Cannot Load Kernel Loadable MOdule...

[mohit.saha]

hi everybody,

I tried to create a new module as given in http://tldp.org/LDP/lkmpg/2.6/html/lkmpg.html, hello-1.c.

/*
* 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");
}

and then created the Makefile as

obj-m += hello-1.o

all:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

and then make that... but the following errors are coming:

[root@dhcp-ptp2-10-177-142-249 LKM]# make
make -C /lib/modules/2.6.22.5/build M=/root/Desktop/LKM modules
make[1]: Entering directory `/usr/src/linux-2.6.22.5'
Building modules, stage 2.
MODPOST 0 modules
WARNING: vmlinux(.text+0xc040116f): Section mismatch: reference to .init.text:start_kernel (between 'is386' and 'check_x87')
WARNING: vmlinux(.text+0xc061fc70): Section mismatch: reference to .init.text: (between 'rest_init' and 'alloc_node_mem_map')
WARNING: vmlinux(.text+0xc062460a): Section mismatch: reference to .init.text: (between 'iret_exc' and '_etext')
WARNING: vmlinux(.text+0xc0624616): Section mismatch: reference to .init.text: (between 'iret_exc' and '_etext')
WARNING: vmlinux(.text+0xc0624622): Section mismatch: reference to .init.text: (between 'iret_exc' and '_etext')
WARNING: vmlinux(.text+0xc062462e): Section mismatch: reference to .init.text: (between 'iret_exc' and '_etext')
WARNING: vmlinux(.text+0xc061fcf0): Section mismatch: reference to .init.text:__alloc_bootmem_node (between 'alloc_node_mem_map' and 'zone_wait_table_init')
WARNING: vmlinux(.text+0xc061fd96): Section mismatch: reference to .init.text:__alloc_bootmem_node (between 'zone_wait_table_init' and 'setup_cpu_cache')
WARNING: vmlinux(.text+0xc061fe11): Section mismatch: reference to .init.text: (between 'setup_cpu_cache' and 'schedule')
WARNING: vmlinux(.text+0xc061fe4b): Section mismatch: reference to .init.text: (between 'setup_cpu_cache' and 'schedule')
WARNING: vmlinux(.text+0xc05066f2): Section mismatch: reference to .init.text:__alloc_bootmem (between 'vgacon_startup' and 'vgacon_scrolldelta')
WARNING: vmlinux(.text+0xc0624dc2): Section mismatch: reference to .init.text: (between 'iret_exc' and '_etext')
make[1]: Leaving directory `/usr/src/linux-2.6.22.5'


can u suggest what is the problem?
Also if anyone can suggest me gd book on Kernel Module Programming for LInux 2.6..

Thanks in advance...:)

[mohit.saha]

I inserted the code:

/*
* 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");
}


module_init(init_module);
module_exit(cleanup_module);


but it is still giving some error...

[mohit@dhcp-ptp2-10-177-142-249 LKM]$ make
make -C /lib/modules/2.6.22.5/build M=/home/mohit/Desktop/LKM modules
make[1]: Entering directory `/usr/src/linux-2.6.22.5'
CC [M] /home/mohit/Desktop/LKM/hello-1.o
/home/mohit/Desktop/LKM/hello-1.c:23: error: redefinition of ‘init_module’
/home/mohit/Desktop/LKM/hello-1.c:8: error: previous definition of ‘init_module’ was here
/home/mohit/Desktop/LKM/hello-1.c:24: error: redefinition of ‘cleanup_module’
/home/mohit/Desktop/LKM/hello-1.c:18: error: previous definition of ‘cleanup_module’ was here
make[2]: *** [/home/mohit/Desktop/LKM/hello-1.o] Error 1
make[1]: *** [_module_/home/mohit/Desktop/LKM] Error 2
make[1]: Leaving directory `/usr/src/linux-2.6.22.5'
make: *** [all] Error 2

Now tell me what is the problem....

[bwkaz]

The module_init and module_exit macros define a function named init_module and cleanup_module, respectively. That function calls the function whose name you pass to module_init and module_exit. Because you've already defined one function named init_module, you can't define a second one (via the macro) with the same name. (Also, you need to include <linux/init.h> in this file if you use those macros. That's the file that defines these macros, and it's always a good idea to avoid relying on inter-include-file dependencies to pull that stuff in.)

On the earlier issue, those were just warnings, so I think the module might have worked. But you should still fix them if possible -- I suspect that adding an __init and __exit to your functions would do that for you. So they'd be something like this:

int __init simple_module_init() { ..... }
void __exit simple_module_cleanup() { ..... }

module_init(simple_module_cleanup);
module_exit(simple_module_cleanup); Of course the function bodies would stay the same (I didn't include them here for brevity). :)