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mateuszvis |
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/* 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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mateuszvis |
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#include <i86.h>
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#include <string.h>
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mateuszvis |
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#include "env.h"
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mateuszvis |
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#include "helpers.h"
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mateuszvis |
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mateuszvis |
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#include "rmod.h"
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#include "rmodinit.h"
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/* returns segment where rmod is installed */
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unsigned short rmod_install(unsigned short envsize) {
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char far *myptr, far *mcb;
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unsigned short far *owner;
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unsigned int rmodseg = 0xffff;
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unsigned int envseg = 0;
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/* read my current env segment from PSP */
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_asm {
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push ax
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push bx
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mov bx, 0x2c
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mov ax, [bx]
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mov envseg, ax
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pop bx
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pop ax
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}
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mateuszvis |
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/* printf("original (PSP) env buffer at %04X\r\n", envseg); */
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mateuszvis |
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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, (rmod_len + 15) / 16
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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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mateuszvis |
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outputnl("malloc error");
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mateuszvis |
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return(0xffff);
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}
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/* copy rmod to its destination */
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myptr = MK_FP(rmodseg, 0);
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_fmemcpy(myptr, rmod, rmod_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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mateuszvis |
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/* mark env memory as "self owned" */
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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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mateuszvis |
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/* write env segment to rmod buffer */
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owner = MK_FP(rmodseg, RMOD_OFFSET_ENVSEG);
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*owner = envseg;
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mateuszvis |
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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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mateuszvis |
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/* set the int22 handler in my PSP to rmod so DOS jumps to rmod after I terminate */
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_asm {
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mateuszvis |
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push ax
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push bx
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mateuszvis |
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mov bx, 0x0a /* int22 handler is at 0x0A of the PSP */
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mov ax, RMOD_OFFSET_ROUTINE
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mov [bx], ax /* int handler offset */
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mov ax, rmodseg
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mov [bx+2], ax /* int handler segment */
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mateuszvis |
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pop bx
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pop ax
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mateuszvis |
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}
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return(rmodseg);
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}
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/* scan memory for rmod, returns its segment if found, 0xffff otherwise */
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unsigned short rmod_find(void) {
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unsigned short i;
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mateuszvis |
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unsigned short far *ptrword;
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unsigned char far *ptrbyte;
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mateuszvis |
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/* iterate over all paragraphs, looking for my signature */
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mateuszvis |
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for (i = 1; i != 65535; i++) {
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ptrword = MK_FP(i, 0);
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if (ptrword[0] != 0x1983) continue;
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if (ptrword[1] != 0x1985) continue;
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if (ptrword[2] != 0x2017) continue;
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if (ptrword[3] != 0x2019) continue;
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/* extra check: make sure the paragraph before is an MCB block and that it
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* belongs to itself. otherwise I could find the rmod code embedded inside
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* the command.com binary... */
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ptrbyte = MK_FP(i - 1, 0);
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if ((*ptrbyte != 'M') && (*ptrbyte != 'Z')) continue; /* not an MCB */
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ptrword = MK_FP(i - 1, 1);
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if (*ptrword != i) continue; /* not belonging to self */
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mateuszvis |
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return(i);
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}
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return(0xffff);
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}
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mateuszvis |
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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(env_seg, "COMSPEC");
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if (comspecfp != NULL) {
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*comspecptr = FP_OFF(comspecfp) + 8; /* +8 to skip the "COMSPEC=" prefix */
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} else {
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*comspecptr = 0;
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}
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}
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