Function Module to read stack values.

Hello,

Is there is any function module to read the stack values.

My requirement is

I have 3 FM modules say FM_A, FM_B & FM_C.

FM_A will call FM_C.

FM_B will call FM_C.

In FM_C, I need to identify whether the call has been made from FM_A or FM_B without changing these two function modules and by changing only FM_C.

Please help me out.

Thx.