Re: Rustc unsoundness on i386
On Sun, 24 Nov 2024 at 13:25:59 +0100, Iustin Pop wrote:
> Are there viable/realistic platforms today that are i386 for real, and
> don't support SSE2? In other words, if Debian as a whole does B) (not
> only for rust), what is the practical impact on any non-toy hardware?
SSE2 is well over 20 years old: in the Intel world, SSE2 was new in the
Pentium 4 (2000), and in the AMD world, SSE2 was new in the first
AMD64 CPUs (2003).
According to Wikipedia, the x86 CPUs without SSE2 since 2000 are:
- 32-bit AMD CPUs (Athlon XP and similar)
- VIA C3
- Transmeta Crusoe
- Intel Quark
We no longer release i386 kernels (since linux_6.11-1~exp1) and it has
already been announced that Debian 13 will not have i386 installation
media, so it is already the case that it is only possible to run trixie
on 32-bit x86 by upgrading from bookworm and keeping the bookworm kernel
(or installing a locally-built kernel).
If we raise the baseline to include SSE2, then we would lose the ability
to do that on Athlon XP, C3, Crusoe or Quark. I don't think that's a
practical problem in 2024: those are all designs from the early 2000s,
except for the Quark, which is a discontinued embedded processor that
we already cannot support in a reasonable way as a result of #738575.
According to Wikipedia, after raising the baseline it would still be
possible in principle to run i386 trixie using a bookworm or locally-built
kernel on some of the later 32-bit Intel CPUs (Pentium 4, Pentium M,
Atom), or on Transmeta Efficeon or VIA C7.
i386 in trixie continues to be available as a multiarch foreign
architecture on x86_64 CPUs, or as an architecture for containers or
chroots running on an x86_64 kernel, but a baseline that includes SSE2
would not harm that use-case, because MMX, SSE and SSE2 are part of the
x86_64 baseline already.
My advice to anyone still running Debian on a 32-bit x86 machine would
be to look into acquiring a second-hand 64-bit laptop, many of which are
already sufficiently old that they're most likely to be disposed of as
e-waste if unsold (so replacing an existing 32-bit machine would not be
a net increase in the amount of e-waste needing disposal). As an example,
here in the UK, eBay tells me I could receive a working Lenovo X200 next
week for £50, or a newer, faster and likely more power-efficient X280
for around £100.
smcv
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