[llvm-dev] Relicensing: Revised Developer Policy

Chris Lattner via llvm-dev llvm-dev at lists.llvm.org
Mon Aug 7 08:53:42 PDT 2017

Hi all,

Now that we’ve settled on the license legalese to get to, we need to start the process of relicensing.  We’re still sorting through all of the details of what this will take, but the first step is clear: new contributions to LLVM will need to be under both the old license structure and the new one (until the old structure is completely phased out).  From a mechanical perspective, this is pretty simple, but I want to make sure that the community is aware of this and has time to digest and discuss any concerns.

In order to spell out what this will look like, we’ve gone ahead and revised http://llvm.org/docs/DeveloperPolicy.html to reflect what the new structure will look like.  While the license text is the canonical truth, the DeveloperPolicy serves a few purposes: it explains to non-lawyers what the license means, provides rationale for the design, and deals with relicensing process topics.

I’ve attached a draft of the revised document below.  Please take a look and let me know if anything should be further clarified or if you have any other questions and comments.  Thanks!


Copyright, License, and Patents

.. note::

   This section deals with legal matters but does not provide legal advice.  We
   are not lawyers --- please seek legal counsel from a licensed attorney.

This section addresses the issues of copyright, license and patents for the LLVM
project.  The copyright for the code is held by the contributors of
the code.  The code is licensed under permissive `open source licensing terms`_,
namely the Apache 2 license, which includes a copyright and `patent license`_.
When you contribute code to the LLVM project, you license it under these terms.

If you have questions or comments about these topics, please contact the
`LLVM Developer's Mailing List <mailto:llvm-dev at lists.llvm.org>`_.  However,
please realize that most compiler developers are not lawyers, and therefore you
will not be getting official legal advice.


The LLVM project does not collect copyright assignments, which means that the
copyright for the code in the project is held by the respective contributors.
Because you (or your company)
retain ownership of the code you contribute, you know it may only be used under
the terms of the open source license you contributed it under: the license for
your contributions cannot be changed in the future without your approval.

Because the LLVM project does not require copyright assignments, changing the
LLVM license requires tracking down the
contributors to LLVM and getting them to agree that a license change is
acceptable for their contributions.  We feel that a high burden for relicensing
is good for the project, because contributors do not have to fear that their
code will be used in a way with which they disagree.


The last paragraph notwithstanding, the LLVM Project is in the middle of a large
effort to change licenses, which aims to solve several problems:

* The old licenses made it difficult to move code from (e.g.) the compiler to
  runtime libraries, because runtime libraries used a different license from the
  rest of the compiler.
* Some contributions were not submitted to LLVM due to concerns that
  the patent grant required by the project was overly broad.
* The patent grant was unique to the LLVM Project, not written by a lawyer, and
  was difficult to determine what was protection was provided (if any).

The scope of relicensing is all code that is considered part of the LLVM
project, including the main LLVM repository, runtime libraries (compiler_rt,
OpenMP, etc), Polly, and all other subprojects.  There are a few exceptions:

* Code imported from other projects (e.g. Google Test, Autoconf, etc) will
  remain as it is.  This code isn't *developed* as part of the LLVM project, it
  is *used* by LLVM.
* Some subprojects are impractical or uninteresting to relicense (e.g. llvm-gcc
  and dragonegg). These will be split off from the LLVM project (e.g. to
  separate Github projects), allowing interested people to continue their
  development elsewhere.

To relicense LLVM, we will be seeking approval from all of the copyright holders
of code in the repository, or potentially remove/rewrite code if we cannot.
This is a large
and challenging project which will take a significant amount of time to
complete.  In the interim, **all contributions to the project will be made under
the terms of both the new license and the legacy license scheme** (each of which
is described below).  The exception to this is the legacy patent grant, which
will not be required for new contributions.

When all of the code in the project has been converted to the new license or
removed, we will drop the requirement to contribute under the legacy license.
This will achieve the goal of having
a single standardized license for the entire codebase.

If you are a prior contributor to LLVM and have not done so already, please do
*TODO* to allow us to use your code. *Add a link to a separate page here, which
is probably a click through web form or something like that.  Details to be
determined later*.

.. _open source licensing terms:

New LLVM Project License Framework

Contributions to LLVM are licensed under the `Apache License, Version 2.0
<https://www.apache.org/licenses/LICENSE-2.0>`_, with two limited
exceptions intended to ensure that LLVM is very permissively licensed.
Collectively, the name of this license is "Apache 2.0 License with LLVM
exceptions".  The exceptions read:


   ---- LLVM Exceptions to the Apache 2.0 License ----

   As an exception, if, as a result of your compiling your source code, portions
   of this Software are embedded into an Object form of such source code, you
   may redistribute such embedded portions in such Object form without complying
   with the conditions of Sections 4(a), 4(b) and 4(d) of the License.

   In addition, if you combine or link compiled forms of this Software with
   software that is licensed under the GPLv2 ("Combined Software") and if a
   court of competent jurisdiction determines that the patent provision (Section
   3), the indemnity provision (Section 9) or other Section of the License
   conflicts with the conditions of the GPLv2, you may retroactively and
   prospectively choose to deem waived or otherwise exclude such Section(s) of
   the License, but only in their entirety and only with respect to the Combined

We intend to keep LLVM perpetually open source and available under a permissive
license - this fosters the widest adoption of LLVM by
**allowing commercial products to be derived from LLVM** with few restrictions
and without a requirement for making any derived works also open source.  In
particular, LLVM's license is not a "copyleft" license like the GPL.

The "Apache 2.0 License with LLVM exceptions" allows you to:

* freely download and use LLVM (in whole or in part) for personal, internal, or
  commercial purposes.
* include LLVM in packages or distributions you create.
* combine LLVM with code licensed under every other major open source
  license (including BSD, MIT, GPLv2, GPLv3...).
* make changes to LLVM code without being required to contribute it back
  to the project - contributions are appreciated though!

However, it imposes these limitations on you:

* You must retain the copyright notice if you redistribute LLVM: You cannot
  strip the copyright headers off or replace them with your own.
* Binaries that include LLVM must reproduce the copyright notice (e.g. in an
  included README file or in an "About" box), unless the LLVM code was added as
  a by-product of compilation.  For example, if an LLVM runtime library like
  compiler_rt or libc++ was automatically included into your application by the
  compiler, you do not need to attribute it.
* You can't use our names to promote your products (LLVM derived or not) -
  though you can make truthful statements about your use of the LLVM code,
  without implying our sponsorship.
* There's no warranty on LLVM at all.

We want LLVM code to be widely used, and believe that this provides a model that
is great for contributors and users of the project.  For more information about
the Apache 2.0 License, please see the `Apache License FAQ
<http://www.apache.org/foundation/license-faq.html>`_, maintained by the
Apache Project.

.. note::

   The LLVM Project includes some really old subprojects (dragonegg,
   llvm-gcc-4.0, and llvm-gcc-4.2), which are licensed under **GPL
   licenses**.  This code is not actively maintained - it does not even
   build successfully.  This code is cleanly separated into distinct SVN
   repositories from the rest of LLVM, and the LICENSE.txt files specifically
   indicate that they contain GPL code.  When LLVM transitions from SVN to Git,
   we plan to drop these code bases from the new repository structure.

.. _patent license:


Section 3 of the Apache 2.0 license is a patent grant under which
contributors of code to the project contribute the rights to use any of
their patents that would otherwise be infringed by that code contribution
(protecting uses of that code).  Further, the patent grant is revoked
from anyone who files a patent lawsuit about code in LLVM - this protects the
community by providing a "patent commons" for the code base and reducing the
odds of patent lawsuits in general.

The license specifically scopes which patents are included with code
contributions.  To help explain this, the `Apache License FAQ
<http://www.apache.org/foundation/license-faq.html>`_ explains this scope using
some questions and answers, which we reproduce here for your convenience (for
reference, the "ASF" is the Apache Software Foundation, the guidance still
holds though)::

   Q1: If I own a patent and contribute to a Work, and, at the time my
   contribution is included in that Work, none of my patent's claims are subject
   to Apache's Grant of Patent License, is there a way any of those claims would
   later become subject to the Grant of Patent License solely due to subsequent
   contributions by other parties who are not licensees of that patent.

   A1: No.

   Q2: If at any time after my contribution, I am able to license other patent
   claims that would have been subject to Apache's Grant of Patent License if
   they were licenseable by me at the time of my contribution, do those other
   claims become subject to the Grant of Patent License?

   A2: Yes.

   Q3: If I own or control a licensable patent and contribute code to a specific
   Apache product, which of my patent claims are subject to Apache's Grant of
   Patent License?

   A3:  The only patent claims that are licensed to the ASF are those you own or
   have the right to license that read on your contribution or on the
   combination of your contribution with the specific Apache product to which
   you contributed as it existed at the time of your contribution. No additional
   patent claims become licensed as a result of subsequent combinations of your
   contribution with any other software. Note, however, that licensable patent
   claims include those that you acquire in the future, as long as they read on
   your original contribution as made at the original time. Once a patent claim
   is subject to Apache's Grant of Patent License, it is licensed under the
   terms of that Grant to the ASF and to recipients of any software distributed
   by the ASF for any Apache software product whatsoever.

Legacy License Structure

.. note::
   The code base was previously licensed under the Terms described here.
   We are in the middle of relicensing to a new approach (described above), but
   until this effort is complete, the code is also still available under these
   terms.  Once we finish the relicensing project, new versions of the code will
   not be available under these terms.  However, nothing takes away your right
   to use old versions under the licensing terms under which they were
   originally released.

We intend to keep LLVM perpetually open source and to use a permissive open
source license.  The code in
LLVM is available under the `University of Illinois/NCSA Open Source License
<http://www.opensource.org/licenses/UoI-NCSA.php>`_, which boils down to

* You can freely distribute LLVM.
* You must retain the copyright notice if you redistribute LLVM.
* Binaries derived from LLVM must reproduce the copyright notice (e.g. in an
  included README file).
* You can't use our names to promote your LLVM derived products.
* There's no warranty on LLVM at all.

We believe this fosters the widest adoption of LLVM because it **allows
commercial products to be derived from LLVM** with few restrictions and without
a requirement for making any derived works also open source (i.e. LLVM's
license is not a "copyleft" license like the GPL). We suggest that you read the
`License <http://www.opensource.org/licenses/UoI-NCSA.php>`_ if further
clarification is needed.

In addition to the UIUC license, the runtime library components of LLVM
(**compiler_rt, libc++, and libclc**) are also licensed under the `MIT License
<http://www.opensource.org/licenses/mit-license.php>`_, which does not contain
the binary redistribution clause.  As a user of these runtime libraries, it
means that you can choose to use the code under either license (and thus don't
need the binary redistribution clause), and as a contributor to the code that
you agree that any contributions to these libraries be licensed under both
licenses.  We feel that this is important for runtime libraries, because they
are implicitly linked into applications and therefore should not subject those
applications to the binary redistribution clause. This also means that it is ok
to move code from (e.g.)  libc++ to the LLVM core without concern, but that code
cannot be moved from the LLVM core to libc++ without the copyright owner's

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