[Solved] Analyze this ARM function:func: PUSH {r4, r5} MOV r4, #7 MOV r5, #14 POP {r4, r5} BX lrIf r4 was 30 before the call, what is its value after returning? | ARM Architecture

ARM Architecture - Subroutines and Stack

Analyze this ARM function:

func:
  PUSH {r4, r5}
  MOV r4, #7
  MOV r5, #14
  POP {r4, r5}
  BX lr

If r4 was 30 before the call, what is its value after returning?

A14

B7

C30

DUndefined

Step-by-Step Solution

Solution:

Step 1: Understand PUSH and POP
PUSH saves original r4 and r5 values on stack.
Step 2: MOV modifies r4 and r5 locally
Values changed inside function but not permanently.
Step 3: POP restores original values
r4 and r5 restored to pre-call values before return.
Final Answer:
30 -> Option C
Quick Check:
Registers restored by POP [OK]

Quick Trick: PUSH/POP restore original register values [OK]

Common Mistakes:

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