Re: [PATCH 0/2] Enable new kprobe event at boot

[Masami Hiramatsu <mhiramat@kernel.org>]

On Tue, 21 May 2019 09:33:17 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Tue, 21 May 2019 16:56:16 +0900
> Masami Hiramatsu <mhiramat@kernel.org> wrote:
> 
> > Note that 'trace_event=' option enables trace event at very early
> > timing, but the events added by 'kprobe_event=' are enabled right
> > before enabling device drivers at this point. It is enough for
> > tracing device driver initialization etc.
> 
> Nice!
> 
> I wonder if we can have this called before the trace_event boot is
> analyzed. Then have the kprobe_event work more like the kprobe_events
> file, and not enable the kprobes but only create them. If you want to
> enable them you do a trace_event=kprobes as well.

Yeah, I considered that, but there are several reasons to not to do that.
- trace_event seems enabled very early point than kprobes itself.(but this can
  be fixable)
- if user specifies kprobes at boot, he/she wants to enable that point at boot.
- it is redundant to specify kprobe_event= and trace_event=, especially command
  line size is very limited.

> Perhaps we could enable kprobes at early init?

It should be possible, I will try to find what blocks it. I guess after we
switch early_text_poke() to text_poke(), we can use kprobes on x86. But
for other archs, I need to investigate more.

> What do you think? Or is there something else in kprobes that prevents
> such an early enabling of it?

As I pointed above, I think we should enable it if user specify it. That's
less typing :). Anyway I'll recheck early kprobe availablity.

Thank you,


-- 
Masami Hiramatsu <mhiramat@kernel.org>