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From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Hao Luo <haoluo@google.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
	Andrii Nakryiko <andrii.nakryiko@gmail.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	dwarves@vger.kernel.org, Yonghong Song <yhs@fb.com>
Subject: Re: [PATCH 0/2] pahole: Make encoding percpu vars into BTF optional.
Date: Mon, 21 Sep 2020 09:27:37 -0300
Message-ID: <20200921122737.GJ1996959@kernel.org> (raw)
In-Reply-To: <CA+khW7i5vWnUMCvHmtEDVUQ92Wy+sLhOmnLjHBgVUdgdMWKQdQ@mail.gmail.com>

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@gmail.com> wrote:
> >
> > On Fri, Sep 18, 2020 at 1:41 PM Hao Luo <haoluo@google.com> 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

      reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-18 20:40 Hao Luo
2020-09-18 20:40 ` [PATCH 1/2] btf_encoder: Make encoding " Hao Luo
2020-09-18 21:24   ` Arnaldo Carvalho de Melo
2020-09-18 21:26     ` Hao Luo
2020-09-18 21:40       ` Arnaldo Carvalho de Melo
2020-09-18 20:40 ` [PATCH 2/2] btf_encoder: Introduce option '--btf_encode_force' Hao Luo
2020-09-19  0:57 ` [PATCH 0/2] pahole: Make encoding percpu vars into BTF optional Alexei Starovoitov
2020-09-19  4:00   ` Hao Luo
2020-09-21 12:27     ` Arnaldo Carvalho de Melo [this message]

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