A large component and service-based software system exists in different forms, as different variants targeting different business needs and users. This kind of systems is provided as a set of "indepen-dent" products and not as a "single whole". The presence of a single model describing the architecture of the whole system may be of great interest for developers of future variants. Indeed, this enables them to see the invariant part of the whole, on top of which new functionality can be built, in addition to the different options they can use. We investigate in this work the use of software product line reverse engineering approaches, and in particular the framework named BUT4Reuse, for reconstructing an architecture model of a Software Architecture Product Line (SAPL), from a set of variants. We propose a generic process for reconstructing an architecture model of such a product line. We have instantiated this process for the OSGi Java framework and experimented it for building the architecture model of Eclipse IDE SPL.