linux-kernel - Re: Subtleties of __attribute_

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20061207094833.GD4942@hasse.suse.de>
Date:	Thu, 7 Dec 2006 10:48:33 +0100
From:	Jan Blunck <jblunck@...e.de>
To:	Phil Endecott <phil_arcwk_endecott@...zphil.org>,
	linux-kernel@...r.kernel.org
Subject: Re: Subtleties of __attribute__((packed))

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.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/