linux-kernel - Re: [PATCH 09/18] tracing: Add indexing of arguments for function based events

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Date:   Thu, 8 Feb 2018 10:43:43 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Namhyung Kim <namhyung@...nel.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 09/18] tracing: Add indexing of arguments for function
 based events

On Thu, 8 Feb 2018 19:59:24 +0900
Namhyung Kim <namhyung@...nel.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.

If the arg (val) is 0xffffffffabcd0000

	u64 val+8

Will return: 0xffffffffabcd0008

	u64 val[1]

will return what's at location 0xffffffffabcd0008

"u64 val+8[0]" is the same as "u64 val[1]"

Note: "u64 val[0]+8" will return what's at location 0xffffffffabcd0000
plus 8.

-- Steve