miscemu/instr.c

   1 /*
   2  * Emulation of priviledged instructions
   3  *
   4  * Copyright 1995 Alexandre Julliard
   5  */
   6
   7 #include "windows.h"
   8 #include "ldt.h"
   9 #include "global.h"
  10 #include "module.h"
  11 #include "miscemu.h"
  12 #include "sig_context.h"
  13 #include "debug.h"
  14
  15
  16 #define STACK_sig(context) \
  17    (IS_SELECTOR_32BIT(SS_sig(context)) ? ESP_sig(context) : SP_sig(context))
  18
  19 #define MAKE_PTR(seg,off) \
  20    (IS_SELECTOR_SYSTEM(seg) ? (void *)(off) : PTR_SEG_OFF_TO_LIN(seg,off))
  21
  22 #define STACK_PTR(context) \
  23    (IS_SELECTOR_SYSTEM(SS_sig(context)) ? (void *)ESP_sig(context) : \
  24     (PTR_SEG_OFF_TO_LIN(SS_sig(context),STACK_sig(context))))
  25
  26
  27 /***********************************************************************
  28  *           INSTR_ReplaceSelector
  29  *
  30  * Try to replace an invalid selector by a valid one.
  31  * The only selector where it is allowed to do "mov ax,40;mov es,ax"
  32  * is the so called 'bimodal' selector 0x40, which points to the BIOS
  33  * data segment. Used by (at least) Borland products (and programs compiled
  34  * using Borland products).
  35  *
  36  * See Undocumented Windows, Chapter 5, __0040.
  37  */
  38 static WORD INSTR_ReplaceSelector( SIGCONTEXT *context, WORD sel)
  39 {
  40     if (sel == 0x40)
  41     {
  42         static WORD sys_timer = 0;
  43         if (!sys_timer)
  44             sys_timer = CreateSystemTimer( 55, (FARPROC16)DOSMEM_Tick );
  45         return DOSMEM_BiosSeg;
  46     }
  47     return 0;  /* Can't replace selector, crashdump */
  48 }
  49
  50
  51 /***********************************************************************
  52  *           INSTR_GetOperandAddr
  53  *
  54  * Return the address of an instruction operand (from the mod/rm byte).
  55  */
  56 static BYTE *INSTR_GetOperandAddr( SIGCONTEXT *context, BYTE *instr,
  57                                    int long_addr, int segprefix, int *len )
  58 {
  59     int mod, rm, base, index = 0, ss = 0, seg = 0, off;
  60
  61 #define GET_VAL(val,type) \
  62     { *val = *(type *)instr; instr += sizeof(type); *len += sizeof(type); }
  63
  64     *len = 0;
  65     GET_VAL( &mod, BYTE );
  66     rm = mod & 7;
  67     mod >>= 6;
  68
  69     if (mod == 3)
  70     {
  71         switch(rm)
  72         {
  73         case 0: return (BYTE *)&EAX_sig(context);
  74         case 1: return (BYTE *)&ECX_sig(context);
  75         case 2: return (BYTE *)&EDX_sig(context);
  76         case 3: return (BYTE *)&EBX_sig(context);
  77         case 4: return (BYTE *)&ESP_sig(context);
  78         case 5: return (BYTE *)&EBP_sig(context);
  79         case 6: return (BYTE *)&ESI_sig(context);
  80         case 7: return (BYTE *)&EDI_sig(context);
  81         }
  82     }
  83
  84     if (long_addr)
  85     {
  86         if (rm == 4)
  87         {
  88             BYTE sib;
  89             GET_VAL( &sib, BYTE );
  90             rm = sib & 7;
  91             ss = sib >> 6;
  92             switch(sib >> 3)
  93             {
  94             case 0: index = EAX_sig(context); break;
  95             case 1: index = ECX_sig(context); break;
  96             case 2: index = EDX_sig(context); break;
  97             case 3: index = EBX_sig(context); break;
  98             case 4: index = 0; break;
  99             case 5: index = EBP_sig(context); break;
 100             case 6: index = ESI_sig(context); break;
 101             case 7: index = EDI_sig(context); break;
 102             }
 103         }
 104
 105         switch(rm)
 106         {
 107         case 0: base = EAX_sig(context); seg = DS_sig(context); break;
 108         case 1: base = ECX_sig(context); seg = DS_sig(context); break;
 109         case 2: base = EDX_sig(context); seg = DS_sig(context); break;
 110         case 3: base = EBX_sig(context); seg = DS_sig(context); break;
 111         case 4: base = ESP_sig(context); seg = SS_sig(context); break;
 112         case 5: base = EBP_sig(context); seg = SS_sig(context); break;
 113         case 6: base = ESI_sig(context); seg = DS_sig(context); break;
 114         case 7: base = EDI_sig(context); seg = DS_sig(context); break;
 115         }
 116         switch (mod)
 117         {
 118         case 0:
 119             if (rm == 5)  /* special case: ds:(disp32) */
 120             {
 121                 GET_VAL( &base, DWORD );
 122                 seg = DS_sig(context);
 123             }
 124             break;
 125
 126         case 1:  /* 8-bit disp */
 127             GET_VAL( &off, BYTE );
 128             base += (signed char)off;
 129             break;
 130
 131         case 2:  /* 32-bit disp */
 132             GET_VAL( &off, DWORD );
 133             base += (signed long)off;
 134             break;
 135         }
 136     }
 137     else  /* short address */
 138     {
 139         switch(rm)
 140         {
 141         case 0:  /* ds:(bx,si) */
 142             base = BX_sig(context) + SI_sig(context);
 143             seg  = DS_sig(context);
 144             break;
 145         case 1:  /* ds:(bx,di) */
 146             base = BX_sig(context) + DI_sig(context);
 147             seg  = DS_sig(context);
 148             break;
 149         case 2:  /* ss:(bp,si) */
 150             base = BP_sig(context) + SI_sig(context);
 151             seg  = SS_sig(context);
 152             break;
 153         case 3:  /* ss:(bp,di) */
 154             base = BP_sig(context) + DI_sig(context);
 155             seg  = SS_sig(context);
 156             break;
 157         case 4:  /* ds:(si) */
 158             base = SI_sig(context);
 159             seg  = DS_sig(context);
 160             break;
 161         case 5:  /* ds:(di) */
 162             base = DI_sig(context);
 163             seg  = DS_sig(context);
 164             break;
 165         case 6:  /* ss:(bp) */
 166             base = BP_sig(context);
 167             seg  = SS_sig(context);
 168             break;
 169         case 7:  /* ds:(bx) */
 170             base = BX_sig(context);
 171             seg  = DS_sig(context);
 172             break;
 173         }
 174
 175         switch(mod)
 176         {
 177         case 0:
 178             if (rm == 6)  /* special case: ds:(disp16) */
 179             {
 180                 GET_VAL( &base, WORD );
 181                 seg  = DS_sig(context);
 182             }
 183             break;
 184
 185         case 1:  /* 8-bit disp */
 186             GET_VAL( &off, BYTE );
 187             base += (signed char)off;
 188             break;
 189
 190         case 2:  /* 16-bit disp */
 191             GET_VAL( &off, WORD );
 192             base += (signed short)off;
 193             break;
 194         }
 195         base &= 0xffff;
 196     }
 197     if (segprefix != -1) seg = segprefix;
 198
 199     /* Make sure the segment and offset are valid */
 200     if (IS_SELECTOR_SYSTEM(seg)) return (BYTE *)(base + (index << ss));
 201     if (((seg & 7) != 7) || IS_SELECTOR_FREE(seg)) return NULL;
 202     if (GET_SEL_LIMIT(seg) < (base + (index << ss))) return NULL;
 203     return (BYTE *)PTR_SEG_OFF_TO_LIN( seg, (base + (index << ss)) );
 204 #undef GET_VAL
 205 }
 206
 207
 208 /***********************************************************************
 209  *           INSTR_EmulateLDS
 210  *
 211  * Emulate the LDS (and LES,LFS,etc.) instruction.
 212  */
 213 static BOOL32 INSTR_EmulateLDS( SIGCONTEXT *context, BYTE *instr, int long_op,
 214                                 int long_addr, int segprefix, int *len )
 215 {
 216     WORD seg;
 217     BYTE *regmodrm = instr + 1 + (*instr == 0x0f);
 218     BYTE *addr = INSTR_GetOperandAddr( context, regmodrm,
 219                                        long_addr, segprefix, len );
 220     if (!addr)
 221         return FALSE;  /* Unable to emulate it */
 222     seg = *(WORD *)(addr + (long_op ? 4 : 2));
 223
 224     if (!(seg = INSTR_ReplaceSelector( context, seg )))
 225         return FALSE;  /* Unable to emulate it */
 226
 227     /* Now store the offset in the correct register */
 228
 229     switch((*regmodrm >> 3) & 7)
 230     {
 231     case 0:
 232         if (long_op) EAX_sig(context) = *(DWORD *)addr;
 233         else AX_sig(context) = *(WORD *)addr;
 234         break;
 235     case 1:
 236         if (long_op) ECX_sig(context) = *(DWORD *)addr;
 237         else CX_sig(context) = *(WORD *)addr;
 238         break;
 239     case 2:
 240         if (long_op) EDX_sig(context) = *(DWORD *)addr;
 241         else DX_sig(context) = *(WORD *)addr;
 242         break;
 243     case 3:
 244         if (long_op) EBX_sig(context) = *(DWORD *)addr;
 245         else BX_sig(context) = *(WORD *)addr;
 246         break;
 247     case 4:
 248         if (long_op) ESP_sig(context) = *(DWORD *)addr;
 249         else SP_sig(context) = *(WORD *)addr;
 250         break;
 251     case 5:
 252         if (long_op) EBP_sig(context) = *(DWORD *)addr;
 253         else BP_sig(context) = *(WORD *)addr;
 254         break;
 255     case 6:
 256         if (long_op) ESI_sig(context) = *(DWORD *)addr;
 257         else SI_sig(context) = *(WORD *)addr;
 258         break;
 259     case 7:
 260         if (long_op) EDI_sig(context) = *(DWORD *)addr;
 261         else DI_sig(context) = *(WORD *)addr;
 262         break;
 263     }
 264
 265     /* Store the correct segment in the segment register */
 266
 267     switch(*instr)
 268     {
 269     case 0xc4: ES_sig(context) = seg; break;  /* les */
 270     case 0xc5: DS_sig(context) = seg; break;  /* lds */
 271     case 0x0f: switch(instr[1])
 272                {
 273                case 0xb2: SS_sig(context) = seg; break;  /* lss */
 274 #ifdef FS_sig
 275                case 0xb4: FS_sig(context) = seg; break;  /* lfs */
 276 #endif
 277 #ifdef GS_sig
 278                case 0xb5: GS_sig(context) = seg; break;  /* lgs */
 279 #endif
 280                }
 281                break;
 282     }
 283
 284     /* Add the opcode size to the total length */
 285
 286     *len += 1 + (*instr == 0x0f);
 287     return TRUE;
 288 }
 289
 290
 291 /***********************************************************************
 292  *           INSTR_EmulateInstruction
 293  *
 294  * Emulate a priviledged instruction. Returns TRUE if emulation successful.
 295  */
 296 BOOL32 INSTR_EmulateInstruction( SIGCONTEXT *context )
 297 {
 298     int prefix, segprefix, prefixlen, len, repX, long_op, long_addr;
 299     SEGPTR gpHandler;
 300     BYTE *instr;
 301
 302     /* Check for page-fault */
 303
 304 #if defined(TRAP_sig) && defined(CR2_sig)
 305     if (TRAP_sig(context) == 0x0e
 306         && VIRTUAL_HandleFault( (LPVOID)CR2_sig(context) )) return TRUE;
 307 #endif
 308
 309     long_op = long_addr = IS_SELECTOR_32BIT(CS_sig(context));
 310     instr = (BYTE *)MAKE_PTR(CS_sig(context),EIP_sig(context));
 311     if (!instr) return FALSE;
 312
 313     /* First handle any possible prefix */
 314
 315     segprefix = -1;  /* no prefix */
 316     prefix = 1;
 317     repX = 0;
 318     prefixlen = 0;
 319     while(prefix)
 320     {
 321         switch(*instr)
 322         {
 323         case 0x2e:
 324             segprefix = CS_sig(context);
 325             break;
 326         case 0x36:
 327             segprefix = SS_sig(context);
 328             break;
 329         case 0x3e:
 330             segprefix = DS_sig(context);
 331             break;
 332         case 0x26:
 333             segprefix = ES_sig(context);
 334             break;
 335 #ifdef FS_sig
 336         case 0x64:
 337             segprefix = FS_sig(context);
 338             break;
 339 #endif
 340 #ifdef GS_sig
 341         case 0x65:
 342             segprefix = GS_sig(context);
 343             break;
 344 #endif
 345         case 0x66:
 346             long_op = !long_op;  /* opcode size prefix */
 347             break;
 348         case 0x67:
 349             long_addr = !long_addr;  /* addr size prefix */
 350             break;
 351         case 0xf0:  /* lock */
 352             break;
 353         case 0xf2:  /* repne */
 354             repX = 1;
 355             break;
 356         case 0xf3:  /* repe */
 357             repX = 2;
 358             break;
 359         default:
 360             prefix = 0;  /* no more prefixes */
 361             break;
 362         }
 363         if (prefix)
 364         {
 365             instr++;
 366             prefixlen++;
 367         }
 368     }
 369
 370     /* Now look at the actual instruction */
 371
 372     switch(*instr)
 373     {
 374         case 0x07: /* pop es */
 375         case 0x17: /* pop ss */
 376         case 0x1f: /* pop ds */
 377             {
 378                 WORD seg = *(WORD *)STACK_PTR( context );
 379                 if ((seg = INSTR_ReplaceSelector( context, seg )) != 0)
 380                 {
 381                     switch(*instr)
 382                     {
 383                     case 0x07: ES_sig(context) = seg; break;
 384                     case 0x17: SS_sig(context) = seg; break;
 385                     case 0x1f: DS_sig(context) = seg; break;
 386                     }
 387                     STACK_sig(context) += long_op ? 4 : 2;
 388                     EIP_sig(context) += prefixlen + 1;
 389                     return TRUE;
 390                 }
 391             }
 392             break;  /* Unable to emulate it */
 393
 394         case 0x0f: /* extended instruction */
 395             switch(instr[1])
 396             {
 397 #ifdef FS_sig
 398             case 0xa1: /* pop fs */
 399                 {
 400                     WORD seg = *(WORD *)STACK_PTR( context );
 401                     if ((seg = INSTR_ReplaceSelector( context, seg )) != 0)
 402                     {
 403                         FS_sig(context) = seg;
 404                         STACK_sig(context) += long_op ? 4 : 2;
 405                         EIP_sig(context) += prefixlen + 2;
 406                         return TRUE;
 407                     }
 408                 }
 409                 break;
 410 #endif  /* FS_sig */
 411
 412 #ifdef GS_sig
 413             case 0xa9: /* pop gs */
 414                 {
 415                     WORD seg = *(WORD *)STACK_PTR( context );
 416                     if ((seg = INSTR_ReplaceSelector( context, seg )) != 0)
 417                     {
 418                         GS_sig(context) = seg;
 419                         STACK_sig(context) += long_op ? 4 : 2;
 420                         EIP_sig(context) += prefixlen + 2;
 421                         return TRUE;
 422                     }
 423                 }
 424                 break;
 425 #endif  /* GS_sig */
 426
 427             case 0xb2: /* lss addr,reg */
 428 #ifdef FS_sig
 429             case 0xb4: /* lfs addr,reg */
 430 #endif
 431 #ifdef GS_sig
 432             case 0xb5: /* lgs addr,reg */
 433 #endif
 434                 if (INSTR_EmulateLDS( context, instr, long_op,
 435                                       long_addr, segprefix, &len ))
 436                 {
 437                     EIP_sig(context) += prefixlen + len;
 438                     return TRUE;
 439                 }
 440                 break;
 441             }
 442             break;  /* Unable to emulate it */
 443
 444         case 0x6c: /* insb     */
 445         case 0x6d: /* insw/d   */
 446         case 0x6e: /* outsb    */
 447         case 0x6f: /* outsw/d  */
 448             {
 449               int typ = *instr;  /* Just in case it's overwritten.  */
 450               int outp = (typ >= 0x6e);
 451               unsigned long count = repX ?
 452                           (long_addr ? ECX_sig(context) : CX_sig(context)) : 1;
 453               int opsize = (typ & 1) ? (long_op ? 4 : 2) : 1;
 454               int step = (EFL_sig(context) & 0x400) ? -opsize : +opsize;
 455               int seg = outp ? DS_sig(context) : ES_sig(context);  /* FIXME: is this right? */
 456
 457               if (outp)
 458                 /* FIXME: Check segment readable.  */
 459                 (void)0;
 460               else
 461                 /* FIXME: Check segment writeable.  */
 462                 (void)0;
 463
 464               if (repX)
 465                 if (long_addr)
 466                   ECX_sig(context) = 0;
 467                 else
 468                   CX_sig(context) = 0;
 469
 470               while (count-- > 0)
 471                 {
 472                   void *data;
 473                   if (outp)
 474                   {
 475                       data = MAKE_PTR(seg,
 476                                long_addr ? ESI_sig(context) : SI_sig(context));
 477                       if (long_addr) ESI_sig(context) += step;
 478                       else SI_sig(context) += step;
 479                   }
 480                   else
 481                   {
 482                       data = MAKE_PTR(seg,
 483                                long_addr ? EDI_sig(context) : DI_sig(context));
 484                       if (long_addr) EDI_sig(context) += step;
 485                       else DI_sig(context) += step;
 486                   }
 487
 488                   switch (typ)
 489                   {
 490                     case 0x6c:
 491                       *((BYTE *)data) = IO_inport( DX_sig(context), 1);
 492                       break;
 493                     case 0x6d:
 494                       if (long_op)
 495                         *((DWORD *)data) = IO_inport( DX_sig(context), 4);
 496                       else
 497                         *((WORD *)data) = IO_inport( DX_sig(context), 2);
 498                       break;
 499                     case 0x6e:
 500                         IO_outport( DX_sig(context), 1, *((BYTE *)data));
 501                         break;
 502                     case 0x6f:
 503                         if (long_op)
 504                             IO_outport( DX_sig(context), 4, *((DWORD *)data));
 505                         else
 506                             IO_outport( DX_sig(context), 2, *((WORD *)data));
 507                         break;
 508                     }
 509                 }
 510               EIP_sig(context) += prefixlen + 1;
 511             }
 512             return TRUE;
 513
 514         case 0x8e: /* mov XX,segment_reg */
 515             {
 516                 WORD seg;
 517                 BYTE *addr = INSTR_GetOperandAddr(context, instr + 1,
 518                                                   long_addr, segprefix, &len );
 519                 if (!addr)
 520                     break;  /* Unable to emulate it */
 521                 seg = *(WORD *)addr;
 522                 if (!(seg = INSTR_ReplaceSelector( context, seg )))
 523                     break;  /* Unable to emulate it */
 524
 525                 switch((instr[1] >> 3) & 7)
 526                 {
 527                 case 0:
 528                     ES_sig(context) = seg;
 529                     EIP_sig(context) += prefixlen + len + 1;
 530                     return TRUE;
 531                 case 1:  /* cs */
 532                     break;
 533                 case 2:
 534                     SS_sig(context) = seg;
 535                     EIP_sig(context) += prefixlen + len + 1;
 536                     return TRUE;
 537                 case 3:
 538                     DS_sig(context) = seg;
 539                     EIP_sig(context) += prefixlen + len + 1;
 540                     return TRUE;
 541                 case 4:
 542 #ifdef FS_sig
 543                     FS_sig(context) = seg;
 544                     EIP_sig(context) += prefixlen + len + 1;
 545                     return TRUE;
 546 #endif
 547                 case 5:
 548 #ifdef GS_sig
 549                     GS_sig(context) = seg;
 550                     EIP_sig(context) += prefixlen + len + 1;
 551                     return TRUE;
 552 #endif
 553                 case 6:  /* unused */
 554                 case 7:  /* unused */
 555                     break;
 556                 }
 557             }
 558             break;  /* Unable to emulate it */
 559
 560         case 0xc4: /* les addr,reg */
 561         case 0xc5: /* lds addr,reg */
 562             if (INSTR_EmulateLDS( context, instr, long_op,
 563                                   long_addr, segprefix, &len ))
 564             {
 565                 EIP_sig(context) += prefixlen + len;
 566                 return TRUE;
 567             }
 568             break;  /* Unable to emulate it */
 569
 570         case 0xcd: /* int <XX> */
 571             if (long_op)
 572             {
 573                 ERR(int, "int xx from 32-bit code is not supported.\n");
 574                 break;  /* Unable to emulate it */
 575             }
 576             else
 577             {
 578                 FARPROC16 addr = INT_GetPMHandler( instr[1] );
 579                 WORD *stack = (WORD *)STACK_PTR( context );
 580                 /* Push the flags and return address on the stack */
 581                 *(--stack) = FL_sig(context);
 582                 *(--stack) = CS_sig(context);
 583                 *(--stack) = IP_sig(context) + prefixlen + 2;
 584                 STACK_sig(context) -= 3 * sizeof(WORD);
 585                 /* Jump to the interrupt handler */
 586                 CS_sig(context)  = HIWORD(addr);
 587                 EIP_sig(context) = LOWORD(addr);
 588             }
 589             return TRUE;
 590
 591         case 0xcf: /* iret */
 592             if (long_op)
 593             {
 594                 DWORD *stack = (DWORD *)STACK_PTR( context );
 595                 EIP_sig(context) = *stack++;
 596                 CS_sig(context)  = *stack++;
 597                 EFL_sig(context) = *stack;
 598                 STACK_sig(context) += 3*sizeof(DWORD);  /* Pop the return address and flags */
 599             }
 600             else
 601             {
 602                 WORD *stack = (WORD *)STACK_PTR( context );
 603                 EIP_sig(context) = *stack++;
 604                 CS_sig(context)  = *stack++;
 605                 FL_sig(context)  = *stack;
 606                 STACK_sig(context) += 3*sizeof(WORD);  /* Pop the return address and flags */
 607             }
 608             return TRUE;
 609
 610         case 0xe4: /* inb al,XX */
 611             AL_sig(context) = IO_inport( instr[1], 1 );
 612             EIP_sig(context) += prefixlen + 2;
 613             return TRUE;
 614
 615         case 0xe5: /* in (e)ax,XX */
 616             if (long_op) EAX_sig(context) = IO_inport( instr[1], 4 );
 617             else AX_sig(context) = IO_inport( instr[1], 2 );
 618             EIP_sig(context) += prefixlen + 2;
 619             return TRUE;
 620
 621         case 0xe6: /* outb XX,al */
 622             IO_outport( instr[1], 1, AL_sig(context) );
 623             EIP_sig(context) += prefixlen + 2;
 624             return TRUE;
 625
 626         case 0xe7: /* out XX,(e)ax */
 627             if (long_op) IO_outport( instr[1], 4, EAX_sig(context) );
 628             else IO_outport( instr[1], 2, AX_sig(context) );
 629             EIP_sig(context) += prefixlen + 2;
 630             return TRUE;
 631
 632         case 0xec: /* inb al,dx */
 633             AL_sig(context) = IO_inport( DX_sig(context), 1 );
 634             EIP_sig(context) += prefixlen + 1;
 635             return TRUE;
 636
 637         case 0xed: /* in (e)ax,dx */
 638             if (long_op) EAX_sig(context) = IO_inport( DX_sig(context), 4 );
 639             else AX_sig(context) = IO_inport( DX_sig(context), 2 );
 640             EIP_sig(context) += prefixlen + 1;
 641             return TRUE;
 642
 643         case 0xee: /* outb dx,al */
 644             IO_outport( DX_sig(context), 1, AL_sig(context) );
 645             EIP_sig(context) += prefixlen + 1;
 646             return TRUE;
 647
 648         case 0xef: /* out dx,(e)ax */
 649             if (long_op) IO_outport( DX_sig(context), 4, EAX_sig(context) );
 650             else IO_outport( DX_sig(context), 2, AX_sig(context) );
 651             EIP_sig(context) += prefixlen + 1;
 652             return TRUE;
 653
 654         case 0xfa: /* cli, ignored */
 655             EIP_sig(context) += prefixlen + 1;
 656             return TRUE;
 657
 658         case 0xfb: /* sti, ignored */
 659             EIP_sig(context) += prefixlen + 1;
 660             return TRUE;
 661     }
 662
 663
 664     /* Check for Win16 __GP handler */
 665     gpHandler = HasGPHandler( PTR_SEG_OFF_TO_SEGPTR( CS_sig(context),
 666                                                      EIP_sig(context) ) );
 667     if (gpHandler)
 668     {
 669         WORD *stack = (WORD *)STACK_PTR( context );
 670         *--stack = CS_sig(context);
 671         *--stack = EIP_sig(context);
 672         STACK_sig(context) -= 2*sizeof(WORD);
 673
 674         CS_sig(context) = SELECTOROF( gpHandler );
 675         EIP_sig(context) = OFFSETOF( gpHandler );
 676         return TRUE;
 677     }
 678
 679     MSG("Unexpected Windows program segfault"
 680                     " - opcode = %x\n", *instr);
 681     return FALSE;  /* Unable to emulate it */
 682 }