linux-kernel - Re: [PATCHv4] kprobes: Introduce kprobe_handle

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Date:	Thu, 10 Jan 2008 00:16:21 +0100
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Harvey Harrison <harvey.harrison@...il.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	David Miller <davem@...emloft.net>, hskinnemoen@...el.com,
	schwidefsky@...ibm.com, tony.luck@...el.com,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	David Wilder <dwilder@...ibm.com>, jkenisto@...ibm.com
Subject: Re: [PATCHv4] kprobes: Introduce kprobe_handle_fault()

>  arch/avr32/mm/fault.c   |   21 +--------------------
>  arch/ia64/mm/fault.c    |   24 +-----------------------
>  arch/powerpc/mm/fault.c |   25 +------------------------
>  arch/s390/mm/fault.c    |   25 +------------------------
>  arch/sparc64/mm/fault.c |   23 +----------------------
>  arch/x86/mm/fault_64.c  |   23 ++---------------------
>  include/linux/kprobes.h |   17 +++++++++++++++++
>  7 files changed, 24 insertions(+), 134 deletions(-)

Somehow I think you missed arch/x86/mm/fault_32.c :)

> This uncovered a possible bug in the s390 version as that purely
> copied the x86 version unconditionally passing 14 as the trapnr
> rather than the error_code parameter.

> diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
> index 2456b52..a9033cf 100644
> --- a/arch/s390/mm/fault.c
> +++ b/arch/s390/mm/fault.c
> @@ -51,29 +51,6 @@ extern int sysctl_userprocess_debug;
> 
>  extern void die(const char *,struct pt_regs *,long);
> 
> -#ifdef CONFIG_KPROBES
> -static inline int notify_page_fault(struct pt_regs *regs, long err)
> -{
> -	int ret = 0;
> -
> -	/* kprobe_running() needs smp_processor_id() */
> -	if (!user_mode(regs)) {
> -		preempt_disable();
> -		if (kprobe_running() && kprobe_fault_handler(regs, 14))
> -			ret = 1;
> -		preempt_enable();
> -	}
> -
> -	return ret;
> -}
> -#else
> -static inline int notify_page_fault(struct pt_regs *regs, long err)
> -{
> -	return 0;
> -}
> -#endif
> -
> -
>  /*
>   * Unlock any spinlocks which will prevent us from getting the
>   * message out.
> @@ -309,7 +286,7 @@ do_exception(struct pt_regs *regs, unsigned long error_code, int write)
>  	int si_code;
>  	int fault;
> 
> -	if (notify_page_fault(regs, error_code))
> +	if (kprobe_handle_fault(regs, 14))
>  		return;

Uhm.. yes. 14 is HFP-Significance exception. That doesn't make too much
sense. Passing error_code here would be the right thing to do.
Also I just checked with David Wilder: system tap itself doesn't have any
fault handlers. So it should be safe to change this.
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