This paper presents a backward stable preprocessing technique for (nearly) ill-posed semidef5 inite programming, SDP, problems, i.e., programs for which the Slater constraint qualification, 6 existence of strictly feasible points, (nearly) fails. 7 Current popular algorithms for semidefinite programming rely on primal-dual interior-point, 8 p-d i-p methods. These algorithms require the Slater c...