Dynamic Linking and Loading in Networked Embedded Systems

We present a holistic dynamic linking and loading mechanism in networked embedded systems. Our design and implementation are guided by four requirements, which are to provide (i) minimal code size (ii) efficient execution and loading speed (iii) portable design (iv) isolated kernel/application development. First, we develop a tool to minimize the standard ELF format via many techniques in order to reduce the code dissemination cost. Second, we employ the techniques of pre-relocating and pre-linking (to kernel functions) to reduce the run-time linking overhead, thus improving the loading speed. Third, based on relocatable ELF and the modular design of the dynamic linker and loader, our approach can be easily ported to different platforms. Fourth, by maintaining a kernel jump table, we provide a clean isolation between kernel and application development. We have implemented the dynamic linking and loading mechanism on SenSpire OS, a micro sensor node operating system. The evaluation results show that our design and implementation meet our design goals: the code size of our SELF format is only 15%-30% of that of standard ELF, 38%-83% of that of CELF, a compact ELF format for the Contiki operating system; the loading speed improvement varies from 40%-50% compared to the standard mechanism; our design is portable to both MicaZ and TelosB motes, and we allow updating both application modules and kernel services in isolation without prior knowledge about the whole system information.