1//===--- SuspiciousMemsetUsageCheck.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 "SuspiciousMemsetUsageCheck.h"
10#include "clang/AST/ASTContext.h"
11#include "clang/ASTMatchers/ASTMatchFinder.h"
12#include "clang/ASTMatchers/ASTMatchers.h"
13#include "clang/Lex/Lexer.h"
14#include "clang/Tooling/FixIt.h"
15
16using namespace clang::ast_matchers;
17
18namespace clang::tidy::bugprone {
19
20void SuspiciousMemsetUsageCheck::registerMatchers(MatchFinder *Finder) {
21 // Match the standard memset:
22 // void *memset(void *buffer, int fill_char, size_t byte_count);
23 auto MemsetDecl =
24 functionDecl(hasName(Name: "::memset"),
25 parameterCountIs(N: 3),
26 hasParameter(N: 0, InnerMatcher: hasType(InnerMatcher: pointerType(pointee(voidType())))),
27 hasParameter(N: 1, InnerMatcher: hasType(InnerMatcher: isInteger())),
28 hasParameter(N: 2, InnerMatcher: hasType(InnerMatcher: isInteger())));
29
30 // Look for memset(x, '0', z). Probably memset(x, 0, z) was intended.
31 Finder->addMatcher(
32 NodeMatch: callExpr(
33 callee(InnerMatcher: MemsetDecl), argumentCountIs(N: 3),
34 hasArgument(N: 1, InnerMatcher: characterLiteral(equals(Value: static_cast<unsigned>('0')))
35 .bind(ID: "char-zero-fill")),
36 unless(hasArgument(
37 N: 0, InnerMatcher: anyOf(hasType(InnerMatcher: pointsTo(InnerMatcher: isAnyCharacter())),
38 hasType(InnerMatcher: arrayType(hasElementType(isAnyCharacter()))))))),
39 Action: this);
40
41 // Look for memset with an integer literal in its fill_char argument.
42 // Will check if it gets truncated.
43 Finder->addMatcher(
44 NodeMatch: callExpr(callee(InnerMatcher: MemsetDecl), argumentCountIs(N: 3),
45 hasArgument(N: 1, InnerMatcher: integerLiteral().bind(ID: "num-fill"))),
46 Action: this);
47
48 // Look for memset(x, y, 0) as that is most likely an argument swap.
49 Finder->addMatcher(
50 NodeMatch: callExpr(callee(InnerMatcher: MemsetDecl), argumentCountIs(N: 3),
51 unless(hasArgument(N: 1, InnerMatcher: anyOf(characterLiteral(equals(
52 Value: static_cast<unsigned>('0'))),
53 integerLiteral()))))
54 .bind(ID: "call"),
55 Action: this);
56}
57
58void SuspiciousMemsetUsageCheck::check(const MatchFinder::MatchResult &Result) {
59 if (const auto *CharZeroFill =
60 Result.Nodes.getNodeAs<CharacterLiteral>(ID: "char-zero-fill")) {
61 // Case 1: fill_char of memset() is a character '0'. Probably an
62 // integer zero was intended.
63
64 SourceRange CharRange = CharZeroFill->getSourceRange();
65 auto Diag =
66 diag(Loc: CharZeroFill->getBeginLoc(), Description: "memset fill value is char '0', "
67 "potentially mistaken for int 0");
68
69 // Only suggest a fix if no macros are involved.
70 if (CharRange.getBegin().isMacroID())
71 return;
72 Diag << FixItHint::CreateReplacement(
73 RemoveRange: CharSourceRange::getTokenRange(R: CharRange), Code: "0");
74 }
75
76 else if (const auto *NumFill =
77 Result.Nodes.getNodeAs<IntegerLiteral>(ID: "num-fill")) {
78 // Case 2: fill_char of memset() is larger in size than an unsigned char
79 // so it gets truncated during conversion.
80
81 const auto UCharMax = (1 << Result.Context->getCharWidth()) - 1;
82 Expr::EvalResult EVResult;
83 if (!NumFill->EvaluateAsInt(EVResult, *Result.Context))
84 return;
85
86 llvm::APSInt NumValue = EVResult.Val.getInt();
87 if (NumValue >= 0 && NumValue <= UCharMax)
88 return;
89
90 diag(Loc: NumFill->getBeginLoc(), Description: "memset fill value is out of unsigned "
91 "character range, gets truncated");
92 }
93
94 else if (const auto *Call = Result.Nodes.getNodeAs<CallExpr>(ID: "call")) {
95 // Case 3: byte_count of memset() is zero. This is most likely an
96 // argument swap.
97
98 const Expr *FillChar = Call->getArg(Arg: 1);
99 const Expr *ByteCount = Call->getArg(Arg: 2);
100
101 // Return if `byte_count` is not zero at compile time.
102 Expr::EvalResult Value2;
103 if (ByteCount->isValueDependent() ||
104 !ByteCount->EvaluateAsInt(Result&: Value2, Ctx: *Result.Context) ||
105 Value2.Val.getInt() != 0)
106 return;
107
108 // Return if `fill_char` is known to be zero or negative at compile
109 // time. In these cases, swapping the args would be a nop, or
110 // introduce a definite bug. The code is likely correct.
111 Expr::EvalResult EVResult;
112 if (!FillChar->isValueDependent() &&
113 FillChar->EvaluateAsInt(Result&: EVResult, Ctx: *Result.Context)) {
114 llvm::APSInt Value1 = EVResult.Val.getInt();
115 if (Value1 == 0 || Value1.isNegative())
116 return;
117 }
118
119 // `byte_count` is known to be zero at compile time, and `fill_char` is
120 // either not known or known to be a positive integer. Emit a warning
121 // and fix-its to swap the arguments.
122 auto D = diag(Loc: Call->getBeginLoc(),
123 Description: "memset of size zero, potentially swapped arguments");
124 StringRef RHSString = tooling::fixit::getText(Node: *ByteCount, Context: *Result.Context);
125 StringRef LHSString = tooling::fixit::getText(Node: *FillChar, Context: *Result.Context);
126 if (LHSString.empty() || RHSString.empty())
127 return;
128
129 D << tooling::fixit::createReplacement(Destination: *FillChar, Source: RHSString)
130 << tooling::fixit::createReplacement(Destination: *ByteCount, Source: LHSString);
131 }
132}
133
134} // namespace clang::tidy::bugprone
135

source code of clang-tools-extra/clang-tidy/bugprone/SuspiciousMemsetUsageCheck.cpp