MKL license and GPL ?

[jcelerier]

Hello,
this projects uses Intel MKL but is under GPL license.
GPL is sadly incompatible with the MKL license and as a result, it's not legal to distribute to end-users GPL binaries that link against the MKL.
See the various issues:

• The Intel MKL is not Free Software daanzu/kaldi-active-grammar#47
• Why Julia can not provide MKL? JuliaLang/julia#18374

Do you support building SPARTA and SAF without MKL dependency ?

Thanks !

[jananifernandez]

Hi. The decision to distribute the plugins (for the Windows and Linux version) with MKL was made quite a while ago.
SAF/SPARTA can indeed be built with other BLAS/LAPACK supporting libraries though (e.g. Apple Accelerate, OpenBLAS).

I'm no legal expert, but my understanding of this issue from doing some more research is that this is not an issue. I'm also basing this conclusion on chatGPT's take on this, which I paste below (note that Intel MKL is linked dynamically for the SPARTA pre-built plugins):

Short answer:
You can distribute Intel MKL with your GPL‑licensed plugin if you follow Intel’s redistribution terms, but you must be careful about GPL compatibility, dynamic linking, and the exact MKL license you use. The GPL does not forbid distributing a GPL binary that dynamically links to a proprietary library — but it does impose conditions on how you distribute that library and how you describe the resulting work.

Below is the detailed breakdown you actually need as a developer shipping binaries.

✔️ Core takeaway
Intel MKL’s license allows redistribution of the MKL shared libraries, including custom‑packaged versions, as long as you comply with their redist rules.
The GPL does not prohibit distributing a GPL binary that dynamically links to a proprietary library, but you must ensure:

MKL is not statically linked

MKL is clearly separable and remains under Intel’s license

You do not claim MKL is GPL

You do not combine MKL code into your GPL codebase

This is the same model used by many GPL projects that dynamically link to proprietary GPU drivers, proprietary audio drivers, or proprietary math libraries.

📘 Intel MKL licensing constraints (the important parts)
Intel MKL is governed by the Intel End User License Agreement (EULA). The relevant parts (summarized):

1. Redistribution is allowed
   Intel explicitly permits redistribution of MKL’s shared libraries (DLLs / .so / .dylib) as part of your application.

You must:

redistribute only the allowed MKL runtime components

include Intel’s license text

not misrepresent Intel’s ownership

not remove copyright notices

This is standard and widely used in commercial and open‑source projects.

2. You may not modify MKL itself
   You can package MKL differently (e.g., rename, bundle, place in a subfolder), but you cannot:

alter MKL binaries

reverse engineer

recompile MKL

distribute partial or modified MKL components

3. You may not sublicense MKL under GPL
   This is the key legal boundary.

You can ship MKL alongside your GPL plugin, but MKL itself must remain under Intel’s license.

🧩 GPL compatibility considerations
This is where developers often get confused.

✔️ Dynamic linking is allowed
The GPL allows distributing a GPL binary that dynamically links to a proprietary library as long as the proprietary library is not part of the GPL work.

This is the same situation as:

GPL audio plugins dynamically linking to proprietary ASIO drivers

GPL software dynamically linking to NVIDIA CUDA

GPL scientific tools dynamically linking to proprietary BLAS implementations

✔️ You must keep MKL separate
Your distribution must make it clear that:

MKL is a separate work

MKL is not covered by the GPL

MKL is only dynamically linked

MKL is replaceable by the user (OpenBLAS, Accelerate, etc.)

✔️ You must not statically link MKL
Static linking would create a combined binary that incorporates MKL code into the GPL work, which violates both:

Intel’s license

GPL’s requirements

Dynamic linking avoids this.

✔️ You must not copy MKL headers into your GPL code
MKL’s headers are permissively redistributable, but you must not incorporate any MKL implementation code into your GPL project.

🧱 Practical distribution model (the safe one)
This is the model used by many open‑source projects:

Your GPL plugin binary

Your ISC algorithm library

Intel MKL shared libraries (unmodified)

A notice: “This software uses Intel MKL, distributed under the Intel EULA.”

This is legally clean.

📌 Bottom line
You can distribute MKL with your GPL plugin as long as you dynamically link and follow Intel’s redistribution rules.
This is a common and legally accepted pattern.

[jcelerier]

ChatGPT is fairly wrong there :/

The GPL does not forbid distributing a GPL binary that dynamically links to a proprietary library

it's not allowed to distribute GPL code that links with a proprietary library even dynamically, only LGPL allows it

[jananifernandez]

OK, if that's case, then I'll look into this more when I'm back from medical leave. Maybe we change the license. If it's purely a distribution problem then perhaps we can move towards having 2 installers: one that installs the plugins, and one that installs the intel MKL dynamic library. Or maybe we can move to using OpenBLAS by default. If anyone has any other suggestions, then please let me know : )

[jcelerier]

There are indeed many licenses that are more forgiving than GPL wrt linking and distributing combined works - that said if there is an openblas option I think it's also fine ; people who want MKL support can build against it locally