Question

Q4 (10 marks): What are the values in registers R1, R2 and R3 at the end of this ARMv7 assembly program? MOV R1, #2 MOV R2, #10 MOV R3, #10 L1: CMP R1, R3 BGE L3 BL L2 ADD R1, R1, #3 BL1 L2: ADD R2, R2, #3 MOV R15, R14 L3: MUL R3, R1, R2 Q5 (10 marks): Please write ARMv7 assembly program for following C programs. Assume that variables are stored in memory and their addresses can be obtained by using ADR pseudo op? i = 10; if(i>j) { a = i+2*j; } else { a = i; j=a-i; } a =a+2;

Answer 1

Q4:

Initially the values stored in the register are :

• R₁ = 2
• R₂ = 10
• R₃ = 10

L1 :

Compare R₁ and R3  ---> 2 > 10 , NO hence it will skip to the next step -- BL L2 => branches to L2

L2 :  R₂ gets updated to R₂ = 10 + 3 => 13 and value in R₁₄  gets stored in R₁₅ .

Next step - R₁ gets updated to R₁ = 2 + 3 => R₁ = 5 and gets stored in R₁ register.

Now, the updated values are :

• R₁ = 5
• R₂ = 13
• R₃ = 10

L1 :

Compare R₁ and R3  ---> 5 > 10 , NO hence it will skip to the next step -- BL L2 => branches to L2

L2 :  R₂ gets updated to R₂ = 13 + 3 => 16 and value in R₁₄  gets stored in R₁₅ .

Next step - R₁ gets updated to R₁ = 5 + 3 => R₁ = 8 and gets stored in R₁ register.

Now, the updated values are :

• R₁ = 8
• R₂ = 16
• R₃ = 10

L1 :

Compare R₁ and R3  ---> 8 > 10 , NO hence it will skip to the next step -- BL L2 => branches to L2

L2 :  R₂ gets updated to R₂ = 16 + 3 => 19 and value in R₁₄  gets stored in R₁₅ .

Next step - R₁ gets updated to R₁ = 8 + 3 => R₁ = 11 and gets stored in R₁ register.

Now, the updated values are :

• R₁ = 11
• R₂ = 19
• R₃ = 10

L1 :

Compare R₁ and R3  ---> 11 > 10 , YES hence it will go to the next step -- BGE L3 => branch on if >= 0 , implied branches to L3

L3 :  R₃gets updated to R₃ = 11 * 19 => 209

Now, the updated values are :

• R₁ = 11
• R₂ = 19
• R₃ = 209

The last values are the final updated values.

Q5:

Please find the below ARMv7 assembly languauge code for the given C language code:

MOV R1, 10
CMP R1, R2
JLE L1
MOV AX, R1
ADD AX, R2
ADD AX, R2
MOV R3, AX
JMP L2
L1:
MOV R3, R1
MOV AX, R1
SUB AX, R1
MOV R2, AX
L2:
MOV AX, R3
ADD AX, 2
MOV R3, AX
INT 03