Learning how to decompile was challenging. It's difficult to find any good learning resources for it and any open-source projects for this are inactive and/or contain little actual learning material.
So I put together Decomp Academy! Decomp Academy is an interactive way to learn how to decompile PowerPC assembly back into C. The site runs a live Metrowerks CodeWarrior GC/2.0 compiler, converts your C into assembly, and then checks how close your assembly matches the target. If even 1 instruction or bit is off, that's a fail. This is the gold standard for video game decompilation and this is much stricter than a normal decompile.
As of writing there are 250+ lessons on the site and the lessons start at the very basics so anyone with a little programming experience should be able to jump straight in, even if you're not a C expert. Some lessons also have real functions taken from live open source decomp projects (Star Fox Adventures, Mario Party 4, Pikmin, Metroid Prime). The idea being you learn everything you need to know to be able to jump in and contribute to a real decompilation project when done.
The site is completely free, open source and you have access to all lessons without having to sign up. All lessons are stored in markdown in the repo (src/curriculum), it's trivial to add or modify lessons. The site is very new and the lessons are rapidly changing every day with a whole C++ section on the way. The site has already been well received by the decomp community and I'm happy to share it with HN. I'm very keen on others to contribute to this project and I hope this becomes the best resource on the internet for learning the art of decompilation. Please let me know what you think!
Basically; can you reverse engineer in bite sized pieces, and recompile/customize their behavior, without needing to do it all at once?
0 - for example: https://github.com/Xeeynamo/sotn-decomp/blob/master/src/boss...
By the way, I was able to "cheat" on the second lesson with
void identity(void) { return; }
As for cheating, the community calls this a fake match. I don't check that the code you submit conforms to what I expect, I only check if the assembly matches. You can do interesting things where you do a series of bit shifts and bit masks, and you can replicate an equality operator `a == b` or a low clamp `x < 0 ? 0 : x`. I'm not sure if I'll lock this down or not, for people who have accounts, I can see their submissions so I think I'll play it by ear and see what happens. If it looks like people are constantly fake matching, I can look at tweaking the lessons or locking it down more
When Fable was around I thought i'd test it by taking an old piece of Windows software from the late 90s/2000s(ModPlug Player) and seeing how well it could convert it to being a native Mac application.
I was blown away at how it got 85% of the way there in one prompt. Things such as writing a PE extractor, recovering the complete skin, menu tree, full accelerator table, all dialogs, and then it delved into the registry value names as well. Some more prompts got it to 99%(I was happy with that and stopped)
I then took an old 1999 DOS demoscene and yet again it did wonderful magic and got me a native mac build.
I dropped everything I was doing and just started going through all these old apps that I couldn't easily enjoy since im on a Mac. It got to the point where I was losing sleep over it(was just so excited).
The fun ended when I was stopped mid-project with the Fable ban. Opus just does not compare and essentially killed all the enthusiasm after the nth failure of it to complete the task.
It made me realize that among the efforts of the RE community, and the emerging capabilities of these frontier models, in the future we could have the possibility living in a renaissance of open computing if we want any software we see on the market to be forever remixed and tailored to our uses and completely open.
I don't know how the business and legal side will deal with this. There needs to be new frameworks and ways of thinking about this stuff.
I'm just happy that hopefully no code will ever be lost to the sands of time ever again.
One of the reasons I went down the path of learning decomp myself was because AI had hit a wall. Matching decomp is quite a bit harder than just normal decomp as even simple things like using an if/else instead of a terney actually change the assembly. AI did an amazing job of getting to 95% matches on nearly all functions, but once it got to that tail end, it started to struggle quite a lot and would often just claim "it's impossible". So that's when I pivoted and started learning actual decomp myself so that I could prompt AI better and finish off the star fox adventures decomp!
USPTO and court precedent is leaning heavily toward LLM output not being transformative on its own, making it mechanical, and no longer fair use and in violation of copyright. This puts a legal gray cloud on a project where most contributors couldn’t defend themselves if a rights holder goes after it, and there’s a high likelihood that they would succeed. On the other hand there’s enough case law protecting human decompilation that even the most litigious game companies don’t go after decomp projects that have historically been done by humans.
(I’m not a lawyer, I’m not your lawyer, this is not legal advice, etc., etc.)
Nicalis and Take-Two have both gone after decompilation projects, also. In particular, Nicalis has gone after a decompilation of Cave Story, but not a black box reimplementation of the same, while Take-Two ended up suing a decompilation developer (albeit settled out of court). However, in some jurisdictions, even clean reimplementations have failed - see Tetris v. Xio.
(I am not a lawyer either, etc etc, but that's my understanding)
CSE2 was distributing binaries as well.
So was SM64 decomp and Nintendo told them to stop, they did and continued to share their source code.
Tetris v. Xio is unrelated to reverse engineering or decompilation.
Distributing binaries should not matter. If the binary is just compiled from the source code, the binary is just an (non-)infringing as the source code.
> They also allegedly violated a EULA
Meaningless. EULAs are not the law.
Also, how to folks obtain binaries? Presumably unless there is a source code breach or vulnerability, source never gets exposed, is thst correct?
Otherwise they reference rips of the original game.
The toolchain would also be easier to match, unless they were using some proprietary compiler you can't get your hands on.
Just lookup how they match the toolchain, and find an agent harness to do decompilation.
I wonder if doing this kind of stuff with more recent software will cause more legal problems though. I am not really sure of the legal status of the resulting code.
On the first lesson, it tells me there's a target on "the right". There isn't anything to the right, I've in clue where to look.