https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105512
David Truby <gnu.w2nnu at simplelogin dot com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |gnu.w2nnu at simplelogin dot com --- Comment #1 from David Truby <gnu.w2nnu at simplelogin dot com> --- I also see this issue and have a reproducer here: ---- main.cpp #include <iostream> #include <string> import test; int main() { std::cout << tester(); } ---- test.cpp module; #include <string> export module test; export std::string tester() { return "hello world\n"; } ---- Interestingly the issue also goes away if -D_GLIBCXX_USE_CXX11_ABI=0 is passed to both TUs so I suspect there's an issue with the module file not exporting the correct ABI for `std::string`