scripts/debian/create-efi-kernel

#!/bin/sh

# EFI related vars
EFI_BASE_LABEL="Debian unified"
EFI_MOUNT_PATH="/boot/efi"

temp_efi_list_file="/tmp/efibootmgr.label.entry.temp"

# OS related vars
ROOT_UUID=$(findmnt -kno UUID /)
ROOT_FSTYPE=$(findmnt -kno FSTYPE /)
CRYPT_PART_UUID=$(blkid | sed -n 's;/dev/.*_crypt.*UUID="\(.*\)".*TYPE=.*;\1;p')

temp_kernel_list_file="/tmp/kernel.list.temp"
temp_kernel_command_file="/tmp/kernel.command.temp"


# Clean old entries {{{

## Install efibootmgr tool if not available
command -v efibootmgr > /dev/null || aptitude install -y efibootmgr

## Get all old entries list with base label
rm -f -- "${temp_efi_list_file}" ; touch "${temp_efi_list_file}"
efibootmgr | grep -E ".*${EFI_BASE_LABEL}.*" | cut -c 5-8 > "${temp_efi_list_file}"

## Remove all matching entries
while IFS= read -r OLD_EFI_ENTRY; do
	printf "%s\n" "Deleting efiboot entry ${OLD_EFI_ENTRY}"
	efibootmgr --delete-bootnum --bootnum "${OLD_EFI_ENTRY}" > /dev/null || exit 1
	#printf "%s\n" "efibootmgr --delete-bootnum --bootnum ${EFI_ENTRY}"
done < "${temp_efi_list_file}"
# }}}
# Clean old kernels {{{
## Rename last version of generic kernel for backup
mv -- "${EFI_MOUNT_PATH}/EFI/debian/linux.debian.efi" "${EFI_MOUNT_PATH}/EFI/debian/backup.debian.efi.$(date +%Y%m%d-%H%M)"
## Keep only the 4 more recent backup kernels
find "${EFI_MOUNT_PATH}/EFI/debian" -type f -iname "backup.debian.efi.*" | sort --reverse --numeric-sort -- | tail --lines=+5 -- | xargs --replace={} rm -- {}

## Remove all previous unified kernels with version in filename
find "${EFI_MOUNT_PATH}/EFI/debian" -type f -iname "linux.debian.*.efi" -delete
# }}}

# Create unified kernels blob and efiboot entries {{{

## Install objcopy tool if not available
command -v objcopy > /dev/null || aptitude install -y binutils

## Put Kernel command line in temp file
rm -f -- "${temp_kernel_command_file}" ; touch "${temp_kernel_command_file}"
printf "%s" "root=UUID=${ROOT_UUID} rootfstype=${ROOT_FSTYPE} add_efi_memmap \
ro cryptdevice=UUID=${CRYPT_PART_UUID}:lvm" >> "${temp_kernel_command_file}"

## Get all kernel versions starting with the oldest
rm -f -- "${temp_kernel_list_file}" ; touch "${temp_kernel_list_file}"
ls -1tr /boot/vmlinuz-* >> "${temp_kernel_list_file}"

## For each version of the kernel {{{
while IFS= read -r KERNEL; do
	### Get kernel version
	KERNEL_VERSION=$(printf "%s" "${KERNEL}" | sed 's;.*vmlinuz-\(.*\);\1;')

	### Ensure EFI device is mounted (excluding systemd-automount line)
	if ! mount | grep -v "autofs" | grep --quiet "${EFI_MOUNT_PATH}"; then
		mount "${EFI_MOUNT_PATH}" || exit 2
	fi

	ESP=$(findmnt -kno SOURCE "${EFI_MOUNT_PATH}" | grep -v systemd | sed s-/dev/--)
	ESP_DISK=$(lsblk /dev/"${ESP}" -no pkname)
	ESP_PART=$(cat /sys/class/block/"${ESP}"/partition)

	### Calculate address values to use for each section
	osrel_offs=$(objdump -h "/usr/lib/systemd/boot/efi/linuxx64.efi.stub" | awk 'NF==7 {size=strtonum("0x"$3); offset=strtonum("0x"$4)} END {print size + offset}')
	cmdline_offs=$((osrel_offs + $(stat -Lc%s "/usr/lib/os-release")))
	linux_offs=$((cmdline_offs + $(stat -Lc%s "${temp_kernel_command_file}")))
	initrd_offs=$((linux_offs + $(stat -Lc%s "/boot/vmlinuz-6.3.0-1-amd64")))

	### Create a unified kernel

	printf "%s\n" "Creating unified kernel for version ${KERNEL_VERSION}..."
	objcopy \
		--add-section .osrel="/usr/lib/os-release" --change-section-vma .osrel=$(printf 0x%x $osrel_offs) \
		--add-section .cmdline="${temp_kernel_command_file}" --change-section-vma .cmdline=$(printf 0x%x $cmdline_offs) \
		--add-section .linux="/boot/vmlinuz-${KERNEL_VERSION}" --change-section-vma .linux=$(printf 0x%x $linux_offs) \
		--add-section .initrd="/boot/initrd.img-${KERNEL_VERSION}" --change-section-vma .initrd=$(printf 0x%x $initrd_offs) \
		/usr/lib/systemd/boot/efi/linuxx64.efi.stub "${EFI_MOUNT_PATH}/EFI/debian/linux.debian.${KERNEL_VERSION}.efi"

	### Create a efiboot entry
	printf "%s\n" "Creating efiboot entry for kernel ${KERNEL_VERSION}"
	efibootmgr --disk /dev/"${ESP_DISK}" --part "${ESP_PART}" --create --label "${EFI_BASE_LABEL} ${KERNEL_VERSION}" --loader "\\EFI\\debian\\linux.debian.${KERNEL_VERSION}.efi"
	#printf "%s\n" "efibootmgr --disk /dev/\"${ESP_DISK}\" --part \"${ESP_PART}\" --create --label \"${EFI_BASE_LABEL} ${KERNEL_VERSION}\" --loader \"\\EFI\\debian\\linux.${KERNEL_VERSION}.efi\""

done < "${temp_kernel_list_file}"
## }}}
## Create generic entry for the last version of the kernel {{{
### Create a unified kernel
printf "%s\n" "Creating unified generic kernel for the last version (${KERNEL_VERSION})..."
objcopy \
	--add-section .osrel="/usr/lib/os-release" --change-section-vma .osrel=$(printf 0x%x $osrel_offs) \
	--add-section .cmdline="${temp_kernel_command_file}" --change-section-vma .cmdline=$(printf 0x%x $cmdline_offs) \
	--add-section .linux="/boot/vmlinuz-${KERNEL_VERSION}" --change-section-vma .linux=$(printf 0x%x $linux_offs) \
	--add-section .initrd="/boot/initrd.img-${KERNEL_VERSION}" --change-section-vma .initrd=$(printf 0x%x $initrd_offs) \
	/usr/lib/systemd/boot/efi/linuxx64.efi.stub "${EFI_MOUNT_PATH}/EFI/debian/linux.debian.efi"

### Create a efiboot entry
printf "%s\n" "Creating efiboot generic entry for the last version (${KERNEL_VERSION})"
efibootmgr --disk /dev/"${ESP_DISK}" --part "${ESP_PART}" --create --label "${EFI_BASE_LABEL}" --loader "\\EFI\\debian\\linux.debian.efi"
#printf "%s\n" "efibootmgr --disk /dev/\"${ESP_DISK}\" --part \"${ESP_PART}\" --create --label \"${EFI_BASE_LABEL} ${KERNEL_VERSION}\" --loader \"\\EFI\\debian\\linux.efi\""

## }}}
# }}}

## Remove temp files
rm -f -- "${temp_efi_list_file}" "${temp_kernel_list_file}" "${temp_kernel_command_file}"

exit 0