![jsix](assets/jsix.svg) # The jsix operating system **jsix** is a custom multi-core x64 operating system that I am building from scratch. It's far from finished, or even being usable - see the *Status and Roadmap* section, below. 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 architectures, and modern commodity hardware. Currently that means x64 systems with Nehalem or newer CPUs and UEFI firmware. (See [this list][cpu_features] for the currently required CPU features.) 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. * Exploration - I'm really mostly doing this to have fun learning and exploring modern OS development. Initial feature implementations may temporarily throw away modular design to allow for exploration of the related hardware. A note on the name: This kernel was originally named Popcorn, but I have since discovered that the Popcorn Linux project is also developing a kernel with that name, started around the same time as this project. So I've renamed this kernel jsix (Always styled _jsix_ or `j6`, never capitalized) as an homage to L4, xv6, and my wonderful wife. [cpu_features]: https://github.com/justinian/jsix/blob/master/src/libraries/cpu/include/cpu/features.inc ## Status and Roadmap The following major feature areas are targets for jsix development: #### UEFI boot loader _Done._ The bootloader loads the kernel and initial userspace programs, and sets up necessary kernel arguments about the memory map and EFI GOP framebuffer. Possible future ideas: - take over more init-time functions from the kernel - rewrite it in Zig #### Memory _Virtual memory: Sufficient._ The kernel manages virtual memory with a number of kinds of `vm_area` objects representing mapped areas, which can belong to one or more `vm_space` objects which represent a whole virtual memory space. (Each process has a `vm_space`, and so does the kernel itself.) Remaining to do: - TLB shootdowns - Page swapping - Large / huge page support _Physical page allocation: Sufficient._ The current physical page allocator implementation uses a group of blocks representing up-to-1GiB areas of usable memory as defined by the bootloader. Each block has a three-level bitmap denoting free/used pages. Future work: - Align blocks so that their first page is 1GiB-aligned, making finding free large/huge pages easier. #### Multitasking _Sufficient._ The global scheduler object keeps separate ready/blocked lists per core. Cores periodically attempt to balance load via work stealing. User-space tasks are able to create threads as well as other processes. Several kernel-only tasks exist, though I'm trying to reduce that. Eventually only the timekeeping task should be a separate kernel-only thread. #### API _In progress._ User-space tasks are able to make syscalls to the kernel via fast SYSCALL/SYSRET instructions. Syscalls made via `libj6` look to both the callee and the caller like standard SysV ABI function calls. The implementations are wrapped in generated wrapper functions which validate the request, check capabilities, and find the appropriate kernel objects or handles before calling the implementation functions. Current work in this area: - The protocol for processes and their children for both initialization and sharing resources. The kernel is ignorant of this, except for providing IPC capabilities. #### Hardware Support * Framebuffer driver: _In progress._ Currently on machines with a video device accessible by UEFI, jsix starts a user-space framebuffer driver that only prints out kernel logs. * Serial driver: _In progress._ The current UART driver does not expose the UART as an output resource yet, it merely gets the kernel logs and sends them over serial. * USB driver: _To do_ * AHCI (SATA) driver: _To do_ ## Building jsix uses the [Ninja][] build tool, and generates the build files for it with the `configure` script. The build also relies on a custom toolchain sysroot, which can be downloaded or built using the scripts in [jsix-os/toolchain][]. [Ninja]: https://ninja-build.org [jsix-os/toolchain]: https://github.com/jsix-os/toolchain Other build dependencies: * [clang][]: the C/C++ compiler * [nasm][]: the assembler * [lld][]: the linker * [mtools][]: for creating the FAT image [clang]: https://clang.llvm.org [nasm]: https://www.nasm.us [lld]: https://lld.llvm.org [mtools]: https://www.gnu.org/software/mtools/ The `configure` script has some Python dependencies - these can be installed via `pip`, though doing so in a python virtual environment is recommended. Installing via `pip` will also install `ninja`. A Debian 11 (Bullseye) system can be configured with the necessary build dependencies by running the following commands from the jsix repository root: ```bash sudo apt install clang lld nasm mtools python3-pip python3-venv python3 -m venv ./venv source venv/bin/activate pip install -r requirements.txt peru sync ``` ### Setting up the sysroot Build or download the toolchain sysroot as mentioned above with [jsix-os/toolchain][], and symlink the built toolchain directory as `sysroot` at the root of this project. ```bash # Example if both the toolchain and this project are cloned under ~/src ln -s ~/src/toolchain/toolchains/llvm-13 ~/src/jsix/sysroot ``` ### Building and running jsix Once the toolchain has been set up, running the `./configure` script (see `./configure --help` for available options) will set up the build configuration, and `ninja -C build` (or wherever you put the build directory) will actually run the build. If you have `qemu-system-x86_64` installed, the `qemu.sh` script will to run jsix in QEMU `-nographic` mode. I personally run this either from a real debian amd64 bullseye machine or a windows WSL debian bullseye installation. Your mileage may vary with other setups and distros. ### Running the test suite jsix now has the `test_runner` userspace program that runs various automated tests. It is not included in the default build, but if you use the `test.yml` manifest it will be built, and can be run with the `test.sh` script or the `qemu.sh` script. ```bash ./configure --manifest=assets/manifests/test.yml if ./test.sh; then echo "All tests passed!"; else echo "Failed."; fi ```