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(nasm.info)Section 4.3.1

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4.3.1. Overloading Multi-Line Macros
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   As with single-line macros, multi-line macros can be overloaded by
defining the same macro name several times with different numbers of
parameters.  This time, no exception is made for macros with no
parameters at all. So you could define

     %macro  prologue 0
     
             push    ebp
             mov     ebp,esp
     
     %endmacro

   to define an alternative form of the function prologue which
allocates no local stack space.

   Sometimes, however, you might want to `overload' a machine
instruction; for example, you might want to define

     %macro  push 2
     
             push    %1
             push    %2
     
     %endmacro

   so that you could code

             push    ebx             ; this line is not a macro call
             push    eax,ecx         ; but this one is

   Ordinarily, NASM will give a warning for the first of the above two
lines, since `push' is now defined to be a macro, and is being invoked
with a number of parameters for which no definition has been given. The
correct code will still be generated, but the assembler will give a
warning. This warning can be disabled by the use of the
`-w-macro-params' command- line option (see *Note Section 2.1.18::).