Cslim: automated extraction of IoT functionalities from legacy C codebases

Many Internet of Things (IoT) devices are resource-poor, possessing limited memory, disk space, and processor capacity. To accommodate such resource scarcity, IoT software cannot include any extraneous functionalities not used in operating the underlying device. Although legacy systems software contains numerous functionalities that can be reused in IoT applications, these functionalities are exposed as part of a larger codebase with multiple complex dependencies and a heavy runtime footprint. To enable programmers to effectively reuse extant systems software in IoT applications, this paper presents Cslim, a cross-package function extraction tool for C. Cslim extracts programmer-specified functions from a source package and generates new source files for a target package, thereby enabling the reuse of systems software in resource-poor execution environments, such as the IoT devices. Cslim resolves all dependencies by recursively extracting required functions, while bypassing the complexities of preprocessor macro variabilities by operating on preprocessed source files. Furthermore, Cslim efficiently traverses and resolves the calling dependencies by maintaining an in-memory relational database. Finally, Cslim is easy to use, as it requires neither manual intervention nor source code modifications. Our prototype implementation of Cslim has successfully extracted a set of functions from SQLite and GlusterFS, producing slimmed down executables that can be deployed on IoT devices.