[Solved] Consider this ARM assembly snippet:BL subroutine MOV R0, #0 B end subroutine: MOV R0, #1 BX LR end:What value will register R0 hold after execution? | ARM Architecture

ARM Architecture - Control Flow Instructions

Consider this ARM assembly snippet:

BL subroutine
MOV R0, #0
B end
subroutine:
MOV R0, #1
BX LR
end:

What value will register R0 hold after execution?

A1

B0

CUndefined

DThe program will crash

Step-by-Step Solution

Solution:

Step 1: Follow the BL instruction
The BL instruction jumps to subroutine and saves the return address (address of MOV R0, #0) in LR.
Step 2: Execute subroutine and return
Inside subroutine, MOV R0, #1 sets R0 to 1, then BX LR returns to MOV R0, #0.
Step 3: Continue after BL
MOV R0, #0 overwrites R0 to 0, followed by B end.
Final Answer:
0 -> Option B
Quick Check:
Post-return MOV R0, #0 overwrites subroutine value [OK]

Quick Trick: BL returns to next instr MOV R0, #0 overwriting subroutine's R0=1 [OK]

Common Mistakes:

Master "Control Flow Instructions" in ARM Architecture

9 interactive learning modes - each teaches the same concept differently

More ARM Architecture Quizzes

Consider this ARM assembly snippet: