Re: Include hwcap as ifunc argument

[Richard Henderson <rth@twiddle.net>]

On 2012-06-08 07:00, Andreas Krebbel wrote:
>From a S/390 perspective AT_PLATFORM would also be more helpful. We do not add every new
> machine feature to the hwcaps vector so it is not possible to deduce the cpu level just
> from the hwcaps vector.

No, but the one important thing in s390's AT_HWCAP is HWCAP_S390_STFLE,
which tells you (without setting up sigill handlers) that you can go ahead
and find out *everything* you want to know via stfle.  More or less exactly
how the x86 port works atm with its cpuid bits.

But again, it depends on what you're trying to test.  Are you looking at
choosing a version based on scheduling, or choosing a version based on
features?

I'd would hope that any multiarch'd version of e.g. feraiseexcept would test
for the ieee-exception-simulation-facility (included in bit 41 of stfle results)
rather than using a strcmp of AT_PLATFORM vs "z109-xx" (or whatever).

Certainly for libatomic I would be most interested in testing for the 
presence of the interlocked-access and compare-and-swap-and-store-2 facilities.
 
> I'm working on the S/390 ifunc support and hope to be able to come up with a patch soon.

Excellent.


r~