Subversion Repositories SvarDOS

/* This file is part of the SvarCOM project and is published under the terms

 * of the MIT license.

 *

 * Copyright (C) 2021-2024 Mateusz Viste

 *

 * Permission is hereby granted, free of charge, to any person obtaining a

 * copy of this software and associated documentation files (the "Software"),

 * to deal in the Software without restriction, including without limitation

 * the rights to use, copy, modify, merge, publish, distribute, sublicense,

 * and/or sell copies of the Software, and to permit persons to whom the

 * Software is furnished to do so, subject to the following conditions:

 *

 * The above copyright notice and this permission notice shall be included in

 * all copies or substantial portions of the Software.

 *

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING

 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER

 * DEALINGS IN THE SOFTWARE.

 */

#include <i86.h>

#include <string.h>

#include "env.h"

#include "helpers.h"

#include "rmodinit.h"

/* returns far pointer to rmod's settings block on success */

struct rmod_props far *rmod_install(unsigned short envsize, unsigned char *rmodcore, unsigned short rmodcore_len) {

  char far *myptr, far *mcb;

  unsigned short far *owner;

  const unsigned short sizeof_rmodandprops_paras = (0x100 + rmodcore_len + sizeof(struct rmod_props) + 15) / 16;

  unsigned short rmodseg = 0xffff;

  unsigned short envseg, origenvseg;

  struct rmod_props far *res;

  /* read my current env segment from PSP and save it */

  envseg = *((unsigned short *)0x2c);

  origenvseg = envseg;

  /* printf("original (PSP) env buffer at %04X\r\n", envseg); */

  /* if envseg is zero, then enforce our own one (MSDOS 5 does not provide a default env) */

  if ((envseg == 0) && (envsize == 0)) envsize = 256;

  /* if custom envsize requested, convert it to number of paragraphs */

  if (envsize != 0) {

    envsize += 15;

    envsize /= 16;

  }

  _asm {

    push bx

    push cx

    push dx

    /* link in the UMB memory chain for enabling high-memory allocation (and save initial status on stack) */

    mov ax, 0x5802  /* GET UMB LINK STATE */

    int 0x21

    xor ah, ah

    push ax         /* save link state on stack */

    mov ax, 0x5803  /* SET UMB LINK STATE */

    mov bx, 1

    int 0x21

    /* get current allocation strategy and save it in DX */

    mov ax, 0x5800

    int 0x21

    push ax

    pop dx

    /* set strategy to 'last fit, try high then low memory' */

    mov ax, 0x5801

    mov bx, 0x0082

    int 0x21

    /* ask for a memory block and save the given segment to rmodseg */

    mov ah, 0x48

    mov bx, sizeof_rmodandprops_paras

    int 0x21

    jc ALLOC_FAIL

    mov rmodseg, ax

    /* ask for a memory block for the environment and save it to envseg (only if custom size requested) */

    mov bx, envsize

    test bx, bx

    jz ALLOC_FAIL

    mov ah, 0x48

    int 0x21

    jc ALLOC_FAIL

    mov envseg, ax

    ALLOC_FAIL:

    /* restore initial allocation strategy */

    mov ax, 0x5801

    mov bx, dx

    int 0x21

    /* restore initial UMB memory link state */

    mov ax, 0x5803

    pop bx       /* pop initial UMB link state from stack */

    int 0x21

    pop dx

    pop cx

    pop bx

  }

  if (rmodseg == 0xffff) {

    outputnl("malloc error");

    return(NULL);

  }

  /* generate a new PSP where RMOD is about to land */

  _asm {

    push dx

    mov ah, 0x26 /* CREATE NEW PROGRAM SEGMENT PREFIX (DOS 1+) */

    mov dx, rmodseg

    int 0x21

    pop dx

  }

  myptr = MK_FP(rmodseg, 0);

  /* patch up RMOD's PSP: Parent's PSP segment @ 0x16-0x17 */

  myptr[0x16] = rmodseg & 0xff; /* RMOD is his own parent */

  myptr[0x17] = rmodseg >> 8;

  /* patch up RMOD's PSP: SS:SP pointer @ 0x2E-0x31  --  I abuse the PSP's

   * command line tail as stack, but I do NOT set the stack at the end of the

   * tail. E. C. Masloch kindly explained why this would be a bad idea:

   *

   * "This is wrong and will potentially overwrite part of your buffers that

   * start past the PSP. This is because the dword [PSP:2Eh] is not used merely

   * to set SS:SP but rather to find the stack frame created by the int 21h

   * call. Therefore the int 21h call that terminates the child process will

   * then pop a number of registers off starting from the address stored in the

   * PSP." <https://github.com/SvarDOS/bugz/issues/38#issuecomment-1817445740>

   */

  myptr[0x2e] = 192; /* middle of the command line tail area so I have 64 bytes */

  myptr[0x2f] = 0;   /* before and 64 bytes in front of me */

  myptr[0x30] = rmodseg & 0xff;

  myptr[0x31] = rmodseg >> 8;

  /* patch up RMOD's PSP: JFT size @ 0x32-0x33 */

  myptr[0x32] = 20; /* default JFT size (max that fits without an extra allocation) */

  myptr[0x33] = 0;

  /* patch up RMOD's PSP: JFT pointer @ 0x34-0x37 */

  myptr[0x34] = 0x18; /* the JFT is in the PSP itself */

  myptr[0x35] = 0;

  myptr[0x36] = rmodseg & 0xff;

  myptr[0x37] = rmodseg >> 8;

  /* patch up RMOD's PSP: pointer to previous PSP @ 0x38-0x3B */

  myptr[0x38] = 0;

  myptr[0x39] = 0;

  myptr[0x3A] = rmodseg & 0xff;

  myptr[0x3B] = rmodseg >> 8;

  /* copy rmod to its destination (right past the PSP I prepared) */

  myptr = MK_FP(rmodseg, 0x100);

  _fmemcpy(myptr, rmodcore, rmodcore_len);

  /* mark rmod memory (MCB) as "self owned" */

  mcb = MK_FP(rmodseg - 1, 0);

  owner = (void far *)(mcb + 1);

  *owner = rmodseg;

  _fmemcpy(mcb + 8, "SVARCOM", 8);

  /* mark env memory (MCB) as "owned by rmod" */

  mcb = MK_FP(envseg - 1, 0);

  owner = (void far *)(mcb + 1);

  *owner = rmodseg;

  _fmemcpy(mcb + 8, "SVARENV", 8);

  /* if env block is newly allocated, fill it with a few NULLs */

  if (envsize != 0) {

    owner = MK_FP(envseg, 0);

    owner[0] = 0;

    owner[1] = 0;

  }

  /* set CTRL+BREAK handler to rmod */

  _asm {

    push ax

    push dx

    push ds

    mov ax, 0x2523

    mov ds, rmodseg

    mov dx, RMOD_OFFSET_BRKHANDLER

    int 0x21

    pop ds

    pop dx

    pop ax

  }

  /* mark the input buffer as empty */

  myptr = MK_FP(rmodseg, RMOD_OFFSET_INPUTBUF);

  myptr[0] = 128;  /* max acceptable length */

  myptr[1] = 0;    /* len of currently stored history string */

  myptr[2] = '\r'; /* string terminator */

  myptr[3] = 0xCA; /* signature to detect stack overflow damaging the buffer */

  myptr[4] = 0xFE; /* 2nd byte of the signature */

  /* prepare result (rmod props) */

  res = MK_FP(rmodseg, 0x100 + rmodcore_len);

  _fmemset(res, 0, sizeof(*res));  /* zero out */

  res->rmodseg = rmodseg;          /* rmod segment */

  res->origenvseg = origenvseg;    /* original environment segment */

  /* write env segment to rmod's PSP */

  owner = MK_FP(rmodseg, RMOD_OFFSET_ENVSEG);

  *owner = envseg;

  /* write boot drive to rmod bootdrive field */

  _asm {

    push ax

    push bx

    push dx

    push ds

    mov ax, 0x3305 /* DOS 4.0+ - GET BOOT DRIVE */

    int 0x21 /* boot drive is in DL now (1=A:, 2=B:, etc) */

    add dl, 'A'-1 /* convert to a proper ASCII letter */

    /* set DS to rmodseg */

    mov ax, rmodseg

    mov ds, ax

    /* write boot drive to rmod bootdrive field */

    mov bx, RMOD_OFFSET_BOOTDRIVE

    mov [bx], dl

    pop ds

    pop dx

    pop bx

    pop ax

  }

  /* save my original int22h handler and parent in rmod's memory */

  res->origint22 = *((unsigned long *)0x0a); /* original int22h handler seg:off is at 0x0a of my PSP */

  res->origparent = *((unsigned short *)0x16); /* PSP segment of my parent is at 0x16 of my PSP */

  /* set the int22 handler in my PSP to rmod so DOS jumps to rmod after I

   * terminate and save the original handler in rmod's memory */

  {

    unsigned short *ptr = (void *)0x0a; /* int22 handler is at 0x0A of the PSP */

    ptr[0] = RMOD_OFFSET_ROUTINE;

    ptr[1] = rmodseg;

  }

  /* set my own parent to RMOD (this is not necessary for MS-DOS nor FreeDOS but

   * might be on other DOS implementations) */

  {

    unsigned short *ptr = (void *)0x16;

    *ptr = rmodseg;

  }

  return(res);

}

/* look up my parent: if it's rmod then return a ptr to its props struct,

 * otherwise return NULL

 * I look at PSP[Ch] to locate RMOD (ie. the "terminate address") */

struct rmod_props far *rmod_find(unsigned short rmodcore_len) {

  unsigned short *parent = (void *)0x0C;

  unsigned short far *ptr;

  const unsigned short sig[] = {0x1983, 0x1985, 0x2017, 0x2019};

  unsigned char *cmdtail = (void *)0x80;

  unsigned char i;

  /* is it rmod? */

  ptr = MK_FP(*parent, 0x100);

  for (i = 0; i < 4; i++) if (ptr[i] != sig[i]) return(NULL);

  /* match successfull (rmod is my parent) - but is it really a respawn?

   * command-line tail should contain a single character '\r' */

  if ((cmdtail[0] != 1) || (cmdtail[1] != '\n')) return(NULL);

  cmdtail[0] = 0;

  cmdtail[1] = '\r';

  /* */

  return(MK_FP(*parent, 0x100 + rmodcore_len));

}

/* update rmod's pointer to comspec */

void rmod_updatecomspecptr(unsigned short rmod_seg, unsigned short env_seg) {

  unsigned short far *comspecptr = MK_FP(rmod_seg, RMOD_OFFSET_COMSPECPTR);

  char far *comspecfp = env_lookup_val(env_seg, "COMSPEC");

  if (comspecfp != NULL) {

    *comspecptr = FP_OFF(comspecfp);

  } else {

    *comspecptr = 0;

  }

}

/* allocates bytes of far memory, flags it as belonging to rmod

 * the new block can be optionally flagged as 'ident' (if not null) and zero

 * out the newly allocated memory.

 * returns a far ptr to the allocated block, or NULL on error */

void far *rmod_fcalloc(unsigned short bytes, unsigned short rmod_seg, char *ident) {

  unsigned short far *owner;

  unsigned short newseg = 0;

  /* ask DOS for a memory block (as high as possible) */

  _asm {

    push bx /* save initial value in BX so I can restore it later */

    /* get current allocation strategy and save it on stack */

    mov ax, 0x5800

    int 0x21

    push ax

    /* set strategy to 'last fit, try high then low memory' */

    mov ax, 0x5801

    mov bx, 0x0082

    int 0x21

    /* ask for a memory block and save the given segment to rmodseg */

    mov ah, 0x48  /* Allocate Memory */

    mov bx, bytes

    add bx, 15    /* convert bytes to paragraphs */

    shr bx, 1     /* bx /= 16 */

    shr bx, 1

    shr bx, 1

    shr bx, 1

    int 0x21

    /* error handling */

    jc FAIL

    /* save newly allocated segment to newseg */

    mov newseg, ax

    FAIL:

    /* restore initial allocation strategy */

    mov ax, 0x5801

    pop bx

    int 0x21

    pop bx /* restore BX to its initial value */

  }

  if (newseg == 0) return(NULL);

  /* mark memory as "owned by rmod" */

  owner = (void far *)(MK_FP(newseg - 1, 1));

  *owner = rmod_seg;

  /* set the MCB description to ident, if provided */

  if (ident) {

    char far *mcbdesc = MK_FP(newseg - 1, 8);

    int i;

    _fmemset(mcbdesc, 0, 8);

    for (i = 0; (i < 8) && (ident[i] != 0); i++) { /* field's length is limited to 8 bytes max */

      mcbdesc[i] = ident[i];

    }

  }

  /* zero out the memory before handing it out */

  _fmemset(MK_FP(newseg, 0), 0, bytes);

  return(MK_FP(newseg, 0));

}

/* free memory previously allocated by rmod_fcalloc() */

void rmod_ffree(void far *ptr) {

  unsigned short ptrseg;

  unsigned short myseg = 0;

  unsigned short far *owner;

  if (ptr == NULL) return;

  ptrseg = FP_SEG(ptr);

  /* get my own segment */

  _asm {

    mov myseg, cs

  }

  /* mark memory in MCB as my own, otherwise DOS might refuse to free it */

  owner = MK_FP(ptrseg - 1, 1);

  *owner = myseg;

  /* free the memory block */

  _asm {

    push es

    mov ah, 0x49  /* Free Memory Block */

    mov es, ptrseg

    int 0x21

    pop es

  }

}

/* free the entire linked list of bat ctx nodes (and set its rmod ptr to NULL) */

void rmod_free_bat_llist(struct rmod_props far *rmod) {

  while (rmod->bat != NULL) {

    struct batctx far *victim = rmod->bat;

    rmod->bat = rmod->bat->parent;

    rmod_ffree(victim);

  }

}