Class 6: Making a Process (Virtualizing Memory)

Posted: Tue 04 February 2014

Problem Set 2 is due Sunday, 9 February. You should sign-up for a team demo using this form.



Gnashing about Gash

Weilin's most evil test:

   curl "" | 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 - Native Client: A Sandbox for Portable, Untrusted x86 Native Code, 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 - 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 - 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?

#include <stdio.h>
#include <stdlib.h>

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]:

How well does the design of Rust espouse the philosophy of growing a language by Guy Steele in the talk?

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