[Solved] Identify the error in this nested subroutine call sequence:funcX: BL funcY BX LR funcY: BL funcZ BX R14 funcZ: BX LR | ARM Architecture

ARM Architecture - Subroutines and Stack

Identify the error in this nested subroutine call sequence:

funcX:
  BL funcY
  BX LR

funcY:
  BL funcZ
  BX R14

funcZ:
  BX LR

AMissing MOV instruction before BL

BNo error present

CIncorrect label names

DUsing BX R14 instead of BX LR in funcY

Step-by-Step Solution

Solution:

Step 1: Understand return instruction conventions
Return from subroutine uses BX LR, where LR holds the return address.
Step 2: Verify register usage
R14 is the link register (LR) alias; BX R14 is equivalent to BX LR and functions correctly in nested calls.
Final Answer:
No error present -> Option B
Quick Check:
BX R14 == BX LR, fully valid [OK]

Quick Trick: BX LR or BX R14 both valid for return [OK]

Common Mistakes:

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