linux-kernel - Re: [RFC][PATCH 00/14 v2] function_graph: Rewrite to allow multiple users

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Date:   Wed, 29 May 2019 05:25:21 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Andy Lutomirski <luto@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Namhyung Kim <namhyung@...nel.org>,
        "Frank Ch. Eigler" <fche@...hat.com>
Subject: Re: [RFC][PATCH 00/14 v2] function_graph: Rewrite to allow multiple
 users

On Wed, 29 May 2019 15:47:40 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:


> Hi Steve,
> 
> I found that these interfaces seem tightly coupled with fgraph_ops. But that
> cause a problem when I'm using it from kretprobe.

I was thinking that the kretprobes could use the fgraph_ops like
kprobes uses ftrace_ops.

> 
> kretprobe has 2 handlers, entry handler and return handler, and both need
> pt_regs. But fgraph_ops's entryfunc and retfunc do not pass the pt_regs.
> That is the biggest issue for me on these APIs.
> Can we expand fgraph_ops with regs parameter?

Ug. Yeah, of course you need that :-/

OK, so this series isn't enough to allow kretprobes to use it yet. OK,
I plan on still keeping it because it does allow for placing function
graph tracer into instances with their own filters.

I'll look into adding a REGS flag like we do with ftrace_ops.

Does the return need all regs? Or is just the return code good enough?

-- Steve