linux-kernel - Re: [PATCH bpf-next v4 2/6] bpf: introduce BPF dispatcher

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Message-ID: <20220815113921.5b3305f5@gandalf.local.home>
Date:   Mon, 15 Aug 2022 11:39:21 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Björn Töpel <bjorn.topel@...il.com>,
        Network Development <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        bpf <bpf@...r.kernel.org>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Edward Cree <ecree@...arflare.com>,
        Toke Høiland-Jørgensen 
        <thoiland@...hat.com>, Jesper Dangaard Brouer <brouer@...hat.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH bpf-next v4 2/6] bpf: introduce BPF dispatcher

On Mon, 15 Aug 2022 11:16:58 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> > It sounds that you've invented nop5 and kernel's ability
> > to replace nop5 with a jump or call.  
> 
> Actually I did invent it.
> 
>    https://lore.kernel.org/lkml/20080210072109.GR4100@elte.hu/
> 
> 
> I'm the one that introduced the code to convert mcount into the 5 byte nop,
> and did the research and development to make it work at run time. I had one
> hiccup along the way that caused the e1000e network card breakage.
> 
> The "daemon" approach was horrible, and then I created the recordmcount.pl
> perl script to accomplish the same thing at compile time.

I guess you were not paying attention to my talk at the Kernel Recipes I
invited you to in 2019. The talk I gave was the history of how fentry came
about.

  https://kernel-recipes.org/en/2019/talks/ftrace-where-modifying-a-running-kernel-all-started/

 ;-)

-- Steve