section .data

codes: db '0123456789ABCDEF'

section .text

global print_hex
print_hex:
    mov  rdi, 1
    mov  rdx, 1
    mov  rcx, 64
    .loop:
    push rax
    sub  rcx, 4
    sar  rax, cl
    and  rax, 0xf
    lea  rsi, [codes + rax]
    mov  rax, 1
    push rcx
    syscall
    pop  rcx
    pop rax
    test rcx, rcx
    jnz .loop
    ret