Today & next lecture Aims of the course Introduction to issues - - PowerPoint PPT Presentation

Chair of Software Engineering

Software Verification

Contracts, Trusted Components and Patterns

Bertrand Meyer Manuel Oriol Till Bay ETH, Fall 2008

Chair of Software Engineering

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Today & next lecture

Aims of the course Introduction to issues of software quality Axiomatic semantics and program correctness (1)

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Aims of this course

To provide a survey of

• Reuse and component technology, with a special

emphasis on object-oriented approaches

• Techniques for quality components
• Software verification techniques

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Topics

• Quality issues in software engineering
• Components and the notion of trusted component
• Designing O-O libraries
• Axiomatic Semantics and Program Correctness
• Componentization: turning patterns into Components
• Automatic component testing techniques
• Program analysis
• Model checking
• Abstract interpretation
• Separation logic (guest lectures by Cristiano Calcagno)
• Proof-Carrying Code

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Basic references

Clemens Szyperski, Component Software, Addison-Wesley, 1998 Bertrand Meyer, Object-Oriented Software Construction, 2nd edition, Prentice Hall, 1997 Bertrand Meyer, Reusable Software, Prentice Hall, 1994 Martin Abadi, Luca Cardelli: A Theory of Objects, Springer-Verlag, 1996 Robert V. Binder: Testing Object-Oriented Systems: Models, Patterns, and Tools, Addison-Wesley, 1999. Karine Arnout: From Patterns to Components, ETH Ph.D. thesis, 2004 Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides: Design Patterns: Elements of Reusable Object-Oriented Software, Addison-Wesley, 1995

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Organization

Course page http://se.ethz.ch/teaching/2008-F/tc-0239/index.html Lectures: Monday: 2 hours Wednesday: 1 hour -- exercises and applications Assistant: Stephan van Staden Stephan.vanStaden@inf.ethz.ch All exercises are optional, but will be corrected. They are an important preparation for the exam and the project. Grading: Written exam on date of 15 December (lecture time): 70% Project (take-home exercise): 30%

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Reading assignment

“Ariane” paper: http://tinyurl.com/xy3s Also read Ken Garlington’s criticism (link in the article) (and optionally) the official report on the Ariane crash Chapter 9 of “Introduction to the Theory of Programming Languages”

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PART 1: Introduction

Issues of Software Quality

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Software quality: external vs internal

External factors: visible to customers (not just end users but e.g. purchasers)

• Examples: ease of use, extendibility, timeliness

Internal factors: perceptible only to developers

• Examples: good programming style, information

hiding Only external factors count in the end, but the internal factors make it possible to obtain them.

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Software quality: product vs process

Product: properties of the resulting software For example: correctness, efficiency Process: properties of the procedures used to produce and “maintain” the software

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External quality factors

Correctness Robustness Security Ease of use Ease of learning Efficiency Extendibility Reusability Portability Timeliness Cost-effectiveness

Security Hostility Robustness Errors Correctness Specification

Process quality:

Product quality (long-term): Product quality (immediate):

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Reliability

Correctness: The systems’ ability to perform according to specification, in cases covered by the specification Robustness: The systems’ ability to perform reasonably in cases not covered by the specification Security (integrity): The systems’ ability to protect itself against hostile use

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Ariane 5, 1996

$500 million, not insured. 40 seconds into flight, exception in Ada program not processed; order given to abort the mission. Exception was caused by an incorrect conversion: a 64-bit real value was incorrectly translated into a 16-bit integer.

• Not a design error.
• Not an implementation error.
• Not a language issue.
• Not really a testing problem.
• Only partly a quality assurance issue.

Systematic analysis had “proved” that the exception could not occur – the 64-bit value (“horizontal bias” of the flight) was proved to be always representable as a 16-bit integer !

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Ariane-5 (Continued)

It was a REUSE error:

• The analysis was correct – for Ariane 4 !
• The assumption was documented – in a design document !

With assertions, the error would almost certainly (if not avoided in the first place) detected by either static inspection or testing:

integer_bias (b: REAL): INTEGER is require representable (b) do … ensure equivalent (b, Result) end

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NIST report on “testing” (2002)

Monetary effect on Developers and User due to “insufficient testing infrastructure”: $59.5 billion (Financial sector: $3.3 billion, auto/aerospace $1.8 billion etc.)

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From reliability to security

Buffer overflow (Morris worm, most viruses) See http://www.cert.org Some_innocuous_public_command “Some message” (Or maybe just inputting text into a browser field)

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Buffer overflow

Memory Setup Max Program Heap Stack

Stack frames

Main Rout1 Routn Stack growth … Stack top Stack bottom

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Calling a routine

Max Program Heap Stack

Stack frames

Main Rout1 Routn …

Args

• f

Rout Locals

• f

Rout

Return address

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Calling a utility

syslogd "Some error message“ finger Some_name some_command "some text" (Text input into some browser field)

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Allocating the buffer

Max Program Heap Stack

Stack frames

Main Rout1 Routn … Args

• f

Rout Return address

Other locals

Buffer

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How was the routine coded?

from i := 1 until i > input_size loop buffer [i] := input [i] i := i + 1 end from i := 1 until i > input_size or i > buffer_size loop buffer [i] := input [i] i := i + 1 end

(1) (2)

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Allocating the buffer

Max Program Heap Stack

Stack frames

Main Rout1 Routn … Args

• f

Rout Return address

Other locals

Buffer

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Getting close

Max Program Heap Stack

Stack frames

Main Rout1 Routn … Return address

Other locals

Buffer

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Getting closer

Max Program Heap Stack

Stack frames

Main Rout1 Routn … Return address

Other locals

Buffer

Available !

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Inserting the code

Max Program Heap Stack

Stack frames

Main Rout1 Routn … Return address

Other locals

Buffer

Available ! Your Code

Modified Return Address

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Buffer overflow: lessons

Lack of specification Lack of specification enforcement Programming techniques Security concepts At the core, a programming methodology issue

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Software quality (through technology)

• A priori (build it right)

Object technology, formal development

• A posteriori (validate and fix it)

Testing, abstract interpretation, model checking

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Management aspects

Process standards: CMMI, ISO 9001 Get software in source from, benefit from public scrutiny Metrics collection and application Code reviews?

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Today’s software is often good enough

Overall: Works most of the time Doesn’t kill too many people Negative effects, esp. financial, are diffuse Significant improvements since early years: Better languages Better tools Better practices (configuration management)

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From “good enough” to good?

Beyond “good enough”, quality is economically bad He who perfects, dies Actual Ideal Quality

1 2 3

Time

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Choose to release?

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The economic argument

Stable system:

• Sum of individual optima = Global optimum

Non-component-based development:

• Individual optimum = “Good Enough Software”
• Improvements: I am responsible!

Component-based development:

• Interest of both consumer and producer: Better

components

• Improvements: Producer does the job

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Quality through reuse

The good news: Reuse scales up everything

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Quality through reuse

The good news: Reuse scales up everything The bad news: Reuse scales up everything

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Trusted components

Confluence of

• Quality engineering
• Reuse

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Classifying components by...

Lifecycle role:

• Analysis
• Design
• Implementation

Flexibility:

• Static
• Dynamic
• Replaceable

Form of use:

• Interface only
• Source only
• Source + hiding

Economics:

• Free
• Purchased
• Rented

Abstraction level:

• Functional (subroutine)
• Casual (package)
• Data (class)
• Cluster (framework)
• System (binary comp.)

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This is a broad view of components

Encompasses patterns and frameworks Software, especially with object technology, permits “pluggable” components (“don’t call us, we’ll call you”), where client programmers can insert their own mechanisms. Supports component families