FreeDOS/kernel/task.c

/****************************************************************/
/*                                                              */
/*                           task.c                             */
/*                                                              */
/*                 Task Manager for DOS Processes               */
/*                                                              */
/*                      Copyright (c) 1995                      */
/*                      Pasquale J. Villani                     */
/*                      All Rights Reserved                     */
/*                                                              */
/* This file is part of DOS-C.                                  */
/*                                                              */
/* DOS-C is free software; you can redistribute it and/or       */
/* modify it under the terms of the GNU General Public License  */
/* as published by the Free Software Foundation; either version */
/* 2, or (at your option) any later version.                    */
/*                                                              */
/* DOS-C 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 General Public License for more details.             */
/*                                                              */
/* You should have received a copy of the GNU General Public    */
/* License along with DOS-C; see the file COPYING.  If not,     */
/* write to the Free Software Foundation, 675 Mass Ave,         */
/* Cambridge, MA 02139, USA.                                    */
/****************************************************************/

#include "portab.h"
#include "globals.h"

#ifdef VERSION_STRINGS
static BYTE *RcsId =
    "$Id$";
#endif

#define toupper(c)	((c) >= 'a' && (c) <= 'z' ? (c) + ('A' - 'a') : (c))

#define LOADNGO 0
#define LOAD    1
#define OVERLAY 3

#define LOAD_HIGH 0x80

/* static exe_header ExeHeader;
                           to save some bytes, both static and on stack,
                           we recycle SecPathBuffer                 TE */

#define ExeHeader (*(exe_header *)(SecPathName + 0))
#define TempExeBlock (*(exec_blk *)(SecPathName + sizeof(exe_header)))
#define Shell (SecPathName + sizeof(exe_header) + sizeof(exec_blk))

#ifdef __TURBOC__ /* this is a Borlandism and doesn't work elsewhere */
 #if sizeof(SecPathName) < sizeof(exe_header) + sizeof(exec_blk) + NAMEMAX
  #error No room in SecPathName to be recycled!
 #endif
#endif

#define CHUNK 32256
#define MAXENV 32768u
#define ENV_KEEPFREE 83         /* keep unallocated by environment variables */
        /* The '65' added to nEnvSize does not cover the additional stuff:
           + 2 bytes: number of strings
           + 80 bytes: maximum absolute filename
           + 1 byte: '\0'
           -- 1999/04/21 ska */

ULONG SftGetFsize(int sft_idx)
{
  sft FAR *s = idx_to_sft(sft_idx);

  /* Get the SFT block that contains the SFT      */
  if (FP_OFF(s) == (size_t) -1)
    return DE_INVLDHNDL;

  /* If SFT entry refers to a device, return the date and time of opening */
  if (s->sft_flags & (SFT_FDEVICE | SFT_FSHARED))
  {
    return s->sft_size;
  }

  /* call file system handler                     */
  return dos_getfsize(s->sft_status);
}

STATIC COUNT ChildEnv(exec_blk * exp, UWORD * pChildEnvSeg, char far * pathname)
{
  BYTE FAR *pSrc;
  BYTE FAR *pDest;
  UWORD nEnvSize;
  COUNT RetCode;
/*  UWORD MaxEnvSize;                                                                                                                                           not used -- 1999/04/21 ska */
  psp FAR *ppsp = MK_FP(cu_psp, 0);

  /* create a new environment for the process             */
  /* copy parent's environment if exec.env_seg == 0       */

  pSrc = exp->exec.env_seg ?
      MK_FP(exp->exec.env_seg, 0) : MK_FP(ppsp->ps_environ, 0);

#if 0
  /* Every process requires an environment because of argv[0]
     -- 1999/04/21 ska */
  */if (!pSrc)                  /* no environment to copy */
  {
    *pChildEnvSeg = 0;
    return SUCCESS;
  }
#endif

  nEnvSize = 1;
  /* This loop had not counted the very last '\0'
     -- 1999/04/21 ska */
  if (pSrc)
  {                             /* if no environment is available, one byte is required */

    for (nEnvSize = 0;; nEnvSize++)
    {
      /* Test env size and abort if greater than max          */
      if (nEnvSize >= MAXENV - ENV_KEEPFREE)
        return DE_INVLDENV;

      if (*(UWORD FAR *) (pSrc + nEnvSize) == 0)
        break;
    }
    nEnvSize += 2;              /* account for trailing \0\0 */
  }

  /* allocate enough space for env + path                 */
  if ((RetCode = DosMemAlloc(long2para(nEnvSize + ENV_KEEPFREE),
                             mem_access_mode, (seg FAR *) pChildEnvSeg,
                             NULL /*(UWORD FAR *) MaxEnvSize ska */ )) < 0)
    return RetCode;
  pDest = MK_FP(*pChildEnvSeg + 1, 0);

  /* fill the new env and inform the process of its       */
  /* location throught the psp                            */

  /* copy the environment */
  if (pSrc)
  {
    fmemcpy(pDest, pSrc, nEnvSize);
    pDest += nEnvSize;
  }
  else
    *pDest++ = '\0';            /* create an empty environment */

  /* initialize 'extra strings' count */
  *((UWORD FAR *) pDest) = 1;
  pDest += sizeof(UWORD) / sizeof(BYTE);

  /* copy complete pathname */
  if ((RetCode = truename(pathname, PriPathName, CDS_MODE_SKIP_PHYSICAL)) < SUCCESS)
  {
    return RetCode;
  }
  fstrcpy(pDest, PriPathName);

  /* Theoretically one could either:
     + resize the already allocated block to best-fit behind the pathname, or
     + generate the filename into a temporary buffer to allocate only the
     minimum required environment -- 1999/04/21 ska */

  return SUCCESS;
}

/* The following code is 8086 dependant                         */
void new_psp(seg para, int psize)
{
  psp FAR *p = MK_FP(para, 0);
  psp FAR *q = MK_FP(cu_psp, 0);
  int i;
        
  /* Clear out new psp first                              */
  fmemset(p, 0, sizeof(psp));

  /* initialize all entries and exits                     */
  /* CP/M-like exit point                                 */
  p->ps_exit = 0x20cd;

  /* CP/M-like entry point - call far to special entry    */
  p->ps_farcall = 0x9a;
  p->ps_reentry = MK_FP(0, 0x30 * 4);
  /* unix style call - 0xcd 0x21 0xcb (int 21, retf)      */
  p->ps_unix[0] = 0xcd;
  p->ps_unix[1] = 0x21;
  p->ps_unix[2] = 0xcb;

  /* Now for parent-child relationships                   */
  /* parent psp segment                                   */
  p->ps_parent = cu_psp;
  /* previous psp pointer                                 */
  p->ps_prevpsp = q;

  /* Environment and memory useage parameters             */
  /* memory size in paragraphs                            */
  p->ps_size = psize;
  /* environment paragraph                                */
  /* p->ps_environ = 0; cleared above */
  /* terminate address                                    */
  p->ps_isv22 = getvec(0x22);
  /* break address                                        */
  p->ps_isv23 = getvec(0x23);
  /* critical error address                               */
  p->ps_isv24 = getvec(0x24);

  /* user stack pointer - int 21                          */
  p->ps_stack = q->ps_stack;

  /* File System parameters                               */
  /* maximum open files                                   */
  p->ps_maxfiles = 20;
  fmemset(p->ps_files, 0xff, 20);

  /* open file table pointer                              */
  p->ps_filetab = p->ps_files;

  /* clone the file table -- 0xff is unused               */
  for (i = 0; i < 20; i++)
    if (CloneHandle(i) >= 0)
      p->ps_files[i] = q->ps_filetab[i];

  /* first command line argument                          */
  /* p->ps_fcb1.fcb_drive = 0; already set                */
  fmemset(p->ps_fcb1.fcb_fname, ' ', FNAME_SIZE + FEXT_SIZE);
  /* second command line argument                         */
  /* p->ps_fcb2.fcb_drive = 0; already set                */
  fmemset(p->ps_fcb2.fcb_fname, ' ', FNAME_SIZE + FEXT_SIZE);

  /* local command line                                   */
  /* p->ps_cmd.ctCount = 0;     command tail, already set */
  p->ps_cmd.ctBuffer[0] = 0xd; /* command tail            */
}

STATIC UBYTE chkdrv(unsigned drive) /* from FCB: 0 = default, 1 = A:, ... */
{
  if (drive)
    drive--; /* 0 = A:, 1 = B:, ... */
  else
    drive = default_drive;
  return get_cds(drive) ? 0 : 0xff; /* return 0 if drive is valid, else 0xff */
}

STATIC UWORD patchPSP(UWORD pspseg, UWORD envseg, exec_blk FAR * exb,
                      BYTE FAR * fnam)
{
  psp FAR *psp;
  mcb FAR *pspmcb;
  int i;
  BYTE FAR *np;

  pspmcb = MK_FP(pspseg, 0);
  ++pspseg;
  psp = MK_FP(pspseg, 0);

  /* complete the psp by adding the command line and FCBs     */
  fmemcpy(&psp->ps_cmd, exb->exec.cmd_line, sizeof(CommandTail));
  if (FP_OFF(exb->exec.fcb_1) != 0xffff)
  {
    fmemcpy(&psp->ps_fcb1, exb->exec.fcb_1, 16);
    fmemcpy(&psp->ps_fcb2, exb->exec.fcb_2, 16);
  }

  /* identify the mcb as this functions'                  */
  pspmcb->m_psp = pspseg;
  /* Patch in environment segment, if present, also adjust its MCB */
  if (envseg)
  {
    ((mcb FAR *) MK_FP(envseg, 0))->m_psp = pspseg;
    envseg++;
  }
  psp->ps_environ = envseg;

  /* use the file name less extension - left adjusted and */
  np = fnam;
  for (;;)
  {
    switch (*fnam++)
    {
      case '\0':
        goto set_name;
      case ':':
      case '/':
      case '\\':
        np = fnam;
    }
  }
set_name:
  for (i = 0; i < 8 && np[i] != '.' && np[i] != '\0'; i++)
  {
    pspmcb->m_name[i] = toupper(np[i]);
  }
  if (i < 8)
    pspmcb->m_name[i] = '\0';

  /* return value: AX value to be passed based on FCB values */
  return chkdrv(psp->ps_fcb1.fcb_drive) |
    (chkdrv(psp->ps_fcb2.fcb_drive) << 8);
}

int load_transfer(UWORD ds, exec_blk *exp, UWORD fcbcode, COUNT mode)
{
  psp FAR *p = MK_FP(ds, 0);
  psp FAR *q = MK_FP(cu_psp, 0);
  
  /* Transfer control to the executable                   */
  p->ps_parent = cu_psp;
  p->ps_prevpsp = q;
  q->ps_stack = (BYTE FAR *)user_r;
  user_r->FLAGS &= ~FLG_CARRY;
  
  cu_psp = ds;
  /* process dta                                          */
  dta = &p->ps_cmd;
  
  if (mode == LOADNGO)
  {
    iregs FAR *irp;
    
    /* build the user area on the stack                     */
    irp = (iregs FAR *)(exp->exec.stack - sizeof(iregs));
    
    /* start allocating REGs (as in MS-DOS - some demos expect them so --LG) */
    /* see http://www.beroset.com/asm/showregs.asm */
    irp->DX = irp->ES = irp->DS = ds;
    irp->CS = FP_SEG(exp->exec.start_addr);
    irp->SI = irp->IP = FP_OFF(exp->exec.start_addr);
    irp->DI = FP_OFF(exp->exec.stack);
    irp->BP = 0x91e; /* this is more or less random but some programs
                        expect 0x9 in the high byte of BP!! */
    irp->AX = irp->BX = fcbcode;
    irp->CX = 0xFF;
    irp->FLAGS = 0x200;
    
    if (InDOS)
      --InDOS;
    exec_user(irp, 1);
    
    /* We should never be here          
       fatal("KERNEL RETURNED!!!");                    */
  }
  /* mode == LOAD */
  exp->exec.stack -= 2;
  *((UWORD FAR *)(exp->exec.stack)) = fcbcode;
  return SUCCESS;
}

/* Now find out how many paragraphs are available
   considering a threshold, trying HIGH then LOW */
STATIC int ExecMemLargest(UWORD *asize, UWORD threshold)
{
  int rc;
  if (mem_access_mode & 0x80)
  {
    mem_access_mode &= ~0x80;
    mem_access_mode |= 0x40;
    rc = DosMemLargest(asize);
    mem_access_mode &= ~0x40;
    /* less memory than the .COM/.EXE file has:
       try low memory first */
    if (rc != SUCCESS || *asize < threshold)
      rc = DosMemLargest(asize);
    mem_access_mode |= 0x80;
  }
  else
    rc = DosMemLargest(asize);
  return (*asize < threshold ? DE_NOMEM : rc);
}

STATIC int ExecMemAlloc(UWORD size, seg *para, UWORD *asize)
{
  /* We can still get an error on first fit if the above  */
  /* returned size was a best fit case                    */
  /* ModeLoadHigh = 80 = try high, then low               */
  int rc = DosMemAlloc(size, mem_access_mode, para, asize);

  if (rc != SUCCESS)
  {
    if (rc == DE_NOMEM)
    {
      rc = DosMemAlloc(0, LARGEST, para, asize);
      if ((mem_access_mode & 0x80) && (rc != SUCCESS))
      {
        mem_access_mode &= ~0x80;
        rc = DosMemAlloc(0, LARGEST, para, asize);
        mem_access_mode |= 0x80;
      }
    }
  }
  else
  {
    /* with no error, we got exactly what we asked for      */
    *asize = size;
  }

  /* This should never happen, but ... */
  if (rc == SUCCESS && *asize < size)
  {
    DosMemFree(*para);
    return DE_NOMEM;
  }
  return rc;
}

COUNT DosComLoader(BYTE FAR * namep, exec_blk * exp, COUNT mode, COUNT fd)
{
  UWORD mem;
  UWORD env, asize = 0;
  
  {
    UWORD com_size;
    {
      ULONG com_size_long = SftGetFsize(fd);
      /* maximally 64k - 256 bytes stack -
         256 bytes psp */
      com_size = ((UWORD)min(com_size_long, 0xfe00u) >> 4) + 0x10;
    }

    if ((mode & 0x7f) != OVERLAY)
    {
      COUNT rc;
      UBYTE UMBstate = uppermem_link;
      UBYTE orig_mem_access = mem_access_mode;
      
      if (mode & 0x80)
      {
        mem_access_mode |= 0x80;
        DosUmbLink(1);            /* link in UMB's */
      }
      
      rc = ChildEnv(exp, &env, namep);
      
      /* COMFILES will always be loaded in largest area. is that true TE */
      /* yes, see RBIL, int21/ah=48 -- Bart */

      if (rc == SUCCESS)
        rc = ExecMemLargest(&asize, com_size);
      
      if (rc == SUCCESS)
        /* Allocate our memory and pass back any errors         */
        rc = ExecMemAlloc(asize, &mem, &asize);

      if (rc != SUCCESS)
        DosMemFree(env);

      if (mode & 0x80)
      {
        DosUmbLink(UMBstate);       /* restore link state */
        mem_access_mode = orig_mem_access;
        mode &= 0x7f;
      }

      if (rc != SUCCESS)
        return rc;

      ++mem;
    }
    else
      mem = exp->load.load_seg;
  }

#ifdef DEBUG
  printf("DosComLoader. Loading '%S' at %04x\n", namep, mem);
#endif
  /* Now load the executable                              */
  {
    BYTE FAR *sp;

    if (mode == OVERLAY)  /* memory already allocated */
      sp = MK_FP(mem, 0);
    else                  /* test the filesize against the allocated memory */
      sp = MK_FP(mem, sizeof(psp));

    /* MS DOS always only loads the very first 64KB - sizeof(psp) bytes.
       -- 1999/04/21 ska */

    /* rewind to start */
    SftSeek(fd, 0, 0);
    /* read everything, but at most 64K - sizeof(PSP)             */
    DosRWSft(fd, 0xff00, sp, XFR_READ);
    DosCloseSft(fd, FALSE);
  }

  if (mode == OVERLAY)
    return SUCCESS;
  
  {
    UWORD fcbcode;
    psp FAR *p;

    /* point to the PSP so we can build it                  */
    setvec(0x22, MK_FP(user_r->CS, user_r->IP));
    new_psp(mem, mem + asize);

    fcbcode = patchPSP(mem - 1, env, exp, namep);
    /* set asize to end of segment */
    if (asize > 0x1000)
      asize = 0x1000;
    if (asize < 0x11)
      return DE_NOMEM;
    asize -= 0x11;
    /* CP/M compatibility--size of first segment for .COM files
       while preserving the far call to 0:00c0 +
       copy in HMA at ffff:00d0 */
    p = MK_FP(mem, 0);
    p->ps_reentry = MK_FP(0xc - asize, asize << 4);
    asize <<= 4;
    asize += 0x10e;
    exp->exec.stack = MK_FP(mem, asize);
    exp->exec.start_addr = MK_FP(mem, 0x100);
    *((UWORD FAR *) MK_FP(mem, asize)) = (UWORD) 0;
    load_transfer(mem, exp, fcbcode, mode);
  }
  return SUCCESS;
}

VOID return_user(void)
{
  psp FAR *p, FAR * q;
  REG COUNT i;
  iregs FAR *irp;
/*  long j;*/

  /* restore parent                                       */
  p = MK_FP(cu_psp, 0);

  /* When process returns - restore the isv               */
  setvec(0x22, p->ps_isv22);
  setvec(0x23, p->ps_isv23);
  setvec(0x24, p->ps_isv24);

  /* And free all process memory if not a TSR return      */
  remote_process_end();         /* might be a good idea to do that after closing
                                   but doesn't help NET either TE */
  if (!tsr)
  {
    remote_close_all();
    for (i = 0; i < p->ps_maxfiles; i++)
    {
      DosClose(i);
    }
    FcbCloseAll();
    FreeProcessMem(cu_psp);
  }

  cu_psp = p->ps_parent;
  q = MK_FP(cu_psp, 0);

  irp = (iregs FAR *) q->ps_stack;

  irp->CS = FP_SEG(p->ps_isv22);
  irp->IP = FP_OFF(p->ps_isv22);

  if (InDOS)
    --InDOS;
  exec_user((iregs FAR *) q->ps_stack, 0);
}

COUNT DosExeLoader(BYTE FAR * namep, exec_blk * exp, COUNT mode, COUNT fd)
{
  UWORD mem, env, start_seg, asize = 0;
  ULONG exe_size;
  {
    ULONG image_size;
    ULONG image_offset;
    
    /* compute image offset from the ExeHeader                 */
    image_offset = (ULONG) ExeHeader.exHeaderSize * 16;

    /* compute image size by removing the offset from the   */
    /* number pages scaled to bytes plus the remainder and  */
    /* the psp                                              */
    /*  First scale the size                                */
    image_size = (ULONG) ExeHeader.exPages * 512;
    /* remove the offset                                    */
    image_size -= image_offset;
    
    /* We should not attempt to allocate
       memory if we are overlaying the current process, because the new
       process will simply re-use the block we already have allocated.
       Jun 11, 2000 - rbc */
    
    if ((mode & 0x7f) != OVERLAY)
    {
      UBYTE UMBstate = uppermem_link;
      UBYTE orig_mem_access = mem_access_mode;
      COUNT rc;
      
      /* and finally add in the psp size                      */
      image_size += sizeof(psp);        /*TE 03/20/01 */
      exe_size = (ULONG) long2para(image_size) + ExeHeader.exMinAlloc;
      
      /* Clone the environement and create a memory arena     */
      if (mode & 0x80)
      {
        DosUmbLink(1);          /* link in UMB's */
        mem_access_mode |= 0x80;
      }
      
      rc = ChildEnv(exp, &env, namep);
      
      if (rc == SUCCESS)
        /* Now find out how many paragraphs are available       */
        rc = ExecMemLargest(&asize, (UWORD)exe_size);
      
      exe_size = (ULONG) long2para(image_size) + ExeHeader.exMaxAlloc;
      if (exe_size > asize)
        exe_size = asize;
      
      /* TE if ExeHeader.exMinAlloc == ExeHeader.exMaxAlloc == 0,
         DOS will allocate the largest possible memory area
         and load the image as high as possible into it.
         discovered (and after that found in RBIL), when testing NET */
      
      if ((ExeHeader.exMinAlloc | ExeHeader.exMaxAlloc) == 0)
        exe_size = asize;
      
      /* Allocate our memory and pass back any errors         */
      if (rc == SUCCESS)
        rc = ExecMemAlloc((UWORD)exe_size, &mem, &asize);
      
      if (rc != SUCCESS)
        DosMemFree(env);
      
      if (mode & 0x80)
      {
        mem_access_mode = orig_mem_access; /* restore old situation */
        DosUmbLink(UMBstate);     /* restore link state */
      }
      if (rc != SUCCESS)
        return rc;
      
      mode &= 0x7f; /* forget about high loading from now on */
      
#ifdef DEBUG
      printf("DosExeLoader. Loading '%S' at %04x\n", namep, mem);
#endif
      
      /* memory found large enough - continue processing      */
      ++mem;
      
/* /// Added open curly brace and "else" clause.  We should not attempt
   to allocate memory if we are overlaying the current process, because
   the new process will simply re-use the block we already have allocated.
   This was causing execl() to fail in applications which use it to
   overlay (replace) the current exe file with a new one.
   Jun 11, 2000 - rbc */
    }
    else /* !!OVERLAY */
    {
      mem = exp->load.load_seg;
    }

    /* Now load the executable                              */
    /* offset to start of image                             */
    if (SftSeek(fd, image_offset, 0) != SUCCESS)
    {
      if (mode != OVERLAY)
      {
        DosMemFree(--mem);
        DosMemFree(env);
      }
      return DE_INVLDDATA;
    }
    
    /* create the start seg for later computations          */
    start_seg = mem;
    exe_size = image_size;
    if (mode != OVERLAY)
    {
      exe_size -= sizeof(psp);
      start_seg += long2para(sizeof(psp));
      if (exe_size > 0 && (ExeHeader.exMinAlloc == 0) && (ExeHeader.exMaxAlloc == 0))
      {
        mcb FAR *mp = MK_FP(mem - 1, 0);
        
        /* then the image should be placed as high as possible */
        start_seg = start_seg + mp->m_size - (UWORD)((image_size + 15) / 16);
      }
    }
  }

  /* read in the image in 32K chunks                      */
  {
    int nBytesRead;
    BYTE FAR *sp = MK_FP(start_seg, 0x0);
    
    while (exe_size > 0)
    {
      nBytesRead =
        (int)DosRWSft(fd,
                (COUNT) (exe_size < CHUNK ? exe_size : CHUNK),
                (VOID FAR *) sp, XFR_READ);
      if (nBytesRead <= 0)
        break;
      sp = add_far((VOID FAR *) sp, nBytesRead);
      exe_size -= nBytesRead;
    }
  }

  {                             /* relocate the image for new segment                   */
    COUNT i;
    UWORD reloc[2];
    seg FAR *spot;

    SftSeek(fd, ExeHeader.exRelocTable, 0);
    for (i = 0; i < ExeHeader.exRelocItems; i++)
    {
      if (DosRWSft
          (fd, sizeof(reloc), (VOID FAR *) & reloc[0], XFR_READ) != sizeof(reloc))
      {
        if (mode != OVERLAY)
        {
          DosMemFree(--mem);
          DosMemFree(env);
        }
        return DE_INVLDDATA;
      }
      if (mode == OVERLAY)
      {
        spot = MK_FP(reloc[1] + mem, reloc[0]);
        *spot += exp->load.reloc;
      }
      else
      {
        /*      spot = MK_FP(reloc[1] + mem + 0x10, reloc[0]); */
        spot = MK_FP(reloc[1] + start_seg, reloc[0]);
        *spot += start_seg;
      }
    }
  }

  /* and finally close the file                           */
  DosCloseSft(fd, FALSE);

  /* exit here for overlay                                */
  if (mode == OVERLAY)
    return SUCCESS;

  {
    UWORD fcbcode;

    /* point to the PSP so we can build it                  */
    setvec(0x22, MK_FP(user_r->CS, user_r->IP));
    new_psp(mem, mem + asize);

    fcbcode = patchPSP(mem - 1, env, exp, namep);
    exp->exec.stack =
      MK_FP(ExeHeader.exInitSS + start_seg, ExeHeader.exInitSP);
    exp->exec.start_addr =
      MK_FP(ExeHeader.exInitCS + start_seg, ExeHeader.exInitIP);

    /* Transfer control to the executable                   */
    load_transfer(mem, exp, fcbcode, mode);
  }
  return SUCCESS;
}

/* mode = LOAD or EXECUTE
   ep = EXE block
   lp = filename to load (string)

   leb = local copy of exe block
 */
COUNT DosExec(COUNT mode, exec_blk FAR * ep, BYTE FAR * lp)
{
  COUNT rc;
  COUNT fd;

  if ((mode & 0x7f) > 3 || (mode & 0x7f) == 2)
    return DE_INVLDFMT; 

  fmemcpy(&TempExeBlock, ep, sizeof(exec_blk));
  /* If file not found - free ram and return error        */

  if (IsDevice(lp) ||        /* we don't want to execute C:>NUL */
      (fd = (short)DosOpenSft(lp, O_LEGACY | O_OPEN | O_RDONLY, 0)) < 0)
  {
    return DE_FILENOTFND;
  }
  
  rc = (int)DosRWSft(fd, sizeof(exe_header), (BYTE FAR *)&ExeHeader, XFR_READ);

  if (rc == sizeof(exe_header) &&
      (ExeHeader.exSignature == MAGIC || ExeHeader.exSignature == OLD_MAGIC))
  {
    rc = DosExeLoader(lp, &TempExeBlock, mode, fd);
  }
  else if (rc != 0)
  {
    rc = DosComLoader(lp, &TempExeBlock, mode, fd);
  }

  DosCloseSft(fd, FALSE);

  if (mode == LOAD && rc == SUCCESS)
    fmemcpy(ep, &TempExeBlock, sizeof(exec_blk));

  return rc;
}

#include "config.h" /* config structure definition */

/* start process 0 (the shell) */
VOID ASMCFUNC P_0(struct config FAR *Config)
{
  BYTE *tailp, *endp;
  exec_blk exb;
  UBYTE mode = Config->cfgP_0_startmode;

  /* build exec block and save all parameters here as init part will vanish! */
  exb.exec.fcb_1 = exb.exec.fcb_2 = (fcb FAR *)-1L;
  exb.exec.env_seg = DOS_PSP + 8;
  fstrcpy(Shell, Config->cfgInit);
  fstrcpy(Shell + strlen(Shell), Config->cfgInitTail); /* join name and tail */
  endp =  Shell + strlen(Shell);

  for ( ; ; )   /* endless shell load loop - reboot or shut down to exit it! */
  {
    BYTE *p;
    /* if there are no parameters, point to end without "\r\n" */
    if((tailp = strchr(Shell,'\t')) == NULL &&
       (tailp = strchr(Shell, ' ')) == NULL)
        tailp = endp - 2;
    /* shift tail to right by 2 to make room for '\0', ctCount */
    for (p = endp - 1; p >= tailp; p--)
      *(p + 2) = *p;
    /* terminate name and tail */
    *tailp =  *(endp + 2) = '\0';
    /* ctCount: just past '\0' do not count the "\r\n" */
    exb.exec.cmd_line = (CommandTail *)(tailp + 1);
    exb.exec.cmd_line->ctCount = endp - tailp - 2;
#ifdef DEBUG
    printf("Process 0 starting: %s%s\n\n", Shell, tailp + 2);
#endif
    res_DosExec(mode, &exb, Shell);
    put_string("Bad or missing Command Interpreter: "); /* failure _or_ exit */
    put_string(Shell);
    put_string(tailp + 2);
    put_string(" Enter the full shell command line: ");
    endp = Shell + res_read(STDIN, Shell, NAMEMAX);
    *endp = '\0';                             /* terminate string for strchr */
  }
}