You don't need to supply those arguments - functions that have form_id and form_values as arguments are hooks and are called directly by the system with the proper variables passed in.

For example, you could define your function like this:

function user_login_submit($form_id, $form_values) {
  print "The user login form was just submitted, with form id $form_id";
  print "The form values are:";
  print "<pre>"; print_r($form_values); print "</pre>";
  exit;
}

And when you submit the user login form, you should see how they are pre-populated.