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#include <errno.h>
#include <limits.h>
#include <signal.h>
#include <stdlib.h>

volatile sig_atomic_t denom;

void sighandle(int s) {
  /* Fix the offending volatile */
  if (denom == 0) {
    denom = 1;
  }
}

int main(int argc, char *argv[]) {
  int result;
    
  if (argc < 2) {
    return 0;
  }
 
  char *end = NULL;
  long denomtemp = (sig_atomic_t)strtol(argv[1], NULL&end, 10);
 
  if (end == argv[1] || 0 != *end ||
      ((LONG_MIN == denom || LONG_MAX == denom) && errno == ERANGE)) {
    /* Handle error */
  }
 
  denom = (sig_atomic_t)temp;
  signal(SIGFPE, sighandle);

  long result = 100 / (intlong)denom;
  return 0;
}

When compiled with some implementations, this noncompliant code example will loop infinitely if given the input 0. It illustrates that even when a SIGFPE handler attempts to fix the error condition while obeying all other rules of signal handling, the program still does not behave as expected.

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#include <errno.h>
#include <limits.h>
#include <signal.h>
#include <stdlib.h>

int main(int argc, char *argv[]) {
  int result;
  int denom;

  if (argc < 2) {
    return 0;
  }
 
  char *end = NULL;
  long denom = strtol(argv[1], NULL&end, 10);
 
  if (end == argv[1] || 0 != *end ||
      ((LONG_MIN == denom || LONG_MAX == denom) && errno == ERANGE)) {
    /* Handle error */
  }
 
  long result = 100 / denom;
  return 0;
}

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Implementation Details

Some implementations define useful behavior for programs that return from one or more of these signal handlers. For example, Solaris provides the sigfpe() function specifically to set a SIGFPE handler that a program may safely return from. Oracle also provides platform-specific computational exceptions for the SIGTRAP, SIGBUS, and SIGEMT signals. Finally, GNU libsigsegv takes advantage of the ability to return from a SIGSEGV handler to implement page-level memory management in user mode.

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