Calling my native functions

[Gustavo Castro]

Hello, i know this must be the dumbest question by far (i think i´m even blushing
myself), but how do i call my own native functions? i did all the steps in the
item_create.* and the item_func.* but when call it from the mysql prompt i always get a
sintax error, even if i call some function of their own like abs which is also defined in
those files. My function is called get_update and it is almost the same as the abs
function.
Thanks!