Stack overflow

A stack overflow results in a segmentation fault. The most common cause of stack overflow is excessively deep or infinite recursion. Now try the code below:

#include <stdio.h>
#include <string.h>
#include <unistd.h>
void recursion(int i) {
    char a[40 * 1024];
    printf("start %d\n", i);
    memset(a, 0, sizeof(a));
    printf("OK! %d\n", i);
    recursion(i+1);
}
int main(int argc, char **argv) {
    char a[8000 * 1024]; // remaining is 192 * 1024
    printf("start\n");
    memset(a, 0, sizeof(a));
    printf("OK!\n");
    recursion(0);
    return 0;
}

Here is the output:img01

What happened?

  • Find out the maximum size of the stack in kilobyte (KB)
    $ ulimit -s
8192
  • So the maximum size of the stack is 8192 KB = 8192 * 1024 bytes.
  • In the main function, we use 8000 * 1024 bytes which remains 192 * 1024 bytes.
  • Four calls to the recursion function use 160 * 1024 bytes.
  • So the fifth call to the recursion function exceeds the maximum size of the stack and triggers the stack overflow.