Build System Changes for Writers

export and unexport deprecation

The export and unexport keywords have been deprecated, and will throw warnings or errors depending on where they are used.

Early in the make system, during product configuration and reading: these will throw a warnings, and will be an error in the future. Device specific configuration should not be able to affect common core build steps -- we're looking at triggering build steps to be invalidated if the set of environment variables they can access changes. If device specific configuration is allowed to change those, switching devices with the same output directory could become significantly more expensive than it already can be.

Later, during files, and later tasks: these will throw errors, since it is increasingly likely that they are being used incorrectly, attempting to change the environment for a single build step, and instead setting it for hundreds of thousands.

It is not recommended to just move the environment variable setting outside of the build (in, or some other configuration script or wrapper). We expect to limit the environment variables that the build respects in the future, others will be cleared. (There will be methods to get custom variables into the build, just not to every build step)

Instead, write the export commands into the rule command lines themselves:

	rm -rf $@
	export MY_ENV_A="$(MY_A)"; make ...

If you want to set many environment variables, and/or use them many times, write them out to a script and source the script:

envsh := $(intermediates)/
	rm -rf $@
	echo 'export MY_ENV_A="$(MY_A)"' >$@
	echo 'export MY_ENV_B="$(MY_B)"' >>$@

$(intermediates)/generated_output.img: PRIVATE_ENV := $(envsh)
$(intermediates)/generated_output.img: $(envsh) a/b/c/
	rm -rf $@
	source $(PRIVATE_ENV); make ...
	source $(PRIVATE_ENV); a/b/c/ ...

Implicit make rules are obsolete

Implicit rules look something like the following:


%.o :

These can have wide ranging effects across unrelated modules, so they're now obsolete. Instead, use static pattern rules, which are similar, but explicitly match the specified outputs:

libs := $(foreach lib,libfoo libbar,$(TARGET_OUT_SHARED_LIBRARIES)/$(lib)

files := $(wildcard $(LOCAL_PATH)/*.foo)
gen := $(patsubst $(LOCAL_PATH)/,$(intermediates)/%.o,$(files))
$(gen): %.o :

Removing ‘/’ from Valid Module Names

The build system uses module names in path names in many places. Having an extra ‘/’ or ‘../’ being inserted can cause problems -- and not just build breaks, but stranger invalid behavior.

In every case we‘ve seen, the fix is relatively simple: move the directory into LOCAL_MODULE_RELATIVE_PATH (or LOCAL_MODULE_PATH if you’re still using it). If this causes multiple modules to be named the same, use unique module names and LOCAL_MODULE_STEM to change the installed file name:

include $(CLEAR_VARS)
LOCAL_MODULE := ver1/code.bin

include $(CLEAR_VARS)
LOCAL_MODULE := ver2/code.bin

Can be rewritten as:

include $(CLEAR_VARS)
LOCAL_MODULE := ver1_code.bin

include $(CLEAR_VARS)
LOCAL_MODULE := ver2_code.bin

You just need to make sure that any other references (PRODUCT_PACKAGES, LOCAL_REQUIRED_MODULES, etc) are converted to the new names.

Valid Module Names

We've adopted lexical requirements very similar to Bazel's requirements for target names. Valid characters are a-z, A-Z, 0-9, and the special characters _.+-=,@~. This currently applies to LOCAL_PACKAGE_NAME, LOCAL_MODULE, and LOCAL_MODULE_SUFFIX, and LOCAL_MODULE_STEM*.

Many other characters already caused problems if you used them, so we don't expect this to have a large effect.

PATH Tools

The build has started restricting the external host tools usable inside the build. This will help ensure that build results are reproducible across different machines, and catch mistakes before they become larger issues.

To start with, this includes replacing the $PATH with our own directory of tools, mirroring that of the host PATH. The only difference so far is the removal of the host GCC tools. Anything that is not explicitly in the configuration as allowed will continue functioning, but will generate a log message. This is expected to become more restrictive over time.

The configuration is located in build/soong/ui/build/paths/config.go, and contains all the common tools in use in many builds. Anything not in that list will currently print a warning in the $OUT_DIR/soong.log file, including the command and arguments used, and the process tree in order to help locate the usage.

In order to fix any issues brought up by these checks, the best way to fix them is to use tools checked into the tree -- either as prebuilts, or building them as host tools during the build.

As a temporary measure, you can set TEMPORARY_DISABLE_PATH_RESTRICTIONS=true in your environment to temporarily turn off the error checks and allow any tool to be used (with logging). Beware that GCC didn't work well with the interposer used for logging, so this may not help in all cases.

Deprecating / obsoleting variables in Makefiles

It is not required to source before running a build. Many scripts, including a majority of our automated build systems, do not do so. Make will transparently make every environment variable available as a make variable. This means that relying on environment variables only set up in will produce different output for local users and scripted users.

Many of these variables also include absolute path names, which we‘d like to keep out of the generated files, so that you don’t need to do a full rebuild if you move the source tree.

To fix this, we‘re marking the variables that are set in as deprecated in the makefiles. This will trigger a warning every time one is read (or written) inside Kati. Once all the warnings have been removed for a particular variable, we’ll switch it to obsolete, and any references will become errors. variables with make equivalents

instead ofuse

All of the make variables may be relative paths from the current directory, or absolute paths if the output directory was specified as an absolute path. If you need an absolute variable, convert it to absolute during a rule, so that it's not expanded into the generated ninja file:

$(PRODUCT_OUT)/gen.img: my/src/path/
	export PRODUCT_OUT=$$(cd $(PRODUCT_OUT); pwd); cd my/src/path; ./ -o $${PRODUCT_OUT}/gen.img


In files, you can always assume that the current directory is the root of the source tree, so this can just be replaced with ‘.’ (which is what $TOP is hardcoded to), or removed entirely. If you need an absolute path, see the instructions above.

Stop using PATH directly

This isn‘t only set by, but it is modified by it. Due to that it’s rather easy for this to change between different shells, and it's not ideal to reread the makefiles every time this changes.

In most cases, you shouldn‘t need to touch PATH at all. When you need to have a rule reference a particular binary that’s part of the source tree or outputs, it's preferrable to just use the path to the file itself (since you should already be adding that as a dependency).

Depending on the rule, passing the file path itself may not be feasible due to layers of unchangable scripts/binaries. In that case, be sure to add the dependency, but modify the PATH within the rule itself:

$(TARGET): myscript my/path/binary
	PATH=my/path:$$PATH myscript -o $@

Stop using PYTHONPATH directly

Like PATH, this isn‘t only set by, but it is modified by it. Due to that it’s rather easy for this to change between different shells, and it's not ideal to reread the makefiles every time.

The best solution here is to start switching to Soong's python building support, which packages the python interpreter, libraries, and script all into one file that no longer needs PYTHONPATH. See fontchain_lint for examples of this:

If you still need to use PYTHONPATH, do so within the rule itself, just like path:

$(TARGET): $(sort $(shell find my/python/lib -name '*.py'))
	PYTHONPATH=my/python/lib:$$PYTHONPATH -o $@


Specify Framework Compatibility Matrix Version in device manifest by adding a target-level attribute to the root element <manifest>. If PRODUCT_COMPATIBILITY_MATRIX_LEVEL_OVERRIDE is 26 or 27, you can add "target-level"="1" to your device manifest instead.


Clang is the default and only supported Android compiler, so there is no reason for this option to exist.

Other variables


These are all exported from, but don‘t have clear equivalents within the makefile system. If you need one of them, you’ll have to set up your own version.