loader/dos/module.c

   1 /*
   2  * DOS (MZ) loader
   3  *
   4  * Copyright 1998 Ove Kåven
   5  *
   6  * This code hasn't been completely cleaned up yet.
   7  */
   8
   9 #include "config.h"
  10
  11 #include <stdio.h>
  12 #include <stdlib.h>
  13 #include <string.h>
  14 #include <errno.h>
  15 #include <fcntl.h>
  16 #include <signal.h>
  17 #include <unistd.h>
  18 #include <sys/types.h>
  19 #include <sys/stat.h>
  20 #include <sys/time.h>
  21 #include "windef.h"
  22 #include "wine/winbase16.h"
  23 #include "winerror.h"
  24 #include "module.h"
  25 #include "neexe.h"
  26 #include "task.h"
  27 #include "selectors.h"
  28 #include "file.h"
  29 #include "ldt.h"
  30 #include "process.h"
  31 #include "miscemu.h"
  32 #include "debugtools.h"
  33 #include "dosexe.h"
  34 #include "dosmod.h"
  35 #include "options.h"
  36 #include "server.h"
  37 #include "vga.h"
  38
  39 DEFAULT_DEBUG_CHANNEL(module)
  40
  41 #ifdef MZ_SUPPORTED
  42
  43 #ifdef HAVE_SYS_MMAN_H
  44 # include <sys/mman.h>
  45 #endif
  46
  47 /* define this to try mapping through /proc/pid/mem instead of a temp file,
  48    but Linus doesn't like mmapping /proc/pid/mem, so it doesn't work for me */
  49 #undef MZ_MAPSELF
  50
  51 #define BIOS_DATA_SEGMENT 0x40
  52 #define START_OFFSET 0
  53 #define PSP_SIZE 0x10
  54
  55 #define SEG16(ptr,seg) ((LPVOID)((BYTE*)ptr+((DWORD)(seg)<<4)))
  56 #define SEGPTR16(ptr,segptr) ((LPVOID)((BYTE*)ptr+((DWORD)SELECTOROF(segptr)<<4)+OFFSETOF(segptr)))
  57
  58 static LPDOSTASK dos_current;
  59
  60 static void MZ_Launch(void);
  61
  62 static void MZ_CreatePSP( LPVOID lpPSP, WORD env )
  63 {
  64  PDB16*psp=lpPSP;
  65
  66  psp->int20=0x20CD; /* int 20 */
  67  /* some programs use this to calculate how much memory they need */
  68  psp->nextParagraph=0x9FFF;
  69  psp->environment=env;
  70  /* FIXME: more PSP stuff */
  71 }
  72
  73 static void MZ_FillPSP( LPVOID lpPSP, LPCSTR cmdline )
  74 {
  75  PDB16*psp=lpPSP;
  76  const char*cmd=cmdline?strchr(cmdline,' '):NULL;
  77
  78  /* copy parameters */
  79  if (cmd) {
  80 #if 0
  81   /* command.com doesn't do this */
  82   while (*cmd == ' ') cmd++;
  83 #endif
  84   psp->cmdLine[0]=strlen(cmd);
  85   strcpy(psp->cmdLine+1,cmd);
  86   psp->cmdLine[psp->cmdLine[0]+1]='\r';
  87  } else psp->cmdLine[1]='\r';
  88  /* FIXME: more PSP stuff */
  89 }
  90
  91 /* default INT 08 handler: increases timer tick counter but not much more */
  92 static char int08[]={
  93  0xCD,0x1C,           /* int $0x1c */
  94  0x50,                /* pushw %ax */
  95  0x1E,                /* pushw %ds */
  96  0xB8,0x40,0x00,      /* movw $0x40,%ax */
  97  0x8E,0xD8,           /* movw %ax,%ds */
  98 #if 0
  99  0x83,0x06,0x6C,0x00,0x01, /* addw $1,(0x6c) */
 100  0x83,0x16,0x6E,0x00,0x00, /* adcw $0,(0x6e) */
 101 #else
 102  0x66,0xFF,0x06,0x6C,0x00, /* incl (0x6c) */
 103 #endif
 104  0xB0,0x20,           /* movb $0x20,%al */
 105  0xE6,0x20,           /* outb %al,$0x20 */
 106  0x1F,                /* popw %ax */
 107  0x58,                /* popw %ax */
 108  0xCF                 /* iret */
 109 };
 110
 111 static void MZ_InitHandlers( LPDOSTASK lpDosTask )
 112 {
 113  WORD seg;
 114  LPBYTE start=DOSMEM_GetBlock(sizeof(int08),&seg);
 115  memcpy(start,int08,sizeof(int08));
 116 /* INT 08: point it at our tick-incrementing handler */
 117  ((SEGPTR*)(lpDosTask->img))[0x08]=PTR_SEG_OFF_TO_SEGPTR(seg,0);
 118 /* INT 1C: just point it to IRET, we don't want to handle it ourselves */
 119  ((SEGPTR*)(lpDosTask->img))[0x1C]=PTR_SEG_OFF_TO_SEGPTR(seg,sizeof(int08)-1);
 120 }
 121
 122 static char enter_xms[]={
 123 /* XMS hookable entry point */
 124  0xEB,0x03,           /* jmp entry */
 125  0x90,0x90,0x90,      /* nop;nop;nop */
 126                       /* entry: */
 127 /* real entry point */
 128 /* for simplicity, we'll just use the same hook as DPMI below */
 129  0xCD,0x31,           /* int $0x31 */
 130  0xCB                 /* lret */
 131 };
 132
 133 static void MZ_InitXMS( LPDOSTASK lpDosTask )
 134 {
 135  LPBYTE start=DOSMEM_GetBlock(sizeof(enter_xms),&(lpDosTask->xms_seg));
 136  memcpy(start,enter_xms,sizeof(enter_xms));
 137 }
 138
 139 static char enter_pm[]={
 140  0x50,                /* pushw %ax */
 141  0x52,                /* pushw %dx */
 142  0x55,                /* pushw %bp */
 143  0x89,0xE5,           /* movw %sp,%bp */
 144 /* get return CS */
 145  0x8B,0x56,0x08,      /* movw 8(%bp),%dx */
 146 /* just call int 31 here to get into protected mode... */
 147 /* it'll check whether it was called from dpmi_seg... */
 148  0xCD,0x31,           /* int $0x31 */
 149 /* we are now in the context of a 16-bit relay call */
 150 /* need to fixup our stack;
 151  * 16-bit relay return address will be lost, but we won't worry quite yet */
 152  0x8E,0xD0,           /* movw %ax,%ss */
 153  0x66,0x0F,0xB7,0xE5, /* movzwl %bp,%esp */
 154 /* set return CS */
 155  0x89,0x56,0x08,      /* movw %dx,8(%bp) */
 156  0x5D,                /* popw %bp */
 157  0x5A,                /* popw %dx */
 158  0x58,                /* popw %ax */
 159  0xCB                 /* lret */
 160 };
 161
 162 static void MZ_InitDPMI( LPDOSTASK lpDosTask )
 163 {
 164  unsigned size=sizeof(enter_pm);
 165  LPBYTE start=DOSMEM_GetBlock(size,&(lpDosTask->dpmi_seg));
 166
 167  lpDosTask->dpmi_sel = SELECTOR_AllocBlock( start, size, SEGMENT_CODE, FALSE, FALSE );
 168
 169  memcpy(start,enter_pm,sizeof(enter_pm));
 170 }
 171
 172 static WORD MZ_InitEnvironment( LPDOSTASK lpDosTask, LPCSTR env, LPCSTR name )
 173 {
 174  unsigned sz=0;
 175  WORD seg;
 176  LPSTR envblk;
 177
 178  if (env) {
 179   /* get size of environment block */
 180   while (env[sz++]) sz+=strlen(env+sz)+1;
 181  } else sz++;
 182  /* allocate it */
 183  envblk=DOSMEM_GetBlock(sz+sizeof(WORD)+strlen(name)+1,&seg);
 184  /* fill it */
 185  if (env) {
 186   memcpy(envblk,env,sz);
 187  } else envblk[0]=0;
 188  /* DOS 3.x: the block contains 1 additional string */
 189  *(WORD*)(envblk+sz)=1;
 190  /* being the program name itself */
 191  strcpy(envblk+sz+sizeof(WORD),name);
 192  return seg;
 193 }
 194
 195 static BOOL MZ_InitMemory( LPDOSTASK lpDosTask )
 196 {
 197  if (lpDosTask->img) return TRUE; /* already allocated */
 198
 199  /* allocate 1MB+64K shared memory */
 200  lpDosTask->img_ofs=START_OFFSET;
 201 #ifdef MZ_MAPSELF
 202  lpDosTask->img=VirtualAlloc(NULL,0x110000,MEM_COMMIT,PAGE_READWRITE);
 203  /* make sure mmap accepts it */
 204  ((char*)lpDosTask->img)[0x10FFFF]=0;
 205 #else
 206  tmpnam(lpDosTask->mm_name);
 207 /* strcpy(lpDosTask->mm_name,"/tmp/mydosimage"); */
 208  lpDosTask->mm_fd=open(lpDosTask->mm_name,O_RDWR|O_CREAT /* |O_TRUNC */,S_IRUSR|S_IWUSR);
 209  if (lpDosTask->mm_fd<0) ERR("file %s could not be opened\n",lpDosTask->mm_name);
 210  /* expand file to 1MB+64K */
 211  ftruncate(lpDosTask->mm_fd,0x110000);
 212  /* map it in */
 213  lpDosTask->img=mmap(NULL,0x110000-START_OFFSET,PROT_READ|PROT_WRITE,MAP_SHARED,lpDosTask->mm_fd,0);
 214 #endif
 215  if (lpDosTask->img==(LPVOID)-1) {
 216   ERR("could not map shared memory, error=%s\n",strerror(errno));
 217   return FALSE;
 218  }
 219  TRACE("DOS VM86 image mapped at %08lx\n",(DWORD)lpDosTask->img);
 220
 221  /* initialize the memory */
 222  TRACE("Initializing DOS memory structures\n");
 223  DOSMEM_Init(TRUE);
 224  MZ_InitHandlers(lpDosTask);
 225  MZ_InitXMS(lpDosTask);
 226  MZ_InitDPMI(lpDosTask);
 227  return TRUE;
 228 }
 229
 230 BOOL MZ_LoadImage( HMODULE module, HANDLE hFile, LPCSTR filename )
 231 {
 232   LPDOSTASK lpDosTask = dos_current;
 233   IMAGE_NT_HEADERS *win_hdr = PE_HEADER(module);
 234   IMAGE_DOS_HEADER mz_header;
 235   DWORD image_start,image_size,min_size,max_size,avail;
 236   BYTE*psp_start,*load_start;
 237   int x, old_com=0, alloc=0;
 238   SEGPTR reloc;
 239   WORD env_seg;
 240   DWORD len;
 241
 242   win_hdr->OptionalHeader.Subsystem = IMAGE_SUBSYSTEM_WINDOWS_CUI;
 243   win_hdr->OptionalHeader.AddressOfEntryPoint = (LPBYTE)MZ_Launch - (LPBYTE)module;
 244
 245   if (!lpDosTask) {
 246     alloc=1;
 247     lpDosTask = HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(DOSTASK));
 248     lpDosTask->mm_fd = -1;
 249     dos_current = lpDosTask;
 250   }
 251
 252  SetFilePointer(hFile,0,NULL,FILE_BEGIN);
 253  if (   !ReadFile(hFile,&mz_header,sizeof(mz_header),&len,NULL)
 254      || len != sizeof(mz_header)
 255      || mz_header.e_magic != IMAGE_DOS_SIGNATURE) {
 256   old_com=1; /* assume .COM file */
 257   image_start=0;
 258   image_size=GetFileSize(hFile,NULL);
 259   min_size=0x10000; max_size=0x100000;
 260   mz_header.e_crlc=0;
 261   mz_header.e_ss=0; mz_header.e_sp=0xFFFE;
 262   mz_header.e_cs=0; mz_header.e_ip=0x100;
 263  } else {
 264   /* calculate load size */
 265   image_start=mz_header.e_cparhdr<<4;
 266   image_size=mz_header.e_cp<<9; /* pages are 512 bytes */
 267   if ((mz_header.e_cblp!=0)&&(mz_header.e_cblp!=4)) image_size-=512-mz_header.e_cblp;
 268   image_size-=image_start;
 269   min_size=image_size+((DWORD)mz_header.e_minalloc<<4)+(PSP_SIZE<<4);
 270   max_size=image_size+((DWORD)mz_header.e_maxalloc<<4)+(PSP_SIZE<<4);
 271  }
 272
 273  MZ_InitMemory(lpDosTask);
 274
 275  /* allocate environment block */
 276  env_seg=MZ_InitEnvironment(lpDosTask,GetEnvironmentStringsA(),filename);
 277
 278  /* allocate memory for the executable */
 279  TRACE("Allocating DOS memory (min=%ld, max=%ld)\n",min_size,max_size);
 280  avail=DOSMEM_Available();
 281  if (avail<min_size) {
 282   ERR("insufficient DOS memory\n");
 283   SetLastError(ERROR_NOT_ENOUGH_MEMORY);
 284   goto load_error;
 285  }
 286  if (avail>max_size) avail=max_size;
 287  psp_start=DOSMEM_GetBlock(avail,&lpDosTask->psp_seg);
 288  if (!psp_start) {
 289   ERR("error allocating DOS memory\n");
 290   SetLastError(ERROR_NOT_ENOUGH_MEMORY);
 291   goto load_error;
 292  }
 293  lpDosTask->load_seg=lpDosTask->psp_seg+(old_com?0:PSP_SIZE);
 294  load_start=psp_start+(PSP_SIZE<<4);
 295  MZ_CreatePSP(psp_start, env_seg);
 296
 297  /* load executable image */
 298  TRACE("loading DOS %s image, %08lx bytes\n",old_com?"COM":"EXE",image_size);
 299  SetFilePointer(hFile,image_start,NULL,FILE_BEGIN);
 300  if (!ReadFile(hFile,load_start,image_size,&len,NULL) || len != image_size) {
 301   SetLastError(ERROR_BAD_FORMAT);
 302   goto load_error;
 303  }
 304
 305  if (mz_header.e_crlc) {
 306   /* load relocation table */
 307   TRACE("loading DOS EXE relocation table, %d entries\n",mz_header.e_crlc);
 308   /* FIXME: is this too slow without read buffering? */
 309   SetFilePointer(hFile,mz_header.e_lfarlc,NULL,FILE_BEGIN);
 310   for (x=0; x<mz_header.e_crlc; x++) {
 311    if (!ReadFile(hFile,&reloc,sizeof(reloc),&len,NULL) || len != sizeof(reloc)) {
 312     SetLastError(ERROR_BAD_FORMAT);
 313     goto load_error;
 314    }
 315    *(WORD*)SEGPTR16(load_start,reloc)+=lpDosTask->load_seg;
 316   }
 317  }
 318
 319  lpDosTask->init_cs=lpDosTask->load_seg+mz_header.e_cs;
 320  lpDosTask->init_ip=mz_header.e_ip;
 321  lpDosTask->init_ss=lpDosTask->load_seg+mz_header.e_ss;
 322  lpDosTask->init_sp=mz_header.e_sp;
 323
 324   TRACE("entry point: %04x:%04x\n",lpDosTask->init_cs,lpDosTask->init_ip);
 325
 326   if (!MZ_InitTask(lpDosTask)) {
 327     MZ_KillTask(lpDosTask);
 328     SetLastError(ERROR_GEN_FAILURE);
 329     return FALSE;
 330   }
 331
 332   return TRUE;
 333
 334 load_error:
 335   if (alloc) {
 336     dos_current = NULL;
 337     if (lpDosTask->mm_name[0]!=0) {
 338       if (lpDosTask->img!=NULL) munmap(lpDosTask->img,0x110000-START_OFFSET);
 339       if (lpDosTask->mm_fd>=0) close(lpDosTask->mm_fd);
 340       unlink(lpDosTask->mm_name);
 341     } else
 342       if (lpDosTask->img!=NULL) VirtualFree(lpDosTask->img,0x110000,MEM_RELEASE);
 343   }
 344
 345   return FALSE;
 346 }
 347
 348 LPDOSTASK MZ_AllocDPMITask( void )
 349 {
 350   LPDOSTASK lpDosTask = HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(DOSTASK));
 351
 352   if (lpDosTask) {
 353     lpDosTask->mm_fd = -1;
 354     dos_current = lpDosTask;
 355     MZ_InitMemory(lpDosTask);
 356   }
 357   return lpDosTask;
 358 }
 359
 360 static void MZ_InitTimer( LPDOSTASK lpDosTask, int ver )
 361 {
 362  if (ver<1) {
 363   /* can't make timer ticks */
 364  } else {
 365   int func;
 366   struct timeval tim;
 367
 368   /* start dosmod timer at 55ms (18.2Hz) */
 369   func=DOSMOD_SET_TIMER;
 370   tim.tv_sec=0; tim.tv_usec=54925;
 371   write(lpDosTask->write_pipe,&func,sizeof(func));
 372   write(lpDosTask->write_pipe,&tim,sizeof(tim));
 373  }
 374 }
 375
 376 BOOL MZ_InitTask( LPDOSTASK lpDosTask )
 377 {
 378   int write_fd[2],x_fd;
 379   pid_t child;
 380   char *fname,*farg,arg[16],fproc[64],path[256],*fpath;
 381   struct get_read_fd_request *r_req = get_req_buffer();
 382   struct get_write_fd_request *w_req = get_req_buffer();
 383
 384   if (!lpDosTask) return FALSE;
 385   /* create pipes */
 386   if (!CreatePipe(&(lpDosTask->hReadPipe),&(lpDosTask->hXPipe),NULL,0)) return FALSE;
 387   if (pipe(write_fd)<0) {
 388     CloseHandle(lpDosTask->hReadPipe);
 389     CloseHandle(lpDosTask->hXPipe);
 390     return FALSE;
 391   }
 392
 393   r_req->handle = lpDosTask->hReadPipe;
 394   server_call_fd( REQ_GET_READ_FD, -1, &lpDosTask->read_pipe );
 395   w_req->handle = lpDosTask->hXPipe;
 396   server_call_fd( REQ_GET_WRITE_FD, -1, &x_fd );
 397
 398   TRACE("win32 pipe: read=%d, write=%d, unix pipe: read=%d, write=%d\n",
 399                lpDosTask->hReadPipe,lpDosTask->hXPipe,lpDosTask->read_pipe,x_fd);
 400   TRACE("outbound unix pipe: read=%d, write=%d, pid=%d\n",write_fd[0],write_fd[1],getpid());
 401
 402   lpDosTask->write_pipe=write_fd[1];
 403
 404   lpDosTask->hConInput=GetStdHandle(STD_INPUT_HANDLE);
 405   lpDosTask->hConOutput=GetStdHandle(STD_OUTPUT_HANDLE);
 406
 407   /* if we have a mapping file, use it */
 408   fname=lpDosTask->mm_name; farg=NULL;
 409   if (!fname[0]) {
 410     /* otherwise, map our own memory image */
 411     sprintf(fproc,"/proc/%d/mem",getpid());
 412     sprintf(arg,"%ld",(unsigned long)lpDosTask->img);
 413     fname=fproc; farg=arg;
 414   }
 415
 416   TRACE("Loading DOS VM support module\n");
 417   if ((child=fork())<0) {
 418     close(write_fd[0]);
 419     close(lpDosTask->read_pipe);
 420     close(lpDosTask->write_pipe);
 421     close(x_fd);
 422     CloseHandle(lpDosTask->hReadPipe);
 423     CloseHandle(lpDosTask->hXPipe);
 424     return FALSE;
 425   }
 426  if (child!=0) {
 427   /* parent process */
 428   int ret;
 429
 430   close(write_fd[0]);
 431   close(x_fd);
 432   lpDosTask->task=child;
 433   /* wait for child process to signal readiness */
 434   while (1) {
 435     if (read(lpDosTask->read_pipe,&ret,sizeof(ret))==sizeof(ret)) break;
 436     if ((errno==EINTR)||(errno==EAGAIN)) continue;
 437     /* failure */
 438     ERR("dosmod has failed to initialize\n");
 439     if (lpDosTask->mm_name[0]!=0) unlink(lpDosTask->mm_name);
 440     return FALSE;
 441   }
 442   /* the child has now mmaped the temp file, it's now safe to unlink.
 443    * do it here to avoid leaving a mess in /tmp if/when Wine crashes... */
 444   if (lpDosTask->mm_name[0]!=0) unlink(lpDosTask->mm_name);
 445   /* start simulated system timer */
 446   MZ_InitTimer(lpDosTask,ret);
 447   if (ret<2) {
 448     ERR("dosmod version too old! Please install newer dosmod properly\n");
 449     ERR("If you don't, the new dosmod event handling system will not work\n");
 450   }
 451   /* all systems are now go */
 452  } else {
 453   /* child process */
 454   close(lpDosTask->read_pipe);
 455   close(lpDosTask->write_pipe);
 456   /* put our pipes somewhere dosmod can find them */
 457   dup2(write_fd[0],0); /* stdin */
 458   dup2(x_fd,1);        /* stdout */
 459   /* now load dosmod */
 460   /* check argv[0]-derived paths first, since the newest dosmod is most likely there
 461    * (at least it was once for Andreas Mohr, so I decided to make it easier for him) */
 462   fpath=strrchr(strcpy(path,full_argv0),'/');
 463   if (fpath) {
 464    strcpy(fpath,"/dosmod");
 465    execl(path,fname,farg,NULL);
 466    strcpy(fpath,"/loader/dos/dosmod");
 467    execl(path,fname,farg,NULL);
 468   }
 469   /* okay, it wasn't there, try in the path */
 470   execlp("dosmod",fname,farg,NULL);
 471   /* last desperate attempts: current directory */
 472   execl("dosmod",fname,farg,NULL);
 473   /* and, just for completeness... */
 474   execl("loader/dos/dosmod",fname,farg,NULL);
 475   /* if failure, exit */
 476   ERR("Failed to spawn dosmod, error=%s\n",strerror(errno));
 477   exit(1);
 478  }
 479  return TRUE;
 480 }
 481
 482 static void MZ_Launch(void)
 483 {
 484   LPDOSTASK lpDosTask = MZ_Current();
 485   BYTE *psp_start = (BYTE*)lpDosTask->img + ((DWORD)lpDosTask->psp_seg << 4);
 486
 487   MZ_FillPSP(psp_start, GetCommandLineA());
 488
 489   DOSVM_Enter(NULL);
 490 }
 491
 492 void MZ_KillTask( LPDOSTASK lpDosTask )
 493 {
 494   DOSEVENT *event,*p_event;
 495   DOSSYSTEM *sys,*p_sys;
 496
 497   TRACE("killing DOS task\n");
 498   VGA_Clean();
 499   if (lpDosTask->mm_name[0]!=0) {
 500     munmap(lpDosTask->img,0x110000-START_OFFSET);
 501     close(lpDosTask->mm_fd);
 502   } else VirtualFree(lpDosTask->img,0x110000,MEM_RELEASE);
 503   close(lpDosTask->read_pipe);
 504   close(lpDosTask->write_pipe);
 505   CloseHandle(lpDosTask->hReadPipe);
 506   CloseHandle(lpDosTask->hXPipe);
 507   kill(lpDosTask->task,SIGTERM);
 508 /* free memory allocated for events and systems */
 509 #define DFREE(var,pvar,svar) \
 510   var = lpDosTask->svar; \
 511   while (var) { \
 512     if (var->data) free(var->data); \
 513     pvar = var->next; free(var); var = pvar; \
 514   }
 515
 516   DFREE(event,p_event,pending)
 517   DFREE(event,p_event,current)
 518   DFREE(sys,p_sys,sys)
 519
 520 #undef DFREE
 521
 522 #if 0
 523   /* FIXME: this seems to crash */
 524   if (lpDosTask->dpmi_sel)
 525     SELECTOR_FreeBlock(lpDosTask->dpmi_sel, 1);
 526 #endif
 527 }
 528
 529 LPDOSTASK MZ_Current( void )
 530 {
 531   return dos_current;
 532 }
 533
 534 #else /* !MZ_SUPPORTED */
 535
 536 BOOL MZ_CreateProcess( HANDLE hFile, LPCSTR filename, LPCSTR cmdline, LPCSTR env,
 537                        LPSECURITY_ATTRIBUTES psa, LPSECURITY_ATTRIBUTES tsa,
 538                        BOOL inherit, DWORD flags, LPSTARTUPINFOA startup,
 539                        LPPROCESS_INFORMATION info )
 540 {
 541  WARN("DOS executables not supported on this architecture\n");
 542  SetLastError(ERROR_BAD_FORMAT);
 543  return FALSE;
 544 }
 545
 546 LPDOSTASK MZ_Current( void )
 547 {
 548   return NULL;
 549 }
 550
 551 #endif