linux-kernel - Re: [PATCH 11/12] hw-breakpoints: ftrace plugin for kernel symbol tracing using HW Breakpoint interfaces

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Date:	Thu, 4 Jun 2009 21:15:00 +0530
From:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	David Daney <ddaney@...iumnetworks.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH 11/12] hw-breakpoints: ftrace plugin for kernel symbol
	tracing using HW Breakpoint interfaces

On Wed, Jun 03, 2009 at 02:38:12AM +0200, Frederic Weisbecker wrote:
> On Tue, Jun 02, 2009 at 04:12:08PM -0700, David Daney wrote:
> > Frederic Weisbecker wrote:
> >> From: K.Prasad <prasad@...ux.vnet.ibm.com>

> > I hate to sound like a broken record, but could some one explain to me  
> > again why it is a good idea to design a new API that requires processor  
> > specific #ifdefs to be sprinkled all around generic kernel code?
> >
> > Back in:
> > http://lkml.org/lkml/2008/12/4/329
> > and
> > http://lkml.org/lkml/2009/5/21/189
> >
> > I raised doubts about this hw-breakpoint thing being generic and the  
> > responses made think that the processor specific portions would be  
> > isolated in the processor specific parts of the kernel.  I now see that  
> > I was wrong.
> >
> > When we add sparc, MIPS, ppc...  Support it would be nice to not have to  
> > add all our own #ifdefs to this, but instead have a generic interface  
> > that will not need changes.
> >
> > David Daney
> 
> I was discussing about it with Prasad few hours ago :)
> 
> The fact is that archs support the hardware breakpoints in
> very different ways each.
> Some of them support read breakpoint, others not (x86).
> Some support addresses range, others (x86).
> 
> But still it would be nice to gather the most common
> breakpoints operations through a real generic wrapper
> that relies on arch specific implmentation in
> background.
> 
> Such as setting very simple x/w/r breakpoints...
> 
> Well Prasad and Alan Stern could tell more about it,
> I wait for their answer.
> 
> Anyway it's a fairly new Api that can still evolve.
> The basis are set but can still be improved and more high level
> and generic things can still be implemented.
> 

I think this concern can be partially addressed, atleast as far as the
breakpoint length is concerned. I've added my comments in the response
to David Daney here: http://lkml.org/lkml/2009/6/4/303.

Hope that the changes proposed there is acceptable to the community.

Thanks,
K.Prasad

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