Resident Evil 4 (GameCube) – complete byte-identical decompilation to C/C++

So having Claude one-shot a NES emulator is almost pointless to me. You're using and looking at source code for an emulator you didn't write -- and you can learn from that, but it's not the same thing and doesn't require you to really understand a CPU the way you would by, say, observing a deviation in game behavior and staring at trace logs to figure out the exact instruction you emulated incorrectly.

It's not all bad -- AI is a great research tool and can automate some of the tedious parts (writing out an instruction decoder by hand is miserable). But using it to just...skip over the effort of doing a project defeats the whole purpose of doing those projects in the first place.

I don't want to be gatekeepy or curmudgeonly or "back in my day..." about it. But for me, my entire career path is due to skills and knowledge I learned spending several years of my life as a teenager figuring out how to write an NES emulator as a relative beginner to programming. And so I feel like using AI for this is depriving the next generation of that learning process. In addition, there are only so many retro games, and fewer popular ones. There's only so much unexplored territory to discover, and doing it with AI deprives another person of that experience and deprives that game's community of someone who might have been able to find a "home" working on projects related to that game.

Boggles my mind that there is hate for AI in retro-gaming. It's all about making existing things work. If it works and plays well, who cares if Claude did it in an afternoon or some human who spent a year of his life. In fact, I'd rather have Claude do it. Humans will get bored, get involved in community drama, disappear, etc. Unfortunate for the humans who are seeing their life's contribution to the scene made obsolete by a few kilowatt-hours in a datacenter, but good for the rest of us.

The reason I’m finding this is much faster than a traditional decomp is that while it’d be nice for the bytes to match, finding the perfect blend of compiler version, compiler args, permitting variables etc to try and find the perfect register assignments, etc is all very time consuming. My ultimate goal is not a byte for byte match, that’s just one way to ensure correctness. I’ve found agents are much faster and effective at reading the original assembly and understanding what’s going on then writing semantically equivalent C.

There is also value in decomps beyond just understanding and general interest. They can also be used to make more advanced mods, better translation patches, etc. The fidelity here matters, like having asm code accessing structures makes it hard to modify structures, but any fidelity improvement beyond pure asm is very welcome.

Of course I still prefer to try to recover the original code that caused the compiler to do what it did, but it's a really challenging problem sometimes. I've been working on decompiling code from old versions of MSVC for literally years now and you accumulate some knowledge of what things impact register allocation or the order of symbols but some of it comes from things that get fully erased from the source. Like for example, debug builds generally seem to retain symbols that aren't actually referenced anywhere, but those symbols only actually make it into an object file if they are. For functions that were only ever inlined and not actually referenced anywhere... They still wind up in the object files and thus in debug builds, despite nothing referencing them. They are also COMDAT any'd because they can appear in multiple objects legally, which means the exact object that winds up retaining it in the final linked executable is arbitrary (and the compilation flags of the object containing it, too - I bet that was fun for developers to debug.) This is incredibly useful but very challenging, needless to say. It may even be feasible to construct examples that would be legitimately infeasible to simply guess back to equivalent source, which I suspect is a major reason why until it was finally shown to be possible in larger scale projects many people wrote fully matching decomps off as a fool's errand..

Maybe someone else comes and helps out here and there.

Heh. I was just looking at the RE family on Steam. Nothing over a fiver.

I guess they really did make it more convenient than piracy.

You took a copyrighted work, did some lossless mathematical transformations on it, and have created an artifact that reproduces the original copyrighted work with perfect fidelity every time. From a legal perspective, this is effectively identical to zipping and unzipping a copyrighted file. You won't have much luck claiming that the intermediate Zip file is somehow free of copyright.

The legal problem is the original taint of using a copyrighted work (expressly contrary to its license), and the fact that nothing transformative is occurring here sufficient to enliven the defense of fair use. (Not even close, and no, this is nowhere near the realm of being arguable. The fact that this spits out a copyrighted work 'byte for byte' is a stake through the heart of any such argument.)

Decomp projects are cool, but if you work on them, please be aware that you're taking a risk, and some video game companies are famously litigious, even for old games.

The main reason you'd avoid this is to stop the first copyright holder from wanting to sue you - not because it's actually invalid.

Doesn't mean I liked them, or that they wouldn't have been better as a 2D game. But IMHO the graphics stopped distracting from fun games... OTOH, I played plenty of games on the Atari 2600 were the player character wasn't much more than a chonky pixel :p

There has been some 2D decomps too, Pokemon Red/Blue being the biggest I can think of. I can also imagine they make more sense for the 3D consoles where games tended to be written in higher level languages than raw assembly.