clang-tools  7.0.0
SuspiciousMemsetUsageCheck.cpp
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1 //===--- SuspiciousMemsetUsageCheck.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/ASTMatchers/ASTMatchers.h"
14 #include "clang/Lex/Lexer.h"
15 #include "clang/Tooling/FixIt.h"
16 
17 using namespace clang::ast_matchers;
18 
19 namespace clang {
20 namespace tidy {
21 namespace bugprone {
22 
23 void SuspiciousMemsetUsageCheck::registerMatchers(MatchFinder *Finder) {
24  // Note: void *memset(void *buffer, int fill_char, size_t byte_count);
25  // Look for memset(x, '0', z). Probably memset(x, 0, z) was intended.
26  Finder->addMatcher(
27  callExpr(
28  callee(functionDecl(hasName("::memset"))),
29  hasArgument(1, characterLiteral(equals(static_cast<unsigned>('0')))
30  .bind("char-zero-fill")),
31  unless(
32  eachOf(hasArgument(0, anyOf(hasType(pointsTo(isAnyCharacter())),
33  hasType(arrayType(hasElementType(
34  isAnyCharacter()))))),
35  isInTemplateInstantiation()))),
36  this);
37 
38  // Look for memset with an integer literal in its fill_char argument.
39  // Will check if it gets truncated.
40  Finder->addMatcher(callExpr(callee(functionDecl(hasName("::memset"))),
41  hasArgument(1, integerLiteral().bind("num-fill")),
42  unless(isInTemplateInstantiation())),
43  this);
44 
45  // Look for memset(x, y, 0) as that is most likely an argument swap.
46  Finder->addMatcher(
47  callExpr(callee(functionDecl(hasName("::memset"))),
48  unless(hasArgument(1, anyOf(characterLiteral(equals(
49  static_cast<unsigned>('0'))),
50  integerLiteral()))),
51  unless(isInTemplateInstantiation()))
52  .bind("call"),
53  this);
54 }
55 
56 void SuspiciousMemsetUsageCheck::check(const MatchFinder::MatchResult &Result) {
57  if (const auto *CharZeroFill =
58  Result.Nodes.getNodeAs<CharacterLiteral>("char-zero-fill")) {
59  // Case 1: fill_char of memset() is a character '0'. Probably an
60  // integer zero was intended.
61 
62  SourceRange CharRange = CharZeroFill->getSourceRange();
63  auto Diag =
64  diag(CharZeroFill->getLocStart(), "memset fill value is char '0', "
65  "potentially mistaken for int 0");
66 
67  // Only suggest a fix if no macros are involved.
68  if (CharRange.getBegin().isMacroID())
69  return;
70  Diag << FixItHint::CreateReplacement(
71  CharSourceRange::getTokenRange(CharRange), "0");
72  }
73 
74  else if (const auto *NumFill =
75  Result.Nodes.getNodeAs<IntegerLiteral>("num-fill")) {
76  // Case 2: fill_char of memset() is larger in size than an unsigned char
77  // so it gets truncated during conversion.
78 
79  llvm::APSInt NumValue;
80  const auto UCharMax = (1 << Result.Context->getCharWidth()) - 1;
81  if (!NumFill->EvaluateAsInt(NumValue, *Result.Context) ||
82  (NumValue >= 0 && NumValue <= UCharMax))
83  return;
84 
85  diag(NumFill->getLocStart(), "memset fill value is out of unsigned "
86  "character range, gets truncated");
87  }
88 
89  else if (const auto *Call = Result.Nodes.getNodeAs<CallExpr>("call")) {
90  // Case 3: byte_count of memset() is zero. This is most likely an
91  // argument swap.
92 
93  const Expr *FillChar = Call->getArg(1);
94  const Expr *ByteCount = Call->getArg(2);
95 
96  // Return if `byte_count` is not zero at compile time.
97  llvm::APSInt Value1, Value2;
98  if (ByteCount->isValueDependent() ||
99  !ByteCount->EvaluateAsInt(Value2, *Result.Context) || Value2 != 0)
100  return;
101 
102  // Return if `fill_char` is known to be zero or negative at compile
103  // time. In these cases, swapping the args would be a nop, or
104  // introduce a definite bug. The code is likely correct.
105  if (!FillChar->isValueDependent() &&
106  FillChar->EvaluateAsInt(Value1, *Result.Context) &&
107  (Value1 == 0 || Value1.isNegative()))
108  return;
109 
110  // `byte_count` is known to be zero at compile time, and `fill_char` is
111  // either not known or known to be a positive integer. Emit a warning
112  // and fix-its to swap the arguments.
113  auto D = diag(Call->getLocStart(),
114  "memset of size zero, potentially swapped arguments");
115  StringRef RHSString = tooling::fixit::getText(*ByteCount, *Result.Context);
116  StringRef LHSString = tooling::fixit::getText(*FillChar, *Result.Context);
117  if (LHSString.empty() || RHSString.empty())
118  return;
119 
120  D << tooling::fixit::createReplacement(*FillChar, RHSString)
121  << tooling::fixit::createReplacement(*ByteCount, LHSString);
122  }
123 }
124 
125 } // namespace bugprone
126 } // namespace tidy
127 } // namespace clang
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//