[aandrejevic] 67669: [FAST486] Duplicate prefixes don't generate #UD. Multiple segment overrides override each other, and so do REP and REPNZ.

Author: aandrejevic
Date: Mon May 11 18:49:10 2015
New Revision: 67669

URL: http://svn.reactos.org/svn/reactos?rev=67669&view=rev
Log:
[FAST486]
Duplicate prefixes don't generate #UD. Multiple segment overrides
override each other, and so do REP and REPNZ.


Modified:
    trunk/reactos/lib/fast486/opcodes.c

Modified: trunk/reactos/lib/fast486/opcodes.c
URL:
http://svn.reactos.org/svn/reactos/trunk/reactos/lib/fast486/opcodes.c?rev=…
==============================================================================
--- trunk/reactos/lib/fast486/opcodes.c	[iso-8859-1] (original)
+++ trunk/reactos/lib/fast486/opcodes.c	[iso-8859-1] Mon May 11 18:49:10 2015
@@ -311,120 +311,74 @@
 
 FAST486_OPCODE_HANDLER(Fast486OpcodePrefix)
 {
-    BOOLEAN Valid = FALSE;
-
     switch (Opcode)
     {
         /* ES: */
         case 0x26:
         {
-            if (!(State->PrefixFlags & FAST486_PREFIX_SEG))
-            {
-                State->PrefixFlags |= FAST486_PREFIX_SEG;
-                State->SegmentOverride = FAST486_REG_ES;
-                Valid = TRUE;
-            }
-
+            State->PrefixFlags |= FAST486_PREFIX_SEG;
+            State->SegmentOverride = FAST486_REG_ES;
             break;
         }
 
         /* CS: */
         case 0x2E:
         {
-            if (!(State->PrefixFlags & FAST486_PREFIX_SEG))
-            {
-                State->PrefixFlags |= FAST486_PREFIX_SEG;
-                State->SegmentOverride = FAST486_REG_CS;
-                Valid = TRUE;
-            }
-
+            State->PrefixFlags |= FAST486_PREFIX_SEG;
+            State->SegmentOverride = FAST486_REG_CS;
             break;
         }
 
         /* SS: */
         case 0x36:
         {
-            if (!(State->PrefixFlags & FAST486_PREFIX_SEG))
-            {
-                State->PrefixFlags |= FAST486_PREFIX_SEG;
-                State->SegmentOverride = FAST486_REG_SS;
-                Valid = TRUE;
-            }
-
+            State->PrefixFlags |= FAST486_PREFIX_SEG;
+            State->SegmentOverride = FAST486_REG_SS;
             break;
         }
 
         /* DS: */
         case 0x3E:
         {
-            if (!(State->PrefixFlags & FAST486_PREFIX_SEG))
-            {
-                State->PrefixFlags |= FAST486_PREFIX_SEG;
-                State->SegmentOverride = FAST486_REG_DS;
-                Valid = TRUE;
-            }
-
+            State->PrefixFlags |= FAST486_PREFIX_SEG;
+            State->SegmentOverride = FAST486_REG_DS;
             break;
         }
 
         /* FS: */
         case 0x64:
         {
-            if (!(State->PrefixFlags & FAST486_PREFIX_SEG))
-            {
-                State->PrefixFlags |= FAST486_PREFIX_SEG;
-                State->SegmentOverride = FAST486_REG_FS;
-                Valid = TRUE;
-            }
-
+            State->PrefixFlags |= FAST486_PREFIX_SEG;
+            State->SegmentOverride = FAST486_REG_FS;
             break;
         }
 
         /* GS: */
         case 0x65:
         {
-            if (!(State->PrefixFlags & FAST486_PREFIX_SEG))
-            {
-                State->PrefixFlags |= FAST486_PREFIX_SEG;
-                State->SegmentOverride = FAST486_REG_GS;
-                Valid = TRUE;
-            }
-
+            State->PrefixFlags |= FAST486_PREFIX_SEG;
+            State->SegmentOverride = FAST486_REG_GS;
             break;
         }
 
         /* OPSIZE */
         case 0x66:
         {
-            if (!(State->PrefixFlags & FAST486_PREFIX_OPSIZE))
-            {
-                State->PrefixFlags |= FAST486_PREFIX_OPSIZE;
-                Valid = TRUE;
-            }
-
+            State->PrefixFlags |= FAST486_PREFIX_OPSIZE;
             break;
         }
 
         /* ADSIZE */
         case 0x67:
         {
-            if (!(State->PrefixFlags & FAST486_PREFIX_ADSIZE))
-            {
-                State->PrefixFlags |= FAST486_PREFIX_ADSIZE;
-                Valid = TRUE;
-            }
+            State->PrefixFlags |= FAST486_PREFIX_ADSIZE;
             break;
         }
 
         /* LOCK */
         case 0xF0:
         {
-            if (!(State->PrefixFlags & FAST486_PREFIX_LOCK))
-            {
-                State->PrefixFlags |= FAST486_PREFIX_LOCK;
-                Valid = TRUE;
-            }
-
+            State->PrefixFlags |= FAST486_PREFIX_LOCK;
             break;
         }
 
@@ -432,13 +386,8 @@
         case 0xF2:
         {
             /* Mutually exclusive with REP */
-            if (!(State->PrefixFlags
-                & (FAST486_PREFIX_REPNZ | FAST486_PREFIX_REP)))
-            {
-                State->PrefixFlags |= FAST486_PREFIX_REPNZ;
-                Valid = TRUE;
-            }
-
+            State->PrefixFlags |= FAST486_PREFIX_REPNZ;
+            State->PrefixFlags &= ~FAST486_PREFIX_REP;
             break;
         }
 
@@ -446,24 +395,16 @@
         case 0xF3:
         {
             /* Mutually exclusive with REPNZ */
-            if (!(State->PrefixFlags
-                & (FAST486_PREFIX_REPNZ | FAST486_PREFIX_REP)))
-            {
-                State->PrefixFlags |= FAST486_PREFIX_REP;
-                Valid = TRUE;
-            }
-
+            State->PrefixFlags |= FAST486_PREFIX_REP;
+            State->PrefixFlags &= ~FAST486_PREFIX_REPNZ;
             break;
         }
-    }
-
-    if (!Valid)
-    {
-        /* Clear all prefixes */
-        State->PrefixFlags = 0;
-
-        /* Throw an exception */
-        Fast486Exception(State, FAST486_EXCEPTION_UD);
+
+        default:
+        {
+            /* Shouldn't happen */
+            ASSERT(FALSE);
+        }
     }
 }