TinySys

An implementation of a kernel entirely from scratch.

Motivation for this Project

I always prefer to know how the things I use on a daily basis work under the hood. One of those things is Linux, which I use on all of my devices.

Maybe I'll get it to the point where it can be considered an operating system, eventually...

Tech Stack: literally just Zig

Many would want to use C/C++ for such a project. So why choose Zig, you may ask? Because it has:

• an amazing build system (check the build.zig),
• the beautiful comptime keyword, instead of C preprocessor macros,
• defer and errdefer, handling 95% of what the borrow checker in Rust is for,
• no hidden control flow, everything is explicit and therefore easier to reason about,
• no hidden allocations, it is all explicit, using the std.mem.Allocator interface,

and because I just wanted to see how Zig does in such a project, at the lowest level of software there is! (aside from firmware maybe)

First Prototype Goals - for the Hack Club Macondo YSWS

finished

• Booting via the SBI boot protocol
• UART driver for basic printing
• A single U-mode process executing -> just a kernel-embedded binary at first -> basic syscalls work: write, exit

Future Goals

• Small TTY/Shell Initial Process:
  • using basic graphics -> bitmap font rendering?
  • environment variables and $PATH lookups
  • coloring support (ANSI? -> maybe something less complex)
• Symmetric Multi-Processing:
  • implement infrastructure for easly declaration of per-CPU state (using the tp register)
  • simple preemptive scheduler, maybe based on fair shares?
• Persistent Filesystem:
  • FAT32 first
  • Ext4 later
• Advanced Graphics Support:
  • windowing/window compositor => Wayland protocol?

Project Structure

• src/ Kernel and Bootloader
• libsys/ System Zig Library, equivalent to a POSIX libc
• apps/ Userspace Applications
  • apps/hello-world: A hello world program, that simply prints to stdout.

Building and Running from Source Code

Requirements:

• Zig 0.16.0
• QEMU installation including qemy-system-riscv to emulate the RISC-V 64-bit ISA

# Run in an optimized build in a headless QEMU with maximum verbose logging
zig build -Dheadless -Dlog-level=debug --release=small run