The Selfie Project provides an educational platform for teaching undergraduate and graduate students the design and implementation of programming languages and runtime systems. The focus is on the construction of compilers, libraries, operating systems, and virtual machine monitors. The common theme is to identify and resolve self-reference in systems code which is seen as the key challenge when teaching systems engineering, hence the name.

Selfie is a self-contained 64-bit, 11-KLOC C implementation of:

• a self-compiling compiler called starc that compiles a tiny but still fast subset of C called C Star (C*) to a tiny and easy-to-teach subset of RISC-V called RISC-U,
• a self-executing emulator called mipster that executes RISC-U code including itself when compiled with starc,
• a self-hosting hypervisor called hypster that provides RISC-U virtual machines that can host all of selfie, that is, starc, mipster, and hypster itself, and
• a tiny C* library called libcstar utilized by selfie.

Selfie generates ELF binaries that run on real RISC-V hardware as well as on QEMU and are compatible with the official RISC-V toolchain, in particular the spike emulator and the pk kernel.

In this Github repository, I'm documenting my journey to write a self-compiling compiler for a subset of the C language. I'm also writing out the details so that, if you want to follow along, there will be an explanation of what I did, why, and with some references back to the theory of compilers.

But not too much theory, I want this to be a practical journey.

Emscripten plugs into llvm-gcc or CLANG and intercepts the intermediate code, which it then translates into JavaScript. That JavaScript then runs natively in modern browsers with little evidence of slowdown. As proofs of concept they compiled Unreal 3, the Nebula3 engine, ScummVM, VICE, OpenSCAD, itself (yes, it's self-hosting), and a half-dozen popular programming languages into JavaScript and run them inside of web browsers.