linux-kernel - Re: [PATCH 0/4] amd64

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Message-ID: <4A2409C3.2000804@zytor.com>
Date:	Mon, 01 Jun 2009 10:02:59 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <petkovbb@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <borislav.petkov@....com>, greg@...ah.com,
	mingo@...e.hu, norsk5@...oo.com, tglx@...utronix.de,
	mchehab@...hat.com, aris@...hat.com, edt@....ca,
	linux-kernel@...r.kernel.org, randy.dunlap@...cle.com
CC:	Sam Ravnborg <sam@...nborg.org>, "H.J. Lu" <hjl.tools@...il.com>
Subject: Re: [PATCH 0/4] amd64_edac: misc fixes

H. Peter Anvin wrote:
> 
> Yes, we would have to do something like that.
> 
> However, if you're doing that you shouldn't use typeof() there...
> instead this should be turned into an inline function with explicit
> 64-bit types.
> 
> It would be good if we could get Kbuild to export some kind of macro
> that we can use to test binutils version, so we can do something like:
> 
> #if BINUTILS_VERSION >= KERNEL_VERSION(2,18,50)
> /* Do the right thing */
> #else
> /* Do the wrong thing */
> #endif
> 

The other option, and perhaps a better option, is to key it on the
version of gcc; then we can use the gcc intrinsics __builtin_popcount(),
__builtin_popcountl() and __builtin_popcountll(), which should produce
better code since gcc can schedule them appropriately.

Probably also means passing -msse4.2 to gcc while hoping that that
doesn't enable any #TS-generating instructions (SSE 4.2 is mostly a
collection of integer instructions).

(H.J., any comments?)

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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