linux-kernel - Re: [RFC PATCH -tip v5 18/27] powerpc/kprobes: Don't call the ->break

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Date:   Thu, 07 Jun 2018 17:07:00 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "H . Peter Anvin" <hpa@...or.com>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Ingo Molnar <mingo@...hat.com>,
        Paul Mackerras <paulus@...ba.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC PATCH -tip v5 18/27] powerpc/kprobes: Don't call the
 ->break_handler() in arm kprobes code

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 <mhiramat@...nel.org>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
> Cc: linuxppc-dev@...ts.ozlabs.org
> ---
>  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...
Acked-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>

- 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.

- Naveen