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From:   Jiri Olsa <olsajiri@gmail.com>
Date:   Mon, 15 Aug 2022 13:29:29 +0200
To:     =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= <bjorn@kernel.org>
Cc:     Jiri Olsa <olsajiri@gmail.com>,
        Chen Zhongjin <chenzhongjin@huawei.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        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>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC] ftrace: Add support to keep some functions out of ftrace
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On Mon, Aug 15, 2022 at 01:01:06PM +0200, Bj?rn T?pel wrote:
> On Mon, 15 Aug 2022 at 10:04, Jiri Olsa <olsajiri@gmail.com> wrote:
> [...]
> > > > >
> > > > > Today, objtool has also got involved, and added an "--mcount" option
> > > > > that will create the section too.
> > > > I overlooked that objtool is involved as well,
> > > > will check on that
> > >
> > > objtool --mcount option only involves mcount_loc generation (see
> > > annotate_call_site) and other validation check call destination directly
> > > (see is_fentry_call).
> > >
> > > Some simply removing --mcount option dose work for this.
> > >
> > >
> > > Another question, it seems we can export and use DEFINE_BPF_DISPATCHER out
> > > of kernel, does that means we should add NO_MCOUNT_FILES for these single
> > > uages as well?
> >
> > yes, cc-ing Bj?rn to make sure it's valid use case for dispatcher
> >
> 
> Hmm, could you expand a bit on how this would work?

the goal here is to remove bpf_dispatcher_<FUNC>_func functions from
ftrace, because it's updated by dispatcher code with bpf_arch_text_poke,
but it's also visible and attachable to ftrace.. and will cause problems
when these 2 updates will race

question was if DEFINE_BPF_DISPATCHER can be used in kernel module,
which would bring another realm of problems ;-)

jirka