linux-kernel - enabling libgcc for 64-bit divisions, was Re: PROBLEM: XFS on ARM corruption 'Structure needs cleaning'

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Message-ID: <20150812062445.GA4520@infradead.org>
Date:	Tue, 11 Aug 2015 23:24:45 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	katsuki.uwatoko@...hiba.co.jp
Cc:	linux-arm-kernel@...ts.infradead.org, david@...morbit.com,
	gangchen@...micro.com, linux@....linux.org.uk,
	karanvir.singh@...t.com, luca@...lable.com,
	christopher.squires@...t.com, edwin@...lable.com,
	wayne.burri@...t.com, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: enabling libgcc for 64-bit divisions, was Re: PROBLEM: XFS on ARM
 corruption 'Structure needs cleaning'

On Wed, Aug 12, 2015 at 12:56:25AM +0000, katsuki.uwatoko@...hiba.co.jp wrote:
> On Sat, 13 Jun 2015 08:52:09 +1000, Dave Chinner wrote:
> 
> > Yup, that's looking like a toolchain bug. Thread about arm directory
> > read corruption:
> 
> I think that this is not a toolchain bug, this is related to 
> Subject: [PATCH v2 1/1] ARM : missing corrupted reg in __do_div_asm
> http://www.spinics.net/lists/arm-kernel/msg426684.html

Maybe it's time to rely on gcc to handle 64 bit divisions now?

I've been pretty annoyed at the amount of 32-bit architecture build
failures due to the lack of support for native 64-bit divisions, and
the ugly do_div hackery to work around it.

We're living in a world where we are using a lot of 64-bit CPUs and
people optimize for them, so it might be a good time to start relying
on the compiler to get these right on older CPUs.

How bad is gcc's code for 64-bit divisions on arm and x86 these days?
Is there still a good case for offloading work the compiler should be
doing on the programmer?
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