Loadable module and kernel gp

Loadable module and kernel gp

[Christian Hildner]

Hi,

does anybody know a simple way for a loadable module to get the gp value 
of the kernel? Is there any sample code?

Christian

Re: Loadable module and kernel gp

[Erich Focht]

At compile time you can get it from the System.map. The symbol is at
the end and called __gp. Of course you might want to have some
cross-checks that you pick up the right System.map. I usually take
some known and exported symbols.

But there's surely some dynamic way, too...

Regards,
Erich

On Friday 23 January 2004 10:52, Christian Hildner wrote:
> does anybody know a simple way for a loadable module to get the gp value
> of the kernel? Is there any sample code?
>
> Christian

Re: Loadable module and kernel gp

[David Mosberger]

>>>>> On Fri, 23 Jan 2004 10:52:00 +0100, Christian Hildner <christian.hildner@hob.de> said:

  Christian> Hi, does anybody know a simple way for a loadable module
  Christian> to get the gp value of the kernel? Is there any sample
  Christian> code?

The safest way is probably to materialize a function pointer for a
function that is known to be in the kernel (and exported) and then to
read the second word.

	--david

RE: Loadable module and kernel gp

[Luck, Tony]

> >>>>> On Fri, 23 Jan 2004 10:52:00 +0100, Christian Hildner 
> <christian.hildner@hob.de> said:
> 
>   Christian> Hi, does anybody know a simple way for a loadable module
>   Christian> to get the gp value of the kernel? Is there any sample
>   Christian> code?
> 
> The safest way is probably to materialize a function pointer for a
> function that is known to be in the kernel (and exported) and then to
> read the second word.

In case "materialzie a function pointer" is total greek:

#include <linux/slab.h>

struct fptr {
	unsigned long func_addr;
	unsigned long gp;
};

your_routine()
{
	struct fptr = (struct fptr *)kmalloc; /*function known to be in kernel */

	printk("Kernel gp is %lx\n", fptr->gp);
}


Untested ... kmalloc is declared "inline" so that might mess things
up.  Just choose some other exported thing if it is.

Re: Loadable module and kernel gp

[Christian Hildner]

Luck, Tony schrieb:

>>>>>>>On Fri, 23 Jan 2004 10:52:00 +0100, Christian Hildner 
>>>>>>>              
>>>>>>>
>><christian.hildner@hob.de> said:
>>
>>  Christian> Hi, does anybody know a simple way for a loadable module
>>  Christian> to get the gp value of the kernel? Is there any sample
>>  Christian> code?
>>
>>The safest way is probably to materialize a function pointer for a
>>function that is known to be in the kernel (and exported) and then to
>>read the second word.
>>
Yes, that's it, thanks. Sometimes good solutions are also simple. I'll 
try it.

>
>In case "materialzie a function pointer" is total greek:
>
>#include <linux/slab.h>
>
>struct fptr {
>	unsigned long func_addr;
>	unsigned long gp;
>};
>
>your_routine()
>{
>	struct fptr = (struct fptr *)kmalloc; /*function known to be in kernel */
>
>	printk("Kernel gp is %lx\n", fptr->gp);
>}
>
>
>Untested ... kmalloc is declared "inline" so that might mess things
>up.  Just choose some other exported thing if it is.
>
I hope the compiler will not explode if I request the pointer to an 
inlined function ;-). I like the idea of using kmalloc since this symbol 
should be present in almost any kernel.

Thanks

Christian