linux-kernel - Re: [PATCH -tip v5 7/7] tracing: add arguments support on kprobe-based event tracer

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Date:	Mon, 11 May 2009 10:35:31 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <mhiramat@...hat.com>
cc:	Ingo Molnar <mingo@...e.hu>, lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	kvm <kvm@...r.kernel.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH -tip v5 7/7] tracing: add arguments support on kprobe-based
 event tracer


On Fri, 8 May 2009, Masami Hiramatsu wrote:

> Support following probe arguments and add fetch functions on kprobe-based
> event tracer.
> 
>   %REG  : Fetch register REG
>   sN    : Fetch Nth entry of stack (N >= 0)
>   @ADDR : Fetch memory at ADDR (ADDR should be in kernel)
>   @SYM[+|-offs] : Fetch memory at SYM +|- offs (SYM should be a data symbol)
>   aN    : Fetch function argument. (N >= 0)
>   rv    : Fetch return value.
>   ra    : Fetch return address.
>   +|-offs(FETCHARG) : fetch memory at FETCHARG +|- offs address.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...hat.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ananth N Mavinakayanahalli <ananth@...ibm.com>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> ---
> 
>  Documentation/trace/ftrace.txt |   47 +++-
>  kernel/trace/trace_kprobe.c    |  431 ++++++++++++++++++++++++++++++++++++++--
>  2 files changed, 441 insertions(+), 37 deletions(-)
> 
> diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
> index 2b8ead6..ce91398 100644
> --- a/Documentation/trace/ftrace.txt

The Documentation/trace/ftrace.txt file is getting too big. Could you make 
a separate "Documentation/trace/kprobes.txt file, and split out the 
kprobe bits.

Thanks,

-- Steve


> +++ b/Documentation/trace/ftrace.txt
> @@ -1329,17 +1329,34 @@ current_tracer, instead of that, just set probe points via
>  /debug/tracing/kprobe_events.
>  
>  Synopsis of kprobe_events:
> -  p SYMBOL[+offs|-offs]|MEMADDR	: set a probe
> -  r SYMBOL[+0]			: set a return probe
> +  p SYMBOL[+offs|-offs]|MEMADDR [FETCHARGS]	: set a probe
> +  r SYMBOL[+0] [FETCHARGS]			: set a return probe
> +
> + FETCHARGS:
> +  %REG	: Fetch register REG
> +  sN	: Fetch Nth entry of stack (N >= 0)
> +  @ADDR	: Fetch memory at ADDR (ADDR should be in kernel)
> +  @SYM[+|-offs]	: Fetch memory at SYM +|- offs (SYM should be a data symbol)
> +  aN	: Fetch function argument. (N >= 0)(*)
> +  rv	: Fetch return value.(**)
> +  ra	: Fetch return address.(**)
> +  +|-offs(FETCHARG) : fetch memory at FETCHARG +|- offs address.(***)
> +
> +  (*) aN may not correct on asmlinkaged functions and at the middle of
> +      function body.
> +  (**) only for return probe.
> +  (***) this is useful for fetching a field of data structures.
>  
>  E.g.
> -  echo p sys_open > /debug/tracing/kprobe_events
> +  echo p do_sys_open a0 a1 a2 a3 > /debug/tracing/kprobe_events
>  
> - This sets a kprobe on the top of sys_open() function.
> + This sets a kprobe on the top of do_sys_open() function with recording
> +1st to 4th arguments.
>  
> -  echo r sys_open >> /debug/tracing/kprobe_events
> +  echo r do_sys_open rv ra >> /debug/tracing/kprobe_events
>  
> - This sets a kretprobe on the return point of sys_open() function.
> + This sets a kretprobe on the return point of do_sys_open() function with
> +recording return value and return address.
>  
>    echo > /debug/tracing/kprobe_events
>  
--
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