Title: Class 6: Making a Process (Virtualizing Memory)
Date: 2014-02-04
Category: Classes
Tags: operating systems, Rust, virtual memory, processes
Author: David Evans
**[Problem Set 2](|filename|../../pages/ps/ps2/ps2.md)** is due Sunday, 9 February. You should sign-up for a team demo using [this form](https://docs.google.com/spreadsheet/ccc?key=0AvXGI69lkg_edGE4dk0taUFlcmVueGg0UExIT1RZSXc&usp=sharing#gid=0).
Weilin's most evil test:
````
curl "http://rust-class.org/pages/ps2.html" | sed "s/[^a-zA-Z ]/ /g" | tr "A-Z " "a-z\n"| grep "[a-z]" | sort -u
````
What is the difference between a background process and foreground process?
What happens when the user types `Ctrl-C`?
# Memory Isolation
How can a program be isolated in memory without hardware support?
[Native Client](https://developers.google.com/native-client/) - [_Native Client: A Sandbox for Portable, Untrusted x86 Native Code_](http://static.googleusercontent.com/external_content/untrusted_dlcp/research.google.com/en/us/pubs/archive/34913.pdf), IEEE Security and Privacy ("Oakland") 2009.
What are the advantages/disadvantages of hardware-based memory isolation over software-based memory isolation?
# Implementing Virtual Memory
Robert C. Daley and Jack B. Dennis, [_Virtual Memory, Processes, and Sharing in
MULTICS_](|filename|./daley-cacm68.pdf) - Symposium on Operating System
Principles (SOSP), 1967.
What must be done to switch processes on MULTICS?
# Virtual Memory on the x86
[Intel x86 Software Develop Manuals](http://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-manual-325462.pdf) - Most of what I covered today is in Volume I, Chapter 3 (_Basic Execution Environment_) with Section 3.3 on Memory Organization. Chapter 5 is all about Protection.
Why is it useful to convert a _logical address_ into a _linear address_, as is done by the segmentation unit?
Where is the Global Descriptor Table stored?
Why is a memory page in the 80386 (32-bit) processor 4K bytes?
What will this program do and why?
````c
#include
#include
int main(int argc, char **argv) {
char *s = (char *) malloc (1);
int i = 0;
while (1) {
printf("%d: %x\n", i, s[i]);
i += 4;
}
}
````
**Challenge:** Write a program that takes _N_ as an input and produces
(nearly) exactly _N_ page faults. A good solution is worth a USS
Hopper patch (even cooler than a Rust sticker!) or an exemption from
Exam 1 or Exam 2.
If you were designing a modern processor today, and not limited by the
need to run legacy operating systems and programs, how would your memory
isolation design be different from x86's virtual memory?
# Growing a Language
Guy L. Steele's _Growing a Language_ [[Transcript](http://www.cs.virginia.edu/~evans/cs655/readings/steele.pdf)]:
How well does the design of Rust espouse the philosophy of growing a
language by Guy Steele in the talk?