www/analyzer/scan-build.html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
          "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
  <title>scan-build: running the analyzer from the command line</title>
  <link type="text/css" rel="stylesheet" href="content.css">
  <link type="text/css" rel="stylesheet" href="menu.css">
  <script type="text/javascript" src="scripts/menu.js"></script>
</head>
<body>

<div id="page">
<!--#include virtual="menu.html.incl"-->
<div id="content">

<h1>scan-build: running the analyzer from the command line</h1>

<table style="margin-top:0px" width="100%" cellpadding="0px" cellspacing="0">
<tr><td>

<h3>What is it?</h3>
<p><b>scan-build</b> is a command line utility that enables a user to run the
static analyzer over their codebase as part of performing a regular build (from
the command line).</p>

<h3>How does it work?</h3>
<p>During a project build, as source files are compiled they are also analyzed
in tandem by the static analyzer.</p>

<p>Upon completion of the build, results are then presented to the user within a
web browser.</p>

<h3>Will it work with any build system?</h3>
<p><b>scan-build</b> has little or no knowledge about how you build your code.
It works by overriding the <tt>CC</tt> and <tt>CXX</tt> environment variables to
(hopefully) change your build to use a &quot;fake&quot; compiler instead of the
one that would normally build your project. This fake compiler executes either
<tt>clang</tt> or <tt>gcc</tt> (depending on the platform) to compile your
code and then executes the static analyzer to analyze your code.</p>

<p>This &quot;poor man's interposition&quot; works amazingly well in many cases
and falls down in others. Please consult the information on this page on making
the best use of <b>scan-build</b>, which includes getting it to work when the
aforementioned hack fails to work.</p>

</td>
<td style="padding-left:10px; text-align:center">
  <img src="images/scan_build_cmd.png" width="450px" alt="scan-build"><br>
  <a href="images/analyzer_html.png"><img src="images/analyzer_html.png" width="450px" alt="analyzer in browser"></a>
<br><b>Viewing static analyzer results in a web browser</b>
</td></tr></table>

<h2>Contents</h2>

<ul>
<li><a href="#scanbuild">Getting Started</a>
 <ul>
  <li><a href="#scanbuild_basicusage">Basic Usage</a></li>
  <li><a href="#scanbuild_forwindowsusers">For Windows Users</a></li>
  <li><a href="#scanbuild_otheroptions">Other Options</a></li>
  <li><a href="#scanbuild_output">Output of scan-build</a></li>
 </ul>
</li>
<li><a href="#recommendedguidelines">Recommended Usage Guidelines</a>
 <ul>
  <li><a href="#recommended_debug">Always Analyze a Project in its &quot;Debug&quot; Configuration</a></li>
  <li><a href="#recommended_verbose">Use Verbose Output when Debugging scan-build</a></li>
  <li><a href="#recommended_autoconf">Run './configure' through scan-build</a></li>
 </ul>
</li>
<li><a href="#iphone">Analyzing iPhone Projects</a></li>
</ul>

<h2 id="scanbuild">Getting Started</h2>

<p>The <tt>scan-build</tt> command can be used to analyze an entire project by
essentially interposing on a project's build process. This means that to run the
analyzer using <tt>scan-build</tt>, you will use <tt>scan-build</tt> to analyze
the source files compiled by <tt>gcc</tt>/<tt>clang</tt> during a project build.
This means that any files that are not compiled will also not be analyzed.</p>

<h3 id="scanbuild_basicusage">Basic Usage</h3>

<p>Basic usage of <tt>scan-build</tt> is designed to be simple: just place the
word &quot;scan-build&quot; in front of your build command:</p>

<pre class="code_example">
$ <span class="code_highlight">scan-build</span> make
$ <span class="code_highlight">scan-build</span> xcodebuild
</pre>

<p>In the first case <tt>scan-build</tt> analyzes the code of a project built
with <tt>make</tt> and in the second case <tt>scan-build</tt> analyzes a project
built using <tt>xcodebuild</tt>.<p>

<p>Here is the general format for invoking <tt>scan-build</tt>:</p>

<pre class="code_example">
$ <span class="code_highlight">scan-build</span> <i>[scan-build options]</i> <span class="code_highlight">&lt;command&gt;</span> <i>[command options]</i>
</pre>

<p>Operationally, <tt>scan-build</tt> literally runs &lt;command&gt; with all of the
subsequent options passed to it. For example, one can pass <tt>-j4</tt> to
<tt>make</tt> get a parallel build over 4 cores:</p>

<pre class="code_example">
$ scan-build make <span class="code_highlight">-j4</span>
</pre>

<p>In almost all cases, <tt>scan-build</tt> makes no effort to interpret the
options after the build command; it simply passes them through. In general,
<tt>scan-build</tt> should support parallel builds, but <b>not distributed
builds</b>.</p>

<p>It is also possible to use <tt>scan-build</tt> to analyze specific
files:</p>

<pre class="code_example">
 $ scan-build gcc -c <span class="code_highlight">t1.c t2.c</span>
</pre>

<p>This example causes the files <tt>t1.c</tt> and <tt>t2.c</tt> to be analyzed.
</p>

<h3 id="scanbuild_forwindowsusers">For Windows Users</h3>

<p>Windows users must have Perl installed to use scan-build. Currently scan-build
is known to work with the msys perl port.</p>

<p>scan-build.bat script allows you to launch scan-build in the same way as it described in the Basic Usage section above.
All you need to be able to invoke scan-build from an arbitrary location is to add the path to scan-build to your PATH environment variable.</p>

<h3 id="scanbuild_otheroptions">Other Options</h3>

<p>As mentioned above, extra options can be passed to <tt>scan-build</tt>. These
options prefix the build command. For example:</p>

<pre class="code_example">
 $ scan-build <span class="code_highlight">-k -V</span> make
 $ scan-build <span class="code_highlight">-k -V</span> xcodebuild
</pre>

<p>Here is a subset of useful options:</p>

<table class="options">
<colgroup><col class="option"><col class="description"></colgroup>
<thead><tr><td>Option</td><td>Description</td></tr></thead>

<tr><td><b>-o</b></td><td>Target directory for HTML report files. Subdirectories
will be created as needed to represent separate "runs" of the analyzer. If this
option is not specified, a directory is created in <tt>/tmp</tt> to store the
reports.</td></tr>

<tr><td><b>-h</b><br><i>(or&nbsp;no&nbsp;arguments)</i></td><td>Display all
<tt>scan-build</tt> options.</td></tr>

<tr><td><b>-k</b><br><b>--keep-going</b></td><td>Add a "keep on
going" option to the specified build command. <p>This option currently supports
<tt>make</tt> and <tt>xcodebuild</tt>.</p> <p>This is a convenience option; one
can specify this behavior directly using build options.</p></td></tr>

<tr><td><b>-v</b></td><td>Verbose output from scan-build and the analyzer. <b>A
second and third "-v" increases verbosity</b>, and is useful for filing bug
reports against the analyzer.</td></tr>

<tr><td><b>-V</b></td><td>View analysis results in a web browser when the build
command completes.</td></tr>

<tr><td><b>--use-analyzer Xcode</b><br><i>or</i><br>
<b>--use-analyzer [path to clang]</b></td><td><tt>scan-build</tt> uses the
'clang' executable relative to itself for static analysis. One can override this
behavior with this option by using the 'clang' packaged with Xcode (on OS X) or
from the PATH.</p></td></tr> </table>

<p>A complete list of options can be obtained by running <tt>scan-build</tt>
with no arguments.</p>

<h3 id="scanbuild_output">Output of scan-build</h3>

<p>
The output of scan-build is a set of HTML files, each one which represents a
separate bug report. A single <tt>index.html</tt> file is generated for
surveying all of the bugs. You can then just open <tt>index.html</tt> in a web
browser to view the bug reports.
</p>

<p>
Where the HTML files are generated is specified with a <b>-o</b> option to
<tt>scan-build</tt>. If <b>-o</b> isn't specified, a directory in <tt>/tmp</tt>
is created to store the files (<tt>scan-build</tt> will print a message telling
you where they are). If you want to view the reports immediately after the build
completes, pass <b>-V</b> to <tt>scan-build</tt>.
</p>


<h2 id="recommendedguidelines">Recommended Usage Guidelines</h2>

<p>This section describes a few recommendations with running the analyzer.</p>

<h3 id="recommended_debug">ALWAYS analyze a project in its &quot;debug&quot; configuration</h3>

<p>Most projects can be built in a &quot;debug&quot; mode that enables assertions.
Assertions are picked up by the static analyzer to prune infeasible paths, which
in some cases can greatly reduce the number of false positives (bogus error
reports) emitted by the tool.</p>

<h3 id="recommend_verbose">Use verbose output when debugging scan-build</h3>

<p><tt>scan-build</tt> takes a <b>-v</b> option to emit verbose output about
what it's doing; two <b>-v</b> options emit more information. Redirecting the
output of <tt>scan-build</tt> to a text file (make sure to redirect standard
error) is useful for filing bug reports against <tt>scan-build</tt> or the
analyzer, as we can see the exact options (and files) passed to the analyzer.
For more comprehensible logs, don't perform a parallel build.</p>

<h3 id="recommended_autoconf">Run './configure' through scan-build</h3>

<p>If an analyzed project uses an autoconf generated <tt>configure</tt> script,
you will probably need to run <tt>configure</tt> script through
<tt>scan-build</tt> in order to analyze the project.</p>

<p><b>Example</b></p>

<pre class="code_example">
$ scan-build ./configure
$ scan-build make
</pre>

<p>The reason <tt>configure</tt> also needs to be run through
<tt>scan-build</tt> is because <tt>scan-build</tt> scans your source files by
<i>interposing</i> on the compiler. This interposition is currently done by
<tt>scan-build</tt> temporarily setting the environment variable <tt>CC</tt> to
<tt>ccc-analyzer</tt>. The program <tt>ccc-analyzer</tt> acts like a fake
compiler, forwarding its command line arguments over to the compiler to perform
regular compilation and <tt>clang</tt> to perform static analysis.</p>

<p>Running <tt>configure</tt> typically generates makefiles that have hardwired
paths to the compiler, and by running <tt>configure</tt> through
<tt>scan-build</tt> that path is set to <tt>ccc-analyzer</tt>.</p>

<!--
<h2 id="Debugging">Debugging the Analyzer</h2>

<p>This section provides information on debugging the analyzer, and troubleshooting
it when you have problems analyzing a particular project.</p>

<h3>How it Works</h3>

<p>To analyze a project, <tt>scan-build</tt> simply sets the environment variable
<tt>CC</tt> to the full path to <tt>ccc-analyzer</tt>. It also sets a few other
environment variables to communicate to <tt>ccc-analyzer</tt> where to dump HTML
report files.</p>

<p>Some Makefiles (or equivalent project files) hardcode the compiler; for such
projects simply overriding <tt>CC</tt> won't cause <tt>ccc-analyzer</tt> to be
called. This will cause the compiled code <b>to not be analyzed.</b></p> If you
find that your code isn't being analyzed, check to see if <tt>CC</tt> is
hardcoded. If this is the case, you can hardcode it instead to the <b>full
path</b> to <tt>ccc-analyzer</tt>.</p>

<p>When applicable, you can also run <tt>./configure</tt> for a project through
<tt>scan-build</tt> so that configure sets up the location of <tt>CC</tt> based
on the environment passed in from <tt>scan-build</tt>:

<pre>
  $ scan-build <b>./configure</b>
</pre>

<p><tt>scan-build</tt> has special knowledge about <tt>configure</tt>, so it in
most cases will not actually analyze the configure tests run by
<tt>configure</tt>.</p>

<p>Under the hood, <tt>ccc-analyzer</tt> directly invokes <tt>gcc</tt> to
compile the actual code in addition to running the analyzer (which occurs by it
calling <tt>clang</tt>). <tt>ccc-analyzer</tt> tries to correctly forward all
the arguments over to <tt>gcc</tt>, but this may not work perfectly (please
report bugs of this kind).
 -->

<h2 id="iphone">Analyzing iPhone Projects</h2>

<p>Conceptually Xcode projects for iPhone applications are nearly the same as
their cousins for desktop applications. <b>scan-build</b> can analyze these
projects as well, but users often encounter problems with just building their
iPhone projects from the command line because there are a few extra preparative
steps they need to take (e.g., setup code signing).</p>

<h3>Recommendation: use &quot;Build and Analyze&quot;</h3>

<p>The absolute easiest way to analyze iPhone projects is to use the <a
href="http://developer.apple.com/mac/library/featuredarticles/StaticAnalysis/index.html"><i>Build
and Analyze</i> feature in Xcode 3.2</a> (which is based on the Clang Static
Analyzer). There a user can analyze their project with the click of a button
without most of the setup described later.</p>

<p><a href="/xcode.html">Instructions are available</a> on this
website on how to use open source builds of the analyzer as a replacement for
the one bundled with Xcode.</p>

<h3>Using scan-build directly</h3>

<p>If you wish to use <b>scan-build</b> with your iPhone project, keep the
following things in mind:</p>

<ul>
 <li>Analyze your project in the <tt>Debug</tt> configuration, either by setting
this as your configuration with Xcode or by passing <tt>-configuration
Debug</tt> to <tt>xcodebuild</tt>.</li>
 <li>Analyze your project using the <tt>Simulator</tt> as your base SDK. It is
possible to analyze your code when targeting the device, but this is much
easier to do when using Xcode's <i>Build and Analyze</i> feature.</li>
 <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>
</ul>

<p>Note that you can most of this without actually modifying your project. For
example, if your application targets iPhoneOS 2.2, you could run
<b>scan-build</b> in the following manner from the command line:</p>

<pre class="code_example">
$ scan-build xcodebuild -configuration Debug -sdk iphonesimulator2.2
</pre>

Alternatively, if your application targets iPhoneOS 3.0:

<pre class="code_example">
$ scan-build xcodebuild -configuration Debug -sdk iphonesimulator3.0
</pre>

<h3>Gotcha: using the right compiler</h3>

<p>Recall that <b>scan-build</b> analyzes your project by using a compiler to
compile the project and <tt>clang</tt> to analyze your project. The script uses
simple heuristics to determine which compiler should be used (it defaults to
<tt>clang</tt> on Darwin and <tt>gcc</tt> on other platforms). When analyzing
iPhone projects, <b>scan-build</b> may pick the wrong compiler than the one
Xcode would use to build your project. For example, this could be because
multiple versions of a compiler may be installed on your system, especially if
you are developing for the iPhone.</p>

<p>When compiling your application to run on the simulator, it is important that <b>scan-build</b>
finds the correct version of <tt>gcc/clang</tt>. Otherwise, you may see strange build
errors that only happen when you run <tt>scan-build</tt>.

<p><b>scan-build</b> provides the <tt>--use-cc</tt> and <tt>--use-c++</tt>
options to hardwire which compiler scan-build should use for building your code.
Note that although you are chiefly interested in analyzing your project, keep in
mind that running the analyzer is intimately tied to the build, and not being
able to compile your code means it won't get fully analyzed (if at all).</p>

<p>If you aren't certain which compiler Xcode uses to build your project, try
just running <tt>xcodebuild</tt> (without <b>scan-build</b>). You should see the
full path to the compiler that Xcode is using, and use that as an argument to
<tt>--use-cc</tt>.</p>

</div>
</div>
</body>
</html>