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

[Jan Polensky]

On Mon, May 18, 2026 at 07:23:09PM +0200, Miguel Ojeda wrote:
> On Mon, May 18, 2026 at 5:19 PM Jan Polensky <japo@xxxxxxxxxxxxx> wrote:
> >
> > thanks for the review.
>
> You're welcome!
>
> > -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.
>
> Yeah, #152432 is the one I linked in our live list.
>
> Sometimes tracking issues are missing, but I think upstream Rust is
> generally OK adding them -- I have created one, tagged and linked it,
> please feel free to modify it, close it, etc. if needed:
>
>   https://github.com/rust-lang/rust/issues/156724
>
> I hope that helps.
>
> > 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.
>
> No, it is meant to work -- we use `-Z` flags (and other unstable
> features) on a regular basis, as you can see in our issue #2 that I
> linked above, e.g. you can see some of them with:
>
>   git grep '\-Z' Makefile
>
> Please see:
>
>   https://rust-for-linux.com/unstable-features
>
> for some more details.
>
> That is why I was suggesting that you test the current beta, because
> it will become soon 1.96. If it doesn't, then it would be wise to try
> to see why it doesn't! :)
>
> Thanks!
>
> Cheers,
> Miguel
Hi Miguel,

Thanks again for creating the tracking issue for -Zpacked-stack and for
all the references, they were very helpful.

Regarding the toolchain: since this works with the Rust-for-Linux
bootstrap mechanism, I tested with rustc 1.96.0-beta.7 (6be5f81e1
2026-05-17) and everything behaves as expected. I’ll update v2
accordingly (min-tool 1.96.0 without the -nightly suffix, and adjust the
wording so it doesn’t imply nightly-only).

Best Regards
Jan