[llvm-dev] RFC: Improving license & patent issues in the LLVM community

[Daniel Berlin via llvm-dev]

On Mon, Oct 19, 2015 at 1:03 PM, Chris Lattner via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>
>> On Oct 19, 2015, at 10:57 AM, Renato Golin <renato.golin at linaro.org> wrote:
>>
>> On 19 October 2015 at 18:12, David Chisnall via llvm-dev
>> <llvm-dev at lists.llvm.org> wrote:
>>> One worry is that Apache 2 is incompatible with GPLv2 (is it incompatible with other licenses?)
>>
>> This is interesting, I did not know that...
>>
>> http://www.apache.org/licenses/GPL-compatibility.html
>>
>> "Despite our best efforts, the FSF has never considered the Apache
>> License to be compatible with GPL version 2, citing the patent
>> termination and indemnification provisions as restrictions not present
>> in the older GPL license."
>>
>> It seems to be compatible with GPLv3, though. But I think most
>> companies that use LLVM are stuck with GPLv2 due to the patents issue.
>
> Yes, this is a known concern with the Apache 2 license, but I don’t know if there is an actual “known” answer to this question.  DannyB or someone else can comment for sure, but my understanding is that the terms of the GPL2 prevent *any* license from including the sort of patent protection that we are looking for.
>

Note: GPLV2 and GPLv3 are *also* incompatible with each other (see
http://www.gnu.org/licenses/gpl-faq.en.html#v2v3Compatibility), so you
have larger issues if you are mixing those ;-).

Besides the obvious ones, there are subtle ones:
For example, it's not okay to use an old GPLv2 version of gcc and a
new version of GPLv3 libgcc with the runtime exception, because old
compiler is not "GPL-compatible" as that license defines it.