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From: Michael Snyder on 12 Aug 2010 13:20
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(a)vmware.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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