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-rw-r--r--docs/reference/services/tfm_attestation_integration_guide.rst17
1 files changed, 15 insertions, 2 deletions
diff --git a/docs/reference/services/tfm_attestation_integration_guide.rst b/docs/reference/services/tfm_attestation_integration_guide.rst
index d3457cd905..5d2986146e 100644
--- a/docs/reference/services/tfm_attestation_integration_guide.rst
+++ b/docs/reference/services/tfm_attestation_integration_guide.rst
@@ -356,8 +356,21 @@ The structure of shared data must be the following:
entry header structure: ``struct shared_data_tlv_entry`` and the data. In
the entry header is a type field ``tlv_type`` which identify the consumer of
the entry in the runtime software and specify the subtype of that data item.
- There is a size field ``tlv_len`` which covers the size of the entry header
- and the data. After this structure comes the actual data.
+
+ .. Note::
+
+ There is a size field ``tlv_len`` which has different definitions in the
+ upstream MCUboot repository and in its TF-M forked version:
+
+ - Upstream MCUboot: Covers only the length of data but not the header
+ size.
+ - TF-M MCUboot: Covers the size of the entry header and the data
+ together.
+
+ This difference is handled by TF-M code based on which bootloader is used
+ along with TF-M runtime.
+
+ After the entry header structure comes the actual data.
.. code-block:: c