Re: [PATCH bpf v2 3/3] tools/resolve_btfids: Skip unresolved symbol warning for empty BTF sets

[Song Liu <song@kernel.org>]

On Mon, Nov 22, 2021 at 6:47 AM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> resolve_btfids prints a warning when it finds an unresolved symbol,
> (id == 0) in id_patch. This can be the case for BTF sets that are empty
> (due to disabled config options), hence printing warnings for certain
> builds, most recently seen in [0].
>
> The reason behind this is because id->cnt aliases id->id in btf_id
> struct, leading to empty set showing up as ID 0 when we get to id_patch,
> which triggers the warning. Since sets are an exception here, accomodate
> by reusing hole in btf_id for bool is_set member, setting it to true for
> BTF set when setting id->cnt, and use that to skip extraneous warning.
>
>   [0]: https://lore.kernel.org/all/1b99ae14-abb4-d18f-cc6a-d7e523b25542@gmail.com
>
> Before:
>
> ; ./tools/bpf/resolve_btfids/resolve_btfids -v -b vmlinux net/ipv4/tcp_cubic.ko
> adding symbol tcp_cubic_kfunc_ids
> WARN: resolve_btfids: unresolved symbol tcp_cubic_kfunc_ids
> patching addr     0: ID       0 [tcp_cubic_kfunc_ids]
> sorting  addr     4: cnt      0 [tcp_cubic_kfunc_ids]
> update ok for net/ipv4/tcp_cubic.ko
>
> After:
>
> ; ./tools/bpf/resolve_btfids/resolve_btfids -v -b vmlinux net/ipv4/tcp_cubic.ko
> adding symbol tcp_cubic_kfunc_ids
> patching addr     0: ID       0 [tcp_cubic_kfunc_ids]
> sorting  addr     4: cnt      0 [tcp_cubic_kfunc_ids]
> update ok for net/ipv4/tcp_cubic.ko
>
> Cc: Jiri Olsa <jolsa@kernel.org>
> Fixes: 0e32dfc80bae ("bpf: Enable TCP congestion control kfunc from modules")
> Reported-by: Pavel Skripkin <paskripkin@gmail.com>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

Acked-by: Song Liu <songliubraving@fb.com>