For a film “based on a true story” — that of Leonard and Phil Chess’ eponymous record label, featuring the likes of Muddy Waters (Jeffrey Wright), Howlin’ Wolf (Eamonn Walker), Etta James (Beyoncé Knowles), and Chuck Berry (Mos Def) — there doesn’t seem to be a single fact contained within writer-director Darnell Martin’s fiction, which renders pre-rock musical history as yet another downer soap opera bloated with smack and sex and premature corpses. For all its copious flaws, Walk Hard: The Dewey Cox Story perfectly nailed the trajectory of every single rockudrama that has tarnished a legend’s legend — the big bang turned sad whimper. In this version — told in flashback, no less, with overwrought narration provided by Cedric the Entertainer as Chess producer, session musician and house songwriter Willie Dixon — there is no Phil Chess, only Leonard, played by an actor, Adrien Brody, who, with his anachronistically tousled hair and Fonzie wardrobe, looks as much like Leonard Chess as he does, well, Howlin’ Wolf. Fabrications in the name of movie mythmaking are, of course, to be expected from a genre that condenses a life into a handful of defining episodes; all biopics reduce and trivialize. But so egregious are the deficiencies and distortions here — in this universe, the Rolling Stones came to the United States and the Beach Boys ripped off Chuck Berry long before anyone had ever heard of Elvis Presley — that it’s almost impossible to discern whether there’s anything decent about the moviemaking itself. With everything so wrong, how can there be anything right about Cadillac Records?