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<h1>Open Projects</h1>
<p>This page lists several projects that would boost analyzer's usability and
power. Most of the projects listed here are infrastructure-related so this list
is an addition to the <a href="potential_checkers.html">potential checkers
list</a>. If you are interested in tackling one of these, please send an email
to the <a href=http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev>cfe-dev
mailing list</a> to notify other members of the community.</p>
<ul>
<li>Core Analyzer Infrastructure
<ul>
<li>Explicitly model standard library functions with <tt>BodyFarm</tt>.
<p><tt><a href="http://clang.llvm.org/doxygen/classclang_1_1BodyFarm.html">BodyFarm</a></tt>
allows the analyzer to explicitly model functions whose definitions are
not available during analysis. Modeling more of the widely used functions
(such as the members of <tt>std::string</tt>) will improve precision of the
analysis.
<i>(Difficulty: Easy, ongoing)</i><p>
</li>
<li>Handle floating-point values.
<p>Currently, the analyzer treats all floating-point values as unknown.
However, we already have most of the infrastructure we need to handle
floats: RangeConstraintManager. This would involve adding a new SVal kind
for constant floats, generalizing the constraint manager to handle floats
and integers equally, and auditing existing code to make sure it doesn't
make untoward assumptions.
<i> (Difficulty: Medium)</i></p>
</li>
<li>Implement generalized loop execution modeling.
<p>Currently, the analyzer simply unrolls each loop <tt>N</tt> times. This
means that it will not execute any code after the loop if the loop is
guaranteed to execute more than <tt>N</tt> times. This results in lost
basic block coverage. We could continue exploring the path if we could
model a generic <tt>i</tt>-th iteration of a loop.
<i> (Difficulty: Hard)</i></p>
</li>
<li>Enhance CFG to model C++ temporaries properly.
<p>There is an existing implementation of this, but it's not complete and
is disabled in the analyzer.
<i>(Difficulty: Medium)</i></p>
<li>Enhance CFG to model exception-handling properly.
<p>Currently exceptions are treated as "black holes", and exception-handling
control structures are poorly modeled (to be conservative). This could be
much improved for both C++ and Objective-C exceptions.
<i>(Difficulty: Medium)</i></p>
<li>Enhance CFG to model C++ <code>new</code> more precisely.
<p>The current representation of <code>new</code> does not provide an easy
way for the analyzer to model the call to a memory allocation function
(<code>operator new</code>), then initialize the result with a constructor
call. The problem is discussed at length in
<a href="http://llvm.org/bugs/show_bug.cgi?id=12014">PR12014</a>.
<i>(Difficulty: Easy)</i></p>
<li>Enhance CFG to model C++ <code>delete</code> more precisely.
<p>Similarly, the representation of <code>delete</code> does not include
the call to the destructor, followed by the call to the deallocation
function (<code>operator delete</code>). One particular issue
(<tt>noreturn</tt> destructors) is discussed in
<a href="http://llvm.org/bugs/show_bug.cgi?id=15599">PR15599</a>
<i>(Difficulty: Easy)</i></p>
<li>Track type info through casts more precisely.
<p>The DynamicTypePropagation checker is in charge of inferring a region's
dynamic type based on what operations the code is performing. Casts are a
rich source of type information that the analyzer currently ignores. They
are tricky to get right, but might have very useful consequences.
<i>(Difficulty: Medium)</i></p>
<li>Design and implement alpha-renaming.
<p>Implement unifying two symbolic values along a path after they are
determined to be equal via comparison. This would allow us to reduce the
number of false positives and would be a building step to more advanced
analyses, such as summary-based interprocedural and cross-translation-unit
analysis.
<i>(Difficulty: Hard)</i></p>
</li>
</ul>
</li>
<li>Bug Reporting
<ul>
<li>Add support for displaying cross-file diagnostic paths in HTML output
(used by <tt>scan-build</tt>).
<p>Currently <tt>scan-build</tt> output does not display reports that span
multiple files. The main problem is that we do not have a good format to
display such paths in HTML output. <i>(Difficulty: Medium)</i> </p>
</li>
<li>Relate bugs to checkers / "bug types"
<p>We need to come up with an API which will relate bug reports
to the checkers that produce them and refactor the existing code to use the
new API. This would allow us to identify the checker from the bug report,
which paves the way for selective control of certain checks.
<i>(Difficulty: Easy-Medium)</i></p>
</li>
<li>Refactor path diagnostic generation in <a href="http://clang.llvm.org/doxygen/BugReporter_8cpp_source.html">BugReporter.cpp</a>.
<p>It would be great to have more code reuse between "Minimal" and
"Extensive" PathDiagnostic generation algorithms. One idea is to create an
IR for representing path diagnostics, which would be later be used to
generate minimal or extensive report output. <i>(Difficulty: Medium)</i></p>
</li>
</ul>
</li>
<li>Other Infrastructure
<ul>
<li>Rewrite <tt>scan-build</tt> (in Python).
<p><i>(Difficulty: Easy)</i></p>
</li>
<li>Do a better job interposing on a compilation.
<p>Currently, <tt>scan-build</tt> just sets the <tt>CC</tt> and <tt>CXX</tt>
environment variables to its wrapper scripts, which then call into an
underlying platform compiler. This is problematic for any project that
doesn't exclusively use <tt>CC</tt> and <tt>CXX</tt> to control its
compilers.
<p><i>(Difficulty: Medium-Hard)</i></p>
</li>
<li>Create an <tt>analyzer_annotate</tt> attribute for the analyzer
annotations.
<p>We would like to put all analyzer attributes behind a fence so that we
could add/remove them without worrying that compiler (not analyzer) users
depend on them. Design and implement such a generic analyzer attribute in
the compiler. <i>(Difficulty: Medium)</i></p>
</li>
</ul>
</li>
<li>Enhanced Checks
<ul>
<li>Implement a production-ready StreamChecker.
<p>A SimpleStreamChecker has been presented in the Building a Checker in 24
Hours talk
(<a href="http://llvm.org/devmtg/2012-11/Zaks-Rose-Checker24Hours.pdf">slides</a>
<a href="http://llvm.org/devmtg/2012-11/videos/Zaks-Rose-Checker24Hours.mp4">video</a>).
We need to implement a production version of the checker with richer set of
APIs and evaluate it by running on real codebases.
<i>(Difficulty: Easy)</i></p>
</li>
<li>Extend Malloc checker with reasoning about custom allocator,
deallocator, and ownership-transfer functions.
<p>This would require extending the MallocPessimistic checker to reason
about annotated functions. It is strongly desired that one would rely on
the <tt>analyzer_annotate</tt> attribute, as described above.
<i>(Difficulty: Easy)</i></p>
</li>
<li>Implement a BitwiseMaskingChecker to handle <a href="http://llvm.org/bugs/show_bug.cgi?id=16615">PR16615</a>.
<p>Symbolic expressions of the form <code>$sym & CONSTANT</code> can range from 0 to <code>CONSTANT-</code>1 if CONSTANT is <code>2^n-1</code>, e.g. 0xFF (0b11111111), 0x7F (0b01111111), 0x3 (0b0011), 0xFFFF, etc. Even without handling general bitwise operations on symbols, we can at least bound the value of the resulting expression. Bonus points for handling masks followed by shifts, e.g. <code>($sym & 0b1100) >> 2</code>.
<i>(Difficulty: Easy)</i></p>
</li>
<li>Implement iterators invalidation checker.
<p><i>(Difficulty: Easy)</i></p>
</li>
<li>Write checkers which catch Copy and Paste errors.
<p>Take a look at the
<a href="http://pages.cs.wisc.edu/~shanlu/paper/TSE-CPMiner.pdf">CP-Miner</a>
paper for inspiration.
<i>(Difficulty: Medium-Hard)</i></p>
</li>
</ul>
</li>
</ul>
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