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
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.
> 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.
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.
As far as I know, ISO c++ is no better than microsoft rust.
It is said microsoft rust syntax is on the same brain damage complexity level than ISO c++. That, and I don't even talk about the technical cost of its runtime (not far from the toxicity of a jvm?)
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.
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.
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.
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.
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.
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.
> 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.
Indeed specifically Rust defines that pointer comparisons are done by address, whereas C doesn't specify what the rules are exactly. This gets sticky if the pointer was invalidated (e.g. you free'd the memory it was pointing at). Rust says - as you might expect - that you can still compare this invalid pointer to another pointer (which may or may not still be valid and indeed might be a valid pointer to the same address!) because we're only comparing the address - but C++ says you mustn't do that and I believe C has the same rule.
> Signed integer overflow is UB in C, defined to wrap/panic in Rust.
This doesn't feel like an interesting difference. C made a weird choice, which was maybe convenient for the usual Worse Is Better reasons 50+ years ago. LLVM doesn't care about that choice, LLVM can cheerfully simulate this behaviour in C if you want that.
> Type-based alias analysis is a big one, does not exist in Rust.
This also doesn't feel relevant but I guess I'm interested in why you think it would make "a big" difference?
Edited: I confirmed C11 has "pointer zap" which is the behaviour I described above, and I believe C23 also still has pointer zap although paulmck and co. are trying to get rid of it or do something on this topic in C2y.
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.
> 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.
> 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.
> 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.
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.
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™
They don’t need to “officially support” Rust in order to ship code written with Rust. Just target the applicable architecture and ABI. It’s a lot easier now that the ABI’s are mostly standard now too.
Source: I wrote a compiler and runtime that ran .NET code (AoT compiled with LLVM) on PS3/Xbox360/Wii and shipped a few games with it.
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.
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
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.
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.
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.
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.
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.
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
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.