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3 <title>Information on using the Static Analyzer ("LLVM Checker")</title>
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28<div id="content">
29
Ted Kremenek43bfbaf2008-06-11 06:01:28 +0000[diff] [blame]30<h1>Information on using the Static Analyzer</h1>
Ted Kremenekce2e3322008-04-25 18:44:36 +0000[diff] [blame]31
Ted Kremenekbe6e5162008-06-11 05:25:12 +0000[diff] [blame]32<p>This documents provides some notes on using the LLVM/clang static analyzer to
33find bugs in C and Objective-C programs.</p>
34
35<p>Please note that this tool is <b>very early</b> in development, and there are
36<b>many planned enhancements</b> to improve both the precision and scope of its
37analysis algorithms as well as the kinds bugs it will find.</p>
Ted Kremenekce2e3322008-04-25 18:44:36 +0000[diff] [blame]38
Ted Kremenekb8a522f2008-06-11 16:09:34 +0000[diff] [blame^]39<h3>High-Level Summary</h3>
40
41<p>Currently the analyzer is invoked as a command-line tool. It is intended to
42run in synchronous with a build of a project or code base. Analysis results are
43deposited in a directory as HTML files, which can then viewed using a web
44browser.</p>
45
46<p>The analyzer performs a variety of checks on code, each requiring different
47levels of analysis precision (more precision = more CPU time). While the
48analyzer is being designed to be as fast and light-weight as possible, please
49<b>do not expect it to be as fast as compiling a program</b> (even with
50optimizations enabled). Some of the algorithms needed to find bugs require in
51the worst case exponential time. The analyzer runs in a reasonable amount of
52time by both bounding the amount of checking work it will do as well as using
53clever algorithms to reduce the amount of work it must do to find bugs.</p>
54
55<h3>Organization</h3>
56
57<p>This page is arranged into the following sections:</p>
Ted Kremenekce2e3322008-04-25 18:44:36 +0000[diff] [blame]58
59<ul>
Ted Kremenekbd317162008-06-09 14:30:01 +0000[diff] [blame]60 <li><a href="#Contents">Obtaining the Analyzer</a></li>
Ted Kremenekce2e3322008-04-25 18:44:36 +0000[diff] [blame]61 <li><a href="#BasicUsage">Basic Usage</a></li>
Ted Kremenek891a3532008-04-25 20:29:37 +0000[diff] [blame]62 <li><a href="#Output">Output of the Analyzer</a></li>
63 <li><a href="#RecommendedUsageGuidelines">Recommended Usage Guidelines</a></li>
64 <li><a href="#Debugging">Debugging the Analyzer</a>
Ted Kremenekce2e3322008-04-25 18:44:36 +0000[diff] [blame]65</ul>
66
Ted Kremenekbd317162008-06-09 14:30:01 +0000[diff] [blame]67<h2 id="ReleaseContents">Obtaining the Analyzer</h2>
Ted Kremenekce2e3322008-04-25 18:44:36 +0000[diff] [blame]68
Ted Kremenekbe6e5162008-06-11 05:25:12 +0000[diff] [blame]69<p> Using the analyzer involves executing <tt>scan-build</tt> (see <a
70href="#BasicUsage">Basic Usage</a>). <tt>scan-build</tt> will first look for a
71<tt>clang</tt> executable in the same directory as <tt>scan-build</tt>, and then
72search your path.</p>
73
74<p>If one is using the analyzer directly from the Clang sources, it suffices to
75just directly execute <tt>scan-build</tt> in the <tt>utils</tt> directory. No
76other special installation is needed.</p>
77
78<h3>Packaged Builds (currently Mac-Only)</h3>
79
80<p>Semi-regular builds of the analyzer on Mac OS X (10.5) are available <a
Ted Kremenekbd317162008-06-09 14:30:01 +0000[diff] [blame]81href="http://keeda.stanford.edu/~kremenek/checker">here</a>. Packaged builds for
82other platforms may eventually be provided, but as the tool is in its early
Ted Kremenekbe6e5162008-06-11 05:25:12 +0000[diff] [blame]83stages we are not actively promoting releases yet. If you wish to help
84contribute regular builds of the analyzer on other platforms, please email the
85<a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">Clang Developers'
86mailing list</a>.</p>
Ted Kremenekbd317162008-06-09 14:30:01 +0000[diff] [blame]87
Ted Kremenekbe6e5162008-06-11 05:25:12 +0000[diff] [blame]88<p>Packaged builds of the analyzer expand to the following files:</p>
Ted Kremenekce2e3322008-04-25 18:44:36 +0000[diff] [blame]89
Ted Kremenekbe6e5162008-06-11 05:25:12 +0000[diff] [blame]90<table id="package">
Ted Kremenekce2e3322008-04-25 18:44:36 +0000[diff] [blame]91<thead><tr><td>File</td><td>Purpose</td></tr></thead>
92<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>
93<tr><td><tt>ccc-analyzer</tt></td><td>GCC interceptor (called by scan-build)</td></tr>
94<tr><td><tt>clang</tt></td><td>Static Analyzer (called by ccc-analyzer)</td><tr>
95<tr><td><tt>sorttable.js</tt></td><td>JavaScript used for displaying error reports</td></tr>
96</table>
97
Ted Kremenekbe6e5162008-06-11 05:25:12 +0000[diff] [blame]98<h3>Other Platforms (Building the Analyzer from Source)</h3>
99
100<p>Packaged builds simply consist of a few files from the Clang source tree,
101meaning that <b>anyone</b> who can build Clang can use the static analyzer.
102Please see the <a href="get_started.html">Getting Started</a> page for more
103details on downloading and compiling Clang.</p>
104
105<p>All files used by the analyzer (and included in packaged builds; <a
106href="#package">see above</a>) other than a compiled <tt>clang</tt> executable
107are found in the <tt>utils</tt> subdirectory in the Clang tree.</p>
Ted Kremenekbd317162008-06-09 14:30:01 +0000[diff] [blame]108
Ted Kremenekce2e3322008-04-25 18:44:36 +0000[diff] [blame]109<h2 id="BasicUsage">Basic Usage</h2>
110
111<p>The analyzer is executed from the command-line. To run the analyzer, you will
112use <tt>scan-build</tt> to analyze the source files compiled by <tt>gcc</tt>
113during a project build.</p>
114
115<p>For example, to analyze the files compiled under a build:</p>
116
117<pre>
118 $ <b>scan-build</b> make
119 $ <b>scan-build</b> xcodebuild
120</pre>
121
122<p> In the first case <tt>scan-build</tt> analyzes the code of a project built
123with <tt>make</tt>, andin the second case <tt>scan-build</tt> analyzes a project
124built using <tt>xcodebuild</tt>. In general, the format is: </p>
125
126<pre>
127 $ <b>scan-build</b> <i>[scan-build options]</i> <b>&lt;command&gt;</b> <i>[command options]</i>
128</pre>
129
130<p> Operationally, <tt>scan-build</tt> literally runs <command> with all of the
131subsequent options passed to it. For example</p>
132
133<pre>
134 $ scan-build make <b>-j4</b>
135</pre>
136
137<p>In this example, <tt>scan-build</tt> makes no effort to interpret the options
138after the build command (in this case, <tt>make</tt>); it just passes them
139through. In general, <tt>scan-build</tt> should support parallel builds, but
140<b>not distributed builds</b>. Similarly, you can use <tt>scan-build</tt> to
141analyze specific files:
142
143<pre>
144 $ scan-build gcc -c <b>t1.c t2.c</b>
145</pre>
146
147<p>
148This example causes the files <tt>t1.c</tt> and <tt>t2.c</tt> to be analyzed.
149</p>
150
151<h3>Other Options</h3>
152
153<p>
154As mentioned above, extra options can be passed to <tt>scan-build</tt>. These
155options prefix the build command. For example:</p>
156
157<pre>
158 $ scan-build <b>-k -V</b> make
159 $ scan-build <b>-k -V</b> xcodebuild
160</pre>
161
162<p>Here are a complete list of options:</p>
163
164<table>
165 <thead><tr><td>Option</td><td>Description</td></tr></thead>
166
Ted Kremenekbe6e5162008-06-11 05:25:12 +0000[diff] [blame]167 <tr><td><b>-a</b></td>
168 <td>The analysis to run. The default analysis is <i>checker-cfref</i>. Valid options are: <i>checker-cfref</i>, <i>fsyntax-only</i>.
169 These translate into options passed down to the <tt>clang</tt> executable, and currently this option is mainly used for debugging.</td></tr>
170
Ted Kremenekce2e3322008-04-25 18:44:36 +0000[diff] [blame]171 <tr><td><b>-o</b></td><td>Target directory for HTML report files. Subdirectories will be
172 created as needed to represent separate "runs" of the analyzer. If this option
173is not specified, a directory is created in <tt>/tmp</tt> to store the
174reports.</td><tr>
175
176 <tr><td><b>-h</b><br><i><nobr>(or no arguments)</nobr></i></td><td>Display <tt>scan-build</tt> options.</td></tr>
177
178 <tr><td><b>-k</b><br><nobr><b>--keep-going</b></nobr></td><td>Add a "keep on going" option to the
179 specified build command. <p>This option currently supports <tt>make</tt> and
180 <tt>xcodebuild</tt>.</p> <p>This is a convenience option; one can specify this
181 behavior directly using build options.</p></td></tr>
182
Ted Kremenekbe6e5162008-06-11 05:25:12 +0000[diff] [blame]183 <tr><td><b>-v<b></td><td>Verbose output from scan-build and the analyzer. <b>A second and third
Ted Kremenekce2e3322008-04-25 18:44:36 +0000[diff] [blame]184 "-v" increases verbosity</b>, and is useful for filing bug reports against the analyzer.</td></tr>
185
186 <tr><td><b>-V</b></td><td>View analysis results in a web browser when the build command completes.</td></tr>
187</table>
188
189<p>These options can also be viewed by running <tt>scan-build</tt> with no
190arguments:</p>
191
192<pre>
193 $ <b>scan-build</b>
194
195 USAGE: scan-build [options] &lt;build command&gt; [build options]
196
197 OPTIONS:
198
Ted Kremenekbe6e5162008-06-11 05:25:12 +0000[diff] [blame]199 -a - The analysis to run. The default is 'checker-cfref'.
200 Valid options are: 'checker-cfref', 'fsyntax-only'
201
Ted Kremenekce2e3322008-04-25 18:44:36 +0000[diff] [blame]202 -o - Target directory for HTML report files. Subdirectories
203 will be created as needed to represent separate "runs" of
204 the analyzer. If this option is not specified, a directory
205 is created in /tmp to store the reports.
206 <b>...</b>
207</pre>
208
209<h2 id="Output">Output of the Analyzer</h2>
210
211<p>
212The output of the analyzer is a set of HTML files, each one which represents a
213separate bug report. A single <tt>index.html</tt> file is generated for
214surveying all of the bugs. You can then just open <tt>index.html</tt> in a web
215browser to view the bug reports.
216</p>
217
218<p>
219Where the HTML files are generated is specified with a <b>-o</b> option to
Ted Kremenek87e795e2008-04-25 20:31:58 +0000[diff] [blame]220<tt>scan-build</tt>. If <b>-o</b> isn't specified, a directory in <tt>/tmp</tt>
Ted Kremenekce2e3322008-04-25 18:44:36 +0000[diff] [blame]221is created to store the files (<tt>scan-build</tt> will print a message telling
222you where they are). If you want to view the reports immediately after the build
223completes, pass <b>-V</b> to <tt>scan-build</tt>.
224</p>
225
226
Ted Kremenek904f1002008-04-25 20:30:34 +0000[diff] [blame]227<h2 id="RecommendedUsageGuidelines">Recommended Usage Guidelines</h2>
Ted Kremenekce2e3322008-04-25 18:44:36 +0000[diff] [blame]228
229Here are a few recommendations with running the analyzer:
230
231<h3>Always Analyze a Project in its "Debug" Configuration</h3>
232
233Most projects can be built in a "debug" mode that enables assertions. Assertions
234are picked up by the static analyzer to prune infeasible paths, which in some
235cases can greatly reduce the number of false positives (bogus error reports)
236emitted by the tool.
237
238<h3>Pass -k to <tt>scan-build</tt></h3>
239
240<p>While <tt>ccc-analyzer</tt> invokes <tt>gcc</tt> to compile code, any
241problems in correctly forwarding arguments to <tt>gcc</tt> may result in a build
242failure. Passing <b>-k</b> to <tt>scan-build</tt> potentially allows you to
243analyze other code in a project for which this problem doesn't occur.</p>
244
245<p> Also, it is useful to analyze a project even if not all of the source files
246are compilable. This is great when using <tt>scan-build</tt> as part of your
247compile-debug cycle.</p>
248
249<h3>Use Verbose Output when Debugging <tt>scan-build</tt></h3>
250
251<tt>scan-build</tt> takes a <b>-v</b> option to emit verbose output about what
252it's doing; two <b>-v</b> options emit more information. Redirecting the output
253of <tt>scan-build</tt> to a text file (make sure to redirect standard error) is
254useful for filing bug reports against <tt>scan-build</tt> or the analyzer, as we
255can see the exact options (and files) passed to the analyzer. For more
256comprehendible logs, don't perform a parallel build.
257
258<h2 id="Debugging">Debugging the Analyzer</h2>
259
260This section provides information on debugging the analyzer, and troubleshooting
261it when you have problems analyzing a particular project.
262
263<h3>How it Works</h3>
264
265To analyze a project, <tt>scan-build</tt> simply sets the environment variable
266<tt>CC</tt> to the full path to <tt>ccc-analyzer</tt>. It also sets a few other
267environment variables to communicate to <tt>ccc-analyzer</tt> where to dump HTML
268report files.
269
270<p>Some Makefiles (or equivalent project files) hardcode the compiler; for such
271projects simply overriding <tt>CC</tt> won't cause <tt>ccc-analyzer</tt> to be
272called. This will cause the compiled code <b>to not be analyzed.</b></p> If you
273find that your code isn't being analyzed, check to see if <tt>CC</tt> is
274hardcoded. If this is the case, you can hardcode it instead to the <b>full
275path</b> to <tt>ccc-analyzer</tt>.</p>
276
277<p>When applicable, you can also run <tt>./configure</tt> for a project through
278<tt>scan-build</tt> so that configure sets up the location of <tt>CC</tt> based
279on the environment passed in from <tt>scan-build</tt>:
280
281<pre>
282 $ scan-build <b>./configure</b>
283</pre>
284
285<p><tt>scan-build</tt> has special knowledge about <tt>configure</tt>, so it in
286most cases will not actually analyze the configure tests run by
287<tt>configure</tt>.</p>
288
289<p>Under the hood, <tt>ccc-analyzer</tt> directly invokes <tt>gcc</tt> to
290compile the actual code in addition to running the analyzer (which occurs by it
291calling <tt>clang</tt>). <tt>ccc-analyzer</tt> tries to correctly forward all
292the arguments over to <tt>gcc</tt>, but this may not work perfectly (please
293report bugs of this kind).
294
295<h3>Filing Bugs</h3>
296
297We encourage users to file bug reports for any problems that they encounter.
Ted Kremenekbe6e5162008-06-11 05:25:12 +0000[diff] [blame]298
299<p><b>Outside Apple</b>: Please <a
300href="http://llvm.org/bugs/enter_bug.cgi?product=clang">file bugs</a> (against
301Clang) in LLVM's Bugzilla database.</p>
302
303<p><b>Apple-internal</b>: Please file bugs in Radar against the <b>llvm - clang</b>
304component.</p>
305
Ted Kremenek20c5f142008-06-11 05:26:52 +0000[diff] [blame]306</div>
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