Type - safe Composition of Object Modules

We describe a facility that enables routine type checking during the linkage of exter nal declarations and de nitions of separately compiled programs in ANSI C The primary advantage of our server style type checked linkage facility is the ability to program the composition of object modules via a suite of strongly typed module combination opera tors Such programmability enables one to easily incorporate programmer de ned data format conversion stubs at link time In ad dition our linkage facility is able to automat ically generate safe coercion stubs for com patible encapsulated data This research was sponsored by the Advanced Research Projects Agency DOD monitored by the Department of the Navy O ce of the Chief of Naval Research under Grant number N J The views and conclusions contained in this document are those of the authors and should not be interpreted as representing o cial policies ei ther expressed or implied of the Advanced Research Projects Agency or the US Government Contact author G Banavar Computer Science MEB University of Utah Salt Lake City UT USA e mail banavar cs utah edu phone fax Introduction It is widely agreed that strong typing in creases the reliability and e ciency of soft ware However compilers for statically typed languages such as C and C in tradi tional non integrated programming environ ments guarantee complete type safety only within a compilation unit but not across such units Longstanding and widely avail able linkers compose separately compiled units by matching symbols purely by name equivalence with no regard to their types Such common denominator linkers accom modate object modules from various source languages by simply ignoring the static se mantics of the language Moreover com monly used object le formats are not de signed to incorporate source language type information in an easily accessible manner In this paper we present a technique to perform type checking of object modules as a routine link time activity Our technique is characterized by i the design of speci c lan guage type systems into a system wide linker ii programmed link time control over indi vidual symbols of object modules and iii C style name mangling does not accomplish complete type safety across compilation units see Section