Remove Unused Material

The inclusion of functions and data that are not used by the object being built, is wasteful. This material bloats the object, which can result in unnecessary relocation overhead and associated paging activity. References to unused dependencies are also wasteful. These references result in the unnecessary loading and processing of other shared objects.

Unused sections are displayed during a link-edit when using the link-editors debugging token -D unused. Sections identified as unused should be removed from the link-edit, or eliminated using the link-editors -z ignore option.

The link-editor identifies a section from a relocatable object as unused if:

• The section is allocatable

• No other sections bind to (relocate) to this section

• The section provides no global symbols

You can improve the link-editors ability to eliminate sections by defining the shared objects external interfaces. By defining an interface, global symbols that are not defined as part of the interface are reduced to locals. These reduced symbols, if unreferenced from other objects, are now clearly identified as candidates for elimination.

Individual functions and data variables can be eliminated by the link-editor if these items are assigned to their own sections. This section refinement is achieved using compiler options such as -xF. Earlier compilers only provided for the assignment of functions to their own sections. Newer compilers have extended the -xF syntax to assign data variables to their own sections. Earlier compilers required C++ exception handling to be disabled when using -xF. This restriction has been dropped with later compilers.

If all allocatable sections from a relocatable object can be eliminated, the entire file is discarded from the link-edit.

In addition to input file elimination, the link-editor also identifies unused dependencies. A dependency is deemed unused if it is not bound to by the object being produced. An object built with the -z ignore option, will have no unused dependencies recorded in it.

The -z ignore option applies only to the files that follow the option on the link-edit command line. The -z ignore option is cancelled with -z record.