platform_build_soong/README.md

Soong

Soong is one of the build systems used in Android. There are altogether three:

• The legacy Make-based build system that is controlled by files called Android.mk.
• Soong, which is controlled by files called Android.bp.
• The upcoming Bazel-based build system that is controlled by files called BUILD.bazel.

Android.bp file are JSON-like declarative descriptions of "modules" to build; a "module" is the basic unit of building that Soong understands, similarly to how "target" is the basic unit of building for Bazel (and Make, although the two kinds of "targets" are very different)

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

Contributing

Code reviews are handled through the usual code review system of Android, available here.

For simple changes (fixing typos, obvious optimizations, etc.), sending a code review request is enough. For more substantial changes, file a bug in our bug tracker or or write us at android-building@googlegroups.com .

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.

The list of valid module types and their properties can be generated by calling m soong_docs. It will be written to $OUT_DIR/soong/docs/soong_build.html. This list for the current version of Soong can be found here.

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 are dynamically typed based on the first assignment, and properties are statically typed 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 contain 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

The + operator:

• Sums integers.
• Concatenates strings and lists.
• Produces the union of maps.

Concatenating maps produces a map whose keys are the union of the given maps' keys, and whose mapped values are the union of the given maps' corresponding mapped values.

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

The presence 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/my/display/lib/Android.bp, its namespace is device/my/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.
• ["//visibility:override"]: Discards any rules inherited from defaults or a creating module. Can only be used at the beginning of a list of visibility rules.
• ["//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.

Conditionals

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

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.

Soong Config Variables

When converting vendor modules that contain conditionals, simple conditionals can be supported through Soong config variables using soong_config_* modules that describe the module types, variables and possible values:

soong_config_module_type {
    name: "acme_cc_defaults",
    module_type: "cc_defaults",
    config_namespace: "acme",
    variables: ["board"],
    bool_variables: ["feature"],
    value_variables: ["width"],
    properties: ["cflags", "srcs"],
}

soong_config_string_variable {
    name: "board",
    values: ["soc_a", "soc_b", "soc_c"],
}

This example describes a new acme_cc_defaults module type that extends the cc_defaults module type, with three additional conditionals based on variables board, feature and width, which can affect properties cflags and srcs. Additionally, each conditional will contain a conditions_default property can affect cflags and srcs in the following conditions:

• bool variable (e.g. feature): the variable is unspecified or not set to a true value
• value variable (e.g. width): the variable is unspecified
• string variable (e.g. board): the variable is unspecified or the variable is set to a string unused in the given module. For example, with board, if the board conditional contains the properties soc_a and conditions_default, when board=soc_b, the cflags and srcs values under conditions_default will be used. To specify that no properties should be amended for soc_b, you can set soc_b: {},.

The values of the variables can be set from a product's BoardConfig.mk file:

$(call soong_config_set,acme,board,soc_a)
$(call soong_config_set,acme,feature,true)
$(call soong_config_set,acme,width,200)

The acme_cc_defaults module type can be used anywhere after the definition in the file where it is defined, or can be imported into another file with:

soong_config_module_type_import {
    from: "device/acme/Android.bp",
    module_types: ["acme_cc_defaults"],
}

It can used like any other module type:

acme_cc_defaults {
    name: "acme_defaults",
    cflags: ["-DGENERIC"],
    soong_config_variables: {
        board: {
            soc_a: {
                cflags: ["-DSOC_A"],
            },
            soc_b: {
                cflags: ["-DSOC_B"],
            },
            conditions_default: {
                cflags: ["-DSOC_DEFAULT"],
            },
        },
        feature: {
            cflags: ["-DFEATURE"],
            conditions_default: {
                cflags: ["-DFEATURE_DEFAULT"],
            },
        },
        width: {
            cflags: ["-DWIDTH=%s"],
            conditions_default: {
                cflags: ["-DWIDTH=DEFAULT"],
            },
        },
    },
}

cc_library {
    name: "libacme_foo",
    defaults: ["acme_defaults"],
    srcs: ["*.cpp"],
}

With the BoardConfig.mk snippet above, libacme_foo would build with cflags: "-DGENERIC -DSOC_A -DFEATURE -DWIDTH=200".

Alternatively, with DefaultBoardConfig.mk:

SOONG_CONFIG_NAMESPACES += acme
SOONG_CONFIG_acme += \
    board \
    feature \
    width \

SOONG_CONFIG_acme_feature := false

then libacme_foo would build with cflags: "-DGENERIC -DSOC_DEFAULT -DFEATURE_DEFAULT -DSIZE=DEFAULT".

Alternatively, with DefaultBoardConfig.mk:

SOONG_CONFIG_NAMESPACES += acme
SOONG_CONFIG_acme += \
    board \
    feature \
    width \

SOONG_CONFIG_acme_board := soc_c

then libacme_foo would build with cflags: "-DGENERIC -DSOC_DEFAULT -DFEATURE_DEFAULT -DSIZE=DEFAULT".

soong_config_module_type modules will work best when used to wrap defaults modules (cc_defaults, java_defaults, etc.), which can then be referenced by all of the vendor's other modules using the normal namespace and visibility rules.

soongConfigTraceMutator enables modules affected by soong config variables to write outputs into a hashed directory path. It does this by recording accesses to soong config variables on each module, and then accumulating records of each module's all dependencies. m soong_config_trace builds information about hashes to $OUT_DIR/soong/soong_config_trace.json.

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.

Environment Variables Config File

Soong can optionally load environment variables from a pre-specified configuration file during startup. These environment variables can be used to control the behavior of the build. For example, these variables can determine whether remote-execution should be used for the build or not.

The ANDROID_BUILD_ENVIRONMENT_CONFIG_DIR environment variable specifies the directory in which the config file should be searched for. The ANDROID_BUILD_ENVIRONMENT_CONFIG variable determines the name of the config file to be searched for within the config directory. For example, the following build comand will load ENV_VAR_1 and ENV_VAR_2 environment variables from the example_config.json file inside the build/soong directory.

ANDROID_BUILD_ENVIRONMENT_CONFIG_DIR=build/soong \
  ANDROID_BUILD_ENVIRONMENT_CONFIG=example_config \
  build/soong/soong_ui.bash

Other documentation

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

Developing for Soong

To load the code of Soong in IntelliJ:

• File -> Open, open the build/soong directory. It will be opened as a new project.
• File -> Settings, then Languages & Frameworks -> Go -> GOROOT, then set it to prebuilts/go/linux-x86
• File -> Project Structure, then, Project Settings -> Modules, then Add Content Root, then add the build/blueprint directory.
• Optional: also add the external/golang-protobuf directory. In practice, IntelliJ seems to work well enough without this, too.

Running Soong in a debugger

Both the Android build driver (soong_ui) and Soong proper (soong_build) are Go applications and can be debugged with the help of the standard Go debugger called Delve. A client (e.g., IntelliJ IDEA) communicates with Delve via IP port that Delve listens to (the port number is passed to it on invocation).

Debugging Android Build Driver

To make soong_ui wait for a debugger connection, use the SOONG_UI_DELVE variable:

SOONG_UI_DELVE=5006 m nothing

Debugging Soong Proper

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

SOONG_DELVE=5006 m nothing

Android build driver invokes soong_build multiple times, and by default each invocation is run in the debugger. Setting SOONG_DELVE_STEPS controls which invocations are run in the debugger, e.g., running

SOONG_DELVE=2345 SOONG_DELVE_STEPS='build,modulegraph' m

results in only build (main build step) and modulegraph being run in the debugger. The allowed step names are bp2build_files, bp2build_workspace, build, modulegraph, queryview, soong_docs.

Note setting or unsetting SOONG_DELVE causes a recompilation of soong_build. This is because in order to debug the binary, it needs to be built with debug symbols.

Delve Troubleshooting

To test the debugger connection, run this command:

dlv connect :5006

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

IntelliJ Setup

To connect to the process using IntelliJ:

• Run -> Edit Configurations...
• Choose "Go Remote" on the left
• Click on the "+" buttion on the top-left
• Give it a nice name and set "Host" to localhost and "Port" to the port in the environment variable (SOONG_UI_DELVE for soong_ui, SOONG_DELVE for soong_build)
• Set the breakpoints where you want application to stop
• Run the build from the command line
• In IntelliJ, click Run -> Debug name
• Observe Connecting... message in the debugger pane. It changes to Connected once the communication with the debugger has been established; the terminal window where the build started will display API server listening at ... message

Sometimes the dlv process hangs on connection. A symptom of this is dlv spinning a core or two. In that case, kill -9 dlv and try again. Anecdotally, it feels like waiting a minute after the start of soong_build helps.

Contact

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