When we run a program that contains a function call, GAWK maintains a stack of all function calls to lead you up to where you are executing. We can see how we got there, where we are and also move inside the stack with the help of the backtrace command or bt or the alias where. Any of these three commands can be used to print the backtrace of function calls (stack frames).
Here, frame 0 is the currently executing innermost frame (function call). Frame 1 is the frame that called the innermost frame 0 and the highest-numbered frame represents the main program:
gawk> backtrace#0 find_add(num1, num2) at `calc.awk':2#1 in calc() at `calc.awk':18#2 in main() at `calc.awk':26gawk>
The output contains the frame number, ...