Expenses allowed on LTCG/STCG on shares

When someone purchases equity shares he pays brokerage stamp duty gst etc., when he sells shares he pays brokerage and all above again. stt is not a expense. So while calculating total expenses, to calculate LTCG/ STCG, Can one add up expenses for buying and selling both? or expenses occured while selling only. What about gst.is it allowed as expense or not?

I will be thankful if somebody clarify above thing