fix: Erase non-aligned bytes with --no-stub

This enables writing to non-aligned address by way of
erasing the bytes before it to the closest aligned address.

esptool/cmds.py

@@ -560,15 +560,24 @@ def write_flash(esp, args):
             print("Will flash %s uncompressed" % argfile.name)
             compress = False
 
-        if args.no_stub:
-            print("Erasing flash...")
-        image = pad_to(
-            argfile.read(), esp.FLASH_ENCRYPTED_WRITE_ALIGN if encrypted else 4
-        )
+        image = argfile.read()
+
         if len(image) == 0:
             print("WARNING: File %s is empty" % argfile.name)
             continue
 
+        image = pad_to(image, esp.FLASH_ENCRYPTED_WRITE_ALIGN if encrypted else 4)
+
+        if args.no_stub:
+            print("Erasing flash...")
+
+            # It is not possible to write to not aligned addresses without stub,
+            # so there are added 0xFF (erase) bytes at the beginning of the image
+            # to align it.
+            bytes_over = address % esp.FLASH_SECTOR_SIZE
+            address -= bytes_over
+            image = b"\xFF" * bytes_over + image
+
         if not esp.secure_download_mode and not esp.get_secure_boot_enabled():
             image = _update_image_flash_params(esp, address, args, image)
         else:

test/test_esptool.py

@@ -667,6 +667,15 @@ def test_erase_before_write(self):
         assert "Chip erase completed successfully" in output
         assert "Hash of data verified" in output
 
+    @pytest.mark.quick_test
+    def test_flash_not_aligned_nostub(self):
+        output = self.run_esptool("--no-stub write_flash 0x1 images/one_kb.bin")
+        assert (
+            "WARNING: Flash address 0x00000001 is not aligned to a 0x1000 byte flash sector. 0x1 bytes before this address will be erased."
+            in output
+        )
+        assert "Hard resetting via RTS pin..." in output
+
 
 @pytest.mark.skipif(
     arg_chip in ["esp8266", "esp32"],