Develop Reference

android - system app jni library load path

If android installed at below path:
/system/product/priv-app/mynative/app-debug.apk
And this apk contains a jni library:
app-debug/lib/arm64-v8a/libnative-lib.so
Where is the path android to load the library libnative-lib.so? I search device and never find that so file.

The answer might be: "it never was on the filesystem to begin with".
Modern Android build infrastructure sets extractNativeLibraries=false by default. This keeps the .so in the APK instead of having a copy linger on your device.
EDIT: I did some source digging, the Android runtime linker can open libraries directly from zip files if the filename contains !/. I think this would just show up as another mapping of the APK in /proc/pid/maps, but I did not investigate beyond that (eg how relocation is done in this case or what namespaces have to do with it).

Packaging external .so files into Android .apk files using Gradle

Recently, I ported my existing Android project from an ancient Gradle version to Gradle 6.6 and Android Studio's Gradle plugin 4.0.1. This project uses an external native library (.so file) that gets used in the Java code via JNI. This .so library has a dependency on libc++_shared.so because it is written in C++.
I realized that if I just copy the .so file into the corresponding platform folder (arm64-v8a, armeabi-v7a, x86, x86_64) within the jniLibs Gradle packages it "properly" into my .apk file.
By "properly" I mean that it automatically adds libc++_shared.so, which my library has a dependency on, as well as my own library to the .apk file. In addition, if I additionally set jniDebuggable to true in the build.gradle file it will also add the gdbserver library which is required to be able to attach the native code debugger.
Now, this is exactly what I want. The problem is that I cannot find any documentation that describes this behavior. The best source I could find is this but it does not mention anything about dependencies being packaged automatically. So, I don't know whether that is an officially supported way of doing things.
I suspect that there is a part of Android's Gradle based build process that automatically analyzes the files in the jniLibs folder and acts accordingly. It would be great to know a bit more to be aware what is really going on.
Does anyone have a reference that confirms my above observations or know which Gradle task (or whatever) accomplishes this? It would also be good to know in which Android Gradle plugin version this behavior was introduced.
Edit:
This answer to another SO question led me to the Android source file https://android.googlesource.com/platform/tools/build/+/master/builder/src/main/java/com/android/builder/internal/packaging/Packager.java
which seems to be the code that packages the .so files and gdbserver into the .apk file. But I have no explanation why libc++_shared.so gets packaged as well.

How to add vendor shared lib to android ndk app

I have added a library under Android aosp vendor folder and successfully created shared lib (lets say, libmyvendor.so) files. And verified that .so files are created under both system/lib and system/lib64. Flashed on a device and working fine here.
To debug my ndk application, I have copied .so files into Android's path sdk/ndk/{versionNumber}/platforms/android-28/arch-x86/usr/lib. Also in archx86_64/usr/lib64 folder. Did invalidate and restart Android Studio. Now I'm trying to find or add libmyvendor library in my ndk application using cmake function
find_library(mVendor libmyvendor)
Tried myvendor instead of libmyvendor. In both cases, cmake couldn't find it.
Then tried copying libmyvendor.so files into ndk application (under jniLibs/x86/ and x86_64/ ). Compiled but app crash at runtime saying
UnSatifiedLinkError: dlopen failed library 'libcrypto.so' not found
Where libcrypto.so is needed as a dependent to libmyvendor project. And I'm stuck here.
As per my assumption, libmyvendor is part of system libs. NDK should be capable of finding it using find_library(), just like we find liblog.so. But it cannot find. Did I miss or mess anything?

Building android app on Qt using additional library (Assimp)

Hi I am trying to port an OpenGL desktop app to android. I have no knowledge of android development so am depending on Qt Creator to package the app. As part of the setup, I have invoked 'make-standalone-toolchain' script in android ndk with following settings
--platform=android-21
--toolchain=arm-linux-androideabi-4.9
--system=linux-x86_64
Then I used android-cmake and passed it the path of my newly created standalone-toolchain, which created libassimp.so, libassimp.so.3, and libassimp.so.3.1.1(ln) inside my assimp directory tree.
I passed the libassimp.so path to Qt creator project build menu under 'additional libraries'. However, on deploying the app on android, it crashes with error:
dlopen("/data/app/org.qtproject.example.a3dqtquick-2/lib/arm/lib3dqtquick.so", RTLD_LAZY) failed: dlopen failed: could not load library "libassimp.so.3" needed by "lib3dqtquick.so"; caused by library "libassimp.so.3" not found
I can even see the libassimp.so (not libassimp.so.3) file inside the project build directory at
../android-build/libs/armeabi-v7a.
Not sure where to go from here, manually placing libassimp.so.3 at this location does not sort out the problem. Thanks for reading. I will add further info on your feedback . please forgive any info deficiency as this is my first experiment with android.
Following is the deployment-settings.json file
"description": "This file is generated by qmake to be read by androiddeployqt and should not be modified by hand.",
"qt": "/home/ubashir/programs/Qt/5.4/android_armv7",
"sdk": "/home/ubashir/programs/android-sdk-linux",
"sdkBuildToolsRevision": "21.1.2",
"ndk": "/home/ubashir/programs/android-ndk-r10d",
"toolchain-prefix": "arm-linux-androideabi",
"tool-prefix": "arm-linux-androideabi",
"toolchain-version": "4.9",
"ndk-host": "linux-x86_64",
"target-architecture": "armeabi-v7a",
"qml-root-path": "/home/ubashir/code/3dqtquick",
"application-binary": "/home/ubashir/code/3dqtquickAndroid/lib3dqtquick.so"
UPDATE:
I have now tried this.. replace all links to assimp.so.3.1.1 with copies of the latter so now my library libassimp.so.3 is a file instead of link to libassimp.so.3.1.1. I manually added libassimp.so.3 to my project subfolder android/libs/aremabi-v71 --- no good. I confirm that my build directory shows all libassimp files as I manually added them so presumably they are being deployed but the error remains :
failed: dlopen failed: could not load library "libassimp.so.3" needed by "lib3dqtquick.so".
As outlined here http://webmail.dev411.com/p/gg/android-ndk/1386vger6e/use-assimp-c-library-in-ndk-ld-error-obj-local-armeabi-v7a-libassimp-so-incompatible-target-for-use-with-vuforia
I even edited the link.txt file after running cmake on my assimp build directory for android, altering the entry -soname,libassimp.so.3 with -soname,libassimp.so but it still creates libassimp.so.3.1.1 with its two links , i.e., libassimp.so.3 and libassimp.so. So still stuck..

I ran into the same problem with a shared library I built with CMake for and Android project. I found a way to fix it. There might be a cleaner solution if you were more familiar with CMake.
Search through the CMakeLists.txt file(s) for "SOVERSION" and "SET_TARGET_PROPERTIES()"
In the SET_TARGET_PROPERTIES() routine comment out the lines for VERSION and SOVERSION as follows
SET_TARGET_PROPERTIES(${PROJECT_NAME} PROPERTIES # create *nix style library versions + symbolic links
DEFINE_SYMBOL DSO_EXPORTS
# VERSION ${PROJECT_VERSION}
# SOVERSION ${PROJECT_SOVERSION}
CLEAN_DIRECT_OUTPUT 1 # allow creating static and shared libs without conflicts
OUTPUT_NAME "${PROJECT_NAME}${PROJECT_DLLVERSION}" # avoid conflicts between library and binary target names
)
Then rerun the configure and generate steps in CMake and rebuild the target. This should give you a .so without any version numbers.

I'll suggest you to take a look at the solution I've found to my problem (that is very similar to yours):
libgdal.so android error: could not load library "libgdal.so.1"
Hope this helps.

Problem loading pre-built library via Android NDK

I am attempting to add a third-party library to my Android app. It utilizes a .jar file and a .so file. This is a pre-built .so file (i.e. not built specifically for the Android app) - which I know will provide me with plenty of problems down the road. I do NOT have access to the source files for the .jar or .so files!
I am attempting to dynamically load the library via a call to System.loadLibrary("foo");. Currently, when attempting to run the app, it crashes with the UnsatisfiedLinkError: Library foo not found. I have the .so file in both the libs/ and the libs/armeabi file in my project.
Am I chasing after a ghost here? I am trying to determine if what I'm after is even feasible. I have no native code that I'm referencing - all my function calls are to the .jar file that is, as I understand it, backed by the .so file. I have not run the Android.mk file as I'm not compiling anything - the .so file is already provided. I could really use some advice as to what direction to proceed from here.

It's possible that the base name given to System.loadLibrary() is expanding to a file (or path) name different than that of the actual prebuilt library. Logcat should show you exactly what it is trying to load. You could also use System.load() with a full path/file name instead of System.loadLibrary() - though you really should get it working with the later.
While I think it would generate a different error message, it's also possible that the .so is not android compatible - it must not only be for a compatible processor type and abi, but not depend on any dynamic libraries (such as a non-bionic libc) not installed on the device.