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  16 <h1>Open Projects</h1>
  17
  18 <p>This page lists several projects that would boost analyzer's usability and
  19 power. Most of the projects listed here are infrastructure-related so this list
  20 is an addition to the <a href="potential_checkers.html">potential checkers
  21 list</a>. If you are interested in tackling one of these, please send an email
  22 to the <a href=http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev>cfe-dev
  23 mailing list</a> to notify other members of the community.</p>
  24
  25 <ul>
  26   <li>Core Analyzer Infrastructure
  27   <ul>
  28     <li>Explicitly model standard library functions with <tt>BodyFarm</tt>.
  29     <p><tt><a href="http://clang.llvm.org/doxygen/classclang_1_1BodyFarm.html">BodyFarm</a></tt>
  30     allows the analyzer to explicitly model functions whose definitions are
  31     not available during analysis. Modeling more of the widely used functions
  32     (such as the members of <tt>std::string</tt>) will improve precision of the
  33     analysis.
  34     <i>(Difficulty: Easy, ongoing)</i><p>
  35     </li>
  36
  37     <li>Handle floating-point values.
  38     <p>Currently, the analyzer treats all floating-point values as unknown.
  39     However, we already have most of the infrastructure we need to handle
  40     floats: RangeConstraintManager. This would involve adding a new SVal kind
  41     for constant floats, generalizing the constraint manager to handle floats
  42     and integers equally, and auditing existing code to make sure it doesn't
  43     make untoward assumptions.
  44     <i> (Difficulty: Medium)</i></p>
  45     </li>
  46
  47     <li>Implement generalized loop execution modeling.
  48     <p>Currently, the analyzer simply unrolls each loop <tt>N</tt> times. This
  49     means that it will not execute any code after the loop if the loop is
  50     guaranteed to execute more than <tt>N</tt> times. This results in lost
  51     basic block coverage. We could continue exploring the path if we could
  52     model a generic <tt>i</tt>-th iteration of a loop.
  53     <i> (Difficulty: Hard)</i></p>
  54     </li>
  55
  56     <li>Enhance CFG to model C++ temporaries properly.
  57     <p>There is an existing implementation of this, but it's not complete and
  58     is disabled in the analyzer.
  59     <i>(Difficulty: Medium; current contact: Alex McCarthy)</i></p>
  60
  61     <li>Enhance CFG to model exception-handling properly.
  62     <p>Currently exceptions are treated as "black holes", and exception-handling
  63     control structures are poorly modeled (to be conservative). This could be
  64     much improved for both C++ and Objective-C exceptions.
  65     <i>(Difficulty: Medium)</i></p>
  66
  67     <li>Enhance CFG to model C++ <code>new</code> more precisely.
  68     <p>The current representation of <code>new</code> does not provide an easy
  69     way for the analyzer to model the call to a memory allocation function
  70     (<code>operator new</code>), then initialize the result with a constructor
  71     call. The problem is discussed at length in
  72     <a href="http://llvm.org/bugs/show_bug.cgi?id=12014">PR12014</a>.
  73     <i>(Difficulty: Easy; current contact: Karthik Bhat)</i></p>
  74
  75     <li>Enhance CFG to model C++ <code>delete</code> more precisely.
  76     <p>Similarly, the representation of <code>delete</code> does not include
  77     the call to the destructor, followed by the call to the deallocation
  78     function (<code>operator delete</code>). One particular issue
  79     (<tt>noreturn</tt> destructors) is discussed in
  80     <a href="http://llvm.org/bugs/show_bug.cgi?id=15599">PR15599</a>
  81     <i>(Difficulty: Easy; current contact: Karthik Bhat)</i></p>
  82
  83     <li>Implement a BitwiseConstraintManager to handle <a href="http://llvm.org/bugs/show_bug.cgi?id=3098">PR3098</a>.
  84     <p>Constraints on the bits of an integer are not easily representable as
  85     ranges. A bitwise constraint manager would model constraints such as "bit 32
  86     is known to be 1". This would help code that made use of bitmasks</code>.
  87     <i>(Difficulty: Medium)</i></p>
  88     </li>
  89
  90     <li>Track type info through casts more precisely.
  91     <p>The DynamicTypePropagation checker is in charge of inferring a region's
  92     dynamic type based on what operations the code is performing. Casts are a
  93     rich source of type information that the analyzer currently ignores. They
  94     are tricky to get right, but might have very useful consequences.
  95     <i>(Difficulty: Medium)</i></p>
  96
  97     <li>Design and implement alpha-renaming.
  98     <p>Implement unifying two symbolic values along a path after they are
  99     determined to be equal via comparison. This would allow us to reduce the
 100     number of false positives and would be a building step to more advanced
 101     analyses, such as summary-based interprocedural and cross-translation-unit
 102     analysis.
 103     <i>(Difficulty: Hard)</i></p>
 104     </li>
 105   </ul>
 106   </li>
 107
 108   <li>Bug Reporting
 109   <ul>
 110     <li>Add support for displaying cross-file diagnostic paths in HTML output
 111     (used by <tt>scan-build</tt>).
 112     <p>Currently <tt>scan-build</tt> output does not display reports that span
 113     multiple files. The main problem is that we do not have a good format to
 114     display such paths in HTML output. <i>(Difficulty: Medium)</i> </p>
 115     </li>
 116
 117     <li>Refactor path diagnostic generation in <a href="http://clang.llvm.org/doxygen/BugReporter_8cpp_source.html">BugReporter.cpp</a>.
 118     <p>It would be great to have more code reuse between "Minimal" and
 119     "Extensive" PathDiagnostic generation algorithms. One idea is to create an
 120     IR for representing path diagnostics, which would be later be used to
 121     generate minimal or extensive report output. <i>(Difficulty: Medium)</i></p>
 122     </li>
 123   </ul>
 124   </li>
 125
 126   <li>Other Infrastructure
 127   <ul>
 128     <li>Rewrite <tt>scan-build</tt> (in Python).
 129     <p><i>(Difficulty: Easy)</i></p>
 130     </li>
 131
 132     <li>Do a better job interposing on a compilation.
 133     <p>Currently, <tt>scan-build</tt> just sets the <tt>CC</tt> and <tt>CXX</tt>
 134     environment variables to its wrapper scripts, which then call into an
 135     underlying platform compiler. This is problematic for any project that
 136     doesn't exclusively use <tt>CC</tt> and <tt>CXX</tt> to control its
 137     compilers.
 138     <p><i>(Difficulty: Medium-Hard)</i></p>
 139     </li>
 140
 141     <li>Create an <tt>analyzer_annotate</tt> attribute for the analyzer
 142     annotations.
 143     <p>We would like to put all analyzer attributes behind a fence so that we
 144     could add/remove them without worrying that compiler (not analyzer) users
 145     depend on them. Design and implement such a generic analyzer attribute in
 146     the compiler. <i>(Difficulty: Medium)</i></p>
 147     </li>
 148   </ul>
 149   </li>
 150
 151   <li>Enhanced Checks
 152   <ul>
 153     <li>Implement a production-ready StreamChecker.
 154     <p>A SimpleStreamChecker has been presented in the Building a Checker in 24
 155     Hours talk
 156     (<a href="http://llvm.org/devmtg/2012-11/Zaks-Rose-Checker24Hours.pdf">slides</a>
 157     <a href="http://llvm.org/devmtg/2012-11/videos/Zaks-Rose-Checker24Hours.mp4">video</a>).
 158     We need to implement a production version of the checker with richer set of
 159     APIs and evaluate it by running on real codebases.
 160     <i>(Difficulty: Easy)</i></p>
 161     </li>
 162
 163     <li>Extend Malloc checker with reasoning about custom allocator,
 164     deallocator, and ownership-transfer functions.
 165     <p>This would require extending the MallocPessimistic checker to reason
 166     about annotated functions. It is strongly desired that one would rely on
 167     the <tt>analyzer_annotate</tt> attribute, as described above.
 168     <i>(Difficulty: Easy)</i></p>
 169     </li>
 170
 171     <li>Implement a BitwiseMaskingChecker to handle <a href="http://llvm.org/bugs/show_bug.cgi?id=16615">PR16615</a>.
 172     <p>Symbolic expressions of the form <code>$sym &amp; CONSTANT</code> can range from 0 to <code>CONSTANT-</code>1 if CONSTANT is <code>2^n-1</code>, e.g. 0xFF (0b11111111), 0x7F (0b01111111), 0x3 (0b0011), 0xFFFF, etc. Even without handling general bitwise operations on symbols, we can at least bound the value of the resulting expression. Bonus points for handling masks followed by shifts, e.g. <code>($sym &amp; 0b1100) >> 2</code>.
 173     <i>(Difficulty: Easy)</i></p>
 174     </li>
 175
 176     <li>Implement iterators invalidation checker.
 177     <p><i>(Difficulty: Easy)</i></p>
 178     </li>
 179
 180     <li>Write checkers which catch Copy and Paste errors.
 181     <p>Take a look at the
 182     <a href="http://pages.cs.wisc.edu/~shanlu/paper/TSE-CPMiner.pdf">CP-Miner</a>
 183     paper for inspiration.
 184     <i>(Difficulty: Medium-Hard; current contacts: Daniel Marjam&auml;ki and Daniel Fahlgren)</i></p>
 185     </li>
 186   </ul>
 187   </li>
 188 </ul>
 189
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