utils: Add kernel_size_time.sh to measure size and boot time

This is what I've been using to measure size and execution times for
a test command (based on muvm) for the previous patches. It's made to
be used in a rebase script, for example:

  x ./utils/kernel_size_time.sh
  pick 12181bf config-libkrunfw_x86_64: Disable processor quirks and features we don't need
  x ./utils/kernel_size_time.sh
  pick 5c5badc config-libkrunfw_x86_64: Drop power management features and cpufreq
  x ./utils/kernel_size_time.sh

it's a bit bigger than what I wanted because of the time -p trick:
nowadays most distributions don't ship /usr/bin/time (at least by
default), but many shells skip support for the POSIX compatibility
mode (-p, which simplifies calculations) in their 'time' built-in,
so, if we need it, we need to re-execute under Bash (assuming it's
not the default non-interactive shell).

Signed-off-by: Stefano Brivio <[email protected]>

utils/kernel_size_time.sh

@@ -0,0 +1,96 @@
+#!/bin/sh -e
+#
+# SPDX-License-Identifier: LGPL-2.1-only
+#
+# utils/kernel_size_time.sh - Check build size, and boot time for given command
+#
+# Copyright (c) 2025 Red Hat GmbH
+# Author: Stefano Brivio <[email protected]>
+
+CONFIG="${CONFIG:-config-libkrunfw_x86_64}"
+RUNS=${RUNS:-10}
+TIME_CMD="${TIME_CMD:-~/muvm/target/release/muvm --mem=64 --vram=0 -c 0,1 -- true}"
+PREV_SIZE_FILE="prev_size"
+PREV_TIME_FILE="prev_time"
+LOG_FILE="log"
+
+find_time_dash_p() {
+	REEXEC_BASH=n
+	if time -p ':'; then
+		TIME_DASH_P='time -p'
+	elif command -v /usr/bin/time; then
+		TIME_DASH_P='/usr/bin/time -p'
+	elif command -v bash; then
+		# Simply re-execute under bash to avoid further eval tricks
+		REEXEC_BASH=y
+	fi
+}
+
+build() {
+	for KERNELDIR in linux-*/; do
+		cp "${CONFIG}" "${KERNELDIR}/.config"
+	done
+
+	rm -f linux-*/vmlinux
+	make clean
+	make -j$(nproc) || make -j$(($(nproc) / 2)) || make
+}
+
+measure_runs() {
+	export LD_PRELOAD=$(ls $(pwd)/libkrunfw.so.*)
+	for i in $(seq 1 ${RUNS}); do eval ${TIME_CMD}; done
+}
+
+measure() {
+	NEW_SIZE=$(stat -c %s linux-*/vmlinux)
+	NEW_TIME="$( eval ${TIME_DASH_P} measure_runs 2>&1 | grep real | tr -dc [:digit:] )5"
+}
+
+log() {
+	BASE_SIZE="$(cat ${PREV_SIZE_FILE} 2>/dev/null || :)"
+	BASE_TIME="$(cat ${PREV_TIME_FILE} 2>/dev/null || :)"
+
+	[ -e "${PREV_SIZE_FILE}" ] || FIRST="y"
+
+	echo "$NEW_SIZE" > "${PREV_SIZE_FILE}"
+	echo "$NEW_TIME" > "${PREV_TIME_FILE}"
+
+	git rev-parse HEAD >> ${LOG_FILE}
+
+	if [ "${FIRST}" = "y" ]; then
+		NEW_TIME="$(echo 'scale=0; '$NEW_TIME' / '${RUNS} | bc -l)"
+		printf "Baseline:
+- %i bytes in the uncompressed kernel image
+
+- %i ms (average of ${RUNS} runs) for:
+    ${TIME_CMD}
+
+" $NEW_SIZE $NEW_TIME >> ${LOG_FILE}
+		exit 0
+	fi
+
+	DIFF_SIZE="$((BASE_SIZE - NEW_SIZE))"
+	DIFF_TIME="$((BASE_TIME - NEW_TIME))"
+
+	DIFF_TIME="$(echo 'scale=0; '$DIFF_TIME' / '${RUNS} | bc -l)"
+	BASE_TIME="$(echo 'scale=0; '$BASE_TIME' / '${RUNS} | bc -l)"
+	NEW_TIME="$(echo 'scale=0; '$NEW_TIME' / '${RUNS} | bc -l)"
+
+	printf "This saves:
+- %i bytes (%i -> %i) in the uncompressed kernel image
+
+- %i ms (%i -> %i, average of ${RUNS} runs) for:
+    ${TIME_CMD}
+
+" $DIFF_SIZE $BASE_SIZE $NEW_SIZE $DIFF_TIME $BASE_TIME $NEW_TIME >> ${LOG_FILE}
+}
+
+build
+find_time_dash_p >/dev/null 2>&1 || { echo "No implementation of 'time -p', exiting"; exit 1; }
+
+if [ ${REEXEC_BASH} = "y" ]; then
+	bash $0
+else
+	measure
+	log
+fi