Re: Linux Kernel GDB tracepoint module demo release

[Michael Snyder]

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@xxxxxxxxxx> 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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