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

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Message-ID: <CALCETrVP1a+NMC1tGLSGQef4eeWHGgFLLh=ayNLrpoMOCWctJg@mail.gmail.com>
Date:	Wed, 12 Aug 2015 15:39:19 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andy Lutomirski <luto@...nel.org>,
	Christoph Hellwig <hch@...radead.org>,
	katsuki.uwatoko@...hiba.co.jp,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Dave Chinner <david@...morbit.com>, gangchen@...micro.com,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	karanvir.singh@...t.com, luca@...lable.com,
	christopher.squires@...t.com, edwin@...lable.com,
	wayne.burri@...t.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: enabling libgcc for 64-bit divisions, was Re: PROBLEM: XFS on ARM
 corruption 'Structure needs cleaning'

On Wed, Aug 12, 2015 at 3:36 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Wed, Aug 12, 2015 at 3:20 PM, Andy Lutomirski <luto@...nel.org> wrote:
>>
>> Does your objection still apply if we supplied our own implementations of a
>> handful of libgcc helpers?
>
> We already do that.
>
> Several architectures actually implement _udivdi3.
>
> However, do_div() is actually the much simpler/better interface.
>
> I don't think we have a single case in the kernel where we really want
> the full 64/64 division, and the 64/32->64 case really is
> fundamentally simpler.
>
> This whole "do_div is so complicated" thing is just BS.
>
> The thing that triggered Christoph to ask was a bug in the
> implementation of that *simpler*  interface. What makes you think that
> making people implement _udivdi3 would magically avoid all such bugs?
>

Nothing.

We could ask gcc to fix this, I suppose (add __udiv_64_over_32 or whatever).

--Andy
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