On Wed, Jul 20, 2005 at 08:41:56AM +0530, Vijay Ram Chitrapu (RCVIJAYD) wrote:
> I am a newbie to programming in kernel.
> I am facing a problem with "insmod".
> I have several files say. test1.c test2.c
> I have compiled all the files with the -o option and created a common .o
> file. Sample of the above files is as below..
>
> int minit(char *a, int argc,char * argv[])
> {
> printk("<1>...argc: %d\r\n",argc);
^^^
Do not use "<1>", use the KERN_ macros in include/linux/kernel.h
instead. If the values of KERN_ change, your module will continue to
work, but only if you use the KERN_ macros. Make the printk():
printk(KERN_ALERT "blablabla\n");
> if (argc < 2)
> {
> printk("<1>\n");
> return 0;
> }
> return 0;
> }
>
> the function minit is prototyped in a header file.
The entry point of a kernel module is the function pointed by the
module_init() macro. The function prototype of the init function is not
like in userland, but: static int init_module(void); . IOW: it takes
*no* arguments.
> All the code files will contains functions similar to this with different
> name and prototypes. None of the files have a init_module function.
Well, that's an error. There should be an entry point to a module,
otherwise there's no way to initialise a module.
> While doing insmod of the final obtained .o file, an error is being
> thrown saying, Floating Point Exception and core is dumped.
> I have debugged the code using GDB and found that the use of the int argc
> in the above function was creating the exception..
That doesn't surprise me at all. The function prototype of a module
init function is:
static int init_module(void);
You created a function like:
int minit(char *, int, char * []);
Your function parameters take whatever was left on the stack (i.e.:
random values)
> Can anybody please clear my doubts
> 1. can i insert a module which does not have a init_module and
> cleanup_module functions?
No, of course not. How should the kernel know what to do with a random
piece of code?
> 2. While doing insmod, is the code executed or somethign simialr
> happens..? This doubt could be silly but..the reason behind this doubt is
> the exception as i said was for local variables.
No, the only thing that gets executed is the function declared in the
module_init() macro.
> 3. under wat conditions do we get a FPE (floating point exception) ?
By creating random junk and trying to load it as a module.
> Basically the above code was actually written for the user space usage
> and am now trying to change it to the kernel space.
Do not even *think* about doing that. The kernel has a very specific
task: to share resources (CPU time, access to devices and files)
between processes and to protect those processes against each other. It
is NOT a place to run userspace programs. Trying to run programs in
kernel space only has disadvantages:
- It doesn't become any faster.
- It's much more difficult.
- Any programming error you make will be fatal and compromise the
stability of the whole system.
> Do we need to take some extra care to make the necessary changes?
I think you should read "Linux Device Drivers, 3rd edition". If you
don't want to buy it, it's available online for free at
http://www.xml.com/ldd/chapter/book/ .
Erik
--
Erik Mouw
J.A.K.Mouw@xxxxxxxxxxxxxx mouw@xxxxxxxxxxxx
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