scripts: imgtool: Compression of no header-padded images

This fixes issues when trying to compress images with no
header padding requested.

Signed-off-by: Michal Kozikowski <michal.kozikowski@nordicsemi.no>

Author: nordic-mik7

scripts/imgtool/image.py

@@ -348,7 +348,6 @@ def load(self, path):
                     self.payload = copy.copy(self.infile_data)
         except FileNotFoundError:
             raise click.UsageError("Input file not found")
-        self.image_size = len(self.payload)
 
         # Add the image header if needed.
         if self.pad_header and self.header_size > 0:
@@ -358,6 +357,8 @@ def load(self, path):
             self.payload = bytes([self.erased_val] * self.header_size) + \
                 self.payload
 
+        self.image_size = len(self.payload) - self.header_size
+
         self.check_header()
 
     def load_compressed(self, data, compression_header):
@@ -366,14 +367,19 @@ def load_compressed(self, data, compression_header):
         self.image_size = len(self.payload)
 
         # Add the image header if needed.
-        if self.pad_header and self.header_size > 0:
-            if self.base_addr:
-                # Adjust base_addr for new header
-                self.base_addr -= self.header_size
-            self.payload = bytes([self.erased_val] * self.header_size) + \
-                self.payload
-
-        self.check_header()
+        if self.header_size > 0:
+            if self.pad_header:
+                if self.base_addr:
+                    # Adjust base_addr for new header
+                    self.base_addr -= self.header_size
+                self.payload = bytes([self.erased_val] * self.header_size) + \
+                    self.payload
+            else:
+                # Fill header padding with zeros to align with what is expected
+                # for uncompressed images when no pad_header is requested
+                # (see self.check_header())
+                self.payload = bytes([0] * self.header_size) + \
+                    self.payload
 
     def save(self, path, hex_addr=None):
         """Save an image from a given file"""

scripts/imgtool/main.py

@@ -542,9 +542,11 @@ def sign(key, public_key_format, align, version, pad_sig, header_size,
         ]
         if compression == "lzma2armthumb":
             compression_filters.insert(0, {"id":lzma.FILTER_ARMTHUMB})
-        compressed_data = lzma.compress(img.get_infile_data(),filters=compression_filters,
-            format=lzma.FORMAT_RAW)
-        uncompressed_size = len(img.get_infile_data())
+
+        infile_offset = 0 if pad_header else header_size
+        compressed_data = lzma.compress(img.get_infile_data()[infile_offset:],
+            filters=compression_filters, format=lzma.FORMAT_RAW)
+        uncompressed_size = len(img.get_infile_data()[infile_offset:])
         compressed_size = len(compressed_data)
         print(f"compressed image size: {compressed_size} bytes")
         print(f"original image size: {uncompressed_size} bytes")