reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git/commit/?id=8cd2c9c9e4c91d99eeb68284c1f5d464a2925963
        git remote add crng-random git://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git
        git fetch --no-tags crng-random vdso-droppable
        git checkout 8cd2c9c9e4c91d99eeb68284c1f5d464a2925963
        make W=1 O=/tmp/kselftest headers
        make W=1 O=/tmp/kselftest -C tools/testing/selftests
        make W=1 O=/tmp/kselftest -C tools/testing/selftests/bpf