LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
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

  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 \
    --subject='Re: [PATCH] Optimize generic get_unaligned / put_unaligned implementations.' \
    /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

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).