An input relocatable object file is determined to be unused if all allocatable sections provided by the relocatable object are unused.
Unused files are diagnosed with the –z guidance option, and can be discarded from the link-edit by using the –z discard-unused=files option.
The –z discard-unused option provides independent control over unused sections and unused files in order to compliment –z guidance processing. Under –z guidance, files that are determined to be unused are identified. Unused files can often easily be removed from a link-edit. However, sections that are determined to be unused are not identified under –z guidance processing. Unused sections can involve much more investigation and effort to remove and can be a consequence of compiler actions that are beyond your control.
By using the –z discard-unused=sections option together with the –z guidance option, unused sections are automatically removed, while unused files are identified for you to remove from the link-edit.