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Re: x86 D flag: what's its status thru the program?
On Mon, Jul 05, 2004 at 03:23:44PM +0200, Lukasz Michal Rak wrote:
>
> Hi all!
>
> The convention is that the D flag in IA32 is cleared. So if you call a
> subroutine you have to clear D flag before making call.
Do you mean that 'I have to clear the D flag if I had set it somewhere
before?' Else what is the sense of the convention?
> The subroutine can change the state of D flag, but before returning
> the routine has to clear the D flag.
If the subroutine can change the flag, that it will violate the
convention, won't it? And what is the strength of the convention,
again?
> Hope I helped.
Thanks, but I still don't understand something. Again: if every
procedure keeps the flag clear at exit, then why the same every
procedure clears it at entry? In a suspicion, that caller has changed
the flag against the rules?
> Regards,
>
> Lukasz
>
>
> > Is this Direction flag (for the movs instructions) has some assumed
> > value (say, as after cld)? I ask because the many program sources
> > show interesting behaviour: from one side, this flag is always set
> > before the string insns (cld or std), but from the other side, if the
> > programs does std then it always does cld after. So, nobody leaves it
> > set, but nevertheless, everybody set it clear. Why?
> > -
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