clang-tools 20.0.0git
SuspiciousMemoryComparisonCheck.cpp
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1//===--- SuspiciousMemoryComparisonCheck.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
10#include "clang/AST/ASTContext.h"
11#include "clang/ASTMatchers/ASTMatchFinder.h"
12#include <optional>
13
14using namespace clang::ast_matchers;
15
16namespace clang::tidy::bugprone {
17
18static std::optional<uint64_t> tryEvaluateSizeExpr(const Expr *SizeExpr,
19 const ASTContext &Ctx) {
20 Expr::EvalResult Result;
21 if (SizeExpr->EvaluateAsRValue(Result, Ctx))
22 return Ctx.toBits(
23 CharUnits::fromQuantity(Result.Val.getInt().getExtValue()));
24 return std::nullopt;
25}
26
28 Finder->addMatcher(
29 callExpr(callee(namedDecl(
30 anyOf(hasName("::memcmp"), hasName("::std::memcmp")))),
31 unless(isInstantiationDependent()))
32 .bind("call"),
33 this);
34}
35
37 const MatchFinder::MatchResult &Result) {
38 const ASTContext &Ctx = *Result.Context;
39 const auto *CE = Result.Nodes.getNodeAs<CallExpr>("call");
40
41 const Expr *SizeExpr = CE->getArg(2);
42 assert(SizeExpr != nullptr && "Third argument of memcmp is mandatory.");
43 std::optional<uint64_t> ComparedBits = tryEvaluateSizeExpr(SizeExpr, Ctx);
44
45 for (unsigned int ArgIndex = 0; ArgIndex < 2; ++ArgIndex) {
46 const Expr *ArgExpr = CE->getArg(ArgIndex);
47 QualType ArgType = ArgExpr->IgnoreImplicit()->getType();
48 const Type *PointeeType = ArgType->getPointeeOrArrayElementType();
49 assert(PointeeType != nullptr && "PointeeType should always be available.");
50 QualType PointeeQualifiedType(PointeeType, 0);
51
52 if (PointeeType->isRecordType()) {
53 if (const RecordDecl *RD =
54 PointeeType->getAsRecordDecl()->getDefinition()) {
55 if (const auto *CXXDecl = dyn_cast<CXXRecordDecl>(RD)) {
56 if (!CXXDecl->isStandardLayout()) {
57 diag(CE->getBeginLoc(),
58 "comparing object representation of non-standard-layout type "
59 "%0; consider using a comparison operator instead")
60 << PointeeQualifiedType;
61 break;
62 }
63 }
64 }
65 }
66
67 if (!PointeeType->isIncompleteType()) {
68 uint64_t PointeeSize = Ctx.getTypeSize(PointeeType);
69 if (ComparedBits && *ComparedBits >= PointeeSize &&
70 !Ctx.hasUniqueObjectRepresentations(PointeeQualifiedType)) {
71 diag(CE->getBeginLoc(),
72 "comparing object representation of type %0 which does not have a "
73 "unique object representation; consider comparing %select{the "
74 "values|the members of the object}1 manually")
75 << PointeeQualifiedType << (PointeeType->isRecordType() ? 1 : 0);
76 break;
77 }
78 }
79 }
80}
81
82} // namespace clang::tidy::bugprone
CaptureExpr CE
NodeType Type
DiagnosticBuilder diag(SourceLocation Loc, StringRef Description, DiagnosticIDs::Level Level=DiagnosticIDs::Warning)
Add a diagnostic with the check's name.
void registerMatchers(ast_matchers::MatchFinder *Finder) override
Override this to register AST matchers with Finder.
void check(const ast_matchers::MatchFinder::MatchResult &Result) override
ClangTidyChecks that register ASTMatchers should do the actual work in here.
static std::optional< uint64_t > tryEvaluateSizeExpr(const Expr *SizeExpr, const ASTContext &Ctx)