Re: [PATCH 2/2] x86: Add generic CPUID data dumper to ld.so --list-diagnostics

[Florian Weimer <fweimer@redhat.com>]

* Adhemerval Zanella Netto:

>> +void
>> +_dl_diagnostics_cpu_kernel (void)
>> +{
>> +#if !HAS_CPUID
>> +  /* CPUID is not supported, so there is nothing to dump.  */
>> +  if (__get_cpuid_max (0, 0) == 0)
>> +    return;
>> +#endif
>
> I think we don't support __i486__ anymore, so we can just assume HAS_CPUID
> at sysdeps/x86/include/cpu-features.h.

We still build an i486 variant in build-many-glibcs.py.
> Why not use the interfaces to work on cpuset? 
>
>   if (length_reference > 0)
>     {
>       int cpu_count = CPU_COUNT_S (length_reference, mask_reference);
>       for (int i = 0; i < cpu_count; i++)
>         {
>           if (CPU_ISSET_S (i, length_reference, mask_reference)
>             {
>               CPU_SET_S (i, length_reference, mask_request);
>               if (INTERNAL_SYSCALL_CALL (sched_setaffinity, 0,
> 					 length_reference, mask_request) == 0)
>                 {
>                   _dl_diagnostics_cpuid_collect (&ccd[i & 1]);
>                   _dl_diagnostics_cpuid_report (processor_index, i, 
> 						&ccd[processor_index & 1],
> 						&ccd[!(processor_index & 1)]);
>                   ++processor_index;
>                 }
>               CPU_CLR_S (i, length_reference, mask_request);
>             }
>         }
>     }
>
> I will iterate over the list twice, but I don't think this would really matter
> here.

I think the macros are somewhat incompatible with direct system calls.
CPU_COUNT_S requires that the tail is zeroed, which the system call
doesn't do.  Maybe we can memset the whole thing before the sched_getcpu
system call.  I haven't tried if we can directly rebuild
__sched_cpucount for ld.so, either.

Thanks,
Florian