Android.mk(a copy of the Google android_mk site)

This page describes the syntax of the 

Android.mk

 build file, which glues your C and C++ source files to the Android NDK.

Overview

The 

Android.mk

 file resides in a subdirectory of your project's 

jni/

 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 more. The 

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 

Android.mk

 file.

The syntax of this file is very close to that used in the 

Android.mk

 files 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.

Basics

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.

An 

Android.mk

 file must begin by defining the 

LOCAL_PATH

 variable:

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 

Android.mk

 file itself).

The next line declares the 

CLEAR_VARS

 variable, whose value the build system provides.

include $(CLEAR_VARS)
      

The 

CLEAR_VARS

 variable points to a special GNU Makefile that clears many 

LOCAL_XXX

 variables for you, such as 

LOCAL_MODULE

, 

LOCAL_SRC_FILES

, and

LOCAL_STATIC_LIBRARIES

. Note that it does not clear 

LOCAL_PATH

. This 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.

Next, the 

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 

libhello-jni.so

.

Note: If your module's name already starts with 

lib

, the build system does not prepend an additional 

lib

 prefix; it takes the module name as-is, and adds the 

.so

 extension. So a source file originally called, for example, 

libfoo.c

 still produces a shared-object file called 

libfoo.so

. This behavior is to support libraries that the Android platform sources generate from 

Android.mk

 files; the names of all such libraries start with 

lib

.

The next line enumerates the source files, with spaces delimiting multiple files:

LOCAL_SRC_FILES := hello-jni.c
      

The 

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:

include $(BUILD_SHARED_LIBRARY)
      

The 

BUILD_SHARED_LIBRARY

 variable points to a GNU Makefile script that collects all the information you defined in 

LOCAL_XXX

 variables since the most recent 

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-activityprovides a detailed explanation of that sample's 

Android.mk

 file. Finally, Variables and Macros provides further information on the variables from this section.

Variables and Macros

The build system provides many possible variables for use in the the 

Android.mk

 file. 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 

  LOCAL_MODULE

  .
• Names that begin with 

  PRIVATE_

  , 

  NDK_

  , or 

  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 recommend prepending 

MY_

 to their names.

NDK-defined 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.

CLEAR_VARS

This variable points to a build script that undefines nearly all 

LOCAL_XXX

 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:

include $(CLEAR_VARS)
      

BUILD_SHARED_LIBRARY

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_MODULE

 and

LOCAL_SRC_FILES

, at a minimum (for more information about these variables, see Module-Description Variables).

The syntax for using this variable is:

include $(BUILD_SHARED_LIBRARY)
      

A shared-library variable causes the build system to generate a library file with a 

.so

 extension.

BUILD_STATIC_LIBRARY

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_STATIC_LIBRARIES

 and 

LOCAL_WHOLE_STATIC_LIBRARIES

, below). The syntax for using this variable is:

include $(BUILD_STATIC_LIBRARY)
      

A static-library variable causes the build system to generate a library with a 

.a

 extension.

PREBUILT_SHARED_LIBRARY

Points to a build script used to specify a prebuilt shared library. Unlike in the case of 

BUILD_SHARED_LIBRARY

 and 

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 variable is:

include $(PREBUILT_SHARED_LIBRARY)
      

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.

PREBUILT_STATIC_LIBRARY

The same as 

PREBUILT_SHARED_LIBRARY

, but for a prebuilt static library. For more information about using prebuilts, see Using Prebuilt Libraries.

TARGET_ARCH

The name of the target CPU architecture as the Android Open Source Project specifies it. For any ARM-compatible build, use 

arm

, independent of the CPU architecture revision or ABI (see TARGET_ARCH_ABI, below).

The value of this variable is taken from the APP_ABI variable that you define in the 

Android.mk

 file, which the system reads ahead of parsing the

Android.mk

 file.

TARGET_PLATFORM

The Android API level number for the build system to target. 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:

TARGET_PLATFORM := android-22
      

TARGET_ARCH_ABI

This variable stores the name of the CPU and architecture to target when the build system parses this 

Android.mk

 file. You can specify one or more of the following values, using a space as a delimiter between multiple targets. Table 1 shows the ABI setting to use for each supported CPU and architecture.

Table 1. ABI settings for different CPUs and architectures.

CPU and architecture	Setting
ARMv5TE	armeabi
ARMv7	armeabi-v7a
ARMv8 AArch64	arm64-v8a
i686	x86
x86-64	x86_64
mips32 (r1)	mips
mips64 (r6)	mips64
All	all

The following example shows how to set ARMv8 AArch64 as the target CPU-and-ABI combination:

TARGET_ARCH_ABI := arm64-v8a
      

Note: Up to Android NDK 1.6_r1, this variable is defined as 

arm

.

For more details about architecture ABIs and associated compatibility issues, refer to ABI Management.

New target ABIs in the future will have different values.

TARGET_ABI

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 specify a 64-bit ARM device running on Android API level 22:

TARGET_ABI := android-22-arm64-v8a
      

Note: Up to Android NDK 1.6_r1, the default value was 

android-3-arm

.

Module-Description Variables

The variables in this section describe your module to the build system. Each module description should follow this basic flow:

• 1. Initialize or undefine the variables associated with the module, using the 

     CLEAR_VARS

      variable.
  2. Assign values to the variables used to describe the module.
  3. Set the NDK build system to use the appropriate build script for the module, using the 

     BUILD_XXX

      variable.

LOCAL_PATH

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 so:

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 

Android.mk

 file describes multiple modules.

LOCAL_MODULE

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 

lib

 prefix or the 

.so

 or 

.a

 file extension; the build system makes these modifications automatically. Throughout your 

Android.mk

 and 

Application.mk

 files, refer to your module by its unmodified name. For example, the following line results in the generation of a shared library module called 

libfoo.so

:

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.

LOCAL_MODULE_FILENAME

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

LOCAL_MODULE

 is 

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 

libnewfoo.so

.

Note: You cannot override filepath or file extension.

LOCAL_SRC_FILES

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 file paths.

We recommend avoiding absolute file paths; relative paths make your 

Android.mk

 file more portable.

Note: Always use Unix-style forward slashes (/) in build files. The build system does not handle Windows-style backslashes (\) properly.

LOCAL_CPP_EXTENSION

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 extension to 

.cxx

. (The setting must include the dot.)

LOCAL_CPP_EXTENSION := .cxx
      

From NDK r7, you can use this variable to specify multiple extensions. For instance:

LOCAL_CPP_EXTENSION := .cxx .cpp .cc
      

LOCAL_CPP_FEATURES

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 

-frtti

 and 

-fexceptions

 directly in your 

LOCAL_CPPFLAGS

 definition.

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.

LOCAL_C_INCLUDES

You can use this optional variable to specify a list of paths, relative to the NDK 

root

 directory, to add to the include search path when compiling all sources (C, C++ and Assembly). For example:

LOCAL_C_INCLUDES := sources/foo
      

Or even:

LOCAL_C_INCLUDES := $(LOCAL_PATH)//foo
      

Define this variable before setting any corresponding inclusion flags via 

LOCAL_CFLAGS

 or 

LOCAL_CPPFLAGS

.

The build system also uses 

LOCAL_C_INCLUDES

 paths automatically when launching native debugging with ndk-gdb.

LOCAL_CFLAGS

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.

Try not to change the optimization/debugging level in your 

Android.mk

 file. The build system can handle this setting automatically for you, using the relevant information in the 

Application.mk

 file. Doing it this way allows the build system to generate useful data files used during debugging.

Note: In android-ndk-1.5_r1, the corresponding flags only applied to C source files, not C++ ones. They now match the full Android build system behavior. (You can now use 

LOCAL_CPPFLAGS

 to specify flags for C++ sources only.)

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 ndk-gdb.

LOCAL_CPPFLAGS

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 command-line.

Note: In android-ndk-1.5_r1, the corresponding flags applied to both C and C++ sources. This has been corrected to match the full Android build system. To specify flags for both C and C++ sources, use 

LOCAL_CFLAGS

.

LOCAL_STATIC_LIBRARIES

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.

LOCAL_SHARED_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.

LOCAL_WHOLE_STATIC_LIBRARIES

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 linker's documentation for the 

--whole-archive

 flag.

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.

LOCAL_LDLIBS

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 time:

LOCAL_LDLIBS := -lz
      

For the list of exposed system libraries against which you can link in this NDK release, see Android NDK Native APIs.

Note: If you define this variable for a static library, the build system ignores it, and 

ndk-build

 prints a warning.

LOCAL_LDFLAGS

The list of other linker flags for the build system to use when building your shared library or executable. For example, the following example uses the

ld.bfd

 linker on ARM/X86 GCC 4.6+, on which 

ld.gold

 is the default

LOCAL_LDFLAGS += -fuse-ld=bfd
      

Note: If you define this variable for a static library, the build system ignores it, and ndk-build prints a warning.

LOCAL_ALLOW_UNDEFINED_SYMBOLS

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.

Note: If you define this variable for a static library, the build system ignores it, and ndk-build prints a warning.

LOCAL_ARM_MODE

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 

arm

 mode by appending 

.arm

 suffix to the 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_ARM_MODE

.

LOCAL_SRC_FILES := foo.c bar.c.arm
      

Note: You can also force the build system to generate ARM binaries by setting 

APP_OPTIM

 in your 

Application.mk

 file to 

debug

. Specifying 

debug

 forces an ARM build because the toolchain debugger does not handle Thumb code properly.

LOCAL_ARM_NEON

This variable only matters when you are targeting the 

armeabi-v7a

 ABI. It allows the use of ARM Advanced SIMD (NEON) GCC 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, see 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, 

bar.c

 with 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 

.neon

.

LOCAL_DISABLE_NO_EXECUTE

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.

LOCAL_DISABLE_RELRO

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 value to 

true

. We do not recommend doing so without a compelling reason.

For more information, see RELRO: RELocation Read-Only and Security enhancements in RedHat Enterprise Linux (section 6).

LOCAL_DISABLE_FORMAT_STRING_CHECKS

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.

LOCAL_EXPORT_CFLAGS

This variable records a set of C/C++ compiler flags to add to the 

LOCAL_CFLAGS

 definition of any other module that uses this one via the

LOCAL_STATIC_LIBRARIES

 or 

LOCAL_SHARED_LIBRARIES

 variables.

For example, consider the following pair of modules: 

foo

 and 

bar

, which depends on 

foo

:

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 

-DFOO=1

 and 

-DBAR=2

 to the compiler when building 

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 

foo

, then 

zoo

 also inherits all flags exported from 

foo

.

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 

foo/foo.c

. To build locally, use 

LOCAL_CFLAGS

 instead.

LOCAL_EXPORT_CPPFLAGS

This variable is the same as 

LOCAL_EXPORT_CFLAGS

, but for C++ flags only.

LOCAL_EXPORT_C_INCLUDES

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 module 

foo

.

LOCAL_EXPORT_LDFLAGS

This variable is the same as 

LOCAL_EXPORT_CFLAGS

, but for linker flags.

LOCAL_EXPORT_LDLIBS

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 module's 

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 

LOCAL_EXPORT_LDLIBS

to 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 

libbar.so

depends on 

foo

, it also depends on the system logging library.

LOCAL_SHORT_COMMANDS

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 use 

@

 syntax for archives containing intermediate object files or linking libraries.

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.

LOCAL_THIN_ARCHIVE

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 contain.

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 

true

, 

false

 or empty. A default value can be set in your 

Application.mk

 file through the 

APP_THIN_ARCHIVE

 variable.

Note: This is ignored for non-static library modules, or prebuilt static library ones.

LOCAL_FILTER_ASM

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:

• 1. The build system generates a temporary assembly file from any C or C++ source file, instead of compiling them into an object file.
  2. The build system executes the shell command in 

     LOCAL_FILTER_ASM

      on any temporary assembly file and on any assembly file listed in

     LOCAL_SRC_FILES

     , thus generating another temporary assembly file.
  3. The build system compiles these filtered assembly files into an object file.

For example:

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.

my-dir

This macro returns the path of the last included makefile, which typically is the current 

Android.mk

's directory. 

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 

my-dir

 defines 

LOCAL_PATH

 as 

$PATH/foo

 instead of 

$PATH

, because that was where its most recent include pointed.

You can avoid this problem by putting additional includes after everything else in the 

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 first 

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
      

all-subdir-makefiles

Returns the list of 

Android.mk

 files located in all subdirectories of the current 

my-dir

 path.

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 containing the 

Android.mk

 file.

this-makefile

Returns the path of the current makefile (from which the build system called the function).

parent-makefile

Returns the path of the parent makefile in the inclusion tree (the path of the makefile that included the current one).

grand-parent-makefile

Returns the path of the grandparent makefile in the inclusion tree (the path of the makefile that included the current one).

import-module

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:

$(call import-module,<name>)
      

In this example, the build system looks for the module tagged 

<name>

 in the list of directories referenced that your 

NDK_MODULE_PATH

 environment variable references, and includes its 

Android.mk

 file automatically for you.