internal/cpu: detect cpu features in internal/cpu package

change hash/crc32 package to use cpu package instead of using
runtime internal variables to check crc32 instruction

Change-Id: I8f88d2351bde8ed4e256f9adf822a08b9a00f532
Reviewed-on: https://go-review.googlesource.com/76490
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>

2 files changed, 54 insertions, 5 deletions

diff --git a/src/internal/cpu/cpu.go b/src/internal/cpu/cpu.go
index 38fedc4e2b..22fc561002 100644
--- a/src/internal/cpu/cpu.go
+++ b/src/internal/cpu/cpu.go
@@ -57,3 +57,21 @@ type ppc64 struct {
 	IsPOWER9   bool // ISA v3.00 (POWER9)
 	_          [CacheLineSize]byte
 }
+
+var ARM64 arm64
+
+// The booleans in arm64 contain the correspondingly named cpu feature bit.
+// The struct is padded to avoid false sharing.
+type arm64 struct {
+	_          [CacheLineSize]byte
+	HasFP      bool
+	HasASIMD   bool
+	HasEVTSTRM bool
+	HasAES     bool
+	HasPMULL   bool
+	HasSHA1    bool
+	HasSHA2    bool
+	HasCRC32   bool
+	HasATOMICS bool
+	_          [CacheLineSize]byte
+}
diff --git a/src/internal/cpu/cpu_arm64.go b/src/internal/cpu/cpu_arm64.go
index 4d071b3a4e..e1278a147a 100644
--- a/src/internal/cpu/cpu_arm64.go
+++ b/src/internal/cpu/cpu_arm64.go
@@ -2,13 +2,44 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build arm64
+
 package cpu
 
 const CacheLineSize = 64
 
-// TODO: delete this once https://go-review.googlesource.com/c/go/+/76490 lands.
-// These will just be false for now.
-var ARM64 struct {
-	HasSHA1 bool
-	HasSHA2 bool
+// arm64 doesn't have a 'cpuid' equivalent, so we rely on HWCAP/HWCAP2.
+// These are linknamed in runtime/os_linux_arm64.go and are initialized by
+// archauxv().
+var arm64_hwcap uint
+var arm64_hwcap2 uint
+
+// HWCAP/HWCAP2 bits. These are exposed by Linux.
+const (
+	_ARM64_FEATURE_HAS_FP      = (1 << 0)
+	_ARM64_FEATURE_HAS_ASIMD   = (1 << 1)
+	_ARM64_FEATURE_HAS_EVTSTRM = (1 << 2)
+	_ARM64_FEATURE_HAS_AES     = (1 << 3)
+	_ARM64_FEATURE_HAS_PMULL   = (1 << 4)
+	_ARM64_FEATURE_HAS_SHA1    = (1 << 5)
+	_ARM64_FEATURE_HAS_SHA2    = (1 << 6)
+	_ARM64_FEATURE_HAS_CRC32   = (1 << 7)
+	_ARM64_FEATURE_HAS_ATOMICS = (1 << 8)
+)
+
+func init() {
+	// HWCAP feature bits
+	ARM64.HasFP = isSet(arm64_hwcap, _ARM64_FEATURE_HAS_FP)
+	ARM64.HasASIMD = isSet(arm64_hwcap, _ARM64_FEATURE_HAS_ASIMD)
+	ARM64.HasEVTSTRM = isSet(arm64_hwcap, _ARM64_FEATURE_HAS_EVTSTRM)
+	ARM64.HasAES = isSet(arm64_hwcap, _ARM64_FEATURE_HAS_AES)
+	ARM64.HasPMULL = isSet(arm64_hwcap, _ARM64_FEATURE_HAS_PMULL)
+	ARM64.HasSHA1 = isSet(arm64_hwcap, _ARM64_FEATURE_HAS_SHA1)
+	ARM64.HasSHA2 = isSet(arm64_hwcap, _ARM64_FEATURE_HAS_SHA2)
+	ARM64.HasCRC32 = isSet(arm64_hwcap, _ARM64_FEATURE_HAS_CRC32)
+	ARM64.HasATOMICS = isSet(arm64_hwcap, _ARM64_FEATURE_HAS_ATOMICS)
+}
+
+func isSet(hwc uint, value uint) bool {
+	return hwc&value != 0
 }