problem with userland exec()

["bbb arc" <arcbbb@gmail.com>]

i am trying grugq's userland exec()  [1]
 but is unable to run with my simple static linked hello world program
 [2]

 because of the random stack start address,I tried added the following
 three lines in the
 save.c:ul_setup_stack():

    stack_top = mmap(0,0x16000, PROT_WRITE |PROT_READ,
                MAP_PRIVATE|MAP_ANONYMOUS|MAP_GROWSDOWN,-1,0);// test
    stack_top +=0x16000;

 the program still segmentation fault at memcpy: 0x804d95f:      rep
 movsl %ds:(%esi),%es:(%edi)

 Does anyone have ideas about it?

 Kind Regards,
 arcbbb

 [1] http://www.phrack.org/issues.html?issue=62&id=8
 [2] my simple hello world compiled with gcc -g -static
     #include <unistd.h>
     #define hello   "Hello World!\n"

     int
     main(void)
     {
             write(1, hello, 13);
             return (0);
     }