This guide shows you how to build Fuchsia to include an example package from Fuchsia source's //examples
directory and run its component on your Fuchsia device.
Open the examples/hello_world/BUILD.gn
file.
This example, written in both C++ and Rust, prints Hello, world!
. Each language-dependent directory has the following:
BUILD.gn
file that defines its Fuchsia package.meta
subdirectory with component manifests (.cmx
) files.In short, GN is a meta build system. Output files from GN serve as inputs to Ninja{:.external}, the actual build system. If you aren't familiar with GN, see Introduction to GN.
In the example package's top level BUILD.gn
file, the hello_world
target is a group containing other dependencies, notably cpp
and rust
. Therefore, this target builds both of them:
group("hello_world") { testonly = true deps = [ ":tests", "cpp", "rust", ] }
To learn more about how GN defines Fuchsia packages, see the build/package.gni
file.
A .cmx
file, known as a component manifest, describes how to run an application on Fuchsia as a component. In other words, a component manifest creates a Fuchsia package.
To include a package in your Fuchsia image, you have the following options:
Base: Packages that are produced by build and included in paving images. These packages are included in over-the-air updates and are always updated as a single unit.
Cache: Packages that are included in paving images, but are not included in over-the-air system updates. These packages can be updated at any time when updates are available.
Universe: Packages that are not included in paving image. These optional packages are fetched and run on-demand,
To include the example package in Universe (so that it can be fetched on-demand), use the --with
flag when setting your product and board environment:
fx set <PRODUCT>.<ARCH> --with //examples/hello_world fx build
For more information on setting up fx
, see fx workflows.
You now have a build that includes the example package in Universe.
To run a Fuchsia component, use its Fuchsia package URL as an argument to the fx shell run
command:
Open a terminal and run fx serve
:
fx serve
Open another terminal and run the example component:
fx shell run fuchsia-pkg://fuchsia.com/hello_world_cpp#meta/hello_world_cpp.cmx
This command prints the following output:
Hello, World!
If fx serve
is not running, the command prints an error message from the device:
fuchsia-pkg://fuchsia.com/hello_world_cpp#meta/hello_world_cpp.cmx: not found.
If fx serve
is running, but the package is not found, then try rebuilding your Fuchsia image to include this package and repaving it to the device. See Include the example package in your Fuchsia image for details.
The fx shell run
command can match a string to a package URL if the string is only mapped to one component in your product configuration. For example:
$ fx shell run hello_world_cpp.cmx
If multiple matches exist, the command prints the list of matches:
$ fx shell run hello_world fuchsia-pkg://fuchsia.com/hello_world_cpp_tests#meta/hello_world_cpp_unittests.cmx fuchsia-pkg://fuchsia.com/hello_world_rust_tests#meta/hello_world_rust_bin_test.cm fuchsia-pkg://fuchsia.com/hello_world_rust_tests#meta/hello_world_rust_bin_test.cmx fuchsia-pkg://fuchsia.com/hello_world_cpp#meta/hello_world_cpp.cmx fuchsia-pkg://fuchsia.com/hello_world_rust#meta/hello_world_rust.cmx fuchsia-pkg://fuchsia.com/hello_world_rust#meta/hello_world_rust.cm Error: "hello_world" matched multiple components
You can explore what components are in your product configuration using the locate
command.
Find your favorite component:
fx shell locate hello_world_cpp
Find all runnable components:
fx shell locate --list cmx
Find multiple test components:
fx shell locate --list test