mainline inclusion
from mainline-5.13-rc1
commit a0964f52
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=a0964f526df6facd4e12a4c416185013026eecf9

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Add Makefile infra to specify multi-file BPF object files (and derivative
skeletons). Add first selftest validating BPF static linker can merge together
successfully two independent BPF object files and resulting object and
skeleton are correct and usable.

Use the same F(F(F(X))) = F(F(X)) identity test on linked object files as for
the case of single BPF object files.
Signed-off-by: NAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210318194036.3521577-13-andrii@kernel.org
(cherry picked from commit a0964f52)
Signed-off-by: NWang Yufen <wangyufen@huawei.com>