[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20071124143441.41657307@poseidon.drzeus.cx>
Date: Sat, 24 Nov 2007 14:34:41 +0100
From: Pierre Ossman <drzeus-list@...eus.cx>
To: Daniel Drake <dsd@...too.org>
Cc: linux-kernel@...r.kernel.org, davem@...emloft.net,
kune@...ne-taler.de, johannes@...solutions.net
Subject: Re: [RFC] Documentation about unaligned memory access
On Fri, 23 Nov 2007 00:15:53 +0000 (GMT)
Daniel Drake <dsd@...too.org> wrote:
> Being spoilt by the luxuries of i386/x86_64 I've never really had a good
> grasp on unaligned memory access problems on other architectures and decided
> it was time to figure it out. As a result I've written this documentation
> which I plan to submit for inclusion as
> Documentation/unaligned_memory_access.txt
>
> Before I do so, any comments on the following?
>
A very nice, and much needed document. I think you should include one thing though:
memcpy() is _only_ safe when one of the pointers is char* or void*. If it is anything more complex than that, gcc will assume alignment and optimise based on that. E.g. memcpy() of two long:s generates the same assembly as doing an assignment.
(Technically it is no different for char* and void*, but since they have byte alignment, gcc can't really do anything creative.)
Rgds
--
-- Pierre Ossman
Linux kernel, MMC maintainer http://www.kernel.org
PulseAudio, core developer http://pulseaudio.org
rdesktop, core developer http://www.rdesktop.org
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists