Re: [PATCH tracing/kprobes v3 4/7] tracing/kprobes: Avoid field name confliction

[Masami Hiramatsu <mhiramat at redhat dot com>]

Frederic Weisbecker wrote:
> On Mon, Oct 12, 2009 at 03:13:51PM -0400, Masami Hiramatsu wrote:
> > Frederic Weisbecker wrote:
> > > The conflict issue might not be obvious for a user desperately trying to set
> > > a kprobe. Even for other failcases, it might not be obvious (blacklisted
> > > symbols, syntax errors...)
> > >
> > > May be should you improve the error granularity and print a KERN_DEBUG
> > > message?
> >
> > Agreed, and kprobes error handling should be improved too (in the most cases,
> > it just returns -EINVAL).
> >
> > Thank you.
>
>
> And btw, I'm enable to create a probe, neither through ftrace nor perf:
>
> 	$ sudo ./perf probe -P 'p:sys_close sys_close $retval'
> 	Adding new event: p:sys_close sys_close+0 $retval
>
> 	Error: Failed to create event: Invalid argument
>
>
> 	# echo 'p:sys_open sys_open $retval'>  /debug/tracing/kprobe_events
> 	bash: echo: write error : Invalid argument
>
> I suspect I missed something very obvious with the syntax :)

Ah, only kretprobe events can use $retval :-)
So, you should specify 'r' instead of 'p'.

-P 'r:sys_close sys_close $retval'


> I've applied your patches in:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/random-tracing.git
> 	tracing/kprobes
>
> Thanks.

Thank you!

--
Masami Hiramatsu

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

e-mail: mhiramat@redhat.com