# 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](https://source.android.com/compatibility/tests/development/blueprints) 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](https://android-review.googlesource.com/dashboard/self). 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](https://issuetracker.google.com/issues/new?component=381517) 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](https://bazel.build/concepts/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](https://ci.android.com/builds/latest/branches/aosp-build-tools/targets/linux/view/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 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. * `["//visibility:any_partition"]`: Any modules of type android_filesystem or android_system_image can use this module. Intended for modules that no one should link against, but should still be included in soong-built partitions. * `["//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](https://golang.org/cmd/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](docs/best_practices.md#removing-conditionals) 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"], list_variables: ["impl"], 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 four additional conditionals based on variables `board`, `feature`, `impl` and `width` which can affect properties `cflags` and `srcs`. The four types of soong variables control properties in the following ways. * bool variable (e.g. `feature`): Properties are applied if set to `true`. * list variable (e.g. `impl`): (lists of strings properties only) Properties are applied for each value in the list, using `%s` substitution. For example, if the property is `["%s.cpp", "%s.h"]` and the list value is `foo bar`, the result is `["foo.cpp", "foo.h", "bar.cpp", "bar.h"]`. * value variable (e.g. `width`): (strings or lists of strings) The value are directly substituted into properties using `%s`. * string variable (e.g. `board`): Properties are applied only if they match the variable's value. Additionally, each conditional containing 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 `true` * list variable (e.g. `impl`): the variable is unspecified * 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` is `soc_b`, the `cflags` and `srcs` values under `conditions_default` is 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,impl,foo.cpp bar.cpp) $(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"], }, }, impl: { srcs: ["impl/%s"], conditions_default: { srcs: ["impl/default.cpp"], }, }, }, } 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"` and `srcs: ["*.cpp", "impl/foo.cpp", "impl/bar.cpp"]`. Alternatively, with `DefaultBoardConfig.mk`: ``` SOONG_CONFIG_NAMESPACES += acme SOONG_CONFIG_acme += \ board \ feature \ impl \ width \ SOONG_CONFIG_acme_feature := false ``` then `libacme_foo` would build with `cflags: "-DGENERIC -DSOC_DEFAULT -DFEATURE_DEFAULT -DSIZE=DEFAULT"` and `srcs: ["*.cpp", "impl/default.cpp"]`. Alternatively, with `DefaultBoardConfig.mk`: ``` SOONG_CONFIG_NAMESPACES += acme SOONG_CONFIG_acme += \ board \ feature \ impl \ width \ SOONG_CONFIG_acme_board := soc_c SOONG_CONFIG_acme_impl := baz ``` then `libacme_foo` would build with `cflags: "-DGENERIC -DSOC_DEFAULT -DFEATURE_DEFAULT -DSIZE=DEFAULT"` and `srcs: ["*.cpp", "impl/baz.cpp"]`. `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](http://godoc.org/github.com/google/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](http://ninja-build.org) 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](docs/best_practices.md) * [Build Performance](docs/perf.md) * [Generating CLion Projects](docs/clion.md) * [Generating YouCompleteMe/VSCode compile\_commands.json file](docs/compdb.md) * Make-specific documentation: [build/make/README.md](https://android.googlesource.com/platform/build/+/main/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=` in the environment. For example: ```bash 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 ```bash 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](https://www.kernel.org/doc/Documentation/security/Yama.txt) using: ```bash 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](http://go/soong) (internal).