My mission is intercept VM syscall insmod (sys_init_module) from hypervisor.
I've dirty xen code to try, specifically in do_guest_trap function in arch/x86/traps.c Xen file. In this function I've added this small part of code:

unit32_t a;
if (v->domain->domain_id != 0) { /* if domain is not Dom0 */
    a=regs->eax;
    if (a == 128) {
          printk("I've intercepted sys_init_module");
    }
}

In this way I'm able to intercept the syscall sys_init_module (number 128) from any DomU, but my problem now is to intercept the insmod parameter and print it with printk.
I've tried to assign a

char __user *myvar = (char __user *)regs->ebx

but I can't print it with

printk("%s",myvar)

This is what happen: when I start my domU and happen an insmod in boot time, my dom0 reboots itself.

Is it true that parameter of my syscall is in regs->ebx register?? What is the way to print it in human readable (for example if in DomU I print in shell "insmod mymodule" I'd like print "mymodule" from hypervisor, not the hex value like 0804b018, but the string).

Can you help me? I'd like only print insmod parameter. I use 3.2.1 xen + linux-2.6.18-xen.hg.

Thanks a lot.

Elena