Linker and Libraries Guide

Runtime Linking

Runtime linking involves the binding of objects, usually generated from one or more previous link-edits, to generate a runnable process. During the generation of these objects by the link-editor, appropriate bookkeeping information is produced to represent the verified binding requirements. This information enables the runtime linker to load, relocate, and complete the binding process.

During process execution, the facilities of the runtime linker are made available. These facilities can be used to extend the process' address space by adding additional shared objects on demand. The two most common components involved in runtime linking are dynamic executables and shared objects.

Dynamic executables are applications that are executed under the control of a runtime linker. These applications usually have dependencies in the form of shared objects, which are located, and bound by the runtime linker to create a runnable process. Dynamic executables are the default output file generated by the link-editor.

Shared objects provide the key building-block to a dynamically linked system. A shared object is similar to a dynamic executable, however, shared objects have not yet been assigned a virtual address.

Dynamic executables usually have dependencies on one or more shared objects. Typically, one or more shared objects must be bound to the dynamic executable to produce a runnable process. Because shared objects can be used by many applications, aspects of their construction directly affect shareability, versioning, and performance.

Shared object processing by the link-editor or the runtime linker can be distinguished by the environment in which the shared object is used.

compilation environment

Shared objects are processed by the link-editor to generate dynamic executables or other shared objects. The shared objects become dependencies of the output file being generated.

runtime environment

Shared objects are processed by the runtime linker, together with a dynamic executable, to produce a runnable process.