Stack frame setup in ARM Architecture - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the Purpose of Stack Frames

What is the main purpose of setting up a stack frame during a function call in ARM architecture?

A To allocate space for local variables and save the return address and previous frame pointer

B To increase the CPU clock speed temporarily during function execution

C To directly access hardware peripherals without using registers

D To clear all registers before executing the function

💡 Hint

Think about what information a function needs to keep track of when it calls another function.

Setting up a stack frame allows the function to reserve space for its local variables and save important information like the return address and the previous frame pointer. This helps in returning control correctly after the function finishes.

📋 Factual

intermediate

Identifying Stack Frame Components

Which register in ARM architecture typically holds the frame pointer used in stack frame setup?

A R14

B R13

C R7

D R15

💡 Hint

It is a general-purpose register often used as a frame pointer in ARM calling conventions.

In many ARM calling conventions, R7 is used as the frame pointer to reference the current stack frame, while R13 is the stack pointer, R14 is the link register, and R15 is the program counter.

🔍 Analysis

advanced

Analyzing Stack Frame Setup Instructions

Consider the following ARM assembly instructions executed at the start of a function:

push {r4, r5, r6, lr}
add r7, sp, #0
sub sp, sp, #16

What is the purpose of these instructions in the context of stack frame setup?

A They save registers, set the frame pointer, and allocate space for local variables

B They clear the stack and reset all registers to zero

C They load function arguments into registers and jump to the function

D They restore saved registers and return from the function

💡 Hint

Look at what each instruction does: pushing registers, setting a pointer, and adjusting the stack pointer.

The push instruction saves registers and the link register to the stack. The add sets the frame pointer (R7) to the current stack pointer. The sub reserves space on the stack for local variables by moving the stack pointer down.

❓ Comparison

advanced

Comparing Stack Pointer and Frame Pointer Roles

Which statement best describes the difference between the stack pointer (SP) and the frame pointer (FP) in ARM stack frame setup?

A SP and FP are the same register with different names

B SP is used only for function arguments; FP stores return addresses

C SP is a general-purpose register; FP is used to access hardware registers

D SP points to the top of the stack and changes during function execution; FP points to a fixed location in the stack frame

💡 Hint

Think about which pointer moves as local variables are pushed or popped and which remains stable during a function.

The stack pointer (SP) moves as data is pushed or popped from the stack, reflecting the current top of the stack. The frame pointer (FP) remains fixed during the function to provide a stable reference point for accessing local variables and parameters.

❓ Reasoning

expert

Determining Stack Frame Size from Assembly

Given the following ARM assembly snippet at function start:

push {r4, r5, r6, lr}
sub sp, sp, #32

What is the total size in bytes of the stack frame allocated for this function, including saved registers and local variables?

A 32 bytes

B 48 bytes

C 16 bytes

D 64 bytes

💡 Hint

Each register pushed uses 4 bytes. Add the space reserved by sub sp, sp, #32.

The push saves 4 registers (r4, r5, r6, lr), each 4 bytes, totaling 16 bytes. The sub sp, sp, #32 reserves 32 bytes for local variables. Total stack frame size is 16 + 32 = 48 bytes.