linux VS unsafe-code-guidelines

> Torvalds answered that, while he used to find problems in the LLVM Clang compiler, now he's more likely to find problems with GCC instead; he now builds with Clang.

https://github.com/ClangBuiltLinux/linux/issues is our bug tracker for known issues (a few are tracked in llvm's issue tracker). Bug reporters and future kernel hackers wanted!

As I mentioned on mastodon, there's lots of bugs still to be fixed everywhere, but even if we don't fix them, providing competition in the toolchain space has been worth it to users.

Linux builds on clang after a decade of dedicated effort to make it happen, and that is with clang overall being comparatively similar to gcc (e.g clang implements many gcc extensions): https://github.com/ClangBuiltLinux/linux/wiki/Project-histor...

We got plenty of bugs for building the kernel with LLVM, if you're looking for tasks, pick one!

There's an semi-official github[0] for this.

AFAICT from the issue, Clang and binutils/LLVM tools work fine with no patches for the mainstream archs and when not trying to be super-fancy with custom flags. The more non-mainstream one goes with arch or flags the more likely one will run into something.

[0] https://github.com/ClangBuiltLinux/linux/issues

If you have any reproducible issues please file them here: https://github.com/ClangBuiltLinux/linux/issues

See if you can build your distro's config. make LLVM=1 localmodconfig olddefconfig bzImage. Any warnings? Any warnings not in the issue tracker? If not, pick one from the issue tracker and see if you can reproduce it. Note: lots of issues are tagged by target ISA, so you'll need to get familiar with cross compiling (setting ARCH= and CROSS_COMPILE=.

It's a pipeline; clang starts, hands off to LLVM.

For a compilation to object file from source code, the vast majority of time for most translation units is spent in the front end of the pipeline, not the middle, or backend.

See also my first plot: https://github.com/ClangBuiltLinux/linux/issues/1086#issueco...

Useful context on the Rust side is this issue [1]. It sounds like some of the author's concerns are addressed already.

[1]: https://github.com/rust-lang/unsafe-code-guidelines/issues/4...

Is this captured by one of the known soundness conflicts? If not then should consider adding it to the list.

There are some competing proposals for different memory models. Stacked borrows is the current proposal, but there are more work in the approproate WG.

Thank you /u/RalfJung for bringing formal methods to Rust, both through models like Stacked Borrows, by developing miri, and by working on unsafe-code-guidelines which aims to specify exactly what is and isn't allowed in unsafe code (surprisingly, it's an open question as 2023!)

You could imagine some way to make this safe for example automatically convert &'short &'long mut T to &'short &'short T, but it's non-trivial to prove they are safe at all, not to mention ensuring this is correctly implemented in the compiler. If you're interested there's also a discussion on whether the opposite (& & T to & &mut T) is sound here.

Agreed! MIRI is so good, it still feels like magic to me. It also comforts me that the Rust team takes improving unsafe semantics seriously, with the past Unsafe Code Guidelines WG and today's operational semantics team (t-opsem).

I think there are some aspects of this rule that are still undecided. See for example:

- https://github.com/rust-lang/unsafe-code-guidelines/issues/8...

- https://github.com/rust-lang/miri/issues/2732

C is much better specified than unsafe Rust. Some things are just not worked out yet in Rust. This may sometimes even bite very experienced devs, such as this issue with Box's aliasing semantics, which tripped up the author of left-right.