough for the profiler. 41 // randomNumber provides better seeding of fastrand. 42 return nanotime() + int64(randomNumber) 43 } 44
