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16<div id="content">
17
18<h1>Clang Compiler User's Manual</h1>
19
20<ul>
21<li><a href="#intro">Introduction</a>
22 <ul>
23 <li><a href="#terminology">Terminology</a></li>
24 <li><a href="#basicusage">Basic Usage</a></li>
25 </ul>
26</li>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]27<li><a href="#commandline">Command Line Options</a>
28 <ul>
29 <li><a href="#cl_diagnostics">Options to Control Error and Warning
30 Messages</a></li>
31 </ul>
32</li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]33<li><a href="#general_features">Language and Target-Independent Features</a>
34 <ul>
35 <li><a href="#diagnostics">Controlling Errors and Warnings</a></li>
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]36 <ul>
37 <li><a href="#diagnostics_display">Controlling How Clang Displays Diagnostics</a></li>
38 <li><a href="#diagnostics_mappings">Diagnostic Mappings</a></li>
Chris Lattner67db8cd2010-05-30 23:42:51 +0000[diff] [blame]39 <li><a href="#diagnostics_categories">Diagnostic Categories</a></li>
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]40 <li><a href="#diagnostics_commandline">Controlling Diagnostics via Command Line Flags</a></li>
41 <li><a href="#diagnostics_pragmas">Controlling Diagnostics via Pragmas</a></li>
Ted Kremenek2fb11eb2010-08-24 18:12:35 +0000[diff] [blame]42 <li><a href="#analyzer_diagnositics">Controlling Static Analyzer Diagnostics</a></li>
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]43 </ul>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]44 <li><a href="#precompiledheaders">Precompiled Headers</a></li>
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]45 <li><a href="#codegen">Controlling Code Generation</a></li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]46 </ul>
47</li>
48<li><a href="#c">C Language Features</a>
49 <ul>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]50 <li><a href="#c_ext">Extensions supported by clang</a></li>
51 <li><a href="#c_modes">Differences between various standard modes</a></li>
52 <li><a href="#c_unimpl_gcc">GCC extensions not implemented yet</a></li>
53 <li><a href="#c_unsupp_gcc">Intentionally unsupported GCC extensions</a></li>
54 <li><a href="#c_ms">Microsoft extensions</a></li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]55 </ul>
56</li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]57<li><a href="#target_features">Target-Specific Features and Limitations</a>
58 <ul>
59 <li><a href="#target_arch">CPU Architectures Features and Limitations</a>
60 <ul>
61 <li><a href="#target_arch_x86">X86</a></li>
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]62 <li><a href="#target_arch_arm">ARM</a></li>
63 <li><a href="#target_arch_other">Other platforms</a></li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]64 </ul>
65 </li>
66 <li><a href="#target_os">Operating System Features and Limitations</a>
67 <ul>
68 <li><a href="#target_os_darwin">Darwin (Mac OS/X)</a></li>
69 <li>Linux, etc.</li>
70 </ul>
71
72 </li>
73 </ul>
74</li>
75</ul>
76
77
78<!-- ======================================================================= -->
79<h2 id="intro">Introduction</h2>
80<!-- ======================================================================= -->
81
82<p>The Clang Compiler is an open-source compiler for the C family of programming
83languages, aiming to be the best in class implementation of these languages.
84Clang builds on the LLVM optimizer and code generator, allowing it to provide
85high-quality optimization and code generation support for many targets. For
86more general information, please see the <a href="http://clang.llvm.org">Clang
87Web Site</a> or the <a href="http://llvm.org">LLVM Web Site</a>.</p>
88
89<p>This document describes important notes about using Clang as a compiler for
90an end-user, documenting the supported features, command line options, etc. If
91you are interested in using Clang to build a tool that processes code, please
92see <a href="InternalsManual.html">the Clang Internals Manual</a>. If you are
93interested in the <a href="http://clang.llvm.org/StaticAnalysis.html">Clang
94Static Analyzer</a>, please see its web page.</p>
95
96<p>Clang is designed to support the C family of programming languages, which
97includes <a href="#c">C</a>, <a href="#objc">Objective-C</a>, <a
98href="#cxx">C++</a>, and <a href="#objcxx">Objective-C++</a> as well as many
99dialects of those. For language-specific information, please see the
100corresponding language specific section:</p>
101
102<ul>
103<li><a href="#c">C Language</a>: K&amp;R C, ANSI C89, ISO C90, ISO C94
104 (C89+AMD1), ISO C99 (+TC1, TC2, TC3). </li>
105<li><a href="#objc">Objective-C Language</a>: ObjC 1, ObjC 2, ObjC 2.1, plus
106 variants depending on base language.</li>
107<li><a href="#cxx">C++ Language Features</a></li>
108<li><a href="#objcxx">Objective C++ Language</a></li>
109</ul>
110
111<p>In addition to these base languages and their dialects, Clang supports a
112broad variety of language extensions, which are documented in the corresponding
113language section. These extensions are provided to be compatible with the GCC,
114Microsoft, and other popular compilers as well as to improve functionality
115through Clang-specific features. The Clang driver and language features are
116intentionally designed to be as compatible with the GNU GCC compiler as
117reasonably possible, easing migration from GCC to Clang. In most cases, code
118"just works".</p>
119
120<p>In addition to language specific features, Clang has a variety of features
121that depend on what CPU architecture or operating system is being compiled for.
Douglas Gregorcd5a5052009-11-09 15:15:41 +0000[diff] [blame]122Please see the <a href="#target_features">Target-Specific Features and
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]123Limitations</a> section for more details.</p>
124
125<p>The rest of the introduction introduces some basic <a
126href="#terminology">compiler terminology</a> that is used throughout this manual
127and contains a basic <a href="#basicusage">introduction to using Clang</a>
128as a command line compiler.</p>
129
130<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
131<h3 id="terminology">Terminology</h3>
132<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
133
134<p>Front end, parser, backend, preprocessor, undefined behavior, diagnostic,
135 optimizer</p>
136
137<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
138<h3 id="basicusage">Basic Usage</h3>
139<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
140
141<p>Intro to how to use a C compiler for newbies.</p>
142<p>
143compile + link
144
145compile then link
146
147debug info
148
149enabling optimizations
150
151picking a language to use, defaults to C99 by default. Autosenses based on
152extension.
153
154using a makefile
155</p>
156
157
158<!-- ======================================================================= -->
159<h2 id="commandline">Command Line Options</h2>
160<!-- ======================================================================= -->
161
162<p>
163This section is generally an index into other sections. It does not go into
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]164depth on the ones that are covered by other sections. However, the first part
165introduces the language selection and other high level options like -c, -g, etc.
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]166</p>
167
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]168
169<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
170<h3 id="cl_diagnostics">Options to Control Error and Warning Messages</h3>
171<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
172
173<p><b>-Werror</b>: Turn warnings into errors.</p>
174<p><b>-Werror=foo</b>: Turn warning "foo" into an error.</p>
175<p><b>-Wno-error=foo</b>: Turn warning "foo" into an warning even if -Werror is
176 specified.</p>
177<p><b>-Wfoo</b>: Enable warning foo</p>
178<p><b>-Wno-foo</b>: Disable warning foo</p>
179<p><b>-w</b>: Disable all warnings.</p>
180<p><b>-pedantic</b>: Warn on language extensions.</p>
181<p><b>-pedantic-errors</b>: Error on language extensions.</p>
182<p><b>-Wsystem-headers</b>: Enable warnings from system headers.</p>
183
Chris Lattner0f0c9632010-04-07 20:49:23 +0000[diff] [blame]184<p><b>-ferror-limit=123</b>: Stop emitting diagnostics after 123 errors have
185 been produced. The default is 20, and the error limit can be disabled with
186 -ferror-limit=0.</p>
187
Douglas Gregor575cf372010-04-20 07:18:24 +0000[diff] [blame]188<p><b>-ftemplate-backtrace-limit=123</b>: Only emit up to 123 template instantiation notes within the template instantiation backtrace for a single warning or error. The default is 10, and the limit can be disabled with -ftemplate-backtrace-limit=0.</p>
189
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]190<!-- ================================================= -->
191<h4 id="cl_diag_formatting">Formatting of Diagnostics</h4>
192<!-- ================================================= -->
193
194<p>Clang aims to produce beautiful diagnostics by default, particularly for new
195users that first come to Clang. However, different people have different
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]196preferences, and sometimes Clang is driven by another program that wants to
197parse simple and consistent output, not a person. For these cases, Clang
198provides a wide range of options to control the exact output format of the
199diagnostics that it generates.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]200
201<dl>
202
203<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
204<dt id="opt_fshow-column"><b>-f[no-]show-column</b>: Print column number in
205diagnostic.</dt>
206<dd>This option, which defaults to on, controls whether or not Clang prints the
207column number of a diagnostic. For example, when this is enabled, Clang will
208print something like:</p>
209
210<pre>
211 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
212 #endif bad
213 ^
214 //
215</pre>
216
217<p>When this is disabled, Clang will print "test.c:28: warning..." with no
218column number.</p>
219</dd>
220
221<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
222<dt id="opt_fshow-source-location"><b>-f[no-]show-source-location</b>: Print
223source file/line/column information in diagnostic.</dt>
224<dd>This option, which defaults to on, controls whether or not Clang prints the
225filename, line number and column number of a diagnostic. For example,
226when this is enabled, Clang will print something like:</p>
227
228<pre>
229 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
230 #endif bad
231 ^
232 //
233</pre>
234
235<p>When this is disabled, Clang will not print the "test.c:28:8: " part.</p>
236</dd>
237
238<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
239<dt id="opt_fcaret-diagnostics"><b>-f[no-]caret-diagnostics</b>: Print source
240line and ranges from source code in diagnostic.</dt>
241<dd>This option, which defaults to on, controls whether or not Clang prints the
242source line, source ranges, and caret when emitting a diagnostic. For example,
243when this is enabled, Clang will print something like:</p>
244
245<pre>
246 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
247 #endif bad
248 ^
249 //
250</pre>
251
252<p>When this is disabled, Clang will just print:</p>
253
254<pre>
Douglas Gregore8d44dd2010-07-09 16:31:58 +0000[diff] [blame]255 <b><font color="black">test.c:28:8: <font color="magenta">warning</font>: extra tokens at end of #endif directive [-Wextra-tokens]</font></b>
256 #endif bad
257 <font color="green">^</font>
258 <font color="green">//</font>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]259</pre>
260
261</dd>
262
263<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Douglas Gregore8d44dd2010-07-09 16:31:58 +0000[diff] [blame]264<dt id="opt_fcolor_diagnostics"><b>-f[no-]color-diagnostics</b>: </dt>
265<dd>This option, which defaults to on when a color-capable terminal is
266 detected, controls whether or not Clang prints diagnostics in color.
267 When this option is enabled, Clang will use colors to highlight
268 specific parts of the diagnostic, e.g.,
269
270<pre>
271<test.c:2:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
272#endif bad
273 ^
274 //
275</pre>
276</dd>'
277<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]278<dt id="opt_fdiagnostics-show-option"><b>-f[no-]diagnostics-show-option</b>:
279Enable <tt>[-Woption]</tt> information in diagnostic line.</dt>
280<dd>This option, which defaults to on,
281controls whether or not Clang prints the associated <A
282href="#cl_diag_warning_groups">warning group</a> option name when outputting
283a warning diagnostic. For example, in this output:</p>
284
285<pre>
286 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
287 #endif bad
288 ^
289 //
290</pre>
291
292<p>Passing <b>-fno-diagnostics-show-option</b> will prevent Clang from printing
293the [<a href="#opt_Wextra-tokens">-Wextra-tokens</a>] information in the
294diagnostic. This information tells you the flag needed to enable or disable the
295diagnostic, either from the command line or through <a
296href="#pragma_GCC_diagnostic">#pragma GCC diagnostic</a>.</dd>
297
Chris Lattner28a43a42010-05-05 01:35:28 +0000[diff] [blame]298<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
299<dt id="opt_fdiagnostics-show-category"><b>-fdiagnostics-show-category=none/id/name</b>:
300Enable printing category information in diagnostic line.</dt>
301<dd>This option, which defaults to "none",
302controls whether or not Clang prints the category associated with a diagnostic
303when emitting it. Each diagnostic may or many not have an associated category,
304if it has one, it is listed in the diagnostic categorization field of the
305diagnostic line (in the []'s).</p>
306
307<p>For example, a format string warning will produce these three renditions
308based on the setting of this option:</p>
309
310<pre>
311 t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat]
312 t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat<b>,1</b>]
313 t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat<b>,Format String</b>]
314</pre>
315
316<p>This category can be used by clients that want to group diagnostics by
317category, so it should be a high level category. We want dozens of these, not
318hundreds or thousands of them.</p>
319</dd>
320
321
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]322
323<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
324<dt id="opt_fdiagnostics-fixit-info"><b>-f[no-]diagnostics-fixit-info</b>:
325Enable "FixIt" information in the diagnostics output.</dt>
326<dd>This option, which defaults to on, controls whether or not Clang prints the
327information on how to fix a specific diagnostic underneath it when it knows.
328For example, in this output:</p>
329
330<pre>
331 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
332 #endif bad
333 ^
334 //
335</pre>
336
337<p>Passing <b>-fno-diagnostics-fixit-info</b> will prevent Clang from printing
338the "//" line at the end of the message. This information is useful for users
339who may not understand what is wrong, but can be confusing for machine
340parsing.</p>
341</dd>
342
343<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]344<dt id="opt_fdiagnostics-print-source-range-info">
345<b>-f[no-]diagnostics-print-source-range-info</b>:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]346Print machine parsable information about source ranges.</dt>
347<dd>This option, which defaults to off, controls whether or not Clang prints
348information about source ranges in a machine parsable format after the
349file/line/column number information. The information is a simple sequence of
350brace enclosed ranges, where each range lists the start and end line/column
351locations. For example, in this output:</p>
352
353<pre>
354exprs.c:47:15:{47:8-47:14}{47:17-47:24}: error: invalid operands to binary expression ('int *' and '_Complex float')
355 P = (P-42) + Gamma*4;
356 ~~~~~~ ^ ~~~~~~~
357</pre>
358
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]359<p>The {}'s are generated by -fdiagnostics-print-source-range-info.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]360</dd>
361
Douglas Gregor4786c152010-08-19 20:24:43 +0000[diff] [blame]362<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
363<dt id="opt_fdiagnostics-parseable-fixits">
364<b>-fdiagnostics-parseable-fixits</b>:
365Print Fix-Its in a machine parseable form.</dt>
366<dd><p>This option makes Clang print available Fix-Its in a machine parseable format at the end of diagnostics. The following example illustrates the format:</p>
367
368<pre>
Douglas Gregorbf5e09d2010-08-20 03:17:33 +0000[diff] [blame]369 fix-it:"t.cpp":{7:25-7:29}:"Gamma"
Douglas Gregor4786c152010-08-19 20:24:43 +0000[diff] [blame]370</pre>
371
Douglas Gregoree45e242010-08-23 14:03:03 +0000[diff] [blame]372<p>The range printed is a half-open range, so in this example the characters at column 25 up to but not including column 29 on line 7 in t.cpp should be replaced with the string "Gamma". Either the range or the replacement string may be empty (representing strict insertions and strict erasures, respectively). Both the file name and the insertion string escape backslash (as "\\"), tabs (as "\t"), newlines (as "\n"), double quotes(as "\"") and non-printable characters (as octal "\xxx").</p>
Douglas Gregor4786c152010-08-19 20:24:43 +0000[diff] [blame]373</dd>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]374
375</dl>
376
377
378
379
380<!-- ===================================================== -->
381<h4 id="cl_diag_warning_groups">Individual Warning Groups</h4>
382<!-- ===================================================== -->
383
384<p>TODO: Generate this from tblgen. Define one anchor per warning group.</p>
385
386
387<dl>
388
389
390<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
391<dt id="opt_Wextra-tokens"><b>-Wextra-tokens</b>: Warn about excess tokens at
392 the end of a preprocessor directive.</dt>
393<dd>This option, which defaults to on, enables warnings about extra tokens at
394the end of preprocessor directives. For example:</p>
395
396<pre>
397 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
398 #endif bad
399 ^
400</pre>
401
402<p>These extra tokens are not strictly conforming, and are usually best handled
403by commenting them out.</p>
404
405<p>This option is also enabled by <a href="">-Wfoo</a>, <a href="">-Wbar</a>,
406 and <a href="">-Wbaz</a>.</p>
407</dd>
408
Jeffrey Yasskin21d07e42010-06-05 01:39:57 +0000[diff] [blame]409<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
410<dt id="opt_Wambiguous-member-template"><b>-Wambiguous-member-template</b>:
411Warn about unqualified uses of a member template whose name resolves
412to another template at the location of the use.</dt>
413<dd>This option, which defaults to on, enables a warning in the
414following code:</p>
415
416<pre>
417template&lt;typename T> struct set{};
418template&lt;typename T> struct trait { typedef const T& type; };
419struct Value {
420 template&lt;typename T> void set(typename trait&lt;T>::type value) {}
421};
422void foo() {
423 Value v;
424 v.set&lt;double>(3.2);
425}
426</pre>
427
428<p>C++ [basic.lookup.classref] requires this to be an error, but,
429because it's hard to work around, Clang downgrades it to a warning as
430an extension.</p>
431</dd>
432
Jeffrey Yasskin57d12fd2010-06-07 15:58:05 +0000[diff] [blame]433<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
434<dt id="opt_Wbind-to-temporary-copy"><b>-Wbind-to-temporary-copy</b>: Warn about
435an unusable copy constructor when binding a reference to a temporary.</dt>
436<dd>This option, which defaults to on, enables warnings about binding a
437reference to a temporary when the temporary doesn't have a usable copy
438constructor. For example:</p>
439
440<pre>
441 struct NonCopyable {
442 NonCopyable();
443 private:
444 NonCopyable(const NonCopyable&);
445 };
446 void foo(const NonCopyable&);
447 void bar() {
448 foo(NonCopyable()); // Disallowed in C++98; allowed in C++0x.
449 }
450</pre>
451<pre>
452 struct NonCopyable2 {
453 NonCopyable2();
454 NonCopyable2(NonCopyable2&);
455 };
456 void foo(const NonCopyable2&);
457 void bar() {
458 foo(NonCopyable2()); // Disallowed in C++98; allowed in C++0x.
459 }
460</pre>
461
462<p>Note that if <tt>NonCopyable2::NonCopyable2()</tt> has a default
463argument whose instantiation produces a compile error, that error will
464still be a hard error in C++98 mode even if this warning is turned
465off.</p>
466
467</dd>
468
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]469</dl>
470
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]471<!-- ======================================================================= -->
472<h2 id="general_features">Language and Target-Independent Features</h2>
473<!-- ======================================================================= -->
474
475
476<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
477<h3 id="diagnostics">Controlling Errors and Warnings</h3>
478<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
479
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]480<p>Clang provides a number of ways to control which code constructs cause it to
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]481emit errors and warning messages, and how they are displayed to the console.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]482
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]483<h4 id="diagnostics_display">Controlling How Clang Displays Diagnostics</h4>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]484
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]485<p>When Clang emits a diagnostic, it includes rich information in the output,
486and gives you fine-grain control over which information is printed. Clang has
487the ability to print this information, and these are the options that control
488it:</p>
489
490<p>
491<ol>
492<li>A file/line/column indicator that shows exactly where the diagnostic occurs
493 in your code [<a href="#opt_fshow-column">-fshow-column</a>, <a
494 href="#opt_fshow-source-location">-fshow-source-location</a>].</li>
495<li>A categorization of the diagnostic as a note, warning, error, or fatal
496 error.</li>
497<li>A text string that describes what the problem is.</li>
498<li>An option that indicates how to control the diagnostic (for diagnostics that
499 support it) [<a
500 href="#opt_fdiagnostics-show-option">-fdiagnostics-show-option</a>].</li>
Chris Lattner3f145382010-05-24 21:35:18 +0000[diff] [blame]501<li>A <a href="#diagnostics_categories">high-level category</a> for the
502 diagnostic for clients that want to group diagnostics by class (for
503 diagnostics that support it) [<a
Chris Lattner28a43a42010-05-05 01:35:28 +0000[diff] [blame]504 href="#opt_fdiagnostics-show-category">-fdiagnostics-show-category</a>].</li>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]505<li>The line of source code that the issue occurs on, along with a caret and
506 ranges that indicate the important locations [<a
507 href="opt_fcaret-diagnostics">-fcaret-diagnostics</a>].</li>
508<li>"FixIt" information, which is a concise explanation of how to fix the
509 problem (when Clang is certain it knows) [<a
510 href="opt_fdiagnostics-fixit-info">-fdiagnostics-fixit-info</a>].</li>
511<li>A machine-parsable representation of the ranges involved (off by
512 default) [<a
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]513 href="opt_fdiagnostics-print-source-range-info">-fdiagnostics-print-source-range-info</a>].</li>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]514</ol></p>
515
516<p>For more information please see <a href="#cl_diag_formatting">Formatting of
517Diagnostics</a>.</p>
518
Chris Lattner3f145382010-05-24 21:35:18 +0000[diff] [blame]519
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]520<h4 id="diagnostics_mappings">Diagnostic Mappings</h4>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]521
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]522<p>All diagnostics are mapped into one of these 5 classes:</p>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]523
524<p>
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]525<ul>
526<li>Ignored</li>
527<li>Note</li>
528<li>Warning</li>
529<li>Error</li>
530<li>Fatal</li>
531</ul></p>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]532
Chris Lattner3f145382010-05-24 21:35:18 +0000[diff] [blame]533<h4 id="diagnostics_categories">Diagnostic Categories</h4>
534
535<p>Though not shown by default, diagnostics may each be associated with a
536 high-level category. This category is intended to make it possible to triage
537 builds that produce a large number of errors or warnings in a grouped way.
538</p>
539
540<p>Categories are not shown by default, but they can be turned on with the
541<a href="#opt_fdiagnostics-show-category">-fdiagnostics-show-category</a> option.
542When set to "<tt>name</tt>", the category is printed textually in the diagnostic
543output. When it is set to "<tt>id</tt>", a category number is printed. The
544mapping of category names to category id's can be obtained by running '<tt>clang
545 --print-diagnostic-categories</tt>'.
546</p>
547
548<h4 id="diagnostics_commandline">Controlling Diagnostics via Command Line
549 Flags</h4>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]550
551<p>-W flags, -pedantic, etc</p>
552
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]553<h4 id="diagnostics_pragmas">Controlling Diagnostics via Pragmas</h4>
554
555<p>Clang can also control what diagnostics are enabled through the use of
556pragmas in the source code. This is useful for turning off specific warnings
557in a section of source code. Clang supports GCC's pragma for compatibility
558with existing source code, as well as several extensions. </p>
559
560<p>The pragma may control any warning that can be used from the command line.
561Warnings may be set to ignored, warning, error, or fatal. The following
562example code will tell Clang or GCC to ignore the -Wall warnings:</p>
563
564<pre>
565#pragma GCC diagnostic ignored "-Wall"
566</pre>
567
568<p>In addition to all of the functionality of provided by GCC's pragma, Clang
569also allows you to push and pop the current warning state. This is particularly
570useful when writing a header file that will be compiled by other people, because
571you don't know what warning flags they build with.</p>
572
573<p>In the below example
574-Wmultichar is ignored for only a single line of code, after which the
575diagnostics return to whatever state had previously existed.</p>
576
577<pre>
578#pragma clang diagnostic push
579#pragma clang diagnostic ignored "-Wmultichar"
580
581char b = 'df'; // no warning.
582
583#pragma clang diagnostic pop
584</pre>
585
586<p>The push and pop pragmas will save and restore the full diagnostic state of
587the compiler, regardless of how it was set. That means that it is possible to
588use push and pop around GCC compatible diagnostics and Clang will push and pop
589them appropriately, while GCC will ignore the pushes and pops as unknown
590pragmas. It should be noted that while Clang supports the GCC pragma, Clang and
591GCC do not support the exact same set of warnings, so even when using GCC
592compatible #pragmas there is no guarantee that they will have identical behaviour
593on both compilers. </p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]594
Ted Kremenek2fb11eb2010-08-24 18:12:35 +0000[diff] [blame]595<h4 id="analyzer_diagnositics">Controlling Static Analyzer Diagnostics</h4>
596
597<p>While not strictly part of the compiler, the diagnostics from Clang's <a
598href="http://clang-analyzer.llvm.org">static analyzer</a> can also be influenced
599by the user via changes to the source code. This can be done in two ways:
600
601<ul>
602
603<li id="analyzer_annotations"><b>Annotations</b>: The static analyzer recognizes various GCC-style
604attributes (e.g., <tt>__attribute__((nonnull)))</tt>) that can either suppress
605static analyzer warnings or teach the analyzer about code invariants which
606enable it to find more bugs. While many of these attributes are standard GCC
607attributes, additional ones have added to Clang to specifically support the
608static analyzer. Detailed information on these annotations can be found in the
609<a href="http://clang-analyzer.llvm.org/annotations.html">analyzer's
610documentation</a>.</li>
611
612<li><b><tt>__clang_analyzer__</tt></b>: When the static analyzer is using Clang
613to parse source files, it implicitly defines the preprocessor macro
614<tt>__clang_analyzer__</tt>. While discouraged, code can use this macro to
615selectively exclude code the analyzer examines. Here is an example:
616
617<pre>
618#ifndef __clang_analyzer__
619// Code not to be analyzed
620#endif
621</pre>
622
623In general, this usage is discouraged. Instead, we prefer that users file bugs
624against the analyzer when it flags false positives. There is also active
625discussion of allowing users in the future to selectively silence specific
626analyzer warnings (some which can already be done using <a
627href="analyzer_annotations">annotations</a>).</li>
628
629</ul>
630
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]631<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
632<h3 id="precompiledheaders">Precompiled Headers</h3>
633<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
634
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]635<p><a href="http://en.wikipedia.org/wiki/Precompiled_header">Precompiled
636headers</a> are a general approach employed by many compilers to reduce
637compilation time. The underlying motivation of the approach is that it is
638common for the same (and often large) header files to be included by
639multiple source files. Consequently, compile times can often be greatly improved
640by caching some of the (redundant) work done by a compiler to process headers.
641Precompiled header files, which represent one of many ways to implement
642this optimization, are literally files that represent an on-disk cache that
643contains the vital information necessary to reduce some of the work
644needed to process a corresponding header file. While details of precompiled
645headers vary between compilers, precompiled headers have been shown to be a
646highly effective at speeding up program compilation on systems with very large
647system headers (e.g., Mac OS/X).</p>
648
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]649<h4>Generating a PCH File</h4>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]650
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]651<p>To generate a PCH file using Clang, one invokes Clang with
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]652the <b><tt>-x <i>&lt;language&gt;</i>-header</tt></b> option. This mirrors the
653interface in GCC for generating PCH files:</p>
654
655<pre>
656 $ gcc -x c-header test.h -o test.h.gch
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]657 $ clang -x c-header test.h -o test.h.pch
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]658</pre>
659
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]660<h4>Using a PCH File</h4>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]661
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]662<p>A PCH file can then be used as a prefix header when a
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]663<b><tt>-include</tt></b> option is passed to <tt>clang</tt>:</p>
664
665<pre>
666 $ clang -include test.h test.c -o test
667</pre>
668
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]669<p>The <tt>clang</tt> driver will first check if a PCH file for <tt>test.h</tt>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]670is available; if so, the contents of <tt>test.h</tt> (and the files it includes)
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]671will be processed from the PCH file. Otherwise, Clang falls back to
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]672directly processing the content of <tt>test.h</tt>. This mirrors the behavior of
673GCC.</p>
674
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]675<p><b>NOTE:</b> Clang does <em>not</em> automatically use PCH files
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]676for headers that are directly included within a source file. For example:</p>
677
678<pre>
Chris Lattnere42ec542009-06-13 20:35:58 +0000[diff] [blame]679 $ clang -x c-header test.h -o test.h.pch
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]680 $ cat test.c
681 #include "test.h"
682 $ clang test.c -o test
683</pre>
684
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]685<p>In this example, <tt>clang</tt> will not automatically use the PCH file for
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]686<tt>test.h</tt> since <tt>test.h</tt> was included directly in the source file
687and not specified on the command line using <tt>-include</tt>.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]688
Douglas Gregore650c8c2009-07-07 00:12:59 +0000[diff] [blame]689<h4>Relocatable PCH Files</h4>
690<p>It is sometimes necessary to build a precompiled header from headers that
691are not yet in their final, installed locations. For example, one might build a
692precompiled header within the build tree that is then meant to be installed
693alongside the headers. Clang permits the creation of "relocatable" precompiled
694headers, which are built with a given path (into the build directory) and can
695later be used from an installed location.</p>
696
697<p>To build a relocatable precompiled header, place your headers into a
698subdirectory whose structure mimics the installed location. For example, if you
699want to build a precompiled header for the header <code>mylib.h</code> that
700will be installed into <code>/usr/include</code>, create a subdirectory
701<code>build/usr/include</code> and place the header <code>mylib.h</code> into
702that subdirectory. If <code>mylib.h</code> depends on other headers, then
703they can be stored within <code>build/usr/include</code> in a way that mimics
704the installed location.</p>
705
706<p>Building a relocatable precompiled header requires two additional arguments.
707First, pass the <code>--relocatable-pch</code> flag to indicate that the
708resulting PCH file should be relocatable. Second, pass
709<code>-isysroot /path/to/build</code>, which makes all includes for your
710library relative to the build directory. For example:</p>
711
712<pre>
713 # clang -x c-header --relocatable-pch -isysroot /path/to/build /path/to/build/mylib.h mylib.h.pch
714</pre>
715
716<p>When loading the relocatable PCH file, the various headers used in the PCH
717file are found from the system header root. For example, <code>mylib.h</code>
718can be found in <code>/usr/include/mylib.h</code>. If the headers are installed
719in some other system root, the <code>-isysroot</code> option can be used provide
720a different system root from which the headers will be based. For example,
721<code>-isysroot /Developer/SDKs/MacOSX10.4u.sdk</code> will look for
722<code>mylib.h</code> in
723<code>/Developer/SDKs/MacOSX10.4u.sdk/usr/include/mylib.h</code>.</p>
724
725<p>Relocatable precompiled headers are intended to be used in a limited number
726of cases where the compilation environment is tightly controlled and the
727precompiled header cannot be generated after headers have been installed.
728Relocatable precompiled headers also have some performance impact, because
729the difference in location between the header locations at PCH build time vs.
730at the time of PCH use requires one of the PCH optimizations,
731<code>stat()</code> caching, to be disabled. However, this change is only
732likely to affect PCH files that reference a large number of headers.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]733
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]734<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
735<h3 id="codegen">Controlling Code Generation</h3>
736<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
737
738<p>Clang provides a number of ways to control code generation. The options are listed below.</p>
739
740<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
741<dt id="opt_fcatch-undefined-behavior"><b>-fcatch-undefined-behavior</b>: Turn
742on runtime code generation to check for undefined behavior.</dt>
743
744<dd>This option, which defaults to off, controls whether or not Clang
745adds runtime checks for undefined runtime behavior. If the check fails,
746<tt>__builtin_trap()</tt> is used to indicate failure.
747The checks are:
748<p>
Mike Stump88b2a172009-12-16 03:25:12 +0000[diff] [blame]749<li>Subscripting where the static type of one operand is variable
750 which is decayed from an array type and the other operand is
751 greater than the size of the array or less than zero.</li>
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]752<li>Shift operators where the amount shifted is greater or equal to the
753 promoted bit-width of the left-hand-side or less than zero.</li>
Mike Stump8f6a3ed2009-12-16 03:18:14 +0000[diff] [blame]754<li>If control flow reaches __builtin_unreachable.
755<li>When llvm implements more __builtin_object_size support, reads and
756 writes for objects that __builtin_object_size indicates we aren't
757 accessing valid memory. Bit-fields and vectors are not yet checked.
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]758</p>
759</dd>
760
Nuno Lopesaa526242009-12-17 10:00:52 +0000[diff] [blame]761<dt id="opt_fno-assume-sane-operator-new"><b>-fno-assume-sane-operator-new</b>:
762Don't assume that the C++'s new operator is sane.</dt>
Nuno Lopesb23f20d2009-12-17 10:15:49 +0000[diff] [blame]763<dd>This option tells the compiler to do not assume that C++'s global new
764operator will always return a pointer that do not
Nuno Lopesaa526242009-12-17 10:00:52 +0000[diff] [blame]765alias any other pointer when the function returns.</dd>
766
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]767<!-- ======================================================================= -->
768<h2 id="c">C Language Features</h2>
769<!-- ======================================================================= -->
770
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]771<p>The support for standard C in clang is feature-complete except for the C99
772floating-point pragmas.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]773
774<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]775<h3 id="c_ext">Extensions supported by clang</h3>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]776<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
777
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]778<p>See <a href="LanguageExtensions.html">clang language extensions</a>.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]779
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]780<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
781<h3 id="c_modes">Differences between various standard modes</h3>
782<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]783
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]784<p>clang supports the -std option, which changes what language mode clang uses.
785The supported modes for C are c89, gnu89, c94, c99, gnu99 and various aliases
786for those modes. If no -std option is specified, clang defaults to gnu99 mode.
787</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]788
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]789<p>Differences between all c* and gnu* modes:</p>
790<ul>
791<li>c* modes define "__STRICT_ANSI__".</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]792<li>Target-specific defines not prefixed by underscores, like "linux", are
793defined in gnu* modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]794<li>Trigraphs default to being off in gnu* modes; they can be enabled by the
795-trigraphs option.</li>
796<li>The parser recognizes "asm" and "typeof" as keywords in gnu* modes; the
797variants "__asm__" and "__typeof__" are recognized in all modes.</li>
Eli Friedmanb0ac5452009-05-16 23:17:30 +0000[diff] [blame]798<li>The Apple "blocks" extension is recognized by default in gnu* modes
799on some platforms; it can be enabled in any mode with the "-fblocks"
800option.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]801</ul>
802
803<p>Differences between *89 and *99 modes:</p>
804<ul>
805<li>The *99 modes default to implementing "inline" as specified in C99, while
806the *89 modes implement the GNU version. This can be overridden for individual
807functions with the __gnu_inline__ attribute.</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]808<li>Digraphs are not recognized in c89 mode.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]809<li>The scope of names defined inside a "for", "if", "switch", "while", or "do"
810statement is different. (example: "if ((struct x {int x;}*)0) {}".)</li>
811<li>__STDC_VERSION__ is not defined in *89 modes.</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]812<li>"inline" is not recognized as a keyword in c89 mode.</li>
813<li>"restrict" is not recognized as a keyword in *89 modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]814<li>Commas are allowed in integer constant expressions in *99 modes.</li>
815<li>Arrays which are not lvalues are not implicitly promoted to pointers in
816*89 modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]817<li>Some warnings are different.</li>
818</ul>
819
820<p>c94 mode is identical to c89 mode except that digraphs are enabled in
821c94 mode (FIXME: And __STDC_VERSION__ should be defined!).</p>
822
823<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
824<h3 id="c_unimpl_gcc">GCC extensions not implemented yet</h3>
825<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
826
827<p>clang tries to be compatible with gcc as much as possible, but some gcc
828extensions are not implemented yet:</p>
829
830<ul>
831<li>clang does not support __label__
832(<a href="http://llvm.org/bugs/show_bug.cgi?id=3429">bug 3429</a>). This is
833a relatively small feature, so it is likely to be implemented relatively
834soon.</li>
835
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]836<li>clang does not support #pragma weak
Eli Friedman4da92552009-06-02 08:21:31 +0000[diff] [blame]837(<a href="http://llvm.org/bugs/show_bug.cgi?id=3679">bug 3679</a>). Due to
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]838the uses described in the bug, this is likely to be implemented at some
839point, at least partially.</li>
840
Eli Friedman4da92552009-06-02 08:21:31 +0000[diff] [blame]841<li>clang does not support code generation for local variables pinned to
842registers (<a href="http://llvm.org/bugs/show_bug.cgi?id=3933">bug 3933</a>).
843This is a relatively small feature, so it is likely to be implemented
844relatively soon.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]845
846<li>clang does not support decimal floating point types (_Decimal32 and
847friends) or fixed-point types (_Fract and friends); nobody has expressed
848interest in these features yet, so it's hard to say when they will be
849implemented.</li>
850
851<li>clang does not support nested functions; this is a complex feature which
852is infrequently used, so it is unlikely to be implemented anytime soon.</li>
853
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]854<li>clang does not support global register variables, this is unlikely
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]855to be implemented soon because it requires additional LLVM backend support.
856</li>
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]857
858<li>clang does not support static initialization of flexible array
859members. This appears to be a rarely used extension, but could be
860implemented pending user demand.</li>
861
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]862<li>clang does not support __builtin_va_arg_pack/__builtin_va_arg_pack_len.
863This is used rarely, but in some potentially interesting places, like the
864glibc headers, so it may be implemented pending user demand. Note that
865because clang pretends to be like GCC 4.2, and this extension was introduced
866in 4.3, the glibc headers will not try to use this extension with clang at
867the moment.</li>
868
869<li>clang does not support the gcc extension for forward-declaring function
870parameters; this has not showed up in any real-world code yet, though, so it
871might never be implemented.</li>
872
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]873</ul>
874
875<p>This is not a complete list; if you find an unsupported extension
876missing from this list, please send an e-mail to cfe-dev. This list
877currently excludes C++; see <a href="#cxx">C++ Language Features</a>.
878Also, this list does not include bugs in mostly-implemented features; please
879see the <a href="http://llvm.org/bugs/buglist.cgi?quicksearch=product%3Aclang+component%3A-New%2BBugs%2CAST%2CBasic%2CDriver%2CHeaders%2CLLVM%2BCodeGen%2Cparser%2Cpreprocessor%2CSemantic%2BAnalyzer">
880bug tracker</a> for known existing bugs (FIXME: Is there a section for
881bug-reporting guidelines somewhere?).</p>
882
883<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
884<h3 id="c_unsupp_gcc">Intentionally unsupported GCC extensions</h3>
885<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
886
Eli Friedman0b326002009-06-12 20:11:05 +0000[diff] [blame]887<ul>
888
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]889<li>clang does not support the gcc extension that allows variable-length arrays
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]890in structures. This is for a few of reasons: one, it is tricky
891to implement, two, the extension is completely undocumented, and three, the
Chris Lattnerb9d511c2010-10-28 02:20:32 +0000[diff] [blame]892extension appears to be rarely used. Note that clang <em>does</em> support
893flexible array members (arrays with a zero or unspecified size at the end of
894a structure).</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]895
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]896<li>clang does not support duplicate definitions of a function where one is
Daniel Dunbarc5f928c2009-06-04 18:37:52 +0000[diff] [blame]897inline. This complicates clients of the AST which normally can expect there is
898at most one definition for each function. Source code using this feature should
899be changed to define the inline and out-of-line definitions in separate
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]900translation units.</li>
Daniel Dunbarc5f928c2009-06-04 18:37:52 +0000[diff] [blame]901
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]902<li>clang does not have an equivalent to gcc's "fold"; this means that
903clang doesn't accept some constructs gcc might accept in contexts where a
904constant expression is required, like "x-x" where x is a variable, or calls
905to C library functions like strlen.</li>
906
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]907<li>clang does not support multiple alternative constraints in inline asm; this
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]908is an extremely obscure feature which would be complicated to implement
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]909correctly.</li>
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]910
911<li>clang does not support __builtin_apply and friends; this extension is
912extremely obscure and difficult to implement reliably.</li>
913
Eli Friedman0b326002009-06-12 20:11:05 +0000[diff] [blame]914</ul>
915
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]916<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
917<h3 id="c_ms">Microsoft extensions</h3>
918<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
919
920<p>clang has some experimental support for extensions from
921Microsoft Visual C++; to enable it, use the -fms-extensions command-line
Eli Friedmana1821b52009-06-08 06:21:03 +0000[diff] [blame]922option. This is the default for Windows targets. Note that the
923support is incomplete; enabling Microsoft extensions will silently drop
924certain constructs (including __declspec and Microsoft-style asm statements).
925</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]926
Michael J. Spencerdae4ac42010-10-21 05:21:48 +0000[diff] [blame]927<li>clang allows setting _MCS_VER with -fmsc-version=. It defaults to 1300 which
928is the same as Visual C/C++ 2003. Any number is supported and can greatly affect
929what Windows SDK and c++stdlib headers clang can compile. This option will be
930removed when clang supports the full set of MS extensions required for these
931headers.</li>
932
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]933<li>clang does not support the Microsoft extension where anonymous
Daniel Dunbar869e0542009-05-13 00:23:53 +0000[diff] [blame]934record members can be declared using user defined typedefs.</li>
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]935
Daniel Dunbar9375ed12009-05-13 21:40:49 +0000[diff] [blame]936<li>clang supports the Microsoft "#pragma pack" feature for
937controlling record layout. GCC also contains support for this feature,
938however where MSVC and GCC are incompatible clang follows the MSVC
939definition.</li>
940
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]941<!-- ======================================================================= -->
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]942<h2 id="target_features">Target-Specific Features and Limitations</h2>
943<!-- ======================================================================= -->
944
945
946<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
947<h3 id="target_arch">CPU Architectures Features and Limitations</h3>
948<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
949
950<!-- ======================== -->
951<h4 id="target_arch_x86">X86</h4>
952<!-- ======================== -->
Daniel Dunbarbcaf7aa2010-09-19 19:26:59 +0000[diff] [blame]953
954<p>The support for X86 (both 32-bit and 64-bit) is considered stable on Darwin
955(Mac OS/X), Linux, FreeBSD, and Dragonfly BSD: it has been tested to correctly
956compile many large C, C++, Objective-C, and Objective-C++ codebases.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]957
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]958<!-- ======================== -->
959<h4 id="target_arch_arm">ARM</h4>
960<!-- ======================== -->
Daniel Dunbarbcaf7aa2010-09-19 19:26:59 +0000[diff] [blame]961
962<p>The support for ARM (specifically ARMv6 and ARMv7) is considered stable on
963Darwin (iOS): it has been tested to correctly compile many large C, C++,
964Objective-C, and Objective-C++ codebases.</p>
965
966<p>It is not quite feature complete, the following areas still need work:</p>
967<ul>
968 <li>Vector support (NEON in particular) is not yet well tested and may have
969 ABI errors.</li>
970 <li>Clang only supports a limited number of ARM architectures. It does not yet
971 fully support ARMv5, for example.</li>
972</ul>
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]973
974<!-- ======================== -->
975<h4 id="target_arch_other">Other platforms</h4>
976<!-- ======================== -->
977clang currently contains some support for PPC and Sparc; however, significant
978pieces of code generation are still missing, and they haven't undergone
979significant testing.
980
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]981<p>clang contains limited support for the MSP430 embedded processor, but both
982the clang support and the LLVM backend support are highly experimental.
983
984<p>Other platforms are completely unsupported at the moment. Adding the
985minimal support needed for parsing and semantic analysis on a new platform
986is quite easy; see lib/Basic/Targets.cpp in the clang source tree. This level
987of support is also sufficient for conversion to LLVM IR for simple programs.
988Proper support for conversion to LLVM IR requires adding code to
989lib/CodeGen/CGCall.cpp at the moment; this is likely to change soon, though.
990Generating assembly requires a suitable LLVM backend.
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]991
992<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
993<h3 id="target_os">Operating System Features and Limitations</h3>
994<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
995
996<!-- ======================================= -->
997<h4 id="target_os_darwin">Darwin (Mac OS/X)</h4>
998<!-- ======================================= -->
999
1000<p>No __thread support, 64-bit ObjC support requires SL tools.</p>
1001
1002</div>
1003</body>
1004</html>