linux-kernel - Re: [PATCH 1/2] x86: Ignore trap bits on single step exceptions

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Date:	Thu, 25 Nov 2010 08:47:50 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Michael Stefaniuc <mstefani@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Maciej Rutecki <maciej.rutecki@...il.com>,
	Alexandre Julliard <julliard@...ehq.org>,
	Jason Wessel <jason.wessel@...driver.com>,
	"All since 2.6.33.x" <stable@...nel.org>
Subject: Re: [PATCH 1/2] x86: Ignore trap bits on single step exceptions

On Wed, Nov 24, 2010 at 09:32:02PM +0100, Michael Stefaniuc wrote:
> Hello Frederic,
> 
> On 11/13/2010 10:37 PM, Frederic Weisbecker wrote:
> >When a single step exception fires, the trap bits, used to
> >signal hardware breakpoints, are in a random state.
> >
> >These trap bits might be set if another exception will follow,
> >like a breakpoint in the next instruction, or a watchpoint in the
> >previous one. Or there can be any junk there.
> >
> >So if we handle these trap bits during the single step exception,
> >we are going to handle an exception twice, or we are going to
> >handle junk.
> >
> >Just ignore them in this case.
> >
> >This fixes https://bugzilla.kernel.org/show_bug.cgi?id=21332
> sorry for the delay in testing this.
> 
> I have cherry-picked this patch on top of v2.6.37-rc3-102-gea49b16
> and the ntdll/exception tests pass now.
> 
> Many thanks
> bye
> 	michael

Thanks for testing!
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