Build system

Fuchsia builds use Generate Ninja (GN), a meta-build system that generates build files consumed by Ninja, which executes the actual build. The build system provides the tools to configure the build for a specific product and templates to build code for Fuchsia targets.

Build targets

You define individual build targets for GN using BUILD.gn files located with your project source code. The Fuchsia build system provides templates as GN imports (.gni) for you to declare Fuchsia artifacts, such as:

fuchsia_component(): Defines an executable component, containing the manifest, program binary, and resources.
fuchsia_package(): Defines a package containing one or more components for distribution in a package repository.
fuchsia_test_package(): Defines a package containing test components.

Below is an example of a BUILD.gn file for a simple component package with tests:

import("//build/components.gni")

executable("bin") {
  sources = [ "main.cc" ]
}

fuchsia_component("hello-world-component") {
  deps = [ ":bin" ]
  manifest = "meta/hello-world.cml"
}

fuchsia_package("hello-world") {
  deps = [
    ":hello-world-component",
  ]
}

fuchsia_component("hello-world-test-component") {
  testonly = true
  deps = [ ":bin_test" ]
  manifest = "meta/hello-world-bin-test.cml"
}

fuchsia_test_package("hello-world-tests") {
  test_components = [ ":hello-world-test-component" ]
}

A unique label composed of the target's name and the path to its BUILD.gn file identifies everything that can participate in the build. In the above example, the hello-world target might have a label that looks like this: //src/examples/basic:hello-world.

Build configuration

The GN front-end configures the build according to the chosen Fuchsia product configuration, collecting all the necessary packages and components required by the build. These targets are defined in various BUILD.gn files throughout the source tree. The output of the GN step is an optimized set of instructions for Ninja in the build directory.

The build system invokes GN when you run the fx set command to configure the build.

fx set minimal.x64

You can also invoke GN directly with fx gn to customize or troubleshoot the build.

You should run the GN configuration step anytime you want to adjust the product configuration or the packages available to the build. GN is also invoked automatically during a build anytime one of the BUILD.gn files in the current configuration is changed.

Boards and products

The Fuchsia build system defines the baseline configuration for a Fuchsia build as a combination of a product and board. Together, these elements form the build configuration you provide to fx set.

Boards define the architecture that the build targets, which may affect what drivers are included and influence device specific kernel parameters.

This codelab targets the x64 board, which supports the Fuchsia emulator (FEMU) running on x64 architecture.

You can discover all the available target boards with fx list-boards.

A product defines the software configuration that a build produces. This configuration may include what services are available and the user-facing experience.

This codelab targets the minimal_eng product.

You can discover all the available target products with fx list-products.

Build

Once the GN build configuration is complete, Ninja consumes the generated build files and runs the appropriate compile, link, and packaging commands to generate the Fuchsia image.

The build system invokes Ninja when you run the fx build command to execute the current build configuration.

fx build

You can also invoke Ninja directly with fx ninja to customize or troubleshoot the build.

Exercise: Build Minimal

In this exercise, you'll build the minimal_eng product configuration from source to run on the x64 emulator board.

Configure the build

Set up the build environment for the minimal product and x64 board:

fx set minimal.x64

This command runs GN on the set of targets defined in the product's build configuration to produce the build instructions. It does not actually perform the build, but instead defines the parameters of what is considered buildable.

You can also ask GN to regenerate the existing build configuration using fx gen without needing to supply the product configuration again. This can be helpful when you are editing BUILD.gn files and want to quickly validate without running a full build.

Inspect the build configuration

Once the build is configured, use fx list-packages to print the set of packages the build is aware of:

fx list-packages

This is a useful tool to determine if a package you need was properly included in the build configuration.

Build Fuchsia Minimal

Build the Minimal target with fx build:

fx build

Restart the emulator

Run the following command to close any emulator instances you currently have open:
```
ffx emu stop --all
```

Start a new emulator instance:

ffx emu start --headless

When startup is complete, the emulator prints the following message and returns:

Logging to "$HOME/.local/share/Fuchsia/ffx/emu/instances/fuchsia-emulator/emulator.log"
Waiting for Fuchsia to start (up to 60 seconds)........
Emulator is ready.

Inspect the device

Open another terminal window and run the following command to print the details of your device target:

ffx target show

Look for the build configuration of the target output:

Version: "2000-01-01T12:00:00+00:00"
Product: "minimal_eng"
Board: "x64"
Commit: "2000-01-01T12:00:00+00:00"

Notice that the configuration points to the build you just completed on your machine.

You are now running your own build of Fuchsia!

Fuchsia source tree

Product packages