Arithmetic, Logical and Control Instructions in IA32 Assembly

This is not a blog post, per se, but rather an example program that contains basic usage of arithmetic, logical and control instructions. For this blog post, I thought that it is better to describe the example program in the program comments and not in separate paragraphs.

We will write a simple program that will have examples of  the following:

  • Arithmetic
    • Addition
    • Subtraction
    • Increment/Decrement
    • Multiplication
    • Division
  • Logical
    • AND
    • OR
    • XOR
    • NOT
  • Control
    • Unconditional Jump
    • Conditional Jump
    • Loop
; Author: HRDARJI
; This program was created to understand arithmetic, logical and control
; instructions of  assembly language programming.

global _start

section .text

_start:

	; ----------- Arithmetic Instructions----------------

	; The below instructions are register based addition.
 <span 				data-mce-type="bookmark" 				id="mce_SELREST_start" 				data-mce-style="overflow:hidden;line-height:0" 				style="overflow:hidden;line-height:0" 			></span>

	mov eax, 0x0
	add eax, 0x10

	; memory based addition

	mov eax, 0x0
	add word [var2], 0x1111

	clc ; clear carry flag
	stc ; set carry flag
	cmc ; complement carry flag

	; subtract

	mov eax, 0x3
	sub eax, 0x2

	; increment and decrement instructions

	inc eax
	dec eax

	; multiplication

	mov eax, 0x0
	mov ebx, 0x0

	mov ax, 0x1111
	mov bx, 0x0002
	mul bx

	; divistion

	mov dx, 0x0
	mov ax, 0x1234
	mov cx, 0x2
	div cx

	; ----------- Logical Instructions----------------

	; AND

	mov al, 0x10
	and al, 0x01

	; AND can also be used for memory locations

	and byte [var1], 0x22

	; OR

	mov al, 0x10
	or al, 0x01

	; XOR

	mov al, 0x10
	xor al, 0x01

	; NOT 

	mov eax, 0xFFFFFFFF
	not eax

	; ----------- Control Instructions----------------

	jmp LabelExample2

	; instructions under LabelExample1 will never be executed.

LabelExample1:

	mov eax, 0x11
	add eax, 0x22	

LabelExample2:

	; we are updating eax to 5 because we will print hello world 5 times
	mov eax, 0x5

PrintString:

	push eax

	; print hello world 5 times

	mov eax, 0x4
	mov ebx, 1
	mov ecx, message
	mov edx, mlen
	int 0x80

	pop eax
	dec eax
	jnz PrintString

	;-------------- loop instruction example ---------------

	mov ecx, 0x5

PrintStringLoop:

	push ecx

	mov eax, 0x4
	mov ebx, 1
	mov ecx, message
	mov edx, mlen
	int 0x80

	pop ecx
	loop PrintStringLoop	

	; exit program 

	mov eax, 1
	mov ebx, 1
	int 0x80

section .data

	var1 db 0x00
	var2 dw 0x0000
	var3 dd 0x00000000

	message: db "Hello World"
	mlen	equ $-message
<span 				data-mce-type="bookmark" 				id="mce_SELREST_start" 				data-mce-style="overflow:hidden;line-height:0" 				style="overflow:hidden;line-height:0" 			></span>

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