Re: Linux Kernel GDB tracepoint module demo release

[Hui Zhu <teawater@gmail.com>]

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@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
>
>