~/build/ipt_xor/kernel # make
make -C /lib/modules/4.9.0-4-amd64/build M=$PWD;
make[1]: Entering directory '/usr/src/linux-headers-4.9.0-4-amd64'
  CC [M]  /root/build/ipt_xor/kernel/xt_XOR.o
/root/build/ipt_xor/kernel/xt_XOR.c:41:49: warning: ‘struct xt_target_param’ declared inside parameter list will not be visible outside of this definition or declaration
 xt_xor_target(struct sk_buff *skb, const struct xt_target_param *par)
                                                 ^~~~~~~~~~~~~~~
/root/build/ipt_xor/kernel/xt_XOR.c: In function ‘xt_xor_target’:
/root/build/ipt_xor/kernel/xt_XOR.c:43:41: error: dereferencing pointer to incomplete type ‘const struct xt_target_param’
     const struct xt_xor_info *info = par->targinfo;
                                         ^~
/root/build/ipt_xor/kernel/xt_XOR.c: At top level:
/root/build/ipt_xor/kernel/xt_XOR.c:108:15: error: initialization from incompatible pointer type [-Werror=incompatible-pointer-types]
     .target = xt_xor_target,
               ^~~~~~~~~~~~~
/root/build/ipt_xor/kernel/xt_XOR.c:108:15: note: (near initialization for ‘xt_xor.target’)
/root/build/ipt_xor/kernel/xt_XOR.c:110:19: error: initialization from incompatible pointer type [-Werror=incompatible-pointer-types]
     .checkentry = xt_xor_checkentry,
                   ^~~~~~~~~~~~~~~~~
/root/build/ipt_xor/kernel/xt_XOR.c:110:19: note: (near initialization for ‘xt_xor.checkentry’)
cc1: some warnings being treated as errors
/usr/src/linux-headers-4.9.0-4-common/scripts/Makefile.build:304: recipe for target '/root/build/ipt_xor/kernel/xt_XOR.o' failed
make[4]: *** [/root/build/ipt_xor/kernel/xt_XOR.o] Error 1
/usr/src/linux-headers-4.9.0-4-common/Makefile:1510: recipe for target '_module_/root/build/ipt_xor/kernel' failed
make[3]: *** [_module_/root/build/ipt_xor/kernel] Error 2
Makefile:150: recipe for target 'sub-make' failed
make[2]: *** [sub-make] Error 2
Makefile:8: recipe for target 'all' failed
make[1]: *** [all] Error 2
make[1]: Leaving directory '/usr/src/linux-headers-4.9.0-4-amd64'
Makefile:8: recipe for target 'all' failed
make: *** [all] Error 2

rwxr-xr-x 1 root root 16960 Apr  2 15:16 /usr/lib/x86_64-linux-gnu/xtables/libxt_XOR.so

rwxr-xr-x 1 root root 14864 Apr  1 16:23 /usr/lib/x86_64-linux-gnu/xtables/libxt_XOR.so

gcc -O2 -Wall -I../include -fPIC -c -o libxt_XOR.o libxt_XOR.c
libxt_XOR.c:119:13: warning: ‘_init’ defined but not used [-Wunused-function]
  119 | static void _init(void)
      |             ^~~~~
gcc -shared -o libxt_XOR.so libxt_XOR.o
rm libxt_XOR.o
make -C /lib/modules/6.1.0-18-amd64/build M=$PWD;
make[1]: Entering directory '/usr/src/linux-headers-6.1.0-18-amd64'
  CC [M]  /tmp/ipt_xor/kernel/xt_XOR.o
  MODPOST /tmp/ipt_xor/kernel/Module.symvers
  CC [M]  /tmp/ipt_xor/kernel/xt_XOR.mod.o
  LD [M]  /tmp/ipt_xor/kernel/xt_XOR.ko
  BTF [M] /tmp/ipt_xor/kernel/xt_XOR.ko
Skipping BTF generation for /tmp/ipt_xor/kernel/xt_XOR.ko due to unavailability of vmlinux