Software Maintenance and Evolution

Transcription

1 Software Maintenance and Evolution Minsoo Ryu Hanyang University

2 Topics Covered 1. Software Maintenance and Evolution 2. Reverse Engineering 3. Reengineering 2 2

3 Software Change Software change is inevitable New requirements emerge when the software is used; The business environment changes; Errors must be repaired; New computers and equipment is added to the system; The performance or reliability of the system may have to be improved A key problem for organizations is implementing and managing change to their existing software systems 3 3

4 Software Maintenance and Evolution Maintenance is modifying a program after it has been put into use The terms, maintenance, evolution, and reengineering can often be used interchangeably Software maintenance is the modification of a software product after delivery to correct faults, to improve performance or other attributes, or to adapt the product to a modified environment. (ISO/IEC 14764) 4 4

5 Types of Maintenance Maintenance to repair software faults Changing a system to correct deficiencies in the way meets its requirements Maintenance to adapt software to a different operating environment Changing a system so that it operates in a different environment (computer, OS, etc.) from its initial implementation Maintenance to add to or modify the system s functionality Modifying the system to satisfy new requirements 5 5

6 Change reports Maintenance Process Every change needed must be first reported, i.e., fault report Change authorization Changes must be checked and authorized Software reengineering Reverse engineering Forward engineering 6 6

7 Reengineering 7 7

8 1. Software Maintenance and Evolution 2. Reverse Engineering Reverse Engineering of Source Code Source code analysis Diagram generation Document generation Reverse Engineering of Binary Software Disassembly Decompilation Reverse Engineering with HW Support 3. Reengineering Topics Covered 8 8

9 Reverse Engineering Reverse engineering is the process of design recovery Analyze a program in an effort to create a representation of the program at a higher level of abstraction It can also be seen as "going backwards through the development cycle In this model, the output of the implementation phase (in source code form) is reverse engineered back to the analysis phase, in an inversion of the traditional waterfall model Reverse engineering is a process of examination only: the software system under consideration is not modified 9 9

10 Two Types of Reverse Engineering In the first case, source code is already available for the software, but higher level aspects of the program, perhaps poorly documented or documented but no longer valid, are discovered In the second case, there is no source code available for the software, and any efforts towards discovering one possible source code for the software are regarded as reverse engineering This second usage of the term is the one most people are familiar with Reverse engineering of software can make use of the clean room design technique to avoid infringing copyrights 10 10

11 Notes on Clean Room Design Clean room design (also known as the Chinese wall technique) is the method of copying a design by reverse engineering and then recreating it without infringing any of the copyrights and trade secrets associated with the original design Clean room design is useful as a defense against copyright and trade secret infringement because it relies on independent invention However, because independent invention is not a defense against patents, clean room designs typically cannot be used to circumvent patent restrictions 11 11

12 Notes on Legality of Reverse Engineering In the United States and many other countries, even if an artifact or process is protected by trade secrets, reverse-engineering the artifact or process is often lawful as long as it is obtained legitimately Patents, on the other hand, need a public disclosure of an invention, and therefore patented items do not necessarily have to be reverse engineered to be studied One common motivation of reverse engineers is to determine whether a competitor's product contains patent infringements or copyright infringements 12 12

13 Reverse Engineering of Source Code Source code analysis tools for C in UNIX ctags: creates an index of functions cxref: shows where each symbol is mentioned in the program cflow: shows which function calls which others cxref cflow 13 13

14 Reverse Engineering of Source Code Producing diagrams from source code Object-oriented implementation can easily be reverse engineered to produce its original design model Java Studio Enterprise 8 (based on NetBeans) can take code sources and reverse engineer the code into a UML model IBM rational Software Modeler can perform reverse transformations source code into a UML model CVF (Code Visual to Flow chart) CVF can automatically generate programming flow chart from source code, help programmers to document, visualize and understand code 14 14

15 Reverse Engineering of Source Code Document generation Some tools can generate documents from commented source code Doxygen is a documentation generator for C++, C, Java, Objective-C, Python, IDL (Corba and Microsoft flavors), Fortran, VHDL, PHP, C#, and to some extent D and ActionScript It runs on most Unix-like systems, including Mac OS X, as well as on Windows Javadoc is a documentation generator from Sun Microsystems for generating API documentation in HTML format from Java source code Javadoc is the industry standard for documenting Java classes Most IDEs will automatically generate Javadoc HTML 15 15

16 Reverse Engineering of Source Code ROBODoc is a documentation tool similar to javadoc and licensed under the GPL ROBODoc works with C, C++, Fortran, Perl, shell scripts, Assembler, DCL, DB/C, Tcl/Tk, Forth, Lisp, COBOL, Occam, Basic, HTML, Clarion 16 16

17 Reverse Engineering of Binary Software Disassembly (machine language assembly language) The raw machine language of the program is read and understood in its own terms, only with the aid of machine language mnemonics The Interactive Disassembler is a particularly popular tool The Interactive Disassembler, more commonly known as simply IDA, is a commercial disassembler widely used for reverse engineering It supports a variety of executable formats for different processors and operating systems including Windows PE, Mac OS X Mach-O, and Linux ELF executables 17 17

18 Reverse Engineering of Binary Software Decompilation A decompiler can perform the reverse operation to that of a compiler It translates a file containing information at a relatively low level of abstraction into a form having a higher level of abstraction (usually designed to be human readable) 18 18

19 Reverse Engineering of Binary Software The dcc decompiler was developed by Cristina Cifuentes while a PhD student at the Queensland University of Technology (QUT), Australia, , under the supervision of Professor John Gough Mike Van Emmerik developed the library signature recognition algorithms while employed by QUT The dcc distribution is made available under the GPL license The dcc decompiler decompiles.exe files from the (i386, DOS) platform to C programs The final C program contains assembler code for any subroutines that are not possible to be decompiled at a higher level than assembler 19 19

20 Reverse Engineering of Binary Software Decompilation using dcc 20 20

21 Reverse Engineering at Low-Level Hardware trace Hardware trace provides a complete history of a microprocessor is doing as software runs Data values read and written Context switching State of microprocessor Hardware trace data is output over a dedicated port from a trace-enabled microprocessor There are several embedded microprocessors available today that can output trace data, including the ARM7, ARM9, and ARM11; the IBM PowerPC 405 and 440; and the PowerPC 5500 and MAC7100 families from Freescale 21 21

22 Reverse Engineering at Low-Level Logic analyzer A logic analyzer is an electronic instrument that displays signals in a digital circuit that are too fast to be observed and presents it to a user so that the user can more easily check correct operation of the digital system They are typically used for capturing data in systems that have too many channels to be examined with an oscilloscope Software running on the logic analyzer can convert the captured data into timing diagrams, protocol decodes, state machine traces, assembly language, or correlate assembly with source-level software 22 22

23 Reverse Engineering with HW Support Packet sniffer A packet sniffer (also known as a network sniffer, network analyzer or protocol analyzer or, for particular types of networks, an Ethernet sniffer or wireless sniffer) is computer software or computer hardware that can intercept and log traffic passing over a digital network or part of a network As data streams flow across the network, the sniffer captures each packet and eventually decodes and analyzes its content according to the appropriate RFC or other specifications A bus analyzer is a type of protocol analyzer 23 23

24 Topics covered 1. Software Maintenance and Evolution 2. Reverse Engineering 3. Reengineering 24 24

25 Reengineering Typical reengineering activities Code restructuring Program structure improvement Program modularization Data restructuring Data abstraction Source code translation (e.g. FORTRAN to C) 25 25

26 Program Structure Improvement (before) Spaghetti logic Start: Get (Time-on, Time-off, Time, Setting, Temp, Switch) if Switch = off goto off if Switch = on goto on goto Cntrld off: if Heating-status = on goto Sw-off goto loop on: if Heating-status = off goto Sw-on goto loop Cntrld: if Time = Time-on goto on if Time = Time-off goto off if Time < Time-on goto Start if Time > Time-off goto Start if Temp > Setting then goto off if Temp < Setting then goto on Sw-off: Heating-status := off goto Switch Sw-on: Heating-status := on Switch: Switch-heating loop: goto Start 26 26

27 Program Structure Improvement (after) loop -- The Get statement finds values for the given variables from the system 뭩 -- environment. Get (Time-on, Time-off, Time, Setting, Temp, Switch) ; case Switch of when On => if Heating-status = off then Switch-heating ; Heating-status := on ; end if ; when Off => if Heating-status = on then Switch-heating ; Heating-status := off ; end if; when Controlled => if Time >= Time-on and Time < = Time-off then if Temp > Setting and Heating-status = on then Switch-heating; Heating-status = off; elsif Temp < Setting and Heating-status = off then Switch-heating; Heating-status := on ; end if; end if ; end case ; end loop ; 27 27

28 Data Restructuring Program 1 Program 2 Program 3 File 1 File 2 File 3 File 4 File 5 File 6 Program 4 Program 5 Program 6 Program 7 Becomes Program 3 Program 4 Program 5 Program 6 Program 2 Program 7 Program 1 Database management system describes Logical and physical data models 28 28

29 Source Code Translation Translation of code in one language into another in different language E.g., Fortran to C or C to C++ PROMULA is a Fortran to C translator This tool translates FORTRAN source code to correct (compilable) and clean (readable and maintainable) C source code The article Object-Oriented Programming with ANSI-C Shows how object-oriented programming is done with ANSI-C and how to translate the notions classes, inheritance, instances, linkage, methods, objects, polymorphisms, and more into the things in ANSI-C 29 29