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

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Date:	Thu, 13 Aug 2015 09:28:35 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	George Spelvin <linux@...izon.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Lutomirski <luto@...nel.org>
Subject: Re: enabling libgcc for 64-bit divisions, was Re: PROBLEM: XFS on ARM
 corruption 'Structure needs cl

On Wed, Aug 12, 2015 at 11:11 PM, George Spelvin <linux@...izon.com> wrote:
>
> Agreed.  But some x86 code I'm working on now, I have a *lot* of
> asm("divl") calls because even do_div isn't great for 64/32->32 division.

Yeah.

I'm not convinced that "64/32->32" is all that generic, though.  If
the dividend in 64-bit, there's no fundamental type-based guarantee
that things will fit.

So your case is rather special, and depends (intimately) on knowing
the actual ranges and how they interact.

That's not a generic situation like "do_div()".

                  Linus
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