Re: [PATCH V6 2/3] rust: Add PowerPC support

[Alice Ryhl <aliceryhl@google.com>]

On Mon, Mar 02, 2026 at 11:25:54AM +0530, Mukesh Kumar Chaurasiya wrote:
> On Tue, Feb 24, 2026 at 09:58:10AM +0100, Ralf Jung wrote:
> > Hi all,
> > 
> > On 23.02.26 16:31, Miguel Ojeda wrote:
> > > On Mon, Feb 23, 2026 at 3:26 AM Mukesh Kumar Chaurasiya
> > > <mkchauras@gmail.com> wrote:
> > > > 
> > > > I think, disabling altivec, fpu and vsx with compiler flag will work.
> > > > 
> > > > What are your opinion on this?
> > > 
> > > It is really up to upstream Rust -- for us, i.e. the kernel, it
> > > usually doesn't really matter much how things like that are
> > > accomplished: whether via flags, a built-in target, a custom target,
> > > etc. However, we need to know what the path to stability is.
> > > 
> > > My understanding (but I may be wrong) is that upstream Rust prefer we
> > > use built-in targets for softfloat instead of disabling via
> > > `-Ctarget-feature` (and that the other options may go away soon and/or
> > > will never be stable) -- at least for some cases. For instance, for
> > > arm64, please this recent change kernel-side regarding `neon` as an
> > > entry point:
> > > 
> > >    446a8351f160 ("arm64: rust: clean Rust 1.85.0 warning using softfloat target")
> > > 
> > > So please ask upstream Rust (probably in their Zulip, e.g. in
> > > t-compiler or rust-for-linux channels) what you should do for powerpc.
> > > They will likely be happy with a PR adding the target (or whatever
> > > they decide) as Alice mentions. And until we reach that minimum
> > > version (in a year or more), we can use something else meanwhile. But
> > > at least we will have a way towards the end goal, if that makes sense.
> > > 
> > > In case it helps, let me Cc Ralf, Jubilee and Matthew who were
> > > involved in some of that discussion in the past, plus the compiler
> > > leads.
> > 
> > Upstream Rust dev here. Indeed we'd strongly prefer if this could use a
> > built-in Rust target; we can work with you on adding a new target if that is
> > needed.
> > The kernel currently uses a custom JSON target on x86 and that's quite the
> > headache for compiler development: JSON targets are highly unstable and
> > directly expose low-level details of how the compiler internally represents
> > targets. When we change that representation, we update all built-in targets,
> > but of course we cannot update JSON targets. So whenever possible we'd like
> > to move towards reducing the number of JSON targets used by the kernel, not
> > increase it. :)
> > 
> > Kind regards,
> > Ralf
> > 
> Hey,
> 
> Sorry for delayed response. I was out of network zone.
> 
> I am not sure about the process of how to get this in rust toolchain.
> Should I raise an issue of github for this?

You would need to add a new file to compiler/rustc_target/src/spec/targets
in the rustc repository.

If you're not sure what to put there, I would suggest coming up with
something that looks plausible, and opening a PR with that. Then others
can help you with filling out the target correctly.

Alice