There are no additional host dependencies. The Bazel toolchain and environment are provided through repo sync. The corresponding entries are in the kernel manifests.
As a convenience, installing a bazel host package allows the use of the bazel command from anywhere in the tree (as opposed to using tools/bazel from the top of the workspace) while still ensuring the correct version of the toolchain drives the build. That works because Bazel binaries by convention search for an executable at $(dirname WORKSPACE)/tools/bazel and defer execution to that if existing. (Similarly, tools/ could be added to PATH, but this creates a dependency on that particular checked out workspace if used across workspaces and also adds additional executables from tools/ to PATH. Hence, this method is not recommended.)
Android Common Kernels define at least a ‘kernel’ rule as part of the build definition in the common/ subdirectory. Building just a kernel is therefore as simple as
$ tools/bazel build //common:kernel
Installing a host version of Bazel allows using that from PATH as a convenience wrapper without affecting hermeticity. For example, you may install bazel with apt:
$ apt-get install bazel
With a bazel in PATH, this reduces to
$ bazel build //common:kernel
and this command can be executed from any subdirectory below the top level workspace directory.
//common:kernel refers by convention to the default kernel target and in the case of the Android Common Kernels (GKI), this will usually be an alias for kernel_aarch64. Further targets can be discovered via bazel's query subcommand:
$ bazel query "kind('py_binary', //common:*)"
Copy build artifacts to DIST_DIR for distribution by running the following command.
$ tools/bazel run //common:kernel_dist
You may override the destination of distribution directory in the command line via the --dist_dir argument. The --dist_dir is an argument to the copy_to_dist_dir script, not to Bazel. Hence, put them after the -- delimiter.
$ tools/bazel run //common:kernel_dist -- --dist_dir=out/dist
$ tools/bazel run //common-modules/virtual-device:virtual_device_x86_64_dist
The kernel_build() macro provided by this package is to be used in BUILD.bazel build files to define kernel build targets. The simplest example is (defining the GKI build):
load("//build/kernel/kleaf:kernel.bzl", "kernel_build")
kernel_build(
name = "kernel",
outs = ["vmlinux"],
build_config = "common/build.config.gki.aarch64",
srcs = glob(["**"]),
)
The kernel_module() macro defines a kernel module target. Example:
load("//build/kernel/kleaf:kernel.bzl", "kernel_module")
kernel_module(
name = "nfc",
srcs = glob(["**"]),
outs = [
"nfc.ko",
],
kernel_build = "//common:kernel",
)
See instructions to build your own kernels and drivers with Bazel in Build your kernels and drivers with Bazel.
See API Reference and Documentation for all rules
Kleaf is available for Android 13 and later kernels.
Question: How can I try it out?
With a recent repo checkout of common-android-mainline, the simplest invocation is tools/bazel build //common:kernel.
Question: Are BUILD_CONFIG files still a thing?
Yes! build.config files still describe the build environment. Though they get treated as hermetic input. Further, some features might not be supported yet or never will be as they do not make sense in a Bazel-based build (e.g. SKIP_MRPROPER is implicit).
Question: Why the name “Kleaf”?
The Android Platform Build with Bazel is sometimes referred to as Roboleaf (Robo=Android, Bazel...Basil...Leaf). The kernel variant of that is Kleaf.