dprobes-list

[Dprobes-list] Segmentation violation compiling dprobes .rpn files

[Peter L. <p.l...@co...>]

I have been trying to get dprobes working to trace some kernel functions 
with LTT. 
 
I am using SuSE 9.2 Professional, but it does not seem to have the LTT 
patches against the kernel. So I pulled a kernel from SLES9, and 
compiled with all the appropriate switches in the .config and changes 
dprobes requires per the README.dpcc.  I can take an LTT trace with the 
default trace points. Since it uses dprobes under the hood, it is safe 
to assume dprobes is working in some fashion?
 
Compiling and running with the SLES9 kernel on SuSE 9.2 seems OK, but 
when I compile something like tut14.dpc or the examples out of the 
dprobes.lang man page, I just get a segmentation violation when it reads 
the symbol table in /usr/src/linux/vmlinux. 
 
dprobes itself seems OK, "dprobes -q -a -x" returns "No information 
returned." as it should. 
 
Please advise what to check to get dprobes working with custom probes. I 
really want to do what is close to the long example 6 back in dprobes.lang.

Is there a beginners guide to writeing and troubleshooting rpn files? 
Most of the stuff I have found is a high level overview of dprobes 
architecture, or really detailed advanced features, not much in between.

Regards, 
Peter

Re: [Dprobes-list] Segmentation violation compiling dprobes .rpn files

[Tom Z. <za...@us...>]

Peter Lauterbach writes:
 > I have been trying to get dprobes working to trace some kernel functions 
 > with LTT. 
 >  
 > I am using SuSE 9.2 Professional, but it does not seem to have the LTT 
 > patches against the kernel. So I pulled a kernel from SLES9, and 
 > compiled with all the appropriate switches in the .config and changes 
 > dprobes requires per the README.dpcc.  I can take an LTT trace with the 
 > default trace points. Since it uses dprobes under the hood, it is safe 
 > to assume dprobes is working in some fashion?

Hi,

LTT doesn't use dprobes under the hood, so you can't assume anything
about dprobes from the fact that LTT is working.

 >  
 > Compiling and running with the SLES9 kernel on SuSE 9.2 seems OK, but 
 > when I compile something like tut14.dpc or the examples out of the 
 > dprobes.lang man page, I just get a segmentation violation when it reads 
 > the symbol table in /usr/src/linux/vmlinux. 

There is a known problem with dpcc in SLES9.  I have a patch that was
supposed to go into SLES9 SP1 to fix that, but it was somehow lost in
the shuffle and never applied.  I'll send that to you tomorrow.

It sounds though that you're getting a segmentation violation with the
dprobes command itself - I haven't seen that, but it sounds like a
misconfiguration if so.

In any case, I'll be happy to help you get it all working and your
custom events out of dprobes and into LTT - I know it all works given
the proper setup, as I've done the same thing myself.  I'll send
more info along with the dpcc patch tomorrow...

Tom