Safe and Secure Software - An Invitation to Ada 2012

160 Pages·2013·3.44 MB·English

by  John Barnes

John Barnes
Ben Brosgol
With contributions by
Safe and Secure Software
An invitation to
Courtesy of
© 2013 AdaCore
www.adacore.com

First printed 2008. Reprinted with revisions 2009, 2013.
V.20130212
Foreword
The aim of this booklet is to show how the study of Ada in general, and the
features introduced by Ada 2005 and Ada 2012 in particular, can help anyone
designing safe and secure software regardless of the programming language in
which the software is eventually written. After all, successful implementers of
safe and secure software write in the spirit of Ada in any language!
Thank you John for showing this throughout your papers, Ada rationales,
books, and this booklet.
AdaCore dedicates this booklet to the memory of Dr. Jean Ichbiah (1940-
2007), the principal designer of the original Ada language, who established the
safe and secure foundations on which succeeding versions of the language have
built.

Franco Gasperoni
Chief Executive Officer, AdaCore
Paris, January 2013

iii

Preface
This revised version of the “Safe and Secure Software” booklet updates the
content to take into account the important new facilities introduced in Ada 2012
which include support for contract-based programming. Ada 2012 marks the
most significant advance in Ada since 1995 and is especially relevant for
software that needs to meet safety and/or security certification standards.
I am very grateful for the assistance of Ben Brosgol of AdaCore in the
preparation of the new content in this version of the booklet. Not only did Ben
draft the new sections but he also ironed out several vague, misleading or plain
incorrect bits in the original, and moreover has added a comprehensive index
which I am sure will be of great value to all readers.

John Barnes
Caversham, England
January 2013

v

Contents
Introduction 1
1 Safe Syntax 5
Equality and assignment 5
Statement groups 7
Named notation 8
Integer literals 10
2 Safe Typing 11
Using distinct types 11
Enumerations and integers 13
Constraints and subtypes 15
Subtype predicates 16
Arrays and constraints 18
Default initialization 20
Real errors 22
3 Safe Pointers 25
References, pointers and addresses 25
Access types and strong typing 27
Access types and accessibility 29
References to subprograms 30
Nested subprograms as parameters 33
4 Safe Architecture 37
Package specifications and bodies 37
Private types 41
Generic contract model 43
Child units 45
Unit testing 46
Mutually dependent types 47
Contract-based programming 49
vii
Safe and Secure Software: An invitation to Ada 2012
5 Safe Object-Oriented Programming 53
Object-Orientation versus Function-Orientation 53
Overriding indicators 58
Dispatchless programming 59
Interfaces and multiple inheritance 60
Substitutability 65
6 Safe Object Construction 69
Variables and constants 69
Constant and variable views 71
Constructor functions 72
Limited types 72
Controlled types 76
7 Safe Memory Management 81
Buffer overflow 81
Heap control 82
Storage pools 85
Restrictions 89
8 Safe Startup 91
Elaboration 91
Elaboration pragmas 93
Dynamic loading 95
9 Safe Communication 97
Representation of data 97
Validity of data 99
Communication with other languages 100
Streams 102
Object factories 104
v i i i
Contents
10 Safe Concurrency 107
Operating systems and tasks 107
Protected objects 109
The rendezvous 114
Restrictions 117
Ravenscar 118
Safe shutdown 119
Timing and scheduling 124
11 Certified Safe with SPARK 127
Contracts 128
Correctness by construction 128
The kernel language 131
Tool support 132
Examples 134
Certification 136
Work in progress 136
Conclusion 137
Bibliography 141
Index 143
ix