Plan 42

**** Plan 42 LIVES! ****

After being left for many years, I've decided to revive Plan 42 using the same base as Sea-DOS. '

This project, forked from uefi-dev, aims to create a public-domain 64-bit Plan 9-like OS.

Status (as at 4th May 2025) - Builds (for me) but boot still drops to UEFI shell.

Acknowledgement

Plan 42 would not be possible without the excellent work of queso-fuego, whose uefi-dev code it is forked from. I also want to give huge thanks to him for making uefi-dev "public domain" under the Unlicense. Plan 42 too will be under the Unlicense.

Queso-fuego's original README for uefi-dev is shown below.

uefi-dev

This repo was originally to go along with the UEFI Development Series: https://www.youtube.com/playlist?list=PLT7NbkyNWaqZYHNLtOZ1MNxOt8myP5K0p

But can act as a basis for an efi application/bootloader example. Those videos are done now for an intro series, and most commits before late 2024 roughly corresponded to a given video in that playlist. Future videos could be done on an as wanted or requested basis.

The goal was to learn EFI development as from-scratch as possible, for freestanding bare metal programs, without using gnu-efi or posix-efi or other 3rd party premade libraries. Only using the UEFI specification and related documents, as feasible.

The current end result is headers for general UEFI definitions and helper functions, and an EFI OS loader application to load an ELF/PE/flat binary file as a starter "kernel", as well as print other various information discoverable/available via UEFI. It builds, runs, and boots in both a QEMU emulated environment and on real hardware for a dell xps 13 laptop ca. 2019.

Supported architectures are currently only x86_64, with stubs for Aarch64.

repo layout

efi_c is the main directory; it should hold the lastest developments and is used for building EFI applications and test kernels.

hello_efi is a directory for what was shown in the first UEFI intro/overview video. It has a basic "hello world" test EFI application.

dependencies

• C compiler supporting -std=c17 or later, and ability to output PE32+ object files. This repo assumes clang or x86_64-w64-mingw32-gcc (MinGW) for the default x86_64 target. Windows users can use the same MinGW gcc compiler. Clang, through LLVM, supports other targets for cross compiling with -target, while gcc has to use a different compiler for different target architectures.
• make; gnu make preferably, unless posix defines ifeq() or other niceties.
• qemu with ovmf firmware, x86_64 is provided as bios64.bin in the "UEFI-GPT-image-creator" directory, aarch64 as QEMU_EFI_AARCH64.raw and VARS raw files.

building

1. NOTE: This git repo uses submodules. To initialize everything use git clone --recurse-submodules https://github.com/queso-fuego/uefi-dev or after cloning use git submodule update --remote or git pull --recurse-submodules.
2. cd /efi_c/ && make (this should build the x86_64 target and launch qemu automatically).

Running/testing thereafter should only need make in the main efi_c directory.

running/testing

• Emulation: Use make in the efi_c directory to run using qemu/ovmf.
• Bare metal: On linux, I recommend using dd to write the disk image to e.g. a USB drive. Use lsblk or another way to find your USB's block device. An example using the default disk image name and assuming /dev/sdB as a USB drive could be dd if=uefi-dev/UEFI-GPT-image-creator/test.hdd of=/dev/sdb bs=1M. Note the 1 megabyte block size to reduce write time, and writing to the drive directly with sdb, not using a partition e.g. sdb1. On Windows, rufus works well to write raw image files directly to a USB drive: https://rufus.ie