runtime: get ppc64x ISA level and hardware capabilities from HWCAP/HWCAP2

This implements a check that can be done at runtime for the ISA level and
hardware capability. It follows the same implementation as in s390x.

These checks will be important as we enable new instructions and write go
asm implementations using those.

Updates #15403
Fixes #16643

Change-Id: Idfee374a3ffd7cf13a7d8cf0a6c83d247d3bee16
Reviewed-on: https://go-review.googlesource.com/32330Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/os_linux.go

@@ -184,6 +184,7 @@ const (
 	_AT_PAGESZ = 6  // System physical page size
 	_AT_HWCAP  = 16 // hardware capability bit vector
 	_AT_RANDOM = 25 // introduced in 2.6.29
+	_AT_HWCAP2 = 26 // hardware capability bit vector 2
 )
 
 func sysargs(argc int32, argv **byte) {

src/runtime/os_linux_noauxv.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !amd64,!arm,!arm64,!mips64,!mips64le,!s390x
+// +build !amd64,!arm,!arm64,!mips64,!mips64le,!s390x,!ppc64,!ppc64le
 
 package runtime
 

src/runtime/os_linux_ppc64x.go

+// Copyright 2016 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 ppc64 ppc64le
+
+package runtime
+
+import (
+	"runtime/internal/sys"
+)
+
+const (
+	// ISA level
+	// Go currently requires POWER5 as a minimum for ppc64, so we need
+	// to check for ISA 2.03 and beyond.
+	_PPC_FEATURE_POWER5_PLUS = 0x00020000 // ISA 2.03 (POWER5+)
+	_PPC_FEATURE_ARCH_2_05   = 0x00001000 // ISA 2.05 (POWER6)
+	_PPC_FEATURE_POWER6_EXT  = 0x00000200 // mffgpr/mftgpr extension (POWER6x)
+	_PPC_FEATURE_ARCH_2_06   = 0x00000100 // ISA 2.06 (POWER7)
+	_PPC_FEATURE2_ARCH_2_07  = 0x80000000 // ISA 2.07 (POWER8)
+
+	// Standalone capabilities
+	_PPC_FEATURE_HAS_ALTIVEC = 0x10000000 // SIMD/Vector unit
+	_PPC_FEATURE_HAS_VSX     = 0x00000080 // Vector scalar unit
+)
+
+type facilities struct {
+	_         [sys.CacheLineSize]byte
+	isPOWER5x bool // ISA 2.03
+	isPOWER6  bool // ISA 2.05
+	isPOWER6x bool // ISA 2.05 + mffgpr/mftgpr extension
+	isPOWER7  bool // ISA 2.06
+	isPOWER8  bool // ISA 2.07
+	hasVMX    bool // Vector unit
+	hasVSX    bool // Vector scalar unit
+	_         [sys.CacheLineSize]byte
+}
+
+// cpu can be tested at runtime in go assembler code to check for
+// a certain ISA level or hardware capability, for example:
+//	  ·cpu+facilities_hasVSX(SB) for checking the availability of VSX
+//	  or
+//	  ·cpu+facilities_isPOWER7(SB) for checking if the processor implements
+//	  ISA 2.06 instructions.
+var cpu facilities
+
+func archauxv(tag, val uintptr) {
+	switch tag {
+	case _AT_HWCAP:
+		cpu.isPOWER5x = val&_PPC_FEATURE_POWER5_PLUS != 0
+		cpu.isPOWER6 = val&_PPC_FEATURE_ARCH_2_05 != 0
+		cpu.isPOWER6x = val&_PPC_FEATURE_POWER6_EXT != 0
+		cpu.isPOWER7 = val&_PPC_FEATURE_ARCH_2_06 != 0
+		cpu.hasVMX = val&_PPC_FEATURE_HAS_ALTIVEC != 0
+		cpu.hasVSX = val&_PPC_FEATURE_HAS_VSX != 0
+	case _AT_HWCAP2:
+		cpu.isPOWER8 = val&_PPC_FEATURE2_ARCH_2_07 != 0
+	}
+}