Making simple linux kernel module

Question

I'm trying to upgrade my daemon code so that instead of it being an executable, it will be a kernel module, but I have difficulty even with using a simple example.

Here's the code I tried:

#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");
}

And because I understand that I can't just compile the code directly, I took a stab at copying and slightly modifying the makefile as follows:

WARN    := -W -Wall -Wstrict-prototypes -Wmissing-prototypes
INCLUDE := -isystem /lib/modules/`uname -r`/build/include
CFLAGS  := -O2 -DMODULE -D__KERNEL__ ${WARN} ${INCLUDE}
CC      := gcc
OBJS    := ${patsubst %.c, %.o, ${wildcard *.c}}

all: ${OBJS}

Then on the command line I executed "make" with the expectation of the program to be installed:

This is my output:

    gcc -O2 -DMODULE -D__KERNEL__ -W -Wall -Wstrict-prototypes -Wmissing-prototypes -isystem /lib/modules/`uname -r`/build/include   -c -o d.o d.c
    In file included from /lib/modules/2.6.21.5-smp/build/include/asm/thread_info.h:16,
                    from /lib/modules/2.6.21.5-smp/build/include/linux/thread_info.h:21,
                    from /lib/modules/2.6.21.5-smp/build/include/linux/preempt.h:9,
                    from /lib/modules/2.6.21.5-smp/build/include/linux/spinlock.h:49,
                    from /lib/modules/2.6.21.5-smp/build/include/linux/module.h:9,
                    from d.c:1:
    /lib/modules/2.6.21.5-smp/build/include/asm/processor.h:82: error: 'CONFIG_X86_L1_CACHE_SHIFT' undeclared here (not in a function)
    /lib/modules/2.6.21.5-smp/build/include/asm/processor.h:82: error: requested alignment is not a constant
    In file included from /lib/modules/2.6.21.5-smp/build/include/linux/sched.h:51,
                    from /lib/modules/2.6.21.5-smp/build/include/linux/utsname.h:35,
                    from /lib/modules/2.6.21.5-smp/build/include/asm/elf.h:12,
                    from /lib/modules/2.6.21.5-smp/build/include/linux/elf.h:7,
                    from /lib/modules/2.6.21.5-smp/build/include/linux/module.h:15,
                    from d.c:1:
    /lib/modules/2.6.21.5-smp/build/include/linux/jiffies.h:33:3: error: #error You lose.
    /lib/modules/2.6.21.5-smp/build/include/linux/jiffies.h:225:31: error: division by zero in #if
    /lib/modules/2.6.21.5-smp/build/include/linux/jiffies.h:225:31: error: division by zero in #if
    /lib/modules/2.6.21.5-smp/build/include/linux/jiffies.h:225:31: error: division by zero in #if
    /lib/modules/2.6.21.5-smp/build/include/linux/jiffies.h:225:31: error: division by zero in #if
    /lib/modules/2.6.21.5-smp/build/include/linux/jiffies.h:225:31: error: division by zero in #if
    /lib/modules/2.6.21.5-smp/build/include/linux/jiffies.h:225:31: error: division by zero in #if
    /lib/modules/2.6.21.5-smp/build/include/linux/jiffies.h:225:31: error: division by zero in #if
    /lib/modules/2.6.21.5-smp/build/include/linux/jiffies.h:225:31: error: division by zero in #if
    /lib/modules/2.6.21.5-smp/build/include/linux/jiffies.h:225:31: error: division by zero in #if
    /lib/modules/2.6.21.5-smp/build/include/linux/jiffies.h:225:31: error: division by zero in #if
    /lib/modules/2.6.21.5-smp/build/include/linux/jiffies.h:225:31: error: division by zero in #if
    /lib/modules/2.6.21.5-smp/build/include/linux/jiffies.h:225:31: error: division by zero in #if
    /lib/modules/2.6.21.5-smp/build/include/linux/jiffies.h:225:31: error: division by zero in #if
    /lib/modules/2.6.21.5-smp/build/include/linux/jiffies.h:225:31: error: division by zero in #if
    /lib/modules/2.6.21.5-smp/build/include/linux/jiffies.h:225:31: error: division by zero in #if
    /lib/modules/2.6.21.5-smp/build/include/linux/jiffies.h:225:31: error: division by zero in #if
    In file included from /lib/modules/2.6.21.5-smp/build/include/linux/module.h:21,
                    from d.c:1:
    /lib/modules/2.6.21.5-smp/build/include/asm/module.h:62:2: error: #error unknown processor family
    make: *** [d.o] Error 1

Why should I be getting all those errors when I'm only dealing with two functions that are well documented? Is my makefile off? Please advise?

Answer 1

nevermind. I found myself an answer from:

https://www.kernel.org/doc/Documentation/kbuild/modules.txt

It states:

To build against the running kernel use:

    $ make -C /lib/modules/`uname -r`/build M=$PWD

    Then to install the module(s) just built, add the target
"modules_install" to the command:

    $ make -C /lib/modules/`uname -r`/build M=$PWD modules_install