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Microsoft OS/2 SDK 03-01-1988

/*
 * Example of DosSetVec usage
 *
 * This call allows a process to register a handler for the 80286
 * exception vectors. This program works Family API.
 *
 * Notes:
 *
 *	When using the divide by zero trap in Family API mode, be
 *	aware that the 8088/86 leaves the instruction pointer one
 *	beyond the faulting instruction, whereas the 286 and 386 in
 *	real mode leave it pointing to the faulting divide instruction.
 *	The example here assumes a 286 or 386 as it tries to restart
 *	the divide instruction.
 *
 *	It is possible, as in this example, to have exception handlers
 *	written in C. In general these will be very simple handlers which
 *	print a message before terminating the program. If you wish to
 *	access the full register set at the time the exception occurred,
 *	or get at the address of the failing instruction, then an assembler
 *	handler is needed. Important caveats for handlers in C:
 *
 *		- disable stack checking in your program (-Gs), since the
 *		  handler is entered with unknown segment registers set up.
 *
 *		- if a program with multiple data segments traps and the
 *		  handler uses the segment registers (which are not saved
 *		  in C), then on return the program will crash. C handlers
 *		  which return to the faulting instruction only work in
 *		  simple cases.
 *
 *	The example here is carefully constructed to successfully return
 *	to the faulting instruction from a C handler. It relies somewhat
 *	on the compiler code generation, and the exact compiler options
 *	used.
 *
 * Compile as: cl -AL -G2 -Gs -Lp setvec.c
 *
 * Created by Microsoft Corp. 1986
 */

#define INCL_DOSMISC

#include <os2def.h>
#include <bsedos.h>

int j = 0;		    /* zero variable for division */

main()
{

  USHORT VecNum;	    /* Exception number (0,4,5,6,7,16) */
  PFN PrevAddress;    /* Storage for old vector address, used to

				reset the vector when finished */
  PFN Dummy;	  /* Dummy variable used when resetting vector */
  int APIENTRY handler();	     /* Name of routine that will handle exception */
  int i = 9;		    /* Variable to be divided by 0 */

    /* Set up handler for Exception 0, 'divide by zero' */
    VecNum = 0;
    DosSetVec(VecNum,handler,&PrevAddress);

    /* Test the handler */
    i = i/j;
    printf("new i = %d\n", i);

    /* Reset handler for exception 0 */
    DosSetVec(VecNum,PrevAddress,&Dummy);
}

/*
 * Handler subroutine for testing DosSetVec above.
 * This is the routine that will get control
 * when the exception occurs.
 */
int APIENTRY handler()
{
      j = 3;    /* Since j=0 caused this exception, setting j=3 will prevent
                   the exception from recurring, when we return */
}

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