linux-kernel - Re: Subtleties of __attribute_

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Message-ID: <1165415082132@dmwebmail.belize.chezphil.org>
Date:	Wed, 06 Dec 2006 14:24:42 +0000
From:	"Phil Endecott" <phil_arcwk_endecott@...zphil.org>
To:	"Frederik Deweerdt" <deweerdt@...e.fr>
Cc:	<linux-kernel@...r.kernel.org>
Subject: Re: Subtleties of __attribute__((packed))

Frederik Deweerdt wrote:
> On Wed, Dec 06, 2006 at 01:20:41PM +0000, Phil Endecott wrote:
>> 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.
>> 
> This is likely a gcc bug isn't it? The gcc info page states:
>   Specifying this attribute for `struct' and `union' types is
>   equivalent to specifying the `packed' attribute on each of the
>   structure or union members.

A gcc *documentation* bug?

I asked on the gcc list about this before posting here, and although 
replies are still coming in the first opinion was "it's doing exactly 
what you asked it to do".

Phil.




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