internal/cpu: consolidate arm64 feature detection

Move code to detect and mask arm64 CPU features from
runtime to internal/cpu.

Change-Id: Ib784e2ff056e8def125d68827b852f07a3eff0db
Reviewed-on: https://go-review.googlesource.com/c/go/+/261878
Trust: Martin Möhrmann <moehrmann@google.com>
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Benny Siegert <bsiegert@gmail.com>

6 files changed, 107 insertions, 12 deletions

diff --git a/src/internal/cpu/cpu_android.go b/src/internal/cpu/cpu_android.go
new file mode 100644
index 0000000000..d995e8d5a7
--- /dev/null
+++ b/src/internal/cpu/cpu_android.go
@@ -0,0 +1,7 @@
+// Copyright 2020 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
+
+const GOOS = "android"
diff --git a/src/internal/cpu/cpu_arm64.go b/src/internal/cpu/cpu_arm64.go
index d9e0c98ca6..533bea2470 100644
--- a/src/internal/cpu/cpu_arm64.go
+++ b/src/internal/cpu/cpu_arm64.go
@@ -6,13 +6,11 @@ package cpu
 
 const CacheLinePadSize = 64
 
-// arm64 doesn't have a 'cpuid' equivalent, so we rely on HWCAP/HWCAP2.
-// These are initialized by archauxv and should not be changed after they are
-// initialized.
+// HWCap may be initialized by archauxv and
+// should not be changed after it was initialized.
 var HWCap uint
-var HWCap2 uint
 
-// HWCAP/HWCAP2 bits. These are exposed by Linux.
+// HWCAP bits. These are exposed by Linux.
 const (
 	hwcap_AES     = 1 << 3
 	hwcap_PMULL   = 1 << 4
@@ -32,15 +30,66 @@ func doinit() {
 		{Name: "atomics", Feature: &ARM64.HasATOMICS},
 	}
 
-	// HWCAP feature bits
-	ARM64.HasAES = isSet(HWCap, hwcap_AES)
-	ARM64.HasPMULL = isSet(HWCap, hwcap_PMULL)
-	ARM64.HasSHA1 = isSet(HWCap, hwcap_SHA1)
-	ARM64.HasSHA2 = isSet(HWCap, hwcap_SHA2)
-	ARM64.HasCRC32 = isSet(HWCap, hwcap_CRC32)
-	ARM64.HasATOMICS = isSet(HWCap, hwcap_ATOMICS)
+	switch GOOS {
+	case "linux", "android":
+		// HWCap was populated by the runtime from the auxillary vector.
+		// Use HWCap information since reading aarch64 system registers
+		// is not supported in user space on older linux kernels.
+		ARM64.HasAES = isSet(HWCap, hwcap_AES)
+		ARM64.HasPMULL = isSet(HWCap, hwcap_PMULL)
+		ARM64.HasSHA1 = isSet(HWCap, hwcap_SHA1)
+		ARM64.HasSHA2 = isSet(HWCap, hwcap_SHA2)
+		ARM64.HasCRC32 = isSet(HWCap, hwcap_CRC32)
+
+		// The Samsung S9+ kernel reports support for atomics, but not all cores
+		// actually support them, resulting in SIGILL. See issue #28431.
+		// TODO(elias.naur): Only disable the optimization on bad chipsets on android.
+		ARM64.HasATOMICS = isSet(HWCap, hwcap_ATOMICS) && GOOS != "android"
+
+	case "freebsd":
+		// Retrieve info from system register ID_AA64ISAR0_EL1.
+		isar0 := getisar0()
+
+		// ID_AA64ISAR0_EL1
+		switch extractBits(isar0, 4, 7) {
+		case 1:
+			ARM64.HasAES = true
+		case 2:
+			ARM64.HasAES = true
+			ARM64.HasPMULL = true
+		}
+
+		switch extractBits(isar0, 8, 11) {
+		case 1:
+			ARM64.HasSHA1 = true
+		}
+
+		switch extractBits(isar0, 12, 15) {
+		case 1, 2:
+			ARM64.HasSHA2 = true
+		}
+
+		switch extractBits(isar0, 16, 19) {
+		case 1:
+			ARM64.HasCRC32 = true
+		}
+
+		switch extractBits(isar0, 20, 23) {
+		case 2:
+			ARM64.HasATOMICS = true
+		}
+	default:
+		// Other operating systems do not support reading HWCap from auxillary vector
+		// or reading privileged aarch64 system registers in user space.
+	}
+}
+
+func extractBits(data uint64, start, end uint) uint {
+	return (uint)(data>>start) & ((1 << (end - start + 1)) - 1)
 }
 
 func isSet(hwc uint, value uint) bool {
 	return hwc&value != 0
 }
+
+func getisar0() uint64
diff --git a/src/internal/cpu/cpu_arm64.s b/src/internal/cpu/cpu_arm64.s
new file mode 100644
index 0000000000..d85914973f
--- /dev/null
+++ b/src/internal/cpu/cpu_arm64.s
@@ -0,0 +1,12 @@
+// Copyright 2020 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.
+
+#include "textflag.h"
+
+// func getisar0() uint64
+TEXT ·getisar0(SB),NOSPLIT,$0
+	// get Instruction Set Attributes 0 into R0
+	MRS	ID_AA64ISAR0_EL1, R0
+	MOVD	R0, ret+0(FP)
+	RET
diff --git a/src/internal/cpu/cpu_freebsd.go b/src/internal/cpu/cpu_freebsd.go
new file mode 100644
index 0000000000..dc37173dac
--- /dev/null
+++ b/src/internal/cpu/cpu_freebsd.go
@@ -0,0 +1,7 @@
+// Copyright 2020 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
+
+const GOOS = "freebsd"
diff --git a/src/internal/cpu/cpu_linux.go b/src/internal/cpu/cpu_linux.go
new file mode 100644
index 0000000000..ec0b84c510
--- /dev/null
+++ b/src/internal/cpu/cpu_linux.go
@@ -0,0 +1,9 @@
+// Copyright 2020 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.
+
+// +build !android
+
+package cpu
+
+const GOOS = "linux"
diff --git a/src/internal/cpu/cpu_other.go b/src/internal/cpu/cpu_other.go
new file mode 100644
index 0000000000..8a15fbe79d
--- /dev/null
+++ b/src/internal/cpu/cpu_other.go
@@ -0,0 +1,11 @@
+// Copyright 2020 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.
+
+// +build !linux
+// +build !freebsd
+// +build !android
+
+package cpu
+
+const GOOS = "other"