Re: Plug-in Licensing

[Justin Seyster <jrseys at gmail dot com>]

Thanks for this advice.  The link to the GCC Exception was especially helpful.

The trick here is that I'm actually releasing a library designed to be
linked into plug-ins.  I want the library itself to be copyleft but
for plug-in authors to retain any licensing flexibility that they
would have when releasing a stand-alone GCC plug-in.

It sounds like the GPLv3 will do that for me, so that's my plan unless
somebody corrects me.
        --Justin

On Tue, Oct 19, 2010 at 4:49 PM, Ian Lance Taylor <iant@google.com> wrote:
> Justin Seyster <jrseys@gmail.com> writes:
>
>> I'm getting ready to release plug-in code, and I want to have a very
>> clear idea about licensing before I release. ?I'm leaning towards
>> releasing everything as GPLv3, but I do want to know exactly what is
>> and isn't allowed.
>
> GPLv3 is fine.
>
>> I know this issue was debated quite intensely before plug-in support
>> got added, but my understanding is that there was a final consensus.
>> I can't find one document though that explains exactly what this
>> consensus was.
>
> The document is here:
>
> http://www.gnu.org/licenses/gcc-exception.html
>
> See also the rationale and FAQ that it links to.
>
> Basically, if you use a plugin with gcc, and the plugin is not
> GPL-compatible, then the resulting compiled code is covered by the GPL.
>
>> I vaguely remember a proposal that there would be no restriction on
>> plug-in licensing but that non-free plug-ins could only be used to
>> compile Free software, but that's not documented anywhere I can find.
>
> That's pretty much it.
>
>> GCC itself now requires that plug-ins export a
>> plugin_is_gpl_compatible symbol, which implies that the plug-in's
>> license need only be compatible with the GPL. ?Is it ok to release
>> LGPL- or BSD-licensed plug-ins?
>
> Sure, both of those licenses are GPL-compatible.
>
>> My understanding is that, in general, only GPLv3 code can link against
>> GPLv3 code, which would imply that my plug-in code must be GPLv3.
>
> That is incorrect. ?You can link code under any GPL-compatible license
> with GPLv3 code, and the resulting executable will be covered the union
> of both licenses. ?Since GPLv3 tends to be stricter than any
> GPL-compatible license, this generally means that the result is under
> GPLv3. ?There is a (non-exhaustive) list of GPL-compatible licenses
> here:
>
> http://www.gnu.org/licenses/license-list.html#GPLCompatibleLicenses
>
> Ian
>