.LINKAGE_PAIR causes a linkage pair to be stored at the current
    location counter. A linkage pair consists of two quadwords. The
    first quadword is the code entry point of the routine indicated
    by the specified identifier. The second quadword is the address
    of the procedure descriptor of the routine indicated by the
    specified identifier. The second quadword is also called the
    procedure value. The specified name should reference a procedure
    descriptor that is either defined within the assembly unit or
    that becomes defined at the time the program is linked.