netdev - Re: "resolve_btfids: unresolved" warnings while building v5.16-rc1

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Date:   Mon, 15 Nov 2021 22:57:03 +0530
From:   Kumar Kartikeya Dwivedi <memxor@...il.com>
To:     Pavel Skripkin <paskripkin@...il.com>
Cc:     ast@...nel.org, Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Andrii Nakryiko <andrii@...nel.org>
Subject: Re: "resolve_btfids: unresolved" warnings while building v5.16-rc1

On Mon, Nov 15, 2021 at 07:47:35PM IST, Kumar Kartikeya Dwivedi wrote:
> On Mon, Nov 15, 2021 at 07:04:51PM IST, Pavel Skripkin wrote:
> > Hi, net/bpf developers!
> >
> > While building newest kernel for fuzzing I met following warnings:
> >
> > ```
> >   BTFIDS  vmlinux
> > WARN: resolve_btfids: unresolved symbol tcp_dctcp_kfunc_ids
> > WARN: resolve_btfids: unresolved symbol tcp_cubic_kfunc_ids
> > WARN: resolve_btfids: unresolved symbol tcp_bbr_kfunc_ids
> >   SORTTAB vmlinux
> >
> > ```

+Cc Andrii

So the reason should be CONFIG_DYNAMIC_FTRACE=n, when that is turned off,
all these three BTF sets should be empty. Earlier they were all part of the
set in bpf_tcp_ca.c, which would never be empty, so there was no warning.

I guess we can demote that warning to debug, but not sure, since it isn't
limited to BTF sets, but also other symbols (e.g. kernel functions referenced in
.BTF_ids).

The other option is to add a dummy function in the set so that set->cnt != 0.

> >
> > I haven't seen such warnings before and have no idea are they important or
> > not. Config is attached.
> >
> > My host is openSUSE Tumbleweed with gcc (SUSE Linux) 10.3.1 20210707
> > [revision 048117e16c77f82598fca9af585500572d46ad73] if it's important :)
> >
> >
>
> I'll take a look later today.
>
> >
> > With regards,
> > Pavel Skripkin
>
> --
> Kartikeya

--
Kartikeya