COFF CALC_ADDEND comment

[Alan Modra]

Old COFF (and AOUT) targets have unusual relocation addends.

	* coffcode.h (<Reading relocations>): Describe COFF addends.

diff --git a/bfd/coffcode.h b/bfd/coffcode.h
index e952bd77d6a..168bb8a55c2 100644
--- a/bfd/coffcode.h
+++ b/bfd/coffcode.h
@@ -5092,6 +5092,14 @@ SUBSUBSECTION
 	structure, in a back end specific way. For instance, the 386
 	uses the @code{r_type} to directly produce an index
 	into a howto table vector.
+
+	o Note that @code{arelent.addend} for COFF is often not what
+	most people understand as a relocation addend, but rather an
+	adjustment to the relocation addend stored in section contents
+	of relocatable object files.  The value found in section
+	contents may also be confusing, depending on both symbol value
+	and addend somewhat similar to the field value for a
+	final-linked object.  See @code{CALC_ADDEND}.
 */
 
 #ifndef CALC_ADDEND

-- 
Alan Modra
Australia Development Lab, IBM