User:Imate900/32-bit assembler bare bones

Difficulty level
Medium

Kernel Designs
Models
Monolithic Kernel Microkernel Exokernel Nano/Picokernel Cache Kernel Virtualizing Kernel Megalithic Kernel
Other Concepts
Modular Kernel Higher Half Kernel 64-bit Kernel Hybrid Kernel

This tutorial will teach you how to make a 32-bit assembler kernel.

GRUB

All we need is something like this (nasm):

%define MBOOT_MAGIC 0x1badb002
%define MBOOT_FLAGS 0x00010002

bits 32
org 0x100000

__entry_point:
   mov edi, 0xB8000
   mov esi, string
   mov ah, 0x0F
   .displaying:
   lodsb
   stosw
   or al, al
   jnz .displaying
   jmp short $

align 4, db 0
header:
   dd MBOOT_MAGIC
   dd MBOOT_FLAGS
   dd 0 - MBOOT_MAGIC - MBOOT_FLAGS
   dd header
   dd __entry_point
   dd end_of_file
   dd end_of_file
   dd __entry_point

string: db "Hello world!", 0

align 4, db 0
end_of_file:

Link with:

nasm -f bin kernel.asm

Make sure you have a GRUB entry...

title Assembler Barebones
kernel (hd0,0)/boot/kernel.bin

Now, reboot, and enjoy!

Without GRUB

If your bootloader loads flat binary images and gives you protected mode for you, use this code as a basis:

_start:
 ; Write kernel here. It might be good to load a new GDT.
   mov edi, 0xB8000
   mov esi, string
   mov ah, 0x0F
   .displaying:
   lodsb
   stosw
   or al, al
   jnz .displaying
   jmp short $

string: db "Hello world!", 0

If you start out in real mode, remember to switch to Protected Mode.

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This page may thus be incomplete. Its content may be changed in the near future.