11.2: Multi-Line Macros

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Multi-line macros can include a varying number of lines (including one). The multi-line macros are more useful and the following sections will focus primarily on multi-line macros.

Macro Definition

Before using a multi-line macro, it must first be defined. The general format is as follows:

     %macro  <name>  <number of arguments>
       ; [body of macro]
     %endmacro

The arguments can be referenced within the macro by %<number>, with %1 being the first argument, and %2 the second argument, and so forth.

In order to use labels, the labels within the macro must be prefixing the label name with a %%.

This will ensure that calling the same macro multiple times will use a different label each time. For example, a macro definition for the absolute value function would be as follows:

     %macro  abs  1
           cmp  %1, 0
           jge %%done            
           neg  %1
     %%done:
     
     %endmacro

Refer to the sample macro program for a complete example.

Using a Macro

In order to use or “invoke” a macro, it must be placed in the code segment and referred to by name with the appropriate number of arguments.

Given a data declaration as follows:

      qVar     dq     4

Then, to invoke the “abs” macro (twice):

      mov     eax, -3 
      abs     eax 
      
      abs     qword [qVar]

The list file will display the code as follows (for the first invocation):

      27 00000000 B8FDFFFFFF         mov  eax, -3
      28                             abs  eax
      29 00000005 3D00000000  <1>  cmp %1, 0
      30 0000000A 7D02        <1>  jge %%done
      31 0000000C F7D8        <1>  neg %1
      32                      <1> %%done:

The macro will be copied from the definition into the code, with the appropriate arguments replaced in the body of the macro, each time it is used. The <1> indicates code copied from a macro definition. In both cases, the %1 argument was replaced with the given argument; eax in this example.

Macros use more memory, but do not require overhead for transfer of control (like functions).