From mboxrd@z Thu Jan  1 00:00:00 1970
From: Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 09/18] tracing: Add indexing of arguments for function
 based events
Date: Thu, 8 Feb 2018 19:19:10 -0500
Message-ID: <20180208191910.6bfdc921@gandalf.local.home>
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        <20180202231018.338259949@goodmis.org>
        <20180208105924.GB26290@sejong>
        <20180208104343.2fa63eda@gandalf.local.home>
        <20180208235615.GA28206@sejong>
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Cc: linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Tom Zanussi <tom.zanussi@linux.intel.com>,
        linux-rt-users@vger.kernel.org, linux-trace-users@vger.kernel.org,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Clark Williams <williams@redhat.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        kernel-team@lge.com
To: Namhyung Kim <namhyung@kernel.org>
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On Fri, 9 Feb 2018 08:56:15 +0900
Namhyung Kim <namhyung@kernel.org> wrote:

> On Thu, Feb 08, 2018 at 10:43:43AM -0500, Steven Rostedt wrote:
> > On Thu, 8 Feb 2018 19:59:24 +0900
> > Namhyung Kim <namhyung@kernel.org> wrote:
> >   
> > > > @@ -347,6 +361,8 @@ static long long get_arg(struct func_arg *arg, unsigned long val)
> > > >  	char buf[8];
> > > >  	int ret;
> > > >  
> > > > +	val += arg->index;
> > > > +
> > > >  	if (!arg->indirect)
> > > >  		return val;    
> > > 
> > > So this also works without the indirect, and just add the immediate to
> > > the value.  
> > 
> > Not sure what you are asking here. The immediate adds to the current
> > value, where as the indirect will then look what's at that location.  
> 
> I expected that the immediate offset is only meaningful with the
> indirect (dereference) as the doc says just about it.  So I asked it
> was intentional or not.
>

Yes it is intentional, but rather useless without an indirect. I mean,
you could just add to the value if you want :-)

The reason it doesn't need the indirect is because there's some types
(arrays and strings) that don't need the indirect. For example, with
the net_device with the perm_addr at 558 bytes away:

 echo 'ip_rcv(NULL, x8[6] perm_addr+558)' > function_events

produces:

          <idle>-0     [003] ..s3  1809.074329: __netif_receive_skb_core->ip_rcv(perm_addr=b4,b5,2f,ce,18,65)

-- Steve