At work, we use a version of GCC provided by a vendor of a proprietary OS. The vendor has modified gcc so that it will only run if it successfully acquires one of a limited number of licenses we've purchased from our license server. This seems very much not in the spirit of free software, and it's very annoying, but is it permitted under the GPL?
Assuming it is, shouldn't I also be able to request the modified source code from the vendor, and then make a new gcc executable without the obnoxious license check? Or could that be a terrible idea for legal reasons I'm ignorant of?