runtime: initialise cpu.HWCap on netbsd/arm64

NetBSD does not supply AT_HWCAP, however we still need to initialise
cpu.HWCaps.  For now specify the bare minimum until we add some form of
capabilities detection. See
https://golang.org/issue/30824#issuecomment-494901591

Follows CL 174129 which did the same for openbsd/arm64.

Updates #30824

Change-Id: I43a86b583bc60d259a66772703de06970124bb7f
Reviewed-on: https://go-review.googlesource.com/c/go/+/257998
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Trust: Benny Siegert <bsiegert@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>

src/runtime/os_netbsd.go

@@ -359,6 +359,7 @@ func sysargs(argc int32, argv **byte) {
 	// now argv+n is auxv
 	auxv := (*[1 << 28]uintptr)(add(unsafe.Pointer(argv), uintptr(n)*sys.PtrSize))
 	sysauxv(auxv[:])
+	archauxv(auxv[:])
 }
 
 const (

src/runtime/os_netbsd_386.go

@@ -14,3 +14,6 @@ func lwp_mcontext_init(mc *mcontextt, stk unsafe.Pointer, mp *m, gp *g, fn uintp
 	mc.__gregs[_REG_EDX] = uint32(uintptr(unsafe.Pointer(gp)))
 	mc.__gregs[_REG_ESI] = uint32(fn)
 }
+
+func archauxv(auxv []uintptr) {
+}

src/runtime/os_netbsd_amd64.go

@@ -14,3 +14,6 @@ func lwp_mcontext_init(mc *mcontextt, stk unsafe.Pointer, mp *m, gp *g, fn uintp
 	mc.__gregs[_REG_R9] = uint64(uintptr(unsafe.Pointer(gp)))
 	mc.__gregs[_REG_R12] = uint64(fn)
 }
+
+func archauxv(auxv []uintptr) {
+}

src/runtime/os_netbsd_arm.go

@@ -32,3 +32,6 @@ func cputicks() int64 {
 	// runtime·nanotime() is a poor approximation of CPU ticks that is enough for the profiler.
 	return nanotime()
 }
+
+func archauxv(auxv []uintptr) {
+}

src/runtime/os_netbsd_arm64.go

@@ -4,7 +4,10 @@
 
 package runtime
 
-import "unsafe"
+import (
+	"internal/cpu"
+	"unsafe"
+)
 
 func lwp_mcontext_init(mc *mcontextt, stk unsafe.Pointer, mp *m, gp *g, fn uintptr) {
 	// Machine dependent mcontext initialisation for LWP.
@@ -21,3 +24,10 @@ func cputicks() int64 {
 	// runtime·nanotime() is a poor approximation of CPU ticks that is enough for the profiler.
 	return nanotime()
 }
+
+func archauxv(auxv []uintptr) {
+	// NetBSD does not supply AT_HWCAP, however we still need to initialise cpu.HWCaps.
+	// For now specify the bare minimum until we add some form of capabilities
+	// detection. See issue https://golang.org/issue/30824#issuecomment-494901591
+	cpu.HWCap = 1<<1 | 1<<0 // ASIMD, FP
+}