assembly - How to reliably detect maximum additional CPUID levels? -


i query cpu features using cpuid instruction. i'm interested in additional cpuid levels, including 0x80000000 , 0xc0000000 (centaur). problem don't see clear way of determining whether particular level supported.

in particular, i'm worried particular bit intel(r) 64 , ia-32 architectures software developer's manual:

two types of information returned: basic , extended function information. if value entered cpuid.eax higher maximum input value basic or extended function processor data highest basic information leaf returned.

this means if query cpuid eax = 0x80000000 or eax = 0xc0000000, can either maximum cpuid level in eax, or output random basic level leaf.

is there reliable , relatively easy way of determining whether particular level supported?

you should start detecting processor vendor identification (12-character text string @ level 0) , continue basing on value. intel, 2 range of levels, since 0 , 0x80000000, supported (the first 1 native intel 1 , second 1 option set compatibility amd); amd, same 2 ranges supported bits can change value; then, other vendors, may own ranges according documentation.


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