The last time I needed to deal with kernel headers was back in the Pleistocene (2.6 or so) and I remember back then that you needed to match your kernel headers not to the kernel you were running but to the kernel version glibc was compiled against. But this was a long time ago and before the kernel exported its own headers.
I have a computer that will be running a 4.15 series kernel, with a C library compiled against 4.4 series headers. Should I export the headers from the kernel I'm running, or use the headers package that my distro (Slackware) provides? (Or, and please say the answer is no, do I need to also rebuild glibc against the new kernel?)