Em Fri, Sep 18, 2020 at 09:00:10PM -0700, Hao Luo escreveu:
> Hi Alexei,
>
> I was syncing with Arnaldo offline on whether the change in Pahole was
> enough for supporting percpu vars in BPF. While I think about it, I
> felt it's better to have a flag in pahole to toggle the feature on and
> off. My concern is mainly malformed BTF caused by the newly introduced
> VAR entries. I've tested over some kernel configurations and compilers
> but not confident enough.
>
> I haven't thought about opt-out. Maybe we should use opt-out instead of opt-in?
Yeah, having an opt-out should be useful as a debugging technique.
- Arnaldo
> Hao
>
> On Fri, Sep 18, 2020 at 5:58 PM Alexei Starovoitov
> <alexei.starovoitov@xxxxxxxxx> wrote:
> >
> > On Fri, Sep 18, 2020 at 1:41 PM Hao Luo <haoluo@xxxxxxxxxx> wrote:
> > >
> > > Previous commit f3d9054ba8ff ("btf_encoder: Teach pahole to store
> > > percpu variables in vmlinux BTF.") introduced a feature in btf_encoder
> > > that encodes global symbols in BTF. However, this feature is not
> > > protected by any flag. In order to avoid surprises after Pahole v1.18
> > > rolls out, make this feature off by default and enable only upon
> > > request. On the kernel side, we can add a Kconfig to enable this
> > > new capability on an opt-in pattern.
> >
> > I think I've missed some earlier discussions and motivation for opt-in.
> > Why opt-out is a problem?
> > I would think the kernel build should always include percpu vars.
--
- Arnaldo
