On Thu, Feb 13, 2025 at 05:41:12PM +0100, Samuel Thibault wrote: > Simon McVittie, le jeu. 13 févr. 2025 16:32:30 +0000, a ecrit: > > The options as I see them, *including* the options that I would personally > > prefer to rule out, are: > > > > - Status quo: don't change anything. As Fabian says, Rust code on i386 > > will sometimes be miscompiled and might crash. > > > > - Raise baseline to i686+SSE2+MMX and make gcc require/assume this > > > > - Raise "official" baseline to i686+SSE2+MMX, leave gcc producing > > code that would have worked with the previous baseline by default, > > but rustc/LLVM may require/assume i686+SSE2+MMX > > Are rustc and LLVM necessarily coupled? AIUI the rustc baseline is > configured in rustc itself, in > ./compiler/rustc_target/src/spec/targets/i686_unknown_linux_gnu.rs : > > base.cpu = "pentiumpro".into(); > > vs > > base.cpu = "pentium4".into(); > > So we could raise the baseline only in rustc.
rustc uses LLVM as its backend compiler, and LLVM on its own is affected by the same issue as LLVM internally assumes Pentium 4 semantics for i686 targets when it does its optimization passes[0]. LLVM in Debian carries a similar patch downgrading the definition of its i686 targets[1]: - // Fallback to p4. - return "pentium4"; + // Fallback to i686. + return "i686"; it just downgrades further (to the pre-bookworm baseline, and not the bookworm and later one). 0: https://github.com/llvm/llvm-project/issues/89885 1: https://salsa.debian.org/pkg-llvm-team/llvm-toolchain/-/blob/19/debian/patches/clang-baseline-fix-i386.patch
