OpenXR+JsonCpp can not be statically linked at the same time (duplicate symbols)

[LordOfDragons]

It is impossible to statically compile and link both OpenXR and JsconCpp (other libraries for example) into the same application. Reason is that OpenXR uses internally compiled JsonCpp library. This causes duplicate jsoncpp symbols in the final link.

Unfortunately due to #314 it is not possible to statically compile a separate jsoncpp and then use "-DBUILD_WITH_SYSTEM_JSONCPP=Yes" to force using this one.

We need a solution for this and the solution can only be to fix the build system to work with system jsoncpp combined with statically building the loader. Otherwise it is not possible to use OpenXR and JsonCpp at the same time.

[rpavlik]

I do not understand the mention of 314 - that looked like user error. Static loader should work fine, though it's not necesarrily recommended (better to build shared library and just open it from your own path if you want) because as you point out, we can't really limit the symbols exposed there

[LordOfDragons]

Here's the logs:

Build OpenXR
-- The C compiler identification is GNU 14.2.1
-- The CXX compiler identification is GNU 14.2.1
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/gcc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/g++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Found Python3: /usr/bin/python3.13 (found version "3.13.2") found components: Interpreter
-- Performing Test HAVE_FILESYSTEM_WITHOUT_LIB
-- Performing Test HAVE_FILESYSTEM_WITHOUT_LIB - Failed
-- Performing Test HAVE_FILESYSTEM_NEEDING_LIBSTDCXXFS
-- Performing Test HAVE_FILESYSTEM_NEEDING_LIBSTDCXXFS - Success
-- Performing Test HAVE_FILESYSTEM_NEEDING_LIBCXXFS
-- Performing Test HAVE_FILESYSTEM_NEEDING_LIBCXXFS - Failed
-- Found OpenGL: /usr/lib64/libOpenGL.so
-- Enabling OpenGL support
-- Found Vulkan: /usr/lib64/libvulkan.so (found version "1.4.304") found components: glslc glslangValidator
-- Enabling Vulkan support
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE
-- Found JsonCpp: /usr/include/jsoncpp
-- Presentation backend selected for hello_xr, loader_test, conformance: xlib
-- Found X11: /usr/include
-- Looking for XOpenDisplay in /usr/lib64/libX11.so;/usr/lib64/libXext.so
-- Looking for XOpenDisplay in /usr/lib64/libX11.so;/usr/lib64/libXext.so - found
-- Looking for gethostbyname
-- Looking for gethostbyname - found
-- Looking for connect
-- Looking for connect - found
-- Looking for remove
-- Looking for remove - found
-- Looking for shmat
-- Looking for shmat - found
-- Looking for IceConnectionNumber in ICE
-- Looking for IceConnectionNumber in ICE - found
-- Found PkgConfig: /usr/bin/pkg-config (found version "2.3.0")
-- Checking for one of the modules 'xcb'
-- Checking for one of the modules 'xcb-glx'
-- Checking for one of the modules 'wayland-client'
-- BUILD_WITH_XLIB_HEADERS: ON
-- BUILD_WITH_XCB_HEADERS: No
-- BUILD_WITH_WAYLAND_HEADERS: No
-- Found glslc: /usr/bin/glslc
-- Looking for secure_getenv
-- Looking for secure_getenv - found
-- Looking for __secure_getenv
-- Looking for __secure_getenv - not found
-- Looking for timespec_get
-- Looking for timespec_get - found
-- OpenXR 1.1.46
-- Found and will use pre-generated xr_generated_dispatch_table.h in source tree
-- Found and will use pre-generated xr_generated_dispatch_table.c in source tree
-- Found and will use pre-generated xr_generated_dispatch_table_core.h in source tree
-- Found and will use pre-generated xr_generated_dispatch_table_core.c in source tree
-- Performing Test SUPPORTS_Wall
-- Performing Test SUPPORTS_Wall - Success
-- Performing Test SUPPORTS_C_Wall
-- Performing Test SUPPORTS_C_Wall - Success
-- Performing Test SUPPORTS_Werrorunusedparameter
-- Performing Test SUPPORTS_Werrorunusedparameter - Success
-- Performing Test SUPPORTS_C_Werrorunusedparameter
-- Performing Test SUPPORTS_C_Werrorunusedparameter - Success
-- Performing Test SUPPORTS_Werrorunusedargument
-- Performing Test SUPPORTS_Werrorunusedargument - Failed
-- Performing Test SUPPORTS_C_Werrorunusedargument
-- Performing Test SUPPORTS_C_Werrorunusedargument - Failed
-- Performing Test SUPPORTS_Wpointerarith
-- Performing Test SUPPORTS_Wpointerarith - Success
-- Performing Test SUPPORTS_C_Wpointerarith
-- Performing Test SUPPORTS_C_Wpointerarith - Success
-- Found and will use pre-generated xr_generated_loader.hpp in source tree
-- Found and will use pre-generated xr_generated_loader.cpp in source tree
-- Configuring done (1.9s)
CMake Error: install(EXPORT "openxr_loader_export" ...) includes target "openxr_loader" which requires target "jsoncpp_interface" that is not in any export set.
CMake Error in src/loader/CMakeLists.txt:
  export called with target "openxr_loader" which requires target
  "jsoncpp_interface" that is not in any export set.


-- Generating done (0.0s)
CMake Generate step failed.  Build files cannot be regenerated correctly.
RunExternalCommand failed for script:
export CC="gcc"
export CXX="g++"
export AS="as"
export AR="ar"
export RANLIB="ranlib"
export CPPFLAGS="-I/home/roland/progs/dragengine/extern/jsoncpp/build/include"
export LDFLAGS="-L/home/roland/progs/dragengine/extern/jsoncpp/build/lib"
cd "/home/roland/progs/dragengine/extern/openxr/build/OpenXR-SDK-release-1.1.46" || exit 1
cmake -DCMAKE_INSTALL_PREFIX="/home/roland/progs/dragengine/extern/openxr/build" -DCMAKE_INSTALL_LIBDIR="/home/roland/progs/dragengine/extern/openxr/build/lib" -DCMAKE_BUILD_TYPE=Release -DBUILD_API_LAYERS=No -DBUILD_TESTS=No -DBUILD_WITH_STD_FILESYSTEM=No -DBUILD_WITH_WAYLAND_HEADERS=No -DBUILD_WITH_XCB_HEADERS=No -DBUILD_WITH_SYSTEM_JSONCPP=Yes -DDYNAMIC_LOADER=No -Wno-dev ../OpenXR-SDK-release-1.1.46 || exit 1
make -j 12 install || exit 1
scons: *** [extern/openxr/build/lib/libopenxr_loader.a] Exception : Failed building OpenXR
Traceback (most recent call last):
  File "/usr/lib/python3.12/site-packages/SCons/Action.py", line 1441, in execute
    result = self.execfunction(target=target, source=rsources, env=env)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/roland/progs/dragengine/extern/openxr/SConscript", line 142, in openxrBuild
    raise Exception('Failed building OpenXR')
Exception: Failed building OpenXR
scons: building terminated because of errors.

[rpavlik]

oh, that part is relatively easy, but awkward. Because making a static library does not include the contents of its dependencies, when you link to a static library, you also have to transitively link to its dependencies.

Which means that if you install a static library, you also need to install the dependencies you build in tree, which is where it gets really weird.

That error message is griping that we didn't install our self-built jsoncpp. (We don't need to in a dynamic build, in that case there is actual linking going on - but a static library is basically just an archive of object files. you can't really link anything into it the way you might expect or the way CMake makes it look.)

(oops sorry not sure why GitHub decided to close this when I commented.)

So... when you build a static library... do we install the built-in jsoncpp, just using a decorated name? do we make it so you can't install a static library, you can only use it in the build tree? do we actually shove the jsoncpp object files in the static library as well instead of linking them later?

I could not decide which of those options was best, which is why I did none of them in the build system. 😅

[LordOfDragons]

What goes for my case I have a statically build jsoncpp and I want a statically build openxr so I can link them into the game engine shared library. The usual way to do this is to provide the include and library path (CPPFLAGS/LDFLAGS). Since this is a static library to be build only the include path is required to obtain the needed header declarations. No symbol resolving is done at that time. Then I link the game engine shared library where all the static libraries are pulled in. Hence the openxr would get its jsoncpp resolved at that time as it should be.

[rpavlik-bot]

An issue (number 2516) has been filed to correspond to this issue in the internal Khronos GitLab (Khronos members only: KHR:openxr/openxr#2516 ), to facilitate working group processes.

This GitHub issue will continue to be the main site of discussion.