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Date:   Wed, 29 May 2019 05:25:21 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Masami Hiramatsu <mhiramat@kernel.org>
Cc:     linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Andy Lutomirski <luto@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Namhyung Kim <namhyung@kernel.org>,
        "Frank Ch. Eigler" <fche@redhat.com>
Subject: Re: [RFC][PATCH 00/14 v2] function_graph: Rewrite to allow multiple
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On Wed, 29 May 2019 15:47:40 +0900
Masami Hiramatsu <mhiramat@kernel.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