ARM Architecture - Control Flow Instructions
Identify the error in this ARM code snippet:
Assuming we want to branch if R1 equals R2.
SUB R0, R1, R2 BEQ equal_label
Assuming we want to branch if R1 equals R2.
Identify the error in this ARM code snippet:
medium📝 Analysis Q6 of 15
Step-by-Step Solution
Solution:
Step 1: Check flag setting instruction
SUB does not update flags; SUBS updates flags needed for conditional branch.Step 2: Confirm branch condition
BEQ depends on zero flag set by SUBS. Without SUBS, flags are not updated, so branch may fail.Final Answer:
SUB should be SUBS to set flags -> Option DQuick Check:
Use SUBS to update flags before BEQ [OK]
Quick Trick: Use SUBS, not SUB, to update flags for branch [OK]
Common Mistakes:
- Using SUB without S suffix
- Changing branch condition incorrectly
- Ignoring flag updates
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