Hi Hans,

I love your patch! Yet something to improve:

[auto build test ERROR on tip/x86/core]
[also build test ERROR on v5.6-rc3 next-20200228]
[cannot apply to tip/auto-latest]
[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/Hans-de-Goede/x86-purgatory-Make-sure-we-fail-the-build-if-purgatory-ro-has-missing-symbols/20200223-040035
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 248ed51048c40d36728e70914e38bffd7821da57
config: x86_64-randconfig-s1-20200229 (attached as .config)
compiler: gcc-4.9 (Debian 4.9.2-10+deb8u1) 4.9.2
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

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

All errors (new ones prefixed by >>):

   ld: arch/x86/purgatory/purgatory.ro: in function `kstrtoull':
>> (.text+0x2b0e): undefined reference to `ftrace_likely_update'

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