On Thu, Dec 04, 2025 at 01:15:34PM +0000, Alice Ryhl wrote: > On Thu, Dec 04, 2025 at 01:49:28PM +0100, Emilio Cobos Álvarez wrote: > > On 12/4/25 12:57 PM, Miguel Ojeda wrote: > > > On Thu, Dec 4, 2025 at 12:11 PM Peter Zijlstra <[email protected]> > > > wrote: > > > > > > > > Right. Earlier I also proposed using libclang to parse the C header and > > > > inject that. This might be a little simpler, in that.. > > > > > > Yeah, that would be closer to the `bindgen` route in that `libclang` > > > gets already involved. > > > > Yeah, so... there are existing tools (c2rust [0] being the actively > > maintained one IIUC) that in theory could do something like that (translate > > the bodies of the functions from C to Rust so that rustc could consume them > > directly rather than via LLVM LTO). > > > > I think the intended use case is more "translate a whole C project into > > rust", but it could be interesting to test how well / poorly it performs > > with the kernel helpers / with a single header translated to Rust. > > > > I personally haven't tried it because for work I need to deal with C++, > > which means that automatic translation to Rust is a lot harder / probably > > impossible in general. So for Firefox we end up relying on bindgen + > > cross-language LTO for this kind of thing, and it works well for us. > > > > If I'm understanding correctly, it seems the kernel needs this extra bit of > > help (__always_inline) to push LLVM to inline C functions into rust, which > > is a bit unfortunate... But this approach seems sensible to me, for now at > > least. > > > > FWIW Bindgen recently gained an option to generate inline functions [1], > > which could help avoid at least the bindgen ifdef in the patch series? > > > > Anyways, it might be interesting to give c2rust a go on the kernel helpers > > if nobody has done so, and see how well / poorly it works in practice? Of > > course probably introducing a new dependency would be kind of a pain, but > > could be a good data point for pushing into adding something like it built > > into rustc... > > I already tried c2rust as an alternative to this patch. It works okay > for many functions, but it's missing support for some features such as > asm goto, though this is fixable. But a larger issue is that some things > simply do not translate to Rust right now. For example: > > * Atomics use the Ir operand. > * static_branch uses the i operand. > > neither of which translate directly to Rust.
Right this. AFAIK Rust simply does not have feature parity with inline asm. Them having picked a wildly different syntax for inline asm didn't help either of course. But Rust is Rust, must have terrible syntax :-)
