clang-tools  3.8.0
ThrowByValueCatchByReferenceCheck.cpp
Go to the documentation of this file.
1 //===--- ThrowByValueCatchByReferenceCheck.cpp - clang-tidy----------------===//
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 
11 #include "clang/AST/ASTContext.h"
12 #include "clang/ASTMatchers/ASTMatchFinder.h"
13 #include "clang/AST/OperationKinds.h"
14 
15 using namespace clang::ast_matchers;
16 
17 namespace clang {
18 namespace tidy {
19 
20 ThrowByValueCatchByReferenceCheck::ThrowByValueCatchByReferenceCheck(
21  StringRef Name, ClangTidyContext *Context)
22  : ClangTidyCheck(Name, Context),
23  CheckAnonymousTemporaries(Options.get("CheckThrowTemporaries", true)) {}
24 
26  // This is a C++ only check thus we register the matchers only for C++
27  if (!getLangOpts().CPlusPlus)
28  return;
29 
30  Finder->addMatcher(cxxThrowExpr().bind("throw"), this);
31  Finder->addMatcher(cxxCatchStmt().bind("catch"), this);
32 }
33 
36  Options.store(Opts, "CheckThrowTemporaries", true);
37 }
38 
40  const MatchFinder::MatchResult &Result) {
41  diagnoseThrowLocations(Result.Nodes.getNodeAs<CXXThrowExpr>("throw"));
42  diagnoseCatchLocations(Result.Nodes.getNodeAs<CXXCatchStmt>("catch"),
43  *Result.Context);
44 }
45 
46 bool ThrowByValueCatchByReferenceCheck::isFunctionParameter(
47  const DeclRefExpr *declRefExpr) {
48  return isa<ParmVarDecl>(declRefExpr->getDecl());
49 }
50 
51 bool ThrowByValueCatchByReferenceCheck::isCatchVariable(
52  const DeclRefExpr *declRefExpr) {
53  auto *valueDecl = declRefExpr->getDecl();
54  if (auto *varDecl = dyn_cast<VarDecl>(valueDecl))
55  return varDecl->isExceptionVariable();
56  return false;
57 }
58 
59 bool ThrowByValueCatchByReferenceCheck::isFunctionOrCatchVar(
60  const DeclRefExpr *declRefExpr) {
61  return isFunctionParameter(declRefExpr) || isCatchVariable(declRefExpr);
62 }
63 
64 void ThrowByValueCatchByReferenceCheck::diagnoseThrowLocations(
65  const CXXThrowExpr *throwExpr) {
66  if (!throwExpr)
67  return;
68  auto *subExpr = throwExpr->getSubExpr();
69  if (!subExpr)
70  return;
71  auto qualType = subExpr->getType();
72  if (qualType->isPointerType()) {
73  // The code is throwing a pointer.
74  // In case it is strng literal, it is safe and we return.
75  auto *inner = subExpr->IgnoreParenImpCasts();
76  if (isa<StringLiteral>(inner))
77  return;
78  // If it's a variable from a catch statement, we return as well.
79  auto *declRef = dyn_cast<DeclRefExpr>(inner);
80  if (declRef && isCatchVariable(declRef)) {
81  return;
82  }
83  diag(subExpr->getLocStart(), "throw expression throws a pointer; it should "
84  "throw a non-pointer value instead");
85  }
86  // If the throw statement does not throw by pointer then it throws by value
87  // which is ok.
88  // There are addition checks that emit diagnosis messages if the thrown value
89  // is not an RValue. See:
90  // https://www.securecoding.cert.org/confluence/display/cplusplus/ERR09-CPP.+Throw+anonymous+temporaries
91  // This behavior can be influenced by an option.
92 
93  // If we encounter a CXXThrowExpr, we move through all casts until you either
94  // encounter a DeclRefExpr or a CXXConstructExpr.
95  // If it's a DeclRefExpr, we emit a message if the referenced variable is not
96  // a catch variable or function parameter.
97  // When encountering a CopyOrMoveConstructor: emit message if after casts,
98  // the expression is a LValue
99  if (CheckAnonymousTemporaries) {
100  bool emit = false;
101  auto *currentSubExpr = subExpr->IgnoreImpCasts();
102  const DeclRefExpr *variableReference =
103  dyn_cast<DeclRefExpr>(currentSubExpr);
104  const CXXConstructExpr *constructorCall =
105  dyn_cast<CXXConstructExpr>(currentSubExpr);
106  // If we have a DeclRefExpr, we flag for emitting a diagnosis message in
107  // case the referenced variable is neither a function parameter nor a
108  // variable declared in the catch statement.
109  if (variableReference)
110  emit = !isFunctionOrCatchVar(variableReference);
111  else if (constructorCall &&
112  constructorCall->getConstructor()->isCopyOrMoveConstructor()) {
113  // If we have a copy / move construction, we emit a diagnosis message if
114  // the object that we copy construct from is neither a function parameter
115  // nor a variable declared in a catch statement
116  auto argIter =
117  constructorCall
118  ->arg_begin(); // there's only one for copy constructors
119  auto *currentSubExpr = (*argIter)->IgnoreImpCasts();
120  if (currentSubExpr->isLValue()) {
121  if (auto *tmp = dyn_cast<DeclRefExpr>(currentSubExpr))
122  emit = !isFunctionOrCatchVar(tmp);
123  else if (isa<CallExpr>(currentSubExpr))
124  emit = true;
125  }
126  }
127  if (emit)
128  diag(subExpr->getLocStart(),
129  "throw expression should throw anonymous temporary values instead");
130  }
131 }
132 
133 void ThrowByValueCatchByReferenceCheck::diagnoseCatchLocations(
134  const CXXCatchStmt *catchStmt, ASTContext &context) {
135  const char *diagMsgCatchReference = "catch handler catches a pointer value; "
136  "should throw a non-pointer value and "
137  "catch by reference instead";
138  if (!catchStmt)
139  return;
140  auto caughtType = catchStmt->getCaughtType();
141  if (caughtType.isNull())
142  return;
143  auto *varDecl = catchStmt->getExceptionDecl();
144  if (const auto *PT = caughtType.getCanonicalType()->getAs<PointerType>()) {
145  // We do not diagnose when catching pointer to strings since we also allow
146  // throwing string literals.
147  if (!PT->getPointeeType()->isAnyCharacterType())
148  diag(varDecl->getLocStart(), diagMsgCatchReference);
149  } else if (!caughtType->isReferenceType()) {
150  // If it's not a pointer and not a reference then it must be thrown "by
151  // value". In this case we should emit a diagnosis message unless the type
152  // is trivial.
153  if (!caughtType.isTrivialType(context))
154  diag(varDecl->getLocStart(), diagMsgCatchReference);
155  }
156 }
157 
158 } // namespace tidy
159 } // namespace clang
LangOptions getLangOpts() const
Returns the language options from the context.
Definition: ClangTidy.h:162
StringHandle Name
std::unique_ptr< ast_matchers::MatchFinder > Finder
Definition: ClangTidy.cpp:188
void registerMatchers(ast_matchers::MatchFinder *Finder) override
Override this to register ASTMatchers with Finder.
Base class for all clang-tidy checks.
Definition: ClangTidy.h:102
void check(const ast_matchers::MatchFinder::MatchResult &Result) override
ClangTidyChecks that register ASTMatchers should do the actual work in here.
void store(ClangTidyOptions::OptionMap &Options, StringRef LocalName, StringRef Value) const
Stores an option with the check-local name LocalName with string value Value to Options.
Definition: ClangTidy.cpp:344
std::map< std::string, std::string > OptionMap
static const char PointerType[]
ClangTidyContext & Context
Definition: ClangTidy.cpp:93
Every ClangTidyCheck reports errors through a DiagnosticsEngine provided by this context.
void storeOptions(ClangTidyOptions::OptionMap &Opts) override
Should store all options supported by this check with their current values or default values for opti...
DiagnosticBuilder diag(SourceLocation Loc, StringRef Description, DiagnosticIDs::Level Level=DiagnosticIDs::Warning)
Add a diagnostic with the check's name.
Definition: ClangTidy.cpp:323
const NamedDecl * Result
Definition: USRFinder.cpp:121