Fails to compile with gcc 10 on Fedora Rawhide.

broken.cpp

void* callback(const char* name);

extern "C" {

inline void f1()
{
	static void (*f)();
	f = (void(*)()) callback("f1");
	f();
}

inline void f2()
{
	static void (*f)();
	f = (void(*)()) callback("f2");
	f();
}

} // extern "C"

int main()
{
	f1();
	f2();
}

That causes a runtime crash, but that's not the point. The point here is that gcc 10 generates two symbols f for lines 10 and 17, and they collide. Previous versions of gcc generate _ZZ2f1E1f and _ZZ2f2E1f respectively, i.e., f1::f and f2::f demangled.

I've removed the implementation of callback() so at least this should no longer be UB. The underlying issue though is as @Enchufa2 says, with duplicate (and non-mangled) names for f generated.