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androidc++cmakeandroid-ndkndk-build

Android How to enable position independent flag -fpic for c++ code

I am using a c++ class in my application to store my constants/urls etc. For that I have configured ndk and CMakeLists.txt file. So I only have two files in my jni folder which is app-config-native-lib.cpp and CMakeLists.txt. Following is my CMakeLists.txt file

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html

# Sets the minimum version of CMake required to build the native library.

cmake_minimum_required(VERSION 3.4.1)

# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.

add_library( # Sets the name of the library.
        app-config-lib

        # Sets the library as a shared library.
        SHARED

        # Provides a relative path to your source file(s).
        app-config-native-lib.cpp)

# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.

find_library( # Sets the name of the path variable.
        log-lib

        # Specifies the name of the NDK library that
        # you want CMake to locate.
        log)

# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.

target_link_libraries( # Specifies the target library.
        app-config-lib

        # Links the target library to the log library
        # included in the NDK.
        ${log-lib})

I want to enable Position independent flag-fpic to adhere the security constraints as it is explained here here. It is explained in this thread that we can pass flag in build gradle file in externalNativeBuild/cmake but I am not sure about it.

My question is how we can enabe PIC executables for native code in Android? What flag should be used? And where to put that flag in build gradle file or CMakeLists file?

Solution

  • The option -fPIC is the default on Android.
    You can add other compiler options in CMakeLists.txt via:
    set_source_files_properties(myfile.c PROPERTIES COMPILE_FLAGS " -mfpu=neon -fno-vectorize")