This section discusses some programming considerations you need
    to be aware of when using the calling-standard macros.

1  –  Making Multiple Calls From the Same Routine

    The $CALL macro generates the following instruction sequence:

     LDQ R26, code_address_offset(Rls)              ; load code address
     LDQ R27, procedure_descriptor_address_offset(Rls) ; load procedure
                                                       ;    descriptor
                                                       ;    address
     JSR R26, R26                                      ;

    The contents of R26 and R27 are erased as a result of using the
    $CALL macro. This is important since Rls in the previous sequence
    is typically R27. Thus, if you require subsequent access to your
    linkage section, such as when making subsequent calls, you need
    to make a working copy of R27 to use after the first call.

    Note that $CALL also overwrites the values in the argument
    registers, and the scratch registers specified or the default
    set by the SCRATCH_REGS argument, when you pass arguments to the
    called routine.

2  –  Nonstandard Linkage

    Under certain circumstances, there may be advantages in using a
    nonstandard routine linkage.

3  –  Routine Restrictions

    Different routine types have different capabilities and
    restrictions. For example, only a stack routine that specifies
    BASE_REG_IS_FP=TRUE can make standard calls.

4  –  Syntax Rules

    You can use either positional or keyword argument association
    or a combination of the two with these macros. For positional
    association, the order of formal arguments is shown with
    the format of each macro. The following syntax rules apply
    when invoking the assembler using the command-line qualifier
    /NAMES=AS_IS:

    o  When specifying macro names, you must use all uppercase or all
       lowercase characters. You cannot mix uppercase and lowercase
       characters.

    o  When specifying keyword arguments, you must use the same
       alphabetic case as the macro name it is associated with. If
       you use lowercase characters with the macro name, you must
       use lowercase characters with the keyword argument. If you
       use uppercase characters with the macro name, you must use
       uppercase characters with the keyword argument.