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Adding Builder Variants using Profiles


This page documents the steps taken to add builders to the ChromeOS testing infrastructure. More specifically, this document will focus on adding new builder variants by adding profiles to existing overlays.

Example CLs are linked throughout this document and are also listed here for quick access:


When changes to the ChromeOS code base are submitted, they are tested with applicable overlays and affected hardware. This process involves automatically building images and running tests with these images on both physical devices and virtual machines.

When more test coverage is desired, changes to the ChromeOS Infrastructure must be made. This can be achieved by adding builders to generate new image variants to be tested. That process is what this document will focus on.

The debug-kernel builders, used for automated debug kernel testing, will be used as an example throughout this document.

The images built by these builders have several additional kernel debugging features enabled. These additional features sacrifice system performance, but provide a vehicle for detecting an array of hard to detect and reproduce bugs - race conditions, improper memory accesses, etc.

The Process

Update Appropriate Overlays

To automatically test new ChromeOS image variants, you first must be able to build them locally. This requires adding profiles to board overlays:

Plan board coverage

Decide which boards you want to add test coverage for. If you need broad coverage, think about which boards differ significantly for your purposes and try to avoid unnecessary overlap. Infrastructure and lab resources are limited, so it is important to think about which boards you really care about. Board overlays are defined in the src/overlays and src/private-overlays directories.

Adding profiles

Add a profile to each overlay you want to create a builder for. This profile will inherit from the overlay's base profile and set the desired build variables. If you plan to add profiles to multiple overlays, see the "Feature Profiles" section below first.

To make your profile inherit from the overlay's base profile, add a parent file containing the line ../base to your new profile directory (Example CL here). package.use files define default USE flag state on a per package basis. For information on other portage profile file types see the Gentoo Portage Profile page

Plan variant details

You also must figure out which build variables you need to set to generate your desired image variants. Typically this will involve setting or masking a USE flag. These can be specified in the profile's package.use file.

For the debug-kernel builders, test coverage was initially only added for Octopus. The only build variable update was enabling USE="debug" for the chromeos-kernel package.

Feature profiles

Feature profiles set the USE flag for every version of a package. You can then use this feature profile as a mix-in for each profile you add to an overlay, ensuring the correct package version will be affected for that overlay. Feature profiles are located in the src/third_party/chromiumos-overlay/profiles/features directory.

For debug-kernel builders, the debug kernel feature profile is located at src/third_party/chromiumos-overly/profiles/features/kernel/debug. This profile contains a package.use file which enables the debug flag for every version of the sys-kernel/chromeos-kernel package. The debug kernel feature profile is then mixed in to the 'debug_kernel' profile in the octopus overlay by adding chromiumos:features/kernel/debug to the parent file. See src/overlays/overlay-octopus/profiles/debug_kernel for this example.

Note that profiles should be public unless there's a specific need to use a private repo (e.g. restrictive licensing, or trying to keep some upcoming new HW or SW secret). However, if a new profile inherits from an existing private profile, it must be in the private repo. Be sure to take into account the fact that settings in private profiles are applied on top of settings in the matching public profile (e.g. octopus-private:base vs. octopus:base).

Testing locally

To verify that the profile you added works, build an image for the corresponding board using your new profile.

  1. setup_board --board=$BOARD --profile=$PROFILE
  2. cros build-packages --board=$BOARD
  3. cros build-image --board=$BOARD -r
  4. Verify that the generated image reflects the updates you specified in the profile.

Update Infra Config

Now that you have successfully created profiles and can build the corresponding images locally, it's time to add builders to the ChromeOS Infrastructure. After the builders are added, your image variants can be generated and used for testing automatically.

To create a new builder, you must define both a new builder and a builder config in the infra config codebase.

Adding new builders

To define a new builder, create a function in infra/config/ which defines the necessary builders and then call your function in infra/config/ There are helper functions in which define common types of builders (cq, postsubmit, etc.) so be sure to look into those options before doing more work than necessary.

It may help to find a builder similar to what you are trying to create and use it as a template. See this CL for an example.

NOTE: It is important that new builders do not upload binary packages. _define_debug_kernel_builder_configs() enforces this by setting packages = None. New builder variants should follow the same behavior.

Adding a new builder config

To define a new builder config, you must add a function in infra/config/builderconfig/ It is here where you can specify which profile the builder should use. You must call this function in as well, ensuring that you call your function defining the builders before defining the corresponding builder configs. The function should look fairly similar to the one which defined the builders themselves.

See _define_debug_kernel_builder_configs() for an example.

Specify test suites to run

To specify which tests suites to run with images built by your builders, you must modify infra/config/builderconfig/ If these tests are expirimental or purely informational, be sure to mark them as non-critical. See this CL for an example.

NOTE: The format of this file has changed substantially since the linked CL was added. Searching for "octopus-debug-kernel" in still provides a good example to follow, however.


To test that you have successfully added builders and corresponding builder configs, run ./ and verify that the changes in the generated files seem to be appropriate.

If more guidance is required after reading this document, please reach out to the ChromeOS Infrastructure team at or message directly.