tools/buildroot: Add support for generating Linux target system images

Integrate buildroot into devlib in order to ease building kernel and
root filesystem images via 'generate-kernel-initrd.sh' helper script.

As its name suggests, the script builds kernel image which also includes
an initial RAM disk per default config files located under
configs/<arch>/.

Provide config files for buildroot and Linux kernel as well as a
post-build.sh script which tweaks (e.g., allowing root login on SSH)
target's root filesystem.

doc/tools.rst talks about details of kernel and rootfs configuration.

Signed-off-by: Metin Kaya <metin.kaya@arm.com>

doc/index.rst

@@ -25,6 +25,7 @@ Contents:
    derived_measurements
    platform
    connection
+   tools
 
 Indices and tables
 ==================

doc/tools.rst

@@ -41,3 +41,45 @@ Android emulator:
    # After ~30 seconds, the emulated device will be ready:
    adb -s emulator-5554 shell "lsmod"
 
+
+Building buildroot
+------------------
+
+``buildroot/generate-kernel-initrd.sh`` helper script downloads and builds
+``buildroot`` per config files located under ``tools/buildroot/configs``
+for the specified architecture.
+
+The script roughly checks out ``2023.11.1`` tag of ``buildroot``, copies config
+files for buildroot (e.g., ``configs/aarch64/arm-power_aarch64_defconfig``) and
+kernel (e.g., ``configs/aarch64/linux.config``) to necessary places under
+buildroot directory, and runs ``make arm-power_aarch64_defconfig && make``
+commands.
+
+As its name suggests, ``generate-kernel-initrd.sh`` builds kernel image with an
+initial RAM disk per default config files.
+
+There is also ``post-build.sh`` script in order to make following tunings on
+root filesystem generated by ``buildroot``:
+- allow root login on SSH.
+- increase number of concurrent SSH connections/channels to let devlib
+  consumers hammering the target system.
+
+In order to keep rootfs minimal, only OpenSSH and util-linux packages
+are enabled in the default configuration files.
+
+DHCP client and SSH server services are enabled on target system startup.
+
+SCHED_MC, SCHED_SMT and UCLAMP_TASK scheduler features are enabled for aarch64
+kernel.
+
+If you need to make changes on ``buildroot``, rootfs or kernel of target
+system, you may want to run commands similar to these:
+
+.. code:: shell
+
+   $ cd tools/buildroot/buildroot-v2023.11.1-aarch64
+   $ make menuconfig    # or 'make linux-menuconfig' if you want to configure kernel
+   $ make
+
+See https://buildroot.org/downloads/manual/manual.html for details.
+

tools/buildroot/.gitignore

@@ -0,0 +1 @@
+buildroot-v2023.11.1-*/

tools/buildroot/configs/aarch64/arm-power_aarch64_defconfig

@@ -0,0 +1,17 @@
+BR2_aarch64=y
+BR2_cortex_a73_a53=y
+BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV=y
+BR2_TARGET_GENERIC_ROOT_PASSWD="root"
+BR2_SYSTEM_DHCP="eth0"
+BR2_ROOTFS_POST_BUILD_SCRIPT="board/arm-power/post-build.sh"
+BR2_LINUX_KERNEL=y
+BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
+BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="board/arm-power/aarch64/linux.config"
+BR2_LINUX_KERNEL_XZ=y
+BR2_PACKAGE_OPENSSH=y
+# BR2_PACKAGE_OPENSSH_SANDBOX is not set
+BR2_PACKAGE_UTIL_LINUX=y
+BR2_PACKAGE_UTIL_LINUX_BINARIES=y
+BR2_TARGET_ROOTFS_CPIO_XZ=y
+BR2_TARGET_ROOTFS_INITRAMFS=y
+# BR2_TARGET_ROOTFS_TAR is not set

tools/buildroot/configs/aarch64/linux.config

@@ -0,0 +1,36 @@
+CONFIG_SCHED_MC=y
+CONFIG_UCLAMP_TASK=y
+CONFIG_SCHED_SMT=y
+CONFIG_KERNEL_XZ=y
+CONFIG_SYSVIPC=y
+CONFIG_IKCONFIG=y
+CONFIG_IKCONFIG_PROC=y
+CONFIG_CGROUPS=y
+CONFIG_BLK_DEV_INITRD=y
+CONFIG_INITRAMFS_SOURCE="${BR_BINARIES_DIR}/rootfs.cpio"
+# CONFIG_RD_GZIP is not set
+# CONFIG_RD_BZIP2 is not set
+# CONFIG_RD_LZMA is not set
+# CONFIG_RD_LZO is not set
+# CONFIG_RD_LZ4 is not set
+# CONFIG_RD_ZSTD is not set
+CONFIG_SMP=y
+# CONFIG_GCC_PLUGINS is not set
+CONFIG_MODULES=y
+CONFIG_MODULE_UNLOAD=y
+CONFIG_NET=y
+CONFIG_PACKET=y
+CONFIG_UNIX=y
+CONFIG_INET=y
+CONFIG_PCI=y
+CONFIG_PCI_HOST_GENERIC=y
+CONFIG_DEVTMPFS=y
+CONFIG_DEVTMPFS_MOUNT=y
+CONFIG_NETDEVICES=y
+CONFIG_VIRTIO_NET=y
+CONFIG_INPUT_EVDEV=y
+CONFIG_SERIAL_AMBA_PL011=y
+CONFIG_SERIAL_AMBA_PL011_CONSOLE=y
+CONFIG_VIRTIO_CONSOLE=y
+CONFIG_VIRTIO_PCI=y
+CONFIG_TMPFS=y

tools/buildroot/configs/post-build.sh

@@ -0,0 +1,15 @@
+#!/bin/sh
+
+set -eux
+
+# Enable root login on SSH
+sed -i 's/#PermitRootLogin.*/PermitRootLogin yes/' "${TARGET_DIR}/etc/ssh/sshd_config"
+
+# Increase the number of available channels so that devlib async code can
+# exploit concurrency better.
+sed -i 's/#MaxSessions.*/MaxSessions 100/' "${TARGET_DIR}/etc/ssh/sshd_config"
+sed -i 's/#MaxStartups.*/MaxStartups 100/' "${TARGET_DIR}/etc/ssh/sshd_config"
+
+# To test Android bindings of ChromeOsTarget
+mkdir -p "${TARGET_DIR}/opt/google/containers/android"
+

tools/buildroot/configs/x86_64/arm-power_x86_64_defconfig

@@ -0,0 +1,16 @@
+BR2_x86_64=y
+BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV=y
+BR2_TARGET_GENERIC_ROOT_PASSWD="root"
+BR2_SYSTEM_DHCP="eth0"
+BR2_ROOTFS_POST_BUILD_SCRIPT="board/arm-power/post-build.sh"
+BR2_LINUX_KERNEL=y
+BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
+BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="board/arm-power/x86_64/linux.config"
+BR2_LINUX_KERNEL_XZ=y
+BR2_PACKAGE_OPENSSH=y
+# BR2_PACKAGE_OPENSSH_SANDBOX is not set
+BR2_PACKAGE_UTIL_LINUX=y
+BR2_PACKAGE_UTIL_LINUX_BINARIES=y
+BR2_TARGET_ROOTFS_CPIO_XZ=y
+BR2_TARGET_ROOTFS_INITRAMFS=y
+# BR2_TARGET_ROOTFS_TAR is not set

tools/buildroot/configs/x86_64/linux.config

@@ -0,0 +1,31 @@
+CONFIG_KERNEL_XZ=y
+CONFIG_SYSVIPC=y
+CONFIG_IKCONFIG=y
+CONFIG_IKCONFIG_PROC=y
+CONFIG_CGROUPS=y
+CONFIG_BLK_DEV_INITRD=y
+CONFIG_INITRAMFS_SOURCE="${BR_BINARIES_DIR}/rootfs.cpio"
+# CONFIG_RD_GZIP is not set
+# CONFIG_RD_BZIP2 is not set
+# CONFIG_RD_LZMA is not set
+# CONFIG_RD_LZO is not set
+# CONFIG_RD_LZ4 is not set
+# CONFIG_RD_ZSTD is not set
+CONFIG_SMP=y
+# CONFIG_GCC_PLUGINS is not set
+CONFIG_MODULES=y
+CONFIG_MODULE_UNLOAD=y
+CONFIG_NET=y
+CONFIG_PACKET=y
+CONFIG_UNIX=y
+CONFIG_INET=y
+CONFIG_PCI=y
+CONFIG_DEVTMPFS=y
+CONFIG_DEVTMPFS_MOUNT=y
+CONFIG_NETDEVICES=y
+CONFIG_VIRTIO_NET=y
+CONFIG_INPUT_EVDEV=y
+CONFIG_SERIAL_8250=y
+CONFIG_SERIAL_8250_CONSOLE=y
+CONFIG_VIRTIO_PCI=y
+CONFIG_TMPFS=y

tools/buildroot/generate-kernel-initrd.sh

@@ -0,0 +1,120 @@
+#!/usr/bin/env bash
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+# Copyright (C) 2024, ARM Limited and contributors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# Forked from LISA/tools/lisa-buildroot-create-rootfs.
+#
+
+set -eu
+
+ARCH="aarch64"
+BUILDROOT_URI="git://git.busybox.net/buildroot"
+KERNEL_IMAGE_NAME="Image"
+
+function print_usage
+{
+	echo "Usage: ${0} [options]"
+	echo "	options:"
+	echo "		-a: set arch (default is aarch64, x86_64 is also supported)"
+	echo "		-p: purge buildroot to force a fresh build"
+	echo "		-h: print this help message"
+}
+
+function set_arch
+{
+	if [[ "${1}" == "aarch64" ]]; then
+		return 0
+	elif [[ "${1}" == "x86_64" ]]; then
+		ARCH="x86_64"
+		KERNEL_IMAGE_NAME="bzImage"
+		return 0
+	fi
+
+	return 1
+}
+
+while getopts "ahp" opt; do
+	case ${opt} in
+	a)
+		shift
+		if ! set_arch "${1}"; then
+			echo "Invalid arch \"${1}\"."
+			exit 1
+		fi
+		;;
+	p)
+		rm -rf "${BUILDROOT_DIR}"
+		exit 0
+		;;
+	h)
+		print_usage
+		exit 0
+		;;
+	*)
+		print_usage
+		exit 1
+		;;
+	esac
+done
+
+# Execute function for once
+function do_once
+{
+	FILE="${BUILDROOT_DIR}/.devlib_${1}"
+	if [ ! -e "${FILE}" ]; then
+		eval "${1}"
+		touch "${FILE}"
+	fi
+}
+
+function br_clone
+{
+	git clone -b ${BUILDROOT_VERSION} -v ${BUILDROOT_URI} "${BUILDROOT_DIR}"
+}
+
+function br_apply_config
+{
+	pushd "${BUILDROOT_DIR}" >/dev/null
+
+	mkdir -p "board/arm-power/${ARCH}/"
+	cp -f "../configs/post-build.sh" "board/arm-power/"
+	cp -f "../configs/${ARCH}/arm-power_${ARCH}_defconfig" "configs/"
+	cp -f "../configs/${ARCH}/linux.config" "board/arm-power/${ARCH}/"
+
+	make "arm-power_${ARCH}_defconfig"
+
+	popd >/dev/null
+}
+
+function br_build
+{
+	pushd "${BUILDROOT_DIR}" >/dev/null
+	make
+	popd >/dev/null
+}
+
+
+BUILDROOT_VERSION=${BUILDROOT_VERSION:-"2023.11.1"}
+BUILDROOT_DIR="$(dirname "$0")/buildroot-v${BUILDROOT_VERSION}-${ARCH}"
+
+do_once br_clone
+
+do_once br_apply_config
+
+br_build
+
+echo "Kernel image \"${BUILDROOT_DIR}/output/images/${KERNEL_IMAGE_NAME}\" is ready."