The question of whether what they've produced is a derivative work of GCC is one for the courts, which tend to take a dim view of creative workarounds.

Absolutely not. The GPL boundary is very clearly defined and intentionally has never been brought to court.

"The broadest and most established definition of derivative work for software is the abstraction, filtration, and comparison test (“the AFC test”) as created and developed by the Second Circuit. Some circuits, including the Ninth Circuit and the First Circuit, have either adopted narrower versions of the AFC test or have expressly rejected the AFC test in favor of a narrower standard. Further, several other circuits have yet to adopt any definition of derivative work for software.

As an introductory matter, it is important to note that literal copying of a significant portion of source code is not always sufficient to establish that a second work is a derivative work of an original program. Conversely, a second work can be a derivative work of an original program even though absolutely no copying of the literal source code of the original program has been made. This is the case because copyright protection does not always extend to all portions of a program’s code, while, at the same time, it can extend beyond the literal code of a program to its non-literal aspects, such as its architecture, structure, sequence, organization, operational modules, and computer-user interface."

https://copyleft.org/guide/comprehensive-gpl-guidech5.html

How so? The GPL grants permission to distribute derivative works in general under the GPL, and additionally to distribute derivative works consisting of object code that is the compiled form of system libraries (narrowly defined) without including that source (though AIUI still under the GPL); that's all. If someone were distributing a derivative work of a GPLed program not under the GPL and therefore without permission (i.e. without being otherwise licensed by the copyright holder), that would be copyright infringement. The question of what is or is not a derivative work in the general case is absolutely a question for the court. The FSF explicitly says as much: https://www.gnu.org/licenses/gpl-faq.html#MereAggregation

All of this is irrelevant. The GPL stops at the process boundary and that's exactly what these compilers do. They provide the modifications to GCC itself under the GPL and then have separate executables that are proprietary that feed things in and out of GCC.

It's still pretty clearly a violation of the intentions of the gcc developers, and something that only exists to wrap one product seems very suspiciously like a derivative work. I'd be curious to see this tested in court.

But the FSF would not be curious to test this in court because they know they lose. I had this conversation many years ago with people that wrote extactly this type of software and the general consensus was that the FSF would stay away from probing the GPL there because there is angood chance that the ruling would set a precedent they don't want. The FUD surrounding the license in that regard is preferrable.

In general it's 2016 and no longer relevant. The world moved on to LLVM and these GCC using toolchains are on their way out for good.

The text of the GPL (nor the FSF FAQ) does not explicitly support the "stops at process boundaries" interpretation, though a form of that's been a popular interpretation since at least the GPLv2 period.

> The GPL stops at the process boundary

No it doesn't, and if it did that would only mean that processes that form derivative works of GPLed programs were unlicensed, and therefore a violation of copyright.

What the FSF wants the boundary of the GPL is irrelevant, since copyright law of the televant jurisdiction determines whether copyright license is even necessary, and the boundary of derivative works in copyright is both often unclear (as noted in sibling comments, different circuits in the US apply different tests that have not been harmonized by the Supreme Court) and differ between jurisdictions.

The GPL cannot create certainty that doesn't exist in the law on which the GPL relies to have any force.