LGPL and prime95

[Prime95]

Any lawyers here?

I get a headache reading LGPL licensing rules. If prime95 calls GMP functions in a GMP shared library will I run afoul of the LGPL license in any way?

Remember that prime95 does not publish all its source code and thus cannot use GPL code.

[Xyzzy]

A possible resource for an answer: https://opensource.stackexchange.com/

[CRGreathouse]

Originally Posted by Prime95

I get a headache reading LGPL licensing rules. If prime95 calls GMP functions in a GMP shared library will I run afoul of the LGPL license in any way?

My understanding is that this is the whole point of the LGPL -- that you can link to a shared LGPL library even if your software is not open-source at all.

[Mysticial]

Yes, you're allowed to link to LGPL from closed-sourced code. But there is a difference between dynamic linking and static linking.

• If you're dynamically linking, there are no issues at all.
• If you're statically linking, you must provide a way for somebody to relink their own version of the LGPL library.

The idea here is that someone must be able to use their own version of the LGPL library. In the case of dynamic linking, they can simply swap out the library. In the case of static linking, that's not possible. Therefore, you're required to provide a way to relink.

There are exceptions though. For example, most of the "system libraries" in Linux (i.e. libc) have a static-linking exception to allow static-linking without the ability to relink. Otherwise, every closed-sourced program compiled with GCC and distributed would be in violation of the LGPL. I don't believe GMP has this static-linking exception.

Disclaimer: I'm not a lawyer and this does not constitute as legal advice.