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[TOOL] c2kpe: C expression to kprobe event format converter

From: Masami Hiramatsu <mhiramat at redhat dot com>
To: Ingo Molnar <mingo at elte dot hu>, Steven Rostedt <rostedt at goodmis dot org>, lkml <linux-kernel at vger dot kernel dot org>
Cc: Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Avi Kivity <avi at redhat dot com>, Andi Kleen <ak at linux dot intel dot com>, Christoph Hellwig <hch at infradead dot org>, "Frank Ch. Eigler" <fche at redhat dot com>, Frederic Weisbecker <fweisbec at gmail dot com>, "H. Peter Anvin" <hpa at zytor dot com>, Jason Baron <jbaron at redhat dot com>, Jim Keniston <jkenisto at us dot ibm dot com>, "K.Prasad" <prasad at linux dot vnet dot ibm dot com>, Lai Jiangshan <laijs at cn dot fujitsu dot com>, Li Zefan <lizf at cn dot fujitsu dot com>, PrzemysÅawPaweÅczyk <przemyslaw at pawelczyk dot it>, Roland McGrath <roland at redhat dot com>, Sam Ravnborg <sam at ravnborg dot org>, Srikar Dronamraju <srikar at linux dot vnet dot ibm dot com>, Tom Zanussi <tzanussi at gmail dot com>, Vegard Nossum <vegard dot nossum at gmail dot com>, systemtap <systemtap at sources dot redhat dot com>, kvm <kvm at vger dot kernel dot org>, DLE <dle-develop at lists dot sourceforge dot net>
Date: Thu, 13 Aug 2009 16:59:19 -0400
Subject: [TOOL] c2kpe: C expression to kprobe event format converter
References: <20090813203403.31965.20973.stgit@localhost.localdomain>

This program converts probe point in C expression to kprobe event
format for kprobe-based event tracer. This helps to define kprobes
events by C source line number or function name, and local variable
name. Currently, this supports only x86(32/64) kernels.


Compile
--------
Before compilation, please install libelf and libdwarf development
packages.
(e.g. elfutils-libelf-devel and libdwarf-devel on Fedora)

$ gcc -Wall -lelf -ldwarf c2kpe.c -o c2kpe


Synopsis
--------
 $ c2kpe [options] FUNCTION[+OFFS][@SRC] [VAR [VAR ...]]
 or
 $ c2kpe [options] @SRC:LINE [VAR [VAR ...]]

  FUNCTION:	Probing function name.
  OFFS:		Offset in bytes.
  SRC:		Source file path.
  LINE:		Line number
  VAR:		Local variable name.
  options:
  -r KREL	Kernel release version (e.g. 2.6.31-rc5)
  -m DEBUGINFO	Dwarf-format binary file (vmlinux or kmodule)


Example
-------
 $ c2kpe sys_read fd buf count
 sys_read+0 %di %si %dx

 $ c2kpe @mm/filemap.c:339 inode pos
 sync_page_range+125 -48(%bp) %r14


Example with kprobe-tracer
--------------------------
Since C expression may be converted multiple results, I recommend to use
readline.

 $ c2kpe sys_read fd buf count | while read i; do \
   echo "p $i" > $DEBUGFS/tracing/kprobe_events ;\
   done


Note
----
 - This requires a kernel compiled with CONFIG_DEBUG_INFO.
 - Specifying @SRC speeds up c2kpe, because we can skip CUs which don't
   include specified SRC file.
 - c2kpe doesn't check whether the offset byte is correctly on the
   instruction boundary. I recommend you to use @SRC:LINE expression for
   tracing function body.
 - This tool doesn't search kmodule file. You need to specify kmodule
   file if you want to probe it.


TODO
----
 - Fix bugs.
 - Support multiple probepoints from stdin.
 - Better kmodule support.
 - Use elfutils-libdw?
 - Merge into trace-cmd or perf-tools?

--
Masami Hiramatsu

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

e-mail: mhiramat@redhat.com

Attachment: c2kpe.c
Description: Text document

References:
- [PATCH -tip v14 00/12] tracing: kprobe-based event tracer and x86 instruction decoder
  - From: Masami Hiramatsu

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