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

From: Steven Rostedt
Date: Wed May 29 2019 - 05:28:52 EST

On Wed, 29 May 2019 15:47:40 +0900
Masami Hiramatsu <mhiramat@xxxxxxxxxx> 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