.PROCEDURE_DESCRIPTOR defines a bivalued global identifier
    that is used to represent a global routine. The first value
    is the procedure value, which is the address of the procedure
    descriptor. This value is defined as the current location counter
    at the point where you use the .PROCEDURE_DESCRIPTOR directive.
    The second value is the code address, which is the code entry-
    point address of the procedure. This value is defined by the
    second argument to the .PROCEDURE_DESCRIPTOR directive. No
    storage is allocated.