1. PROGRAM AT RUNTIME Subject code: CSCI-620
Subject name: Operating Systems Security
Lecture No.:
Unit: 02
Unit topic: Basic program execution flow control
Professor : R. A. Mihajlović
School year: /2013
© R. A. Mihajlovic, Reproduction is prohibited

2. CSCI-620 Operating Systems Security
Topics
Program lifetime phases
Typical C program development phases
Program statistics
Run time
Compile time
CSCI-620 Operating Systems Security
Lecture 2.2 2

3. Typical Program Lifetime Phases
Typical Program Lifetime Phases
One program or software goes through 3 general life time phases:
Static or development phase, compile time
Transient or loading phase, load time
Dynamic or runtime phase, runtime
Additional lifetime phase is deployment/installation/roll-out time, which may be of essence with regard to security.
CSCI-620 Operating Systems Security
Lecture 2.2

4. Typical C Program Development Steps
Typical C Program Development Steps
Phases of some typical C/C++ program evolution:
Editing (Static)
Preprocessing (Static)
Compiling (Static)
Linking (Static)
Loading (Transient)
Executing (Dynamic)
CSCI-620 Operating Systems Security
Lecture 2.2

5. Typical C Program Development Steps
Typical C Program Development Steps
Program source text is created in the editor and stored on disk.
Preprocessor program
processes the source code text.
Loader puts program in memory.
Compiler & Assembler create object code and stores it on disk.
Linker links the object code modules with the libraries
Loader
Primary
Memory
Compiler
Editor
Preprocessor
Linker
Primary Memory .
Disk
CPU
Static or
Compile Time
Transient or
Load Time
Dynamic or
Run Time
CPU fetches each object code instruction and executes it.

6. Source Code Text Processing
Compiler (Static time)
“Translates” program written in "source" language to "target" language
Interpreter (Dynamic time translation & execution)
Translates source text line/instruction into object code and immediately executes
CSCI-620 Operating Systems Security
Lecture 2.2

7. Source Code Text Processing (Transformation)
Assembler (Static time)
Translates Assembly language text into the object binary code (machine “language” not human language) for particular machine/CPU
Macro Processor (Static time)
Textual substitutions, (Parses text, finds its directives and executes these directives by replacing them with the macro-text)
Example: Macro assembler replaces Macro Assembly instructions with the block of assembly instructions (With the Macro code)
Example: C preprocessor replaces preprocessor directives with the result of their execution (#include, #define, #ifdef,…)
CSCI-620 Operating Systems Security
Lecture 2.2

8. CSCI-620 Operating Systems Security
Run time statistics
Good estimate is that out of all programs running at any given time anywhere in the world, 90% were written in C.
CSCI-620 Operating Systems Security
Lecture 2.2

9. Compile time statistics
Good estimate is that out of all programs that exist on the storage of any computing machine in the world 10% were written in C.

10. CSCI-620 Operating Systems Security
Reference
[1] John W. Backus, 82, Fortran Developer, Dies, NY Times, March 20, 2007 [2] Additional material
CSCI-620 Operating Systems Security
Lecture 2.2

11. CSCI-620 Operating Systems Security
The End
J.W. Backus Inventor of Fortran 1957
CSCI-620 Operating Systems Security
Lecture 2.2