Re: Linux Kernel GDB tracepoint module demo release
From: Michael Snyder
Date: Wed Aug 11 2010 - 17:11:01 EST
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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