ABAP--如何擷取ABAP的程式的調用堆棧

REPORT demo_mod_tech_perform_int .

DATA: num1 TYPE i,

      num2 TYPE i,

      sum  TYPE i.

num1 = 2. num2 = 4.

PERFORM addit.

FORM addit.

  sum = num1 + num2.

  PERFORM out.

ENDFORM.                    "addit

FORM out.

  field-symbols: <fs> type any.

  data l_cstack_tab  type SYS_CALLST.

  WRITE: / 'Sum of', num1, 'and', num2, 'is', sum.

  CALL FUNCTION 'SYSTEM_CALLSTACK'

    IMPORTING

      et_callstack = l_cstack_tab. " internal table

* l_cstack_tab 裡就是abap的調用堆棧   

ENDFORM.                    "out