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243 строки
9.3 KiB
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<title>Information on using the Static Analyzer ("LLVM Checker")</title>
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<h1>Information on using the Static Analyzer ("LLVM Checker")</h1>
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<p>
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This documents provides some notes on using the LLVM/clang static analyzer to
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find bugs in C and Objective-C programs.
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<p>This document is arranged into the following sections:</p>
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<ul>
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<li><a href="#Contents">Downloadable Package Contents</a></li>
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<li><a href="#BasicUsage">Basic Usage</a></li>
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<li><a href="#Output">Output of the Analyzer</a></li>
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<li><a href="#RecommendedUsageGuidelines">Recommended Usage Guidelines</a></li>
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<li><a href="#Debugging">Debugging the Analyzer</a>
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</ul>
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<h2 id="ReleaseContents">Package Contents</h2>
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<p>The static analyzer is released as a single tarball:
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<tt>checker-XXX.tar.gz</tt>, where <b>XXX</b> is the release tag. The tarball
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expands to the following files:</p>
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<table>
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<thead><tr><td>File</td><td>Purpose</td></tr></thead>
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<tr><td><tt><b>scan-build</b></tt></td><td>Script for running the analyzer over a project build. <b>This is the only file you care about.</b></td></tr>
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<tr><td><tt>ccc-analyzer</tt></td><td>GCC interceptor (called by scan-build)</td></tr>
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<tr><td><tt>clang</tt></td><td>Static Analyzer (called by ccc-analyzer)</td><tr>
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<tr><td><tt>sorttable.js</tt></td><td>JavaScript used for displaying error reports</td></tr>
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</table>
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<h2 id="BasicUsage">Basic Usage</h2>
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<p>The analyzer is executed from the command-line. To run the analyzer, you will
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use <tt>scan-build</tt> to analyze the source files compiled by <tt>gcc</tt>
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during a project build.</p>
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<p>For example, to analyze the files compiled under a build:</p>
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<pre>
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$ <b>scan-build</b> make
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$ <b>scan-build</b> 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>, andin the second case <tt>scan-build</tt> analyzes a project
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built using <tt>xcodebuild</tt>. In general, the format is: </p>
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<pre>
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$ <b>scan-build</b> <i>[scan-build options]</i> <b><command></b> <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</p>
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<pre>
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$ scan-build make <b>-j4</b>
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</pre>
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<p>In this example, <tt>scan-build</tt> makes no effort to interpret the options
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after the build command (in this case, <tt>make</tt>); it just passes them
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through. In general, <tt>scan-build</tt> should support parallel builds, but
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<b>not distributed builds</b>. Similarly, you can use <tt>scan-build</tt> to
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analyze specific files:
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<pre>
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$ scan-build gcc -c <b>t1.c t2.c</b>
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</pre>
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<p>
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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>Other Options</h3>
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<p>
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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>
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$ scan-build <b>-k -V</b> make
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$ scan-build <b>-k -V</b> xcodebuild
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</pre>
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<p>Here are a complete list of options:</p>
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<table>
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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 will be
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created as needed to represent separate "runs" of the analyzer. If this option
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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 <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 going" option to the
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specified build command. <p>This option currently supports <tt>make</tt> and
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<tt>xcodebuild</tt>.</p> <p>This is a convenience option; one can specify this
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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 second
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"-v" increases verbosity</b>, and is useful for filing bug 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 command completes.</td></tr>
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</table>
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<p>These options can also be viewed by running <tt>scan-build</tt> with no
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arguments:</p>
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<pre>
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$ <b>scan-build</b>
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USAGE: scan-build [options] <build command> [build options]
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OPTIONS:
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-o - Target directory for HTML report files. Subdirectories
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will be created as needed to represent separate "runs" of
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the analyzer. If this option is not specified, a directory
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is created in /tmp to store the reports.
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<b>...</b>
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</pre>
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<h2 id="Output">Output of the Analyzer</h2>
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<p>
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The output of the analyzer 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="RecommendedUsageGuidelines">Recommended Usage Guidelines</h2>
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Here are a few recommendations with running the analyzer:
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<h3>Always Analyze a Project in its "Debug" Configuration</h3>
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Most projects can be built in a "debug" mode that enables assertions. Assertions
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are picked up by the static analyzer to prune infeasible paths, which in some
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cases can greatly reduce the number of false positives (bogus error reports)
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emitted by the tool.
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<h3>Pass -k to <tt>scan-build</tt></h3>
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<p>While <tt>ccc-analyzer</tt> invokes <tt>gcc</tt> to compile code, any
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problems in correctly forwarding arguments to <tt>gcc</tt> may result in a build
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failure. Passing <b>-k</b> to <tt>scan-build</tt> potentially allows you to
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analyze other code in a project for which this problem doesn't occur.</p>
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<p> Also, it is useful to analyze a project even if not all of the source files
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are compilable. This is great when using <tt>scan-build</tt> as part of your
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compile-debug cycle.</p>
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<h3>Use Verbose Output when Debugging <tt>scan-build</tt></h3>
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<tt>scan-build</tt> takes a <b>-v</b> option to emit verbose output about what
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it's doing; two <b>-v</b> options emit more information. Redirecting the output
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of <tt>scan-build</tt> to a text file (make sure to redirect standard error) is
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useful for filing bug reports against <tt>scan-build</tt> or the analyzer, as we
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can see the exact options (and files) passed to the analyzer. For more
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comprehendible logs, don't perform a parallel build.
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<h2 id="Debugging">Debugging the Analyzer</h2>
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This section provides information on debugging the analyzer, and troubleshooting
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it when you have problems analyzing a particular project.
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<h3>How it Works</h3>
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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.
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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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<h3>Filing Bugs</h3>
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We encourage users to file bug reports for any problems that they encounter.
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Apple-internal users should file bugs in Radar against the <b>llvm - clang</b>
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component. External-Apple users should file bugs in <a
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href="http://llvm.org/bugs/enter_bug.cgi?product=clang">LLVM's Bugzilla against
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clang</a>.
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