FYI, using the same BKM (Best Known Method) I succeeded in running my ioctl.ko on my rpi3mb platform. My next move is to develop an IOCTL app to very my IOCTL kernel module.

I did not change my setting. After lunch I tried the steps again. It surprisingly works: The rpi3mb console log shows: [427889.087724] Hello World! [427915.237325] Goodbye World My next move is the replacement of hello_work.c with my ioctl.ko.

Your building steps work for me. I have been looking for such solutions for a while; yours is the simplest one. Thanks. Now I am encountering an insmod problem: insmod ./hell0_world.ko ERROR: could not load module ./hell0_world.ko: No such file or directory I am using buildroot master branch in my ubuntu host. My KDIR string is /home/tclee/buildroot/output/build/linux-custom tclee@tclee-Latitude-E6230:~/buildroot/output/build/linux-custom$ make kernelversion 6.12.20 My rpi3mb target is running a different kernel version: Linux buildroot 6.12.20-v7 #1 SMP Tue Jun 3 20:03:35 PDT 2025 armv7l GNU/Linux I am wondering if the kernel version difference is the cause of this failure. I am resolving this problem; your comment is welcome.