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Initial K-Boot support
K-Boot is a bootloader based on Linux kexec. The binary is generated from these projects: - linux (external project) - busybox (external project) - kexec-tools (external project) - kbootd K-Boot doesn't manage linux project neither provide the defconfig, the user take care of the linux project and must follow "Linux requirements" section from the README. busybox and kexec-tools project have been added as git submodules: - busybox: version 1.36.0 - kexec-tools: version 2.0.26 The reference HEAD will always point to the latest release. K-Boot daemon (kbootd) is executed by init and fulfilled these tasks: - read/write on MMC - read/list MMC partitions - read/write on USB (fastboot gadget) - support main fastboot commands (erase, flash, getvar, reboot ...) - multi-thread flashing (one thread read USB, one thread write MMC) - extract Boot Android partition: Kernel, ramdisk, dtb and cmdline Once we have extracted all Android components, kexec will boot on Android kernel. All the compilation is done through build scripts (build instructions in the README). In the future we will add the support for different SoC or linux distribution, most of the part are already generic. Signed-off-by: Julien Masson <[email protected]>
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‎.github/workflows/ci.yml

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name: CI
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on: pull_request
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jobs:
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lint:
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name: Lint
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runs-on: ubuntu-latest
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strategy:
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matrix:
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path:
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- 'kbootd'
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steps:
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- uses: actions/checkout@v3
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- name: Run clang-format
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uses: jidicula/[email protected]
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with:
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clang-format-version: '13'
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check-path: ${{ matrix.path }}
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build:
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name: Build
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runs-on: ubuntu-latest
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steps:
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- name: Set up environment
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run: |
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sudo apt update
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sudo apt install meson
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- uses: actions/checkout@v3
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with:
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submodules: 'true'
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- name: Download musl toolchain
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run: |
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mkdir toolchain
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cd toolchain
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wget https://musl.cc/aarch64-linux-musl-cross.tgz
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tar zxvf aarch64-linux-musl-cross.tgz
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echo "$PWD/aarch64-linux-musl-cross/bin" >> $GITHUB_PATH
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- name: Build busybox
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run: |
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./build/build_busybox.sh
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- name: Build kexec
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run: |
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./build/build_kexec.sh
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- name: Build kbootd
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run: |
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./build/build_kbootd.sh

‎.gitignore

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initramfs/bin/busybox
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initramfs/bin/kbootd
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initramfs/bin/kexec
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k-boot-*.bin

‎.gitmodules

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[submodule "kexec-tools"]
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path = kexec-tools
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url = https://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
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[submodule "busybox"]
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path = busybox
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url = https://git.busybox.net/busybox

‎README.md

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# K-Boot
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K-Boot is a bootloader based on Linux kexec.
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There is several benefits with this kind of bootloader solution:
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- no need to duplicate/integrate drivers from Kernel
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- no need to maintain another bootloader project
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- same kernel source code used between Linux and K-Boot
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- better boot/flashing performance
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- easier to extend or debug (many tools available)
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- use/contribute existing reliable projects
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For now K-Boot target only `arm64` hardware.
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### Setup environment
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Fetch K-Boot project:
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``` console
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$ git clone --recurse-submodules [email protected]:baylibre/k-boot.git
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```
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Download toolchains and add to `$PATH`:
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``` console
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# aarch64-linux-musl toolchain for userspace binaries
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$ wget https://musl.cc/aarch64-linux-musl-cross.tgz
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$ tar zxvf aarch64-linux-musl-cross.tgz
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# aarch64-none-linux toolchain for linux
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$ wget https://developer.arm.com/-/media/Files/downloads/gnu-a/10.3-2021.07/binrel/gcc-arm-10.3-2021.07-x86_64-aarch64-none-linux-gnu.tar.xz
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$ tar -xvf gcc-arm-10.3-2021.07-x86_64-aarch64-none-linux-gnu.tar.xz
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```
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### Linux requirements
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K-Boot doesn't manage linux project neither provide the defconfig.
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However the user must set in the defconfig:
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```
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CONFIG_INITRAMFS_SOURCE="usr/initramfs/setup"
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CONFIG_KEXEC=y
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```
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### Build K-Boot
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``` console
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$ ./build/build_all.sh --linux=~/src/linux --defconfig=kboot_defconfig
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```
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All others build scripts can be run independently (`--help` for more infos).
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### Intregration with Arm Trusted Firmware (ATF)
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In the ARM boot flow, K-Boot will be used as `BL33`.
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According to [Booting AArch64 Linux](https://docs.kernel.org/arm64/booting.html):
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> Primary CPU general-purpose register settings:
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> - x0 = physical address of device tree blob (dtb) in system RAM.
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Thus the device tree must be loaded before booting to K-Boot and `x0` must be set to the physical address where the device tree has been loaded.
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This task can be fulfilled by the `BL2`.
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ATF Boot Flow example with K-Boot:
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1. MMC BOOT0 contains BL2 + Device Tree for K-Boot
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2. BL1 (ROM code) copy MMC BOOT0 to SRAM
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3. BL1 jump to SRAM and execute BL2
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4. BL2 initialize DDR, extract from fip image: BL31 (pm runtime services), BL32 (OP-TEE) and BL33 (K-Boot)
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5. BL2 copy the Device Tree for K-Boot found in SRAM to DDR and set x0 register
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6. BL2 jump to BL31
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7. BL31 boot and jump to OP-TEE
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8. OP-TEE boot and jump to K-Boot
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9. K-Boot kernel start, find init process in initramfs and execute K-Boot daemon (kbootd)
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### Tips
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Send `kbootd` over serial:
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``` console
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# On host
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$ sx kbootd < /dev/ttyUSB0 > /dev/ttyUSB0
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# On device, make sure kbootd is not running
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# rx /bin/kbootd
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```
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### Contributions
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`kbootd` coding style:
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``` console
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$ clang-format -i kbootd/src/*
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```

‎build/build_all.sh

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#!/bin/bash
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set -e
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set -u
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set -o pipefail
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SRC=$(dirname "$(readlink -e "$0")")
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source "${SRC}/build_busybox.sh"
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source "${SRC}/build_kbootd.sh"
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source "${SRC}/build_kexec.sh"
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source "${SRC}/build_linux.sh"
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source "${SRC}/utils.sh"
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function build_all {
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local clean="$1"
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local mode="$2"
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local linux="$3"
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local defconfig="$4"
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build_busybox "${clean}" "${mode}"
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build_kexec "${clean}" "${mode}"
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build_kbootd "${clean}" "${mode}"
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build_linux "$@"
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cp "${linux}/arch/arm64/boot/Image" "${ROOT}/k-boot-${mode}.bin"
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}
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function usage {
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cat <<DELIM__
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usage: $(basename "$0") [options]
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$ $(basename "$0") --linux=~/src/linux --defconfig=kboot_defconfig
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Options:
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--linux Linux project path
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--defconfig Linux defconfig
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--clean (OPTIONAL) clean before build
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--mode (OPTIONAL) [release|debug|factory] mode (default: release)
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--help (OPTIONAL) display usage
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DELIM__
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}
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function main {
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local script=$(basename "$0")
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local build="${script%.*}"
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local clean=false
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local defconfig=""
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local linux=""
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local mode="release"
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local opts_args="clean,defconfig:,help,linux:,mode:"
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local opts=$(getopt -o '' -l "${opts_args}" -- "$@")
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eval set -- "${opts}"
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while true; do
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case "$1" in
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--clean) clean=true; shift ;;
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--defconfig) defconfig="$2"; shift 2 ;;
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--linux) linux=$(find_path "$2"); shift 2 ;;
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--mode) mode="$2"; shift 2 ;;
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--help) usage; exit 0 ;;
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--) shift; break ;;
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esac
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done
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# check arguments
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[ -z "${linux}" ] && error_usage_exit "Cannot find linux project"
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[ -z "${defconfig}" ] && error_usage_exit "defconfig not provided"
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! [[ " ${MODES[*]} " =~ " ${mode} " ]] && error_usage_exit "${mode} mode not supported"
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# build
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build_all "${clean}" "${mode}" "${linux}" "${defconfig}"
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}
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if [ "$0" = "$BASH_SOURCE" ]; then
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main "$@"
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fi

‎build/build_busybox.sh

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#!/bin/bash
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set -e
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set -u
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set -o pipefail
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SRC=$(dirname "$(readlink -e "$0")")
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source "${SRC}/utils.sh"
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BUSYBOX="${ROOT}/busybox"
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function build_busybox {
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local clean="$1"
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local mode="$2"
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display_current_build "busybox" "${mode}"
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pushd "${BUSYBOX}"
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export CROSS_COMPILE=aarch64-linux-musl-
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[[ "${clean}" == true ]] && make clean
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[ ! -f .config ] && make defconfig
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make -j"$(nproc)" LDFLAGS="--static"
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cp busybox "${INITRAMFS}/bin/"
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unset CROSS_COMPILE
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popd
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}
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if [ "$0" = "$BASH_SOURCE" ]; then
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main "$@"
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fi

‎build/build_kbootd.sh

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#!/bin/bash
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set -e
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set -u
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set -o pipefail
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SRC=$(dirname "$(readlink -e "$0")")
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source "${SRC}/utils.sh"
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KBOOTD="${ROOT}/kbootd"
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function build_kbootd {
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local clean="$1"
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local mode="$2"
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display_current_build "kbootd" "${mode}"
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pushd "${KBOOTD}"
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export CROSS_COMPILE=aarch64-linux-musl-
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[[ "${clean}" == true ]] && rm -rf build
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if [ ! -d build ]; then
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meson setup build --prefix "${INITRAMFS}" --cross-file meson.cross
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fi
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ninja -C build install
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unset CROSS_COMPILE
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popd
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}
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if [ "$0" = "$BASH_SOURCE" ]; then
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main "$@"
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fi

‎build/build_kexec.sh

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#!/bin/bash
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set -e
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set -u
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set -o pipefail
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SRC=$(dirname "$(readlink -e "$0")")
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source "${SRC}/utils.sh"
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KEXEC="${ROOT}/kexec-tools"
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function build_kexec {
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local clean="$1"
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local mode="$2"
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display_current_build "kexec" "${mode}"
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pushd "${KEXEC}"
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export CROSS_COMPILE=aarch64-linux-musl-
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[[ "${clean}" == true ]] && make clean
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[ ! -f configure ] && ./bootstrap
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[ ! -f Makefile ] && LDFLAGS=-static ./configure --host=aarch64-linux-musl
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make -j"$(nproc)"
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aarch64-linux-musl-strip build/sbin/kexec
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cp build/sbin/kexec "${INITRAMFS}/bin/"
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unset CROSS_COMPILE
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popd
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}
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if [ "$0" = "$BASH_SOURCE" ]; then
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main "$@"
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fi

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