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Date: Wed, 6 Jun 2007 14:42:29 +0200
From: Arnd Bergmann <arnd@...db.de>
To: David Woodhouse <dwmw2@...radead.org>
Cc: Segher Boessenkool <segher@...nel.crashing.org>,
Kyle Moffett <mrmacman_g4@....com>,
John Stoffel <john@...ffel.org>, Willy Tarreau <w@....eu>,
Evgeniy Polyakov <johnpol@....mipt.ru>, CaT <cat@....com.au>,
Ondrej Zajicek <santiago@...reenet.org>,
linux-kernel@...r.kernel.org, Bill Davidsen <davidsen@....com>,
Jan Engelhardt <jengelh@...ux01.gwdg.de>,
Thomas Gleixner <tglx@...utronix.de>,
Dongjun Shin <djshin90@...il.com>,
Pekka Enberg <penberg@...helsinki.fi>,
Albert Cahalan <acahalan@...il.com>,
linux-fsdevel@...r.kernel.org, linux-mtd@...ts.infradead.org,
Artem Bityutskiy <dedekind@...radead.org>,
Sam Ravnborg <sam@...nborg.org>,
Jamie Lokier <jamie@...reable.org>,
Roland Dreier <rdreier@...co.com>,
Jörn Engel <joern@...ybastard.org>,
Pavel Machek <pavel@....cz>,
Ulisses Furquim <ulissesf@...il.com>, akpm@...l.org,
David Weinehall <tao@....umu.se>
Subject: Re: [Patch 04/18] include/linux/logfs.h
On Wednesday 06 June 2007, David Woodhouse wrote:
> And if I had something like this (which is admittedly contrived, but
> hardware people _do_ do stupid things to us):
> { uint32_t, uint8_t, uint16_t, uint8_t, uint32_t, uint32_t }
>
> With the 'packed' attribute the compiler would assume arbitrary
> alignment of all the 32-bit integers. But in reality it's only necessary
> for the uint16_t in the middle. A 'nopadding' attribute would deal with
> that correctly.
I would argue that a newly invented 'nopadding' attribute should reject
such a structure as invalid, because it should not let members be
unaligned. Unfortunately, this also gets tricky if you consider
struct {
uint32_t a;
uint64_t b;
uint32_t c;
};
which does have an unaligned member by default in i386, but not on
any modern platform.
Arnd <><
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