Re: [RFC] x86: xsave/xrstor support, ucontext_t extensions

From: Roland McGrath
Date: Thu May 22 2008 - 22:12:50 EST

> hmm.. so the kernel needs to export all the cpuid info (that the kernel
> enables and supports) to the user through some mechanism then?

For a cheap interface, we use AT_HWCAP for this. Unfortunately that only
covers the first 32 bits of CPUID info. (For another cheap interface,
giving all the CPUID bits in the vDSO would be easy.)

For a clunky interface that already exists and is "simple" to use,
there is /dev/cpu/0/cpuid now. I wonder if having a device node and
opening it too much for applications that consider the vDSO too complex.

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