According to my experience, though it may be incorrect, on Windows if no translation unit exports any symbol then all symbols are implicitly exported when building a DLL with GNU C++ compiler. In contrast, if there is any translation unit exports any symbol, then all others symbols in the DLL are NOT implicitly exported.
In other words, if there is a header we #include declares a symbol with __declspec(dllexport), then we have to manually insert __declspec(dllexport) to every single declarations of other symbols. Otherwise, those symbols will not get exported.
Is there a convenient way in CMake world that we don't have to add __declspec(dllexport) ourselves? I've tried
set_target_properties(foo PROPERTIES WINDOWS_EXPORT_ALL_SYMBOLS TRUE)
but it doesn't work. Any suggestion? Thanks.
Reedit: (2021-09-03 8:34:40 UTC)
Below is an example to recreate the problem.
example/CMakeLists.txt:
cmake_minimum_required(VERSION 3.21)
project(example VERSION 1.0)
add_executable(myapp main.cpp)
add_subdirectory(foo)
add_subdirectory(bar)
target_link_libraries(myapp PRIVATE foo)
example/main.cpp:
#include "foo.hpp" // for function foo_func
int main(int argc, char *argv[])
{
foo_func();
return 0;
}
example/foo/CMakeLists.txt:
add_library(foo SHARED foo.cpp)
target_include_directories(foo INTERFACE "${CMAKE_CURRENT_SOURCE_DIR}")
target_link_libraries(foo PRIVATE bar)
example/foo/foo.hpp:
#ifndef FOO_HPP
#define FOO_HPP
void foo_func(void);
#endif
example/foo/foo.cpp:
#include "bar.hpp" // for function bar_funcA
void foo_func(void)
{
bar_funcA();
}
example/bar/CMakeLists.txt
add_library(bar SHARED bar.cpp)
target_include_directories(bar INTERFACE ${CMAKE_CURRENT_SOURCE_DIR})
set_target_properties(bar PROPERTIES WINDOWS_EXPORT_ALL_SYMBOLS TRUE)
example/bar/bar.hpp:
#ifndef BAR_HPP
#define BAR_HPP
void bar_funcA(void);
void bar_funcB(void);
#endif
example/bar/bar.cpp:
#include <cstdio> // for function printf
void bar_funcA(void)
{
std::printf("%s\n", __func__);
}
__declspec(dllexport) void bar_funcB(void)
{
std::printf("%s\n", __func__);
}
My environment:
Windows 10
MSYS2
CMake 3.21.2
Result:
$ cmake -G 'Unix Makefiles' -S example/ -B build/
$ cmake --build build/
[ 16%] Building CXX object bar/CMakeFiles/bar.dir/bar.cpp.obj
[ 33%] Linking CXX shared library libbar.dll
[ 33%] Built target bar
Consolidate compiler generated dependencies of target foo
[ 50%] Building CXX object foo/CMakeFiles/foo.dir/foo.cpp.obj
[ 66%] Linking CXX shared library libfoo.dll
C:/msys64/mingw64/x86_64-w64-mingw32/bin/ld.exe: CMakeFiles/foo.dir/objects.a(foo.cpp.obj):foo.cpp:(.text+0x9): undefined reference to `bar_funcA()'
collect2.exe: error: ld returned 1 exit status
make[2]: *** [foo/CMakeFiles/foo.dir/build.make:102: foo/libfoo.dll] Error 1
make[1]: *** [CMakeFiles/Makefile2:144: foo/CMakeFiles/foo.dir/all] Error 2
make: *** [Makefile:91: all] Error 2
According to Dependency Walker, the only symbol that gets exported from libbar.dll is bar_funcB.
