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 #include <utility> 21 22 using namespace clang; 23 using namespace ento; 24 25 namespace { 26 27 class UndefBranchChecker : public Checker<check::BranchCondition> { 28 mutable std::unique_ptr<BuiltinBug> BT; 29 30 struct FindUndefExpr { 31 ProgramStateRef St; 32 const LocationContext *LCtx; 33 34 FindUndefExpr(ProgramStateRef S, const LocationContext *L) 35 : St(std::move(S)), LCtx(L) {} 36 37 const Expr *FindExpr(const Expr *Ex) { 38 if (!MatchesCriteria(Ex)) 39 return nullptr; 40 41 for (const Stmt *SubStmt : Ex->children()) 42 if (const Expr *ExI = dyn_cast_or_null<Expr>(SubStmt)) 43 if (const Expr *E2 = FindExpr(ExI)) 44 return E2; 45 46 return Ex; 47 } 48 49 bool MatchesCriteria(const Expr *Ex) { 50 return St->getSVal(Ex, LCtx).isUndef(); 51 } 52 }; 53 54 public: 55 void checkBranchCondition(const Stmt *Condition, CheckerContext &Ctx) const; 56 }; 57 58 } 59 60 void UndefBranchChecker::checkBranchCondition(const Stmt *Condition, 61 CheckerContext &Ctx) const { 62 SVal X = Ctx.getState()->getSVal(Condition, Ctx.getLocationContext()); 63 if (X.isUndef()) { 64 // Generate a sink node, which implicitly marks both outgoing branches as 65 // infeasible. 66 ExplodedNode *N = Ctx.generateErrorNode(); 67 if (N) { 68 if (!BT) 69 BT.reset(new BuiltinBug( 70 this, "Branch condition evaluates to a garbage value")); 71 72 // What's going on here: we want to highlight the subexpression of the 73 // condition that is the most likely source of the "uninitialized 74 // branch condition." We do a recursive walk of the condition's 75 // subexpressions and roughly look for the most nested subexpression 76 // that binds to Undefined. We then highlight that expression's range. 77 78 // Get the predecessor node and check if is a PostStmt with the Stmt 79 // being the terminator condition. We want to inspect the state 80 // of that node instead because it will contain main information about 81 // the subexpressions. 82 83 // Note: any predecessor will do. They should have identical state, 84 // since all the BlockEdge did was act as an error sink since the value 85 // had to already be undefined. 86 assert (!N->pred_empty()); 87 const Expr *Ex = cast<Expr>(Condition); 88 ExplodedNode *PrevN = *N->pred_begin(); 89 ProgramPoint P = PrevN->getLocation(); 90 ProgramStateRef St = N->getState(); 91 92 if (Optional<PostStmt> PS = P.getAs<PostStmt>()) 93 if (PS->getStmt() == Ex) 94 St = PrevN->getState(); 95 96 FindUndefExpr FindIt(St, Ctx.getLocationContext()); 97 Ex = FindIt.FindExpr(Ex); 98 99 // Emit the bug report. 100 auto R = llvm::make_unique<BugReport>(*BT, BT->getDescription(), N); 101 bugreporter::trackNullOrUndefValue(N, Ex, *R); 102 R->addRange(Ex->getSourceRange()); 103 104 Ctx.emitReport(std::move(R)); 105 } 106 } 107 } 108 109 void ento::registerUndefBranchChecker(CheckerManager &mgr) { 110 mgr.registerChecker<UndefBranchChecker>(); 111 } 112
