Dynamic objects can supply code that provides for runtime initialization and termination processing. The initialization code of a dynamic object is executed once each time the dynamic object is loaded in a process. The termination code of a dynamic object is executed once each time the dynamic object is unloaded from a process or at process termination.
Before transferring control to an application, the runtime linker processes any initialization sections found in the application and any loaded dependencies. If new dynamic objects are loaded during process execution, their initialization sections are processed as part of loading the object. The initialization sections .preinit_array, .init_array, and .init are created by the link-editor when a dynamic object is built.
The runtime linker executes functions whose addresses are contained in the .preinit_array and .init_array sections. These functions are executed in the same order in which their addresses appear in the array. The runtime linker executes an .init section as an individual function. If an object contains both .init and .init_array sections, the .init section is processed before the functions defined by the .init_array section for that object.
A dynamic executable can provide pre-initialization functions in a .preinit_array section. These functions are executed after the runtime linker has built the process image and performed relocations but before any other initialization functions. Pre-initialization functions are not permitted in shared objects.
Dynamic objects can also provide termination sections. The termination sections .fini_array and .fini are created by the link-editor when a dynamic object is built.
Any termination sections are passed to atexit(3C). These termination routines are called when the process calls exit(2). Termination sections are also called when objects are removed from the running process with dlclose(3C).
The runtime linker executes functions whose addresses are contained in the .fini_array section. These functions are executed in the reverse order in which their addresses appear in the array. The runtime linker executes a .fini section as an individual function. If an object contains both .fini and .fini_array sections, the functions defined by the .fini_array section are processed before the .fini section for that object.
For more information on the creation of initialization and termination sections by the link-editor see Initialization and Termination Sections.