Messages in this thread | | | Date | Tue, 15 Dec 1998 04:42:29 +0100 (CET) | From | Chipzz <> | Subject | NOP instruction |
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On Mon, 14 Dec 1998, Riley Williams wrote:
> From: Riley Williams <rhw@bigfoot.com> > Subject: Re: [PATCH] i386 entry.S alignment tweak > > Hi Jamie. > > > BTW, they're not nop instructions these days: they're the largest > > filler instructions gas can put in, so an alignment of a few bytes > > needn't take any longer to execute than a single byte alignment. > > I remember seeing some assembly that had the following sequence in the > middle thereof (not for gcc but you can probably decode it): > > LOCK > SEG ES > MOV DI,DI > > The first time I read through that, I wondered what on earth it was > supposed to do, and only later did I realise it was effectively a > rather verbose NOP instruction...
I've always wondered... A much used NOP "instruction" is OR AX,AX (or similar); But doesn't this, as well as MOV DI,DI, set the zero flag??? As a NOP instruction is supposed to do nothing, would this then be wrong? (Nothing meaning not setting any flags?)
Hmmm... Where's the time from the good ol' Z80 when you HAD a real NOP instruction? *Sigh* :-)
Chipzz AKA Jan Van Buggenhout
-------------------------------------------------------------------------- UNIX isn't dead - It just smells funny Chipzz@Ace.ULYSSIS.Student.KULeuven.Ac.Be --------------------------------------------------------------------------
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