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Rust to C compiler – 95.9% test pass rate, odd platforms

fractalfir.github.io

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Re: Rust to C compiler – 95.9% test pass rate, odd platforms

#71

Post by lmm »

uecker wrote: post #65
lmm wrote: post #63

Earlier quoted context omitted.

> a given C compiler + platform will behave completetly deterministically and you can test the output and see what it does, regardless of UB or not. Sure[1], but that doesn't mean it's safe to publish that C code - the next version of that same compiler on that same platform might do something very different. With machine code (especially x86, with its very friendly memory model) that's unlikely. (There are cases lik…

It is not terribly hard to generate C code that does not use undefined behavior.

Maybe. But when carefully investigated, the overwhelming majority of C code does in fact use undefined behaviour, and there is no practical way to verify that any given code doesn't.

Re: Rust to C compiler – 95.9% test pass rate, odd platforms

#72

Post by lmm »

baq wrote: post #64
lmm wrote: post #63

Earlier quoted context omitted.

> a given C compiler + platform will behave completetly deterministically and you can test the output and see what it does, regardless of UB or not. Sure[1], but that doesn't mean it's safe to publish that C code - the next version of that same compiler on that same platform might do something very different. With machine code (especially x86, with its very friendly memory model) that's unlikely. (There are cases lik…

CPUs get microcode updates all the time, too. Nothing is safe from bitrot unless you’re dedicated to 100% reproducible builds and build on the exact same box you’re running on. (…I’m not, for the record - but the more, the merrier.)

> CPUs get microcode updates all the time, too.

To fix bugs, sure. They don't generally get updates that contain new optimizations that radically break existing machine code, justifying this by saying that the existing code violated some spec.

Re: Rust to C compiler – 95.9% test pass rate, odd platforms

#73

Post by epage »

dilawar wrote: post #13

Is it LLVM IR --> C? Or Rust AST to C?

It is a rustc backend, ie an alternative to llvm, gcc, or the cranelift backends.

It started as a .NET backend but they found that their approach could easily support C code generation as well so they added that. They do this by turning what rustc gives them into their own IR.

Re: Rust to C compiler – 95.9% test pass rate, odd platforms

#75

Post by fpoling »

chii wrote: post #17
GolDDranks wrote: post #12

Earlier quoted context omitted.

If the transpilation itself is bug-free, why not? For static guarantees, provided we transpile Rust code that already compiles on a normal Rust compiler, the guarantees are already checked and there, and the dynamic ones such as bounds checking can be implemented runtime in C with no problems.

this assumes the rusty guarantees are transitive. There's no reason to believe it isn't, but it'd be nice to see some sort of proof, or at least an argument for it.

Rust does not generate machine code itself. It uses LLVM to do that and there is no proof that the transformations done by that continue to keep the borrow checker guarantees. One just assumes with sufficient testing all bugs will be discovered.

Then the machine code generated by LLVM is not run directly by modern CPUs and is translated into internal representation first. And the future CPUs will behave like JIT-compilers with even more complex transformations.

The intermediate C code generated by this project just adds yet another transformation not fundamentally different from any of the above.

Re: Rust to C compiler – 95.9% test pass rate, odd platforms

#77

Post by sitkack »

CryZe wrote: post #67
Aurornis wrote: post #9

Earlier quoted context omitted.

> C to Rust would be fantastic. This would have to go into one big unsafe block for any nontrivial program. C doesn’t convey all of the explicit things you need to know about the code to make it even compile in Rust.

I once implemented a WASM to Rust compiler that due to WASM's safety compiles to fully safe Rust. So I was able to compile C -> WASM -> Rust and ended up with fully safe code. Though of course, just like in WASM, the C code is still able to corrupt its own linear memory, just can't escape the "sandbox". Firefox has employed a similar strategy: https://hacks.mozilla.org/2020/02/securing-firefox-with-weba...

I'd love to check that out. Did it unroll a wasm interpreter into wasm_op function calls?

Re: Rust to C compiler – 95.9% test pass rate, odd platforms

#78

Post by carlmr »

olivermuty wrote: post #69
kreetx wrote: post #54

Earlier quoted context omitted.

Borrow checker, and more generally any type checkers, are essentially terminating programs ran during compilation process, thus safety guarantees given by them are ensured before the code is transformed into some target language.

Thats assuming lossless transpilation though

That's a problem for almost every language, not just Rust. C++ also compiles to intermediate representations, and then to machine code. Errors happen on that path. Rust just get rid of a lot of errors that could have been in the original specification (the source code).

Re: Rust to C compiler – 95.9% test pass rate, odd platforms

#79

Post by carlmr »

lmm wrote: post #72
baq wrote: post #64

Earlier quoted context omitted.

CPUs get microcode updates all the time, too. Nothing is safe from bitrot unless you’re dedicated to 100% reproducible builds and build on the exact same box you’re running on. (…I’m not, for the record - but the more, the merrier.)

> CPUs get microcode updates all the time, too. To fix bugs, sure. They don't generally get updates that contain new optimizations that radically break existing machine code, justifying this by saying that the existing code violated some spec.

>To fix bugs, sure.

Maybe your program worked due to the bug they fixed.

Re: Rust to C compiler – 95.9% test pass rate, odd platforms

#80

Post by Someone »

drdeca wrote: post #36
jokoon wrote: post #34

At first I read it as C to rust compiler. What is the point of compiling rust to C?

I think there are probably C compilers for more platforms than there are rust compilers. So, if you want to compile your rust project on some obscure platform that doesn’t have a rust compiler for it yet, you could compile to C and then compile the resulting C code for that platform? Just a guess.

This project doesn’t have that as a goal. In fact, it doesn’t even have “Rust to C compiler” as a goal. https://github.com/FractalFir/rustc_codegen_clr:

“ The project aims to provide a way to easily use Rust libraries in .NET. It comes with a Rust/.NET interop layer, which allows you to easily interact with .NET code from Rust

[…]

While .NET is the main focus of my work, this project can also be used to compile Rust to C, by setting the C_MODE enviroment flag to 1.

This may seem like a strange and unrelated feature, but the project was written in such a way that this is not only possible, but relatively easy.”

It also doesn’t mention for which version of C it produces code. That may or may not hinder attempts to use this to run rust on obscure platforms.

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