Ada also has no exception allowed profiles and other mechanisms.
HN is not the place to hold a lecture on Ada features.
It is not a maybe, rather lack of knowledge.
We can lead academic discussions about which language is safer/better/leaner/whatever-er, but the fact is that Rust has a larger and growing mindshare so this effort is unsurprising. For Ada, the solution isn't to try and prove to anonymous forum goers it would've been better choice if only people recognized the fact. The solution is to mobilize the Ada community to put the same amount of effort into the publicity and marketing (yes, the bad M word) of their ecosystem.
Ada clearly lives on in many safety critical systems, but judging by the admittedly biased topic frequency on HN and other technical sites, it has a tiny community who mostly keep to themselves. That's fine, but then don't be surprised when it's Hip Language X that gets the headlines and these sort of efforts.
My only point is how many in the Rust community advocate as if Rust would be the first language having features, that actually were already in Ada for the past decades.
As for Ada on Linux, naturally Linus would never go along it.
A C kernel guy liking a language with Pascal syntax, a community that worships a paper that hasn't been true in the Pascal world since early 80's, not even at gunpoint.
If you want to see a use case where Ada was chosen against Rust, check NVidia's project for self driving vehicles firmware.
Plenty of safety conscious language have had followings since ALGOL, this is the point that many miss when praising Rust, while ignoring our computing history.
I think that is a false perception created by the dev-blogging community. Based on GitHub activity (https://madnight.github.io/githut/#/pull_requests/2021/2) Rust usage is declining (absolute numbers show little growth). Based on developer surveys (https://www.jetbrains.com/lp/devecosystem-2020/) very few people use rust outside of hobby development.
I think the concern is that the core argument that "I think Linux should adopt rust for safety" is a bit dishonest, given that there are a large number of well-vetted alternatives. "I think Linux should adopt rust because I like rust for social reasons" would probably be more correct. That Google staff seem to think rust is good for the Linux kernel but not, say, Zircon, would be surprising if those same people actually believed that any legal rust program is safe and inherently trustworthy. "Embrace, extend, extinguish" wasn't that long ago.
I mean, neither Ada nor Zircon are even on the lists, so in terms of mindshare, they are clearly blown out of the water by Rust (from the evidence you provide). To discount Rust based on usage when the alternatives being suggested don't even make the rankings is also a bit dishonest.
In fact, the argument "I think Linux should adopt rust for safety" makes perfect sense. Here's finally a safety conscious language that seems to be embraced by a larger community, and even the big tech players. Instead we get people suggesting arcane alternatives that may be technically better, but have a snowball's chance in hell to become commonplace any time soon.
In the meantime, Google makes extensive use of Rust in new components of both Fuchsia and Android and even rewrites some legacy components where it makes sense.
I think you and 'grumblenum should team up and write a working kernel module in Ada/Spark and then we can have a fruitful discussion about it, instead of just theorizing about whether it could be done. I'm interested in seeing the problems solved, and I'm indifferent to technology. If you think Ada/Spark can solve them, that would be awesome!
(Editing to reply to a small claim in another subthread, "Linus would never go for it" - we believed the same thing when we started. We were originally thinking that we'd pitch this directly at Linux distros shipping out-of-tree modules that they didn't want to keep having to push security updates for. https://github.com/fishinabarrel/linux-kernel-module-rust was out-of-tree and we tried to keep compatibility with kernels 4.4 onwards. But it turned out Linus isn't opposed to it.)
I think the first problem is some kind of language specification. That it's not possible to know what behavior one should expect from rustc means that it isn't a solution. It's another problem. You should check out Ken Thompson's great speech on why this is an issue. https://www.cs.cmu.edu/~rdriley/487/papers/Thompson_1984_Ref...
Or do you think it's wrong to regard unauditable enhancements to free software paid for by Google with suspicion?
Here's a way to address the issue he brings up in that speech that does not involve language specifications: https://dwheeler.com/trusting-trust/
https://www.adacore.com/academia/projects/muen-project
https://www.adacore.com/company/partners/nvidia
https://genode.org/about/road-map
https://www.ptc.com/-/media/Files/PDFs/Developer-Tools/apexa... (ApexAda Exec)
https://www.ghs.com/products/safety_critical/integrity_178_e...
https://www.windriver.com/products/helix (Wind River Helix Bare Metal partitions)
Muen: If I am reading the allocator in https://git.codelabs.ch/?p=muen.git;a=tree;f=tools/liballoc/... correctly, it simply has no deallocator function at all. It does have a "Clear" function, but there's no sign that it has any ability to statically check that calling it is safe. That is exactly what we're talking about.
Nvidia: No public source code, and it's not obvious what actually exists here, beyond a compiler to Nvidia hardware.
Genode: This project is mostly written in C++. There is a very tiny, experimental amount of Ada in it (< 400 lines of code). There's certainly nothing that speaks to the questions discussed in this thread (safe dynamic allocation/deallocation, security, etc.).
ApexAda: This is a marketing brochure. Also this marketing brochure talks about "significant deployments in satellite communications, avionics, weapons control systems, and a myriad of other mil/aero applications," all of which - as discussed elsewhere in these comment - are applications that neither need nor want dynamic allocation (and are generally not exposed to deeply-structured untrusted input, for that matter).
Green Hills: This looks interesting - there's a POSIX filesystem and a UDP socket implementation, both of which (probably) want dynamic memory allocation. That is, at last, an application that needs dynamic allocation. Is it actually written in Ada? I see that the RTOS itself supports development in C, C++, and Ada, and they claim to offer a BSD socket implementation, so they at least have C bindings. I don't see any claim about what language it's written in, and Green Hills seems to do a lot of C work (see e.g. https://www.ghs.com/products/micro_velosity.html). If it's in Ada, then I think this gets the closest to what would be needed for the Linux kernel - do you know how their filesystem and socket implementations handle dynamic allocation? (I'll also note that they lost their certification many years ago, so if the answer is that they have safe code because they spent a whole lot of time perfecting a single version of an OS, then that's a very different problem space from Linux, which is constantly changing.)
Wind River: This is a marketing page without much detail, but it looks like it's a hypervisor to run general-purpose OSes on top of, not a general-purpose OS itself, which means it probably does not need dynamic memory allocation, or that if it does, the safety of deallocation can be verified by hand.
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No Ada developer has done what's being done in this patchset, and it's pretty insulting to the folks putting in the work to claim it's been done and Gish-gallop a bunch of random links and expect people to put in the time to figure out what exactly you're claiming already exists. Everyone knows it's possible to write code in Ada. Nobody is asking if Ada can be used for completely unrelated purposes. You may as well link to GORILLAS.BAS and ask why the Linux kernel isn't using QBasic, a memory-safe language if you use the subset without PEEK and POKE.
Write - or point to - a kernel driver for a UNIX-like operating system written in Ada, that safely handles dynamic allocation. That's the clear bright-line goal. If you think that's not the right goal, say why.