func subdir() (pkgpath string, underGoRoot bool, err error) {
	cwd, err := os.Getwd()
	if err != nil {
		return "", false, err
	}
	cwd, err = filepath.EvalSymlinks(cwd)
	if err != nil {
		log.Fatal(err)
	}
	goroot, err := filepath.EvalSymlinks(runtime.GOROOT())
	if err != nil {
		return "", false, err
	}
	if strings.HasPrefix(cwd, goroot) {
		subdir, err := filepath.Rel(goroot, cwd)
		if err != nil {