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Re: sse{2,3,4.2}, altivec, neon, ...

On Sat, Aug 05, 2017 at 11:50:42PM +0200, Guus Sliepen wrote:
> On Sat, Aug 05, 2017 at 07:53:02PM +0200, Adam Borowski wrote:
> > Thus, here's a proposed solution: in unstable, there's now a bunch of
> > packages that do such checking in preinst, and thus refuse (overridably) to
> > even install such software.
> [...]
> A big issue here is that install-time is different than run-time. I see
> at least two possible scenarios where this construction fails:
> - Motherboard dies, move harddisks to old computer with older CPU,
>   suddenly things start failing at run-time again.
> - Preparing a Debian image on a fast new machine, use the image on an
>   older/embedded device.

Hmm right, this one indeed might be an issue.  We wouldn't be worse off
than the current state, though.  Do you perhaps have any ideas?

> Also conversely, trying to install something on an old machine, or in a
> limitted VM environment, with the intention of later using it on a newer
> machine, will now fail.

A limited VM is ok, as no check looks at /proc or something that may be
missing, just tests on the CPU itself.

As for a foreign machine:
* ISA_IGNORE=y apt install »package«
* if installing for a wholly different architecture (and without qemu), the
  check is skipped -- no way to probe the target machine anyway

> Maybe a debconf question can be asked when installing one of these
> proposed packages to allow installation anyway even if the current host
> machine does not support the requested instruction set.

I thought about it but decided against, as it seemed to me it's a situation
too unlikely to happen (usually it's the big computer installing something
for a SoC or a museal piece) -- at least not likely enough to warrant
confusing new users.

If you guys disagree, though, it's not a big change.

There's a reason why I raised this thread instead of rushing on a mass bug

⢀⣴⠾⠻⢶⣦⠀ What Would Jesus Do, MUD/MMORPG edition:
⣾⠁⢰⠒⠀⣿⡁ • multiplay with an admin char to benefit your mortal
⢿⡄⠘⠷⠚⠋⠀ • abuse item cloning bugs (the five fishes + two breads affair)
⠈⠳⣄⠀⠀⠀⠀ • use glitches to walk on water