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

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Date:   Fri, 9 Feb 2018 12:18:40 -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 17/18] tracing: Add indirect to indirect access for
 function based events

On Fri, 9 Feb 2018 10:47:58 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> Good catch!
> 
> It should have been:
> 
> 		return process_redirects(arg, val, buf);

Although I need to add this :-p

diff --git a/kernel/trace/trace_event_ftrace.c b/kernel/trace/trace_event_ftrace.c
index 673336e352be..2690d4e46322 100644
--- a/kernel/trace/trace_event_ftrace.c
+++ b/kernel/trace/trace_event_ftrace.c
@@ -562,7 +564,7 @@ process_event(struct func_event *fevent, const char *token, enum func_states sta
                ret = add_arg_redirect(fevent->last_arg, val, 0);
                if (ret)
                        break;
-               return FUNC_STATE_VAR;
+               return FUNC_STATE_BRACKET_END;
 
        case FUNC_STATE_REDIRECT_BRACKET:
                if (WARN_ON(!fevent->last_arg))
@@ -656,6 +658,7 @@ static unsigned long process_redirects(struct func_arg *arg, unsigned long val,
                        ret = probe_kernel_read(buf, (void *)val, sizeof(long));
                        if (ret)
                                return 0;
+                       val = *(unsigned long *)buf;
                }
        }
        return val;

Because it wasn't parsing properly, and then not getting the redirect.

-- Steve