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421 mateuszvis 1
/* This file is part of the SvarCOM project and is published under the terms
2
 * of the MIT license.
3
 *
949 mateusz.vi 4
 * Copyright (C) 2021-2022 Mateusz Viste
421 mateuszvis 5
 *
6
 * Permission is hereby granted, free of charge, to any person obtaining a
7
 * copy of this software and associated documentation files (the "Software"),
8
 * to deal in the Software without restriction, including without limitation
9
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
10
 * and/or sell copies of the Software, and to permit persons to whom the
11
 * Software is furnished to do so, subject to the following conditions:
12
 *
13
 * The above copyright notice and this permission notice shall be included in
14
 * all copies or substantial portions of the Software.
15
 *
16
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
19
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
21
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
22
 * DEALINGS IN THE SOFTWARE.
23
 */
351 mateuszvis 24
 
25
#include <i86.h>
26
#include <string.h>
27
 
367 mateuszvis 28
#include "env.h"
369 mateuszvis 29
#include "helpers.h"
367 mateuszvis 30
 
351 mateuszvis 31
#include "rmodinit.h"
32
 
33
 
449 mateuszvis 34
/* returns far pointer to rmod's settings block on success */
479 mateuszvis 35
struct rmod_props far *rmod_install(unsigned short envsize, unsigned char *rmodcore, unsigned short rmodcore_len) {
351 mateuszvis 36
  char far *myptr, far *mcb;
37
  unsigned short far *owner;
478 mateuszvis 38
  const unsigned short sizeof_rmodandprops_paras = (0x100 + rmodcore_len + sizeof(struct rmod_props) + 15) / 16;
453 mateuszvis 39
  unsigned short rmodseg = 0xffff;
454 mateuszvis 40
  unsigned short envseg, origenvseg;
465 mateuszvis 41
  struct rmod_props far *res;
351 mateuszvis 42
 
453 mateuszvis 43
  /* read my current env segment from PSP and save it */
454 mateuszvis 44
  envseg = *((unsigned short *)0x2c);
45
  origenvseg = envseg;
351 mateuszvis 46
 
369 mateuszvis 47
  /* printf("original (PSP) env buffer at %04X\r\n", envseg); */
449 mateuszvis 48
 
49
  /* if envseg is zero, then enforce our own one (MSDOS 5 does not provide a default env) */
50
  if ((envseg == 0) && (envsize == 0)) envsize = 256;
51
 
351 mateuszvis 52
  /* if custom envsize requested, convert it to number of paragraphs */
53
  if (envsize != 0) {
54
    envsize += 15;
55
    envsize /= 16;
56
  }
57
 
58
  _asm {
59
    /* link in the UMB memory chain for enabling high-memory allocation (and save initial status on stack) */
60
    mov ax, 0x5802  /* GET UMB LINK STATE */
61
    int 0x21
62
    xor ah, ah
63
    push ax         /* save link state on stack */
64
    mov ax, 0x5803  /* SET UMB LINK STATE */
65
    mov bx, 1
66
    int 0x21
67
    /* get current allocation strategy and save it in DX */
68
    mov ax, 0x5800
69
    int 0x21
70
    push ax
71
    pop dx
72
    /* set strategy to 'last fit, try high then low memory' */
73
    mov ax, 0x5801
74
    mov bx, 0x0082
75
    int 0x21
76
    /* ask for a memory block and save the given segment to rmodseg */
77
    mov ah, 0x48
449 mateuszvis 78
    mov bx, sizeof_rmodandprops_paras
351 mateuszvis 79
    int 0x21
80
    jc ALLOC_FAIL
81
    mov rmodseg, ax
82
    /* ask for a memory block for the environment and save it to envseg (only if custom size requested) */
83
    mov bx, envsize
84
    test bx, bx
85
    jz ALLOC_FAIL
86
    mov ah, 0x48
87
    int 0x21
88
    jc ALLOC_FAIL
89
    mov envseg, ax
90
 
91
    ALLOC_FAIL:
92
    /* restore initial allocation strategy */
93
    mov ax, 0x5801
94
    mov bx, dx
95
    int 0x21
96
    /* restore initial UMB memory link state */
97
    mov ax, 0x5803
98
    pop bx       /* pop initial UMB link state from stack */
99
    int 0x21
100
  }
101
 
102
  if (rmodseg == 0xffff) {
369 mateuszvis 103
    outputnl("malloc error");
449 mateuszvis 104
    return(NULL);
351 mateuszvis 105
  }
106
 
1587 mateusz.vi 107
  /* copy my own PSP where RMOD is about to land, so it has a proper PSP as well */
108
  /* take care to init the JFT (20 bytes starting at offset 0x18) to 0xff, which
109
   * essentially means "empty JFT slot" */
351 mateuszvis 110
  myptr = MK_FP(rmodseg, 0);
459 mateuszvis 111
  {
112
    unsigned short i;
113
    char *mypsp = (void *)0;
114
    for (i = 0; i < 0x100; i++) myptr[i] = mypsp[i];
1590 mateusz.vi 115
    /* for (i = 0x18; i < 0x18+20; i++) myptr[i] = 0xff; */ /* do NOT close file handlers, RMOD's children might need stdin/stdout/etc */
459 mateuszvis 116
  }
1587 mateusz.vi 117
 
118
  /* patch up RMOD's PSP: Parent's PSP segment @ 0x16-0x17 */
119
  myptr[0x16] = rmodseg & 0xff; /* RMOD is his own parent */
120
  myptr[0x17] = rmodseg >> 8;
121
 
1589 mateusz.vi 122
  /* patch up RMOD's PSP: SS:SP pointer @ 0x2E-0x31  --  I abuse the PSP's
1590 mateusz.vi 123
   * command line tail as stack, but I do NOT set the stack at the end of the
1589 mateusz.vi 124
   * tail. E. C. Masloch kindly explained why this would be a bad idea:
125
   *
126
   * "This is wrong and will potentially overwrite part of your buffers that
127
   * start past the PSP. This is because the dword [PSP:2Eh] is not used merely
128
   * to set SS:SP but rather to find the stack frame created by the int 21h
129
   * call. Therefore the int 21h call that terminates the child process will
130
   * then pop a number of registers off starting from the address stored in the
131
   * PSP." <https://github.com/SvarDOS/bugz/issues/38#issuecomment-1817445740>
132
   */
133
  myptr[0x2e] = 192; /* middle of the command line tail area so I have 64 bytes */
134
  myptr[0x2f] = 0;   /* before and 64 bytes in front of me */
1587 mateusz.vi 135
  myptr[0x30] = rmodseg & 0xff;
136
  myptr[0x31] = rmodseg >> 8;
137
 
138
  /* patch up RMOD's PSP: JFT size @ 0x32-0x33 */
1588 mateusz.vi 139
  myptr[0x32] = 20; /* default JFT size (max that fits without an extra allocation) */
1587 mateusz.vi 140
  myptr[0x33] = 0;
141
 
142
  /* patch up RMOD's PSP: JFT pointer @ 0x34-0x37 */
143
  myptr[0x34] = 0x18; /* the JFT is in the PSP itself */
144
  myptr[0x35] = 0;
145
  myptr[0x36] = rmodseg & 0xff;
146
  myptr[0x37] = rmodseg >> 8;
147
 
148
  /* patch up RMOD's PSP: pointer to previous PSP @ 0x38-0x3B */
149
  myptr[0x38] = 0;
150
  myptr[0x39] = 0;
151
  myptr[0x3A] = rmodseg & 0xff;
152
  myptr[0x3B] = rmodseg >> 8;
153
 
154
  /* copy rmod to its destination (right past the PSP I prepared) */
459 mateuszvis 155
  myptr = MK_FP(rmodseg, 0x100);
478 mateuszvis 156
  _fmemcpy(myptr, rmodcore, rmodcore_len);
351 mateuszvis 157
 
1587 mateusz.vi 158
  /* mark rmod memory (MCB) as "self owned" */
351 mateuszvis 159
  mcb = MK_FP(rmodseg - 1, 0);
160
  owner = (void far *)(mcb + 1);
161
  *owner = rmodseg;
162
  _fmemcpy(mcb + 8, "SVARCOM", 8);
163
 
1587 mateusz.vi 164
  /* mark env memory (MCB) as "owned by rmod" */
359 mateuszvis 165
  mcb = MK_FP(envseg - 1, 0);
166
  owner = (void far *)(mcb + 1);
167
  *owner = rmodseg;
168
  _fmemcpy(mcb + 8, "SVARENV", 8);
351 mateuszvis 169
 
449 mateuszvis 170
  /* if env block is newly allocated, fill it with a few NULLs */
171
  if (envsize != 0) {
172
    owner = MK_FP(envseg, 0);
173
    owner[0] = 0;
174
    owner[1] = 0;
175
  }
176
 
537 mateuszvis 177
  /* set CTRL+BREAK handler to rmod */
178
  _asm {
179
    push ax
180
    push dx
181
    push ds
182
    mov ax, 0x2523
183
    mov ds, rmodseg
184
    mov dx, RMOD_OFFSET_BRKHANDLER
185
    int 0x21
186
    pop ds
187
    pop dx
188
    pop ax
189
  }
190
 
983 mateusz.vi 191
  /* mark the input buffer as empty */
192
  myptr = MK_FP(rmodseg, RMOD_OFFSET_INPUTBUF);
987 mateusz.vi 193
  myptr[0] = 128;  /* max acceptable length */
194
  myptr[1] = 0;    /* len of currently stored history string */
195
  myptr[2] = '\r'; /* string terminator */
196
  myptr[3] = 0xCA; /* signature to detect stack overflow damaging the buffer */
197
  myptr[4] = 0xFE; /* 2nd byte of the signature */
983 mateusz.vi 198
 
449 mateuszvis 199
  /* prepare result (rmod props) */
478 mateuszvis 200
  res = MK_FP(rmodseg, 0x100 + rmodcore_len);
450 mateuszvis 201
  _fmemset(res, 0, sizeof(*res));  /* zero out */
202
  res->rmodseg = rmodseg;          /* rmod segment */
453 mateuszvis 203
  res->origenvseg = origenvseg;    /* original environment segment */
449 mateuszvis 204
 
459 mateuszvis 205
  /* write env segment to rmod's PSP */
351 mateuszvis 206
  owner = MK_FP(rmodseg, RMOD_OFFSET_ENVSEG);
207
  *owner = envseg;
208
 
366 mateuszvis 209
  /* write boot drive to rmod bootdrive field */
210
  _asm {
211
    push ax
212
    push bx
213
    push dx
214
    push ds
215
    mov ax, 0x3305 /* DOS 4.0+ - GET BOOT DRIVE */
216
    int 0x21 /* boot drive is in DL now (1=A:, 2=B:, etc) */
217
    add dl, 'A'-1 /* convert to a proper ASCII letter */
218
    /* set DS to rmodseg */
219
    mov ax, rmodseg
220
    mov ds, ax
221
    /* write boot drive to rmod bootdrive field */
222
    mov bx, RMOD_OFFSET_BOOTDRIVE
223
    mov [bx], dl
224
    pop ds
225
    pop dx
226
    pop bx
227
    pop ax
228
  }
229
 
450 mateuszvis 230
  /* save my original parent in rmod's memory */
231
  res->origparent = *((unsigned long *)0x0a); /* original parent seg:off is at 0x0a of my PSP */
232
 
448 mateuszvis 233
  /* set the int22 handler in my PSP to rmod so DOS jumps to rmod after I
234
   * terminate and save the original handler in rmod's memory */
454 mateuszvis 235
  {
236
    unsigned short *ptr = (void *)0x0a; /* int22 handler is at 0x0A of the PSP */
237
    ptr[0] = RMOD_OFFSET_ROUTINE;
238
    ptr[1] = rmodseg;
351 mateuszvis 239
  }
240
 
449 mateuszvis 241
  return(res);
351 mateuszvis 242
}
243
 
244
 
449 mateuszvis 245
/* look up my parent: if it's rmod then return a ptr to its props struct,
975 mateusz.vi 246
 * otherwise return NULL
983 mateusz.vi 247
 * I look at PSP[Ch] to locate RMOD (ie. the "terminate address") */
479 mateuszvis 248
struct rmod_props far *rmod_find(unsigned short rmodcore_len) {
983 mateusz.vi 249
  unsigned short *parent = (void *)0x0C;
448 mateuszvis 250
  unsigned short far *ptr;
251
  const unsigned short sig[] = {0x1983, 0x1985, 0x2017, 0x2019};
465 mateuszvis 252
  unsigned char *cmdtail = (void *)0x80;
448 mateuszvis 253
  unsigned char i;
254
  /* is it rmod? */
459 mateuszvis 255
  ptr = MK_FP(*parent, 0x100);
449 mateuszvis 256
  for (i = 0; i < 4; i++) if (ptr[i] != sig[i]) return(NULL);
465 mateuszvis 257
  /* match successfull (rmod is my parent) - but is it really a respawn?
258
   * command-line tail should contain a single character '\r' */
259
  if ((cmdtail[0] != 1) || (cmdtail[1] != '\n')) return(NULL);
260
  cmdtail[0] = 0;
261
  cmdtail[1] = '\r';
262
  /* */
478 mateuszvis 263
  return(MK_FP(*parent, 0x100 + rmodcore_len));
351 mateuszvis 264
}
367 mateuszvis 265
 
266
 
267
/* update rmod's pointer to comspec */
268
void rmod_updatecomspecptr(unsigned short rmod_seg, unsigned short env_seg) {
269
  unsigned short far *comspecptr = MK_FP(rmod_seg, RMOD_OFFSET_COMSPECPTR);
439 mateuszvis 270
  char far *comspecfp = env_lookup_val(env_seg, "COMSPEC");
367 mateuszvis 271
  if (comspecfp != NULL) {
439 mateuszvis 272
    *comspecptr = FP_OFF(comspecfp);
367 mateuszvis 273
  } else {
274
    *comspecptr = 0;
275
  }
276
}
949 mateusz.vi 277
 
278
 
279
/* allocates bytes of far memory, flags it as belonging to rmod
957 mateusz.vi 280
 * the new block can be optionally flagged as 'ident' (if not null) and zero
281
 * out the newly allocated memory.
949 mateusz.vi 282
 * returns a far ptr to the allocated block, or NULL on error */
957 mateusz.vi 283
void far *rmod_fcalloc(unsigned short bytes, unsigned short rmod_seg, char *ident) {
949 mateusz.vi 284
  unsigned short far *owner;
285
  unsigned short newseg = 0;
286
 
287
  /* ask DOS for a memory block (as high as possible) */
288
  _asm {
289
    push bx /* save initial value in BX so I can restore it later */
290
 
291
    /* get current allocation strategy and save it on stack */
292
    mov ax, 0x5800
293
    int 0x21
294
    push ax
295
 
296
    /* set strategy to 'last fit, try high then low memory' */
297
    mov ax, 0x5801
298
    mov bx, 0x0082
299
    int 0x21
300
 
301
    /* ask for a memory block and save the given segment to rmodseg */
302
    mov ah, 0x48  /* Allocate Memory */
303
    mov bx, bytes
304
    add bx, 15    /* convert bytes to paragraphs */
305
    shr bx, 1     /* bx /= 16 */
306
    shr bx, 1
307
    shr bx, 1
308
    shr bx, 1
309
    int 0x21
310
 
311
    /* error handling */
312
    jc FAIL
313
 
314
    /* save newly allocated segment to newseg */
315
    mov newseg, ax
316
 
317
    FAIL:
318
    /* restore initial allocation strategy */
319
    mov ax, 0x5801
320
    pop bx
321
    int 0x21
322
 
323
    pop bx /* restore BX to its initial value */
324
  }
325
 
326
  if (newseg == 0) return(NULL);
327
 
328
  /* mark memory as "owned by rmod" */
329
  owner = (void far *)(MK_FP(newseg - 1, 1));
330
  *owner = rmod_seg;
331
 
332
  /* set the MCB description to ident, if provided */
333
  if (ident) {
334
    char far *mcbdesc = MK_FP(newseg - 1, 8);
335
    int i;
336
    _fmemset(mcbdesc, 0, 8);
337
    for (i = 0; (i < 8) && (ident[i] != 0); i++) { /* field's length is limited to 8 bytes max */
338
      mcbdesc[i] = ident[i];
339
    }
340
  }
341
 
957 mateusz.vi 342
  /* zero out the memory before handing it out */
343
  _fmemset(MK_FP(newseg, 0), 0, bytes);
344
 
949 mateusz.vi 345
  return(MK_FP(newseg, 0));
346
}
347
 
348
 
957 mateusz.vi 349
/* free memory previously allocated by rmod_fcalloc() */
949 mateusz.vi 350
void rmod_ffree(void far *ptr) {
351
  unsigned short ptrseg;
352
  unsigned short myseg = 0;
353
  unsigned short far *owner;
354
  if (ptr == NULL) return;
355
  ptrseg = FP_SEG(ptr);
356
 
357
  /* get my own segment */
358
  _asm {
359
    mov myseg, cs
360
  }
361
 
362
  /* mark memory in MCB as my own, otherwise DOS might refuse to free it */
363
  owner = MK_FP(ptrseg - 1, 1);
364
  *owner = myseg;
365
 
366
  /* free the memory block */
367
  _asm {
368
    push es
369
    mov ah, 0x49  /* Free Memory Block */
370
    mov es, ptrseg
371
    int 0x21
372
    pop es
373
  }
374
}
963 mateusz.vi 375
 
376
 
377
/* free the entire linked list of bat ctx nodes (and set its rmod ptr to NULL) */
378
void rmod_free_bat_llist(struct rmod_props far *rmod) {
379
  while (rmod->bat != NULL) {
380
    struct batctx far *victim = rmod->bat;
381
    rmod->bat = rmod->bat->parent;
382
    rmod_ffree(victim);
383
  }
384
}