[Pkg-rust-maintainers] Bug#1106779: gpg: "No good signature" when doing `apt- update`

[Fabian Grünbichler]

On Fri, May 30, 2025, at 11:13 PM, Stefan Monnier wrote:
>>>I just confirmed now that downgrading to the version of `sqv` in
>>>Debian stable (which also downgraded `apt` and `apt-utils`) brings the
>>>system back to a usable state.
>>
>> The architecture baseline for i386 was raised.
>
> According to https://wiki.debian.org/ArchitectureSpecificsMemo#i386-1
> [ FWIW, it was difficult to find that page, because the natural search
>   terms like "baseline" are missing.  ]:
>
>     - i686 since Debian 12 'bookworm'. There's no MMX nor SSE.
>     - Before that, "almost" i686 (no "long NOP"/NOPL) since Debian 9 
> 'stretch' (gcc-6 6.1.1-1).
>     - Before that, i586 since gcc-4.9 4.9-20140411-1 (2014).
>     - Before that, i486 since gcc-4.1 4.1ds7-0exp7 (2006).
>     - Before that, i386.

That page is not yet updated for Trixie, see below.

> Whereas my processor is a Pentium-III (mobile), i.e. an evolution of the
> Pentium-II itself an evolution of the famous Pentium Pro (aka *the*
> original i686).  It has SSE but not SSE2 which only came a bit later.
>
> [ The vast majority of CPUs after i686 are already supported via amd64,
>   so I don't understand what would be the benefit of raising the baseline
>   even further.  ]

See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1095863 and
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1095862 (and related/cloned
LLVM bugs and upstream references) for details.

The TL;DR gist: LLVM (which rustc uses as codegen backend) is broken for
non-SSE2 targets with no intention upstream of fixing it, so Trixie+ will
use targets which include/require SSE2 for what Debian calls i386 (which
is called i686 by LLVM and rustc, but might otherwise be called i786 if
that term ever had taken off ;)).