It's not an obvious legal argument that it is not a derivative work of the compiled code or the original source code that produced that. Clean room reverse engineering is meant to give you a strong argument for that, and while it's not necessarily required to prevail against a copyright case (or actually sufficient) it's gonna make things harder if you don't. (All of this is made more murky because copyright is meant to only cover expressions of human creativity, and code is kind of a mix of creativity and mechanical details: the clean room approach is meant to separate out the mechanical details)
replyAlso, If it is an unauthorized derivative work, as I understand it then it might not even qualify for copyright protection itself.
A decompilation is not clean room, nor is it "created from scratch". If that was the case, you could just compile a program to remove the copyright, because the machine code doesn't resemble the source code at all either.
replyA reimplementation or a behavior-based clone is an entirely different legal world from decompilation.
The compiled binary is protected and the property of the original company. The source code written by people doing decompilation is owned by the people doing the decompilation. That source code can compile to a lot of different binary representations, just like a lot of code representations (infinitely many) could compile to the original binary.
replyIn fact, the goal of most decomp not to produce the same binary, that’s just used as a validation.
>is owned by the people doing the decompilation
replyTrue, but as a derivative work of the original source code they don't have rights to do anything with that code without infringing copyright.