orOS — Monolithic 64-bit Kernel in Rust

Overview​

orOS is a 64-bit monolithic operating system kernel written entirely in Rust — no C, no assembly beyond what the bootloader provides. It runs in a #![no_std] freestanding environment, managing the full x86_64 CPU state without an underlying OS or standard library.

The project serves as a deep-dive into low-level systems programming: configuring the interrupt subsystem (GDT, IDT, PIC), setting up virtual memory with page tables, implementing multiple heap allocator strategies, driving the VGA text buffer and pixel-based framebuffer, and running a cooperative async task executor. It targets the x86_64-unknown-none triple and requires the Rust nightly toolchain.

Key Features​

• Freestanding execution: #![no_std] + #![no_main] — no standard library, no host OS, bare-metal boot via GRUB2 or UEFI
• Interrupt subsystem: Global Descriptor Table (GDT) with Task State Segment (TSS) for double-fault handling, Interrupt Descriptor Table (IDT) with handlers for breakpoint, double fault, page fault, timer (PIC IRQ0), and keyboard (PIC IRQ1)
• Memory management: Page table setup via OffsetPageTable, physical frame allocation from bootloader memory regions, virtual memory mapping for heap pages
• Three heap allocators: Bump allocator (linear), fixed-size block allocator (9 size classes with free lists), and linked-list allocator with free region merging — all behind Locked<T> using spin::Mutex
• VGA text-mode driver: Memory-mapped I/O to 0xb8000 (80×25 text mode), 16-color palette, line scrolling, thread-safe via spinlock + interrupt-disabled critical sections
• Framebuffer output: Pixel-based writer using noto-sans-mono-bitmap font rasterizer, supporting RGB, BGR, and U8 pixel formats
• Async task system: Cooperative executor with custom TaskWaker, BTreeMap-backed task registry, sleep-on-idle via hlt, and an async keyboard input stream
• Custom test framework: #![custom_test_frameworks] with QEMU exit-code integration — tests run in the actual kernel on real hardware emulation

Architecture​

A monolithic kernel organized into 7 subsystems:

┌─────────────────────────────────────────┐
│          init.rs (boot sequence)        │
│  IDT → GDT → PIC → paging → allocator  │
└──────────────┬──────────────────────────┘
               │
    ┌──────────┼──────────┬──────────┬──────────┐
    ▼          ▼          ▼          ▼          ▼
 interrupts  memory     screen     task       port
  gdt, idt   page tbl   vga        executor   serial
  handlers    frame     frame-buf  keyboard   qemu exit
  pic         bump      color
              fixed     macros
              linked

Tech Stack​