Crashlytics NDK symbol building from command line

Question

I'm trying to add Crashlytics support to my Android project, which uses NDK and gradle CMake. This means that I need symbols for my shared projects. So if I want to create the symbols for release build I'll call gradlew crashlyticsUploadSymbolsRelease

The official document in https://docs.fabric.io/android/crashlytics/ndk.html says that The symbol generation and upload process assumes a standard project structure: src/main/obj for debug binaries, and src/main/libs for release binaries as produced by ndk-build.

In the gradle file this means a new block which is like the following:

crashlytics {
    enableNdk true
    androidNdkOut 'src/main/obj'
    androidNdkLibsOut 'src/main/libs'
}

Because I am using the gradle CMake integration to build my native libs, the default paths of course are not working. My native libraries in release mode are built into a build/intermediates/cmake/release/obj directory and in debug mode they go to build/intermediates/cmake/debug/obj directory.

From trial and error I figured that if I want my release build to work, I'll have to put the path to release mode native libraries into both lines, as illustrated below.

crashlytics {
    enableNdk true
    androidNdkOut 'build/intermediates/cmake/release/obj'
    androidNdkLibsOut 'build/intermediates/cmake/release/obj'
}

I just really don't understand the difference between androidNdkOut and androidNdkLibsOut variables, because at least in my scenario they point to same directory. Fortunately this isn't a problem for me because I just need Crashlytics to work with my release binaries.

So my questions are:

1) What is really the difference between androidNdkOut and androidNdkLibsOut? Why I cannot put a path to my debug binaries in one and path to release binaries to other? A concrete example would be nice in addition to explanation.

2) How should I modify my gradle file if some day I want to include symbols for my debug libraries as well? Meaning that the command gradlew crashlyticsUploadSymbolsRelease as well as gradlew crashlyticsUploadSymbolsDebug would work?

There is a discussion about this in the threads Crashlytics NDK symbols and Gradle tasks and Crashlytics NDK multi androidNdkOut path support but they really don't answer to these two questions.

Answer 1

I work on the Fabric team that maintains our Crashlytics NDK support.

To give some context - our symbol upload tool is based on the ndk-build process which produces 2 sets of binaries: your production binaries, which are stripped of symbol data, and debug binaries, which have symbol data intact for debugging purposes.

The Gradle properties map to variables in the ndk-build process, specifically:

• androidNdkOut is the directory under which the unstripped, debug binaries are placed (equivalent to the $NDK_OUT variable in ndk-build) called obj by default.
• androidNdkLibsOut is the directory under which the stripped, release binaries are placed (equivalent to the $NDK_LIBS_OUT variable in ndk-build) called libs by default.

The expected contents of these paths are the architecture-specific directories for your libraries, so for example:

obj/
  — armeabi
    — lib1.so
    — lib2.so
  — x86
    — lib1.so
    — lib2.so

libs/
  — armeabi
    — lib1.so
    — lib2.so
  — x86
    — lib1.so
    — lib2.so

All you’ll need to do for our symbol upload to work is to generate these same sets of binaries from CMake, and then set your androidNdkOut and androidNdkLibsOut to the appropriate top-level directories where those libraries can be found.

EDIT/UPDATE July 7, 2017

We've just released version 1.23.0 of the Fabric plugin for Gradle which supports automatically resolving the appropriate native library paths when you're using the Android Gradle plugin 2.2.0+ with the externalNativeBuild DSL, so you no longer have to set androidNdkOut and androidNdkLibsOut if you're using the latest Android Gradle plugin. Check out more info here: https://docs.fabric.io/android/crashlytics/ndk.html#specifying-the-path-to-debug-and-release-binaries