Fix standalone GC on ARM32 (#38970)

* Fix standalone GC on ARM32

The standalone build of GC on ARM32 was missing the FEATURE_64BIT_ALIGNMENT,
which caused aligment failures at runtime for objects that require align
on 8 byte boundary and were not getting it.

This change fixes that. I had to modify the copy of MethodTable that the
standalone GC uses so that the RequireAlign8 flag can be checked.

* Move the FEATURE_64BIT_ALIGNMENT setting to gcenv.object.h

* Fix debug build where an assert required MethodTable::IsValueType

diff --git a/src/coreclr/src/gc/env/gcenv.object.h b/src/coreclr/src/gc/env/gcenv.object.h
index 7a8976f..c5c6d42 100644 (file)
--- a/src/coreclr/src/gc/env/gcenv.object.h
+++ b/src/coreclr/src/gc/env/gcenv.object.h
@@ -4,6 +4,13 @@
 #ifndef __GCENV_OBJECT_H__
 #define __GCENV_OBJECT_H__
 
+// ARM requires that 64-bit primitive types are aligned at 64-bit boundaries for interlocked-like operations.
+// Additionally the platform ABI requires these types and composite type containing them to be similarly
+// aligned when passed as arguments.
+#ifdef TARGET_ARM
+#define FEATURE_64BIT_ALIGNMENT
+#endif
+
 //-------------------------------------------------------------------------------------------------
 //
 // Low-level types describing GC object layouts.
@@ -35,18 +42,25 @@ public:
 
 static_assert(sizeof(ObjHeader) == sizeof(uintptr_t), "this assumption is made by the VM!");
 
-#define MTFlag_ContainsPointers     0x0100
-#define MTFlag_HasCriticalFinalizer 0x0800
-#define MTFlag_HasFinalizer         0x0010
-#define MTFlag_IsArray              0x0008
-#define MTFlag_Collectible          0x1000
-#define MTFlag_HasComponentSize     0x8000
+#define MTFlag_RequireAlign8            0x00001000
+#define MTFlag_Category_ValueType       0x00040000
+#define MTFlag_Category_ValueType_Mask  0x000C0000
+#define MTFlag_ContainsPointers         0x01000000
+#define MTFlag_HasCriticalFinalizer     0x08000000
+#define MTFlag_HasFinalizer             0x00100000
+#define MTFlag_IsArray                  0x00080000
+#define MTFlag_Collectible              0x10000000
+#define MTFlag_HasComponentSize         0x80000000
 
 class MethodTable
 {
 public:
-    uint16_t    m_componentSize;
-    uint16_t    m_flags;
+    union
+    {
+        uint16_t    m_componentSize;
+        uint32_t    m_flags;
+    };
+
     uint32_t    m_baseSize;
 
     MethodTable * m_pRelatedType;
@@ -55,8 +69,8 @@ public:
     void InitializeFreeObject()
     {
         m_baseSize = 3 * sizeof(void *);
-        m_componentSize = 1;
         m_flags = MTFlag_HasComponentSize | MTFlag_IsArray;
+        m_componentSize = 1;
     }
 
     uint32_t GetBaseSize()
@@ -84,6 +98,16 @@ public:
         return ContainsPointers() || Collectible();
     }
 
+    bool RequiresAlign8()
+    {
+        return (m_flags & MTFlag_RequireAlign8) != 0;
+    }
+
+    bool IsValueType()
+    {
+        return (m_flags & MTFlag_Category_ValueType_Mask) == MTFlag_Category_ValueType;
+    }
+
     bool HasComponentSize()
     {
         // Note that we can't just check m_componentSize != 0 here. The VM