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From: Jan Blunck <>
To: Phil Endecott <>,
Subject: Re: Subtleties of __attribute__((packed))
Date: Thu, 7 Dec 2006 10:48:33 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Wed, Dec 06, Russell King wrote:

> On Wed, Dec 06, 2006 at 04:54:39PM +0100, Jan Blunck wrote:
> > Maybe the arm backend is somehow broken. AFAIK (and I verfied it on S390 and
> > i386) the alignment shouldn't change.

Once again: I refered to "packed attribute on the struct vs. packed attribute
on each member of the struct". The alignment shouldn't be different.

> Please read the info pages:
> `packed'
>      This attribute, attached to an `enum', `struct', or `union' type
>      definition, specifies that the minimum required memory be used to
>      represent the type.
>      Specifying this attribute for `struct' and `union' types is
>      equivalent to specifying the `packed' attribute on each of the
>      structure or union members.  Specifying the `-fshort-enums' flag
>      on the line is equivalent to specifying the `packed' attribute on
>      all `enum' definitions.
> Note that it says *nothing* about alignment.  It says "minimum required
> memory be used to represent the type." which implies that the internals
> of the structure are packed together as tightly as possible.
> It does not say "and as such the struct may be aligned to any alignment".

And this is why it makes sense to think about align attribute when you use

  parent reply	other threads:[~2006-12-07  9:48 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2006-12-06 13:20 Subtleties of __attribute__((packed)) Phil Endecott
2006-12-06 14:01 ` Frederik Deweerdt
2006-12-06 14:24   ` Phil Endecott
2006-12-06 15:04 ` Jan Blunck
2006-12-06 15:22   ` Phil Endecott
2006-12-06 15:54     ` Jan Blunck
2006-12-06 16:02       ` Andreas Schwab
2006-12-06 16:41         ` Jan Blunck
2006-12-06 17:28           ` Andreas Schwab
2006-12-06 16:13       ` Phil Endecott
2006-12-06 16:26         ` Jan Blunck
2006-12-06 17:54       ` Russell King
2006-12-06 18:05         ` David Miller
2006-12-07  9:48         ` Jan Blunck [this message]
2006-12-07 10:30           ` Andreas Schwab

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