Clean up multi byte nop support on x64 to more closely match IA32.

src/x64/disasm-x64.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 91 matching lines @@
   { 0x8B, REG_OPER_OP_ORDER,      "mov" },
   { 0x8D, REG_OPER_OP_ORDER,      "lea" },
   { -1, UNSET_OP_ORDER, "" }
 };
 
 
 static const ByteMnemonic zero_operands_instr[] = {
   { 0xC3, UNSET_OP_ORDER, "ret" },
   { 0xC9, UNSET_OP_ORDER, "leave" },
   { 0xF4, UNSET_OP_ORDER, "hlt" },
+  { 0xFC, UNSET_OP_ORDER, "cld" },
   { 0xCC, UNSET_OP_ORDER, "int3" },
   { 0x60, UNSET_OP_ORDER, "pushad" },
   { 0x61, UNSET_OP_ORDER, "popad" },
   { 0x9C, UNSET_OP_ORDER, "pushfd" },
   { 0x9D, UNSET_OP_ORDER, "popfd" },
   { 0x9E, UNSET_OP_ORDER, "sahf" },
   { 0x99, UNSET_OP_ORDER, "cdq" },
   { 0x9B, UNSET_OP_ORDER, "fwait" },
   { 0xA4, UNSET_OP_ORDER, "movs" },
   { 0xA5, UNSET_OP_ORDER, "movs" },
@@ skipping 905 matching lines @@
          // roundsd xmm, xmm/m64, imm8
         AppendToBuffer("roundsd %s, ", NameOfCPURegister(regop));
         current += PrintRightOperand(current);
         AppendToBuffer(", %d", (*current) & 3);
         current += 1;
       } else {
         UnimplementedInstruction();
       }
     } else {
       get_modrm(*current, &mod, &regop, &rm);
-      if (opcode == 0x28) {
+      if (opcode == 0x1f) {
+        current++;
+        if (rm == 4) {  // SIB byte present.
+          current++;
+        }
+        if (mod == 1) {  // Byte displacement.
+          current += 1;
+        } else if (mod == 2) {  // 32-bit displacement.
+          current += 4;
+        }  // else no immediate displacement.
+        AppendToBuffer("nop");
+      } else if (opcode == 0x28) {
         AppendToBuffer("movapd %s, ", NameOfXMMRegister(regop));
         current += PrintRightXMMOperand(current);
       } else if (opcode == 0x29) {
         AppendToBuffer("movapd ");
         current += PrintRightXMMOperand(current);
         AppendToBuffer(", %s", NameOfXMMRegister(regop));
       } else if (opcode == 0x6E) {
         AppendToBuffer("mov%c %s,",
                        rex_w() ? 'q' : 'd',
                        NameOfXMMRegister(regop));
@@ skipping 123 matching lines @@
       AppendToBuffer("movq %s, ", NameOfXMMRegister(regop));
       current += PrintRightXMMOperand(current);
     } else {
       UnimplementedInstruction();
     }
   } else if (opcode == 0x1F) {
     // NOP
     int mod, regop, rm;
     get_modrm(*current, &mod, &regop, &rm);
     current++;
-    if (regop == 4) {  // SIB byte present.
+    if (rm == 4) {  // SIB byte present.
       current++;
     }
     if (mod == 1) {  // Byte displacement.
       current += 1;
     } else if (mod == 2) {  // 32-bit displacement.
       current += 4;
     }  // else no immediate displacement.
     AppendToBuffer("nop");
 
   } else if (opcode == 0x28) {
@@ skipping 633 matching lines @@
     for (int i = 6 - static_cast<int>(pc - prev_pc); i >= 0; i--) {
       fprintf(f, "  ");
     }
     fprintf(f, "  %s\n", buffer.start());
   }
 }
 
 }  // namespace disasm
 
 #endif  // V8_TARGET_ARCH_X64