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mov EAX, 80000008h
cpuid
;AL = 160+ decimal
;AH = 160+ decimal
;Then I invoke again the same command...
mov EAX, 80000008h
cpuid
;AL = 36 decimal
;AH = 48 decimal
;This looks more appropriate result
CPUID can be executed at any privilege level to serialize instruction execution. Serializing instruction execution guarantees that any modifications to flags, registers, and memory for previous instructions are completed before the next instruction is fetched and executed.
?????In that case it's likely to be a problem elsewhere (e.g. in the code you're using to display the values returned by CPUID, rather than in the code to use CPUID or in the CPU itself).nikito wrote:The CPU supports all the CPUID instructions I have tried, but in the second time, not the first.
Short answer: This isn't the problem.nikito wrote:I guess it is due a thing that I do not understand at all, an thing called "serializing instructions".
CPUID can be executed at any privilege level to serialize instruction execution. Serializing instruction execution guarantees that any modifications to flags, registers, and memory for previous instructions are completed before the next instruction is fetched and executed.
](./images/smilies/eusa_wall.gif "Brick wall"){kind=small}
