[Solved] Analyze the following ARM assembly code:BL subroutine MOV R1, #3 B finish subroutine: MOV R1, #7 BX LR finish:What value will register R1 contain after execution reaches finish? | ARM Architecture

ARM Architecture - Control Flow Instructions

Analyze the following ARM assembly code:

BL subroutine
MOV R1, #3
B finish
subroutine:
MOV R1, #7
BX LR
finish:

What value will register R1 contain after execution reaches finish?

A3

B7

C0

DUndefined

Step-by-Step Solution

Solution:

Step 1: Follow the flow
The BL instruction branches to subroutine and saves the return address in LR.
Step 2: Execute subroutine
Inside subroutine, R1 is set to 7, then BX LR returns to the instruction after BL.
Step 3: Continue after BL
After returning, MOV R1, #3 executes, overwriting R1 with 3.
Step 4: Branch to finish
The B finish instruction jumps to finish.
Final Answer:
3 -> Option A
Quick Check:
Post-subroutine code overwrites R1 [OK]

Quick Trick: Post-call instructions overwrite register values [OK]

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