[CMake] transitive linkage of OBJECT library targets

[Richard Szabo]

The reason going to object libs instead of static libs is the
limitation of windows dynamic libraries that export simbols must be in
the liner command line object it can not be added to the static
libraries linked to the dlls.
with gcc this problem can be solved with

-Wl,--whole-archive
.... libs with export
-Wl,--no-whole-archive

but I did not find something similar to MSVC .... and have the problem
that I have have code generators between user code and core runtime
which generate c++ code in separate libs.

So my idea was to use object libs to solve the problem but now I face
the issue with the transitive linkage. :(.

Cheers
Richard





On Wed, 22 May 2019 at 20:33, Richard Szabo <sz.richard at gmail.com> wrote:
>
> With Public it is still the same problem :(
>
> cmake_minimum_required(VERSION 3.14)
> project(test_object_lib_nesting)
>
> set(CMAKE_CXX_STANDARD 14)
>
> add_library(first_object_lib OBJECT first.cpp)
>
> add_library(second_object_lib OBJECT second.cpp)
>
> target_link_libraries(second_object_lib PUBLIC first_object_lib)
>
> add_executable(test_object_lib_nesting main.cpp)
>
> target_link_libraries(test_object_lib_nesting second_object_lib)
>
>
> /cmake -E cmake_link_script
> CMakeFiles/test_object_lib_nesting.dir/link.txt --verbose=1
> /usr/bin/clang++-6.0  -g
> CMakeFiles/test_object_lib_nesting.dir/main.cpp.o
> CMakeFiles/second_object_lib.dir/second.cpp.o  -o
> test_object_lib_nesting
> CMakeFiles/second_object_lib.dir/second.cpp.o: In function
> `Second::get_second()':
> /home/csita/CLionProjects/test_object_lib_nesting/second.cpp:10:
> undefined reference to `First::get_first() const'
> clang: error: linker command failed with exit code 1 (use -v to see invocation)
>
> I read the issue and it seems that there is no solution jet ....
>
> Is there an easy / not so easy workaround ?
> I have a dependency tree which can go down to 20 - 30 libs. (code
> generator ) also diamond graph. :(.
>
> Cheers
> Richard
>
> On Wed, 22 May 2019 at 14:25, Robert Maynard <robert.maynard at kitware.com> wrote:
> >
> > This is a known limitation of the current design. Only directly linked
> > object library objects are propagated.
> >
> > For more details on why see: https://gitlab.kitware.com/cmake/cmake/issues/18090
> >
> > On Wed, May 22, 2019 at 1:48 AM Richard Szabo <sz.richard at gmail.com> wrote:
> > >
> > > Hi cmakers
> > >
> > > I'm trying to get the following example working:
> > > ```
> > > cmake_minimum_required(VERSION 3.14)
> > > project(test_object_lib_nesting)
> > >
> > > set(CMAKE_CXX_STANDARD 14)
> > >
> > > add_library(first_object_lib OBJECT first.cpp)
> > >
> > > add_library(second_object_lib OBJECT second.cpp)
> > >
> > > target_link_libraries(second_object_lib first_object_lib)
> > >
> > > add_executable(test_object_lib_nesting main.cpp)
> > >
> > > target_link_libraries(test_object_lib_nesting second_object_lib)
> > > ```
> > >
> > > The problem I have that the linker command line will have only the
> > > second.cpp.o for linking the first.cpp.o will not be added as link
> > > object to the exe. Causing missing symbols on exe linkage.
> > >
> > > How to transitively resolve and link "nested" Object library targets ?.
> > > --
> > >
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