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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Mon, 15 Aug 2022 08:49:11 -0700
Message-ID: <CAADnVQ+QTMRnCpmqPcovcbAXmtVz2Kefyr0E++P7CTRq6=PCVw@mail.gmail.com>
Subject: Re: [RFC] ftrace: Add support to keep some functions out of ftrace
To:     Peter Zijlstra <peterz@infradead.org>
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>
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On Mon, Aug 15, 2022 at 8:41 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, Aug 15, 2022 at 05:28:02PM +0200, Peter Zijlstra 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.
> >
> > The whole problem is that it isn't a notrace function and you're abusing
> > a __fentry__ site.
>
> https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/commit/?h=x86/fineibt&id=8d075bdf11193f1d276bf19fa56b4b8dfe24df9e

Brand new stuff.
Awesome. That should fit perfectly.

> foo.c:
>
> __attribute__((__no_instrument_function__))
> __attribute__((patchable_function_entry(5)))

Interesting. Didn't know about this attribute.

> void my_func(void)
> {
> }
>
> void my_foo(void)
> {
> }

Great.
Jiri, could you please revise your patch with this approach?