# Android Build System

Status: Draft (as of May 18, 2006)

Contents

## Objective

The primary goals of reworking the build system are (1) to make dependencies work more reliably, so that when files need to rebuilt, they are, and (2) to improve performance of the build system so that unnecessary modules are not rebuilt, and so doing a top-level build when little or nothing needs to be done for a build takes as little time as possible.

## Principles and Use Cases and Policy

Given the above objective, these are the overall principles and use cases that we will support. This is not an exhaustive list.

### Multiple Targets

It needs to be possible to build the Android platform for multiple targets. This means:

- The build system will support building tools for the host platform, both ones that are used in the build process itself, and developer tools like the simulator.
- The build system will need to be able to build tools on Linux (definitely Goobuntu and maybe Grhat), MacOS, and to some degree on Windows.
- The build system will need to be able to build the OS on Linux, and in the short-term, MacOS. Note that this is a conscious decision to stop building the OS on Windows. We are going to rely on the emulator there and not attempt to use the simulator. This is a requirement change now that the emulator story is looking brighter.

### Non-Recursive Make

To achieve the objectives, the build system will be rewritten to use make non-recursively. For more background on this, read Recursive Make Considered Harmful. For those that don't want PDF, here is the Google translated version.

### Rapid Compile-Test Cycles

When developing a component, for example a C++ shared library, it must be possible to easily rebuild just that component, and not have to wait more than a couple seconds for dependency checks, and not have to wait for unneeded components to be built.

### Both Environment and Config File Based Settings

To set the target, and other options, some people on the team like to have a configuration file in a directory so they do not have an environment setup script to run, and others want an environment setup script to run so they can run builds in different terminals on the same tree, or switch back and forth in one terminal. We will support both.

### Object File Directory / make clean

Object files and other intermediate files will be generated into a directory that is separate from the source tree. The goal is to have make clean be "rm -rf <obj>" in the tree root directory. The primary goals of this are to simplify searching the source tree, and to make "make clean" more reliable.

### SDK

The SDK will be a tarball that will allow non-OS-developers to write apps. The apps will actually be built by first building the SDK, and then building the apps against that SDK. This will hopefully (1) make writing apps easier for us, because we won't have to rebuild the OS as much, and we can use the standard java-app development tools, and (2) allow us to dog-food the SDK, to help ensure its quality. Cedric has suggested (and I agree) that apps built from the SDK should be built with ant. Stay tuned for more details as we figure out exactly how this will work.

### Dependecies

Dependencies should all be automatic. Unless there is a custom tool involved (e.g. the webkit has several), the dependencies for shared and static libraries, .c, .cpp, .h, .java, java libraries, etc., should all work without intervention in the Android.mk file.

### Wildcard source files

Wildcarding source file will be discouraged. It may be useful in some scenarios. The default `$(wildcard *)` will not work due to the current directory being set to the root of the build tree.

### Multiple targets in one directory

It will be possible to generate more than one target from a given subdirectory. For example, libutils generates a shared library for the target and a static library for the host.

### Makefile fragments for modules

Android.mk is the standard name for the makefile fragments that control the building of a given module. Only the top directory should have a file named "Makefile".

### Use shared libraries

Currently, the simulator is not built to use shared libraries. This should be fixed, and now is a good time to do it. This implies getting shared libraries to work on Mac OS.

## Nice to Have

These things would be nice to have, and this is a good place to record them, however these are not promises.

### Simultaneous Builds

The hope is to be able to do two builds for different combos in the same tree at the same time, but this is a stretch goal, not a requirement. Doing two builds in the same tree, not at the same time must work. (update: it's looking like we'll get the two builds at the same time working)

### Deleting headers (or other dependecies)

Problems can arise if you delete a header file that is referenced in ".d" files. The easy way to deal with this is "make clean". There should be a better way to handle it. (from fadden)

One way of solving this is introducing a dependency on the directory. The problem is that this can create extra dependecies and slow down the build. It's a tradeoff.

### Multiple builds

General way to perform builds across the set of known platforms. This would make it easy to perform multiple platform builds when testing a change, and allow a wide-scale "make clean". Right now the buildspec.mk or environment variables need to be updated before each build. (from fadden)

### Aftermarket Locales and Carrier

We will eventually need to add support for creating locales and carrier customizations to the SDK, but that will not be addressed right now.

## Usage

You've read (or scrolled past) all of the motivations for this build system, and you want to know how to use it. This is the place.

### Your first build

The Building document describes how do do builds.

### build/envsetup.sh functions

If you source the file build/envsetup.sh into your bash environment, `. build/envsetup.sh`you'll get a few helpful shell functions:

- printconfig - Prints the current configuration as set by the lunch and choosecombo commands.
- m - Runs `make` from the top of the tree. This is useful because you can run make from within subdirectories. If you have the `TOP` environment variable set, it uses that. If you don't, it looks up the tree from the current directory, trying to find the top of the tree.
- croot - `cd` to the top of the tree.
- sgrep - grep for the regex you provide in all .c, .cpp, .h, .java, and .xml files below the current directory.

### Build flavors/types

When building for a particular product, it's often useful to have minor variations on what is ultimately the final release build. These are the currently-defined "flavors" or "types" (we need to settle on a real name for these).

`eng```

This is the default flavor. A plain "`make`" is the same as "`make eng`". `droid` is an alias for `eng`.

- Installs modules tagged with: `eng`, `debug`, `user`, and/or `development`.
- Installs non-APK modules that have no tags specified.
- Installs APKs according to the product definition files, in addition to tagged APKs.
- `ro.secure=0`
- `ro.debuggable=1`
- `ro.kernel.android.checkjni=1`
- `adb` is enabled by default.

`user```

"`make user`"

This is the flavor intended to be the final release bits.

- Installs modules tagged with `user`.
- Installs non-APK modules that have no tags specified.
- Installs APKs according to the product definition files; tags are ignored for APK modules.
- `ro.adb.secure=1`
- `ro.secure=1`
- `ro.debuggable=0`
- `adb` is disabled by default.

`userdebug```

"`make userdebug`"

The same as `user`, except:

- Also installs modules tagged with `debug`.
- `ro.debuggable=1`
- `adb` is enabled by default.

If you build one flavor and then want to build another, you should run "`make installclean`" between the two makes to guarantee that you don't pick up files installed by the previous flavor. "`make clean`" will also suffice, but it takes a lot longer.

### More pseudotargets

Sometimes you want to just build one thing. The following pseudotargets are there for your convenience:

- droid - `make droid` is the normal build. This target is here because the default target has to have a name.
- all - `make all` builds everything `make droid` does, plus everything whose `LOCAL_MODULE_TAGS` do not include the "droid" tag. The build server runs this to make sure that everything that is in the tree and has an Android.mk builds.
- clean-$(LOCAL_MODULE) and clean-$(LOCAL_PACKAGE_NAME) - Let you selectively clean one target. For example, you can type `make clean-libutils` and it will delete libutils.so and all of the intermediate files, or you can type `make clean-Home` and it will clean just the Home app.
- clean - `make clean` deletes all of the output and intermediate files for this configuration. This is the same as `rm -rf out/<configuration>/`
- clobber - `make clobber` deletes all of the output and intermediate files for all configurations. This is the same as `rm -rf out/`.
- dataclean - `make dataclean` deletes contents of the data directory inside the current combo directory. This is especially useful on the simulator and emulator, where the persistent data remains present between builds.
- LOCAL_MODULE - Anything you specify as a `LOCAL_MODULE` in an Android.mk is made into a pseudotarget. For example, `make runtime` might be shorthand for `make out/linux-x86-debug/system/bin/runtime` (which would work), and `make libkjs` might be shorthand for `make out/linux-x86-debug/system/lib/libkjs.so` (which would also work).
- targets - `make targets` will print a list of all of the LOCAL_MODULE names you can make.

### How to add another component to the build - Android.mk templates

You have a new library, a new app, or a new executable. For each of the common types of modules, there is a corresponding file in the templates directory. It will usually be enough to copy one of these, and fill in your own values. Some of the more esoteric values are not included in the templates, but are instead just documented here, as is the documentation on using custom tools to generate files.

Mostly, you can just look for the TODO comments in the templates and do what it says. Please remember to delete the TODO comments when you're done to keep the files clean. The templates have minimal documentation in them, because they're going to be copied, and when that gets stale, the copies just won't get updated. So read on...

#### Apps

Use the `templates/apps` file.

This template is pretty self-explanitory. See the variables below for more details.

#### Java Libraries

Use the `templates/java_library` file.

The interesting thing here is the value of LOCAL_MODULE, which becomes the name of the jar file. (Actually right now, we're not making jar files yet, just directories of .class files, but the directory is named according to what you put in LOCAL_MODULE). This name will be what goes in the LOCAL_JAVA_LIBRARIES variable in modules that depend on your java library.

#### C/C++ Executables

Use the `templates/executable` file, or the `templates/executable_host` file.

This template has a couple extra options that you usually don't need. Please delete the ones you don't need, and remove the TODO comments. It makes the rest of them easier to read, and you can always refer back to the templates if you need them again later.

By default, on the target these are built into /system/bin, and on the host, they're built into <combo>/host/bin. These can be overridden by setting `LOCAL_MODULE_PATH` or `LOCAL_MODULE_RELATIVE_PATH`. See Putting targets elsewhere for more.

#### Shared Libraries

Use the `templates/shared_library` file, or the `templates/shared_library_host` file.

Remember that on the target, we use shared libraries, and on the host, we use static libraries, since executable size isn't as big an issue, and it simplifies distribution in the SDK.

#### Static Libraries

Use the `templates/static_library` file, or the `templates/static_library_host` file.

Remember that on the target, we use shared libraries, and on the host, we use static libraries, since executable size isn't as big an issue, and it simplifies distribution in the SDK.

#### Using Custom Tools

If you have a tool that generates source files for you, it's possible to have the build system get the dependencies correct for it. Here are a couple of examples. `$@` is the make built-in variable for "the current target." The red parts are the parts you'll need to change.

You need to put this after you have declared `LOCAL_PATH` and `LOCAL_MODULE`, because the `$(local-generated-sources-dir)` and `$(local-host-generated-sources-dir)` macros use these variables to determine where to put the files.

##### Example 1

Here, there is one generated file, called chartables.c, which doesn't depend on anything. And is built by the tool built to $(HOST_OUT_EXECUTABLES)/dftables. Note on the second to last line that a dependency is created on the tool.

    intermediates:= $(local-generated-sources-dir)
    GEN := $(intermediates)/chartables.c
    $(GEN): PRIVATE_CUSTOM_TOOL = $(HOST_OUT_EXECUTABLES)/dftables $@
    $(GEN): $(HOST_OUT_EXECUTABLES)/dftables
    	$(transform-generated-source)
    LOCAL_GENERATED_SOURCES += $(GEN)

##### Example 2

Here as a hypothetical example, we use use cat as if it were to transform a file. Pretend that it does something useful. Note how we use a target-specific variable called PRIVATE_INPUT_FILE to store the name of the input file.

    intermediates:= $(local-generated-sources-dir)
    GEN := $(intermediates)/file.c
    $(GEN): PRIVATE_INPUT_FILE := $(LOCAL_PATH)/input.file
    $(GEN): PRIVATE_CUSTOM_TOOL = cat $(PRIVATE_INPUT_FILE) > $@
    $(GEN): $(LOCAL_PATH)/input.file
    	$(transform-generated-source)
    LOCAL_GENERATED_SOURCES += $(GEN)

##### Example 3

If you have several files that are all similar in name, and use the same tool, you can combine them. (here the *.lut.h files are the generated ones, and the *.cpp files are the input files)

    intermediates:= $(local-generated-sources-dir)
    GEN := $(addprefix $(intermediates)/kjs/, \
                array_object.lut.h \
                bool_object.lut.h \
            )
    $(GEN): PRIVATE_CUSTOM_TOOL = perl libs/WebKitLib/WebKit/JavaScriptCore/kjs/create_hash_table $< -i > $@
    $(GEN): $(intermediates)/%.lut.h : $(LOCAL_PATH)/%.cpp
    	$(transform-generated-source)
    LOCAL_GENERATED_SOURCES += $(GEN)

### Unbundled build

Unbundled build has several meanings by the context. Let me explain the meaning by the flags related to "unbundled build"

#### TARGET_BUILD_UNBUNDLED

The source tree might not have the full platform sources. It turns on `TARGET_BUILD_USE_PREBUILT_SDKS`, unless `UNBUNDLED_BUILD_SDKS_FROM_SOURCE` is set. It is always set if `TARGET_BUILD_APPS` or `TARGET_BUILD_UNBUNDLED_IMAGE` is set.

#### TARGET_BUILD_USE_PREBUILT_SDKS

It is an internal flag. If it is set, prebuilt SDKs are used, even if a module's `LOCAL_SDK_VERSION` is `current` (including `system_current`, `core_current`, and so on). If it is unset, build current SDKs, and use them as usual.

#### DISABLE_PREOPT

It is an internal flag as well. If it is set, dexpreopt is disabled. It is always set if `TARGET_BUILD_APPS` or `TARGET_BUILD_UNBUNDLED_IMAGE` is set, because dexpreopt tightly depends on the platform.

#### TARGET_BUILD_APPS

Build the apps that can be distributed outside the platform, so it turns on `TARGET_BUILD_UNBUNDLED` and `DISABLE_PREOPT`. Also, it turns on `TARGET_BUILD_USE_PREBUILT_SDKS`, unless `UNBUNDLED_BUILD_SDKS_FROM_SOURCE` is set.

#### TARGET_BUILD_UNBUNDLED_IMAGE

It is similar to `TARGET_BUILD_APPS`, but its target is an unbundled partition (such as the vendor partition). Accordingly, it sets `TARGET_BUILD_UNBUNDLED` and `DISABLE_PREOPT`. We can call the partition unbundled, because the partition can be distributed outside the platform. And also, it turns on `TARGET_BUILD_USE_PREBUILT_SDKS`, unless `UNBUNDLED_BUILD_SDKS_FROM_SOURCE` is set.

### Platform specific conditionals

Sometimes you need to set flags specifically for different platforms. Here is a list of which values the different build-system defined variables will be set to and some examples.

HOST_OS linux darwin | HOST_ARCH x86 x86_64 | HOST_BUILD_TYPE release debug
TARGET_ARCH arm arm64 x86 x86_64 | TARGET_BUILD_TYPE release debug

There are also special variables to use instead of conditionals. Many of the normal variables (LOCAL_SRC_FILES, LOCAL_CFLAGS, etc) can be conditionally added to with _{arch} _{32|64}, and for the host, _{os}.

#### Some Examples

    ifeq ($(TARGET_BUILD_TYPE),release)
    LOCAL_CFLAGS += -DNDEBUG=1
    endif

    LOCAL_CFLAGS_arm += -DTARGET_IS_ARM

    LOCAL_CFLAGS_64 += -DBIG_POINTER

    # from libutils
    # Use the futex based mutex and condition variable
    # implementation from android-arm because it's shared mem safe
    LOCAL_SRC_FILES_linux += futex_synchro.c
    LOCAL_LDLIBS_linux += -lrt -ldl

### Putting modules elsewhere

If you have modules that normally go somewhere, and you need to have them build somewhere else, read this.

If you have modules that need to go in a subdirectory of their normal location, for example HAL modules that need to go in /system/lib/hw or /vendor/lib/hw, set LOCAL_MODULE_RELATIVE_PATH in your Android.mk, for example:

    LOCAL_MODULE_RELATIVE_PATH := hw

If you have modules that need to go in an entirely different location, for example the root filesystem instead of in /system, add these lines to your Android.mk:

    LOCAL_MODULE_PATH := $(TARGET_ROOT_OUT)
    LOCAL_UNSTRIPPED_PATH := $(TARGET_ROOT_OUT_UNSTRIPPED)

For executables and libraries, you need to specify a `LOCAL_UNSTRIPPED_PATH` location if you specified a `LOCAL_MODULE_PATH`, because on target builds, we keep the unstripped executables so GDB can find the symbols. `LOCAL_UNSTRIPPED_PATH` is not necessary if you only specified `LOCAL_MODULE_RELATIVE_PATH`.

Look in `core/envsetup.mk` for all of the variables defining places to build things.

### Android.mk variables

These are the variables that you'll commonly see in Android.mk files, listed alphabetically.

But first, a note on variable naming:

- LOCAL_ - These variables are set per-module. They are cleared by the `include $(CLEAR_VARS)` line, so you can rely on them being empty after including that file. Most of the variables you'll use in most modules are LOCAL_ variables.
- PRIVATE_ - These variables are make-target-specific variables. That means they're only usable within the commands for that module. It also means that they're unlikely to change behind your back from modules that are included after yours. This link to the make documentation describes more about target-specific variables. Please note that there are a couple of these laying around the tree that aren't prefixed with PRIVATE_. It is safe, and they will be fixed as they are discovered. Sorry for the confusion.
- INTERNAL_ - These variables are critical to functioning of the build system, so you shouldn't create variables named like this, and you probably shouldn't be messing with these variables in your makefiles.
- HOST_ and TARGET_ - These contain the directories and definitions that are specific to either the host or the target builds. Do not set variables that start with HOST_ or TARGET_ in your makefiles.
- HOST_CROSS_ - These contain the directories and definitions that are specific to cross-building host binaries. The common case is building windows host tools on linux. Do not set variables that start with HOST_CROSS_ in your makefiles.
- BUILD_ and CLEAR_VARS - These contain the names of well-defined template makefiles to include. Some examples are CLEAR_VARS and BUILD_HOST_PACKAGE.
- Any other name is fair-game for you to use in your Android.mk. However, remember that this is a non-recursive build system, so it is possible that your variable will be changed by another Android.mk included later, and be different when the commands for your rule / module are executed.

#### LOCAL_ANNOTATION_PROCESSORS

Set this to a list of modules built with `BUILD_HOST_JAVA_LIBRARY` to have their jars passed to javac with -processorpath for use as annotation processors.

#### LOCAL_ANNOTATION_PROCESSOR_CLASSES

Set this to a list of classes to be passed to javac as -processor arguments. This list is would be unnecessary, as javac will autodetect annotation processor classes, except that the Grok tool that is used on the Android source code does not autodetect them and requires listing them manually.

#### LOCAL_ASSET_FILES

In Android.mk files that `include $(BUILD_PACKAGE)` set this to the set of files you want built into your app. Usually:

`LOCAL_ASSET_FILES += $(call find-subdir-assets)`

This will probably change when we switch to ant for the apps' build system.

#### LOCAL_CC

If you want to use a different C compiler for this module, set LOCAL_CC to the path to the compiler. If LOCAL_CC is blank, the appropriate default compiler is used.

#### LOCAL_CXX

If you want to use a different C++ compiler for this module, set LOCAL_CXX to the path to the compiler. If LOCAL_CXX is blank, the appropriate default compiler is used.

#### LOCAL_CFLAGS

If you have additional flags to pass into the C or C++ compiler, add them here. For example:

`LOCAL_CFLAGS += -DLIBUTILS_NATIVE=1`

#### LOCAL_CPPFLAGS

If you have additional flags to pass into only the C++ compiler, add them here. For example:

`LOCAL_CPPFLAGS += -ffriend-injection`

`LOCAL_CPPFLAGS` is guaranteed to be after `LOCAL_CFLAGS` on the compile line, so you can use it to override flags listed in `LOCAL_CFLAGS`.

#### LOCAL_CPP_EXTENSION

If your C++ files end in something other than "`.cpp`", you can specify the custom extension here. For example:

`LOCAL_CPP_EXTENSION := .cc`

Note that all C++ files for a given module must have the same extension; it is not currently possible to mix different extensions.

#### LOCAL_NO_DEFAULT_COMPILER_FLAGS

Normally, the compile line for C and C++ files includes global include paths and global cflags. If `LOCAL_NO_DEFAULT_COMPILER_FLAGS` is non-empty, none of the default includes or flags will be used when compiling C and C++ files in this module. `LOCAL_C_INCLUDES`, `LOCAL_CFLAGS`, and `LOCAL_CPPFLAGS` will still be used in this case, as will any `DEBUG_CFLAGS` that are defined for the module.

#### LOCAL_COPY_HEADERS

This will be going away.

The set of files to copy to the install include tree. You must also supply `LOCAL_COPY_HEADERS_TO`.

This is going away because copying headers messes up the error messages, and may lead to people editing those headers instead of the correct ones. It also makes it easier to do bad layering in the system, which we want to avoid. We also aren't doing a C/C++ SDK, so there is no ultimate requirement to copy any headers.

#### LOCAL_COPY_HEADERS_TO

This will be going away.

The directory within "include" to copy the headers listed in `LOCAL_COPY_HEADERS` to.

This is going away because copying headers messes up the error messages, and may lead to people editing those headers instead of the correct ones. It also makes it easier to do bad layering in the system, which we want to avoid. We also aren't doing a C/C++ SDK, so there is no ultimate requirement to copy any headers.

#### LOCAL_C_INCLUDES

Additional directories to instruct the C/C++ compilers to look for header files in. These paths are rooted at the top of the tree. Use `LOCAL_PATH` if you have subdirectories of your own that you want in the include paths. For example:

`LOCAL_C_INCLUDES += extlibs/zlib-1.2.3
LOCAL_C_INCLUDES += $(LOCAL_PATH)/src`

You should not add subdirectories of include to `LOCAL_C_INCLUDES`, instead you should reference those files in the `#include` statement with their subdirectories. For example:

`#include <utils/KeyedVector.h>`
not `#include <KeyedVector.h>`

There are some components that are doing this wrong, and should be cleaned up.

#### LOCAL_MODULE_TAGS

Set `LOCAL_MODULE_TAGS` to any number of whitespace-separated tags. If the tag list is empty or contains `droid`, the module will get installed as part of a `make droid`. Otherwise, it will only get installed by running `make <your-module>` or with the `make all` pseudotarget.

#### LOCAL_REQUIRED_MODULES

Set `LOCAL_REQUIRED_MODULES` to any number of whitespace-separated module names, like "libblah" or "Email". If this module is installed, all of the modules that it requires will be installed as well. This can be used to, e.g., ensure that necessary shared libraries or providers are installed when a given app is installed.

#### LOCAL_FORCE_STATIC_EXECUTABLE

If your executable should be linked statically, set `LOCAL_FORCE_STATIC_EXECUTABLE:=true`. There is a very short list of libraries that we have in static form (currently only libc).

#### LOCAL_GENERATED_SOURCES

Files that you add to `LOCAL_GENERATED_SOURCES` will be automatically generated and then linked in when your module is built. See the Custom Tools template makefile for an example.

#### LOCAL_JAVACFLAGS

If you have additional flags to pass into the javac compiler, add them here. For example:

`LOCAL_JAVACFLAGS += -Xlint:deprecation`

#### LOCAL_ERROR_PRONE_FLAGS

If you have additional flags to pass into the error prone compiler, add them here. For example:

`LOCAL_ERROR_PRONE_FLAGS += -Xep:ClassCanBeStatic:ERROR`

#### LOCAL_JAVA_LIBRARIES

When linking Java apps and libraries, `LOCAL_JAVA_LIBRARIES` specifies which sets of java classes to include. Currently there are two of these: `core` and `framework`. In most cases, it will look like this:

`LOCAL_JAVA_LIBRARIES := core framework`

Note that setting `LOCAL_JAVA_LIBRARIES` is not necessary (and is not allowed) when building an APK with "`include $(BUILD_PACKAGE)`". The appropriate libraries will be included automatically.

#### LOCAL_LDFLAGS

You can pass additional flags to the linker by setting `LOCAL_LDFLAGS`. Keep in mind that the order of parameters is very important to ld, so test whatever you do on all platforms.

#### LOCAL_LDLIBS

`LOCAL_LDLIBS` allows you to specify additional libraries that are not part of the build for your executable or library. Specify the libraries you want in -lxxx format; they're passed directly to the link line. However, keep in mind that there will be no dependency generated for these libraries. It's most useful in simulator builds where you want to use a library preinstalled on the host. The linker (ld) is a particularly fussy beast, so it's sometimes necessary to pass other flags here if you're doing something sneaky. Some examples:

`LOCAL_LDLIBS += -lcurses -lpthread
LOCAL_LDLIBS += -Wl,-z,origin`

#### LOCAL_NO_MANIFEST

If your package doesn't have a manifest (AndroidManifest.xml), then set `LOCAL_NO_MANIFEST:=true`. The common resources package does this.

#### LOCAL_PACKAGE_NAME

`LOCAL_PACKAGE_NAME` is the name of an app. For example, Dialer, Contacts, etc. This will probably change or go away when we switch to an ant-based build system for the apps.

#### LOCAL_PATCH_MODULE (experimental option)

As of January 2018, you almost certainly don't need this option, so please ask and only use it if you understand what you're doing. This feature is experimental and may go away in future.

When compiling language level 9+ .java code in packages that are part of a a system module, `LOCAL_PATCH_MODULE` names the module that your sources and dependencies should be patched into. The Android runtime currently (Jan 2018) doesn't implement the JEP 261 module system so this option is only supported at compile time. It should only be needed to compile tests in packages that exist in libcore and which are inconvenient to move elsewhere.

#### LOCAL_PATH

The directory your Android.mk file is in. You can set it by putting the following as the first line in your Android.mk:

`LOCAL_PATH := $(my-dir)`

The `my-dir` macro uses the `MAKEFILE_LIST` variable, so you must call it before you include any other makefiles. Also, consider that any subdirectories you inlcude might reset LOCAL_PATH, so do your own stuff before you include them. This also means that if you try to write several `include` lines that reference `LOCAL_PATH`, it won't work, because those included makefiles might reset LOCAL_PATH.

#### LOCAL_POST_PROCESS_COMMAND

For host executables, you can specify a command to run on the module after it's been linked. You might have to go through some contortions to get variables right because of early or late variable evaluation:

`module := $(HOST_OUT_EXECUTABLES)/$(LOCAL_MODULE)
LOCAL_POST_PROCESS_COMMAND := /Developer/Tools/Rez -d __DARWIN__ -t APPL\
-d __WXMAC__ -o $(module) Carbon.r`

#### LOCAL_PREBUILT_EXECUTABLES

When including $(BUILD_MULTI_PREBUILT) or $(BUILD_HOST_PREBUILT), set these to executables that you want copied. They're located automatically into the right bin directory.

#### LOCAL_PREBUILT_LIBS

When including $(BUILD_MULTI_PREBUILT) or $(BUILD_HOST_PREBUILT), set these to libraries that you want copied. They're located automatically into the right lib directory.

#### LOCAL_SHARED_LIBRARIES

These are the libraries you directly link against. You don't need to pass transitively included libraries. Specify the name without the suffix:

`LOCAL_SHARED_LIBRARIES := \
libutils \
libui \
libaudio \
libexpat \
libsgl`

#### LOCAL_SRC_FILES

The build system looks at `LOCAL_SRC_FILES` to know what source files to compile -- .cpp .c .y .l .java. For lex and yacc files, it knows how to correctly do the intermediate .h and .c/.cpp files automatically. If the files are in a subdirectory of the one containing the Android.mk, prefix them with the directory name:

`LOCAL_SRC_FILES := \
file1.cpp \
dir/file2.cpp`

#### LOCAL_STATIC_LIBRARIES

These are the static libraries that you want to include in your module. Mostly, we use shared libraries, but there are a couple of places, like host executables where we use static libraries instead.

`LOCAL_STATIC_LIBRARIES := \
libutils \
libtinyxml`

#### LOCAL_MODULE

`LOCAL_MODULE` is the name of what's supposed to be generated from your Android.mk. For exmample, for libkjs, the `LOCAL_MODULE` is "libkjs" (the build system adds the appropriate suffix -- .so .dylib .dll). For app modules, use `LOCAL_PACKAGE_NAME` instead of `LOCAL_MODULE`. We're planning on switching to ant for the apps, so this might become moot.

#### LOCAL_MODULE_PATH

Instructs the build system to put the module somewhere other than what's normal for its type. If you override this, make sure you also set `LOCAL_UNSTRIPPED_PATH` if it's an executable or a shared library so the unstripped binary has somewhere to go. An error will occur if you forget to.

See Putting modules elsewhere for more.

#### LOCAL_MODULE_RELATIVE_PATH

Instructs the build system to put the module in a subdirectory under the directory that is normal for its type. If you set this you do not need to set `LOCAL_UNSTRIPPED_PATH`, the unstripped binaries will also use the relative path.

See Putting modules elsewhere for more.

#### LOCAL_MODULE_HOST_OS

This specifies which OSes are supported by this host module. It is not used for target builds. The accepted values here are combinations of `linux`, `darwin`, and `windows`. By default, linux and darwin(MacOS) are considered to be supported. If a module should build under windows, you must specify windows, and any others to be supported. Some examples:

`LOCAL_MODULE_HOST_OS := linux
LOCAL_MODULE_HOST_OS := darwin linux windows`

#### LOCAL_UNSTRIPPED_PATH

Instructs the build system to put the unstripped version of the module somewhere other than what's normal for its type. Usually, you override this because you overrode `LOCAL_MODULE_PATH` for an executable or a shared library. If you overrode `LOCAL_MODULE_PATH`, but not `LOCAL_UNSTRIPPED_PATH`, an error will occur.

See Putting modules elsewhere for more.

#### LOCAL_WHOLE_STATIC_LIBRARIES

These are the static libraries that you want to include in your module without allowing the linker to remove dead code from them. This is mostly useful if you want to add a static library to a shared library and have the static library's content exposed from the shared library.

`LOCAL_WHOLE_STATIC_LIBRARIES := \
libsqlite3_android
`

#### LOCAL_YACCFLAGS

Any flags to pass to invocations of yacc for your module. A known limitation here is that the flags will be the same for all invocations of YACC for your module. This can be fixed. If you ever need it to be, just ask.

`LOCAL_YACCFLAGS := -p kjsyy`

## Implementation Details

You should never have to touch anything in the config directory unless you're adding a new platform, new tools, or adding new features to the build system. In general, please consult with the build system owner(s) (android-build-team) before you go mucking around in here. That said, here are some notes on what's going on under the hood.

### Environment Setup / buildspec.mk Versioning

In order to make easier for people when the build system changes, when it is necessary to make changes to buildspec.mk or to rerun the environment setup scripts, they contain a version number in the variable BUILD_ENV_SEQUENCE_NUMBER. If this variable does not match what the build system expects, it fails printing an error message explaining what happened. If you make a change that requires an update, you need to update two places so this message will be printed.

- In core/envsetup.mk, increment the CORRECT_BUILD_ENV_SEQUENCE_NUMBER definition.
- In buildspec.mk.default, update the BUILD_ENV_SEQUENCE_DUMBER definition to match the one in core/envsetup.mk

The scripts automatically get the value from the build system, so they will trigger the warning as well.

### Additional makefile variables

You probably shouldn't use these variables. Please consult android-build-team before using them. These are mostly there for workarounds for other issues, or things that aren't completely done right.

#### LOCAL_ADDITIONAL_DEPENDENCIES

If your module needs to depend on anything else that isn't actually built in to it, you can add those make targets to `LOCAL_ADDITIONAL_DEPENDENCIES`. Usually this is a workaround for some other dependency that isn't created automatically.

#### LOCAL_BUILT_MODULE

This should not be used, since multiple binaries are now created from a single module defintiion.

When a module is built, the module is created in an intermediate directory then copied to its final location. LOCAL_BUILT_MODULE is the full path to the intermediate file. See LOCAL_INSTALLED_MODULE for the path to the final installed location of the module.

#### LOCAL_IS_HOST_MODULE

Set by the host_xxx.mk includes to tell base_rules.mk and the other includes that we're building for the host.

#### LOCAL_INSTALLED_MODULE

This should not be used, since multiple binaries are now created from a single module defintiion.

The fully qualified path name of the final location of the module. See LOCAL_BUILT_MODULE for the location of the intermediate file that the make rules should actually be constructing.

#### LOCAL_MODULE_CLASS

Which kind of module this is. This variable is used to construct other variable names used to locate the modules. See base_rules.mk and envsetup.mk.

#### LOCAL_MODULE_SUFFIX

The suffix that will be appended to `LOCAL_MODULE` to form `LOCAL_MODULE_NAME`. For example, .so, .a, .dylib.

#### LOCAL_STRIP_MODULE

If set to true (the default), the binary will be stripped and a debug link will be set up so that GDB will still work. If set to no_debuglink, the binary will be stripped, but no debug link will be added. If set to keep_symbols, it will strip the debug information, but keep the symbol table. Any other value will prevent stripping.

#### LOCAL_SYSTEM_SHARED_LIBRARIES

Used while building the base libraries: libc, libm, libdl. Usually it should be set to "none," as it is in $(CLEAR_VARS). When building these libraries, it's set to the ones they link against. For example, libc, libstdc++ and libdl don't link against anything, and libm links against libc. Normally, when the value is none, these libraries are automatically linked in to executables and libraries, so you don't need to specify them manually.