[Mono-bugs] [Bug 58881][Maj] Changed - [patch] marshalling of struct params to functions passed as unmanaged delegates broken

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Changed by vladimir@pobox.com.

http://bugzilla.ximian.com/show_bug.cgi?id=58881

--- shadow/58881	2004-05-26 16:36:39.000000000 -0400
+++ shadow/58881.tmp.21777	2004-05-26 21:36:26.000000000 -0400
@@ -141,6 +141,23 @@
 managed delegate, the unmanaged code never gets those modifications (i
 and j == 0 after return from invoking the managed delegate).  The
 runtime never copies the contents back, I assume because it's treating
 the ref SomeStruct as [In] only?  (I assume that ref should imply
 In/Out; otherwise, you have different behaviour depending on whether
 your ref argument is blittable or not.)
+
+------- Additional Comments From vladimir@pobox.com  2004-05-26 21:36 -------
+This is related to struct layout alignment; according to
+http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfsystemruntimeinteropservicesstructlayoutattributeclasspacktopic.asp
+managed types have a default alignment of 8, "except for unmanaged
+structures that typically have a default packing size of 4."  I'm not
+sure how their runtime decides what an "unmanaged structure" is. 
+We're trying to blit types that have a managed alignment of 8 to
+unmanaged blocks of memory with a different alignment.  There's two
+fixes that I can think of -- one is to simply check if instance_size
+is different from mono_class_native_size(), and if so, set blittable
+to false.  This means that we can't blit within the managed side of
+things either.  The other fix is to introduce a new native_blittable
+flag within klass->marshal_info, and use that when deciding whether we
+can blit to/from unmanaged data types.  I think the latter is a better
+fix.
+