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<h1>scan-build: running the analyzer from the command line</h1>
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<table style="margin-top:0px" width="100%" border="0" cellpadding="0px" cellspacing="0">
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<tr><td>
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<h3>What is it?</h3>
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<p><b>scan-build</b> is a command line utility that enables a user to run the
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static analyzer over their codebase as part of performing a regular build (from
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the command line).</p>
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<h3>How does it work?</h3>
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<p>During a project build, as source files are compiled they are also analyzed
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in tandem by the static analyzer.</p>
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<p>Upon completion of the build, results are then presented to the user within a
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web browser.</p>
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<h3>Will it work with any build system?</h3>
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<p><b>scan-build</b> has little or no knowledge about how you build your code.
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It works by overriding the <tt>CC</tt> and <tt>CXX</tt> environment variables to
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(hopefully) change your build to use a "fake" compiler instead of the
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one that would normally build your project. By default, this fake compiler
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executes <tt>gcc</tt> to compile your code (assuming that <tt>gcc</tt> is your
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compiler) and then executes the static analyzer to analyze your code.</p>
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<p>This "poor man's interposition" works amazingly well in many cases
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and falls down in others. Please consult the information on this page on making
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the best use of <b>scan-build</b>, which includes getting it to work when the
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aforementioned hack fails to work.</p>
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</td>
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<td style="padding-left:10px">
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<center>
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<img src="images/scan_build_cmd.png" width="450px" border=0><br>
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<a href="images/analyzer_html.png"><img src="images/analyzer_html.png" width="450px" border=0></a>
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<br><b>Viewing static analyzer results in a web browser</b></center>
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</td></tr></table>
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<h2>Contents</h2>
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<ul id="collapsetree" class="dbtree onclick multiple">
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<li><a href="#scanbuild">Getting Started</a>
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<ul>
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<li><a href="#scanbuild_basicusage">Basic Usage</a></li>
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<li><a href="#scanbuild_otheroptions">Other Options</a></li>
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<li><a href="#scanbuild_output">Output of scan-build</a></li>
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</ul>
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</li>
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<li><a href="#recommendedguidelines">Recommended Usage Guidelines</a>
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<ul>
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<li><a href="#recommended_debug">Always Analyze a Project in its "Debug" Configuration</a></li>
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<li><a href="#recommended_verbose">Use Verbose Output when Debugging scan-build</a></li>
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<li><a href="#recommended_autoconf">Run './configure' through scan-build</a></li>
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</ul>
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</li>
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<li><a href="#iphone">Analyzing iPhone Projects</a></li>
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</ul>
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<h2 id="scanbuild">Getting Started</h2>
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<p>The <tt>scan-build</tt> command can be used to analyze an entire project by
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essentially interposing on a project's build process. This means that to run the
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analyzer using <tt>scan-build</tt>, you will use <tt>scan-build</tt> to analyze
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the source files compiled by <tt>gcc</tt> during a project build. This means
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that any files that are not compiled will also not be analyzed.</p>
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<h3 id="scanbuild_basicusage">Basic Usage</h3>
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<p>Basic usage of <tt>scan-build</tt> is designed to be simple: just place the
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word "scan-build" in front of your build command:</p>
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<pre class="code_example">
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$ <span class="code_highlight">scan-build</span> make
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$ <span class="code_highlight">scan-build</span> xcodebuild
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</pre>
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<p>In the first case <tt>scan-build</tt> analyzes the code of a project built
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with <tt>make</tt> and in the second case <tt>scan-build</tt> analyzes a project
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built using <tt>xcodebuild</tt>.<p>
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<p>Here is the general format for invoking <tt>scan-build</tt>:</p>
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<pre class="code_example">
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$ <span class="code_highlight">scan-build</span> <i>[scan-build options]</i> <span class="code_highlight"><command></span> <i>[command options]</i>
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</pre>
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<p>Operationally, <tt>scan-build</tt> literally runs <command> with all of the
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subsequent options passed to it. For example, one can pass <nobr><tt>-j4</tt></nobr> to
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<tt>make</tt> get a parallel build over 4 cores:</p>
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<pre class="code_example">
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$ scan-build make <span class="code_highlight">-j4</span>
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</pre>
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<p>In almost all cases, <tt>scan-build</tt> makes no effort to interpret the
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options after the build command; it simply passes them through. In general,
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<tt>scan-build</tt> should support parallel builds, but <b>not distributed
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builds</b>.</p>
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<p>It is also possible to use <tt>scan-build</tt> to analyze specific
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files:</p>
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<pre class="code_example">
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$ scan-build gcc -c <span class="code_highlight">t1.c t2.c</span>
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</pre>
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<p>This example causes the files <tt>t1.c</tt> and <tt>t2.c</tt> to be analyzed.
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</p>
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<h3 id="scanbuild_otheroptions">Other Options</h3>
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<p>As mentioned above, extra options can be passed to <tt>scan-build</tt>. These
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options prefix the build command. For example:</p>
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<pre class="code_example">
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$ scan-build <span class="code_highlight">-k -V</span> make
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$ scan-build <span class="code_highlight">-k -V</span> xcodebuild
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</pre>
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<p>Here is a subset of useful options:</p>
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<table class="options">
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<thead><tr><td>Option</td><td>Description</td></tr></thead>
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<tr><td><b>-o</b></td><td>Target directory for HTML report files. Subdirectories
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will be created as needed to represent separate "runs" of the analyzer. If this
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option is not specified, a directory is created in <tt>/tmp</tt> to store the
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reports.</td><tr>
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<tr><td><b>-h</b><br><i><nobr>(or no arguments)</nobr></i></td><td>Display all
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<tt>scan-build</tt> options.</td></tr>
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<tr><td><b>-k</b><br><nobr><b>--keep-going</b></nobr></td><td>Add a "keep on
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going" option to the specified build command. <p>This option currently supports
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<tt>make</tt> and <tt>xcodebuild</tt>.</p> <p>This is a convenience option; one
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can specify this behavior directly using build options.</p></td></tr>
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<tr><td><b>-v<b></td><td>Verbose output from scan-build and the analyzer. <b>A
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second and third "-v" increases verbosity</b>, and is useful for filing bug
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reports against the analyzer.</td></tr>
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<tr><td><b>-V</b></td><td>View analysis results in a web browser when the build
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command completes.</td></tr> </table>
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<p>A complete list of options can be obtained by running <tt>scan-build</tt>
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with no arguments.</p>
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<h3 id="scanbuild_output">Output of scan-build</h3>
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<p>
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The output of scan-build is a set of HTML files, each one which represents a
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separate bug report. A single <tt>index.html</tt> file is generated for
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surveying all of the bugs. You can then just open <tt>index.html</tt> in a web
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browser to view the bug reports.
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</p>
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<p>
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Where the HTML files are generated is specified with a <b>-o</b> option to
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<tt>scan-build</tt>. If <b>-o</b> isn't specified, a directory in <tt>/tmp</tt>
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is created to store the files (<tt>scan-build</tt> will print a message telling
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you where they are). If you want to view the reports immediately after the build
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completes, pass <b>-V</b> to <tt>scan-build</tt>.
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</p>
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<h2 id="recommendedguidelines">Recommended Usage Guidelines</h2>
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<p>This section describes a few recommendations with running the analyzer.</p>
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<h3 id="recommended_debug">ALWAYS analyze a project in its "debug" configuration</h3>
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<p>Most projects can be built in a "debug" mode that enables assertions.
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Assertions are picked up by the static analyzer to prune infeasible paths, which
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in some cases can greatly reduce the number of false positives (bogus error
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reports) emitted by the tool.</p>
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<h3 id="recommend_verbose">Use verbose output when debugging scan-build</h3>
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<p><tt>scan-build</tt> takes a <b>-v</b> option to emit verbose output about
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what it's doing; two <b>-v</b> options emit more information. Redirecting the
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output of <tt>scan-build</tt> to a text file (make sure to redirect standard
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error) is useful for filing bug reports against <tt>scan-build</tt> or the
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analyzer, as we can see the exact options (and files) passed to the analyzer.
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For more comprehensible logs, don't perform a parallel build.</p>
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<h3 id="recommended_autoconf">Run './configure' through scan-build</h3>
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<p>If an analyzed project uses an autoconf generated <tt>configure</tt> script,
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you will probably need to run <tt>configure</tt> script through
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<tt>scan-build</tt> in order to analyze the project.</p>
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<p><b>Example</b></p>
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<pre class="code_example">
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$ scan-build ./configure
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$ scan-build make
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</pre>
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<p>The reason <tt>configure</tt> also needs to be run through
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<tt>scan-build</tt> is because <tt>scan-build</tt> scans your source files by
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<i>interposing</i> on the compiler. This interposition is currently done by
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<tt>scan-build</tt> temporarily setting the environment variable <tt>CC</tt> to
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<tt>ccc-analyzer</tt>. The program <tt>ccc-analyzer</tt> acts like a fake
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compiler, forwarding its command line arguments over to <tt>gcc</tt> to perform
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regular compilation and <tt>clang</tt> to perform static analysis.</p>
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<p>Running <tt>configure</tt> typically generates makefiles that have hardwired
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paths to the compiler, and by running <tt>configure</tt> through
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<tt>scan-build</tt> that path is set to <tt>ccc-analyzer</tt>.</p.>
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<!--
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<h2 id="Debugging">Debugging the Analyzer</h2>
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<p>This section provides information on debugging the analyzer, and troubleshooting
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it when you have problems analyzing a particular project.</p>
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<h3>How it Works</h3>
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<p>To analyze a project, <tt>scan-build</tt> simply sets the environment variable
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<tt>CC</tt> to the full path to <tt>ccc-analyzer</tt>. It also sets a few other
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environment variables to communicate to <tt>ccc-analyzer</tt> where to dump HTML
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report files.</p>
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<p>Some Makefiles (or equivalent project files) hardcode the compiler; for such
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projects simply overriding <tt>CC</tt> won't cause <tt>ccc-analyzer</tt> to be
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called. This will cause the compiled code <b>to not be analyzed.</b></p> If you
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find that your code isn't being analyzed, check to see if <tt>CC</tt> is
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hardcoded. If this is the case, you can hardcode it instead to the <b>full
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path</b> to <tt>ccc-analyzer</tt>.</p>
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<p>When applicable, you can also run <tt>./configure</tt> for a project through
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<tt>scan-build</tt> so that configure sets up the location of <tt>CC</tt> based
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on the environment passed in from <tt>scan-build</tt>:
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<pre>
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$ scan-build <b>./configure</b>
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</pre>
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<p><tt>scan-build</tt> has special knowledge about <tt>configure</tt>, so it in
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most cases will not actually analyze the configure tests run by
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<tt>configure</tt>.</p>
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<p>Under the hood, <tt>ccc-analyzer</tt> directly invokes <tt>gcc</tt> to
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compile the actual code in addition to running the analyzer (which occurs by it
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calling <tt>clang</tt>). <tt>ccc-analyzer</tt> tries to correctly forward all
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the arguments over to <tt>gcc</tt>, but this may not work perfectly (please
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report bugs of this kind).
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-->
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<h2 id="iphone">Analyzing iPhone Projects</h2>
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<p>Conceptually Xcode projects for iPhone applications are nearly the same as
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their cousins for desktop applications. <b>scan-build</b> can analyze these
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projects as well, but users often encounter problems with just building their
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iPhone projects from the command line because there are a few extra preparative
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steps they need to take (e.g., setup code signing).</p>
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<h3>Recommendation: use "Build and Analyze"</h3>
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<p>The absolute easiest way to analyze iPhone projects is to use the <a
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href="http://developer.apple.com/mac/library/featuredarticles/StaticAnalysis/index.html"><i>Build
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and Analyze</i> feature in Xcode 3.2</a> (which is based on the Clang Static
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Analyzer). There a user can analyze their project with the click of a button
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without most of the setup described later.</p>
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<p><a href="/xcode.html">Instructions are available</a> on this
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website on how to use open source builds of the analyzer as a replacement for
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the one bundled with Xcode.</p>
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<h3>Using scan-build directly</h3>
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<p>If you wish to use <b>scan-build</b> with your iPhone project, keep the
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following things in mind:</p>
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<ul>
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<li>Analyze your project in the <tt>Debug</tt> configuration, either by setting
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this as your configuration with Xcode or by passing <tt>-configuration
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Debug</tt> to <tt>xcodebuild</tt>.</li>
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<li>Analyze your project using the <tt>Simulator</tt> as your base SDK. It is
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possible to analyze your code when targeting the device, but this is much
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easier to do when using Xcode's <i>Build and Analyze</i> feature.</li>
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<li>Check that your code signing SDK is set to the simulator SDK as well, and make sure this option is set to <tt>Don't Code Sign</tt>.</li>
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</ul>
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<p>Note that you can most of this without actually modifying your project. For
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example, if your application targets iPhoneOS 2.2, you could run
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<b>scan-build</b> in the following manner from the command line:</p>
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<pre class="code_example">
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$ scan-build xcodebuild -configuration Debug -sdk iphonesimulator2.2
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</pre>
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Alternatively, if your application targets iPhoneOS 3.0:
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<pre class="code_example">
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$ scan-build xcodebuild -configuration Debug -sdk iphonesimulator3.0
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</pre>
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<h3>Gotcha: using the right compiler</h3>
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<p>Recall that <b>scan-build</b> analyzes your project by using <tt>gcc</tt> to
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compile the project and <tt>clang</tt> to analyze your project. When analyzing
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iPhone projects, <b>scan-build</b> may pick the wrong compiler than the one
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Xcode would use to build your project. This is because multiple versions of
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<tt>gcc</tt> may be installed on your system, especially if you are developing
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for the iPhone.</p>
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<p>Where this particularly might be a problem is if you are using Mac OS 10.5
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(Leopard) to develop for iPhone OS 3.0. The default desktop compiler on Leopard
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is gcc-4.0, while the compiler for iPhone OS 3.0 is gcc-4.2. When compiling your
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application to run on the simulator, it is important that <b>scan-build</b>
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finds the correct version of <tt>gcc</tt>. Otherwise, you may see strange build
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errors that only happen when you run <tt>scan-build</tt>.
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<p><b>scan-build</b> provides the <tt>--use-cc</tt> and <tt>--use-c++</tt>
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options to hardwire which compiler scan-build should use for building your code.
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Note that although you are chiefly interested in analyzing your project, keep in
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mind that running the analyzer is intimately tied to the build, and not being
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able to compile your code means it won't get fully analyzed (if at all).</p>
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<p>If you aren't certain which compiler Xcode uses to build your project, try
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just running <tt>xcodebuild</tt> (without <b>scan-build</b>). You should see the
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full path to the compiler that Xcode is using, and use that as an argument to
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<tt>--use-cc</tt>.</p>
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