[Solved] What is the problem with this ARM code snippet?func: PUSH {r4} MOV r4, #15 BX lrAssuming r4 is callee-saved. | ARM Architecture

ARM Architecture - Subroutines and Stack

What is the problem with this ARM code snippet?

func:
  PUSH {r4}
  MOV r4, #15
  BX lr

Assuming r4 is callee-saved.

Ar4 is saved but not restored before return

BPUSH instruction is invalid

CMOV instruction cannot assign immediate values

DNo problem, code is correct

Step-by-Step Solution

Solution:

Step 1: Check preservation completeness
r4 is saved with PUSH but never restored with POP before returning.
Step 2: Consequence of missing restore
Without restoring, the original value of r4 is lost after function returns.
Final Answer:
r4 is saved but not restored before return -> Option A
Quick Check:
Save without restore = data loss [OK]

Quick Trick: Always restore registers after saving [OK]

Common Mistakes:

Master "Subroutines and Stack" in ARM Architecture

9 interactive learning modes - each teaches the same concept differently

More ARM Architecture Quizzes

What is the problem with this ARM code snippet?