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Date:   Mon, 15 Aug 2022 17:48:44 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     Jiri Olsa <olsajiri@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Ingo Molnar <mingo@redhat.com>, bpf <bpf@vger.kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@chromium.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [RFC] ftrace: Add support to keep some functions out of ftrace
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On Mon, Aug 15, 2022 at 08:35:53AM -0700, Alexei Starovoitov wrote:
> On Mon, Aug 15, 2022 at 8:28 AM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Mon, Aug 15, 2022 at 08:17:42AM -0700, Alexei Starovoitov wrote:
> > > It's hiding a fake function from ftrace, since it's not a function
> > > and ftrace infra shouldn't show it tracing logs.
> > > In other words it's a _notrace_ function with nop5.
> >
> > Then make it a notrace function with a nop5 in it. That isn't hard.
> 
> That's exactly what we're trying to do.

All the while claiming ftrace is broken while it is not.

> Jiri's patch is one way to achieve that.

Fairly horrible way.

> What is your suggestion?

Mailed it already.

> Move it from C to asm ?

Would be much better than proposed IMO.

> Make it naked function with explicit inline asm?

Can be made to work but is iffy because the compiler can do horrible
things with placing the asm().