Tool qualification for safety related systems

Tools used in the development of safety related software applications need to be qualified as safe. That is, the tools cannot be allowed to introduce hazardous faults into the application, e.g., a compiler shall not generate dangerous code due to failure of the compiler. In many cases laws and regulations require the product development of safety related applications to comply with industry sector specific safety standards. Examples of such standards include EN50129/50128 for railway applications, ISO/EN13849 for machines with moving parts, DO-178B/C for avionics, or IS026262 for cars. These standards require the use of a rigorous development and maintenance process. The standards are also mainly intended to be used when developing systems from scratch. However, most development and test tools are not developed from scratch according to the rigorous processes of these standards. In order to address this issue, some of the standards provide means for qualifying existing tools as a more lightweight and pragmatic alternative to a regular certification process. In this paper we analyze the concept of these qualification approaches. The result of the analysis in our contribution includes a set of approaches that can be applied individually or as a combination in order to reduce the effort needed for qualifying tools. As a running example we use one of the most flexible but at the same time dangerous, even prohibited, maintenance techniques available: dynamic instrumentation of executing code. With this example, we describe how exceptions in these standards can be utilized in order to qualify a dynamic instrumentation tool with a minimal effort, without following the process of tool certification as defined by the standards.