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
--
.''`. John Paul Adrian Glaubitz
: :' : Debian Developer
`. `' Physicist
`- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913
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