Elimination of unused sections
Elimination of unused sections is the most significant optimization on image size that is performed by the linker.
Unused section elimination:
-
Removes unreachable code and data from the final image.
-
Is suppressed in cases that might result in the removal of all sections.
To control this optimization use the --remove,
--no_remove, --first, --last, and
--keep linker options.
Unused section elimination requires an entry point. Therefore, if there is no entry point
specified for an image, use the --entry linker option to specify an entry
point and permit unused section elimination to work, if it is enabled.
Use the --info unused linker option to instruct the linker to generate a
list of the unused sections that it eliminates.
An input section is retained in the final image when:
It contains an entry point.
It is referred to, directly or indirectly, by a non-weak reference from an input section containing an entry point.
It is specified as the first or last input section by the
--firstor--lastoption (or a scatter-loading equivalent).It is marked as unremovable by the
--keepoption.
Note
Compilers usually collect functions and data together and emit one section for each category. The linker can only eliminate a section if it is entirely unused.
You can also use the -ffunction-sections compiler command-line option to
instruct the compiler to generate one ELF section for each function in the source
file.