Subject: Re: [Patch 3/4] PPC64-HWBKPT: Handle concurrent alignment interrupts

From: "K.Prasad" <[email-masked]>
Date: Fri, 28 May 2010 13:11:35 +0530

On Thu, May 27, 2010 at 04:20:44PM +1000, Paul Mackerras wrote:
> On Tue, May 25, 2010 at 02:44:35PM +0530, K.Prasad wrote:
> 
> > An alignment interrupt may intervene between a DSI/hw-breakpoint exception
> > and the single-step exception. Enable the alignment interrupt (through
> > modifications to emulate_single_step()) to notify the single-step exception
> > handler for proper restoration of hw-breakpoints.
> > 
> > Signed-off-by: K.Prasad <[email-masked]>
> > ---
> >  arch/powerpc/kernel/traps.c |    7 ++-----
> >  1 file changed, 2 insertions(+), 5 deletions(-)
> > 
> > Index: linux-2.6.ppc64_test/arch/powerpc/kernel/traps.c
> > ===================================================================
> > --- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/traps.c
> > +++ linux-2.6.ppc64_test/arch/powerpc/kernel/traps.c
> > @@ -602,7 +602,7 @@ void RunModeException(struct pt_regs *re
> >  
> >  void __kprobes single_step_exception(struct pt_regs *regs)
> >  {
> > -	regs->msr &= ~(MSR_SE | MSR_BE);  /* Turn off 'trace' bits */
> > +	clear_single_step(regs);
> >  
> >  	if (notify_die(DIE_SSTEP, "single_step", regs, 5,
> >  					5, SIGTRAP) == NOTIFY_STOP)
> > @@ -621,10 +621,7 @@ void __kprobes single_step_exception(str
> >   */
> >  static void emulate_single_step(struct pt_regs *regs)
> >  {
> > -	if (single_stepping(regs)) {
> > -		clear_single_step(regs);
> > -		_exception(SIGTRAP, regs, TRAP_TRACE, 0);
> > -	}
> > +	single_step_exception(regs);
> >  }
> 
> We still need the if (single_stepping(regs)) in emulate_single_step.
> We don't want to send the process a SIGTRAP every time it gets an
> alignment interrupt. :)
> 
> Paul.

Agreed, and made changes to that effect in version XXII (as seen in
patch linuxppc-dev message-id: [email-masked]).

Thanks,
K.Prasad