Subject: Re: [Patch 2/2] PPC64-HWBKPT: Implement hw-breakpoints for PPC64

From: "K.Prasad" <[email-masked]>
Date: Wed, 12 May 2010 09:04:34 +0530

On Wed, May 05, 2010 at 02:03:03AM +0530, K.Prasad wrote:
> On Mon, May 03, 2010 at 04:23:30PM +1000, Paul Mackerras wrote:
> > On Wed, Apr 14, 2010 at 09:18:27AM +0530, K.Prasad wrote:
> > 
[snipped]
> 
> It has been pointed out to me before (Roland's mail Ref:linuxppc-dev
> message-id: [email-masked]) that there will
> be too many corner cases that will be difficult to foresee, however your
> above list appears to be exhaustive. While the alternatives to this being
> a fallback to one-shot breakpoints (thereby leading to confusing
> hw-breakpoint interface semantics), this is an attempt to generate
> continuous and 'trigger-after-execute' (for non-ptrace requests)
> breakpoint exceptions. I believe that, with the addressal of concerns
> cited above, the resultant patchset would be one that achieves the
> stated design goals with no loss to existing functionality.
> 

Hi Paul,

> I intend to send out another version of this patchset with fixes as
> described in my replies above (unless I hear objections to it :-)).
> 

Meanwhile, a little sickness had kept me away from working on this
patchset. I have now posted a new version of the same here () which
contains changes as described above.

A few more changes to the patch is impending post merger
of Frederic's patches (which are now in -tip) into mainline (ref: commit
73266fc1df2f94cf72b3beba3eee3b88ed0b0664 to
777d0411cd1e384115985dac5ccd42031e3eee2b);
mainly due to the new ability for a per-task breakpoint to request
kernel-space breakpoints (the notion of kernel- vs user-bp would also
become obsolete, it is better to call them per-cpu vs per-task
breakpoints).

Also, I find that possibility of a kernel-thread specific breakpoint
(which can migrate across CPUs) has not been thought and implemented well
in this patch (will be much easier after merger of Frederic's patch). I
would prefer to have atleast some version of the patch included in
mainline before bringing in support for the same.

Thanks,
K.Prasad