docs/fuchsia_build_instructions.md

# Checking out and building on Fuchsia

***Note that the Fuchsia port is in the early stages, and things are likely to
frequently be broken. Try #cr-fuchsia on Freenode or Slack if something seems
awry.***

There are instructions for other platforms linked from the
[get the code](get_the_code.md) page.

[TOC]

## System requirements

*   A 64-bit Intel machine with at least 8GB of RAM. More than 16GB is highly
    recommended.
*   At least 100GB of free disk space.
*   You must have Git and Python installed already.

Most development is done on Ubuntu. Mac build is supported on a best-effort
basis.

## Install `depot_tools`

Clone the `depot_tools` repository:

```shell
$ git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
```

Add `depot_tools` to the end of your PATH (you will probably want to put this
in your `~/.bashrc` or `~/.zshrc`). Assuming you cloned `depot_tools` to
`/path/to/depot_tools`:

```shell
$ export PATH="$PATH:/path/to/depot_tools"
```

## Get the code

Create a `chromium` directory for the checkout and change to it (you can call
this whatever you like and put it wherever you like, as long as the full path
has no spaces):

```shell
$ mkdir ~/chromium && cd ~/chromium
```

Run the `fetch` tool from depot_tools to check out the code and its
dependencies.

```shell
$ fetch --nohooks chromium
```

Expect the command to take 30 minutes on even a fast connection, and many
hours on slower ones.

If you've already installed the build dependencies on the machine (from another
checkout, for example), you can omit the `--nohooks` flag and `fetch`
will automatically execute `gclient runhooks` at the end.

When `fetch` completes, it will have created a hidden `.gclient` file and a
directory called `src` in the working directory.

### Configure for building on Fuchsia

Edit `.gclient` to include (this is a list, so it could also include `android`,
etc. if necessary.)

```
target_os = ['fuchsia']
```

Note that this should be added as a top-level statement in the `.gclient` file,
not an entry inside the `solutions` dict. An example `.gclient` file would look
as follows:

```
solutions = [
  {
    "url": "https://chromium.googlesource.com/chromium/src.git",
    "managed": False,
    "name": "src",
    "custom_deps": {},
    "custom_vars": {}
  }
]
target_os = ['fuchsia']
```

You will then need to run:

```shell
$ gclient sync
```

This makes sure the Fuchsia SDK is available in third\_party and keeps it up to
date.

The remaining instructions assume you have switched to the `src` directory:

```shell
$ cd src
```

### (Linux-only) Install any required host packages

Chromium relies on some platform packages to be present in order to build.
You can install the current set of required packages with:

```shell
$ build/install-build-deps.sh
```

Note that you need to do this only once, and thereafter only if new dependencies
are added - these will be announced to the chromium-dev@ group.

### Update your checkout

To update an existing checkout, you can run

```shell
$ git rebase-update
$ gclient sync
```

The first command updates the primary Chromium source repository and rebases
any of your local branches on top of tip-of-tree (aka the Git branch
`origin/master`). If you don't want to use this script, you can also just use
`git pull` or other common Git commands to update the repo.

The second command syncs dependencies to the appropriate versions and re-runs
hooks as needed. `gclient sync` updates dependencies to the versions specified
in `DEPS`, so any time that file is modified (pulling, changing branches, etc.)
`gclient sync` should be run.

## (Mac-only) Download additional required Clang binaries

Go to [this page](https://chrome-infra-packages.appspot.com/p/fuchsia/clang/mac-amd64/+/)
and download the most recent build. Extract `bin/llvm-ar` to the clang folder
in Chromium:

```shell
$ unzip /path/to/clang.zip bin/llvm-ar -d ${CHROMIUM_SRC}/third_party/llvm-build/Release+Asserts
```

## Setting up the build

Chromium uses [Ninja](https://ninja-build.org) as its main build tool along with
a tool called [GN](https://gn.googlesource.com/gn/+/master/docs/quick_start.md)
to generate `.ninja` files. You can create any number of *build directories*
with different configurations. To create a build directory, run:

```shell
$ gn gen out/fuchsia --args="is_debug=false dcheck_always_on=true is_component_build=false target_os=\"fuchsia\""
```

You can also build for Debug, with `is_debug=true`, but since we don't currently
have any Debug build-bots, it may be more broken than Release.

`use_goma=true` is fine to use also if you're a Googler.

Architecture options are x64 (default) and arm64. This can be set with
`target_cpu=arm64`.

## Build

All targets included in the GN build should build successfully. You can also
build a specific binary, for example, base\_unittests:

```shell
$ autoninja -C out/fuchsia base_unittests
```

(`autoninja` is a wrapper that automatically provides optimal values for the
arguments passed to `ninja`.)

## Run

Once you've built a package, you'll want to run it!

### (Recommended)(Linux-only) Enable KVM acceleration

Under Linux, if your host and target CPU architectures are the same (e.g. you're
building for Fuchsia/x64 on a Linux/x64 host) then you can benefit from QEMU's
support for the KVM hypervisor:

1. Install the KVM module for your kernel, to get a /dev/kvm device.
2. Ensure that your system has a "kvm" group, and it owns /dev/kvm.
You can do that by installing the QEMU system common package:
```shell
$ sudo apt-get install qemu-system-common
```
3. Add users to the "kvm" group, and have them login again, to pick-up the new
group.
```shell
$ sudo adduser <user> kvm
$ exit
[log in again]
```

### Running test suites

Building test suites generate a launcher script to run them on an emulator
or a physical device. These scripts are generated at `out/fuchsia/bin`. For
instance,to run the `base_unittests` target, launch:

```shell
$ out/fuchsia/bin/run_base_unittests
```

Common gtest arguments such as `--gtest_filter=...` are supported by the run
script. The launcher script also symbolizes backtraces.

The test suite, by default, will run on QEMU. AEMU can be used for running
tests that interact with Fuchsia's window manager, Scenic. To change the device
that Fuchsia will run on, use `--device={aemu|qemu|device}`.

To run a test suite on an *unprovisioned device* in a zedboot state, simply add
`-d` to the test runner script arguments. Subsequent runs of the test runner
script will be able to pick up the same device.

To run a test suite on a device that is *already provisioned*, add the following
arguments to the test runner script:

* `-d` to run the test suite on a device.
* `--fuchsia-out-dir=[/path/to/fuchsia/out/directory]` or
  `--ssh-config=[/path/to/ssh_config]` to specify the SSH configuration used for
  connecting to the target device.
* (Optional) `--host=[IP]` to specify the test device IP. Typically, this is the
value obtained from the command `fx netaddr --fuchsia`.
* (Optional) `--port=[port]` to specify the SSH port, if different from 22.

### Troubleshooting a test

To troubleshoot a specific test, consider a combination of the following
arguments to the test runner script:

* `--gtest_filter="[TestSuite.TestName]"` to only run a specific test, or a
  comma-separated list to run a set of tests. Wildcards can also be used to run
  a set of tests or an entire test suite, e.g. `--gtest_filter="[TestSuite.*]"`.
* `--test-launcher-jobs=1` to only have one batch of tests running at a time.
  This bypasses the test launcher buffering of test log output, making it
  possible to access the log output from successful test runs.
* `--single-process-tests` to run all the tests in the same process. Unlike the
  above option, this will run the tests directly in the test launcher process,
  making it easier to attach a debugger.
* `system-log-file=[/path/to/syslog]` to specify the file to write system logs
  to. Or `system-log-file=-` to write the system logs to stdout. By default,
  Chromium logs are written to the system log on Fuchsia. This argument is known
  to cause `IOError` python exceptions with a QEMU target.
* `--gtest_repeat=[number] --gtest_break_on_failure` to run a test or test suite
  a certain number of times until it fails. This is useful to investigate flaky
  tests.