linux-kernel - Re: [uml-devel] [PATCH 2/6] UML: Don't valgrind userspace

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Message-ID: <20080906221231.GA9359@c2.user-mode-linux.org>
Date:	Sat, 6 Sep 2008 18:12:31 -0400
From:	Jeff Dike <jdike@...toit.com>
To:	John Reiser <jreiser@...Wagon.com>
Cc:	Steve VanDeBogart <vandebo-lkml@...dBox.Net>, jiayingz@...gle.com,
	linux-kernel@...r.kernel.org,
	user-mode-linux-devel@...ts.sourceforge.net, dkegel@...gle.com
Subject: Re: [uml-devel] [PATCH 2/6] UML: Don't valgrind userspace

On Sat, Sep 06, 2008 at 01:55:34PM -0700, John Reiser wrote:
> > This is effectively appropriating part of the kernel's ABI for
> > valgrind's use.  
> 
> UML is part of the kernel, so getting a memory reference checker (valgrind)
> running in UML is part of the kernel, too.  The concept of "escape from the
> virtualizer" eventually occurs to more than just memory reference checkers.

Irrelevant - what if UML, or anything else for that matter, starts
using CLONE_IO?  All of a sudden, valgrind will start letting those
threads go.

> Why wouldn't that be a race between the next _NR_clone from this thread
> and the next _NR_clone from any other existing thread [in the same
> process]?

Yeah, if you cloned in a signal handler, that would be a problem.

How about sticking the annotation in the thread itself?  This may be
what you're suggesting here - I can't really tell.

> Valgrind can pre-pend a block of code at the start of the new thread,
> but almost immediately that code will want to "unvirtualize."
> Doing so at _NR_clone itself is convenient all around.

  	      		Jeff

-- 
Work email - jdike at linux dot intel dot com
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