UninitializedValues.cpp revision f8fd82ba49827db0f6a6ba00c55a7b56b12a19fa
1//==- UninitializedValues.cpp - Find Uninitialized Values -------*- 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 implements Uninitialized Values analysis for source-level CFGs. 11// 12//===----------------------------------------------------------------------===// 13 14#include "clang/Analysis/Analyses/UninitializedValues.h" 15#include "clang/Analysis/Visitors/CFGRecStmtDeclVisitor.h" 16#include "clang/Analysis/AnalysisDiagnostic.h" 17#include "clang/AST/ASTContext.h" 18#include "clang/Analysis/FlowSensitive/DataflowSolver.h" 19 20#include "llvm/ADT/SmallPtrSet.h" 21 22using namespace clang; 23 24//===----------------------------------------------------------------------===// 25// Dataflow initialization logic. 26//===----------------------------------------------------------------------===// 27 28namespace { 29 30class RegisterDecls 31 : public CFGRecStmtDeclVisitor<RegisterDecls> { 32 33 UninitializedValues::AnalysisDataTy& AD; 34public: 35 RegisterDecls(UninitializedValues::AnalysisDataTy& ad) : AD(ad) {} 36 37 void VisitVarDecl(VarDecl* VD) { AD.Register(VD); } 38 CFG& getCFG() { return AD.getCFG(); } 39}; 40 41} // end anonymous namespace 42 43void UninitializedValues::InitializeValues(const CFG& cfg) { 44 RegisterDecls R(getAnalysisData()); 45 cfg.VisitBlockStmts(R); 46} 47 48//===----------------------------------------------------------------------===// 49// Transfer functions. 50//===----------------------------------------------------------------------===// 51 52namespace { 53class TransferFuncs 54 : public CFGStmtVisitor<TransferFuncs,bool> { 55 56 UninitializedValues::ValTy V; 57 UninitializedValues::AnalysisDataTy& AD; 58public: 59 TransferFuncs(UninitializedValues::AnalysisDataTy& ad) : AD(ad) {} 60 61 UninitializedValues::ValTy& getVal() { return V; } 62 CFG& getCFG() { return AD.getCFG(); } 63 64 void SetTopValue(UninitializedValues::ValTy& X) { 65 X.setDeclValues(AD); 66 X.resetBlkExprValues(AD); 67 } 68 69 bool VisitDeclRefExpr(DeclRefExpr* DR); 70 bool VisitBinaryOperator(BinaryOperator* B); 71 bool VisitUnaryOperator(UnaryOperator* U); 72 bool VisitStmt(Stmt* S); 73 bool VisitCallExpr(CallExpr* C); 74 bool VisitDeclStmt(DeclStmt* D); 75 bool VisitConditionalOperator(ConditionalOperator* C); 76 bool BlockStmt_VisitObjCForCollectionStmt(ObjCForCollectionStmt* S); 77 78 bool Visit(Stmt *S); 79 bool BlockStmt_VisitExpr(Expr* E); 80 81 void VisitTerminator(CFGBlock* B) { } 82}; 83 84static const bool Initialized = false; 85static const bool Uninitialized = true; 86 87bool TransferFuncs::VisitDeclRefExpr(DeclRefExpr* DR) { 88 89 if (VarDecl* VD = dyn_cast<VarDecl>(DR->getDecl())) 90 if (VD->isBlockVarDecl()) { 91 92 if (AD.Observer) 93 AD.Observer->ObserveDeclRefExpr(V, AD, DR, VD); 94 95 // Pseudo-hack to prevent cascade of warnings. If an accessed variable 96 // is uninitialized, then we are already going to flag a warning for 97 // this variable, which a "source" of uninitialized values. 98 // We can otherwise do a full "taint" of uninitialized values. The 99 // client has both options by toggling AD.FullUninitTaint. 100 101 if (AD.FullUninitTaint) 102 return V(VD,AD); 103 } 104 105 return Initialized; 106} 107 108static VarDecl* FindBlockVarDecl(Expr* E) { 109 110 // Blast through casts and parentheses to find any DeclRefExprs that 111 // refer to a block VarDecl. 112 113 if (DeclRefExpr* DR = dyn_cast<DeclRefExpr>(E->IgnoreParenCasts())) 114 if (VarDecl* VD = dyn_cast<VarDecl>(DR->getDecl())) 115 if (VD->isBlockVarDecl()) return VD; 116 117 return NULL; 118} 119 120bool TransferFuncs::VisitBinaryOperator(BinaryOperator* B) { 121 122 if (VarDecl* VD = FindBlockVarDecl(B->getLHS())) 123 if (B->isAssignmentOp()) { 124 if (B->getOpcode() == BinaryOperator::Assign) 125 return V(VD,AD) = Visit(B->getRHS()); 126 else // Handle +=, -=, *=, etc. We do want '&', not '&&'. 127 return V(VD,AD) = Visit(B->getLHS()) & Visit(B->getRHS()); 128 } 129 130 return VisitStmt(B); 131} 132 133bool TransferFuncs::VisitDeclStmt(DeclStmt* S) { 134 for (DeclStmt::decl_iterator I=S->decl_begin(), E=S->decl_end(); I!=E; ++I) { 135 VarDecl *VD = dyn_cast<VarDecl>(*I); 136 if (VD && VD->isBlockVarDecl()) { 137 if (Stmt* I = VD->getInit()) 138 V(VD,AD) = AD.FullUninitTaint ? V(cast<Expr>(I),AD) : Initialized; 139 else { 140 // Special case for declarations of array types. For things like: 141 // 142 // char x[10]; 143 // 144 // we should treat "x" as being initialized, because the variable 145 // "x" really refers to the memory block. Clearly x[1] is 146 // uninitialized, but expressions like "(char *) x" really do refer to 147 // an initialized value. This simple dataflow analysis does not reason 148 // about the contents of arrays, although it could be potentially 149 // extended to do so if the array were of constant size. 150 if (VD->getType()->isArrayType()) 151 V(VD,AD) = Initialized; 152 else 153 V(VD,AD) = Uninitialized; 154 } 155 } 156 } 157 return Uninitialized; // Value is never consumed. 158} 159 160bool TransferFuncs::VisitCallExpr(CallExpr* C) { 161 VisitChildren(C); 162 return Initialized; 163} 164 165bool TransferFuncs::VisitUnaryOperator(UnaryOperator* U) { 166 switch (U->getOpcode()) { 167 case UnaryOperator::AddrOf: { 168 VarDecl* VD = FindBlockVarDecl(U->getSubExpr()); 169 if (VD && VD->isBlockVarDecl()) 170 return V(VD,AD) = Initialized; 171 break; 172 } 173 174 default: 175 break; 176 } 177 178 return Visit(U->getSubExpr()); 179} 180 181bool 182TransferFuncs::BlockStmt_VisitObjCForCollectionStmt(ObjCForCollectionStmt* S) { 183 // This represents a use of the 'collection' 184 bool x = Visit(S->getCollection()); 185 186 if (x == Uninitialized) 187 return Uninitialized; 188 189 // This represents an initialization of the 'element' value. 190 Stmt* Element = S->getElement(); 191 VarDecl* VD = 0; 192 193 if (DeclStmt* DS = dyn_cast<DeclStmt>(Element)) 194 VD = cast<VarDecl>(DS->getSingleDecl()); 195 else { 196 Expr* ElemExpr = cast<Expr>(Element)->IgnoreParens(); 197 198 // Initialize the value of the reference variable. 199 if (DeclRefExpr* DR = dyn_cast<DeclRefExpr>(ElemExpr)) 200 VD = cast<VarDecl>(DR->getDecl()); 201 else 202 return Visit(ElemExpr); 203 } 204 205 V(VD,AD) = Initialized; 206 return Initialized; 207} 208 209 210bool TransferFuncs::VisitConditionalOperator(ConditionalOperator* C) { 211 Visit(C->getCond()); 212 213 bool rhsResult = Visit(C->getRHS()); 214 // Handle the GNU extension for missing LHS. 215 if (Expr *lhs = C->getLHS()) 216 return Visit(lhs) & rhsResult; // Yes: we want &, not &&. 217 else 218 return rhsResult; 219} 220 221bool TransferFuncs::VisitStmt(Stmt* S) { 222 bool x = Initialized; 223 224 // We don't stop at the first subexpression that is Uninitialized because 225 // evaluating some subexpressions may result in propogating "Uninitialized" 226 // or "Initialized" to variables referenced in the other subexpressions. 227 for (Stmt::child_iterator I=S->child_begin(), E=S->child_end(); I!=E; ++I) 228 if (*I && Visit(*I) == Uninitialized) x = Uninitialized; 229 230 return x; 231} 232 233bool TransferFuncs::Visit(Stmt *S) { 234 if (AD.isTracked(static_cast<Expr*>(S))) return V(static_cast<Expr*>(S),AD); 235 else return static_cast<CFGStmtVisitor<TransferFuncs,bool>*>(this)->Visit(S); 236} 237 238bool TransferFuncs::BlockStmt_VisitExpr(Expr* E) { 239 bool x = static_cast<CFGStmtVisitor<TransferFuncs,bool>*>(this)->Visit(E); 240 if (AD.isTracked(E)) V(E,AD) = x; 241 return x; 242} 243 244} // end anonymous namespace 245 246//===----------------------------------------------------------------------===// 247// Merge operator. 248// 249// In our transfer functions we take the approach that any 250// combination of uninitialized values, e.g. 251// Uninitialized + ___ = Uninitialized. 252// 253// Merges take the same approach, preferring soundness. At a confluence point, 254// if any predecessor has a variable marked uninitialized, the value is 255// uninitialized at the confluence point. 256//===----------------------------------------------------------------------===// 257 258namespace { 259 typedef StmtDeclBitVector_Types::Union Merge; 260 typedef DataflowSolver<UninitializedValues,TransferFuncs,Merge> Solver; 261} 262 263//===----------------------------------------------------------------------===// 264// Uninitialized values checker. Scan an AST and flag variable uses 265//===----------------------------------------------------------------------===// 266 267UninitializedValues_ValueTypes::ObserverTy::~ObserverTy() {} 268 269namespace { 270class UninitializedValuesChecker 271 : public UninitializedValues::ObserverTy { 272 273 ASTContext &Ctx; 274 Diagnostic &Diags; 275 llvm::SmallPtrSet<VarDecl*,10> AlreadyWarned; 276 277public: 278 UninitializedValuesChecker(ASTContext &ctx, Diagnostic &diags) 279 : Ctx(ctx), Diags(diags) {} 280 281 virtual void ObserveDeclRefExpr(UninitializedValues::ValTy& V, 282 UninitializedValues::AnalysisDataTy& AD, 283 DeclRefExpr* DR, VarDecl* VD) { 284 285 assert ( AD.isTracked(VD) && "Unknown VarDecl."); 286 287 if (V(VD,AD) == Uninitialized) 288 if (AlreadyWarned.insert(VD)) 289 Diags.Report(Ctx.getFullLoc(DR->getSourceRange().getBegin()), 290 diag::warn_uninit_val); 291 } 292}; 293} // end anonymous namespace 294 295namespace clang { 296void CheckUninitializedValues(CFG& cfg, ASTContext &Ctx, Diagnostic &Diags, 297 bool FullUninitTaint) { 298 299 // Compute the uninitialized values information. 300 UninitializedValues U(cfg); 301 U.getAnalysisData().FullUninitTaint = FullUninitTaint; 302 Solver S(U); 303 S.runOnCFG(cfg); 304 305 // Scan for DeclRefExprs that use uninitialized values. 306 UninitializedValuesChecker Observer(Ctx,Diags); 307 U.getAnalysisData().Observer = &Observer; 308 S.runOnAllBlocks(cfg); 309} 310} // end namespace clang 311