Re: [Minios-devel] [UNIKRAFT PATCH v3 5/8] plat: Add global struct to keep x86 CPU information

[Florian Schmidt <Florian.Schmidt@xxxxxxxxx>]

Hi Yuri,

On 1/2/19 3:19 PM, Yuri Volchkov wrote:
> > @@ -150,6 +153,10 @@ void _liblinuxuplat_entry(int argc, char *argv[])
> >         int ret;
> >         void *pret;
> >   
> > +#if defined __X86_64__
> > +       _init_cpufeatures();
> > +#endif
> Would it make sense to add a stub-function _init_cpufeatures for arm?
That's a good question. I actually am not sure whether an equivalent of 
it (checking CPU features with CPUID and saving that information for 
later use) would make sense on Arm. How do you get your CPU's 
capabilities on Arm? I just checked quickly, and there's a "cpuid" 
instruction, but it seems to be much less intricate than the x86 one 
and, crucially, a privileged instruction, so wouldn't work for Linux 
userspace anyway. Or do you use the device tree?
How do you even get CPU feature information on Arm as a non-privileged 
user? After all, there are legitimate use cases for that, like figuring 
out which instruction sets or registers are available, so a user can 
choose at runtime which optimized version of code to run?
Bottom line: of course I could add a dummy function like that to make 
the boot process similar, but I'm trying to think of whether that's even 
the right way to do it on Arm...
Cheers,
Florian

--
Dr. Florian Schmidt
フローリアン・シュミット
Research Scientist,
Systems and Machine Learning Group
NEC Laboratories Europe
Kurfürsten-Anlage 36, D-69115 Heidelberg
Tel.     +49 (0)6221 4342-265
Fax:     +49 (0)6221 4342-155
e-mail:  florian.schmidt@xxxxxxxxx
============================================================
Registered at Amtsgericht Mannheim, Germany, HRB728558

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