This provides information on creating Rust projects for installation within Chrome OS and Chrome OS SDK. All commands and paths given are from within the SDK's chroot.
cros-rust.eclass is an eclass that supports first-party and third-party crate dependencies. Rust project's ebuild should inherit the eclass to support Rust building in Chrome OS build system.
WARNING: Some legacy projects are still using cargo.eclass. These two eclasses can't be used together in a single project. Rust projects with dependencies should all use
cros-rust.eclass.
All the Rust projects using cros-rust.eclass will get dependent crates from /build/${BOARD}/usr/lib/cros_rust_registry instead of crates.io. You'll learn how to publish first-party and third-party crates to cros_rust_registry in the following sections.
To import a third-party crate, we need to create an ebuild for it in ~/chromiumos/src/third_party/chromiumos-overlay/dev-rust/<crate_name>/<crate_name>-<crate_version>.ebuild. For an example crate with SemVer dependencies:
[dependencies] crate1 = "^0.4" crate2 = "^1.2" crate3 = "~1.3"
Here is its ebuild:
# Copyright <copyright_year> The Chromium OS Authors. All rights reserved. # Distributed under the terms of the GNU General Public License v2 EAPI="6" inherit cros-rust DESCRIPTION="An example library" HOMEPAGE="url/to/the/homepage" SRC_URI="https://crates.io/api/v1/crates/${PN}/${PV}/download -> ${P}.crate" LICENSE="|| ( <fill in license> )" SLOT="${PV}/${PR}" KEYWORDS="*" DEPEND=" =dev-rust/crate1-0.4*:= >=dev-rust/crate2-1.2:= !>=dev-rust/crate2-2 =dev-rust/crate3-1.3*:= "
DESCRIPTION, HOMEPAGE, SRC_URI and LICENSE should be found from Cargo.toml or crates.io.cros-rust ebuild and be listed in DEPEND section.ebuild example.ebuild digest to generate Manifest.After creating the ebuild file, running emerge-${BOARD} <crate_name> will install the crate's package to cros-rust-registry.
If some third-party crates are dependent on some unused crates (e.g., dependencies uses by unused features or they're in dev-dependencies) and we want to mock those unused crates out, we could create empty-crate ebuilds for them. Here is an empty ebuild for example crate:
# Copyright <copyright_year> The Chromium OS Authors. All rights reserved. # Distributed under the terms of the GNU General Public License v2 EAPI="6" CROS_RUST_EMPTY_CRATE=1 inherit cros-rust DESCRIPTION="Empty example crate" HOMEPAGE="" LICENSE="BSD-Google" SLOT="${PV}/${PR}" KEYWORDS="*"
You can create your Rust project in anywhere in the Chrome OS system and it's ebuild in a suitable place in chromiumos-overlay with name <category>/<crate_name>-9999.ebuild. Here is an ebuild for an example first-party crate:
# Copyright <copyright_year> The Chromium OS Authors. All rights reserved. # Distributed under the terms of the GNU General Public License v2 EAPI="6" CROS_WORKON_LOCALNAME="example" CROS_WORKON_PROJECT="path/to/project/repository" # We don't use CROS_WORKON_OUTOFTREE_BUILD here since project's Cargo.toml is # using "provided by ebuild" macro which supported by cros-rust. CROS_WORKON_SUBTREE="path/to/project/subtree" inherit cros-workon cros-rust DESCRIPTION="An example first party project" HOMEPAGE="home_page_url" LICENSE="BSD-Google" SLOT="${PV}/${PR}" KEYWORDS="~*" IUSE="test" DEPEND=" dev-rust/third_party_crate:= example2/first_party_crate:= " src_unpack() { cros-workon_src_unpack S+="/path/to/project/subtree" cros-rust_src_unpack } src_compile() { ecargo_build use test && ecargo_test --no-run } src_test() { if use x86 || use amd64; then ecargo_test else elog "Skipping rust unit tests on non-x86 platform" fi } src_install() { # You can # 1. Publish this library for other first-party crates by cros-rust_publish "${PN}" "$(cros-rust_get_crate_version)" # 2. Install the binary to image by dobin "$(cros-rust_get_build_dir)/example_bin" }
If the Rust project will be used by other first-party crates, remember to publish it by using the cros-rust_publish command.
WARNING: Please make sure your project could be built by both steps for engineering productivity:
From chroot with
emerge-${BOARD} CRATE-EBUILD-NAMETips: You can set
USE=-ltoto speed up build times when using emerge. This turns off link time optimization, which is useful for release builds but significantly increases build times and isn't really needed during development.From project root directory with
cargo buildWe add two macros to resolve conflicts between these two build system. Check details from the following section.
Using cros-rust ebuild could support building crates in Chrome OS build system, but it will break local cargo build in some situations. We add two macros which are recognized by ebuild for Cargo.toml to keep both build system work.
Provided by ebuild
This macro introduces a replacement of:
[dependencies] data_model = { path = "../data_model" } # provided by ebuild
with:
[dependencies] data_model = { version = "*" }
Example usage: Add dependency to first-party crate
Cargo.toml but with # provided by ebuild macro:[dependencies] data_model = { path = "../data_model" } # provided by ebuild
Ignored by ebuild
We will use this to discard parts of [patch.crates-io] which should be applied to local developer builds but not to ebuilds.
This macro introduces a replacement of:
audio_streams = { path = "../../third_party/adhd/audio_streams" } # ignored by ebuild
with empty line while building with emerge.
Example usage: Add dependency to first-party crate for sub-crates from root crate.
[patch.crates-io] section in root crate's Cargo.toml but with # ignored by ebuild macro:[patch.crates-io] audio_streams = { path = "../../third_party/adhd/audio_streams" } # ignored by ebuild
Because the sources for all ebuilds in Chrome OS must be available at localmirror, you will have to upload all third-party crate dependencies for the project to localmirror.
The following will download a crate, upload it to localmirror, and make it accessible for download:
WARNING: localmirror is shared by all Chrome OS developers. If you break it, everybody will have a bad day.
curl -L 'https://crates.io/api/v1/crates/<crate_name>/<crate_version>/download' >/tmp/crates/<crate_name>-<crate_version>.crate gsutil cp -a public-read /tmp/crates/<crate_name>-<crate_version>.crate gs://chromeos-localmirror/distfiles/
The toolchain that is installed by default is targetable to the following triples:
| Target Triple | Description |
|---|---|
x86_64-pc-linux-gnu | (default) Used exclusively for packages installed in the chroot |
armv7a-cros-linux-gnueabihf | Used by 32-bit usermode ARM devices |
aarch64-cros-linux-gnu | Used by 64-bit usermode ARM devices (none of these exist as of November 30th, 2018) |
x86_64-cros-linux-gnu | Used by x86_64 devices |
When building Rust projects for development, a non-default target can be selected as follows:
cargo build --target=<target_triple>
If a specific board is being targeted, that board's sysroot can be used for compiling and linking purposes by setting the SYSROOT environment variable as follows:
export SYSROOT="/build/<board>"
If C files are getting compiled with a build script that uses the cc or gcc crates, you may also need to set the TARGET_CC environment variable to point at the appropriate C compiler.
export TARGET_CC="<target_triple>-clang"
If a C/C++ package is being pulled in via pkg-config, the PKG_CONFIG_ALLOW_CROSS environment variable should be exposed. Without this, you might see CrossCompilation as part of an error message during build script execution.
export PKG_CONFIG_ALLOW_CROSS=1