Symbol Lookup

When the runtime linker needs to look up a symbol, it does so by searching in each object, starting with the dynamic executable, and progressing through each shared object in the same order that the objects are mapped. In many instances, the shared object that requires a symbolic relocation will turn out to be the provider of the symbol definition.

If this is the case, and the symbol used for this relocation is not required as part of the shared object's interface, then this symbol is a strong candidate for conversion to a static or automatic variable. A symbol reduction can also be applied to removed symbols from a shared objects interface (see "Reducing Symbol Scope" for more details). By making these conversions the link-editor will incur the expense of processing any symbolic relocation against these symbols during the shared object's creation.

The only global data items that should be visible from a shared object are those that contribute to its user interface. However, frequently this is a hard goal to accomplish, as global data are often defined to allow reference from two or more functions located in different source files. Nevertheless, any reduction in the number of global symbols exported from a shared object will result in lower relocation costs and an overall performance improvement.