Re: [PATCH v9.1 07/11] tracing/probes: Add $$args meta argument for all function args

Masami Hiramatsu
2023-05-14T03:02:46Z

On Fri, 5 May 2023 17:48:56 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Tue, 2 May 2023 11:18:21 +0900
> "Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:
>
> > From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> >
> > Add the '$$args' meta fetch argument for function-entry probe events. This
>
> Hmm, couldn't we just use $args ? That would be different from $arg1,
> $arg2, etc.
>
> The $$ to me would be either the bash pid of current, or perhaps it would
> be just to use a dollar sign. I don't see the precedence of $$args being a
> "full expand".

OK, I just thought it required a bit special prefix because it will be
expanded to several arguments (it is different from other $-params) and,
internally, it should be handled in the different path from the other
$-params. But the latter is internal reason, we should not care about that.
(of course I will leave a comment it.)

Thank you!

>
> -- Steve
>
>
> > will be expanded to the all arguments of the function and the tracepoint
> > using BTF function argument information.
> >
> > e.g.
> > # echo 'p vfs_read $$args' >> dynamic_events
> > # echo 'f vfs_write $$args' >> dynamic_events
> > # echo 't sched_overutilized_tp $$args' >> dynamic_events
> > # cat dynamic_events
> > p:kprobes/p_vfs_read_0 vfs_read file=file buf=buf count=count pos=pos
> > f:fprobes/vfs_write__entry vfs_write file=file buf=buf count=count pos=pos
> > t:tracepoints/sched_overutilized_tp sched_overutilized_tp rd=rd overutilized=overutilized
> >
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > ---

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>