section .data

%macro full_line 1
    times %1 db "X"
    db 0x0a
%endmacro

%macro hollow_line 1
    db "X"
    times %1-2 db " "
    db "X", 0x0a
%endmacro

%macro box 2 ; width, height
    full_line %1
    %rep %2
        hollow_line %1
    %endrep
    full_line %1
%endmacro

board:
    box 80, 25

board_size  equ     $ - board

section .text

global main

main:
    mov rax, 0x2000004          ; syscall: SYS_write
    mov rdi, 1                  ; file descriptor: STDOUT_FILENO
    mov rsi, board              ; buf
    mov rdx, board_size         ; nbytes
    syscall

    mov rax, 0x2000001          ; syscall: exit
    mov rdi, 0                  ; exit code
    syscall