MODPOST __copy_from_user module compilation issue

Question

Hello!  I'm encountering a problem while compiling USB modules under Nios2Linux-MMU.  In Kernel config I select USB Host driver support and execute 'make modules'. At the end of the process I get the following errors:  
Building modules, stage 2.
  MODPOST 21 modules
ERROR: "__copy_from_user"  undefined!
ERROR: "__copy_to_user"  undefined!
Does anyone know good documentation about this modpost stuff? Actually I have no clue and can't find anything on this topic...  Btw, also when I use the __copy_*_user and copy_*_user in my own modules it results in the same error. As a workaround 've been using the put_user and get_user functions. But this couldn't be a solution.  regards  steron

altera_forum · Answer

It seems nobody can help me. I'm still trying to fix that and found out some things:  Now I'm trying to compile my own module where I use the function mentioned above.   The module is a char device driver and the important parts are the following:  # include &lt;linux/init.h&gt;# include &lt;linux/module.h&gt;# include &lt;linux/ioport.h&gt;# include &lt;linux/fs.h&gt;# include &lt;asm/io.h&gt;# include &lt;asm/uaccess.h&gt;
__copy_from_user(cmd,buffer,2);
Now i don't get the errors anymore, but warnings instead:  
  Building modules, stage 2.
  MODPOST 1 modules
WARNING: "__copy_from_user"  undefined!
The Makefile: (for building outside the kernel tree)  
obj-m := mymod.o
all:
  $(MAKE) -C ../../../uClinux-dist SUBDIRS=$(PWD) modules
Eventually the module is built, but when I try to plug it into the running kernel, I get this error: 
root:~&gt; insmod mymod.ko
mymod: Unknown symbol __copy_from_user
insmod: can't insert 'mymod.ko': unknown symbol in module, or unknown parameter
Am I missing something here? Cause the symbol _is_ actually defined, as I can see from /proc/kallsyms:  
root:~&gt; cat /proc/kallsyms | grep copy_from_user
c8006854 T __copy_from_user
c8008210 T copy_from_user_page
c805075c t __iovec_copy_from_user_inatomic
c805081c T iov_iter_copy_from_user
c80508ac T iov_iter_copy_from_user_atomic
c8086654 t pipe_iov_copy_from_user
c8123d58 T csum_partial_copy_from_user
One other thing I've found is this post on the forum: http://www.alteraforum.com/forum/showthread.php?t=14426 (http://www.alteraforum.com/forum/showthread.php?t=14426&amp;highlight=copy_from_user)  wentao suggests to include another EXPORT_SYMBOL in the according file. I did the same in arch/nios/mm/uaccess.c but it didn't help.  Thanks for your support  steron

altera_forum · Answer

Hi,

--- Quote Start ---

It seems nobody can help me. I'm still trying to fix that and found out some things:

--- Quote End ---

Before complaining to forum members, please 'grep' the kernel source directories and find the definition of '__copy_from_user'. Maybe it exists in the file

/nios2-linux/linux-2.6/arch/nios2/mm/uaccess.c

and its header file is

/nios2-linux/linux-2.6/arch/nios2/include/uaccess.h

And please check again whether your 'include path' is right or not.

Kazu

altera_forum · Answer

Hi!

--- Quote Start ---

Before complaining to forum members

--- Quote End ---

Complaining was not my intention. I'm sorry if it sounded like that. I just wanted to give you more information because the error messages from my first were probably not enough.

I checked the definition of the function and the include path. Eventually I put the EXPORT_SYMBOL(__copy_from_user); line into the arch/nios2/mm/uaccess.c file.

Don't know if it's only a workaround, because it seems strange that other users haven't encountered such errors.

By the way, in my last post when I wrote

--- Quote Start ---

I did the same in arch/nios/mm/uaccess.c but it didn't help.

--- Quote End ---

I just got confused with the directories in my kernel tree. Surprisingly I got another 'nios2' directory below 'arch/nios2' but this seems to be a result of any messy copying action.

altera_forum · Answer

Hi,    --- Quote Start ---   I checked the definition of the function and the include path. Eventually I put the EXPORT_SYMBOL(__copy_from_user); line into the arch/nios2/mm/uaccess.c file.  Don't know if it's only a workaround, because it seems strange that other users haven't encountered such errors.   --- Quote End ---     You mean that you don't have the description EXPORT_SYMBOL(__copy_from_user); in your 'uaccess.c' file ?  Modules are loaded dynamically and the linker must resolve the locations. To do this, the kernel must expose the symbol's location, and you need the macro 'EXPORT_SYMBOL(symbol)' if you want to use the 'symbol' in your module. In fact, the symbols  
EXPORT_SYMBOL(__copy_from_user);
EXPORT_SYMBOL(copy_from_user);
EXPORT_SYMBOL(__copy_to_user);
EXPORT_SYMBOL(copy_to_user);
EXPORT_SYMBOL(get_ds);
EXPORT_SYMBOL(get_fs);
EXPORT_SYMBOL(set_fs);
are exported in my 'arch/nios2/mm/uaccess.c'.  The macro 'EXPORT_SYMBOL' exports symbols as follows 
/* For every exported symbol, place a struct in the __ksymtab section */# define __EXPORT_SYMBOL(sym, sec)                
    extern typeof(sym) sym;                    
    __CRC_SYMBOL(sym, sec)                    
    static const char __kstrtab_##sym            
    __attribute__((section("__ksymtab_strings"), aligned(1))) 
    = MODULE_SYMBOL_PREFIX# sym;                        
    static const struct kernel_symbol __ksymtab_##sym    
    __used                            
    __attribute__((section("__ksymtab" sec), unused))    
    = { (unsigned long)&amp;sym, __kstrtab_##sym }
# define EXPORT_SYMBOL(sym)                    
    __EXPORT_SYMBOL(sym, "")
  And it seems that Wind River guys did not test the module loadings at all. Please see this  http://www.alteraforum.com/forum/showpost.php?p=78791&amp;postcount=48 .  Kazu

altera_forum · Answer

Shame on me, I actually got confused with file versioning. In the recent versions there are the correct macro calls in 'arch/nios2/mm/uaccess.c' and others. Thanks for the hint!  steron

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MODPOST __copy_from_user module compilation issue

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