ARM Architecture - Subroutines and Stack
You want to organize a complex ARM program by splitting tasks into subroutines that call each other. Which is the best practice for nested subroutine calls to avoid errors?
You want to organize a complex ARM program by splitting tasks into subroutines that call each other. Which is the best practice for nested subroutine calls to avoid errors?
hard📝 Application Q15 of 15
Step-by-Step Solution
Solution:
Step 1: Understand call and return instructions
BL saves return address in LR and branches to subroutine; BX LR returns to caller.Step 2: Handle nested calls safely
If a subroutine calls another, it must save LR (e.g., on stack) before calling to avoid losing return address.Final Answer:
Always use BL to call and BX LR to return, saving LR if calling another subroutine -> Option AQuick Check:
BL call + BX LR return + save LR for nested calls [OK]
Quick Trick: Save LR before nested BL calls, return with BX LR [OK]
Common Mistakes:
- Using BX LR to call instead of BL
- Not saving LR before nested calls
- Jumping with MOV ignoring LR
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