From debbae89f9faf47b95bd1c86058cd232783f3c3f Mon Sep 17 00:00:00 2001 From: Bernhard Schommer Date: Thu, 4 Jul 2019 12:59:33 +0200 Subject: Added new diagnostic for non-linear conditionals The new diagnostics is triggered if a conditional is used that may not be transformed into linear code by the later by the if conversion. The new diagnostic is emitted if a conditional may contain an unsafe expression or is contained within another conditional, logical and or logical or expression. An expression is unsafe if it contains a call, changes memory or if its evaluation leads to undefined behavior, for example division and modulo. Also fixes a small typo in a comment in Cutil. --- cparser/Checks.ml | 163 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 163 insertions(+) (limited to 'cparser/Checks.ml') diff --git a/cparser/Checks.ml b/cparser/Checks.ml index 94570f4e..e79e3ccf 100644 --- a/cparser/Checks.ml +++ b/cparser/Checks.ml @@ -212,3 +212,166 @@ let unused_variables p = traverse_program ~fundef:fundef p + +(* Warning for conditionals that cannot be transformed into linear code *) + +(* Compute the set of local variables that do not have their address taken *) + +let rec non_stack_locals_expr vars e = + match e.edesc with + | ECast (_,e) -> non_stack_locals_expr vars e + | EUnop (Oaddrof,e) -> + begin match e.edesc with + | EVar id -> + IdentSet.remove id vars + | _ -> vars + end + | EUnop (Oderef, e) -> + (* Special optimization *(& ...) is removed in SimplExpr *) + begin match e.edesc with + | EUnop (Oaddrof,e) -> non_stack_locals_expr vars e + | _ -> non_stack_locals_expr vars e + end + | EUnop (_, e) -> + non_stack_locals_expr vars e + | EBinop (_,e1,e2,_) -> + let vars = non_stack_locals_expr vars e1 in + non_stack_locals_expr vars e2 + | EConditional (e1,e2,e3) -> + let vars = non_stack_locals_expr vars e1 in + let vars = non_stack_locals_expr vars e2 in + non_stack_locals_expr vars e3 + | ECompound (_,init) -> non_stack_locals_init vars init + | ECall (e,p) -> + let vars = non_stack_locals_expr vars e in + List.fold_left non_stack_locals_expr vars p + | _ -> vars + +and non_stack_locals_init vars init = + fold_over_init ~expr:non_stack_locals_expr vars init + +let add_vars env vars (id,ty) = + let volatile = List.mem AVolatile (attributes_of_type env ty) in + if not volatile then + IdentSet.add id vars + else + vars + +let non_stack_locals_stmt env vars s = + let decl vars loc (sto, id, ty, init) = + let vars = match init with + | Some init -> non_stack_locals_init vars init + | None -> vars in + add_vars env vars (id,ty) in + fold_over_stmt ~expr:non_stack_locals_expr ~decl:decl + vars s + +(* Check whether an expression is safe and can be always evaluated *) + +let safe_cast env tfrom tto = + match unroll env tfrom, unroll env tto with + | (TInt _ | TPtr _ | TArray _ | TFun _ | TEnum _), + (TInt _ | TPtr _ | TEnum _) -> true + | TFloat _, TFloat _ -> true + | _, _ -> equal_types env tfrom tto + +let safe_expr vars env e = + let rec expr e = + match e.edesc with + | EConst _ | ESizeof _ | EAlignof _ | ECompound _ -> true + | EVar id -> (IdentSet.mem id vars) || not (is_scalar_type env e.etyp) + | ECast (ty, e) -> + safe_cast env e.etyp ty && expr e + | EUnop (op, e) -> + unop op e + | EBinop (op, e1, e2, ty) -> + binop op e1 e2 + | EConditional _ -> false + | ECall _ -> false + and binop op e1 e2 = + let is_long_long_type ty = + match unroll env ty with + | TInt (ILongLong, _) + | TInt (IULongLong, _) -> true + | _ -> false in + match op with + | Oadd | Osub | Omul | Oand | Oor | Oxor | Oshl | Oshr -> + expr e1 && expr e2 + | Oeq | One | Olt | Ogt | Ole | Oge -> + let not_long_long = not (is_long_long_type e1.etyp) && not (is_long_long_type e2.etyp) in + not_long_long && expr e1 && expr e2 + | _ -> false + (* x.f if f has array or struct or union type *) + and unop op e = + match op with + | Ominus | Onot | Olognot | Oplus -> expr e + | Oaddrof -> + begin match e.edesc with + (* skip &*e *) + | EUnop (Oderef, e) -> expr e + (* skip &(e.f) *) + | EUnop (Odot f, e) -> expr e + | _ -> expr e + end + (* skip *&e *) + | Oderef -> + begin match e.edesc with + | EUnop (Oaddrof,e) -> expr e + | _ -> expr e + end + (* e.f is okay if f has array or composite type *) + | Odot m -> + let fld = field_of_dot_access env e.etyp m in + (is_array_type env fld.fld_typ || is_composite_type env fld.fld_typ) && expr e + | _ -> false in + expr e + +(* Check expressions if they contain conditionals that cannot be transformed in + linear code. The inner_cond parameter is used to mimic the translation of short + circuit logical or and logical and as well as conditional to if statements in + SimplExpr. *) + +let rec non_linear_cond_expr inner_cond vars env loc e = + match e.edesc with + | EConst _ | ESizeof _ | EAlignof _ | EVar _ -> () + | ECast (_ , e) | EUnop (_, e)-> non_linear_cond_expr false vars env loc e + | EBinop (op, e1, e2, ty) -> + let inner_cond = match op with + | Ocomma -> inner_cond + | Ologand | Ologor -> true + | _ -> false + in + non_linear_cond_expr false vars env loc e1; + non_linear_cond_expr inner_cond vars env loc e2 + | EConditional (c, e1, e2) -> + let can_cast = safe_cast env e1.etyp e.etyp && safe_cast env e2.etyp e.etyp in + if not can_cast || inner_cond || not (safe_expr vars env e1) || not (safe_expr vars env e2) then + warning loc Non_linear_cond_expr "conditional expression may not be linearized"; + non_linear_cond_expr true vars env loc e1; + non_linear_cond_expr true vars env loc e2; + | ECompound (ty, init) -> non_linear_cond_init vars env loc init + | ECall (e, params) -> + non_linear_cond_expr false vars env loc e; + List.iter (non_linear_cond_expr false vars env loc) params + +and non_linear_cond_init vars env loc init = + iter_over_init ~expr:(non_linear_cond_expr false vars env loc) init + +let non_linear_cond_stmt vars env s = + let decl loc (sto, id, ty, init) = + match init with + | None -> () + | Some init -> non_linear_cond_init vars env loc init in + iter_over_stmt_loc ~expr:(non_linear_cond_expr false vars env) ~decl:decl s + +let non_linear_conditional p = + if active_warning Non_linear_cond_expr then begin + let fundef env loc fd = + let vars = List.fold_left (add_vars env) IdentSet.empty fd.fd_params in + let vars = non_stack_locals_stmt env vars fd.fd_body in + non_linear_cond_stmt vars env fd.fd_body; + in + traverse_program + ~fundef:fundef + p + end -- cgit