Implement GenericComCallStub

Author: jkotas

src/coreclr/vm/comtoclrcall.h

@@ -325,12 +325,6 @@ class ComCallMethodDesc
         return -COMMETHOD_PREPAD;
     }
 
-    static DWORD GetOffsetOfMethodDesc()
-    {
-        LIMITED_METHOD_CONTRACT;
-        return ((DWORD) offsetof(class ComCallMethodDesc, m_pMD));
-    }
-
     //get call sig
     PCCOR_SIGNATURE GetSig(DWORD *pcbSigSize = NULL)
     {

src/coreclr/vm/dllimportcallback.h

@@ -308,12 +308,6 @@ class UMEntryThunk
         RETURN m_pMD;
     }
 
-    static DWORD GetOffsetOfMethodDesc()
-    {
-        LIMITED_METHOD_CONTRACT;
-        return offsetof(class UMEntryThunk, m_pMD);
-    }
-
     static DWORD GetCodeOffset()
     {
         LIMITED_METHOD_CONTRACT;

src/coreclr/vm/frames.h

@@ -1820,20 +1820,6 @@ class UnmanagedToManagedFrame : public Frame
         return m_pvDatum;
     }
 
-    static int GetOffsetOfDatum()
-    {
-        LIMITED_METHOD_CONTRACT;
-        return offsetof(UnmanagedToManagedFrame, m_pvDatum);
-    }
-
-#ifdef TARGET_X86
-    static int GetOffsetOfCalleeSavedRegisters()
-    {
-        LIMITED_METHOD_CONTRACT;
-        return offsetof(UnmanagedToManagedFrame, m_calleeSavedRegisters);
-    }
-#endif
-
     int GetFrameType()
     {
         LIMITED_METHOD_DAC_CONTRACT;

src/coreclr/vm/i386/asmconstants.h

@@ -212,6 +212,8 @@ ASMCONSTANTS_C_ASSERT(OFFSETOF__FrameHandlerExRecord__m_pEntryFrame == offsetof(
 #define STACK_OVERWRITE_BARRIER_VALUE 0xabcdefab
 #endif
 
+#define COMMETHOD_PREPAD_ASM  8
+ASMCONSTANTS_C_ASSERT(COMMETHOD_PREPAD_ASM == COMMETHOD_PREPAD)
 #endif
 
 #define CLRToCOMCallMethodDesc__m_pCLRToCOMCallInfo DBG_FRE(0x20, 0xC)

src/coreclr/vm/i386/asmhelpers.asm

@@ -46,6 +46,7 @@ EXTERN _TheUMEntryPrestubWorker@4:PROC
 
 ifdef FEATURE_COMINTEROP
 EXTERN _CLRToCOMWorker@8:PROC
+EXTERN _COMToCLRWorker@4:PROC
 endif
 
 EXTERN _ExternalMethodFixupWorker@16:PROC
@@ -1237,7 +1238,44 @@ _GenericCLRToCOMCallStub@0 proc public
 _GenericCLRToCOMCallStub@0 endp
 
 _GenericComCallStub@0 proc public
-    int 3
+
+    ; Pop ComCallMethodDesc* pushed by prestub
+    pop         eax
+
+    ; push ebp-frame
+    push        ebp
+    mov         ebp,esp
+
+    ; save CalleeSavedRegisters
+    push        ebx
+    push        esi
+    push        edi
+
+    push        eax         ; datum
+    sub         esp, 3*4    ; next, vtable, gscookie
+
+    lea         eax, [esp+4]
+
+    push        eax
+    call        _COMToCLRWorker@4
+
+    add         esp, 3*4
+
+    ; pop the MethodDesc*
+    pop         ecx
+
+    ; pop CalleeSavedRegisters
+    pop         edi
+    pop         esi
+    pop         ebx
+    pop         ebp
+
+    sub         ecx, COMMETHOD_PREPAD_ASM
+    jmp         ecx
+
+    ; This will never be executed. It is just to help out stack-walking logic
+    ; which disassembles the epilog to unwind the stack.
+    ret
 
 _GenericComCallStub@0 endp