Re: Problems compiling kernel modules

["Richard B. Johnson" <root@chaos.analogic.com>]

On Mon, 23 Aug 2004, Lei Yang wrote:

> Hi friends,
>
> I've askeed questions about errors compiling kernel modules caused by
> including <stdio.h> and got some very helpful info here.
>
> I changed those I/O stream and file operation in the code and get the
> module compiled, however, there would be warnings like
>
> In file included from /home/lei/modules/test.c:49:
> /home/lei/modules/Kcomp.h:21: warning: function declaration isn't a
> prototype
> /home/lei/modules/Kcomp.h:27: warning: function declaration isn't a
> prototype
> /home/lei/modules/Kcomp.h:69: warning: function declaration isn't a
> prototype
>
> And the no prototype fuction looks like
>
> int preset() // with no arguments
> {
> 	p = &nodes[0][0];
> 	return 0;
> }
>

A function looks like this:

int present()
{

}

A prototype for the same function looks like this:

int present(void);

Functions always have "{}". Prototypes never do.
-- Yes there's some troll who might cite some obscure
case... ignore them.

If you compile above a certain warning-level, then prototypes
are required. The prototype usually goes in header files
and the function (the actual code) goes in the source files.

>
> So when I tried to install the module with insmod ./test.ko ,
> there would be an error,
>
> insmod: error inserting './test.ko': -1 Unknown symbol in module
>
> Could anyone tell me what is wrong here? Is that because of the no
> prototype function declaration?
>

Do `depmod -e test.ko` to see what it's complaining about. You
can see all the symbols by using `nm`. Try it. Your code
probably didn't define the necessary stuff to make a module.
You need to look at a typical module (driver) that comes with the
kernel. Just find one of the shortest ".c" files in the driver
tree.


Cheers,
Dick Johnson
Penguin : Linux version 2.4.26 on an i686 machine (5570.56 BogoMips).
            Note 96.31% of all statistics are fiction.