• 08/31/13 01:54 AM
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    Checking the Open-Source Multi Theft Auto Game

    General and Gameplay Programming

    We haven't used PVS-Studio to check games for a long time. So, this time we decided to return to this practice and picked out the MTA project. Multi Theft Auto (MTA) is a multiplayer modification for PC versions of the Grand Theft Auto: San Andreas game by Rockstar North that adds online multiplayer functionality. As Wikipedia tells us, the specific feature of the game is "well optimized code with fewest bugs possible". OK, let's ask our analyzer for its opinion.

    Introduction

    This time I decided to omit the texts of diagnostic messages generated by PVS-Studio for every particular defect. I comment upon examples anyway, so if you want to find out in which particular line and by which diagnostic rule a certain bug was found, see the file mtasa-review.txt. When looking through the project, I noted in the mtasa-review.txt file those code fragments which I found suspicious and used it to prepare the article. Important! I added only those code fragments which I personally didn't like. I'm not a MTA developer, so I'm not familiar with its logic and principles. That's why I must have made a few mistakes attacking correct code fragments and missing genuine bugs. Also, when studying certain fragments, I felt lazy indeed to describe some slightly incorrect printf() function calls. So, I'm asking MTA Team developers not to rely on this article and consider checking the project by themselves. It is pretty large, so the demo version of PVS-Studio won't be enough. However, we support free open-source projects. If you're an open source developer, contact us and we'll discuss the question of giving you a free registration key. So, Multi Theft Auto is an open-source project in C/C++: Analysis was performed by the PVS-Studio 5.05 analyzer:
    • tool page;
    • download (the demo version's only limitation concerns the number of click jumps from the message list to source code);
    • bug database.
    Now let's see what bugs PVS-Studio has managed to find in the game. They aren't numerous, and most of them are found in rarely-used parts of the program (error handlers). It's no wonder: most bugs are found and fixed through other, more expensive and slow, methods. To use static analysis properly is to use it regularly. By the way, PVS-Studio can be called to analyze recently modified and compiled files only (see incremental analysis mode). This mechanism allows the developer to find and fix many bugs and misprints immediately, which makes it much faster and cheaper than detecting errors through testing. This subject was discussed in detail in the article "Leo Tolstoy and static code analysis". It's a worthy article, and I do recommend reading the introduction to understand the ideology of using PVS-Studio and other static analysis tools.

    Strange Colors

    // c3dmarkersa.cpp SColor C3DMarkerSA::GetColor() { DEBUG_TRACE("RGBA C3DMarkerSA::GetColor()"); // From ABGR unsigned long ulABGR = this->GetInterface()->rwColour; SColor color; color.A = ( ulABGR >> 24 ) && 0xff; color.B = ( ulABGR >> 16 ) && 0xff; color.G = ( ulABGR >> 8 ) && 0xff; color.R = ulABGR && 0xff; return color; } By mistake '&&' is used instead of '&'. The color is torn into bits and pieces to leave only 0 or 1. The same problem is found in the file "ccheckpointsa.cpp". One more problem with colors. // cchatechopacket.h class CChatEchoPacket : public CPacket { .... inline void SetColor( unsigned char ucRed, unsigned char ucGreen, unsigned char ucBlue ) { m_ucRed = ucRed; m_ucGreen = ucGreen; m_ucRed = ucRed; }; .... } Red is copied twice, while blue is not copied at all. The fixed code should look like this: { m_ucRed = ucRed; m_ucGreen = ucGreen; m_ucBlue = ucBlue; }; The same problem is found in the file cdebugechopacket.h. By the way, quite a number of bugs of the game are duplicated in two files which, I suspect, refer to the client-side and the server-side correspondingly. Do you feel the great power of the Copy-Paste technology? :).

    Something Wrong with utf8

    // utf8.h int utf8_wctomb (unsigned char *dest, wchar_t wc, int dest_size) { if (!dest) return 0; int count; if (wc < 0x80) count = 1; else if (wc < 0x800) count = 2; else if (wc < 0x10000) count = 3; else if (wc < 0x200000) count = 4; else if (wc < 0x4000000) count = 5; else if (wc <= 0x7fffffff) count = 6; else return RET_ILSEQ; .... } The size of the wchar_t type in Windows is 2 bytes. Its value range is [0..65535], which means that comparing it to values 0x10000, 0x200000, 0x4000000, 0x7fffffff is pointless. I guess the code should be written in some different way.

    Missing break

    // cpackethandler.cpp void CPacketHandler::Packet_ServerDisconnected (....) { .... case ePlayerDisconnectType::BANNED_IP: strReason = _("Disconnected: You are banned.\nReason: %s"); strErrorCode = _E("CD33"); bitStream.ReadString ( strDuration ); case ePlayerDisconnectType::BANNED_ACCOUNT: strReason = _("Disconnected: Account is banned.\nReason: %s"); strErrorCode = _E("CD34"); break; .... } The break operator is missing in this code. It results in processing the situation BANNED_IP in the same way as BANNED_ACCOUNT.

    Strange Checks

    // cvehicleupgrades.cpp bool CVehicleUpgrades::IsUpgradeCompatible ( unsigned short usUpgrade ) { .... case 402: return ( us == 1009 || us == 1009 || us == 1010 ); .... } The variable is compared twice to the number 1009. A bit ahead in the code there is a similar double comparison. Another strange comparison: // cclientplayervoice.h bool IsTempoChanged(void) { return m_fSampleRate != 0.0f || m_fSampleRate != 0.0f || m_fTempo != 0.0f; } This error was also copied into the cclientsound.h file.

    Null Pointer Dereferencing

    // cgame.cpp void CGame::Packet_PlayerJoinData(CPlayerJoinDataPacket& Packet) { .... // Add the player CPlayer* pPlayer = m_pPlayerManager->Create (....); if ( pPlayer ) { .... } else { // Tell the console CLogger::LogPrintf( "CONNECT: %s failed to connect " "(Player Element Could not be created.)\n", pPlayer->GetSourceIP() ); } .... } If the object player can't be created, the program will attempt printing the corresponding error message into the console. It will fail because it's a bad idea to use a null pointer when calling the function pPlayer->GetSourceIP(). Another null pointer is dereferenced in the following fragment: // clientcommands.cpp void COMMAND_MessageTarget ( const char* szCmdLine ) { if ( !(szCmdLine || szCmdLine[0]) ) return; .... } If the szCmdLine pointer is null, it will be dereferenced. The fixed code must look like this, I suppose: if ( !(szCmdLine && szCmdLine[0]) ) The following code fragment I like most of all: // cdirect3ddata.cpp void CDirect3DData::GetTransform (....) { switch ( dwRequestedMatrix ) { case D3DTS_VIEW: memcpy (pMatrixOut, &m_mViewMatrix, sizeof(D3DMATRIX)); break; case D3DTS_PROJECTION: memcpy (pMatrixOut, &m_mProjMatrix, sizeof(D3DMATRIX)); break; case D3DTS_WORLD: memcpy (pMatrixOut, &m_mWorldMatrix, sizeof(D3DMATRIX)); break; default: // Zero out the structure for the user. memcpy (pMatrixOut, 0, sizeof ( D3DMATRIX ) ); break; } .... } Very nice Copy-Paste. The function memset() must be called instead of the last memcpy() function.

    Uncleared Arrays

    There are a number of errors related to uncleared arrays. They all can be arranged into two categories. The first includes unremoved items, the second includes partial array clearing errors.

    Unremoved Items

    // cperfstat.functiontiming.cpp std::map < SString, SFunctionTimingInfo > m_TimingMap; void CPerfStatFunctionTimingImpl::DoPulse ( void ) { .... // Do nothing if not active if ( !m_bIsActive ) { m_TimingMap.empty (); return; } .... } The function empty() only checks whether or not the container contains items. To remove items from the m_TimingMap container one should call the clear() function. Another example: // cclientcolsphere.cpp void CreateSphereFaces ( std::vector < SFace >& faceList, int iIterations ) { int numFaces = (int)( pow ( 4.0, iIterations ) * 8 ); faceList.empty (); faceList.reserve ( numFaces ); .... } Some more similar bugs are found in the file cresource.cpp.
    If you have started reading the article from the middle and therefore skipped the beginning, see the file mtasa-review.txt to find out exact locations of all the bugs.

    Partial Array Clearing Errors

    // crashhandler.cpp LPCTSTR __stdcall GetFaultReason(EXCEPTION_POINTERS * pExPtrs) { .... PIMAGEHLP_SYMBOL pSym = (PIMAGEHLP_SYMBOL)&g_stSymbol ; FillMemory ( pSym , NULL , SYM_BUFF_SIZE ) ; .... } Everything looks alright at the first sight. But FillMemory() will in fact have no effect. FillMemory() and memset() are different functions. Have a look at this fragment: #define RtlFillMemory(Destination,Length,Fill) \ memset((Destination),(Fill),(Length)) #define FillMemory RtlFillMemory The second and the third arguments are swapped. That's why the correct code should look like this: FillMemory ( pSym , SYM_BUFF_SIZE, 0 ) ; The same thing is found in the file ccrashhandlerapi.cpp. And here is the last error sample of this type. Only one byte gets cleared. // hash.hpp unsigned char m_buffer[64]; void CMD5Hasher::Finalize ( void ) { .... // Zeroize sensitive information memset ( m_buffer, 0, sizeof (*m_buffer) ); .... } Asterisk '*' should be removed: sizeof (m_buffer).

    Uninitialized Variable

    // ceguiwindow.cpp Vector2 Window::windowToScreen(const UVector2& vec) const { Vector2 base = d_parent ? d_parent->windowToScreen(base) + getAbsolutePosition() : getAbsolutePosition(); .... } The variable base initializes itself. Another bug of this kind can be found a few lines ahead.

    Array Index out of Bounds

    // cjoystickmanager.cpp struct { bool bEnabled; long lMax; long lMin; DWORD dwType; } axis[7]; bool CJoystickManager::IsXInputDeviceAttached ( void ) { .... m_DevInfo.axis[6].bEnabled = 0; m_DevInfo.axis[7].bEnabled = 0; .... } The last line m_DevInfo.axis[7].bEnabled = 0; is not needed. Another error of this kind // cwatermanagersa.cpp class CWaterPolySAInterface { public: WORD m_wVertexIDs[3]; }; CWaterPoly* CWaterManagerSA::CreateQuad ( const CVector& vecBL, const CVector& vecBR, const CVector& vecTL, const CVector& vecTR, bool bShallow ) { .... pInterface->m_wVertexIDs [ 0 ] = pV1->GetID (); pInterface->m_wVertexIDs [ 1 ] = pV2->GetID (); pInterface->m_wVertexIDs [ 2 ] = pV3->GetID (); pInterface->m_wVertexIDs [ 3 ] = pV4->GetID (); .... } One more: // cmainmenu.cpp #define CORE_MTA_NEWS_ITEMS 3 CGUILabel* m_pNewsItemLabels[CORE_MTA_NEWS_ITEMS]; CGUILabel* m_pNewsItemShadowLabels[CORE_MTA_NEWS_ITEMS]; void CMainMenu::SetNewsHeadline (....) { .... for ( char i=0; i <= CORE_MTA_NEWS_ITEMS; i++ ) { m_pNewsItemLabels[ i ]->SetFont ( szFontName ); m_pNewsItemShadowLabels[ i ]->SetFont ( szFontName ); .... } .... } At least one more error of this kind can be found in the file cpoolssa.cpp. But I decided not to describe it in the article because that would be a pretty large sample and I didn't know how to make it brief and clear. As I've already said, this and all the rest of the bugs can be found in the detailed report.

    The Word 'throw' is Missing

    // fallistheader.cpp ListHeaderSegment* FalagardListHeader::createNewSegment(const String& name) const { if (d_segmentWidgetType.empty()) { InvalidRequestException( "FalagardListHeader::createNewSegment - " "Segment widget type has not been set!"); } return ....; } The correct line is throw InvalidRequestException(....). Another code fragment. // ceguistring.cpp bool String::grow(size_type new_size) { // check for too big if (max_size() <= new_size) std::length_error( "Resulting CEGUI::String would be too big"); .... } The correct code should look like this: throw std::length_error(....).

    Oops: free(new T[n])

    // cresourcechecker.cpp int CResourceChecker::ReplaceFilesInZIP(....) { .... // Load file into a buffer buf = new char[ ulLength ]; if ( fread ( buf, 1, ulLength, pFile ) != ulLength ) { free( buf ); buf = NULL; } .... } The new operator is used to allocate memory, while the function free() is used to release it. The result is unpredictable.

    Always True/False Conditions

    // cproxydirect3ddevice9.cpp #define D3DCLEAR_ZBUFFER 0x00000002l HRESULT CProxyDirect3DDevice9::Clear(....) { if ( Flags | D3DCLEAR_ZBUFFER ) CGraphics::GetSingleton(). GetRenderItemManager()->SaveReadableDepthBuffer(); .... } The programmer wanted to check a particular bit in the Flag variable. By mistake he wrote the '|' operation instead of '&'. This results in the condition being always true. A similar mess-up is found in the file cvehiclesa.cpp. Another bug in a check is found here: unsigned_value < 0. // crenderitem.effectcloner.cpp unsigned long long Get ( void ); void CEffectClonerImpl::MaybeTidyUp ( void ) { .... if ( m_TidyupTimer.Get () < 0 ) return; .... } The Get() function returns the value of the unsigned unsigned long long type. It means that the check m_TidyupTimer.Get () < 0 is pointless. Other errors of this type can be found in the files csettings.cpp, cmultiplayersa_1.3.cpp and cvehiclerpcs.cpp.

    This Code May Work, but You'd Better Refactor It

    Many PVS-Studio diagnostics detected bugs which will most likely in no way manifest themselves. I don't like describing such bugs because they are not interesting. So, here are just a couple of examples. // cluaacldefs.cpp int CLuaACLDefs::aclListRights ( lua_State* luaVM ) { char szRightName [128]; .... strncat ( szRightName, (*iter)->GetRightName (), 128 ); .... } The third argument of the strncat() function refers, instead of the buffer size, to the number of characters you can put into the buffer. A buffer overflow can theoretically occur here, but in practice it will most probably never happen. This type of error is described in detail in the V645 diagnostic's description. The second example. // cscreenshot.cpp void CScreenShot::BeginSave (....) { .... HANDLE hThread = CreateThread ( NULL, 0, (LPTHREAD_START_ROUTINE)CScreenShot::ThreadProc, NULL, CREATE_SUSPENDED, NULL ); .... } In many game fragments, the functions CreateThread()/ExitThread() are used. This is in most cases a bad idea. You should use the functions _beginthreadex()/_endthreadex() instead. For details on this issue see the V513 diagnostic's description.

    I Have to Stop Somewhere

    I have described only a part of all the defects I noticed. But I have to stop here: the article is already big enough. See the file mtasa-review.txt for other bug samples. There you will find bugs which I haven't mentioned in the article:
    • identical branches in the conditional operator if () { aa } else { aa };
    • checking a pointer returned by the new operator for being a null pointer: p = new T; if (!p) { aa };
    • a poor way of using #pragma to suppress compiler warnings (instead of push/pop);
    • classes contain virtual functions but no virtual destructors;
    • a pointer gets dereferenced first and only then checked for being a null pointer;
    • identical conditions: if (X) { if (X) { aa } };
    • miscellaneous.

    Conclusion

    The PVS-Studio analyzer can be efficiently used to eliminate various bugs at early development stages both in game projects and projects of any other type. It won't find algorithmic errors of course (it needs AI to do that), but it will help save a lot of time programmers usually waste searching for silly mistakes and misprints. Developers actually spend much more time on finding plain defects than they may think. Even debugged and tested code contains numbers of such errors, while 10 times more of them get fixed when writing new code.


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