probing based on kernel source

probing based on kernel source

[Jun Koi]

Hi,

Is it possible to probe a place coresponding to a particular line of a
particular file in Linux kernel souce code? If so, what is the syntax?

Thanks a lot,
Jun

Re: probing based on kernel source

[Wenji Huang]

Jun Koi wrote:
> Hi,
> 
> Is it possible to probe a place coresponding to a particular line of a
> particular file in Linux kernel souce code? If so, what is the syntax?
> 
> Thanks a lot,
> Jun
See reference
http://sourceware.org/systemtap/langref/

4.2.2 kernel.statement, module().statement
The .statement variant places a probe at the exact spot, exposing those 
local variables that are visible there.

General syntax:

     kernel.statement("func@file:linenumber")
     module("modname").statement("func@file:linenumber")

Example:

     # Refers to the statement at line 2917 within the
     # kernel/sched.c file:
     kernel.statement("*@kernel/sched.c:2917")

Regards,
Wenji

Re: probing based on kernel source

[Ananth N Mavinakayanahalli]

On Tue, Sep 09, 2008 at 01:46:13PM +0900, Jun Koi wrote:
> Hi,
> 
> Is it possible to probe a place coresponding to a particular line of a
> particular file in Linux kernel souce code? If so, what is the syntax?

See
http://sourceware.org/systemtap/langref/node6.html#SECTION00062200000000000000

If the particular line you are trying to probe can't be probed due to
compiler optimizations, etc., stap will give you alternatives too.

Ananth

Re: probing based on kernel source

[Jun Koi]

On Tue, Sep 9, 2008 at 1:55 PM, Ananth N Mavinakayanahalli
<ananth@in.ibm.com> wrote:
> On Tue, Sep 09, 2008 at 01:46:13PM +0900, Jun Koi wrote:
>> Hi,
>>
>> Is it possible to probe a place coresponding to a particular line of a
>> particular file in Linux kernel souce code? If so, what is the syntax?
>
> See
> http://sourceware.org/systemtap/langref/node6.html#SECTION00062200000000000000
>
> If the particular line you are trying to probe can't be probed due to
> compiler optimizations, etc., stap will give you alternatives too.

So I suppose that stap returns a list of (kernel) addresses that might
be suitable to put the probe? If so, how can we know which one is
correct??

Thanks,
Jun

Re: probing based on kernel source

[Ananth N Mavinakayanahalli]

On Tue, Sep 09, 2008 at 02:54:06PM +0900, Jun Koi wrote:
> On Tue, Sep 9, 2008 at 1:55 PM, Ananth N Mavinakayanahalli
> <ananth@in.ibm.com> wrote:
> > On Tue, Sep 09, 2008 at 01:46:13PM +0900, Jun Koi wrote:
> >> Hi,
> >>
> >> Is it possible to probe a place coresponding to a particular line of a
> >> particular file in Linux kernel souce code? If so, what is the syntax?
> >
> > See
> > http://sourceware.org/systemtap/langref/node6.html#SECTION00062200000000000000
> >
> > If the particular line you are trying to probe can't be probed due to
> > compiler optimizations, etc., stap will give you alternatives too.
> 
> So I suppose that stap returns a list of (kernel) addresses that might
> be suitable to put the probe? If so, how can we know which one is
> correct??

Please try the suggestion.. it returns alternative line numbers not
virtual addresses, and that, only if your specified line number can't be
probed. In that case, you'll need to take the call which one of the
alternatives is appropriate.

Ananth

Re: probing based on kernel source

[Theodore Tso]

On Tue, Sep 09, 2008 at 11:36:29AM +0530, Ananth N Mavinakayanahalli wrote:
> > So I suppose that stap returns a list of (kernel) addresses that might
> > be suitable to put the probe? If so, how can we know which one is
> > correct??
> 
> Please try the suggestion.. it returns alternative line numbers not
> virtual addresses, and that, only if your specified line number can't be
> probed. In that case, you'll need to take the call which one of the
> alternatives is appropriate.

When did stap started doing this?  I don't recall it providing
alternate line numbers the last time I tried it.  Just as a gentle
reminder, if something requires using a development snapshot of stap,
it's good to mention that.  Some poeple are still using whatever
version of stap was packaged with their distribution.  (Remember, it
wasn't *all* that long ago that people could easily build stap at
least on some distributions, and when pressed, the party line was that
was the distribution's responsibility and users should use whatever
their distribution packaged up for them --- or switch to another
distribution.)

	   	    	     	  	- Ted

Re: probing based on kernel source

[Masami Hiramatsu]

Theodore Tso wrote:
> On Tue, Sep 09, 2008 at 11:36:29AM +0530, Ananth N Mavinakayanahalli wrote:
>>> So I suppose that stap returns a list of (kernel) addresses that might
>>> be suitable to put the probe? If so, how can we know which one is
>>> correct??
>> Please try the suggestion.. it returns alternative line numbers not
>> virtual addresses, and that, only if your specified line number can't be
>> probed. In that case, you'll need to take the call which one of the
>> alternatives is appropriate.
> 
> When did stap started doing this?  I don't recall it providing
> alternate line numbers the last time I tried it.  Just as a gentle
> reminder, if something requires using a development snapshot of stap,
> it's good to mention that.  Some poeple are still using whatever
> version of stap was packaged with their distribution.  (Remember, it
> wasn't *all* that long ago that people could easily build stap at
> least on some distributions, and when pressed, the party line was that
> was the distribution's responsibility and users should use whatever
> their distribution packaged up for them --- or switch to another
> distribution.)

Hi Ted,

According to systemtap/Changelog,
---
2007-08-24  Frank Ch. Eigler  <fche@redhat.com>

        PR 4899
        * tapsets.cxx (dwflpp::has_single_line_record): Extended,
        abstraction violated.
        (iterate_over_srcfile_lines): Remove exactly line number match
        logic.  Improve error message to offered better-checked alternative
        line numbers.
        (query_srcfile_line): Whoops, pass scope_die down for statement("...")
        probes, to enable $target var processing.
---
From here, maybe that feature was merged. And also,
---
2007-08-14  David Smith  <dsmith@redhat.com>
[...]
        * configure.ac: Version increase to 0.6 and checks for libcap
        availability.  Removed stp_check reference.
        * configure: Regenerated.
        * stp_check.in: Removed.
---
So, you can use it with stap version 0.6 or later.

Thank you,


-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com