linux-kernel - Re: [PATCH] Force same size of struct autofs_v5_packet on x86 and x86

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Message-ID: <1316404368.3206.21.camel@perseus.themaw.net>
Date:	Mon, 19 Sep 2011 11:52:48 +0800
From:	Ian Kent <raven@...maw.net>
To:	Thomas Meyer <thomas@...3r.de>
Cc:	Al Viro <viro@...IV.linux.org.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	dhowells@...hat.com
Subject: Re: [PATCH] Force same size of struct autofs_v5_packet on x86 and
 x86_64

On Sun, 2011-09-18 at 10:01 +0200, Thomas Meyer wrote:
> Am Freitag, den 16.09.2011, 18:38 +0800 schrieb Ian Kent:
> > On Fri, 2011-09-16 at 11:19 +0100, Al Viro wrote:
> > > On Fri, Sep 16, 2011 at 12:06:38PM +0200, Thomas Meyer wrote:
> > > > autofs_v5_packet is 300 bytes on x86 and 304 bytes on x86_64.
> > > > This difference is wrong and leads to a hang in systemd when running
> > > > a x86 userspace on an x86_64 kernel.
> > > 
> > > NAK.
> > > 
> > > You are talking about the userland ABI.  With existing users.  Changing
> > > it might help systemd (what the hell is it doing with autofs, anyway?),
> > > but breaking existing binaries (you know, ones that *do* have some business
> > > dealing with autofs) is not acceptable.
> > 
> > That's right.
> > 
> > Certainly my mistake (made a long time ago) and when I realized it I
> > decided I would need to handle it in user space for the same reasons Al
> > has mentioned.
> > 
> 
> btw. where are the padding bytes are added? how to tell gcc to display
> this?

It's also been a long time since I looked into this so I don't remember
the processor alignment details.

Not sure if there is a compiler option that would report this, sorry,
anyone else?

Ian

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