(a)  
#include "aprobe.h"
probe thread
{
  probe "fstat" in "libc.so"
  {  /* Parameter one is $1, Parameter two is $2, etc */
      on_entry
        log ("St_dev is ", $2-> st_dev);
        log ("Whole st_stat is ", *$2);
  }
}

(b)
St_dev  is 0
Whole st_stat is {
  st_dev = 0
  st_pad1 = {
      [0] = 0
      [1] = 0
      [2] = 0
  }
  st_ino = 0
  st_mode = 0
  st_nlink = 0
  st_uid = 0
  st_gid = 0
  st_rdev = 0
  st_pad2 = {
      [0] = -276903488
      [1] = 143764
}

Example 1: (a) Aprobe log function; (b) resulting output.