The state of the kernel Rust experiment | Hacker News Reader

The state of the kernel Rust experiment

lwn.net

119 pointsdochtman130 comments

>Bergmann agreed with declaring the experiment over, worrying only that Rust still "doesn't work on architectures that nobody uses".

I love you Arnd. More seriously, this will become an issue when someone starts the process of integrating Rust code into a core subsystem. I wonder whether this will lead to the kernel dropping support for some architectures, or to Rust doing the necessary work. Probably a bit of both.

There are two separate ongoing projects to make a rust compiler that uses GCC as a backend (one on the gcc side adding a c++ frontend that directly reads rust, one on the rustc side to make rustc emit an intermediate format that gcc can ingest).

The long-term solution is for either of those to mature to the point where there is rust support everywhere that gcc supports.

I wonder how good a LLVM backend for these rare architectures would have to be for that to be “good enough” for the kernel team. Obviously correctness should be non-negotiable, but how important is it that the generated e.g. Alpha code is performant for somebody’s hobby?

I suspect more the latter than anything. It could be that by the time Rust gets used in the kernel core, one or both of the GCC implementations would be functional enough to compile the kernel.

I'm curious though, if someone has an ancient/niche architecture, what's the benefit of wanting newer kernels to the point where it'd be a concern for development?

I presume that outside of devices and drivers, there's little to no new developments in those architectures. In which case, why don't the users/maintainers of those archs use a pre-6.1 kernel (IIRC when Rust was introduced) and backport what they need?

No one is doing any kind of serious computing on 30 year old CPUs. But the point of the hobby isn’t turning on the computer and doing nothing with it. The hobby is putting together all the pieces you need to turn it on, turning it on and then doing nothing with it.

There’s an asymmetry in what the retro computing enthusiasts are asking for and the amount of effort they’re willing to put in. This niche hobby benefits from the free labour of open source maintaining support for their old architectures. If the maintainers propose dropping support because of the cost of maintenance the hobbyists rarely step up. Instead they make it seem like the maintainers are the bad guys doing a reprehensible thing.

You propose they get their hands dirty and cherry pick changes from newer kernels. But they don’t want to put in effort like that. And they might just feel happier that they’re using the “real” latest kernel.

> I'm curious though, if someone has an ancient/niche architecture, what's the benefit of wanting newer kernels to the point where it'd be a concern for development?

Wanting big fixes (including security fixes, because old machines can still be networked) and feature improvements, just like anyone else?

> I presume that outside of devices and drivers, there's little to no new developments in those architectures.

There's also core/shared features. I could very easily imagine somebody wanting eg. ebpf features to get more performance out of ancient hardware.

> In which case, why don't the users/maintainers of those archs use a pre-6.1 kernel (IIRC when Rust was introduced) and backport what they need?

Because backporting bits and pieces is both hard and especially hard to do reliably without creating more problems.

The kernel must adapt to Rust, not the other way around. Rust is the way!

From the comment section:

> To me the more salient questions are how long before (a) we get Rust in a core subsystem (thus making Rust truly _required_ instead of "optional unless you have hardware foo"), and (b) requiring Rust for _all_ new code.

Previously, the position was that C developers would not be forced to learn Rust.

And a few days ago a security vulnerability was found in the Rust Linux kernel code.

https://news.ycombinator.com/item?id=46309536

Where did anyone promise that the Rust bits will never have security issues? That CVE was a fantastic demonstration of just how much better the situation is in Rust code and I don't think there's a realistic argument that the experiment has been anything other than successful.

Was it? It seems more a fantastic demonstration how the same type of errors can also occur in Rust code.

In C this kind of issue is so common it wouldn't raise to the status of "CVE". People would just shrug and say "git gud".

This is certainly not true. But also arguments about "common" are completely misleading as long as there is many orders of magnitude more C code than Rust code.

Maybe you haven't been paying much attention in this space. Google found empirically that error density in _unsafe_ Rust is still much lower than in C/C++. And only a small portion of code is unsafe. So per LOC Rust has orders of magnitudes fewer errors than C/C++ in real world Android development. And these are not small sample sizes. By now more code is being written in Rust than C++ at Google:

https://security.googleblog.com/2025/11/rust-in-android-move...

But don't take my word for it, you can hear about the benefits of Rust directly from GKH:

www.youtube.com/watch?v=HX0GH-YJbGw

There really isn't a good faith argument here. You can make mistakes in Rust? No one denies that. There is more C code so of course there are more mistakes in C code than in Rust? Complete red herring.

Hey, it was my point that the number of CVEs is red herring.

And no, I do not care or even believe what Google says. There are so many influencing factors.

I would expect that the largest factor is cultural, and of course it's possible to inculcate safety culture in a team working on a C or C++ codebase, but it seems to me that we've shown it's actually easier to import the culture with a language which supports it.

Essentially Weak Sapir–Whorf but for programming languages rather than natural languages. Which is such a common idea that it's the subject of a Turing Award speech. Because the code you read and write in Rust usually has these desirable safety properties, that's how you tend to end up thinking about the problems expressed in that code. You could think this way in C, or C++ but the provided tooling and standard libraries don't support that way of using them so well.

I also think that the largest factor is cultural. But my conclusion from this is not that one should import it with a new language while pretending achieving similar results is not possible otherwise. This just gives an excuse for not caring for the existing code anymore, which I suspect is one reason some parts of the industry like Rust ("nobody can expect us to care about the legacy code, nothing can be done until it is rewritten in Rust")

Of course highly correct C code is possible [1]. But ADA makes it easier. Rust makes it easier. You can write anything in any language, that is _not_ the argument. How could you plausibly advocate for a culture that invests a lot of effort [1] into making codes correct, and not also advocate for tools and languages that make it easier to check important aspects of correctness? A craftsman is responsible for his tools. Using subpar tools with the argument that with sufficient knowledge, skill and an appropriate culture you can overcome their shortcomings is absurd.

Rust is also often not the right tool. I looked at it fairly deeply some years ago for my team to transition away from Python/C hybrids, but settled on a fully garbage-collected language in the end. That was definitely the right choice for us.

[1] e.g. MISRA C, or https://en.wikipedia.org/wiki/The_Power_of_10:_Rules_for_Dev...

The thing is. There always was a strong theoretical case that Rust should improve software quality (not just because of the fact that you have a lifetime system). The only reasonable counterpoint was that this is theory, and large scale experience is missing. Maybe in high quality code bases the mental overhead of using Rust would outweigh the theoretical guarantees, and the type of mistakes prevented are already caught by C/C++ tooling anyways?

The (in recent years) rapid adoption of Rust in industry clearly shows that this is not the case.

> And a few days ago a security vulnerability was found in the Rust Linux kernel code.

was it a security vulnerability? I'm pretty sure it was "just" a crash. Though maybe someone smarter than me could have turned that into something more.

I have no dog in this race, I really like the idea of Rust drivers but can very much understand retiscience at getting Rust to be handling more core parts of the kernel, just because Rust's value seems to pay off way more in higher level code where you have these invariants to maintain across large code paths (meanwhile writing a bunch of doubly-linked lists in unsafe Rust seems a bit like busy work, modulo the niceties Rust itself can give you)

> was it a security vulnerability? I'm pretty sure it was "just" a crash.

It's a race condition resulting in memory corruption.[1][2] That corruption is shown to result in a crash. I don't think the implication is that it can result only in crashes, but this is not mentioned in the CVE.

Whether it is a vulnerability that an attacker can crash a system depends on your security model, I guess. In general it is not expected to happen and it stops other software from running, and can be controlled by entities or software who should not have that level of control, so it's considered a vulnerability.

[1] https://www.cve.org/CVERecord/?id=CVE-2025-68260 [2] https://lore.kernel.org/linux-cve-announce/2025121614-CVE-20...

It is entertaining to observe that how - after the bullshit and propaganda phase - Rust now slowly enters reality and the excuses for problems that did not magically disappear are now exactly the same as what we saw before from C programmers and which Rust proponents would have completely dismissed as unacceptable in the past ("this CVE is not exploitable", "all programmers make mistakes", "unwrap should never been used in production", "this really is an example how fantastic Rust is").

You have a wild amount of confirmation bias going on here, though.

Of course, this bug was in an `unsafe` block, which is exactly what you would expect given Rust's promises.

The promise of Rust was never that it is magical. The promise is that it is significantly easier to manage these types of problems.

There were certainly a lot of people running around claiming that "Rust eliminates the whole class of memory safety bugs." Of course, not everybody made such claims, but some did.

Whether it is "significantly easier" to manage these types of problems and at what cost remains to be seen.

I do not understand you comment about "confirmation bias" as did not make a quantitative prediction that could have bias.

> There were certainly a lot of people running around claiming that "Rust eliminates the whole class of memory safety bugs."

Safe Rust does do this. Dropping into unsafe Rust is the prerogative of the programmer who wants to take on the burden of preventing bugs themselves. Part of the technique of Rust programming is minimising the unsafe part so memory errors are eliminated as much as possible.

If the kernel could be written in 100% safe Rust, then any memory error would be a compiler bug.

Yes, but this is the marketing bullshit I am calling out. "Safe Rust" != "Rust" and it is not "Safe Rust" which is competing with C it is "Rust".

> it is not "Safe Rust" which is competing with C it is "Rust".

It is intended that Safe Rust be the main competitor to C. You are not meant to write your whole program in unsafe Rust using raw pointers - that would indicate a significant failure of Rust’s expressive power.

Its true that many Rust programs involve some element of unsafe Rust, but that unsafety is meant to be contained and abstracted, not pervasive throughout the program. That’s a significant difference from how C’s unsafety works.

But there are more than 2000 uses of "unsafe" even in the tiny amount of Rust use in the Linux kernel. And you would need to compare to C code where an equally amount of effort was done to develop safe abstractions. So essentially this is part of the fallacy Rust marketing exploits: comparing an idealized "Safe Rust" scenario compared to real-word resource-constrained usage of C by overworked maintainers.

The C code comparison exists because people have written DRM drivers in Rust that were of exceedengly high quality and safety compared to the C equivalents.

This is just so obtuse. Be serious.

Even if you somehow manage to ignore the very obvious theoretical argument why it works, the amount of quantitative evidence at this point is staggering: Rust, including unsafe warts and all, substantially improve the ability of any competent team to deliver working software. By a huge margin.

This is the programming equivalent of vaccine denialism.

There is a lot of science showing vaccines work. For Rust showing that it is better this is still lacking. And no Google's blog posts are not science.

So kernel devs claiming Rust works isn't good enough? CloudFlare? Mozilla? Your're raising the bar to a place where no software will be good enough for you.

Safe Rust absolutely eliminates entire categories of bugs

> Of course, this bug was in an `unsafe` block, which is exactly what you would expect given Rust's promises.

The fix was outside of any Rust unsafe blocks. Which confused a lot of Rust developers on Reddit and elsewhere. Since fans of Rust have often repeated that only unsafe blocks have to be checked. Despite the Rustonomicon clearly spelling out that much more than the unsafe blocks might need to be checked in order to avoid UB.

The unsafe code relied on an assumption that was not true; the chosen fix was to make that assumption be true. Makes perfect sense to me.

Rust fanboys on Reddit are not contributing to the Linux kernel. What matters here is that Rust helps serious people deliver great code.

Is it any more or less amusimg, or perhaps tedious, watching the first Rust Linux kernel CVE be pounced on as evidence that "problems .. did not magically disappear"?

Does anyone involved in any of this work believe that a CVE in an unsafe block could not happen?

In case anyone is keen for an explanation of the vulnerability, LowLevelTV has done a video on this:

https://youtu.be/dgPI7NfKCiQ?si=BVBQ0MxuDpsbCvOk

The TLDR is that this race condition happened with unsafe code, which was needed to interact with existing C code. This was not a vulnerability with Rust's model.

That said, you can absolutely use bad coding practices in Rust that can cause issues, even for a regular programmer.

Using unwrap without dealing with all return cases is one example. Of course, there is a right way to dealing with return methods, but it's up to the programmer to follow it

As Rust's advantages over C continue to be proven, a shift in position to "suck it up, C devs" is to be expected.

Agree. As a dev I've had to pivot a dozen times in my career. If you're a dev you should be able to learn a new language fairly quickly, all the core elements are the same, just the vocabulary is a little different. Since nobody has "fixed" C to avoid these bugs, and we're not going to go as far as put Java or .Net in the kernel, then I think Rust is probably the best, most pragmatic solution we have right now.

Eh, these are highly skilled individuals that just don't like learning a new thing, no matter how useful. That attitude is a problem to be managed, but these people deserve a certain amount of respect. Anyone saying "suck it" or similar should get a grip.

I think you’ve said the quiet part out loud by mentioning learning Rust.

The learning seems to be the only legitimate issue that people have. But they avoid mentioning it because it sounds intellectually lazy.

And it is intellectually lazy.

Well yeah, that's the strategy.

"You don't need to learn it or use it, we just want to do our own separate things with it over here"

.. some time later ..

"Oh yeah it's working good for us, we think it'd be useful to use it in these additional places, think about the benefits!"

.. some time later ..

"Now it's going to be core and required, either deal with it or get out"

They know they could never jump straight to the last step without revolt, so they shove their foot in the door with fake promises and smiles and then slowly over time force the door all the way open until they eventually get what they wanted from the beginning.

There are lots of vulnerabilities in the C code, too. Should we remove C or do we accept that fact that no language is perfect since they are used by humans and continue to make improvements and use tools that help us along as time goes forward?

The cherry picking for this one Rust vulnerability to the ~150 C vulnerabilities is such a weird take that I can't help but think people have some weird hatred of Rust.

> Should we remove C or

Your post is curious, for the post I quoted basically argued for just that eventuality for all new code. Even as the new language introduces undefined behavior vulnerabilities.

The promises as stated previously, and the goal as stated by that lwn.net post now, are starkly different. And the poster did not even wait until the new language has proven its worth. And then a UB CVE comes by in the code in the new language.

What Linus wrote in the past:

https://www.phoronix.com/news/Torvalds-On-Rust-Maintainers

> So when you change the C interfaces, the Rust people will have to deal with the fallout, and will have to fix the Rust bindings. That's kind of the promise here: there's that "wall of protection" around C developers that don't want to deal with Rust issues in the promise that they don't have to deal with Rust.

That both you and that lwn.net poster writes these things, is extraordinarily weird and strange.

But this sounds like hubris and user error, then, and not a language discussion at all?

I do not think it is weird. Every C bug was taken as clear evidence that we need to abandon C and switch to Rust. So the fact that there are also such bugs in Rust is - while obvious - also important to highlight. So it is not weird hatred against Rust, but hatred against bullshit. And considering that most of the code is C, your 150 C vulnerabilities is a meaningless number, so you still continue with this nonsense.

One C bug was not taken as clear evidence that we need to abandon C and switch to Rust. Hundreds of thousands of very similar bugs, over decades, in common code patterns were. I’ve never understood how other C or C++ developers could seriously question whether Rust solves any safety problems at all. Maybe the tradeoffs aren’t worth it for a particular use case, but how could you find it unimaginable that even just enforced bounds checks would catch lots of bugs that (normal, non-verified) C would miss? Do you doubt that Python code corrupts memory a lot less because you saw a CPython CVE once?

What language do you think Graydon Hoare was spending most of this time writing while he started working of Rust as a side project? Hint: it sure wasn’t Java. Rust is not the product of some developer who has only used 2 scripting languages and had to read the definition of stack-smashing off of Wikipedia showing those C developers how to live in the future. It’s not old enough for many of the developers working on it to have only ever used Rust. It’s mostly C and C++ developers trying to build a new option for solving their same problems.

> It’s mostly C and C++ developers trying to build a new option for solving their same problems.

I've observed that a lot of the folks I used to meet at ruby conferences have moved to Rust. No idea what led to this, but maybe it's just folks that were generally curious about new programming languages that moved to ruby when it became better known and that the same interest led to adopting Rust.

I worked on a Ruby codebase that moved to Rust - I think that part is mostly cargo-culting cool things in the news to be perfectly honest. There’s type safety advantages, but if Ruby’s performance envelope was even conceivably acceptable for your use-case there are likely better options. I strongly suspect a lot of the friction between Rust and only-C/C++ developers is the product of a bunch of people coming at Rust from higher level languages parroting lines about safety, and then looking at you blankly if you ask how it handles nested pointer indirection.

But I don’t think that applies to the people actually driving the language forward, just those talking a big game on HN/Reddit.

Giving the size and age of the C ecosystem, the number of bugs is not really a valid argument. We will see an increasing numbers with Rust as Rust is increasingly used. I also do not question that Rust solves some problems. It just solves them rather badly and at high cost while bringing new problems.

I looked at firefox code a decade ago, it was a complete complex nightmare mix of different languages. I can see that this motivated starting something new, but it was not a clean C code base (and not even C).

What number of CVEs is Rust kernel code allowed to have before we have good evidence it’s a categorical failure? Do you turn off KASLR for your Linux machines because there exist CVEs it doesn’t protect against?

As long as the kernel will be developed, there will be CVEs - even with Rust. So at what point the number is so high that we should drop Rust and move to formal verification? And even then, there will be CVEs... This whole argument is nonsense.

But I also do not agree that memory safety is of much higher importance than other issues. Memory safety is highly critical if you have a monopolistic walled garden spyware ecosystem - such as Android. Not that I do not want memory safety, but the people I know who got hacked, did not get hacked because of memory safety issue, but because of weak passwords or unpatched software. And at least the later problems gets harder with Rust...

Your priorities do not match that of most kernel developers or most operators of network-connected Linux systems (even if we ignore Android). So I don’t think your problem is with Rust at all, you’ll need to fork Linux if you want the project to stop putting huge amounts of effort into memory safety (as it has for decades).

You are right, I do not have a problem with Rust as a language nor with the kernel improving memory safety. My issue is solely with exaggerated claims and aggressive marketing of Rust.

(And I am operating network-connected Linux devices since 30 years myself. Memory safety is not the known issue, at the moment I worry more about limited security updates due to Rust.)

The number of memory related bugs is absolutely a valid issue with C when the same bugs are impossible in Rust. The C memory model is a disaster when every computer is connected to the Internet.

You are saying the Rust bug in the kernel was impossible? How did it happen then? Come on guys.

> Every C bug was taken as clear evidence that we need to abandon C and switch to Rust.

I think more charitably it's every "simple" C bug that tends to provoke that reaction. Buffer overflows, use-after-frees, things for which mechanically-enforceable solutions have existed and been widespread for a while. I think more exotic bugs tend to produce more interesting discussions since the techniques for avoiding those bugs tend to be similarly exotic.

> So the fact that there are also such bugs in Rust

Similarly, I think you need to be careful about what exactly "such bugs" encompasses. This bug wasn't one of the above "simple" bugs IMHO, so I would guess an equivalent bug in C code would at least avoid the worst of the more strident calls you so dislike. Hard to say for sure, though, given our unfortunate lack of a time machine.

I agree with you that this is more nuanced and that I oversimplified this a bit in my comment.

Okay, fair that since the majority of the codebase is C and that 150 vulnerabilities is probably negligible in comparison since we're talking about ratios, but if we're to be THAT nuanced then we also need to consider that code has been iterated upon for decades, so, I think the point is moot.

The claim has never, ever, been that Rust is bug free. The objective was to help reduce bugs, which is an outcome I've seen first hand in projects I work on. You still seem to speak in aggro terms, so it still feels like an emotional response to Rust.

What features do you like the most in Rust? Are pattern matching and enums some of them?

Ah, credibility attacks. Nice.

Safe Rust eliminates some of the more common memory bugs in C. The bug under discussion was written in unsafe Rust—but even that doesn't obviate the huge advantages Rust has over C. Even unsafe Rust, for instance, has far fewer UB gotchas than C. And with Rust, you can isolate the tricky bits in 'unsafe' blocks and write higher-level logic in safe Rust, giving your code an extra layer of protection. C is 100% unsafe—"unsafe at any speed" as I like to say.

IMHO, "C is 100% unsafe" is a misleading way to look at it and the kind of exaggeration which I criticize. Also in C only specific language features are unsafe and not all code, and you can screen for these features and also isolate critical code in helper functions. Saying these features could appear everywhere is no difference from "unsafe" possibly appearing everywhere in Rust. I agree that "unsafe" is easier to find as a keyword, but I do not think this is a fundamental advantage, especially in projects where you have a lot of such "unsafe" blocks.

> Saying these features could appear everywhere is no difference from "unsafe" possibly appearing everywhere in Rust.

That's not true in practice: Unsafe code is clearly delineated and can be 100% correctly identified. In C, usage of dangerous features can occur at any point and is much harder to clearly separate.

First, if "unsafe" worked so well 100% time, why did we have this bug? (and many other) So this already obviously wrong statement.

Then yes, you can use dangerous features in C at any time, but obviously you can also use "unsafe" at any time. The only difference is that "unsafe" is clearer to recognize. But how much this is worth is unclear. First, if you do not invalidly reduce the discussion to only memory safety, you need to review all other code anyway! But even then, it is also not true that only the code marked with "unsafe" is relevant. This is major myth. The "unsafe" code can cause UB outside "unsafe" and logic bugs outside "unsafe" can cause bugs unsafe. This does not perfectly decouple if you Rust repeat this nonsense over and over again.

Don't get me wrong, I think the unsafe keyword is good idea. But the magical powers Rust fans attribute to it and the "SAFETY" comment they put next to it tells me they are a bit delusional.

> logic bugs outside "unsafe" can cause bugs unsafe.

This is the wrong understanding of Rust's unsafety encapsulation. For example, no logic bug outside of `unsafe` can cause undefined behavior of Rust std's `Vec` abstraction, which is using underlying unsafe to build.

The point that "because unsafe is used so the entire Rust program is also unsafe" is a real major myth. It's as absurd as saying "because Java runtime using unsafe underlying to build so Java is also unsafe".

Two questions:

Why was the fix to this unsafe memory safety bug [0] only changes to code outside of unsafe Rust blocks?[1][2]

Why does the Rustonomicon[3] say the following?

> This code is 100% Safe Rust but it is also completely unsound. Changing the capacity violates the invariants of Vec (that cap reflects the allocated space in the Vec). This is not something the rest of Vec can guard against. It has to trust the capacity field because there's no way to verify it.

> Because it relies on invariants of a struct field, this unsafe code does more than pollute a whole function: it pollutes a whole module. Generally, the only bullet-proof way to limit the scope of unsafe code is at the module boundary with privacy.

[0] https://social.kernel.org/notice/B1JLrtkxEBazCPQHDM

[1] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux...

[2] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux...

[3] https://doc.rust-lang.org/nomicon/working-with-unsafe.html

If a logic bug inside Vec and outside any unsafe blocks inside Vec happens, and that logic bug violates any invariants and requirements of the unsafe blocks, that can cause memory unsafety.

That would be the unsoundness of `Vec` itself, but if the abstraction of `Vec` is sound, there would be no way to use `Vec` outside of `unsafe` that can cause memory unsafety.

The point coming back to abstraction and responsibility, in Rust, you can build abstraction that is sound and guarantee memory safety from there. There can be soundness bug inside your abstraction, but it will be a massively smaller surface for auditing and expert required to write such abstraction. Also, when soundness bug appears, the responsibility is solely on the abstraction writer, not the user.

Whereas in C, without those safe abstraction, the surface of doing thing right to avoid memory safety issue is your entire codebase, and responsibility of "holding the knife correctly" is on the user.

> There can be soundness bug inside your abstraction, but it will be a massively smaller surface for auditing and expert required to write such abstraction.

If all of the Vec has to be "audited", or checked and reviewed, including all the code that is not inside unsafe blocks, how would the surface be any smaller?

> The point coming back to abstraction and responsibility, in Rust, you can build abstraction that is sound and guarantee memory safety from there.

Isn't it normal for programming languages to support building abstractions that can help with not only memory safety, but general correctness? C is a bit barebones, but lots of other programming languages, like C#, C++, Haskell and Scala support building abstractions that are harder to misuse.

All of `Vec` is much smaller than all of the place using Vec. IIRC, Vec is around 3k LoC. And for even low level code like Oxide & Android core, they are observed less than 4% of their code is inside or related to unsafe, that’s a massive improvement.

Yes, Rust is not new in term of allow building hard to misuse abstraction, it’s just allow abstraction over memory safety without relying on GC or runtime checks. Rust achieve this by adding capability to enforce shared XOR mutability with its borrowck which C++ couldn’t.

> in C only specific language features are unsafe and not all code

Using rust's definition of unsafe which is roughly "can cause undefined behaviour" then it seems to me isolating use of these features isn't possible. What is C without:

* Dereferencing pointers * Array access * Incrementing signed integers

You can do all of the above without invoking UB, but you can't separate the features in C that can cause UB from the ones that can't.

The first misunderstanding is that safety is a property of the language or not. Rust marketing convinced many people that this is so, but C can be safe or unsafe. Fil-C shows that even all of C can be memory safe (but at a substantial cost in performance). But even just with GCC and Clang, array access and signed integer can be made safe with a compiler flag, and a violation then traps and this is similar to a Rust panic. The cases which can not be dealt with easily are pointer arithmetic, unions, and free and concurrently related issues. And it is very well possible to isolate and review all of these. This will not find all bugs, but neither does this work perfectly for Rust "unsafe" as this bug (and many others) nicely illustrates.

I guess that means you're using the colloquial meaning of the word safety/unsafe rather than the rust definition. It's worth being explicit about that (or choosing a different word) in these discussions to prevent confusion.

For Rust safety (meaning no UB) most definitely is a property of the language. If a module does not contain unsafe and the modules it uses that do contain unsafe are implemented soundly then there is no UB.

In C UB is a part of the language.

No, in the comment you reply to, I am using safe/unsafe in the Rust sense. E.g. signed overflow changed to trap avoids the UB.

Also "If .. are implemented soundly" sounds harmless but simply means there is no safety guarantee (in contrast to Fil-C or formally verified C, for example). It relies on best-effort manual review. (but even without "unsafe" use anywhere, there are various issues in Rust's type system which would still allow UB but I agree that this is not that critical)

In C UB is part of the ISO language specification, but not necessarily part of a specific implementation of ISO C. If you argue that the ISO spec matters so much, I like to point out that Rust does not even have one, so from this perspective it is completely UB.

> Also "If .. are implemented soundly" sounds harmless but simply means there is no safety guarantee (in contrast to Fil-C or formally verified C, for example).

Don't those also depend on implementations being sound? Fil-C has its own unsafe implementation, formal verification tools have their trusted kernels, it's turtles all the way down.

The implementation itself being sound, yes. And yes, in Rust if you only use sound libraries (in combination), never use unsafe yourself and ignore the known defects in Rust, then it is also guaranteed to be safe. But in system programming, you usually have to use "unsafe" in your own code, and then there is no guarantee and you make sure the could has no UB yourself, just like in C.

Sure. My point is mostly that the problem is less that your safety guarantees rely on correct implementations (since that applies to all "safe" systems as long as we're running on unsafe hardware) and more that the trusted codebase tends to be quite a bit larger for (current?) Rust compared to Fil-C/formal verification tools. There are efforts to improve the situation there, but it'll take time.

Does make me wonder how easy porting Fil-C to Rust/Zig/etc. would be. IIRC most of the work is done via LLVM pass(es?) and changes to frontends were relatively minor, so it might be an interesting alternative to MIRI/ASan.

The safest computer is a rock.

The point is that when you start using rust in the real world to get real work done a lot of the promises that were made about safety have to be dropped because you need to boot your computer before the heat death of the universe. The result will be that we end up with something about as safe as C is currently - because CPUs are fundamentally unsafe and we need them to work somehow.

Rust is from the universe in which micro kernels weren't a dead end and we could avoid all the drivers being written in C.

> when you start using rust in the real world to get real work done a lot of the promises that were made about safety have to be dropped because you need to boot your computer before the heat death of the universe.

Safe rust isn't slow like Python, Go or Fil-C. It gets compiled to normal native code just like C and C++. It generally runs just as fast as C. At least, almost all the time. Arrays have runtime bounds checks. And ... thats about it.

> The result will be that we end up with something about as safe as C is currently - because CPUs are fundamentally unsafe and we need them to work somehow.

Nah. Most rust is safe rust. Even in the kernel, not much code actually interacts directly with raw hardware. The argument in favour of moving to rust isn't that it will remove 100% of memory safety bugs. Just that it'll hopefully remove most of them.

A million memory error bugs is used as a valid argument to stop using C and switch to rust where such bugs are impossible.

Once again, congrats to the R4L team! It's a big milestone and I'm looking forwards to future developments!.

There was a lot of interesting discussion on the previous post [0], but one thing I didn't see was much discussion about this bit:

> The DRM (graphics) subsystem has been an early adopter of the Rust language. It was still perhaps surprising, though, when Airlie (the DRM maintainer) said that the subsystem is only "about a year away" from disallowing new drivers written in C and requiring the use of Rust.

I was a bit surprised when I first read this. Is this meant to be read in a way that is more just a description of the state of Rust bindings (e.g., the DRM subsystem is about a year away from being able to require the use of Rust, but isn't actually planning on doing so), or it is describing actual plans (e.g., the DRM subsystem is about a year away from actually requiring the use of Rust)? I was originally more inclined to go for the former interpretation, but this other bit:

> With regard to adding core-kernel dependencies on Rust code, Airlie said that it shouldn't happen for another year or two.

Makes me think that perhaps the devs are actually considering the latter. Is anyone more in-the-know able to comment on this?

[0]: https://news.ycombinator.com/item?id=46213585

I'm not more "in the know" but it makes sense that new drivers could require it. New drivers, after all, are pretty much always written for newer platforms that Rust has support for. The main issue with enabling Rust (let alone requiring it) is that Linux still supports platforms which Rust does not.

Is DRM considered core kernel dependencies?

I don't know. My line of thinking is that if the Linux devs are comfortable with using Rust in core Linux then they might also be comfortable requiring Rust for new drivers as well. No idea if that makes sense, though.

If you build a house out of inflammable bricks instead of magnesium ones you can at least rule out magnesium fires.

Now the question is: If we live in a world where magnesium fires are common, can we afford to not at least try building with the inflammable bricks?

I know this topic stokes emotions, but if you haven't tried Rust as someone with C/C++ experience, give it a go. You will come out wiser on the other side, even if you never use the language for anything.

Inflammable doesn’t mean not flammable. It means able to be inflamed. Language changes over time but this word is particularly problematic, so I’d avoid it to avoid confusion.

Thanks for the correction, English is not my first language.

Somewhat related, a kernel in Rust: https://github.com/jgarzik/hk

If you're going to plug your own project, you might want to mention that in your comment.

There's dozens of rust osdev projects. Its an open question if any become relevant like linux.

It's so tiresome.

Offtopic but this title makes me want to create an alternate-universe version of the HN front page where every title is shrill/spectacular/hysterical/urgent/clickbaity. Such as:

The Absolute State of the Kernel Rust Experiment Right Now

And every comment has its confidence/aggressiveness taken up to 11 (tho still within site rules).

This author is not someone who should be reporting on Rust especially in the kernel: https://www.youtube.com/watch?v=gVC1gp2PS8U&t=1538s

Mind elaborating on what exactly is wrong in that video? Or how that is relevant to the article's contents?

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