macros

Macros in Assembly

Macros in Assembly

Macros are reusable blocks of code that are substituted during assembly. They simplify repetitive tasks and improve code readability.

Defining a Macro

Macros are defined using the %macro directive, and invoked like regular instructions.

Syntax

%macro macro_name num_params
    ; Macro body
%endmacro

Example: Simple Macro

This macro writes a string to the screen using a system call.

%macro write_string 2
    mov rax, 1          ; System call: write
    mov rdi, 1          ; File descriptor: stdout
    mov rsi, %1         ; String address
    mov rdx, %2         ; String length
    syscall
%endmacro

section .data
    msg db 'Hello, Macro!', 0xA
    len equ $ - msg

section .text
    global _start

_start:
    write_string msg, len  ; Call the macro
    mov rax, 60            ; System call: exit
    xor rdi, rdi           ; Exit code: 0
    syscall

Example: Reusable Arithmetic Macro

This macro adds two numbers and stores the result in a register.

%macro add_two_numbers 3
    mov %1, %2      ; Move the first number to the target register
    add %1, %3      ; Add the second number
%endmacro

section .text
    global _start

_start:
    add_two_numbers rax, 5, 10 ; Adds 5 and 10, stores the result in rax
    mov rax, 60                ; System call: exit
    xor rdi, rdi               ; Exit code: 0
    syscall

Benefits of Macros