[CMake] Win cmake belives I am building a .dll, but the only target is an .exe file

[Timothy Madden]

Hello,

In my CMakeLists.txt I have a simple executable target like:

cmake_minimum_required(VERSION 3.2)  # I actually have 3.10 installed
project(cl-tool CXX)

set(OPENCL_INCLUDE_SEARCH_PATHS ...)
set(OPENCL_LIBRARY_64_SEARCH_PATHS ...)

if (CYGWIN)
    set(CMAKE_FIND_LIBRARY_SUFFIXES .lib)
    set(OCL_LIB_SUFFIX .lib)
endif()

set(OPENCL_LIBRARY_SEARCH_PATHS ${OPENCL_LIBRARY_64_SEARCH_PATHS})
set(FIND_LIBRARY_USE_LIB64_PATHS ON)

find_path(OPENCL_INCLUDE_DIRS CL/cl.h PATHS ENV OpencCL_INCPATH
${OPENCL_INCLUDE_SEARCH_PATHS})
find_path(OPENCL2_HPP_INCLUDE_DIRS CL/cl2.hpp PATHS ENV OpencCL_INCPATH
${OPENCL_INCLUDE_SEARCH_PATHS})

find_library(OPENCL_LIBRARIES NAMES OpenCL DOC "OpenCL library" PATHS ENV
OpenCL_LIBPATH ${OPENCL_LIBRARY_SEARCH_PATHS})
find_package(Threads)

set(CL_INFO_SOURCES cl-matrix-mult.hh cl-matrix-mult.cc cl-platform-info.hh
cl-platform-info.cc cl-tool.cc)
*add_executable(cl-tool ${CL_INFO_SOURCES})*
target_compile_features(cl-tool PRIVATE cxx_std_14)
target_compile_definitions(cl-tool PRIVATE CL_HPP_TARGET_OPENCL_VERSION=120
CL_HPP_MINIMUM_OPENCL_VERSION=110 CL_HPP_CL_1_2_DEFAULT_BUILD
CL_HPP_ENABLE_EXCEPTIONS)
target_compile_definitions(cl-tool PRIVATE __CL_ENABLE_EXCEPTIONS
CL_VERSION_1_2)
target_include_directories(cl-tool PRIVATE ${OPENCL_INCLUDE_DIRS}
${OPENCL2_HPP_INCLUDE_DIRS})
target_compile_options(cl-tool PRIVATE -Wno-ignored-attributes
-fvisibility=hidden)
target_link_libraries(cl-tool ${OPENCL_LIBRARIES} Threads::Threads)

But then at build time with:

   cd build && cmake .. -G "MinGW ..." -DCMAKE_CXX_COMPILER=g++
   gmake VERBOSE=1

I get bellow unexpected behaviour:

CMake is building a static archive with `ar` containing all 3 objects in my
target executable cl-tool.exe.
The static archive is then linked in the executable with
-Wl,--whole-archive. CMake also wants to output an import library,
Although the target is clearly an executable named cl-tool.exe, on the same
g++ command line used for linking.

My objects use some templates that are instantiated in 2 of the 3 objects,
and using --Wl,--whole-archive with these object files,
results in multiple definitions for the instantiations.

Normally the linker would see the multiple symbols as weak references and
discard duplicates, but now CMake insists on using
--whole-archive on the linker command line, so duplicates now result in an
error.

I have Win10 up-to-date, CMake 3.10, and g++ 7.1, from the MinGW
installation that comes packaged with Strawberry Perl.
Also Intel OpenCL SDKincluded and linked with.

This unexpected behaviour is breaking my build, and I am also worried about
the duplicate / unused code in the resulting executable.
Is there a proper solution to this problem please ?

Why does CMake go to the trouble of:
  - creating a separate static archive with the 3 object files (which is
not requested from the CMakeLists.txt file) ?
  - using --whole-archive on the resulting .a file instead of linking
normally ?
  - attempt to output the import library for an .exe module ?

Apparently CMake believes my target is a .dll (shared library), but nowhere
in the CMakeLists is a .dll ever created.

I set ENABLE_EXPORTS and CMAKE_WIN32_EXPORT_ENABLE to "OFF", with no effect.

--
Thank you,
Timothy Madden
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