This page describes the syntax of the
Android.mk build file, which glues your
C and C++ source files to the Android NDK.
Android.mk file resides in a subdirectory of your project's
directory, and describes your sources and shared libraries to the build system.
It is really a tiny GNU makefile fragment that the build system parses once or
Android.mk file is useful for defining project-wide settings that
Application.mk, the build system, and your environment variables leave
undefined. It can also override project-wide settings for specific modules.
The syntax of the
Android.mk allows you to group your sources into modules.
A module is either a static library, a shared library, or a standalone
executable. You can define one or more modules in each
Android.mk file, and
you can use the same source file in multiple modules. The build system only
places shared libraries into your application package. In addition, static
libraries can generate shared libraries.
In addition to packaging libraries, the build system handles a variety of other
details for you. For example, you don't need to list header files or explicit
dependencies between generated files in your
Android.mk file. The NDK build
system computes these relationships automatically for you. As a result, you
should be able to benefit from new toolchain/platform support in future NDK
releases without having to touch your
The syntax of this file is very close to that used in the
distributed with the full Android Open Source Project. While the build system
implementation that uses them is different, their similarity is an intentional
design decision aimed at making it easier for application developers to reuse
source code for external libraries.
Before exploring the syntax in detail, it is useful to start by understanding
the basics of what a
Android.mk file contains. This section uses the
Android.mk file in the Hello-JNI sample toward that end, explaining the role
that each line in the file plays.
Android.mk file must begin by defining the
LOCAL_PATH := $(call my-dir)
This variable indicates the location of the source files in the development
tree. Here, the macro function
my-dir, provided by the build system, returns
the path of the current directory (the directory containing the
The next line declares the
CLEAR_VARS variable, whose value the build system
CLEAR_VARS variable points to a special GNU Makefile that clears many
LOCAL_XXX variables for you, such as
LOCAL_STATIC_LIBRARIES. Note that it does not clear
variable must retain its value because the system parses all build control files
in a single GNU Make execution context where all variables are global. You must
(re-)declare this variable before describing each module.
LOCAL_MODULE variable stores the name of the module that you wish to
build. Use this variable once per module in your application.
LOCAL_MODULE := hello-jni
Each module name must be unique and not contain any spaces. The build system,
when it generates the final shared-library file, automatically adds the proper
prefix and suffix to the name that you assign to
LOCAL_MODULE. For example,
the example that appears above results in generation of a library called
The next line enumerates the source files, with spaces delimiting multiple files:
LOCAL_SRC_FILES := hello-jni.c
LOCAL_SRC_FILES variable must contain a list of C and/or C++ source files
to build into a module.
The last line helps the system tie everything together:
BUILD_SHARED_LIBRARY variable points to a GNU Makefile script that
collects all the information you defined in
LOCAL_XXX variables since the most
include. This script determines what to build, and how to do it.
There are more complex examples in the samples directories, with commented
Android.mk files that you can look at. In addition, Sample: native-activity
provides a detailed explanation of that sample's
Android.mk file. Finally,
Variables and Macros provides further information on the variables from this
Variables and Macros
The build system provides many possible variables for use in the
Many of these variables come with preassigned values. Others, you assign.
In addition to these variables, you can also define your own arbitrary ones. If you do so, keep in mind that the NDK build system reserves the following variable names:
- Names that begin with
LOCAL_, such as
- Names that begin with
APP. The build system uses these internally.
- Lower-case names, such as
my-dir. The build system uses these internally, as well.
If you need to define your own convenience variables in an
Android.mk file, we
MY_ to their names.
NDK-defined include variables
This section discusses the GNU Make variables that the build system defines
before parsing your
Android.mk file. Under certain circumstances, the NDK
might parse your
Android.mk file several times, using a different definition
for some of these variables each time.
This variable points to a build script that undefines nearly all
variables listed in the "Developer-defined variables" section below. Use this
variable to include this script before describing a new module. The syntax for
using it is:
This variable points to a build script that collects all the information about
the module you provided in your
LOCAL_XXX variables, and determines how to
build a target shared library from the sources you listed. Note that using this
script requires that you have already assigned values to
LOCAL_SRC_FILES, at a minimum (for more information about these variables, see
The syntax for using this variable is:
A shared-library variable causes the build system to generate a library file
A variant of
BUILD_SHARED_LIBRARY that is used to build a static library. The
build system does not copy static libraries into your project/packages, but it
can use them to build shared libraries (see
LOCAL_WHOLE_STATIC_LIBRARIES, below). The syntax for using this variable is:
A static-library variable causes the build system to generate a library with a
Points to a build script used to specify a prebuilt shared library. Unlike in
the case of
BUILD_STATIC_LIBRARY, here the value of
LOCAL_SRC_FILES cannot be a source file. Instead, it must be a single path to
a prebuilt shared library, such as
foo/libfoo.so. The syntax for using this
You can also reference a prebuilt library in another module by using the
LOCAL_PREBUILTS variable. For more information about using prebuilts, see
Using Prebuilt Libraries.
The same as
PREBUILT_SHARED_LIBRARY, but for a prebuilt static library. For
more information about using prebuilts, see Using Prebuilt Libraries.
Target information variables
The build system parses
Android.mk once per ABI specified by the
variable, which is typically defined in your
Application.mk file. If
all, then the build system parses
Android.mk once per ABI the NDK
supports. This section describes variables the build system defines each time it
The CPU family the build system is targeting as it parses this
file. This variable will be one of:
The Android API level number the build system is targeting as it parses this
Android.mk file. For example, the Android 5.1 system images correspond to
Android API level 22:
android-22. For a complete list of platform names and
corresponding Android system images, see Android NDK Native APIs. The
following example shows the syntax for using this variable:
ifeq ($(TARGET_PLATFORM),android-22) # ... do something ... endif
The ABI the build system is targeting as it parses this
Table 1 shows the ABI setting used for each supported CPU and architecture.
|CPU and architecture||Setting|
The following example shows how to check for ARMv8 AArch64 as the target CPU-and-ABI combination:
ifeq ($(TARGET_ARCH_ABI),arm64-v8a) # ... do something ... endif
For more details about architecture ABIs and associated compatibility issues, refer to ABI Management.
New target ABIs in the future will have different values.
A concatenation of target Android API level and ABI. It is especially useful when you want to test against a specific target system image for a real device. For example, to check for a 64-bit ARM device running on Android API level 22:
ifeq ($(TARGET_ABI),android-22-arm64-v8a) # ... do something ... endif
The variables in this section describe your module to the build system. Each module description should follow this basic flow:
- Initialize or undefine the variables associated with the module, using the
- Assign values to the variables used to describe the module.
- Set the NDK build system to use the appropriate build script for the module,
This variable is used to give the path of the current file. You must define it
at the start of your
Android.mk file. The following example shows how to do
LOCAL_PATH := $(call my-dir)
The script to which
CLEAR_VARS points does not clear this variable. Therefore,
you only need to define it a single time, even if your
describes multiple modules.
This variable stores the name of your module. It must be unique among all module
names, and must not contain any spaces. You must define it before including any
scripts (other than the one for
CLEAR_VARS). You need not add either the
prefix or the
.a file extension; the build system makes these
modifications automatically. Throughout your
files, refer to your module by its unmodified name. For example, the following
line results in the generation of a shared library module called
LOCAL_MODULE := "foo"
If you want the generated module to have a name other than
lib + the value of
LOCAL_MODULE, you can use the
LOCAL_MODULE_FILENAME variable to give the
generated module a name of your own choosing, instead.
This optional variable allows you to override the names that the build system
uses by default for files that it generates. For example, if the name of your
foo, you can force the system to call the file it generates
libnewfoo. The following example shows how to accomplish this:
LOCAL_MODULE := foo LOCAL_MODULE_FILENAME := libnewfoo
For a shared library module, this example would generate a file called
This variable contains the list of source files that the build system uses to
generate the module. Only list the files that the build system actually passes
to the compiler, since the build system automatically computes any associated
depencies. Note that you can use both relative (to
LOCAL_PATH) and absolute
We recommend avoiding absolute file paths; relative paths make your
file more portable.
You can use this optional variable to indicate a file extension other than
.cpp for your C++ source files. For example, the following line changes the
.cxx. (The setting must include the dot.)
LOCAL_CPP_EXTENSION := .cxx
You can use this variable to specify multiple extensions. For instance:
LOCAL_CPP_EXTENSION := .cxx .cpp .cc
You can use this optional variable to indicate that your code relies on specific
C++ features. It enables the right compiler and linker flags during the build
process. For prebuilt binaries, this variable also declares which features the
binary depends on, thus helping ensure the final linking works correctly. We
recommend that you use this variable instead of enabling
-fexceptions directly in your
Using this variable allows the build system to use the appropriate flags for
each module. Using
LOCAL_CPPFLAGS causes the compiler to use all specified
flags for all modules, regardless of actual need.
For example, to indicate that your code uses RTTI (RunTime Type Information), write:
LOCAL_CPP_FEATURES := rtti
To indicate that your code uses C++ exceptions, write:
LOCAL_CPP_FEATURES := exceptions
You can also specify multiple values for this variable. For example:
LOCAL_CPP_FEATURES := rtti features
The order in which you describe the values does not matter.
You can use this optional variable to specify a list of paths, relative to the
root directory, to add to the include search path when compiling all
sources (C, C++ and Assembly). For example:
LOCAL_C_INCLUDES := sources/foo
LOCAL_C_INCLUDES := $(LOCAL_PATH)/<subdirectory>/foo
Define this variable before setting any corresponding inclusion flags via
The build system also uses
LOCAL_C_INCLUDES paths automatically when launching
native debugging with ndk-gdb.
This optional variable sets compiler flags for the build system to pass when
building C and C++ source files. The ability to do so can be useful for
specifying additional macro definitions or compile options. Use
to specify flags for C++ only.
Try not to change the optimization/debugging level in your
The build system can handle this setting automatically for you, using the
relevant information in the [pplication.mk] file. Doing it this way allows the
build system to generate useful data files used during debugging.
It is possible to specify additional include paths by writing:
LOCAL_CFLAGS += -I<path>,
It is better, however, to use
LOCAL_C_INCLUDES for this purpose, since doing
so also makes it possible to use the paths available for native debugging with
An optional set of compiler flags that will be passed when building C++ source
files only. They will appear after the
LOCAL_CFLAGS on the compiler's
LOCAL_CFLAGS to specify flags for both C and C++.
This variable stores the list of static libraries modules on which the current module depends.
If the current module is a shared library or an executable, this variable will force these libraries to be linked into the resulting binary.
If the current module is a static library, this variable simply indicates that other modules depending on the current one will also depend on the listed libraries.
This variable is the list of shared libraries modules on which this module depends at runtime. This information is necessary at link time, and to embed the corresponding information in the generated file.
This variable is a variant of
LOCAL_STATIC_LIBRARIES, and expresses that the
linker should treat the associated library modules as whole archives. For
more information on whole archives, see the GNU ld documentation for the
This variable is useful when there are circular dependencies among several static libraries. When you use this variable to build a shared library, it will force the build system to add all object files from your static libraries to the final binary. The same is not true, however, when generating executables.
This variable contains the list of additional linker flags for use in building
your shared library or executable. It enables you to use the
-l prefix to pass
the name of specific system libraries. For example, the following example tells
the linker to generate a module that links to
/system/lib/libz.so at load
LOCAL_LDLIBS := -lz
For the list of exposed system libraries against which you can link in this NDK release, see Android NDK Native APIs.
The list of other linker flags for the build system to use when building your
shared library or executable. For example, to use the
ld.bfd linker on
LOCAL_LDFLAGS += -fuse-ld=bfd
By default, when the build system encounters an undefined reference encountered while trying to build a shared, it will throw an undefined symbol error. This error can help you catch catch bugs in your source code.
To disable this check, set this variable to
true. Note that this setting may
cause the shared library to load at runtime.
By default, the build system generates ARM target binaries in thumb mode,
where each instruction is 16 bits wide and linked with the STL libraries in the
thumb/ directory. Defining this variable as
arm forces the build system to
generate the module's object files in 32-bit
arm mode. The following example
shows how to do this:
LOCAL_ARM_MODE := arm
You can also instruct the build system to only build specific sources in
mode by appending
.arm suffix to the source filenames. For example, the
following example tells the build system to always compile
bar.c in ARM mode,
but to build
foo.c according to the value of
LOCAL_SRC_FILES := foo.c bar.c.arm
This variable only matters when you are targeting the
armeabi-v7a ABI. It
allows the use of ARM Advanced SIMD (NEON) compiler intrinsics in your C and C++
sources, as well as NEON instructions in Assembly files.
Note that not all ARMv7-based CPUs support the NEON instruction set extensions. For this reason, you must perform runtime detection to be able to safely use this code at runtime. For more information, se NEON Support and the cpufeatures Library.
Alternatively, you can use the
.neon suffix to specify that the build system
only compile specific source files with NEON support. In the following example,
the build system compiles
foo.c with thumb and neon support,
thumb support, and
zoo.c with support for ARM and NEON:
LOCAL_SRC_FILES = foo.c.neon bar.c zoo.c.arm.neon
If you use both suffixes,
.arm must precede
Android NDK r4 added support for the "NX bit" security feature. It is enabled by
default, but you can disable it by setting this variable to
true. We do not
recommend doing so without a compelling reason.
This feature does not modify the ABI, and is only enabled on kernels targeting ARMv6+ CPU devices. Machine code with this feature enabled will run unmodified on devices running earlier CPU architectures. For more information, see Wikipedia: NX bit and The GNU stack kickstart.
By default, the NDK compiles code with read-only relocations and GOT protection. This variable instructs the runtime linker to mark certain regions of memory as read-only after relocation, making certain security exploits (such as GOT overwrites) more difficult. Note that these protections are only effective on Android API level 16 and higher. On lower API levels, the code will still run, but without memory protections.
This variable is turned on by default, but you can disable it by setting its
true. We do not recommend doing so without a compelling reason.
By default, the build system compiles code with format string protection. Doing
so forces a compiler error if a non-constant format string is used in a
printf-style function. This protection is on by default, but you can disable
it by setting the value of this variable to
true. We do not recommend doing so
without a compelling reason.
This variable records a set of C/C++ compiler flags to add to the
definition of any other module that uses this one via the
For example, consider the following pair of modules:
include $(CLEAR_VARS) LOCAL_MODULE := foo LOCAL_SRC_FILES := foo/foo.c LOCAL_EXPORT_CFLAGS := -DFOO=1 include $(BUILD_STATIC_LIBRARY) include $(CLEAR_VARS) LOCAL_MODULE := bar LOCAL_SRC_FILES := bar.c LOCAL_CFLAGS := -DBAR=2 LOCAL_STATIC_LIBRARIES := foo include $(BUILD_SHARED_LIBRARY)
Here, the build system passes the flags
-DBAR=2 to the compiler
bar.c. It also prepends exported flags to your your module's
LOCAL_CFLAGS so you can easily override them.
In addition, the relationship among modules is transitive: If
zoo depends on
bar, which in turn depends on
zoo also inherits all flags
Finally, the build system does not use exported flags when building locally
(i.e., building the module whose flags it is exporting). Thus, in the example
above, it does not pass
-DFOO=1 to the compiler when building
build locally, use
This variable is the same as
LOCAL_EXPORT_CFLAGS, but for C++ flags only.
This variable is the same as
LOCAL_EXPORT_CFLAGS, but for C include paths. It
is useful in cases where, for example,
bar.c needs to include headers from
This variable is the same as
LOCAL_EXPORT_CFLAGS, but for linker flags.
This variable is the same as
LOCAL_EXPORT_CFLAGS, telling the build system to
pass names of specific system libraries to the compiler. Prepend
-l to the
name of each library you specify.
Note that the build system appends imported linker flags to the value of your
LOCAL_LDLIBS variable. It does this due to the way Unix linkers work.
This variable is typically useful when module
foo is a static library and has
code that depends on a system library. You can then use
to export the dependency. For example:
include $(CLEAR_VARS) LOCAL_MODULE := foo LOCAL_SRC_FILES := foo/foo.c LOCAL_EXPORT_LDLIBS := -llog include $(BUILD_STATIC_LIBRARY) include $(CLEAR_VARS) LOCAL_MODULE := bar LOCAL_SRC_FILES := bar.c LOCAL_STATIC_LIBRARIES := foo include $(BUILD_SHARED_LIBRARY)
In this example, the build system puts
-llog at the end of the linker command
when it builds
libbar.so. Doing so tells the linker that, because
foo, it also depends on the system logging library.
Set this variable to
true when your module has a very high number of sources
and/or dependent static or shared libraries. Doing so forces the build system to
@ syntax for archives containing intermediate object files or linking
This feature can be useful on Windows, where the command line accepts a maximum of only of 8191 characters, which can be too small for complex projects. It also impacts the compilation of individual source files, placing nearly all compiler flags inside list files, too.
Note that any value other than
true will revert to the default behaviour. You
can also define
APP_SHORT_COMMANDS in your
Application.mk file to force
this behavior for all modules in your project.
We do not recommend enabling this feature by default, since it makes the build slower.
Set this variable to
true when building static libraries. Doing so will
generate a thin archive, a library file that does not contain object files,
but instead just file paths to the actual objects that it would normally
This is useful to reduce the size of your build output. The drawback is that such libraries cannot be moved to a different location (all paths inside them are relative).
Valid values are
false or empty. A default value can be set in your
Application.mk file through the
Define this variable as a shell command that the build system will use to filter
the assembly files extracted or generated from the files you specified for
LOCAL_SRC_FILES. Defining this variable causes the following things to occur:
- The build system generates a temporary assembly file from any C or C++ source file, instead of compiling them into an object file.
- The build system executes the shell command in
LOCAL_FILTER_ASMon any temporary assembly file and on any assembly file listed in
LOCAL_SRC_FILES, thus generating another temporary assembly file.
- The build system compiles these filtered assembly files into an object file.
LOCAL_SRC_FILES := foo.c bar.S LOCAL_FILTER_ASM := foo.c --1--> $OBJS_DIR/foo.S.original --2--> $OBJS_DIR/foo.S --3--> $OBJS_DIR/foo.o bar.S --2--> $OBJS_DIR/bar.S --3--> $OBJS_DIR/bar.o
"1" corresponds to the compiler, "2" to the filter, and "3" to the assembler. The filter must be a standalone shell command that takes the name of the input file as its first argument, and the name of the output file as the second one. For example:
myasmfilter $OBJS_DIR/foo.S.original $OBJS_DIR/foo.S myasmfilter bar.S $OBJS_DIR/bar.S
NDK-provided function macros
This section explains GNU Make function macros that the NDK provides. Use
$(call <function>) to evaluate them; they return textual information.
This macro returns the path of the last included makefile, which typically is
my-dir is useful for defining
LOCAL_PATH at the start of your
Android.mk file. For example:
LOCAL_PATH := $(call my-dir)
Due to the way GNU Make works, what this macro really returns is the path of the
last makefile that the build system included when parsing the build scripts. For
this reason, you should not call
my-dir after including another file.
For example, consider the following example:
LOCAL_PATH := $(call my-dir) # ... declare one module include $(LOCAL_PATH)/foo/`Android.mk` LOCAL_PATH := $(call my-dir) # ... declare another module
The problem here is that the second call to
$PATH/foo instead of
$PATH, because that was where its most recent include
You can avoid this problem by putting additional includes after everything else
Android.mk file. For example:
LOCAL_PATH := $(call my-dir) # ... declare one module LOCAL_PATH := $(call my-dir) # ... declare another module # extra includes at the end of the Android.mk file include $(LOCAL_PATH)/foo/Android.mk
If it is not feasible to structure the file in this way, save the value of the
my-dir call into another variable. For example:
MY_LOCAL_PATH := $(call my-dir) LOCAL_PATH := $(MY_LOCAL_PATH) # ... declare one module include $(LOCAL_PATH)/foo/`Android.mk` LOCAL_PATH := $(MY_LOCAL_PATH) # ... declare another module
Returns the list of
Android.mk files located in all subdirectories of the
You can use this function to provide deep-nested source directory hierarchies to
the build system. By default, the NDK only looks for files in the directory
Returns the path of the current makefile (from which the build system called the function).
Returns the path of the parent makefile in the inclusion tree (the path of the makefile that included the current one).
Returns the path of the grandparent makefile in the inclusion tree (the path of the makefile that included the current one).
A function that allows you to find and include a module's
Android.mk file by
the name of the module. A typical example is as follows:
In this example, the build system looks for the module tagged
the list of directories referenced that your
variable references, and includes its
Android.mk file automatically for you.