linux-kernel - Re: lib/klist.c: bit 0 in pointer can't be used as flag

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Message-ID: <20090114110257.GI19262@axis.com>
Date:	Wed, 14 Jan 2009 12:02:57 +0100
From:	Jesper Nilsson <Jesper.Nilsson@...s.com>
To:	David Miller <davem@...emloft.net>
Cc:	"roucaries.bastien@...il.com" <roucaries.bastien@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tj@...nel.org" <tj@...nel.org>, "gregkh@...e.de" <gregkh@...e.de>,
	"stern@...land.harvard.edu" <stern@...land.harvard.edu>,
	"jens.axboe@...cle.com" <jens.axboe@...cle.com>,
	"hinko.kocevar@...rtapot.si" <hinko.kocevar@...rtapot.si>
Subject: Re: lib/klist.c: bit 0 in pointer can't be used as flag

On Wed, Jan 14, 2009 at 11:45:28AM +0100, David Miller wrote:
> From: Jesper Nilsson <Jesper.Nilsson@...s.com>
> Date: Wed, 14 Jan 2009 11:36:24 +0100
> 
> > On Wed, Jan 14, 2009 at 11:21:40AM +0100, David Miller wrote:
> > > From: Jesper Nilsson <Jesper.Nilsson@...s.com>
> > > Date: Wed, 14 Jan 2009 11:19:08 +0100
> > > > The following patch works for CRIS, and is less intrusive than
> > > > my earlier patch. If this the way to go I can resubmit a proper patch.
> > > 
> > > Out of curiosity, is there a way to get gcc to output code such
> > > that data objects are aligned more naturally?  Some option or
> > > similar?
> > 
> > There's flags for alignment of objects, but no flags for changing
> > structure layout or size, which is probably what we run into here.
> 
> Really?

A quick test using 32bit alignment didn't work, but it could be
that I've missed a place to modify cflags.

> I thought the problem is that the base object can have any odd
> alignment in the kernel image.  And this is why the problem isn't run
> into for objects allocated using dynamic allocation.

I reasoned that the struct klist is actually allocated as a part of
another struct, which due to no padding got the odd alignment.
I'll research this more fully.

/^JN - Jesper Nilsson
-- 
               Jesper Nilsson -- jesper.nilsson@...s.com
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