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

[Mathieu Desnoyers]

* 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