CSE120, Fall 2005, Homework 1
Due: October 4, in class

1. [Silberschatz] In most modern OSes, several users share the system 
simultaneously.  This situation can result in various security problems.  
What are 3 such problems?  How, if possible, can we ensure the same 
degree of security in a shared machine as in a dedicated one?

2. Why must the OS verify and copy system call arguments into kernel 
memory?

3. [Silberschatz] Describe 3 general methods for passing parameters to 
the operating system.

4. Suppose user processes could disable timer interrupts.  What problems 
could this cause?  Why might this be beneficial for certain applications 
or computing environments?

5. Suppose the architecture provided no explicit system call support, 
but provided dedicated system call registers.  How could the OS still 
enable a user process to make "system calls"?

6. What are the advantages and disadvantages to having system calls not
restart on interrupt (the UNIX default) vs. being automatically restarted
by the kernel?

7. What are the advantages and disadvantages to storing handles to OS 
resources (open files, network sockets) per process rather than shared 
across all processes?

8. Suppose the architecture provided no priviledged mode of operation.  
What problems could this cause?  Could you build a conventional (e.g. 
UNIX-like) OS on it?  How?

9. Upon fork(), why might it not be a good idea to copy the process's 
entire address space?

10. [McKusick] After a process has exited, it may enter the state of 
being a zombie, before disappearing from the system entirely.  What is 
the purpose of the zombie state?  What event causes a process to exit 
from the zombie state?