WARNING: Unknown commit id 'cc937dad85ae', maybe rebased or not pulled?
#16: 
The culprit is commit cc937dad85ae ("selftests: centralize -D_GNU_SOURCE= to

WARNING: Unknown link reference '0:', use 'Link:' or 'Closes:' instead
#25: 
0: https://stackoverflow.com/questions/11670581/why-is-gnu-source-defined-by-default-and-how-to-turn-it-off

total: 0 errors, 2 warnings, 0 checks, 8 lines checked

NOTE: For some of the reported defects, checkpatch may be able to
      mechanically convert to the typical style using --fix or --fix-inplace.

Commit ed43586dfca0 ("selftests/bpf: Filter out _GNU_SOURCE when compiling test_cpp") has style problems, please review.

NOTE: Ignored message types: ALLOC_SIZEOF_STRUCT BAD_REPORTED_BY_LINK CAMELCASE COMMIT_LOG_LONG_LINE GIT_COMMIT_ID MACRO_ARG_REUSE NO_AUTHOR_SIGN_OFF

NOTE: If any of the errors are false positives, please report
      them to the maintainer, see CHECKPATCH in MAINTAINERS.
total: 0 errors, 2 warnings, 0 checks, 8 lines checked