#Null-pointer Dereference In xv6 , currenlty the address space of a user program starts at address location 0, Hence NULL pointer deference doesnt throw an error.

• I have modified the code so that the first page of address is not used, hence any deference to a NULL pointer will throw and trap error.
• Have modifed the pointer deference in a system call to check if the address is not in the 0th page else throw error.

The xv6 address space is currently set up like this:

code stack (fixed-sized, one page) heap (grows towards the high-end of the address space)

In this part of the xv6 project, I have changed the address space to look like this:

code heap (grows towards the high-end of the address space) ... (gap) stack (at end of address space; grows backwards)