platform_build/Changes.md

Build System Changes for Android.mk Writers

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 envsetup.sh variables in Makefiles

It is not required to source envsetup.sh 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 envsetup.sh 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 envsetup.sh 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.

envsetup.sh variables with make equivalents

instead of	use
OUT {#OUT}	OUT_DIR
ANDROID_HOST_OUT {#ANDROID_HOST_OUT}	HOST_OUT
ANDROID_PRODUCT_OUT {#ANDROID_PRODUCT_OUT}	PRODUCT_OUT
ANDROID_HOST_OUT_TESTCASES {#ANDROID_HOST_OUT_TESTCASES}	HOST_OUT_TESTCASES
ANDROID_TARGET_OUT_TESTCASES {#ANDROID_TARGET_OUT_TESTCASES}	TARGET_OUT_TESTCASES

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

ANDROID_BUILD_TOP

In Android.mk 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 envsetup.sh, 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 envsetup.sh, 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:

• external/fonttools/Lib/fontTools/Android.bp for python_library_host
• frameworks/base/Android.bp for python_binary_host
• frameworks/base/data/fonts/Android.mk to execute the python binary

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

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

Stop using PRODUCT_COMPATIBILITY_MATRIX_LEVEL_OVERRIDE directly

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.

Stop using USE_CLANG_PLATFORM_BUILD

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

Other envsetup.sh variables

• ANDROID_TOOLCHAIN
• ANDROID_TOOLCHAIN_2ND_ARCH
• ANDROID_DEV_SCRIPTS
• ANDROID_EMULATOR_PREBUILTS
• ANDROID_PRE_BUILD_PATHS

These are all exported from envsetup.sh, 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.