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

[Brian Gerst]

On Sat, Dec 17, 2011 at 9:58 AM, Nai Xia <nai.xia@xxxxxxxxx> 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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The i386 ELF ABI states "The direction flag must be set to the
ââforwardââ (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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