Category : Files from Magazines
Archive   : CGAZV4N2.ZIP
Filename : BLOWSTK.C

/**********************************************************************
* blowstk.c - demonstrate stack overflow checking
*
* Author: John Rex
* Date: July, 1989
* Compilers: Turbo C 2.0, MSC 5.1
* Memory model: any
* Compile time switches:
* SAFETY_MARGIN - minimum number of bytes that we are willing to
* leave free on the stack for system interrupts,
* calls to error handling routines, etc.
*
* Usage: Just compile and invoke. It runs a recursive routine to blow
* the stack. The number of successful calls is reported.
*
* Sources: This code was derived from study of the Turbo C and Microsoft
* C run-time libraries and startup code.
*
* Source code and object code may be used freely.
********************************************************************/

#define SAFETY_MARGIN 500

#if defined(__TURBOC__)
#if defined(__SMALL__) || defined(__MEDIUM__) || defined(__TINY__)
#define TURBOSMALL
#else
#define TURBOLARGE
#endif
#else
#define MSC
#endif

int count; /* set to max # of calls we were able to make */

void blowstack(int i)
{
/* stack check protocols */

#if defined(TURBOSMALL)
extern unsigned __brklvl;

if (_SP < (__brklvl + SAFETY_MARGIN)) { /* true if blown */
count = i;
return;
}
#endif

#if defined(TURBOLARGE)
if (_SP < SAFETY_MARGIN) { /* true if blown */
count = i;
return;
}
#endif

#if defined(MSC)
unsigned getsp();
extern int end;

if ( getsp() < (((unsigned) &end) + SAFETY_MARGIN)) { /* true if blown */
count = i;
return;
}
#endif

/* otherwise, recurse! */
blowstack(i+1);
}

#include
void main()
{
blowstack(1);
printf("Blowstack() made %d calls\n", count);
}