sys_call_table is not exported anymore for kernel modules to
tinker with (for a number of good reasons mentioned elsewhere).
This code is groping in the kernel address space to figure
out the location of the sys_call_table.
On Fri, Jan 31, 2003 at 05:24:06PM +0530, Mohanasundaram C wrote:
> Hi All,
>
> I tried to understand the code below but could not. Can any one please explain me.
>
> Regards,
> Mohan.
>
> #include <linux/syscall.h>
> #include <asm/unistd.h>
>
> static void **sys_call_table;
>
> //nearest exported symbol to syscalls in my kernel,
> //i hope in others kernels too
> //but in other form you can look at your kernel sources
>
> extern void *system_utsname;
>
> ....
>
> static int locate_sys_call_table(void) {
> unsigned long *begin;
> int i;
>
> begin=(unsigned long *) &system_utsname;
> for (i=0;i<1024;i++) {
> if (*(begin+i)==(unsigned long) sys_socketcall) {
> sys_call_table=(void *) (begin+i-__NR_socketcall);
> //are you sure?
> if (sys_call_table[__NR_exit]==(void *) sys_exit) {
> printk("success: located sys_call_table: %X\n",(unsigned
> int) sys_call_table);
> return(1);
> }
> }
> }
> return(0);
> }
>
>
> int __init init_exportmodule (void)
> {
>
> if (!locate_sys_call_table()) {
> // ... cry again and return error
> }
>
> //.....sys_call_table[] works now!!
> //......do something like export symbol
> //.... or intercept any syscall
>
> }
> --
> Kernelnewbies: Help each other learn about the Linux kernel.
> Archive: http://mail.nl.linux.org/kernelnewbies/
> FAQ: http://kernelnewbies.org/faq/
>
--
Vamsi Krishna S.
Linux Technology Center,
IBM Software Lab, Bangalore.
Ph: +91 80 5044959
Internet: vamsi@in.ibm.com
--
Kernelnewbies: Help each other learn about the Linux kernel.
Archive: http://mail.nl.linux.org/kernelnewbies/
FAQ: http://kernelnewbies.org/faq/
