gem5: add run -l option to restore latest checkpoint with directory timestamps

run

@@ -18,6 +18,7 @@ extra_flags_qemu=
 extra_opts=
 gem5opts=
 gem5_fsbiglittle=false
+gem5_restore_last_checkpoint=
 lkmc_eval=
 initrd=false
 initramfs=false
@@ -33,7 +34,7 @@ trace_enabled=false
 # just to prevent QEMU from emitting a warning that '' is not valid.
 trace_type=pr_manager_run
 vnc=
-while getopts a:c:DdE:e:F:f:G:ghIiKkL:M:m:N:n:PQ:RrT:t:U:uVX:x OPT; do
+while getopts a:c:DdE:e:F:f:G:ghIiKkL:l:M:m:N:n:PQ:RrT:t:U:uVX:x OPT; do
   case "$OPT" in
     a)
       common_arch="$OPTARG"
@@ -91,6 +92,9 @@ while getopts a:c:DdE:e:F:f:G:ghIiKkL:M:m:N:n:PQ:RrT:t:U:uVX:x OPT; do
     L)
       common_linux_variant="$OPTARG"
       ;;
+    l)
+      gem5_restore_last_checkpoint="${OPTARG}"
+      ;;
     M)
       common_gem5_variant="$OPTARG"
       ;;
@@ -194,6 +198,13 @@ if "$common_gem5"; then
   else
     gem5_arch=ARM
   fi
+  if [ -n "$gem5_restore_last_checkpoint" ]; then
+    cpt_pref='^cpt\.'
+    latest_cpt_basename="$(ls -crt "$common_m5out_dir" | grep -E "$cpt_pref" | tail -n "$gem5_restore_last_checkpoint" | head -n 1)"
+    n="$(ls -1 "$common_m5out_dir" | grep -E "$cpt_pref" | sort -k 2 -n -t . | grep -n "$latest_cpt_basename" | cut -d : -f 1)"
+    extra_flags="${extra_flags}-r ${n} \\
+"
+  fi
   if "$trace_enabled"; then
     gem5opts="${gem5opts} --debug-flags='${trace_type}' \\
 "