On Fri, 15 May 2009, K.Prasad wrote:
> I see that you're referring to this code in __switch_to() :
> if (unlikely(__get_cpu_var(current_dabr) != new->thread.dabr))
> set_dabr(new->thread.dabr);
>
> arch_install_thread_hw_breakpoint()<--switch_to_thread_hw_breakpoint()
> <--__switch_to() implementation is also similar.
>
> In __switch_to(),
> if (unlikely(test_tsk_thread_flag(new, TIF_DEBUG)))
> switch_to_thread_hw_breakpoint(new);
>
> happens only when TIF_DEBUG flag is set. This flag is cleared when the
> process unregisters any breakpoints it had requested earlier. So, the
> set_dabr() call is avoided for processes not using the debug register.
In the x86 code, shouldn't arch_update_user_hw_breakpoint set or clear
TIF_DEBUG, depending on whether or not there are any user breakpoints
remaining?
> > > +int __kprobes hw_breakpoint_handler(struct die_args *args)
> > > +{
> > > + int rc = NOTIFY_STOP;
> > > + struct hw_breakpoint *bp;
> > > + struct pt_regs *regs = args->regs;
> > > + unsigned long dar;
> > > + int cpu, stepped, is_kernel;
> > > +
> > > + /* Disable breakpoints during exception handling */
> > > + set_dabr(0);
> > > +
> > > + dar = regs->dar & (~HW_BREAKPOINT_ALIGN);
> > > + is_kernel = (dar >= TASK_SIZE) ? 1 : 0;
> >
> > is_kernel_addr() ?
> >
>
> Ok.
Shouldn't this test hbp_kernel_pos instead?
> > > + if (is_kernel)
> > > + bp = hbp_kernel[0];
> > > + else {
> > > + bp = current->thread.hbp[0];
> > > + /* Lazy debug register switching */
> > > + if (!bp)
> > > + return rc;
Shouldn't this test be moved outside the "if" statement, as in the x86
code?
Alan Stern
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