Date:	Thu, 02 Apr 2009 13:24:05 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Jim Keniston <jkenisto@...ibm.com>
CC:	kvm@...r.kernel.org, systemtap-ml <systemtap@...rces.redhat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer

Hi,

Here are the patches of kprobe-based event tracer for x86, version 4.

This version supports only x86(-32/-64) (If someone is interested in
porting this to other architectures, he just needs to port
kprobes/kretprobes and ptrace enhancement[PATCH 2/6]).

I added x86 insn decoder on this version. It might be better
integrated with KVM's decoder, and kprobes x86 code should be
rewritten with it.


This can be applied on the linux-2.6-tip tree.

This patchset includes following changes:
- Fix kernel_trap_sp() on x86 according to systemtap runtime. [1/6]
- Add arch-dep register and stack fetching functions [2/6]
- Add x86 instruction decoder [3/6]
- Check insertion point safety in kprobe [4/6]
- Add kprobe-tracer plugin [5/6]
- Support fetching various status (register/stack/memory/etc.) [6/6]

Done items:
- Add kernel_trap_sp() and fetch_*() on other archs.
- Support name-based register fetching (ax, bx, and so on)
- Support indirect memory fetch from registers etc.
- Check insertion point safety by using instruction decoder.

Future items:
- .init function tracing support.
- Support primitive types(long, ulong, int, uint, etc) for args.


kprobe-based event tracer
---------------------------

This tracer is similar to the events tracer which is based on Tracepoint
infrastructure. Instead of Tracepoint, this tracer is based on kprobes(kprobe
and kretprobe). It probes anywhere where kprobes can probe(this means, all
functions body except for __kprobes functions).

Unlike the function tracer, this tracer can probe instructions inside of
kernel functions. It allows you to check which instruction has been executed.

Unlike the Tracepoint based events tracer, this tracer can add new probe points
on the fly.

Similar to the events tracer, this tracer doesn't need to be activated via
current_tracer, instead of that, just set probe points via
/debug/tracing/kprobe_probes.

Synopsis of kprobe_probes:
  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 do_sys_open a0 a1 a2 a3 > /debug/tracing/kprobe_probes

 This sets a kprobe on the top of do_sys_open() function with recording
1st to 4th arguments.

  echo r do_sys_open rv rp >> /debug/tracing/kprobe_probes

 This sets a kretprobe on the return point of do_sys_open() function with
recording return value and return address.

  echo > /debug/tracing/kprobe_probes

 This clears all probe points. and you can see the traced information via
/debug/tracing/trace.

  cat /debug/tracing/trace
# tracer: nop
#
#           TASK-PID    CPU#    TIMESTAMP  FUNCTION
#              | |       |          |         |
           <...>-2376  [001]   262.389131: do_sys_open: @do_sys_open+0 0xffffff9c 0x98db83e 0x8880 0x0
           <...>-2376  [001]   262.391166: sys_open: <-do_sys_open+0 0x5 0xc06e8ebb
           <...>-2376  [001]   264.384876: do_sys_open: @do_sys_open+0 0xffffff9c 0x98db83e 0x8880 0x0
           <...>-2376  [001]   264.386880: sys_open: <-do_sys_open+0 0x5 0xc06e8ebb
           <...>-2084  [001]   265.380330: do_sys_open: @do_sys_open+0 0xffffff9c 0x804be3e 0x0 0x1b6
           <...>-2084  [001]   265.380399: sys_open: <-do_sys_open+0 0x3 0xc06e8ebb

 @SYMBOL means that kernel hits a probe, and <-SYMBOL means kernel returns
from SYMBOL(e.g. "sys_open: <-do_sys_open+0" means kernel returns from
do_sys_open to sys_open).


 Documentation/ftrace.txt      |   70 ++++
 arch/x86/include/asm/insn.h   |  130 +++++++
 arch/x86/include/asm/ptrace.h |   70 ++++-
 arch/x86/kernel/kprobes.c     |   51 +++
 arch/x86/kernel/ptrace.c      |   59 +++
 arch/x86/lib/Makefile         |    1 +
 arch/x86/lib/insn.c           |  627 ++++++++++++++++++++++++++++++++
 kernel/trace/Kconfig          |    9 +
 kernel/trace/Makefile         |    1 +
 kernel/trace/trace_kprobe.c   |  789 +++++++++++++++++++++++++++++++++++++++++
 10 files changed, 1805 insertions(+), 2 deletions(-)

Thank you,


-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com



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