Subject: Re: [RFC PATCH -tip v5 18/27] powerpc/kprobes: Don't call the ->break_handler() in arm kprobes code

From: Masami Hiramatsu <[email-masked]>
Date: Thu, 7 Jun 2018 23:28:02 +0900

On Thu, 07 Jun 2018 17:07:00 +0530
"Naveen N. Rao" <[email-masked]> wrote:

> Masami Hiramatsu wrote:
> > Don't call the ->break_handler() from the arm kprobes code,
> 					    ^^^ powerpc
> 
> > because it was only used by jprobes which got removed.
> > 
> > This also makes skip_singlestep() a static function since
> > only ftrace-kprobe.c is using this function.
> > 
> > Signed-off-by: Masami Hiramatsu <[email-masked]>
> > Cc: Benjamin Herrenschmidt <[email-masked]>
> > Cc: Paul Mackerras <[email-masked]>
> > Cc: Michael Ellerman <[email-masked]>
> > Cc: "Naveen N. Rao" <[email-masked]>
> > Cc: [email-masked]
> > ---
> >  arch/powerpc/include/asm/kprobes.h   |   10 ----------
> >  arch/powerpc/kernel/kprobes-ftrace.c |   16 +++-------------
> >  arch/powerpc/kernel/kprobes.c        |   31 +++++++++++--------------------
> >  3 files changed, 14 insertions(+), 43 deletions(-)
> 
> With 2 small comments...

2 ? or 1 ?

> Acked-by: Naveen N. Rao <[email-masked]>
> 
> - Naveen
> 
> > 
> > diff --git a/arch/powerpc/include/asm/kprobes.h b/arch/powerpc/include/asm/kprobes.h
> > index 674036db558b..785c464b6588 100644
> > --- a/arch/powerpc/include/asm/kprobes.h
> > +++ b/arch/powerpc/include/asm/kprobes.h
> > @@ -102,16 +102,6 @@ extern int kprobe_exceptions_notify(struct notifier_block *self,
> >  extern int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
> >  extern int kprobe_handler(struct pt_regs *regs);
> >  extern int kprobe_post_handler(struct pt_regs *regs);
> > -#ifdef CONFIG_KPROBES_ON_FTRACE
> > -extern int skip_singlestep(struct kprobe *p, struct pt_regs *regs,
> > -			   struct kprobe_ctlblk *kcb);
> > -#else
> > -static inline int skip_singlestep(struct kprobe *p, struct pt_regs *regs,
> > -				  struct kprobe_ctlblk *kcb)
> > -{
> > -	return 0;
> > -}
> > -#endif
> >  #else
> >  static inline int kprobe_handler(struct pt_regs *regs) { return 0; }
> >  static inline int kprobe_post_handler(struct pt_regs *regs) { return 0; }
> > diff --git a/arch/powerpc/kernel/kprobes-ftrace.c b/arch/powerpc/kernel/kprobes-ftrace.c
> > index 1b316331c2d9..3869b0e5d5c7 100644
> > --- a/arch/powerpc/kernel/kprobes-ftrace.c
> > +++ b/arch/powerpc/kernel/kprobes-ftrace.c
> > @@ -26,8 +26,8 @@
> >  #include <linux/ftrace.h>
> > 
> >  static nokprobe_inline
> > -int __skip_singlestep(struct kprobe *p, struct pt_regs *regs,
> > -		      struct kprobe_ctlblk *kcb, unsigned long orig_nip)
> > +int skip_singlestep(struct kprobe *p, struct pt_regs *regs,
> > +		    struct kprobe_ctlblk *kcb, unsigned long orig_nip)
> >  {
> >  	/*
> >  	 * Emulate singlestep (and also recover regs->nip)
> > @@ -44,16 +44,6 @@ int __skip_singlestep(struct kprobe *p, struct pt_regs *regs,
> >  	return 1;
> >  }
> > 
> > -int skip_singlestep(struct kprobe *p, struct pt_regs *regs,
> > -		    struct kprobe_ctlblk *kcb)
> > -{
> > -	if (kprobe_ftrace(p))
> > -		return __skip_singlestep(p, regs, kcb, 0);
> > -	else
> > -		return 0;
> > -}
> > -NOKPROBE_SYMBOL(skip_singlestep);
> > -
> >  /* Ftrace callback handler for kprobes */
> >  void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip,
> >  			   struct ftrace_ops *ops, struct pt_regs *regs)
> > @@ -82,7 +72,7 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip,
> >  		__this_cpu_write(current_kprobe, p);
> >  		kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> >  		if (!p->pre_handler || !p->pre_handler(p, regs))
> > -			__skip_singlestep(p, regs, kcb, orig_nip);
> > +			skip_singlestep(p, regs, kcb, orig_nip);
> 
> We can probably get rid of skip_singlestep() completely along with 
> orig_nip since instructions are always 4 bytes on powerpc. So, the 
> changes we do to nip should help to recover the value automatically.

Good point! Yes, skip_singlestep() is no more exported, so we just consolidate
it into kprobe_ftrace_handler() for simplifying operation.

Thank you!
> - Naveen

-- 
Masami Hiramatsu <[email-masked]>