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Gabriel Ferreira, Momin Malik, Christian Kästner, Jurgen Pfeffer, Sven Apel.  2016.  Do #ifdefs influence the occurrence of vulnerabilities? an empirical study of the linux kernel SPLC '16 Proceedings of the 20th International Systems and Software Product Line Conference. :65-73.

Preprocessors support the diversification of software products with #ifdefs, but also require additional effort from developers to maintain and understand variable code. We conjecture that #ifdefs cause developers to produce more vulnerable code because they are required to reason about multiple features simultaneously and maintain complex mental models of dependencies of configurable code.

We extracted a variational call graph across all configurations of the Linux kernel, and used configuration complexity metrics to compare vulnerable and non-vulnerable functions considering their vulnerability history. Our goal was to learn about whether we can observe a measurable influence of configuration complexity on the occurrence of vulnerabilities.

Our results suggest, among others, that vulnerable functions have higher variability than non-vulnerable ones and are also constrained by fewer configuration options. This suggests that developers are inclined to notice functions appear in frequently-compiled product variants. We aim to raise developers' awareness to address variability more systematically, since configuration complexity is an important, but often ignored aspect of software product lines.

Momin Malik, Jurgen Pfeffer, Gabriel Ferreira, Christian Kästner.  2016.  Visualizing the variational callgraph of the Linux Kernel: An approach for reasoning about dependencies. HotSos '16 Proceedings of the Symposium and Bootcamp on the Science of Security.

Software developers use #ifdef statements to support code configurability, allowing software product diversification. But because functions can be in many executions paths that depend on complex combinations of configuration options, the introduction of an #ifdef for a given purpose (such as adding a new feature to a program) can enable unintended function calls, which can be a source of vulnerabilities. Part of the difficulty lies in maintaining mental models of all dependencies. We propose analytic visualizations of thevariational callgraph to capture dependencies across configurations and create visualizations to demonstrate how it would help developers visually reason through the implications of diversification, for example through visually doing change impact analysis.