[Solved] What will be the output in R0 after calling this recursive ARM function with R0=3?func: CMP R0, #1 BLE end PUSH {LR} SUB R0, R0, #1 BL func POP {LR} ADD R0, R0, #2 end: BX LR | ARM Architecture

ARM Architecture - Subroutines and Stack

What will be the output in R0 after calling this recursive ARM function with R0=3?

func:
    CMP R0, #1
    BLE end
    PUSH {LR}
    SUB R0, R0, #1
    BL func
    POP {LR}
    ADD R0, R0, #2
end:
    BX LR

A5

B1

C3

D7

Step-by-Step Solution

Solution:

Step 1: Trace recursion calls
func(3) calls func(2), which calls func(1). func(1) returns immediately.
Step 2: Calculate return values
func(1) returns 1; func(2) adds 2 to 1 = 3; func(3) adds 2 to 3 = 5.
Step 3: Re-examine base case
Since CMP R0, #1 and BLE end, func(1) returns R0=1 without addition.
Final Answer:
5 -> Option A
Quick Check:
Recursive addition accumulates to 5 [OK]

Quick Trick: Add after recursive call accumulates result [OK]

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What will be the output in R0 after calling this recursive ARM function with R0=3?