compiling a module with gcc

mathman0 · 11-06-2004, 07:42 PM

writing a simple module trying to learn about writing device drivers...but i cant seem to get my code to compile properly
hello_module.c:

Code:

#include <linux/module.h>
                                                                             
#if defined(CONFIG_SMP)
#define __SMP__
#endif
                                                                             
#if defined(CONFIG_MODVERSIONS)
#define MODVERSIONS
#include <linux/modversions.h>
#endif
                                                                             
#include <linux/kernel.h>
                                                                             
int init_module(void)
{
        printk("<7>Hello kernel!\n");
        return 0;
}
                                                                             
void cleanup_module(void)
{
        printk("<7>Good-bye kernel!\n");
}

however when i try to compile and insert it i get this:
[root@localhost root]# gcc -D __KERNEL -D MODULE -O2 -W -Wall -c hello_module.c
hello_module.c: In function `init_module':
hello_module.c:16: warning: implicit declaration of function `printk'
[root@localhost root]# insmod hello_module.o
insmod: error inserting 'hello_module.o': -1 Invalid module format

if anyone could point me in the right direction it'd be greatly appreciated

23,1 All

foo_bar_foo · 11-06-2004, 09:21 PM

well for one thing fedora 2 kernel (modern) uses .ko modules
have no idea if they really differ from regular object files though ?????
first try -- just rename it.

mathman0 · 11-06-2004, 10:46 PM

well thanks for the info,renaming it however didn't work....but need to look into why they're doing this............heard alot of good things about FC2 but not that impressed

mathman0 · 11-06-2004, 10:48 PM

found a few errors in my command,am now using
[root@localhost root]# gcc -D__KERNEL__ -D__SMP__ -DMODULE -DMODVERSIONS -I/lib/modules/2.6.5-1.358/build/include -Wall -O2 -o hello_module.o -c hello_module.c
In file included from /lib/modules/2.6.5-1.358/build/include/asm/processor.h:18,
from /lib/modules/2.6.5-1.358/build/include/asm/thread_info.h:16,
from /lib/modules/2.6.5-1.358/build/include/linux/thread_info.h:21,
from /lib/modules/2.6.5-1.358/build/include/linux/spinlock.h:12,
from /lib/modules/2.6.5-1.358/build/include/linux/capability.h:45,
from /lib/modules/2.6.5-1.358/build/include/linux/sched.h:7, from /lib/modules/2.6.5-1.358/build/include/linux/module.h:10,
from hello_module.c:1:
/lib/modules/2.6.5-1.358/build/include/asm/system.h: In function `__set_64bit_var':
/lib/modules/2.6.5-1.358/build/include/asm/system.h:193: warning: dereferencing type-punned pointer will break strict-aliasing rules
/lib/modules/2.6.5-1.358/build/include/asm/system.h:193: warning: dereferencing type-punned pointer will break strict-aliasing rules

but still the same error from insmod

foo_bar_foo · 11-07-2004, 01:19 PM

Quote:

Originally posted by mathman0
...but need to look into why they're doing this...........

new kernel is a good think you just have an old example trythis

Code:

    #include <linux/init.h>
    #include <linux/module.h>
    #include <linux/kernel.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);

Makefile

Code:

obj-m += hello.o
default:
make -C /lib/modules/$(shell uname -r)/build/ SUBDIRS=$(PWD) modules

put a TAB before make in the Makefile

sorry i cant try this to see if it works cause my kernel is very different (compiled with icc)

mathman0 · 11-07-2004, 03:13 PM

thank you,it now compiles and after inserting operated fine,now i can move on to read more about device drivers thank you