模块-kernel 模块编译（Makefile编写）

发现自己以前写的2.4的模块无法在2.6下面编译使用了，需要用新的Makefile才行。简单的说就像这个样子：                                            

                                                                                                                                            

    obj-m := mytest.o                                                                                                                       

                                                                                                                                            

    KDIR := /lib/modules/$(shell uname -r)/build                                                                                            

                                                                                                                                            

    PWD := $(shell pwd)                                                                                                                     

                                                                                                                                            

    default:                                                                                                                                

                                                                                                                                            

     $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules                                                                                              

                                                                                                                                            

                                                                                                                                            

                                                                                                                                            

    就可以了，模块的名称是mytest，最后编译出来是mytest.ko，剩下的系统搞定。当然这里有一些隐含规则了，就是mytest.o由                         

                                                                                                                                            

    mytest.c或者mytest.S编译出来。如果模块是由多个源文件搞定的，那么建议去参考                                                              

                                                                                                                                            

    ~linuxsrc/Documentation/kbuild/下的一些文档。                                                                                           

                                                                                                                                            

    --- add on 2005年11月16日 ---                                                                                                           

                                                                                                                                            

    如果是多个源文件编译出一个模块，那么假设模块名是mytest.ko，那么源文件名不能有mytest.c，下面是一个例子：                                 

                                                                                                                                            

    obj-m := mytest.o                                                                                                                       

                                                                                                                                            

    mytest-objs := file1.o file2.o file3.o                                                                                                  

                                                                                                                                            

    KDIR := /lib/modules/$(shell uname -r)/build                                                                                            

                                                                                                                                            

    PWD := $(shell pwd)                                                                                                                     

                                                                                                                                            

    default:                                                                                                                                

                                                                                                                                            

     $(MAKE) -C $(KDIR) M=$(PWD) modules                                                                                                    

                                                                                                                                            

    这里比较奇怪的是makefile里面没有用SUBDIRS=，而是用了M=                                                                                  

                                                                                                                                            

    --- end of add on 2005年11月16日 ---                                                                                                    

                                                                                                                                            

    --- add on 2006年5月20日 ---                                                                                                            

                                                                                                                                            

    关于前面的makefile当中用M=代替SUBDIR=，效果是一样的，但是M=更明确，参见《从 2.4 到 2.6：Linux 内核可装载模块机制的改变对设备驱动的影响》

                                                                                                                                            

    http://www-128.ibm.com/developerworks/cn/linux/l-module26/                                                                              

                                                                                                                                            

    对于Makefile，其中建议为（将上面的改成）：                                                                                              

                                                                                                                                            

    ifneq ($(KERNELRELEASE),)                                                                                                               

                                                                                                                                            

    obj-m := mytest.o                                                                                                                       

                                                                                                                                            

    mytest-objs := file1.o file2.o file3.o                                                                                                  

                                                                                                                                            

    else                                                                                                                                    

                                                                                                                                            

    KDIR := /lib/modules/$(shell uname -r)/build                                                                                            

                                                                                                                                            

    PWD := $(shell pwd)                                                                                                                     

                                                                                                                                            

    default:                                                                                                                                

                                                                                                                                            

     $(MAKE) -C $(KDIR) M=$(PWD) modules                                                                                                    

                                                                                                                                            

    endif                                                                                                                                   

                                                                                                                                            

    解释为：                                                                                                                                

                                                                                                                                            

    KERNELRELEASE                                                                                                                           

                                                                                                                                            

    是在内核源码的顶层Makefile中定义的一个变量，在第一次读取执行此Makefile时，KERNELRELEASE没有被定义，                                     

                                                                                                                                            

    所以make将读取执行else之后的内容。如果make的目标是clean，直接执行clean操作，然后结束。当make的目标为all时，-C                           

                                                                                                                                            

    $(KDIR) 指明跳转到内核源码目录下读取那里的Makefile；M=$(PWD)                                                                            

                                                                                                                                            

    表明然后返回到当前目录继续读入、执行当前的Makefile。当从内核源码目录返回时，KERNELRELEASE已被被定义，kbuild也被启动去                   

                                                                                                                                            

    解析kbuild语法的语句，make将继续读取else之前的内容。else之前的内容为kbuild语法的语句,                                                   

                                                                                                                                            

    指明模块源码中各文件的依赖关系，以及要生成的目标模块名。mytest-objs := file1.o file2.o                                                  

                                                                                                                                            

    file3.o表示mytest.o 由file1.o，file2.o与file3.o 连接生成。obj-m :=                                                                      

                                                                                                                                            

    mytest.o表示编译连接后将生成mytest.o模块。                                                                                              

                                                                                                                                            

    --- end of add on 2006年5月20日 ---                                                                                                     

                                                                                                                                            

     另外，编译完内核以后用make INSTALL_MOD_PATH=/pathyouwant modules_install可以把内核模块装到指定目录