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cppcheck/lib/fwdanalysis.cpp

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/*
* Cppcheck - A tool for static C/C++ code analysis
* Copyright (C) 2007-2021 Cppcheck team.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include "fwdanalysis.h"
#include "astutils.h"
#include "config.h"
#include "library.h"
#include "symboldatabase.h"
#include "token.h"
#include "vfvalue.h"
#include <string>
static bool isUnchanged(const Token *startToken, const Token *endToken, const std::set<nonneg int> &exprVarIds, bool local)
{
for (const Token *tok = startToken; tok != endToken; tok = tok->next()) {
if (!local && Token::Match(tok, "%name% (") && !Token::simpleMatch(tok->linkAt(1), ") {"))
// TODO: this is a quick bailout
return false;
if (tok->varId() == 0 || exprVarIds.find(tok->varId()) == exprVarIds.end())
continue;
const Token *parent = tok;
while (parent->astParent() && !parent->astParent()->isAssignmentOp() && parent->astParent()->tokType() != Token::Type::eIncDecOp) {
if (parent->str() == "," || parent->isUnaryOp("&"))
// TODO: This is a quick bailout
return false;
parent = parent->astParent();
}
if (parent->astParent()) {
if (parent->astParent()->tokType() == Token::Type::eIncDecOp)
return false;
else if (parent->astParent()->isAssignmentOp() && parent == parent->astParent()->astOperand1())
return false;
}
}
return true;
}
static bool hasFunctionCall(const Token *tok)
{
if (!tok)
return false;
if (Token::Match(tok, "%name% ("))
// todo, const/pure function?
return true;
return hasFunctionCall(tok->astOperand1()) || hasFunctionCall(tok->astOperand2());
}
static bool hasGccCompoundStatement(const Token *tok)
{
if (!tok)
return false;
if (tok->str() == "{" && Token::simpleMatch(tok->previous(), "( {"))
return true;
return hasGccCompoundStatement(tok->astOperand1()) || hasGccCompoundStatement(tok->astOperand2());
}
static bool nonLocal(const Variable* var, bool deref)
{
return !var || (!var->isLocal() && !var->isArgument()) || (deref && var->isArgument() && var->isPointer()) || var->isStatic() || var->isReference() || var->isExtern();
}
static bool hasVolatileCastOrVar(const Token *expr)
{
bool ret = false;
visitAstNodes(expr,
[&ret](const Token *tok) {
if (tok->variable() && tok->variable()->isVolatile())
ret = true;
else if (Token::simpleMatch(tok, "( volatile"))
ret = true;
return ret ? ChildrenToVisit::none : ChildrenToVisit::op1_and_op2;
});
return ret;
}
struct FwdAnalysis::Result FwdAnalysis::checkRecursive(const Token *expr, const Token *startToken, const Token *endToken, const std::set<nonneg int> &exprVarIds, bool local, bool inInnerClass, int depth)
{
// Parse the given tokens
if (++depth > 1000)
return Result(Result::Type::BAILOUT);
for (const Token* tok = startToken; precedes(tok, endToken); tok = tok->next()) {
if (Token::simpleMatch(tok, "try {")) {
// TODO: handle try
return Result(Result::Type::BAILOUT);
}
if (Token::simpleMatch(tok, "break ;")) {
return Result(Result::Type::BREAK, tok);
}
if (Token::simpleMatch(tok, "goto"))
return Result(Result::Type::BAILOUT);
if (!inInnerClass && tok->str() == "{" && tok->scope()->isClassOrStruct()) {
// skip returns from local class definition
FwdAnalysis::Result result = checkRecursive(expr, tok, tok->link(), exprVarIds, local, true, depth);
if (result.type != Result::Type::NONE)
return result;
tok=tok->link();
}
if (tok->str() == "continue")
// TODO
return Result(Result::Type::BAILOUT);
if (const Token *lambdaEndToken = findLambdaEndToken(tok)) {
tok = lambdaEndToken;
const Result lambdaResult = checkRecursive(expr, lambdaEndToken->link()->next(), lambdaEndToken, exprVarIds, local, inInnerClass, depth);
if (lambdaResult.type == Result::Type::READ || lambdaResult.type == Result::Type::BAILOUT)
return lambdaResult;
}
if (Token::Match(tok, "return|throw")) {
// TODO: Handle these better
// Is expr variable used in expression?
const Token* opTok = tok->astOperand1();
if (!opTok)
opTok = tok->next();
std::pair<const Token*, const Token*> startEndTokens = opTok->findExpressionStartEndTokens();
FwdAnalysis::Result result =
checkRecursive(expr, startEndTokens.first, startEndTokens.second->next(), exprVarIds, local, true, depth);
if (result.type != Result::Type::NONE)
return result;
// #9167: if the return is inside an inner class, it does not tell us anything
if (!inInnerClass) {
if (!local && mWhat == What::Reassign)
return Result(Result::Type::BAILOUT);
return Result(Result::Type::RETURN);
}
}
if (tok->str() == "}") {
// Known value => possible value
if (tok->scope() == expr->scope())
mValueFlowKnown = false;
if (tok->scope()->isLoopScope()) {
// check condition
const Token *conditionStart = nullptr;
const Token *conditionEnd = nullptr;
if (Token::simpleMatch(tok->link()->previous(), ") {")) {
conditionEnd = tok->link()->previous();
conditionStart = conditionEnd->link();
} else if (Token::simpleMatch(tok->link()->previous(), "do {") && Token::simpleMatch(tok, "} while (")) {
conditionStart = tok->tokAt(2);
conditionEnd = conditionStart->link();
}
if (conditionStart && conditionEnd) {
bool used = false;
for (const Token *condTok = conditionStart; condTok != conditionEnd; condTok = condTok->next()) {
if (exprVarIds.find(condTok->varId()) != exprVarIds.end()) {
used = true;
break;
}
}
if (used)
return Result(Result::Type::BAILOUT);
}
// check loop body again..
const struct FwdAnalysis::Result &result = checkRecursive(expr, tok->link(), tok, exprVarIds, local, inInnerClass, depth);
if (result.type == Result::Type::BAILOUT || result.type == Result::Type::READ)
return result;
}
}
if (Token::simpleMatch(tok, "else {"))
tok = tok->linkAt(1);
if (Token::simpleMatch(tok, "asm ("))
return Result(Result::Type::BAILOUT);
if (mWhat == What::ValueFlow && (Token::Match(tok, "while|for (") || Token::simpleMatch(tok, "do {"))) {
const Token *bodyStart = nullptr;
const Token *conditionStart = nullptr;
if (Token::simpleMatch(tok, "do {")) {
bodyStart = tok->next();
if (Token::simpleMatch(bodyStart->link(), "} while ("))
conditionStart = bodyStart->link()->tokAt(2);
} else {
conditionStart = tok->next();
if (Token::simpleMatch(conditionStart->link(), ") {"))
bodyStart = conditionStart->link()->next();
}
if (!bodyStart || !conditionStart)
return Result(Result::Type::BAILOUT);
// Is expr changed in condition?
if (!isUnchanged(conditionStart, conditionStart->link(), exprVarIds, local))
return Result(Result::Type::BAILOUT);
// Is expr changed in loop body?
if (!isUnchanged(bodyStart, bodyStart->link(), exprVarIds, local))
return Result(Result::Type::BAILOUT);
}
if (mWhat == What::ValueFlow && Token::simpleMatch(tok, "if (") && Token::simpleMatch(tok->linkAt(1), ") {")) {
const Token *bodyStart = tok->linkAt(1)->next();
const Token *conditionStart = tok->next();
const Token *condTok = conditionStart->astOperand2();
if (condTok->hasKnownIntValue()) {
const bool cond = condTok->values().front().intvalue;
if (cond) {
FwdAnalysis::Result result = checkRecursive(expr, bodyStart, bodyStart->link(), exprVarIds, local, true, depth);
if (result.type != Result::Type::NONE)
return result;
} else if (Token::simpleMatch(bodyStart->link(), "} else {")) {
bodyStart = bodyStart->link()->tokAt(2);
FwdAnalysis::Result result = checkRecursive(expr, bodyStart, bodyStart->link(), exprVarIds, local, true, depth);
if (result.type != Result::Type::NONE)
return result;
}
}
tok = bodyStart->link();
if (isReturnScope(tok, &mLibrary))
return Result(Result::Type::BAILOUT);
if (Token::simpleMatch(tok, "} else {"))
tok = tok->linkAt(2);
if (!tok)
return Result(Result::Type::BAILOUT);
// Is expr changed in condition?
if (!isUnchanged(conditionStart, conditionStart->link(), exprVarIds, local))
return Result(Result::Type::BAILOUT);
// Is expr changed in condition body?
if (!isUnchanged(bodyStart, bodyStart->link(), exprVarIds, local))
return Result(Result::Type::BAILOUT);
}
if (!local && Token::Match(tok, "%name% (") && !Token::simpleMatch(tok->linkAt(1), ") {")) {
// TODO: this is a quick bailout
return Result(Result::Type::BAILOUT);
}
if (mWhat == What::Reassign &&
Token::simpleMatch(tok, ";") &&
Token::simpleMatch(tok->astParent(), ";") &&
Token::simpleMatch(tok->astParent()->astParent(), "(") &&
Token::simpleMatch(tok->astParent()->astParent()->previous(), "for (") &&
!isUnchanged(tok, tok->astParent()->astParent()->link(), exprVarIds, local))
// TODO: This is a quick bailout to avoid FP #9420, there are false negatives (TODO_ASSERT_EQUALS)
return Result(Result::Type::BAILOUT);
if (expr->isName() && Token::Match(tok, "%name% (") && tok->str().find("<") != std::string::npos && tok->str().find(expr->str()) != std::string::npos)
return Result(Result::Type::BAILOUT);
if (exprVarIds.find(tok->varId()) != exprVarIds.end()) {
const Token *parent = tok;
bool other = false;
bool same = tok->astParent() && isSameExpression(mCpp, false, expr, tok, mLibrary, true, false, nullptr);
while (!same && Token::Match(parent->astParent(), "*|.|::|[|(|%cop%")) {
parent = parent->astParent();
if (parent->str() == "(" && !parent->isCast())
break;
if (isSameExpression(mCpp, false, expr, parent, mLibrary, true, false, nullptr)) {
same = true;
if (mWhat == What::ValueFlow) {
KnownAndToken v;
v.known = mValueFlowKnown;
v.token = parent;
mValueFlow.push_back(v);
}
}
if (Token::Match(parent, ". %var%") && parent->next()->varId() && exprVarIds.find(parent->next()->varId()) == exprVarIds.end() &&
isSameExpression(mCpp, false, expr->astOperand1(), parent->astOperand1(), mLibrary, true, false, nullptr)) {
other = true;
break;
}
}
if (mWhat != What::ValueFlow && same && Token::simpleMatch(parent->astParent(), "[") && parent == parent->astParent()->astOperand2()) {
return Result(Result::Type::READ);
}
if (other)
continue;
if (Token::simpleMatch(parent->astParent(), "=") && parent == parent->astParent()->astOperand1()) {
if (!local && hasFunctionCall(parent->astParent()->astOperand2())) {
// TODO: this is a quick bailout
return Result(Result::Type::BAILOUT);
}
if (hasOperand(parent->astParent()->astOperand2(), expr)) {
if (mWhat == What::Reassign)
return Result(Result::Type::READ);
continue;
}
const auto startEnd = parent->astParent()->astOperand2()->findExpressionStartEndTokens();
for (const Token* tok2 = startEnd.first; tok2 != startEnd.second; tok2 = tok2->next()) {
if (tok2->tokType() == Token::eLambda)
return Result(Result::Type::BAILOUT);
// TODO: analyze usage in lambda
}
// ({ .. })
if (hasGccCompoundStatement(parent->astParent()->astOperand2()))
return Result(Result::Type::BAILOUT);
const bool reassign = isSameExpression(mCpp, false, expr, parent, mLibrary, false, false, nullptr);
if (reassign)
return Result(Result::Type::WRITE, parent->astParent());
return Result(Result::Type::READ);
} else if (mWhat == What::Reassign && parent->valueType() && parent->valueType()->pointer && Token::Match(parent->astParent(), "%assign%") && parent == parent->astParent()->astOperand1()) {
return Result(Result::Type::READ);
} else if (Token::Match(parent->astParent(), "%assign%") && !parent->astParent()->astParent() && parent == parent->astParent()->astOperand1()) {
if (mWhat == What::Reassign)
return Result(Result::Type::BAILOUT, parent->astParent());
if (mWhat == What::UnusedValue && (!parent->valueType() || parent->valueType()->reference != Reference::None))
return Result(Result::Type::BAILOUT, parent->astParent());
continue;
} else if (mWhat == What::UnusedValue && parent->isUnaryOp("&") && Token::Match(parent->astParent(), "[,(]")) {
// Pass variable to function the writes it
const Token *ftok = parent->astParent();
while (Token::simpleMatch(ftok, ","))
ftok = ftok->astParent();
if (ftok && Token::Match(ftok->previous(), "%name% (")) {
const std::vector<const Token *> args = getArguments(ftok);
int argnr = 0;
while (argnr < args.size() && args[argnr] != parent)
argnr++;
if (argnr < args.size()) {
const Library::Function* functionInfo = mLibrary.getFunction(ftok->astOperand1());
if (functionInfo) {
const auto it = functionInfo->argumentChecks.find(argnr + 1);
if (it != functionInfo->argumentChecks.end() && it->second.direction == Library::ArgumentChecks::Direction::DIR_OUT)
continue;
}
}
}
return Result(Result::Type::BAILOUT, parent->astParent());
} else {
// TODO: this is a quick bailout
return Result(Result::Type::BAILOUT, parent->astParent());
}
}
if (Token::Match(tok, ")|do {")) {
if (tok->str() == ")" && Token::simpleMatch(tok->link()->previous(), "switch ("))
// TODO: parse switch
return Result(Result::Type::BAILOUT);
const Result &result1 = checkRecursive(expr, tok->tokAt(2), tok->linkAt(1), exprVarIds, local, inInnerClass, depth);
if (result1.type == Result::Type::READ || result1.type == Result::Type::BAILOUT)
return result1;
if (mWhat == What::ValueFlow && result1.type == Result::Type::WRITE)
mValueFlowKnown = false;
if (mWhat == What::Reassign && result1.type == Result::Type::BREAK) {
const Token *scopeEndToken = findNextTokenFromBreak(result1.token);
if (scopeEndToken) {
const Result &result2 = checkRecursive(expr, scopeEndToken->next(), endToken, exprVarIds, local, inInnerClass, depth);
if (result2.type == Result::Type::BAILOUT)
return result2;
}
}
if (Token::simpleMatch(tok->linkAt(1), "} else {")) {
const Token *elseStart = tok->linkAt(1)->tokAt(2);
const Result &result2 = checkRecursive(expr, elseStart, elseStart->link(), exprVarIds, local, inInnerClass, depth);
if (mWhat == What::ValueFlow && result2.type == Result::Type::WRITE)
mValueFlowKnown = false;
if (result2.type == Result::Type::READ || result2.type == Result::Type::BAILOUT)
return result2;
if (result1.type == Result::Type::WRITE && result2.type == Result::Type::WRITE)
return result1;
tok = elseStart->link();
} else {
tok = tok->linkAt(1);
}
}
}
return Result(Result::Type::NONE);
}
bool FwdAnalysis::isGlobalData(const Token *expr) const
{
return ::isGlobalData(expr, mCpp);
}
std::set<nonneg int> FwdAnalysis::getExprVarIds(const Token* expr, bool* localOut, bool* unknownVarIdOut) const
{
// all variable ids in expr.
std::set<nonneg int> exprVarIds;
bool local = true;
bool unknownVarId = false;
visitAstNodes(expr,
[&](const Token *tok) {
if (tok->str() == "[" && mWhat == What::UnusedValue)
return ChildrenToVisit::op1;
if (tok->varId() == 0 && tok->isName() && tok->previous()->str() != ".") {
// unknown variable
unknownVarId = true;
return ChildrenToVisit::none;
}
if (tok->varId() > 0) {
exprVarIds.insert(tok->varId());
if (!Token::simpleMatch(tok->previous(), ".")) {
const Variable *var = tok->variable();
if (var && var->isReference() && var->isLocal() && Token::Match(var->nameToken(), "%var% [=(]") && !isGlobalData(var->nameToken()->next()->astOperand2()))
return ChildrenToVisit::none;
const bool deref = tok->astParent() && (tok->astParent()->isUnaryOp("*") || (tok->astParent()->str() == "[" && tok == tok->astParent()->astOperand1()));
local &= !nonLocal(tok->variable(), deref);
}
}
return ChildrenToVisit::op1_and_op2;
});
if (localOut)
*localOut = local;
if (unknownVarIdOut)
*unknownVarIdOut = unknownVarId;
return exprVarIds;
}
FwdAnalysis::Result FwdAnalysis::check(const Token* expr, const Token* startToken, const Token* endToken)
{
// all variable ids in expr.
bool local = true;
bool unknownVarId = false;
std::set<nonneg int> exprVarIds = getExprVarIds(expr, &local, &unknownVarId);
if (unknownVarId)
return Result(FwdAnalysis::Result::Type::BAILOUT);
if (mWhat == What::Reassign && isGlobalData(expr))
local = false;
// In unused values checking we do not want to check assignments to
// global data.
if (mWhat == What::UnusedValue && isGlobalData(expr))
return Result(FwdAnalysis::Result::Type::BAILOUT);
Result result = checkRecursive(expr, startToken, endToken, exprVarIds, local, false);
// Break => continue checking in outer scope
while (mWhat!=What::ValueFlow && result.type == FwdAnalysis::Result::Type::BREAK) {
const Token *scopeEndToken = findNextTokenFromBreak(result.token);
if (!scopeEndToken)
break;
result = checkRecursive(expr, scopeEndToken->next(), endToken, exprVarIds, local, false);
}
return result;
}
bool FwdAnalysis::hasOperand(const Token *tok, const Token *lhs) const
{
if (!tok)
return false;
if (isSameExpression(mCpp, false, tok, lhs, mLibrary, false, false, nullptr))
return true;
return hasOperand(tok->astOperand1(), lhs) || hasOperand(tok->astOperand2(), lhs);
}
const Token *FwdAnalysis::reassign(const Token *expr, const Token *startToken, const Token *endToken)
{
if (hasVolatileCastOrVar(expr))
return nullptr;
mWhat = What::Reassign;
Result result = check(expr, startToken, endToken);
return result.type == FwdAnalysis::Result::Type::WRITE ? result.token : nullptr;
}
bool FwdAnalysis::unusedValue(const Token *expr, const Token *startToken, const Token *endToken)
{
if (isEscapedAlias(expr))
return false;
if (hasVolatileCastOrVar(expr))
return false;
mWhat = What::UnusedValue;
Result result = check(expr, startToken, endToken);
return (result.type == FwdAnalysis::Result::Type::NONE || result.type == FwdAnalysis::Result::Type::RETURN) && !possiblyAliased(expr, startToken);
}
bool FwdAnalysis::possiblyAliased(const Token *expr, const Token *startToken) const
{
if (expr->isUnaryOp("*"))
return true;
const bool macro = false;
const bool pure = false;
const bool followVar = false;
for (const Token *tok = startToken; tok; tok = tok->previous()) {
if (tok->str() == "{" && tok->scope()->type == Scope::eFunction && !(tok->astParent() && tok->astParent()->str() == ","))
break;
if (Token::Match(tok, "%name% (") && !Token::Match(tok, "if|while|for")) {
// Is argument passed by reference?
const std::vector<const Token*> args = getArguments(tok);
for (int argnr = 0; argnr < args.size(); ++argnr) {
if (!Token::Match(args[argnr], "%name%|.|::"))
continue;
if (tok->function() && tok->function()->getArgumentVar(argnr) && !tok->function()->getArgumentVar(argnr)->isReference() && !tok->function()->isConst())
continue;
for (const Token *subexpr = expr; subexpr; subexpr = subexpr->astOperand1()) {
if (isSameExpression(mCpp, macro, subexpr, args[argnr], mLibrary, pure, followVar)) {
const Scope* scope = expr->scope(); // if there is no other variable, assume no aliasing
if (scope->varlist.size() > 1)
return true;
}
}
}
continue;
}
const Token *addrOf = nullptr;
if (Token::Match(tok, "& %name% ="))
addrOf = tok->tokAt(2)->astOperand2();
else if (tok->isUnaryOp("&"))
addrOf = tok->astOperand1();
else if (Token::simpleMatch(tok, "std :: ref ("))
addrOf = tok->tokAt(3)->astOperand2();
else
continue;
for (const Token *subexpr = expr; subexpr; subexpr = subexpr->astOperand1()) {
if (isSameExpression(mCpp, macro, subexpr, addrOf, mLibrary, pure, followVar))
return true;
}
}
return false;
}
bool FwdAnalysis::isEscapedAlias(const Token* expr)
{
for (const Token *subexpr = expr; subexpr; subexpr = subexpr->astOperand1()) {
for (const ValueFlow::Value &val : subexpr->values()) {
if (!val.isLocalLifetimeValue())
continue;
const Variable* var = val.tokvalue->variable();
if (!var)
continue;
if (!var->isLocal())
return true;
if (var->isArgument())
return true;
}
}
return false;
}
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