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Makefile

The Makefile in the root of the Linux kernel source tree is essentially used to build

vmlinux (the resident kernel image), and
module files
documentation (generated in Documentation/output from files under Documentation/)
other development related stuff like tag files etc.

The top level Makefile includes arch/$SRCARCH/Makefile which supplies architecture-specific information to the top Makefile.

Version variables

The top of the Makefile defines a few version related variables:

VERSION = 6
PATCHLEVEL = 5
SUBLEVEL = 0
EXTRAVERSION = -rc7
NAME = Hurr durr I'ma ninja sloth

$ make -s kernelversion
6.5.0-rc7

Compare with include/config/kernel.release (if it exists) and include/generated/uapi/linux/version.h (if it exists).