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Date:      Wed, 19 Feb 2003 13:23:26 +0100 (CET)
From:      Vaclav Haisman <V.Haisman@sh.cvut.cz>
To:        freebsd-hackers@freebsd.org
Subject:   Raising SIGSEGV in SIGSEGV handler makes FreeBSD loop
Message-ID:  <20030219131316.F68704-100000@logout.sh.cvut.cz>
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Hi,

I have been playing with signals handling and I've found one thing where
FreeBSD differes from other unix systems that I have access to. This test loops
endlessly in FreeBSD but terminates in SunOS 9 and GNU/Linux. It is as test for
what happens when a program raises SIGSEGV in SIGSEGV handler. If this touches
undefined behaviour then I think the behaviour of the other two systems is
saner.

Vaclav Haisman


#include <signal.h>
#include <iostream>

int f (int * x);

void handler (int, siginfo_t * info, ucontext_t * uap)
{
  std::cerr << "SIGSEGV caught, dumping core" << std::endl;
  struct sigaction mysig;
  mysig.sa_handler = SIG_IGN;
  mysig.sa_sigaction = NULL;
  mysig.sa_flags = 0;
  if (sigaction(SIGSEGV, &mysig, NULL) == -1)
    {
      std::cerr << "Error in sigaction()" << std::endl;
      return;
    }

  f((int*)NULL);

  mysig.sa_handler = SIG_DFL;
  mysig.sa_sigaction = NULL;
  mysig.sa_flags = 0;
  if (sigaction(SIGSEGV, &mysig, NULL) == -1)
    {
      std::cerr << "Error in sigaction()" << std::endl;
      return;
    }
}

int f (int * x)
{
  int y = *x;
  return y;
}

int main ()
{
  struct sigaction mysig;
  mysig.sa_handler = NULL;
  mysig.sa_sigaction = (void (*)(int, __siginfo *, void *))handler;
  sigemptyset(&mysig.sa_mask);
  sigaddset(&mysig.sa_mask, SIGSEGV);
  mysig.sa_flags = SA_SIGINFO;

  if (sigaction(SIGSEGV, &mysig, NULL) == -1)
    {
      std::cerr << "Error in sigaction()" << std::endl;
      return 1;
    }

  int * x = NULL;
  int y;
  y = f(x);
  return y;
}


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