ARM Architecture - Subroutines and Stack
You want to implement a nested subroutine call where funcA calls funcB, and funcB calls funcC. funcC modifies R2 and returns. How should you preserve R2's original value across these calls?
You want to implement a nested subroutine call where funcA calls funcB, and funcB calls funcC. funcC modifies R2 and returns. How should you preserve R2's original value across these calls?
hard📝 Application Q8 of 15
Step-by-Step Solution
Solution:
Step 1: Understand register preservation in nested calls
Registers like R2 can be overwritten in nested calls, so saving/restoring is needed.Step 2: Use stack to save R2 in funcB
Push R2 onto the stack at funcB start and pop it before returning preserves original value across calls.Final Answer:
Push R2 onto the stack at funcB start and pop before returning -> Option BQuick Check:
Save registers on stack to preserve values in nested calls [OK]
Quick Trick: Save registers on stack to keep values safe [OK]
Common Mistakes:
- Assuming registers auto-preserve
- Only copying registers without saving original
Master "Subroutines and Stack" in ARM Architecture
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