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

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Message-ID: <195c7a900901131511l7077eebar8396267e3f2b670b@mail.gmail.com>
Date:	Wed, 14 Jan 2009 00:11:32 +0100
From:	"Bastien ROUCARIES" <roucaries.bastien@...il.com>
To:	"Jesper Nilsson" <jesper.nilsson@...s.com>,
	linux-kernel@...r.kernel.org, "David Miller" <davem@...emloft.net>
Subject: Re: lib/klist.c: bit 0 in pointer can't be used as flag

On Tue, Jan 13, 2009 at 11:45 PM, David Miller <davem@...emloft.net> wrote:
> From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Date: Wed, 14 Jan 2009 07:40:19 +0900
>
>> > It may be that we've worked around the other spots, although I haven't
>> > seen anything like that, we might just have been lucky until now.
>> >
>> > Can you recall another place where this trick is used?
>>
>> rmap.
>> Don't CRIS use mmu?
>
> I'm beginning to suspect the issue is only with objects
> in the kernel image itself.  Dynamically allocated memory
> is properly aligned and therefore the "low bit status bits
> in pointer" trick works.

Perhaps using a pointerhackalign trick on this structure where
#define pointerhackalign(x) __attribute__ ((aligned (x)))
and declare
struct klist_node {
...
}  pointerhackalign(2);

Because  __attribute__ ((aligned (x))) could only increase alignment
it will safe to do that and serve as documentation purpose :)

Regards

Bastien
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