exec_copyin_args
error = exec_copyin_args(&args, uap->fname, uap->argv, uap->envv);
error = exec_copyin_args(&args, NULL, uap->argv, uap->envv);
error = exec_copyin_args(&args, uap->fname, uap->argv, uap->envv);
int exec_copyin_args(struct image_args *, const char *, char **, char **);