crustc: entirety of `rustc`, translated to C

https://github.com/FractalFir/crustc

by Philpax • 20 days ago

386 92 20 days ago

github.com

Tiberium• 20 days ago

I wonder how the performance looks like, because this can be interesting even for non-porting reasons ;)

adastra22• 20 days ago

It is very unlikely that it would be faster.

gerdesj• 20 days ago

Faster than what? Please finish your sentence.

ronsor2• 20 days ago

I put my left hand in a blender. The blender won. (Still have all my fingers, just some stitches). I will not elaborate further.

What a shame. I would've read an article about this.

cozzyd• 20 days ago

I mean I get confused every time I use blender too but not to the point of losing fingers...

iwassayinbourns• 20 days ago

I desperately want to know more.

RustyRussell• 20 days ago

Nobody who would code this up would be entirely sane. But I can't help thinking "these are my people" when I read this...

gpvos• 19 days ago

He wrote 14 Rust to C compilers. Sanity has gone out of the window already.

luke-stanley• 20 days ago

But did it Blender open the source?

Cadwhisker• 20 days ago

The primary goal of this is support for old/obscure hardware with no LLVM/GCC support. There are still some systems out there that don't support Rust but support C.

The landing page mentions Plan 9 as one of the systems.

lioeters4• 20 days ago

For the past 3 years, I have been working on compiling Rust to C. .. This is, by my count, the 14th attempt: cilly

Gotta respect the dedication to a niche interest.

The primary goal of this is support for old/obscure hardware with no LLVM/GCC support.

I remember reading about the bootstrapping question, how it typically requires a Rust compiler to build the Rust compiler from source. https://bootstrapping.miraheze.org/wiki/Bootstrapping_Specif...

Oh, but I see there's a C++ implementation of the Rust compiler. https://github.com/thepowersgang/mrustc

Anyway, this part sounds useful too, that crustc can compile across network and devices.

You build a small C server on your Blorbo OS, run rustc on some normal platform like Linux, and let cilly talk over the wire.

zadikian• 20 days ago

So the author made a Rust to C transpiler and immediately used it to transpile... the Rust compiler. I love it.

Animats• 20 days ago

It makes sense as a porting tool, if you need to port the Rust compiler to some target that has a C compiler.

But it doesn't mean rustc generates code for that target, only that you can run it there. You'd still have to teach LLVM about the target. Although that might already have been done.

It's not that useful for retro computers because the Rust compiler needs too much memory for most machines of the 32-bit era.

lispwitch2• 20 days ago

Guix uses mrustc for bootstrapping Rust, as required for compiler packages; it's a really impressive project and has worked well in that role for some time. This new project is interesting for other reasons though, because mrustc is targeted at the de fact "subset" of Rust in use by rustc at any given time. This looks like it could have broader applications, like compiling Rust programs for platforms not supported by LLVM. If it really targets ANSI C (C89 or so), that's potentially many more platforms than are possible with ordinary rustc

More on the Rust bootstrapping process (2018): https://guix.gnu.org/blog/2018/bootstrapping-rust/

xvilka• 19 days ago

compiling Rust programs for platforms not supported by LLVM

For this, gcc-rs[1][2] is the most promising candidate.

[1] https://rust-gcc.github.io/

[2] https://github.com/Rust-GCC/gccrs

lioeters4• 19 days ago

I might have seen that Bootstrapping Rust article, how interesting. I've been curious about Guix for a while, one of these days I need to dive in and explore deeper. I really enjoyed their article on full-source bootstrap, it's relevant now more than ever.

Building from Source All the Way Down - https://guix.gnu.org/en/blog/2023/the-full-source-bootstrap-...

radarsat1• 19 days ago

The primary goal of this is support for old/obscure hardware with no LLVM/GCC support.

If you're going to go to all this effort for an old target though, wouldn't the effort be better spent on making it an LLVM target? Then you'd get Rust and a bunch of other languages for free.

But maybe there are required parts of the LLVM IR that make this undesirable for certain targets, maybe requiring specific hardware features, I don't know. I guess also WASM-as-IR is a possible way to go. (Is that a thing?)

Edit: sorry I see that this point was already raised in this thread by ivanjermakov. Ignore.

lioeters4• 19 days ago

WASM-as-IR .. (Is that a thing?)

Yes, actually I've heard of some projects compiling a language to Wasm, then using wasm2c to translate to C.

https://github.com/WebAssembly/wabt/blob/main/wasm2c/README....

The Zig project does something similar for their bootstrapping process with a custom wasm2c implementation with just the features they need.

https://github.com/ziglang/zig/blob/master/stage1/wasm2c.c

I get the feeling this is an underappreciated technique with more potential.

taris2• 20 days ago

Have you tried Diverse Double-Compiling (DDC) to test if the official rust compiler has a backdoor?

Use crustc to compile the rust source code, producing a new compiler. Then use this new compiler and the official rustc binary, both with deterministic flags, to compile the rust source code again. The two outputs should match bit for bit.

amir734jj• 20 days ago

Awesome idea!

swalberg• 20 days ago

This reminds me of https://www.cs.cmu.edu/~rdriley/487/papers/Thompson_1984_Ref...

lioeters4• 20 days ago

Reflections on Trusting TRust.

laughinghan• 20 days ago

The sole and entire purpose of Diverse Double-Compiling is addressing Thompson's Trusting Trust: https://dwheeler.com/trusting-trust/

gmzamz• 19 days ago

I'm also a fan of https://www.teamten.com/lawrence/writings/coding-machines/

steveklabnik• 20 days ago

This was done with mrustc, which produced byte identical output.

rcxdude• 20 days ago

Better than that, you can get a bootstrapped rust from the Guix project, which has bootstrapped its entire system from source code from only a tiny verifiable binary.

wmanley• 20 days ago

It's not diverse in that case - it's the same compiler source compiled to binaries twice - it's just that with one compiler you've gone via a C intermediate representation. For the purposes of diversity it's the same as compiling rustc with the cranelift/gcc backend.

moltonel2• 19 days ago

From a "trusting trust" point of view, compiling rustc-translated-to-C with a C compiler (and comparing the result to normally-compiled rustc) is a valid demonstration, because we're again starting from code and can eliminate the possibility of a binary-resident compromise.

The actual issue here is that the translation was done using a rustc backend, and therefore an existing rustc binary which could be compromised and inject a "if (user=="wmanley") {...}" that isn't present in the original Rust code. If cilly was completely standalone (like mrustc), or if you had a rustc+cilly build you trusted, there would be no issue.

Imustaskforhelp• 20 days ago

This could be used within https://bootstrappable.org/projects.html to make bootstrappability of rust incredibly much easier other than the previous route of OCaml and other things.

I know some folks within the bootstrappable OS projects community are on Hackernews and I hope that they could take a look at this. I feel as if this project could drastically shrink down the efforts needed to get a working rust compiler in a bootstrappable manner.

hkalbasi• 20 days ago

Not really. This C code is more like a binary and compiler artifact than a source code. So it won't match the standards of bootstrap.

afdbcreid4• 20 days ago

Depending on what your goal is. If it is eliminating trusting trust attacks, yes this is no enough. But more commonly you only want to compile rustc for a platform it was never compiled on, and for that this project is definitely enough.

lispwitch2• 20 days ago

mrustc (a handwritten Rust compiler in C++) is already used for that in Guix and likely other distros: https://guix.gnu.org/blog/2018/bootstrapping-rust/ This would have other benefits though, as it's both a second bootstrapping path and could potentially compile Rust programs for platforms not supported by LLVM

levkk• 20 days ago

Very cool. At first, I thought it was yet another LLM-generated demo, but no: original work of art. Super cool. Transpiling into C does seem easier than LLVM IR, and letting GCC optimize seems like this might actually work.

Excited to see the compiler implementation when it's out -- a lot to learn from.

ahartmetz• 20 days ago

Wait, I thought LLVM had a C backend which could be used for the purpose of transpiling Rust to C? Turns out not for a long time, but now maybe again: https://discourse.llvm.org/t/re-ann-llvm-c-backend-still-abl...

simonask• 20 days ago

This approach is harder than you might imagine. LLVM can do a lot of things that don't map to C language constructs. You cannot generally roundtrip arbitrary LLVM IR through some C representation. You can emulate most things, but you won't necessarily get the same LLVM IR in the other end.

afdbcreid4• 20 days ago

FWIW, Rust can also do a lot of things that do not easily map to C (at least standard C) constructs. For example:

- You can compare any two pointers, while in C they must point to the same allocation. This is possible to solve by converting to integers first.

- Signed integer overflow is UB in C, defined to wrap/panic in Rust.

- Type-based alias analysis is a big one, does not exist in Rust.

SpecialistK• 20 days ago

I wonder if this could be used in PPC Mac OS X, where LLVM isn't supported and most graphical applications need to use GCC 4 with Apple's SDK.

layer8• 20 days ago

Finally we can rewrite all the Rust in C. ;)

avadodin• 20 days ago

As long as we rewrite all the C++ in Rust first.

pjmlp2• 19 days ago

Starting by the compiler infrastructure rustc depends on.

dangoodmanUT• 20 days ago

i believe the author is confused

this is the wrong direction

(jk i read the readme)

sylware4• 19 days ago

Nope, and c++ should get the same thing.

But we now all know rust is microsoft and c++ ISO. I don't think we can trust much more ISO than microsoft to produce less feature creep over the currently known planned obsolescence cycle of 5-10 years.

groos• 20 days ago

As an ex C++ compiler developer, I heartily approve of this project. Kudos.

nxtfari• 20 days ago

this is really cool but it seems very unlikely that someone targeting an exotic system not supported by rust (mostly embedded and ancient mainframe targets) would be willing to trust a beta transpiler to not inject any bugs or leaks in the process of turning rust to c. nevertheless, very cool.

npalli• 20 days ago

Rewrite in C is the new Rewrite in Rust.

keyle• 20 days ago

GTA VI out in Rust before C++?

roflcopter693• 20 days ago

Wake me up when consoles officially support Rust. Until then there's no real way around C/C++ if you want to publish a real game to real consoles. But there's https://akaganite.com so it might become possible soon™

linzhangrun• 20 days ago

Quite an interesting project, lol. I like the name `crustc` :)

casey2• 20 days ago

Not to be confused with crust [1] the dialect of rust B [2][3] is written in.

[1] https://github.com/tsoding/crust [2] https://github.com/bext-lang/b [3] https://www.nokia.com/bell-labs/about/dennis-m-ritchie/kbman...

unjuno• 20 days ago

The most interesting part of this to me is not “Rust to C” by itself, but the fact that it widens the pool of people who can help debug portability problems.

There are relatively few people who understand Rust’s compiler internals, LLVM backends, and obscure target support deeply. But there are many engineers who understand C compilers, ABIs, linkers, makefiles, cross-compilation, old operating systems, and weird platform-specific compiler behavior.

If Rust can be lowered into target-specific C, then some problems stop being exclusively “Rust compiler problems” and also become C toolchain problems. That means more people can inspect the generated C, build failures, linker errors, ABI mismatches, and compiler-specific behavior.

C is obviously not a magic portability layer. ABI details, integer widths, alignment, TLS, aliasing, and undefined behavior still matter. But as an ecosystem boundary, C gives many more engineers a way to participate in debugging and porting work.

I think that social/maintenance aspect may be more important than the language translation itself.

jolmg2• 20 days ago

Guideline:

Don't post generated text or AI-edited text. HN is for conversation between humans.

jdw643• 20 days ago

I saw the reply, and it's not GenAI text. It's just that in the process of translation, people usually use machine translation or LLM translation. The problem is the vocabulary we East Asians use. I experience this issue too.

Probably because in East Asia, we tend to emphasize things with things like "xx" a lot.

jdw643• 20 days ago

I think you're probably using DeepL or some other AI translation. When you use DeepL, most sentences become flat and end up being judged as GenAI. I also used DeepL to communicate on Hacker News in the early days.I had a similar problem

moezd• 20 days ago

Let Rust vs C battle commence with renewed haste!

fithisux• 20 days ago

Kudos.

adithyassekhar• 20 days ago

I'll wait for rustcrustc

ivanjermakov• 20 days ago

The primary goal of this is support for old/obscure hardware with no LLVM/GCC support

Wouldn't it be easier to add old hardware support to LLVM/GCC instead? I adore the project scale and determination, but for this goal extending existing projects seems more logical than building a language translator.

claudex• 20 days ago

Some architecture lacks documentation, if you have a working C compiler, it's easier to use it than working on a compiler to target it.

Liquid_Fire• 19 days ago

Presumably you still need a C++ compiler for LLVM itself though. Or... a C++ to C translator.

Edit: On second thought, that's only needed if you want to run rustc itself on the old hardware, which is probably not super useful given the main reason you would need to do this is if LLVM can't target that hardware.

For building code written in Rust for such old hardware, this would be sufficient.

Perz1val• 20 days ago

Wouldn't it be easier to add old hardware support to LLVM/GCC instead?

No, in fact it's much, much harded. You have no idea of the scope. I have no idea of the scope. Nobody does. There are obscure machines we've never heard about and there are C compilers for them. Targeting and supporting them from modern toolchains is a fool's errand.

jitl• 19 days ago

rust to c supports infinite platforms that already have a c compiler by implementing a single rust to c program

on the other hand, porting llvm to an infinite number of platforms requires an infinite amount of work

so, it is less work this way

micheleeet• 20 days ago

Rust is finally memory safe enough to become C

Sharlin• 20 days ago

"You have become the very thing you swore to destroy"

sylware4• 19 days ago

The real salvation is assembly written software with a wordwide non-IP-locked ISA (for instance RISC-V). Then very high language interpreters would be written directly in such assembly.

db48x• 20 days ago

We should port it to Rust.

westurner• 19 days ago

There are discussions of round-trip between Rust and C;

Would this be useful for this too?

From https://news.ycombinator.com/item?id=46265855 :

To better port C to Rust: 3C (Checked C), c2rust, Crown ownership analysis, RustMap, c2saferrust (LLM), Laertes

C -> Checked C -> Rust

Because Checked C will annotate the raw and other C pointers first.

kube-system• 19 days ago

What sort of hardware would this be useful for?

Archit3ch2• 19 days ago

If I understand this correctly, you could run this compiler on iPadOS (since it's plain C). But you cannot mark it's output executable, since that would require JIT entitlement.

ronsor2• 19 days ago

Target WASM then

Archit3ch2• 19 days ago

Sure, that works. Caveats:

1. Your frontend needs to support emitting WASM. Ok for Rust, not for every language out there.

2. 2x-4x performance overhead.

crustc: entirety of `rustc`, translated to C

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