From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Tue, 04 Dec 2007 22:35:51 -0800 (PST) Received: from larry.melbourne.sgi.com (larry.melbourne.sgi.com [134.14.52.130]) by oss.sgi.com (8.12.11.20060308/8.12.10/SuSE Linux 0.7) with SMTP id lB56ZDcw022473 for ; Tue, 4 Dec 2007 22:35:18 -0800 Message-ID: <475646C8.6070700@sgi.com> Date: Wed, 05 Dec 2007 17:35:52 +1100 From: Lachlan McIlroy Reply-To: lachlan@sgi.com MIME-Version: 1.0 Subject: Re: [Patch] xfs_lowbit64 broken on ia32 References: <20071203211620.GN115527101@sgi.com> <475608D8.4070402@sgi.com> <20071205032128.GB115527101@sgi.com> <475638FD.9090208@sgi.com> <20071205054421.GD115527101@sgi.com> In-Reply-To: <20071205054421.GD115527101@sgi.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com List-Id: xfs To: David Chinner Cc: xfs-oss , xfs-dev David Chinner wrote: > On Wed, Dec 05, 2007 at 04:37:01PM +1100, Lachlan McIlroy wrote: >> David Chinner wrote: >>> On Wed, Dec 05, 2007 at 01:11:36PM +1100, Lachlan McIlroy wrote: >>>> David Chinner wrote: >>>>> The recent change to the internals of xfs_lowbit64 broke it on >>>>> ia32 - the code treats the 64bit value as an unsigned long >>>>> which is only 32 bits on ia32 and hence throws away the high 32 >>>>> bits. 64 bit platforms are not affected. >>>>> >>>>> Tested with a userspace implementation comparing the original >>>>> code with the new code. >>>>> >>>>> Signed-off-by: Dave Chinner >>>>> --- >>>>> fs/xfs/xfs_bit.h | 4 ++-- >>>>> 1 file changed, 2 insertions(+), 2 deletions(-) >>>>> >>>>> Index: 2.6.x-xfs-new/fs/xfs/xfs_bit.h >>>>> =================================================================== >>>>> --- 2.6.x-xfs-new.orig/fs/xfs/xfs_bit.h 2007-11-02 >>>>> 13:44:45.000000000 +1100 >>>>> +++ 2.6.x-xfs-new/fs/xfs/xfs_bit.h 2007-12-03 14:43:33.169851481 +1100 >>>>> @@ -68,8 +68,8 @@ static inline int xfs_lowbit32(__uint32_ >>>>> /* Get low bit set out of 64-bit argument, -1 if none set */ >>>>> static inline int xfs_lowbit64(__uint64_t v) >>>>> { >>>>> - unsigned long t = v; >>>>> - return (v) ? find_first_bit(&t, 64) : -1; >>>>> + unsigned long long t = v; >>>> Why create a local copy? Why not just pass v into find_first_bit()? >>> Because I thought that taking the address of a function parameter >>> was a big no-no because the result is undefined (i.e. platform and >>> compiler dependent)? >>> >> Really? Didn't occur to me but then I can't say for sure I've ever >> used the address of an argument. If we need a local copy then why >> not use __unit64_t instead of unsigned long long? > > Whatever. They are both the same. > > xfs/xfs_types.h 41 typedef unsigned long long int __uint64_t; > Figured they would be. Using the same type probably would have avoided the bug in the first place. Otherwise the change is good.