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ARM Assembly

A collection of ARM 32-bit assembly learning resources: a programming guide in PDF format and corrected exercise solutions with complete assembly code.

ARM 32-bit Assembly Programming Guide

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ARM 32bit Assembly Exercises

All exercises and their complete source code are included below. Expand a program to inspect its solution.

Program 1: Sum 1 to 5

Question: Write an ARM assembly program to calculate the sum of the integers from 1 through 5 and return the result.

Expected: 15

.section .text
.global _start
_start:
    mov r0, #0
    mov r1, #1
    mov r2, #5
loop:
    add r0, r0, r1
    add r1, r1, #1
    cmp r1, r2
    ble loop
exit:
    mov r7, #1
    svc #0

Program 2: Max element

Question: Given an integer array, write an ARM assembly program to find and return its maximum element.

Expected: 23

.section .data
nums: .word 4, 17, 9, 23, 5
len:  .word 5
.section .text
.global _start
_start:
    ldr r3, =nums
    ldr r2, =len
    ldr r2, [r2]
    ldr r0, [r3]
    mov r1, #1
loop:
    cmp r1, r2
    bge exit
    ldr r4, [r3, r1, LSL #2]
    cmp r4, r0
    movgt r0, r4
    add r1, r1, #1
    b loop
exit:
    mov r7, #1
    svc #0

Program 3: Sum of all elements

Question: Given an integer array, write an ARM assembly program to calculate the sum of all its elements.

Expected: 30

.section .data
nums: .word 2, 4, 6, 8, 10
len:  .word 5
.section .text
.global _start
_start:
    mov r0, #0
    mov r1, #0
    ldr r2, =len
    ldr r2, [r2]
    ldr r3, =nums
arr_loop:
    cmp r1, r2
    bge exit
    ldr r4, [r3, r1, LSL #2]
    add r0, r0, r4
    add r1, r1, #1
    b arr_loop
exit:
    mov r7, #1
    svc #0

Program 4: Sum elements divisible by 3

Question: Given an integer array, write an ARM assembly program to add only the elements that are divisible by 3.

Expected: 24. Requires an ARM CPU supporting sdiv.

.section .data
nums: .word 3, 5, 9, 10, 12, 14
len: .word 6
.section .text
.global _start
_start:
    mov r0, #0
    mov r1, #0
    ldr r2, =len
    ldr r2, [r2]
    mov r5, #3
    ldr r3, =nums
arr_loop:
    cmp r1, r2
    bge exit
    ldr r4, [r3, r1, LSL #2]
    sdiv r6, r4, r5
    mul r6, r6, r5
    subs r6, r4, r6
    bne next_loop
    add r0, r0, r4
next_loop:
    add r1, r1, #1
    b arr_loop
exit:
    mov r7, #1
    svc #0

Program 5: Minimum element

Question: Given an integer array that may contain negative values, write an ARM assembly program to find its minimum element.

Expected: -8 (exit status 248)

.section .data
nums: .word 7, -3, 12, -8, 5
len: .word 5
.section .text
.global _start
_start:
    ldr r2, =len
    ldr r2, [r2]
    ldr r3, =nums
    ldr r0, [r3]
    mov r1, #1
arr_loop:
    cmp r1, r2
    bge exit
    ldr r4, [r3, r1, LSL #2]
    cmp r4, r0
    movlt r0, r4
    add r1, r1, #1
    b arr_loop
exit:
    mov r7, #1
    svc #0

Program 6: Maximum absolute value

Question: Given an integer array containing positive and negative values, write an ARM assembly program to find the largest absolute value among its elements.

Expected: 22. The loop comparison must be cmp r1, r2, not cmp r2, r1.

.section .data
nums: .word 4, -15, 9, -22, 7
len: .word 5
.section .text
.global _start
_start:
    mov r1, #0
    ldr r2, =len
    ldr r2, [r2]
    ldr r3, =nums
    ldr r4, [r3, r1, LSL #2]
    cmp r4, #0
    rsblt r0, r4, #0
    movge r0, r4
    add r1, r1, #1
arr_loop:
    cmp r1, r2
    bge exit
    ldr r4, [r3, r1, LSL #2]
    cmp r4, #0
    rsblt r5, r4, #0
    movge r5, r4
    cmp r5, r0
    movgt r0, r5
    add r1, r1, #1
    b arr_loop
exit:
    mov r7, #1
    svc #0

Program 7: Index of maximum value

Question: Given an integer array, write an ARM assembly program to find the index of its maximum element. Use zero-based indexing.

Expected: 3

.section .data
nums: .word 6, 18, 3, 25, 10
len: .word 5
.section .text
.global _start
_start:
    ldr r2, =len
    ldr r2, [r2]
    ldr r3, =nums
    ldr r0, [r3]
    mov r5, #0
    mov r1, #1
arr_loop:
    cmp r1, r2
    bge exit
    ldr r4, [r3, r1, LSL #2]
    cmp r4, r0
    ble next_loop
    mov r0, r4
    mov r5, r1
next_loop:
    add r1, r1, #1
    b arr_loop
exit:
    mov r0, r5
    mov r7, #1
    svc #0

Program 8: Count values divisible by 4

Question: Given an integer array, write an ARM assembly program to count how many elements are divisible by 4.

Expected: 4

.section .data
nums: .word 4, 7, 12, 16, 5, 20
len: .word 6
.section .text
.global _start
_start:
    mov r0, #0
    mov r1, #0
    ldr r2, =len
    ldr r2, [r2]
    ldr r3, =nums
arr_loop:
    cmp r1, r2
    bge exit
    ldr r4, [r3, r1, LSL #2]
    ands r5, r4, #3
    bne next_loop
    add r0, r0, #1
next_loop:
    add r1, r1, #1
    b arr_loop
exit:
    mov r7, #1
    svc #0

Program 9: Index of first even element

Question: Given an integer array, write an ARM assembly program to find the zero-based index of the first even element. Return -1 if no even element exists.

Expected: 3

.section .data
nums: .word 7, 9, 5, 12, 3, 8
len: .word 6
.section .text
.global _start
_start:
    mov r0, #-1
    mov r1, #0
    ldr r2, =len
    ldr r2, [r2]
    ldr r3, =nums
arr_loop:
    cmp r1, r2
    bge exit
    ldr r4, [r3, r1, LSL #2]
    ands r5, r4, #1
    bne next_loop
    mov r0, r1
    b exit
next_loop:
    add r1, r1, #1
    b arr_loop
exit:
    mov r7, #1
    svc #0

Program 10: Last index of element greater than 10

Question: Given an integer array, write an ARM assembly program to find the zero-based index of the last element greater than 10. Return -1 if no such element exists.

Expected: 5

.section .data
nums: .word 4, 7, 3, 15, 8, 20
len: .word 6
.section .text
.global _start
_start:
    mov r0, #-1
    mov r1, #0
    ldr r2, =len
    ldr r2, [r2]
    ldr r3, =nums
arr_loop:
    cmp r1, r2
    bge exit
    ldr r4, [r3, r1, LSL #2]
    cmp r4, #10
    ble next_loop
    mov r0, r1
next_loop:
    add r1, r1, #1
    b arr_loop
exit:
    mov r7, #1
    svc #0

Program 11: Count negative numbers

Question: Given an integer array, write an ARM assembly program to count the number of negative elements.

Expected: 3

.section .data
nums: .word 5, -3, 12, -7, 9, -1
len: .word 6
.section .text
.global _start
_start:
    mov r0, #0
    mov r1, #0
    ldr r2, =len
    ldr r2, [r2]
    ldr r3, =nums
arr_loop:
    cmp r1, r2
    bge exit
    ldr r4, [r3, r1, LSL #2]
    cmp r4, #0
    bge next_loop
    add r0, r0, #1
next_loop:
    add r1, r1, #1
    b arr_loop
exit:
    mov r7, #1
    svc #0

Program 12: Smallest negative number

Question: Given an integer array, write an ARM assembly program to find the smallest (most negative) negative element. Return 0 if the array contains no negative values.

Expected: -7 (exit status 249)

.section .data
nums: .word 5, -3, 12, -7, 9, -1
len: .word 6
.section .text
.global _start
_start:
    mov r0, #0
    mov r1, #0
    ldr r2, =len
    ldr r2, [r2]
    ldr r3, =nums
arr_loop:
    cmp r1, r2
    bge exit
    ldr r4, [r3, r1, LSL #2]
    cmp r4, #0
    bge next_loop
    cmp r4, r0
    bge next_loop
    mov r0, r4
next_loop:
    add r1, r1, #1
    b arr_loop
exit:
    mov r7, #1
    svc #0

Program 13: Index of smallest negative number

Question: Given an integer array, write an ARM assembly program to find the zero-based index of the smallest negative element. Return -1 if no negative element exists.

Expected: 3

.section .data
nums: .word 5, -3, 12, -7, 9, -1
len: .word 6
.section .text
.global _start
_start:
    mov r0, #-1
    mov r5, #0
    mov r1, #0
    ldr r2, =len
    ldr r2, [r2]
    ldr r3, =nums
arr_loop:
    cmp r1, r2
    bge exit
    ldr r4, [r3, r1, LSL #2]
    cmp r4, #0
    bge next_loop
    cmp r0, #-1
    beq update
    cmp r4, r5
    bge next_loop
update:
    mov r5, r4
    mov r0, r1
next_loop:
    add r1, r1, #1
    b arr_loop
exit:
    mov r7, #1
    svc #0

Program 14: Sum of even numbers

Question: Given an integer array, write an ARM assembly program to calculate the sum of all even elements, including negative even values.

Expected: 24

.section .data
nums: .word 5, -3, 12, -7, 9, -1, 8, 4
len: .word 8
.section .text
.global _start
_start:
    mov r0, #0
    mov r1, #0
    ldr r2, =len
    ldr r2, [r2]
    ldr r3, =nums
arr_loop:
    cmp r1, r2
    bge exit
    ldr r4, [r3, r1, LSL #2]
    tst r4, #1
    bne next_loop
    add r0, r0, r4
next_loop:
    add r1, r1, #1
    b arr_loop
exit:
    mov r7, #1
    svc #0

Program 15: Count multiples of 8

Question: Given an integer array, write an ARM assembly program to count the elements that are multiples of 8.

Expected: 4

.section .data
nums: .word 5, 8, 12, 16, 24, 7, 32
len: .word 7
.section .text
.global _start
_start:
    mov r0, #0
    mov r1, #0
    ldr r2, =len
    ldr r2, [r2]
    ldr r3, =nums
arr_loop:
    cmp r1, r2
    bge exit
    ldr r4, [r3, r1, LSL #2]
    ands r5, r4, #7
    bne next_loop
    add r0, r0, #1
next_loop:
    add r1, r1, #1
    b arr_loop
exit:
    mov r7, #1
    svc #0

Program 16: Structure, set READY bit

Question: Given a structure in memory with an ID field, a value field, and a status field, write an ARM assembly routine that sets bit 0 (READY) in the status field without changing the other status bits.

Expected: 1. Fixed .global _start spacing and pop {lr}.

.section .data
device:
    .word 100
    .word 55
    .word 0
.section .text
.global _start
_start:
    ldr r0, =device
    bl set_ready
    ldr r1, [r0, #8]
    mov r0, r1
    mov r7, #1
    svc #0
set_ready:
    push {lr}
    ldr r1, [r0, #8]
    orr r1, r1, #1
    str r1, [r0, #8]
    pop {lr}
    bx lr

Program 17: Function sum_array

Question: Write an ARM assembly function named sum_array that accepts an array address and its length, then returns the sum of all array elements.

Expected: 100. Fixed array addressing to use loop index r4.

.section .data
nums: .word 10, 20, 30, 40
len: .word 4
.section .text
.global _start
_start:
    ldr r0, =nums
    ldr r1, =len
    ldr r1, [r1]
    bl sum_array
    mov r7, #1
    svc #0
sum_array:
    push {r4-r6, lr}
    mov r4, #0
    mov r5, #0
arr_loop:
    cmp r4, r1
    bge done
    ldr r6, [r0, r4, LSL #2]
    add r5, r5, r6
    add r4, r4, #1
    b arr_loop
done:
    mov r0, r5
    pop {r4-r6, lr}
    bx lr

Program 18: Function max_array

Question: Write an ARM assembly function named max_array that accepts an array address and its length, then returns the maximum element.

Expected: 99. Fixed invalid mov r5, [r0] to ldr r5, [r0] and corrected the max update direction.

.section .data
nums: .word 10, 55, 23, 99, 41
len: .word 5
.section .text
.global _start
_start:
    ldr r0, =nums
    ldr r1, =len
    ldr r1, [r1]
    bl max_array
    mov r7, #1
    svc #0
max_array:
    push {r4-r6, lr}
    ldr r5, [r0]
    mov r4, #1
arr_loop:
    cmp r4, r1
    bge done
    ldr r6, [r0, r4, LSL #2]
    cmp r6, r5
    ble next_loop
    mov r5, r6
next_loop:
    add r4, r4, #1
    b arr_loop
done:
    mov r0, r5
    pop {r4-r6, lr}
    bx lr

Program 19: Function min_max

Question: Write an ARM assembly function named min_max that accepts an array address and its length, then returns the minimum element in r0 and the maximum element in r1.

Expected: min = 3 (r0), max = 88 (r1). The exit code displays the low 8 bits of r0.

.section .data
nums: .word 42, 7, 19, 3, 88, 25
len: .word 6
.section .text
.global _start
_start:
    ldr r0, =nums
    ldr r1, =len
    ldr r1, [r1]
    bl min_max
    mov r7, #1
    svc #0
min_max:
    push {r4-r7, lr}
    ldr r6, [r0]
    mov r7, r6
    mov r4, #1
arr_loop:
    cmp r4, r1
    bge done
    ldr r5, [r0, r4, LSL #2]
    cmp r5, r6
    movlt r6, r5
    cmp r5, r7
    movgt r7, r5
    add r4, r4, #1
    b arr_loop
done:
    mov r0, r6
    mov r1, r7
    pop {r4-r7, lr}
    bx lr

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