netdev - Re: [PATCHv6 bpf] bpf: Move iterator functions into special init section

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Date:   Wed, 11 Nov 2020 12:09:26 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Jiri Olsa <jolsa@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andriin@...com>, Yonghong Song <yhs@...com>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: Re: [PATCHv6 bpf] bpf: Move iterator functions into special init section

On Wed, Nov 11, 2020 at 4:38 AM Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
>
> Em Wed, Nov 11, 2020 at 09:37:38AM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Wed, Nov 11, 2020 at 12:26:29PM +0100, Daniel Borkmann escreveu:
> > > On 11/10/20 4:40 PM, Jiri Olsa wrote:
> > > > With upcoming changes to pahole, that change the way how and
> > > > which kernel functions are stored in BTF data, we need a way
> > > > to recognize iterator functions.
> > > >
> > > > Iterator functions need to be in BTF data, but have no real
> > > > body and are currently placed in .init.text section, so they
> > > > are freed after kernel init and are filtered out of BTF data
> > > > because of that.
> > > >
> > > > The solution is to place these functions under new section:
> > > >    .init.bpf.preserve_type
> > > >
> > > > And add 2 new symbols to mark that area:
> > > >    __init_bpf_preserve_type_begin
> > > >    __init_bpf_preserve_type_end
> > > >
> > > > The code in pahole responsible for picking up the functions will
> > > > be able to recognize functions from this section and add them to
> > > > the BTF data and filter out all other .init.text functions.
> > > >
> > > > Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> > > > Suggested-by: Yonghong Song <yhs@...com>
> > > > Signed-off-by: Jiri Olsa <jolsa@...hat.com>
> > >
> > > LGTM, applied, thanks! Also added a reference to the pahole commit
> >
> > Applied to what branch? I'm trying to test it now :-)
>
> Nevermind, bpf/master, I was looking at bpf-next/master.

I've dropped this patch from bpf tree.
I think we need to agree on the whole approach first.
This filtering based on section name with special handling in pahole doesn't
feel like solid long term direction.
I think we have to brainstorm more on it.
I'm not saying we will not go back to a special section approach.
This revert is only buying us time to discuss what's the right path here.
Mainly I reverted to unbreak bpf tree CI which currently fails due to
two tests in test_progs
failing with the latest pahole and this patch.