linux-kernel - Re: [PATCH] Introduce compat_u64 and compat

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Date:	Fri, 15 Jun 2007 13:38:32 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dave Airlie <airlied@...ux.ie>, linux-arch@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] Introduce compat_u64 and compat_s64 types

On Fri, 2007-06-15 at 06:11 -0600, Matthew Wilcox wrote:
> You're relying on compat_[us]64 being only used in structures which are
> already packed. 

In which case the whole exercise is pointless, on account of the
structure being already packed. It was _already_ laid out the same on
32-bit and 64-bit builds.

>  If someone uses them in a non-packed struct, they won't
> decrease the alignment.  I think it would be more effective to specify
> it as:
> __attribute__((aligned(4), packed))

Good point. Yes, it looks like we need the additional 'packed' in order
for the aligned(4) to be anything other than a no-op.

-- 
dwmw2

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