Clean Room Development Guide

December 24, 2025 · View on GitHub

This document outlines the clean room development process for building a Win32-compatible operating system in the custom Hexa programming language, using ReactOS as a reference. The goal is to ensure legal safety and avoid intellectual property infringement, particularly with respect to Microsoft's proprietary Windows code.

Win32 compatibility is implemented as a plugin—operating system is operable without its presence. This further strengthens legal safety by openly demonstrating that Greentea OS is not a competitive threat to Microsoft's currently active commercial products (e.g. Windows 11), as required by the law.

Purpose

Clean room development ensures our OS is functionally compatible with the Win32 API without copying proprietary code.

In this example, ReactOS, an open-source OS under the GNU GPL, serves as a third-party reference for understanding Win32 behavior and OS architecture.

Due to Greentea OS being new, independent project in different programming language, ReactOS works as a "clean room source of the third-party knowledge" in relation to it. The same applies to other projects.

Clean Room Principles

Clean room states that replication of Win32 functionality should happen without copying proprietary code, using only public specifications and third-party references like ReactOS. This requirement is relaxed to a degree according to directives related to reverse engineering, but still is a strong general approach to maximize legal safeguards. You may learn more about the directives from the README in the root of this repo.

  1. Reference, Don’t Copy:

    • Use ReactOS’s source code (available on GitHub) to study Win32 API behavior, kernel structures (e.g., ntoskrnl), and driver interfaces (e.g., ntoskrnl/io).

  2. Leverage Public Documentation:

    • Rely on Microsoft’s public resources (e.g., MSDN, Windows SDK) for Win32 API specifications to minimize dependence on ReactOS.
    • Use public documentation to define expected behavior for APIs and kernel components.

  3. Custom Language Advantage:

    • Implement all code in the Hexa programming language, which inherently distances our implementation from ReactOS’s and Microsoft's C/C++ codebases.
    • Hexa’s unique syntax forces reengineering of low-level components, strengthening our clean room claim.

  4. Document the Process:

    • Maintain records of development, showing that ReactOS was used only as a functional reference (e.g., for API behavior or system design).
    • Log how each component was designed and implemented independently in Hexa.
    • This is not a strict requirement, and generally satisfied with the presence of the Git commit history.
    • A separate log or design document alongside Git history would be more robust for legal defense.

  5. Avoid LGPL Conflicts:

    • Do not incorporate third-party licensed code into the project unless the code part in question is LGPL-compatible, as this is the primary Greentea OS license.
    • We do not accept proprietary code.

Implementation Guidelines

Win32 compatibility is a modular plugin, ensuring Greentea OS operates independently and does not compete with Microsoft’s active products, per legal requirements.

  • Study References: Analyze ReactOS’s ntoskrnl (kernel), win32k (graphics), and dll/win32 (Win32 APIs) to understand Win32-compatible OS architecture.
  • Write Original Code: Implement all functionality in Hexa, focusing on replicating observed behavior (e.g., API inputs/outputs/side effects) rather than code structure.
  • Test Independently: Use Microsoft’s tools (e.g., Application Verifier, Driver Verifier) to validate Win32 compatibility, reducing reliance on ReactOS’s test suite.
  • Testing with Microsoft’s tools ensures we’re aligning with official Win32 specs, not just ReactOS’s implementation.
  • Consult an intellectual property lawyer to review the development process and ensure compliance with clean room principles.
  • Avoid any direct use of Microsoft’s proprietary code or documentation not publicly available.
  • If in doubt, prioritize public Win32 API specifications over ReactOS’s implementation details.

Commitment

By following these guidelines, we ensure our OS is a legally independent implementation of a Win32-compatible system, leveraging ReactOS as a reference while maintaining clean room integrity.