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Date:   Mon, 21 Oct 2019 21:05:33 -0700
From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
        Nadav Amit <nadav.amit@gmail.com>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Song Liu <songliubraving@fb.com>,
        Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [PATCH 3/3] x86/ftrace: Use text_poke()
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On Mon, Oct 21, 2019 at 11:19:04PM -0400, Steven Rostedt wrote:
> On Mon, 21 Oct 2019 23:16:30 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
> 
> > > what bugs you're seeing?
> > > The IPI frequency that was mentioned in this thread or something else?
> > > I'm hacking ftrace+bpf stuff in the same spot and would like to
> > > base my work on the latest and greatest.  
> 
> I'm also going to be touching some of this code too, as I'm waiting for
> Peter's code to settle down. What are you touching? I'm going to be
> working on making the dyn_ftrace records smaller, and this is going to
> change the way the iterations work on modifying the code.

I'm not touching dyn_ftrace.
Actually calling my stuff ftrace+bpf is probably not correct either.
I'm reusing code patching of nop into call that ftrace does. That's it.
Turned out I cannot use 99% of ftrace facilities.
ftrace_caller, ftrace_call, ftrace_ops_list_func and the whole ftrace api
with ip, parent_ip and pt_regs cannot be used for this part of the work.
bpf prog needs to access raw function arguments. To achieve that I'm
generating code on the fly. Just like bpf jits do.
As soon as I have something reviewable I'll share it.
That's the stuff I mentioned to you at KR.
First nop of a function will be replaced with a call into bpf.
Very similar to what existing kprobe+bpf does, but faster and safer.
Second part of calling real ftrace from bpf is on todo list.