linux-kernel - Re: Bug#609371: linux-image-2.6.37-trunk-sparc64: module scsi

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Message-ID: <20110119161857.GC15031@Krystal>
Date:	Wed, 19 Jan 2011 11:18:57 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	David Miller <davem@...emloft.net>, rostedt@...dmis.org,
	richm@...elvet.org.uk, 609371@...s.debian.org, ben@...adent.org.uk,
	sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org,
	fweisbec@...il.com, mingo@...hat.com
Subject: Re: Bug#609371: linux-image-2.6.37-trunk-sparc64: module scsi_mod:
	Unknown relocation: 36

* Sam Ravnborg (sam@...nborg.org) wrote:
> > 
> > If my memory serves me correctly, I think "long long" is aligned on 4 bytes on
> > ppc32, but on 8 bytes on x86_32 (yeah, that's weird). How about we create a
> > #define __long_long_aligned __attribute__((__aligned__(__alignof__(long long))))
> 
> #define __u64_aligned __attribute__((__aligned__(__alignof__(long long))))
> 
> A bit shorter but maybe less obvious.

Yep, that would make sense.

I'm tempted to try creating

#defined __u64_packed_aligned __attribute__((__packed__, __aligned__(__alignof__(long long))))

in the hope that gcc sees this as a strict alignment requirement (including a
max bound) rather than just a hint. From what I gather in my reading of 

http://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html

"The aligned attribute can only increase the alignment; but you can decrease it
by specifying packed as well. See below."

gcc seems to support having both specified. I think this would provide the kind
of alignment guarantees we really need here: both specifying the minimum _and_
maximum alignment.

Thoughts ?

Mathieu

> 
> 	Sam

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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