fibonacci in asm(gas)

.section .text
.global main
.intel_syntax noprefix

# takes value in rdi and returns in rax
fib:
  cmp rdi, 1
  jl .br1                         # if (n < 1)
  je .br2                         # else if (n == 1)
  jmp .normal                     # else

.br1:
  mov rax, 0                      # return 0;
  ret

.br2:
  mov rax, 1                      # return 1;
  ret

.normal:
  # int x = fib(n - 1);
  push rdi
  sub rdi, 1
  call fib

  # int y = fib(n - 2);
  pop rdi
  sub rdi, 2
  push rax
  call fib

  # int result = x + y;
  mov rbx, rax
  pop rax
  add rbx, rax

  # return result;
  mov rax, rbx
  ret

main:
  push rbp
  mov rbp, rsp
  sub rsp, 16

  # printf("Enter n: ");
  lea rdi, qword ptr [rip+.fmt_prompt]
  xor rax, rax
  call printf@plt

  # scanf("%d", &n);
  lea rdi, qword ptr [rip+.fmt_scanf]
  lea rsi, qword ptr [rip+n]
  xor rax, rax
  call scanf@plt

  # int result = fib(n);
  mov rdi, qword ptr [rip+n]
  call fib@plt

  # printf("Fibonacci of %d is %d", n, result);
  lea rdi, qword ptr [rip+.fmt_printf]
  mov rsi, qword ptr [rip+n]
  mov rdx, rax
  xor rax, rax
  call printf@plt

  add rsp, 16
  pop rbp

  # return 0;
  xor rax, rax
  ret

.section .bss
n:
  .zero 8

.section .rodata
.fmt_prompt:
  .asciz "Enter n: "

.fmt_scanf:
  .asciz "%d"

.fmt_printf:
  .asciz "Fibonacci of %d is %d\n"