1 //=== UndefBranchChecker.cpp -----------------------------------*- C++ -*--===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file defines UndefBranchChecker, which checks for undefined branch 10 // condition. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "clang/AST/StmtObjC.h" 15 #include "clang/AST/Type.h" 16 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h" 17 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h" 18 #include "clang/StaticAnalyzer/Core/Checker.h" 19 #include "clang/StaticAnalyzer/Core/CheckerManager.h" 20 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" 21 #include <utility> 22 23 using namespace clang; 24 using namespace ento; 25 26 namespace { 27 28 class UndefBranchChecker : public Checker<check::BranchCondition> { 29 mutable std::unique_ptr<BuiltinBug> BT; 30 31 struct FindUndefExpr { 32 ProgramStateRef St; 33 const LocationContext *LCtx; 34 35 FindUndefExpr(ProgramStateRef S, const LocationContext *L) 36 : St(std::move(S)), LCtx(L) {} 37 38 const Expr *FindExpr(const Expr *Ex) { 39 if (!MatchesCriteria(Ex)) 40 return nullptr; 41 42 for (const Stmt *SubStmt : Ex->children()) 43 if (const Expr *ExI = dyn_cast_or_null<Expr>(SubStmt)) 44 if (const Expr *E2 = FindExpr(ExI)) 45 return E2; 46 47 return Ex; 48 } 49 50 bool MatchesCriteria(const Expr *Ex) { 51 return St->getSVal(Ex, LCtx).isUndef(); 52 } 53 }; 54 55 public: 56 void checkBranchCondition(const Stmt *Condition, CheckerContext &Ctx) const; 57 }; 58 59 } // namespace 60 61 void UndefBranchChecker::checkBranchCondition(const Stmt *Condition, 62 CheckerContext &Ctx) const { 63 // ObjCForCollection is a loop, but has no actual condition. 64 if (isa<ObjCForCollectionStmt>(Condition)) 65 return; 66 SVal X = Ctx.getSVal(Condition); 67 if (X.isUndef()) { 68 // Generate a sink node, which implicitly marks both outgoing branches as 69 // infeasible. 70 ExplodedNode *N = Ctx.generateErrorNode(); 71 if (N) { 72 if (!BT) 73 BT.reset(new BuiltinBug( 74 this, "Branch condition evaluates to a garbage value")); 75 76 // What's going on here: we want to highlight the subexpression of the 77 // condition that is the most likely source of the "uninitialized 78 // branch condition." We do a recursive walk of the condition's 79 // subexpressions and roughly look for the most nested subexpression 80 // that binds to Undefined. We then highlight that expression's range. 81 82 // Get the predecessor node and check if is a PostStmt with the Stmt 83 // being the terminator condition. We want to inspect the state 84 // of that node instead because it will contain main information about 85 // the subexpressions. 86 87 // Note: any predecessor will do. They should have identical state, 88 // since all the BlockEdge did was act as an error sink since the value 89 // had to already be undefined. 90 assert (!N->pred_empty()); 91 const Expr *Ex = cast<Expr>(Condition); 92 ExplodedNode *PrevN = *N->pred_begin(); 93 ProgramPoint P = PrevN->getLocation(); 94 ProgramStateRef St = N->getState(); 95 96 if (Optional<PostStmt> PS = P.getAs<PostStmt>()) 97 if (PS->getStmt() == Ex) 98 St = PrevN->getState(); 99 100 FindUndefExpr FindIt(St, Ctx.getLocationContext()); 101 Ex = FindIt.FindExpr(Ex); 102 103 // Emit the bug report. 104 auto R = std::make_unique<PathSensitiveBugReport>( 105 *BT, BT->getDescription(), N); 106 bugreporter::trackExpressionValue(N, Ex, *R); 107 R->addRange(Ex->getSourceRange()); 108 109 Ctx.emitReport(std::move(R)); 110 } 111 } 112 } 113 114 void ento::registerUndefBranchChecker(CheckerManager &mgr) { 115 mgr.registerChecker<UndefBranchChecker>(); 116 } 117 118 bool ento::shouldRegisterUndefBranchChecker(const CheckerManager &mgr) { 119 return true; 120 } 121