Application.mk

This document explains the Application.mk build file used by ndk-build.

We recommend that you read the Concepts and Android.mk pages before this one. Doing so will help maximize your understanding of the material on this page.

Overview

The Application.mk file is really a tiny GNU Makefile fragment that defines several variables for compilation. It usually resides under $PROJECT/jni/, where $PROJECT points to your application's project directory. Another alternative is to place it under a sub-directory of the top-level $NDK/apps/ directory. For example:

$NDK/apps/<myapp>/Application.mk

Here, <myapp> is a short name used to describe your app to the NDK build system. It doesn't actually go into your generated shared libraries or your final packages.

Variables

APP_PROJECT_PATH

This variable stores the absolute path to your app's project-root directory. The build system uses this information to place stripped-down versions of the generated JNI shared libraries into a specific location known to the APK-generating tools.

If you place your Application.mk file under $NDK/apps/<myapp>/, you must define this variable. If you place it under $PROJECT/jni/, it is optional.

APP_MODULES

If this variable is defined, it tells ndk-build to build only the corresponding modules and those that they depend on. It must be a space-separated list of module names as they appear in the LOCAL_MODULE definition of Android.mk files.

If the variable is undefined, ndk-build looks for the list of all installable top-level modules, i.e. those listed by your Android.mk file and any file it includes directly. Imported modules are not top-level though.

An installable module is either a shared library or executable, which will generate a file in libs/$ABI/.

If the variable is undefined, and there are no installable top-level modules in your project, then ndk-build builds all top-level static libraries and their dependencies instead. These libraries are placed at the usual location under obj/ or obj-debug/.

APP_OPTIM

Define this optional variable as either release or debug. You use it to alter the optimization level when building your application's modules.

Release mode is the default, and generates highly optimized binaries. Debug mode generates unoptimized binaries that are much easier to debug.

Note that you can debug either release or debug binaries. Release binaries, however, provide less information during debugging. For example, the build system optimizes out some variables, preventing you from inspecting them. Also, code re-ordering can make it more difficult to step through the code; stack traces may not be reliable.

Declaring android:debuggable in your application manifest's <application> tag will cause this variable to default to debug instead of release. Override this default value by setting APP_OPTIM to release.

APP_CFLAGS

This variable stores a set of C compiler flags that the build system passes to the compiler when compiling any C or C++ source code for any of the modules. You can use this variable to change the build of a given module according to the application that needs it, instead of having to modify the Android.mk file itself. Use APP_CPPFLAGS to specify flags for C++ only.

All paths in these flags should be relative to the top-level NDK directory. For example, if you have the following setup:

sources/foo/Android.mk
sources/bar/Android.mk

To specify in foo/Android.mk that you want to add the path to the bar sources during compilation, you should use:

APP_CFLAGS += -Isources/bar

Or, alternatively:

APP_CFLAGS += -I$(LOCAL_PATH)/../bar

-I../bar will not work since it is equivalent to -I$NDK_ROOT/../bar.

APP_CPPFLAGS

This variable contains a set of C++ compiler flags that the build system passes to the compiler when building only C++ sources. Use APP_CFLAGS to specify flags for C and C++.

APP_LDFLAGS

A set of linker flags that the build system passes when linking the application. This variable is only relevant when the build system is building shared libraries and executables. When the build system builds static libraries, it ignores these flags.

APP_BUILD_SCRIPT

By default, the NDK build system looks under jni/ for a file named Android.mk.

If you want to override this behavior, you can define APP_BUILD_SCRIPT to point to an alternate build script. The build system always interprets a non-absolute path as relative to the NDK's top-level directory.

APP_ABI

By default, the NDK build system generates machine code for all non-deprecated ABIs. You can use the APP_ABI setting to generate machine code for specific ABIs. Table 1 shows the APP_ABI settings for different instruction sets.

Table 1. APP_ABI settings for different instruction sets.

Instruction set Value
Hardware FPU instructions on ARMv7 based devices APP_ABI := armeabi-v7a
ARMv8 AArch64 APP_ABI := arm64-v8a
IA-32 APP_ABI := x86
Intel64 APP_ABI := x86_64
All supported instruction sets APP_ABI := all

You can also specify multiple values by placing them on the same line, delimited by spaces. For example:

APP_ABI := armeabi-v7a arm64-v8a x86

For the list of all supported ABIs and details about their usage and limitations, refer to ABI Management.

APP_PLATFORM

This variable contains the minimum Android platform version you want to support. For example, a value of android-15 specifies that your library uses APIs that are not available below Android 4.0.3 (API level 15) and can't be used on devices running a lower platform version. For a complete list of platform names and corresponding Android system images, see Android NDK Native APIs.

Instead of changing this flag directly, you should set the minSdkVersion property in the defaultConfig or productFlavors blocks of your module-level build.gradle file. This makes sure your library is used only by apps installed on devices running an adequate version of Android. The ndk-build toolchain uses the following logic to choose the minimum platform version for your library based the ABI you're building and the minSdkVersion you specify:

  1. If there exists a platform version for the ABI equal to minSdkVersion, ndk-build uses that version.
  2. Otherwise, if there exists platform versions lower than minSdkVersion for the ABI, ndk-build uses the highest of those platform versions. This is a reasonable choice because a missing platform version typically means that there were no changes to the native platform APIs since the previous available version.
  3. Otherwise, ndk-build uses the next available platform version higher than minSdkVersion.

APP_STL

The NDK build system defaults to STL system. Other choices are c++_shared, c++_static, and none. See NDK Runtimes and Features.

APP_SHORT_COMMANDS

The equivalent of LOCAL_SHORT_COMMANDS in Application.mk for your whole project. For more information, see the documentation for this variable on Android.mk.

APP_THIN_ARCHIVE

Sets the default value of LOCAL_THIN_ARCHIVE in the Android.mk file for all static library modules in this project. For more information, see the documentation for LOCAL_THIN_ARCHIVE on Android.mk.