Set the heap start address in C program?

Question

Is there a way to set the heap start address in GCC compiled C program in linux? In x86_64 system,my test program sets the heap address to 4 byte referenced address ( less than FFFFFFFF). I want to set this to 8 byte referenced address for some testing ( > FFFFFFFF). Does GCC provide any way to set the heap start address?

Answer 1

You can do this a bit indirectly using sbrk():

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

int main(void)
{
  sbrk(0xFFFFFFFF);
  printf("%p\n", malloc(1));
  return 0;
}

This works by "allocating" 0xFFFFFFFF bytes at the very start, so that the next thing malloc() can allocate is a higher address.