Recursive function in assembly in ARM Architecture - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the base case in ARM recursive functions

In a recursive ARM assembly function calculating factorial, what is the purpose of the base case?

A To increase the stack pointer to allocate more space

B To jump to the start of the program

C To call the function again with the same input

D To stop the recursion by returning a known value when input is 0 or 1

💡 Hint

Think about how recursion ends to avoid infinite loops.

The base case stops recursion by returning a fixed value when the input reaches 0 or 1, preventing infinite calls.

🔍 Analysis

intermediate

Stack usage in ARM recursive calls

What happens to the stack pointer (SP) during each recursive call in an ARM assembly function?

A SP remains unchanged

B SP increases to allocate more space

C SP decreases to allocate space for return address and local variables

D SP is reset to zero

💡 Hint

Consider how the stack grows when functions call themselves.

Each recursive call pushes data onto the stack, so SP decreases to allocate space.

📋 Factual

advanced

Register preservation in ARM recursion

Which registers must be preserved (saved and restored) by a recursive ARM assembly function to maintain correct execution?

A Callee-saved registers like R4-R11 and LR

B Only R0 and R1

C All registers including R0-R3

D No registers need preservation

💡 Hint

Think about which registers the function must keep unchanged across calls.

Callee-saved registers (R4-R11 and LR) must be preserved to avoid corrupting data during recursion.

🚀 Application

advanced

Output of ARM recursive factorial function

Given an ARM assembly recursive factorial function called with input 4, what is the returned result?

ARM Architecture

Input: R0 = 4
Function: factorial(n) returns n! recursively

A 24

B 10

C 16

D 120

💡 Hint

Recall the factorial values for small numbers.

Factorial of 4 is 4 × 3 × 2 × 1 = 24.

❓ Reasoning

expert

Identifying error in ARM recursive function code snippet

What error will occur if the link register (LR) is not saved before a recursive call in ARM assembly?

ARM Architecture

Recursive call without pushing LR onto stack

A Stack overflow immediately

B Return address overwritten causing incorrect return

C No error, function works fine

D Processor halts due to invalid instruction

💡 Hint

Consider what happens to LR during nested calls.

Not saving LR causes it to be overwritten on recursive calls, so the function returns to wrong address.