User:Imate900/32-bit assembler bare bones
This tutorial will teach you how to make a 32-bit Assembly kernel.
Most OSes are in C, but you may consider it in Assembly. This is moderate-easy, and requires knowing GRUB and Assembly.
All we need is something like this (Nasm):
%define MBOOT_MAGIC 0x1badb002 %define MBOOT_FLAGS 0x00010002 bits 32 org 0x100000 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 align 0, db 0 __entry_point: mov edi, 0xB8000 mov esi, string mov ah, 0x0F .displaying: lodsb stosw or al, al jnz .displaying jmp short $ string: db "Hello world!", 0 align 4, db 0 end_of_file:
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!
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.
Good luck writing your 32-bit Assembly kernel! But, there ARE catch-yas!
- As soon as possible, load a new GDT.
- You must not depend on the BIOS to do everything for you. Most prominent are disk access, printing to the screen (this tutorial has a way to printing: writing to 0xb8000) and reading keys from the keyboard. No BIOS ints will help and only cause a GPF.