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

From	Andy Lutomirski <luto@amacapital.net>
Newsgroups	linux.kernel
Subject	Re: [PATCH 1/2] x86/CPU: Add native CPUID variants returning a single datum
Date	2017-01-03 19:40 +0100
Message-ID	<sVCa6-1SP-11@gated-at.bofh.it> (permalink)
References	(2 earlier) <sTkAG-7wR-9@gated-at.bofh.it> <sTqZs-3sy-11@gated-at.bofh.it> <sTFlL-4Oj-17@gated-at.bofh.it> <sUhr3-5cP-1@gated-at.bofh.it> <sUpRE-2d9-7@gated-at.bofh.it>
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On Sat, Dec 31, 2016 at 3:09 AM, Borislav Petkov <bp@alien8.de> wrote:
> 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?

That's why I didn't type "volatile". :)

>
>> 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 :-)

Okay.  Anyway, this particular nit is minor and I'll shut up.

>
> --
> Regards/Gruss,
>     Boris.
>
> ECO tip #101: Trim your mails when you reply.
> --



-- 
Andy Lutomirski
AMA Capital Management, LLC

Thread

[PATCH] x86: Fix Intel microcode revision detection Junichi Nomura <j-nomura@ce.jp.nec.com> - 2016-12-28 05:50 +0100
  [PATCH 1/2] x86/CPU: Add native CPUID variants returning a single  datum Borislav Petkov <bp@alien8.de> - 2016-12-28 12:30 +0100
    Re: [PATCH 1/2] x86/CPU: Add native CPUID variants returning a single datum Andy Lutomirski <luto@amacapital.net> - 2016-12-28 19:20 +0100
      Re: [PATCH 1/2] x86/CPU: Add native CPUID variants returning a  single datum Borislav Petkov <bp@alien8.de> - 2016-12-29 10:40 +0100
        Re: [PATCH 1/2] x86/CPU: Add native CPUID variants returning a single datum Andy Lutomirski <luto@amacapital.net> - 2016-12-31 03:20 +0100
          Re: [PATCH 1/2] x86/CPU: Add native CPUID variants returning a  single datum Borislav Petkov <bp@alien8.de> - 2016-12-31 12:20 +0100
            Re: [PATCH 1/2] x86/CPU: Add native CPUID variants returning a single datum Andy Lutomirski <luto@amacapital.net> - 2017-01-03 19:40 +0100
              Re: [PATCH 1/2] x86/CPU: Add native CPUID variants returning a  single datum Borislav Petkov <bp@alien8.de> - 2017-01-03 20:50 +0100
  [PATCH 2/2] x86/microcode: Use native CPUID to tickle out microcode  revision Borislav Petkov <bp@alien8.de> - 2016-12-28 12:30 +0100
    [PATCH 3/2] x86/microcode/intel: Add a helper which gives the  microcode revision Borislav Petkov <bp@alien8.de> - 2016-12-28 14:00 +0100
      Re: [PATCH 3/2] x86/microcode/intel: Add a helper which gives the  microcode revision Andy Lutomirski <luto@amacapital.net> - 2016-12-28 19:20 +0100
        Re: [PATCH 3/2] x86/microcode/intel: Add a helper which gives the  microcode revision Borislav Petkov <bp@alien8.de> - 2016-12-29 10:40 +0100
      Re: [PATCH 3/2] x86/microcode/intel: Add a helper which gives the  microcode revision Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-12-28 20:30 +0100
        Re: [PATCH 3/2] x86/microcode/intel: Add a helper which gives the  microcode revision Borislav Petkov <bp@alien8.de> - 2016-12-29 10:40 +0100
  Re: [PATCH] x86: Fix Intel microcode revision detection Borislav Petkov <bp@alien8.de> - 2016-12-28 12:30 +0100
    Re: [PATCH] x86: Fix Intel microcode revision detection Borislav Petkov <bp@alien8.de> - 2017-01-05 10:50 +0100

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