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X-Envelope-From: pavel@bug.ucw.cz
Date: Thu, 24 Oct 2002 13:24:12 +0200
From: Pavel Machek <pavel@suse.cz>
To: Andi Kleen <ak@muc.de>
Cc: Jeff Dike <jdike@karaya.com>, john stultz <johnstul@us.ibm.com>,
       Linus Torvalds <torvalds@transmeta.com>, andrea <andrea@suse.de>,
       lkml <linux-kernel@vger.kernel.org>,
       george anzinger <george@mvista.com>,
       Stephen Hemminger <shemminger@osdl.org>
Subject: Re: [PATCH] linux-2.5.43_vsyscall_A0
Message-ID: <20021024112411.GA783@elf.ucw.cz>
References: <1034981832.4042.58.camel@cog> <200210190352.WAA05769@ccure.karaya.com> <20021019031002.GA16404@averell>
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Hi!

> > > Since no one really brought up any issues with the code itself
> > > (correct me if I'm wrong), here is the i386 vsyscall gettimeofday port
> > > I sent last night, synced up and ready for integration.
> > 
> > This vsyscall implementation breaks UML.  Any app that's run inside UML
> > that uses vsyscalls will get the host's vsyscalls rather than the UML
> > vsyscalls.
> 
> Ugh.
> 
> Guess you'll have some problems then with UML on x86-64, which always uses
> vgettimeofday. But it's only used for gettimeofday() currently, perhaps it's 
> not that bad when the UML child runs with the host's time.

Well, if you want to use UML for time shifting (pretty common use,
AFAICS)...

> I guess it would be possible to add some support for UML
> to map own code over the vsyscall reserved locations. UML would need
> to use the syscalls then. But it'll be likely ugly.

I guess this is the right solution. [Or UML could simply unmap that
area and handle the faults...].
								Pavel
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