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Sat, 8 Aug 2026 03:21:21 +0000 Message-ID: Date: Fri, 7 Aug 2026 20:21:18 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] x86/build/64: Prevent native builds from generating APX instructions To: Miguel Ojeda CC: , , , , , , , , , , , , , , , , , , , , , , Omar Avelar , References: <20260807151715.7247-1-chang.seok.bae@intel.com> Content-Language: en-US From: "Chang S. 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Bae 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. Yes, I intended “the commit” to refer to the one in the Fixes: tag. To make it explicit, I can add the commit back here: ea1dcca1de12 ("x86/kbuild/64: Add the CONFIG_X86_NATIVE_CPU ...") >> 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 Passing `-apxf` through the generated target JSON avoids this warning: warning: unstable feature specified for `-Ctarget-feature`: `apxf` | = note: this feature is not stably supported; its behavior can change in the future I’ll add the link to reference the status of the Rust support. Thanks. >> 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: stable@vger.kernel.org Yes, I have included it. Thanks, Chang