Re: Rust version requirement (was: [PATCH V2 3/3] powerpc: Enable Rust for ppc64le)

[Alice Ryhl <aliceryhl@google.com>]

On Mon, Feb 16, 2026 at 12:23:16PM +0100, J. Neuschäfer wrote:
> On Thu, Feb 05, 2026 at 09:12:01PM +0530, Mukesh Kumar Chaurasiya wrote:
> [...]
> > use rust version nightly-2026-01-28
> > 
> > the latest one has some issue. I just raised a bug for the rustc
> > here[1].
> > 
> > [1] https://github.com/rust-lang/rust/issues/152177
> 
> Another reason to use a nightly version is that Rust inline assembly for
> PowerPC will only be stabilized[1] in version 1.94, so current release
> versions fail like this (tested with 1.91.1):
> 
>     error[E0658]: inline assembly is not stable yet on this architecture
>       --> ../rust/kernel/sync/barrier.rs:19:14
>        |
>     19 |     unsafe { core::arch::asm!("") };
>        |              ^^^^^^^^^^^^^^^^^^^^
>        |
>        = note: see issue #93335 <https://github.com/rust-lang/rust/issues/93335> for more information
>        = help: add `#![feature(asm_experimental_arch)]` to the crate attributes to enable
>        = note: this compiler was built on 2025-11-07; consider upgrading it if it is out of date
> 
> This is somewhat at odds with Documentation/process/changes.rst which
> only requires Rust 1.78. I wonder if the rust version requirement should
> generally be bumped, or if there should be arch-specific requirements
> somewhere in changes.rst or rust/arch-support.rst.
> 
> Best regards,
> J. Neuschäfer
> 
> [1]: https://github.com/rust-lang/rust/pull/147996

The MSRV is planned to be bumped to 1.85.

If it's available as a nightly feature on 1.78, then you can just add
#![feature(asm_experimental_arch)] to lib.rs, which already enables
several other stabilized feature on older compilers.

Otherwise powerpc support can always be gated to require a larger
rustc version than other platforms.

Alice