Historical view of linking and loading in AIX

The linker and system loader on AIX are designed so that modules are self contained entities with well defined sets of imported and exported symbols. Symbol resolution is performed at link-time, simplifying the work of the system loader when a module is loaded. The system loader looks up symbols to relocate references, but does not perform symbol resolution. As a result, a shared module and its dependents can be pre-relocated in global memory. Once a set of modules has been pre-relocated, a program using the modules can be loaded more effectively since symbol lookup and relocation in the pre-relocated modules does not have to be performed.

However, there has been several circumstances where the traditional AIX linking mechanism did not satisfy the application programmers’ requirements. For example, in many new applications, the location of some symbol definitions may not be known at link-time.

To address this requirement, AIX has been supporting the run-time linking method, which provide more flexibility in how and when symbol resolution takes place (see 2.5, “Run-time linking” on page 68).