From: Ralf Baechle <ralf@linux-mips.org>
To: "Maciej W. Rozycki" <macro@linux-mips.org>
Cc: Atsushi Nemoto <anemo@mba.ocn.ne.jp>,
u1@terran.org, linux-mips@linux-mips.org
Subject: Re: MIPS checksum bug
Date: Fri, 19 Sep 2008 13:23:04 +0200 [thread overview]
Message-ID: <20080919112304.GB13440@linux-mips.org> (raw)
In-Reply-To: <Pine.LNX.4.55.0809190112090.22686@cliff.in.clinika.pl>
On Fri, Sep 19, 2008 at 11:12:22AM +0100, Maciej W. Rozycki wrote:
> > Which is a truely weird operation - but MIPS R2 happens to have a wonderful
> > instruction for this operation, WSBH / DSBH.
>
> Ah, finally a justification for the R2 ISA!
As you may recall the real reason is that this instruction was designed
not by engineers but patent law. Which is f*cked into the head but ...
> Seriously though, I smell a caller somewhere fails to call csum_fold() on
> the result obtained from csum_partial() where it should, so it would be
> good to fix the bug rather than trying to cover it. Bryan, would you be
> able to track down the caller?
Not quite. Internally the IP stack maintains the checksum as a 32-bit
value for performance sake. It only folds it to 16-bit when it has to.
> I can see you have done the microoptimisation I had in mind meanwhile --
> thanks for saving me the effort. ;) There is a delay slot to fill left
> though -- will you take care of it too?
Will do - just couldn't be bothered (too) late last night ...
Ralf
next prev parent reply other threads:[~2008-09-19 11:23 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <072748C6-07A9-4167-A8A5-80D0F7D9C784@darkforest.org>
2008-09-17 5:15 ` MIPS checksum bug Bryan Phillippe
2008-09-17 10:40 ` Maciej W. Rozycki
2008-09-17 13:23 ` Atsushi Nemoto
2008-09-17 14:46 ` Maciej W. Rozycki
2008-09-17 15:27 ` Atsushi Nemoto
2008-09-17 18:21 ` Maciej W. Rozycki
2008-09-18 22:07 ` Ralf Baechle
2008-09-19 10:12 ` Maciej W. Rozycki
2008-09-19 11:23 ` Ralf Baechle [this message]
2008-09-19 11:47 ` [PATCH] MIPS checksum fix Ralf Baechle
2008-09-19 12:07 ` Ralf Baechle
2008-09-19 12:15 ` Maciej W. Rozycki
2008-09-19 14:09 ` Atsushi Nemoto
2008-09-19 15:02 ` Maciej W. Rozycki
2008-09-20 15:09 ` Ralf Baechle
2008-09-23 21:52 ` Bryan Phillippe
2008-09-23 22:06 ` Ralf Baechle
2008-09-29 15:28 ` Atsushi Nemoto
2008-09-19 12:26 ` MIPS checksum bug Maciej W. Rozycki
2008-09-19 16:04 ` Bryan Phillippe
2008-09-17 22:52 ` Bryan Phillippe
2008-09-18 16:17 ` Atsushi Nemoto
2008-09-19 1:14 ` Ralf Baechle
2008-09-19 15:43 ` Atsushi Nemoto
2008-09-19 16:09 ` Maciej W. Rozycki
2008-09-19 16:35 ` Thiemo Seufer
2008-09-19 23:18 ` Maciej W. Rozycki
2008-09-20 0:13 ` Ralf Baechle
2008-09-20 13:45 ` Atsushi Nemoto
2008-09-18 4:43 ` Bryan Phillippe
2008-09-18 10:06 ` Maciej W. Rozycki
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