Recently, the people behind the re3 project (public decompilation of the games GTA III and GTA Vice City) were served a civol lawsuit by Take Two, the owning company of the games.
What the group did was run the binaries through decompilers, such as IDA, and making a recreation of equivalent high-level C++ source code.
From my underdstanding of law and jurisprudence, this would not breach copyright law. My reasoning is the following:
Computer programs are only covered by copyright because their source code is, therefore so is the resulting object code. However, the processes and sequences of operations that make the program do what it does aren't copyrightable (a patent would be better suited for those things).
Taking that into account, by decompiling the object code into new, re-arranged source code, the only elements that would remain are the specific sequences and processes that are represented by it. No copyrighted works remain, neither the object code nor the original source code the engineers wrote and later compiled.
I have what I believe to be a good analogy to explain it better.
Suppose there is a recording (object code/binary) of an orchestral performance (original source code) of a song that is in the public domain (processes/sequences of operations) Wouldn't the decompilation project be the equivalent of me running the recording through a program which would recognize the individual notes and throw together a music sheet? The recording and performance are copyrighted, but the core concept in which they are based on is not (in this case because the song is on the public domain, however keep in mind I only used this to have an example of an "non-copyrighted" thing. processes/sequences of operations can never enjoy copyright protections at all)
While of course noting that we cannot predict the future: could this argument hold up? If not, what are its flaws?