Monday, January 24, 2011

Running the code through PVS-Studio

I was generously offered a temporary license to PVS-Studio to do static analysis on my code and the following is the result.

The Hardware

OS: Windows XP Professional x64 Edition (5.2, Build 3790) Service Pack 2
Processor: AMD64 (8 CPUs), ~2.7GHz
Memory: 4094MB RAM

Performance was not much of an issue and analysis took a few minutes per project, but I figured I should port the hardware used for reference.

The Install

Install was painless and it integrated itself into Visual Studio 2010 as a menu item. You can analyze a file, a project or whole solution. You can also load/save analysis.

The Analysis

I analyzed most of the base libraries used by AObjectServer, then base modules and then the actual server code. I also analyzed the load test tool I use (which comes as a command like tool and a Win32 GUI). Overall it was 11 DLLs, 3 EXE. Analysis per project is about 2-5 minutes (depending on files I suppose).

The Results

Results are divided into 3 levels.

Start with Level 1 issues.

MESSAGE: V550 An odd precise comparison: - 1.0 == m_stateTimeLimit. It's probably better to use a comparison with defined precision: fabs(A - B) '<' Epsilon.
return (INVALID_TIME_INTERVAL == m_stateTimeLimit || m_stateTimer.getInterval() < m_stateTimeLimit ? false : true);

FIX: return (0.0 > m_stateTimeLimit || m_stateTimer.getInterval() < m_stateTimeLimit ? false : true);
NOTE: This is definitely a good find

MESSAGE: V550 An odd precise comparison: 0.0 == difftime (t). It's probably better to use a comparison with defined precision: fabs(A - B) '<' Epsilon.
CODE: return (0.0 == difftime(t) ? true : false);
FIX: According to the API reference return of 0 from difftime
NOTE: This is a tougher one, this tests to see if difftime returns 0 which means that it is the same time. I did notice that this function was operating on time_t structure which defined on Windows as __int64 so comparing to another time_t should be fine. I made this change, but I am not sure if other operating systems may use something else for time_t.


Next are Level 2 issues. Almost all were V112 type that flags usage of numbers that relate to memory sizes (like 4, 8 32, etc); all of these were false positives for me. Few of the messages were interesting.

MESSAGE: V401 The structure's size can be decreased via changing the fields' order. The size can be reduced from 32 to 24 bytes.
CODE: in dbghelp.h (part of Microsft SDK)
DWORD ThreadId;
ULONG64 ExceptionRecord;
ULONG64 ContextRecord;
BOOL ClientPointers;
FIX: None, it's part of the Microsoft SDK but interesting.

MESSAGE: 2776 V801 Decreased performance. It is better to redefine the first function argument as a reference. Consider replacing 'const .. path' with 'const .. &path'.
FIX: I accidentally used pass object instead of pass by reference, while not critical in this instance since it was part of initialization call, this message is very useful.

MESSAGE: 297 V112 Dangerous magic number 4 used
NOTE: The tool is fixated on numbers that may be associated with memory word sizes like 4, in all my cases 4 represents a 4 and not a memory size (I use sizeof if I need word sizes). So this resulted in many false positived and probably should have been level 3.


Now on to Level 3 here are the more interesting ones.

MESSAGE: V547 Expression 'findFromFront (p) >= 0' is always true. Unsigned type value is always >= 0.
CODE: AASSERT(this, findFromFront(p) >= 0);
FIX: This was not needed since size_t is the result from findFromFront and it is always >=0, this I suspect is leftover code from changeover from int to size_t.
NOTE: Good to clean dead code even if it is harmless

MESSAGE: V547 Expression 'moveSize < 0' is always false. Unsigned type value is never < 0.
NOTE: These were very useful since they are a result of another porting project that replaced int with size_t and went from signed to unsigned. Most of the warning were harmless and inside assert statements but nevertheless, cleaner code is always better.

MESSAGE: V509 The 'throw' operator inside the destructor should be placed within the try..catch block. Raising exception inside the destructor is illegal.
NOTE: Great catch, this was a result of a conversion from assert() to a macro which throws an execption and this was inside a destructor which is a bid thing.

The Summary

Overall I liked the tool, it did find a few non-critical issues with the server code, but to be fair I have ran most of my code through FlexeLint and BoundChecker (until my license expired that is). I also have Visual Studio warning level 4 turned on for debug builds and that catches a lot of issues.

The main benefit of PVS-Studio is that it is good at finding issues that may affect porting 32-bit code to 64-bits.

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