gistfile1.txt

#include <unistd.h>
#include <mach/mach.h>
#include <mach/mach_vm.h>
#include <mach-o/dyld.h>

int
main (int argc, char * argv[])
{
  volatile char * library;
  const mach_vm_size_t page_size = getpagesize ();
  const mach_vm_size_t buffer_size = 3 * page_size;
  char buffer[buffer_size];
  mach_vm_size_t result_size;

  library = (char *) _dyld_get_image_header (1);
  mach_vm_protect (mach_task_self (), (mach_vm_address_t) (library + page_size), page_size, FALSE, VM_PROT_READ | VM_PROT_WRITE | VM_PROT_COPY | VM_PROT_EXECUTE);
  library[page_size]++;
  library[page_size]--;
  result_size = 0;
  mach_vm_read_overwrite (mach_task_self (), (mach_vm_address_t) library, buffer_size, (mach_vm_address_t) buffer, &result_size);

  return 0;
}