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17 <h1>scan-build: running the analyzer from the command line</h1>
19 <table style="margin-top:0px" width="100%" cellpadding="0px" cellspacing="0">
23 <p><b>scan-build</b> is a command line utility that enables a user to run the
24 static analyzer over their codebase as part of performing a regular build (from
25 the command line).</p>
27 <h3>How does it work?</h3>
28 <p>During a project build, as source files are compiled they are also analyzed
29 in tandem by the static analyzer.</p>
31 <p>Upon completion of the build, results are then presented to the user within a
34 <h3>Will it work with any build system?</h3>
35 <p><b>scan-build</b> has little or no knowledge about how you build your code.
36 It works by overriding the <tt>CC</tt> and <tt>CXX</tt> environment variables to
37 (hopefully) change your build to use a "fake" compiler instead of the
38 one that would normally build your project. This fake compiler executes either
39 <tt>clang</tt> or <tt>gcc</tt> (depending on the platform) to compile your
40 code and then executes the static analyzer to analyze your code.</p>
42 <p>This "poor man's interposition" works amazingly well in many cases
43 and falls down in others. Please consult the information on this page on making
44 the best use of <b>scan-build</b>, which includes getting it to work when the
45 aforementioned hack fails to work.</p>
48 <td style="padding-left:10px; text-align:center">
49 <img src="images/scan_build_cmd.png" width="450px" alt="scan-build"><br>
50 <a href="images/analyzer_html.png"><img src="images/analyzer_html.png" width="450px" alt="analyzer in browser"></a>
51 <br><b>Viewing static analyzer results in a web browser</b>
56 <ul id="collapsetree" class="dbtree onclick multiple">
57 <li><a href="#scanbuild">Getting Started</a>
59 <li><a href="#scanbuild_basicusage">Basic Usage</a></li>
60 <li><a href="#scanbuild_forwindowsusers">For Windows Users</a></li>
61 <li><a href="#scanbuild_otheroptions">Other Options</a></li>
62 <li><a href="#scanbuild_output">Output of scan-build</a></li>
65 <li><a href="#recommendedguidelines">Recommended Usage Guidelines</a>
67 <li><a href="#recommended_debug">Always Analyze a Project in its "Debug" Configuration</a></li>
68 <li><a href="#recommended_verbose">Use Verbose Output when Debugging scan-build</a></li>
69 <li><a href="#recommended_autoconf">Run './configure' through scan-build</a></li>
72 <li><a href="#iphone">Analyzing iPhone Projects</a></li>
75 <h2 id="scanbuild">Getting Started</h2>
77 <p>The <tt>scan-build</tt> command can be used to analyze an entire project by
78 essentially interposing on a project's build process. This means that to run the
79 analyzer using <tt>scan-build</tt>, you will use <tt>scan-build</tt> to analyze
80 the source files compiled by <tt>gcc</tt>/<tt>clang</tt> during a project build.
81 This means that any files that are not compiled will also not be analyzed.</p>
83 <h3 id="scanbuild_basicusage">Basic Usage</h3>
85 <p>Basic usage of <tt>scan-build</tt> is designed to be simple: just place the
86 word "scan-build" in front of your build command:</p>
88 <pre class="code_example">
89 $ <span class="code_highlight">scan-build</span> make
90 $ <span class="code_highlight">scan-build</span> xcodebuild
93 <p>In the first case <tt>scan-build</tt> analyzes the code of a project built
94 with <tt>make</tt> and in the second case <tt>scan-build</tt> analyzes a project
95 built using <tt>xcodebuild</tt>.<p>
97 <p>Here is the general format for invoking <tt>scan-build</tt>:</p>
99 <pre class="code_example">
100 $ <span class="code_highlight">scan-build</span> <i>[scan-build options]</i> <span class="code_highlight"><command></span> <i>[command options]</i>
103 <p>Operationally, <tt>scan-build</tt> literally runs <command> with all of the
104 subsequent options passed to it. For example, one can pass <tt>-j4</tt> to
105 <tt>make</tt> get a parallel build over 4 cores:</p>
107 <pre class="code_example">
108 $ scan-build make <span class="code_highlight">-j4</span>
111 <p>In almost all cases, <tt>scan-build</tt> makes no effort to interpret the
112 options after the build command; it simply passes them through. In general,
113 <tt>scan-build</tt> should support parallel builds, but <b>not distributed
116 <p>It is also possible to use <tt>scan-build</tt> to analyze specific
119 <pre class="code_example">
120 $ scan-build gcc -c <span class="code_highlight">t1.c t2.c</span>
123 <p>This example causes the files <tt>t1.c</tt> and <tt>t2.c</tt> to be analyzed.
126 <h3 id="scanbuild_forwindowsusers">For Windows Users</h3>
128 <p>Windows users must have Perl installed to use scan-build. Currently scan-build
129 is known to work with the msys perl port.</p>
131 <p>scan-build.bat script allows you to launch scan-build in the same way as it described in the Basic Usage section above.
132 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>
134 <h3 id="scanbuild_otheroptions">Other Options</h3>
136 <p>As mentioned above, extra options can be passed to <tt>scan-build</tt>. These
137 options prefix the build command. For example:</p>
139 <pre class="code_example">
140 $ scan-build <span class="code_highlight">-k -V</span> make
141 $ scan-build <span class="code_highlight">-k -V</span> xcodebuild
144 <p>Here is a subset of useful options:</p>
146 <table class="options">
147 <colgroup><col class="option"><col class="description"></colgroup>
148 <thead><tr><td>Option</td><td>Description</td></tr></thead>
150 <tr><td><b>-o</b></td><td>Target directory for HTML report files. Subdirectories
151 will be created as needed to represent separate "runs" of the analyzer. If this
152 option is not specified, a directory is created in <tt>/tmp</tt> to store the
155 <tr><td><b>-h</b><br><i>(or no arguments)</i></td><td>Display all
156 <tt>scan-build</tt> options.</td></tr>
158 <tr><td><b>-k</b><br><b>--keep-going</b></td><td>Add a "keep on
159 going" option to the specified build command. <p>This option currently supports
160 <tt>make</tt> and <tt>xcodebuild</tt>.</p> <p>This is a convenience option; one
161 can specify this behavior directly using build options.</p></td></tr>
163 <tr><td><b>-v</b></td><td>Verbose output from scan-build and the analyzer. <b>A
164 second and third "-v" increases verbosity</b>, and is useful for filing bug
165 reports against the analyzer.</td></tr>
167 <tr><td><b>-V</b></td><td>View analysis results in a web browser when the build
168 command completes.</td></tr>
170 <tr><td><b>--use-analyzer Xcode</b><br><i>or</i><br>
171 <b>--use-analyzer [path to clang]</b></td><td><tt>scan-build</tt> uses the
172 'clang' executable relative to itself for static analysis. One can override this
173 behavior with this option by using the 'clang' packaged with Xcode (on OS X) or
174 from the PATH.</p></td></tr> </table>
176 <p>A complete list of options can be obtained by running <tt>scan-build</tt>
177 with no arguments.</p>
179 <h3 id="scanbuild_output">Output of scan-build</h3>
182 The output of scan-build is a set of HTML files, each one which represents a
183 separate bug report. A single <tt>index.html</tt> file is generated for
184 surveying all of the bugs. You can then just open <tt>index.html</tt> in a web
185 browser to view the bug reports.
189 Where the HTML files are generated is specified with a <b>-o</b> option to
190 <tt>scan-build</tt>. If <b>-o</b> isn't specified, a directory in <tt>/tmp</tt>
191 is created to store the files (<tt>scan-build</tt> will print a message telling
192 you where they are). If you want to view the reports immediately after the build
193 completes, pass <b>-V</b> to <tt>scan-build</tt>.
197 <h2 id="recommendedguidelines">Recommended Usage Guidelines</h2>
199 <p>This section describes a few recommendations with running the analyzer.</p>
201 <h3 id="recommended_debug">ALWAYS analyze a project in its "debug" configuration</h3>
203 <p>Most projects can be built in a "debug" mode that enables assertions.
204 Assertions are picked up by the static analyzer to prune infeasible paths, which
205 in some cases can greatly reduce the number of false positives (bogus error
206 reports) emitted by the tool.</p>
208 <h3 id="recommend_verbose">Use verbose output when debugging scan-build</h3>
210 <p><tt>scan-build</tt> takes a <b>-v</b> option to emit verbose output about
211 what it's doing; two <b>-v</b> options emit more information. Redirecting the
212 output of <tt>scan-build</tt> to a text file (make sure to redirect standard
213 error) is useful for filing bug reports against <tt>scan-build</tt> or the
214 analyzer, as we can see the exact options (and files) passed to the analyzer.
215 For more comprehensible logs, don't perform a parallel build.</p>
217 <h3 id="recommended_autoconf">Run './configure' through scan-build</h3>
219 <p>If an analyzed project uses an autoconf generated <tt>configure</tt> script,
220 you will probably need to run <tt>configure</tt> script through
221 <tt>scan-build</tt> in order to analyze the project.</p>
223 <p><b>Example</b></p>
225 <pre class="code_example">
226 $ scan-build ./configure
230 <p>The reason <tt>configure</tt> also needs to be run through
231 <tt>scan-build</tt> is because <tt>scan-build</tt> scans your source files by
232 <i>interposing</i> on the compiler. This interposition is currently done by
233 <tt>scan-build</tt> temporarily setting the environment variable <tt>CC</tt> to
234 <tt>ccc-analyzer</tt>. The program <tt>ccc-analyzer</tt> acts like a fake
235 compiler, forwarding its command line arguments over to the compiler to perform
236 regular compilation and <tt>clang</tt> to perform static analysis.</p>
238 <p>Running <tt>configure</tt> typically generates makefiles that have hardwired
239 paths to the compiler, and by running <tt>configure</tt> through
240 <tt>scan-build</tt> that path is set to <tt>ccc-analyzer</tt>.</p>
243 <h2 id="Debugging">Debugging the Analyzer</h2>
245 <p>This section provides information on debugging the analyzer, and troubleshooting
246 it when you have problems analyzing a particular project.</p>
248 <h3>How it Works</h3>
250 <p>To analyze a project, <tt>scan-build</tt> simply sets the environment variable
251 <tt>CC</tt> to the full path to <tt>ccc-analyzer</tt>. It also sets a few other
252 environment variables to communicate to <tt>ccc-analyzer</tt> where to dump HTML
255 <p>Some Makefiles (or equivalent project files) hardcode the compiler; for such
256 projects simply overriding <tt>CC</tt> won't cause <tt>ccc-analyzer</tt> to be
257 called. This will cause the compiled code <b>to not be analyzed.</b></p> If you
258 find that your code isn't being analyzed, check to see if <tt>CC</tt> is
259 hardcoded. If this is the case, you can hardcode it instead to the <b>full
260 path</b> to <tt>ccc-analyzer</tt>.</p>
262 <p>When applicable, you can also run <tt>./configure</tt> for a project through
263 <tt>scan-build</tt> so that configure sets up the location of <tt>CC</tt> based
264 on the environment passed in from <tt>scan-build</tt>:
267 $ scan-build <b>./configure</b>
270 <p><tt>scan-build</tt> has special knowledge about <tt>configure</tt>, so it in
271 most cases will not actually analyze the configure tests run by
272 <tt>configure</tt>.</p>
274 <p>Under the hood, <tt>ccc-analyzer</tt> directly invokes <tt>gcc</tt> to
275 compile the actual code in addition to running the analyzer (which occurs by it
276 calling <tt>clang</tt>). <tt>ccc-analyzer</tt> tries to correctly forward all
277 the arguments over to <tt>gcc</tt>, but this may not work perfectly (please
278 report bugs of this kind).
281 <h2 id="iphone">Analyzing iPhone Projects</h2>
283 <p>Conceptually Xcode projects for iPhone applications are nearly the same as
284 their cousins for desktop applications. <b>scan-build</b> can analyze these
285 projects as well, but users often encounter problems with just building their
286 iPhone projects from the command line because there are a few extra preparative
287 steps they need to take (e.g., setup code signing).</p>
289 <h3>Recommendation: use "Build and Analyze"</h3>
291 <p>The absolute easiest way to analyze iPhone projects is to use the <a
292 href="http://developer.apple.com/mac/library/featuredarticles/StaticAnalysis/index.html"><i>Build
293 and Analyze</i> feature in Xcode 3.2</a> (which is based on the Clang Static
294 Analyzer). There a user can analyze their project with the click of a button
295 without most of the setup described later.</p>
297 <p><a href="/xcode.html">Instructions are available</a> on this
298 website on how to use open source builds of the analyzer as a replacement for
299 the one bundled with Xcode.</p>
301 <h3>Using scan-build directly</h3>
303 <p>If you wish to use <b>scan-build</b> with your iPhone project, keep the
304 following things in mind:</p>
307 <li>Analyze your project in the <tt>Debug</tt> configuration, either by setting
308 this as your configuration with Xcode or by passing <tt>-configuration
309 Debug</tt> to <tt>xcodebuild</tt>.</li>
310 <li>Analyze your project using the <tt>Simulator</tt> as your base SDK. It is
311 possible to analyze your code when targeting the device, but this is much
312 easier to do when using Xcode's <i>Build and Analyze</i> feature.</li>
313 <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>
316 <p>Note that you can most of this without actually modifying your project. For
317 example, if your application targets iPhoneOS 2.2, you could run
318 <b>scan-build</b> in the following manner from the command line:</p>
320 <pre class="code_example">
321 $ scan-build xcodebuild -configuration Debug -sdk iphonesimulator2.2
324 Alternatively, if your application targets iPhoneOS 3.0:
326 <pre class="code_example">
327 $ scan-build xcodebuild -configuration Debug -sdk iphonesimulator3.0
330 <h3>Gotcha: using the right compiler</h3>
332 <p>Recall that <b>scan-build</b> analyzes your project by using a compiler to
333 compile the project and <tt>clang</tt> to analyze your project. The script uses
334 simple heuristics to determine which compiler should be used (it defaults to
335 <tt>clang</tt> on Darwin and <tt>gcc</tt> on other platforms). When analyzing
336 iPhone projects, <b>scan-build</b> may pick the wrong compiler than the one
337 Xcode would use to build your project. For example, this could be because
338 multiple versions of a compiler may be installed on your system, especially if
339 you are developing for the iPhone.</p>
341 <p>When compiling your application to run on the simulator, it is important that <b>scan-build</b>
342 finds the correct version of <tt>gcc/clang</tt>. Otherwise, you may see strange build
343 errors that only happen when you run <tt>scan-build</tt>.
345 <p><b>scan-build</b> provides the <tt>--use-cc</tt> and <tt>--use-c++</tt>
346 options to hardwire which compiler scan-build should use for building your code.
347 Note that although you are chiefly interested in analyzing your project, keep in
348 mind that running the analyzer is intimately tied to the build, and not being
349 able to compile your code means it won't get fully analyzed (if at all).</p>
351 <p>If you aren't certain which compiler Xcode uses to build your project, try
352 just running <tt>xcodebuild</tt> (without <b>scan-build</b>). You should see the
353 full path to the compiler that Xcode is using, and use that as an argument to
354 <tt>--use-cc</tt>.</p>