Re: Linux kernel marker questions

[Mike Mason <mmlnx at us dot ibm dot com>]

David Smith wrote:
> Mike Mason wrote:
> > David,
> >
> > Is there enough marker support in CVS now that we can write scripts 
> > against it?  I tried using the latest CVS against a kernel with a few 
> > markers, but I'm seeing errors.
> >
> > Here's the script:
> > global sem_up_cnt
> > probe kernel.mark("sem_up") { sem_up_cnt++ }
> > probe end { printf("sem_up_cnt = %d\n", sem_up_cnt)}
> >
> > Here's the marker I'm trying to access in __up() in semaphore-sleepers.c:
> >
> > MARK(sem_down, "%ul", (unsigned long) sem);
> >
> > Here are the errors I'm seeing:
> >
> > semantic error: bad __markers_string section?
> > semantic error: no match for probe point while resolving probe point 
> > kernel.mark("sem_up")
> >
> > Should this work yet?
>
> Yes it should work - depending on which version of Mathieu's patches 
> you've got.  I've bet we've got differing versions if you are getting 
> the "bad __markers_string section" message.  I've been using the version 
> of Mathieu's patches that Andrew Morton has.  I can send you a copy of 
> the patches I've been using if you'd like.

I'm using a version of the Andrew's patches, but perhaps not the latest.  Please send me what you're using.

> One more thing - your marker is called "sem_down", but you look to be 
> putting a probe on "sem_up"...

Oops, cut-and-paste error.  I do have a "sem_up" marker as well.

BTW, what data can be accessed in a SystemTap marker probe handler?  Can it access the data defined by the marker or any local or global variables?

Thanks,
Mike