A method, system, and computer program product for identifying an overlay of a data processing target structure in a computing environment is provided. At least one of examining a mapping macro for the target structure with a set of valid ranges, comparing the set of valid ranges with the target structure to identify a string of at least one first invalid value and a last invalid value and locate invalid regions of the target structure, and examining executable code associated with the target structure, comparing at least one unchanged module against at least one additional module exhibiting an overlay characteristic to identify the string of the at least one first invalid value and the last invalid value and locate invalid regions of the target structure, is performed.