A flexible bootloader.

I want to write a small bootloader that can boot literally everywhere and anything, and that lets you easily add new platforms. This project builds upon my previous work on the following projects:

• povOS
• rpi3b-OS
• hello-efi
• santOS

To start off, I am planning to implement booting on the following platforms:

• UEFI (x86_64, ARM)
• Legacy BIOS (x86_64)
• Qemu Virt (ARM)
• Raspberry Pi 3 (ARM)
• Grub (x86_64)

Eventually I will support RISC-V and other boards like the BeagleBone Black, Raspberry Pi Pico 2, the STM32s and many others.

Design

To make the bootloader work with multiple platforms and load many operating systems, we need to design some abstractions:

• backend: the code that gets executed right after the CPU powers on, or after some other firmware
• core: the internal API exposed by the backend and used by the frontend, and common code
• frontend: the frontend sets up the CPU in a well defined state for the OS. This is the API that is presented to the OS, and it must be architecture specific.

The boot process itself is divided in multiple phases, inspired by coreboot:

• bootblock: the first stage executed after CPU reset, sets up an environment to run C
• romstage: initialize DRAM
• postcar: leave CAR (Cache As Ram) and load ramstage
• ramstage: main device init
• iperboot proper: common initialization and bootloader logic, loads the OS in memory
• payload (the OS)

This project also defines a fully custom frontend API, iperboot-protocol, inspired by multiboot and Linux's boot protocol.

Usage

git clone --recurse-submodules https://github.com/San7o/iperboot.git
cd iperboot

make
make img
make qemu

Select which backend to use (defualt is uefi):

make BACKEND=bios
make img BACKEND=bios
make qemu BACKEND=bios