System for linking program units by binding symbol vector index in the

Abstract

An improved method for linking images at program activation is provided by use of a symbol vector in a sharable code image. The symbol vector is automatically constructed which the linker and operating system use to effect fast lookup of symbol values at program activation, thus providing flexibility similar to that of link-time binding. For each sharable image being constructed, the programmer provides a list of symbols which are to be made visible outside of the image. These symbols may be procedure names, data cells, absolute values, or any other valid use of a symbolic value. The order of this list must remain fixed from one image build to the next. From this list, the 'symbol vector' is constructed (as by the linker) of the value of each of the identified symbols, and the symbol vector is associated with the sharable image. A symbol table is also associated with the sharable image, where each symbol has the value of its index in the symbol vector. When resolving references to other images, the linker does a symbolic lookup in the symbol table of the target image and obtains the index into the target symbol vector. That index is bound into the calling image. Then, at program activation, the image activator uses the index bound into a calling image to obtain the current value of the symbol in the target image.