FableOS

A from-scratch x86-64 hobby kernel written in C, booted with Limine, and developed in QEMU. The long-term goal is a compact OS that can run LLM inference on bare metal.

Current features

• Boot: Limine (BIOS + UEFI hybrid ISO), higher-half kernel, physical memory reached through Limine's higher-half direct map (HHDM).
• Serial console: COM1 at 115200 baud, a small printf, and leveled logging.
• Physical memory manager: buddy allocator for 4 KiB to 2 MiB blocks, using per-order free lists and bitmaps, with an invariant checker (pmm_check).
• Kernel heap: kmalloc / kfree with slab caches for 16 to 2048 byte objects and direct page allocation for larger requests. Initialized at boot.

Future plans

• Interrupts: IDT and exception handlers
• Timer
• Paging and a virtual memory manager
• Scheduler

Building and running

Requirements:

• x86_64-elf-gcc and x86_64-elf-ld (cross toolchain)
• xorriso and qemu-system-x86_64
• Limine's prebuilt binaries in ./limine (or point LIMINE_DIR at them)

make          # build build/fableos.elf
make run      # build the ISO and boot it in QEMU; serial output goes to the terminal
make test     # build and run the host-side unit tests
make clean

Testing

200+ host-side unit tests cover the console, string utilities, PMM, and heap. They run against a simulated physical memory arena under AddressSanitizer and UndefinedBehaviorSanitizer. I design the allocators and specify what to test; Claude Code writes the test code.