第一个内核模块hello world

1、源码树的下载和编译（只是研究内核模块的话，应该不需要源码树的）

下载很简单，压缩包解压

编译：make menuconfig   

make bzImage -j4

参考

2、

cd  /usr/src/linux-4.12.10/drivers/char

建立demo目录，用来存放自己的内核模块

demo目录下新建hello.c 和 Makefile文件

//hello.c

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

MODULE_LICENSE("Dual BSD/GPL");

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

static void hello_exit(void)
{
    printk(KERN_ALERT "goodbye!\n");
}

module_init(hello_init);
module_exit(hello_exit);



//Makefile

ifeq ($(KERNELRELEASE),)
KERNELDIR ?= /lib/modules/$(shell uname -r)/build 
PWD := $(shell pwd)
modules:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules
modules_install:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules_install
clean:
    rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions Module* modules*
.PHONY: modules modules_install clean
else
obj-m := hello.o
endif

参考

  编译结果：

ninjame@ubuntu1604:/usr/src/linux-4.12.10/drivers/char/demo$ sudo make
make -C /lib/modules/4.4.80-040480-generic/build  M=/usr/src/linux-4.12.10/drivers/char/demo modules
make[1]: Entering directory '/usr/src/linux-headers-4.4.80-040480-generic'
  CC [M]  /usr/src/linux-4.12.10/drivers/char/demo/hello.o
  Building modules, stage 2.
  MODPOST 1 modules
  CC      /usr/src/linux-4.12.10/drivers/char/demo/hello.mod.o
  LD [M]  /usr/src/linux-4.12.10/drivers/char/demo/hello.ko
make[1]: Leaving directory '/usr/src/linux-headers-4.4.80-040480-generic'

模块加载和效果

ninjame@ubuntu1604:/usr/src/linux-4.12.10/drivers/char/demo$ sudo insmod hello.ko 
ninjame@ubuntu1604:/usr/src/linux-4.12.10/drivers/char/demo$ dmesg | tail
[   15.300169] r8169 0000:01:00.0 enp1s0: link down
[   15.300185] r8169 0000:01:00.0 enp1s0: link down
[   15.300230] IPv6: ADDRCONF(NETDEV_UP): enp1s0: link is not ready
[   16.840866] r8169 0000:01:00.0 enp1s0: link up
[   16.840873] IPv6: ADDRCONF(NETDEV_CHANGE): enp1s0: link becomes ready
[   18.016626] Bluetooth: BNEP (Ethernet Emulation) ver 1.3
[   18.016628] Bluetooth: BNEP filters: protocol multicast
[   18.016631] Bluetooth: BNEP socket layer initialized
[12219.748060] hello: module verification failed: signature and/or required key missing - tainting kernel
[12219.748268] hello world!