[PATCH] RISC-V: Fix building rust when using GCC toolchain

[Conor Dooley]

On Thu, Sep 26, 2024 at 05:40:19PM +0200, Miguel Ojeda wrote:
> On Tue, Sep 17, 2024 at 5:26 PM Conor Dooley <conor at kernel.org> wrote:
> >
> > Yes, but unfortunately I already knew how it worked. It's not flags I am worried about, it is extensions.
> > Even using a libclang that doesn't match clang could be a problem, but we can at least declare that unsupported.
> > Not digging it out on an airport bus, but we discussed the lack of GCC support on the original patch adding riscv, and decided against it.
> 
> Do you mean you would prefer to avoid supporting the mixed GCC-Clang
> builds?

Mixed builds are allowed on the c side, since we can figure out what the
versions of each tool are. If there's a way to detect the version of
libclang in use by the rust side, then I would be okay with mixed gcc +
rustc builds.

> If so, do you mean you would prefer to not pick the patch,
> i.e. avoid supporting this at all?

Yes, I would rather this was not applied at all. My plan was to send a
patch making HAVE_RUST depend on CC_IS_CLANG, but just ain't got around
to it yet, partly cos I was kinda hoping to mention this to you guys at
LPC last week, but I never got the chance to talk to any rust people (or
go to any rust talks either!).

> (If so, then perhaps it would be a
> good idea to add a comment there and perhaps a note to
> https://docs.kernel.org/rust/arch-support.html).

Sure, I can add a comment there. 

> Otherwise, please let me know if I am misunderstanding -- thanks!

In sorta related news, is there a plan for config "options" that will
allow us to detect gcc-rs or the gcc rust backend?

Cheers,
Conor.
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