[PATCH v3 1/3] implement cmp instruction

[Etaash Mathamsetty]

From: Etaash Mathamsetty

with opcode 0x38 and 0x39
---
 dlls/ntoskrnl.exe/instr.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/dlls/ntoskrnl.exe/instr.c b/dlls/ntoskrnl.exe/instr.c
index 8f1aa4d45a3..c9c61513a33 100644
--- a/dlls/ntoskrnl.exe/instr.c
+++ b/dlls/ntoskrnl.exe/instr.c
@@ -890,7 +890,39 @@ static DWORD emulate_instruction( EXCEPTION_RECORD *rec, CONTEXT *context )
         }
         break;  /* Unable to emulate it */
     }
+    case 0x38:
+    case 0x39: /* cmp r/m r/m*/
+    {
+        BYTE *data = INSTR_GetOperandAddr(context, instr + 1, prefixlen + 1, long_addr, rex, segprefix, &len);
+        BYTE *data2 = INSTR_GetOperandAddr(context, instr + 2, prefixlen + 2, long_addr, rex, segprefix, &len);
+        SIZE_T offset = data - user_shared_data;
+        SIZE_T offset2 = data2 - user_shared_data;
+        SIZE_T data_size = get_op_size(long_op, rex);
+        if(offset <= KSHARED_USER_DATA_PAGE_SIZE - data_size)
+        {
+            if(offset2 <= KSHARED_USER_DATA_PAGE_SIZE - data_size)
+            {
+                data2 = wine_user_shared_data + offset2;
+                TRACE("USD offset2 %#x at %#p", (unsigned int)offset, (void*)context->Rip);
+            }
+            TRACE("USD offset %#x at %#p\n",(unsigned int) offset, (void*)context->Rip);
+
+            /* clear ZF and CF */
+            context->EFlags &= ~(1UL << 6);
+            context->EFlags &= ~(1UL);

+            if(*(wine_user_shared_data + offset) == *data2)
+            {
+                context->EFlags |= (1UL << 6); /* ZF */
+            }
+            else if(*(wine_user_shared_data + offset) < *data2){
+                context->EFlags |= 1UL; /* CF */
+            }
+            context->Rip += prefixlen + len + 1;
+            return ExceptionContinueExecution;
+        }
+        break;
+    }
     case 0xa0: /* mov Ob, AL */
     case 0xa1: /* mov Ovqp, rAX */
     {