Cross-compile on linux for windows won't output DLL file

Question

compile on linux for windows such that it outputs a windows DLL fuil that can be run natively on windows (no need for cygwin or anything like that). Basically the same as if i ran the compilation on a windows box, which I'd rather avoid.

I've tried many things, most of which seem to compile successfully leave me with *.la or *.so files and never a *.dll.

My configure.ac file:

AC_INIT([libaparapi], [1.4.2], [syncleus@syncleus.com])
AC_ENABLE_SHARED(yes)
AC_ENABLE_STATIC(no)
LT_INIT
AC_CONFIG_MACRO_DIRS([m4])
AM_INIT_AUTOMAKE([subdir-objects])
AC_PROG_CXX
AC_CONFIG_FILES([Makefile])
AC_CANONICAL_HOST
case $host_os in
  darwin* )
        AC_LDFLAGS="-framework OpenCL -version-info 5:2:4"
    AC_CPPFLAGS="-Iinclude -I/opt/AMDAPP/SDK/include -Isrc/cpp -Isrc/cpp/runKernel -Isrc/cpp/invoke -I${JAVA_HOME}/include/darwin -I${JAVA_HOME}/include -I/System/Library/Frameworks/JavaVM.framework/Versions/Current/Headers/ -DCL_USE_DEPRECATED_OPENCL_1_1_APIS"
        ;;
  mingw*)
        AC_LDFLAGS="-no-undefined -lOpenCL -version-info 5:2:4  -no-undefined"
          AC_CPPFLAGS="-Iinclude -I/opt/AMDAPP/SDK/include -Isrc/cpp -Isrc/cpp/runKernel -Isrc/cpp/invoke -I/usr/lib/jvm/java-11-openjdk-amd64/include -I/usr/lib/jvm/java-11-openjdk-amd64/include/linux -I/usr/lib/jvm/java-8-openjdk/include -I/usr/lib/jvm/java-8-openjdk/include/linux -I/usr/lib/jvm/java-8-openjdk-amd64/include -I/usr/lib/jvm/java-8-openjdk-amd64/include/linux -I/usr/lib/jvm/java-8-oracle/include -I/usr/lib/jvm/java-8-oracle/include/linux -I/System/Library/Frameworks/JavaVM.framework/Versions/Current/Headers/ -DCL_USE_DEPRECATED_OPENCL_1_1_APIS -fpermissive"
        ;;
  *)
        AC_LDFLAGS="-lOpenCL -version-info 5:2:4  -no-undefined"
    AC_CPPFLAGS="-Iinclude -I/opt/AMDAPP/SDK/include -Isrc/cpp -Isrc/cpp/runKernel -Isrc/cpp/invoke -I/usr/lib/jvm/default/include -I/usr/lib/jvm/default/include/linux -I/usr/lib/jvm/default-java/include -I/usr/lib/jvm/default-java/include/linux -I/usr/lib/jvm/java-8-openjdk/include -I/usr/lib/jvm/java-8-openjdk/include/linux -I/usr/lib/jvm/java-8-openjdk-amd64/include -I/usr/lib/jvm/java-8-openjdk-amd64/include/linux -I/usr/lib/jvm/java-8-oracle/include -I/usr/lib/jvm/java-8-oracle/include/linux -I/System/Library/Frameworks/JavaVM.framework/Versions/Current/Headers/ -DCL_USE_DEPRECATED_OPENCL_1_1_APIS  -fpermissive"
        ;;
esac
AC_SUBST(AC_LDFLAGS)
AC_SUBST(AC_CPPFLAGS)
AC_OUTPUT

In the above case it appears to be the *) case that is provoked, the ming*) case can be ignored it was part of a failed earlier attempt and not called here.

My makefile.am:

ACLOCAL_AMFLAGS = -I m4
AUTOMAKE_OPTIONS = foreign
EXTRA_DIST = include src/cpp/CLHelper.h src/cpp/classtools.h src/cpp/invoke/JavaArgs.h src/cpp/invoke/OpenCLMem.h src/cpp/invoke/OpenCLKernel.h src/cpp/invoke/OpenCLJNI.h src/cpp/invoke/OpenCLArgDescriptor.h src/cpp/invoke/OpenCLProgram.h src/cpp/CLException.h src/cpp/JNIHelper.h src/cpp/Common.h src/cpp/runKernel/KernelArg.h src/cpp/runKernel/Range.h src/cpp/runKernel/ProfileInfo.h src/cpp/runKernel/AparapiBuffer.h src/cpp/runKernel/Config.h src/cpp/runKernel/Aparapi.h src/cpp/runKernel/ArrayBuffer.h src/cpp/runKernel/JNIContext.h src/cpp/runKernel/List.h
lib_LTLIBRARIES = libaparapi.la
libaparapi_la_CPPFLAGS = $(AC_CPPFLAGS)
libaparapi_la_LDFLAGS = $(AC_LDFLAGS)
libaparapi_la_SOURCES = src/cpp/runKernel/Aparapi.cpp src/cpp/runKernel/ArrayBuffer.cpp src/cpp/runKernel/AparapiBuffer.cpp src/cpp/runKernel/Config.cpp src/cpp/runKernel/JNIContext.cpp src/cpp/runKernel/KernelArg.cpp src/cpp/runKernel/ProfileInfo.cpp src/cpp/runKernel/Range.cpp src/cpp/invoke/OpenCLJNI.cpp src/cpp/invoke/OpenCLArgDescriptor.cpp src/cpp/invoke/OpenCLMem.cpp src/cpp/CLHelper.cpp src/cpp/classtools.cpp src/cpp/JNIHelper.cpp src/cpp/agent.cpp
all-local:

I tried using dockcross but had the same problems as when doing it natively, so ill share the commands I invoked to compile natively. As you can see below I installed clang for cross compiling as I'm told its the only way to get a truly native DLL, things like mingw will need to package most libraries statically to work at all.

git clean -xdf
cp -r ../include/ .
mkdir -p m4
aclocal --force
libtoolize --force --copy
automake --foreign --add-missing --copy --force
autoconf --force
CC=clang ./configure --target=windows-shared-x64
CC=clang make && ls .libs

When run the following is the output from the configure stage, no errors are produced when running the above commands so its the only relevant tidbit.

checking build system type... x86_64-pc-linux-gnu
checking host system type... x86_64-pc-linux-gnu
checking how to print strings... printf
checking for gcc... clang
checking whether the C compiler works... yes
checking for C compiler default output file name... a.out
checking for suffix of executables... 
checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether clang accepts -g... yes
checking for clang option to accept ISO C89... none needed
checking whether clang understands -c and -o together... yes
checking for a sed that does not truncate output... /usr/bin/sed
checking for grep that handles long lines and -e... /usr/bin/grep
checking for egrep... /usr/bin/grep -E
checking for fgrep... /usr/bin/grep -F
checking for ld used by clang... /usr/bin/ld
checking if the linker (/usr/bin/ld) is GNU ld... yes
checking for BSD- or MS-compatible name lister (nm)... /usr/bin/nm -B
checking the name lister (/usr/bin/nm -B) interface... BSD nm
checking whether ln -s works... yes
checking the maximum length of command line arguments... 1572864
checking how to convert x86_64-pc-linux-gnu file names to x86_64-pc-linux-gnu format... func_convert_file_noop
checking how to convert x86_64-pc-linux-gnu file names to toolchain format... func_convert_file_noop
checking for /usr/bin/ld option to reload object files... -r
checking for objdump... objdump
checking how to recognize dependent libraries... pass_all
checking for dlltool... no
checking how to associate runtime and link libraries... printf %s\n
checking for ar... ar
checking for archiver @FILE support... @
checking for strip... strip
checking for ranlib... ranlib
checking for gawk... gawk
checking command to parse /usr/bin/nm -B output from clang object... ok
checking for sysroot... no
checking for a working dd... /usr/bin/dd
checking how to truncate binary pipes... /usr/bin/dd bs=4096 count=1
checking for mt... no
checking if : is a manifest tool... no
checking how to run the C preprocessor... clang -E
checking for ANSI C header files... yes
checking for sys/types.h... yes
checking for sys/stat.h... yes
checking for stdlib.h... yes
checking for string.h... yes
checking for memory.h... yes
checking for strings.h... yes
checking for inttypes.h... yes
checking for stdint.h... yes
checking for unistd.h... yes
checking for dlfcn.h... yes
checking for objdir... .libs
checking if clang supports -fno-rtti -fno-exceptions... yes
checking for clang option to produce PIC... -fPIC -DPIC
checking if clang PIC flag -fPIC -DPIC works... yes
checking if clang static flag -static works... yes
checking if clang supports -c -o file.o... yes
checking if clang supports -c -o file.o... (cached) yes
checking whether the clang linker (/usr/bin/ld -m elf_x86_64) supports shared libraries... yes
checking whether -lc should be explicitly linked in... no
checking dynamic linker characteristics... GNU/Linux ld.so
checking how to hardcode library paths into programs... immediate
checking whether stripping libraries is possible... yes
checking if libtool supports shared libraries... yes
checking whether to build shared libraries... yes
checking whether to build static libraries... no
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for a thread-safe mkdir -p... /usr/bin/mkdir -p
checking whether make sets $(MAKE)... yes
checking whether make supports the include directive... yes (GNU style)
checking whether make supports nested variables... yes
checking dependency style of clang... gcc3
checking for g++... g++
checking whether we are using the GNU C++ compiler... yes
checking whether g++ accepts -g... yes
checking how to run the C++ preprocessor... g++ -E
checking for ld used by g++... /usr/bin/ld -m elf_x86_64
checking if the linker (/usr/bin/ld -m elf_x86_64) is GNU ld... yes
checking whether the g++ linker (/usr/bin/ld -m elf_x86_64) supports shared libraries... yes
checking for g++ option to produce PIC... -fPIC -DPIC
checking if g++ PIC flag -fPIC -DPIC works... yes
checking if g++ static flag -static works... yes
checking if g++ supports -c -o file.o... yes
checking if g++ supports -c -o file.o... (cached) yes
checking whether the g++ linker (/usr/bin/ld -m elf_x86_64) supports shared libraries... yes
checking dynamic linker characteristics... (cached) GNU/Linux ld.so
checking how to hardcode library paths into programs... immediate
checking dependency style of g++... gcc3
checking that generated files are newer than configure... done
configure: creating ./config.status
config.status: creating Makefile
config.status: executing libtool commands
config.status: executing depfiles commands

Finally the ls command at the end clearly shows no DLL was produced:

libaparapi.la  libaparapi.lai  libaparapi.so  libaparapi.so.1  libaparapi.so.1.4.2

Any idea what im doing wrong? I am very new to cross compiling.

Answer 1

GCC can't build Windows DLLs if undefined symbols are allowed. You can usually fix this by adding LDFLAGS="-Wl,-no-undefined" at the end of the ./configure line. But I have seen some cases where that doesn't help, but running this line after ./configure fixes it:

sed -i.bak -e "s/\(allow_undefined=\)yes/\1no/" libtool

Then there is the import part where you actually have to declare your functions as dllexport. One way of doing this is to add something like this at the top of your header file(s):

# if defined(_WIN32) && (defined(BUILD_MYLIB_DLL) || defined (MyLib_EXPORT))
#  define DLL_EXPORT_MYLIB __declspec(dllexport)
# elif defined(_WIN32) && !defined(STATIC) && !defined(BUILD_MYLIB_STATIC) && !defined(BUILD_MYLIB)
#  define DLL_EXPORT_MYLIB __declspec(dllimport)
# else
#  define DLL_EXPORT_MYLIB
# endif
#endif

and then add DLL_EXPORT_MYLIB before the definition of each function you need to be available from the DLL. For example:

DLL_EXPORT_MYLIB const char* mylib_get_version ();

As the above header code only exports when BUILD_MYLIB_DLL is defined you will also need to add CFLAGS="-DBUILD_MYLIB_DLL"and/or CXXFLAGS="-DBUILD_MYLIB_DLL" at the end of the ./configure line.

Note that there are other ways (like using .def files) to build DLLs, but I find this the cleanest and most portable way, in particular when using autoconf tools.

Have you considered using CMake?

When using CMake a bit easier. There it's just a matter of adding SHARED to the add_library() command. The header modification above is still needed though. For example this line in CMakeLists.txt:

add_library(MyLib SHARED mylib.c)

will automatically try to build a DLL and define MyLib_EXPORT in C/C++ so it can be detected in the header file to use dllexport.

Answer 2

So, it seems that you're setting target to windows, not host, therefore everything is set up to host on Linux, hence .so files are produced. The target triple proved to --target does not look right as well. Doing configure --host=x86_64-w64-mingw32 would likely solve the problem.