What exactly does -rdynamic (or --export-dynamic at the linker level) do and how does it relate to symbol visibility as defined by the -fvisibility* flags or visibility pragmas and __attribute__s?
For --export-dynamic, ld(1) mentions:
... 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. ...
I'm not sure I completely understand this. Could you please provide an example that doesn't work without -rdynamic but does with it?
Edit:
I actually tried compiling a couple of dummy libraries (single file, multi-file, various -O levels, some inter-function calls, some hidden symbols, some visible), with and without -rdynamic, and so far I've been getting byte-identical outputs (when keeping all other flags constant of course), which is quite puzzling.