Stack frame setup in ARM Architecture - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to push the link register onto the stack at the start of a function.

ARM Architecture

push [1]

Drag options to blanks, or click blank then click option'

A{r0}

B{pc}

C{sp}

D{lr}

Attempts:

3 left

💡 Hint

Common Mistakes

Using {pc} instead of {lr} will push the program counter, which is not typical for function prologue.

Pushing {sp} or {r0} is incorrect for saving return address.

In ARM assembly, the link register (lr) holds the return address. Pushing {lr} saves it on the stack for later return.

2fill in blank

medium

Complete the code to allocate 16 bytes on the stack for local variables.

ARM Architecture

sub sp, sp, [1]

Drag options to blanks, or click blank then click option'

A#4

B#8

C#16

D#32

Attempts:

3 left

💡 Hint

Common Mistakes

Using #8 only allocates 8 bytes, which may be insufficient.

Using #32 allocates too much space unnecessarily.

Subtracting 16 bytes from the stack pointer reserves space for local variables in the stack frame.

3fill in blank

hard

Fix the error in the instruction that restores the stack pointer after a function call.

ARM Architecture

add sp, sp, [1]

Drag options to blanks, or click blank then click option'

A#16

B#12

C#8

D#4

Attempts:

3 left

💡 Hint

Common Mistakes

Adding back #8 or #12 bytes will not fully restore the stack pointer.

Adding #4 bytes is too little and causes stack corruption.

The stack pointer must be incremented by the same amount it was decremented to restore the stack frame correctly. If 16 bytes were allocated, add back 16 bytes.

4fill in blank

hard

Fill both blanks to correctly save and restore the frame pointer (r7) in the function prologue and epilogue.

ARM Architecture

push [1]
...
pop [2]

Drag options to blanks, or click blank then click option'

A{r7}

B{lr}

C{r6}

D{sp}

Attempts:

3 left

💡 Hint

Common Mistakes

Pushing {lr} instead of {r7} will save the return address, not the frame pointer.

Using different registers for push and pop causes errors.

The frame pointer register (r7) is saved at the start and restored at the end of the function to maintain the stack frame.

5fill in blank

hard

Fill all three blanks to create a stack frame setup that saves lr and r7, allocates 12 bytes, and restores them properly.

ARM Architecture

push [1]
sub sp, sp, [2]
...
add sp, sp, [3]

Drag options to blanks, or click blank then click option'

A{lr, r7}

B#12

D{r7}

Attempts:

3 left

💡 Hint

Common Mistakes

Using {r7} alone in push does not save lr.

Allocating different amounts in sub and add causes stack imbalance.

The push instruction saves both lr and r7 registers. Then 12 bytes are allocated on the stack. Finally, 12 bytes are added back to restore the stack pointer.