Re: [Patch 00/11] Hardware Breakpoint interfaces

K.Prasad
2009-03-28T08:47:19Z

On Wed, Mar 25, 2009 at 03:48:31PM -0400, Alan Stern wrote:
> > +
> > +/*
> > + * Handle debug exception notifications.
> > + */
> > +int __kprobes hw_breakpoint_handler(struct die_args *args)
> > +{
> > + int i, rc = NOTIFY_DONE;
> > + struct hw_breakpoint *bp;
> > + /* The DR6 value is stored in args->err */
> > + unsigned long dr7, dr6 = args->err;
>
> Please change this. (I should have changed it long ago, but I never
> got around to it.) Instead of passing the DR6 value in args->err,
> pass a pointer to the dr6 variable in do_debug(). That way the
> handler routines can turn off bits in that variable and do_debug() can
> see which bits remain set at the end.
>
> Of course, this will require a corresponding change to the
> post_kprobe_handler() routine.
>

As I looked at the code with an intention of changing it, I don't find a
place - in hw_breakpoint_handler() and in functions called by
kprobe_exceptions_notify() where bits in dr6 are written into.
The thread-specific thread->debugreg6 is updated with causative bits in
ptrace_triggered() to help send signals to the user-space. I don't see a
user for the change you propose.

I should send out the revised patchset sometime tomorrow. Kindly let me
know your comments about them.

Thanks,
K.Prasad