@jay - I hope this helps you: - issue 1: i386, i486, i586, i686 are considered as Pentium 4 in LLVM, which might be relevant if Rust is compiled with it: https://github.com/llvm/llvm-project/issues/61347 - issue 2: Rust considers i686 as Pentium 4, and i586 as Pentium: https://github.com/rust-lang/rust/issues/82435
So, what I'm thinking is: - When building the Rust toolchain itself, if Debian uses LLVM for it, it might be a good idea to set the CPU target explicitly to pentiumpro in LLVM's flags (fix issue 1) (It could also be a good idea to set this for LLVM in general if possible, if not already done so). -- Also compile the i586 Rust toolchain, not the i686 one (fix issue 2). - For Rust programs, I'd probably recommend setting the target for all (?) of them to i586 (fix issue 2). One can also try to add "-C target-cpu=pentiumpro -C target-feature=-mmx -C target-feature=-sse -C target-feature=-sse2" to RUSTFLAGS, if the above doesn't work. Most of this is assumptions, but I hope it brings some progress. Best of luck and thank you.