SmPL: A Domain-Specific Language for Specifying Collateral Evolutions in Linux Device Drivers

Collateral evolutions are a pervasive problem in large-scale software development. Such evolutions occur when an evolution that affects the interface of a generic library entails modifications, i.e., collateral evolutions, in all library clients. Performing these collateral evolutions requires identifying the affected files and modifying all of the code fragments in these files that in some way depend on the changed interface. We have studied the collateral evolution problem in the context of Linux device drivers [1]. Collateral evolution is a significant problem in this context because device drivers make up over half of the Linux source code and are highly dependent on the kernel and driver support libraries for functions and data structures. Our EuroSys study [1] has shown that from one version of Linux to the next, collateral evolutions can account for up to 35% of the lines modified in such code. Moreover, those collateral evolutions may be complex, entailing substantial code reorganizations. Currently, collateral evolutions in Linux are mostly done manually using a text editor, or with tools such as sed. The large number of Linux drivers, and complexity of the collateral evolutions, however, implies that these approaches are time-consuming and unreliable, leading to subtle errors when modifications are not done consistently. To address these problems, we propose a transformation language, SmPL,1 to specify collateral evolutions. Because Linux programmers are used to exchange, read, and manipulate program modifications in terms of patches, we have built our language around the idea and syntax of a patch, extending patches to semantic patches. Two important characteristics of semantic patches are: