Re: [PATCH 4/4] s390: enable Rust support

[Jan Polensky]

On Tue, May 12, 2026 at 02:10:52PM +0200, Miguel Ojeda wrote:
> On Tue, May 12, 2026 at 1:00 PM Jan Polensky <japo@xxxxxxxxxxxxx> wrote:
> >
> > Signed-off-by: Jan Polensky <japo@xxxxxxxxxxxxx>
>
> Closes: https://github.com/Rust-for-Linux/linux/issues/106
>
> I am happy to see IBM getting involved and being able to close a 5
> year issue! :)
:)
>
> I backlinked there this thread.
>
> > +KBUILD_RUSTFLAGS += --target=s390x-unknown-none-softfloat -Zpacked-stack -Ctarget-feature=+backchain
>
> I added `-Zpacked-stack` and a bunch of related links to:
>
>   https://github.com/Rust-for-Linux/linux/issues/2
>
> Is there a tracking issue for it? I linked
> https://github.com/rust-lang/rust/issues/150259 for the backchain
> feature.
>
> > +       if [ "$SRCARCH" = "s390" ]; then
> > +               echo 1.97.0-nightly
>
> `-Zpacked-stack` landed for 1.96. Is there something queued for 1.97?
> If not, does the beta work?
>
> Either way, I would prefer waiting until we know the actual version
> number, i.e. without `-nightly`. It is just a few weeks away anyway.
>
> Thanks!
>
> Cheers,
> Miguel

Hi Miguel,

thanks for the review.

-Zpacked-stack: I’m not aware of a dedicated rust-lang/rust tracking
issue for this flag. The implementation landed via rust-lang/rust PR
152432, but it doesn’t appear to reference a tracking issue.

backchain: ack, the s390x target-feature tracking issue you linked is the
right umbrella reference.

minimum toolchain version / beta: as long as we pass -Zpacked-stack in
KBUILD_RUSTFLAGS, we need a nightly compiler; beta/stable won’t accept -Z
flags. In v2 I’ll drop the 1.97.0-nightly guess and set the minimum to
1.96.0-nightly (the first release line that includes -Zpacked-stack).
We’ll keep the “-nightly” suffix while this remains a -Z flag. If it gets
stabilized and nothing blocks, the earliest stable release that could
plausibly carry it would be 1.98.

Thanks,
Jan