The NDK supports the use of prebuilt libraries, both static and shared. There are two principal use cases for this functionality:
- Distributing your own libraries to third-party NDK developers without distributing your sources.
- Using a prebuilt version of your own libraries to speed up your build.
This page explains how to use prebuilt libraries.
Declaring a Prebuilt Library
You must declare each prebuilt library you use as an independent module. To do so, perform the following steps:
- Give the module a name. This name does not need to be the same as that of the prebuilt library, itself.
In the module's Android.mk file, assign to
LOCAL_SRC_FILESthe path to the prebuilt library you are providing. Specify the path relative to the value of your
PREBUILT_STATIC_LIBRARY, depending on whether you are using a shared (
.so) or static (
Here is a trivial example that assumes the prebuilt library
in the same directory as the Android.mk file that describes it.
LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) LOCAL_MODULE := foo-prebuilt LOCAL_SRC_FILES := libfoo.so include $(PREBUILT_SHARED_LIBRARY)
In this example, the name of the module is the same as that of the prebuilt library.
The build system places a copy of your prebuilt shared library into
$PROJECT/obj/local, and another copy, stripped of debug information, into
$PROJECT is the root directory of your project.
Referencing the Prebuilt Library from Other Modules
To reference a prebuilt library from other modules, specify its name as the
value of the
LOCAL_SHARED_LIBRARIES variable in
the Android.mk files associated with those other modules.
For example, the description of a module using
libfoo.so might be as follows:
include $(CLEAR_VARS) LOCAL_MODULE := foo-user LOCAL_SRC_FILES := foo-user.c LOCAL_SHARED_LIBRARIES := foo-prebuilt include $(BUILD_SHARED_LIBRARY)
LOCAL_MODULE is the name of the module referring to the prebuilt;
LOCAL_SHARED_LIBRARIES is the name of the prebuilt, itself.
Exporting Headers for Prebuilt Libraries
The code in
foo-user.c depends on specific declarations that normally reside
in a header file, such as
foo.h, distributed with the prebuilt library. For
foo-user.c might have a line like the following:
In such a case, you need to provide the header and its include path to the
compiler when you build the
foo-user module. A simple way to accomplish this
task is to use exports in the prebuilt module definition. For example, as long
foo.h is located under the
include directory associated with the
prebuilt module, you can declare it as follows:
include $(CLEAR_VARS) LOCAL_MODULE := foo-prebuilt LOCAL_SRC_FILES := libfoo.so LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/include include $(PREBUILT_SHARED_LIBRARY)
LOCAL_EXPORT_C_INCLUDES definition here ensures that the build system
exports the path to the prebuilt library's
include directory, prepending that
path onto the value of the
LOCAL_C_INCLUDES for the module dependent on it.
This operation allows the build system to find the necessary headers.
Debugging Prebuilt Libraries
We recommend that you provide prebuilt shared libraries containing debug
symbols. The NDK build system always strips the symbols from the version of the
library that it installs into
$PROJECT/libs/<abi>/, but you can use the debug
version for debugging with
Selecting ABIs for Prebuilt Libraries
You must make sure to select the right version of your prebuilt shared library
for your targeted ABI. The
variable in the Android.mk file can point the build system at the appropriate
version of the library.
For example, assume that your project contains two versions of library
The following snippet shows how to use
TARGET_ARCH_ABI so that the build
system selects the appropriate version of the library:
include $(CLEAR_VARS) LOCAL_MODULE := foo-prebuilt LOCAL_SRC_FILES := $(TARGET_ARCH_ABI)/libfoo.so LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/include include $(PREBUILT_SHARED_LIBRARY)
If you have specified
armeabi as the value of
TARGET_ARCH_ABI, the build
system uses the version of
libfoo.so located in the
armeabi directory. If
you have specified
x86 as the value
TARGET_ARCH_ABI, the build system uses
the version in the