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mateuszvis |
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#include <i86.h>
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#include <stdio.h>
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#include <string.h>
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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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printf("original (PSP) env buffer at %04X\r\n", envseg);
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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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puts("malloc error");
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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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/* 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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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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}
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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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