section .data
title db "———————————————————————————————————————————"
    db 10, "ALP to reverse a given string"
    db 10, "———————————————————————————————————————————",10
title_len equ $-title

input db "Enter the string "
input_len equ $-input

output db 10, "Reverse string is "
output_len equ $-output

end db 10, "———————————————————————————————————————————",10
end_len equ $-end

section .bss
    string resb 50
    count resb 01
    reverse resb 01

%macro display 4
    mov rax,%1
    mov rdi,%2
    mov rsi,%3
    mov rdx,%4
    syscall
%endm

section .text
global _start
_start:
    display 1,1,title,title_len
    display 1,1,input,input_len
    display 0,0,string,50

    dec al
    mov [count],al

    display 1,1,output,output_len
    mov rcx,0
    mov rsi,string
    mov rdi,reverse
    mov cl,[count]
    add rsi,rcx
    sub rsi,1

up2:
    mov al,[rsi]
    mov [rdi],al
    inc rdi
    dec rsi
    loop up2
    display 1,1,reverse,count
    display 1,1,end,end_len

exit:
    mov rax,60
    mov rbx,0
    syscall

codeaft@codeaft:~$ nasm -felf64 codeaft.asm
codeaft@codeaft:~$ ld codeaft.o && ./a.out
———————————————————————————————————————————
ALP to reverse a given string
———————————————————————————————————————————
Enter the string CODEAFT

Reverse string is WODNIWGNIDOK
———————————————————————————————————————————
codeaft@codeaft:~$