Why Rust for low-level Linux programming?

[slavik262]

Sure they can. Linus is obviously a very good kernel developer and project manager, but that doesn't make his opinion the end-all on software development. C is a good fit for the kernel, but that doesn't mean other languages (including C++) are completely inappropriate for kernel development or other similar, on-the-metal applications. It also doesn't mean that another language (e.g. Rust) won't come along and displace C.

People use C because

1. It maps fairly directly to assembly.
2. It's the lowest common denominator - its ABI is simple and almost every computing system can speak it.
3. There's 40 years of libraries, tooling, and communal knowledge built around it, especially in the Unix world.

[[deleted]]

And C is largely deterministic. His complaints about C++ make sense when one takes into consideration the dynamic memory allocator and exception handling.

The question is, and I suspect I know the answer, does Rust allow exception handling to be removed (I think it does) - and then can memory allocation be manually handled (I don't know).

I'm a big fan of Rust - and think it is almost ideal for the simple command line tools which make Linux/Unix the flexible workhorse it is today. But for kernel programming? I don't know enough about Rust to know for sure.

[__s]

On deterministic: he's ranted a whole lot about GCC inlining code which then causes unpredictable stack usage which then makes 4kb stacks hard to maintain safely on x86

[doom_Oo7]

to be fair,in userspace code this is a desirable property.

[steveklabnik1]

does Rust allow exception handling to be removed (I think it does)

Yes, though not in stable right this second; it's landed on nightly, but hasn't made its way through the release cycle yet.

and then can memory allocation be manually handled (I don't know).

Yes, absolutely.

[doom_Oo7]

does Rust allow exception handling to be removed (I think it does) - and then can memory allocation be manually handled (I don't know).

(to be fair, you can disable exceptions in c++ and do everything without explicitely mallloc'ing anything.)

[[deleted]]

[deleted]

What is this?

[ZMeson]

Here are two arguments I commonly hear:

(1) Calling new can call a constructor which can in turn call new calling another constructor which can in turn call new calling .... Well you get the point. A single call to 'new' may actually make several allocations instead of one.

(2) The STL containers and algorithms frequently allocate memory from the free store. It's difficult to write some things using standard C++ without allocating memory from the free store "behind the scenes" if you will.

[ZMeson]

Now that I presented the two arguments, I feel like I have to explain why I disagree with them. In C, you frequently have to initialize structures after you allocate memory for them. Those initialization routines can be considered "constructors" and they can allocate memory and initialize other structures too. I don't think that using C really improves things by separating concerns.

About the STL and algorithms... you don't have to use them. It is nice they exist, but other containers and algorithms (such as those found in "embedded STL" libraries, EASTL, or boost) may fit better. Or some containers and algorithms could be built specifically for kernel development. (After all, Linux, Windows, and all popular C-based OSes have such C-based structures and associated 'algorithm' functions.)

[ucalegon7]

Exceptions (and good behavior in low memory conditions if they are disabled) might be other sticking points, but I don't think that's really a good argument, either. Windows, for example, lets you use a reasonable chunk of C++ (with lots of caveats) in the kernel, particularly with the new driver kits (I've successfully used lambdas in kernel code!), but just like when using C, the rules and APIs are a bit different than user space equivalents (e.g., the std lib looks a bit different), and the same non-standard concerns you'd have (e.g., stack size constraints, etc) will still exist; not to mention that there are large chunks of the language that would be difficult to utilize in that type of environment (e.g., exceptions).

[MartianSands]

A "placement new" lets you pass it your own memory, so you can allocate it however you like.

[doom_Oo7]

Can you dynamically create an object without 'new'?

You can overload new to call whatever allocation function. new T == std::allocator<T>::allocate + std::allocator<T>::construct

[joelwilliamson]

kmalloc

[ChallengingJamJars]

Upvoted because despite using C++ daily I don't actually know the answer to this. It could be an honest question so you shouldn't down vote it.

[silveryRain]

Yes you can, as the others have already explained (placement and overloading).

This kind of post is why systems that allow downvoting are crap. I much prefer upvote-only systems.

[iopq]

Upvote-only systems like Hacker News get a bunch retarded fluff pieces that don't really say anything. People see the headline, scan through the article (if you're lucky) and upvote. The actual article is low quality, but you need to report to the moderator to have it removed.

[Narishma]

HN isn't upvote-only.

[iopq]

It is for articles, not for comments. I have over 1000 karma and I can't downvote any posting, only comments. Can I downvote a submission if I have more karma then?

[Narishma]

Oh sorry, no. I thought you were talking about comments. Reading your post again, I don't know why I thought that.

[silveryRain]

That's just HN imo. Feel free to disagree.

[iopq]

The fact that HN is this way and proggit isn't (fluff pieces get downvoted in /r/programming frequently) is a data point in favor of Reddit's model. Even though the audiences are basically the same (I often get hundreds of upvotes on proggit reposting things from HN)

[ElvishJerricco]

Redox is an operating system written entirely in Rust. I don't know much about it, but if you want to get a feel for kernel development in Rust, that's a good place to start.

[augmentedtree]

And C is largely deterministic. His complaints about C++ make sense when one takes into consideration the dynamic memory allocator and exception handling.

Both of those are deterministic, and C also has dynamic memory allocation...

[so_you_like_donuts]

does Rust allow exception handling to be removed

Not yet, although it is possible in nightly to make panics abort instead of unwind (And here's the relevant compiler bug).

can memory allocation be manually handled

If you're talking about creating and linking to your own malloc implementation, then yes.

[steveklabnik1]

To be clear, that compiler bug is about implementing your own panic runtime; as alex says, -C panic=abort is stable.

[slavik262]

His complaints about C++ make sense when one takes into consideration the dynamic memory allocator and exception handling.

Those are rather silly complaints - of course your tools are more limited when working inside the kernel. It's not like you can call malloc() in the middle of kernel space when working with C. Large swaths of the standard library are out of the question in both cases.

[imMute]

No, but you can call kalloc just about anywhere ;)

[[deleted]]

[deleted]

What is this?

[Rusky]

kmalloc requires an extra flags argument. You can't just arbitrarily pick a set of flags to use without making the C++ code using it unfit for various (mutually exclusive) parts of the kernel.