Messages in this thread | | | From | Andy Lutomirski <> | Date | Fri, 30 Dec 2016 18:13:24 -0800 | Subject | Re: [PATCH 1/2] x86/CPU: Add native CPUID variants returning a single datum |
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On Thu, Dec 29, 2016 at 1:30 AM, Borislav Petkov <bp@alien8.de> wrote: > On Wed, Dec 28, 2016 at 10:11:22AM -0800, Andy Lutomirski wrote: >> On a very quick read, it looks like none of your new call sites >> actually use the return value at all. Since you also appear to be >> consolidating them all, would it make sense to just open-code the >> single (?) remaining user? > > I've got stuff coming up which will use the retval but it is not fully > cooked yet. And also, we want to have generic helpers so that people do > not reimplement them left and right.
Okay, but I still think that a variant that says "do cpuid and ignore the return value" would make sense. Imagine a very clever implementation of native_cpuid_eax like:
asm ("cpuid" : "=a" (eax) : ...); return eax;
Now you call it and ignore the return value and the compiler optimizes it out :) Also, someone reading the code might scratch their head and wonder why you picked eax and not ebx, ecx, or edx.
--Andy
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