ICSE '13 Doctoral Symposium

1. A Study of Variability Spaces
in Open Source Software
Sarah Nadi
University of Waterloo, Canada
PhD Advisor: Richard C. Holt
ICSE ’13 Doctoral Symposium – May 21st 2013
San Francisco, USA

2. Variability in Real Life
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• Integrated Garage Door Opener
• Electronic Compass
Command navigation package
• Heated Front Seats
• Exterior Power Folding Mirrors
Premium Package

3. Example of Software Variability
The Linux kernel
I want usb
support on
ARM
architecture!
User 1
I want sound
support on
x86
architecture!
User 2
Variant 2 Variant 1
Sarah Nadi Study of Variability Spaces - ICSE DS 2013 3

4. What functionality
will each choice
provide?
Code Space
Supporting Variability
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What can I
configure?
How will my choices
select the right
implementation
parts?
Configuration
Space
Build Space
[Czarnecki & Eisenecker., 2000] [Svahnberg et al., 2005] [Tartler et al., 2011]
Feature1 -> Feature2
Block1 -> Feature2
File1 -> Feature1
(e.g., Kconfig files)
(e.g., C code files) (e.g., Makefiles)

5. Build Space
Code Space
Configuration
Space
Previous Work
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Change evolution
[Adams et al.
2008, McIntosh et al.
2011]
Feasibility of mapping
extraction [Berger et
al., 2010]
Change evolution (Lotufo et
al. 2009 & 2011)
Use of feature modeling
concepts [She et al.,
2010][Berger et al., 2010]
Consistency with code
space
[Tartler et al. 2011]
Studying & extracting
implemented variability
[Liebig et al., 2010, Sincero et
al, 2010]
Variability aware parsing
[Kaestner et al.,2011]
Consistency with
configuration space [Tartler et
al. 2011]

6. What is the origin of these
anomalies? How are they
fixed?
What variability constraints
does each space provide?
So, What’s the Problem?
?
??
?
?
? Are the spaces consistent?
Sarah Nadi Study of Variability Spaces - ICSE DS 2013 6
?
What role does the Build
Space play?

7. Examples of Systems Supporting Build-
time Variability
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BusyBoxLinux kernel
> 12,000 features > 1,000 features > 800 features

8. RQ1: Variability Constraints in 3 Spaces?
Sarah Nadi Study of Variability Spaces - ICSE DS 2013 8
Build SpaceCode Space
Configuration
Space
= ?
• Identify overlap in constraints
• Identify constraints that are only
in one side
Challenges
• Accurately extract code constraints
• Meaningfully compare constraints
Benefits
• Uncover limits of static analysis
• Accurate reverse engineering
• Better maintenance
BusyBox

9. RQ2: Role of Build System in Variability?
Sarah Nadi Study of Variability Spaces - ICSE DS 2013 9
Makefile
Constraint
Extractor
Build Space
Constraints
≈ 50% of configuration space features are only
used in the build space!
[Nadi & Holt, JSEP ‘13]
[Liebig et al., 2010]
Limitations
• Extractor specific to Kbuild
• Relies on text parsing of Makefiles
Benefits
• Show which parts of the system
control most of variability

10. RQ3: Is Variability Consistent?
Sarah Nadi Study of Variability Spaces - ICSE DS 2013 10
Code Space
Configuration
Space
Build Space
[Tartler et al., 2011]
Syntactic Anomalies
• Don’t deal with constraints
• Related to the setup of conditional
compilation in Kbuild
Semantic Anomalies
• Conflicts between constraints
• Requires a SAT solver
• Dead (never selected) &
undead (always selected) code
blocks and files

11. RQ3 Cont’d: Detecting Syntactic Anomalies
X
XX
X
X
Variable Not
Used anomaly
X
File Not Used
anomaly
Feature Not
Defined anomaly
Sarah Nadi Study of Variability Spaces - ICSE DS 2013 11
[Nadi & Holt, WCRE ‘11]

12. RQ3 Cont’d: Detecting Semantic Variability
Anomalies
• '
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[Nadi&Holt, CSMR ‘12]
More anomalies detected when build space
constraints are considered!

13. #ifdef X
//B1
#else
//B2
#endif
foo.c
(Code Space)
RQ3 Cont’d: Example of a Code Block
Anomaly
Undead block!
Dead block!
foo.c => X
Build Space
foo.c will be
compiled
only if X is
selected“Testing X inside foo.c is a waste
of text, since foo.c is built only
when X is selected”
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14. RQ4: Intro. & Fix of Variability Anomalies?
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1 Exploratory study with existing patches
2 Mine git repository across
several releases to confirm patterns
Variability Anomalies
[Nadi et al., MSR ’13]
Incomplete
configuration
patches
Code patches
Time
cause fix
14% 26%
Avoid future anomalies & provide automatic fix solutions!

15. Limitations & Future Work
• Build time variability
• External validity
• Focused on certain types of anomalies
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Future Work
• Study other systems
• Analyze other types of anomalies

16. Overall Contributions & Benefits
• Contributions
• Established the importance of build system variability
• Quantified build system variability
• Detected variability anomalies in the Linux kernel
• Studied causes and fixes of variability anomalies
• Benefits
• Guide future variability analysis by determining overlaps between
variability spaces
• Decrease variability anomalies in software systems
• Improve maintainability of variable software
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17. Acknowledgements
• University of Waterloo
• Ric Holt (Supervisor)
• Krzysztof Czarnecki
• Mike Godfrey
• Friedrich-Alexander-Universität Erlangen-Nürnberg
• Christian Dietrich
• Reinhard Tartler
• Daniel Lohmann
• Leipzig University
• Thorsten Berger
• Carnegie Mellon University
• Christian Kästner
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18. Sarah Nadi Study of Variability Spaces - ICSE DS 2013 18
Time2011
WCRE ‘11
CSMR ‘12
2012 2013 2014
MSR ‘13
In progress
JSEP ‘13
BusyBox
Other anomalies
Questions?
snadi@uwaterloo.ca
http://swag.uwaterloo.ca/~snadi