ThreadSafety.cpp revision 0fed26d94553881011aa7ec30cee3ed0da71c7a1
1//===- ThreadSafety.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// A intra-procedural analysis for thread safety (e.g. deadlocks and race 11// conditions), based off of an annotation system. 12// 13// See http://gcc.gnu.org/wiki/ThreadSafetyAnnotation for the gcc version. 14// 15//===----------------------------------------------------------------------===// 16 17#include "clang/Analysis/Analyses/ThreadSafety.h" 18#include "clang/Basic/SourceManager.h" 19#include "clang/Basic/SourceLocation.h" 20#include "clang/AST/DeclCXX.h" 21#include "clang/AST/ExprCXX.h" 22#include "clang/AST/StmtCXX.h" 23#include "clang/AST/StmtVisitor.h" 24#include "clang/Analysis/AnalysisContext.h" 25#include "clang/Analysis/CFG.h" 26#include "clang/Analysis/CFGStmtMap.h" 27#include "llvm/ADT/BitVector.h" 28#include "llvm/ADT/FoldingSet.h" 29#include "llvm/ADT/ImmutableMap.h" 30#include "llvm/ADT/PostOrderIterator.h" 31#include "llvm/ADT/SmallVector.h" 32#include "llvm/ADT/StringRef.h" 33#include <algorithm> 34#include <vector> 35 36using namespace clang; 37using namespace thread_safety; 38 39// Helper functions 40static Expr *getParent(Expr *Exp) { 41 if (MemberExpr *ME = dyn_cast<MemberExpr>(Exp)) 42 return ME->getBase(); 43 if (CXXMemberCallExpr *CE = dyn_cast<CXXMemberCallExpr>(Exp)) 44 return CE->getImplicitObjectArgument(); 45 return 0; 46} 47 48namespace { 49/// \brief Implements a set of CFGBlocks using a BitVector. 50/// 51/// This class contains a minimal interface, primarily dictated by the SetType 52/// template parameter of the llvm::po_iterator template, as used with external 53/// storage. We also use this set to keep track of which CFGBlocks we visit 54/// during the analysis. 55class CFGBlockSet { 56 llvm::BitVector VisitedBlockIDs; 57 58public: 59 // po_iterator requires this iterator, but the only interface needed is the 60 // value_type typedef. 61 struct iterator { 62 typedef const CFGBlock *value_type; 63 }; 64 65 CFGBlockSet() {} 66 CFGBlockSet(const CFG *G) : VisitedBlockIDs(G->getNumBlockIDs(), false) {} 67 68 /// \brief Set the bit associated with a particular CFGBlock. 69 /// This is the important method for the SetType template parameter. 70 bool insert(const CFGBlock *Block) { 71 // Note that insert() is called by po_iterator, which doesn't check to make 72 // sure that Block is non-null. Moreover, the CFGBlock iterator will 73 // occasionally hand out null pointers for pruned edges, so we catch those 74 // here. 75 if (Block == 0) 76 return false; // if an edge is trivially false. 77 if (VisitedBlockIDs.test(Block->getBlockID())) 78 return false; 79 VisitedBlockIDs.set(Block->getBlockID()); 80 return true; 81 } 82 83 /// \brief Check if the bit for a CFGBlock has been already set. 84 /// This method is for tracking visited blocks in the main threadsafety loop. 85 /// Block must not be null. 86 bool alreadySet(const CFGBlock *Block) { 87 return VisitedBlockIDs.test(Block->getBlockID()); 88 } 89}; 90 91/// \brief We create a helper class which we use to iterate through CFGBlocks in 92/// the topological order. 93class TopologicallySortedCFG { 94 typedef llvm::po_iterator<const CFG*, CFGBlockSet, true> po_iterator; 95 96 std::vector<const CFGBlock*> Blocks; 97 98public: 99 typedef std::vector<const CFGBlock*>::reverse_iterator iterator; 100 101 TopologicallySortedCFG(const CFG *CFGraph) { 102 Blocks.reserve(CFGraph->getNumBlockIDs()); 103 CFGBlockSet BSet(CFGraph); 104 105 for (po_iterator I = po_iterator::begin(CFGraph, BSet), 106 E = po_iterator::end(CFGraph, BSet); I != E; ++I) { 107 Blocks.push_back(*I); 108 } 109 } 110 111 iterator begin() { 112 return Blocks.rbegin(); 113 } 114 115 iterator end() { 116 return Blocks.rend(); 117 } 118}; 119 120/// \brief A MutexID object uniquely identifies a particular mutex, and 121/// is built from an Expr* (i.e. calling a lock function). 122/// 123/// Thread-safety analysis works by comparing lock expressions. Within the 124/// body of a function, an expression such as "x->foo->bar.mu" will resolve to 125/// a particular mutex object at run-time. Subsequent occurrences of the same 126/// expression (where "same" means syntactic equality) will refer to the same 127/// run-time object if three conditions hold: 128/// (1) Local variables in the expression, such as "x" have not changed. 129/// (2) Values on the heap that affect the expression have not changed. 130/// (3) The expression involves only pure function calls. 131/// The current implementation assumes, but does not verify, that multiple uses 132/// of the same lock expression satisfies these criteria. 133/// 134/// Clang introduces an additional wrinkle, which is that it is difficult to 135/// derive canonical expressions, or compare expressions directly for equality. 136/// Thus, we identify a mutex not by an Expr, but by the set of named 137/// declarations that are referenced by the Expr. In other words, 138/// x->foo->bar.mu will be a four element vector with the Decls for 139/// mu, bar, and foo, and x. The vector will uniquely identify the expression 140/// for all practical purposes. 141/// 142/// Note we will need to perform substitution on "this" and function parameter 143/// names when constructing a lock expression. 144/// 145/// For example: 146/// class C { Mutex Mu; void lock() EXCLUSIVE_LOCK_FUNCTION(this->Mu); }; 147/// void myFunc(C *X) { ... X->lock() ... } 148/// The original expression for the mutex acquired by myFunc is "this->Mu", but 149/// "X" is substituted for "this" so we get X->Mu(); 150/// 151/// For another example: 152/// foo(MyList *L) EXCLUSIVE_LOCKS_REQUIRED(L->Mu) { ... } 153/// MyList *MyL; 154/// foo(MyL); // requires lock MyL->Mu to be held 155class MutexID { 156 SmallVector<NamedDecl*, 2> DeclSeq; 157 ThreadSafetyHandler &Handler; 158 159 /// Build a Decl sequence representing the lock from the given expression. 160 /// Recursive function that bottoms out when the final DeclRefExpr is reached. 161 void buildMutexID(Expr *Exp, Expr *Parent) { 162 if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(Exp)) { 163 NamedDecl *ND = cast<NamedDecl>(DRE->getDecl()->getCanonicalDecl()); 164 DeclSeq.push_back(ND); 165 } else if (MemberExpr *ME = dyn_cast<MemberExpr>(Exp)) { 166 NamedDecl *ND = ME->getMemberDecl(); 167 DeclSeq.push_back(ND); 168 buildMutexID(ME->getBase(), Parent); 169 } else if (isa<CXXThisExpr>(Exp)) { 170 if (!Parent) 171 return; 172 buildMutexID(Parent, 0); 173 } else if (CastExpr *CE = dyn_cast<CastExpr>(Exp)) 174 buildMutexID(CE->getSubExpr(), Parent); 175 else 176 Handler.handleInvalidLockExp(Exp->getExprLoc()); 177 } 178 179public: 180 MutexID(ThreadSafetyHandler &Handler, Expr *LExpr, Expr *ParentExpr) 181 : Handler(Handler) { 182 buildMutexID(LExpr, ParentExpr); 183 assert(!DeclSeq.empty()); 184 } 185 186 bool operator==(const MutexID &other) const { 187 return DeclSeq == other.DeclSeq; 188 } 189 190 bool operator!=(const MutexID &other) const { 191 return !(*this == other); 192 } 193 194 // SmallVector overloads Operator< to do lexicographic ordering. Note that 195 // we use pointer equality (and <) to compare NamedDecls. This means the order 196 // of MutexIDs in a lockset is nondeterministic. In order to output 197 // diagnostics in a deterministic ordering, we must order all diagnostics to 198 // output by SourceLocation when iterating through this lockset. 199 bool operator<(const MutexID &other) const { 200 return DeclSeq < other.DeclSeq; 201 } 202 203 /// \brief Returns the name of the first Decl in the list for a given MutexID; 204 /// e.g. the lock expression foo.bar() has name "bar". 205 /// The caret will point unambiguously to the lock expression, so using this 206 /// name in diagnostics is a way to get simple, and consistent, mutex names. 207 /// We do not want to output the entire expression text for security reasons. 208 StringRef getName() const { 209 return DeclSeq.front()->getName(); 210 } 211 212 void Profile(llvm::FoldingSetNodeID &ID) const { 213 for (SmallVectorImpl<NamedDecl*>::const_iterator I = DeclSeq.begin(), 214 E = DeclSeq.end(); I != E; ++I) { 215 ID.AddPointer(*I); 216 } 217 } 218}; 219 220/// \brief This is a helper class that stores info about the most recent 221/// accquire of a Lock. 222/// 223/// The main body of the analysis maps MutexIDs to LockDatas. 224struct LockData { 225 SourceLocation AcquireLoc; 226 227 /// \brief LKind stores whether a lock is held shared or exclusively. 228 /// Note that this analysis does not currently support either re-entrant 229 /// locking or lock "upgrading" and "downgrading" between exclusive and 230 /// shared. 231 /// 232 /// FIXME: add support for re-entrant locking and lock up/downgrading 233 LockKind LKind; 234 235 LockData(SourceLocation AcquireLoc, LockKind LKind) 236 : AcquireLoc(AcquireLoc), LKind(LKind) {} 237 238 bool operator==(const LockData &other) const { 239 return AcquireLoc == other.AcquireLoc && LKind == other.LKind; 240 } 241 242 bool operator!=(const LockData &other) const { 243 return !(*this == other); 244 } 245 246 void Profile(llvm::FoldingSetNodeID &ID) const { 247 ID.AddInteger(AcquireLoc.getRawEncoding()); 248 ID.AddInteger(LKind); 249 } 250}; 251 252/// A Lockset maps each MutexID (defined above) to information about how it has 253/// been locked. 254typedef llvm::ImmutableMap<MutexID, LockData> Lockset; 255 256/// \brief We use this class to visit different types of expressions in 257/// CFGBlocks, and build up the lockset. 258/// An expression may cause us to add or remove locks from the lockset, or else 259/// output error messages related to missing locks. 260/// FIXME: In future, we may be able to not inherit from a visitor. 261class BuildLockset : public StmtVisitor<BuildLockset> { 262 ThreadSafetyHandler &Handler; 263 Lockset LSet; 264 Lockset::Factory &LocksetFactory; 265 266 // Helper functions 267 void removeLock(SourceLocation UnlockLoc, Expr *LockExp, Expr *Parent); 268 void addLock(SourceLocation LockLoc, Expr *LockExp, Expr *Parent, 269 LockKind LK); 270 const ValueDecl *getValueDecl(Expr *Exp); 271 void warnIfMutexNotHeld (const NamedDecl *D, Expr *Exp, AccessKind AK, 272 Expr *MutexExp, ProtectedOperationKind POK); 273 void checkAccess(Expr *Exp, AccessKind AK); 274 void checkDereference(Expr *Exp, AccessKind AK); 275 276 template <class AttrType> 277 void addLocksToSet(LockKind LK, Attr *Attr, CXXMemberCallExpr *Exp); 278 279 /// \brief Returns true if the lockset contains a lock, regardless of whether 280 /// the lock is held exclusively or shared. 281 bool locksetContains(MutexID Lock) const { 282 return LSet.lookup(Lock); 283 } 284 285 /// \brief Returns true if the lockset contains a lock with the passed in 286 /// locktype. 287 bool locksetContains(MutexID Lock, LockKind KindRequested) const { 288 const LockData *LockHeld = LSet.lookup(Lock); 289 return (LockHeld && KindRequested == LockHeld->LKind); 290 } 291 292 /// \brief Returns true if the lockset contains a lock with at least the 293 /// passed in locktype. So for example, if we pass in LK_Shared, this function 294 /// returns true if the lock is held LK_Shared or LK_Exclusive. If we pass in 295 /// LK_Exclusive, this function returns true if the lock is held LK_Exclusive. 296 bool locksetContainsAtLeast(MutexID Lock, LockKind KindRequested) const { 297 switch (KindRequested) { 298 case LK_Shared: 299 return locksetContains(Lock); 300 case LK_Exclusive: 301 return locksetContains(Lock, KindRequested); 302 } 303 } 304 305public: 306 BuildLockset(ThreadSafetyHandler &Handler, Lockset LS, Lockset::Factory &F) 307 : StmtVisitor<BuildLockset>(), Handler(Handler), LSet(LS), 308 LocksetFactory(F) {} 309 310 Lockset getLockset() { 311 return LSet; 312 } 313 314 void VisitUnaryOperator(UnaryOperator *UO); 315 void VisitBinaryOperator(BinaryOperator *BO); 316 void VisitCastExpr(CastExpr *CE); 317 void VisitCXXMemberCallExpr(CXXMemberCallExpr *Exp); 318}; 319 320/// \brief Add a new lock to the lockset, warning if the lock is already there. 321/// \param LockLoc The source location of the acquire 322/// \param LockExp The lock expression corresponding to the lock to be added 323void BuildLockset::addLock(SourceLocation LockLoc, Expr *LockExp, Expr *Parent, 324 LockKind LK) { 325 // FIXME: deal with acquired before/after annotations 326 MutexID Mutex(Handler, LockExp, Parent); 327 LockData NewLock(LockLoc, LK); 328 329 // FIXME: Don't always warn when we have support for reentrant locks. 330 if (locksetContains(Mutex)) 331 Handler.handleDoubleLock(Mutex.getName(), LockLoc); 332 LSet = LocksetFactory.add(LSet, Mutex, NewLock); 333} 334 335/// \brief Remove a lock from the lockset, warning if the lock is not there. 336/// \param LockExp The lock expression corresponding to the lock to be removed 337/// \param UnlockLoc The source location of the unlock (only used in error msg) 338void BuildLockset::removeLock(SourceLocation UnlockLoc, Expr *LockExp, 339 Expr *Parent) { 340 MutexID Mutex(Handler, LockExp, Parent); 341 342 Lockset NewLSet = LocksetFactory.remove(LSet, Mutex); 343 if(NewLSet == LSet) 344 Handler.handleUnmatchedUnlock(Mutex.getName(), UnlockLoc); 345 346 LSet = NewLSet; 347} 348 349/// \brief Gets the value decl pointer from DeclRefExprs or MemberExprs 350const ValueDecl *BuildLockset::getValueDecl(Expr *Exp) { 351 if (const DeclRefExpr *DR = dyn_cast<DeclRefExpr>(Exp)) 352 return DR->getDecl(); 353 354 if (const MemberExpr *ME = dyn_cast<MemberExpr>(Exp)) 355 return ME->getMemberDecl(); 356 357 return 0; 358} 359 360/// \brief Warn if the LSet does not contain a lock sufficient to protect access 361/// of at least the passed in AccessType. 362void BuildLockset::warnIfMutexNotHeld(const NamedDecl *D, Expr *Exp, 363 AccessKind AK, Expr *MutexExp, 364 ProtectedOperationKind POK) { 365 LockKind LK = getLockKindFromAccessKind(AK); 366 Expr *Parent = getParent(Exp); 367 MutexID Mutex(Handler, MutexExp, Parent); 368 if (!locksetContainsAtLeast(Mutex, LK)) 369 Handler.handleMutexNotHeld(D, POK, Mutex.getName(), LK, Exp->getExprLoc()); 370} 371 372 373/// \brief This method identifies variable dereferences and checks pt_guarded_by 374/// and pt_guarded_var annotations. Note that we only check these annotations 375/// at the time a pointer is dereferenced. 376/// FIXME: We need to check for other types of pointer dereferences 377/// (e.g. [], ->) and deal with them here. 378/// \param Exp An expression that has been read or written. 379void BuildLockset::checkDereference(Expr *Exp, AccessKind AK) { 380 UnaryOperator *UO = dyn_cast<UnaryOperator>(Exp); 381 if (!UO || UO->getOpcode() != clang::UO_Deref) 382 return; 383 Exp = UO->getSubExpr()->IgnoreParenCasts(); 384 385 const ValueDecl *D = getValueDecl(Exp); 386 if(!D || !D->hasAttrs()) 387 return; 388 389 if (D->getAttr<PtGuardedVarAttr>() && LSet.isEmpty()) 390 Handler.handleNoMutexHeld(D, POK_VarDereference, AK, Exp->getExprLoc()); 391 392 const AttrVec &ArgAttrs = D->getAttrs(); 393 for(unsigned i = 0, Size = ArgAttrs.size(); i < Size; ++i) 394 if (PtGuardedByAttr *PGBAttr = dyn_cast<PtGuardedByAttr>(ArgAttrs[i])) 395 warnIfMutexNotHeld(D, Exp, AK, PGBAttr->getArg(), POK_VarDereference); 396} 397 398/// \brief Checks guarded_by and guarded_var attributes. 399/// Whenever we identify an access (read or write) of a DeclRefExpr or 400/// MemberExpr, we need to check whether there are any guarded_by or 401/// guarded_var attributes, and make sure we hold the appropriate mutexes. 402void BuildLockset::checkAccess(Expr *Exp, AccessKind AK) { 403 const ValueDecl *D = getValueDecl(Exp); 404 if(!D || !D->hasAttrs()) 405 return; 406 407 if (D->getAttr<GuardedVarAttr>() && LSet.isEmpty()) 408 Handler.handleNoMutexHeld(D, POK_VarAccess, AK, Exp->getExprLoc()); 409 410 const AttrVec &ArgAttrs = D->getAttrs(); 411 for(unsigned i = 0, Size = ArgAttrs.size(); i < Size; ++i) 412 if (GuardedByAttr *GBAttr = dyn_cast<GuardedByAttr>(ArgAttrs[i])) 413 warnIfMutexNotHeld(D, Exp, AK, GBAttr->getArg(), POK_VarAccess); 414} 415 416/// \brief For unary operations which read and write a variable, we need to 417/// check whether we hold any required mutexes. Reads are checked in 418/// VisitCastExpr. 419void BuildLockset::VisitUnaryOperator(UnaryOperator *UO) { 420 switch (UO->getOpcode()) { 421 case clang::UO_PostDec: 422 case clang::UO_PostInc: 423 case clang::UO_PreDec: 424 case clang::UO_PreInc: { 425 Expr *SubExp = UO->getSubExpr()->IgnoreParenCasts(); 426 checkAccess(SubExp, AK_Written); 427 checkDereference(SubExp, AK_Written); 428 break; 429 } 430 default: 431 break; 432 } 433} 434 435/// For binary operations which assign to a variable (writes), we need to check 436/// whether we hold any required mutexes. 437/// FIXME: Deal with non-primitive types. 438void BuildLockset::VisitBinaryOperator(BinaryOperator *BO) { 439 if (!BO->isAssignmentOp()) 440 return; 441 Expr *LHSExp = BO->getLHS()->IgnoreParenCasts(); 442 checkAccess(LHSExp, AK_Written); 443 checkDereference(LHSExp, AK_Written); 444} 445 446/// Whenever we do an LValue to Rvalue cast, we are reading a variable and 447/// need to ensure we hold any required mutexes. 448/// FIXME: Deal with non-primitive types. 449void BuildLockset::VisitCastExpr(CastExpr *CE) { 450 if (CE->getCastKind() != CK_LValueToRValue) 451 return; 452 Expr *SubExp = CE->getSubExpr()->IgnoreParenCasts(); 453 checkAccess(SubExp, AK_Read); 454 checkDereference(SubExp, AK_Read); 455} 456 457/// \brief This function, parameterized by an attribute type, is used to add a 458/// set of locks specified as attribute arguments to the lockset. 459template <typename AttrType> 460void BuildLockset::addLocksToSet(LockKind LK, Attr *Attr, 461 CXXMemberCallExpr *Exp) { 462 typedef typename AttrType::args_iterator iterator_type; 463 SourceLocation ExpLocation = Exp->getExprLoc(); 464 Expr *Parent = Exp->getImplicitObjectArgument(); 465 AttrType *SpecificAttr = cast<AttrType>(Attr); 466 467 if (SpecificAttr->args_size() == 0) { 468 // The mutex held is the "this" object. 469 addLock(ExpLocation, Parent, Parent, LK); 470 return; 471 } 472 473 for (iterator_type I = SpecificAttr->args_begin(), 474 E = SpecificAttr->args_end(); I != E; ++I) 475 addLock(ExpLocation, *I, Parent, LK); 476} 477 478/// \brief When visiting CXXMemberCallExprs we need to examine the attributes on 479/// the method that is being called and add, remove or check locks in the 480/// lockset accordingly. 481/// 482/// FIXME: For classes annotated with one of the guarded annotations, we need 483/// to treat const method calls as reads and non-const method calls as writes, 484/// and check that the appropriate locks are held. Non-const method calls with 485/// the same signature as const method calls can be also treated as reads. 486/// 487/// FIXME: We need to also visit CallExprs to catch/check global functions. 488void BuildLockset::VisitCXXMemberCallExpr(CXXMemberCallExpr *Exp) { 489 NamedDecl *D = dyn_cast_or_null<NamedDecl>(Exp->getCalleeDecl()); 490 491 SourceLocation ExpLocation = Exp->getExprLoc(); 492 Expr *Parent = Exp->getImplicitObjectArgument(); 493 494 if(!D || !D->hasAttrs()) 495 return; 496 497 AttrVec &ArgAttrs = D->getAttrs(); 498 for(unsigned i = 0; i < ArgAttrs.size(); ++i) { 499 Attr *Attr = ArgAttrs[i]; 500 switch (Attr->getKind()) { 501 // When we encounter an exclusive lock function, we need to add the lock 502 // to our lockset with kind exclusive. 503 case attr::ExclusiveLockFunction: 504 addLocksToSet<ExclusiveLockFunctionAttr>(LK_Exclusive, Attr, Exp); 505 break; 506 507 // When we encounter a shared lock function, we need to add the lock 508 // to our lockset with kind shared. 509 case attr::SharedLockFunction: 510 addLocksToSet<SharedLockFunctionAttr>(LK_Shared, Attr, Exp); 511 break; 512 513 // When we encounter an unlock function, we need to remove unlocked 514 // mutexes from the lockset, and flag a warning if they are not there. 515 case attr::UnlockFunction: { 516 UnlockFunctionAttr *UFAttr = cast<UnlockFunctionAttr>(Attr); 517 518 if (UFAttr->args_size() == 0) { // The lock held is the "this" object. 519 removeLock(ExpLocation, Parent, Parent); 520 break; 521 } 522 523 for (UnlockFunctionAttr::args_iterator I = UFAttr->args_begin(), 524 E = UFAttr->args_end(); I != E; ++I) 525 removeLock(ExpLocation, *I, Parent); 526 break; 527 } 528 529 case attr::ExclusiveLocksRequired: { 530 // FIXME: Also use this attribute to add required locks to the initial 531 // lockset when processing a CFG for a function annotated with this 532 // attribute. 533 ExclusiveLocksRequiredAttr *ELRAttr = 534 cast<ExclusiveLocksRequiredAttr>(Attr); 535 536 for (ExclusiveLocksRequiredAttr::args_iterator 537 I = ELRAttr->args_begin(), E = ELRAttr->args_end(); I != E; ++I) 538 warnIfMutexNotHeld(D, Exp, AK_Written, *I, POK_FunctionCall); 539 break; 540 } 541 542 case attr::SharedLocksRequired: { 543 // FIXME: Also use this attribute to add required locks to the initial 544 // lockset when processing a CFG for a function annotated with this 545 // attribute. 546 SharedLocksRequiredAttr *SLRAttr = cast<SharedLocksRequiredAttr>(Attr); 547 548 for (SharedLocksRequiredAttr::args_iterator I = SLRAttr->args_begin(), 549 E = SLRAttr->args_end(); I != E; ++I) 550 warnIfMutexNotHeld(D, Exp, AK_Read, *I, POK_FunctionCall); 551 break; 552 } 553 554 case attr::LocksExcluded: { 555 LocksExcludedAttr *LEAttr = cast<LocksExcludedAttr>(Attr); 556 for (LocksExcludedAttr::args_iterator I = LEAttr->args_begin(), 557 E = LEAttr->args_end(); I != E; ++I) { 558 MutexID Mutex(Handler, *I, Parent); 559 if (locksetContains(Mutex)) 560 Handler.handleFunExcludesLock(D->getName(), Mutex.getName(), 561 ExpLocation); 562 } 563 break; 564 } 565 566 case attr::LockReturned: 567 // FIXME: Deal with this attribute. 568 break; 569 570 // Ignore other (non thread-safety) attributes 571 default: 572 break; 573 } 574 } 575} 576 577} // end anonymous namespace 578 579/// \brief Flags a warning for each lock that is in LSet2 but not LSet1, or 580/// else mutexes that are held shared in one lockset and exclusive in the other. 581static Lockset warnIfNotInFirstSetOrNotSameKind(ThreadSafetyHandler &Handler, 582 const Lockset LSet1, 583 const Lockset LSet2, 584 Lockset Intersection, 585 Lockset::Factory &Fact) { 586 for (Lockset::iterator I = LSet2.begin(), E = LSet2.end(); I != E; ++I) { 587 const MutexID &LSet2Mutex = I.getKey(); 588 const LockData &LSet2LockData = I.getData(); 589 if (const LockData *LD = LSet1.lookup(LSet2Mutex)) { 590 if (LD->LKind != LSet2LockData.LKind) { 591 Handler.handleExclusiveAndShared(LSet2Mutex.getName(), 592 LSet2LockData.AcquireLoc, 593 LD->AcquireLoc); 594 if (LD->LKind != LK_Exclusive) 595 Intersection = Fact.add(Intersection, LSet2Mutex, LSet2LockData); 596 } 597 } else { 598 Handler.handleMutexHeldEndOfScope(LSet2Mutex.getName(), 599 LSet2LockData.AcquireLoc); 600 } 601 } 602 return Intersection; 603} 604 605 606/// \brief Compute the intersection of two locksets and issue warnings for any 607/// locks in the symmetric difference. 608/// 609/// This function is used at a merge point in the CFG when comparing the lockset 610/// of each branch being merged. For example, given the following sequence: 611/// A; if () then B; else C; D; we need to check that the lockset after B and C 612/// are the same. In the event of a difference, we use the intersection of these 613/// two locksets at the start of D. 614static Lockset intersectAndWarn(ThreadSafetyHandler &Handler, 615 const Lockset LSet1, const Lockset LSet2, 616 Lockset::Factory &Fact) { 617 Lockset Intersection = LSet1; 618 Intersection = warnIfNotInFirstSetOrNotSameKind(Handler, LSet1, LSet2, 619 Intersection, Fact); 620 621 for (Lockset::iterator I = LSet1.begin(), E = LSet1.end(); I != E; ++I) { 622 if (!LSet2.contains(I.getKey())) { 623 const MutexID &Mutex = I.getKey(); 624 const LockData &MissingLock = I.getData(); 625 Handler.handleMutexHeldEndOfScope(Mutex.getName(), 626 MissingLock.AcquireLoc); 627 Intersection = Fact.remove(Intersection, Mutex); 628 } 629 } 630 return Intersection; 631} 632 633/// \brief Returns the location of the first Stmt in a Block. 634static SourceLocation getFirstStmtLocation(CFGBlock *Block) { 635 SourceLocation Loc; 636 for (CFGBlock::const_iterator BI = Block->begin(), BE = Block->end(); 637 BI != BE; ++BI) { 638 if (const CFGStmt *CfgStmt = dyn_cast<CFGStmt>(&(*BI))) { 639 Loc = CfgStmt->getStmt()->getLocStart(); 640 if (Loc.isValid()) return Loc; 641 } 642 } 643 if (Stmt *S = Block->getTerminator().getStmt()) { 644 Loc = S->getLocStart(); 645 if (Loc.isValid()) return Loc; 646 } 647 return Loc; 648} 649 650/// \brief Warn about different locksets along backedges of loops. 651/// This function is called when we encounter a back edge. At that point, 652/// we need to verify that the lockset before taking the backedge is the 653/// same as the lockset before entering the loop. 654/// 655/// \param LoopEntrySet Locks before starting the loop 656/// \param LoopReentrySet Locks in the last CFG block of the loop 657static void warnBackEdgeUnequalLocksets(ThreadSafetyHandler &Handler, 658 const Lockset LoopReentrySet, 659 const Lockset LoopEntrySet, 660 SourceLocation FirstLocInLoop, 661 Lockset::Factory &Fact) { 662 assert(FirstLocInLoop.isValid()); 663 // Warn for locks held at the start of the loop, but not the end. 664 for (Lockset::iterator I = LoopEntrySet.begin(), E = LoopEntrySet.end(); 665 I != E; ++I) { 666 if (!LoopReentrySet.contains(I.getKey())) { 667 // We report this error at the location of the first statement in a loop 668 Handler.handleNoLockLoopEntry(I.getKey().getName(), FirstLocInLoop); 669 } 670 } 671 672 // Warn for locks held at the end of the loop, but not at the start. 673 warnIfNotInFirstSetOrNotSameKind(Handler, LoopEntrySet, LoopReentrySet, 674 LoopReentrySet, Fact); 675} 676 677 678namespace clang { namespace thread_safety { 679/// \brief Check a function's CFG for thread-safety violations. 680/// 681/// We traverse the blocks in the CFG, compute the set of mutexes that are held 682/// at the end of each block, and issue warnings for thread safety violations. 683/// Each block in the CFG is traversed exactly once. 684void runThreadSafetyAnalysis(AnalysisContext &AC, 685 ThreadSafetyHandler &Handler) { 686 CFG *CFGraph = AC.getCFG(); 687 if (!CFGraph) return; 688 const Decl *D = AC.getDecl(); 689 if (D && D->getAttr<NoThreadSafetyAnalysisAttr>()) return; 690 691 Lockset::Factory LocksetFactory; 692 693 // FIXME: Swith to SmallVector? Otherwise improve performance impact? 694 std::vector<Lockset> EntryLocksets(CFGraph->getNumBlockIDs(), 695 LocksetFactory.getEmptyMap()); 696 std::vector<Lockset> ExitLocksets(CFGraph->getNumBlockIDs(), 697 LocksetFactory.getEmptyMap()); 698 699 // We need to explore the CFG via a "topological" ordering. 700 // That way, we will be guaranteed to have information about required 701 // predecessor locksets when exploring a new block. 702 TopologicallySortedCFG SortedGraph(CFGraph); 703 CFGBlockSet VisitedBlocks(CFGraph); 704 705 for (TopologicallySortedCFG::iterator I = SortedGraph.begin(), 706 E = SortedGraph.end(); I!= E; ++I) { 707 const CFGBlock *CurrBlock = *I; 708 int CurrBlockID = CurrBlock->getBlockID(); 709 710 VisitedBlocks.insert(CurrBlock); 711 712 // Use the default initial lockset in case there are no predecessors. 713 Lockset &Entryset = EntryLocksets[CurrBlockID]; 714 Lockset &Exitset = ExitLocksets[CurrBlockID]; 715 716 // Iterate through the predecessor blocks and warn if the lockset for all 717 // predecessors is not the same. We take the entry lockset of the current 718 // block to be the intersection of all previous locksets. 719 // FIXME: By keeping the intersection, we may output more errors in future 720 // for a lock which is not in the intersection, but was in the union. We 721 // may want to also keep the union in future. As an example, let's say 722 // the intersection contains Mutex L, and the union contains L and M. 723 // Later we unlock M. At this point, we would output an error because we 724 // never locked M; although the real error is probably that we forgot to 725 // lock M on all code paths. Conversely, let's say that later we lock M. 726 // In this case, we should compare against the intersection instead of the 727 // union because the real error is probably that we forgot to unlock M on 728 // all code paths. 729 bool LocksetInitialized = false; 730 for (CFGBlock::const_pred_iterator PI = CurrBlock->pred_begin(), 731 PE = CurrBlock->pred_end(); PI != PE; ++PI) { 732 733 // if *PI -> CurrBlock is a back edge 734 if (*PI == 0 || !VisitedBlocks.alreadySet(*PI)) 735 continue; 736 737 int PrevBlockID = (*PI)->getBlockID(); 738 if (!LocksetInitialized) { 739 Entryset = ExitLocksets[PrevBlockID]; 740 LocksetInitialized = true; 741 } else { 742 Entryset = intersectAndWarn(Handler, Entryset, 743 ExitLocksets[PrevBlockID], LocksetFactory); 744 } 745 } 746 747 BuildLockset LocksetBuilder(Handler, Entryset, LocksetFactory); 748 for (CFGBlock::const_iterator BI = CurrBlock->begin(), 749 BE = CurrBlock->end(); BI != BE; ++BI) { 750 if (const CFGStmt *CfgStmt = dyn_cast<CFGStmt>(&*BI)) 751 LocksetBuilder.Visit(const_cast<Stmt*>(CfgStmt->getStmt())); 752 } 753 Exitset = LocksetBuilder.getLockset(); 754 755 // For every back edge from CurrBlock (the end of the loop) to another block 756 // (FirstLoopBlock) we need to check that the Lockset of Block is equal to 757 // the one held at the beginning of FirstLoopBlock. We can look up the 758 // Lockset held at the beginning of FirstLoopBlock in the EntryLockSets map. 759 for (CFGBlock::const_succ_iterator SI = CurrBlock->succ_begin(), 760 SE = CurrBlock->succ_end(); SI != SE; ++SI) { 761 762 // if CurrBlock -> *SI is *not* a back edge 763 if (*SI == 0 || !VisitedBlocks.alreadySet(*SI)) 764 continue; 765 766 CFGBlock *FirstLoopBlock = *SI; 767 SourceLocation FirstLoopLocation = getFirstStmtLocation(FirstLoopBlock); 768 769 assert(FirstLoopLocation.isValid()); 770 771 // Fail gracefully in release code. 772 if (!FirstLoopLocation.isValid()) 773 continue; 774 775 Lockset PreLoop = EntryLocksets[FirstLoopBlock->getBlockID()]; 776 Lockset LoopEnd = ExitLocksets[CurrBlockID]; 777 warnBackEdgeUnequalLocksets(Handler, LoopEnd, PreLoop, FirstLoopLocation, 778 LocksetFactory); 779 } 780 } 781 782 Lockset FinalLockset = ExitLocksets[CFGraph->getExit().getBlockID()]; 783 if (!FinalLockset.isEmpty()) { 784 for (Lockset::iterator I=FinalLockset.begin(), E=FinalLockset.end(); 785 I != E; ++I) { 786 const MutexID &Mutex = I.getKey(); 787 const LockData &MissingLock = I.getData(); 788 789 std::string FunName = "<unknown>"; 790 if (const NamedDecl *ContextDecl = dyn_cast<NamedDecl>(AC.getDecl())) { 791 FunName = ContextDecl->getDeclName().getAsString(); 792 } 793 794 Handler.handleNoUnlock(Mutex.getName(), FunName, MissingLock.AcquireLoc); 795 } 796 } 797} 798 799/// \brief Helper function that returns a LockKind required for the given level 800/// of access. 801LockKind getLockKindFromAccessKind(AccessKind AK) { 802 switch (AK) { 803 case AK_Read : 804 return LK_Shared; 805 case AK_Written : 806 return LK_Exclusive; 807 } 808} 809}} // end namespace clang::thread_safety 810