Unable to build mavsdk_server for armv7 android device

[gparrow]

Hello,

I'm having difficulty building the backend (C++) for armeabi-v7a. Following the instructions for building from source do not seem to work (get a message about the system no longer using makefiles, instructions coming later?) but I've made what seems to be progress by using the following below, strung together from a variety of web sources for each issue that comes up. It seems the biggest problem is getting gRPC, error below:

CMake Error at cmake/cares.cmake:38 (find_package): Could not find a package configuration file provided by "c-ares" with any of the following names:

c-aresConfig.cmake
c-ares-config.cmake

Add the installation prefix of "c-ares" to CMAKE_PREFIX_PATH or set "c-ares_DIR" to a directory containing one of the above files. If "c-ares" provides a separate development package or SDK, be sure it has been installed. Call Stack (most recent call first): CMakeLists.txt:135 (include)

command I've attempted (hopefully you can suggest something simpler??) that seems to get somewhere: cmake -G"Unix Makefiles" -DCMAKE_SYSTEM_NAME="Android" -DCMAKE_INSTALL_PREFIX=install -DCMAKE_SYSTEM_VERSION=21 -DCMAKE_ANDROID_NDK=${HOME}/Android/android-ndk-r18b -DCMAKE_TOOLCHAIN_FILE=${HOME}/Android/android-ndk-r18b/build/cmake/android.toolchain.cmake -DCMAKE_ANDROID_ARCH_ABI="armeabi-v7a" -DCMAKE_BUILD_TYPE=Release -DBUILD_SHARED_LIBS=OFF -DBUILD_BACKEND=ON -DgRPC_INSTALL=ON -DgRPC_BUILD_TESTS=OFF -DgRPC_PROTOBUF_PROVIDER=package -DgRPC_ZLIB_PROVIDER=package -DgRPC_CARES_PROVIDER=package -DgRPC_SSL_PROVIDER=package -DRUN_HAVE_STD_REGEX=0 -DRUN_HAVE_POSIX_REGEX=0 -DRUN_HAVE_STEADY_CLOCK=0 -Bbuild/android -H.

Please let me know if I'm doing anything wrong? I've attempted this on both OSX (10.14.6) and Ubuntu 18.04

I'm looking to build mavsdk_server to install on an armv7 android device. I attempted to use a few different NDK versions as well, 20b, 18b, 17c.

[julianoes]

We suggest to use dockcross as described here: https://mavsdk.mavlink.io/develop/en/contributing/build.html#cross_compilation_dockcross

[gparrow]

ok, so using dockcross at least builds something, but deploying to the device I get ./mavsdk_server": error: Android 5.0 and later only support position-independent executables (-fPIE).

I've tried passing the desired flags (and setting android-platform=21) and rebuilding but have not been able to get something to run using either dockcross-android-arm or dockcross-android-arm64, but its quite possible I'm not passing things quite right - e.g. below

./dockcross-android-arm64 cmake -DANDROID_PLATFORM=android-21  -DCMAKE_BUILD_TYPE=Release -DBUILD_BACKEND=ON -DBUILD_SHARED_LIBS=OFF -DCMAKE_POSITION_INDEPENDENT_CODE=ON -Bbuild/android-arm64 -S.

./dockcross-android-arm64 cmake  --build build/android-arm64 -j 8

Any further suggestions?

[julianoes]

@JonasVautherin do you have an idea here?

[gparrow]

Success! I added the below lines to the root CMakeLists.txt and now have mavsdk_server running on the device!

# Use "-fPIC" / "-fPIE" for all targets by default, including static libs
set(CMAKE_POSITION_INDEPENDENT_CODE ON)

# CMake doesn't add "-pie" by default for executables (CMake issue #14983)
set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -pie")

Once above added, used the command

./dockcross-android-arm64 cmake -DCMAKE_BUILD_TYPE=Release -DBUILD_BACKEND=ON -DBUILD_SHARED_LIBS=OFF  -Bbuild/android-arm64 -S.
  ./dockcross-android-arm64 cmake  --build build/android-arm64 -j 8

[JonasVautherin]

Great!

BTW, I see that the issue mentions armv7, and you use arm64 in the solution. There is an arm64-v8a version released on mavenCentral already, and used in the android example.

[gparrow]

OK Thanks! can confirm the android-arm dockcross builds (and runs) for armv7 too, for anyone who comes looking