Question

Yes, as the title, I don’t know how to program and compile “Hello World” code in kernel mode of linux , please help me in the shortest and easy to understand way. Thank you !
(Any related document is welcomed too, I’m just new to this)

Answer 1

You can start Here:

/*  
 *  hello-1.c - The simplest kernel module.
 */
#include <linux/module.h>   /* Needed by all modules */
#include <linux/kernel.h>   /* Needed for KERN_INFO */

int init_module(void)
{
    printk(KERN_INFO "Hello world 1.\n");

    /* 
     * 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.\n");
}