(Florian Mueller said) "But the implicit patent grant under the GPLv2 does not help if modified code infringes the same patent."
I don't think this is right. Surely the point is that any uses of code covered by patents held by its distributor are protected by the (implicit) GPL2 patent grant. In this particular case, *any* Sun/Oracle patents reading on *anything* done by GPL Java are granted to *all* derivative code of same. What is not granted is licence to patents that are not exercised in the original code.
In other words, "The implicit patent grant under the GPLv2 should be of great help if derivative code infringes on the same patent."
As I mentioned in a comment above, it seems to me that it would be quite feasible for Google to recreate Dalvik as a derivative work of GPL Java. It would be very interesting if Google did this:
- there would be a really free telephone
- the GPL2 patent grant might be tested in court (I suspect it has remained untested for good a reason)