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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/AST/DeclTemplate.h"
     17 #include "clang/AST/StmtVisitor.h"
     18 #include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
     19 #include "clang/StaticAnalyzer/Core/Checker.h"
     20 #include "llvm/ADT/SmallString.h"
     21 #include "llvm/Support/raw_ostream.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 (!TD->isInStdNamespace())
     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   const Decl *DeclWithIssue;
    119   BugReporter &BR;
    120   const CheckerBase *Checker;
    121 
    122 public:
    123   StringRefCheckerVisitor(const Decl *declWithIssue, BugReporter &br,
    124                           const CheckerBase *checker)
    125       : DeclWithIssue(declWithIssue), BR(br), Checker(checker) {}
    126   void VisitChildren(Stmt *S) {
    127     for (Stmt::child_iterator I = S->child_begin(), E = S->child_end() ;
    128       I != E; ++I)
    129       if (Stmt *child = *I)
    130         Visit(child);
    131   }
    132   void VisitStmt(Stmt *S) { VisitChildren(S); }
    133   void VisitDeclStmt(DeclStmt *DS);
    134 private:
    135   void VisitVarDecl(VarDecl *VD);
    136 };
    137 } // end anonymous namespace
    138 
    139 static void CheckStringRefAssignedTemporary(const Decl *D, BugReporter &BR,
    140                                             const CheckerBase *Checker) {
    141   StringRefCheckerVisitor walker(D, BR, Checker);
    142   walker.Visit(D->getBody());
    143 }
    144 
    145 void StringRefCheckerVisitor::VisitDeclStmt(DeclStmt *S) {
    146   VisitChildren(S);
    147 
    148   for (auto *I : S->decls())
    149     if (VarDecl *VD = dyn_cast<VarDecl>(I))
    150       VisitVarDecl(VD);
    151 }
    152 
    153 void StringRefCheckerVisitor::VisitVarDecl(VarDecl *VD) {
    154   Expr *Init = VD->getInit();
    155   if (!Init)
    156     return;
    157 
    158   // Pattern match for:
    159   // StringRef x = call() (where call returns std::string)
    160   if (!IsLLVMStringRef(VD->getType()))
    161     return;
    162   ExprWithCleanups *Ex1 = dyn_cast<ExprWithCleanups>(Init);
    163   if (!Ex1)
    164     return;
    165   CXXConstructExpr *Ex2 = dyn_cast<CXXConstructExpr>(Ex1->getSubExpr());
    166   if (!Ex2 || Ex2->getNumArgs() != 1)
    167     return;
    168   ImplicitCastExpr *Ex3 = dyn_cast<ImplicitCastExpr>(Ex2->getArg(0));
    169   if (!Ex3)
    170     return;
    171   CXXConstructExpr *Ex4 = dyn_cast<CXXConstructExpr>(Ex3->getSubExpr());
    172   if (!Ex4 || Ex4->getNumArgs() != 1)
    173     return;
    174   ImplicitCastExpr *Ex5 = dyn_cast<ImplicitCastExpr>(Ex4->getArg(0));
    175   if (!Ex5)
    176     return;
    177   CXXBindTemporaryExpr *Ex6 = dyn_cast<CXXBindTemporaryExpr>(Ex5->getSubExpr());
    178   if (!Ex6 || !IsStdString(Ex6->getType()))
    179     return;
    180 
    181   // Okay, badness!  Report an error.
    182   const char *desc = "StringRef should not be bound to temporary "
    183                      "std::string that it outlives";
    184   PathDiagnosticLocation VDLoc =
    185     PathDiagnosticLocation::createBegin(VD, BR.getSourceManager());
    186   BR.EmitBasicReport(DeclWithIssue, Checker, desc, "LLVM Conventions", desc,
    187                      VDLoc, Init->getSourceRange());
    188 }
    189 
    190 //===----------------------------------------------------------------------===//
    191 // CHECK: Clang AST nodes should not have fields that can allocate
    192 //   memory.
    193 //===----------------------------------------------------------------------===//
    194 
    195 static bool AllocatesMemory(QualType T) {
    196   return IsStdVector(T) || IsStdString(T) || IsSmallVector(T);
    197 }
    198 
    199 // This type checking could be sped up via dynamic programming.
    200 static bool IsPartOfAST(const CXXRecordDecl *R) {
    201   if (IsClangStmt(R) || IsClangType(R) || IsClangDecl(R) || IsClangAttr(R))
    202     return true;
    203 
    204   for (const auto &BS : R->bases()) {
    205     QualType T = BS.getType();
    206     if (const RecordType *baseT = T->getAs<RecordType>()) {
    207       CXXRecordDecl *baseD = cast<CXXRecordDecl>(baseT->getDecl());
    208       if (IsPartOfAST(baseD))
    209         return true;
    210     }
    211   }
    212 
    213   return false;
    214 }
    215 
    216 namespace {
    217 class ASTFieldVisitor {
    218   SmallVector<FieldDecl*, 10> FieldChain;
    219   const CXXRecordDecl *Root;
    220   BugReporter &BR;
    221   const CheckerBase *Checker;
    222 
    223 public:
    224   ASTFieldVisitor(const CXXRecordDecl *root, BugReporter &br,
    225                   const CheckerBase *checker)
    226       : Root(root), BR(br), Checker(checker) {}
    227 
    228   void Visit(FieldDecl *D);
    229   void ReportError(QualType T);
    230 };
    231 } // end anonymous namespace
    232 
    233 static void CheckASTMemory(const CXXRecordDecl *R, BugReporter &BR,
    234                            const CheckerBase *Checker) {
    235   if (!IsPartOfAST(R))
    236     return;
    237 
    238   for (auto *I : R->fields()) {
    239     ASTFieldVisitor walker(R, BR, Checker);
    240     walker.Visit(I);
    241   }
    242 }
    243 
    244 void ASTFieldVisitor::Visit(FieldDecl *D) {
    245   FieldChain.push_back(D);
    246 
    247   QualType T = D->getType();
    248 
    249   if (AllocatesMemory(T))
    250     ReportError(T);
    251 
    252   if (const RecordType *RT = T->getAs<RecordType>()) {
    253     const RecordDecl *RD = RT->getDecl()->getDefinition();
    254     for (auto *I : RD->fields())
    255       Visit(I);
    256   }
    257 
    258   FieldChain.pop_back();
    259 }
    260 
    261 void ASTFieldVisitor::ReportError(QualType T) {
    262   SmallString<1024> buf;
    263   llvm::raw_svector_ostream os(buf);
    264 
    265   os << "AST class '" << Root->getName() << "' has a field '"
    266      << FieldChain.front()->getName() << "' that allocates heap memory";
    267   if (FieldChain.size() > 1) {
    268     os << " via the following chain: ";
    269     bool isFirst = true;
    270     for (SmallVectorImpl<FieldDecl*>::iterator I=FieldChain.begin(),
    271          E=FieldChain.end(); I!=E; ++I) {
    272       if (!isFirst)
    273         os << '.';
    274       else
    275         isFirst = false;
    276       os << (*I)->getName();
    277     }
    278   }
    279   os << " (type " << FieldChain.back()->getType().getAsString() << ")";
    280   os.flush();
    281 
    282   // Note that this will fire for every translation unit that uses this
    283   // class.  This is suboptimal, but at least scan-build will merge
    284   // duplicate HTML reports.  In the future we need a unified way of merging
    285   // duplicate reports across translation units.  For C++ classes we cannot
    286   // just report warnings when we see an out-of-line method definition for a
    287   // class, as that heuristic doesn't always work (the complete definition of
    288   // the class may be in the header file, for example).
    289   PathDiagnosticLocation L = PathDiagnosticLocation::createBegin(
    290                                FieldChain.front(), BR.getSourceManager());
    291   BR.EmitBasicReport(Root, Checker, "AST node allocates heap memory",
    292                      "LLVM Conventions", os.str(), L);
    293 }
    294 
    295 //===----------------------------------------------------------------------===//
    296 // LLVMConventionsChecker
    297 //===----------------------------------------------------------------------===//
    298 
    299 namespace {
    300 class LLVMConventionsChecker : public Checker<
    301                                                 check::ASTDecl<CXXRecordDecl>,
    302                                                 check::ASTCodeBody > {
    303 public:
    304   void checkASTDecl(const CXXRecordDecl *R, AnalysisManager& mgr,
    305                     BugReporter &BR) const {
    306     if (R->isCompleteDefinition())
    307       CheckASTMemory(R, BR, this);
    308   }
    309 
    310   void checkASTCodeBody(const Decl *D, AnalysisManager& mgr,
    311                         BugReporter &BR) const {
    312     CheckStringRefAssignedTemporary(D, BR, this);
    313   }
    314 };
    315 }
    316 
    317 void ento::registerLLVMConventionsChecker(CheckerManager &mgr) {
    318   mgr.registerChecker<LLVMConventionsChecker>();
    319 }
    320