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

[Masami Hiramatsu]

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

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