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[Blog] Q & A - picking our noes
#1
Quality Assurance

Quality & assurance is a full time job and it is a complex topic. Quality always comes with a trade-off of time vs cost. By definition, open source projects make a false start here. Spending $100,000 on a formal analysis tool isn't possible. Neither is dedicating the only dev to full-time testing. Fortunately, some tools are free (even open source) such as Valgrind or Clang-Tidy and some services are free to use, such as Coverity. We currently don't have a high number of committers, but we have lots of dedicated testers and users. Big thanks to all of them, because without them nothing would have been possible. So quality is possible. Maybe we can't reach the 100% perfect quality state but we can reach a decent level.

The project took various actions in order to improve the quality and robustness of PCSX2. Some actions started a long time ago, most of them are still on-going, some are still planned. You won't find any ground-breaking methodology here. Nevertheless, I wanted to do a summary of what is going on.

Continuous Integration

The first step of QA is called Continuous Integration. The goal is to ensure correctness of the project at every commit done. That's easy to say but quite hard to do.

* Most of you know about the PCSX2 buildbot. It provides compiled snapshots regularly. It allows testers and users to play with the latest features. It also gives them the opportunity to report regressions much sooner in the development. Therefore, we can fix them better. Regressions are the highest priority bug reports for me.

* The migration to Github allowed us to add additional bots to ensure compilation works fine with various compilers. PCSX2's buildbot is limited to a single version of the Microsoft compiler. Appveyor & Travis allow us to test multiple versions of Visual Studio (VS2013 & VS2015) but also clang/gcc. We even have a 64 bits compilation test validation.

* The buildbot is limited to Windows, therefore a daily PPA build was added too.

Compiler

The 2nd step of QA is compiler support. The compiler is the first tool of any developer. Of course, compilation errors are bad, but compilers can also report constructs that are prone to errors. These are called compiler warnings. Often there are false positives, the code is correct and behaves as expected but the compiler still reports it as dangerous. You could say "It's not a big deal.", but when you have thousands of false positives, you don't see the bad warnings anymore. So the goal is to have 0 warnings for all compilers. Note that some warnings were disabled because they report too many false positives. But they are a conscious exception and additional work has been done to re-enable them when possible.

* GCC warning counts are rather low (less than 20) but not 0 yet. And we even enabled most of the extra warnings.
* Clang reports lots of warnings because I asked clang to report some old code that I marked as deprecated. Otherwise we'd be around 50. I'm sure we can do better here too.

Global status is rather good but not yet perfect. GCC used to have 500+ warnings with less warnings enabled. Clang used to be unable to compile the code. The road was quite long but we started to see the light Smile
    
        
 Formal/Lint Tool
Compilers are nice at reporting various problems but it isn't their main job. So dedicated tools were created with the single objective of finding all your bugs. In reality it is closer to "some bugs" but less bugs is always nice and good for e-reputation of a project. I decided to integrate those tools with the Linux build.sh script. This way, you can easily run them. If you want a report, I will gladly send it to you.

I) Cppcheck

Cppcheck is an open-source lint tool to check code quality. For the 1.2/1.4 release we tried to fix the big errors. So far it reports 838 warnings. The number is quite high but warnings are very minor (micro-optimization and style). It would require some analysis/fixes to improve the situation. I guess some minor style warning could be filtered.

II) Coverity

Coverity is an expensive lint tool to ensure code robustness. It is very nice of Synopsys to allow open source projects to use it for free. Coverity is based on a compiler back-end so it tries harder than Cppcheck to find issues. Coverity found a couple of nasty ones but also various false positives. We're currently around 70 issue reports. I'm not sure we will be able to fix all the reports but we can target a goal of nearly 0 Coverity issues.

III) Clang-tidy

Clang-tidy is an open-source lint tool based on the Clang/LLVM compiler. It is based on rule checks from the Clang / C++ core guidelines and C++ ISO certification. The tool reports a massive number of warnings, currently 49000+ !!!

I can hear you yelling "This is insane, PCSX2 code must suck so bad". But when you look at the report, the huge number comes from C/C++ constructs that are sane but not safe. There is a strong bias on robustness/pure C++, rather than performance/C. For example, every time you access an array, you must check the array boundary. For sure, this is robust but it is also slow. I'm not sure we want this kind of robustness in performance critical code. That being said, all cold paths (i.e. code that doesn't impact performance) would be better with safer code. Another recommendation is to use Boost classes. Boost is a nice beast but it is a mammoth. The full include on my system is 155MB ! I think we will wait until the interesting bits are included in the C++ library. A lot of warnings remain to be fixed but we are now far from the 49K number.


For the record, here is the current summary report on the latest master. You can google the rule name to find what the exact issue is.
cert (665)
                        cert-dcl50-cpp => 85
                        cert-err52-cpp => 3
                        cert-err58-cpp => 360
                        cert-err60-cpp => 148
                        cert-err61-cpp => 69

        clang (496)
                        clang-diagnostic-deprecated-declarations => 475
                        clang-diagnostic-missing-braces => 2
                        clang-diagnostic-shift-negative-value => 3
                        clang-diagnostic-sign-compare => 4
                        clang-diagnostic-unused-const-variable => 10
                        clang-diagnostic-unused-variable => 2

        cppcoreguidelines (33701)
                        cppcoreguidelines-pro-bounds-array-to-pointer-decay => 2883
                        cppcoreguidelines-pro-bounds-constant-array-index => 7697
                        cppcoreguidelines-pro-bounds-pointer-arithmetic => 3763
                        cppcoreguidelines-pro-type-const-cast => 66
                        cppcoreguidelines-pro-type-cstyle-cast => 3478
                        cppcoreguidelines-pro-type-reinterpret-cast => 42
                        cppcoreguidelines-pro-type-static-cast-downcast => 83
                        cppcoreguidelines-pro-type-union-access => 12405
                        cppcoreguidelines-pro-type-vararg => 3284

        misc (905)
                        misc-macro-parentheses => 157
                        misc-throw-by-value-catch-by-reference => 18
                        misc-unused-alias-decls => 1
                        misc-unused-parameters => 729

        modernize (2527)
                        modernize-loop-convert => 146
                        modernize-make-unique => 20
                        modernize-pass-by-value => 6
                        modernize-redundant-void-arg => 35
                        modernize-use-auto => 127
                        modernize-use-default => 107
                        modernize-use-nullptr => 1824
                        modernize-use-override => 262

        readability (10996)
                        readability-braces-around-statements => 6739
                        readability-else-after-return => 124
                        readability-function-size => 1
                        readability-implicit-bool-cast => 3760
                        readability-inconsistent-declaration-parameter-name => 326
                        readability-named-parameter => 36
                        readability-simplify-boolean-expr => 10
                        

                        

To conclude this section, lint tools are quite powerful. They can find bugs that will take days of tests. But they're also dull as they reports tons of false positives. Therefore it is required to filter the results. It is clearly not feasible nor desirable to reach a 0 warnings target. However we can target a better and saner status.

Dynamic Tools


Formal tools can't find all classes of bugs. Luckily for me, Linux comes with 2 additional tools to ensure correct behavior at run time.

I) Valgrind

Valgrind is a virtual machine or a X86 CPU emulator. So yes, we are running an emulator inside an emulator Wink The interesting stuff with virtual machines is that they can see all memory accesses. It comes with a cost, it is damn slow. Another drawback is that Valgrind doesn't support all SIMD instruction such as AVX. Running the tool allows you to detect memory leaks (ouch), memory overflows (ouch, ouch), code execution that depends on uninitialized values (ouch, ouch, ouch). Quite a nice tool; You even find bugs in 3rd party libraries/drivers...

II) Address sanitizer

Valgrind is very powerful but too slow. The address sanitizer is a much faster alternative but less powerful. The code will be instrumented during the compilation. So every time you do a memory access, a small check is done. The main goal is to ensure the correctness of the memory access, a big source of crashes and security flaws of all programs. It greatly helps us to find wrong stack management on the recompiler.

Dynamic tools can greatly help to detect very bad stuff. Unlike formal tools that give you a status in 2 minutes, you need to actually run the program and play some games. So it is time consuming.

Code Formatting

Last but not least, code formatting. The project is a mix of various plugins of various developers with various coding styles. It became even worse recently. We spend too much time in external contributions, reviewing the formatting rather than the real patch improvement.

As we said, desperate times call for desperate measures. So I decided that we will automatically format the code with the help of the clang-format tool. The tool isn't perfect unlike us, Humans Wink But it will give us a much nicer consistency.

Contributing will be easier as you don't need to learn the current coding style of the current file. I hope to provide a git hook on Linux to automatically format the code before the commit. Reviewing will be faster as the syntax will be automatically checked by the build bot. This way we could concentrate on the meat. So far a couple of plugins were converted to the new syntax. The remaining code will be converted step by step in order to avoid conflicts with current Pull Requests.

Conclusion
To conclude this blog post, we have plenty of tools and methods to improve the projects quality. We've worked on it for a long time and slowly it's getting better and better. In the end, QA is like ageing wine, it's a slow process that requires time.
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#2
Thanks for the blog post!
I had no idea you had custom tools for QA.
Hey,  I'm writing yet another PCSX2 frontend. Source code is being hosted at GitHub.
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#3
Thanks for you're reading. I don't have tool but I use external tool to improve the situation.
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#4
Very interesting post, thanks for sharing!
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#5
I attempted today to run Valgind's callgrind on the lastest git revision and it threw an exception (I don't remember exactly which atm) that I set to ignore. From that point I let it sit for a few minutes but it didn't seem to be progressing in emulation. In your experience is the performance significantly slower, minutes per frame? I may dig into the exception later if I find some time.

Edit: Also it would be handy if it was possible to load a state save at startup so as to skip the extra time it takes to boot up and then load state when running under Valgrind.
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