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