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
23using namespace clang;
24using namespace ento;
25
26//===----------------------------------------------------------------------===//
27// Generic type checking routines.
28//===----------------------------------------------------------------------===//
29
30static 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.
41static 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
51static 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
67static bool IsClangType(const RecordDecl *RD) {
68  return RD->getName() == "Type" && InNamespace(RD, "clang");
69}
70
71static bool IsClangDecl(const RecordDecl *RD) {
72  return RD->getName() == "Decl" && InNamespace(RD, "clang");
73}
74
75static bool IsClangStmt(const RecordDecl *RD) {
76  return RD->getName() == "Stmt" && InNamespace(RD, "clang");
77}
78
79static bool IsClangAttr(const RecordDecl *RD) {
80  return RD->getName() == "Attr" && InNamespace(RD, "clang");
81}
82
83static 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
97static 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
116namespace {
117class StringRefCheckerVisitor : public StmtVisitor<StringRefCheckerVisitor> {
118  const Decl *DeclWithIssue;
119  BugReporter &BR;
120  const CheckerBase *Checker;
121
122public:
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);
134private:
135  void VisitVarDecl(VarDecl *VD);
136};
137} // end anonymous namespace
138
139static void CheckStringRefAssignedTemporary(const Decl *D, BugReporter &BR,
140                                            const CheckerBase *Checker) {
141  StringRefCheckerVisitor walker(D, BR, Checker);
142  walker.Visit(D->getBody());
143}
144
145void 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
153void 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
195static 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.
200static 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
216namespace {
217class ASTFieldVisitor {
218  SmallVector<FieldDecl*, 10> FieldChain;
219  const CXXRecordDecl *Root;
220  BugReporter &BR;
221  const CheckerBase *Checker;
222
223public:
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
233static 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
244void 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
261void 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
299namespace {
300class LLVMConventionsChecker : public Checker<
301                                                check::ASTDecl<CXXRecordDecl>,
302                                                check::ASTCodeBody > {
303public:
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
317void ento::registerLLVMConventionsChecker(CheckerManager &mgr) {
318  mgr.registerChecker<LLVMConventionsChecker>();
319}
320