Re: glibc regression on alpha with 2.34+

Hi!

On 12/13/22 08:44, Michael Cree wrote:
>> So what baseline do we want? Would EV56 be sufficient? Because that would
>> still work with my AlphaStation 433au and XP1000 and gets us BWX.
> 
> Yes.  The first extension added is the byte-word extension which came
> in with EV56.  That provides CPU instructions for byte and word (16-bit)
> memory accesses. That is the most important one: possibly a third of
> the bugs in the repository extend from non-atomic byte and word
> accesses.  The kernel developers have expressed a view that they would
> like to assume on all arches that byte and word memory accesses are
> atomic and the only architecture that is holding them back from that
> assumption are old Alphas without BWX.  There is an old open bug on
> gcc related to the non-atomic memory accesses of old Alphas and that
> one is basically cannot fix.
> 
> If we went to BWX (i.e. EV56) then as you say that means the personal
> workstations (e.g. PWS433au and PWS500au), which a lot of Alpha users
> have and AlphaStations such as the 433au will still be supported.

Thanks for the confirmation and clarification!

>> I don't want to use something like EV67 as I think that would limit the
>> usable hardware too much.
> 
> Yes, that's the problem going fully to EV67.  The CPU extensions we
> would get are MVI (motion video instructions) that came in with
> PCA56, CIX (count integer instructions with the like of counting
> trailing zeros) that came in with EV67 and FIX (floating point
> extensions primarily for efficient conversion between float and
> integer and a sqrt instruction) with EV6, but these are nowhere
> near as important as BWX in terms of reducing bug fixing workload
> in maintaining the port.

OK, so EV56 sounds like a very good compromise. I guess we can still
keep the -ev67 glibc package for people with these CPUs.

>> I guess I can live with dropping EV4 since NetBSD
>> and Gentoo would still run on these.
> 
> Gentoo has the advantage (and disadvantage) of compiling from
> source so one can optimise their own installation for their
> hardware.

Yes, of couse.

>> I am still interested in fixing the glibc bug and will work on bisecting it.
>>
>> If EV56 is the baseline we can agree on, please go ahead and rebuild glibc
>> and gcc using this baseline.
> 
> I am currently building gcc-12 to default to EV56/BWX.  In the test
> suite now so probably won't be finished till tomorrow.  Then I will try
> building latest glibc (2.36-6) with that gcc. I suspect there will
> still be a couple of test suite failures so there will probably be
> a further delay before I have it ready to upload to the repository. In
> any case I will give fair warning before I do.

Feel free to open bugs against glibc and gcc to request the raise of the
baseline.

Adrian