Hi Andrii,

I love your patch! Yet something to improve:

[auto build test ERROR on bpf-next/master]
[also build test ERROR on bpf/master cgroup/for-next net/master net-next/master v5.7-rc3 next-20200428]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Andrii-Nakryiko/bpf_link-observability-APIs/20200428-215720
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
config: sh-randconfig-a001-20200428 (attached as .config)
compiler: sh4-linux-gcc (GCC) 9.3.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day GCC_VERSION=9.3.0 make.cross ARCH=sh 

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

All errors (new ones prefixed by >>):

   sh4-linux-ld: kernel/bpf/syscall.o: in function `bpf_raw_tp_link_fill_link_info':
>> kernel/bpf/syscall.c:2570: undefined reference to `__get_user_unknown'

vim +2570 kernel/bpf/syscall.c

  2547	
  2548	static int bpf_raw_tp_link_fill_link_info(const struct bpf_link *link,
  2549						  struct bpf_link_info *info,
  2550						  const struct bpf_link_info *uinfo,
  2551						  u32 info_len)
  2552	{
  2553		struct bpf_raw_tp_link *raw_tp_link =
  2554			container_of(link, struct bpf_raw_tp_link, link);
  2555		u64 ubuf_ptr;
  2556		char __user *ubuf = u64_to_user_ptr(uinfo->raw_tracepoint.tp_name);
  2557		const char *tp_name = raw_tp_link->btp->tp->name;
  2558		size_t tp_len;
  2559		u32 ulen;
  2560	
  2561		if (get_user(ulen, &uinfo->raw_tracepoint.tp_name_len))
  2562			return -EFAULT;
  2563		if (get_user(ubuf_ptr, &uinfo->raw_tracepoint.tp_name))
  2564			return -EFAULT;
  2565		ubuf = u64_to_user_ptr(ubuf_ptr);
  2566	
  2567		if (ulen && !ubuf)
  2568			return -EINVAL;
  2569		if (!ubuf)
> 2570			return 0;
  2571	
  2572		tp_len = strlen(raw_tp_link->btp->tp->name);
  2573		info->raw_tracepoint.tp_name_len = tp_len + 1;
  2574		info->raw_tracepoint.tp_name = (u64)(unsigned long)ubuf;
  2575	
  2576		if (ulen >= tp_len + 1) {
  2577			if (copy_to_user(ubuf, tp_name, tp_len + 1))
  2578				return -EFAULT;
  2579		} else {
  2580			char zero = '\0';
  2581	
  2582			if (copy_to_user(ubuf, tp_name, ulen - 1))
  2583				return -EFAULT;
  2584			if (put_user(zero, ubuf + ulen - 1))
  2585				return -EFAULT;
  2586			return -ENOSPC;
  2587		}
  2588	
  2589		return 0;
  2590	}
  2591	

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