Zythos

A minimal, embeddable operating system written from scratch in C.

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About

Zythos is a from-scratch, x86 (32-bit protected mode) operating system built for minimalism and embeddability. It boots via a custom real-mode stage1/stage2 bootloader, runs a hand-written kernel, and is paired with its own toolchain — including a compiler, assembler, linker, C library, and coreutils — built specifically for the system rather than ported wholesale from Linux.

powerpc / powerpc64 support is planned as a future architecture target.

Features

• Custom bootloader — 16-bit real-mode stage1 (FAT12/16/32 BPB, BIOS disk read via CHS/LBA) and stage2, loading the kernel at 0x100000
• Kernel — memory management (custom kmalloc/kfree allocator), IDT and int 0x80 syscall dispatch, ELF32 loader
• BCC — a minimal, purpose-built C compiler/interpreter (inspired by c4)
• Own toolchain — an in-progress binutils suite: a freestanding assembler with a custom object format, and a linker based on tiny-link
• zlibc — a custom C library with multi-arch raw syscall wrappers
• Userland — a non-Unix shell (zsh), a minimal nolibc-based shell, and coreutils (including ls, built directly against FAT32 structures)
• ttar — a "Tiny tar" implementation supporting create/extract of ustar-format archives
• sysfetch — a neofetch-style system info tool
• Lua - standard lua without some tools.

you probably need the zlibc library to run userland programs.

Repository Layout

arch/      # architecture-specific code (boot.asm, etc.)
base/      # base subsystem tree
core/      # core subsystem
drivers/   # device drivers
fs/        # filesystem code (FAT32; ext2 under consideration)
include/   # shared headers (kernel + imported Linux-style headers)
init/      # kernel init sequence
input/     # input handling (keyboard, etc.)
kernel/    # kernel core (main.c, syscalls, IDT)
mm/        # memory management
net/       # networking
scripts/   # build/dev scripts
userland/  # userland programs
usr/       # usr tree

Building

Zythos is developed in a Linux container (GitHub Codespaces). Build instructions and toolchain requirements are being finalized as the custom binutils suite matures.

make run

This produces a bootable disk image that can be run in an emulator such as QEMU:

qemu-system-i386 -drive format=raw,file=zythos.img

Status

Zythos currently boots and runs a working userland shell with basic syscalls (read/write/exit), memory allocation, and an ELF32 loader. Development is active and many subsystems (filesystem choice, paging/VMM, process model) are still evolving.

Credits

• moshego189 — tiny-link, the basis for Zythos's linker
• seancfoley — Java-side reference work
• tayoky — tvi headers and Zemulate
• ndevilla — iniparser
• wtarreau — libc reference. Huge thanks
• fsantanna — SDL
• Robert-van-Engelen — Lisp reference
• The Lua Team — Lua
• rswier — c4
• Rui314 — other cc (chibicc)
• pardeep-singh — SQLite
• wkozek — zlib tools
• Ferki-git-crestor — ttar
• keyboard.h, keycodes.h, and keymap.h originally from BoredOS by Lluciocc, used under GPL.
• Bootloader design informed by the NanoByte OS tutorial series.

License

GPL-2.0