Hi Jonathan, thank you for your reply!
On Tue, 2022-08-30 at 17:09 +0100, Jonathan Wakely wrote: > > > On Tue, 30 Aug 2022, 15:48 Anton Wöllert via Gcc, <gcc@gcc.gnu.org> > wrote: > > If this libstdc++ is > > newer than the one one the target, I get undefined references > > (because > > there are some newer implementation details and things like that). > > Then you're not telling the executable how find the new libstdc++. > > https://gcc.gnu.org/onlinedocs/libstdc++/faq.html#faq.how_to_set_paths > > I tried to do that. If I let the toolchain use it's own libstdc++.so, then I get at runtime unresolved symbols due to the version mismatch (these GLIBCXX errors). This is clear. If I force the toolchain to link against the older target libstdc++, then I get undefined symbols at compile time, because it is still using it's own shipped headers for the newer libstdc++, which have implementation details that use newer "functions/symbols" that are not available in the old libstdc++. If I furthermore remove the shipped headers and force it to include the c++ headers from the older libstdc++, then everything works out. But this whole "patching" seems very hacky. > > Is > > it possible to tell G++/GCC to use the libstdc++.so from the target > > and > > also to use the C++ headers (like iostream) from the target? > > It's possible, but unsupported and probably won't work. So it seems to be indeed possible, but not intended. > > > If not, is there any reason this is hard-coded? > > The libstdc++ headers are tightly coupled to the GCC version, so > headers from a given GCC release might not even compile with a newer > or older GCC. I would see an argument if you're trying to compile an newer libstdc++ with an older gcc - but why not the other way around? C++ in general tries to be very good in backward compatibility. This essentially means that you can't use newer compilers with more features/bugfixes to compile software for older targets. Is there any obvious reason this is not supported? Clang, for example, also seems to be able to compile/link against different libstdc++ versions. I'm just wondering. Best, Anton
