dlls/krnl386.exe16/dosmem.c

   1 /*
   2  * DOS memory emulation
   3  *
   4  * Copyright 1995 Alexandre Julliard
   5  * Copyright 1996 Marcus Meissner
   6  *
   7  * This library is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.1 of the License, or (at your option) any later version.
  11  *
  12  * This library is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with this library; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
  20  */
  21
  22 #include "config.h"
  23 #include "wine/port.h"
  24
  25 #include <signal.h>
  26 #include <stdarg.h>
  27 #include <stdlib.h>
  28 #include <string.h>
  29 #include <sys/types.h>
  30 #ifdef HAVE_SYS_MMAN_H
  31 # include <sys/mman.h>
  32 #endif
  33
  34 #include "windef.h"
  35 #include "winbase.h"
  36 #include "excpt.h"
  37 #include "winternl.h"
  38 #include "wine/winbase16.h"
  39
  40 #include "kernel16_private.h"
  41 #include "dosexe.h"
  42 #include "wine/debug.h"
  43
  44 WINE_DEFAULT_DEBUG_CHANNEL(dosmem);
  45 WINE_DECLARE_DEBUG_CHANNEL(selector);
  46
  47 WORD DOSMEM_0000H;        /* segment at 0:0 */
  48 WORD DOSMEM_BiosDataSeg;  /* BIOS data segment at 0x40:0 */
  49 WORD DOSMEM_BiosSysSeg;   /* BIOS ROM segment at 0xf000:0 */
  50
  51 /* DOS memory highest address (including HMA) */
  52 #define DOSMEM_SIZE             0x110000
  53 #define DOSMEM_64KB             0x10000
  54
  55 /*
  56  * Memory Control Block (MCB) definition
  57  * FIXME: implement Allocation Strategy
  58  */
  59
  60 #define MCB_DUMP(mc) \
  61     TRACE ("MCB_DUMP base=%p type=%02xh psp=%04xh size=%04xh\n", mc, mc->type, mc->psp , mc->size )
  62
  63 #define MCB_NEXT(mc) \
  64     (MCB*) ((mc->type==MCB_TYPE_LAST) ? NULL : (char*)(mc) + ((mc->size + 1) << 4) )
  65
  66 /* FIXME: should we check more? */
  67 #define MCB_VALID(mc) \
  68     ((mc->type==MCB_TYPE_NORMAL) || (mc->type==MCB_TYPE_LAST))
  69
  70
  71 #define MCB_TYPE_NORMAL    0x4d
  72 #define MCB_TYPE_LAST      0x5a
  73
  74 #define MCB_PSP_DOS        0x0060
  75 #define MCB_PSP_FREE       0
  76
  77 #include "pshpack1.h"
  78 typedef struct {
  79     BYTE type;
  80     WORD psp;     /* segment of owner psp */
  81     WORD size;    /* in paragraphs */
  82     BYTE pad[3];
  83     BYTE name[8];
  84 } MCB;
  85 #include "poppack.h"
  86
  87 /*
  88 #define __DOSMEM_DEBUG__
  89  */
  90
  91 #define VM_STUB(x) (0x90CF00CD|(x<<8)) /* INT x; IRET; NOP */
  92 #define VM_STUB_SEGMENT 0xf000         /* BIOS segment */
  93
  94 /* FIXME: this should be moved to the LOL */
  95 static MCB* DOSMEM_root_block;
  96
  97 /* when looking at DOS and real mode memory, we activate in three different
  98  * modes, depending the situation.
  99  * 1/ By default (protected mode), the first MB of memory (actually 0x110000,
 100  *    when you also look at the HMA part) is always reserved, whatever you do.
 101  *    We allocated some PM selectors to this memory, even if this area is not
 102  *    committed at startup
 103  * 2/ if a program tries to use the memory through the selectors, we actually
 104  *    commit this memory, made of: BIOS segment, but also some system
 105  *    information, usually low in memory that we map for the circumstance also
 106  *    in the BIOS segment, so that we keep the low memory protected (for NULL
 107  *    pointer deref catching for example). In this case, we're still in PM
 108  *    mode, accessing part of the "physical" real mode memory. In fact, we don't
 109  *    map all the first meg, we keep 64k uncommitted to still catch NULL
 110  *    pointers dereference
 111  * 3/ if the process enters the real mode, then we (also) commit the full first
 112  *    MB of memory (and also initialize the DOS structures in it).
 113  */
 114
 115 /* DOS memory base (linear in process address space) */
 116 static char *DOSMEM_dosmem;
 117 static char *DOSMEM_sysmem;
 118 /* number of bytes protected from _dosmem. 0 when DOS memory is initialized,
 119  * 64k otherwise to trap NULL pointers deref */
 120 static DWORD DOSMEM_protect;
 121
 122 static LONG WINAPI dosmem_handler(EXCEPTION_POINTERS* except);
 123
 124 /***********************************************************************
 125  *           DOSMEM_FillIsrTable
 126  *
 127  * Fill the interrupt table with fake BIOS calls to BIOSSEG (0xf000).
 128  *
 129  * NOTES:
 130  * Linux normally only traps INTs performed from or destined to BIOSSEG
 131  * for us to handle, if the int_revectored table is empty. Filling the
 132  * interrupt table with calls to INT stubs in BIOSSEG allows DOS programs
 133  * to hook interrupts, as well as use their familiar retf tricks to call
 134  * them, AND let Wine handle any unhooked interrupts transparently.
 135  */
 136 static void DOSMEM_FillIsrTable(void)
 137 {
 138     SEGPTR *isr = (SEGPTR*)DOSMEM_sysmem;
 139     int x;
 140
 141     for (x=0; x<256; x++) isr[x]=MAKESEGPTR(VM_STUB_SEGMENT,x*4);
 142 }
 143
 144 static void DOSMEM_MakeIsrStubs(void)
 145 {
 146     DWORD *stub = (DWORD*)(DOSMEM_dosmem + (VM_STUB_SEGMENT << 4));
 147     int x;
 148
 149     for (x=0; x<256; x++) stub[x]=VM_STUB(x);
 150 }
 151
 152 BIOSDATA* DOSVM_BiosData(void)
 153 {
 154     return (BIOSDATA *)(DOSMEM_sysmem + 0x400);
 155 }
 156
 157 /**********************************************************************
 158  *          DOSMEM_GetTicksSinceMidnight
 159  *
 160  * Return number of clock ticks since midnight.
 161  */
 162 static DWORD DOSMEM_GetTicksSinceMidnight(void)
 163 {
 164     SYSTEMTIME time;
 165
 166     /* This should give us the (approximately) correct
 167      * 18.206 clock ticks per second since midnight.
 168      */
 169
 170     GetLocalTime( &time );
 171
 172     return (((time.wHour * 3600 + time.wMinute * 60 +
 173               time.wSecond) * 18206) / 1000) +
 174              (time.wMilliseconds * 1000 / 54927);
 175 }
 176
 177 /***********************************************************************
 178  *           DOSMEM_FillBiosSegments
 179  *
 180  * Fill the BIOS data segment with dummy values.
 181  */
 182 static void DOSMEM_FillBiosSegments(void)
 183 {
 184     BYTE *pBiosSys = (BYTE*)DOSMEM_dosmem + 0xf0000;
 185     BYTE *pBiosROMTable = pBiosSys+0xe6f5;
 186     BIOSDATA *pBiosData = DOSVM_BiosData();
 187     static const char bios_date[] = "13/01/99";
 188
 189       /* Clear all unused values */
 190     memset( pBiosData, 0, sizeof(*pBiosData) );
 191
 192     /* FIXME: should check the number of configured drives and ports */
 193     pBiosData->Com1Addr             = 0x3f8;
 194     pBiosData->Com2Addr             = 0x2f8;
 195     pBiosData->Lpt1Addr             = 0x378;
 196     pBiosData->Lpt2Addr             = 0x278;
 197     pBiosData->InstalledHardware    = 0x5463;
 198     pBiosData->MemSize              = 640;
 199     pBiosData->NextKbdCharPtr       = 0x1e;
 200     pBiosData->FirstKbdCharPtr      = 0x1e;
 201     pBiosData->VideoMode            = 3;
 202     pBiosData->VideoColumns         = 80;
 203     pBiosData->VideoPageSize        = 80 * 25 * 2;
 204     pBiosData->VideoPageStartAddr   = 0xb800;
 205     pBiosData->VideoCtrlAddr        = 0x3d4;
 206     pBiosData->Ticks                = DOSMEM_GetTicksSinceMidnight();
 207     pBiosData->NbHardDisks          = 2;
 208     pBiosData->KbdBufferStart       = 0x1e;
 209     pBiosData->KbdBufferEnd         = 0x3e;
 210     pBiosData->RowsOnScreenMinus1   = 24;
 211     pBiosData->BytesPerChar         = 0x10;
 212     pBiosData->ModeOptions          = 0x64;
 213     pBiosData->FeatureBitsSwitches  = 0xf9;
 214     pBiosData->VGASettings          = 0x51;
 215     pBiosData->DisplayCombination   = 0x08;
 216     pBiosData->DiskDataRate         = 0;
 217
 218     /* fill ROM configuration table (values from Award) */
 219     *(pBiosROMTable+0x0)        = 0x08; /* number of bytes following LO */
 220     *(pBiosROMTable+0x1)        = 0x00; /* number of bytes following HI */
 221     *(pBiosROMTable+0x2)        = 0xfc; /* model */
 222     *(pBiosROMTable+0x3)        = 0x01; /* submodel */
 223     *(pBiosROMTable+0x4)        = 0x00; /* BIOS revision */
 224     *(pBiosROMTable+0x5)        = 0x74; /* feature byte 1 */
 225     *(pBiosROMTable+0x6)        = 0x00; /* feature byte 2 */
 226     *(pBiosROMTable+0x7)        = 0x00; /* feature byte 3 */
 227     *(pBiosROMTable+0x8)        = 0x00; /* feature byte 4 */
 228     *(pBiosROMTable+0x9)        = 0x00; /* feature byte 5 */
 229
 230     /* BIOS date string */
 231     memcpy(pBiosSys+0xfff5, bios_date, sizeof bios_date);
 232
 233     /* BIOS ID */
 234     *(pBiosSys+0xfffe) = 0xfc;
 235
 236     /* Reboot vector (f000:fff0 or ffff:0000) */
 237     *(DWORD*)(pBiosSys + 0xfff0) = VM_STUB(0x19);
 238 }
 239
 240 /***********************************************************************
 241  *           BiosTick
 242  *
 243  * Increment the BIOS tick counter. Called by timer signal handler.
 244  */
 245 static void CALLBACK BiosTick( LPVOID arg, DWORD low, DWORD high )
 246 {
 247     BIOSDATA *pBiosData = arg;
 248     pBiosData->Ticks++;
 249 }
 250
 251 /***********************************************************************
 252  *           timer_thread
 253  */
 254 static DWORD CALLBACK timer_thread( void *arg )
 255 {
 256     LARGE_INTEGER when;
 257     HANDLE timer;
 258
 259     if (!(timer = CreateWaitableTimerA( NULL, FALSE, NULL ))) return 0;
 260
 261     when.u.LowPart = when.u.HighPart = 0;
 262     SetWaitableTimer( timer, &when, 55 /* actually 54.925 */, BiosTick, arg, FALSE );
 263     for (;;) SleepEx( INFINITE, TRUE );
 264 }
 265
 266 /***********************************************************************
 267  *           DOSMEM_Collapse
 268  *
 269  * Helper function for internal use only.
 270  * Attach all following free blocks to this one, even if this one is not free.
 271  */
 272 static void DOSMEM_Collapse( MCB* mcb )
 273 {
 274     MCB* next = MCB_NEXT( mcb );
 275
 276     while (next && next->psp == MCB_PSP_FREE)
 277     {
 278         mcb->size = mcb->size + next->size + 1;
 279         mcb->type = next->type;    /* make sure keeping MCB_TYPE_LAST */
 280         next = MCB_NEXT( next );
 281     }
 282 }
 283
 284 /******************************************************************
 285  *              DOSMEM_InitDosMemory
 286  */
 287 BOOL DOSMEM_InitDosMemory(void)
 288 {
 289     static int done;
 290     static HANDLE hRunOnce;
 291
 292     if (done) return TRUE;
 293
 294     /* FIXME: this isn't 100% thread safe, as we won't catch accesses while initializing */
 295     if (hRunOnce == 0)
 296     {
 297         HANDLE hEvent = CreateEventW( NULL, TRUE, FALSE, NULL );
 298         if (InterlockedCompareExchangePointer( &hRunOnce, hEvent, 0 ) == 0)
 299         {
 300             BOOL ret;
 301             DWORD reserve;
 302
 303             /* ok, we're the winning thread */
 304             if (!(ret = VirtualProtect( DOSMEM_dosmem + DOSMEM_protect,
 305                                         DOSMEM_SIZE - DOSMEM_protect,
 306                                         PAGE_READWRITE, NULL )))
 307                 ERR("Cannot load access low 1Mb, DOS subsystem unavailable\n");
 308             RtlRemoveVectoredExceptionHandler( dosmem_handler );
 309
 310             /*
 311              * Reserve either:
 312              * - lowest 64k for NULL pointer catching (Win16)
 313              * - lowest 1k for interrupt handlers and
 314              *   another 0.5k for BIOS, DOS and intra-application
 315              *   areas (DOS)
 316              */
 317             if (DOSMEM_dosmem != DOSMEM_sysmem)
 318                 reserve = 0x10000; /* 64k */
 319             else
 320                 reserve = 0x600; /* 1.5k */
 321
 322             /*
 323              * Set DOS memory base and initialize conventional memory.
 324              */
 325             DOSMEM_FillBiosSegments();
 326             DOSMEM_FillIsrTable();
 327
 328             /* align root block to paragraph */
 329             DOSMEM_root_block = (MCB*)(DOSMEM_dosmem + reserve);
 330             DOSMEM_root_block->type = MCB_TYPE_LAST;
 331             DOSMEM_root_block->psp = MCB_PSP_FREE;
 332             DOSMEM_root_block->size = (DOSMEM_dosmem + 0x9fffc  - ((char*)DOSMEM_root_block)) >> 4;
 333
 334             TRACE("DOS conventional memory initialized, %d bytes free.\n",
 335                   DOSMEM_Available());
 336
 337             DOSVM_InitSegments();
 338             CloseHandle( CreateThread( NULL, 0, timer_thread, DOSVM_BiosData(), 0, NULL ));
 339
 340             SetEvent( hRunOnce );
 341             done = 1;
 342             return ret;
 343         }
 344         /* someone beat us here... */
 345         CloseHandle( hEvent );
 346     }
 347
 348     /* and wait for the winner to have finished */
 349     WaitForSingleObject( hRunOnce, INFINITE );
 350     return TRUE;
 351 }
 352
 353 /******************************************************************
 354  *              dosmem_handler
 355  *
 356  * Handler to catch access to our 1MB address space reserved for real memory
 357  */
 358 static LONG WINAPI dosmem_handler(EXCEPTION_POINTERS* except)
 359 {
 360     if (except->ExceptionRecord->ExceptionCode == EXCEPTION_ACCESS_VIOLATION)
 361     {
 362         char *addr = (char *)except->ExceptionRecord->ExceptionInformation[1];
 363         if (addr >= DOSMEM_dosmem + DOSMEM_protect && addr < DOSMEM_dosmem + DOSMEM_SIZE)
 364         {
 365             if (DOSMEM_InitDosMemory()) return EXCEPTION_CONTINUE_EXECUTION;
 366         }
 367     }
 368     return EXCEPTION_CONTINUE_SEARCH;
 369 }
 370
 371 /***********************************************************************
 372  *           DOSMEM_Init
 373  *
 374  * Create the dos memory segments, and store them into the KERNEL
 375  * exported values.
 376  */
 377 BOOL DOSMEM_Init(void)
 378 {
 379     void *addr = (void *)1;
 380     SIZE_T size = DOSMEM_SIZE - 1;
 381
 382     if (NtAllocateVirtualMemory( GetCurrentProcess(), &addr, 0, &size,
 383                                  MEM_RESERVE | MEM_COMMIT, PAGE_NOACCESS ))
 384     {
 385         ERR( "Cannot allocate DOS memory\n" );
 386         ExitProcess(1);
 387     }
 388
 389     if (addr <= (void *)DOSMEM_64KB)
 390     {
 391         DOSMEM_dosmem = 0;
 392         DOSMEM_protect = DOSMEM_64KB;
 393         DOSMEM_sysmem = (char *)0xf0000;  /* store sysmem in high addresses for now */
 394     }
 395     else
 396     {
 397         WARN( "First megabyte not available for DOS address space.\n" );
 398         DOSMEM_dosmem = addr;
 399         DOSMEM_protect = 0;
 400         DOSMEM_sysmem = DOSMEM_dosmem;
 401     }
 402
 403     RtlAddVectoredExceptionHandler(FALSE, dosmem_handler);
 404     DOSMEM_0000H = GLOBAL_CreateBlock( GMEM_FIXED, DOSMEM_sysmem,
 405                                        DOSMEM_64KB, 0, WINE_LDT_FLAGS_DATA );
 406     DOSMEM_BiosDataSeg = GLOBAL_CreateBlock( GMEM_FIXED, DOSMEM_sysmem + 0x400,
 407                                              0x100, 0, WINE_LDT_FLAGS_DATA );
 408     DOSMEM_BiosSysSeg = GLOBAL_CreateBlock( GMEM_FIXED, DOSMEM_dosmem + 0xf0000,
 409                                             DOSMEM_64KB, 0, WINE_LDT_FLAGS_DATA );
 410
 411     return TRUE;
 412 }
 413
 414 /***********************************************************************
 415  *           DOSMEM_MapLinearToDos
 416  *
 417  * Linear address to the DOS address space.
 418  */
 419 UINT DOSMEM_MapLinearToDos(LPVOID ptr)
 420 {
 421     if (((char*)ptr >= DOSMEM_dosmem) &&
 422         ((char*)ptr < DOSMEM_dosmem + DOSMEM_SIZE))
 423           return (char *)ptr - DOSMEM_dosmem;
 424     return (UINT)ptr;
 425 }
 426
 427
 428 /***********************************************************************
 429  *           DOSMEM_MapDosToLinear
 430  *
 431  * DOS linear address to the linear address space.
 432  */
 433 LPVOID DOSMEM_MapDosToLinear(UINT ptr)
 434 {
 435     if (ptr < DOSMEM_SIZE) return DOSMEM_dosmem + ptr;
 436     return (LPVOID)ptr;
 437 }
 438
 439
 440 /***********************************************************************
 441  *           DOSMEM_MapRealToLinear
 442  *
 443  * Real mode DOS address into a linear pointer
 444  */
 445 LPVOID DOSMEM_MapRealToLinear(DWORD x)
 446 {
 447    LPVOID       lin;
 448
 449    lin = DOSMEM_dosmem + HIWORD(x) * 16 + LOWORD(x);
 450    TRACE_(selector)("(0x%08x) returns %p.\n", x, lin );
 451    return lin;
 452 }
 453
 454 /***********************************************************************
 455  *           DOSMEM_AllocBlock
 456  *
 457  * Carve a chunk of the DOS memory block (without selector).
 458  */
 459 LPVOID DOSMEM_AllocBlock(UINT size, UINT16* pseg)
 460 {
 461     MCB *curr;
 462     MCB *next = NULL;
 463     WORD psp = DOSVM_psp;
 464
 465     DOSMEM_InitDosMemory();
 466
 467     curr = DOSMEM_root_block;
 468     if (!(psp = DOSVM_psp)) psp = MCB_PSP_DOS;
 469
 470     *pseg = 0;
 471
 472     TRACE( "(%04xh)\n", size );
 473
 474     /* round up to paragraph */
 475     size = (size + 15) >> 4;
 476
 477 #ifdef __DOSMEM_DEBUG__
 478     DOSMEM_Available();     /* checks the whole MCB list */
 479 #endif
 480
 481     /* loop over all MCB and search the next large enough MCB */
 482     while (curr)
 483     {
 484         if (!MCB_VALID (curr))
 485         {
 486             ERR( "MCB List Corrupt\n" );
 487             MCB_DUMP( curr );
 488             return NULL;
 489         }
 490         if (curr->psp == MCB_PSP_FREE)
 491         {
 492             DOSMEM_Collapse( curr );
 493             /* is it large enough (one paragraph for the MCB)? */
 494             if (curr->size >= size)
 495             {
 496                 if (curr->size > size)
 497                 {
 498                     /* split curr */
 499                     next = (MCB *) ((char*) curr + ((size+1) << 4));
 500                     next->psp = MCB_PSP_FREE;
 501                     next->size = curr->size - (size+1);
 502                     next->type = curr->type;
 503                     curr->type = MCB_TYPE_NORMAL;
 504                     curr->size = size;
 505                 }
 506                 /* curr is the found block */
 507                 curr->psp = psp;
 508                 if( pseg ) *pseg = (((char*)curr) + 16 - DOSMEM_dosmem) >> 4;
 509                 return (LPVOID) ((char*)curr + 16);
 510             }
 511         }
 512         curr = MCB_NEXT(curr);
 513     }
 514     return NULL;
 515 }
 516
 517 /***********************************************************************
 518  *           DOSMEM_FreeBlock
 519  */
 520 BOOL DOSMEM_FreeBlock(void* ptr)
 521 {
 522     MCB* mcb = (MCB*) ((char*)ptr - 16);
 523
 524     TRACE( "(%p)\n", ptr );
 525
 526 #ifdef __DOSMEM_DEBUG__
 527     DOSMEM_Available();
 528 #endif
 529
 530     if (!MCB_VALID (mcb))
 531     {
 532         ERR( "MCB invalid\n" );
 533         MCB_DUMP( mcb );
 534         return FALSE;
 535     }
 536
 537     mcb->psp = MCB_PSP_FREE;
 538     DOSMEM_Collapse( mcb );
 539     return TRUE;
 540 }
 541
 542 /***********************************************************************
 543  *           DOSMEM_ResizeBlock
 544  *
 545  * Resize DOS memory block in place. Returns block size or -1 on error.
 546  *
 547  * If exact is TRUE, returned value is either old or requested block
 548  * size. If exact is FALSE, block is expanded even if there is not
 549  * enough space for full requested block size.
 550  *
 551  * TODO: return also biggest block size
 552  */
 553 UINT DOSMEM_ResizeBlock(void *ptr, UINT size, BOOL exact)
 554 {
 555     MCB* mcb = (MCB*) ((char*)ptr - 16);
 556     MCB* next;
 557
 558     TRACE( "(%p,%04xh,%s)\n", ptr, size, exact ? "TRUE" : "FALSE" );
 559
 560     /* round up to paragraph */
 561     size = (size + 15) >> 4;
 562
 563 #ifdef __DOSMEM_DEBUG__
 564     DOSMEM_Available();
 565 #endif
 566
 567     if (!MCB_VALID (mcb))
 568     {
 569         ERR( "MCB invalid\n" );
 570         MCB_DUMP( mcb );
 571         return -1;
 572     }
 573
 574     /* resize needed? */
 575     if (mcb->size == size)
 576         return size << 4;
 577
 578     /* collapse free blocks */
 579     DOSMEM_Collapse( mcb );
 580
 581     /* shrink mcb ? */
 582     if (mcb->size > size)
 583     {
 584         next = (MCB *) ((char*)mcb + ((size+1) << 4));
 585         next->type = mcb->type;
 586         next->psp = MCB_PSP_FREE;
 587         next->size = mcb->size - (size+1);
 588         mcb->type = MCB_TYPE_NORMAL;
 589         mcb->size = size;
 590         return size << 4;
 591     }
 592
 593     if (!exact)
 594     {
 595         return mcb->size << 4;
 596     }
 597
 598     return -1;
 599 }
 600
 601 /***********************************************************************
 602  *           DOSMEM_Available
 603  */
 604 UINT DOSMEM_Available(void)
 605 {
 606     UINT  available = 0;
 607     UINT  total = 0;
 608     MCB *curr = DOSMEM_root_block;
 609     /* loop over all MCB and search the largest free MCB */
 610     while (curr)
 611     {
 612 #ifdef __DOSMEM_DEBUG__
 613         MCB_DUMP( curr );
 614 #endif
 615         if (!MCB_VALID (curr))
 616         {
 617             ERR( "MCB List Corrupt\n" );
 618             MCB_DUMP( curr );
 619             return 0;
 620         }
 621         if (curr->psp == MCB_PSP_FREE &&
 622             curr->size > available )
 623             available = curr->size;
 624
 625         total += curr->size + 1;
 626         curr = MCB_NEXT( curr );
 627     }
 628     TRACE( " %04xh of %04xh paragraphs available\n", available, total );
 629     return available << 4;
 630 }
 631
 632 /******************************************************************
 633  *              DOSMEM_MapDosLayout
 634  *
 635  * Initialize the first MB of memory to look like a real DOS setup
 636  */
 637 BOOL DOSMEM_MapDosLayout(void)
 638 {
 639     static int already_mapped;
 640
 641     if (!already_mapped)
 642     {
 643         if (DOSMEM_dosmem || !VirtualProtect( NULL, DOSMEM_SIZE, PAGE_EXECUTE_READWRITE, NULL ))
 644         {
 645             ERR( "Need full access to the first megabyte for DOS mode\n" );
 646             ExitProcess(1);
 647         }
 648         /* copy the BIOS and ISR area down */
 649         memcpy( DOSMEM_dosmem, DOSMEM_sysmem, 0x400 + 0x100 );
 650         DOSMEM_sysmem = DOSMEM_dosmem;
 651         SetSelectorBase( DOSMEM_0000H, 0 );
 652         SetSelectorBase( DOSMEM_BiosDataSeg, 0x400 );
 653         /* we may now need the actual interrupt stubs, and since we've just moved the
 654          * interrupt vector table away, we can fill the area with stubs instead... */
 655         DOSMEM_MakeIsrStubs();
 656         already_mapped = 1;
 657     }
 658     return TRUE;
 659 }