From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Ralf Baechle <ralf@linux-mips.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Atsushi Nemoto <anemo@mba.ocn.ne.jp>,
linux-mips@linux-mips.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Optimize generic get_unaligned / put_unaligned implementations.
Date: Thu, 15 Feb 2007 15:05:36 -0800 [thread overview]
Message-ID: <45D4E740.9020504@goop.org> (raw)
In-Reply-To: <20070215221839.GA14103@linux-mips.org>
Ralf Baechle wrote:
> Gcc info page says:
>
> [...]
> `packed'
> The `packed' attribute specifies that a variable or structure field
> should have the smallest possible alignment--one byte for a
> variable, and one bit for a field, unless you specify a larger
> value with the `aligned' attribute.
> [...]
>
> Qed?
So that the compiler has to assume that if its accessing this __packed
structure, it may be embedded unaligned within something else? And
because the pointer is cast through (void *) it isn't allowed to use
alias analysis to notice that the pointer wasn't originally (apparently)
unaligned.
Seems sound to me.
J
next prev parent reply other threads:[~2007-02-15 23:05 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20050830104056.GA4710@linux-mips.org>
[not found] ` <20060306.203218.69025300.nemoto@toshiba-tops.co.jp>
2006-03-07 1:05 ` [PATCH] 64bit unaligned access on 32bit kernel Andrew Morton
2006-03-07 2:03 ` Atsushi Nemoto
2006-03-07 18:09 ` Ralf Baechle
2006-03-08 4:58 ` Atsushi Nemoto
2006-03-08 5:12 ` Andrew Morton
2007-02-14 21:42 ` [PATCH] Optimize generic get_unaligned / put_unaligned implementations Ralf Baechle
2007-02-15 4:39 ` Andrew Morton
2007-02-15 8:35 ` Marcel Holtmann
2007-02-15 14:34 ` Ralf Baechle
2007-02-15 21:53 ` Andrew Morton
2007-02-15 22:18 ` Ralf Baechle
2007-02-15 23:05 ` Jeremy Fitzhardinge [this message]
2007-02-15 23:38 ` Andrew Morton
2007-02-16 0:13 ` Jeremy Fitzhardinge
2007-02-16 0:43 ` Ralf Baechle
2007-02-16 1:27 ` Andrew Morton
2007-02-16 1:59 ` Ralf Baechle
2007-02-20 13:50 ` Pavel Machek
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=45D4E740.9020504@goop.org \
--to=jeremy@goop.org \
--cc=akpm@linux-foundation.org \
--cc=anemo@mba.ocn.ne.jp \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mips@linux-mips.org \
--cc=ralf@linux-mips.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