1 //=== UndefBranchChecker.cpp -----------------------------------*- C++ -*--===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file defines UndefBranchChecker, which checks for undefined branch 11 // condition. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "ClangSACheckers.h" 16 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h" 17 #include "clang/StaticAnalyzer/Core/Checker.h" 18 #include "clang/StaticAnalyzer/Core/CheckerManager.h" 19 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" 20 21 using namespace clang; 22 using namespace ento; 23 24 namespace { 25 26 class UndefBranchChecker : public Checker<check::BranchCondition> { 27 mutable std::unique_ptr<BuiltinBug> BT; 28 29 struct FindUndefExpr { 30 ProgramStateRef St; 31 const LocationContext *LCtx; 32 33 FindUndefExpr(ProgramStateRef S, const LocationContext *L) 34 : St(S), LCtx(L) {} 35 36 const Expr *FindExpr(const Expr *Ex) { 37 if (!MatchesCriteria(Ex)) 38 return nullptr; 39 40 for (const Stmt *SubStmt : Ex->children()) 41 if (const Expr *ExI = dyn_cast_or_null<Expr>(SubStmt)) 42 if (const Expr *E2 = FindExpr(ExI)) 43 return E2; 44 45 return Ex; 46 } 47 48 bool MatchesCriteria(const Expr *Ex) { 49 return St->getSVal(Ex, LCtx).isUndef(); 50 } 51 }; 52 53 public: 54 void checkBranchCondition(const Stmt *Condition, CheckerContext &Ctx) const; 55 }; 56 57 } 58 59 void UndefBranchChecker::checkBranchCondition(const Stmt *Condition, 60 CheckerContext &Ctx) const { 61 SVal X = Ctx.getState()->getSVal(Condition, Ctx.getLocationContext()); 62 if (X.isUndef()) { 63 // Generate a sink node, which implicitly marks both outgoing branches as 64 // infeasible. 65 ExplodedNode *N = Ctx.generateErrorNode(); 66 if (N) { 67 if (!BT) 68 BT.reset(new BuiltinBug( 69 this, "Branch condition evaluates to a garbage value")); 70 71 // What's going on here: we want to highlight the subexpression of the 72 // condition that is the most likely source of the "uninitialized 73 // branch condition." We do a recursive walk of the condition's 74 // subexpressions and roughly look for the most nested subexpression 75 // that binds to Undefined. We then highlight that expression's range. 76 77 // Get the predecessor node and check if is a PostStmt with the Stmt 78 // being the terminator condition. We want to inspect the state 79 // of that node instead because it will contain main information about 80 // the subexpressions. 81 82 // Note: any predecessor will do. They should have identical state, 83 // since all the BlockEdge did was act as an error sink since the value 84 // had to already be undefined. 85 assert (!N->pred_empty()); 86 const Expr *Ex = cast<Expr>(Condition); 87 ExplodedNode *PrevN = *N->pred_begin(); 88 ProgramPoint P = PrevN->getLocation(); 89 ProgramStateRef St = N->getState(); 90 91 if (Optional<PostStmt> PS = P.getAs<PostStmt>()) 92 if (PS->getStmt() == Ex) 93 St = PrevN->getState(); 94 95 FindUndefExpr FindIt(St, Ctx.getLocationContext()); 96 Ex = FindIt.FindExpr(Ex); 97 98 // Emit the bug report. 99 auto R = llvm::make_unique<BugReport>(*BT, BT->getDescription(), N); 100 bugreporter::trackNullOrUndefValue(N, Ex, *R); 101 R->addRange(Ex->getSourceRange()); 102 103 Ctx.emitReport(std::move(R)); 104 } 105 } 106 } 107 108 void ento::registerUndefBranchChecker(CheckerManager &mgr) { 109 mgr.registerChecker<UndefBranchChecker>(); 110 } 111
