VMS Help System Services, $CMEXEC 64 (Alpha Only), Arguments  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 routin_64

    OpenVMS usage:procedure
    type:         procedure value
    access:       call without stack unwinding
    mechanism:    by 32- or 64-bit reference
    Routine to be executed while the process is in executive mode.
    The routin_64 argument is the 32- or 64-bit address of this
    routine.

 arglst_64

    OpenVMS usage:arg_list
    type:         quadword (unsigned)
    access:       read only
    mechanism:    by 32- or 64-bit reference
    Argument list to be passed to the routine specified by the
    routin_64 argument. The arglst_64 argument is the 32- or 64-bit
    address of this argument list.

    If the arglst value is nonzero and is not accessible as an
    address or if the routine is inaccessible, the service returns
    SS$_ACCVIO.

    Alpha systems require a pointer to a valid argument list or a
    value of 0 in the arglst_64 argument. This means that the arglst_
    64 argument, if nonzero, must contain an accessible virtual
    address for an argument list, the first quadword of which must
    be a number between 0 and 255 specifying the number of quadwords
    that follow it on the list.