/usr/src/xtables-addons-2.6/extensions/pknock/Kbuild is in xtables-addons-dkms 2.6-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 | # -*- Makefile -*-
EXTRA_CFLAGS = -I${src}/..
obj-m += xt_pknock.o
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