Floating Point Exception Core Dump

user_835887 0
Viewed 7275

I am newbie on the Linux signals, please help. The following code get core dump when run in Linux 2.6 gcc.

$ ./a.out
Floating point exception (core dumped)

The questions:
1. Since a process signal mask is installed, shouldn't the "SIGFPGE" generated by line 40 volatile int z = x/y; be blocked?
2. If it is not blocked, since a signal handler has been installed, shouldn't the "SIGFPE" be captured by the signal handler, instead of a core dump?
3. If I commented out line 40volatile int z = x/y;, and use line 42 raise(SIGFPE); instead, then everything works as I expected. What is the difference between x/0 and raise SIGFPE here?

Here is the code:

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

    void sig_handler(int signum)
    {
       printf("sig_handler() received signal %d\n", signum);
    }


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

       // setup signal mask, block all signals
       sigset_t set;
       sigfillset(&set);

       if(sigprocmask(SIG_BLOCK, &set, NULL)<0)
       {
          perror("failed to set sigmask");
          return -1;
       }

       // install signal handler for SIGFPE
       struct sigaction act;
       act.sa_handler = sig_handler;
       act.sa_mask = set;
       act.sa_flags = 0;
       if(sigaction( SIGFPE, &act, NULL)<0)
       {
          perror("sigaction failed");
          exit(-1);
       }

       volatile int x =1;
       volatile int y =0;
       volatile int z = x/y; //line 40

       //raise(SIGFPE); //line 42

       printf("point 1000\n");

       return 0;
    }
sigfpe signals linux c
2 Answers

man signal

According to POSIX, the behavior of a process is undefined after it ignores a SIGFPE, SIGILL, or SIGSEGV signal that was not generated by kill(2) or raise(3). Integer division by zero has undefined result.

On some architectures it will generate a SIGFPE signal. (Also dividing the most negative integer by -1 may generate SIGFPE). Ignoring this signal might lead to an endless loop.

I discovered this after trying to work out why negative/positive infinity resulted from a division by zero: IEEE 754, division by zero

This is a place you never want to get:

void divZeroHdlr(int sig) {
  printf("div by zero: %d\n",sig)
  exit(1);}

int main(int argc, char *argv[]) {
  signal(SIGFPE, divZeroHdlr)
  int n = 1/0}
user_91844340
Related