Re: Request to reconsider i386 (x86) port for Debian 13
On Sat, Aug 16 2025, Simon McVittie wrote:
> On Sat, 16 Aug 2025 at 07:28:24 -0500, John Goerzen wrote:
>>Without getting into a debate over whether i386 should or should not be
>>dropped, as someone that runs other 32-bit archs, I wonder why armhf and
>>armel weren't similarly targeted?
>
> Each of these 32-bit ports has different characteristics and different
> tradeoffs.
Thank you, Simon. Your message (and your other one about compilers
being unable to compile software within 4GB of VRAM) was very helpful
and clarified a lot of points for me.
John
>
> i386-without-SSE2 on real 32-bit CPUs (as opposed to i386 as a compatibility
> architecture on newer CPUs) is a problematic porting target because it has
> non-IEEE floating-point behaviour that frequently causes trouble: test suites
> often expect to see the same exact values, simulations (e.g. networked games)
> want to see deterministic results from running the same simulation on different
> CPUs, and the thing that finally prompted raising the baseline was that it
> turned out that it even harms soundness (ability to generate correct machine
> code) in LLVM/rustc. i386-with-SSE2 is a lot easier, because it has the same
> IEEE floating point as every other release architecture, but there were only a
> few CPU generations that have SSE2 but not 64-bit support (I think the Pentium 4
> around 20 years ago was the most common example).
>
> armel is also on its way out, because it has a *different* characteristic that
> makes it a problematic porting target: unlike every other release architecture,
> it doesn't have atomic operations in the baseline instruction set, and they have
> to be emulated. For example this is why mozjs/gjs had to be removed from armel
> in trixie. I suspect we would have lost armel already if it wasn't for the fact
> that it's the newest/highest-functionality Debian port that will run unmodified
> on first-generation Raspberry Pi hardware, because ARMv6 is slightly too old for
> official Debian's armhf baseline; Raspberry Pi OS, a Debian derivative, works
> around this by recompiling armhf with a lower baseline.
>
> armhf has had CPUs that can run it but not its successor manufactured more
> recently than i386 or armel, has normal IEEE floating-point unlike i386, and has
> normal atomic operations unlike armel, so it is both less painful to support and
> more likely to be useful as a "bare metal" OS when compared with either i386 or
> armel.
>
> (I do think that armhf's useful lifetime is limited, too, though.)
>
> smcv
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