Add comments and fix FaultingExceptionFrame on amd64

Author: Mike McLaughlin

src/coreclr/vm/amd64/asmconstants.h

@@ -449,11 +449,11 @@ ASMCONSTANTS_C_ASSERT(OFFSETOF__CONTEXT__VectorRegister
 ASMCONSTANTS_C_ASSERT(SIZEOF__FaultingExceptionFrame
                     == sizeof(FaultingExceptionFrame));
 
-#define               OFFSETOF__FaultingExceptionFrame__m_fFilterExecuted 0x10
+#define               OFFSETOF__FaultingExceptionFrame__m_fFilterExecuted (SIZEOF__Frame + 0x8)
 ASMCONSTANTS_C_ASSERT(OFFSETOF__FaultingExceptionFrame__m_fFilterExecuted
                     == offsetof(FaultingExceptionFrame, m_fFilterExecuted));
 
-#define               OFFSETOF__FaultingExceptionFrame__m_SSP (0x20 + SIZEOF__CONTEXT)
+#define               OFFSETOF__FaultingExceptionFrame__m_SSP (SIZEOF__Frame)
 ASMCONSTANTS_C_ASSERT(OFFSETOF__FaultingExceptionFrame__m_SSP
                     == offsetof(FaultingExceptionFrame, m_SSP));
 

src/coreclr/vm/frames.h

@@ -933,6 +933,10 @@ class FaultingExceptionFrame : public Frame
 {
     friend class CheckAsmOffsets;
 
+#ifdef TARGET_AMD64
+    TADDR                   m_SSP;
+#endif
+
 #ifndef FEATURE_EH_FUNCLETS
 #ifdef TARGET_X86
     DWORD                   m_Esp;
@@ -944,13 +948,11 @@ class FaultingExceptionFrame : public Frame
 #else // FEATURE_EH_FUNCLETS
     BOOL                    m_fFilterExecuted;  // Flag for FirstCallToHandler
     TADDR                   m_ReturnAddress;
+    // This T_CONTEXT field needs to be the last field in the class because it is a
+    // different size between Linux (pal.h) and the Windows cross-DAC (winnt.h).
     T_CONTEXT               m_ctx;
 #endif // !FEATURE_EH_FUNCLETS
 
-#ifdef TARGET_AMD64
-    TADDR                   m_SSP;
-#endif
-
 public:
 #ifndef DACCESS_COMPILE
     FaultingExceptionFrame() : Frame(FrameIdentifier::FaultingExceptionFrame) {
@@ -1042,6 +1044,8 @@ class SoftwareExceptionFrame : public Frame
 {
     TADDR                           m_ReturnAddress;
     T_KNONVOLATILE_CONTEXT_POINTERS m_ContextPointers;
+    // This T_CONTEXT field needs to be the last field in the class because it is a
+    // different size between Linux (pal.h) and the Windows cross-DAC (winnt.h).
     T_CONTEXT                       m_Context;
 
 public: