linux-kernel - Re: [Patch 00/11] Hardware Breakpoint interfaces

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Message-ID: <20090424155710.GA5008@in.ibm.com>
Date:	Fri, 24 Apr 2009 21:27:10 +0530
From:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@....ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	maneesh@...ux.vnet.ibm.com, Roland McGrath <roland@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [Patch 00/11] Hardware Breakpoint interfaces

On Fri, Apr 24, 2009 at 10:16:07AM -0400, Alan Stern wrote:
> On Fri, 24 Apr 2009, K.Prasad wrote:
> 
> > The arch_update_kernel_hw_breakpoints() was designed to work like this -
> > it updates all registers beginning 'hbp_kernel_pos' to (HB_NUM - 1) with
> > the values stored in hbp_kernel[] array.
> > 
> > When inserting a new breakpoint, hbp_kernel_pos is decremented *before*
> > invoking arch_update_kernel_hw_breakpoints() so that the new value is
> > also written onto the physical debug register.
> > 
> > On removal, 'hbp_kernel_pos' is incremented *after*
> > arch_update_kernel_hw_breakpoints() so that the physical debug registers
> > i.e. both DR7 and DR<pos> are updated with the changes post removal and
> > compaction. I'm ready to make changes but don't see where the code
> > actually goes wrong. Can you explain that?
> 
> I'm sorry; I misread the code in arch_update_kernel_hw_breakpoints().  
> It isn't actually wrong, and you are correct to increment
> hbp_kernel_pos where you do.  Your code is different from my original
> version, which would update all the debug registers at once instead of
> doing the kernel and userspace breakpoints separately -- that's what 
> confused me.
> 
> There is one change you could make to improve the routine, however.  In 
> arch_update_kernel_hw_breakpoints(), the line
> 
> 	kdr7 &= ~kdr7_masks[hbp_kernel_pos];
> 
> really should be
> 
> 	kdr7 = 0;
> 
> since kdr7 never contains anything other than kernel breakpoint
> settings.  (You could update the comment in the preceding line as
> well.)
> 
> Alan Stern

Sure, I'd make that change (in the subsequent iteration) - it's much simpler.

Do you think that the patchset is now in a form that can be submitted
for upstream (-tip tree) acceptance?

Thanks,
K.Prasad

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