popcorn: A toy OS kernel

popcorn is the kernel for the hobby OS that I am currently building. It's far from finished, or even being usable. Instead, it's a sandbox for me to play with kernel-level code and explore architectures.

The design goals of the project are:

• Modernity - I'm not interested in designing for legacy systems, or running on all hardware out there. My target is only 64 bit architecutres, and modern commodity hardware. Currently that means x64 systems with Nehalem or newer CPUs and UEFI firmware. Eventually I'd like to work on an AArch64 port, partly to force myself to factor out the architecture-dependent pieces of the code base.

• Modularity - I'd like to pull as much of the system out into separate processes as possible, in the microkernel fashion. A sub-goal of this is to explore where the bottlenecks of such a microkernel are now, and whether eschewing legacy hardware will let me design a system that's less bogged down by the traditional microkernel problems. Given that there are no processes yet, the kernel is monolithic by default.

• Exploration - I'm really mostly doing this to have fun learning and exploring modern OS development. Modular design may be tossed out (hopefully temporarily) in some places to allow me to play around with the related hardware.

Building

Popcorn uses the ninja build tool, and generates the build files for it with the generate_build.py script. The other requirements are:

• python 3 for generating the build config
  • The Jinja2 package is also required
• clang
• mtools
• ninja
• curl for downloading the toolchain

Setting up the cross toolchain

If you have clang and curl installed, runing the scripts/build_sysroot_clang.sh script will download and build a nasm/binutils/LLVM toolchain configured for building Popcorn host binaries.

Building and running Popcorn

Once the toolchain has been set up, running generate_build.py will set up the build configuration, and ninja -C build will actually run the build. If you have qemu-system-x86_64 installed, the qemu.sh script will to run Popcorn in QEMU -nographic mode.

I personally run this either from a real debian amd64 testing/buster machine or a windows WSL debian testing/buster installation. The following should be enough to set up such a system to build the kernel:

sudo apt install qemu-system-x86 nasm clang-6.0 mtools
sudo update-alternatives /usr/bin/clang clang /usr/bin/clang-6.0 1000
sudo update-alternatives /usr/bin/clang++ clang++ /usr/bin/clang++-6.0 1000