* Jonathan Wakely: > On Mon, 16 Aug 2021 at 10:59, Florian Weimer wrote: >> >> * Jonathan Wakely via Gcc-help: >> >> > I'm not sure if GCC should change, or if the linker should be changed >> > to permit a single non-weak non-UNIQUE definition to be merged with >> > zero or more UNIQUE definitions. As a workaround you can compile the >> > C++17 code with -fno-gnu-unique so that GCC uses a weak symbol, but >> > that isn't a good solution in general (the unique binding exists for >> > good reasons). >> >> What are those reasons, exactly? > > I think it was added to ensure uniqueness of static objects across > libraries opened with RTLD_LOCAL. Hmm, that makes some sense. The glibc implementation is not really structured in such a way that it is obvious that this is the goal. (glibc knows what it has loaded, so it could search just that, and not construct a separate hash table.) >> I've been trying to find a rationale and specification of >> STB_GNU_UNIQUE, but have not been successful. >> >> The glibc implementation does not handle symbol versions, it ignores >> them. It's not entirely clear to me if this is a bug. > > Does anybody use it with more than one symbol version though? libstdc++? > Using symbol versioning on a STB_GNU_UNIQUE symbol would seem to > violate its uniqueness. > >> Furthermore, I haven't seen a case yet which would require >> STB_GNU_UNIQUE and could not have been handled equally well via symbol >> interposition. > > Does that work for RTLD_LOCAL though? No, I don't think so. Thanks, Florian
