linux-kernel - Re: [RFC Patch 1/9] Introducing generic hardware breakpoint handler interfaces

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Date:	Sat, 18 Oct 2008 11:23:11 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Roland McGrath <roland@...hat.com>
cc:	prasad@...ux.vnet.ibm.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	<akpm@...ux-foundation.org>, <mingo@...e.hu>,
	<jason.wessel@...driver.com>, <avi@...ranet.com>,
	<richardj_moore@...ibm.com>
Subject: Re: [RFC Patch 1/9] Introducing generic hardware breakpoint handler
 interfaces

On Fri, 17 Oct 2008, Roland McGrath wrote:

> > There's another RF-related issue which the patch currently ignores.  
> > Namely, what should happen if a new user breakpoint is registered at
> > the current PC address?  We should force the RF flag to 0 so that the
> > breakpoint will be triggered when execution resumes.  The problem is
> > that it's not easy to tell whether the current PC corresponds to the
> > same linear address as that registered for the breakpoint -- i.e., I
> > don't know how the code should go about translating from virtual
> > addresses to linear addresses.  Would this in fact always be the
> > identity mapping?  Presumably not if we're in VM86 mode.
> 
> Um, punt?  There is the hair in step.c:convert_ip_to_linear, but, bah.

Punting is exactly what the patch does now.  Together with a FIXME 
comment.

Alan Stern

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