[Bug kprobes/4384] New: Problem in making kprobe modules portable across all the archtecture.

[Bug kprobes/4384] New: Problem in making kprobe modules portable across all the archtecture.

[srinivasa at in dot ibm dot com]

When data symbols are not present in kernel image, one has to add dot(".")
before function name, that he wants to probe in kprobe module on ppc64. 
Hence kernel module may not become portable across all the architecture.

When data symbols are missing on ppc64,
====================
[root@llm27lp1 ~]# cat /proc/kallsyms | grep do_fork
c00000000006283c T .do_fork
==============================
kp.symbol_name = ".do_fork";
============================
But if data symbols were included, then it looks like this
================
llm27lp2:~ # cat /proc/kallsyms |grep do_fork
c00000000005de28 T .do_fork
c0000000005fbe88 D do_fork
======================
kp.symbol_name = ".do_fork";
===============================

Iam attaching patch here, which solves this problem. Please let me know your
comments on this.

Thanks
 Srinivasa DS

-- 
           Summary: Problem in making kprobe modules portable across all the
                    archtecture.
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: kprobes
        AssignedTo: systemtap at sources dot redhat dot com
        ReportedBy: srinivasa at in dot ibm dot com
                CC: ananth at in dot ibm dot com,anil dot s dot
                    keshavamurthy at intel dot com,jkenisto at us dot ibm
                    dot com,prasanna at in dot ibm dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=4384

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[Bug kprobes/4384] Problem in making kprobe modules portable across all the archtecture.

[srinivasa at in dot ibm dot com]

------- Additional Comments From srinivasa at in dot ibm dot com  2007-04-17 13:29 -------
Created an attachment (id=1725)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=1725&action=view)
Patch to solve this problem.

This patch just appends "." to the function name the user wants to probe and
hence user need not have to bother, whether data symbols are present or not.

Thanks 
 Srinivasa DS


-- 


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[Bug kprobes/4384] Problem in making kprobe modules portable across all the archtecture.

[ananth at in dot ibm dot com]

------- Additional Comments From ananth at in dot ibm dot com  2007-04-17 15:43 -------
Srinivasa,
The patch looks fine.... you'll need to fix the codingstyle:

 	}								\
+	else {								\
       ^^^^^
+		char dot_name[KSYM_NAME_LEN+1];				\
+		dot_name[0] = '.';					\
+		strncat(dot_name, name, KSYM_NAME_LEN);			\
+		addr = (kprobe_opcode_t *)kallsyms_lookup_name(dot_name); \
+	}								\
 }

Please include a short description and post it to powerpc-dev list for
inclusion. Feel free to put my signed-off once you've successfully tested the patch.

-- 


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[Bug kprobes/4384] Problem in making kprobe modules portable across all the archtecture.

[fche at redhat dot com]

------- Additional Comments From fche at redhat dot com  2007-04-17 17:27 -------
Note that this would not fix systemtap, as we do not use the kprobes-level symbol
lookup facilities.  It sounds like, for the PPC, systemtap itself should prefix
function symbols with "." unconditionally, and not treat it as a conditional 
fallback heuristic.


-- 


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[Bug kprobes/4384] Problem in making kprobe modules portable across all the archtecture.

[ananth at in dot ibm dot com]

------- Additional Comments From ananth at in dot ibm dot com  2007-04-18 04:50 -------
Subject: Re:  Problem in making kprobe modules portable across all the archtecture.

On Tue, Apr 17, 2007 at 04:27:38PM -0000, fche at redhat dot com wrote:
> 
> ------- Additional Comments From fche at redhat dot com  2007-04-17 17:27 -------
> Note that this would not fix systemtap, as we do not use the kprobes-level symbol
> lookup facilities.  It sounds like, for the PPC, systemtap itself should prefix
> function symbols with "." unconditionally, and not treat it as a conditional 
> fallback heuristic.

Yes, that would always work, but you may need to check the module:symbol
type address lookups.

That begs the question... till RHEL5, the compiler used in RHEL would
include both text and data symbols for powerpc. But, RHEL5 has some
compiler modifications that causes the data symbol (eg., "do_fork") to
be discarded and only the text symbol (".do_fork") is visible for
kallsyms lookup. Even upstream kernels built on RHEL5 have a similar
issue. Any specific reasons for this?


-- 


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[Bug kprobes/4384] Problem in making kprobe modules portable across all the archtecture.

[ananth at in dot ibm dot com]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|systemtap at sources dot    |srinivasa at in dot ibm dot
                   |redhat dot com              |com
             Status|NEW                         |ASSIGNED


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