Hi Francis,

[auto build test ERROR on net-next/master]

url:    https://github.com/0day-ci/linux/commits/Yuchung-Cheng/tcp-sender-chronographs-instrumentation/20161127-041428
config: arm-spear6xx_defconfig (attached as .config)
compiler: arm-linux-gnueabi-gcc (Debian 6.1.1-9) 6.1.1 20160705
reproduce:
        wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=arm 

All errors (new ones prefixed by >>):

   net/built-in.o: In function `__skb_tstamp_tx':
>> net/core/skbuff.c:3846: undefined reference to `tcp_get_timestamping_opt_stats'

vim +3846 net/core/skbuff.c

  3840			return;
  3841	
  3842		if (tsonly) {
  3843			if ((sk->sk_tsflags & SOF_TIMESTAMPING_OPT_STATS) &&
  3844			    sk->sk_protocol == IPPROTO_TCP &&
  3845			    sk->sk_type == SOCK_STREAM)
> 3846				skb = tcp_get_timestamping_opt_stats(sk);
  3847			else
  3848				skb = alloc_skb(0, GFP_ATOMIC);
  3849		} else {

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