C++ BX_ERROR函數代碼示例

void BX_CPU_C::real_mode_int(Bit8u vector, bx_bool push_error, Bit16u error_code)
{
  if ((vector*4+3) > BX_CPU_THIS_PTR idtr.limit) {
    BX_ERROR(("interrupt(real mode) vector > idtr.limit"));
    exception(BX_GP_EXCEPTION, 0);
  }

  push_16((Bit16u) read_eflags());
  push_16(BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].selector.value);
  push_16(IP);

  Bit16u new_ip = system_read_word(BX_CPU_THIS_PTR idtr.base + 4 * vector);
  // CS.LIMIT can't change when in real/v8086 mode
  if (new_ip > BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].cache.u.segment.limit_scaled) {
    BX_ERROR(("interrupt(real mode): instruction pointer not within code segment limits"));
    exception(BX_GP_EXCEPTION, 0);
  }

  Bit16u cs_selector = system_read_word(BX_CPU_THIS_PTR idtr.base + 4 * vector + 2);
  load_seg_reg(&BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS], cs_selector);
  EIP = new_ip;

  /* INT affects the following flags: I,T */
  BX_CPU_THIS_PTR clear_IF();
  BX_CPU_THIS_PTR clear_TF();
#if BX_CPU_LEVEL >= 4
  BX_CPU_THIS_PTR clear_AC();
#endif
  BX_CPU_THIS_PTR clear_RF();
}

int bx_sound_linux_c::alsa_pcm_write()
{
  int ret;

  if (alsa_pcm[0].buffer == NULL) {
    alsa_pcm[0].buffer = (char *)malloc(alsa_pcm[0].alsa_bufsize);
  }
  while (alsa_pcm[0].audio_bufsize >= alsa_pcm[0].alsa_bufsize) {
    memcpy(alsa_pcm[0].buffer, audio_buffer[0], alsa_pcm[0].alsa_bufsize);
    ret = snd_pcm_writei(alsa_pcm[0].handle, alsa_pcm[0].buffer, alsa_pcm[0].frames);
    if (ret == -EAGAIN)
      continue;
    if (ret == -EPIPE) {
      /* EPIPE means underrun */
      BX_ERROR(("ALSA: underrun occurred"));
      snd_pcm_prepare(alsa_pcm[0].handle);
    } else if (ret < 0) {
      BX_ERROR(("ALSA: error from writei: %s", snd_strerror(ret)));
    }  else if (ret != (int)alsa_pcm[0].frames) {
      BX_ERROR(("ALSA: short write, write %d frames", ret));
    }
    alsa_pcm[0].audio_bufsize -= alsa_pcm[0].alsa_bufsize;
    memcpy(audio_buffer[0], audio_buffer[0]+alsa_pcm[0].alsa_bufsize, alsa_pcm[0].audio_bufsize);
  }
  if ((alsa_pcm[0].audio_bufsize == 0) && (alsa_pcm[0].buffer != NULL)) {
    free(alsa_pcm[0].buffer);
    alsa_pcm[0].buffer = NULL;
  }

  return BX_SOUNDLOW_OK;
}

static bx_bool pcidev_mem_read_handler(bx_phy_address addr, unsigned len, void *data, void *param)
{
    struct region_struct *region = (struct region_struct *)param;
    bx_pcidev_c *pcidev = region->pcidev;
    int fd = pcidev->pcidev_fd;
    int ret = -1;

    if (fd == -1)
        return false; /* we failed to handle the request, so let a default handler do it for us */

    BX_INFO(("Reading I/O memory at 0x%08x", (unsigned)addr));
    struct pcidev_io_struct io;
    io.address = addr + region->host_start - region->start;
    switch(len) {
        case 1:
            ret = ioctl(fd, PCIDEV_IOCTL_READ_MEM_BYTE, &io);
            *(Bit8u *)data = io.value;
            break;
        case 2:
            ret = ioctl(fd, PCIDEV_IOCTL_READ_MEM_WORD, &io);
            *(Bit16u *)data = io.value;
            break;
        case 4:
            ret = ioctl(fd, PCIDEV_IOCTL_READ_MEM_DWORD, &io);
            *(Bit32u *)data = io.value;
            break;
        default:
            BX_ERROR(("Unsupported pcidev read mem operation"));
            break;
    }
    if (ret == -1) {
        BX_ERROR(("pcidev read mem error"));
    }
    return true; // ok, we handled the request
}

void BX_CPU_C::branch_far64(bx_selector_t *selector, 
           bx_descriptor_t *descriptor, bx_address rip, Bit8u cpl)
{
#if BX_SUPPORT_X86_64
  if (descriptor->u.segment.l)
  {
    if (! IsCanonical(rip)) {
      BX_ERROR(("branch_far: canonical RIP violation"));
      exception(BX_GP_EXCEPTION, 0, 0);
    }
  }
  else
#endif
  {
    /* instruction pointer must be in code segment limit else #GP(0) */
    if (rip > descriptor->u.segment.limit_scaled) {
      BX_ERROR(("branch_far: RIP > limit"));
      exception(BX_GP_EXCEPTION, 0, 0);
    }
  }

  /* Load CS:IP from destination pointer */
  /* Load CS-cache with new segment descriptor */
  load_cs(selector, descriptor, cpl);

  /* Change the RIP value */
  RIP = rip;
}

int bx_sound_linux_c::sendwavepacket(int length, Bit8u data[])
{
#if BX_HAVE_ALSASOUND
  if (use_alsa_pcm) {
    if ((alsa_pcm[0].audio_bufsize+length) <= BX_SOUND_LINUX_BUFSIZE) {
      memcpy(audio_buffer[0]+alsa_pcm[0].audio_bufsize, data, length);
      alsa_pcm[0].audio_bufsize += length;
    } else {
      BX_ERROR(("ALSA: audio buffer overflow"));
      return BX_SOUNDLOW_ERR;
    }
    if (alsa_pcm[0].audio_bufsize < alsa_pcm[0].alsa_bufsize) {
      return BX_SOUNDLOW_OK;
    } else {
      return alsa_pcm_write();
    }
  }
#endif
  int ret = write(wave_fd[0], data, length);

  if (ret == length) {
    return BX_SOUNDLOW_OK;
  } else {
    BX_ERROR(("OSS: write error"));
    return BX_SOUNDLOW_ERR;
  }
}

void bx_tap_pktmover_c::rx_timer()
{
  int nbytes;
  Bit8u buf[BX_PACKET_BUFSIZE];
  Bit8u *rxbuf;
  if (fd<0) return;
#if defined(__sun__)
  struct strbuf sbuf;
  int f = 0;
  sbuf.maxlen = sizeof(buf);
  sbuf.buf = (char *)buf;
  nbytes = getmsg(fd, NULL, &sbuf, &f) >=0 ? sbuf.len : -1;
#else
  nbytes = read (fd, buf, sizeof(buf));
#endif

  // hack: discard first two bytes
#if defined(__FreeBSD__) || defined(__FreeBSD_kernel__) || defined(__APPLE__) || defined(__sun__) // Should be fixed for other *BSD
  rxbuf = buf;
#else
  rxbuf = buf+2;
  nbytes-=2;
#endif

#if defined(__linux__)
  // hack: TAP device likes to create an ethernet header which has
  // the same source and destination address FE:FD:00:00:00:00.
  // Change the dest address to FE:FD:00:00:00:01.
  if (!memcmp(&rxbuf[0], &rxbuf[6], 6)) {
    rxbuf[5] = guest_macaddr[5];
  }
#endif

  if (nbytes>0)
    BX_DEBUG(("tap read returned %d bytes", nbytes));
  if (nbytes<0) {
    if (errno != EAGAIN)
      BX_ERROR(("tap read error: %s", strerror(errno)));
    return;
  }
#if BX_ETH_TAP_LOGGING
  if (nbytes > 0) {
    BX_DEBUG(("receive packet length %u", nbytes));
    // dump raw bytes to a file, eventually dump in pcap format so that
    // tcpdump -r FILE can interpret them for us.
    int n = fwrite(rxbuf, nbytes, 1, rxlog);
    if (n != 1) BX_ERROR(("fwrite to rxlog failed, nbytes = %d", nbytes));
    // dump packet in hex into an ascii log file
    write_pktlog_txt(rxlog_txt, rxbuf, nbytes, 1);
    // flush log so that we see the packets as they arrive w/o buffering
    fflush(rxlog);
  }
#endif
  BX_DEBUG(("eth_tap: got packet: %d bytes, dst=%x:%x:%x:%x:%x:%x, src=%x:%x:%x:%x:%x:%x\n", nbytes, rxbuf[0], rxbuf[1], rxbuf[2], rxbuf[3], rxbuf[4], rxbuf[5], rxbuf[6], rxbuf[7], rxbuf[8], rxbuf[9], rxbuf[10], rxbuf[11]));
  if (nbytes < 60) {
    BX_INFO(("packet too short (%d), padding to 60", nbytes));
    nbytes = 60;
  }
  (*rxh)(netdev, rxbuf, nbytes);
}

bx_bool usb_msd_device_c::init()
{
  if (d.type == USB_DEV_TYPE_DISK) {
    s.hdimage = DEV_hdimage_init_image(s.image_mode, 0, s.journal);
    if (s.hdimage->open(s.fname) < 0) {
      BX_ERROR(("could not open hard drive image file '%s'", s.fname));
      return 0;
    } else {
      s.scsi_dev = new scsi_device_t(s.hdimage, 0, usb_msd_command_complete, (void*)this);
    }
    sprintf(s.info_txt, "USB HD: path='%s', mode='%s'", s.fname, hdimage_mode_names[s.image_mode]);
  } else if (d.type == USB_DEV_TYPE_CDROM) {
#ifdef LOWLEVEL_CDROM
    s.cdrom = DEV_hdimage_init_cdrom(s.fname);
    if (!s.cdrom->insert_cdrom()) {
      BX_ERROR(("could not open cdrom image file '%s'", s.fname));
      return 0;
    } else {
      s.scsi_dev = new scsi_device_t(s.cdrom, 0, usb_msd_command_complete, (void*)this);
    }
    sprintf(s.info_txt, "USB CD: path='%s'", s.fname);
#else
    BX_PANIC(("missing LOWLEVEL_CDROM support"));
    return 0;
#endif
  }
  s.scsi_dev->register_state(s.sr_list, "scsidev");
  s.mode = USB_MSDM_CBW;
  d.connected = 1;
  return 1;
}

BX_CPU_C::read_RMW_virtual_dword(unsigned s, bx_address offset)
{
  bx_address laddr;
  bx_segment_reg_t *seg = &BX_CPU_THIS_PTR sregs[s];
  Bit32u data;
  BX_INSTR_MEM_DATA_ACCESS(BX_CPU_ID, s, offset, 4, BX_RW);

  if (seg->cache.valid & SegAccessWOK4G) {
accessOK:
    laddr = BX_CPU_THIS_PTR get_laddr(s, offset);
#if BX_SupportGuest2HostTLB
    unsigned tlbIndex = BX_TLB_INDEX_OF(laddr, 3);
    bx_address lpf = AlignedAccessLPFOf(laddr, 3);
    bx_TLB_entry *tlbEntry = &BX_CPU_THIS_PTR TLB.entry[tlbIndex];
    if (tlbEntry->lpf == lpf) {
      // See if the TLB entry privilege level allows us write access
      // from this CPL.
      if (tlbEntry->accessBits & (0x10 << CPL)) {
        bx_hostpageaddr_t hostPageAddr = tlbEntry->hostPageAddr;
        Bit32u pageOffset = PAGE_OFFSET(laddr);
        BX_INSTR_LIN_ACCESS(BX_CPU_ID, laddr, tlbEntry->ppf | pageOffset, 4, BX_RW);
        Bit32u *hostAddr = (Bit32u*) (hostPageAddr | pageOffset);
#if BX_SUPPORT_ICACHE
        pageWriteStampTable.decWriteStamp(tlbEntry->ppf);
#endif
        ReadHostDWordFromLittleEndian(hostAddr, data);
        BX_CPU_THIS_PTR address_xlation.pages = (bx_ptr_equiv_t) hostAddr;
        BX_DBG_LIN_MEMORY_ACCESS(BX_CPU_ID, laddr,
            tlbEntry->ppf | pageOffset, 4, CPL, BX_READ, (Bit8u*) &data);
        return data;
      }
    }
#endif
#if BX_SUPPORT_X86_64
    if (! IsCanonical(laddr)) {
      BX_ERROR(("read_RMW_virtual_dword(): canonical failure"));
      exception(int_number(seg), 0, 0);
    }
#endif
#if BX_CPU_LEVEL >= 4 && BX_SUPPORT_ALIGNMENT_CHECK
    if (BX_CPU_THIS_PTR alignment_check()) {
      if (laddr & 3) {
        BX_ERROR(("read_RMW_virtual_dword(): #AC misaligned access"));
        exception(BX_AC_EXCEPTION, 0, 0);
      }
    }
#endif
    access_read_linear(laddr, 4, CPL, BX_RW, (void *) &data);
    return data;
  }

  if (seg->cache.valid & SegAccessWOK) {
    if (Is64BitMode() || (offset < (seg->cache.u.segment.limit_scaled-2)))
      goto accessOK;
  }
  write_virtual_checks(seg, offset, 4);
  goto accessOK;
}

int BX_CPU_C::v86_redirect_interrupt(Bit8u vector)
{
#if BX_CPU_LEVEL >= 5
  if (BX_CPU_THIS_PTR cr4.get_VME())
  {
    bx_address tr_base = BX_CPU_THIS_PTR tr.cache.u.segment.base;
    if (BX_CPU_THIS_PTR tr.cache.u.segment.limit_scaled < 103) {
      BX_ERROR(("INT_Ib(): TR.limit < 103 in VME"));
      exception(BX_GP_EXCEPTION, 0);
    }

    Bit32u io_base = system_read_word(tr_base + 102), offset = io_base - 32 + (vector >> 3);
    if (offset > BX_CPU_THIS_PTR tr.cache.u.segment.limit_scaled) {
      BX_ERROR(("INT_Ib(): failed to fetch VME redirection bitmap"));
      exception(BX_GP_EXCEPTION, 0);
    }

    Bit8u vme_redirection_bitmap = system_read_byte(tr_base + offset);
    if (!(vme_redirection_bitmap & (1 << (vector & 7))))
    {
      // redirect interrupt through virtual-mode idt
      Bit16u temp_flags = (Bit16u) read_eflags();

      Bit16u temp_CS = system_read_word(vector*4 + 2);
      Bit16u temp_IP = system_read_word(vector*4);

      if (BX_CPU_THIS_PTR get_IOPL() < 3) {
        temp_flags |= EFlagsIOPLMask;
        if (BX_CPU_THIS_PTR get_VIF())
          temp_flags |=  EFlagsIFMask;
        else
          temp_flags &= ~EFlagsIFMask;
      }

      Bit16u old_IP = IP;
      Bit16u old_CS = BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].selector.value;

      push_16(temp_flags);
      // push return address onto new stack
      push_16(old_CS);
      push_16(old_IP);

      load_seg_reg(&BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS], (Bit16u) temp_CS);
      EIP = temp_IP;

      BX_CPU_THIS_PTR clear_TF();
      BX_CPU_THIS_PTR clear_RF();
      if (BX_CPU_THIS_PTR get_IOPL() == 3)
        BX_CPU_THIS_PTR clear_IF();
      else
        BX_CPU_THIS_PTR clear_VIF();

      return 1;
    }
  }

int bx_sound_linux_c::alsa_seq_open(const char *alsadev)
{
  char *mididev, *ptr;
  int client, port, ret = 0;
  int length = strlen(alsadev) + 1;

  mididev = new char[length];

  if (mididev == NULL)
    return BX_SOUNDLOW_ERR;

  strcpy(mididev, alsadev);
  ptr = strtok(mididev, ":");
  if (ptr == NULL) {
    BX_ERROR(("ALSA sequencer setup: missing client parameters"));
    return BX_SOUNDLOW_ERR;
  }
  client = atoi(ptr);
  ptr = strtok(NULL, ":");
  if (ptr == NULL) {
    BX_ERROR(("ALSA sequencer setup: missing port parameter"));
    return BX_SOUNDLOW_ERR;
  }
  port = atoi(ptr);

  delete(mididev);

  if (snd_seq_open(&alsa_seq.handle, "default", SND_SEQ_OPEN_OUTPUT, 0) < 0) {
    BX_ERROR(("Couldn't open ALSA sequencer for midi output"));
    return BX_SOUNDLOW_ERR;
  }
  ret = snd_seq_create_simple_port(alsa_seq.handle, NULL,
    SND_SEQ_PORT_CAP_WRITE |
    SND_SEQ_PORT_CAP_SUBS_WRITE |
    SND_SEQ_PORT_CAP_READ,
    SND_SEQ_PORT_TYPE_MIDI_GENERIC);
  if (ret < 0) {
    BX_ERROR(("ALSA sequencer: error creating port %s", snd_strerror(errno)));
  } else {
    alsa_seq.source_port = ret;
    ret = snd_seq_connect_to(alsa_seq.handle, alsa_seq.source_port, client, port);
    if (ret < 0) {
      BX_ERROR(("ALSA sequencer: could not connect to port %d:%d", client, port));
    }
  }
  if (ret < 0) {
    snd_seq_close(alsa_seq.handle);
    return BX_SOUNDLOW_ERR;
  } else {
    return BX_SOUNDLOW_OK;
  }
}

BX_CPU_C::read_RMW_virtual_qword_64(unsigned s, Bit64u offset)
{
  BX_ASSERT(BX_CPU_THIS_PTR cpu_mode == BX_MODE_LONG_64);

  bx_segment_reg_t *seg = &BX_CPU_THIS_PTR sregs[s];
  Bit64u data;
  BX_INSTR_MEM_DATA_ACCESS(BX_CPU_ID, s, offset, 8, BX_RW);

  Bit64u laddr = BX_CPU_THIS_PTR get_laddr64(s, offset);
#if BX_SupportGuest2HostTLB
  unsigned tlbIndex = BX_TLB_INDEX_OF(laddr, 7);
  Bit64u lpf = AlignedAccessLPFOf(laddr, 7);
  bx_TLB_entry *tlbEntry = &BX_CPU_THIS_PTR TLB.entry[tlbIndex];
  if (tlbEntry->lpf == lpf) {
    // See if the TLB entry privilege level allows us write access
    // from this CPL.
    if (tlbEntry->accessBits & (0x10 << CPL)) {
      bx_hostpageaddr_t hostPageAddr = tlbEntry->hostPageAddr;
      Bit32u pageOffset = PAGE_OFFSET(laddr);
      BX_INSTR_LIN_ACCESS(BX_CPU_ID, laddr, tlbEntry->ppf | pageOffset, 8, BX_RW);
      Bit64u *hostAddr = (Bit64u*) (hostPageAddr | pageOffset);
#if BX_SUPPORT_ICACHE
      pageWriteStampTable.decWriteStamp(tlbEntry->ppf);
#endif
      ReadHostQWordFromLittleEndian(hostAddr, data);
      BX_CPU_THIS_PTR address_xlation.pages = (bx_ptr_equiv_t) hostAddr;
      BX_DBG_LIN_MEMORY_ACCESS(BX_CPU_ID, laddr,
          tlbEntry->ppf | pageOffset, 8, CPL, BX_READ, (Bit8u*) &data);
      return data;
    }
  }
#endif

  if (! IsCanonical(laddr)) {
    BX_ERROR(("read_RMW_virtual_qword_64(): canonical failure"));
    exception(int_number(seg), 0, 0);
  }

#if BX_CPU_LEVEL >= 4 && BX_SUPPORT_ALIGNMENT_CHECK
  if (BX_CPU_THIS_PTR alignment_check()) {
    if (laddr & 7) {
      BX_ERROR(("read_RMW_virtual_qword_64(): #AC misaligned access"));
      exception(BX_AC_EXCEPTION, 0, 0);
    }
  }
#endif

  access_read_linear(laddr, 8, CPL, BX_RW, (void *) &data);
  return data;
}

BX_INSF_TYPE BX_CPP_AttrRegparmN(1) BX_CPU_C::BSWAP_RX(bxInstruction_c *i)
{
  BX_ERROR(("BSWAP with 16-bit opsize: undefined behavior !"));
  BX_WRITE_16BIT_REG(i->rm(), 0);

  BX_NEXT_INSTR(i);
}

void serial_raw::transmit(Bit8u byte)
{
#ifdef WIN32
  DWORD DErr, Len2;
  OVERLAPPED tx_ovl;
#endif

  BX_DEBUG (("transmit %d", byte));
  if (present) {
#ifdef WIN32
    if (DCBchanged) {
      setup_port();
    } else {
      ClearCommError(hCOM, &DErr, NULL);
    }
    memset(&tx_ovl, 0, sizeof(OVERLAPPED));
    tx_ovl.hEvent = CreateEvent(NULL,TRUE,TRUE,"transmit");
    if (!WriteFile(hCOM, &byte, 1, &Len2, &tx_ovl)) {
      if (GetLastError() == ERROR_IO_PENDING) {
        if (WaitForSingleObject(tx_ovl.hEvent, 100) == WAIT_OBJECT_0) {
          GetOverlappedResult(hCOM, &tx_ovl, &Len2, FALSE);
        }
      }
    }
    if (Len2 != 1) BX_ERROR(("transmit failed: len = %d", Len2));
    ClearCommError(hCOM, &DErr, NULL);
    CloseHandle(tx_ovl.hEvent);
#endif
  }
}

void BX_CPU_C::real_mode_int(Bit8u vector, bx_bool is_INT, bx_bool is_error_code, Bit16u error_code)
{
  // real mode interrupt
  Bit16u cs_selector, ip;

  if ((vector*4+3) > BX_CPU_THIS_PTR idtr.limit) {
    BX_ERROR(("interrupt(real mode) vector > idtr.limit"));
    exception(BX_GP_EXCEPTION, 0, 0);
  }

  push_16((Bit16u) read_eflags());

  cs_selector = BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS].selector.value;
  push_16(cs_selector);
  ip = EIP;
  push_16(ip);

  access_read_linear(BX_CPU_THIS_PTR idtr.base + 4 * vector,     2, 0, BX_READ, &ip);
  EIP = (Bit32u) ip;
  access_read_linear(BX_CPU_THIS_PTR idtr.base + 4 * vector + 2, 2, 0, BX_READ, &cs_selector);
  load_seg_reg(&BX_CPU_THIS_PTR sregs[BX_SEG_REG_CS], cs_selector);

  /* INT affects the following flags: I,T */
  BX_CPU_THIS_PTR clear_IF();
  BX_CPU_THIS_PTR clear_TF();
#if BX_CPU_LEVEL >= 4
  BX_CPU_THIS_PTR clear_AC();
#endif
  BX_CPU_THIS_PTR clear_RF();
}

void BX_CPU_C::task_switch_load_selector(bx_segment_reg_t *seg,
                 bx_selector_t *selector, Bit16u raw_selector, Bit8u cs_rpl)
{
  bx_descriptor_t descriptor;
  Bit32u dword1, dword2;

  // NULL selector is OK, will leave cache invalid
  if ((raw_selector & 0xfffc) != 0)
  {
    bx_bool good = fetch_raw_descriptor2(selector, &dword1, &dword2);
    if (!good) {
      BX_ERROR(("task_switch(%s): bad selector fetch !", strseg(seg)));
      exception(BX_TS_EXCEPTION, raw_selector & 0xfffc, 0);
    }

    parse_descriptor(dword1, dword2, &descriptor);

    /* AR byte must indicate data or readable code segment else #TS(selector) */
    if (descriptor.segment==0 || (IS_CODE_SEGMENT(descriptor.type) &&
        IS_CODE_SEGMENT_READABLE(descriptor.type) == 0))
    {
      BX_ERROR(("task_switch(%s): not data or readable code !", strseg(seg)));
      exception(BX_TS_EXCEPTION, raw_selector & 0xfffc, 0);
    }

    /* If data or non-conforming code, then both the RPL and the CPL
     * must be less than or equal to DPL in AR byte else #GP(selector) */
    if (IS_DATA_SEGMENT(descriptor.type) ||
        IS_CODE_SEGMENT_NON_CONFORMING(descriptor.type))
    {
      if ((selector->rpl > descriptor.dpl) || (cs_rpl > descriptor.dpl)) {
        BX_ERROR(("load_seg_reg(%s): RPL & CPL must be <= DPL", strseg(seg)));
        exception(BX_TS_EXCEPTION, raw_selector & 0xfffc, 0);
      }
    }

    if (! IS_PRESENT(descriptor)) {
      BX_ERROR(("task_switch(%s): descriptor not present !", strseg(seg)));
      exception(BX_NP_EXCEPTION, raw_selector & 0xfffc, 0);
    }

    // All checks pass, fill in shadow cache
    seg->cache = descriptor;
  }
}