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      1 //=== LLVMConventionsChecker.cpp - Check LLVM codebase conventions ---*- 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 defines LLVMConventionsChecker, a bunch of small little checks
     11 // for checking specific coding conventions in the LLVM/Clang codebase.
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #include "ClangSACheckers.h"
     16 #include "clang/StaticAnalyzer/Core/Checker.h"
     17 #include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
     18 #include "clang/AST/DeclTemplate.h"
     19 #include "clang/AST/StmtVisitor.h"
     20 #include <string>
     21 #include "llvm/ADT/StringRef.h"
     22 
     23 using namespace clang;
     24 using namespace ento;
     25 
     26 //===----------------------------------------------------------------------===//
     27 // Generic type checking routines.
     28 //===----------------------------------------------------------------------===//
     29 
     30 static bool IsLLVMStringRef(QualType T) {
     31   const RecordType *RT = T->getAs<RecordType>();
     32   if (!RT)
     33     return false;
     34 
     35   return StringRef(QualType(RT, 0).getAsString()) ==
     36           "class StringRef";
     37 }
     38 
     39 /// Check whether the declaration is semantically inside the top-level
     40 /// namespace named by ns.
     41 static bool InNamespace(const Decl *D, StringRef NS) {
     42   const NamespaceDecl *ND = dyn_cast<NamespaceDecl>(D->getDeclContext());
     43   if (!ND)
     44     return false;
     45   const IdentifierInfo *II = ND->getIdentifier();
     46   if (!II || !II->getName().equals(NS))
     47     return false;
     48   return isa<TranslationUnitDecl>(ND->getDeclContext());
     49 }
     50 
     51 static bool IsStdString(QualType T) {
     52   if (const ElaboratedType *QT = T->getAs<ElaboratedType>())
     53     T = QT->getNamedType();
     54 
     55   const TypedefType *TT = T->getAs<TypedefType>();
     56   if (!TT)
     57     return false;
     58 
     59   const TypedefNameDecl *TD = TT->getDecl();
     60 
     61   if (!InNamespace(TD, "std"))
     62     return false;
     63 
     64   return TD->getName() == "string";
     65 }
     66 
     67 static bool IsClangType(const RecordDecl *RD) {
     68   return RD->getName() == "Type" && InNamespace(RD, "clang");
     69 }
     70 
     71 static bool IsClangDecl(const RecordDecl *RD) {
     72   return RD->getName() == "Decl" && InNamespace(RD, "clang");
     73 }
     74 
     75 static bool IsClangStmt(const RecordDecl *RD) {
     76   return RD->getName() == "Stmt" && InNamespace(RD, "clang");
     77 }
     78 
     79 static bool IsClangAttr(const RecordDecl *RD) {
     80   return RD->getName() == "Attr" && InNamespace(RD, "clang");
     81 }
     82 
     83 static bool IsStdVector(QualType T) {
     84   const TemplateSpecializationType *TS = T->getAs<TemplateSpecializationType>();
     85   if (!TS)
     86     return false;
     87 
     88   TemplateName TM = TS->getTemplateName();
     89   TemplateDecl *TD = TM.getAsTemplateDecl();
     90 
     91   if (!TD || !InNamespace(TD, "std"))
     92     return false;
     93 
     94   return TD->getName() == "vector";
     95 }
     96 
     97 static bool IsSmallVector(QualType T) {
     98   const TemplateSpecializationType *TS = T->getAs<TemplateSpecializationType>();
     99   if (!TS)
    100     return false;
    101 
    102   TemplateName TM = TS->getTemplateName();
    103   TemplateDecl *TD = TM.getAsTemplateDecl();
    104 
    105   if (!TD || !InNamespace(TD, "llvm"))
    106     return false;
    107 
    108   return TD->getName() == "SmallVector";
    109 }
    110 
    111 //===----------------------------------------------------------------------===//
    112 // CHECK: a StringRef should not be bound to a temporary std::string whose
    113 // lifetime is shorter than the StringRef's.
    114 //===----------------------------------------------------------------------===//
    115 
    116 namespace {
    117 class StringRefCheckerVisitor : public StmtVisitor<StringRefCheckerVisitor> {
    118   BugReporter &BR;
    119 public:
    120   StringRefCheckerVisitor(BugReporter &br) : BR(br) {}
    121   void VisitChildren(Stmt *S) {
    122     for (Stmt::child_iterator I = S->child_begin(), E = S->child_end() ;
    123       I != E; ++I)
    124       if (Stmt *child = *I)
    125         Visit(child);
    126   }
    127   void VisitStmt(Stmt *S) { VisitChildren(S); }
    128   void VisitDeclStmt(DeclStmt *DS);
    129 private:
    130   void VisitVarDecl(VarDecl *VD);
    131 };
    132 } // end anonymous namespace
    133 
    134 static void CheckStringRefAssignedTemporary(const Decl *D, BugReporter &BR) {
    135   StringRefCheckerVisitor walker(BR);
    136   walker.Visit(D->getBody());
    137 }
    138 
    139 void StringRefCheckerVisitor::VisitDeclStmt(DeclStmt *S) {
    140   VisitChildren(S);
    141 
    142   for (DeclStmt::decl_iterator I = S->decl_begin(), E = S->decl_end();I!=E; ++I)
    143     if (VarDecl *VD = dyn_cast<VarDecl>(*I))
    144       VisitVarDecl(VD);
    145 }
    146 
    147 void StringRefCheckerVisitor::VisitVarDecl(VarDecl *VD) {
    148   Expr *Init = VD->getInit();
    149   if (!Init)
    150     return;
    151 
    152   // Pattern match for:
    153   // StringRef x = call() (where call returns std::string)
    154   if (!IsLLVMStringRef(VD->getType()))
    155     return;
    156   ExprWithCleanups *Ex1 = dyn_cast<ExprWithCleanups>(Init);
    157   if (!Ex1)
    158     return;
    159   CXXConstructExpr *Ex2 = dyn_cast<CXXConstructExpr>(Ex1->getSubExpr());
    160   if (!Ex2 || Ex2->getNumArgs() != 1)
    161     return;
    162   ImplicitCastExpr *Ex3 = dyn_cast<ImplicitCastExpr>(Ex2->getArg(0));
    163   if (!Ex3)
    164     return;
    165   CXXConstructExpr *Ex4 = dyn_cast<CXXConstructExpr>(Ex3->getSubExpr());
    166   if (!Ex4 || Ex4->getNumArgs() != 1)
    167     return;
    168   ImplicitCastExpr *Ex5 = dyn_cast<ImplicitCastExpr>(Ex4->getArg(0));
    169   if (!Ex5)
    170     return;
    171   CXXBindTemporaryExpr *Ex6 = dyn_cast<CXXBindTemporaryExpr>(Ex5->getSubExpr());
    172   if (!Ex6 || !IsStdString(Ex6->getType()))
    173     return;
    174 
    175   // Okay, badness!  Report an error.
    176   const char *desc = "StringRef should not be bound to temporary "
    177                      "std::string that it outlives";
    178   PathDiagnosticLocation VDLoc =
    179     PathDiagnosticLocation::createBegin(VD, BR.getSourceManager());
    180   BR.EmitBasicReport(desc, "LLVM Conventions", desc,
    181                      VDLoc, Init->getSourceRange());
    182 }
    183 
    184 //===----------------------------------------------------------------------===//
    185 // CHECK: Clang AST nodes should not have fields that can allocate
    186 //   memory.
    187 //===----------------------------------------------------------------------===//
    188 
    189 static bool AllocatesMemory(QualType T) {
    190   return IsStdVector(T) || IsStdString(T) || IsSmallVector(T);
    191 }
    192 
    193 // This type checking could be sped up via dynamic programming.
    194 static bool IsPartOfAST(const CXXRecordDecl *R) {
    195   if (IsClangStmt(R) || IsClangType(R) || IsClangDecl(R) || IsClangAttr(R))
    196     return true;
    197 
    198   for (CXXRecordDecl::base_class_const_iterator I = R->bases_begin(),
    199                                                 E = R->bases_end(); I!=E; ++I) {
    200     CXXBaseSpecifier BS = *I;
    201     QualType T = BS.getType();
    202     if (const RecordType *baseT = T->getAs<RecordType>()) {
    203       CXXRecordDecl *baseD = cast<CXXRecordDecl>(baseT->getDecl());
    204       if (IsPartOfAST(baseD))
    205         return true;
    206     }
    207   }
    208 
    209   return false;
    210 }
    211 
    212 namespace {
    213 class ASTFieldVisitor {
    214   SmallVector<FieldDecl*, 10> FieldChain;
    215   const CXXRecordDecl *Root;
    216   BugReporter &BR;
    217 public:
    218   ASTFieldVisitor(const CXXRecordDecl *root, BugReporter &br)
    219     : Root(root), BR(br) {}
    220 
    221   void Visit(FieldDecl *D);
    222   void ReportError(QualType T);
    223 };
    224 } // end anonymous namespace
    225 
    226 static void CheckASTMemory(const CXXRecordDecl *R, BugReporter &BR) {
    227   if (!IsPartOfAST(R))
    228     return;
    229 
    230   for (RecordDecl::field_iterator I = R->field_begin(), E = R->field_end();
    231        I != E; ++I) {
    232     ASTFieldVisitor walker(R, BR);
    233     walker.Visit(*I);
    234   }
    235 }
    236 
    237 void ASTFieldVisitor::Visit(FieldDecl *D) {
    238   FieldChain.push_back(D);
    239 
    240   QualType T = D->getType();
    241 
    242   if (AllocatesMemory(T))
    243     ReportError(T);
    244 
    245   if (const RecordType *RT = T->getAs<RecordType>()) {
    246     const RecordDecl *RD = RT->getDecl()->getDefinition();
    247     for (RecordDecl::field_iterator I = RD->field_begin(), E = RD->field_end();
    248          I != E; ++I)
    249       Visit(*I);
    250   }
    251 
    252   FieldChain.pop_back();
    253 }
    254 
    255 void ASTFieldVisitor::ReportError(QualType T) {
    256   llvm::SmallString<1024> buf;
    257   llvm::raw_svector_ostream os(buf);
    258 
    259   os << "AST class '" << Root->getName() << "' has a field '"
    260      << FieldChain.front()->getName() << "' that allocates heap memory";
    261   if (FieldChain.size() > 1) {
    262     os << " via the following chain: ";
    263     bool isFirst = true;
    264     for (SmallVectorImpl<FieldDecl*>::iterator I=FieldChain.begin(),
    265          E=FieldChain.end(); I!=E; ++I) {
    266       if (!isFirst)
    267         os << '.';
    268       else
    269         isFirst = false;
    270       os << (*I)->getName();
    271     }
    272   }
    273   os << " (type " << FieldChain.back()->getType().getAsString() << ")";
    274   os.flush();
    275 
    276   // Note that this will fire for every translation unit that uses this
    277   // class.  This is suboptimal, but at least scan-build will merge
    278   // duplicate HTML reports.  In the future we need a unified way of merging
    279   // duplicate reports across translation units.  For C++ classes we cannot
    280   // just report warnings when we see an out-of-line method definition for a
    281   // class, as that heuristic doesn't always work (the complete definition of
    282   // the class may be in the header file, for example).
    283   PathDiagnosticLocation L = PathDiagnosticLocation::createBegin(
    284                                FieldChain.front(), BR.getSourceManager());
    285   BR.EmitBasicReport("AST node allocates heap memory", "LLVM Conventions",
    286                      os.str(), L);
    287 }
    288 
    289 //===----------------------------------------------------------------------===//
    290 // LLVMConventionsChecker
    291 //===----------------------------------------------------------------------===//
    292 
    293 namespace {
    294 class LLVMConventionsChecker : public Checker<
    295                                                 check::ASTDecl<CXXRecordDecl>,
    296                                                 check::ASTCodeBody > {
    297 public:
    298   void checkASTDecl(const CXXRecordDecl *R, AnalysisManager& mgr,
    299                     BugReporter &BR) const {
    300     if (R->isCompleteDefinition())
    301       CheckASTMemory(R, BR);
    302   }
    303 
    304   void checkASTCodeBody(const Decl *D, AnalysisManager& mgr,
    305                         BugReporter &BR) const {
    306     CheckStringRefAssignedTemporary(D, BR);
    307   }
    308 };
    309 }
    310 
    311 void ento::registerLLVMConventionsChecker(CheckerManager &mgr) {
    312   mgr.registerChecker<LLVMConventionsChecker>();
    313 }
    314