[Solved] Given this ARM assembly snippet for a recursive sum function:sum: CMP R0, #0 BEQ end PUSH {LR} SUB R0, R0, #1 BL sum POP {LR} ADD R0, R0, R1 end: BX LRWhat is the main issue with this code? | ARM Architecture

ARM Architecture - Subroutines and Stack

Given this ARM assembly snippet for a recursive sum function:

sum:
    CMP R0, #0
    BEQ end
    PUSH {LR}
    SUB R0, R0, #1
    BL sum
    POP {LR}
    ADD R0, R0, R1
end:
    BX LR

What is the main issue with this code?

ALR is not saved before recursive call

BR1 is never initialized before use

CThe base case is incorrect

DStack pointer is not adjusted

Step-by-Step Solution

Solution:

Step 1: Analyze register usage
The code adds R0 and R1 after recursion, but R1 is never set.
Step 2: Identify missing initialization
Without initializing R1, the addition uses garbage value causing wrong result.
Final Answer:
R1 is never initialized before use -> Option B
Quick Check:
Uninitialized register use = R1 [OK]

Quick Trick: Always initialize registers before use in recursion [OK]

Common Mistakes:

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Given this ARM assembly snippet for a recursive sum function: