cppcheck/lib/checktype.cpp

/*
 * Cppcheck - A tool for static C/C++ code analysis
 * Copyright (C) 2007-2015 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 "checktype.h"
#include "mathlib.h"
#include "symboldatabase.h"

#include <stack>
//---------------------------------------------------------------------------

// Register this check class (by creating a static instance of it)
namespace {
    CheckType instance;
}

static bool astIsIntResult(const Token *tok)
{
    if (!tok)
        return false;
    if (tok->astOperand1())
        return astIsIntResult(tok->astOperand1()) && astIsIntResult(tok->astOperand2());
    // todo: handle numbers
    if (!tok->variable())
        return false;
    const Token *type = tok->variable()->typeStartToken();
    return Token::Match(type, "char|short|int") && !type->isLong();
}

static bool astGetSizeSign(const Settings *settings, const Token *tok, unsigned int *size, char *sign)
{
    if (!tok)
        return false;
    if (tok->isArithmeticalOp()) {
        if (!astGetSizeSign(settings, tok->astOperand1(), size, sign))
            return false;
        return !tok->astOperand2() || astGetSizeSign(settings, tok->astOperand2(), size, sign);
    }
    if (tok->isNumber() && MathLib::isInt(tok->str())) {
        if (tok->str().find('L') != std::string::npos)
            return false;
        MathLib::bigint value = MathLib::toLongNumber(tok->str());
        unsigned int sz;
        if (value >= -(1<<7) && value <= (1<<7)-1)
            sz = 8;
        else if (value >= -(1<<15) && value <= (1<<15)-1)
            sz = 16;
        else if (value >= -(1LL<<31) && value <= (1LL<<31)-1)
            sz = 32;
        else
            return false;
        if (sz < 8 * settings->sizeof_int)
            sz = 8 * settings->sizeof_int;
        if (*size < sz)
            *size = sz;
        if (tok->str().find('U') != std::string::npos)
            *sign = 'u';
        if (*sign != 'u')
            *sign = 's';
        return true;
    }
    if (tok->isName()) {
        const Variable *var = tok->variable();
        if (!var)
            return false;
        unsigned int sz = 0;
        for (const Token *type = var->typeStartToken(); type; type = type->next()) {
            if (type->str() == "*")
                return false;  // <- FIXME: handle pointers
            if (Token::Match(type, "char|short|int")) {
                sz = 8 * settings->sizeof_int;
                if (type->isUnsigned())
                    *sign = 'u';
                else if (*sign != 'u')
                    *sign = 's';
            } else if (Token::Match(type, "float|double|long")) {
                return false;
            } else {
                // TODO: try to lookup type info in library
            }
            if (type == var->typeEndToken())
                break;
        }
        if (sz == 0)
            return false;
        if (*size < sz)
            *size = sz;
        return true;
    }
    return false;
}

//---------------------------------------------------------------------------
// Checking for shift by too many bits
//---------------------------------------------------------------------------

void CheckType::checkTooBigBitwiseShift()
{
    const bool printWarnings = _settings->isEnabled("warning");
    const bool printInconclusive = _settings->inconclusive;

    // unknown sizeof(int) => can't run this checker
    if (_settings->platformType == Settings::Unspecified)
        return;

    const SymbolDatabase *symbolDatabase = _tokenizer->getSymbolDatabase();
    const std::size_t functions = symbolDatabase->functionScopes.size();
    for (std::size_t i = 0; i < functions; ++i) {
        const Scope * scope = symbolDatabase->functionScopes[i];
        for (const Token* tok = scope->classStart->next(); tok != scope->classEnd; tok = tok->next()) {
            if (tok->str() != "<<" && tok->str() != ">>")
                continue;

            if (!tok->astOperand1() || !tok->astOperand2())
                continue;

            // get number of bits of lhs
            const Variable *var = tok->astOperand1()->variable();
            if (!var)
                continue;
            int lhsbits = 0;
            for (const Token *type = var->typeStartToken(); type; type = type->next()) {
                if (Token::Match(type,"char|short|int") && !type->isLong()) {
                    lhsbits = _settings->sizeof_int * 8;
                    break;
                }
                if (type == var->typeEndToken() || type->str() == "<")
                    break;
            }
            if (lhsbits == 0)
                continue;

            // Get biggest rhs value. preferably a value which doesn't have 'condition'.
            const ValueFlow::Value *value = tok->astOperand2()->getValueGE(lhsbits, _settings);
            if (!value)
                continue;
            if (value->condition && !printWarnings)
                continue;
            if (value->inconclusive && !printInconclusive)
                continue;
            tooBigBitwiseShiftError(tok, lhsbits, *value);
        }
    }
}

void CheckType::tooBigBitwiseShiftError(const Token *tok, int lhsbits, const ValueFlow::Value &rhsbits)
{
    std::list<const Token*> callstack;
    callstack.push_back(tok);
    if (rhsbits.condition)
        callstack.push_back(rhsbits.condition);
    std::ostringstream errmsg;
    errmsg << "Shifting " << lhsbits << "-bit value by " << rhsbits.intvalue << " bits is undefined behaviour";
    if (rhsbits.condition)
        errmsg << ". See condition at line " << rhsbits.condition->linenr() << ".";
    reportError(callstack, rhsbits.condition ? Severity::warning : Severity::error, "shiftTooManyBits", errmsg.str(), 0U, rhsbits.inconclusive);
}

//---------------------------------------------------------------------------
// Checking for integer overflow
//---------------------------------------------------------------------------

void CheckType::checkIntegerOverflow()
{
    // unknown sizeof(int) => can't run this checker
    if (_settings->platformType == Settings::Unspecified)
        return;

    // max int value according to platform settings.
    const MathLib::bigint maxint = (1LL << (8 * _settings->sizeof_int - 1)) - 1;

    const SymbolDatabase *symbolDatabase = _tokenizer->getSymbolDatabase();
    const std::size_t functions = symbolDatabase->functionScopes.size();
    for (std::size_t i = 0; i < functions; ++i) {
        const Scope * scope = symbolDatabase->functionScopes[i];
        for (const Token* tok = scope->classStart->next(); tok != scope->classEnd; tok = tok->next()) {
            if (!tok->isArithmeticalOp())
                continue;

            // is there a overflow result value
            const ValueFlow::Value *value = tok->getValueGE(maxint + 1, _settings);
            if (!value)
                value = tok->getValueLE(-maxint - 2, _settings);
            if (!value)
                continue;

            // get size and sign of result..
            unsigned int size = 0;
            char sign = 0;
            if (!astGetSizeSign(_settings, tok, &size, &sign))
                continue;
            if (sign != 's')  // only signed integer overflow is UB
                continue;

            integerOverflowError(tok, *value);
        }
    }
}

void CheckType::integerOverflowError(const Token *tok, const ValueFlow::Value &value)
{
    const std::string expr(tok ? tok->expressionString() : "");
    const std::string cond(value.condition ?
                           ". See condition at line " + MathLib::toString(value.condition->linenr()) + "." :
                           "");

    reportError(tok,
                value.condition ? Severity::warning : Severity::error,
                "integerOverflow",
                "Signed integer overflow for expression '"+expr+"'"+cond,
                0U,
                value.inconclusive);
}

//---------------------------------------------------------------------------
// Checking for sign conversion when operand can be negative
//---------------------------------------------------------------------------

void CheckType::checkSignConversion()
{
    if (!_settings->isEnabled("warning"))
        return;

    const SymbolDatabase *symbolDatabase = _tokenizer->getSymbolDatabase();
    const std::size_t functions = symbolDatabase->functionScopes.size();
    for (std::size_t i = 0; i < functions; ++i) {
        const Scope * scope = symbolDatabase->functionScopes[i];
        for (const Token* tok = scope->classStart->next(); tok != scope->classEnd; tok = tok->next()) {
            if (!tok->isArithmeticalOp() || Token::Match(tok,"+|-"))
                continue;

            unsigned int size = 0;
            char sign = 0;
            if (!astGetSizeSign(_settings, tok, &size, &sign))
                continue;

            if (sign != 'u')
                continue;

            // Check if there are signed operands that can be negative..
            std::stack<const Token *> tokens;
            tokens.push(tok->astOperand1());
            tokens.push(tok->astOperand2());
            while (!tokens.empty()) {
                const Token *tok1 = tokens.top();
                tokens.pop();
                if (!tok1)
                    continue;
                if (tok1->str() == "(")
                    continue; // Todo: properly handle casts, function calls, etc
                const Variable *var = tok1->variable();
                if (var && tok1->getValueLE(-1,_settings)) {
                    bool signedvar = true;  // assume that variable is signed since it can have a negative value
                    for (const Token *type = var->typeStartToken();; type = type->next()) {
                        if (type->isUnsigned()) {
                            signedvar = false;
                            break;
                        }
                        if (type->isSigned())
                            break;
                        if (type->isName() && !Token::Match(type, "char|short|int|long|const")) {
                            signedvar = false;
                            break;
                        }
                        if (type == var->typeEndToken())
                            break;
                    }
                    if (signedvar) {
                        signConversionError(tok1);
                        break;
                    }
                }
            }
        }
    }
}

void CheckType::signConversionError(const Token *tok)
{
    const std::string varname(tok ? tok->str() : "var");

    reportError(tok,
                Severity::warning,
                "signConversion",
                "Suspicious code: sign conversion of " + varname + " in calculation, even though " + varname + " can have a negative value");
}


//---------------------------------------------------------------------------
// Checking for long cast of int result   const long x = var1 * var2;
//---------------------------------------------------------------------------

void CheckType::checkLongCast()
{
    if (!_settings->isEnabled("style"))
        return;

    // Assignments..
    for (const Token *tok = _tokenizer->tokens(); tok; tok = tok->next()) {
        if (!Token::Match(tok, "%var% ="))
            continue;
        if (!tok->variable() || !tok->variable()->isConst() || tok->variable()->typeStartToken()->str() != "long")
            continue;
        if (!tok->variable()->typeStartToken()->originalName().empty())
            continue;
        if (Token::Match(tok->next()->astOperand2(), "*|<<") && astIsIntResult(tok->next()->astOperand2()))
            longCastAssignError(tok);
    }

    // Return..
    const SymbolDatabase *symbolDatabase = _tokenizer->getSymbolDatabase();
    const std::size_t functions = symbolDatabase->functionScopes.size();
    for (std::size_t i = 0; i < functions; ++i) {
        const Scope * scope = symbolDatabase->functionScopes[i];

        // function must return long data
        const Token * def = scope->classDef;
        bool islong = false;
        while (Token::Match(def, "%type%|::")) {
            if (def->str() == "long" && def->originalName().empty()) {
                islong = true;
                break;
            }
            def = def->previous();
        }
        if (!islong)
            continue;

        // find return statement
        // todo.. this is slow, we should only check last statement in each child scope
        const Token *ret = nullptr;
        for (const Token *tok = scope->classStart; tok != scope->classEnd; tok = tok->next()) {
            if (tok->str() == "return") {
                if (!ret)
                    ret = tok;
                else {
                    ret =  nullptr;
                    break;
                }
            }
        }

        if (ret && Token::Match(ret->astOperand1(), "*|<<") && astIsIntResult(ret->astOperand1()))
            longCastReturnError(ret);
    }
}

void CheckType::longCastAssignError(const Token *tok)
{
    reportError(tok,
                Severity::style,
                "truncLongCastAssignment",
                "int result is assigned to long variable. If the variable is long to avoid loss of information, then you have loss of information.\n"
                "int result is assigned to long variable. If the variable is long to avoid loss of information, then there is loss of information. To avoid loss of information you must cast a calculation operand to long, for example 'l = a * b;' => 'l = (long)a * b;'.");
}

void CheckType::longCastReturnError(const Token *tok)
{
    reportError(tok,
                Severity::style,
                "truncLongCastReturn",
                "int result is returned as long value. If the return value is long to avoid loss of information, then you have loss of information.\n"
                "int result is returned as long value. If the return value is long to avoid loss of information, then there is loss of information. To avoid loss of information you must cast a calculation operand to long, for example 'return a*b;' => 'return (long)a*b'.");
}