Re: [PATCH V16 4/7] rust/powerpc: Set min rustc version for powerpc

On Tue, May 26, 2026 at 02:22:49PM +0530, Mukesh Kumar Chaurasiya wrote:

On Mon, May 25, 2026 at 08:16:53PM +0200, Miguel Ojeda wrote:

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On Wed, May 20, 2026 at 8:48 AM Mukesh Kumar Chaurasiya (IBM)
[off-list ref] wrote:

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Minimum `rustc` version required for powerpc is 1.95 as some critical
features required for compiling rust code for kernel are not there.

Which critical features?

Hey Miguel,

Right now i can only think of inline asm. I can rerun the whole thing
with 1.85 and figure out the issues with 1.85. I'll get back on this.

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For example Stable inline asm support which got merged in 1.95.

It is not needed that the support is stable, but rather that
everything you may need works.

I wanted inline asm be stable, I was skeptical about inline asm to be
unstable and potentially messing up the whole system. That's the reason
I waited for the stable support to get merged before sending out this
patch series.

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From a quick test (with a dummy example that may not be
representative), ppc64 inline assembly seems to work for a long time,
way before Rust 1.95.

So, which is the actual version that it is needed? i.e. 1.95.0 doesn't
seem to be required at least due to that.

Yeah it may be true. I'll test out the 1.85 rustc and come back with the
results.

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That is why I am asking about the critical features above, because it
may be that this works since earlier versions.

(I wonder if this patch and s390's similar one influenced each other?)

I am not aware of s390x way of approaching support for rust so can't say
anything about that.

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Thanks!

Cheers,
Miguel

Regards,
Mukesh

Hey Miguel,

Sorry about delayed response on this.
I ran it with rustc 1.85.1.
CONFIG_RUSTC_VERSION_TEXT="rustc 1.85.1 (4eb161250 2025-03-15)"

I got a linker error with this.
ld.lld: error: undefined symbol: __subsf3

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referenced by core.7dc3da321ed68c1f-cgu.0
              rust/core.o:(<core::core_arch::powerpc::altivec::vector_float as core::ops::arith::Neg>::neg) in archive vmlinux.a
referenced by core.7dc3da321ed68c1f-cgu.0
              rust/core.o:(<core::core_arch::powerpc::altivec::vector_float as core::ops::arith::Neg>::neg) in archive vmlinux.a
referenced by core.7dc3da321ed68c1f-cgu.0
              rust/core.o:(<core::core_arch::powerpc::altivec::vector_float as core::ops::arith::Neg>::neg) in archive vmlinux.a
referenced 1 more times

make[2]: *** [scripts/Makefile.vmlinux:72: vmlinux.unstripped] Error 1
make[1]: *** [/home/mkchauras/src/linux/Makefile:1367: vmlinux] Error 2
make: *** [Makefile:248: __sub-make] Error 2

This corresponds to a floating point instruction. Although we have
disabled fpu, vsx and altivec we are still generating these. Seems like
we have some issue with the rustc here. I didn't dive deeper into this.

Is it ok if we keep 1.95 as base for powerpc64le?

Regards,
Mukesh