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

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Date:   Sun, 14 May 2023 12:02:36 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Florent Revest <revest@...omium.org>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Martin KaFai Lau <martin.lau@...ux.dev>, bpf@...r.kernel.org
Subject: Re: [PATCH v9.1 07/11] tracing/probes: Add $$args meta argument for
 all function args

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

> On Tue,  2 May 2023 11:18:21 +0900
> "Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:
> 
> > From: Masami Hiramatsu (Google) <mhiramat@...nel.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@...nel.org>
> > ---


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