From mboxrd@z Thu Jan  1 00:00:00 1970
From: greg@kroah.com (Greg KH)
Date: Fri, 24 Jul 2015 10:10:18 -0700
Subject: Do you know the bug of EXPORT_SYMBOL()
In-Reply-To: <20150724054941.GA17034@debian>
References: <20150724054941.GA17034@debian>
Message-ID: <20150724171018.GA8358@kroah.com>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

On Fri, Jul 24, 2015 at 01:49:42PM +0800, Navy wrote:
> Hi
> To my understanding, EXPORT_SYMBOL() is used to export a symbol in 
> kernel/modules. The the address of the all sysbols is in /proc/kallsyms. 
> Only symbols exported by EXPORT_SYMBOL() is listed its CRC information 
> in Module.symvers. So I think the CRC is the key to export a symbol.
> I do an experiment:
> 	
>        ---mdir
>            |
>            |---Mod1
>            |    |---mod1.c
>            |    |---Makefile
>            |
>            |---Mod2
>                 |---mod2.c
>                 |---Makefile
> 		
> mod1.c define function *void myfunc(void)* and exported by EXPORT_SYMBOL() 
> and the CRC info is showed in Module.symvers. mod2.c reference *myfunc* and
> compiled successfully. BUT when mod2.ko is insmoded, "unknown symbol" is 
> complained. mod2.ko CAN'T BE INSMOD.

Use 'modprobe' after "properly" installing the kernel modules to the
correct location, and then all will be fine.

greg k-h