linux-kernel - Re: [PATCH] ubi: kill homegrown endian macros

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Date:	Fri, 18 May 2007 10:39:19 +0800
From:	David Woodhouse <dwmw2@...radead.org>
To:	Matthieu CASTET <castet.matthieu@...e.fr>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ubi: kill homegrown endian macros

On Thu, 2007-05-17 at 20:30 +0000, Matthieu CASTET wrote:
> On Thu, 17 May 2007 10:29:31 -0700, Andrew Morton wrote:
> 
> > On Thu, 17 May 2007 18:09:50 +0300 Artem Bityutskiy
> > <dedekind@...radead.org> wrote:
> > 
> > umm..  I'd say what you've done in there is an improvement to the
> > exiting stuff: getting gcc to check it is better than having to use
> > sparse.
> > 
> > I'd have expected gcc to generate poorer code with your approach but I'm
> > showing zero text size changes from Christoph's patch (gcc-4.1 and
> > gcc-3.4.5).
> > 
> >
> On which arch did you try ?
> X86 where unaligned access are ok ?
> 
> On arch that don't support aligned access, packed struct access will be 
> done byte per byte (but it could be the expected behavior if there 
> unaligned access).

When I tested this on ARM, the output for je32_to_cpu et al was fine.
For _other_ structures where I'd used __attribute__((packed)) to be
safe, gcc would emit code to handle unaligned loads. But not in the
simple case where the struct has only one member.

Are you suggesting that this has changed since I did my testing?

-- 
dwmw2

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