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Computer Systems &
Programming (CS 367)
Prof. Richard Carver
George Mason University
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Course Goals
Previous courses (CS 112, CS 211): high-level
programming in Java/C++
This course: exposes you to C and assembly
programming
- C is a procedural language (not object-oriented)
- Commonly used for “low-level” systems programming and embedded systems
Theme of the course: strip away abstractions provided by
high-level languages such as Java and let you understand
what goes on “under the hood”
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Course Goals cont’d
Abstractions have limits
- Especially in the presence of bugs
- Need to understand underlying implementations
Useful outcomes
- Become more effective programmers Able to find and eliminate bugs efficiently Able to tune program performance
- Prepare for later “systems” classes in CS & ECE Compilers, Operating Systems, Networks, Computer Architecture
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Great Reality #
Int’s are not Integers, Float’s are not Reals
Examples
- is x^2 0? Float’s: Yes! Int’s: - 40000 * 40000 --> 1600000000 - 50000 * 50000 --> ??
- is (x + y) + z = x + (y + z)? Unsigned & Signed Int’s: Yes! Float’s: - (1e20 + -1e20) + 3.14 --> 3. - 1e20 + (-1e20 + 3.14) --> ??
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Great Reality #
Memory Matters
Memory is not unbounded
- It must be allocated and managed
- Many applications are memory dominated
Memory referencing bugs especially pernicious
- Effects are distant in both time and space
Memory performance is not uniform
- Cache and virtual memory effects can greatly affect program performance
- Adapting program to characteristics of memory system can lead to major speed improvements
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Memory Referencing Bug Example
main () { long int a[2]; double d = 3.14; a[2] = 1073741824; / Out of bounds reference / printf("d = %.15g\n", d); exit(0); }
main () { long int a[2]; double d = 3.14; a[2] = 1073741824; / Out of bounds reference / printf("d = %.15g\n", d); exit(0); }
Alpha MIPS Linux -g 5.30498947741318e-315 3.1399998664856 3. -O 3.14 3.14 3.
(Linux version gives correct result, but implementing as separate function gives segmentation fault.)
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Memory Referencing Errors
C and C++ do not provide any memory protection
- Out of bounds array references
- Invalid pointer values
- Abuses of malloc/free Can lead to nasty bugs
- Whether or not bug has any effect depends on system and compiler
- Action at a distance Corrupted object logically unrelated to one being accessed Effect of bug may be first observed long after it is generated How can I deal with this?
- Program in Java, Lisp, or ML
- Understand what possible interactions may occur
- Use or develop tools to detect referencing errors
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Course Perspective
Most Systems Courses are Builder-Centric
- Computer Architecture Design pipelined processor
- Operating Systems Implement portions of operating system
- Compilers Write compiler for simple language
- Networking Implement and simulate network protocols
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Textbooks
Randal E. Bryant and David R. O’Hallaron,
- “Computer Systems: A Programmer’s Perspective”, Prentice Hall 2003.
- csapp.cs.cmu.edu
Brian Kernighan and Dennis Ritchie,
- “The C Programming Language, Second Edition”, Prentice Hall, 1988
- You can use any book on C
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Course Outline
Programming in C (2 weeks)
Data Representation (2 weeks)
Program Representation (5 weeks)
Linking (1 week)
Exceptional Control Flow & Virtual Memory (3 weeks)
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Programming in C
Assumption: You are comfortable programming in Java
and/or C++
C is a procedural (imperative) programming language
Topics
- C Standard I/O library for input/output
- Bit-level operators
- Pointers & Structures
- Memory allocation and deallocation
Assignment
- P1: Write a non-trivial program in C
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Machine-level Representation of Data and
Programs
Topics
- Bits operations, arithmetic, assembly language programs, representation of C control and data structures
- Includes aspects of of architecture and compilers
Assignments
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Logistics
Grading
- Programming Assignments and Homework (50%) All programs will be tested on a Linux platform for grading - You need to obtain an IT&E Unix Cluster account (See syllabus)
- Midterm (25%) & Final (25%) Class TA
- Raimi Rufai ([email protected])
- Office Hrs: TBD My office hrs
- T 3:45-4:30pm, S&T II, Room 343
- Also available at other times (e.g., before class)
- Always available via email
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Policies
Classroom:
- Set phones to vibrate mode if you must leave them on
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Cheating
What is cheating?
- Sharing code: either by copying, retyping, looking at, or supplying a copy of a file.
What is NOT cheating?
- Helping others use systems or tools.
- Helping others with high-level design issues.
- Helping others debug their code.
Penalty for cheating:
- Removal from course with failing grade.
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Logistics cont’d
Class Web Page
- http://www.cs.gmu.edu/~rcarver/cs
- Lecture Slides, Assignments, Useful Links
