[lttng-dev] New LTTNG user : Question about Kprobe and function commandline options

[Mathieu Desnoyers]

* tarek slaymia (tarek.slaymia at gmail.com) wrote:
> Hi,
> 
> can we retrieve kernel data structures addresses or contents using LTTng ?

With "--probe", not yet. With static tracepoints, yes, but the
instrumentation needs to be either already in or added to the kernel
code.

Thanks,

Mathieu

> 
> regards.
> 
> 
> 2013/6/23 Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> 
> > * Jessica Foest (jessica.foest at gmail.com) wrote:
> > > Hi,
> > > i tried to apply kprobe to a system call , so i used probe and function
> > > option :
> > >
> > > lttng enable-event aname -k --probe sys_open+0x0
> > > this command returns ip value
> > >
> > > lttng enable-event aname -k --function sys_open
> > > this command returns ip and parent_ip values .
> > >
> > > what does these values ip and parent_ip means ?
> >
> > ip: instruction pointer of the function,
> > parent_ip: instruction pointer of the caller.
> >
> > >
> > > I try to apply probe and function options to some kernel symbols like
> > > initialized date (like xen_vcpu_info symbol), read only data (like
> > > linux_prob_banner symbol) and code (like reserve_ebda_region symbol) it
> > > displays to me : Enable kernel event failed ,warning some command went(s)
> > > wrong.
> > > Did i make a mistake or it's a limitation in LTTng ?
> >
> > It's kprobes: you can only add breakpoints to code, not data.
> >
> > Thanks,
> >
> > Mathieu
> >
> > > regards.
> >
> > > _______________________________________________
> > > lttng-dev mailing list
> > > lttng-dev at lists.lttng.org
> > > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
> >
> >
> > --
> > Mathieu Desnoyers
> > EfficiOS Inc.
> > http://www.efficios.com
> >
> > _______________________________________________
> > lttng-dev mailing list
> > lttng-dev at lists.lttng.org
> > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
> >

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com