Question 12 Consider the following snippet of code from xv6: void syscall(void) { int num; struct proc *curproc = myproc(); num = curproc->tf->eax; if(num > 0 && num tf->eax = syscalls [num](; } else { cprintf("%d %s: unknown sys call %d ", curproc->pid, curproc->name, num); curproc->tf->eax = -1; } } How is the system call number (read into num) first loaded into curproc->tf->eax? the kernel saves all the general purpose registers onto the kernel stack as part of the trap frame, after an interrupt the kernel copies it there as a result of a preceding call to argint the user places the argument to the system call here before calling int it is saved onto the kernel stack by the hardware as part of the int instruction behavior