LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Jan Blunck <jblunck@suse.de>
To: Phil Endecott <phil_arcwk_endecott@chezphil.org>,
	linux-kernel@vger.kernel.org
Subject: Re: Subtleties of __attribute__((packed))
Date: Thu, 7 Dec 2006 10:48:33 +0100	[thread overview]
Message-ID: <20061207094833.GD4942@hasse.suse.de> (raw)
In-Reply-To: <20061206175423.GA9959@flint.arm.linux.org.uk>

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
packed.

  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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20061207094833.GD4942@hasse.suse.de \
    --to=jblunck@suse.de \
    --cc=linux-kernel@vger.kernel.org \
    --cc=phil_arcwk_endecott@chezphil.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).