1// SValBuilder.cpp - Basic class for all SValBuilder implementations -*- 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 SValBuilder, the base class for all (complete) SValBuilder
11//  implementations.
12//
13//===----------------------------------------------------------------------===//
14
15#include "clang/StaticAnalyzer/Core/PathSensitive/SValBuilder.h"
16#include "clang/AST/DeclCXX.h"
17#include "clang/AST/ExprCXX.h"
18#include "clang/StaticAnalyzer/Core/PathSensitive/BasicValueFactory.h"
19#include "clang/StaticAnalyzer/Core/PathSensitive/MemRegion.h"
20#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
21#include "clang/StaticAnalyzer/Core/PathSensitive/SVals.h"
22
23using namespace clang;
24using namespace ento;
25
26//===----------------------------------------------------------------------===//
27// Basic SVal creation.
28//===----------------------------------------------------------------------===//
29
30void SValBuilder::anchor() { }
31
32DefinedOrUnknownSVal SValBuilder::makeZeroVal(QualType type) {
33  if (Loc::isLocType(type))
34    return makeNull();
35
36  if (type->isIntegralOrEnumerationType())
37    return makeIntVal(0, type);
38
39  // FIXME: Handle floats.
40  // FIXME: Handle structs.
41  return UnknownVal();
42}
43
44NonLoc SValBuilder::makeNonLoc(const SymExpr *lhs, BinaryOperator::Opcode op,
45                                const llvm::APSInt& rhs, QualType type) {
46  // The Environment ensures we always get a persistent APSInt in
47  // BasicValueFactory, so we don't need to get the APSInt from
48  // BasicValueFactory again.
49  assert(lhs);
50  assert(!Loc::isLocType(type));
51  return nonloc::SymbolVal(SymMgr.getSymIntExpr(lhs, op, rhs, type));
52}
53
54NonLoc SValBuilder::makeNonLoc(const llvm::APSInt& lhs,
55                               BinaryOperator::Opcode op, const SymExpr *rhs,
56                               QualType type) {
57  assert(rhs);
58  assert(!Loc::isLocType(type));
59  return nonloc::SymbolVal(SymMgr.getIntSymExpr(lhs, op, rhs, type));
60}
61
62NonLoc SValBuilder::makeNonLoc(const SymExpr *lhs, BinaryOperator::Opcode op,
63                               const SymExpr *rhs, QualType type) {
64  assert(lhs && rhs);
65  assert(!Loc::isLocType(type));
66  return nonloc::SymbolVal(SymMgr.getSymSymExpr(lhs, op, rhs, type));
67}
68
69NonLoc SValBuilder::makeNonLoc(const SymExpr *operand,
70                               QualType fromTy, QualType toTy) {
71  assert(operand);
72  assert(!Loc::isLocType(toTy));
73  return nonloc::SymbolVal(SymMgr.getCastSymbol(operand, fromTy, toTy));
74}
75
76SVal SValBuilder::convertToArrayIndex(SVal val) {
77  if (val.isUnknownOrUndef())
78    return val;
79
80  // Common case: we have an appropriately sized integer.
81  if (Optional<nonloc::ConcreteInt> CI = val.getAs<nonloc::ConcreteInt>()) {
82    const llvm::APSInt& I = CI->getValue();
83    if (I.getBitWidth() == ArrayIndexWidth && I.isSigned())
84      return val;
85  }
86
87  return evalCastFromNonLoc(val.castAs<NonLoc>(), ArrayIndexTy);
88}
89
90nonloc::ConcreteInt SValBuilder::makeBoolVal(const CXXBoolLiteralExpr *boolean){
91  return makeTruthVal(boolean->getValue());
92}
93
94DefinedOrUnknownSVal
95SValBuilder::getRegionValueSymbolVal(const TypedValueRegion* region) {
96  QualType T = region->getValueType();
97
98  if (!SymbolManager::canSymbolicate(T))
99    return UnknownVal();
100
101  SymbolRef sym = SymMgr.getRegionValueSymbol(region);
102
103  if (Loc::isLocType(T))
104    return loc::MemRegionVal(MemMgr.getSymbolicRegion(sym));
105
106  return nonloc::SymbolVal(sym);
107}
108
109DefinedOrUnknownSVal SValBuilder::conjureSymbolVal(const void *SymbolTag,
110                                                   const Expr *Ex,
111                                                   const LocationContext *LCtx,
112                                                   unsigned Count) {
113  QualType T = Ex->getType();
114
115  // Compute the type of the result. If the expression is not an R-value, the
116  // result should be a location.
117  QualType ExType = Ex->getType();
118  if (Ex->isGLValue())
119    T = LCtx->getAnalysisDeclContext()->getASTContext().getPointerType(ExType);
120
121  return conjureSymbolVal(SymbolTag, Ex, LCtx, T, Count);
122}
123
124DefinedOrUnknownSVal SValBuilder::conjureSymbolVal(const void *symbolTag,
125                                                   const Expr *expr,
126                                                   const LocationContext *LCtx,
127                                                   QualType type,
128                                                   unsigned count) {
129  if (!SymbolManager::canSymbolicate(type))
130    return UnknownVal();
131
132  SymbolRef sym = SymMgr.conjureSymbol(expr, LCtx, type, count, symbolTag);
133
134  if (Loc::isLocType(type))
135    return loc::MemRegionVal(MemMgr.getSymbolicRegion(sym));
136
137  return nonloc::SymbolVal(sym);
138}
139
140
141DefinedOrUnknownSVal SValBuilder::conjureSymbolVal(const Stmt *stmt,
142                                                   const LocationContext *LCtx,
143                                                   QualType type,
144                                                   unsigned visitCount) {
145  if (!SymbolManager::canSymbolicate(type))
146    return UnknownVal();
147
148  SymbolRef sym = SymMgr.conjureSymbol(stmt, LCtx, type, visitCount);
149
150  if (Loc::isLocType(type))
151    return loc::MemRegionVal(MemMgr.getSymbolicRegion(sym));
152
153  return nonloc::SymbolVal(sym);
154}
155
156DefinedOrUnknownSVal
157SValBuilder::getConjuredHeapSymbolVal(const Expr *E,
158                                      const LocationContext *LCtx,
159                                      unsigned VisitCount) {
160  QualType T = E->getType();
161  assert(Loc::isLocType(T));
162  assert(SymbolManager::canSymbolicate(T));
163
164  SymbolRef sym = SymMgr.conjureSymbol(E, LCtx, T, VisitCount);
165  return loc::MemRegionVal(MemMgr.getSymbolicHeapRegion(sym));
166}
167
168DefinedSVal SValBuilder::getMetadataSymbolVal(const void *symbolTag,
169                                              const MemRegion *region,
170                                              const Expr *expr, QualType type,
171                                              unsigned count) {
172  assert(SymbolManager::canSymbolicate(type) && "Invalid metadata symbol type");
173
174  SymbolRef sym =
175      SymMgr.getMetadataSymbol(region, expr, type, count, symbolTag);
176
177  if (Loc::isLocType(type))
178    return loc::MemRegionVal(MemMgr.getSymbolicRegion(sym));
179
180  return nonloc::SymbolVal(sym);
181}
182
183DefinedOrUnknownSVal
184SValBuilder::getDerivedRegionValueSymbolVal(SymbolRef parentSymbol,
185                                             const TypedValueRegion *region) {
186  QualType T = region->getValueType();
187
188  if (!SymbolManager::canSymbolicate(T))
189    return UnknownVal();
190
191  SymbolRef sym = SymMgr.getDerivedSymbol(parentSymbol, region);
192
193  if (Loc::isLocType(T))
194    return loc::MemRegionVal(MemMgr.getSymbolicRegion(sym));
195
196  return nonloc::SymbolVal(sym);
197}
198
199DefinedSVal SValBuilder::getFunctionPointer(const FunctionDecl *func) {
200  return loc::MemRegionVal(MemMgr.getFunctionTextRegion(func));
201}
202
203DefinedSVal SValBuilder::getBlockPointer(const BlockDecl *block,
204                                         CanQualType locTy,
205                                         const LocationContext *locContext,
206                                         unsigned blockCount) {
207  const BlockTextRegion *BC =
208    MemMgr.getBlockTextRegion(block, locTy, locContext->getAnalysisDeclContext());
209  const BlockDataRegion *BD = MemMgr.getBlockDataRegion(BC, locContext,
210                                                        blockCount);
211  return loc::MemRegionVal(BD);
212}
213
214/// Return a memory region for the 'this' object reference.
215loc::MemRegionVal SValBuilder::getCXXThis(const CXXMethodDecl *D,
216                                          const StackFrameContext *SFC) {
217  return loc::MemRegionVal(getRegionManager().
218                           getCXXThisRegion(D->getThisType(getContext()), SFC));
219}
220
221/// Return a memory region for the 'this' object reference.
222loc::MemRegionVal SValBuilder::getCXXThis(const CXXRecordDecl *D,
223                                          const StackFrameContext *SFC) {
224  const Type *T = D->getTypeForDecl();
225  QualType PT = getContext().getPointerType(QualType(T, 0));
226  return loc::MemRegionVal(getRegionManager().getCXXThisRegion(PT, SFC));
227}
228
229Optional<SVal> SValBuilder::getConstantVal(const Expr *E) {
230  E = E->IgnoreParens();
231
232  switch (E->getStmtClass()) {
233  // Handle expressions that we treat differently from the AST's constant
234  // evaluator.
235  case Stmt::AddrLabelExprClass:
236    return makeLoc(cast<AddrLabelExpr>(E));
237
238  case Stmt::CXXScalarValueInitExprClass:
239  case Stmt::ImplicitValueInitExprClass:
240    return makeZeroVal(E->getType());
241
242  case Stmt::ObjCStringLiteralClass: {
243    const ObjCStringLiteral *SL = cast<ObjCStringLiteral>(E);
244    return makeLoc(getRegionManager().getObjCStringRegion(SL));
245  }
246
247  case Stmt::StringLiteralClass: {
248    const StringLiteral *SL = cast<StringLiteral>(E);
249    return makeLoc(getRegionManager().getStringRegion(SL));
250  }
251
252  // Fast-path some expressions to avoid the overhead of going through the AST's
253  // constant evaluator
254  case Stmt::CharacterLiteralClass: {
255    const CharacterLiteral *C = cast<CharacterLiteral>(E);
256    return makeIntVal(C->getValue(), C->getType());
257  }
258
259  case Stmt::CXXBoolLiteralExprClass:
260    return makeBoolVal(cast<CXXBoolLiteralExpr>(E));
261
262  case Stmt::IntegerLiteralClass:
263    return makeIntVal(cast<IntegerLiteral>(E));
264
265  case Stmt::ObjCBoolLiteralExprClass:
266    return makeBoolVal(cast<ObjCBoolLiteralExpr>(E));
267
268  case Stmt::CXXNullPtrLiteralExprClass:
269    return makeNull();
270
271  case Stmt::ImplicitCastExprClass: {
272    const CastExpr *CE = cast<CastExpr>(E);
273    if (CE->getCastKind() == CK_ArrayToPointerDecay) {
274      Optional<SVal> ArrayVal = getConstantVal(CE->getSubExpr());
275      if (!ArrayVal)
276        return None;
277      return evalCast(*ArrayVal, CE->getType(), CE->getSubExpr()->getType());
278    }
279    // FALLTHROUGH
280  }
281
282  // If we don't have a special case, fall back to the AST's constant evaluator.
283  default: {
284    // Don't try to come up with a value for materialized temporaries.
285    if (E->isGLValue())
286      return None;
287
288    ASTContext &Ctx = getContext();
289    llvm::APSInt Result;
290    if (E->EvaluateAsInt(Result, Ctx))
291      return makeIntVal(Result);
292
293    if (Loc::isLocType(E->getType()))
294      if (E->isNullPointerConstant(Ctx, Expr::NPC_ValueDependentIsNotNull))
295        return makeNull();
296
297    return None;
298  }
299  }
300}
301
302//===----------------------------------------------------------------------===//
303
304SVal SValBuilder::makeSymExprValNN(ProgramStateRef State,
305                                   BinaryOperator::Opcode Op,
306                                   NonLoc LHS, NonLoc RHS,
307                                   QualType ResultTy) {
308  if (!State->isTainted(RHS) && !State->isTainted(LHS))
309    return UnknownVal();
310
311  const SymExpr *symLHS = LHS.getAsSymExpr();
312  const SymExpr *symRHS = RHS.getAsSymExpr();
313  // TODO: When the Max Complexity is reached, we should conjure a symbol
314  // instead of generating an Unknown value and propagate the taint info to it.
315  const unsigned MaxComp = 10000; // 100000 28X
316
317  if (symLHS && symRHS &&
318      (symLHS->computeComplexity() + symRHS->computeComplexity()) <  MaxComp)
319    return makeNonLoc(symLHS, Op, symRHS, ResultTy);
320
321  if (symLHS && symLHS->computeComplexity() < MaxComp)
322    if (Optional<nonloc::ConcreteInt> rInt = RHS.getAs<nonloc::ConcreteInt>())
323      return makeNonLoc(symLHS, Op, rInt->getValue(), ResultTy);
324
325  if (symRHS && symRHS->computeComplexity() < MaxComp)
326    if (Optional<nonloc::ConcreteInt> lInt = LHS.getAs<nonloc::ConcreteInt>())
327      return makeNonLoc(lInt->getValue(), Op, symRHS, ResultTy);
328
329  return UnknownVal();
330}
331
332
333SVal SValBuilder::evalBinOp(ProgramStateRef state, BinaryOperator::Opcode op,
334                            SVal lhs, SVal rhs, QualType type) {
335
336  if (lhs.isUndef() || rhs.isUndef())
337    return UndefinedVal();
338
339  if (lhs.isUnknown() || rhs.isUnknown())
340    return UnknownVal();
341
342  if (Optional<Loc> LV = lhs.getAs<Loc>()) {
343    if (Optional<Loc> RV = rhs.getAs<Loc>())
344      return evalBinOpLL(state, op, *LV, *RV, type);
345
346    return evalBinOpLN(state, op, *LV, rhs.castAs<NonLoc>(), type);
347  }
348
349  if (Optional<Loc> RV = rhs.getAs<Loc>()) {
350    // Support pointer arithmetic where the addend is on the left
351    // and the pointer on the right.
352    assert(op == BO_Add);
353
354    // Commute the operands.
355    return evalBinOpLN(state, op, *RV, lhs.castAs<NonLoc>(), type);
356  }
357
358  return evalBinOpNN(state, op, lhs.castAs<NonLoc>(), rhs.castAs<NonLoc>(),
359                     type);
360}
361
362DefinedOrUnknownSVal SValBuilder::evalEQ(ProgramStateRef state,
363                                         DefinedOrUnknownSVal lhs,
364                                         DefinedOrUnknownSVal rhs) {
365  return evalBinOp(state, BO_EQ, lhs, rhs, getConditionType())
366      .castAs<DefinedOrUnknownSVal>();
367}
368
369/// Recursively check if the pointer types are equal modulo const, volatile,
370/// and restrict qualifiers. Also, assume that all types are similar to 'void'.
371/// Assumes the input types are canonical.
372static bool shouldBeModeledWithNoOp(ASTContext &Context, QualType ToTy,
373                                                         QualType FromTy) {
374  while (Context.UnwrapSimilarPointerTypes(ToTy, FromTy)) {
375    Qualifiers Quals1, Quals2;
376    ToTy = Context.getUnqualifiedArrayType(ToTy, Quals1);
377    FromTy = Context.getUnqualifiedArrayType(FromTy, Quals2);
378
379    // Make sure that non-cvr-qualifiers the other qualifiers (e.g., address
380    // spaces) are identical.
381    Quals1.removeCVRQualifiers();
382    Quals2.removeCVRQualifiers();
383    if (Quals1 != Quals2)
384      return false;
385  }
386
387  // If we are casting to void, the 'From' value can be used to represent the
388  // 'To' value.
389  if (ToTy->isVoidType())
390    return true;
391
392  if (ToTy != FromTy)
393    return false;
394
395  return true;
396}
397
398// FIXME: should rewrite according to the cast kind.
399SVal SValBuilder::evalCast(SVal val, QualType castTy, QualType originalTy) {
400  castTy = Context.getCanonicalType(castTy);
401  originalTy = Context.getCanonicalType(originalTy);
402  if (val.isUnknownOrUndef() || castTy == originalTy)
403    return val;
404
405  if (castTy->isBooleanType()) {
406    if (val.isUnknownOrUndef())
407      return val;
408    if (val.isConstant())
409      return makeTruthVal(!val.isZeroConstant(), castTy);
410    if (!Loc::isLocType(originalTy) &&
411        !originalTy->isIntegralOrEnumerationType() &&
412        !originalTy->isMemberPointerType())
413      return UnknownVal();
414    if (SymbolRef Sym = val.getAsSymbol(true)) {
415      BasicValueFactory &BVF = getBasicValueFactory();
416      // FIXME: If we had a state here, we could see if the symbol is known to
417      // be zero, but we don't.
418      return makeNonLoc(Sym, BO_NE, BVF.getValue(0, Sym->getType()), castTy);
419    }
420    // Loc values are not always true, they could be weakly linked functions.
421    if (Optional<Loc> L = val.getAs<Loc>())
422      return evalCastFromLoc(*L, castTy);
423
424    Loc L = val.castAs<nonloc::LocAsInteger>().getLoc();
425    return evalCastFromLoc(L, castTy);
426  }
427
428  // For const casts, casts to void, just propagate the value.
429  if (!castTy->isVariableArrayType() && !originalTy->isVariableArrayType())
430    if (shouldBeModeledWithNoOp(Context, Context.getPointerType(castTy),
431                                         Context.getPointerType(originalTy)))
432      return val;
433
434  // Check for casts from pointers to integers.
435  if (castTy->isIntegralOrEnumerationType() && Loc::isLocType(originalTy))
436    return evalCastFromLoc(val.castAs<Loc>(), castTy);
437
438  // Check for casts from integers to pointers.
439  if (Loc::isLocType(castTy) && originalTy->isIntegralOrEnumerationType()) {
440    if (Optional<nonloc::LocAsInteger> LV = val.getAs<nonloc::LocAsInteger>()) {
441      if (const MemRegion *R = LV->getLoc().getAsRegion()) {
442        StoreManager &storeMgr = StateMgr.getStoreManager();
443        R = storeMgr.castRegion(R, castTy);
444        return R ? SVal(loc::MemRegionVal(R)) : UnknownVal();
445      }
446      return LV->getLoc();
447    }
448    return dispatchCast(val, castTy);
449  }
450
451  // Just pass through function and block pointers.
452  if (originalTy->isBlockPointerType() || originalTy->isFunctionPointerType()) {
453    assert(Loc::isLocType(castTy));
454    return val;
455  }
456
457  // Check for casts from array type to another type.
458  if (const ArrayType *arrayT =
459                      dyn_cast<ArrayType>(originalTy.getCanonicalType())) {
460    // We will always decay to a pointer.
461    QualType elemTy = arrayT->getElementType();
462    val = StateMgr.ArrayToPointer(val.castAs<Loc>(), elemTy);
463
464    // Are we casting from an array to a pointer?  If so just pass on
465    // the decayed value.
466    if (castTy->isPointerType() || castTy->isReferenceType())
467      return val;
468
469    // Are we casting from an array to an integer?  If so, cast the decayed
470    // pointer value to an integer.
471    assert(castTy->isIntegralOrEnumerationType());
472
473    // FIXME: Keep these here for now in case we decide soon that we
474    // need the original decayed type.
475    //    QualType elemTy = cast<ArrayType>(originalTy)->getElementType();
476    //    QualType pointerTy = C.getPointerType(elemTy);
477    return evalCastFromLoc(val.castAs<Loc>(), castTy);
478  }
479
480  // Check for casts from a region to a specific type.
481  if (const MemRegion *R = val.getAsRegion()) {
482    // Handle other casts of locations to integers.
483    if (castTy->isIntegralOrEnumerationType())
484      return evalCastFromLoc(loc::MemRegionVal(R), castTy);
485
486    // FIXME: We should handle the case where we strip off view layers to get
487    //  to a desugared type.
488    if (!Loc::isLocType(castTy)) {
489      // FIXME: There can be gross cases where one casts the result of a function
490      // (that returns a pointer) to some other value that happens to fit
491      // within that pointer value.  We currently have no good way to
492      // model such operations.  When this happens, the underlying operation
493      // is that the caller is reasoning about bits.  Conceptually we are
494      // layering a "view" of a location on top of those bits.  Perhaps
495      // we need to be more lazy about mutual possible views, even on an
496      // SVal?  This may be necessary for bit-level reasoning as well.
497      return UnknownVal();
498    }
499
500    // We get a symbolic function pointer for a dereference of a function
501    // pointer, but it is of function type. Example:
502
503    //  struct FPRec {
504    //    void (*my_func)(int * x);
505    //  };
506    //
507    //  int bar(int x);
508    //
509    //  int f1_a(struct FPRec* foo) {
510    //    int x;
511    //    (*foo->my_func)(&x);
512    //    return bar(x)+1; // no-warning
513    //  }
514
515    assert(Loc::isLocType(originalTy) || originalTy->isFunctionType() ||
516           originalTy->isBlockPointerType() || castTy->isReferenceType());
517
518    StoreManager &storeMgr = StateMgr.getStoreManager();
519
520    // Delegate to store manager to get the result of casting a region to a
521    // different type.  If the MemRegion* returned is NULL, this expression
522    // Evaluates to UnknownVal.
523    R = storeMgr.castRegion(R, castTy);
524    return R ? SVal(loc::MemRegionVal(R)) : UnknownVal();
525  }
526
527  return dispatchCast(val, castTy);
528}
529