Re: glibc 2.35 failures in elf/tst-cpu-features-cpuinfo-static.

[Carlos O'Donell <carlos@redhat.com>]

On 1/14/22 16:11, Florian Weimer wrote:
> * Carlos O'Donell:
> 
>> Can we make our testing detect this and mark the test XFAIL?
> 
> If we treat this as our bug, we'd have to run CPUID on *all* CPUs during
> glibc startup.  The bug is visible to applications as well.  I don't
> think this is feasible.

I thought we already ran cpuid at startup for all cpus?

In cpu-features.c (init_cpu_features) we call __cpuid() unconditionally, and that
is called via ARCH_INIT_CPU_FEATURES() in LIBC_START_MAIN (static), and
DL_PLATFORM_INIT in ld.so (shared).

In fact we might call cpuid five or six times during startup?

>> Or as HJ say, blacklist the CPU from the test e.g. UNSUPPORTED?
> 
> I think the bug isn't CPU-specific.

Could you expand in this a bit more?

My concern is that testing should be robust and not return false positives to
the extent that we can prevent that. False positives, regardless of who is at
fault, call into question the validity of the test infrastructure. There is a
cost to such prevention of false positives, for certain, there is a practical
limit to the work we can do.

-- 
Cheers,
Carlos.