LddFirstModule < Training2

%SECTION0{name=LddFirstModule}% A first hello_world module

*Code:*

<verbatim>
/*                                                                                                                                               
 * A first simple hello_world kernel module                                                                                                      
 */

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

static int hello_init(void)
{
        printk(KERN_ALERT "Hello world!\n");
        return 0;
}

static void hello_exit(void)
{
        printk(KERN_ALERT "Goodbye, cruel world\n");
}

module_init(hello_init);
module_exit(hello_exit);

</verbatim>

*Makefile:*

<verbatim>
obj-m := hello.o
</verbatim>

*Build it:*

<verbatim>
make -C ~/git/linux-denx/ M=`pwd` modules ARCH=powerpc
</verbatim>

*loading*
   * insmod
   * modprobe

*Extentions:*

   * =__init, __initdata, __exit, __exitdata= (=include/linux/init.h=)

   * =__devinit= / =__devexit= (normal function if =!CONFIG_HOTPLUG=, else equal =__init= / =__exit=

   * =MODULE_AUTHOR, MODULE_LICENSE, MODULE_DESCRIPTION=

   * Kernel symbol visibility: =static=, =EXPORT_SYMBOL[_GPL[_FUTURE]](a)=

   * check out kernel symbols: =/proc/kallsyms= (=nm(1)=)

5.2.1. Configuring and building the Linux kernel		1. Denx Training Topics		5.2.3. Linux kernel makefiles
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