Re: [PATCH 1/2] x86/CPU: Add native CPUID variants returning a single datum

From: Borislav Petkov
Date: Sat Dec 31 2016 - 06:10:16 EST

On Fri, Dec 30, 2016 at 06:13:24PM -0800, Andy Lutomirski wrote:
> Now you call it and ignore the return value and the compiler optimizes
> it out :)

Does it, really?

It is an inlined asm volatile. I checked all call sites and the CPUID
call is there. gcc 6 simply issues the CPUID and then later code
overwrites rAX. I.e., it looks ok to me.

Or what example scenario do you have in mind?

> Also, someone reading the code might scratch their head and
> wonder why you picked eax and not ebx, ecx, or edx.

We have comments for her/him :-)


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