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

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Date:   Wed, 29 May 2019 15:47:40 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.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, 22 May 2019 10:40:27 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Wed, 22 May 2019 23:19:55 +0900
> Masami Hiramatsu <mhiramat@...nel.org> wrote:
> 
> > >  void *fgraph_reserve_data(int size_in_bytes)
> > > 
> > >     Allows the entry function to reserve up to 4 words of data on
> > >     the shadow stack. On success, a pointer to the contents is returned.
> > >     This may be only called once per entry function.
> > > 
> > >  void *fgraph_retrieve_data(void)
> > > 
> > >     Allows the return function to retrieve the reserved data that was
> > >     allocated by the entry function.  
> > 
> > Nice! this seems good for kretprobe too. I'll review and try to port
> > kretprobe on this framework.
> 
> If you rather pull from my git repo and not download all the patches,
> they are currently available in my ftrace/fgraph-multi branch.

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.

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?

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>