cmake 从 object 库构建共享库导致未定义符号

Question

I'm building a shared library using cmake. Here are the steps that I take, starting with building a shared library A_shared using an object library A_obj .

add_library(A_obj OBJECT ${A_SRCS})
add_library(A_shared SHARED)
target_link_libraries(A_shared PUBLIC A_obj)

This process works. Now I wish to build another shared library that uses A_shared and its own sources. So I have:

add_library(B_obj OBJECT ${B_SRCS})
target_link_libraries(B_obj PUBLIC A_shared)
add_library(B_shared SHARED)
target_link_libraries(B_shared PUBLIC B_obj)

It seems to me that this should be valid, because I'm building objects B_obj which have dependence on a shared libraries A_shared , and then using these objects to construct shared library B_shared and at the same time transitively passing the dependence on A_shared using the call to target_link_libraries .

However, this results in undefined symbols when building in MSVC. When linking B_shared.dll , I get unresolved external dependencies on global variables that were defined in ${A_SRCS} and used in ${B_srcs} , and not anything else (like functions). Strangely, the object files B_obj compile fine.

• If I instead link B_shared to A_obj , it works fine. But this gives me the impression that B_shared will actually contain the object files from A_obj , but all I want it only to link to A_shared .
• If I link B_obj to A_obj , nothing changes and I still get unresolved dependencies.

With gcc, B_shared is successfully linked.

Therefore, my question is: am I doing the correct thing in cmake to achieve what I want? I'm wondering what I'm misunderstanding, because I've researched this extensively and I can't find the fault in my process, so I would greatly appreciate any clarification.

Answer 1

This comes from the behaviour of shared libraries on Windows in general: See this question . I have to manually export the symbols. The interaction with the object library wasn't creating issues.