由于未定义的引用，无法在 Windows 下编译共享库

Question

I'm using the same waf script, both for Linux and for Windows , to compile a shared-library for a program (which is able to load shared libraries at run-time).

To create this library I import some headers of the main program, so I can call main program's function in the library, and symbols are resolved at run-time, and this works under Linux.

Under Windows I'm not able to build the library because it says undefined reference for every function of the main program I call in the library.

What's the difference between Windows and Linux in that case? Why do I have to resolve symbols at linking-time under Windows ? Is there a flag or something like that to avoid this?

Answer 1

Linux allows unresolved symbols in a shared library, but Windows does not. I have no good knowledge of the reasons of this difference. In https://lists.gnu.org/archive/html/libtool/2007-04/msg00070.html for example you can see one opinion that on Linux it is "to allow circular references in shared libraries".

On Windows you can get the same behavior as on Linux with the /FORCE:UNRESOLVED linker parameter (see https://docs.microsoft.com/en-us/cpp/build/reference/force-force-file-output?view=msvc-170 ), but it has a restriction, namely your DLL must have an entry point.

On Linux you can get the same behavior as on Windows with -Wl,-no-undefined linker parameter. Additionally you can use a parameter -Wl,--no-allow-shlib-undefined to disallow undefined symbols only in shared libraries which you link against (see https://linux.die.net/man/1/ld ).