linux-kernel - Re: Linux Kernel GDB tracepoint module demo release

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Date:	Thu, 12 Aug 2010 10:13:49 -0700
From:	Michael Snyder <msnyder@...are.com>
To:	Hui Zhu <teawater@...il.com>
CC:	"gdb@...rceware.org" <gdb@...rceware.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Linux Kernel GDB tracepoint module demo release

Very interesting then.  I'd like to see you continue this work.


Hui Zhu wrote:
> KGTP use Kprobes, I think it can work with most part of kernel.
> 
> Thanks,
> Hui
> 
> On Thu, Aug 12, 2010 at 05:10, Michael Snyder <msnyder@...are.com> wrote:
>> Actually, this is kind of interesting.
>> Can your system set a tracepoint at any arbitrary location in the
>> kernel?  If so, I think that makes it more powerful than existing
>> systems such as LTTng, which can only trace statically pre-determined
>> locations.
>>
>> Hui Zhu wrote:
>>> Hi,
>>>
>>> GDB Tracepoint
>>> (http://sourceware.org/gdb/current/onlinedocs/gdb/Tracepoints.html)
>>> is new feature that make GDB can debug real-time program.
>>> I think this feature is very fit for debug Linux Kernel.  So I make a
>>> lkm to make kernel support it. You can get it in
>>> https://code.google.com/p/kgtp/
>>>
>>> I just release the demo for it.  It just support collect $reg in
>>> x86_32.  I will add the other tracepoint support in the future.
>>>
>>> For example:
>>> tar vxjf gtp_20100811.tar.bz2
>>> cd gtp
>>> make
>>> insmod gtp.ko
>>> gdb ./vmlinux
>>> GNU gdb (GDB) 7.2.50.20100720-cvs
>>> Copyright (C) 2010 Free Software Foundation, Inc.
>>> License GPLv3+: GNU GPL version 3 or later
>>> <http://gnu.org/licenses/gpl.html>
>>> This is free software: you are free to change and redistribute it.
>>> There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
>>> and "show warranty" for details.
>>> This GDB was configured as "i686-pc-linux-gnu".
>>> For bug reporting instructions, please see:
>>> <http://www.gnu.org/software/gdb/bugs/>...
>>> Reading symbols from /vmlinux...done.
>>> (gdb) target remote /proc/gtp
>>> Remote debugging using /proc/gtp
>>> 0x00000000 in ?? ()
>>> (gdb) trace vfs_readdir
>>> Tracepoint 1 at 0xc01a1ac0: file
>>> /home/teawater/kernel/linux-2.6/fs/readdir.c, line 23.
>>> (gdb) actions
>>> Enter actions for tracepoint 1, one per line.
>>> End with a line saying just "end".
>>>> collect $reg
>>>> end
>>> (gdb) tstart
>>> (gdb) shell ls
>>> (gdb) tstop
>>> (gdb) tfind
>>> Found trace frame 0, tracepoint 1
>>> #0  0xc01a1ac1 in vfs_readdir (file=0xc5528d00, filler=0xc01a1900
>>> <filldir64>,
>>>    buf=0xc0d09f90) at /home/teawater/kernel/linux-2.6/fs/readdir.c:23
>>> 23      /home/teawater/kernel/linux-2.6/fs/readdir.c: No such file or
>>> directory.
>>>        in /home/teawater/kernel/linux-2.6/fs/readdir.c
>>> (gdb) info reg
>>> eax            0xc5528d00       -984445696
>>> ecx            0xc0d09f90       -1060069488
>>> edx            0xc01a1900       -1072031488
>>> ebx            0xfffffff7       -9
>>> esp            0xc0d09f8c       0xc0d09f8c
>>> ebp            0x0      0x0
>>> esi            0x8061480        134616192
>>> edi            0xc5528d00       -984445696
>>> eip            0xc01a1ac1       0xc01a1ac1 <vfs_readdir+1>
>>> eflags         0x286    [ PF SF IF ]
>>> cs             0x60     96
>>> ss             0x8061480        134616192
>>> ds             0x7b     123
>>> es             0x7b     123
>>> fs             0x0      0
>>> gs             0x0      0
>>> (gdb) tfind
>>> Found trace frame 1, tracepoint 1
>>> 0xc01a1ac1      23      in /home/teawater/kernel/linux-2.6/fs/readdir.c
>>> (gdb) info reg
>>> eax            0xc5528d00       -984445696
>>> ecx            0xc0d09f90       -1060069488
>>> edx            0xc01a1900       -1072031488
>>> ebx            0xfffffff7       -9
>>> esp            0xc0d09f8c       0xc0d09f8c
>>> ebp            0x0      0x0
>>> esi            0x8061480        134616192
>>> edi            0xc5528d00       -984445696
>>> eip            0xc01a1ac1       0xc01a1ac1 <vfs_readdir+1>
>>> eflags         0x286    [ PF SF IF ]
>>> cs             0x60     96
>>> ss             0x8061480        134616192
>>> ds             0x7b     123
>>> es             0x7b     123
>>> fs             0x0      0
>>> gs             0x0      0
>>> (gdb) tfind
>>> Found trace frame 2, tracepoint 1
>>> #0  0xc01a1ac1 in vfs_readdir (file=0xc5528300, filler=0xc01a19e0
>>> <filldir>,
>>>    buf=0xc6c2df90) at /home/teawater/kernel/linux-2.6/fs/readdir.c:23
>>> 23      in /home/teawater/kernel/linux-2.6/fs/readdir.c
>>> (gdb)
>>> Found trace frame 3, tracepoint 1
>>> 0xc01a1ac1      23      in /home/teawater/kernel/linux-2.6/fs/readdir.c
>>> (gdb)
>>> Target failed to find requested trace frame.
>>> (gdb) quit
>>> A debugging session is active.
>>>
>>>        Inferior 1 [Remote target] will be killed.
>>>
>>> Quit anyway? (y or n) y
>>>
>>> Thanks,
>>> Hui
>>

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