The build system supports building binaries for two target CPU architectures, 32 bit and 64 bit, in the same build. This two-target build is known as a multilib build.
For built-in static libraries and shared libraries, the build system sets up
rules to build binaries for both architectures. The product configuration
PRODUCT_PACKAGES), together with the dependency graph, determines which
binaries are built and installed to the system image.
For executables and apps, the build system builds only the 64-bit version by
default, but you can override this setting with a global
BoardConfig.mk variable or a module-scoped variable.
Identify a second CPU architecture and ABI
BoardConfig.mk includes the following variables to configure the second CPU
architecture and application binary interface (ABI):
For an example makefile that uses these variables, see
In a multilib build, module names in
both the 32-bit and 64-bit binaries, as long as they're defined by the build
system. For libraries included by dependency, a 32-bit or 64-bit library is
installed only if it's required by another 32-bit or 64-bit library or
However, module names on the
make command line cover only the
64-bit version. For example, after running
make libc builds only the 64-bit libc. To
build the 32-bit libc, you need to run
Define module architecture in Android.mk
You can use the
LOCAL_MULTILIB variable to configure your build
for 32 bit and 64 bit and override the global
LOCAL_MULTILIB to one of the
bothbuilds both 32 bit and 64 bit.
32builds only 32 bit.
64builds only 64 bit.
firstbuilds for only the first architecture (32 bit in 32-bit devices and 64 bit in 64-bit devices).
LOCAL_MULTILIB isn't set and the build system decides which
architecture to build based on the module class and other
LOCAL_* variables, such as
If you want to build your module for specific architectures, use the following variables:
LOCAL_MODULE_TARGET_ARCH- Set this variable to a list of architectures, such as
arm x86 arm64. If the architecture being built is in that list, the current module is included by the build system.
LOCAL_MODULE_UNSUPPORTED_TARGET_ARCH- This variable is the opposite of
LOCAL_MODULE_TARGET_ARCH. If the architecture being built is
notin that list, the current module is included by the build system.
There are minor variants of these two variables:
The build system warns if the current module is skipped because of the architectures listed.
To set up build flags for a particular architecture, use the
LOCAL_* variables where
* is an architecture-specific suffix, for example:
These variables are applied only if a binary is being built for that architecture.
Sometimes it's easier to set up flags based on whether the binary is
being built for 32-bit or 64-bit. Use the
variable with a
_64 suffix, for example:
Set library installation path
For a non-multilib build, you can use
LOCAL_MODULE_PATH to install a library
to a location other than the default location. For example,
LOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)/hw.
However, in a multilib build, use
LOCAL_MODULE_RELATIVE_PATH := hw
With this format, both the 64-bit and 32-bit libraries are installed in the correct location.
If you build an executable as both 32 bit and 64 bit, use one of the following variables to distinguish the install path:
LOCAL_MODULE_STEM_32, LOCAL_MODULE_STEM_64- Specifies the installed filename.
LOCAL_MODULE_PATH_32, LOCAL_MODULE_PATH_64- Specifies the install path.
Obtain intermediate directory for source files
In a multilib build, if you generate source files to
with explicit variables), it doesn't work reliably. That's
because the intermediate generated sources are required by both the 32-bit and
64-bit builds, but
$(local-intermediates-dir) points to only one of
the two intermediate directories.
The build system provides a dedicated, multilib-friendly,
intermediate directory for generating sources. To retrieve the intermediate
directory's path, use the
$(generated-sources-dir-for) macro. The uses of these macros are similar to
If a source file is generated to this dedicated directory and picked up
LOCAL_GENERATED_SOURCES, it's built for both 32 bit and 64 bit
in a multilib build.
Indicate system architecture of prebuilt binary targets
In a multilib build, you can't use
TARGET_ARCH combined with
TARGET_2ND_ARCH, to indicate the system architecture of the prebuilt
binary targets. Instead, use the
With these variables, the build system can choose the corresponding 32-bit prebuilt binary even if it's working on a 64-bit multilib build.
If you want to use the chosen architecture to compute the source path for the
prebuilt binary, call
Ensure 32-bit and 64-bit ODEX file generation
For 64-bit devices, by default Google generates both 32-bit and 64-bit ODEX
files for the boot image and any Java libraries. For APKs, by default Google
generates ODEX only for the primary 64-bit architecture. If an app is launched
in both 32-bit and 64-bit processes, use
LOCAL_MULTILIB := both to make sure
that both 32-bit and 64-bit ODEX files are generated. If the app has any 32-bit
or 64-bit JNI libraries, that flag also tells the build system to include them.