How to compile a kernel module for Raspberry pi?

Question

I'm having trouble compiling a kernel module for a raspberry pi. I want to compile a "hello world" kernel module using the raspberry pi itself. I am using raspbian wheezy 3.6.11+. I tried following the directions at http://elinux.org/RPi_Kernel_Compilation. Here is the Makefile I am using: ``` obj-m += hello-1.o all: make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules clean: make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean ``` Here is the source code for hello-1.c: ``` /* * hello-1.c - The simplest kernel module. */ #include /* Needed by all modules */ #include /* Needed for KERN_INFO */ int init_module(void) { printk(KERN_INFO "Hello world 1. "); /* * A non 0 return means init_module failed; module can't be loaded. */ return 0; } void cleanup_module(void) { printk(KERN_INFO "Goodbye world 1. "); } ``` Here's what I get when I try to make the project: ``` root@raspberrypi:/home/pi/hello-module# make make -C /lib/modules/3.6.11+/…

Accepted Answer

Here are the steps I used to build the Hello World kernel module on Raspbian.

Perform `sudo rpi-update`

See https://github.com/Hexxeh/rpi-update for details on `rpi-update`. You have to be on the latest firmware and associated kernel to be able to perform the next step.

Install and run `rpi-source` to install the source code that built the latest kernel that you are running. This will create the correct entry in `/lib/modules` for the kernel that you are running. Note: you don't need to be root to run this, however the script will perform certain tasks using `sudo` and the root password will be requested during the script execution.

Instructions to install `rpi-source` can be found at https://github.com/notro/rpi-source/wiki

Once those steps are performed you should be able to `make` the Hello World kernel module.

```
johnma@raspberrypi ~/HelloWorld $ make
make -C /lib/modules/3.12.19+/build M=/home/johnma/HelloWorld modules
make[1]: Entering directory `/home/johnma/linux-c3db7205bcd8988cf7c185e50c8849542554b1f5'
  CC [M]  /home/johnma/HelloWorld/hello.o
  Building modules, stage 2.
  MODPOST 1 modules
  CC      /home/johnma/HelloWorld/hello.mod.o
  LD [M]  /home/johnma/HelloWorld/hello.ko
make[1]: Leaving directory `/home/johnma/linux-c3db7205bcd8988cf7c185e50c8849542554b1f5'

johnma@raspberrypi ~/HelloWorld $ sudo insmod hello.ko
johnma@raspberrypi ~/HelloWorld $ tail -1 /var/log/syslog
May 15 13:45:39 raspberrypi kernel: [59789.169461] Hello World :)

johnma@raspberrypi ~/HelloWorld $ sudo rmmod hello.ko
johnma@raspberrypi ~/HelloWorld $ tail -1 /var/log/syslog
May 15 13:46:10 raspberrypi kernel: [59819.503503] Goodbye World!
```

How to compile a kernel module for Raspberry pi?

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