linux-kernel - Re: [PATCH 17/18] tracing: Add indirect to indirect access for function based events

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Message-ID: <20180213092737.GJ31513@sejong>
Date:   Tue, 13 Feb 2018 18:27:37 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        linux-rt-users@...r.kernel.org, linux-trace-users@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Clark Williams <williams@...hat.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        kernel-team@....com
Subject: Re: [PATCH 17/18] tracing: Add indirect to indirect access for
 function based events

Hi Steve,

On Mon, Feb 12, 2018 at 12:23:54PM -0500, Steven Rostedt wrote:
> On Mon, 12 Feb 2018 11:15:34 +0900
> Namhyung Kim <namhyung@...nel.org> wrote:
> 
> > > It should have been:
> > > 
> > > 		return process_redirects(arg, val, buf);  
> > 
> > But I think you need to consider data type of the arg when
> > dereferencing the last redirect.
> 
> What for?

Otherwise it'd return a value of unsigned long type regardless of the
type of the arg.  I thought it should have same logic as indirect
args.

But it seems not matter since record_entry() would copy it only for
the arg->size.  Then type check in __get_arg() might be unnecessary
too.

> 
> Also this code has also changed. I haven't posted new patches but my
> latest is in my git tree in the branch ftrace/dynamic-ftrace-events.

I've checked it.  And it seems to have another problem for indirect
(but not redirect) arrays and strings.  Like 'x32[1] foo[2]'?

Thanks,
Namhyung