Re: [PATCH V13 5/7] rust: Make __udivdi3() and __umoddi3() panic

Miguel Ojeda
2026-04-24T10:34:41Z

On Fri, Apr 24, 2026 at 12:21 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> How hard would it be to have a private copy of the parts of the core
> crate that the kernel actually needs? Since Linux is neither quite
> hosted (using a full libc) nor entirely freestanding (still using
> some library interfaces), the C implementation on most architectures
> has a small subset of the libgcc that we ship with the kernel.
>
> I assume the core crate is larger than libgcc, but I don't know how
> much of it is actually needed here.

It is fairly tied to the compiler version, so it would be a
substantial effort to support across a bunch of versions. Instead of
that, initially we asked to have some `cfg`s (i.e. conditional
compilation) to customize it in the few places we need. We already
pass `--cfg no_fp_fmt_parse` for instance.

There were concerns about combinatorial explosion of `cfg`s, so we
suggested `cfg(linux_kernel)` or similar instead, though nothing
happened so far.

The other option is to at least lint against certain operations, but I
think it would be better to have a way to tell the compiler we really
don't want them generated to begin with.

Cheers,
Miguel