fibanocci in x64

fib_x64.s

# compile: gcc -o fib_x64 fib_x64.s -m64
# run: ./fib <number>
.global main
.data
    formatstr: .asciz "fib(%d)= %d\n"

main:
    push %r12
    movq 8(%rsi),%rdi
    call atoi

    movq %rax,%rdi
    movq %rax,%r12
    call fib

    movq $formatstr,%rdi
    movq %r12,%rsi
    movq %rax,%rdx
    movq $0,%rax
    call printf
    call exit
fib:
    push %rbp
	movq %rsp, %rbp

    cmpq $1,%rdi
    je fib_base
    cmpq $0,%rdi
    je fib_base

    decq %rdi
    push %rdi
    call fib
    pop %rdi
    subq $8, %rsp
    movq %rax, (%rsp)

    decq %rdi
    push %rdi
    call fib
    pop %rdi
    movq (%rsp), %rcx
    addq $8, %rsp
    addq %rcx,%rax
    leave
    ret
fib_base:
    movq $1,%rax
    leave
    ret