linux-kernel - Re: [PATCH 2/5 -v2.1] x86: Detect CPUID support early at boot

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Message-ID: <168505a3-2aba-4d4a-b1e7-d37c79ae306c@email.android.com>
Date:	Sun, 10 Feb 2013 07:10:56 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH 2/5 -v2.1] x86: Detect CPUID support early at boot

Sure it does... it takes time.

Borislav Petkov <bp@...en8.de> wrote:

>On Sat, Feb 09, 2013 at 08:34:53PM -0800, H. Peter Anvin wrote:
>> I wouldn't really call it a "side effect". Perhaps the right thing
>> here is to say something like "we want to start out with %eflags
>> unambiguously clear".
>>
>> (Note also we have had to CLD earlier because we have already copied
>> the command line.)
>
>Ok, let's make it even more verbose so that people know in the future:
>
>"... we want to start out with EFLAGS unambiguously clear. That means
>DF
>in particular (even though we have cleared it earlier after copying the
>command line) because GCC expects it."
>
>How does that sound?
>
>Also, I was wondering about the whole reasoning behind that: do you
>know
>why DF=0 is a GCC requirement? I mean, nothing hurts GCC from issuing a
>CLD each time?
>
>Thanks.

-- 
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