package goblint-cil
A front-end for the C programming language that facilitates program analysis and transformation
Install
Dune Dependency
Authors
Maintainers
Sources
goblint-cil-2.0.1.tbz
sha256=5f81cb3f25c09770e77b5eb4092e6621e456122b6d1219dcc304c062075f9572
sha512=31bb753031e0ef321a2ef065373009270881b1cce7f23167b378845188aed9cb49f18a165edd2e11f751f2c7a7b84ab5ac1da50ba1f5cb975e6e8a97157838ed
doc/src/goblint-cil/dataflow.ml.html
Source file dataflow.ml
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module IH = Inthash module E = Errormsg open Cil open Pretty (** A framework for data flow analysis for CIL code. Before using this framework, you must initialize the Control-flow Graph for your program, e.g using {!Cfg.computeFileCFG} *) type 't action = Default (** The default action *) | Done of 't (** Do not do the default action. Use this result *) | Post of ('t -> 't) (** The default action, followed by the given transformer *) type 't stmtaction = SDefault (** The default action *) | SDone (** Do not visit this statement or its successors *) | SUse of 't (** Visit the instructions and successors of this statement as usual, but use the specified state instead of the one that was passed to doStmt *) (* For if statements *) type 't guardaction = GDefault (** The default state *) | GUse of 't (** Use this data for the branch *) | GUnreachable (** The branch will never be taken. *) (****************************************************************** ********** ********** FORWARDS ********** ********************************************************************) module type ForwardsTransfer = sig val name: string (** For debugging purposes, the name of the analysis *) val debug: bool ref (** Whether to turn on debugging *) type t (** The type of the data we compute for each block start. May be imperative. *) val copy: t -> t (** Make a deep copy of the data *) val stmtStartData: t Inthash.t (** For each statement id, the data at the start. Not found in the hash table means nothing is known about the state at this point. At the end of the analysis this means that the block is not reachable. *) val pretty: unit -> t -> Pretty.doc (** Pretty-print the state *) val computeFirstPredecessor: Cil.stmt -> t -> t (** Give the first value for a predecessors, compute the value to be set for the block *) val combinePredecessors: Cil.stmt -> old:t -> t -> t option (** Take some old data for the start of a statement, and some new data for the same point. Return None if the combination is identical to the old data. Otherwise, compute the combination, and return it. *) val doInstr: Cil.instr -> t -> t action (** The (forwards) transfer function for an instruction. The {!Cil.currentLoc} is set before calling this. The default action is to continue with the state unchanged. *) val doStmt: Cil.stmt -> t -> t stmtaction (** The (forwards) transfer function for a statement. The {!Cil.currentLoc} is set before calling this. The default action is to do the instructions in this statement, if applicable, and continue with the successors. *) val doGuard: Cil.exp -> t -> t guardaction (** Generate the successor to an If statement assuming the given expression is nonzero. Analyses that don't need guard information can return GDefault; this is equivalent to returning GUse of the input. A return value of GUnreachable indicates that this half of the branch will not be taken and should not be explored. This will be called twice per If, once for "then" and once for "else". *) val filterStmt: Cil.stmt -> bool (** Whether to put this statement in the worklist. This is called when a block would normally be put in the worklist. *) end module ForwardsDataFlow = functor (T : ForwardsTransfer) -> struct (** Keep a worklist of statements to process. It is best to keep a queue, because this way it is more likely that we are going to process all predecessors of a statement before the statement itself. *) let worklist: Cil.stmt Queue.t = Queue.create () (** We call this function when we have encountered a statement, with some state. *) let reachedStatement (s: stmt) (d: T.t) : unit = let loc = get_stmtLoc s.skind in if loc != locUnknown then currentLoc := get_stmtLoc s.skind; (* see if we know about it already *) E.pushContext (fun _ -> dprintf "Reached statement %d with %a" s.sid T.pretty d); let newdata: T.t option = try let old = IH.find T.stmtStartData s.sid in match T.combinePredecessors s ~old:old d with None -> (* We are done here *) if !T.debug then ignore (E.log "FF(%s): reached stmt %d with %a\n implies the old state %a\n" T.name s.sid T.pretty d T.pretty old); None | Some d' -> begin (* We have changed the data *) if !T.debug then ignore (E.log "FF(%s): weaken data for block %d: %a\n" T.name s.sid T.pretty d'); Some d' end with Not_found -> (* was bottom before *) let d' = T.computeFirstPredecessor s d in if !T.debug then ignore (E.log "FF(%s): set data for block %d: %a\n" T.name s.sid T.pretty d'); Some d' in E.popContext (); match newdata with None -> () | Some d' -> IH.replace T.stmtStartData s.sid d'; if T.filterStmt s && not (Queue.fold (fun exists s' -> exists || s'.sid = s.sid) false worklist) then Queue.add s worklist (** Get the two successors of an If statement *) let ifSuccs (s:stmt) : stmt * stmt = let fstStmt blk = match blk.bstmts with [] -> Cil.dummyStmt | fst::_ -> fst in match s.skind with If(e, b1, b2, _, _) -> let thenSucc = fstStmt b1 in let elseSucc = fstStmt b2 in let oneFallthrough () = let fallthrough = List.filter (fun s' -> thenSucc != s' && elseSucc != s') s.succs in match fallthrough with [] -> E.s (bug "Bad CFG: missing fallthrough for If.") | [s'] -> s' | _ -> E.s (bug "Bad CFG: multiple fallthrough for If.") in (* If thenSucc or elseSucc is Cil.dummyStmt, it's an empty block. So the successor is the statement after the if *) let stmtOrFallthrough s' = if s' == Cil.dummyStmt then oneFallthrough () else s' in (stmtOrFallthrough thenSucc, stmtOrFallthrough elseSucc) | _-> E.s (bug "ifSuccs on a non-If Statement.") (** Process a statement *) let processStmt (s: stmt) : unit = currentLoc := get_stmtLoc s.skind; if !T.debug then ignore (E.log "FF(%s).stmt %d at %t\n" T.name s.sid d_thisloc); (* It must be the case that the block has some data *) let init: T.t = try T.copy (IH.find T.stmtStartData s.sid) with Not_found -> E.s (E.bug "FF(%s): processing block without data" T.name) in (* See what the custom says *) match T.doStmt s init with SDone -> () | (SDefault | SUse _) as act -> begin let curr = match act with SDefault -> init | SUse d -> d | SDone -> E.s (bug "SDone") in (* Do the instructions in order *) let handleInstruction (s: T.t) (i: instr) : T.t = currentLoc := get_instrLoc i; (* Now handle the instruction itself *) let s' = let action = T.doInstr i s in match action with | Done s' -> s' | Default -> s (* do nothing *) | Post f -> f s in s' in let after: T.t = match s.skind with Instr il -> (* Handle instructions starting with the first one *) List.fold_left handleInstruction curr il | Goto _ | ComputedGoto _ | Break _ | Continue _ | If _ | Switch _ | Loop _ | Return _ | Block _ -> curr in currentLoc := get_stmtLoc s.skind; (* Handle If guards *) let succsToReach = match s.skind with If (e, _, _, _, _) -> begin let not_e = UnOp(LNot, e, intType) in let thenGuard = T.doGuard e after in let elseGuard = T.doGuard not_e after in if thenGuard = GDefault && elseGuard = GDefault then (* this is the common case *) s.succs else begin let doBranch succ guard = match guard with GDefault -> reachedStatement succ after | GUse d -> reachedStatement succ d | GUnreachable -> if !T.debug then ignore (E.log "FF(%s): Not exploring branch to %d\n" T.name succ.sid); () in let thenSucc, elseSucc = ifSuccs s in doBranch thenSucc thenGuard; doBranch elseSucc elseGuard; [] end end | _ -> s.succs in (* Reach the successors *) List.iter (fun s' -> reachedStatement s' after) succsToReach; end (** Compute the data flow. Must have the CFG initialized *) let compute (sources: stmt list) = Queue.clear worklist; List.iter (fun s -> Queue.add s worklist) sources; (* All initial stmts must have non-bottom data *) List.iter (fun s -> if not (IH.mem T.stmtStartData s.sid) then E.s (E.error "FF(%s): initial stmt %d does not have data" T.name s.sid)) sources; if !T.debug then ignore (E.log "\nFF(%s): processing\n" T.name); let rec fixedpoint () = if !T.debug && not (Queue.is_empty worklist) then ignore (E.log "FF(%s): worklist= %a\n" T.name (docList (fun s -> num s.sid)) (List.rev (Queue.fold (fun acc s -> s :: acc) [] worklist))); let keepgoing = try let s = Queue.take worklist in processStmt s; true with Queue.Empty -> if !T.debug then ignore (E.log "FF(%s): done\n\n" T.name); false in if keepgoing then fixedpoint () in fixedpoint () end (****************************************************************** ********** ********** BACKWARDS ********** ********************************************************************) module type BackwardsTransfer = sig val name: string (* For debugging purposes, the name of the analysis *) val debug: bool ref (** Whether to turn on debugging *) type t (** The type of the data we compute for each block start. In many presentations of backwards data flow analysis we maintain the data at the block end. This is not easy to do with JVML because a block has many exceptional ends. So we maintain the data for the statement start. *) val pretty: unit -> t -> Pretty.doc (** Pretty-print the state *) val stmtStartData: t Inthash.t (** For each block id, the data at the start. This data structure must be initialized with the initial data for each block *) val funcExitData: t (** The data at function exit. Used for statements with no successors. This is usually bottom, since we'll also use doStmt on Return statements. *) val combineStmtStartData: Cil.stmt -> old:t -> t -> t option (** When the analysis reaches the start of a block, combine the old data with the one we have just computed. Return None if the combination is the same as the old data, otherwise return the combination. In the latter case, the predecessors of the statement are put on the working list. *) val combineSuccessors: t -> t -> t (** Take the data from two successors and combine it *) val doStmt: Cil.stmt -> t action (** The (backwards) transfer function for a branch. The {!Cil.currentLoc} is set before calling this. If it returns None, then we have some default handling. Otherwise, the returned data is the data before the branch (not considering the exception handlers) *) val doInstr: Cil.instr -> t -> t action (** The (backwards) transfer function for an instruction. The {!Cil.currentLoc} is set before calling this. If it returns None, then we have some default handling. Otherwise, the returned data is the data before the branch (not considering the exception handlers) *) val filterStmt: Cil.stmt -> Cil.stmt -> bool (** Whether to put this predecessor block in the worklist. We give the predecessor and the block whose predecessor we are (and whose data has changed) *) end module BackwardsDataFlow = functor (T : BackwardsTransfer) -> struct let getStmtStartData (s: stmt) : T.t = try IH.find T.stmtStartData s.sid with Not_found -> E.s (E.bug "BF(%s): stmtStartData is not initialized for %d: %a" T.name s.sid d_stmt s) (** Process a statement and return true if the set of live return addresses on its entry has changed. *) let processStmt (s: stmt) : bool = if !T.debug then ignore (E.log "FF(%s).stmt %d\n" T.name s.sid); (* Find the state before the branch *) currentLoc := get_stmtLoc s.skind; let d: T.t = match T.doStmt s with Done d -> d | (Default | Post _) as action -> begin (* Do the default one. Combine the successors *) let res = match s.succs with [] -> T.funcExitData | fst :: rest -> List.fold_left (fun acc succ -> T.combineSuccessors acc (getStmtStartData succ)) (getStmtStartData fst) rest in (* Now do the instructions *) let res' = match s.skind with Instr il -> (* Now scan the instructions in reverse order. This may Stack_overflow on very long blocks ! *) let handleInstruction (i: instr) (s: T.t) : T.t = currentLoc := get_instrLoc i; (* First handle the instruction itself *) let action = T.doInstr i s in match action with | Done s' -> s' | Default -> s (* do nothing *) | Post f -> f s in (* Handle instructions starting with the last one *) List.fold_right handleInstruction il res | _ -> res in match action with Post f -> f res' | _ -> res' end in (* See if the state has changed. The only changes are that it may grow.*) let s0 = getStmtStartData s in match T.combineStmtStartData s ~old:s0 d with None -> (* The old data is good enough *) false | Some d' -> (* We have changed the data *) if !T.debug then ignore (E.log "BF(%s): set data for block %d: %a\n" T.name s.sid T.pretty d'); IH.replace T.stmtStartData s.sid d'; true (** Compute the data flow. Must have the CFG initialized *) let compute (sinks: stmt list) = let worklist: Cil.stmt Queue.t = Queue.create () in List.iter (fun s -> Queue.add s worklist) sinks; if !T.debug && not (Queue.is_empty worklist) then ignore (E.log "\nBF(%s): processing\n" T.name); let rec fixedpoint () = if !T.debug && not (Queue.is_empty worklist) then ignore (E.log "BF(%s): worklist= %a\n" T.name (docList (fun s -> num s.sid)) (List.rev (Queue.fold (fun acc s -> s :: acc) [] worklist))); let keepgoing = try let s = Queue.take worklist in let changes = processStmt s in if changes then begin (* We must add all predecessors of block b, only if not already in and if the filter accepts them. *) List.iter (fun p -> if not (Queue.fold (fun exists s' -> exists || p.sid = s'.sid) false worklist) && T.filterStmt p s then Queue.add p worklist) s.preds; end; true with Queue.Empty -> if !T.debug then ignore (E.log "BF(%s): done\n\n" T.name); false in if keepgoing then fixedpoint (); in fixedpoint (); end (** Helper utility that finds all of the statements of a function. It also lists the return statments (including statements that fall through the end of a void function). Useful when you need an initial set of statements for BackwardsDataFlow.compute. *) let sink_stmts = ref [] let all_stmts = ref [] let sinkFinder = object(self) inherit nopCilVisitor method! vstmt s = all_stmts := s ::(!all_stmts); match s.succs with [] -> (sink_stmts := s :: (!sink_stmts); DoChildren) | _ -> DoChildren end (* returns (all_stmts, return_stmts). *) let find_stmts (fdec:fundec) : (stmt list * stmt list) = ignore(visitCilFunction (sinkFinder) fdec); let all = !all_stmts in let ret = !sink_stmts in all_stmts := []; sink_stmts := []; all, ret
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