--- kmod-hello-world.scm
;; guix build -f kmod-hello-world.scm
(use-modules
 (guix build-system linux-module)
 (guix gexp)
 ((guix licenses) #:prefix license:)
 (guix packages))

(package
  (name "kmod-hello-world")
  (version "1.0.0")
  (source
   (local-file "hello" #:recursive? #t))
  (build-system linux-module-build-system)
  (arguments
   (list #:tests? #f))
  (synopsis "")
  (description "")
  (home-page "")
  (license license:gpl2+))

--- hello/Kbuild
CFLAGS_MODULE := -Wall -Werror
obj-m := hello_world.o

--- hello/hello_world.c
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Me");
MODULE_DESCRIPTION("Hello world");
MODULE_VERSION("1.0.0");

static int __init hello_world_init(void) {
  printk(KERN_INFO "hello_world: init\n");
  return 0;
}

static void __exit hello_world_exit(void) {
  printk(KERN_INFO "hello_world: exit\n");
}

module_init(hello_world_init);
module_exit(hello_world_exit);