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//===--- SuspiciousMemsetUsageCheck.cpp - clang-tidy-----------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "SuspiciousMemsetUsageCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "clang/ASTMatchers/ASTMatchers.h"
#include "clang/Lex/Lexer.h"
#include "clang/Tooling/FixIt.h"
using namespace clang::ast_matchers;
namespace clang::tidy::bugprone {
void SuspiciousMemsetUsageCheck::registerMatchers(MatchFinder *Finder) {
// Match the standard memset:
// void *memset(void *buffer, int fill_char, size_t byte_count);
auto MemsetDecl =
functionDecl(hasName("::memset"),
parameterCountIs(3),
hasParameter(0, hasType(pointerType(pointee(voidType())))),
hasParameter(1, hasType(isInteger())),
hasParameter(2, hasType(isInteger())));
// Look for memset(x, '0', z). Probably memset(x, 0, z) was intended.
Finder->addMatcher(
callExpr(
callee(MemsetDecl), argumentCountIs(3),
hasArgument(1, characterLiteral(equals(static_cast<unsigned>('0')))
.bind("char-zero-fill")),
unless(hasArgument(
0, anyOf(hasType(pointsTo(isAnyCharacter())),
hasType(arrayType(hasElementType(isAnyCharacter()))))))),
this);
// Look for memset with an integer literal in its fill_char argument.
// Will check if it gets truncated.
Finder->addMatcher(
callExpr(callee(MemsetDecl), argumentCountIs(3),
hasArgument(1, integerLiteral().bind("num-fill"))),
this);
// Look for memset(x, y, 0) as that is most likely an argument swap.
Finder->addMatcher(
callExpr(callee(MemsetDecl), argumentCountIs(3),
unless(hasArgument(1, anyOf(characterLiteral(equals(
static_cast<unsigned>('0'))),
integerLiteral()))))
.bind("call"),
this);
}
void SuspiciousMemsetUsageCheck::check(const MatchFinder::MatchResult &Result) {
if (const auto *CharZeroFill =
Result.Nodes.getNodeAs<CharacterLiteral>("char-zero-fill")) {
// Case 1: fill_char of memset() is a character '0'. Probably an
// integer zero was intended.
SourceRange CharRange = CharZeroFill->getSourceRange();
auto Diag =
diag(CharZeroFill->getBeginLoc(), "memset fill value is char '0', "
"potentially mistaken for int 0");
// Only suggest a fix if no macros are involved.
if (CharRange.getBegin().isMacroID())
return;
Diag << FixItHint::CreateReplacement(
CharSourceRange::getTokenRange(CharRange), "0");
}
else if (const auto *NumFill =
Result.Nodes.getNodeAs<IntegerLiteral>("num-fill")) {
// Case 2: fill_char of memset() is larger in size than an unsigned char
// so it gets truncated during conversion.
const auto UCharMax = (1 << Result.Context->getCharWidth()) - 1;
Expr::EvalResult EVResult;
if (!NumFill->EvaluateAsInt(EVResult, *Result.Context))
return;
llvm::APSInt NumValue = EVResult.Val.getInt();
if (NumValue >= 0 && NumValue <= UCharMax)
return;
diag(NumFill->getBeginLoc(), "memset fill value is out of unsigned "
"character range, gets truncated");
}
else if (const auto *Call = Result.Nodes.getNodeAs<CallExpr>("call")) {
// Case 3: byte_count of memset() is zero. This is most likely an
// argument swap.
const Expr *FillChar = Call->getArg(1);
const Expr *ByteCount = Call->getArg(2);
// Return if `byte_count` is not zero at compile time.
Expr::EvalResult Value2;
if (ByteCount->isValueDependent() ||
!ByteCount->EvaluateAsInt(Value2, *Result.Context) ||
Value2.Val.getInt() != 0)
return;
// Return if `fill_char` is known to be zero or negative at compile
// time. In these cases, swapping the args would be a nop, or
// introduce a definite bug. The code is likely correct.
Expr::EvalResult EVResult;
if (!FillChar->isValueDependent() &&
FillChar->EvaluateAsInt(EVResult, *Result.Context)) {
llvm::APSInt Value1 = EVResult.Val.getInt();
if (Value1 == 0 || Value1.isNegative())
return;
}
// `byte_count` is known to be zero at compile time, and `fill_char` is
// either not known or known to be a positive integer. Emit a warning
// and fix-its to swap the arguments.
auto D = diag(Call->getBeginLoc(),
"memset of size zero, potentially swapped arguments");
StringRef RHSString = tooling::fixit::getText(*ByteCount, *Result.Context);
StringRef LHSString = tooling::fixit::getText(*FillChar, *Result.Context);
if (LHSString.empty() || RHSString.empty())
return;
D << tooling::fixit::createReplacement(*FillChar, RHSString)
<< tooling::fixit::createReplacement(*ByteCount, LHSString);
}
}
} // namespace clang::tidy::bugprone
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