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421 mateuszvis 1
/* This file is part of the SvarCOM project and is published under the terms
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 * of the MIT license.
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 *
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 * Copyright (C) 2021 Mateusz Viste
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 *
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 * Permission is hereby granted, free of charge, to any person obtaining a
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 * copy of this software and associated documentation files (the "Software"),
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 * to deal in the Software without restriction, including without limitation
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 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
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 * and/or sell copies of the Software, and to permit persons to whom the
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 * Software is furnished to do so, subject to the following conditions:
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 *
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 * The above copyright notice and this permission notice shall be included in
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 * all copies or substantial portions of the Software.
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 *
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 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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 * DEALINGS IN THE SOFTWARE.
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 */
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#include <i86.h>
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#include <string.h>
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#include "env.h"
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#include "helpers.h"
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#include "rmodinit.h"
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/* returns far pointer to rmod's settings block on success */
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struct rmod_props far *rmod_install(unsigned short envsize, unsigned char *rmodcore, unsigned short rmodcore_len) {
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  char far *myptr, far *mcb;
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  unsigned short far *owner;
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  const unsigned short sizeof_rmodandprops_paras = (0x100 + rmodcore_len + sizeof(struct rmod_props) + 15) / 16;
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  unsigned short rmodseg = 0xffff;
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  unsigned short envseg, origenvseg;
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  struct rmod_props far *res;
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453 mateuszvis 43
  /* read my current env segment from PSP and save it */
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  envseg = *((unsigned short *)0x2c);
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  origenvseg = envseg;
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  /* printf("original (PSP) env buffer at %04X\r\n", envseg); */
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  /* if envseg is zero, then enforce our own one (MSDOS 5 does not provide a default env) */
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  if ((envseg == 0) && (envsize == 0)) envsize = 256;
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  /* if custom envsize requested, convert it to number of paragraphs */
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  if (envsize != 0) {
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    envsize += 15;
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    envsize /= 16;
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  }
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  _asm {
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    /* link in the UMB memory chain for enabling high-memory allocation (and save initial status on stack) */
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    mov ax, 0x5802  /* GET UMB LINK STATE */
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    int 0x21
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    xor ah, ah
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    push ax         /* save link state on stack */
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    mov ax, 0x5803  /* SET UMB LINK STATE */
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    mov bx, 1
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    int 0x21
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    /* get current allocation strategy and save it in DX */
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    mov ax, 0x5800
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    int 0x21
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    push ax
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    pop dx
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    /* set strategy to 'last fit, try high then low memory' */
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    mov ax, 0x5801
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    mov bx, 0x0082
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    int 0x21
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    /* ask for a memory block and save the given segment to rmodseg */
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    mov ah, 0x48
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    mov bx, sizeof_rmodandprops_paras
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    int 0x21
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    jc ALLOC_FAIL
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    mov rmodseg, ax
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    /* ask for a memory block for the environment and save it to envseg (only if custom size requested) */
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    mov bx, envsize
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    test bx, bx
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    jz ALLOC_FAIL
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    mov ah, 0x48
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    int 0x21
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    jc ALLOC_FAIL
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    mov envseg, ax
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    ALLOC_FAIL:
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    /* restore initial allocation strategy */
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    mov ax, 0x5801
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    mov bx, dx
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    int 0x21
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    /* restore initial UMB memory link state */
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    mov ax, 0x5803
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    pop bx       /* pop initial UMB link state from stack */
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    int 0x21
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  }
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  if (rmodseg == 0xffff) {
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    outputnl("malloc error");
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    return(NULL);
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  }
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  /* copy rmod to its destination, prefixed with a copy of my own PSP */
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  myptr = MK_FP(rmodseg, 0);
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  {
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    unsigned short i;
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    char *mypsp = (void *)0;
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    for (i = 0; i < 0x100; i++) myptr[i] = mypsp[i];
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  }
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  myptr = MK_FP(rmodseg, 0x100);
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  _fmemcpy(myptr, rmodcore, rmodcore_len);
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  /* mark rmod memory as "self owned" */
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  mcb = MK_FP(rmodseg - 1, 0);
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  owner = (void far *)(mcb + 1);
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  *owner = rmodseg;
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  _fmemcpy(mcb + 8, "SVARCOM", 8);
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448 mateuszvis 123
  /* mark env memory as "owned by rmod" */
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  mcb = MK_FP(envseg - 1, 0);
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  owner = (void far *)(mcb + 1);
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  *owner = rmodseg;
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  _fmemcpy(mcb + 8, "SVARENV", 8);
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449 mateuszvis 129
  /* if env block is newly allocated, fill it with a few NULLs */
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  if (envsize != 0) {
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    owner = MK_FP(envseg, 0);
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    owner[0] = 0;
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    owner[1] = 0;
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  }
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  /* set CTRL+BREAK handler to rmod */
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  _asm {
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    push ax
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    push dx
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    push ds
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    mov ax, 0x2523
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    mov ds, rmodseg
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    mov dx, RMOD_OFFSET_BRKHANDLER
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    int 0x21
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    pop ds
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    pop dx
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    pop ax
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  }
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  /* prepare result (rmod props) */
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  res = MK_FP(rmodseg, 0x100 + rmodcore_len);
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  _fmemset(res, 0, sizeof(*res));  /* zero out */
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  res->rmodseg = rmodseg;          /* rmod segment */
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  res->inputbuf[0] = 128;          /* input buffer for INT 0x21, AH=0Ah*/
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  res->origenvseg = origenvseg;    /* original environment segment */
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  /* write env segment to rmod's PSP */
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  owner = MK_FP(rmodseg, RMOD_OFFSET_ENVSEG);
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  *owner = envseg;
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  /* write boot drive to rmod bootdrive field */
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  _asm {
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    push ax
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    push bx
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    push dx
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    push ds
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    mov ax, 0x3305 /* DOS 4.0+ - GET BOOT DRIVE */
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    int 0x21 /* boot drive is in DL now (1=A:, 2=B:, etc) */
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    add dl, 'A'-1 /* convert to a proper ASCII letter */
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    /* set DS to rmodseg */
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    mov ax, rmodseg
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    mov ds, ax
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    /* write boot drive to rmod bootdrive field */
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    mov bx, RMOD_OFFSET_BOOTDRIVE
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    mov [bx], dl
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    pop ds
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    pop dx
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    pop bx
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    pop ax
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  }
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450 mateuszvis 182
  /* save my original parent in rmod's memory */
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  res->origparent = *((unsigned long *)0x0a); /* original parent seg:off is at 0x0a of my PSP */
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448 mateuszvis 185
  /* set the int22 handler in my PSP to rmod so DOS jumps to rmod after I
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   * terminate and save the original handler in rmod's memory */
454 mateuszvis 187
  {
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    unsigned short *ptr = (void *)0x0a; /* int22 handler is at 0x0A of the PSP */
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    ptr[0] = RMOD_OFFSET_ROUTINE;
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    ptr[1] = rmodseg;
351 mateuszvis 191
  }
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449 mateuszvis 193
  return(res);
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}
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449 mateuszvis 197
/* look up my parent: if it's rmod then return a ptr to its props struct,
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 * otherwise return NULL */
479 mateuszvis 199
struct rmod_props far *rmod_find(unsigned short rmodcore_len) {
448 mateuszvis 200
  unsigned short *parent = (void *)0x0C; /* parent's seg in PSP[Ch] ("prev. int22 handler") */
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  unsigned short far *ptr;
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  const unsigned short sig[] = {0x1983, 0x1985, 0x2017, 0x2019};
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  unsigned char *cmdtail = (void *)0x80;
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  unsigned char i;
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  /* is it rmod? */
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  ptr = MK_FP(*parent, 0x100);
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  for (i = 0; i < 4; i++) if (ptr[i] != sig[i]) return(NULL);
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  /* match successfull (rmod is my parent) - but is it really a respawn?
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   * command-line tail should contain a single character '\r' */
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  if ((cmdtail[0] != 1) || (cmdtail[1] != '\n')) return(NULL);
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  cmdtail[0] = 0;
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  cmdtail[1] = '\r';
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  /* */
478 mateuszvis 214
  return(MK_FP(*parent, 0x100 + rmodcore_len));
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}
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/* update rmod's pointer to comspec */
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void rmod_updatecomspecptr(unsigned short rmod_seg, unsigned short env_seg) {
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  unsigned short far *comspecptr = MK_FP(rmod_seg, RMOD_OFFSET_COMSPECPTR);
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  char far *comspecfp = env_lookup_val(env_seg, "COMSPEC");
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  if (comspecfp != NULL) {
439 mateuszvis 223
    *comspecptr = FP_OFF(comspecfp);
367 mateuszvis 224
  } else {
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    *comspecptr = 0;
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  }
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}