Learn coding with amol

Hello my name is amol sharma or vineet and this is my 9th part of learn coding with amol and in this part we are going to learn assembly.


 ASSEMBLY PART - 9 


Learn Assembly Programming | Amol Sharma

Complete Assembly Programming Guide

Assembly language is a low-level programming language that is closely related to machine code. It is used to write programs that directly interact with the hardware. This guide will take you from beginner to advanced level.

1. Basics of Assembly Language

Assembly language uses mnemonics to represent machine instructions. Each processor architecture (like x86, ARM) has its own instruction set.

  • Registers: Small storage locations in CPU (e.g., AX, BX, CX, DX in x86).
  • Memory: Used to store data, accessed via addresses.
  • Instructions: Commands like MOV, ADD, SUB, JMP.
  • Comments: Denoted by ; in x86.

2. Basic Structure of an x86 Program


; This is a simple program in x86 assembly

section .data          ; Data section

    msg db 'Hello, World!',0

section .text          ; Code section

    global _start

_start:

    ; write syscall

    mov edx,13         ; message length

    mov ecx,msg        ; message to write

    mov ebx,1          ; file descriptor (stdout)

    mov eax,4          ; syscall number (sys_write)

    int 0x80           ; call kernel

    ; exit syscall

    mov eax,1          ; syscall number (sys_exit)

    int 0x80           ; call kernel

3. Common x86 Instructions

  • MOV - Moves data between registers or memory
  • ADD - Adds values
  • SUB - Subtracts values
  • INC / DEC - Increment/Decrement
  • PUSH / POP - Stack operations
  • CMP - Compare values
  • JMP, JE, JNE - Jump instructions
  • INT - Software interrupt

4. Data Types

  • db - Define byte
  • dw - Define word (2 bytes)
  • dd - Define double word (4 bytes)
  • dq - Define quad word (8 bytes)

5. Loops and Conditions


section .text

global _start

_start:

    mov ecx,5          ; counter

loop_start:

    ; do something

    dec ecx

    jnz loop_start     ; jump if not zero

    mov eax,1          ; exit syscall

    int 0x80

6. Procedures / Functions


section .text

global _start

print_hello:

    ; print "Hello"

    ret                ; return to caller

_start:

    call print_hello    ; call function

    mov eax,1

    int 0x80

7. Input / Output (Syscalls)

On Linux x86, syscalls are used for input/output:

  • sys_write - Write to stdout (eax=4)
  • sys_read - Read from stdin (eax=3)
  • sys_exit - Exit program (eax=1)

8. Advanced Topics

  • Interrupts and Exception Handling
  • Bit Manipulation (AND, OR, XOR, SHL, SHR)
  • Stack and Memory Management
  • Calling Conventions (cdecl, stdcall)
  • Optimization Techniques

9. Recommended Tools

  • Assembler: NASM, MASM
  • Debugger: GDB, OllyDbg
  • IDE: Visual Studio, VS Code

10. Practice Programs


; Program to add two numbers

section .data

    num1 db 5

    num2 db 10

    sum db 0

section .text

global _start

_start:

    mov al,[num1]

    add al,[num2]

    mov [sum],al

    mov eax,1

    int 0x80

With this guide, you now have a complete start-to-advanced overview of Assembly programming for x86. Practice is key to mastering it!

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