feat: initial scalable x86_64 microkernel skeleton with Limine, Rust, C HAL, and C++20 IPC
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RarDog
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# opencoreC: High-Performance x86_64 Microkernel OS
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**opencoreC** is a modern, modular, capability-based microkernel operating system written in **Rust (`#![no_std]`)**, **Freestanding C**, and **Modern C++20**. It is designed around principles of strict hardware isolation, capability security, and zero-copy / fast-path inter-process communication (IPC).
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---
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## 🏛️ Architecture Overview
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The system follows a pure microkernel design paradigm where only the essential primitives reside in **Ring 0**, while device drivers, file systems, and system servers operate in isolated **Ring 3** user spaces.
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```mermaid
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graph TD
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subgraph Ring 3 [User Space - Ring 3]
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INIT["init_server (C++20 Root Server)"]
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PROCMGR["procmgr (Process & Server Manager)"]
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UART_DRV["uart_driver (16550 COM1 Driver)"]
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FS["VFS / Storage Server (Future)"]
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end
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subgraph Ring 0 [Microkernel - Ring 0]
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IPC["Fast-Path IPC Dispatcher (Registers + SHM)"]
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CAP["Capability Table & CNode Tracker"]
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VMM["Virtual Memory Manager (PML4 4-Level Paging)"]
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PFA["Physical Frame Allocator (Bitmap Allocator)"]
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SCHED["Thread Scheduler & Context Switch (ASM)"]
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end
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INIT -- "Fast-Path IPC (Syscall)" --> IPC
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PROCMGR -- "Fast-Path IPC (Syscall)" --> IPC
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UART_DRV -- "Fast-Path IPC (Syscall)" --> IPC
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IPC --> CAP
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IPC --> SCHED
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```
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### 🔀 Language & Subsystem Distribution
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| Component | Language | Privilege | Responsibilities |
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| :--- | :--- | :--- | :--- |
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| **Microkernel Core** | **Rust** (`#![no_std]`) | Ring 0 | PFA (Physical Memory), VMM (Paging), Capabilities, Fast IPC dispatcher, Scheduler. |
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| **Low-Level Glue** | **x86_64 ASM** | Ring 0 / 3 | `_start`, `switch_to` context switch, `syscall_entry` / `sysretq`, IDT vectors. |
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| **HAL & Hardware** | **C** (`-ffreestanding`) | Ring 3 / Ring 0 | Minimal bare-metal libc, 16550 UART COM driver, PCI bus scanning, APIC/IOAPIC. |
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| **User Services** | **C++20** (`-nostdlib`) | Ring 3 | System servers, process management, RAII IPC endpoints (`ipc::Endpoint`, `ipc::SharedBuffer`). |
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---
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## 📁 Repository Structure
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```text
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opencoreC/
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├── Cargo.toml # Root Rust workspace manifest
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├── rust-toolchain.toml # Fixed toolchain (x86_64-unknown-none)
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├── Makefile # Unified root build system
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├── CMakeLists.txt # Alternative CMake build for C/C++ components
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├── limine.conf # Limine bootloader configuration
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├── config/
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│ ├── linker.ld # Higher-half kernel linker script (0xffffffff80000000)
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│ └── user.ld # Userspace ELF linker script (0x400000)
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├── include/
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│ └── abi/
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│ ├── types.h # ABI primitive types (cap_t, sysret_t, vaddr_t)
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│ ├── syscalls.h # Syscall numbers and inline assembly wrappers
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│ └── ipc.h # Fast-Path IPC register layout and SHM headers
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├── kernel/ # Microkernel crate (Rust)
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│ ├── Cargo.toml
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│ ├── asm/
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│ │ ├── context.S # Cooperative/Preemptive context switcher
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│ │ └── syscall_entry.S # x86_64 fast syscall trampoline
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│ └── src/
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│ ├── main.rs # Kernel entry point & self-tests
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│ ├── limine_requests.rs # Limine protocol responses (HHDM, Memmap)
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│ ├── arch/ # GDT, TSS, IDT, Syscall MSRs
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│ ├── mm/ # Physical Frame Allocator & 4-Level Paging
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│ ├── ipc/ # Register-based Fast-Path IPC
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│ └── sched/ # Thread control blocks & scheduler
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├── lib/
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│ ├── libc/ # Minimal freestanding C library
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│ └── libipc_cpp/ # Modern C++ RAII IPC client library
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├── hal/ # Hardware Abstraction Layer (UART, PCI, APIC)
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└── servers/ # Ring 3 User-space servers (init, procmgr, uart_driver)
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```
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---
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## ⚡ Fast-Path IPC Specification
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Short messages (up to 32 bytes of arguments) are passed directly through CPU registers without memory allocations or deep kernel stack copies:
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* **`RAX`**: Syscall Number (`SYS_IPC_CALL = 1`, `SYS_IPC_REPLY_RECV = 2`, etc.)
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* **`RDI`**: Target Capability Handle (`cap_t dest_cap`)
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* **`RSI`**: IPC Opcode / Interface Method ID
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* **`RDX`**: Argument 0 (`uint64_t`)
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* **`R8`** : Argument 1 (`uint64_t`)
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* **`R9`** : Argument 2 (`uint64_t`)
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* **`R10`**: Argument 3 / SHM token (`uint64_t`)
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* **Return Registers**: `RAX` (Status code), `RDX` (Result 0), `R8` (Result 1)
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---
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## 🚀 Building & Running
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### Prerequisites
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* `rustc` & `cargo` (with target `x86_64-unknown-none`)
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* `gcc` & `g++` (supporting C11 and C++20)
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* `qemu-system-x86_64`
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### Quick Start
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1. **Build all components:**
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```bash
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make all
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```
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2. **Run in QEMU with Serial Console Output:**
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```bash
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make run
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```
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3. **Clean build artifacts:**
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```bash
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make clean
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```
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---
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## 🗺️ Roadmap
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- [x] Higher-Half Limine bootloader protocol initialization (HHDM).
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- [x] Physical Frame Allocator (PFA) via bitmap.
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- [x] 4-Level Paging (VMM) with dynamic page table allocation.
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- [x] Fast-Path register IPC infrastructure (`syscall`/`sysretq`).
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- [x] Freestanding bare-metal libc and 16550 UART driver.
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- [x] Modern C++ RAII IPC wrappers and initial userspace servers.
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- [ ] **Phase 1:** ELF Loader, User Address Space isolation, and `iretq` jump to Ring 3.
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- [ ] **Phase 2:** Synchronous IPC Rendezvous (blocking call / reply loop).
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- [ ] **Phase 3:** Preemptive Multi-Tasking via LAPIC Timer interrupts.
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- [ ] **Phase 4:** Userspace device driver model & interrupt forwarding.
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---
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## 📜 License
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Distributed under the MIT / Apache-2.0 License.
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