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

[Ralf Jung <post@ralfj.de>]

Hi all,

On 02.03.26 08:29, Alice Ryhl wrote:
> 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.

Also see the documentation at 
<https://doc.rust-lang.org/rustc/target-tier-policy.html#adding-a-new-target>.

Kind regards,
Ralf