Question about kernel module debug

[Yuxin_Zhuang at emc dot com]

Hi,Systemtap users:

I've installed systemtap 0.5.8 on RHEL4 with kernel 2.6.9-42. I wanna
use systemtap to debug a kernel module which is not built into the
kernel and I got some questions.

1. Is the 'debuginfo' of the module needed by systemtap is just the
stuff created by gcc with option '-g'? Will an additional '-O2' make a
lot of difference?

2. I've put the '.ko' file which is built with options '-g -O2' under
the proper search path and created a symbol link with the suffix
'.ko.debug' to it. Before the systemtap is run, the module has been
loaded and works well. But systemtap reported that it can not find the
module's debuginfo. 
The output is: 

Pass 1: parsed user script and 25 library script(s) in
80usr/10sys/136real ms.
semantic error: cannot find module my_module debuginfo: r_offset is
bogus
semantic error: no match for probe point
while: resolving probe point module("my_module").function("*")
Pass 2: analyzed script: 2 probe(s), 0 function(s), 0 global(s) in
0usr/30sys/43real ms.
Pass 2: analysis failed.  Try again with more '-v' (verbose) options.

And I straced the stap, the output before printing the error is as
follows :

......
open("/usr/lib/systemtap/../lib/systemtap/libebl_i386.so", O_RDONLY) =
-1 ENOENT (No such file or directory)
open("/usr/lib/systemtap/libebl_i386.so", O_RDONLY) = 5
read(5, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0`\6\0\000"...,
512) = 512
fstat64(5, {st_mode=S_IFREG|0755, st_size=7724, ...}) = 0
old_mmap(NULL, 10596, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 5,
0) = 0xcf5000
old_mmap(0xcf7000, 4096, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 5, 0x1000) = 0xcf7000
close(5)                                = 0
open("/lib/modules/2.6.9-42.ELsmp/kernel/fs/my_module/my_module.ko.debug
", O_RDONLY|O_LARGEFILE) = 5
fcntl64(5, F_GETFL)                     = 0x8000 (flags
O_RDONLY|O_LARGEFILE)
fstat64(5, {st_mode=S_IFREG|0755, st_size=2734531, ...}) = 0
mmap2(NULL, 2734531, PROT_READ|PROT_WRITE, MAP_PRIVATE, 5, 0) =
0xb589f000
open("/sys/module/my_module/sections/.text", O_RDONLY) = 6
fstat64(6, {st_mode=S_IFREG|0444, st_size=4096, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0) = 0xb589e000
read(6, "0xd0e0c000\n", 4096)           = 11
read(6, "", 4096)                       = 0
close(6)                                = 0
munmap(0xb589e000, 4096)                = 0
open("/sys/module/my_module/sections/.rodata", O_RDONLY) = 6
fstat64(6, {st_mode=S_IFREG|0444, st_size=4096, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0) = 0xb589e000
read(6, "0xd0e29c90\n", 4096)           = 11
read(6, "", 4096)                       = 0
close(6)                                = 0
munmap(0xb589e000, 4096)                = 0
write(2, "semantic error: ", 16semantic error: )        = 16
...... 

What can be the reason for the error?? 
Any suggestions will be appreciated, thanks a lot!


ZHUANG Yuxin