Bochs/bochs/cpu/proc_ctrl.cc

/////////////////////////////////////////////////////////////////////////
// $Id: proc_ctrl.cc,v 1.159 2006-09-10 16:56:55 sshwarts Exp $
/////////////////////////////////////////////////////////////////////////
//
//  Copyright (C) 2001  MandrakeSoft S.A.
//
//    MandrakeSoft S.A.
//    43, rue d'Aboukir
//    75002 Paris - France
//    http://www.linux-mandrake.com/
//    http://www.mandrakesoft.com/
//
//  This library is free software; you can redistribute it and/or
//  modify it under the terms of the GNU Lesser General Public
//  License as published by the Free Software Foundation; either
//  version 2 of the License, or (at your option) any later version.
//
//  This library is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
//  Lesser General Public License for more details.
//
//  You should have received a copy of the GNU Lesser General Public
//  License along with this library; if not, write to the Free Software
//  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA


#define NEED_CPU_REG_SHORTCUTS 1
#include "bochs.h"
#include "cpu.h"
#define LOG_THIS BX_CPU_THIS_PTR


#if BX_SUPPORT_X86_64==0
// Make life easier for merging code.
#define RAX EAX
#define RBX EBX
#define RCX ECX
#define RDX EDX
#endif

void BX_CPU_C::UndefinedOpcode(bxInstruction_c *i)
{
  BX_DEBUG(("UndefinedOpcode: %02x causes exception 6", (unsigned) i->b1()));
  exception(BX_UD_EXCEPTION, 0, 0);
}

void BX_CPU_C::NOP(bxInstruction_c *i)
{
  // No operation.
}

void BX_CPU_C::PREFETCH(bxInstruction_c *i)
{
#if BX_SUPPORT_3DNOW || BX_SUPPORT_SSE >= 1
  BX_INSTR_PREFETCH_HINT(BX_CPU_ID, i->nnn(), i->seg(), RMAddr(i));
#else
  UndefinedOpcode(i);
#endif
}

//
// The shutdown state is very similar to the state following the exection 
// if HLT instruction. In this mode the processor stops executing 
// instructions until #NMI, #SMI, #RESET or #INIT is received. If 
// shutdown occurs why in NMI interrupt handler or in SMM, a hardware 
// reset must be used to restart the processor execution.
//
void BX_CPU_C::shutdown(void)
{
  BX_PANIC(("Entering to shutdown state still not implemented"));

  BX_CPU_THIS_PTR clear_IF();

  // artificial trap bit, why use another variable.
  BX_CPU_THIS_PTR debug_trap |= BX_DEBUG_TRAP_HALT_STATE; // artificial trap
  BX_CPU_THIS_PTR async_event = 1; // so processor knows to check
  // Execution of this instruction completes.  The processor
  // will remain in a halt state until one of the above conditions
  // is met.

  BX_INSTR_HLT(BX_CPU_ID);

#if BX_USE_IDLE_HACK  
  bx_gui->sim_is_idle ();
#endif /* BX_USE_IDLE_HACK */  

  longjmp(BX_CPU_THIS_PTR jmp_buf_env, 1); // go back to main decode loop
}

void BX_CPU_C::HLT(bxInstruction_c *i)
{
  // hack to panic if HLT comes from BIOS
  if (BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].selector.value == 0xf000)
    BX_PANIC(("HALT instruction encountered in the BIOS ROM"));

  if (!real_mode() && CPL!=0) {
    BX_ERROR(("HLT: %s priveledge check failed, CPL=%d, generate #GP(0)",
        cpu_mode_string(BX_CPU_THIS_PTR cpu_mode), CPL));
    exception(BX_GP_EXCEPTION, 0, 0);
    return;
  }

  if (! BX_CPU_THIS_PTR get_IF()) {
    BX_INFO(("WARNING: HLT instruction with IF=0!"));
  }

  // stops instruction execution and places the processor in a
  // HALT state.  An enabled interrupt, NMI, or reset will resume
  // execution.  If interrupt (including NMI) is used to resume
  // execution after HLT, the saved CS:eIP points to instruction
  // following HLT.

  // artificial trap bit, why use another variable.
  BX_CPU_THIS_PTR debug_trap |= BX_DEBUG_TRAP_HALT_STATE; // artificial trap
  BX_CPU_THIS_PTR async_event = 1; // so processor knows to check
  // Execution of this instruction completes.  The processor
  // will remain in a halt state until one of the above conditions
  // is met.

  BX_INSTR_HLT(BX_CPU_ID);

#if BX_USE_IDLE_HACK  
  bx_gui->sim_is_idle ();
#endif /* BX_USE_IDLE_HACK */  
}

void BX_CPU_C::CLTS(bxInstruction_c *i)
{
  // #GP(0) if CPL is not 0
  if (!real_mode() && CPL!=0) {
    BX_ERROR(("CLTS: priveledge check failed, generate #GP(0)"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }

  BX_CPU_THIS_PTR cr0.ts = 0;
  BX_CPU_THIS_PTR cr0.val32 &= ~0x08;
}

void BX_CPU_C::INVD(bxInstruction_c *i)
{
#if BX_CPU_LEVEL >= 4
  invalidate_prefetch_q();

  // protected or v8086 mode
  if (BX_CPU_THIS_PTR cr0.pe) {
    if (CPL!=0) {
      BX_ERROR(("INVD: priveledge check failed, generate #GP(0)"));
      exception(BX_GP_EXCEPTION, 0, 0);
    }
  }

  BX_DEBUG(("INVD: Flush caches and TLB !"));
  BX_INSTR_CACHE_CNTRL(BX_CPU_ID, BX_INSTR_INVD);
  TLB_flush(1); // 1 = Flush Global entries too
#if BX_SUPPORT_ICACHE
  flushICaches();
#endif

#else
  BX_INFO(("INVD: required 486 support, use --enable-cpu-level=4 option"));
  UndefinedOpcode(i);
#endif
}

void BX_CPU_C::WBINVD(bxInstruction_c *i)
{
#if BX_CPU_LEVEL >= 4
  invalidate_prefetch_q();

  if (BX_CPU_THIS_PTR cr0.pe) {
    if (CPL!=0) {
      BX_ERROR(("WBINVD: priveledge check failed, generate #GP(0)"));
      exception(BX_GP_EXCEPTION, 0, 0);
    }
  }

  BX_DEBUG(("WBINVD: Flush caches and TLB !"));
  BX_INSTR_CACHE_CNTRL(BX_CPU_ID, BX_INSTR_WBINVD);
  TLB_flush(1); // 1 = Flush Global entries too
#if BX_SUPPORT_ICACHE
  flushICaches();
#endif

#else
  BX_INFO(("WBINVD: required 486 support, use --enable-cpu-level=4 option"));
  UndefinedOpcode(i);
#endif
}

#if BX_CPU_LEVEL >= 3
void BX_CPU_C::MOV_DdRd(bxInstruction_c *i)
{
  Bit32u val_32;

  if (!real_mode() && CPL!=0) {
    BX_ERROR(("MOV_DdRd: CPL!=0 not in real mode"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }

  /* NOTES:
   *   32bit operands always used
   *   r/m field specifies general register
   *   reg field specifies which special register
   */

  /* This instruction is always treated as a register-to-register,
   * regardless of the encoding of the MOD field in the MODRM byte.   
   */
  if (!i->modC0())
    BX_PANIC(("MOV_DdRd(): rm field not a register!"));

  invalidate_prefetch_q();

  val_32 = BX_READ_32BIT_REG(i->rm());
  if (bx_dbg.dreg)
    BX_INFO(("MOV_DdRd: DR[%u]=%08xh unhandled",
      (unsigned) i->nnn(), (unsigned) val_32));

  switch (i->nnn()) {
    case 0: // DR0
      BX_CPU_THIS_PTR dr0 = val_32;
      break;
    case 1: // DR1
      BX_CPU_THIS_PTR dr1 = val_32;
      break;
    case 2: // DR2
      BX_CPU_THIS_PTR dr2 = val_32;
      break;
    case 3: // DR3
      BX_CPU_THIS_PTR dr3 = val_32;
      break;

    case 4: // DR4
      // DR4 aliased to DR6 by default.  With Debug Extensions on,
      // access to DR4 causes #UD
#if BX_CPU_LEVEL >= 4
      if (BX_CPU_THIS_PTR cr4.get_DE()) {
        // Debug extensions CR4.DE is ON
        BX_INFO(("MOV_DdRd: access to DR4 causes #UD"));
        UndefinedOpcode(i);
      }
#endif
      // Fall through to DR6 case
    case 6: // DR6
#if BX_CPU_LEVEL <= 4
      // On 386/486 bit12 is settable
      BX_CPU_THIS_PTR dr6 = (BX_CPU_THIS_PTR dr6 & 0xffff0ff0) |
                            (val_32 & 0x0000f00f);
#else
      // On Pentium+, bit12 is always zero
      BX_CPU_THIS_PTR dr6 = (BX_CPU_THIS_PTR dr6 & 0xffff0ff0) |
                            (val_32 & 0x0000e00f);
#endif
      break;

    case 5: // DR5
      // DR5 aliased to DR7 by default.  With Debug Extensions on,
      // access to DR5 causes #UD
#if BX_CPU_LEVEL >= 4
      if (BX_CPU_THIS_PTR cr4.get_DE()) {
        // Debug extensions CR4.DE is ON
        BX_INFO(("MOV_DdRd: access to DR5 causes #UD"));
        UndefinedOpcode(i);
      }
#endif
      // Fall through to DR7 case
    case 7: // DR7
      // Note: 486+ ignore GE and LE flags.  On the 386, exact
      // data breakpoint matching does not occur unless it is enabled
      // by setting the LE and/or GE flags.

      // Some sanity checks...
      if (val_32 & 0x00002000) {
        BX_INFO(("MOV_DdRd: GD bit not supported yet"));
        // Note: processor clears GD upon entering debug exception
        // handler, to allow access to the debug registers
      }
      if ( (((val_32>>16) & 3)==2) ||
           (((val_32>>20) & 3)==2) ||
           (((val_32>>24) & 3)==2) ||
           (((val_32>>28) & 3)==2) ) {
        // IO breakpoints (10b) are not yet supported.
        BX_PANIC(("MOV_DdRd: write of %08x contains IO breakpoint", val_32));
      }
      if ( (((val_32>>18) & 3)==2) ||
           (((val_32>>22) & 3)==2) ||
           (((val_32>>26) & 3)==2) ||
           (((val_32>>30) & 3)==2) ) {
        // LEN0..3 contains undefined length specifier (10b)
        BX_PANIC(("MOV_DdRd: write of %08x contains undefined LENx", val_32));
      }
      if ( ((((val_32>>16) & 3)==0) && (((val_32>>18) & 3)!=0)) ||
           ((((val_32>>20) & 3)==0) && (((val_32>>22) & 3)!=0)) ||
           ((((val_32>>24) & 3)==0) && (((val_32>>26) & 3)!=0)) ||
           ((((val_32>>28) & 3)==0) && (((val_32>>30) & 3)!=0)) )
      {
        // Instruction breakpoint with LENx not 00b (1-byte length)
        BX_PANIC(("MOV_DdRd: write of %08x, R/W=00b LEN!=00b", val_32));
      }
#if BX_CPU_LEVEL <= 4
      // 386/486: you can play with all the bits except b10 is always 1
      BX_CPU_THIS_PTR dr7 = val_32 | 0x00000400;
#else
      // Pentium+: bits15,14,12 are hardwired to 0, rest are settable.
      // Even bits 11,10 are changeable though reserved.
      BX_CPU_THIS_PTR dr7 = (val_32 & 0xffff2fff) | 0x00000400;
#endif
      // if we have breakpoints enabled then we must check
      // breakpoints condition in cpu loop
      if(BX_CPU_THIS_PTR dr7 & 0xff)
        BX_CPU_THIS_PTR async_event = 1;
      break;

    default:
      BX_PANIC(("MOV_DdRd: control register index out of range"));
      break;
  }
}

void BX_CPU_C::MOV_RdDd(bxInstruction_c *i)
{
  Bit32u val_32;

  if (!real_mode() && CPL!=0) {
    BX_ERROR(("MOV_RdDd: CPL!=0 not in real mode"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }

  /* This instruction is always treated as a register-to-register,
   * regardless of the encoding of the MOD field in the MODRM byte.   
   */
  if (!i->modC0())
    BX_PANIC(("MOV_RdDd(): rm field not a register!"));

  if (bx_dbg.dreg)
    BX_INFO(("MOV_RdDd: DR%u not implemented yet", i->nnn()));

  switch (i->nnn()) {
    case 0: // DR0
      val_32 = BX_CPU_THIS_PTR dr0;
      break;
    case 1: // DR1
      val_32 = BX_CPU_THIS_PTR dr1;
      break;
    case 2: // DR2
      val_32 = BX_CPU_THIS_PTR dr2;
      break;
    case 3: // DR3
      val_32 = BX_CPU_THIS_PTR dr3;
      break;

    case 4: // DR4
      // DR4 aliased to DR6 by default.  With Debug Extensions on,
      // access to DR4 causes #UD
#if BX_CPU_LEVEL >= 4
      if (BX_CPU_THIS_PTR cr4.get_DE()) {
        // Debug extensions CR4.DE is ON
        BX_INFO(("MOV_RdDd: access to DR4 causes #UD"));
        UndefinedOpcode(i);
      }
#endif
      // Fall through to DR6 case
    case 6: // DR6
      val_32 = BX_CPU_THIS_PTR dr6;
      break;

    case 5: // DR5
      // DR5 aliased to DR7 by default.  With Debug Extensions on,
      // access to DR5 causes #UD
#if BX_CPU_LEVEL >= 4
      if (BX_CPU_THIS_PTR cr4.get_DE()) {
        // Debug extensions CR4.DE is ON
        BX_INFO(("MOV_RdDd: access to DR5 causes #UD"));
        UndefinedOpcode(i);
      }
#endif
      // Fall through to DR7 case
    case 7: // DR7
      val_32 = BX_CPU_THIS_PTR dr7;
      break;

    default:
      BX_PANIC(("MOV_RdDd: control register index out of range"));
      val_32 = 0;
  }
  BX_WRITE_32BIT_REGZ(i->rm(), val_32);
}

#if BX_SUPPORT_X86_64
void BX_CPU_C::MOV_DqRq(bxInstruction_c *i)
{
  BX_ASSERT(protected_mode());

  /* NOTES:
   *   64bit operands always used
   *   r/m field specifies general register
   *   reg field specifies which special register
   */

  /* This instruction is always treated as a register-to-register,
   * regardless of the encoding of the MOD field in the MODRM byte.   
   */
  if (!i->modC0())
    BX_PANIC(("MOV_DqRq(): rm field not a register!"));

  invalidate_prefetch_q();

  /* #GP(0) if CPL is not 0 */
  if (CPL != 0) {
    BX_ERROR(("MOV_DqRq: #GP(0) if CPL is not 0"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }

  Bit64u val_64 = BX_READ_64BIT_REG(i->rm());
  if (bx_dbg.dreg)
    BX_INFO(("MOV_DqRq: DR[%u]=%08xh unhandled", i->nnn(), (unsigned) val_64));

  switch (i->nnn()) {
    case 0: // DR0
      BX_CPU_THIS_PTR dr0 = val_64;
      break;
    case 1: // DR1
      BX_CPU_THIS_PTR dr1 = val_64;
      break;
    case 2: // DR2
      BX_CPU_THIS_PTR dr2 = val_64;
      break;
    case 3: // DR3
      BX_CPU_THIS_PTR dr3 = val_64;
      break;

    case 4: // DR4
      // DR4 aliased to DR6 by default.  With Debug Extensions on,
      // access to DR4 causes #UD
      if (BX_CPU_THIS_PTR cr4.get_DE()) {
        // Debug extensions CR4.DE is ON
        BX_INFO(("MOV_DqRq: access to DR4 causes #UD"));
        UndefinedOpcode(i);
      }
      // Fall through to DR6 case
    case 6: // DR6
      // On Pentium+, bit12 is always zero
      BX_CPU_THIS_PTR dr6 = (BX_CPU_THIS_PTR dr6 & 0xffff0ff0) |
                            (val_64 & 0x0000e00f);
      break;

    case 5: // DR5
      // DR5 aliased to DR7 by default.  With Debug Extensions on,
      // access to DR5 causes #UD
      if (BX_CPU_THIS_PTR cr4.get_DE()) {
        // Debug extensions CR4.DE is ON
        BX_INFO(("MOV_DqRq: access to DR5 causes #UD"));
        UndefinedOpcode(i);
      }
      // Fall through to DR7 case
    case 7: // DR7
      // Note: 486+ ignore GE and LE flags.  On the 386, exact
      // data breakpoint matching does not occur unless it is enabled
      // by setting the LE and/or GE flags.

      // Some sanity checks...
      if (val_64 & 0x00002000) {
        BX_PANIC(("MOV_DqRq: GD bit not supported yet"));
        // Note: processor clears GD upon entering debug exception
        // handler, to allow access to the debug registers
      }
      if ( (((val_64>>16) & 3)==2) ||
           (((val_64>>20) & 3)==2) ||
           (((val_64>>24) & 3)==2) ||
           (((val_64>>28) & 3)==2) )
      {
        // IO breakpoints (10b) are not yet supported.
        BX_PANIC(("MOV_DqRq: write of %08x:%08x contains IO breakpoint", 
          (Bit32u)(val_64 >> 32), (Bit32u)(val_64 & 0xFFFFFFFF)));
      }
      if ( (((val_64>>18) & 3)==2) ||
           (((val_64>>22) & 3)==2) ||
           (((val_64>>26) & 3)==2) ||
           (((val_64>>30) & 3)==2) )
      {
        // LEN0..3 contains undefined length specifier (10b)
        BX_PANIC(("MOV_DqRq: write of %08x:%08x contains undefined LENx",
          (Bit32u)(val_64 >> 32), (Bit32u)(val_64 & 0xFFFFFFFF)));
      }
      if ( ((((val_64>>16) & 3)==0) && (((val_64>>18) & 3)!=0)) ||
           ((((val_64>>20) & 3)==0) && (((val_64>>22) & 3)!=0)) ||
           ((((val_64>>24) & 3)==0) && (((val_64>>26) & 3)!=0)) ||
           ((((val_64>>28) & 3)==0) && (((val_64>>30) & 3)!=0)) )
      {
        // Instruction breakpoint with LENx not 00b (1-byte length)
        BX_PANIC(("MOV_DqRq: write of %08x:%08x , R/W=00b LEN!=00b",
          (Bit32u)(val_64 >> 32), (Bit32u)(val_64 & 0xFFFFFFFF)));
      }

      // Pentium+: bits15,14,12 are hardwired to 0, rest are settable.
      // Even bits 11,10 are changeable though reserved.
      BX_CPU_THIS_PTR dr7 = (val_64 & 0xffff2fff) | 0x00000400;
      break;

    default:
      BX_PANIC(("MOV_DqRq: control register index out of range"));
      break;
  }
}

void BX_CPU_C::MOV_RqDq(bxInstruction_c *i)
{
  Bit64u val_64;

  BX_ASSERT(protected_mode());

  /* This instruction is always treated as a register-to-register,
   * regardless of the encoding of the MOD field in the MODRM byte.   
   */
  if (!i->modC0())
    BX_PANIC(("MOV_RqDq(): rm field not a register!"));

  /* #GP(0) if CPL is not 0 */
  if (CPL != 0) {
    BX_ERROR(("MOV_RqDq: #GP(0) if CPL is not 0"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }

  if (bx_dbg.dreg)
    BX_INFO(("MOV_RqDq: DR%u not implemented yet", i->nnn()));

  switch (i->nnn()) {
    case 0: // DR0
      val_64 = BX_CPU_THIS_PTR dr0;
      break;
    case 1: // DR1
      val_64 = BX_CPU_THIS_PTR dr1;
      break;
    case 2: // DR2
      val_64 = BX_CPU_THIS_PTR dr2;
      break;
    case 3: // DR3
      val_64 = BX_CPU_THIS_PTR dr3;
      break;

    case 4: // DR4
      // DR4 aliased to DR6 by default.  With Debug Extensions on,
      // access to DR4 causes #UD
      if (BX_CPU_THIS_PTR cr4.get_DE()) {
        // Debug extensions CR4.DE is ON
        BX_INFO(("MOV_RqDq: access to DR4 causes #UD"));
        UndefinedOpcode(i);
      }
      // Fall through to DR6 case
    case 6: // DR6
      val_64 = BX_CPU_THIS_PTR dr6;
      break;

    case 5: // DR5
      // DR5 aliased to DR7 by default.  With Debug Extensions on,
      // access to DR5 causes #UD
      if (BX_CPU_THIS_PTR cr4.get_DE()) {
        // Debug extensions CR4.DE is ON
        BX_INFO(("MOV_RqDq: access to DR5 causes #UD"));
        UndefinedOpcode(i);
      }
      // Fall through to DR7 case
    case 7: // DR7
      val_64 = BX_CPU_THIS_PTR dr7;
      break;

    default:
      BX_PANIC(("MOV_RqDq: control register index out of range"));
      val_64 = 0;
  }
  BX_WRITE_64BIT_REG(i->rm(), val_64);
}
#endif // #if BX_SUPPORT_X86_64

void BX_CPU_C::MOV_CdRd(bxInstruction_c *i)
{
  // mov general register data to control register
  Bit32u val_32;

  if (!real_mode() && CPL!=0) {
    BX_ERROR(("MOV_CdRd: CPL!=0 not in real mode"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }

  /* NOTES:
   *   32bit operands always used
   *   r/m field specifies general register
   *   reg field specifies which special register
   */

  /* This instruction is always treated as a register-to-register,
   * regardless of the encoding of the MOD field in the MODRM byte.   
   */
  if (!i->modC0())
    BX_PANIC(("MOV_CdRd(): rm field not a register!"));

  invalidate_prefetch_q();

  val_32 = BX_READ_32BIT_REG(i->rm());

  switch (i->nnn()) {
    case 0: // CR0 (MSW)
      SetCR0(val_32);
      break;

    case 1: /* CR1 */
      BX_PANIC(("MOV_CdRd: CR1 not implemented yet"));
      break;
    case 2: /* CR2 */
      BX_DEBUG(("MOV_CdRd:CR2 = %08x", (unsigned) val_32));
      BX_CPU_THIS_PTR cr2 = val_32;
      break;
    case 3: // CR3
      BX_DEBUG(("MOV_CdRd:CR3 = %08x", (unsigned) val_32));
      // Reserved bits take on value of MOV instruction
      CR3_change(val_32);
      BX_INSTR_TLB_CNTRL(BX_CPU_ID, BX_INSTR_MOV_CR3, val_32);
      break;
    case 4: // CR4
#if BX_CPU_LEVEL == 3
      BX_PANIC(("MOV_CdRd: write to CR4 of 0x%08x on 386", val_32));
      UndefinedOpcode(i);
#else
      // Protected mode: #GP(0) if attempt to write a 1 to
      // any reserved bit of CR4
      if (! SetCR4(val_32))
        exception(BX_GP_EXCEPTION, 0, 0);
#endif
      break;
    default:
      BX_PANIC(("MOV_CdRd: control register index out of range"));
      break;
  }
}

void BX_CPU_C::MOV_RdCd(bxInstruction_c *i)
{
  // mov control register data to register
  Bit32u val_32;

  if (!real_mode() && CPL!=0) {
    BX_ERROR(("MOV_RdCd: CPL!=0 not in real mode"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }

  /* NOTES:
   *   32bit operands always used
   *   r/m field specifies general register
   *   reg field specifies which special register
   */

  /* This instruction is always treated as a register-to-register,
   * regardless of the encoding of the MOD field in the MODRM byte.   
   */
  if (!i->modC0())
    BX_PANIC(("MOV_RdCd(): rm field not a register!"));

  switch (i->nnn()) {
    case 0: // CR0 (MSW)
      val_32 = BX_CPU_THIS_PTR cr0.val32;
      break;
    case 1: /* CR1 */
      BX_PANIC(("MOV_RdCd: CR1 not implemented yet"));
      val_32 = 0;
      break;
    case 2: /* CR2 */
      BX_DEBUG(("MOV_RdCd: reading CR2"));
      val_32 = BX_CPU_THIS_PTR cr2;
      break;
    case 3: // CR3
      BX_DEBUG(("MOV_RdCd: reading CR3"));
      val_32 = BX_CPU_THIS_PTR cr3;
      break;
    case 4: // CR4
#if BX_CPU_LEVEL < 4
      val_32 = 0;
      BX_INFO(("MOV_RdCd: read of CR4 causes #UD"));
      UndefinedOpcode(i);
#else
      BX_DEBUG(("MOV_RdCd: read of CR4"));
      val_32 = BX_CPU_THIS_PTR cr4.getRegister();
#endif
      break;
    default:
      BX_PANIC(("MOV_RdCd: control register index out of range"));
      val_32 = 0;
  }
  BX_WRITE_32BIT_REGZ(i->rm(), val_32);
}

#if BX_SUPPORT_X86_64
void BX_CPU_C::MOV_CqRq(bxInstruction_c *i)
{
  // mov general register data to control register
  Bit64u val_64;

  BX_ASSERT(protected_mode());

  /* NOTES:
   *   64bit operands always used
   *   r/m field specifies general register
   *   reg field specifies which special register
   */

  /* This instruction is always treated as a register-to-register,
   * regardless of the encoding of the MOD field in the MODRM byte.   
   */
  if (!i->modC0())
    BX_PANIC(("MOV_CqRq(): rm field not a register!"));

  invalidate_prefetch_q();

  /* #GP(0) if CPL is not 0 */
  if (CPL!=0) {
    BX_ERROR(("MOV_CqRq: #GP(0) if CPL is not 0"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }

  val_64 = BX_READ_64BIT_REG(i->rm());

  switch (i->nnn()) {
    case 0: // CR0 (MSW)
      SetCR0(val_64);
      break;
    case 1: /* CR1 */
      BX_PANIC(("MOV_CqRq: CR1 not implemented yet"));
      break;
    case 2: /* CR2 */
      BX_DEBUG(("MOV_CqRq: write to CR2 of %08x:%08x", 
          (Bit32u)(val_64 >> 32), (Bit32u)(val_64 & 0xFFFFFFFF)));
      BX_CPU_THIS_PTR cr2 = val_64;
      break;
    case 3: // CR3
      BX_DEBUG(("MOV_CqRq: write to CR3 of %08x:%08x", 
          (Bit32u)(val_64 >> 32), (Bit32u)(val_64 & 0xFFFFFFFF)));
      // Reserved bits take on value of MOV instruction
      CR3_change(val_64);
      BX_INSTR_TLB_CNTRL(BX_CPU_ID, BX_INSTR_MOV_CR3, val_64);
      break;
    case 4: // CR4
      //  Protected mode: #GP(0) if attempt to write a 1 to
      //  any reserved bit of CR4
      BX_DEBUG(("MOV_CqRq: write to CR4 of %08x:%08x", 
          (Bit32u)(val_64 >> 32), (Bit32u)(val_64 & 0xFFFFFFFF)));
      if (! SetCR4(val_64))
        exception(BX_GP_EXCEPTION, 0, 0);
      break;
#if BX_SUPPORT_APIC
    case 8: // CR8
      // CR8 is aliased to APIC->TASK PRIORITY register
      //   APIC.TPR[7:4] = CR8[3:0]
      //   APIC.TPR[3:0] = 0
      // Reads of CR8 return zero extended APIC.TPR[7:4]
      // Write to CR8 update APIC.TPR[7:4]
      BX_CPU_THIS_PTR local_apic.set_tpr((val_64 & 0xF) << 0x4);
      break;
#endif
    default:
      BX_PANIC(("MOV_CqRq: control register index out of range"));
      break;
  }
}

void BX_CPU_C::MOV_RqCq(bxInstruction_c *i)
{
  // mov control register data to register
  Bit64u val_64;

  BX_ASSERT(protected_mode());

  /* NOTES:
   *   64bit operands always used
   *   r/m field specifies general register
   *   reg field specifies which special register
   */

  /* This instruction is always treated as a register-to-register,
   * regardless of the encoding of the MOD field in the MODRM byte.   
   */
  if (!i->modC0())
    BX_PANIC(("MOV_RqCq(): rm field not a register!"));

  /* #GP(0) if CPL is not 0 */
  if (CPL!=0) {
    BX_ERROR(("MOV_RqCq: #GP(0) if CPL is not 0"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }

  switch (i->nnn()) {
    case 0: // CR0 (MSW)
      val_64 = BX_CPU_THIS_PTR cr0.val32;
      break;
    case 1: /* CR1 */
      BX_PANIC(("MOV_RqCq: CR1 not implemented yet"));
      val_64 = 0;
      break;
    case 2: /* CR2 */
      BX_DEBUG(("MOV_RqCq: read of CR2"));
      val_64 = BX_CPU_THIS_PTR cr2;
      break;
    case 3: // CR3
      BX_DEBUG(("MOV_RqCq: read of CR3"));
      val_64 = BX_CPU_THIS_PTR cr3;
      break;
    case 4: // CR4
      BX_DEBUG(("MOV_RqCq: read of CR4"));
      val_64 = BX_CPU_THIS_PTR cr4.getRegister();
      break;
#if BX_SUPPORT_APIC
    case 8: // CR8
      // CR8 is aliased to APIC->TASK PRIORITY register
      //   APIC.TPR[7:4] = CR8[3:0]
      //   APIC.TPR[3:0] = 0
      // Reads of CR8 return zero extended APIC.TPR[7:4]
      // Write to CR8 update APIC.TPR[7:4]
      val_64 = (BX_CPU_THIS_PTR local_apic.get_tpr() & 0xF) >> 4;
      break;
#endif
    default:
      BX_PANIC(("MOV_RqCq: control register index out of range"));
      val_64 = 0;
  }

  BX_WRITE_64BIT_REG(i->rm(), val_64);
}
#endif // #if BX_SUPPORT_X86_64

#endif // #if BX_CPU_LEVEL >= 3

#if BX_CPU_LEVEL >= 2
void BX_CPU_C::LMSW_Ew(bxInstruction_c *i)
{
  Bit16u msw;
  Bit32u cr0;

  invalidate_prefetch_q();

  if (!real_mode() && CPL!=0) {
    BX_ERROR(("LMSW: CPL!=0 not in real mode"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }

  if (i->modC0()) {
    msw = BX_READ_16BIT_REG(i->rm());
  }
  else {
    read_virtual_word(i->seg(), RMAddr(i), &msw);
  }

  // LMSW does not affect PG,CD,NW,AM,WP,NE,ET bits, and cannot clear PE

  // LMSW cannot clear PE
  if (BX_CPU_THIS_PTR cr0.pe)
    msw |= 0x0001; // adjust PE bit to current value of 1

  msw &= 0x000f; // LMSW only affects last 4 flags
  cr0 = (BX_CPU_THIS_PTR cr0.val32 & 0xfffffff0) | msw;
  SetCR0(cr0);
}

void BX_CPU_C::SMSW_Ew(bxInstruction_c *i)
{
  Bit16u msw;

#if BX_CPU_LEVEL == 2
  msw = 0xfff0; /* 80286 init value */
  msw |= (BX_CPU_THIS_PTR cr0.ts << 3) |
         (BX_CPU_THIS_PTR cr0.em << 2) |
         (BX_CPU_THIS_PTR cr0.mp << 1) |
         (BX_CPU_THIS_PTR cr0.pe);
#else /* 386+ */
  msw = BX_CPU_THIS_PTR cr0.val32 & 0xffff;
#endif

  if (i->modC0()) {
    if (i->os32L()) {
      BX_WRITE_32BIT_REGZ(i->rm(), msw);  // zeros out high 16bits
    }
    else {
      BX_WRITE_16BIT_REG(i->rm(), msw);
    }
  }
  else {
    write_virtual_word(i->seg(), RMAddr(i), &msw);
  }
}
#endif

void BX_CPU_C::MOV_TdRd(bxInstruction_c *i)
{
#if BX_CPU_LEVEL <= 4
  BX_PANIC(("MOV_TdRd: Still not implemented"));
#else
  // Pentium+ does not have TRx.  They were redesigned using the MSRs.
  BX_INFO(("MOV_TdRd: causes #UD"));
  UndefinedOpcode(i);
#endif
}

void BX_CPU_C::MOV_RdTd(bxInstruction_c *i)
{
#if BX_CPU_LEVEL <= 4
  BX_PANIC(("MOV_RdTd: Still not implemented"));
#else
  // Pentium+ does not have TRx.  They were redesigned using the MSRs.
  BX_INFO(("MOV_RdTd: causes #UD"));
  UndefinedOpcode(i);
#endif
}

#if BX_CPU_LEVEL == 2
void BX_CPU_C::LOADALL(bxInstruction_c *i)
{
  Bit16u msw, tr, flags, ip, ldtr;
  Bit16u ds_raw, ss_raw, cs_raw, es_raw;
  Bit16u di, si, bp, sp, bx, dx, cx, ax;
  Bit16u base_15_0, limit;
  Bit8u  base_23_16, access;

  if (v8086_mode()) BX_PANIC(("proc_ctrl: LOADALL in v8086 mode unsupported"));

  if (BX_CPU_THIS_PTR cr0.pe) 
  {
    BX_PANIC(("LOADALL not yet supported for protected mode"));
  }

  BX_PANIC(("LOADALL: handle CR0.val32"));
  /* MSW */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x806, 2, &msw);
  BX_CPU_THIS_PTR cr0.pe = (msw & 0x01); msw >>= 1;
  BX_CPU_THIS_PTR cr0.mp = (msw & 0x01); msw >>= 1;
  BX_CPU_THIS_PTR cr0.em = (msw & 0x01); msw >>= 1;
  BX_CPU_THIS_PTR cr0.ts = (msw & 0x01);

  if (BX_CPU_THIS_PTR cr0.pe || BX_CPU_THIS_PTR cr0.mp || BX_CPU_THIS_PTR cr0.em || BX_CPU_THIS_PTR cr0.ts)
    BX_PANIC(("LOADALL set PE, MP, EM or TS bits in MSW!"));

  /* TR */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x816, 2, &tr);
  BX_CPU_THIS_PTR tr.selector.value = tr;
  BX_CPU_THIS_PTR tr.selector.rpl   = (tr & 0x03); tr >>= 2;
  BX_CPU_THIS_PTR tr.selector.ti    = (tr & 0x01); tr >>= 1;
  BX_CPU_THIS_PTR tr.selector.index = tr;
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x860, 2, &base_15_0);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x862, 1, &base_23_16);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x863, 1, &access);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x864, 2, &limit);

  BX_CPU_THIS_PTR tr.cache.valid =
  BX_CPU_THIS_PTR tr.cache.p           = (access & 0x80) >> 7;
  BX_CPU_THIS_PTR tr.cache.dpl         = (access & 0x60) >> 5;
  BX_CPU_THIS_PTR tr.cache.segment     = (access & 0x10) >> 4;
  // don't allow busy bit in tr.cache.type, so bit 2 is masked away too.
  BX_CPU_THIS_PTR tr.cache.type        = (access & 0x0d);
  BX_CPU_THIS_PTR tr.cache.u.system.base  = (base_23_16 << 16) | base_15_0;
  BX_CPU_THIS_PTR tr.cache.u.system.limit = limit;

  if ((BX_CPU_THIS_PTR tr.selector.value & 0xfffc) == 0) {
    BX_CPU_THIS_PTR tr.cache.valid = 0;
  }
  if (BX_CPU_THIS_PTR tr.cache.u.system.limit < 43 ||
      BX_CPU_THIS_PTR tr.cache.type != BX_SYS_SEGMENT_AVAIL_286_TSS ||
      BX_CPU_THIS_PTR tr.cache.segment)
  {
    BX_CPU_THIS_PTR tr.cache.valid = 0;
  }
  if (BX_CPU_THIS_PTR tr.cache.valid==0)
  {
    BX_CPU_THIS_PTR tr.selector.value    = 0;
    BX_CPU_THIS_PTR tr.selector.index    = 0;
    BX_CPU_THIS_PTR tr.selector.ti       = 0;
    BX_CPU_THIS_PTR tr.selector.rpl      = 0;
    BX_CPU_THIS_PTR tr.cache.u.system.base  = 0;
    BX_CPU_THIS_PTR tr.cache.u.system.limit = 0;
    BX_CPU_THIS_PTR tr.cache.p           = 0;
  }

  /* FLAGS */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x818, 2, &flags);
  write_flags(flags, 1, 1);

  /* IP */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x81a, 2, &ip);
  IP = ip;

  /* LDTR */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x81c, 2, &ldtr);
  BX_CPU_THIS_PTR ldtr.selector.value = ldtr;
  BX_CPU_THIS_PTR ldtr.selector.rpl   = (ldtr & 0x03); ldtr >>= 2;
  BX_CPU_THIS_PTR ldtr.selector.ti    = (ldtr & 0x01); ldtr >>= 1;
  BX_CPU_THIS_PTR ldtr.selector.index = ldtr;
  if ((BX_CPU_THIS_PTR ldtr.selector.value & 0xfffc) == 0)
  {
    BX_CPU_THIS_PTR ldtr.cache.valid   = 0;
    BX_CPU_THIS_PTR ldtr.cache.p       = 0;
    BX_CPU_THIS_PTR ldtr.cache.segment = 0;
    BX_CPU_THIS_PTR ldtr.cache.type    = 0;
    BX_CPU_THIS_PTR ldtr.cache.u.system.base = 0;
    BX_CPU_THIS_PTR ldtr.cache.u.system.limit = 0;
    BX_CPU_THIS_PTR ldtr.selector.value = 0;
    BX_CPU_THIS_PTR ldtr.selector.index = 0;
    BX_CPU_THIS_PTR ldtr.selector.ti    = 0;
  }
  else {
    BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x854, 2, &base_15_0);
    BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x856, 1, &base_23_16);
    BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x857, 1, &access);
    BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x858, 2, &limit);
    BX_CPU_THIS_PTR ldtr.cache.valid      =
    BX_CPU_THIS_PTR ldtr.cache.p          = access >> 7;
    BX_CPU_THIS_PTR ldtr.cache.dpl        = (access >> 5) & 0x03;
    BX_CPU_THIS_PTR ldtr.cache.segment    = (access >> 4) & 0x01;
    BX_CPU_THIS_PTR ldtr.cache.type       = (access & 0x0f);
    BX_CPU_THIS_PTR ldtr.cache.u.system.base = (base_23_16 << 16) | base_15_0;
    BX_CPU_THIS_PTR ldtr.cache.u.system.limit = limit;

    if (access == 0) {
      BX_PANIC(("loadall: LDTR case access byte=0."));
    }
    if (BX_CPU_THIS_PTR ldtr.cache.valid==0) {
      BX_PANIC(("loadall: ldtr.valid=0"));
    }
    if (BX_CPU_THIS_PTR ldtr.cache.segment) { /* not a system segment */
      BX_INFO(("         AR byte = %02x", (unsigned) access));
      BX_PANIC(("loadall: LDTR descriptor cache loaded with non system segment"));
    }
    if (BX_CPU_THIS_PTR ldtr.cache.type != BX_SYS_SEGMENT_LDT) {
      BX_PANIC(("loadall: LDTR.type(%u) != LDT", (unsigned) (access & 0x0f)));
    }
  }

  /* DS */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x81e, 2, &ds_raw);
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_DS].selector.value = ds_raw;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_DS].selector.rpl   = (ds_raw & 0x03);  ds_raw >>= 2;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_DS].selector.ti    = (ds_raw & 0x01);  ds_raw >>= 1;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_DS].selector.index = ds_raw;
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x848, 2, &base_15_0);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x84a, 1, &base_23_16);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x84b, 1, &access);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x84c, 2, &limit);
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_DS].cache.u.segment.base = (base_23_16 << 16) | base_15_0;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_DS].cache.u.segment.limit = limit;
  set_ar_byte(BX_CPU_THIS_PTR sregs[BX_SEG_REG_DS].cache, access);

  if ((BX_CPU_THIS_PTR sregs[BX_SEG_REG_DS].selector.value & 0xfffc) == 0) {
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_DS].cache.valid = 0;
  }
  else {
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_DS].cache.valid = 1;
  }
  if (BX_CPU_THIS_PTR sregs[BX_SEG_REG_DS].cache.valid==0 ||
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_DS].cache.segment==0)
  {
    BX_PANIC(("loadall: DS invalid"));
  }

  /* SS */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x820, 2, &ss_raw);
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].selector.value = ss_raw;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].selector.rpl   = (ss_raw & 0x03); ss_raw >>= 2;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].selector.ti    = (ss_raw & 0x01); ss_raw >>= 1;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].selector.index = ss_raw;
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x842, 2, &base_15_0);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x844, 1, &base_23_16);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x845, 1, &access);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x846, 2, &limit);
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.base = (base_23_16 << 16) | base_15_0;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.limit = limit;
  set_ar_byte(BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache, access);

  if ((BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].selector.value & 0xfffc) == 0) {
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.valid = 0;
  }
  else {
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.valid = 1;
  }
  if (BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.valid==0 ||
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.segment==0)
  {
    BX_PANIC(("loadall: SS invalid"));
  }
  
  /* CS */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x822, 2, &cs_raw);
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].selector.value = cs_raw;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].selector.rpl   = (cs_raw & 0x03); cs_raw >>= 2;

  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].selector.ti    = (cs_raw & 0x01); cs_raw >>= 1;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].selector.index = cs_raw;
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x83c, 2, &base_15_0);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x83e, 1, &base_23_16);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x83f, 1, &access);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x840, 2, &limit);
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.base = (base_23_16 << 16) | base_15_0;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.limit = limit;
  set_ar_byte(BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache, access);

  if ((BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].selector.value & 0xfffc) == 0) {
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.valid = 0;
  }
  else {
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.valid = 1;
  }
  if (BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.valid==0 ||
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.segment==0)
  {
    BX_PANIC(("loadall: CS invalid"));
  }

#if BX_SUPPORT_ICACHE
  BX_CPU_THIS_PTR updateFetchModeMask();
#endif

  /* ES */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x824, 2, &es_raw);
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_ES].selector.value = es_raw;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_ES].selector.rpl   = (es_raw & 0x03); es_raw >>= 2;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_ES].selector.ti    = (es_raw & 0x01); es_raw >>= 1;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_ES].selector.index = es_raw;
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x836, 2, &base_15_0);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x838, 1, &base_23_16);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x839, 1, &access);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x83a, 2, &limit);
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_ES].cache.u.segment.base = (base_23_16 << 16) | base_15_0;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_ES].cache.u.segment.limit = limit;
  set_ar_byte(BX_CPU_THIS_PTR sregs[BX_SEG_REG_ES].cache, access);

  if ((BX_CPU_THIS_PTR sregs[BX_SEG_REG_ES].selector.value & 0xfffc) == 0) {
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_ES].cache.valid = 0;
  }
  else {
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_ES].cache.valid = 1;
  }
  if (BX_CPU_THIS_PTR sregs[BX_SEG_REG_ES].cache.valid==0 ||
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_ES].cache.segment==0)
  {
    BX_PANIC(("loadall: ES invalid"));
  }

#if 0
    BX_INFO(("cs.dpl = %02x", (unsigned) BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.dpl));
    BX_INFO(("ss.dpl = %02x", (unsigned) BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.dpl));
    BX_INFO(("BX_CPU_THIS_PTR sregs[BX_SEG_REG_DS].dpl = 0x%02x", (unsigned) BX_CPU_THIS_PTR ds.cache.dpl));
    BX_INFO(("BX_CPU_THIS_PTR sregs[BX_SEG_REG_ES].dpl = 0x%02x", (unsigned) BX_CPU_THIS_PTR es.cache.dpl));
    BX_INFO(("LOADALL: setting cs.selector.rpl to %u",
      (unsigned) BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].selector.rpl));
    BX_INFO(("LOADALL: setting ss.selector.rpl to %u",
      (unsigned) BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].selector.rpl));
    BX_INFO(("LOADALL: setting ds.selector.rpl to %u",
      (unsigned) BX_CPU_THIS_PTR sregs[BX_SEG_REG_DS].selector.rpl));
    BX_INFO(("LOADALL: setting es.selector.rpl to %u",
      (unsigned) BX_CPU_THIS_PTR sregs[BX_SEG_REG_ES].selector.rpl));
#endif

  /* DI */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x826, 2, &di);
  DI = di;

  /* SI */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x828, 2, &si);
  SI = si;

  /* BP */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x82a, 2, &bp);
  BP = bp;

  /* SP */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x82c, 2, &sp);
  SP = sp;

  /* BX */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x82e, 2, &bx);
  BX = bx;

  /* DX */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x830, 2, &dx);
  DX = dx;

  /* CX */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x832, 2, &cx);
  CX = cx;

  /* AX */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x834, 2, &ax);
  AX = ax;

  /* GDTR */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x84e, 2, &base_15_0);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x850, 1, &base_23_16);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x851, 1, &access);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x852, 2, &limit);
  BX_CPU_THIS_PTR gdtr.base = (base_23_16 << 16) | base_15_0;
  BX_CPU_THIS_PTR gdtr.limit = limit;

#if 0
  if (access)
      BX_INFO(("LOADALL: GDTR access bits not 0 (%02x)", (unsigned) access));
#endif

  /* IDTR */
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x85a, 2, &base_15_0);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x85c, 1, &base_23_16);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x85d, 1, &access);
  BX_CPU_THIS_PTR mem->readPhysicalPage(BX_CPU_THIS, 0x85e, 2, &limit);
  BX_CPU_THIS_PTR idtr.base = (base_23_16 << 16) | base_15_0;
  BX_CPU_THIS_PTR idtr.limit = limit;
}
#endif

void BX_CPU_C::handleCpuModeChange(void)
{
#if BX_SUPPORT_X86_64
  if (BX_CPU_THIS_PTR msr.lma) {
    if (! BX_CPU_THIS_PTR cr0.pe) {
      BX_PANIC(("change_cpu_mode: EFER.LMA is set when CR0.PE=0 !"));
    }
    if (BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.l) {
      BX_CPU_THIS_PTR cpu_mode = BX_MODE_LONG_64;
      BX_DEBUG(("Long Mode Activated"));
    }
    else {
      BX_CPU_THIS_PTR cpu_mode = BX_MODE_LONG_COMPAT;
      BX_DEBUG(("Compatibility Mode Activated"));
    }
  }
  else 
#endif
  {
    if (BX_CPU_THIS_PTR cr0.pe) {
      if (BX_CPU_THIS_PTR get_VM()) {
        BX_CPU_THIS_PTR cpu_mode = BX_MODE_IA32_V8086;
        BX_DEBUG(("VM8086 Mode Activated"));
      }
      else {
        BX_CPU_THIS_PTR cpu_mode = BX_MODE_IA32_PROTECTED;
        BX_DEBUG(("Protected Mode Activated"));
      }
    }
    else {
      BX_CPU_THIS_PTR cpu_mode = BX_MODE_IA32_REAL;
      BX_DEBUG(("Real Mode Activated"));
    }
  }
}

void BX_CPU_C::SetCR0(Bit32u val_32)
{
  bx_bool pe = val_32 & 0x01;
  bx_bool nw = (val_32 >> 29) & 0x01;
  bx_bool cd = (val_32 >> 30) & 0x01;
  bx_bool pg = (val_32 >> 31) & 0x01;

  if (pg && !pe) {
    BX_INFO(("SetCR0: GP(0) when attempt to set CR0.PG with CR0.PE cleared !"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }

  if (nw && !cd) {
    BX_INFO(("SetCR0: GP(0) when attempt to set CR0.NW with CR0.CD cleared !"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }

  if (pe && BX_CPU_THIS_PTR get_VM()) BX_PANIC(("EFLAGS.VM=1, enter_PM"));

  // from either MOV_CdRd() or debug functions
  // protection checks made already or forcing from debug
  Bit32u oldCR0 = BX_CPU_THIS_PTR cr0.val32, newCR0;

  bx_bool prev_pe = BX_CPU_THIS_PTR cr0.pe;
#if BX_SUPPORT_X86_64
  bx_bool prev_pg = BX_CPU_THIS_PTR cr0.pg;
#endif

  BX_CPU_THIS_PTR cr0.pe = pe;
  BX_CPU_THIS_PTR cr0.mp = (val_32 >> 1) & 0x01;
  BX_CPU_THIS_PTR cr0.em = (val_32 >> 2) & 0x01;
  BX_CPU_THIS_PTR cr0.ts = (val_32 >> 3) & 0x01;
  // cr0.et is hardwired to 1
#if BX_CPU_LEVEL >= 4
  BX_CPU_THIS_PTR cr0.ne = (val_32 >> 5)  & 0x01;
  BX_CPU_THIS_PTR cr0.wp = (val_32 >> 16) & 0x01;
  BX_CPU_THIS_PTR cr0.am = (val_32 >> 18) & 0x01;
  BX_CPU_THIS_PTR cr0.nw = nw;
  BX_CPU_THIS_PTR cr0.cd = cd;
#endif
  BX_CPU_THIS_PTR cr0.pg = pg;

#if BX_CPU_LEVEL >= 4
  if (BX_CPU_THIS_PTR cr0.am) {
    BX_DEBUG(("WARNING: Alignment check enabled but not implemented !"));
  }
#endif

  // handle reserved bits behaviour
#if BX_CPU_LEVEL == 3
  newCR0 = val_32 | 0x7ffffff0;
#elif BX_CPU_LEVEL == 4
  newCR0 = (val_32 | 0x00000010) & 0xe005003f;
#elif BX_CPU_LEVEL == 5
  newCR0 = val_32 | 0x00000010;
#elif BX_CPU_LEVEL == 6
  newCR0 = (val_32 | 0x00000010) & 0xe005003f;
#else
#error "MOV_CdRd: implement reserved bits behaviour for this CPU_LEVEL"
#endif
  BX_CPU_THIS_PTR cr0.val32 = newCR0;

  if (prev_pe==0 && BX_CPU_THIS_PTR cr0.pe) {
    BX_DEBUG(("Enter Protected Mode"));
    BX_CPU_THIS_PTR cpu_mode = BX_MODE_IA32_PROTECTED;
  }
  else if (prev_pe==1 && BX_CPU_THIS_PTR cr0.pe==0) {
    BX_DEBUG(("Enter Real Mode"));
    BX_CPU_THIS_PTR cpu_mode = BX_MODE_IA32_REAL;
  }

#if BX_SUPPORT_X86_64
  if (prev_pg==0 && BX_CPU_THIS_PTR cr0.pg) {
    if (BX_CPU_THIS_PTR msr.lme) {
      if (!BX_CPU_THIS_PTR cr4.get_PAE()) {
        BX_ERROR(("SetCR0: attempt to enter x86-64 LONG mode without enabling CR4.PAE !"));
        exception(BX_GP_EXCEPTION, 0, 0);
      }
      BX_CPU_THIS_PTR msr.lma = 1;
    }
  }
  else if (prev_pg==1 && BX_CPU_THIS_PTR cr0.pg==0) {
    if (BX_CPU_THIS_PTR msr.lma) {
      if (BX_CPU_THIS_PTR dword.rip_upper != 0) {
        BX_PANIC(("SetCR0: attempt to leave x86-64 LONG mode with RIP upper != 0 !!!"));
      }
      BX_CPU_THIS_PTR msr.lma = 0;
    }
  }
#endif  // #if BX_SUPPORT_X86_64

  handleCpuModeChange();

  // Give the paging unit a chance to look for changes in bits
  // it cares about, like {PG,PE}, so it can flush cache entries etc.
  pagingCR0Changed(oldCR0, newCR0);
}

#if BX_CPU_LEVEL >= 4
bx_bool BX_CPU_C::SetCR4(Bit32u val_32)
{
  Bit32u oldCR4 = BX_CPU_THIS_PTR cr4.getRegister();
  Bit32u allowMask = 0;

  // CR4 bit definitions from AMD Hammer manual:
  //   [63-11] Reserved, Must be Zero
  //   [10]    OSXMMEXCPT: Operating System Unmasked Exception Support R/W
  //   [9]     OSFXSR: Operating System FXSAVE/FXRSTOR Support R/W
  //   [8]     PCE: Performance-Monitoring Counter Enable R/W
  //   [7]     PGE: Page-Global Enable R/W
  //   [6]     MCE: Machine Check Enable R/W
  //   [5]     PAE: Physical-Address Extension R/W
  //   [4]     PSE: Page Size Extensions R/W
  //   [3]     DE: Debugging Extensions R/W
  //   [2]     TSD: Time Stamp Disable R/W
  //   [1]     PVI: Protected-Mode Virtual Interrupts R/W
  //   [0]     VME: Virtual-8086 Mode Extensions R/W

#if BX_SUPPORT_VME
  allowMask |= (1<<0) | (1<<1);  /* VME */
#endif

#if BX_CPU_LEVEL >= 5
  allowMask |= (1<<2);   /* TSD */
#endif

  allowMask |= (1<<3);   /* DE  */

#if BX_SUPPORT_4MEG_PAGES
  allowMask |= (1<<4);
#endif

#if BX_SUPPORT_PAE
  allowMask |= (1<<5);
#endif

#if BX_CPU_LEVEL >= 5
  // NOTE: exception 18 never appears in Bochs
  allowMask |= (1<<6);   /* MCE */
#endif

#if BX_SUPPORT_GLOBAL_PAGES
  allowMask |= (1<<7);
#endif

#if BX_CPU_LEVEL >= 6
  allowMask |= (1<<8);   /* PCE */
  allowMask |= (1<<9);   /* OSFXSR */
#endif

#if BX_SUPPORT_SSE
  allowMask |= (1<<10);  /* OSXMMECPT */
#endif

#if BX_SUPPORT_X86_64
  // need to GP(0) if LMA=1 and PAE=1->0
  if ((BX_CPU_THIS_PTR msr.lma)
      && (!(val_32 >> 5) & 1)
      && (BX_CPU_THIS_PTR cr4.get_PAE())) 
  {
    BX_ERROR(("SetCR4: attempt to change PAE when LMA=1"));
    return 0;
  }
#endif

  // Need to GPF if trying to set undefined bits.
  if (val_32 & ~allowMask) {
    BX_INFO(("#GP(0): SetCR4: Write of 0x%08x not supported (allowMask=0x%x)", val_32, allowMask));
    return 0;
  }

  val_32 &= allowMask; // Screen out unsupported bits. (not needed, for good measure)
  BX_CPU_THIS_PTR cr4.setRegister(val_32);
  pagingCR4Changed(oldCR4, BX_CPU_THIS_PTR cr4.getRegister());
  return 1;
}
#endif

void BX_CPU_C::RDPMC(bxInstruction_c *i)
{
/* We need to be Pentium with MMX or later */
#if ((BX_CPU_LEVEL >= 6) || (BX_SUPPORT_MMX && BX_CPU_LEVEL == 5))
  bx_bool pce = BX_CPU_THIS_PTR cr4.get_PCE();

  if ((pce==1) || (CPL==0) || real_mode())
  {
    /* According to manual, Pentium 4 has 18 counters,
     * previous versions have two.  And the P4 also can do
     * short read-out (EDX always 0).  Otherwise it is
     * limited to 40 bits.
     */

#if (BX_CPU_LEVEL == 6 && BX_SUPPORT_SSE >= 2) // Pentium 4 processor (see cpuid.cc)
    if ((ECX & 0x7fffffff) >= 18)
      exception(BX_GP_EXCEPTION, 0, 0);
#else //
    if ((ECX & 0xffffffff) >= 2)
      exception(BX_GP_EXCEPTION, 0, 0);
#endif
    // Most counters are for hardware specific details, which
    // we anyhow do not emulate (like pipeline stalls etc)

    // Could be interesting to count number of memory reads,
    // writes.  Misaligned etc...  But to monitor bochs, this
    // is easier done from the host.

    EAX = 0;
    EDX = 0; // if P4 and ECX & 0x10000000, then always 0 (short read 32 bits)

    BX_ERROR(("RDPMC: Performance Counters Support not reasonably implemented yet"));
  } else {
    // not allowed to use RDPMC!
    exception(BX_GP_EXCEPTION, 0, 0);
  }
#else
  UndefinedOpcode(i);
#endif
}

#if BX_CPU_LEVEL >= 5
Bit64u BX_CPU_C::get_TSC ()
{
  return bx_pc_system.time_ticks() - BX_CPU_THIS_PTR msr.tsc_last_reset;
}

void BX_CPU_C::set_TSC (Bit32u newval)
{
  // compute the correct setting of tsc_last_reset so that a get_TSC()
  // will return newval
  BX_CPU_THIS_PTR msr.tsc_last_reset = 
            bx_pc_system.time_ticks() - (Bit64u) newval;

  // verify
  BX_ASSERT (get_TSC() == (Bit64u) newval);
}
#endif

void BX_CPU_C::RDTSC(bxInstruction_c *i)
{
#if BX_CPU_LEVEL >= 5
  bx_bool tsd = BX_CPU_THIS_PTR cr4.get_TSD();
  if ((tsd==0) || (tsd==1 && CPL==0)) {
    // return ticks
    Bit64u ticks = BX_CPU_THIS_PTR get_TSC();
    RAX = (Bit32u) (ticks & 0xffffffff);
    RDX = (Bit32u) ((ticks >> 32) & 0xffffffff);
  } else {
    // not allowed to use RDTSC!
    BX_ERROR(("RDTSC: incorrect usage of RDTSC instruction !"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }
#else
  BX_INFO(("RDTSC: Pentium CPU required, use --enable-cpu=5"));
  UndefinedOpcode(i);
#endif
}

#if BX_SUPPORT_X86_64
void BX_CPU_C::RDTSCP(bxInstruction_c *i)
{
  RDTSC(i);
  RCX = MSR_TSC_AUX;
}
#endif

void BX_CPU_C::RDMSR(bxInstruction_c *i)
{
#if BX_CPU_LEVEL >= 5
  invalidate_prefetch_q();

  if (!real_mode() && CPL!=0) {
    BX_ERROR(("RDMSR: CPL!=0 not in real mode"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }

  /* We have the requested MSR register in ECX */
  switch(ECX) {

#if BX_SUPPORT_SEP
    case BX_MSR_SYSENTER_CS:
      RAX = BX_CPU_THIS_PTR msr.sysenter_cs_msr;  
      RDX = 0; 
      return;

    case BX_MSR_SYSENTER_ESP: 
      RAX = BX_CPU_THIS_PTR msr.sysenter_esp_msr; 
      RDX = 0; 
      return;

    case BX_MSR_SYSENTER_EIP: 
      RAX = BX_CPU_THIS_PTR msr.sysenter_eip_msr; 
      RDX = 0; 
      return;
#endif 

#if BX_CPU_LEVEL == 5
    /* The following registers are defined for Pentium only */
    case BX_MSR_P5_MC_ADDR:
    case BX_MSR_MC_TYPE:
      /* TODO */
      return;

    case BX_MSR_CESR:
      /* TODO */
      return;
#else
    /* These are noops on i686... */
    case BX_MSR_P5_MC_ADDR:
    case BX_MSR_MC_TYPE:
      /* do nothing */
      return;

    /* ... And these cause an exception on i686 */
    case BX_MSR_CESR:
    case BX_MSR_CTR0:
    case BX_MSR_CTR1:
      goto do_exception;
#endif  /* BX_CPU_LEVEL == 5 */

    case BX_MSR_TSC:
      RDTSC(i);
      return;

    /* MSR_APICBASE
       0:7    Reserved
       8     This is set if its the BSP
       9:10    Reserved
       11    APIC Global Enable bit (1=enabled 0=disabled)
       12:35  APIC Base Address
       36:63  Reserved
    */
#if BX_SUPPORT_APIC
    case BX_MSR_APICBASE:
      RAX = BX_CPU_THIS_PTR msr.apicbase;
      RDX = 0;
      BX_INFO(("RDMSR: Read %08x:%08x from MSR_APICBASE", EDX, EAX));
      return;
#endif

#if BX_SUPPORT_X86_64
    case BX_MSR_EFER:
      RAX = (Bit64u) BX_CPU_THIS_PTR get_EFER();
      RDX = 0;
      return;

    case BX_MSR_STAR:
      RAX = MSR_STAR & 0xffffffff;
      RDX = MSR_STAR >> 32;
      return;

    case BX_MSR_LSTAR:
      RAX = MSR_LSTAR & 0xffffffff;
      RDX = MSR_LSTAR >> 32;
      return;

    case BX_MSR_CSTAR:
      RAX = MSR_CSTAR & 0xffffffff;
      RDX = MSR_CSTAR >> 32;
      return;

    case BX_MSR_FMASK:
      RAX = MSR_FMASK & 0xffffffff;
      RDX = MSR_FMASK >> 32;
      return;

    case BX_MSR_FSBASE:
      RAX = MSR_FSBASE & 0xffffffff;
      RDX = MSR_FSBASE >> 32;
      return;

    case BX_MSR_GSBASE:
      RAX = MSR_GSBASE & 0xffffffff;
      RDX = MSR_GSBASE >> 32;
      return;

    case BX_MSR_KERNELGSBASE:
      RAX = MSR_KERNELGSBASE & 0xffffffff;
      RDX = MSR_KERNELGSBASE >> 32;
      return;

    case BX_MSR_TSC_AUX:
      RAX = MSR_TSC_AUX;   // 32 bit MSR
      RDX = 0;
      return;
#endif  // #if BX_SUPPORT_X86_64

    default:
      BX_ERROR(("RDMSR: Unknown register %#x", ECX));
#if BX_IGNORE_BAD_MSR
      RAX = 0;
      RDX = 0;
      return;
#endif
  }

do_exception:
  exception(BX_GP_EXCEPTION, 0, 0);

#else  /* BX_CPU_LEVEL >= 5 */
  BX_INFO(("RDMSR: Pentium CPU required"));
  UndefinedOpcode(i);
#endif
}

void BX_CPU_C::WRMSR(bxInstruction_c *i)
{
#if BX_CPU_LEVEL >= 5
  invalidate_prefetch_q();

  if (!real_mode() && CPL!=0) {
    BX_ERROR(("WRMSR: CPL!=0 not in real mode"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }

  BX_INSTR_WRMSR(BX_CPU_ID, ECX, ((Bit64u) EDX << 32) + EAX);

  /* ECX has the MSR to write to */
  switch(ECX) {

#if BX_SUPPORT_SEP
    case BX_MSR_SYSENTER_CS: {
      // not a bug according to book ... but very stOOpid
      if (EAX & 3) BX_PANIC(("writing sysenter_cs_msr with non-kernel mode selector %X", EAX));
      BX_CPU_THIS_PTR msr.sysenter_cs_msr  = EAX;
      return;
    }

    case BX_MSR_SYSENTER_ESP:
      BX_CPU_THIS_PTR msr.sysenter_esp_msr = EAX; 
      return;

    case BX_MSR_SYSENTER_EIP: 
      BX_CPU_THIS_PTR msr.sysenter_eip_msr = EAX; 
      return;
#endif

#if BX_CPU_LEVEL == 5
    /* The following registers are defined for Pentium only */
    case BX_MSR_P5_MC_ADDR:
    case BX_MSR_MC_TYPE:
    case BX_MSR_CESR:
      /* TODO */
      return;
#else
    /* These are noops on i686... */
    case BX_MSR_P5_MC_ADDR:
    case BX_MSR_MC_TYPE:
      /* do nothing */
      return;

    /* ... And these cause an exception on i686 */
    case BX_MSR_CESR:
    case BX_MSR_CTR0:
    case BX_MSR_CTR1:
      goto do_exception;
#endif  /* BX_CPU_LEVEL == 5 */

    case BX_MSR_TSC:
      BX_CPU_THIS_PTR set_TSC(EAX); /* ignore the high 32bits */
      BX_INFO(("WRMSR: wrote 0x%08x to MSR_TSC", EAX));
      return;

    /* MSR_APICBASE
       0:7    Reserved
       8     This is set if its the BSP
       9:10    Reserved
       11    APIC Global Enable bit (1=enabled 0=disabled)
       12:35  APIC Base Address (in Bochs 12:31 because of 32-bit physical addr)
       36:63  Reserved
    */
#if BX_SUPPORT_APIC
    case BX_MSR_APICBASE:
      if (BX_CPU_THIS_PTR msr.apicbase & 0x800) {
        BX_INFO(("WRMSR: wrote %08x:%08x to MSR_APICBASE", EDX, EAX));
        BX_CPU_THIS_PTR msr.apicbase = EAX; /* ignore the high 32bits */
        if (EDX != 0) {
            BX_PANIC(("MSR_APICBASE: Only 32 bit physical address space is emulated !"));
        }
        BX_CPU_THIS_PTR local_apic.set_base(BX_CPU_THIS_PTR msr.apicbase);
        // TLB flush is required for emulation correctness
        TLB_flush(1);  // don't care about performance of apic relocation
      }
      else {
        BX_INFO(("WRMSR: MSR_APICBASE APIC global enable bit cleared !"));
      }
      return;
#endif

#if BX_SUPPORT_X86_64
    case BX_MSR_EFER:
      // GPF #0 if lme 0->1 and cr0.pg = 1
      // GPF #0 if lme 1->0 and cr0.pg = 1
      if ((BX_CPU_THIS_PTR msr.lme != ((EAX >> 8) & 1)) &&
          (BX_CPU_THIS_PTR cr0.pg == 1))
      {
        BX_ERROR(("WRMSR: attempt to change LME when CR0.PG=1"));
        exception(BX_GP_EXCEPTION, 0, 0);
      }
      BX_CPU_THIS_PTR msr.sce   = (EAX >> 0)  & 1;
      BX_CPU_THIS_PTR msr.lme   = (EAX >> 8)  & 1;
      BX_CPU_THIS_PTR msr.nxe   = (EAX >> 11) & 1;
      BX_CPU_THIS_PTR msr.ffxsr = (EAX >> 14) & 1;
      return;

    case BX_MSR_STAR:
      MSR_STAR   = ((Bit64u) EDX << 32) + EAX;
      return;

    case BX_MSR_LSTAR:
      MSR_LSTAR  = ((Bit64u) EDX << 32) + EAX;
      return;

    case BX_MSR_CSTAR:
      MSR_CSTAR  = ((Bit64u) EDX << 32) + EAX;
      return;

    case BX_MSR_FMASK:
      MSR_FMASK  = ((Bit64u) EDX << 32) + EAX;
      return;

    case BX_MSR_FSBASE:
      MSR_FSBASE = ((Bit64u) EDX << 32) + EAX;
      return;

    case BX_MSR_GSBASE:
      MSR_GSBASE = ((Bit64u) EDX << 32) + EAX;
      return;

    case BX_MSR_KERNELGSBASE:
      MSR_KERNELGSBASE = ((Bit64u) EDX << 32) + EAX;
      return;

    case BX_MSR_TSC_AUX:
      MSR_TSC_AUX = EAX;
      return;
#endif  // #if BX_SUPPORT_X86_64

    default:
      BX_ERROR(("WRMSR: Unknown register %#x", ECX));
#if BX_IGNORE_BAD_MSR
      return;
#endif
  }

do_exception:
  exception(BX_GP_EXCEPTION, 0, 0);

#else  /* BX_CPU_LEVEL >= 5 */
  BX_INFO(("RDMSR: Pentium CPU required"));
  UndefinedOpcode(i);
#endif
}

void BX_CPU_C::SYSENTER(bxInstruction_c *i)
{
#if BX_SUPPORT_SEP
  if (!protected_mode()) {
    BX_ERROR(("sysenter not from protected mode !"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }
  if ((BX_CPU_THIS_PTR msr.sysenter_cs_msr & BX_SELECTOR_RPL_MASK) == 0) {
    BX_ERROR(("sysenter with zero sysenter_cs_msr !"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }

  invalidate_prefetch_q();

  BX_CPU_THIS_PTR clear_VM();       // do this just like the book says to do
  BX_CPU_THIS_PTR clear_IF();
  BX_CPU_THIS_PTR clear_RF();

  parse_selector(BX_CPU_THIS_PTR msr.sysenter_cs_msr & BX_SELECTOR_RPL_MASK,
                       &BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].selector);

  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.valid   = 1;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.p       = 1;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.dpl     = 0;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.segment = 1;  /* data/code segment */
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.type    = BX_CODE_EXEC_READ_ACCESSED;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.base         = 0;          // base address
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.limit        = 0xFFFF;     // segment limit
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.limit_scaled = 0xFFFFFFFF; // scaled segment limit
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.g            = 1;          // 4k granularity
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.d_b          = 1;          // 32-bit mode
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.avl          = 0;          // available for use by system

#if BX_SUPPORT_ICACHE
  BX_CPU_THIS_PTR updateFetchModeMask();
#endif

  parse_selector((BX_CPU_THIS_PTR msr.sysenter_cs_msr + 8) & BX_SELECTOR_RPL_MASK,
                       &BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].selector);

  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.valid    = 1;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.p        = 1;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.dpl      = 0;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.segment  = 1; /* data/code segment */
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.type     = BX_DATA_READ_WRITE_ACCESSED;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.base         = 0;          // base address
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.limit        = 0xFFFF;     // segment limit
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.limit_scaled = 0xFFFFFFFF; // scaled segment limit
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.g            = 1;          // 4k granularity
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.d_b          = 1;          // 32-bit mode
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.avl          = 0;          // available for use by system

  ESP = BX_CPU_THIS_PTR msr.sysenter_esp_msr;
  EIP = BX_CPU_THIS_PTR msr.sysenter_eip_msr;
#else
  BX_INFO(("SYSENTER: use --enable-sep to enable SYSENTER/SYSEXIT support"));
  UndefinedOpcode (i);
#endif
}

void BX_CPU_C::SYSEXIT(bxInstruction_c *i)
{
#if BX_SUPPORT_SEP
  if (!protected_mode()) {
    BX_ERROR(("sysexit not from protected mode !"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }
  if ((BX_CPU_THIS_PTR msr.sysenter_cs_msr & BX_SELECTOR_RPL_MASK) == 0) {
    BX_ERROR(("sysexit with zero sysenter_cs_msr !"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }
  if (CPL != 0) {
    BX_INFO(("sysexit at non-zero cpl %u !", CPL));
    exception(BX_GP_EXCEPTION, 0, 0);
  }

  invalidate_prefetch_q();

  parse_selector((BX_CPU_THIS_PTR msr.sysenter_cs_msr + 16) | 3, 
                       &BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].selector);

  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.valid   = 1;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.p       = 1;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.dpl     = 3;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.segment = 1;  /* data/code segment */
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.type    = BX_CODE_EXEC_READ_ACCESSED;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.base         = 0;           // base address
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.limit        = 0xFFFF;      // segment limit
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.limit_scaled = 0xFFFFFFFF;  // scaled segment limit
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.g            = 1;           // 4k granularity
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.d_b          = 1;           // 32-bit mode
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.avl          = 0;           // available for use by system

#if BX_SUPPORT_ICACHE
  BX_CPU_THIS_PTR updateFetchModeMask();
#endif

  parse_selector((BX_CPU_THIS_PTR msr.sysenter_cs_msr + 24) | 3,
                       &BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].selector);

  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.valid    = 1;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.p        = 1;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.dpl      = 3;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.segment  = 1; /* data/code segment */
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.type     = BX_DATA_READ_WRITE_ACCESSED;
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.base         = 0;           // base address
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.limit        = 0xFFFF;      // segment limit
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.limit_scaled = 0xFFFFFFFF;  // scaled segment limit
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.g            = 1;           // 4k granularity
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.d_b          = 1;           // 32-bit mode
  BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.avl          = 0;           // available for use by system

  ESP = ECX;
  EIP = EDX;
#else
  BX_INFO(("SYSEXIT: use --enable-sep to enable SYSENTER/SYSEXIT support"));
  UndefinedOpcode (i);
#endif
}

#if BX_SUPPORT_X86_64
void BX_CPU_C::SYSCALL(bxInstruction_c *i)
{

/* pseudo code from AMD manual.

SYSCALL_START:

  IF (MSR_EFER.SCE = 0) // Check if syscall/sysret are enabled.
    EXCEPTION [#UD]

  IF (LONG_MODE)
    SYSCALL_LONG_MODE
  ELSE // (LEGACY_MODE)
    SYSCALL_LEGACY_MODE


SYSCALL_LONG_MODE:

  RCX.q = next_RIP
  R11.q = RFLAGS // with rf cleared

  IF (64BIT_MODE)
      temp_RIP.q = MSR_LSTAR
  ELSE // (COMPATIBILITY_MODE)
      temp_RIP.q = MSR_CSTAR

  CS.sel = MSR_STAR.SYSCALL_CS AND 0xFFFC
  CS.attr = 64-bit code,dpl0 // Always switch to 64-bit mode in long mode.
  CS.base = 0x00000000
  CS.limit = 0xFFFFFFFF

  SS.sel = MSR_STAR.SYSCALL_CS + 8
  SS.attr = 64-bit stack,dpl0
  SS.base = 0x00000000
  SS.limit = 0xFFFFFFFF

  RFLAGS = RFLAGS AND ~MSR_SFMASK
  RFLAGS.RF = 0

  CPL = 0

  RIP = temp_RIP
  EXIT

SYSCALL_LEGACY_MODE:

  RCX.d = next_RIP

  temp_RIP.d = MSR_STAR.EIP

  CS.sel = MSR_STAR.SYSCALL_CS AND 0xFFFC
  CS.attr = 32-bit code,dpl0 // Always switch to 32-bit mode in legacy mode.
  CS.base = 0x00000000
  CS.limit = 0xFFFFFFFF

  SS.sel = MSR_STAR.SYSCALL_CS + 8
  SS.attr = 32-bit stack,dpl0
  SS.base = 0x00000000
  SS.limit = 0xFFFFFFFF

  RFLAGS.VM,IF,RF=0

  CPL = 0

  RIP = temp_RIP
  EXIT

*/

  bx_address temp_RIP;

  BX_DEBUG(("Execute SYSCALL instruction"));

  if (!BX_CPU_THIS_PTR msr.sce) {
    exception(BX_UD_EXCEPTION, 0, 0);
  }

  invalidate_prefetch_q();

  if (BX_CPU_THIS_PTR msr.lma)
  {
    RCX = RIP;
    R11 = read_eflags() & ~(EFlagsRFMask);

    if (BX_CPU_THIS_PTR cpu_mode == BX_MODE_LONG_64) {
      temp_RIP = MSR_LSTAR;
    }
    else {
      temp_RIP = MSR_CSTAR;
    }

    // set up CS segment, flat, 64-bit DPL=0
    parse_selector((MSR_STAR >> 32) & BX_SELECTOR_RPL_MASK,
                       &BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].selector);

    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.valid   = 1;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.p       = 1;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.dpl     = 0;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.segment = 1;  /* data/code segment */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.type    = BX_CODE_EXEC_READ_ACCESSED;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.base         = 0; /* base address */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.limit        = 0xFFFF;      /* segment limit */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.limit_scaled = 0xFFFFFFFF;  /* scaled segment limit */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.g            = 1; /* 4k granularity */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.d_b          = 0;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.l            = 1; /* 64-bit code */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.avl          = 0; /* available for use by system */

#if BX_SUPPORT_ICACHE
    BX_CPU_THIS_PTR updateFetchModeMask();
#endif

    // set up SS segment, flat, 64-bit DPL=0
    parse_selector(((MSR_STAR >> 32) + 8) & BX_SELECTOR_RPL_MASK,
                       &BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].selector);

    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.valid   = 1;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.p       = 1;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.dpl     = 0;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.segment = 1; /* data/code segment */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.type    = BX_DATA_READ_WRITE_ACCESSED;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.base         = 0; /* base address */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.limit        = 0xFFFF;      /* segment limit */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.limit_scaled = 0xFFFFFFFF;  /* scaled segment limit */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.g            = 1; /* 4k granularity */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.d_b          = 1; /* 32 bit stack */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.l            = 0;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.avl          = 0; /* available for use by system */

    writeEFlags(read_eflags() & (~MSR_FMASK), EFlagsValidMask);
    BX_CPU_THIS_PTR clear_RF();
    RIP = temp_RIP;
  }
  else {
    // legacy mode

    ECX = EIP;
    temp_RIP = MSR_STAR & 0xFFFFFFFF;

    // set up CS segment, flat, 32-bit DPL=0
    parse_selector((MSR_STAR >> 32) & BX_SELECTOR_RPL_MASK,
                       &BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].selector);

    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.valid   = 1;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.p       = 1;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.dpl     = 0;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.segment = 1;  /* data/code segment */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.type    = BX_CODE_EXEC_READ_ACCESSED;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.base         = 0; /* base address */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.limit        = 0xFFFF;      /* segment limit */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.limit_scaled = 0xFFFFFFFF;  /* scaled segment limit */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.g            = 1; /* 4k granularity */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.d_b          = 1;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.l            = 0; /* 32-bit code */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.avl          = 0; /* available for use by system */

#if BX_SUPPORT_ICACHE
    BX_CPU_THIS_PTR updateFetchModeMask();
#endif

    // set up SS segment, flat, 32-bit DPL=0
    parse_selector(((MSR_STAR >> 32) + 8) & BX_SELECTOR_RPL_MASK,
                       &BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].selector);

    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.valid   = 1;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.p       = 1;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.dpl     = 0;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.segment = 1; /* data/code segment */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.type    = BX_DATA_READ_WRITE_ACCESSED;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.base         = 0; /* base address */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.limit        = 0xFFFF;      /* segment limit */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.limit_scaled = 0xFFFFFFFF;  /* scaled segment limit */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.g            = 1; /* 4k granularity */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.d_b          = 1; /* 32 bit stack */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.l            = 0;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.u.segment.avl          = 0; /* available for use by system */

    BX_CPU_THIS_PTR clear_VM();
    BX_CPU_THIS_PTR clear_IF();
    BX_CPU_THIS_PTR clear_RF();
    RIP = temp_RIP;
  }
}

void BX_CPU_C::SYSRET(bxInstruction_c *i)
{
/* from AMD manual

SYSRET_START:

  IF (MSR_EFER.SCE = 0) // Check if syscall/sysret are enabled.
    EXCEPTION [#UD]

  IF ((!PROTECTED_MODE) || (CPL != 0))
    EXCEPTION [#GP(0)] // SYSRET requires protected mode, cpl0

  IF (64BIT_MODE)
    SYSRET_64BIT_MODE
  ELSE // (!64BIT_MODE)
    SYSRET_NON_64BIT_MODE

SYSRET_64BIT_MODE:
  IF (OPERAND_SIZE = 64) // Return to 64-bit mode.
  {
    CS.sel = (MSR_STAR.SYSRET_CS + 16) OR 3
    CS.base = 0x00000000
    CS.limit = 0xFFFFFFFF
    CS.attr = 64-bit code,dpl3
    temp_RIP.q = RCX
  }
  ELSE // Return to 32-bit compatibility mode.
  {
    CS.sel = MSR_STAR.SYSRET_CS OR 3
    CS.base = 0x00000000
    CS.limit = 0xFFFFFFFF
    CS.attr = 32-bit code,dpl3
    temp_RIP.d = RCX
  }
  SS.sel = MSR_STAR.SYSRET_CS + 8 // SS selector is changed,
  // SS base, limit, attributes unchanged.
  RFLAGS.q = R11 // RF=0,VM=0
  CPL = 3
  RIP = temp_RIP
  EXIT

SYSRET_NON_64BIT_MODE:
  CS.sel = MSR_STAR.SYSRET_CS OR 3 // Return to 32-bit legacy protected mode.
  CS.base = 0x00000000
  CS.limit = 0xFFFFFFFF
  CS.attr = 32-bit code,dpl3
  temp_RIP.d = RCX
  SS.sel = MSR_STAR.SYSRET_CS + 8 // SS selector is changed.
  // SS base, limit, attributes unchanged.
  RFLAGS.IF = 1
  CPL = 3
  RIP = temp_RIP
  EXIT

*/

  bx_address temp_RIP;

  BX_DEBUG(("Execute SYSRET instruction"));

  if (!BX_CPU_THIS_PTR msr.sce) {
    exception(BX_UD_EXCEPTION, 0, 0);
  }

  if(real_mode() || CPL != 0) {
    BX_ERROR(("SYSRET: priveledge check failed, generate #GP(0)"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }

  invalidate_prefetch_q();
  
  if (BX_CPU_THIS_PTR cpu_mode == BX_MODE_LONG_64)
  {
    if (i->os64L()) {
      // Return to 64-bit mode, set up CS segment, flat, 64-bit DPL=3
      parse_selector(((MSR_STAR >> 48) + 16) | 3,
                       &BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].selector);

      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.valid   = 1;
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.p       = 1;
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.dpl     = 3;
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.segment = 1;  /* data/code segment */
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.type    = BX_CODE_EXEC_READ_ACCESSED;
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.base         = 0; /* base address */
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.limit        = 0xFFFF;      /* segment limit */
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.limit_scaled = 0xFFFFFFFF;  /* scaled segment limit */
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.g            = 1; /* 4k granularity */
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.d_b          = 0;
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.l            = 1; /* 64-bit code */
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.avl          = 0; /* available for use by system */

      temp_RIP = RCX;
    }
    else {
      // Return to 32-bit compatibility mode, set up CS segment, flat, 32-bit DPL=3
      parse_selector((MSR_STAR >> 48) | 3,
                       &BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].selector);

      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.valid   = 1;
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.p       = 1;
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.dpl     = 3;
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.segment = 1;  /* data/code segment */
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.type    = BX_CODE_EXEC_READ_ACCESSED;
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.base         = 0; /* base address */
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.limit        = 0xFFFF;      /* segment limit */
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.limit_scaled = 0xFFFFFFFF;  /* scaled segment limit */
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.g            = 1; /* 4k granularity */
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.d_b          = 1;
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.l            = 0; /* 32-bit code */
      BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.avl          = 0; /* available for use by system */

      temp_RIP = ECX;
    }

#if BX_SUPPORT_ICACHE
    BX_CPU_THIS_PTR updateFetchModeMask();
#endif

    // SS base, limit, attributes unchanged
    parse_selector((MSR_STAR >> 48) + 8,
                       &BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].selector);

    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.valid   = 1;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.p       = 1;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.dpl     = 3;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.segment = 1;  /* data/code segment */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.type    = BX_DATA_READ_WRITE_ACCESSED;

    writeEFlags(R11, EFlagsValidMask);

    RIP = temp_RIP;
  }
  else { // (!64BIT_MODE)
    // Return to 32-bit legacy mode, set up CS segment, flat, 32-bit DPL=3
    parse_selector((MSR_STAR >> 48) | 3,
                     &BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].selector);

    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.valid   = 1;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.p       = 1;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.dpl     = 3;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.segment = 1;  /* data/code segment */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.type    = BX_CODE_EXEC_READ_ACCESSED;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.base         = 0; /* base address */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.limit        = 0xFFFF;      /* segment limit */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.limit_scaled = 0xFFFFFFFF;  /* scaled segment limit */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.g            = 1; /* 4k granularity */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.d_b          = 1;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.l            = 0; /* 32-bit code */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.avl          = 0; /* available for use by system */

#if BX_SUPPORT_ICACHE
    BX_CPU_THIS_PTR updateFetchModeMask();
#endif

    // SS base, limit, attributes unchanged
    parse_selector((MSR_STAR >> 48) + 8,
                     &BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].selector);

    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.valid   = 1;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.p       = 1;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.dpl     = 3;
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.segment = 1;  /* data/code segment */
    BX_CPU_THIS_PTR sregs[BX_SEG_REG_SS].cache.type    = BX_DATA_READ_WRITE_ACCESSED;

    BX_CPU_THIS_PTR assert_IF();
    temp_RIP = ECX;
  }

  RIP = temp_RIP;
}

void BX_CPU_C::SWAPGS(bxInstruction_c *i)
{
  Bit64u temp_GS_base;

  BX_ASSERT(protected_mode());

  if(CPL != 0)
    exception(BX_GP_EXCEPTION, 0, 0);

  temp_GS_base = MSR_GSBASE;
  MSR_GSBASE = MSR_KERNELGSBASE;
  MSR_KERNELGSBASE = temp_GS_base;
}
#endif

#if BX_X86_DEBUGGER
Bit32u BX_CPU_C::hwdebug_compare(bx_address laddr_0, unsigned size,
                          unsigned opa, unsigned opb)
{
  // Support x86 hardware debug facilities (DR0..DR7)
  Bit32u dr7 = BX_CPU_THIS_PTR dr7;

  bx_bool ibpoint_found = 0;
  bx_address laddr_n = laddr_0 + (size - 1);
  static bx_address alignment_mask[4] =
    // 00b=1  01b=2  10b=undef  11b=4
    {  0x0,   0x1,   0x0,       0x3   };

  Bit32u len0 = (dr7>>18) & 3;
  Bit32u len1 = (dr7>>22) & 3;
  Bit32u len2 = (dr7>>26) & 3;
  Bit32u len3 = (dr7>>30) & 3;

  bx_address dr0 = (BX_CPU_THIS_PTR dr0) & ~(alignment_mask[len0]);
  bx_address dr1 = (BX_CPU_THIS_PTR dr1) & ~(alignment_mask[len1]);
  bx_address dr2 = (BX_CPU_THIS_PTR dr2) & ~(alignment_mask[len2]);
  bx_address dr3 = (BX_CPU_THIS_PTR dr3) & ~(alignment_mask[len3]);

  bx_address dr0_n = dr0 + len0;
  bx_address dr1_n = dr1 + len1;
  bx_address dr2_n = dr2 + len2;
  bx_address dr3_n = dr3 + len3;

  Bit32u dr0_op = (dr7>>16) & 3;
  Bit32u dr1_op = (dr7>>20) & 3;
  Bit32u dr2_op = (dr7>>24) & 3;
  Bit32u dr3_op = (dr7>>28) & 3;

  // See if this instruction address matches any breakpoints
  if ((dr7 & 0x00000003)) {
    if ((dr0_op==opa || dr0_op==opb) &&
         (laddr_0 <= dr0_n) &&
         (laddr_n >= dr0))
      ibpoint_found = 1;
  }
  if ((dr7 & 0x0000000c)) {
    if ((dr1_op==opa || dr1_op==opb) &&
         (laddr_0 <= dr1_n) &&
         (laddr_n >= dr1))
      ibpoint_found = 1;
  }
  if ((dr7 & 0x00000030)) {
    if ((dr2_op==opa || dr2_op==opb) &&
         (laddr_0 <= dr2_n) &&
         (laddr_n >= dr2))
      ibpoint_found = 1;
  }
  if ((dr7 & 0x000000c0)) {
    if ((dr3_op==opa || dr3_op==opb) &&
         (laddr_0 <= dr3_n) &&
         (laddr_n >= dr3))
      ibpoint_found = 1;
  }

  // If *any* enabled breakpoints matched, then we need to
  // set status bits for *all* breakpoints, even disabled ones,
  // as long as they meet the other breakpoint criteria.
  // This code is similar to that above, only without the
  // breakpoint enabled check.  Seems weird to duplicate effort,
  // but its more efficient to do it this way.
  if (ibpoint_found) {
    // dr6_mask is the return value.  These bits represent the bits to
    // be OR'd into DR6 as a result of the debug event.
    Bit32u dr6_mask=0;
    if ((dr0_op==opa || dr0_op==opb) &&
         (laddr_0 <= dr0_n) &&
         (laddr_n >= dr0))
      dr6_mask |= 0x01;
    if ((dr1_op==opa || dr1_op==opb) &&
         (laddr_0 <= dr1_n) &&
         (laddr_n >= dr1))
      dr6_mask |= 0x02;
    if ((dr2_op==opa || dr2_op==opb) &&
         (laddr_0 <= dr2_n) &&
         (laddr_n >= dr2))
      dr6_mask |= 0x04;
    if ((dr3_op==opa || dr3_op==opb) &&
         (laddr_0 <= dr3_n) &&
         (laddr_n >= dr3))
      dr6_mask |= 0x08;
    return(dr6_mask);
  }

  return(0);
}
#endif

/*
void BX_CPU_C::LFENCE(bxInstruction_c *i) {}
void BX_CPU_C::MFENCE(bxInstruction_c *i) {}
void BX_CPU_C::SFENCE(bxInstruction_c *i) {}
*/