Throw an exception when we try to marshal a non-blittable fixed buffer. (#20263)

* Throw an exception when we try to marshal a non-blittable fixed buffer.

* Move function prototype into fieldmarshaler.cpp

2 files changed, 18 insertions, 2 deletions

diff --git a/src/vm/classnames.h b/src/vm/classnames.h
index 1c1c545451..f62f4a8e19 100644
--- a/src/vm/classnames.h
+++ b/src/vm/classnames.h
@@ -156,6 +156,7 @@
 #define g_UnmanagedFunctionPointerAttribute "System.Runtime.InteropServices.UnmanagedFunctionPointerAttribute"
 #define g_DefaultDllImportSearchPathsAttribute "System.Runtime.InteropServices.DefaultDllImportSearchPathsAttribute"
 #define g_NativeCallableAttribute "System.Runtime.InteropServices.NativeCallableAttribute"
+#define g_FixedBufferAttribute "System.Runtime.CompilerServices.FixedBufferAttribute"
 
 #define g_CompilerServicesTypeDependencyAttribute "System.Runtime.CompilerServices.TypeDependencyAttribute"
 
diff --git a/src/vm/fieldmarshaler.cpp b/src/vm/fieldmarshaler.cpp
index 9cee183f4b..2f93130856 100644
--- a/src/vm/fieldmarshaler.cpp
+++ b/src/vm/fieldmarshaler.cpp
@@ -34,7 +34,8 @@
 // forward declaration
 BOOL CheckForPrimitiveType(CorElementType elemType, CQuickArray<WCHAR> *pStrPrimitiveType);
 TypeHandle ArraySubTypeLoadWorker(const SString &strUserDefTypeName, Assembly* pAssembly);
-TypeHandle GetFieldTypeHandleWorker(MetaSig *pFieldSig);  
+TypeHandle GetFieldTypeHandleWorker(MetaSig *pFieldSig);
+BOOL IsFixedBuffer(mdFieldDef field, IMDInternalImport *pInternalImport);
 
 
 //=======================================================================
@@ -659,7 +660,14 @@ do                                                      \
                 {
                     if (IsStructMarshalable(thNestedType))
                     {
-                        INITFIELDMARSHALER(NFT_NESTEDVALUECLASS, FieldMarshaler_NestedValueClass, (thNestedType.GetMethodTable()));
+                        if (IsFixedBuffer(pfwalk->m_MD, pInternalImport) && !thNestedType.GetMethodTable()->IsBlittable())
+                        {
+                            INITFIELDMARSHALER(NFT_ILLEGAL, FieldMarshaler_Illegal, (IDS_EE_BADMARSHAL_NOTMARSHALABLE));
+                        }
+                        else
+                        {
+                            INITFIELDMARSHALER(NFT_NESTEDVALUECLASS, FieldMarshaler_NestedValueClass, (thNestedType.GetMethodTable()));
+                        }
                     }
                     else
                     {
@@ -1228,6 +1236,13 @@ BOOL IsStructMarshalable(TypeHandle th)
     return TRUE;
 }
 
+BOOL IsFixedBuffer(mdFieldDef field, IMDInternalImport *pInternalImport)
+{
+    HRESULT hr = pInternalImport->GetCustomAttributeByName(field, g_FixedBufferAttribute, NULL, NULL);
+
+    return hr == S_OK ? TRUE : FALSE;
+}
+
 
 //=======================================================================
 // Called from the clsloader to load up and summarize the field metadata