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Message-ID: <4de7f8a60612060704k7d7c1ea3o1d43bee6c5e372d4@mail.gmail.com>
Date: Wed, 6 Dec 2006 16:04:22 +0100
From: "Jan Blunck" <jblunck@suse.de>
To: "Phil Endecott" <phil_arcwk_endecott@chezphil.org>
Subject: Re: Subtleties of __attribute__((packed))
Cc: linux-kernel@vger.kernel.org
In-Reply-To: <1165411241721@dmwebmail.belize.chezphil.org>
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On 12/6/06, Phil Endecott <phil_arcwk_endecott@chezphil.org> wrote:
> Dear All,
>
> I used to think that this:
>
> struct foo {
>    int a  __attribute__((packed));
>    char b __attribute__((packed));
>    ... more fields, all packed ...
> };
>
> was exactly the same as this:
>
> struct foo {
>    int a;
>    char b;
>    ... more fields ...
> } __attribute__((packed));
>
> but it is not, in a subtle way.
>

The same code is generated. The difference is that usually packing the
whole struct isn't as error-prone as packing every element. Besides
that the gcc warns about packing objects that have an alignment of 1.
This is the reason why we should use the second approach.
-
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