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//===--- MemsetZeroLengthCheck.cpp - clang-tidy -------------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "MemsetZeroLengthCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "clang/ASTMatchers/ASTMatchers.h"
#include "clang/Lex/Lexer.h"
using namespace clang::ast_matchers;
namespace clang {
namespace tidy {
namespace google {
namespace runtime {
void
MemsetZeroLengthCheck::registerMatchers(ast_matchers::MatchFinder *Finder) {
// Look for memset(x, y, 0) as those is most likely an argument swap.
// TODO: Also handle other standard functions that suffer from the same
// problem, e.g. memchr.
Finder->addMatcher(
callExpr(callee(functionDecl(hasName("::memset"))), argumentCountIs(3),
unless(isInTemplateInstantiation())).bind("decl"),
this);
}
/// \brief Get a StringRef representing a SourceRange.
static StringRef getAsString(const MatchFinder::MatchResult &Result,
SourceRange R) {
const SourceManager &SM = *Result.SourceManager;
// Don't even try to resolve macro or include contraptions. Not worth emitting
// a fixit for.
if (R.getBegin().isMacroID() ||
!SM.isWrittenInSameFile(R.getBegin(), R.getEnd()))
return StringRef();
const char *Begin = SM.getCharacterData(R.getBegin());
const char *End = SM.getCharacterData(Lexer::getLocForEndOfToken(
R.getEnd(), 0, SM, Result.Context->getLangOpts()));
return StringRef(Begin, End - Begin);
}
void MemsetZeroLengthCheck::check(const MatchFinder::MatchResult &Result) {
const auto *Call = Result.Nodes.getNodeAs<CallExpr>("decl");
// Note, this is:
// void *memset(void *buffer, int fill_char, size_t byte_count);
// Arg1 is fill_char, Arg2 is byte_count.
const Expr *Arg1 = Call->getArg(1);
const Expr *Arg2 = Call->getArg(2);
// Return if `byte_count` is not zero at compile time.
llvm::APSInt Value1, Value2;
if (Arg2->isValueDependent() ||
!Arg2->EvaluateAsInt(Value2, *Result.Context) || Value2 != 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.
if (!Arg1->isValueDependent() &&
Arg1->EvaluateAsInt(Value1, *Result.Context) &&
(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->getLocStart(),
"memset of size zero, potentially swapped arguments");
SourceRange LHSRange = Arg1->getSourceRange();
SourceRange RHSRange = Arg2->getSourceRange();
StringRef RHSString = getAsString(Result, RHSRange);
StringRef LHSString = getAsString(Result, LHSRange);
if (LHSString.empty() || RHSString.empty())
return;
D << FixItHint::CreateReplacement(CharSourceRange::getTokenRange(LHSRange),
RHSString)
<< FixItHint::CreateReplacement(CharSourceRange::getTokenRange(RHSRange),
LHSString);
}
} // namespace runtime
} // namespace google
} // namespace tidy
} // namespace clang
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