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Open-source Firmware and Bootloaders

Version History
Date Description
Dec 7, 2020 add iPXE
May 6, 2020 Initial Version

In this blog post, I will review the current firmware and bootloader ecosystem.

Landscape

I admire those firmware projects, maybe because that’s where I started. At first I used SeaBIOS (the default one used by QEMU) to build OS. Then I came across UEFI, though I have never used it.

There are a lot open-source firmware projects. I was trying to understand their relationship. After some research, I drew the following landscape figure.

20200506-on-firmware-landscape.png

Bottom-up:

  • Coreboot/Libreboot/UEFI: for motherboard init, e.g., init memory controller.
  • UEFI/BIOS
  • iPXE
  • GRUB2/U-Boto: Bootloader
  • OS

Projects

  • Coreboot and Libreboot
    • Coreboot seems very interesting. It’s only doing one job, which is initialize the very low-level memory controller and on-board resources. It uses cache as memory.
  • SeaBIOS: the default BIOS used by QEMU
  • qboot: an alternative and lightweight BIOS for QEMU
    • Those are massive hackers, respect.
    • My experience about BIOS is calling them while the kernel (LegoOS) is running at 16-bit. BIOS is the OS for a just-booted kernel. I remember the lower 1MB is never cleared, maybe we could invoke the BIOS at 32 or 64-bit mode?
  • UEFI
    • UEFI EDK II
      • “EDK II is a firmware development environment for the UEFI and UEFI Platform Initialization (PI) specifications”
      • Part of the TianoCore project, an open-source UEFI platform
      • The Unified Extensible Firmware Interface (UEFI) is a specification that defines a software interface between an operating system and platform firmware. UEFI is designed to replace the Basic Input/Output System (BIOS) firmware interface.
      • OVMF: OVMF is an EDK II based project to enable UEFI support for Virtual Machines. OVMF contains sample UEFI firmware for QEMU and KVM.
    • Microsoft Project Mu, a separate fork of EDK II
      • “Project Mu is a modular adaptation of TianoCore’s edk2 tuned for building modern devices using a scalable, maintainable, and reusable pattern”
      • It’s homepage explains the motivation behind it. Microsoft Surface is using it.
    • A book: Beyond BIOS Developing with the Unified Extensible Firmware Interface.
  • Then boot loaders such as GRUB and U-Boot
  • iPXE, network bootloader, this is an open-source version. As their website says, iPXE allows you to: 
    boot from a web server via HTTP
boot from an iSCSI SAN
boot from a Fibre Channel SAN via FCoE
boot from an AoE SAN
boot from a wireless network
boot from a wide-area network
boot from an Infiniband network
control the boot process with a script

If you are using a normal laptop or desktop, chances are, none of those firmware is used. Normally machines are shipped with commercial firmwares.

To me, I like SeaBIOS project the most. It’s simple and can boot everything we need. (For example, Linux, LegoOS as well).

Last update: December 23, 2020

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