info ld

[...]
`-E'
`--export-dynamic'
When creating a dynamically linked executable, add all symbols to
the dynamic symbol table. The dynamic symbol table is the set of
symbols which are visible from dynamic objects at run time.

If you do not use this option, the dynamic symbol table will
normally contain only those symbols which are referenced by some
dynamic object mentioned in the link.

If you use `dlopen' to load a dynamic object which needs to refer
back to the symbols defined by the program, rather than some other
dynamic object, then you will probably need to use this option when
linking the program itself.

You can also use the version script to control what symbols should
be added to the dynamic symbol table if the output format supports
it. See the description of `--version-script' in VERSION.
[...]