Category: Programming

I’ve pretty much run out of linker topics. Unless I think of something new, I’ll make tomorrow’s post be the last one, for a total of 20. __start and __stop Symbols A quick note about another GNU linker extension. If the linker sees a section in the output file which can be part of a…

Incremental Linking Often a programmer will make change a single source file and recompile and relink the application. A standard linker will need to read all the input objects and libraries in order to regenerate the executable with the change. For a large application, this is a lot of work. If only one input object…

Warning Symbols The GNU linker supports a weird extension to ELF used to issue warnings when symbols are referenced at link time. This was originally implemented for a.out using a special symbol type. For ELF, I implemented it using a special section name. If you create a section named .gnu.warning.SYMBOL, then if and when the…

C++ Template Instantiation There is still more C++ fun at link time, though somewhat less related to the linker proper. A C++ program can declare templates, and instantiate them with specific types. Ideally those specific instantiations will only appear once in a program, not once per source file which instantiates the templates. There are a…

COMDAT sections In C++ there are several constructs which do not clearly live in a single place. Examples are inline functions defined in a header file, virtual tables, and typeinfo objects. There must be only a single instance of each of these constructs in the final linked program (actually we could probably get away with…