VMS Help MACRO, /MIGRATION, Macros for 64-Bit Addressing, $CALL64, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    This macro calls the specified routine, assuming $SETUP_CALL64
    has been used to specify the argument count, and $PUSH_ARG64 has
    been used to push the quadword arguments. This macro checks that
    the number of pushes matches what was specified in the setup
    call.

    The call_target operand must not be AP- or SP-based.

    The macros in this section are used for checking certain values
    and directing program flow based on the outcome of the check.