Bochs/bochs/cpu/cpu.cc

/////////////////////////////////////////////////////////////////////////
// $Id$
/////////////////////////////////////////////////////////////////////////
//
//  Copyright (C) 2001-2012  The Bochs Project
//
//  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., 51 Franklin St, Fifth Floor, Boston, MA B 02110-1301 USA
/////////////////////////////////////////////////////////////////////////

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

#define InstrumentICACHE 0

#if InstrumentICACHE
static unsigned iCacheLookups=0;
static unsigned iCacheMisses=0;

#define InstrICache_StatsMask 0xffffff

#define InstrICache_Stats() {\
  if ((iCacheLookups & InstrICache_StatsMask) == 0) { \
    BX_INFO(("ICACHE lookups: %u, misses: %u, hit rate = %6.2f%% ", \
          iCacheLookups, \
          iCacheMisses,  \
          (iCacheLookups-iCacheMisses) * 100.0f / iCacheLookups)); \
    iCacheLookups = iCacheMisses = 0; \
  } \
}
#define InstrICache_Increment(v) (v)++
#else
#define InstrICache_Stats()
#define InstrICache_Increment(v)
#endif

void BX_CPU_C::cpu_loop(void)
{
#if BX_DEBUGGER
  BX_CPU_THIS_PTR break_point = 0;
  BX_CPU_THIS_PTR magic_break = 0;
  BX_CPU_THIS_PTR stop_reason = STOP_NO_REASON;
#endif

  if (setjmp(BX_CPU_THIS_PTR jmp_buf_env)) {
    // can get here only from exception function or VMEXIT
    BX_CPU_THIS_PTR icount++;
    BX_SYNC_TIME_IF_SINGLE_PROCESSOR(0);
#if BX_DEBUGGER || BX_GDBSTUB
    if (dbg_instruction_epilog()) return;
#endif
#if BX_GDBSTUB
    if (bx_dbg.gdbstub_enabled) return;
#endif
  }

  // If the exception() routine has encountered a nasty fault scenario,
  // the debugger may request that control is returned to it so that
  // the situation may be examined.
#if BX_DEBUGGER
  if (bx_guard.interrupt_requested) return;
#endif

  // We get here either by a normal function call, or by a longjmp
  // back from an exception() call.  In either case, commit the
  // new EIP/ESP, and set up other environmental fields.  This code
  // mirrors similar code below, after the interrupt() call.
  BX_CPU_THIS_PTR prev_rip = RIP; // commit new EIP
  BX_CPU_THIS_PTR speculative_rsp = 0;

  while (1) {

    // check on events which occurred for previous instructions (traps)
    // and ones which are asynchronous to the CPU (hardware interrupts)
    if (BX_CPU_THIS_PTR async_event) {
      if (handleAsyncEvent()) {
        // If request to return to caller ASAP.
        return;
      }
    }

    bxICacheEntry_c *entry = getICacheEntry();
    bxInstruction_c *i = entry->i;

#if BX_SUPPORT_HANDLERS_CHAINING_SPEEDUPS
    for(;;) {

      // want to allow changing of the instruction inside instrumentation callback
      BX_INSTR_BEFORE_EXECUTION(BX_CPU_ID, i);
      RIP += i->ilen();
      // when handlers chaining is enabled this single call will execute entire trace
      BX_CPU_CALL_METHOD(i->execute1, (i)); // might iterate repeat instruction

      BX_SYNC_TIME_IF_SINGLE_PROCESSOR(0);

      if (BX_CPU_THIS_PTR async_event) break;

      i = getICacheEntry()->i;
    }
#else // BX_SUPPORT_HANDLERS_CHAINING_SPEEDUPS == 0

    bxInstruction_c *last = i + (entry->tlen);

    for(;;) {

#if BX_DEBUGGER
      if (BX_CPU_THIS_PTR trace)
        debug_disasm_instruction(BX_CPU_THIS_PTR prev_rip);
#endif

      // want to allow changing of the instruction inside instrumentation callback
      BX_INSTR_BEFORE_EXECUTION(BX_CPU_ID, i);
      RIP += i->ilen();
      BX_CPU_CALL_METHOD(i->execute1, (i)); // might iterate repeat instruction
      BX_CPU_THIS_PTR prev_rip = RIP; // commit new RIP
      BX_INSTR_AFTER_EXECUTION(BX_CPU_ID, i);
      BX_CPU_THIS_PTR icount++;

      BX_SYNC_TIME_IF_SINGLE_PROCESSOR(0);

      // note instructions generating exceptions never reach this point
#if BX_DEBUGGER || BX_GDBSTUB
      if (dbg_instruction_epilog()) return;
#endif

      if (BX_CPU_THIS_PTR async_event) break;

      if (++i == last) {
        entry = getICacheEntry();
        i = entry->i;
        last = i + (entry->tlen);
      }
    }
#endif

    // clear stop trace magic indication that probably was set by repeat or branch32/64
    BX_CPU_THIS_PTR async_event &= ~BX_ASYNC_EVENT_STOP_TRACE;

  }  // while (1)
}

#if BX_SUPPORT_SMP

void BX_CPU_C::cpu_run_trace(void)
{
  if (setjmp(BX_CPU_THIS_PTR jmp_buf_env)) {
    // can get here only from exception function or VMEXIT
    BX_CPU_THIS_PTR icount++;
    return;
  }

  // check on events which occurred for previous instructions (traps)
  // and ones which are asynchronous to the CPU (hardware interrupts)
  if (BX_CPU_THIS_PTR async_event) {
    if (handleAsyncEvent()) {
      // If request to return to caller ASAP.
      return;
    }
  }

  bxICacheEntry_c *entry = getICacheEntry();
  bxInstruction_c *i = entry->i;

#if BX_SUPPORT_HANDLERS_CHAINING_SPEEDUPS
  // want to allow changing of the instruction inside instrumentation callback
  BX_INSTR_BEFORE_EXECUTION(BX_CPU_ID, i);
  RIP += i->ilen();
  // when handlers chaining is enabled this single call will execute entire trace
  BX_CPU_CALL_METHOD(i->execute1, (i)); // might iterate repeat instruction

  if (BX_CPU_THIS_PTR async_event) {
    // clear stop trace magic indication that probably was set by repeat or branch32/64
    BX_CPU_THIS_PTR async_event &= ~BX_ASYNC_EVENT_STOP_TRACE;
  }
#else
  bxInstruction_c *last = i + (entry->tlen);

  for(;;) {
    // want to allow changing of the instruction inside instrumentation callback
    BX_INSTR_BEFORE_EXECUTION(BX_CPU_ID, i);
    RIP += i->ilen();
    BX_CPU_CALL_METHOD(i->execute1, (i)); // might iterate repeat instruction
    BX_CPU_THIS_PTR prev_rip = RIP; // commit new RIP
    BX_INSTR_AFTER_EXECUTION(BX_CPU_ID, i);
    BX_CPU_THIS_PTR icount++;

    if (BX_CPU_THIS_PTR async_event) {
      // clear stop trace magic indication that probably was set by repeat or branch32/64
      BX_CPU_THIS_PTR async_event &= ~BX_ASYNC_EVENT_STOP_TRACE;
      break;
    }

    if (++i == last) break;
  }
#endif // BX_SUPPORT_HANDLERS_CHAINING_SPEEDUPS
}

#endif

bxICacheEntry_c* BX_CPU_C::getICacheEntry(void)
{
  bx_address eipBiased = RIP + BX_CPU_THIS_PTR eipPageBias;

  if (eipBiased >= BX_CPU_THIS_PTR eipPageWindowSize) {
    prefetch();
    eipBiased = RIP + BX_CPU_THIS_PTR eipPageBias;
  }

  InstrICache_Increment(iCacheLookups);
  InstrICache_Stats();

  bx_phy_address pAddr = BX_CPU_THIS_PTR pAddrFetchPage + eipBiased;
  bxICacheEntry_c *entry = BX_CPU_THIS_PTR iCache.find_entry(pAddr, BX_CPU_THIS_PTR fetchModeMask);

  if (entry == NULL)
  {
    // iCache miss. No validated instruction with matching fetch parameters
    // is in the iCache.
    InstrICache_Increment(iCacheMisses);
    entry = serveICacheMiss(entry, (Bit32u) eipBiased, pAddr);
  }

  return entry;
}

#if BX_SUPPORT_HANDLERS_CHAINING_SPEEDUPS

// The function is called after taken branch instructions and tries to link the branch to the next trace
BX_INSF_TYPE BX_CPP_AttrRegparmN(1) BX_CPU_C::linkTrace(bxInstruction_c *i)
{
#if BX_SUPPORT_SMP
  if (BX_SMP_PROCESSORS > 1)
    return;
#endif

  if (BX_CPU_THIS_PTR async_event) return;

  Bit32u delta = (Bit32u) (BX_CPU_THIS_PTR icount - BX_CPU_THIS_PTR icount_last_sync);
  if(delta >= bx_pc_system.getNumCpuTicksLeftNextEvent())
    return;

  bxInstruction_c *next = i->getNextTrace();
  if (next) {
    BX_EXECUTE_INSTRUCTION(next);
    return;
  }

  bx_address eipBiased = EIP + BX_CPU_THIS_PTR eipPageBias;
  if (eipBiased >= BX_CPU_THIS_PTR eipPageWindowSize) {
/*
    prefetch();
    eipBiased = RIP + BX_CPU_THIS_PTR eipPageBias;
*/
    // You would like to have the prefetch() instead of this return; statement and link also
    // branches that cross page boundary but this potentially could cause functional failure.
    // An OS might modify the page tables and invalidate the TLB but it won't affect Bochs
    // execution because of a trace linked into another old trace with data before the page
    // invalidation. The case would be detected if doing prefetch() properly.

    return;
  }

  InstrICache_Increment(iCacheLookups);
  InstrICache_Stats();

  bx_phy_address pAddr = BX_CPU_THIS_PTR pAddrFetchPage + eipBiased;
  bxICacheEntry_c *entry = BX_CPU_THIS_PTR iCache.find_entry(pAddr, BX_CPU_THIS_PTR fetchModeMask);

  if (entry != NULL) // link traces - handle only hit cases
  {
    i->setNextTrace(entry->i);
    i = entry->i;
    BX_EXECUTE_INSTRUCTION(i);
  }
}

#endif

#define BX_REPEAT_TIME_UPDATE_INTERVAL (BX_MAX_TRACE_LENGTH-1)

void BX_CPP_AttrRegparmN(2) BX_CPU_C::repeat(bxInstruction_c *i, BxRepIterationPtr_tR execute)
{
  // non repeated instruction
  if (! i->repUsedL()) {
    BX_CPU_CALL_REP_ITERATION(execute, (i));
    return;
  }

#if BX_X86_DEBUGGER
  BX_CPU_THIS_PTR in_repeat = 0;
#endif

#if BX_SUPPORT_X86_64
  if (i->as64L()) {
    while(1) {
      if (RCX != 0) {
        BX_CPU_CALL_REP_ITERATION(execute, (i));
        BX_INSTR_REPEAT_ITERATION(BX_CPU_ID, i);
        RCX --;
      }
      if (RCX == 0) return;

#if BX_DEBUGGER == 0
      if (BX_CPU_THIS_PTR async_event)
#endif
        break; // exit always if debugger enabled

      BX_CPU_THIS_PTR icount++;

      BX_SYNC_TIME_IF_SINGLE_PROCESSOR(BX_REPEAT_TIME_UPDATE_INTERVAL);
    }
  }
  else
#endif
  if (i->as32L()) {
    while(1) {
      if (ECX != 0) {
        BX_CPU_CALL_REP_ITERATION(execute, (i));
        BX_INSTR_REPEAT_ITERATION(BX_CPU_ID, i);
        RCX = ECX - 1;
      }
      if (ECX == 0) return;

#if BX_DEBUGGER == 0
      if (BX_CPU_THIS_PTR async_event)
#endif
        break; // exit always if debugger enabled

      BX_CPU_THIS_PTR icount++;

      BX_SYNC_TIME_IF_SINGLE_PROCESSOR(BX_REPEAT_TIME_UPDATE_INTERVAL);
    }
  }
  else  // 16bit addrsize
  {
    while(1) {
      if (CX != 0) {
        BX_CPU_CALL_REP_ITERATION(execute, (i));
        BX_INSTR_REPEAT_ITERATION(BX_CPU_ID, i);
        CX --;
      }
      if (CX == 0) return;

#if BX_DEBUGGER == 0
      if (BX_CPU_THIS_PTR async_event)
#endif
        break; // exit always if debugger enabled

      BX_CPU_THIS_PTR icount++;

      BX_SYNC_TIME_IF_SINGLE_PROCESSOR(BX_REPEAT_TIME_UPDATE_INTERVAL);
    }
  }

#if BX_X86_DEBUGGER
  BX_CPU_THIS_PTR in_repeat = 1;
#endif

  RIP = BX_CPU_THIS_PTR prev_rip; // repeat loop not done, restore RIP

  // assert magic async_event to stop trace execution
  BX_CPU_THIS_PTR async_event |= BX_ASYNC_EVENT_STOP_TRACE;
}

void BX_CPP_AttrRegparmN(2) BX_CPU_C::repeat_ZF(bxInstruction_c *i, BxRepIterationPtr_tR execute)
{
  unsigned rep = i->repUsedValue();

  // non repeated instruction
  if (! rep) {
    BX_CPU_CALL_REP_ITERATION(execute, (i));
    return;
  }

#if BX_X86_DEBUGGER
  BX_CPU_THIS_PTR in_repeat = 0;
#endif

  if (rep == 3) { /* repeat prefix 0xF3 */
#if BX_SUPPORT_X86_64
    if (i->as64L()) {
      while(1) {
        if (RCX != 0) {
          BX_CPU_CALL_REP_ITERATION(execute, (i));
          BX_INSTR_REPEAT_ITERATION(BX_CPU_ID, i);
          RCX --;
        }
        if (! get_ZF() || RCX == 0) return;

#if BX_DEBUGGER == 0
        if (BX_CPU_THIS_PTR async_event)
#endif
          break; // exit always if debugger enabled

        BX_CPU_THIS_PTR icount++;

        BX_SYNC_TIME_IF_SINGLE_PROCESSOR(BX_REPEAT_TIME_UPDATE_INTERVAL);
      }
    }
    else
#endif
    if (i->as32L()) {
      while(1) {
        if (ECX != 0) {
          BX_CPU_CALL_REP_ITERATION(execute, (i));
          BX_INSTR_REPEAT_ITERATION(BX_CPU_ID, i);
          RCX = ECX - 1;
        }
        if (! get_ZF() || ECX == 0) return;

#if BX_DEBUGGER == 0
        if (BX_CPU_THIS_PTR async_event)
#endif
          break; // exit always if debugger enabled

        BX_CPU_THIS_PTR icount++;

        BX_SYNC_TIME_IF_SINGLE_PROCESSOR(BX_REPEAT_TIME_UPDATE_INTERVAL);
      }
    }
    else  // 16bit addrsize
    {
      while(1) {
        if (CX != 0) {
          BX_CPU_CALL_REP_ITERATION(execute, (i));
          BX_INSTR_REPEAT_ITERATION(BX_CPU_ID, i);
          CX --;
        }
        if (! get_ZF() || CX == 0) return;

#if BX_DEBUGGER == 0
        if (BX_CPU_THIS_PTR async_event)
#endif
          break; // exit always if debugger enabled

        BX_CPU_THIS_PTR icount++;

        BX_SYNC_TIME_IF_SINGLE_PROCESSOR(BX_REPEAT_TIME_UPDATE_INTERVAL);
      }
    }
  }
  else {          /* repeat prefix 0xF2 */
#if BX_SUPPORT_X86_64
    if (i->as64L()) {
      while(1) {
        if (RCX != 0) {
          BX_CPU_CALL_REP_ITERATION(execute, (i));
          BX_INSTR_REPEAT_ITERATION(BX_CPU_ID, i);
          RCX --;
        }
        if (get_ZF() || RCX == 0) return;

#if BX_DEBUGGER == 0
        if (BX_CPU_THIS_PTR async_event)
#endif
          break; // exit always if debugger enabled

        BX_CPU_THIS_PTR icount++;

        BX_SYNC_TIME_IF_SINGLE_PROCESSOR(BX_REPEAT_TIME_UPDATE_INTERVAL);
      }
    }
    else
#endif
    if (i->as32L()) {
      while(1) {
        if (ECX != 0) {
          BX_CPU_CALL_REP_ITERATION(execute, (i));
          BX_INSTR_REPEAT_ITERATION(BX_CPU_ID, i);
          RCX = ECX - 1;
        }
        if (get_ZF() || ECX == 0) return;

#if BX_DEBUGGER == 0
        if (BX_CPU_THIS_PTR async_event)
#endif
          break; // exit always if debugger enabled

        BX_CPU_THIS_PTR icount++;

        BX_SYNC_TIME_IF_SINGLE_PROCESSOR(BX_REPEAT_TIME_UPDATE_INTERVAL);
      }
    }
    else  // 16bit addrsize
    {
      while(1) {
        if (CX != 0) {
          BX_CPU_CALL_REP_ITERATION(execute, (i));
          BX_INSTR_REPEAT_ITERATION(BX_CPU_ID, i);
          CX --;
        }
        if (get_ZF() || CX == 0) return;

#if BX_DEBUGGER == 0
        if (BX_CPU_THIS_PTR async_event)
#endif
          break; // exit always if debugger enabled

        BX_CPU_THIS_PTR icount++;

        BX_SYNC_TIME_IF_SINGLE_PROCESSOR(BX_REPEAT_TIME_UPDATE_INTERVAL);
      }
    }
  }

#if BX_X86_DEBUGGER
  BX_CPU_THIS_PTR in_repeat = 1;
#endif

  RIP = BX_CPU_THIS_PTR prev_rip; // repeat loop not done, restore RIP

  // assert magic async_event to stop trace execution
  BX_CPU_THIS_PTR async_event |= BX_ASYNC_EVENT_STOP_TRACE;
}

// boundaries of consideration:
//
//  * physical memory boundary: 1024k (1Megabyte) (increments of...)
//  * A20 boundary:             1024k (1Megabyte)
//  * page boundary:            4k
//  * ROM boundary:             2k (dont care since we are only reading)
//  * segment boundary:         any

void BX_CPU_C::prefetch(void)
{
  bx_address laddr;
  unsigned pageOffset;

#if BX_SUPPORT_X86_64
  if (long64_mode()) {
    if (! IsCanonical(RIP)) {
      BX_ERROR(("prefetch: #GP(0): RIP crossed canonical boundary"));
      exception(BX_GP_EXCEPTION, 0);
    }

    // linear address is equal to RIP in 64-bit long mode
    pageOffset = PAGE_OFFSET(EIP);
    laddr = RIP;

    // Calculate RIP at the beginning of the page.
    BX_CPU_THIS_PTR eipPageBias = pageOffset - RIP;
    BX_CPU_THIS_PTR eipPageWindowSize = 4096;
  }
  else
#endif
  {

#if BX_CPU_LEVEL >= 5
    if (USER_PL && BX_CPU_THIS_PTR get_VIP() && BX_CPU_THIS_PTR get_VIF()) {
      if (BX_CPU_THIS_PTR cr4.get_PVI() | (v8086_mode() && BX_CPU_THIS_PTR cr4.get_VME())) {
        BX_ERROR(("prefetch: inconsistent VME state"));
        exception(BX_GP_EXCEPTION, 0);
      }
    }
#endif

    BX_CLEAR_64BIT_HIGH(BX_64BIT_REG_RIP); /* avoid 32-bit EIP wrap */
    laddr = get_laddr32(BX_SEG_REG_CS, EIP);
    pageOffset = PAGE_OFFSET(laddr);

    // Calculate RIP at the beginning of the page.
    BX_CPU_THIS_PTR eipPageBias = (bx_address) pageOffset - EIP;

    Bit32u limit = BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.limit_scaled;
    if (EIP > limit) {
      BX_ERROR(("prefetch: EIP [%08x] > CS.limit [%08x]", EIP, limit));
      exception(BX_GP_EXCEPTION, 0);
    }

    BX_CPU_THIS_PTR eipPageWindowSize = 4096;
    if (limit + BX_CPU_THIS_PTR eipPageBias < 4096) {
      BX_CPU_THIS_PTR eipPageWindowSize = (Bit32u)(limit + BX_CPU_THIS_PTR eipPageBias + 1);
    }
  }

#if BX_X86_DEBUGGER
  if (hwbreakpoint_check(laddr, BX_HWDebugInstruction, BX_HWDebugInstruction)) {
    signal_event(BX_EVENT_CODE_BREAKPOINT_ASSIST);
    if (! interrupts_inhibited(BX_INHIBIT_DEBUG)) {
       // The next instruction could already hit a code breakpoint but
       // async_event won't take effect immediatelly.
       // Check if the next executing instruction hits code breakpoint

       // check only if not fetching page cross instruction
       // this check is 32-bit wrap safe as well
       if (EIP == (Bit32u) BX_CPU_THIS_PTR prev_rip) {
         Bit32u dr6_bits = code_breakpoint_match(laddr);
         if (dr6_bits & BX_DEBUG_TRAP_HIT) {
           BX_ERROR(("#DB: x86 code breakpoint catched"));
           BX_CPU_THIS_PTR debug_trap |= dr6_bits;
           exception(BX_DB_EXCEPTION, 0);
         }
       }
    }
  }
  else {
    clear_event(BX_EVENT_CODE_BREAKPOINT_ASSIST);
  }
#endif

  BX_CPU_THIS_PTR clear_RF();

  bx_address lpf = LPFOf(laddr);
  unsigned TLB_index = BX_TLB_INDEX_OF(lpf, 0);
  bx_TLB_entry *tlbEntry = &BX_CPU_THIS_PTR TLB.entry[TLB_index];
  Bit8u *fetchPtr = 0;

  if ((tlbEntry->lpf == lpf) && !(tlbEntry->accessBits & (0x4 | USER_PL))) {
    BX_CPU_THIS_PTR pAddrFetchPage = tlbEntry->ppf;
    fetchPtr = (Bit8u*) tlbEntry->hostPageAddr;
  }  
  else {
    bx_phy_address pAddr = translate_linear(laddr, USER_PL, BX_EXECUTE);
    BX_CPU_THIS_PTR pAddrFetchPage = PPFOf(pAddr);
  }

  if (fetchPtr) {
    BX_CPU_THIS_PTR eipFetchPtr = fetchPtr;
  }
  else {
    BX_CPU_THIS_PTR eipFetchPtr = (const Bit8u*) getHostMemAddr(BX_CPU_THIS_PTR pAddrFetchPage, BX_EXECUTE);

    // Sanity checks
    if (! BX_CPU_THIS_PTR eipFetchPtr) {
      bx_phy_address pAddr = BX_CPU_THIS_PTR pAddrFetchPage + pageOffset;
      if (pAddr >= BX_MEM(0)->get_memory_len()) {
        BX_PANIC(("prefetch: running in bogus memory, pAddr=0x" FMT_PHY_ADDRX, pAddr));
      }
      else {
        BX_PANIC(("prefetch: getHostMemAddr vetoed direct read, pAddr=0x" FMT_PHY_ADDRX, pAddr));
      }
    }
  }
}

#if BX_DEBUGGER || BX_GDBSTUB
bx_bool BX_CPU_C::dbg_instruction_epilog(void)
{
#if BX_DEBUGGER
  bx_address debug_eip = RIP;
  Bit16u cs = BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].selector.value;

  BX_CPU_THIS_PTR guard_found.cs  = cs;
  BX_CPU_THIS_PTR guard_found.eip = debug_eip;
  BX_CPU_THIS_PTR guard_found.laddr = get_laddr(BX_SEG_REG_CS, debug_eip);
  BX_CPU_THIS_PTR guard_found.code_32_64 = BX_CPU_THIS_PTR fetchModeMask;

  //
  // Take care of break point conditions generated during instruction execution
  //

  // Check if we hit read/write or time breakpoint
  if (BX_CPU_THIS_PTR break_point) {
    Bit64u tt = bx_pc_system.time_ticks();
    switch (BX_CPU_THIS_PTR break_point) {
    case BREAK_POINT_TIME:
      BX_INFO(("[" FMT_LL "d] Caught time breakpoint", tt));
      BX_CPU_THIS_PTR stop_reason = STOP_TIME_BREAK_POINT;
      return(1); // on a breakpoint
    case BREAK_POINT_READ:
      BX_INFO(("[" FMT_LL "d] Caught read watch point", tt));
      BX_CPU_THIS_PTR stop_reason = STOP_READ_WATCH_POINT;
      return(1); // on a breakpoint
    case BREAK_POINT_WRITE:
      BX_INFO(("[" FMT_LL "d] Caught write watch point", tt));
      BX_CPU_THIS_PTR stop_reason = STOP_WRITE_WATCH_POINT;
      return(1); // on a breakpoint
    default:
      BX_PANIC(("Weird break point condition"));
    }
  }

  if (BX_CPU_THIS_PTR magic_break) {
    BX_INFO(("[" FMT_LL "d] Stopped on MAGIC BREAKPOINT", bx_pc_system.time_ticks()));
    BX_CPU_THIS_PTR stop_reason = STOP_MAGIC_BREAK_POINT;
    return(1); // on a breakpoint
  }

  // see if debugger requesting icount guard 
  if (bx_guard.guard_for & BX_DBG_GUARD_ICOUNT) {
    if (get_icount() >= BX_CPU_THIS_PTR guard_found.icount_max) {
      return(1);
    }
  }

  // convenient point to see if user requested debug break or typed Ctrl-C
  if (bx_guard.interrupt_requested) {
    return(1);
  }

  // support for 'show' command in debugger
  extern unsigned dbg_show_mask;
  if(dbg_show_mask) {
    int rv = bx_dbg_show_symbolic();
    if (rv) return(rv);
  }

  // Just committed an instruction, before fetching a new one
  // see if debugger is looking for iaddr breakpoint of any type
  if (bx_guard.guard_for & BX_DBG_GUARD_IADDR_ALL) {
#if (BX_DBG_MAX_VIR_BPOINTS > 0)
    if (bx_guard.guard_for & BX_DBG_GUARD_IADDR_VIR) {
      for (unsigned n=0; n<bx_guard.iaddr.num_virtual; n++) {
        if (bx_guard.iaddr.vir[n].enabled &&
           (bx_guard.iaddr.vir[n].cs  == cs) &&
           (bx_guard.iaddr.vir[n].eip == debug_eip))
        {
          BX_CPU_THIS_PTR guard_found.guard_found = BX_DBG_GUARD_IADDR_VIR;
          BX_CPU_THIS_PTR guard_found.iaddr_index = n;
          return(1); // on a breakpoint
        }
      }
    }
#endif
#if (BX_DBG_MAX_LIN_BPOINTS > 0)
    if (bx_guard.guard_for & BX_DBG_GUARD_IADDR_LIN) {
      for (unsigned n=0; n<bx_guard.iaddr.num_linear; n++) {
        if (bx_guard.iaddr.lin[n].enabled &&
           (bx_guard.iaddr.lin[n].addr == BX_CPU_THIS_PTR guard_found.laddr))
        {
          BX_CPU_THIS_PTR guard_found.guard_found = BX_DBG_GUARD_IADDR_LIN;
          BX_CPU_THIS_PTR guard_found.iaddr_index = n;
          return(1); // on a breakpoint
        }
      }
    }
#endif
#if (BX_DBG_MAX_PHY_BPOINTS > 0)
    if (bx_guard.guard_for & BX_DBG_GUARD_IADDR_PHY) {
      bx_phy_address phy;
      bx_bool valid = dbg_xlate_linear2phy(BX_CPU_THIS_PTR guard_found.laddr, &phy);
      if (valid) {
        for (unsigned n=0; n<bx_guard.iaddr.num_physical; n++) {
          if (bx_guard.iaddr.phy[n].enabled && (bx_guard.iaddr.phy[n].addr == phy))
          {
            BX_CPU_THIS_PTR guard_found.guard_found = BX_DBG_GUARD_IADDR_PHY;
            BX_CPU_THIS_PTR guard_found.iaddr_index = n;
            return(1); // on a breakpoint
          }
        }
      }
    }
#endif
  }
#endif

#if BX_GDBSTUB
  if (bx_dbg.gdbstub_enabled) {
    unsigned reason = bx_gdbstub_check(EIP);
    if (reason != GDBSTUB_STOP_NO_REASON) return(1);
  }
#endif

  return(0);
}
#endif // BX_DEBUGGER || BX_GDBSTUB