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SubjectRe: Linux Kernel GDB tracepoint module demo release
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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