From:	Roman Suzi <nuser AT rsuzi DOT pgu DOT karelia DOT ru>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: General Protection Fault interception vs. Checking stack
Date:	Sat, 08 Nov 97 09:40:38 +0300
Distribution:	su
Organization:	unknown
Message-ID:	<ABcb0PqSO6@rsuzi.pgu.karelia.ru>
Sender:	news-service AT sampo DOT karelia DOT ru
Reply-To:	nuser AT rsuzi DOT pgu DOT karelia DOT ru
Lines:	70
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Hi!

Nate Eldredge (was it in private letter?) wrote:

        This example worked for me under both CWSDPMI r3 and Windows 3.1.

        #include <stdio.h>
        #include <signal.h>

        void handler(int sig)
        {
          printf("Received signal %d\n",sig);
          fflush(stdout);
          /* clean up */
          exit(1); /* or whatever else */
        }

        int main(void)
        {
          signal(SIGSEGV,handler);
          /* Overflow the stack */
          alloca(1000000);
          /* Touch the stack to cause a fault */
          printf("This isn't going to work");
          return 0;
        }

        Running it prints "Received signal 291", which is evidently SIGSEGV.

Yes, the example works. And this one doesn't under the same circumstances
(dont optimize to preserve recursion!):


#include <stdio.h>
#include <signal.h>

void handler(int sig)
{
  fprintf(stderr, "Received signal %d\n",sig);
  fflush(stderr);
  exit(1); /* or whatever else */
}

/* deeply recursive */
int myproc(int a, double t)
{
  if (a<0) return 1;
  else return myproc(a-1, a+0.23);
}

int main(void)
{
  signal(SIGSEGV,handler);

  /* Overflow the stack with recursive calls */
  myproc(1000000, 23.4);

  printf("No stack overflow.");
  return 0;
}




--
 --               *                            --
--  Roman A. Suzi * Petrozavodsk Karelia Russia --
 --    http://sampo.karelia.ru/~rnd            --

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