linux-kernel - Re: Question about missing "cld" in x86 string assembly code

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Message-ID: <4EF35243.9030600@gmail.com>
Date:	Thu, 22 Dec 2011 23:52:35 +0800
From:	"nai.xia" <nai.xia@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Brian Gerst <brgerst@...il.com>, Andi Kleen <ak@...ux.intel.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Question about missing "cld" in x86 string assembly code



On 2011年12月18日 02:39, Linus Torvalds wrote:
> On Sat, Dec 17, 2011 at 9:08 AM, Brian Gerst<brgerst@...il.com>  wrote:
>>
>> The i386 ELF ABI states "The direction flag must be set to the
>> ‘‘forward’’ (that is, zero) direction before entry and upon exit from
>> a function."  Therefore it can be assumed to be clear, unless
>> explicitly set.
>
> The exception, of course, being bootup, fault and interrupt handlers,
> and after we've called out to foreign code (ie BIOS).

Yeah, I think I see these cld's now. Thanks for the answers!


Nai
>
> So there *are* a few cld's sprinkled around, they are just fairly rare.
>
>                      Linus
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