[PATCH v6 4/6] fix potential logic error

[Etaash Mathamsetty]

From: Etaash Mathamsetty

---
 dlls/ntoskrnl.exe/instr.c | 31 +++++++++++++++++--------------
 1 file changed, 17 insertions(+), 14 deletions(-)

diff --git a/dlls/ntoskrnl.exe/instr.c b/dlls/ntoskrnl.exe/instr.c
index b4c646bb3b2..55a3ea8d0d3 100644
--- a/dlls/ntoskrnl.exe/instr.c
+++ b/dlls/ntoskrnl.exe/instr.c
@@ -893,31 +893,34 @@ static DWORD emulate_instruction( EXCEPTION_RECORD *rec, CONTEXT *context )
     case 0x38:
     case 0x39: /* cmp r/m r/m*/
     {
-        BYTE* data = NULL;
-        BYTE* data2 = NULL;
-        data = INSTR_GetOperandAddr(context, instr + 1, prefixlen + 1, long_addr, rex, segprefix, &len);
-        data2 = INSTR_GetOperandAddr(context, instr + 2, prefixlen + 2, long_addr, rex, segprefix, &len);
+        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);
+        BOOL is_user_shared_data = FALSE;
         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 */
+            TRACE("USD offset %#x at %p\n",(unsigned int) offset, (void*) context->Rip);
+            data = wine_user_shared_data + offset;
+            is_user_shared_data = TRUE;
+        }
+        if(offset2 <= KSHARED_USER_DATA_PAGE_SIZE - data_size)
+        {
+            TRACE("USD offset %#x at %p", (unsigned int) offset2, (void*) context->Rip);
+            data2 = wine_user_shared_data + offset2;
+            is_user_shared_data = TRUE;
+        }
+        if(is_user_shared_data){
+             /* clear ZF and CF */
             context->EFlags &= ~(1UL << 6);
             context->EFlags &= ~(1UL);

-            if(*(wine_user_shared_data + offset) == *data2)
+            if(*data == *data2)
             {
                 context->EFlags |= (1UL << 6); /* ZF */
             }
-            else if(*(wine_user_shared_data + offset) < *data2){
+            else if(*data < *data2){
                 context->EFlags |= 1UL; /* CF */
             }
             context->Rip += prefixlen + len + 1;