Re: [PATCH v2] x86/build/64: Prevent native builds from generating APX instructions

On Fri, Aug 7, 2026 at 5:43 PM Chang S. Bae <[email protected]> wrote:
>
> Omar reported this broad concern to me, when resolving a separate issue
> with his custom module. CONFIG_X86_NATIVE_CPU=y allows builds to
> opportunistically emit APX instructions when the build host supports APX
> since the commit.

I think this sentence may be cut? I guess this refers to the commit in
the Fixes tag.

> For Rust, APX must be explicitly disabled because any backend supporting
> APX may otherwise emit APX instructions with target-cpu=native. Pass
> features=-apxf through the generated JSON to avoid unstable-feature
> warnings.

So, just to confirm: is Rust 1.88 (with a new enough LLVM) enough to
avoid the warnings? Maybe a link to the tracking issue would be nice:

  https://github.com/rust-lang/rust/issues/139284

> Support for this gating also depends on the Rust/LLVM combination. Rust
> 1.88 introduced the `apxf` feature option, but versions prior to 1.93 may
> emit an `apxf` attribute which LLVM 23 or later can interpret. Restrict
> native Rust builds accordingly.
>
> Fixes: ea1dcca1de12 ("x86/kbuild/64: Add the CONFIG_X86_NATIVE_CPU option to locally optimize the kernel with '-march=native'")

This looks like it exists in 6.18.y+, so I assume this should have:

Cc: [email protected]

Thanks!

Cheers,
Miguel