[wyldfire]

From https://llvm.org/foundation/relicensing/LICENSE.txt

    --- 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
    Software.

[billyoneal]

>Now, can anyone ELI5 the high-level goal of this exception?

I am not a lawyer; this is my extremely limited understanding.

1. Normally the Apache license requires attribution, even in binary forms. We can't say "You said #include <string>, now you must staple this to all your binaries". libstdc++ has a similar exception to the GPL for the same reason: http://gcc.gnu.org/onlinedocs/libstdc++/manual/license.html

2. Keep GPL folks happy :)

[corysama]

Thanks!

Now, can anyone ELI5 the high-level goal of this exception? At a glance it looks like GPL2 folks are still not happy with the patent provisions of Apache 2.0 and this is added to appease them.

[jcranmer]

There's two pieces to the exception.

The first piece is standard for compilers, and essentially says "our compiler linking in bits of this code into your code doesn't count." It means the license matters if you're modifying the compiler and support libraries yourself, but not if you're merely using the compiler.

The second piece revolves around the concerns of mixing licenses: Apache 2 and *GPLv3 are happy in combination, but that's because of some explicit compatibility text in GPLv3; this extends the compatibility text to GPLv2.