Module code

Copyright 1997 Robert de Bath and Alistair Riddoch

I have implemented a simple module implementation in the kernel based on code
sent to me by Rob de Bath. It allows drivers to be loaded into and unloaded
from a slot in the kernel. The module text is loaded into the kernel at
module_init(), and the data at module_data both of which are defined in
kernel/module.c.

An example module and the tools required to build it are found in the
modules directory. The key files in this directory are:

serial.c	- The module. Slightly modified arch/i86/driver/char/serial.c

symchop.ask	- Script that is used to generate modlink.s which defines all
		  the kernel symbols, to be linked to the module.

objchop.c	- Program that takes the compiled, linked module and splits it
		  into text and data images to be directly loaded into the
		  kernel.

vals.c		- Program that chops the empty bits off the text and data 
		  images.

Because the module is linked to the kernel symbols at compile time, the module
must be recompiled if the kernel is changed in such a way that the symbols
module_init and module_data are diferent. If in doubt, re-compile.

The utility insmod used to load modules into the kernel is found in the
elkscmd packages in elkscmd/sysutils. It uses the new insmod(2) system call
to load and initialise the module. To keep the amount of kernel code
required to a minimum, the /dev/mem device is used to copy the module
images into kernel memory.