Recursive Fibonacci in MASM Assembly

Question

So I am creating a program to give the nth term of the Fibonacci sequence. I am supposed to implement the following logic using recursive MASM assembly.

int fib(int n){ 
 if ((n == 1) || (n == 2)) 
     return n - 1; 
 else 
     return fib(n-1) + fib(n-2); 
}

The issue I seem to be having is retaining the values as the program cycles through until reaching 1. I am fairly unexperienced with recursion and I feel like I am missing something in that aspect. I am not sure how to retain the values to add them.

.code
main PROC
    mov ecx,0
    push 4          ; calculate the nth fib
    call Fib            ; calculate fib (eax)
    call WriteDec
    call Crlf
    exit
main ENDP

Fib PROC
    add ecx,1
    push ebp
    mov  ebp,esp
    mov  eax,[ebp+8]    ; get n
    cmp  eax,2      ; n == 2?
    je   exception2     
    cmp  eax,1      ; n == 1?
    je   exception2         
    dec eax
    push eax            ; Fib(n-1)
    call fib

    add eax,
    jmp Quit


Exception2:
    dec eax
Quit:
    pop  ebp            ; return EAX
    ret  4          ; clean up stack
Fib ENDP

END main

Answer 1

At the end of the procedure you must restore ESP not only EBP.

ret 4 (stdcall) is in this case not convenient because you can reuse the value on the stack for the second call.

For the result of the first call you can use a local variable which will be created on the "current" stack.

Don't mix lower and upper case in symbols even if an OPTION-directive allows it!

I changed your code accordingly:

include Irvine32.inc

.code
main PROC
    mov ecx,0
    push 10             ; calculate the nth fib
    call fib            ; calculate fib (eax)
    add esp, 4          ; clean up the stack

    call WriteDec
    call Crlf
    exit
main ENDP

fib PROC C
    add ecx,1
    push ebp
    mov  ebp,esp
    sub  esp, 4         ; space for a local dword [ebp-4]
    mov  eax,[ebp+8]    ; get n

    ; if ((n == 1) || (n == 2)) return 1;
    cmp  eax,2          ; n == 2?
    je   exception2
    cmp  eax,1          ; n == 1?
    je   exception2

    ;else return fib(n-1) + fib(n-2);
    dec eax
    push eax            ; Fib(n-1)
    call fib
    mov [ebp-4], eax    ; store first result

    dec dword ptr [esp] ; (n-1) on the stack -> (n-2)
    call fib
    add esp, 4          ; clean up stack

    add eax, [ebp-4]    ; add result and stored first result

    jmp Quit

exception2:
    mov eax, 1          ; start values: 1, 1
    ; dec eax           ; start values: 0, 1
Quit:
    mov esp, ebp        ; restore esp
    pop ebp             ; restore ebp

    ret                 ; return EAX, stack not cleaned up
fib ENDP

END main