diosix

This is a lightweight and secure multiprocessor microkernel operating system written in Rust for 32-bit and 64-bit RISC-V systems.

It is a work in progress: I'm starting from scratch after previously writing a working microkernel for 32-bit SMP x86 computers in C and assembly.

I learned a lot from that first foray, and this is the second iteration of diosix. Crucially, it will be written in Rust, a C/C++-like programming language that has a fierce emphasis on guaranteed memory safety, threads without data races, and other security features. I chose RISC-V because it's an interesting new ground to explore, whereas there are countless x86 and Arm operating system kernels out there.

Dependencies

To build diosix for a 32-bit RISC-V system, make sure you've cross-compiled and installed the latest RISC-V port (v2.30) of GNU binutils as the kernel requires this toolkit. You'll next need to use rustup to install the nightly toolchain of Rust. The default target must be the build host's architecture (likely x86_64) and you must install the riscv32imac-unknown-none-elf target, too. (Currently, Rust only supports 32-bit RISC-V. As soon as 64-bit support appears, I'll target that as well.)

If in doubt, here's a list of steps to create your RISC-V Rust cross-compiler toolchain for diosix on a Debian-like system, which I recommend running in a container or virtual machine to avoid polluting your main environment:

sudo apt-get update
sudo apt-get install flex bison m4 sed texinfo
mkdir $HOME/cross
mkdir $HOME/src
cd $HOME/src
git clone -b riscv-binutils-2.30 https://github.com/riscv/riscv-binutils-gdb.git
cd riscv-binutils-gdb
./configure --prefix $HOME/cross --target=riscv32-elf
make
make install
rustup toolchain install nightly
rustup default nightly
rustup target install riscv32imac-unknown-none-elf

Make sure your paths are set up to find Rust and Cargo – I use this in my ~/.bashrc:

source $HOME/.cargo/env
export PATH=$PATH:$HOME/cross/bin

Then you should be ready to clone diosix...

cd $HOME/src
git clone https://github.com/diodesign/diosix.git
cd diosix

...and follow the instructions below to build and run it.

Building and running

You must use the supplied build.sh script, which sets up Cargo to compile, assemble, and link the project. Its syntax is:

./build.sh --triple [build triple] --platform [target platform]

Supported triples and platforms are listed in the build.sh file. The compiled kernel executable can be found in target/triple/release/kernel for the given build triple. So, for example,

./build.sh --triple riscv32imac-unknown-none-elf --platform sifive_u34
qemu-system-riscv32 -machine sifive_u -kernel target/riscv32imac-unknown-none-elf/release/kernel -nographic

...will build a kernel for a 32-bit RISC-V CPU in a SiFive Freedom U34-compatible system, and run it in Qemu. To build and run diosix on Qemu's multi-processor Virt hardware environment, try:

./build.sh --triple riscv32imac-unknown-none-elf --platform qemu32_virt
qemu-system-riscv32 -machine virt -kernel target/riscv32imac-unknown-none-elf/release/kernel -nographic -smp 4

Right now, the kernel assumes 16MB or more of DRAM is present. Qemu defaults to 128MB. Here's a screenshot of the kernel booting in a 32-bit quad-core Qemu Virt hardware environment, and writing some debug out to the virtual serial port:

Branches

All current development work is done in master and targets RISC-V. The x86 branch holds an early port of the Rust microkernel for Intel-compatible PC systems. The x86hypervisor branch holds an early attempt to build hypervisor features into the x86 branch. You're welcome to update these so they catch up with master, however my focus will be on the RISC-V port.

Contact

Feel free to email me, Chris Williams, if you have any questions, want to get involved, have source to contribute, or found a security flaw. You can also find me, diodesign, on Freenode IRC in the #osdev channel, or on Twitter.

Copyright, license, and thanks

Copyright © Chris Williams and contributors, 2018. See LICENSE for source code and binary distribution and use.

src/contrib/hermit-dtb: Copyright © 2018 Colin Finck, RWTH Aachen University.

With thanks to Philipp Oppermann for his guide to writing kernel-level Rust code, David Craven and everyone else who helped port Rust to RISC-V, and to the OSdev community for its notes and documentation.