linux-kernel - Re: [patch 14/24] Immediate Values

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Message-ID: <476B335C.5080905@zytor.com>
Date:	Thu, 20 Dec 2007 19:30:36 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@....de>,
	Chuck Ebbert <cebbert@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [patch 14/24] Immediate Values - x86 Optimization

Mathieu Desnoyers wrote:
> 
> Argh.. Rusty asked to have a simplified version first, and then to
> implement the "more complex" one on top of it. However, in order to get
> the reentrancy I need for the markers, I need the complex version of the
> immediate values. Therefore, you find, in this patchset, the simple
> version first, and then, the more complex one implemented on top.
> 
> About this patch header, the initial idea was to use the "Q" and "R"
> constraints, but, as stated just below, the "q" and "r" constraints are
> used instead to make sure the REX prefixed opcodes for 1, 2, and 4 bytes
> immediate values are never used. So the complete header follows the
> source code, it's just that this paragraph could be clearer.
> 

Then you have it backwards.  "Q" and "R" avoid REX prefixes, "q" and "r" 
DO NOT.

	-hpa
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