1 //===--- StringConstructorCheck.cpp - clang-tidy---------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include "StringConstructorCheck.h"
10 #include "../utils/OptionsUtils.h"
11 #include "clang/AST/ASTContext.h"
12 #include "clang/ASTMatchers/ASTMatchFinder.h"
13 #include "clang/Tooling/FixIt.h"
14 
15 using namespace clang::ast_matchers;
16 
17 namespace clang {
18 namespace tidy {
19 namespace bugprone {
20 
21 namespace {
22 AST_MATCHER_P(IntegerLiteral, isBiggerThan, unsigned, N) {
23   return Node.getValue().getZExtValue() > N;
24 }
25 
26 const char DefaultStringNames[] =
27     "::std::basic_string;::std::basic_string_view";
28 
29 static std::vector<StringRef>
30 removeNamespaces(const std::vector<std::string> &Names) {
31   std::vector<StringRef> Result;
32   Result.reserve(Names.size());
33   for (StringRef Name : Names) {
34     std::string::size_type ColonPos = Name.rfind(':');
35     Result.push_back(
36         Name.substr(ColonPos == std::string::npos ? 0 : ColonPos + 1));
37   }
38   return Result;
39 }
40 
41 } // namespace
42 
43 StringConstructorCheck::StringConstructorCheck(StringRef Name,
44                                                ClangTidyContext *Context)
45     : ClangTidyCheck(Name, Context),
46       WarnOnLargeLength(Options.get("WarnOnLargeLength", true)),
47       LargeLengthThreshold(Options.get("LargeLengthThreshold", 0x800000)),
48       StringNames(utils::options::parseStringList(
49           Options.get("StringNames", DefaultStringNames))) {}
50 
51 void StringConstructorCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
52   Options.store(Opts, "WarnOnLargeLength", WarnOnLargeLength);
53   Options.store(Opts, "LargeLengthThreshold", LargeLengthThreshold);
54   Options.store(Opts, "StringNames", DefaultStringNames);
55 }
56 
57 void StringConstructorCheck::registerMatchers(MatchFinder *Finder) {
58   const auto ZeroExpr = expr(ignoringParenImpCasts(integerLiteral(equals(0))));
59   const auto CharExpr = expr(ignoringParenImpCasts(characterLiteral()));
60   const auto NegativeExpr = expr(ignoringParenImpCasts(
61       unaryOperator(hasOperatorName("-"),
62                     hasUnaryOperand(integerLiteral(unless(equals(0)))))));
63   const auto LargeLengthExpr = expr(ignoringParenImpCasts(
64       integerLiteral(isBiggerThan(LargeLengthThreshold))));
65   const auto CharPtrType = type(anyOf(pointerType(), arrayType()));
66 
67   // Match a string-literal; even through a declaration with initializer.
68   const auto BoundStringLiteral = stringLiteral().bind("str");
69   const auto ConstStrLiteralDecl = varDecl(
70       isDefinition(), hasType(constantArrayType()), hasType(isConstQualified()),
71       hasInitializer(ignoringParenImpCasts(BoundStringLiteral)));
72   const auto ConstPtrStrLiteralDecl = varDecl(
73       isDefinition(),
74       hasType(pointerType(pointee(isAnyCharacter(), isConstQualified()))),
75       hasInitializer(ignoringParenImpCasts(BoundStringLiteral)));
76   const auto ConstStrLiteral = expr(ignoringParenImpCasts(anyOf(
77       BoundStringLiteral, declRefExpr(hasDeclaration(anyOf(
78                               ConstPtrStrLiteralDecl, ConstStrLiteralDecl))))));
79 
80   // Check the fill constructor. Fills the string with n consecutive copies of
81   // character c. [i.e string(size_t n, char c);].
82   Finder->addMatcher(
83       cxxConstructExpr(
84           hasDeclaration(cxxMethodDecl(hasName("basic_string"))),
85           hasArgument(0, hasType(qualType(isInteger()))),
86           hasArgument(1, hasType(qualType(isInteger()))),
87           anyOf(
88               // Detect the expression: string('x', 40);
89               hasArgument(0, CharExpr.bind("swapped-parameter")),
90               // Detect the expression: string(0, ...);
91               hasArgument(0, ZeroExpr.bind("empty-string")),
92               // Detect the expression: string(-4, ...);
93               hasArgument(0, NegativeExpr.bind("negative-length")),
94               // Detect the expression: string(0x1234567, ...);
95               hasArgument(0, LargeLengthExpr.bind("large-length"))))
96           .bind("constructor"),
97       this);
98 
99   // Check the literal string constructor with char pointer and length
100   // parameters. [i.e. string (const char* s, size_t n);]
101   Finder->addMatcher(
102       cxxConstructExpr(
103           hasDeclaration(cxxConstructorDecl(ofClass(
104               cxxRecordDecl(hasAnyName(removeNamespaces(StringNames)))))),
105           hasArgument(0, hasType(CharPtrType)),
106           hasArgument(1, hasType(isInteger())),
107           anyOf(
108               // Detect the expression: string("...", 0);
109               hasArgument(1, ZeroExpr.bind("empty-string")),
110               // Detect the expression: string("...", -4);
111               hasArgument(1, NegativeExpr.bind("negative-length")),
112               // Detect the expression: string("lit", 0x1234567);
113               hasArgument(1, LargeLengthExpr.bind("large-length")),
114               // Detect the expression: string("lit", 5)
115               allOf(hasArgument(0, ConstStrLiteral.bind("literal-with-length")),
116                     hasArgument(1, ignoringParenImpCasts(
117                                        integerLiteral().bind("int"))))))
118           .bind("constructor"),
119       this);
120 
121   // Check the literal string constructor with char pointer.
122   // [i.e. string (const char* s);]
123   Finder->addMatcher(
124       traverse(TK_AsIs,
125                cxxConstructExpr(
126                    hasDeclaration(cxxConstructorDecl(ofClass(cxxRecordDecl(
127                        hasAnyName(removeNamespaces(StringNames)))))),
128                    hasArgument(0, expr().bind("from-ptr")),
129                    // do not match std::string(ptr, int)
130                    // match std::string(ptr, alloc)
131                    // match std::string(ptr)
132                    anyOf(hasArgument(1, unless(hasType(isInteger()))),
133                          argumentCountIs(1)))
134                    .bind("constructor")),
135       this);
136 }
137 
138 void StringConstructorCheck::check(const MatchFinder::MatchResult &Result) {
139   const ASTContext &Ctx = *Result.Context;
140   const auto *E = Result.Nodes.getNodeAs<CXXConstructExpr>("constructor");
141   assert(E && "missing constructor expression");
142   SourceLocation Loc = E->getBeginLoc();
143 
144   if (Result.Nodes.getNodeAs<Expr>("swapped-parameter")) {
145     const Expr *P0 = E->getArg(0);
146     const Expr *P1 = E->getArg(1);
147     diag(Loc, "string constructor parameters are probably swapped;"
148               " expecting string(count, character)")
149         << tooling::fixit::createReplacement(*P0, *P1, Ctx)
150         << tooling::fixit::createReplacement(*P1, *P0, Ctx);
151   } else if (Result.Nodes.getNodeAs<Expr>("empty-string")) {
152     diag(Loc, "constructor creating an empty string");
153   } else if (Result.Nodes.getNodeAs<Expr>("negative-length")) {
154     diag(Loc, "negative value used as length parameter");
155   } else if (Result.Nodes.getNodeAs<Expr>("large-length")) {
156     if (WarnOnLargeLength)
157       diag(Loc, "suspicious large length parameter");
158   } else if (Result.Nodes.getNodeAs<Expr>("literal-with-length")) {
159     const auto *Str = Result.Nodes.getNodeAs<StringLiteral>("str");
160     const auto *Lit = Result.Nodes.getNodeAs<IntegerLiteral>("int");
161     if (Lit->getValue().ugt(Str->getLength())) {
162       diag(Loc, "length is bigger than string literal size");
163     }
164   } else if (const auto *Ptr = Result.Nodes.getNodeAs<Expr>("from-ptr")) {
165     Expr::EvalResult ConstPtr;
166     if (!Ptr->isInstantiationDependent() &&
167         Ptr->EvaluateAsRValue(ConstPtr, Ctx) &&
168         ((ConstPtr.Val.isInt() && ConstPtr.Val.getInt().isNullValue()) ||
169          (ConstPtr.Val.isLValue() && ConstPtr.Val.isNullPointer()))) {
170       diag(Loc, "constructing string from nullptr is undefined behaviour");
171     }
172   }
173 }
174 
175 } // namespace bugprone
176 } // namespace tidy
177 } // namespace clang
178