Chromium OS Docs

GN in platform2

New packages should use GN, not GYP, to build binaries.

See the official step-by-step introduction for the GN basics. This article discusses platform2 specific stuff.

How to build your package with GN

Example: arc/adbd/BUILD.gn

  • Put BUILD.gn in your package directory, which is determined by PLATFORM_SUBDIR in your ebuild. Existence of BUILD.gn indicates to the platform2 build system that GN should be used to build this package.
  • Have a target named "all" in the BUILD.gn. It‘s the root target built by the platform2 build system. Typically it’s a group target depends on all the targets to be built.
  • common-mk/ contains common templates or common settings, which your build files can utilize.
    • pkg_config.gni defines the pkg_config rule to generate configs for package dependencies.
    • BUILDCONFIG.gn defines the default configs for each target type (e.g. executable). You can remove default configs in individual target with configs -= if needed (example: hammard/BUILD.gn). (TODO(oka): Replace the URL after the CL is submitted)

How to write ebuilds

Example: arc-adbd-9999.ebuild

Note we should add .gn in CROS_WORKON_SUBTREE so that the platform2 build system can access the file.

How to check USE flags in GN

Example: hammerd/BUILD.gn (TODO(oka): update the link after the CL is submitted)

In GN files, USE flags can be referred as use.foo.

Only whitelisted USE flags can be used. If you need to use new USE flags, update the following files:

  • _IUSE constant in platform2/common-mk/platform2.py
  • IUSE variable in your ebuild file

How to write unit tests

use.test flag is set to true on unit testing. Enclose test only targets with if (use.test) {} to reduce compile time on production. The test targets are typically executables which depend on //common-mk:test to use gtest and gmock.

How to run unit tests is same as before: In chroot, run cros_workon --board=$BOARD start $package_name if you haven't. Then run

cros_workon_make --board=$BOARD --test $package_name

.

Prepend VERBOSE=1 to see the commands run by GN (plus other logs).