include openssl library on native android project - android-ndk

Question

I want to create wrapper module to openssl library for android that will use most of the main functions for security.
I know there are people that say they already did it and publish thier work on github but for security reasons we can't use it.
I compiled the openssl library to android and add to the CMakeList.txt as described here:
https://developer.android.com/studio/projects/configure-cmake#add-other-library
My steps that i have made :
1. I download from here: https://www.openssl.org/source/ version 1.1.1c
2. Compiled sucessfully:
export ANDROID_NDK_HOME=/home/user/Android/Sdk/ndk-bundle
PATH=$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/linux-x86_64/bin:$PATH
./Configure android-arm64
make
I put the entire folder here:
Project/app/src/main/cpp/openssl-1.1.1c
4.thats how the CMakeList looks like:
cmake_minimum_required(VERSION 3.4.1)
set(CMAKE_VERBOSE_MAKEFILE ON)
add_library(openssl-wrapper-lib
SHARED
openssl-c-wrapper.cpp)
#===v===v===v===v===v===v===openssl-include===v===v===v===v===v===v===
add_library(
crypto
SHARED
IMPORTED
)
set_target_properties(
crypto
PROPERTIES IMPORTED_LOCATION
${CMAKE_CURRENT_SOURCE_DIR}/openssl-1.1.1c/libcrypto.so
)
include_directories(openssl-1.1.1c/include)
#===^===^===^===^===^===^===openssl-include===^===^===^===^===^===^===
find_library(log-lib
log)
target_link_libraries( # Specifies the target library.
openssl-wrapper-lib
crypto
${log-lib})
the error when i build is this:
Error while executing process /home/user/Android/Sdk/cmake/3.6.4111459/bin/cmake with arguments {--build /home/user/AndroidStudioProjects/EncryptionModule/app/.externalNativeBuild/cmake/debug/x86_64 --target openssl-wrapper-lib}
[1/1] Linking CXX shared library /home/user/AndroidStudioProjects/EncryptionModule/app/build/intermediates/cmake/debug/obj/x86_64/libopenssl-wrapper-lib.so
FAILED: : && /home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ --target=x86_64-none-linux-android21 --gcc-toolchain=/home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64 --sysroot=/home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/sysroot -fPIC -g -DANDROID -fdata-sections -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -fno-addrsig -Wa,--noexecstack -Wformat -Werror=format-security -v -O0 -fno-limit-debug-info -Wl,--exclude-libs,libgcc.a -Wl,--exclude-libs,libatomic.a -static-libstdc++ -Wl,--build-id -Wl,--warn-shared-textrel -Wl,--fatal-warnings -Wl,--no-undefined -Qunused-arguments -Wl,-z,noexecstack -shared -Wl,-soname,libopenssl-wrapper-lib.so -o /home/user/AndroidStudioProjects/EncryptionModule/app/build/intermediates/cmake/debug/obj/x86_64/libopenssl-wrapper-lib.so CMakeFiles/openssl-wrapper-lib.dir/openssl-c-wrapper.cpp.o /home/user/AndroidStudioProjects/EncryptionModule/app/src/main/cpp/openssl-1.1.1c/libcrypto.so /home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/lib/x86_64-linux-android/21/liblog.so -latomic -lm && :
Android (5220042 based on r346389c) clang version 8.0.7 (https://android.googlesource.com/toolchain/clang b55f2d4ebfd35bf643d27dbca1bb228957008617) (https://android.googlesource.com/toolchain/llvm 3c393fe7a7e13b0fba4ac75a01aa683d7a5b11cd) (based on LLVM 8.0.7svn)
Target: x86_64-none-linux-android21
Thread model: posix
InstalledDir: /home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin
Found candidate GCC installation: /home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/lib/gcc/i686-linux-android/4.9.x
Found candidate GCC installation: /home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/lib/gcc/x86_64-linux-android/4.9.x
Selected GCC installation: /home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/lib/gcc/x86_64-linux-android/4.9.x
Candidate multilib: .;#m64
Selected multilib: .;#m64
"/home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/lib/gcc/x86_64-linux-android/4.9.x/../../../../x86_64-linux-android/bin/ld" --sysroot=/home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/sysroot -z now -z relro --hash-style=gnu --hash-style=both --enable-new-dtags --eh-frame-hdr -m elf_x86_64 -shared -o /home/user/AndroidStudioProjects/EncryptionModule/app/build/intermediates/cmake/debug/obj/x86_64/libopenssl-wrapper-lib.so /home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/lib/x86_64-linux-android/21/crtbegin_so.o -L/home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/lib64/clang/8.0.7/lib/linux/x86_64 -L/home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/lib/gcc/x86_64-linux-android/4.9.x -L/home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/lib/gcc/x86_64-linux-android/4.9.x/../../../../x86_64-linux-android/lib/../lib64 -L/home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/lib/x86_64-linux-android/21 -L/home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/lib/x86_64-linux-android -L/home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/lib/gcc/x86_64-linux-android/4.9.x/../../../../x86_64-linux-android/lib -L/home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/lib --exclude-libs libgcc.a --exclude-libs libatomic.a --build-id --warn-shared-textrel --fatal-warnings --no-undefined -z noexecstack -soname libopenssl-wrapper-lib.so CMakeFiles/openssl-wrapper-lib.dir/openssl-c-wrapper.cpp.o /home/user/AndroidStudioProjects/EncryptionModule/app/src/main/cpp/openssl-1.1.1c/libcrypto.so /home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/lib/x86_64-linux-android/21/liblog.so -latomic -lm -Bstatic -lc++ -Bdynamic -lm -lgcc -ldl -lc -lgcc -ldl /home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/lib/x86_64-linux-android/21/crtend_so.o
/home/user/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/lib/gcc/x86_64-linux-android/4.9.x/../../../../x86_64-linux-android/bin/ld: error: /home/user/AndroidStudioProjects/EncryptionModule/app/src/main/cpp/openssl-1.1.1c/libcrypto.so: incompatible target
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: subcommand failed.
please help me understand what am I doing wrong

Answer 1

You built the library for arm64, but you're also building for Android's other ABIs. You need to build those libraries for each architecture your application supports. i.e., repeat your initial steps:
./Configure android-arm
make
./Configure android-arm64
make
./Configure android-x86
make
./Configure android-x86_64
make
(Note that you probably need to run each of those builds in a separate directory, unless the build scripts you're using will install libraries for each arch independently for you.)
You'll then want to do something like the following (adjust as needed based on your actual install paths) to import the libraries into CMake:
set_target_properties(
crypto
PROPERTIES IMPORTED_LOCATION
# The change happens here: each of the architectures gets its own subdirectory.
${CMAKE_CURRENT_SOURCE_DIR}/openssl-1.1.1c/${ANDROID_ABI}/libcrypto.so
)
The other option, if you only care about supporting 64-bit ARM, would be to disable the other architectures in your build.gradle, as described by https://google.github.io/android-gradle-dsl/current/com.android.build.gradle.internal.dsl.NdkOptions.html:
android {
// Similar to other properties in the defaultConfig block, you can override
// these properties for each product flavor in your build configuration.
defaultConfig {
ndk {
// Tells Gradle to build outputs for the following ABIs and package
// them into your APK.
abiFilters 'arm64-v8a'
}
}
}