How to prevent “error: 'symbol' undeclared here” despite EXPORT_SYMBOL in a Linux kernel module?

Question

I\'m embedding some driver into a Linux kernel when I get this error (I\'m adding the device in the board file and registering it):

error: \'kxtf9_get_slave_         


        

Answer 1

EXPORT_SYMBOL exports the symbol for dynamic linking. What you have is not a linking error but a compilation error due to a missing function declaration. You have to either write a header file for the C file and include that header file, or you declare the function the C file you're compiling.

Option 1:

kxtf9.h:

#ifndef KXTF9_H
#define KXTF9_H

struct ext_slave_descr *kxtf9_get_slave_descr(void);

#endif

your_file.c:

#include "kxtf9.h"
/* your code where you use the function ... */

Option 2:

your_file.c:

struct ext_slave_descr *kxtf9_get_slave_descr(void);
/* your code where you use the function ... */

Also note that the EXPORT_SYMBOL in the file kxtf9.c has #ifdef __KERNEL__ around it, so you have to have set up your build environment (Makefile) correctly - otherwise you'll get a link error.