Linux kernel module compiling

Question

Hello,

I try to compile simple linux kernel module:

#include <linux/module.h>    
#include <linux/kernel.h>       

int init_module(void)
{
        printk("Hello world 1.\n");
        return 0;
}

void cleanup_module(void)
{
        printk(KERN_ALERT "Goodbye world 1.\n");
}

My makefile:

obj-m = testmodule.o
KVERSION = $(shell uname -r)
all:
        make -C /lib/modules/$(KVERSION)/build M=$(PWD) modules
clean:
        make -C /lib/modules/$(KVERSION)/build M=$(PWD) clean

Now i haven't errors in my .c file.

But when i try make in terminal: make: Nothing to be done for `all'.

What's wrong?

Thank you.

Answer 1

You really don't give enough information to determine the correct answer, but I'll give you some things to look into.

How are you compiling it? Do you have the correct include path in your build? Build paths are specified with the -I option to gcc. Make sure you are pointing to your kernel source tree.

Have you build the kernel? When you do a make, certain things are setup that allows you to build. Doing a make doesn't build everything (like modules) but will get the initial stuff setup for you.

Answer 2

Make sure your have your distributions the kernel header/development packages installed that provide these include files.

If they are installed, search where these include files are located on your computer and add these directories to your compilers include search path (the -I option).

Answer 3

The default command in your makefile is

make -C /lib/modules/$(KVERSION)/build M=$(PWD) modules

That instructs make to cd to /lib/modules/$(KVERSION)/build and run

make module m=YOUR_CURRENT_DIR

In turn, that makefile is not finding anything to do. Presumably, that makefile expects to find some particular structure in your current directory.

You need to more carefully read whatever instructions led you to set up this makefile.