`aarch64-unknown-fuchsia` and `x86_64-unknown-fuchsia`

Tier: 2

Fuchsia is a modern open source operating system that's simple, secure, updatable, and performant.

Target maintainers

Tyler Mandry (@tmandry)
Dan Johnson (@computerdruid)
David Koloski (@djkoloski)
Andrew Pollack (@andrewpollack)
Joseph Ryan (@P1n3appl3)

As the team evolves over time, the specific members listed here may differ from the members reported by the API. The API should be considered to be authoritative if this occurs. Instead of pinging individual members, use @rustbot ping fuchsia to contact the team on GitHub.

Requirements
Walkthrough structure
Compiling a Rust binary targeting Fuchsia
1. Targeting Fuchsia with rustup and cargo
2. Targeting Fuchsia with a compiler built from source
Creating a Fuchsia package
1. Creating a Fuchsia component
2. Building a Fuchsia package
Publishing a Fuchsia package
1. Creating a Fuchsia package repository
2. Publishing Fuchsia package to repository
Running a Fuchsia component on an emulator
.gitignore extensions
Testing
1. Running unit tests
2. Running the compiler test suite
Debugging

Requirements

This target is cross-compiled from a host environment. You will need a recent copy of the Fuchsia SDK, which provides the tools, libraries, and binaries required to build and link programs for Fuchsia.

Development may also be done from the source tree.

Fuchsia targets support std and follow the sysv64 calling convention on x86_64. Fuchsia binaries use the ELF file format.

Walkthrough structure

This walkthrough will cover:

Compiling a Rust binary targeting Fuchsia.
Building a Fuchsia package.
Publishing and running a Fuchsia package to a Fuchsia emulator.

For the purposes of this walkthrough, we will only target x86_64-unknown-fuchsia.

Compiling a Rust binary targeting Fuchsia

Today, there are two main ways to build a Rust binary targeting Fuchsia using the Fuchsia SDK:

Allow rustup to handle the installation of Fuchsia targets for you.
Build a toolchain locally that can target Fuchsia.

Targeting Fuchsia with rustup and cargo

The easiest way to build a Rust binary targeting Fuchsia is by allowing rustup to handle the installation of Fuchsia targets for you. This can be done by issuing the following commands:

rustup target add x86_64-unknown-fuchsia
rustup target add aarch64-unknown-fuchsia

After installing our Fuchsia targets, we can now compile a Rust binary that targets Fuchsia.

To create our Rust project, we can use cargo as follows:

From base working directory

cargo new hello_fuchsia

The rest of this walkthrough will take place from hello_fuchsia, so we can change into that directory now:

cd hello_fuchsia

Note: From this point onwards, all commands will be issued from the hello_fuchsia/ directory, and all hello_fuchsia/ prefixes will be removed from references for sake of brevity.

We can edit our src/main.rs to include a test as follows:

src/main.rs

fn main() {
    println!("Hello Fuchsia!");
}

#[test]
fn it_works() {
    assert_eq!(2 + 2, 4);
}

In addition to the standard workspace created, we will want to create a .cargo/config.toml file to link necessary libraries during compilation:

.cargo/config.toml

[target.x86_64-unknown-fuchsia]

rustflags = [
    "-Lnative=<SDK_PATH>/arch/x64/lib",
    "-Lnative=<SDK_PATH>/arch/x64/sysroot/lib"
]

Note: Make sure to fill out <SDK_PATH> with the path to the downloaded Fuchsia SDK.

These options configure the following:

-Lnative=${SDK_PATH}/arch/${ARCH}/lib: Link against Fuchsia libraries from the SDK
-Lnative=${SDK_PATH}/arch/${ARCH}/sysroot/lib: Link against Fuchsia sysroot libraries from the SDK

In total, our new project will look like:

Current directory structure

hello_fuchsia/
┣━ src/
┃  ┗━ main.rs
┣━ Cargo.toml
┗━ .cargo/
   ┗━ config.toml

Finally, we can build our rust binary as:

cargo build --target x86_64-unknown-fuchsia

Now we have a Rust binary at target/x86_64-unknown-fuchsia/debug/hello_fuchsia, targeting our desired Fuchsia target.

Current directory structure

hello_fuchsia/
┣━ src/
┃  ┗━ main.rs
┣━ target/
┃  ┗━ x86_64-unknown-fuchsia/
┃     ┗━ debug/
┃        ┗━ hello_fuchsia
┣━ Cargo.toml
┗━ .cargo/
   ┗━ config.toml

Targeting Fuchsia with a compiler built from source

An alternative to the first workflow is to target Fuchsia by using rustc built from source.

Before building Rust for Fuchsia, you'll need a clang toolchain that supports Fuchsia as well. A recent version (14+) of clang should be sufficient to compile Rust for Fuchsia.

x86-64 and AArch64 Fuchsia targets can be enabled using the following configuration in config.toml:

[build]
target = ["<host_platform>", "aarch64-unknown-fuchsia", "x86_64-unknown-fuchsia"]

[rust]
lld = true

[llvm]
download-ci-llvm = false

[target.x86_64-unknown-fuchsia]
cc = "clang"
cxx = "clang++"

[target.aarch64-unknown-fuchsia]
cc = "clang"
cxx = "clang++"

Though not strictly required, you may also want to use clang for your host target as well:

[target.<host_platform>]
cc = "clang"
cxx = "clang++"

By default, the Rust compiler installs itself to /usr/local on most UNIX systems. You may want to install it to another location (e.g. a local install directory) by setting a custom prefix in config.toml:

[install]
# Make sure to use the absolute path to your install directory
prefix = "<RUST_SRC_PATH>/install"

Next, the following environment variables must be configured. For example, using a script we name config-env.sh:

# Configure this environment variable to be the path to the downloaded SDK
export SDK_PATH="<SDK path goes here>"

export CFLAGS_aarch64_unknown_fuchsia="--target=aarch64-unknown-fuchsia --sysroot=${SDK_PATH}/arch/arm64/sysroot -I${SDK_PATH}/pkg/fdio/include"
export CXXFLAGS_aarch64_unknown_fuchsia="--target=aarch64-unknown-fuchsia --sysroot=${SDK_PATH}/arch/arm64/sysroot -I${SDK_PATH}/pkg/fdio/include"
export LDFLAGS_aarch64_unknown_fuchsia="--target=aarch64-unknown-fuchsia --sysroot=${SDK_PATH}/arch/arm64/sysroot -L${SDK_PATH}/arch/arm64/lib"
export CARGO_TARGET_AARCH64_UNKNOWN_FUCHSIA_RUSTFLAGS="-C link-arg=--sysroot=${SDK_PATH}/arch/arm64/sysroot -Lnative=${SDK_PATH}/arch/arm64/sysroot/lib -Lnative=${SDK_PATH}/arch/arm64/lib"
export CFLAGS_x86_64_unknown_fuchsia="--target=x86_64-unknown-fuchsia --sysroot=${SDK_PATH}/arch/x64/sysroot -I${SDK_PATH}/pkg/fdio/include"
export CXXFLAGS_x86_64_unknown_fuchsia="--target=x86_64-unknown-fuchsia --sysroot=${SDK_PATH}/arch/x64/sysroot -I${SDK_PATH}/pkg/fdio/include"
export LDFLAGS_x86_64_unknown_fuchsia="--target=x86_64-unknown-fuchsia --sysroot=${SDK_PATH}/arch/x64/sysroot -L${SDK_PATH}/arch/x64/lib"
export CARGO_TARGET_X86_64_UNKNOWN_FUCHSIA_RUSTFLAGS="-C link-arg=--sysroot=${SDK_PATH}/arch/x64/sysroot -Lnative=${SDK_PATH}/arch/x64/sysroot/lib -Lnative=${SDK_PATH}/arch/x64/lib"

Finally, the Rust compiler can be built and installed:

(source config-env.sh && ./x.py install)

Once rustc is installed, we can create a new working directory to work from, hello_fuchsia along with hello_fuchsia/src:

mkdir hello_fuchsia
cd hello_fuchsia
mkdir src

Note: From this point onwards, all commands will be issued from the hello_fuchsia/ directory, and all hello_fuchsia/ prefixes will be removed from references for sake of brevity.

There, we can create a new file named src/hello_fuchsia.rs:

src/hello_fuchsia.rs

fn main() {
    println!("Hello Fuchsia!");
}

#[test]
fn it_works() {
    assert_eq!(2 + 2, 4);
}

Current directory structure

hello_fuchsia/
┗━ src/
    ┗━ hello_fuchsia.rs

Using your freshly installed rustc, you can compile a binary for Fuchsia using the following options:

--target x86_64-unknown-fuchsia/--target aarch64-unknown-fuchsia: Targets the Fuchsia platform of your choice
-Lnative ${SDK_PATH}/arch/${ARCH}/lib: Link against Fuchsia libraries from the SDK
-Lnative ${SDK_PATH}/arch/${ARCH}/sysroot/lib: Link against Fuchsia sysroot libraries from the SDK

Putting it all together:

# Configure these for the Fuchsia target of your choice
TARGET_ARCH="<x86_64-unknown-fuchsia|aarch64-unknown-fuchsia>"
ARCH="<x64|aarch64>"

rustc \
    --target ${TARGET_ARCH} \
    -Lnative=${SDK_PATH}/arch/${ARCH}/lib \
    -Lnative=${SDK_PATH}/arch/${ARCH}/sysroot/lib \
    --out-dir bin src/hello_fuchsia.rs

Current directory structure

hello_fuchsia/
┣━ src/
┃   ┗━ hello_fuchsia.rs
┗━ bin/
   ┗━ hello_fuchsia

Creating a Fuchsia package

Before moving on, double check your directory structure:

Current directory structure

hello_fuchsia/
┣━ src/                         (if using rustc)
┃   ┗━ hello_fuchsia.rs         ...
┣━ bin/                         ...
┃  ┗━ hello_fuchsia             ...
┣━ src/                         (if using cargo)
┃  ┗━ main.rs                   ...
┗━ target/                      ...
   ┗━ x86_64-unknown-fuchsia/   ...
      ┗━ debug/                 ...
         ┗━ hello_fuchsia       ...

With our Rust binary built, we can move to creating a Fuchsia package. On Fuchsia, a package is the unit of distribution for software. We'll need to create a new package directory where we will place files like our finished binary and any data it may need.

To start, make the pkg, and pkg/meta directories:

mkdir pkg
mkdir pkg/meta

Current directory structure

hello_fuchsia/
┗━ pkg/
   ┗━ meta/

Now, create the following files inside:

pkg/meta/package

{
  "name": "hello_fuchsia",
  "version": "0"
}

The package file describes our package's name and version number. Every package must contain one.

pkg/hello_fuchsia.manifest if using cargo

bin/hello_fuchsia=target/x86_64-unknown-fuchsia/debug/hello_fuchsia
lib/ld.so.1=<SDK_PATH>/arch/x64/sysroot/dist/lib/ld.so.1
lib/libfdio.so=<SDK_PATH>/arch/x64/dist/libfdio.so
meta/package=pkg/meta/package
meta/hello_fuchsia.cm=pkg/meta/hello_fuchsia.cm

pkg/hello_fuchsia.manifest if using rustc

bin/hello_fuchsia=bin/hello_fuchsia
lib/ld.so.1=<SDK_PATH>/arch/x64/sysroot/dist/lib/ld.so.1
lib/libfdio.so=<SDK_PATH>/arch/x64/dist/libfdio.so
meta/package=pkg/meta/package
meta/hello_fuchsia.cm=pkg/meta/hello_fuchsia.cm

Note: Relative manifest paths are resolved starting from the working directory of pm. Make sure to fill out <SDK_PATH> with the path to the downloaded SDK.

The .manifest file will be used to describe the contents of the package by relating their location when installed to their location on the file system. The bin/hello_fuchsia= entry will be different depending on how your Rust binary was built, so choose accordingly.

Current directory structure

hello_fuchsia/
┗━ pkg/
   ┣━ meta/
   ┃  ┗━ package
   ┗━ hello_fuchsia.manifest

Creating a Fuchsia component

On Fuchsia, components require a component manifest written in Fuchsia's markup language called CML. The Fuchsia devsite contains an overview of CML and a reference for the file format. Here's a basic one that can run our single binary:

pkg/hello_fuchsia.cml

{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/hello_fuchsia",
    },
}

Current directory structure

hello_fuchsia/
┗━ pkg/
   ┣━ meta/
   ┃  ┗━ package
   ┣━ hello_fuchsia.manifest
   ┗━ hello_fuchsia.cml

Now we can compile that CML into a component manifest:

${SDK_PATH}/tools/${ARCH}/cmc compile \
    pkg/hello_fuchsia.cml \
    --includepath ${SDK_PATH}/pkg \
    -o pkg/meta/hello_fuchsia.cm

Note: --includepath tells the compiler where to look for includes from our CML. In our case, we're only using syslog/client.shard.cml.

Current directory structure

hello_fuchsia/
┗━ pkg/
   ┣━ meta/
   ┃  ┣━ package
   ┃  ┗━ hello_fuchsia.cm
   ┣━ hello_fuchsia.manifest
   ┗━ hello_fuchsia.cml

Building a Fuchsia package

Next, we'll build a package manifest as defined by our manifest:

${SDK_PATH}/tools/${ARCH}/pm \
    -api-level $(${SDK_PATH}/tools/${ARCH}/ffx version -v | grep "api-level" | head -1 |  awk -F ' ' '{print $2}') \
    -o pkg/hello_fuchsia_manifest \
    -m pkg/hello_fuchsia.manifest \
    build \
    -output-package-manifest pkg/hello_fuchsia_package_manifest

This will produce pkg/hello_fuchsia_manifest/ which is a package manifest we can publish directly to a repository.

Current directory structure

hello_fuchsia/
┗━ pkg/
   ┣━ meta/
   ┃  ┣━ package
   ┃  ┗━ hello_fuchsia.cm
   ┣━ hello_fuchsia_manifest/
   ┃  ┗━ ...
   ┣━ hello_fuchsia.manifest
   ┣━ hello_fuchsia.cml
   ┗━ hello_fuchsia_package_manifest

We are now ready to publish the package.

Publishing a Fuchsia package

With our package and component manifests setup, we can now publish our package. The first step will be to create a Fuchsia package repository to publish to.

Creating a Fuchsia package repository

We can set up our repository with:

${SDK_PATH}/tools/${ARCH}/pm newrepo \
    -repo pkg/repo

Current directory structure

hello_fuchsia/
┗━ pkg/
   ┣━ meta/
   ┃  ┣━ package
   ┃  ┗━ hello_fuchsia.cm
   ┣━ hello_fuchsia_manifest/
   ┃  ┗━ ...
   ┣━ repo/
   ┃  ┗━ ...
   ┣━ hello_fuchsia.manifest
   ┣━ hello_fuchsia.cml
   ┗━ hello_fuchsia_package_manifest

Publishing Fuchsia package to repository

We can publish our new package to that repository with:

${SDK_PATH}/tools/${ARCH}/pm publish \
    -repo pkg/repo \
    -lp -f <(echo "pkg/hello_fuchsia_package_manifest")

Then we can add the repository to ffx's package server as hello-fuchsia using:

${SDK_PATH}/tools/${ARCH}/ffx repository add-from-pm \
    pkg/repo \
    -r hello-fuchsia

Running a Fuchsia component on an emulator

At this point, we are ready to run our Fuchsia component. For reference, our final directory structure will look like:

Final directory structure

hello_fuchsia/
┣━ src/                         (if using rustc)
┃   ┗━ hello_fuchsia.rs         ...
┣━ bin/                         ...
┃  ┗━ hello_fuchsia             ...
┣━ src/                         (if using cargo)
┃  ┗━ main.rs                   ...
┣━ target/                      ...
┃  ┗━ x86_64-unknown-fuchsia/   ...
┃     ┗━ debug/                 ...
┃        ┗━ hello_fuchsia       ...
┗━ pkg/
   ┣━ meta/
   ┃  ┣━ package
   ┃  ┗━ hello_fuchsia.cm
   ┣━ hello_fuchsia_manifest/
   ┃  ┗━ ...
   ┣━ repo/
   ┃  ┗━ ...
   ┣━ hello_fuchsia.manifest
   ┣━ hello_fuchsia.cml
   ┗━ hello_fuchsia_package_manifest

Starting the Fuchsia emulator

Start a Fuchsia emulator in a new terminal using:

${SDK_PATH}/tools/${ARCH}/ffx product-bundle get workstation_eng.qemu-${ARCH}
${SDK_PATH}/tools/${ARCH}/ffx emu start workstation_eng.qemu-${ARCH} --headless

Watching emulator logs

Once the emulator is running, open a separate terminal to watch the emulator logs:

In separate terminal

${SDK_PATH}/tools/${ARCH}/ffx log \
    --since now

Serving a Fuchsia package

Now, start a package repository server to serve our package to the emulator:

${SDK_PATH}/tools/${ARCH}/ffx repository server start

Once the repository server is up and running, register it with the target Fuchsia system running in the emulator:

${SDK_PATH}/tools/${ARCH}/ffx target repository register \
    --repository hello-fuchsia

Running a Fuchsia component

Finally, run the component:

${SDK_PATH}/tools/${ARCH}/ffx component run \
    /core/ffx-laboratory:hello_fuchsia \
    fuchsia-pkg://hello-fuchsia/hello_fuchsia_manifest#meta/hello_fuchsia.cm

On reruns of the component, the --recreate argument may also need to be passed.

${SDK_PATH}/tools/${ARCH}/ffx component run \
    --recreate \
    /core/ffx-laboratory:hello_fuchsia \
    fuchsia-pkg://hello-fuchsia/hello_fuchsia_manifest#meta/hello_fuchsia.cm

`.gitignore` extensions

Optionally, we can create/extend our .gitignore file to ignore files and directories that are not helpful to track:

pkg/repo
pkg/meta/hello_fuchsia.cm
pkg/hello_fuchsia_manifest
pkg/hello_fuchsia_package_manifest

Testing

Running unit tests

Tests can be run in the same way as a regular binary.

If using cargo, you can simply pass test --no-run to the cargo invocation and then repackage and rerun the Fuchsia package. From our previous example, this would look like cargo test --target x86_64-unknown-fuchsia --no-run, and moving the executable binary path found from the line Executable unittests src/main.rs (target/x86_64-unknown-fuchsia/debug/deps/hello_fuchsia-<HASH>) into pkg/hello_fuchsia.manifest.
If using the compiled rustc, you can simply pass --test to the rustc invocation and then repackage and rerun the Fuchsia package.

The test harness will run the applicable unit tests.

Often when testing, you may want to pass additional command line arguments to your binary. Additional arguments can be set in the component manifest:

pkg/hello_fuchsia.cml

{
    include: [ "syslog/client.shard.cml" ],
    program: {
        runner: "elf",
        binary: "bin/hello_fuchsia",
        args: ["it_works"],
    },
}

This will pass the argument it_works to the binary, filtering the tests to only those tests that match the pattern. There are many more configuration options available in CML including environment variables. More documentation is available on the Fuchsia devsite.

Running the compiler test suite

The commands in this section assume that they are being run from inside your local Rust source checkout:

cd ${RUST_SRC_PATH}

To run the Rust test suite on an emulated Fuchsia device, you must install the Rust compiler locally. See "Targeting Fuchsia with a compiler built from source" for the steps to build locally.

You'll also need to download a copy of the Fuchsia SDK. The current minimum supported SDK version is 9.20220726.1.1.

Fuchsia's test runner interacts with the Fuchsia emulator and is located at src/ci/docker/scripts/fuchsia-test-runner.py. We can use it to start our test environment with:

src/ci/docker/scripts/fuchsia-test-runner.py start
    --rust ${RUST_SRC_PATH}/install
    --sdk ${SDK_PATH}
    --target-arch {x64,arm64}

Where ${RUST_SRC_PATH}/install is the prefix set in config.toml and ${SDK_PATH} is the path to the downloaded and unzipped SDK.

Once our environment is started, we can run our tests using x.py as usual. The test runner script will run the compiled tests on an emulated Fuchsia device. To run the full tests/ui test suite:

( \
    source config-env.sh &&                                                   \
    ./x.py                                                                    \
    --config config.toml                                                      \
    --stage=2                                                                 \
    test tests/ui                                                             \
    --target x86_64-unknown-fuchsia                                           \
    --run=always --jobs 1                                                     \
    --test-args --target-rustcflags                                           \
    --test-args -L                                                            \
    --test-args --target-rustcflags                                           \
    --test-args ${SDK_PATH}/arch/{x64|arm64}/sysroot/lib                      \
    --test-args --target-rustcflags                                           \
    --test-args -L                                                            \
    --test-args --target-rustcflags                                           \
    --test-args ${SDK_PATH}/arch/{x64|arm64}/lib                              \
    --test-args --target-rustcflags                                           \
    --test-args -Cpanic=abort                                                 \
    --test-args --target-rustcflags                                           \
    --test-args -Zpanic_abort_tests                                           \
    --test-args --remote-test-client                                          \
    --test-args src/ci/docker/scripts/fuchsia-test-runner.py                  \
)

Note: The test suite cannot be run in parallel at the moment, so x.py must be run with --jobs 1 to ensure only one test runs at a time.

When finished, the test runner can be used to stop the test environment:

src/ci/docker/scripts/fuchsia-test-runner.py stop

Debugging

`zxdb`

Debugging components running on a Fuchsia emulator can be done using the console-mode debugger: zxdb. We will demonstrate attaching necessary symbol paths to debug our hello-fuchsia component.

Attaching `zxdb`

In a separate terminal, issue the following command from our hello_fuchsia directory to launch zxdb:

In separate terminal

${SDK_PATH}/tools/${ARCH}/ffx debug connect -- \
    --symbol-path target/x86_64-unknown-fuchsia/debug

--symbol-path gets required symbol paths, which are necessary for stepping through your program.

The "displaying source code in zxdb" section describes how you can display Rust and/or Fuchsia source code in your debugging session.

Using `zxdb`

Once launched, you will be presented with the window:

Connecting (use "disconnect" to cancel)...
Connected successfully.
👉 To get started, try "status" or "help".
[zxdb]

To attach to our program, we can run:

[zxdb] attach hello_fuchsia

Expected output

Waiting for process matching "hello_fuchsia".
Type "filter" to see the current filters.

Next, we can create a breakpoint at main using "b main":

[zxdb] b main

Expected output

Created Breakpoint 1 @ main

Finally, we can re-run the "hello_fuchsia" component from our original terminal:

${SDK_PATH}/tools/${ARCH}/ffx component run \
    --recreate \
    fuchsia-pkg://hello-fuchsia/hello_fuchsia_manifest#meta/hello_fuchsia.cm

Once our component is running, our zxdb window will stop execution in our main as desired:

Expected output

Breakpoint 1 now matching 1 addrs for main
🛑 on bp 1 hello_fuchsia::main() • main.rs:2
   1 fn main() {
 ▶ 2     println!("Hello Fuchsia!");
   3 }
   4
[zxdb]

zxdb has similar commands to other debuggers like gdb. To list the available commands, run "help" in the zxdb window or visit the zxdb documentation.

[zxdb] help

Expected output

Help!

  Type "help <command>" for command-specific help.

Other help topics (see "help <topic>")
...

Displaying source code in `zxdb`

By default, the debugger will not be able to display source code while debugging. For our user code, we displayed source code by pointing our debugger to our debug binary via the --symbol-path arg. To display library source code in the debugger, you must provide paths to the source using --build-dir. For example, to display the Rust and Fuchsia source code:

${SDK_PATH}/tools/${ARCH}/ffx debug connect -- \
    --symbol-path target/x86_64-unknown-fuchsia/debug \
    --build-dir ${RUST_SRC_PATH}/rust \
    --build-dir ${FUCHSIA_SRC_PATH}/fuchsia/out/default

--build-dir links against source code paths, which are not strictly necessary for debugging, but is a nice-to-have for displaying source code in zxdb.

Linking to a Fuchsia checkout can help with debugging Fuchsia libraries, such as fdio.

The rustc book

`aarch64-unknown-fuchsia` and `x86_64-unknown-fuchsia`

Target maintainers

Table of contents

Requirements

Walkthrough structure

Compiling a Rust binary targeting Fuchsia

Targeting Fuchsia with rustup and cargo

Targeting Fuchsia with a compiler built from source

Creating a Fuchsia package

Creating a Fuchsia component

Building a Fuchsia package

Publishing a Fuchsia package

Creating a Fuchsia package repository

Publishing Fuchsia package to repository

Running a Fuchsia component on an emulator

Starting the Fuchsia emulator

Watching emulator logs

Serving a Fuchsia package

Running a Fuchsia component

`.gitignore` extensions

Testing

Running unit tests

Running the compiler test suite

Debugging

`zxdb`

Attaching `zxdb`

Using `zxdb`

Displaying source code in `zxdb`