Kwast (will be) an operating system, written in Rust, running WebAssembly. It uses a microkernel architecture for flexibility.
Since WebAssembly was designed to be a safe language, we can run it without having to use hardware usermode and multiple address spaces (optionally). Processes can be run in the same address space (multiple SIPs in a single hardware protection domain), or in seperate address spaces. This enables low-cost context switches, low-cost syscalls, and a microkernel design without a big performance hit. Another interesting thing is that it means the software is cross-platform and that the compiler could enable platform-specific optimisations.
For notes on Spectre, Meltdown and other related issues, see #10. An additional idea is to allow to use optional hardware protection domains in the future if requested.
Contents
Current status
Currently, it runs basic WebAssembly code in a basic multitasked environment. The heap uses a slab allocator design, and the virtual memory areas are managed by an AVL tree. For the ABI, I started with implementing WASI.
Here's a screenshot of a WASI compiled Rust program (userspace/wasm-test).
Getting started
These instructions help you get started with building the source and getting it to run.
Requirements
- make
- grub-mkrescue (you might also need to install xorriso)
- qemu-system-x86_64
- Rust and Cargo
- Optionally wasm-strip (from wabt), which reduces the binary size
Setting up a toolchain
You can setup your toolchain using the following steps:
# (Inside the project root folder.) # You'll need to get the rust nightly and install the wasi toolchain: rustup component add rust-src rustup target add wasm32-wasi # You'll also need a cross-compile binutils, I wrote a bash script that builds this for you. cd toolchain ./setup_cross_binutils.sh
Now you're ready to build and run the project!
Building & Running
There's currently a Makefile in the kernel folder. The Makefile there provides some rules:
# (Inside the project root folder.) make run # Builds iso and start a QEMU virtual machine # If you don't want to run, but only build a bootable ISO: make iso # You can make a release build using: make iso BUILD=release # (or run) # You can run tests using ./run_tests
Short-term goals
- Simple PS/2 server & similar small servers
- Run basic programs
- SMP
Built with
-
Cranelift - Code generator used to parse & run WebAssembly. Kwast uses a fork of Cranelift to let it work in a no_std environment.
-
To integrate Cranelift, wasmtime has been used as a reference implementation, which is licensed under the Apache License 2.0.
-
Spleen font - Spleen is a monospaced bitmap font licensed under the BSD 2-Clause "Simplified" License.