So what's the point of GPL if it's written in assembler?
This is exactly why Richard Stallman objects to the term "open source" and prefers "free software": because the point of the thing is that you are legally free to modify and distribute it. Access to source code is just a prerequisite to be able to practically exercise those freedoms. (I'm making no commentary on whether he's right about this. Personally I tend to say "open source" more often, because that term has basically won out and I'm more likely to be understood.)
By the way, years ago when Microsoft was apparently going to war against open source/free software, there was a bit from some Microsoft executive who said something like, "Open source is pointless. If our customers want to see our source code, they can just ask. But nobody does. Nobody cares about source code." He was exploiting people's misconceptions about what "open source" means. Indeed, nobody cares much about source code if they're not allowed to do anything with it.
(Plus, disassembling a binary is a massive pain compared to just using the commented and labelled assembly file.)
Depending on the GPL, this would also ensure this OS doesn't run on restrictive platforms like iOS.
[0] Quotes around “running” because Bochs isn’t so much of an emulator as it is an interpreter. It’s still an emulator, but it runs by interpreting each instruction instead of binary translation like “modern” emulators.
GPL ensures that you're allowed these things and that anyone, who does modify it, has to then again allow these things to anyone who uses their version.
Yes, a good chunk of GPL – that the source code has to be published along with the software, is pointless here, so a simpler license could have been chosen, but I guess, they went with GPL anyways, as it's a proven license which has already had a few courts look over it.
Whilst that similarity makes it easier to disassemble (i.e. decompile) back to working assembly, the structure of the code can be lost, especially if code is organised in a modular way (using macros, etc...). As modularity improves maintainability, there is a technical benefit to having code written in assembly protected under the GPL.
https://github.com/openssl/openssl/blob/master/crypto/md5/as...
Don't let the perl extension fool you. It's mostly ASM, the perl is there to help with the build.
It was pretty easy to find someone that had copied it and violated their license by removing the copyright text, and further claiming to release it into the public domain. Perhaps not on purpose, but...
https://github.com/GaloisInc/hacrypto/blob/master/src/C/libs...
[0]: Or whatever it’s called on $(OS)