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From: Anton Altaparmakov <aia21@cam.ac.uk>
To: Andi Kleen <ak@suse.de>, Andrew Morton <akpm@osdl.org>,
	Linus Torvalds <torvalds@osdl.org>
Cc: lkml <linux-kernel@vger.kernel.org>,
	yuri@acronis.com, ntfs-dev <linux-ntfs-dev@lists.sourceforge.net>
Subject: [2.6.6-BK] x86_64 has buggy ffs() implementation
Date: Wed, 12 May 2004 14:43:37 +0100	[thread overview]
Message-ID: <1084369416.16624.53.camel@imp.csi.cam.ac.uk> (raw)

Hi Andi, Andrew, Linus,

x86_64 has incorrect include/asm-x86_64/bitops.h::ffs() implementation. 
It uses "g" instead of "rm" in the insline assembled bsfl instruction. 
(This was spotted by Yuri Per.)

bsfl does not accept constant values but only memory ones.  On i386 the
correct "rm" is used.

This causes NTFS build to fail as gcc optimizes a variable into a
constant and ffs() then fails to assemble.

Please apply below patch.  Thanks!

Best regards,

	Anton
-- 
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
Linux NTFS maintainer / IRC: #ntfs on irc.freenode.net
WWW: http://linux-ntfs.sf.net/ &
http://www-stu.christs.cam.ac.uk/~aia21/

--- bklinux-2.6/include/asm-x86_64/bitops.h.old	2004-05-12
14:40:32.524022336 +0100
+++ bklinux-2.6/include/asm-x86_64/bitops.h	2004-05-12
14:41:22.595410328 +0100
@@ -458,7 +458,7 @@ static __inline__ int ffs(int x)
 
 	__asm__("bsfl %1,%0\n\t"
 		"cmovzl %2,%0" 
-		: "=r" (r) : "g" (x), "r" (-1));
+		: "=r" (r) : "rm" (x), "r" (-1));
 	return r+1;
 }
 



             reply	other threads:[~2004-05-12 13:44 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2004-05-12 13:43 Anton Altaparmakov [this message]
2004-05-12 14:02 ` Andi Kleen
2004-05-12 20:31 ` H. Peter Anvin
2004-05-12 21:08   ` Anton Altaparmakov
2004-05-12 21:11   ` Gabriel Paubert
2004-05-12 22:29     ` H. Peter Anvin

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