Preserving callee-saved registers in ARM Architecture - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to save a callee-saved register before using it.

ARM Architecture

push [1]

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

Ar0

Br1

Cr4

Dr2

Attempts:

3 left

💡 Hint

Common Mistakes

Saving caller-saved registers like r0 instead of callee-saved.

Not saving any register before use.

In ARM architecture, registers r4 to r11 are callee-saved. Saving r4 with push r4 preserves its value across function calls.

2fill in blank

medium

Complete the code to restore a callee-saved register after use.

ARM Architecture

pop [1]

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

Ar5

Br0

Cr3

Dr1

Attempts:

3 left

💡 Hint

Common Mistakes

Restoring caller-saved registers instead of callee-saved.

Forgetting to restore the register.

Register r5 is callee-saved in ARM. Restoring it with pop r5 returns its original value after the function finishes.

3fill in blank

hard

Fix the error in the code to properly preserve callee-saved registers.

ARM Architecture

push [1]
// function code
pop r4

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

Ar5

Br1

Cr0

Dr2

Attempts:

3 left

💡 Hint

Common Mistakes

Pushing one register and popping a different one.

Using caller-saved registers for preservation.

The code pushes r5 but pops r4, which is incorrect. Both push and pop must use the same register to preserve its value properly.

4fill in blank

hard

Fill both blanks to save and restore two callee-saved registers correctly.

ARM Architecture

push [1], [2]
// function code
pop r7, r8

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

Ar7

Br8

Cr4

Dr0

Attempts:

3 left

💡 Hint

Common Mistakes

Saving registers that are not callee-saved.

Mismatch between push and pop registers.

Registers r7 and r8 are callee-saved. Saving them with push r7, r8 and restoring with pop r7, r8 preserves their values across the function.

5fill in blank

hard

Fill all three blanks to create a dictionary mapping callee-saved registers to their save instructions.

ARM Architecture

registers = [1]: '[2]', [3]: 'push [3]'

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

Ar4

Br5

Cpush r4

Dr7

Attempts:

3 left

💡 Hint

Common Mistakes

Using caller-saved registers as keys.

Incorrect push instruction strings.

This dictionary maps r4 to its save instruction push r4 and r7 to push r7. Both are callee-saved registers.