Subversion Repositories SvarDOS

/*

 * SvarCOM is a command-line interpreter.

 *

 * a little memory area is allocated as high as possible. it contains:

 *  - a signature (like XMS drivers do)

 *  - a routine for exec'ing programs

 *  - a "last command" buffer for input history

 *

 * when svarcom starts, it tries locating the routine in memory.

 *

 * if found:

 *   waits for user input and processes it. if execing something is required, set the "next exec" field in routine's memory and quit.

 *

 * if not found:

 *   installs it by creating a new PSP, set int 22 vector to the routine, set my "parent PSP" to the routine

 *   and quit.

 *

 *

 *

 * good lecture about PSP and allocating memory

 * https://retrocomputing.stackexchange.com/questions/20001/how-much-of-the-program-segment-prefix-area-can-be-reused-by-programs-with-impun/20006#20006

 *

 * PSP structure

 * http://www.piclist.com/techref/dos/psps.htm

 *

 *

 *

 * === MCB ===

 *

 * each time that DOS allocates memory, it prefixes the allocated memory with

 * a 16-bytes structure called a "Memory Control Block" (MCB). This control

 * block has the following structure:

 *

 * Offset  Size     Description

 *   00h   byte     'M' =  non-last member of the MCB chain

 *                  'Z' = indicates last entry in MCB chain

 *                  other values cause "Memory Allocation Failure" on exit

 *   01h   word     PSP segment address of the owner (Process Id)

 *                  possible values:

 *                    0 = free

 *                    8 = Allocated by DOS before first user pgm loaded

 *                    other = Process Id/PSP segment address of owner

 *   03h  word      number of paragraphs related to this MCB (excluding MCB)

 *   05h  11 bytes  reserved

 *   10h  ...       start of actual allocated memory block

 */

#include <i86.h>

#include <dos.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <process.h>

#include "cmd.h"

#include "env.h"

#include "helpers.h"

#include "rmodinit.h"

struct config {

  int locate;

  int install;

  int envsiz;

} cfg;

static void parse_argv(struct config *cfg, int argc, char **argv) {

  int i;

  memset(cfg, 0, sizeof(*cfg));

  for (i = 1; i < argc; i++) {

    if (strcmp(argv[i], "/locate") == 0) {

      cfg->locate = 1;

    }

    if (strstartswith(argv[i], "/e:") == 0) {

      cfg->envsiz = atoi(argv[i]+3);

      if (cfg->envsiz < 64) cfg->envsiz = 0;

    }

  }

}

static void buildprompt(char *s, const char *fmt) {

  for (; *fmt != 0; fmt++) {

    if (*fmt != '$') {

      *s = *fmt;

      s++;

      continue;

    }

    /* escape code ($P, etc) */

    fmt++;

    switch (*fmt) {

      case 'Q':  /* $Q = = (equal sign) */

      case 'q':

        *s = '=';

        s++;

        break;

      case '$':  /* $$ = $ (dollar sign) */

        *s = '$';

        s++;

        break;

      case 'T':  /* $t = current time */

      case 't':

        s += sprintf(s, "00:00"); /* TODO */

        break;

      case 'D':  /* $D = current date */

      case 'd':

        s += sprintf(s, "1985-07-29"); /* TODO */

        break;

      case 'P':  /* $P = current drive and path */

      case 'p':

        _asm {

          mov ah, 0x19    /* DOS 1+ - GET CURRENT DRIVE */

          int 0x21

          mov bx, s

          mov [bx], al  /* AL = drive (00 = A:, 01 = B:, etc */

        }

        *s += 'A';

        s++;

        *s = ':';

        s++;

        *s = '\\';

        s++;

        _asm {

          mov ah, 0x47    /* DOS 2+ - CWD - GET CURRENT DIRECTORY */

          xor dl,dl       /* DL = drive number (00h = default, 01h = A:, etc) */

          mov si, s       /* DS:SI -> 64-byte buffer for ASCIZ pathname */

          int 0x21

        }

        while (*s != 0) s++; /* move ptr forward to end of pathname */

        break;

      case 'V':  /* $V = DOS version number */

      case 'v':

        s += sprintf(s, "VER"); /* TODO */

        break;

      case 'N':  /* $N = current drive */

      case 'n':

        _asm {

          mov ah, 0x19    /* DOS 1+ - GET CURRENT DRIVE */

          int 0x21

          mov bx, s

          mov [bx], al  /* AL = drive (00 = A:, 01 = B:, etc */

        }

        *s += 'A';

        s++;

        break;

      case 'G':  /* $G = > (greater-than sign) */

      case 'g':

        *s = '>';

        s++;

        break;

      case 'L':  /* $L = < (less-than sign) */

      case 'l':

        *s = '<';

        s++;

        break;

      case 'B':  /* $B = | (pipe) */

      case 'b':

        *s = '|';

        s++;

        break;

      case 'H':  /* $H = backspace (erases previous character) */

      case 'h':

        *s = '\b';

        s++;

        break;

      case 'E':  /* $E = Escape code (ASCII 27) */

      case 'e':

        *s = 27;

        s++;

        break;

      case '_':  /* $_ = CR+LF */

        *s = '\r';

        s++;

        *s = '\n';

        s++;

        break;

    }

  }

  *s = '$';

}

static void run_as_external(const char far *cmdline) {

  char buff[256];

  char const *argvlist[256];

  int i, n;

  /* copy buffer to a near var (incl. trailing CR), insert a space before

     every slash to make sure arguments are well separated */

  n = 0;

  i = 0;

  for (;;) {

    if (cmdline[i] == '/') buff[n++] = ' ';

    buff[n++] = cmdline[i++];

    if (buff[n] == 0) break;

  }

  cmd_explode(buff, cmdline, argvlist);

  /* for (i = 0; argvlist[i] != NULL; i++) printf("arg #%d = '%s'\r\n", i, argvlist[i]); */

  /* must be an external command then. this call should never return, unless

   * the other program failed to be executed. */

  execvp(argvlist[0], argvlist);

}

static void set_comspec_to_self(unsigned short envseg) {

  unsigned short *psp_envseg = (void *)(0x2c); /* pointer to my env segment field in the PSP */

  char far *myenv = MK_FP(*psp_envseg, 0);

  unsigned short varcount;

  char buff[256] = "COMSPEC=";

  char *buffptr = buff + 8;

  /* who am i? look into my own environment, at the end of it should be my EXEPATH string */

  while (*myenv != 0) {

    /* consume a NULL-terminated string */

    while (*myenv != 0) myenv++;

    /* move to next string */

    myenv++;

  }

  /* get next word, if 1 then EXEPATH follows */

  myenv++;

  varcount = *myenv;

  myenv++;

  varcount |= (*myenv << 8);

  myenv++;

  if (varcount != 1) return; /* NO EXEPATH FOUND */

  while (*myenv != 0) {

    *buffptr = *myenv;

    buffptr++;

    myenv++;

  }

  *buffptr = 0;

  /* printf("EXEPATH: '%s'\r\n", buff); */

  env_setvar(envseg, buff);

}

int main(int argc, char **argv) {

  struct config cfg;

  unsigned short rmod_seg;

  unsigned short far *rmod_envseg;

  unsigned short far *lastexitcode;

  parse_argv(&cfg, argc, argv);

  rmod_seg = rmod_find();

  if (rmod_seg == 0xffff) {

    rmod_seg = rmod_install(cfg.envsiz);

    if (rmod_seg == 0xffff) {

      puts("ERROR: rmod_install() failed");

      return(1);

    }

    printf("rmod installed at seg 0x%04X\r\n", rmod_seg);

  } else {

    printf("rmod found at seg 0x%04x\r\n", rmod_seg);

  }

  rmod_envseg = MK_FP(rmod_seg, RMOD_OFFSET_ENVSEG);

  lastexitcode = MK_FP(rmod_seg, RMOD_OFFSET_LEXITCODE);

  /* make COMPSEC point to myself */

  set_comspec_to_self(*rmod_envseg);

  {

    unsigned short envsiz;

    unsigned short far *sizptr = MK_FP(*rmod_envseg - 1, 3);

    envsiz = *sizptr;

    envsiz *= 16;

    printf("rmod_inpbuff at %04X:%04X, env_seg at %04X:0000 (env_size = %u bytes)\r\n", rmod_seg, RMOD_OFFSET_INPBUFF, *rmod_envseg, envsiz);

  }

  for (;;) {

    char far *cmdline = MK_FP(rmod_seg, RMOD_OFFSET_INPBUFF + 2);

    /* revert input history terminator to \r */

    if (cmdline[-1] != 0) {

      cmdline[(unsigned short)(cmdline[-1])] = '\r';

    }

    {

      /* print shell prompt */

      char buff[256];

      char *promptptr = buff;

      buildprompt(promptptr, "$p$g"); /* TODO: prompt should be configurable via environment */

      _asm {

        push ax

        push dx

        mov ah, 0x09

        mov dx, promptptr

        int 0x21

        pop dx

        pop ax

      }

    }

    /* wait for user input */

    _asm {

      push ax

      push bx

      push cx

      push dx

      push ds

      /* is DOSKEY support present? (INT 2Fh, AX=4800h, returns non-zero in AL if present) */

      mov ax, 0x4800

      int 0x2f

      mov bl, al /* save doskey status in BL */

      /* set up buffered input */

      mov ax, rmod_seg

      push ax

      pop ds

      mov dx, RMOD_OFFSET_INPBUFF

      /* execute either DOS input or DOSKEY */

      test bl, bl /* zf set if no DOSKEY present */

      jnz DOSKEY

      mov ah, 0x0a

      int 0x21

      jmp short DONE

      DOSKEY:

      mov ax, 0x4810

      int 0x2f

      DONE:

      pop ds

      pop dx

      pop cx

      pop bx

      pop ax

    }

    printf("\r\n");

    /* if nothing entered, loop again */

    if (cmdline[-1] == 0) continue;

    /* replace \r by a zero terminator */

    cmdline[(unsigned char)(cmdline[-1])] = 0;

    /* move pointer forward to skip over any leading spaces */

    while (*cmdline == ' ') cmdline++;

    /* update rmod's ptr to COMPSPEC so it is always up to date */

    rmod_updatecomspecptr(rmod_seg, *rmod_envseg);

    /* try matching (and executing) an internal command */

    {

      int ecode = cmd_process(*rmod_envseg, cmdline);

      if (ecode >= 0) *lastexitcode = ecode;

      if (ecode >= -1) continue; /* internal command executed */

    }

    /* if here, then this was not an internal command */

    run_as_external(cmdline);

    /* execvp() replaces the current process by the new one

    if I am still alive then external command failed to execute */

    puts("Bad command or file name");

  }

  return(0);

}