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Microdroid kernel

This directory contains prebuilt images of the Linux kernel that is used in Microdroid. The kernel is built from the same source tree as Generic Kernel Image (GKI), but with a different config where most of the config items are turned off to make the kernel fast & slim.

How to build the Microdroid kernels

Checkout the GKI source code.

repo init -u https://android.googlesource.com/kernel/manifest -b common-android15-6.6
repo sync

Build the Microdroid kernels manually

For ARM64

tools/bazel clean
tools/bazel run --config=fast //common:kernel_aarch64_microdroid_dist -- --destdir=out/dist

For x86_64,

tools/bazel clean
tools/bazel run --config=fast //common:kernel_x86_64_microdroid_dist -- --destdir=out/dist

Note that --config=fast is not mandatory, but will make your build much faster.

The build may fail in case you are doing an incremental build and the config has changed (b/257288175). Until that issue is fixed, do the clean build by invoking tools/bazel clean before the build command.

Change the kernel configs

For ARM64

tools/bazel run //common:kernel_aarch64_microdroid_config -- menuconfig

For x86_64

tools/bazel run //common:kernel_x86_64_microdroid_config -- menuconfig

How to update Microdroid kernel prebuilts

For manually built kernels (only for your own development)

Copy the built kernel image to the Android source tree directly, and build the virt APEX.

For ARM64,

cp out/dist/Image <android_checkout>/packages/modules/Virtualization/guest/kernel/android15-6.6/arm64/kernel-6.6

For x86_64,

cp out/dist/bzImage <android_checkout>/packages/modules/Virtualization/guest/kernel/android15-6.6/x86_64/kernel-6.6

For new kernel versions added that did not exist before

Make a new directory with the Android version and the kernel version.

mkdir -p <android_checkout>/packages/modules/Virtualization/guest/kernel/android17-6.18/

Then add a directory for each architecture (arm64 | x86_64) and copy the kernels.

Modify the Android.bp select statements to include the new kernels.

Finally, modify https://source.corp.google.com/h/googleplex-android/platform/superproject/main/+/main:build/release/flag_values/trunk_staging/RELEASE_AVF_MICRODROID_KERNEL_VERSION.textproto;l=3?q=RELEASE_AVF_MICRODROID_KERNEL_VERSION&sq=git:googleplex-android%2Fplatform%2Fsuperproject%2Fmain@refs%2Fheads%2Fmain

Debugging microdroid using GDB

Debugging documentation located at:

<android_checkout>/packages/modules/Virtualization/docs/debug/gdb_kernel.md

For official updates

Use the download_from_ci script to automatically fetch the built images from a specific <build_id> and make commits with nice history in the message.

cd <android_checkout>/packages/modules/Virtualization
repo start <topic_name>
cd <kernel_checkout>
ANDROID_BUILD_TOP=<android_checkout> ./build/kernel/gki/download_from_ci  --update-microdroid -b <bug_id> <build_id>
cd <android_checkout>/packages/modules/Virtualization
repo upload .