heads/initrd/etc/functions

#!/bin/bash
# Shell functions for most initialization scripts
. /etc/ash_functions

# Print <hidden> or <empty> depending on whether $1 is empty.  Useful to mask an
# optional password parameter.
mask_param() {
	if [ -z "$1" ]; then
		echo "<empty>"
	else
		echo "<hidden>"
	fi
}

# Trace a command with DEBUG, then execute it.
# A password parameter can be masked by passing --mask-position N before the
# command to execute, the debug trace will just indicate whether the password
# was empty or nonempty (which is important when use of a password is optional).
# N=0 is the name of the command to be executed, N=1 is its first parameter,
# etc.
DO_WITH_DEBUG() {
	if [ "$1" == "--mask-position" ]; then
		mask_position="$2"
		shift
		shift
		DEBUG_ARGS=("$@")

		DEBUG_ARGS[$mask_position]="$(mask_param "${DEBUG_ARGS[$mask_position]}")"
		DEBUG "${DEBUG_ARGS[@]}"
	else
		DEBUG "$@"
	fi
	"$@"
}

pcrs() {
	if [ "$CONFIG_TPM2_TOOLS" = "y" ]; then
		tpm2 pcrread sha256
	elif [ "$CONFIG_TPM" = "y" ]; then
		head -8 /sys/class/tpm/tpm0/pcrs
	fi
}

confirm_totp()
{
	TRACE "Under /etc/functions:confirm_totp"
	prompt="$1"
	last_half=X
	unset totp_confirm

	while true; do

		# update the TOTP code every thirty seconds
		date=`date "+%Y-%m-%d %H:%M:%S"`
		seconds=`date "+%s"`
		half=`expr \( $seconds % 60 \) / 30`
		if [ "$CONFIG_TPM" != "y" ]; then
			TOTP="NO TPM"
		elif [ "$half" != "$last_half" ]; then
			last_half=$half;
			TOTP=`unseal-totp` \
			|| recovery "TOTP code generation failed"
		fi

		echo -n "$date $TOTP: "

		# read the first character, non-blocking
		read \
			-t 1 \
			-n 1 \
			-s \
			-p "$prompt" \
			totp_confirm \
		&& break

		# nothing typed, redraw the line
		echo -ne '\r'
	done

	# clean up with a newline
	echo
}

reseal_tpm_disk_decryption_key()
{
	TRACE "Under /etc/functions:reseal_tpm_disk_decryption_key"
	#Can be called only on resealing, not on tpm reset:
	#otherise primary handle and rollback would change.
	if ! grep -q /boot /proc/mounts ; then
		mount -o ro /boot \
		|| recovery "Unable to mount /boot"
	fi

	if [ -s /boot/kexec_key_devices.txt ] || [ -s /boot/kexec_key_lvm.txt ]; then
		warn "A TPM disk decryption key previoulsy sealed is now invalid since firmware measurements cannot be unsealed" 
		warn "Renewing LUKS Disk Unlock Key to be unsealed by TPM Disk Unlock Key passphrase"
		while ! kexec-seal-key /boot; do
			warn "Recovery disk encryption key passphrase invalid. Try again!"
		done
		warn "LUKS header hash changed under of /boot/kexec_luks_hdr_hash.txt" 
		warn "Updating checksums and signing all files under /boot/kexec.sig"
		while ! update_checksums; do
		warn "Checksums were not signed. Bad GPG PIN provided?" 
		warn "Please update checksums and provide a valid GPG PIN"
		done
		warn "Rebooting in 3 seconds to enable booting default boot option"
		sleep 3
		reboot
	else
		DEBUG "No TPM disk decryption key to reseal"
	fi
}

# Enable USB storage (if not already enabled), and wait for storage devices to
# be detected.  If USB storage was already enabled, no wait occurs, this would
# have happened already when USB storage was enabled.
enable_usb_storage()
{
	if ! lsmod | grep -q usb_storage; then
		timeout=0
		echo "Scanning for USB storage devices..."
		insmod /lib/modules/usb-storage.ko >/dev/null 2>&1 \
		|| die "usb_storage: module load failed"
		while [[ $(list_usb_storage | wc -l) -eq 0 ]]; do 
			[[ $timeout -ge 8 ]] && break
			sleep 1
			timeout=$(($timeout+1))
		done
	fi
}

list_usb_storage()
{
	TRACE "Under /etc/functions:list_usb_storage"
	# List all USB storage devices, including partitions unless we received argument stating we want drives only
	# The output is a list of device names, one per line.

	if [ "$1" = "disks" ]; then
		DEBUG "Listing USB storage devices (disks only) since list_usb_storage was called with 'disks' argument"
	else
		DEBUG "Listing USB storage devices (including partitions)"
	fi

	stat -c %N /sys/block/sd* 2>/dev/null | grep usb |
		cut -f1 -d ' ' |
		sed "s/[']//g" |
		while read b; do
			# Ignore devices of size 0, such as empty SD card
			# readers on laptops attached via USB.
			if [ "$(cat "$b/size")" -gt 0 ]; then
				DEBUG "USB storage device of size greater then 0: $b"
				echo "$b"
			fi
		done |
		sed "s|/sys/block|/dev|" |
		while read b; do
			# If the device has a partition table, ignore it and
			# include the partitions instead - even if the kernel
			# hasn't detected the partitions yet.  Such a device is
			# never usable directly, and this allows the "wait for
			# disks" loop in mount-usb to correctly wait for the
			# partitions.
			# This check: [ $(fdisk -l "$b" | wc -l) -eq 5 ]
			# covers the case of a device without partition table but
			# formatted as fat32, which contains a sortof partition table.
			# this causes fdisk to not print the invalid partition table
			# message and instead it'll print an empty table with header.
			# In both cases the output is 5 lines: 3 about device info,
			# 1 empty line and the 5th will be the table header or the
			# unvalid message.
			DISK_DATA=$(fdisk -l "$b")
			if echo "$DISK_DATA" | grep -q "doesn't contain a valid partition table" || [ $(echo "$DISK_DATA" | wc -l) -eq 5 ]; then
				# No partition table, include this device
				DEBUG "USB storage device without partition table: $b"
				echo "$b"
			#Bypass the check for partitions if we want only disks
			elif [ "$1" = "disks" ]; then
				# disks only were requested, so we don't list partitions
				DEBUG "USB storage device with partition table: $b"
				DEBUG "We asked for disks only, so we don't want to list partitions"
				echo "$b"
			else
				# Has a partition table, include partitions
				DEBUG "USB storage device with partition table: $b"
				ls -1 "$b"* | awk 'NR!=1 {print $0}'
			fi
		done
}

confirm_gpg_card()
{
	TRACE "Under /etc/functions:confirm_gpg_card"
	read \
		-n 1 \
		-p "Please confirm that your GPG card is inserted [Y/n]: " \
		card_confirm
	echo

	if [ "$card_confirm" != "y" \
		-a "$card_confirm" != "Y" \
		-a -n "$card_confirm" ] \
	; then
		die "gpg card not confirmed"
	fi

	# setup the USB so we can reach the GPG card
	enable_usb

	echo -e "\nVerifying presence of GPG card...\n"
	# ensure we don't exit without retrying
	errexit=$(set -o | grep errexit | awk '{print $2}')
	set +e
	gpg --card-status > /dev/null
	if [ $? -ne 0 ]; then
	  # prompt for reinsertion and try a second time
	  read -n1 -r -p \
	      "Can't access GPG key; remove and reinsert, then press Enter to retry. " \
	      ignored
	  # restore prev errexit state
	  if [ "$errexit" = "on" ]; then
	    set -e
	  fi
	  # retry card status
	  gpg --card-status > /dev/null \
	  	|| die "gpg card read failed"
	fi
	# restore prev errexit state
	if [ "$errexit" = "on" ]; then
	  set -e
	fi
}

# Prompt for an owner password if it is not already set in tpm_password.  Sets
# tpm_password.  Tools should optionally accept a TPM password on the command
# line, since some flows need it multiple times and only one prompt is ideal.
prompt_tpm_password() {
	if [ -n "$tpm_password" ]; then
		return 0;
	fi

	read -s -p "TPM Owner password: " tpm_password
	echo # new line after password prompt
}

# Prompt for a new owner password when resetting the TPM.  Returned in
# key_password.  The password must be 1-32 characters and must be entered twice,
# the script will loop until this is met.
prompt_new_owner_password() {
	local key_password2
	key_password=1
	key_password2=2
	while [ "$key_password" != "$key_password2" ] || [ "${#key_password}" -gt 32 ] || [ -z "$key_password" ]; do
		read -s -p "New TPM owner passphrase (2 words suggested, 1-32 characters max): " key_password
		echo

		read -s -p "Repeat chosen TPM owner passphrase: " key_password2
		echo

		if [ "$key_password" != "$key_password2" ]; then
			echo "Passphrases entered do not match. Try again!"
			echo
		fi
	done
}

check_tpm_counter()
{
  TRACE "Under /etc/functions:check_tpm_counter"
  LABEL=${2:-3135106223}
  tpm_password="$3"
	# if the /boot.hashes file already exists, read the TPM counter ID
	# from it.
	if [ -r "$1" ]; then
		TPM_COUNTER=`grep counter- "$1" | cut -d- -f2`
	else
		warn "$1 does not exist; creating new TPM counter"
		prompt_tpm_password
		tpmr counter_create \
			-pwdo "$tpm_password" \
			-pwdc '' \
			-la $LABEL \
		| tee /tmp/counter \
		|| die "Unable to create TPM counter"
		TPM_COUNTER=`cut -d: -f1 < /tmp/counter`
	fi

	if [ -z "$TPM_COUNTER" ]; then
		die "$1: TPM Counter not found?"
	fi
}

read_tpm_counter()
{
	TRACE "Under /etc/functions:read_tpm_counter"
	tpmr counter_read -ix "$1" | tee "/tmp/counter-$1" \
	|| die "Counter read failed"
}

increment_tpm_counter()
{
	TRACE "Under /etc/functions:increment_tpm_counter"
	tpmr counter_increment -ix "$1" -pwdc '' \
		| tee /tmp/counter-$1 \
	|| die "Counter increment failed"
}

check_config() {
	TRACE "Under /etc/functions:check_config"
	if [ ! -d /tmp/kexec ]; then
		mkdir /tmp/kexec \
		|| die 'Failed to make kexec tmp dir'
	else
		rm -rf /tmp/kexec/* \
		|| die 'Failed to empty kexec tmp dir'
	fi

	if [ ! -r $1/kexec.sig -a "$CONFIG_BASIC" != "y" ]; then
		return
	fi

	if [ `find $1/kexec*.txt | wc -l` -eq 0 ]; then
		return
	fi

	if [ "$2" != "force" ]; then
		if ! sha256sum `find $1/kexec*.txt` | gpgv $1/kexec.sig - ; then
			die 'Invalid signature on kexec boot params'
		fi
	fi

	echo "+++ Found verified kexec boot params"
	cp $1/kexec*.txt /tmp/kexec \
	|| die "Failed to copy kexec boot params to tmp"
}

# Replace a file in a ROM (add it if the file does not exist)
replace_rom_file() {
	ROM="$1"
	ROM_FILE="$2"
	NEW_FILE="$3"
	
	if (cbfs.sh -o "$ROM" -l | grep -q "$ROM_FILE") then
		cbfs.sh -o "$ROM" -d "$ROM_FILE"
	fi
	cbfs.sh -o "$ROM" -a "$ROM_FILE" -f "$NEW_FILE"
}

replace_config() {
	TRACE "Under /etc/functions:replace_config"
	CONFIG_FILE=$1
	CONFIG_OPTION=$2
	NEW_SETTING=$3

	touch $CONFIG_FILE
# first pull out the existing option from the global config and place in a tmp file
	awk "gsub(\"^export ${CONFIG_OPTION}=.*\",\"export ${CONFIG_OPTION}=\\\"${NEW_SETTING}\\\"\")" /tmp/config > ${CONFIG_FILE}.tmp
	awk "gsub(\"^${CONFIG_OPTION}=.*\",\"${CONFIG_OPTION}=\\\"${NEW_SETTING}\\\"\")" /tmp/config >> ${CONFIG_FILE}.tmp

# then copy any remaining settings from the existing config file, minus the option you changed
	grep -v "^export ${CONFIG_OPTION}=" ${CONFIG_FILE} | grep -v "^${CONFIG_OPTION}=" >> ${CONFIG_FILE}.tmp || true
  sort ${CONFIG_FILE}.tmp | uniq > ${CONFIG_FILE}
	rm -f ${CONFIG_FILE}.tmp
}

# Set a config variable in a specific file to a given value - replace it if it
# exists, or add it.  If added, the variable will be exported.
set_config() {
	CONFIG_FILE="$1"
	CONFIG_OPTION="$2"
	NEW_SETTING="$3"
	
	if grep -q "$CONFIG_OPTION" "$CONFIG_FILE"; then
		replace_config "$CONFIG_FILE" "$CONFIG_OPTION" "$NEW_SETTING"
	else
		echo "export $CONFIG_OPTION=\"$NEW_SETTING\"" >>"$CONFIG_FILE"
	fi
}

# Set a value in config.user, re-combine configs, and update configs in the
# environment.
set_user_config() {
	CONFIG_OPTION="$1"
	NEW_SETTING="$2"

	set_config /etc/config.user "$CONFIG_OPTION" "$NEW_SETTING"
	combine_configs
	. /tmp/config
}

# Load a config value to a variable, defaulting to empty.  Does not fail if the
# config is not set (since it would expand to empty by default).
load_config_value()
{
  local config_name="$1"
  if grep -q "$config_name=" /tmp/config; then
    grep "$config_name=" /tmp/config | tail -n1 | cut -f2 -d '=' | tr -d '"'
  fi
}

# Generate a secret for TPM-less HOTP by reading the ROM.  Output is the
# sha256sum of the ROM (binary, not printable), which can be truncated to the
# supported secret length.
secret_from_rom_hash() {
	local ROM_IMAGE="/tmp/coreboot-notpm.rom"

	echo -e "\nTPM not detected; measuring ROM directly\n" 1>&2

	# Read the ROM if we haven't read it yet
	if [ ! -f "${ROM_IMAGE}" ]; then
		flash.sh -r "${ROM_IMAGE}" >/dev/null 2>&1 || return 1
	fi

	sha256sum "${ROM_IMAGE}" | cut -f1 -d ' ' | fromhex_plain
}

update_checksums()
{
	TRACE "Under /etc/functions:update_checksums"
	# ensure /boot mounted
	if ! grep -q /boot /proc/mounts ; then
		mount -o ro /boot \
		|| recovery "Unable to mount /boot"
	fi

	# remount RW
	mount -o rw,remount /boot

	# sign and auto-roll config counter
	extparam=
	if [ "$CONFIG_TPM" = "y" ];then
		if [ "$CONFIG_IGNORE_ROLLBACK" != "y" ]; then
			extparam=-r
		fi
	fi
	if ! kexec-sign-config -p /boot -u $extparam ; then
		rv=1
	else
		rv=0
	fi

	# switch back to ro mode
	mount -o ro,remount /boot

	return $rv
}

print_tree() {
	TRACE "Under /etc/functions:print_tree"
	find ./ ! -path './kexec*' -print0 | sort -z
}

# Escape zero-delimited standard input to safely display it to the user in e.g.
# `whiptail`, `less`, `echo`, `cat`. Doesn't produce shell-escaped output.
# Most printable characters are passed verbatim (exception: \).
# These escapes are used to replace their corresponding characters: #n#r#t#v#b
# Other characters are rendered as hexadecimal escapes.
# escape_zero [prefix] [escape character]
# prefix: \0 in the input will result in \n[prefix]
# escape character: character to use for escapes (default: #); \ may be interpreted by `whiptail`
escape_zero() {
	local prefix="$1"
	local echar="${2:-#}"
	local todo=""
	local echar_hex="$(echo -n "$echar" | xxd -p -c1)"
	[ ${#echar_hex} -eq 2 ] || die "Invalid escape character $echar passed to escape_zero(). Programming error?!"

	echo -e -n "$prefix"
	xxd -p -c1 | tr -d '\n' |
	{
		while IFS= read -r -n2 -d '' ; do
			if [ -n "$todo" ] ; then
				#REPLY == "  " is EOF
				[[ "$REPLY" == "  " ]] && echo '' || echo -e -n "$todo"
				todo=""
			fi

			case "$REPLY" in
				00)
					todo="\n$prefix"
					;;
				08)
					echo -n "${echar}b"
					;;
				09)
					echo -n "${echar}t"
					;;
				0a)
					echo -n "${echar}n"
					;;
				0b)
					echo -n "${echar}v"
					;;
				0d)
					echo -n "${echar}r"
					;;
				"$echar_hex")
					echo -n "$echar$echar"
					;;
				#interpreted characters:
				2[0-9a-f]|3[0-9a-f]|4[0-9a-f]|5[0-9abd-f]|6[0-9a-f]|7[0-9a-e])
					echo -e -n '\x'"$REPLY"
					;;
				# All others are escaped
				*)
					echo -n "${echar}x$REPLY"
					;;
			esac
		done
	}
}

# Currently heads doesn't support signing file names with certain characters
# due to https://bugs.busybox.net/show_bug.cgi?id=14226. Also, certain characters
# may be intepreted by `whiptail`, `less` et al (e.g. \n, \b, ...).
assert_signable() {
	TRACE "Under /etc/functions:assert_signable"
	# ensure /boot mounted
	if ! grep -q /boot /proc/mounts ; then
		mount -o ro /boot || die "Unable to mount /boot"
	fi

	find /boot -print0 > /tmp/signable.ref
	local del='\001-\037\134\177-\377'
	LC_ALL=C tr -d "$del" < /tmp/signable.ref > /tmp/signable.del || die "Failed to execute tr."
	if ! cmp -s "/tmp/signable.ref" "/tmp/signable.del" &> /dev/null ; then
		local user_out="/tmp/hash_output_mismatches"
		local add="Please investigate!"
		[ -f "$user_out" ] && add="Please investigate the following relative paths to /boot (where # are sanitized invalid characters):"$'\n'"$(cat "$user_out")"
		recovery "Some /boot file names contain characters that are currently not supported by heads: $del"$'\n'"$add"
	fi
	rm -f /tmp/signable.*
}

verify_checksums()
{
	TRACE "Under /etc/functions:verify_checksums"
	local boot_dir="$1"
	local gui="${2:-y}"

	(
		set +e -o pipefail
		local ret=0
		cd "$boot_dir" || ret=1
		sha256sum -c "$TMP_HASH_FILE" > /tmp/hash_output || ret=1

		# also make sure that the file & directory structure didn't change
		# (sha256sum won't detect added files)
		print_tree > /tmp/tree_output || ret=1
		if ! cmp -s "$TMP_TREE_FILE" /tmp/tree_output &> /dev/null ; then
			ret=1
			[[ "$gui" != "y" ]] && exit "$ret"
			# produce a diff that can safely be presented to the user
			# this is relatively hard as file names may e.g. contain backslashes etc.,
			# which are interpreted by whiptail, less, ...
			escape_zero "(new) " < "$TMP_TREE_FILE" > "${TMP_TREE_FILE}.user"
			escape_zero "(new) " < /tmp/tree_output > /tmp/tree_output.user
			diff "${TMP_TREE_FILE}.user" /tmp/tree_output.user | grep -E '^\+\(new\).*$' | sed -r 's/^\+\(new\)/(new)/g' >> /tmp/hash_output
			rm -f "${TMP_TREE_FILE}.user"
			rm -f /tmp/tree_output.user
		fi
		exit $ret
	)
	return $?
}

# detect and set /boot device
# mount /boot if successful
detect_boot_device()
{
	TRACE "Under /etc/functions:detect_boot_device"
	# unmount /boot to be safe
	cd / && umount /boot 2>/dev/null

	# check $CONFIG_BOOT_DEV if set/valid
	if [ -e "$CONFIG_BOOT_DEV" ]; then
		if mount -o ro $CONFIG_BOOT_DEV /boot >/dev/null 2>&1; then
			if ls -d /boot/grub* >/dev/null 2>&1; then
				# CONFIG_BOOT_DEV is valid device and contains an installed OS
				return 0
			fi
		fi
	fi

	# generate list of possible boot devices
	fdisk -l | grep "Disk /dev/" | cut -f2 -d " " | cut -f1 -d ":" > /tmp/disklist

	# filter out extraneous options
	> /tmp/boot_device_list
	for i in `cat /tmp/disklist`; do
		# remove block device from list if numeric partitions exist, since not bootable
		DEV_NUM_PARTITIONS=$((`ls -1 $i* | wc -l`-1))
		if [ ${DEV_NUM_PARTITIONS} -eq 0 ]; then
			echo $i >> /tmp/boot_device_list
		else
			ls $i* | tail -${DEV_NUM_PARTITIONS} >> /tmp/boot_device_list
		fi
	done

	# iterate thru possible options and check for grub dir
	for i in `cat /tmp/boot_device_list`; do
		umount /boot 2>/dev/null
		if mount -o ro $i /boot >/dev/null 2>&1; then
			if ls -d /boot/grub* >/dev/null 2>&1; then
				CONFIG_BOOT_DEV="$i"
				return 0
			fi
		fi
	done

	# no valid boot device found
	echo "Unable to locate /boot files on any mounted disk"
	umount /boot 2>/dev/null
	return 1
}

scan_boot_options()
{
	local bootdir config option_file
	bootdir="$1"
	config="$2"
	option_file="$3"

	if [ -r $option_file ]; then rm $option_file; fi
	for i in `find $bootdir -name "$config"`; do
		DO_WITH_DEBUG kexec-parse-boot "$bootdir" "$i" >> $option_file
	done
	# FC29/30+ may use BLS format grub config files
	# https://fedoraproject.org/wiki/Changes/BootLoaderSpecByDefault
	# only parse these if $option_file is still empty
	if [ ! -s $option_file ] && [ -d "$bootdir/loader/entries" ]; then
		for i in `find $bootdir -name "$config"`; do
			kexec-parse-bls "$bootdir" "$i" "$bootdir/loader/entries" >> $option_file
		done
	fi
}

calc()
{ 
	awk "BEGIN { print "$*" }"; 
}

# truncate a file to a size only if it is longer (busybox truncate lacks '<' and
# always sets the file size)
truncate_max_bytes() {
	local bytes="$1"
	local file="$2"
	if [ "$(stat -c %s "$file")" -gt "$bytes" ]; then
		truncate -s "$bytes" "$file"
	fi
}

# Busybox xxd -p pads the last line with spaces to 60 columns, which not only
# trips up many scripts, it's very difficult to diagnose by looking at the
# output.  Delete line breaks and spaces to really get plain hex output.
tohex_plain() {
	xxd -p | tr -d '\n '
}

# Busybox xxd -p -r silently truncates lines longer than 60 hex chars.
# Shorter lines are OK, spaces are OK, and even splitting a byte across lines is
# allowed, so just fold the text to maximum 60 column lines.
# Note that also unlike GNU xxd, non-hex chars in input corrupt the output (GNU
# xxd ignores them).
fromhex_plain() {
	fold -w 60 | xxd -p -r
}

print_battery_health()
{
	if [ -d /sys/class/power_supply/BAT* ]; then
        	battery_health=$(calc $(cat /sys/class/power_supply/BAT*/charge_full)/$(cat /sys/class/power_supply/BAT*/charge_full_design)*100 | awk -F "." {'print $1'})
		echo "$battery_health"
	fi
}

print_battery_charge()
{
	if [ -d /sys/class/power_supply/BAT* ]; then
                battery_charge=$(calc $(cat /sys/class/power_supply/BAT*/charge_now)/$(cat /sys/class/power_supply/BAT*/charge_full)*100 | awk -F "." {'print $1'})
                echo "$battery_charge"
        fi
}

generate_random_mac_address()
{
	#Borrowed from https://stackoverflow.com/questions/42660218/bash-generate-random-mac-address-unicast
	hexdump -n 6 -ve '1/1 "%.2x "' /dev/urandom | awk -v a="2,6,a,e" -v r="$RANDOM" 'BEGIN{srand(r);}NR==1{split(a,b,",");r=int(rand()*4+1);printf "%s%s:%s:%s:%s:%s:%s\n",substr($1,0,1),b[r],$2,$3,$4,$5,$6}'
}

# Add a command to be invoked at exit.  (Note that trap EXIT replaces any
# existing handler.)  Commands are invoked in reverse order, so they can be used
# to clean up resources, etc.
# The parameters are all executed as-is and do _not_ require additional quoting
# (unlike trap).  E.g.:
# at_exit shred "$file" #<-- file is expanded when calling at_exit, no extra quoting needed
at_exit() {
	AT_EXIT_HANDLERS+=("$@") # Command and args
	AT_EXIT_HANDLERS+=("$#") # Number of elements in this command
}

# Array of all exit handler command arguments with lengths of each command at
# the end.  For example:
#   at_exit echo hello
#   at_exit echo a b c
# results in:
# AT_EXIT_HANDLERS=(echo hello 2 echo a b c 4)

AT_EXIT_HANDLERS=()
# Each handler is an array AT_EXIT_HANDLER_{i}
run_at_exit_handlers() {
	local cmd_pos cmd_len
	cmd_pos="${#AT_EXIT_HANDLERS[@]}"
	# Silence trace if there are no handlers, this is common and occurs a lot
	[ "$cmd_pos" -gt 0 ] && DEBUG "Running at_exit handlers"
	while [ "$cmd_pos" -gt 0 ]; do
		cmd_pos="$((cmd_pos-1))"
		cmd_len="${AT_EXIT_HANDLERS[$cmd_pos]}"
		cmd_pos="$((cmd_pos-cmd_len))"
		"${AT_EXIT_HANDLERS[@]:$cmd_pos:$cmd_len}"
	done
}
trap run_at_exit_handlers EXIT