internal/syscall/windows: add GetModuleFileName

For os.Executable. Updates #12773.

Change-Id: Iff6593514b7453b6c5e1f20079e35cb4992cc74a
Reviewed-on: https://go-review.googlesource.com/32877Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/internal/syscall/windows/syscall_windows.go

@@ -110,6 +110,7 @@ const (
 //sys	GetAdaptersAddresses(family uint32, flags uint32, reserved uintptr, adapterAddresses *IpAdapterAddresses, sizePointer *uint32) (errcode error) = iphlpapi.GetAdaptersAddresses
 //sys	GetComputerNameEx(nameformat uint32, buf *uint16, n *uint32) (err error) = GetComputerNameExW
 //sys	MoveFileEx(from *uint16, to *uint16, flags uint32) (err error) = MoveFileExW
+//sys	GetModuleFileName(module syscall.Handle, fn *uint16, len uint32) (n uint32, err error) = kernel32.GetModuleFileNameW
 
 const (
 	ComputerNameNetBIOS                   = 0

src/internal/syscall/windows/zsyscall_windows.go

@@ -44,6 +44,7 @@ var (
 	procGetAdaptersAddresses  = modiphlpapi.NewProc("GetAdaptersAddresses")
 	procGetComputerNameExW    = modkernel32.NewProc("GetComputerNameExW")
 	procMoveFileExW           = modkernel32.NewProc("MoveFileExW")
+	procGetModuleFileNameW    = modkernel32.NewProc("GetModuleFileNameW")
 	procGetACP                = modkernel32.NewProc("GetACP")
 	procGetConsoleCP          = modkernel32.NewProc("GetConsoleCP")
 	procMultiByteToWideChar   = modkernel32.NewProc("MultiByteToWideChar")
@@ -89,6 +90,19 @@ func MoveFileEx(from *uint16, to *uint16, flags uint32) (err error) {
 	return
 }
 
+func GetModuleFileName(module syscall.Handle, fn *uint16, len uint32) (n uint32, err error) {
+	r0, _, e1 := syscall.Syscall(procGetModuleFileNameW.Addr(), 3, uintptr(module), uintptr(unsafe.Pointer(fn)), uintptr(len))
+	n = uint32(r0)
+	if n == 0 {
+		if e1 != 0 {
+			err = errnoErr(e1)
+		} else {
+			err = syscall.EINVAL
+		}
+	}
+	return
+}
+
 func GetACP() (acp uint32) {
 	r0, _, _ := syscall.Syscall(procGetACP.Addr(), 0, 0, 0, 0)
 	acp = uint32(r0)