linux-kernel - Re: [patch 4/7] Immediate Values

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Message-ID: <20070918224444.GC5773@one.firstfloor.org>
Date:	Wed, 19 Sep 2007 00:44:44 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Chuck Ebbert <cebbert@...hat.com>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [patch 4/7] Immediate Values - i386 Optimization

On Tue, Sep 18, 2007 at 03:29:50PM -0700, Jeremy Fitzhardinge wrote:
> Andi Kleen wrote:
> > Jeremy Fitzhardinge <jeremy@...p.org> writes:
> >   
> >> It's a pity that gas seems to generate plain 0x90 nops rather than
> >> long-nop forms here.  I thought it could do that.
> >>     
> >
> > .p2align does it
> 
> Just .p2align?  Not align, balign, org or skip?  Seems... strange.

The problem is that you cannot always safely jump into the middle of the 
longer form nops. So I suppose they didn't risk breakage on older
code relying on this.

-Andi
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