taviso

Here's an interesting problem, how can I make this simple program crash? (assume IA32)

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

int main(int argc, char **argv)
{
    int a, b;

    if (argc != 3)
        return 1;

    a = atoi(argv[1]);
    b = atoi(argv[2]);

    return b ? a / b : 0;
}

scroll down for the solution.

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The code correctly checks for divide by zero, so attempting this wont work:

$ ./a.out 42 0; echo $?
0
$

But not every invalid operation has been checked, while every programmer knows to avoid dividing by zero, very few are aware that it's also illegal to divide INT_MIN by -1. The reason is obvious, on a twos complement system |INT_MIN| is one greater than INT_MAX, so the result of the operation simply cannot fit in an integer.

This little known fact is almost guaranteed to crash any system that uses integer division on user controlled values as so few developers check for this unusual case.

$ ./a.out -2147483648 -1; echo $?
Floating point exception (core dumped)
136