runtime: move s390x HWCap CPU feature detection to internal/cpu

Change-Id: I7d9e31c3b342731ddd7329962426fdfc80e9ed87
Reviewed-on: https://go-review.googlesource.com/c/go/+/263803
Trust: Martin Möhrmann <moehrmann@google.com>
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

src/internal/cpu/cpu_s390x.go

@@ -6,6 +6,8 @@ package cpu
 
 const CacheLinePadSize = 256
 
+var HWCap uint
+
 // bitIsSet reports whether the bit at index is set. The bit index
 // is in big endian order, so bit index 0 is the leftmost bit.
 func bitIsSet(bits []uint64, index uint) bool {
@@ -95,8 +97,10 @@ const (
 	// vector facilities
 	vxe facility = 135 // vector-enhancements 1
 
-	// Note: vx and highgprs are excluded because they require
-	// kernel support and so must be fetched from HWCAP.
+	// Note: vx requires kernel support
+	// and so must be fetched from HWCAP.
+
+	hwcap_VX = 1 << 11 // vector facility
 )
 
 // facilityList contains the result of an STFLE call.
@@ -188,7 +192,14 @@ func doinit() {
 			S390X.HasEDDSA = kdsa.Has(eddsaVerifyEd25519, eddsaSignEd25519, eddsaVerifyEd448, eddsaSignEd448)
 		}
 	}
+
+	S390X.HasVX = isSet(HWCap, hwcap_VX)
+
 	if S390X.HasVX {
 		S390X.HasVXE = facilities.Has(vxe)
 	}
 }
+
+func isSet(hwc uint, value uint) bool {
+	return hwc&value != 0
+}

src/runtime/os_linux_s390x.go

@@ -6,15 +6,10 @@ package runtime
 
 import "internal/cpu"
 
-const (
-	// bit masks taken from bits/hwcap.h
-	_HWCAP_S390_VX = 2048 // vector facility
-)
-
 func archauxv(tag, val uintptr) {
 	switch tag {
-	case _AT_HWCAP: // CPU capability bit flags
-		cpu.S390X.HasVX = val&_HWCAP_S390_VX != 0
+	case _AT_HWCAP:
+		cpu.HWCap = uint(val)
 	}
 }