runtime: parse auxv for page size on netbsd

Decode AT_PAGESZ to determine physPageSize on netbsd.

Also rename vdso_none.go to auxv_none.go which matches its purpose more
closely.

Akin to CL 99780 which did the same for freebsd.

Change-Id: Iea4322f861ff0f3515e9051585dbb442f024326b
Reviewed-on: https://go-review.googlesource.com/102677
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/vdso_none.go → src/runtime/auxv_none.go

@@ -5,6 +5,7 @@
 // +build !linux
 // +build !darwin
 // +build !freebsd
+// +build !netbsd
 
 package runtime
 

src/runtime/os_netbsd.go

@@ -6,6 +6,7 @@ package runtime
 
 import (
 	"runtime/internal/atomic"
+	"runtime/internal/sys"
 	"unsafe"
 )
 
@@ -223,7 +224,9 @@ func netbsdMstart() {
 
 func osinit() {
 	ncpu = getncpu()
-	physPageSize = getPageSize()
+	if physPageSize == 0 {
+		physPageSize = getPageSize()
+	}
 }
 
 var urandom_dev = []byte("/dev/urandom\x00")
@@ -325,3 +328,34 @@ func sigdelset(mask *sigset, i int) {
 
 func (c *sigctxt) fixsigcode(sig uint32) {
 }
+
+func sysargs(argc int32, argv **byte) {
+	n := argc + 1
+
+	// skip over argv, envp to get to auxv
+	for argv_index(argv, n) != nil {
+		n++
+	}
+
+	// skip NULL separator
+	n++
+
+	// now argv+n is auxv
+	auxv := (*[1 << 28]uintptr)(add(unsafe.Pointer(argv), uintptr(n)*sys.PtrSize))
+	sysauxv(auxv[:])
+}
+
+const (
+	_AT_NULL   = 0 // Terminates the vector
+	_AT_PAGESZ = 6 // Page size in bytes
+)
+
+func sysauxv(auxv []uintptr) {
+	for i := 0; auxv[i] != _AT_NULL; i += 2 {
+		tag, val := auxv[i], auxv[i+1]
+		switch tag {
+		case _AT_PAGESZ:
+			physPageSize = val
+		}
+	}
+}