1 // Copyright 2020 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 //go:build arm64 && linux 6 7 package cpu 8 9 import _ "unsafe" // for linkname 10 11 // HWCap may be initialized by archauxv and 12 // should not be changed after it was initialized. 13 // 14 // Other widely used packages 15 // access HWCap using linkname as well, most notably: 16 // - github.com/klauspost/cpuid/v2 17 // 18 // Do not remove or change the type signature. 19 // See go.dev/issue/67401. 20 // 21 //go:linkname HWCap 22 var HWCap uint 23 24 // HWCAP bits. These are exposed by Linux. 25 const ( 26 hwcap_AES = 1 << 3 27 hwcap_PMULL = 1 << 4 28 hwcap_SHA1 = 1 << 5 29 hwcap_SHA2 = 1 << 6 30 hwcap_CRC32 = 1 << 7 31 hwcap_ATOMICS = 1 << 8 32 hwcap_CPUID = 1 << 11 33 hwcap_SHA512 = 1 << 21 34 ) 35 36 func hwcapInit(os string) { 37 // HWCap was populated by the runtime from the auxiliary vector. 38 // Use HWCap information since reading aarch64 system registers 39 // is not supported in user space on older linux kernels. 40 ARM64.HasAES = isSet(HWCap, hwcap_AES) 41 ARM64.HasPMULL = isSet(HWCap, hwcap_PMULL) 42 ARM64.HasSHA1 = isSet(HWCap, hwcap_SHA1) 43 ARM64.HasSHA2 = isSet(HWCap, hwcap_SHA2) 44 ARM64.HasCRC32 = isSet(HWCap, hwcap_CRC32) 45 ARM64.HasCPUID = isSet(HWCap, hwcap_CPUID) 46 ARM64.HasSHA512 = isSet(HWCap, hwcap_SHA512) 47 48 // The Samsung S9+ kernel reports support for atomics, but not all cores 49 // actually support them, resulting in SIGILL. See issue #28431. 50 // TODO(elias.naur): Only disable the optimization on bad chipsets on android. 51 ARM64.HasATOMICS = isSet(HWCap, hwcap_ATOMICS) && os != "android" 52 53 // Check to see if executing on a Neoverse core and in order to do that, 54 // check the AUXV for the CPUID bit. The getMIDR function executes an 55 // instruction which would normally be an illegal instruction, but it's 56 // trapped by the kernel, the value sanitized and then returned. 57 // Without the CPUID bit the kernel will not trap the instruction and the 58 // process will be terminated with SIGILL. 59 if ARM64.HasCPUID { 60 midr := getMIDR() 61 part_num := uint16((midr >> 4) & 0xfff) 62 implementer := byte((midr >> 24) & 0xff) 63 64 // d0c - NeoverseN1 65 // d40 - NeoverseV1 66 // d49 - NeoverseN2 67 // d4f - NeoverseV2 68 if implementer == 'A' && (part_num == 0xd0c || part_num == 0xd40 || 69 part_num == 0xd49 || part_num == 0xd4f) { 70 ARM64.IsNeoverse = true 71 } 72 } 73 } 74 75 func isSet(hwc uint, value uint) bool { 76 return hwc&value != 0 77 } 78