make_kernel_busybox_image.sh

#!/bin/bash

# Copyright 2020 Amazon.com, Inc. or its affiliates. All Rights Reserved.
# SPDX-License-Identifier: Apache-2.0 OR BSD-3-Clause

# This script illustrates the build steps for kernel images used with the Miniball.

set -e

SOURCE=$(readlink -f "$0")
TEST_RESOURCE_DIR="$(dirname "$SOURCE")"

trap "exit 1" TERM
export TOP_PID=$$

source "$TEST_RESOURCE_DIR/make_busybox.sh"
source "$TEST_RESOURCE_DIR/make_kernel.sh"
source "$TEST_RESOURCE_DIR/configs.sh"

# Reset index for cmdline arguments for the following `getopts`.
OPTIND=1
# Flag for optionally building a guest that halts.
HALT=
# Number of CPUs to use during the kernel build process.
MAKEPROCS=1
# Flag for optionally cleaning the workdir and recompiling the kernel.
CLEAN=
# Working directory. Defaults to a unique tmpdir.
WORKDIR=$(mktemp -d)
# Kernel binary format.
KERNEL_FMT=
# Destination kernel binary name.
KERNEL_BINARY_NAME=

USAGE="
Usage: $(basename $SOURCE) -f (elf|bzimage|pe) [-j nprocs] [-k kernel] [-w workdir] [-c] [-h]

Options:
  -f elf|bzimage|pe    Kernel image format (either elf, bzimage or pe).
  -j nprocs            Number of CPUs to use for the kernel build.
  -k kernel            Name of the resulting kernel image. Has the '-halt' suffix if '-h' is passed.
  -w workdir           Working directory for the kernel build.
  -c                   Clean up the working directory after the build.
  -h                   Create a kernel image that halts immediately after boot.
"
export USAGE

while getopts ":chf:j:k:w:" opt; do
    case "$opt" in
    c)  CLEAN=1
        ;;
    h)  HALT=1
        ;;
    f)  KERNEL_FMT=$(validate_kernel_format "$OPTARG")
        ;;
    j)  MAKEPROCS=$OPTARG
        ;;
    k)  KERNEL_BINARY_NAME=$OPTARG
        ;;
    w)  rm -rf "$WORKDIR"
        WORKDIR=$OPTARG
        ;;
    *)  echo "$USAGE"
        exit 1
    esac
done
shift $((OPTIND-1))

cleanup() {
    if [ -n "$CLEAN" ]; then
        echo "Cleaning $WORKDIR..."
        rm -rf "$WORKDIR"
    fi
}

# Step 0: clean up the workdir, if the user wants to.
cleanup

# Step 1: what are we building?
[ -z "$KERNEL_BINARY_NAME" ] && KERNEL_BINARY_NAME=$(kernel_binary "$KERNEL_FMT")
[ -n "$HALT" ] && KERNEL_BINARY_NAME="$KERNEL_BINARY_NAME-halt"

# Step 2: start from scratch.
mkdir -p "$WORKDIR" && cd "$WORKDIR"

# Step 3: acquire kernel sources & config.
extract_kernel_srcs "$KERNEL_VERSION"
kernel_dir="$WORKDIR/linux-$KERNEL_VERSION"
make_kernel_config "$TEST_RESOURCE_DIR/$KERNEL_CFG" "$kernel_dir"

# Step 4: make the initramfs.
make_busybox "$WORKDIR" "$TEST_RESOURCE_DIR/$BUSYBOX_CFG"   \
    "$BUSYBOX_VERSION" "$MAKEPROCS"
make_initramfs "$kernel_dir" "$WORKDIR/busybox_rootfs" "$HALT"

# Step 5: put them together.
target=$(kernel_target "$KERNEL_FMT")
make_kernel "$kernel_dir" "$KERNEL_FMT" "$target" "$MAKEPROCS" "$KERNEL_BINARY_NAME"

# Final step: profit!
echo "Done!"
echo "Kernel binary placed in: $kernel_dir/$KERNEL_BINARY_NAME"
cleanup
exit 0