commit f5b33d8b9d61e77227cf44c01d95f1a367e137c8
author David Brown <david.brown@linaro.org> Fri Sep 01 10:58:27 2017 -0600
committer David Brown <davidb@davidb.org> Wed Sep 06 16:16:58 2017 -0600
tree 282418a02dfade076f6583512065b1daa26e81e2
parent 43cda33c5aecd6594e4adae66d7d922364b2ce84

Place TLV size into TLV itself

To allow the signatures to be replaced, move the size of the TLV into a
small "info" header at the start of the TLV.

Note that this causes image swapping to lose robustness.  This is fixed
by a later commit.

Based on work by Marko Kiiskila <marko@runtime.io>

Signed-off-by: Marko Kiiskila <marko@runtime.io>
Signed-off-by: David Brown <david.brown@linaro.org>
JIRA: MCUB-65

scripts/imgtool/image.py

diff --git a/scripts/imgtool/image.py b/scripts/imgtool/image.py
index 9a9225f..7eb6c0c 100644
--- a/scripts/imgtool/image.py
+++ b/scripts/imgtool/image.py
@@ -21,6 +21,8 @@
         'ECDSA224': 0x21,
         'ECDSA256': 0x22, }
 
+TLV_INFO_SIZE = 4
+TLV_INFO_MAGIC = 0x6907
 TLV_HEADER_SIZE = 4
 
 # Sizes of the image trailer, depending on flash write size.
@@ -46,7 +48,8 @@
         self.buf += payload
 
     def get(self):
-        return bytes(self.buf)
+        header = struct.pack('<HH', TLV_INFO_MAGIC, TLV_INFO_SIZE + len(self.buf))
+        return header + bytes(self.buf)
 
 class Image():
     @classmethod