[Solved] Identify the error in this ARM function snippet:func: MOV r4, #10 MOV r5, #20 BX lrAssuming r4 and r5 are callee-saved registers. | ARM Architecture

ARM Architecture - Subroutines and Stack

Identify the error in this ARM function snippet:

func:
  MOV r4, #10
  MOV r5, #20
  BX lr

Assuming r4 and r5 are callee-saved registers.

AMOV instructions are invalid here

BThe function uses incorrect branch instruction

CNo error, code is correct

DRegisters r4 and r5 are not preserved before modification

Step-by-Step Solution

Solution:

Step 1: Check preservation of callee-saved registers
r4 and r5 are callee-saved and must be saved/restored if modified.
Step 2: Identify missing preservation
The code modifies r4 and r5 without saving/restoring, violating the preservation rule.
Final Answer:
Registers r4 and r5 are not preserved before modification -> Option D
Quick Check:
Modifying callee-saved without saving = error [OK]

Quick Trick: Always save callee-saved before modifying [OK]

Common Mistakes:

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