Stack Switching

gistfile1.c

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

#define STACK_SIZE (1 << 26)
#define STACK_PAD 128

int rec(int n) {
  return n == 0 ? 0 : rec(n - 1) + 1;
}

int main() {
  /* Allocate a new stack to use first.  Because stacks grow to lower addresses
   * we want to use just a little before the end of the allocation. */
  char* nstack = (char*)malloc(STACK_SIZE) + STACK_SIZE - STACK_PAD;

  /* Adjust the stack pointer to fall right in our newly allocated stack.
   * "char stack_hack[sz];" has the effect of subtracting sz from the stack
   * pointer. */
  char stack_hack[(char*)&nstack - nstack];

  /* Now we can recurse deeply.  If you comment out the definition of stack_hack
   * then (on my system's limits, anyway) the second one will segfault. */
  printf("%d\n", rec(100000));
  printf("%d\n", rec(1000000));

  return 1;
}