fix: Derive NT5 boot load size from extracted image (#1991)

src/image.sh

@@ -1044,18 +1044,34 @@ EOC
 getBootLoadSize() {
 
   local iso="$1"
-  local desc="$2"
+  local dir="$2"
-  local boot_info value
+  local desc="$3"
-
+  local boot_info size value
-  if ! boot_info=$(isoinfo -d -i "$iso"); then
 
   case "${DETECTED,,}" in
     "win2k"* | "winxp"* | "win2003"* )
-        BOOT_LOAD_SIZE=4
-        return 0
-        ;;
-    esac
 
+      if [ ! -s "$dir/$ETFS" ]; then
+        error "Failed to locate file \"$ETFS\" in $desc ISO image!"
+        return 1
+      fi
+
+      if ! size=$(stat -c%s "$dir/$ETFS"); then
+        error "Failed to determine boot image size from $desc ISO!"
+        return 1
+      fi
+
+      if (( size < 512 || size % 512 != 0 )); then
+        error "Invalid boot image size found in $desc ISO!"
+        return 1
+      fi
+
+      BOOT_LOAD_SIZE=$((size / 512))
+      ;;
+
+    * )
+
+      if ! boot_info=$(isoinfo -d -i "$iso"); then
         error "Failed to read boot image information from $desc ISO!"
         return 1
       fi
@@ -1063,14 +1079,6 @@ getBootLoadSize() {
       value=$(awk '/Nsect / { print $NF; exit }' <<< "$boot_info")
 
       if [ -z "$value" ]; then
-
-    case "${DETECTED,,}" in
-      "win2k"* | "winxp"* | "win2003"* )
-        BOOT_LOAD_SIZE=4
-        return 0
-        ;;
-    esac
-
         error "Failed to determine boot image load size from $desc ISO!"
         return 1
       fi
@@ -1081,6 +1089,8 @@ getBootLoadSize() {
       fi
 
       BOOT_LOAD_SIZE=$((10#$value))
+      ;;
+  esac
 
   if (( BOOT_LOAD_SIZE < 1 || BOOT_LOAD_SIZE > 65535 )); then
     error "Invalid boot image load size found in $desc ISO!"

src/install.sh

@@ -784,7 +784,7 @@ prepareImage() {
 
   if [[ "${BOOT_MODE,,}" == "windows_legacy" &&
     "${DETECTED,,}" != "win9"* ]]; then
-    getBootLoadSize "$iso" "$desc" || return 1
+    getBootLoadSize "$iso" "$dir" "$desc" || return 1
   fi
 
   skipVersion "$DETECTED" && return 0