linux-kernel - Re: [PATCH] autofs4: fix 32-bit userspace vs 64-bit kernel communications

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Message-Id: <1213191629.4994.61.camel@raven.themaw.net>
Date:	Wed, 11 Jun 2008 21:40:29 +0800
From:	Ian Kent <raven@...maw.net>
To:	Pavel Emelyanov <xemul@...nvz.org>
Cc:	autofs mailing list <autofs@...ux.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Subject: Re: [PATCH] autofs4: fix 32-bit userspace vs
	64-bit	kernel	communications


On Wed, 2008-06-11 at 17:25 +0400, Pavel Emelyanov wrote:
> > Does the test_thread_flag(TIF_IA32) macro only return true for a 32-bit
> > user-space process running within a 64-bit user space environment
> > (perhaps I can do away with the check in the autofs daemon, perhaps it
> > doesn't quite work correctly)?
> 
> Hm... If we fix it in the user level that would also be OK, I
> suppose...
> 
> > Oh .. so maybe the answer to my question is yes?
> 
> It is - we check *only* for the process, that is to receive the 
> packet.

Right, since the send is done in user context.

> 
> > What about other arches offer 32-bit within a 64-bit environment (has
> > this been the case on sparc64 at some point)?
> > What about the compiler padding on these?
> 
> We have no technical ability to check this. First I wanted to
> get your opinion about this particular fix for x86 machines.
> 
> As far as sparc(64) and other 32-to-64 are concerned - I can
> start talking to their users/maintainers to check.

I investigated only x86_64 and sparc64 but that was a quite a while ago
now. My sparc machine doesn't even have a Linux install atm.

If we can find a general and consistent solution I'm happy to remove the
check from the daemon and cope with the bit of pain it might cause.

> 
> > Don't get me wrong, I'm not against fixing this, in fact I'd like to,
> > but I'm concerned it may end up a bit of a can of worms.

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