Macros can be nested, i.e., a macro may invoke another macro. When macros are expanded, the nesting level is shown on the left of each expanded statement.

Example: Let us write a macro to copy a string using two other macros to save and restore registers.

SAVE_REGS MACRO R1, R2, R3

PUSH R1

PUSH R2

PUSH R3

ENDM

RESTORE_REGS MACRO R1, R2, R3

POP R1

POP R2

POP R3

ENDM

COPYS MACRO SOURCE, DESTINATION, LENGTH

SAVE_REGS CX, SI, DI

LEA SI, SOURCE

LEA DI, DESTINATION

CLD

MOV CX, LENGTH

REP MOVSB

RESTORE_REGS DI, SI, CX

ENDM

Example: Show the code that the assembler will generate when it encounters the macro invocation COPYS STRING1, STRING2, 15.

PUSH CX

PUSH SI

PUSH DI

LEA SI, STRING1

LEA DI, STRING2

CLD

MOV CX, 15

REP MOVSB

POP DI

POP SI

POP CX

Recursive Macros

A macro may invoke itself; such macros are called recursive macros.