[Pkg-rust-maintainers] Bug#973414: rustc: produces non-baseline opcodes for compiler_builtins::int::udiv::__udivmoddi4 on i386

[Samuel Thibault]

Hello,

Paul Gevers, le mer. 26 avril 2023 22:09:53 +0200, a ecrit:
> We discussed this during the Release Team IRC meeting [1]
> http://meetbot.debian.net/debian-release/2023/debian-release.2023-04-26-18.59.html
> , and we decided that it's too late in the release cycle to fix
> this. We'll accept the de-facto baseline bump for bookworm and
> document the fact in the Release Notes.
> 
> Having said that, without having discussed it, I don't think we object
> having support for the previous baseline in trixie, if we still release i386
> with it.

AIUI in the end rustc is patching i686 to make it pentiumpro-based, so
not actually a baseline bump?

This patching is being questioned:
https://github.com/rust-lang/rust/issues/136495#issuecomment-2632546175
(without apparently realizing that the question should be asked here,
not there...)

The issue is that without SSE2 it's apparently very hard for rustc to
produce correct floating-point results, so the Debian patching makes
some software not really behave correctly, which then gets reported
to rust upstream, which thus get annoyed because "works for us" (with
SSE2).

I'm wondering: since Debian 13 won't provide an i386 kernel and thus
only support i386 chroots on otherwise-x86_64 machines, perhaps
we can indeed really bump the i386 ABI to SSE2 and thus avoid the
floating-point issues and avoid departing from upstream?

Samuel