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Minimum CPUID extended level in longmode?
Posted: Wed Aug 06, 2014 8:41 am
by tehmav
Hi!
Since my OS is 64bit only, with a 16/32bit bootstrap, I just wanted to ask if there is a minimum extended level (higher than 0x8000_0001 of course) of CPUID required by longmode.
It would be just nice to know
Cheers!
Re: Minimum CPUID extended level in longmode?
Posted: Wed Aug 06, 2014 10:33 am
by stlw
Yes, leaf 0x80000008 present for every CPU with long to state maximum virtual address width.
Stanislav
Re: Minimum CPUID extended level in longmode?
Posted: Fri Aug 08, 2014 7:10 am
by tehmav
Thank you for your answer!
And just to be sure: This means that in long mode CPUID will always report a supported extended level of atleast 0x8000_0008?
Re: Minimum CPUID extended level in longmode?
Posted: Fri Aug 08, 2014 12:07 pm
by stlw
tehmav wrote:Thank you for your answer!
And just to be sure: This means that in long mode CPUID will always report a supported extended level of atleast 0x8000_0008?
Yes. But why should you care for CPUID leafs which you don't get useful information from ?
Re: Minimum CPUID extended level in longmode?
Posted: Sat Aug 09, 2014 4:47 am
by tehmav
This is more of a thing which, for me personally, could be good to know.