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From:   Song Liu <song@kernel.org>
Date:   Fri, 15 Apr 2022 16:24:41 -0700
Message-ID: <CAPhsuW42Sv2EkMzVoh2+i=2NN2yMRHOqDN8wmXGPax2-cz8ynA@mail.gmail.com>
Subject: Re: [PATCH bpf-next 02/11] bpf: always emit struct bpf_perf_link BTF
To:     Alexander Lobakin <alobakin@pm.me>
Cc:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
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On Thu, Apr 14, 2022 at 3:45 PM Alexander Lobakin <alobakin@pm.me> wrote:
>
> When building bpftool with !CONFIG_PERF_EVENTS:
>
> skeleton/pid_iter.bpf.c:47:14: error: incomplete definition of type 'struct bpf_perf_link'
>         perf_link = container_of(link, struct bpf_perf_link, link);
>                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_helpers.h:74:22: note: expanded from macro 'container_of'
>                 ((type *)(__mptr - offsetof(type, member)));    \
>                                    ^~~~~~~~~~~~~~~~~~~~~~
> tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_helpers.h:68:60: note: expanded from macro 'offsetof'
>  #define offsetof(TYPE, MEMBER)  ((unsigned long)&((TYPE *)0)->MEMBER)
>                                                   ~~~~~~~~~~~^
> skeleton/pid_iter.bpf.c:44:9: note: forward declaration of 'struct bpf_perf_link'
>         struct bpf_perf_link *perf_link;
>                ^
>
> &bpf_perf_link is being defined and used only under the ifdef.
> Move it out of the block and explicitly emit a BTF to fix
> compilation.
>
> Fixes: cbdaf71f7e65 ("bpftool: Add bpf_cookie to link output")
> Signed-off-by: Alexander Lobakin <alobakin@pm.me>

Similar to v1, this fix is weird to me. I hope we have can fix it in user
space.