MMUKO QEMU Boot Scaffold

This turns the MMUKO boot idea into a tiny QEMU-bootable kernel.

Important distinction:

• mmuko-boot.c from the gist is a normal hosted C program. It uses printf, malloc, calloc, and the host OS C runtime.
• QEMU boots firmware, boot sectors, kernels, or disk images. At boot time there is no hosted C runtime, so MMUKO needs to run as freestanding code.

This scaffold supports two boot paths.

Path A: Direct BIOS Boot On This Windows Machine

This path uses the tools already common in a MinGW + QEMU setup:

• as
• gcc
• ld
• qemu-system-i386

Build the raw boot image:

:::powershell
.\build-direct.ps1

Run it:

:::powershell
qemu-system-i386 -drive format=raw,file=build\mmuko-direct.img,if=ide,index=0 -display none -serial stdio -no-reboot

The kernel deliberately halts at the end, so QEMU will keep running until you stop it with Ctrl+C.

The direct boot path works like this:

1. boot16.s starts as a 512-byte BIOS boot sector.
2. It loads kernel-flat.bin from disk LBA 1 into memory at 0x10000.
3. It switches to 32-bit protected mode.
4. It jumps into kernel-entry.s.
5. kernel-entry.s calls kernel_main() in kernel.c.

Path B: GRUB Multiboot

The GRUB path uses GRUB Multiboot as the loader:

1. GRUB starts the kernel in 32-bit protected mode.
2. kernel_main() initializes screen and serial output.
3. mmuko_boot() runs the MMUKO boot phases.
4. mmuko_program_main() runs after boot succeeds.

Files

• boot.asm - Multiboot entry point and stack setup.
• boot16.s - Direct BIOS boot sector.
• kernel-entry.s - Direct boot flat-kernel entry point.
• kernel.c - Freestanding MMUKO boot model and example MMUKO program.
• linker.ld - Places the kernel at 1 MiB for GRUB.
• linker-flat.ld - Places the direct boot kernel at 0x10000.
• grub.cfg - GRUB menu entry.
• Makefile - Builds an ISO and runs it in QEMU.
• build-direct.ps1 - Builds the direct BIOS boot image on Windows.

Toolchain

The easiest path on Windows is WSL or MSYS2 with:

• nasm
• i686-elf-gcc
• grub-mkrescue
• grub-file
• xorriso
• qemu-system-i386
• make

On a Debian/Ubuntu-like environment, QEMU/GRUB/NASM can usually be installed with:

:::sh
sudo apt install make nasm grub-pc-bin grub-common xorriso qemu-system-x86

You still need an i686-elf-gcc cross compiler. If you do not have one yet, use an OSDev-style cross compiler, or adapt the Makefile to your existing freestanding i386 compiler.

GRUB Build And Run

:::sh
make
make run

QEMU will show VGA text, and the same log is also written to serial with -serial stdio.

Where To Write Your Program

Edit this function in kernel.c:

:::c
static void mmuko_program_main(MMUKO_System *sys)

That function is the first MMUKO "program" in this scaffold. It only runs after mmuko_boot(sys) returns BOOT_OK.

Later, you can replace it with a loader that reads a separate payload from disk and jumps to it, but compiling the program into the kernel is the simplest way to experiment with QEMU first.