Preparation

The Cross Compiler is ready.

boot.s

i686-elf-as boot.s -o boot.o

Why bootstrap must be written by assembly but cannot written in C?

C requires a stack, but bootstrap code runs BEFORE any stack exists.

Bottom line: Assembly = "create universe from nothing". C = "work within universe". Bootstrap needs the former

kernel.c

i686-elf-gcc -c kernel.c -o kernel.o -std=gnu99 -ffreestanding -O2 -Wall -Wextra

linker.ld

Build the kernel myos.bin from boot.o and kernel.o

i686-elf-gcc -T linker.ld -o myos.bin -ffreestanding -O2 -nostdlib boot.o kernel.o -lgcc

Building a bootable cdrom image

Need to install:

sudo apt-get install xorriso
sudo apt-get install mtools
sudo apt-get install qemu-system-x86

grub.cfg:

menuentry "myos" {
	multiboot /boot/myos.bin
}

grub-mkrescue -o myos.iso isodir

And it works!

qemu-system-i386 -cdrom myos.iso
qemu-system-i386 -kernel myos.bin

It works in read hardware too! (Well, not exactly working, some VGA mode not support. But i think it is ok for now.)

sudo dd if=myos.iso of=/dev/sdx && sync

Reference: https://wiki.osdev.org/Bare_Bones

Created: 20251225