syscall: support windows/arm

Updates #26148

Change-Id: I008502232642237270b7c8a2efb4a378345d06fd
Reviewed-on: https://go-review.googlesource.com/128716
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/syscall/syscall_windows.go

@@ -9,6 +9,7 @@ package syscall
 import (
 	errorspkg "errors"
 	"internal/race"
+	"runtime"
 	"sync"
 	"unicode/utf16"
 	"unsafe"
@@ -340,12 +341,19 @@ const ptrSize = unsafe.Sizeof(uintptr(0))
 // See https://msdn.microsoft.com/en-us/library/windows/desktop/aa365542(v=vs.85).aspx
 func setFilePointerEx(handle Handle, distToMove int64, newFilePointer *int64, whence uint32) error {
 	var e1 Errno
-	if ptrSize == 8 {
+	switch runtime.GOARCH {
+	default:
+		panic("unsupported architecture")
+	case "amd64":
 		_, _, e1 = Syscall6(procSetFilePointerEx.Addr(), 4, uintptr(handle), uintptr(distToMove), uintptr(unsafe.Pointer(newFilePointer)), uintptr(whence), 0, 0)
-	} else {
+	case "386":
 		// distToMove is a LARGE_INTEGER:
 		// https://msdn.microsoft.com/en-us/library/windows/desktop/aa383713(v=vs.85).aspx
 		_, _, e1 = Syscall6(procSetFilePointerEx.Addr(), 5, uintptr(handle), uintptr(distToMove), uintptr(distToMove>>32), uintptr(unsafe.Pointer(newFilePointer)), uintptr(whence), 0)
+	case "arm":
+		// distToMove must be 8-byte aligned per ARM calling convention
+		// https://msdn.microsoft.com/en-us/library/dn736986.aspx#Anchor_7
+		_, _, e1 = Syscall6(procSetFilePointerEx.Addr(), 6, uintptr(handle), 0, uintptr(distToMove), uintptr(distToMove>>32), uintptr(unsafe.Pointer(newFilePointer)), uintptr(whence))
 	}
 	if e1 != 0 {
 		return errnoErr(e1)

src/syscall/types_windows_arm.go

+// Copyright 2018 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 syscall
+
+type WSAData struct {
+	Version      uint16
+	HighVersion  uint16
+	Description  [WSADESCRIPTION_LEN + 1]byte
+	SystemStatus [WSASYS_STATUS_LEN + 1]byte
+	MaxSockets   uint16
+	MaxUdpDg     uint16
+	VendorInfo   *byte
+}
+
+type Servent struct {
+	Name    *byte
+	Aliases **byte
+	Port    uint16
+	Proto   *byte
+}