Why is manual symlink to vmlinux in the kernel source required for module build of

Devs, Building kernel modules on an old 15.4 install, I get the warning: Skipping BTF generation for /home/david/dev/src-c/tmp/tst/kmgpio/gpioblink.ko due to unavailability of vmlinux Tracking the issue down, I ended up creating the symlink in the kernel source directory linux-5.14.21-150400.24.100-obj/x86_64/default: # ln -s /sys/kernel/btf/vmlinux The build proceeds fine then. My question is "is this normal to have to manually create the vmlinux symlink, and if not how should it be properly handled?" -- David C. Rankin, J.D.,P.E.