演示coredump后出现？的情况

void run()
{
  int m = 2;
}

int main()
{
  int *m = new int;
  run();
  return 0;

}

(gdb) tbreak main
Temporary breakpoint 1 at 0x804869b: file test4.c, line 20.
(gdb) r
Starting program: /home/linxp/test/a.out 


Temporary breakpoint 1, main () at test4.c:20
20  int *m = new int;
(gdb) n
21  run();
(gdb) i r ebp
ebp            0xbffff708 0xbffff708
(gdb) set *0xbffff70c=0x10
(gdb) c
Continuing.

Program received signal SIGSEGV, Segmentation fault.
0x00000010 in ?? ()
(gdb) bt
#0  0x00000010 in ?? ()