COMP 40
Machine Structure and Assembly-Language Programming
Tufts University
Fall 2011

What's this class about and why am I taking it?

• Machine structure shows how data is represented at the machine level.
• Assembly language is how code is represented at the machine level.

• The construction of very high-level abstractions and programming languages on top of very low-level hardware is one of the great intellectual achievements of computer science, and every computer scientist should know about it.
• The data and code model of any particular machine, called its instruction-set architecture, represents a contractual agreement between hardware designers and systems programmers that allows a collection of programs to run on any hardware which conforms to the instruction-set architecture. The exploitation of instruction-set architecture to enable both hardware and software to be changed independently and reused with each other is one of the great engineering achievements of computer science, and every computer scientist should know about it.
  (Some of the fruits of this exploitation include operating systems that will run on any x86-compliant hardware; the ability to buy new, more advanced CPUs without having to replace your software; and the ability to create and use ``virtualization environments'' such as VMware, QEMU, Xen, and so on.)
• A programmer may understand a high-level program's outputs and interactions by understanding only the model of computation presented by the programming language. But to understand how a program performs, one needs a working knowledge of computation at the machine level.
• When something goes wrong in a software system, diagnosing the fault often requires the ability to break the abstraction barriers presented by programming languages and to inspect the state and behavior of the machine at its own level, not the level of programs' source code.
• Much software that is critical to the world's computing infrastructure is written in the languages C and C++, and to understand how this ``systems software'' works, one must understand machine-level computation.

• You will be able to understand and improve the real performance of programs written in high-level languages.
• You will be able to diagnose and fix bugs that can't be explained without appealing to the underlying machine model. Many important bugs in C and C++ programs fall into this class.
• You will have started learning how to exploit the underlying hardware in ways that are not possible using high-level languages alone.

Should I actually buy the books?

Not everyone can afford to buy all the books required for the course, and some people just don't like to spend money on books. No one plan works for everyone, but here's what I believe:

• You should have a copy of Hanson's C Interfaces and Implementations before class starts. You'll use it intensively throughout the term, but especially the first few weeks.

  The devil's advocate says that the code is online and so is a PDF quick reference, so you don't need the book. You can definitely live without it, but it will cost you time. How much extra time are you willing to put in so that you don't have to buy this book?

• Kernighan and Ritchie is the canonical book about C, and it is one of the best books ever written about any programming language, ever. You can get it used, cheap. If you are serious about software, sooner or later you will want to own Kernighan and Ritchie. But that doesn't mean you have to own it now.

  The devil's advocate says that the Internet has plenty of good information about C and there is no need to buy a book. You'll need to know how effectively you can work with online information, vs a book you can write in, put stickies on pages, and so on.

• Many students get through the entire semester without using Bryant and O'Hallaron. The book is useful primarily if you have trouble following lectures or if you need more depth than lectures can provide. (Lectures are intense and fast-paced, so many people do have trouble following lectures in real time.) And there are a few topics, like caches and assembly code, which may be hard to understand without some sort of book. I've advised people to pick up a used copy or even a used copy of the first edition.

  The devil's advocate says that every year, a few students say that they found Bryant and O'Hallaron incredibly helpful. They say that they couldn't have gotten through 40 without it, or that it saved them lots of time and effort. The problem is I have no way of telling if you are going to be one of those students.

How can I find out more?

Course admin and course materials

• Photos so you can recognize the course staff
• Sketch of course Syllabus and Schedule
• Lecture notes I prepare for class
• Homework Assignments and solutions. See also How to Analyze a Programming Problem.
• You can see testing results from the lab on removing black edges. Every good test that was submitted was run against all the binaries.
• We have statistics about binary bombs.
• You can view a statistical information about grades on the midterm.
• Lab handouts
• Grading standards
• Pair programming with the course staff
• Other details for which you are responsible
  • Prerequisites
  • Policies and procedures (homework, etc.), including what sorts of collaboration are permissible.
  • Computer software and accounts for the course
• Code that you may find helpful for labs or homework

Technical information

• Idioms for C programmers
• Compiling quickly using a text editor (includes info for emacs and vim).
• Design checklists:
  For a single abstraction
  For a whole program
  For problem-solving
• How to write documentation for COMP 40
• How to analyze a complex problem, with examples from the image-compression project
• C Interfaces and Implementations Quick Reference
• How to connect to linux.cs.tufts.edu using VNC
• Highlighted handouts and advice:
  • How to Write Compile Scripts—all about compiling and linking.
  • Pair programming: What to do when you're not holding the keyboard
• Dinkumware's documentation for the Standard C Library and C99 library overview.
• Useful links to AMD64 information
• Readings
• Noah Daniels's performance tips
• The Univeral Machine Macro Assembler
• Search for answers on Stackoverflow:
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Thanks to Chloe Lopez, you can send an anonymous comment on lecture (or anything else) at any time.