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From: pozar@hoptoad.uucp (Tim Pozar)
Newsgroups: comp.sys.ibm.pc
Subject: Finding the address of functions in MSC, and the ^C interupt
Message-ID: <2042@hoptoad.uucp>
Date: Fri, 24-Apr-87 22:58:10 EDT
Article-I.D.: hoptoad.2042
Posted: Fri Apr 24 22:58:10 1987
Date-Received: Sun, 26-Apr-87 20:17:46 EDT
Reply-To: pozar@hoptoad.UUCP (Tim Pozar)
Organization: Syncstream (San Francisco)
Lines: 210


   I was wondering how one finds the address of a function and would 
apply it to setting a vector interupt with it.  This is the code that
I came up with.  It compiles with one error (see below).  If anyone
has any insite on how this could be better done, I would like to 
hear it.
            Tim Pozar

---
/*
 * CTLC.C
 *
 *    A control-break or ^C handler demo. 
 *
 *    This programme will push the "DOS CONTROL-C Exit Address" vector
 * and set it to the "bye()" function.  bye() should pop the old 
 * address and then executes the users code.  The old vector should
 * be restored if the programme ends through the remaped vector or before
 * a standard exit().  bye() should also come before the retrival of the 
 * function's address with the way MSC is set up.
 *
 *    This is a way to make graceful exits from complex programmes that
 * may have several files open or be communication programmes that need
 * to handle the comm paths a paticular way to exit properly.  (Well, *I* 
 * thought it was an interesting hack in "C" !)
 *
 *    CTLC will count 20 seconds and exit, or if the user types a ^C or 
 * a CONTROL-BREAK the programme will exit with our routine.  If a char
 * is typed before the ^C is entered, the programme will exit normally 
 * because the keyboard buffer is not polled.  To correct this, keep 
 * checking on the kbhit() function supplied with MSC 4.0 and call on 
 * the console input, or keep watching the int 9 (KB_INT) for a keyboard
 * hit while you're in your routine.
 *
 *    I would guess you could make this function return back into the 
 * programme by having it call a assembly function that would pop an 
 * appropiate number off the stack and then execute an "iret". (messy)
 *
 * BUGS:
 *    Because we don't disable the interupts, if an interupt occurs while 
 * the programme is in the middle of stuffing the new or old address, your
 * up the creek.
 *    Also do not change the vector to the BIOS ^C vector (1Ah).  It seems 
 * that DOS has a go at the keyboard break first and so it exits leaving 
 * the modified vector unrestored.
 *
 *    This source is complier dependent.  It was written for the Microsoft
 * C Compiler 4.0.  And it goes without saying, it is VERY DOS dependent.
 *    
 *    At this point there is a complie waring at "funcp = bye;" in the 
 * main function.  But everything works perfectly.  Has anyone any ideas
 * on how to make this compile cleanly?
 *
 *    Tim Pozar -- 24.April.1987
 *    pozar@hoptoad.UUCP or Tim Pozar at Fido 125/406
 *    KLOK-FM
 *    77 Maiden Lane
 *    San Francisco CA 94108
 *    (415) 788-2022
 *
 *    Copyright 1987 Timothy M. Pozar -- All rights reserved.
 *
 */
 
#include <stdio.h>
#include <dos.h>
 
#define CNTLBK 0x23
#define SET_VECTOR 0x25
#define GET_TIME 0x2c
#define GET_VECTOR 0x35	
 
typedef struct timetype {
    unsigned hour;
    unsigned minute;
    unsigned sec;
    unsigned hsec;
} TIME, *TIME_PTR;
 
unsigned int pvoff;
unsigned int pvseg;
 
/*
 *  bye()
 * 
 *  If a keyboard break occurs, this routine is executed.
 *  This routine needs to be stuck into the vector table and taken out 
 *  properly when the programme exits.
 *
 */
 
bye()
{
  set_int(CNTLBK,pvseg,pvoff);	/* reset old vector */
 
/*
 *       Put code here.
 */
 
  printf("Restoreing old keyboard vector and exiting. \n");
  exit(0);
}
 
main()
{
char far *funcp;
unsigned int off;
unsigned int seg;
 
  funcp = bye;
  off = FP_OFF(funcp);
  seg = FP_SEG(funcp);
 
  set_int(CNTLBK,seg,off);
 
  printf("bye() is located at %04X:%04X.\n",seg,off);
  printf("The breakint was located at %04X:%04X.\n",pvseg,pvoff);
 
  sleep(20);
  printf("No keyboard break.  Exiting normally.\n");
  bye();
}
 
/*
 * set_int(n,segm,offs)
 *
 *   Set the interupt speced with the segment and offset passed to it,
 * and push its old address vector.
 *
 */
 
set_int(n,segm,offs)
int n;				/* interupt number */
unsigned int segm, offs;	/* segment and offset to point to */
{
  union REGS inregs;
  union REGS outregs;
  struct SREGS segregs;
 
  inregs.h.ah = GET_VECTOR;	/* get orginal vector */
  inregs.h.al = n;
  intdosx(&inregs, &outregs, &segregs);
  pvoff = outregs.x.bx;		/* push it old vector offset */
  pvseg = segregs.es;		/* and segment */
 
  inregs.h.ah = SET_VECTOR;	/* set new vector */
  inregs.h.al = n;
  inregs.x.dx = offs;
  segregs.ds = segm;
  intdosx(&inregs, &outregs, &segregs);
 
  return(0);
}
 
/*
 *
 * get_time(n)
 * TIME_PTR n;
 *
 *    Fills timetype structure n with current time.  This function could
 * be replace by calles to time() and then gmtime() to get a structor,
 * but since were fooling with vectors anyway...
 *
 */
 
get_time(n)
TIME_PTR n;
{
  union REGS inregs;
  union REGS outregs;
 
  inregs.h.ah = GET_TIME;
 
  intdos(&inregs, &outregs);
 
  n->hour = outregs.h.ch;
  n->minute  = outregs.h.cl;
  n->sec  = outregs.h.dh;
  n->hsec = outregs.h.dl;
 
  return(0);
}
 
sleep(x)
int x;
{
  int i;
  unsigned s;
  TIME n;               	/* current time record */
 
  i = 0;
  get_time(&n);
  s = n.sec;
 
  while (i < x){
  printf("secs = %d \r",i);	/* for debug only */
    while (s == n.sec)          /* while Mickey's hand hasn't moved... */
      get_time(&n);
    s = n.sec;			/* if Mickey's hand moved... */
    ++i;			/* increment the counter */
  }
}

-- 
        Tim Pozar
UUCP    pozar@hoptoad.UUCP
Fido    125/406
USNail  KLOK-FM
	77 Maiden Lane
	San Francisco CA 94108