From: Brian Gerst <brgerst@gmail.com>
To: nai.xia@gmail.com
Cc: Andi Kleen <ak@linux.intel.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: Question about missing "cld" in x86 string assembly code
Date: Sat, 17 Dec 2011 12:08:36 -0500 [thread overview]
Message-ID: <CAMzpN2inHxaSnaYaYXZ4Ya3rK+MWXqR6dN5NVNZy3=OvP04uQA@mail.gmail.com> (raw)
In-Reply-To: <201112172258.24221.nai.xia@gmail.com>
On Sat, Dec 17, 2011 at 9:58 AM, Nai Xia <nai.xia@gmail.com> wrote:
> Hi Andi,
>
> Seems I used a stale email address of you from a related git commit log,
> so this is a resend, sorry.
>
> =======
> Hi,
>
> I notice that all x86 assembly code for string operations containing
> "scasb, lodsb", etc does not have "cld" at the beginning.
> Is this 100% safe?
> Or in other words, how could we be sure that
> there is no "std" generated by compiler somewhere just before
> the string operations?
>
>
> Thanks,
>
> Nai
> --
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> Please read the FAQ at http://www.tux.org/lkml/
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.
--
Brian Gerst
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next prev parent reply other threads:[~2011-12-17 17:08 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-17 14:58 Nai Xia
2011-12-17 17:08 ` Brian Gerst [this message]
2011-12-17 18:39 ` Linus Torvalds
2011-12-22 15:52 ` nai.xia
2011-12-22 15:34 ` nai.xia
-- strict thread matches above, loose matches on Subject: below --
2011-12-17 14:52 Nai Xia
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