HelloWorld.asm

 ;adding two numbers(user input)

section .data
msg1 db "Enter the first number : ",0xa
len1 equ $ - msg1
msg2 db "Enter the 2nd number : ",0xa
len2 equ $ - msg2

msg3 db "The sum is: "
len3 equ $- msg3

section .bss
num1 resb 2
num2 resb 2 
res resb 1

section .text
global _start
_start :
  
  ;typing the first msg
  mov edx,len1
  mov ecx,msg1
  mov ebx,1 
  mov eax,4
  int 0x80
  
  ;getting the user input for the first number 
  mov edx,2 
  mov ecx,num1
  mov ebx,0 
  mov eax,3
  int 0x80
  
  ;typing the second msg 
  mov edx,len2
  mov ecx,msg2
  mov ebx,1 
  mov eax,4
  int 0x80
  
  ;getting the 2nd user input
  mov edx,2 
  mov ecx,num2
  mov ebx,0 
  mov eax,3
  int 0x80
  
  ; moving the first number to eax register and second number to ebx
  mov eax,[num1]
  sub eax,'0' ; subtract to convert ascii into decimal
  mov ebx,[num2]
  sub ebx,'0'
  
  add eax,ebx
  add eax,'0' ; to convert decimal into ascii again
  
  mov [res],eax ; storing the sum in res memory location
  
  ;typing the third msg 
  mov edx,len3
  mov ecx,msg3
  mov ebx,1 
  mov eax,4
  int 0x80
  
  ;printing the sum
  mov edx,1
  mov ecx,res
  mov ebx,1 
  mov eax,4
  int 0x80
  
  
  
  ;exiting
  mov ebx,0
  mov eax,1 
  int 0x80

created 2 years ago by Venom Viper

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About Assembly

Assembly language(asm) is a low-level programming language, where the language instructions will be more similar to machine code instructions.

Every assembler may have it's own assembly language designed for a specific computers or an operating system.

Assembly language requires less execution time and memory. It is more helful for direct hardware manipulation, real-time critical applications. It is used in device drivers, low-level embedded systems etc.

Syntax help

Assembly language usually consists of three sections,

Data section
To initialize variables and constants, buffer size these values doesn't change at runtime.
bss section
To declare variables
text section
_start specifies the starting of this section where the actually code is written.

Variables

There are various define directives to allocate space for variables for both initialized and uninitialized data.

1. To allocate storage space to Initialized data

Syntax

variable-name    define-directive    initial-value

Define Directive	Description	Allocated Space
DB	Define Byte	1 byte
DW	Define Word	2 bytes
DD	Define Doubleword	4 bytes
DQ	Define Quadword	8 bytes
DT	Define Ten Bytes	10 bytes

2. To allocate storage space to un-initialized data

Define Directive	Description
RESB	Reserve a Byte
RESW	Reserve a Word
RESD	Reserve a Doubleword
RESQ	Reserve a Quadword
REST	Reserve a Ten Bytes

Constants

Constants can be defined using

1. equ

To define numeric constants

CONSTANT_NAME EQU regular-exp or value

2. %assign

To define numeric constants.

%assign constant_name value

3. %define

To define numeric or string constants.

%define constant_name value

Loops

Loops are used to iterate a set of statements for a specific number of times.

mov ECX,n
L1:
;<loop body>
loop L1

where n specifies the no of times loops should iterate.

Procedures

Procedure is a sub-routine which contains set of statements. Usually procedures are written when multiple calls are required to same set of statements which increases re-usuability and modularity.

procedure_name:
   ;procedure body
   ret