Hi Cong,

First bad commit (maybe != root cause):

tree:   https://github.com/congwang/linux.git sockmap-v4
head:   cf1c3194b23432234a4939bf82f6e2038901efa4
commit: 1c9cd5c3bd0fad0b1b571e5aab78c49819845c97 [12/16] af_unix: add bpf proto support
config: powerpc-allmodconfig (attached as .config)
compiler: powerpc64-linux-gcc (GCC) 9.3.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/congwang/linux/commit/1c9cd5c3bd0fad0b1b571e5aab78c49819845c97
        git remote add congwang https://github.com/congwang/linux.git
        git fetch --no-tags congwang sockmap-v4
        git checkout 1c9cd5c3bd0fad0b1b571e5aab78c49819845c97
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=powerpc 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

>> powerpc64-linux-ld: net/unix/unix_bpf.o:(.toc+0x0): undefined reference to `unix_proto'

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0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org