Re: [RFC] ftrace: Add support to keep some functions out of ftrace

Jiri Olsa
2022-08-15T11:29:39Z

On Mon, Aug 15, 2022 at 01:01:06PM +0200, Björn Töpel 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 Björn 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