⚠️ Historical design document. This predates the implementation and describes original intent, not the shipped system. For the as-built architecture see the Architecture Decision Records and the CHANGELOG; where they disagree with this file, they are correct.

QuantumOS Kernel Implementation Roadmap

First Principles Foundation

Core Tenets

1. Minimal Trusted Core - Only what cannot be in user space
2. Quantum Resources as First-Class Citizens - Not abstractions, but kernel-managed primitives
3. Capability-Based Security - No ambient authority, explicit grants only
4. Hardware-Agnostic but Hardware-Aware - Support multiple architectures natively

Phase 0.1: Bootstrap Kernel (v0.1)

Minimal Viable Kernel

• Entry Point: kernel/core/boot.c
• Memory Management: Basic paging, no heap yet
• Interrupt Handling: IDT setup, basic exceptions
• Serial Output: Early debugging via UART
• GDT/IDT: Basic x86_64 protection

Files to Create

kernel/core/
├── boot.c              # Entry point, arch-specific initialization
├── memory.c            # Basic paging setup
├── interrupts.c        # IDT, exception handlers
├── gdt.c              # Global descriptor table
└── console.c          # Early serial output

kernel/include/
├── boot.h
├── memory.h
├── interrupts.h
└── types.h

Makefile                # Cross-compiler build system

Phase 0.2: IPC Foundation (v0.1)

Message Passing Core

• IPC Primitives: Synchronous message passing only
• Capability System: Basic capability tokens
• Process Isolation: Separate address spaces
• Scheduler Stub: Round-robin for now

Key Files

kernel/ipc/
├── message.c          # Message passing implementation
├── capability.c       # Capability management
└── process.c          # Process creation/destruction

kernel/scheduler/
└── roundrobin.c       # Basic scheduler

Phase 0.3: HAL Abstraction (v0.2)

Hardware Abstraction Layer

• Architecture Support: x86_64 → ARM64 → RISC-V
• Device Detection: Basic PCI/ACPI enumeration
• Timer Support: Platform-agnostic timers
• Interrupt Routing: Architecture-agnostic IRQ handling

HAL Structure

kernel/hal/
├── x86_64/
│   ├── arch.c        # x86_64 specific code
│   ├── interrupts.c
│   └── timer.c
├── arm64/
│   ├── arch.c
│   ├── interrupts.c
│   └── timer.c
├── riscv64/
│   ├── arch.c
│   ├── interrupts.c
│   └── timer.c
└── common/
    ├── hal.c         # Architecture-agnostic interface
    └── device.c

Success Criteria for v0.1

• Kernel boots on x86_64 hardware
• Basic IPC between two processes
• Memory protection working
• Serial console output
• Cross-compilation working

Next Steps Toward v0.2

• Quantum resource abstractions
• User-space service spawning
• Advanced scheduling
• Device driver framework

Development Principles

1. No Optimizations Early - Correctness first
2. Test Each Component - Unit tests in kernel space
3. Document Assumptions - Clear comments on hardware dependencies
4. Keep It Small - Resist feature creep in kernel

Build System Requirements

• Cross-Compiler: GCC for target architectures
• Linker Script: Custom memory layout
• Debug Symbols: GDB support from day one
• CI Pipeline: Automated testing across architectures