Recursion in Assembly Language

Recursion in assembly language involves a subroutine or function calling itself. Implementing recursion in assembly requires careful management of the stack since each recursive call needs its own set of local variables and a return address. Below is a simple example of recursion in x86 assembly language using the NASM syntax. This example calculates the factorial of a number:

assembly
Copy code
section .data
n db 5 ; Factorial of 5

section .text
global _start

_start:
; Set up parameters and call the recursive function
mov eax, 1 ; Initialize the result to 1
mov ecx, n ; Set the value for which factorial is to be calculated
call factorial

; Result is in eax, you can use it as needed

; Exit the program
mov eax, 1 ; syscall number for sys_exit
xor ebx, ebx ; return code 0
int 0x80 ; make syscall

factorial:
; Check for the base case (n == 0)
cmp ecx, 0
je .base_case

; Save registers that will be modified
push eax
push ecx

; Recursive call: factorial(n-1)
dec ecx
call factorial

; Multiply the result by n
pop ecx
imul eax, ecx

; Restore registers
pop eax

; Return from the subroutine
ret

.base_case:
; Base case: return 1
mov eax, 1
ret
In this example:

The _start section initializes the parameters and calls the factorial function.
The factorial function checks for the base case (n == 0) and returns 1.
If n is not 0, the function makes a recursive call with the argument n-1 and multiplies the result by n.
Remember that the x86 architecture uses the stack for storing return addresses and local variables during function calls. Therefore, when making recursive calls, you need to save and restore the registers that will be modified to avoid conflicts.

Recursion in assembly requires a solid understanding of the stack and careful management of registers. The example provided is simple, and real-world applications may involve more complex recursive algorithms.