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

[Samuel Thibault]

Samuel Thibault, le mar. 04 févr. 2025 12:09:57 +0100, a ecrit:
> 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?

And it was discussed on
https://lists.debian.org/debian-devel/2024/11/msg00328.html
and again today on IRC. Consensus seems to be to raise to SSE2, which
would fix the x87 unsoundness.

Samuel

> 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