I used the following to print the %rsp/%esp value:
```
/* $Id: print_sp.c,v 1.2 2019/07/26 21:12:13 kostik Exp kostik $ */
#include <stdio.h>
int
main(void)
{
unsigned long sp;
#ifdef _LP64
__asm volatile("movq\t%%rsp,%0" : "=r" (sp));
#else
__asm volatile("movl\t%%esp,%0" : "=r" (sp));
#endif
printf("sp %#lx\n", sp);
}
```