mainline inclusion
from mainline-5.13-rc1
commit 42869d28
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5EUVD
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=42869d28527695a75346c988ceeedbba7e3880b7

-------------------------------------------------

Make skip_mods_and_typedefs(), btf_kind_str(), and btf_func_linkage() helpers
available outside of libbpf.c, to be used by static linker code.

Also do few cleanups (error code fixes, comment clean up, etc) that don't
deserve their own commit.
Signed-off-by: NAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210423181348.1801389-9-andrii@kernel.org
(cherry picked from commit 42869d28)
Signed-off-by: NWang Yufen <wangyufen@huawei.com>