Question

So I wrote a toy C program that would intentionally cause a stack overflow, just to play around with the limits of my system:

#include <stdio.h>

int kefladhen(int i) {
    int j = i + 1;
    printf("j is %d\n",j);
    kefladhen(j);
}

int main() {
    printf("Hello!:D\n");
    kefladhen(0);
}

I was surprised to find that the last line printed before a segmentation fault was “j is 174651”. Of course the exact number it got to varied a little each time I ran it, but in general I’m surprised that 174-thousand odd stack frames are enough to exhaust the memory for a process on my 4GB linux laptop. I thought that maybe printf was incurring some overhead, but printf returns before I call kefladhen() recursively so the stack pointer should be back where it was before. I’m storing exactly one int per call, so each stack frame should only be 8 bytes total, right? So 174-thousand odd of them is only about a megabyte and a half of actual memory used, which seems way low to me. What am I misunderstanding here?

Answer 1

I think that the key misunderstanding here is that the stack does not grow dynamically by itself. It is set statically to a relatively small number, but you can change it in runtime (here is a link to an answer explaining how it is done with setrlimit call).