Soong

Soong is the replacement for the old Android make-based build system. It replaces Android.mk files with Android.bp files, which are JSON-like simple declarative descriptions of modules to build.

See Simple Build Configuration on source.android.com to read how Soong is configured for testing.

Android.bp file format

By design, Android.bp files are very simple. There are no conditionals or control flow statements - any complexity is handled in build logic written in Go. The syntax and semantics of Android.bp files are intentionally similar to Bazel BUILD files when possible.

Modules

A module in an Android.bp file starts with a module type, followed by a set of properties in name: value, format:

cc_binary {
    name: "gzip",
    srcs: ["src/test/minigzip.c"],
    shared_libs: ["libz"],
    stl: "none",
}

Every module must have a name property, and the value must be unique across all Android.bp files.

For a list of valid module types and their properties see $OUT_DIR/soong/docs/soong_build.html.

File lists

Properties that take a list of files can also take glob patterns and output path expansions.

• Glob patterns can contain the normal Unix wildcard *, for example "*.java".

  Glob patterns can also contain a single ** wildcard as a path element, which will match zero or more path elements. For example, java/**/*.java will match java/Main.java and java/com/android/Main.java.

• Output path expansions take the format :module or :module{.tag}, where module is the name of a module that produces output files, and it expands to a list of those output files. With the optional {.tag} suffix, the module may produce a different list of outputs according to tag.

  For example, a droiddoc module with the name "my-docs" would return its .stubs.srcjar output with ":my-docs", and its .doc.zip file with ":my-docs{.doc.zip}".

  This is commonly used to reference filegroup modules, whose output files consist of their srcs.

Variables

An Android.bp file may contain top-level variable assignments:

gzip_srcs = ["src/test/minigzip.c"],

cc_binary {
    name: "gzip",
    srcs: gzip_srcs,
    shared_libs: ["libz"],
    stl: "none",
}

Variables are scoped to the remainder of the file they are declared in, as well as any child Android.bp files. Variables are immutable with one exception - they can be appended to with a += assignment, but only before they have been referenced.

Comments

Android.bp files can contain C-style multiline /* */ and C++ style single-line // comments.

Types

Variables and properties are strongly typed, variables dynamically based on the first assignment, and properties statically by the module type. The supported types are:

• Bool (true or false)
• Integers (int)
• Strings ("string")
• Lists of strings (["string1", "string2"])
• Maps ({key1: "value1", key2: ["value2"]})

Maps may values of any type, including nested maps. Lists and maps may have trailing commas after the last value.

Strings can contain double quotes using \", for example "cat \"a b\"".

Operators

Strings, lists of strings, and maps can be appended using the + operator. Integers can be summed up using the + operator. Appending a map produces the union of keys in both maps, appending the values of any keys that are present in both maps.

Defaults modules

A defaults module can be used to repeat the same properties in multiple modules. For example:

cc_defaults {
    name: "gzip_defaults",
    shared_libs: ["libz"],
    stl: "none",
}

cc_binary {
    name: "gzip",
    defaults: ["gzip_defaults"],
    srcs: ["src/test/minigzip.c"],
}

Packages

The build is organized into packages where each package is a collection of related files and a specification of the dependencies among them in the form of modules.

A package is defined as a directory containing a file named Android.bp, residing beneath the top-level directory in the build and its name is its path relative to the top-level directory. A package includes all files in its directory, plus all subdirectories beneath it, except those which themselves contain an Android.bp file.

The modules in a package's Android.bp and included files are part of the module.

For example, in the following directory tree (where .../android/ is the top-level Android directory) there are two packages, my/app, and the subpackage my/app/tests. Note that my/app/data is not a package, but a directory belonging to package my/app.

.../android/my/app/Android.bp
.../android/my/app/app.cc
.../android/my/app/data/input.txt
.../android/my/app/tests/Android.bp
.../android/my/app/tests/test.cc

This is based on the Bazel package concept.

The package module type allows information to be specified about a package. Only a single package module can be specified per package and in the case where there are multiple .bp files in the same package directory it is highly recommended that the package module (if required) is specified in the Android.bp file.

Unlike most module type package does not have a name property. Instead the name is set to the name of the package, e.g. if the package is in top/intermediate/package then the package name is //top/intermediate/package.

E.g. The following will set the default visibility for all the modules defined in the package and any subpackages that do not set their own default visibility (irrespective of whether they are in the same .bp file as the package module) to be visible to all the subpackages by default.

package {
    default_visibility: [":__subpackages"]
}

Referencing Modules

A module libfoo can be referenced by its name

cc_binary {
    name: "app",
    shared_libs: ["libfoo"],
}

Obviously, this works only if there is only one libfoo module in the source tree. Ensuring such name uniqueness for larger trees may become problematic. We might also want to use the same name in multiple mutually exclusive subtrees (for example, implementing different devices) deliberately in order to describe a functionally equivalent module. Enter Soong namespaces.

Namespaces

A presense of the soong_namespace {..} in an Android.bp file defines a namespace. For instance, having

soong_namespace {
    ...
}
...

in device/google/bonito/Android.bp informs Soong that within the device/google/bonito package the module names are unique, that is, all the modules defined in the Android.bp files in the device/google/bonito/ tree have unique names. However, there may be modules with the same names outside device/google/bonito tree. Indeed, there is a module "pixelstats-vendor" both in device/google/bonito/pixelstats and in device/google/coral/pixelstats.

The name of a namespace is the path of its directory. The name of the namespace in the example above is thus device/google/bonito.

An implicit global namespace corresponds to the source tree as a whole. It has empty name.

A module name's scope is the smallest namespace containing it. Suppose a source tree has device/my and device/my/display namespaces. If libfoo module is defined in device/co/display/lib/Android.bp, its namespace is device/co/display.

The name uniqueness thus means that module's name is unique within its scope. In other words, "//scope:name" is globally unique module reference, e.g, "//device/google/bonito:pixelstats-vendor". Note that the name of the namespace for a module may be different from module's package name: libfoo belongs to device/my/display namespace but is contained in device/my/display/lib package.

Name Resolution

The form of a module reference determines how Soong locates the module.

For a global reference of the "//scope:name" form, Soong verifies there is a namespace called "scope", then verifies it contains a "name" module and uses it. Soong verifies there is only one "name" in "scope" at the beginning when it parses Android.bp files.

A local reference has "name" form, and resolving it involves looking for a module "name" in one or more namespaces. By default only the global namespace is searched for "name" (in other words, only the modules not belonging to an explicitly defined scope are considered). The imports attribute of the soong_namespaces allows to specify where to look for modules . For instance, with device/google/bonito/Android.bp containing

soong_namespace {
    imports: [
        "hardware/google/interfaces",
        "hardware/google/pixel",
        "hardware/qcom/bootctrl",
    ],
}

a reference to "libpixelstats" will resolve to the module defined in hardware/google/pixel/pixelstats/Android.bp because this module is in hardware/google/pixel namespace.

TODO: Conventionally, languages with similar concepts provide separate constructs for namespace definition and name resolution (namespace and using in C++, for instance). Should Soong do that, too?

Referencing modules in makefiles

While we are gradually converting makefiles to Android.bp files, Android build is described by a mixture of Android.bp and Android.mk files, and a module defined in an Android.mk file can reference a module defined in Android.bp file. For instance, a binary still defined in an Android.mk file may have a library defined in already converted Android.bp as a dependency.

A module defined in an Android.bp file and belonging to the global namespace can be referenced from a makefile without additional effort. If a module belongs to an explicit namespace, it can be referenced from a makefile only after after the name of the namespace has been added to the value of PRODUCT_SOONG_NAMESPACES variable.

Note that makefiles have no notion of namespaces and exposing namespaces with the same modules via PRODUCT_SOONG_NAMESPACES may cause Make failure. For instance, exposing both device/google/bonito and device/google/coral namespaces will cause Make failure because it will see two targets for the pixelstats-vendor module.

Visibility

The visibility property on a module controls whether the module can be used by other packages. Modules are always visible to other modules declared in the same package. This is based on the Bazel visibility mechanism.

If specified the visibility property must contain at least one rule.

Each rule in the property must be in one of the following forms:

• ["//visibility:public"]: Anyone can use this module.
• ["//visibility:private"]: Only rules in the module's package (not its subpackages) can use this module.
• ["//some/package:__pkg__", "//other/package:__pkg__"]: Only modules in some/package and other/package (defined in some/package/*.bp and other/package/*.bp) have access to this module. Note that sub-packages do not have access to the rule; for example, //some/package/foo:bar or //other/package/testing:bla wouldn't have access. __pkg__ is a special module and must be used verbatim. It represents all of the modules in the package.
• ["//project:__subpackages__", "//other:__subpackages__"]: Only modules in packages project or other or in one of their sub-packages have access to this module. For example, //project:rule, //project/library:lib or //other/testing/internal:munge are allowed to depend on this rule (but not //independent:evil)
• ["//project"]: This is shorthand for ["//project:__pkg__"]
• [":__subpackages__"]: This is shorthand for ["//project:__subpackages__"] where //project is the module's package, e.g. using [":__subpackages__"] in packages/apps/Settings/Android.bp is equivalent to //packages/apps/Settings:__subpackages__.
• ["//visibility:legacy_public"]: The default visibility, behaves as //visibility:public for now. It is an error if it is used in a module.

The visibility rules of //visibility:public and //visibility:private cannot be combined with any other visibility specifications, except //visibility:public is allowed to override visibility specifications imported through the defaults property.

Packages outside vendor/ cannot make themselves visible to specific packages in vendor/, e.g. a module in libcore cannot declare that it is visible to say vendor/google, instead it must make itself visible to all packages within vendor/ using //vendor:__subpackages__.

If a module does not specify the visibility property then it uses the default_visibility property of the package module in the module's package.

If the default_visibility property is not set for the module's package then it will use the default_visibility of its closest ancestor package for which a default_visibility property is specified.

If no default_visibility property can be found then the module uses the global default of //visibility:legacy_public.

The visibility property has no effect on a defaults module although it does apply to any non-defaults module that uses it. To set the visibility of a defaults module, use the defaults_visibility property on the defaults module; not to be confused with the default_visibility property on the package module.

Once the build has been completely switched over to soong it is possible that a global refactoring will be done to change this to //visibility:private at which point all packages that do not currently specify a default_visibility property will be updated to have default_visibility = [//visibility:legacy_public] added. It will then be the owner's responsibility to replace that with a more appropriate visibility.

Formatter

Soong includes a canonical formatter for Android.bp files, similar to gofmt. To recursively reformat all Android.bp files in the current directory:

bpfmt -w .

The canonical format includes 4 space indents, newlines after every element of a multi-element list, and always includes a trailing comma in lists and maps.

Convert Android.mk files

Soong includes a tool perform a first pass at converting Android.mk files to Android.bp files:

androidmk Android.mk > Android.bp

The tool converts variables, modules, comments, and some conditionals, but any custom Makefile rules, complex conditionals or extra includes must be converted by hand.

Differences between Android.mk and Android.bp

• Android.mk files often have multiple modules with the same name (for example for static and shared version of a library, or for host and device versions). Android.bp files require unique names for every module, but a single module can be built in multiple variants, for example by adding host_supported: true. The androidmk converter will produce multiple conflicting modules, which must be resolved by hand to a single module with any differences inside target: { android: { }, host: { } } blocks.

Build logic

The build logic is written in Go using the blueprint framework. Build logic receives module definitions parsed into Go structures using reflection and produces build rules. The build rules are collected by blueprint and written to a ninja build file.

Other documentation

• Best Practices
• Build Performance
• Generating CLion Projects
• Generating YouCompleteMe/VSCode compile_commands.json file
• Make-specific documentation: build/make/README.md

FAQ

How do I write conditionals?

Soong deliberately does not support conditionals in Android.bp files. We suggest removing most conditionals from the build. See Best Practices for some examples on how to remove conditionals.

In cases where build time conditionals are unavoidable, complexity in build rules that would require conditionals are handled in Go through Soong plugins. This allows Go language features to be used for better readability and testability, and implicit dependencies introduced by conditionals can be tracked. Most conditionals supported natively by Soong are converted to a map property. When building the module one of the properties in the map will be selected, and its values appended to the property with the same name at the top level of the module.

For example, to support architecture specific files:

cc_library {
    ...
    srcs: ["generic.cpp"],
    arch: {
        arm: {
            srcs: ["arm.cpp"],
        },
        x86: {
            srcs: ["x86.cpp"],
        },
    },
}

When building the module for arm the generic.cpp and arm.cpp sources will be built. When building for x86 the generic.cpp and 'x86.cpp' sources will be built.

Developing for Soong

To load Soong code in a Go-aware IDE, create a directory outside your android tree and then:

apt install bindfs
export GOPATH=<path to the directory you created>
build/soong/scripts/setup_go_workspace_for_soong.sh

This will bind mount the Soong source directories into the directory in the layout expected by the IDE.

Running Soong in a debugger

To run the soong_build process in a debugger, install dlv and then start the build with SOONG_DELVE=<listen addr> in the environment. For example:

SOONG_DELVE=:1234 m nothing

and then in another terminal:

dlv connect :1234

If you see an error:

Could not attach to pid 593: this could be caused by a kernel
security setting, try writing "0" to /proc/sys/kernel/yama/ptrace_scope

you can temporarily disable Yama's ptrace protection using:

sudo sysctl -w kernel.yama.ptrace_scope=0

Contact

Email android-building@googlegroups.com (external) for any questions, or see go/soong (internal).