Recursion

Recall

Recursion is when a function calls itself.

int sum(int length, int [] arr, int index){
    if (index==length) return 0;
    return arr[index] +  sum(length, arr, index+1); 
}

In x86, it follows the same idea, however you need to consider the aspects of a function.

First, remember which variables are preserved and which are temporary. If you use rax in your function, and it calls itself, it will overwrite your previous rax. Thus, you may need to preserve certain registers before calling.

Additionally, you must preserve the

Example

Caution: The following example is unchecked and may be incorrect. Verify important info.

global sum
	sum:
	push rbp
	mov rbp, rsi
	push r12
	;  if (index == length)
	cmp edx, edi
	jne nonBaseCase
	; return 0
	mov eax, 0 
	jmp prologue
	nonBaseCase:
	; return arr[index] + sum(length, arr, index+1)
	push rdx
	inc edx
	call sum
	pop rdx
	mov r10, eax
	mov eax, dword[rdi+rax*8]
	add eax, 10
	prologue:
	pop r12
	pop rbp
	ret