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<html>
<head>
<title>Clang Compiler User's Manual</title>
<link type="text/css" rel="stylesheet" href="../menu.css" />
<link type="text/css" rel="stylesheet" href="../content.css" />
<style type="text/css">
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vertical-align: top;
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<body>
<!--#include virtual="../menu.html.incl"-->
<div id="content">
<h1>Clang Compiler User's Manual</h1>
<ul>
<li><a href="#intro">Introduction</a>
<ul>
<li><a href="#terminology">Terminology</a></li>
<li><a href="#basicusage">Basic Usage</a></li>
</ul>
</li>
<li><a href="#commandline">Command Line Options</a>
<ul>
<li><a href="#cl_diagnostics">Options to Control Error and Warning
Messages</a></li>
</ul>
</li>
<li><a href="#general_features">Language and Target-Independent Features</a>
<ul>
<li><a href="#diagnostics">Controlling Errors and Warnings</a></li>
<li><a href="#precompiledheaders">Precompiled Headers</a></li>
</ul>
</li>
<li><a href="#c">C Language Features</a>
<ul>
<li><a href="#c_ext">Extensions supported by clang</a></li>
<li><a href="#c_modes">Differences between various standard modes</a></li>
<li><a href="#c_unimpl_gcc">GCC extensions not implemented yet</a></li>
<li><a href="#c_unsupp_gcc">Intentionally unsupported GCC extensions</a></li>
<li><a href="#c_ms">Microsoft extensions</a></li>
</ul>
</li>
<li><a href="#objc">Objective-C Language Features</a>
<ul>
<li><a href="#objc_incompatibilities">Intentional Incompatibilities with
GCC</a></li>
</ul>
</li>
<li><a href="#cxx">C++ Language Features</a>
<ul>
<li>...</li>
</ul>
</li>
<li><a href="#objcxx">Objective C++ Language Features</a>
<ul>
<li>...</li>
</ul>
</li>
<li><a href="#target_features">Target-Specific Features and Limitations</a>
<ul>
<li><a href="#target_arch">CPU Architectures Features and Limitations</a>
<ul>
<li><a href="#target_arch_x86">X86</a></li>
<li>PPC</li>
<li>ARM</li>
</ul>
</li>
<li><a href="#target_os">Operating System Features and Limitations</a>
<ul>
<li><a href="#target_os_darwin">Darwin (Mac OS/X)</a></li>
<li>Linux, etc.</li>
</ul>
</li>
</ul>
</li>
</ul>
<!-- ======================================================================= -->
<h2 id="intro">Introduction</h2>
<!-- ======================================================================= -->
<p>The Clang Compiler is an open-source compiler for the C family of programming
languages, aiming to be the best in class implementation of these languages.
Clang builds on the LLVM optimizer and code generator, allowing it to provide
high-quality optimization and code generation support for many targets. For
more general information, please see the <a href="http://clang.llvm.org">Clang
Web Site</a> or the <a href="http://llvm.org">LLVM Web Site</a>.</p>
<p>This document describes important notes about using Clang as a compiler for
an end-user, documenting the supported features, command line options, etc. If
you are interested in using Clang to build a tool that processes code, please
see <a href="InternalsManual.html">the Clang Internals Manual</a>. If you are
interested in the <a href="http://clang.llvm.org/StaticAnalysis.html">Clang
Static Analyzer</a>, please see its web page.</p>
<p>Clang is designed to support the C family of programming languages, which
includes <a href="#c">C</a>, <a href="#objc">Objective-C</a>, <a
href="#cxx">C++</a>, and <a href="#objcxx">Objective-C++</a> as well as many
dialects of those. For language-specific information, please see the
corresponding language specific section:</p>
<ul>
<li><a href="#c">C Language</a>: K&R C, ANSI C89, ISO C90, ISO C94
(C89+AMD1), ISO C99 (+TC1, TC2, TC3). </li>
<li><a href="#objc">Objective-C Language</a>: ObjC 1, ObjC 2, ObjC 2.1, plus
variants depending on base language.</li>
<li><a href="#cxx">C++ Language Features</a></li>
<li><a href="#objcxx">Objective C++ Language</a></li>
</ul>
<p>In addition to these base languages and their dialects, Clang supports a
broad variety of language extensions, which are documented in the corresponding
language section. These extensions are provided to be compatible with the GCC,
Microsoft, and other popular compilers as well as to improve functionality
through Clang-specific features. The Clang driver and language features are
intentionally designed to be as compatible with the GNU GCC compiler as
reasonably possible, easing migration from GCC to Clang. In most cases, code
"just works".</p>
<p>In addition to language specific features, Clang has a variety of features
that depend on what CPU architecture or operating system is being compiled for.
Please see the <a href="target_features">Target-Specific Features and
Limitations</a> section for more details.</p>
<p>The rest of the introduction introduces some basic <a
href="#terminology">compiler terminology</a> that is used throughout this manual
and contains a basic <a href="#basicusage">introduction to using Clang</a>
as a command line compiler.</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h3 id="terminology">Terminology</h3>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<p>Front end, parser, backend, preprocessor, undefined behavior, diagnostic,
optimizer</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h3 id="basicusage">Basic Usage</h3>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<p>Intro to how to use a C compiler for newbies.</p>
<p>
compile + link
compile then link
debug info
enabling optimizations
picking a language to use, defaults to C99 by default. Autosenses based on
extension.
using a makefile
</p>
<!-- ======================================================================= -->
<h2 id="commandline">Command Line Options</h2>
<!-- ======================================================================= -->
<p>
This section is generally an index into other sections. It does not go into
depth on the ones that are covered by other sections. However, the first part
introduces the language selection and other high level options like -c, -g, etc.
</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h3 id="cl_diagnostics">Options to Control Error and Warning Messages</h3>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<p><b>-Werror</b>: Turn warnings into errors.</p>
<p><b>-Werror=foo</b>: Turn warning "foo" into an error.</p>
<p><b>-Wno-error=foo</b>: Turn warning "foo" into an warning even if -Werror is
specified.</p>
<p><b>-Wfoo</b>: Enable warning foo</p>
<p><b>-Wno-foo</b>: Disable warning foo</p>
<p><b>-w</b>: Disable all warnings.</p>
<p><b>-pedantic</b>: Warn on language extensions.</p>
<p><b>-pedantic-errors</b>: Error on language extensions.</p>
<p><b>-Wsystem-headers</b>: Enable warnings from system headers.</p>
<!-- ================================================= -->
<h4 id="cl_diag_formatting">Formatting of Diagnostics</h4>
<!-- ================================================= -->
<p>Clang aims to produce beautiful diagnostics by default, particularly for new
users that first come to Clang. However, different people have different
preferences, and sometimes Clang is driven by another program that wants to
parse simple and consistent output, not a person. For these cases, Clang
provides a wide range of options to control the exact output format of the
diagnostics that it generates.</p>
<dl>
<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
<dt id="opt_fshow-column"><b>-f[no-]show-column</b>: Print column number in
diagnostic.</dt>
<dd>This option, which defaults to on, controls whether or not Clang prints the
column number of a diagnostic. For example, when this is enabled, Clang will
print something like:</p>
<pre>
test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
#endif bad
^
//
</pre>
<p>When this is disabled, Clang will print "test.c:28: warning..." with no
column number.</p>
</dd>
<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
<dt id="opt_fshow-source-location"><b>-f[no-]show-source-location</b>: Print
source file/line/column information in diagnostic.</dt>
<dd>This option, which defaults to on, controls whether or not Clang prints the
filename, line number and column number of a diagnostic. For example,
when this is enabled, Clang will print something like:</p>
<pre>
test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
#endif bad
^
//
</pre>
<p>When this is disabled, Clang will not print the "test.c:28:8: " part.</p>
</dd>
<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
<dt id="opt_fcaret-diagnostics"><b>-f[no-]caret-diagnostics</b>: Print source
line and ranges from source code in diagnostic.</dt>
<dd>This option, which defaults to on, controls whether or not Clang prints the
source line, source ranges, and caret when emitting a diagnostic. For example,
when this is enabled, Clang will print something like:</p>
<pre>
test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
#endif bad
^
//
</pre>
<p>When this is disabled, Clang will just print:</p>
<pre>
test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
</pre>
</dd>
<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
<dt id="opt_fdiagnostics-show-option"><b>-f[no-]diagnostics-show-option</b>:
Enable <tt>[-Woption]</tt> information in diagnostic line.</dt>
<dd>This option, which defaults to on,
controls whether or not Clang prints the associated <A
href="#cl_diag_warning_groups">warning group</a> option name when outputting
a warning diagnostic. For example, in this output:</p>
<pre>
test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
#endif bad
^
//
</pre>
<p>Passing <b>-fno-diagnostics-show-option</b> will prevent Clang from printing
the [<a href="#opt_Wextra-tokens">-Wextra-tokens</a>] information in the
diagnostic. This information tells you the flag needed to enable or disable the
diagnostic, either from the command line or through <a
href="#pragma_GCC_diagnostic">#pragma GCC diagnostic</a>.</dd>
<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
<dt id="opt_fdiagnostics-fixit-info"><b>-f[no-]diagnostics-fixit-info</b>:
Enable "FixIt" information in the diagnostics output.</dt>
<dd>This option, which defaults to on, controls whether or not Clang prints the
information on how to fix a specific diagnostic underneath it when it knows.
For example, in this output:</p>
<pre>
test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
#endif bad
^
//
</pre>
<p>Passing <b>-fno-diagnostics-fixit-info</b> will prevent Clang from printing
the "//" line at the end of the message. This information is useful for users
who may not understand what is wrong, but can be confusing for machine
parsing.</p>
</dd>
<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
<dt id="opt_fdiagnostics-print-source-range-info">
<b>-f[no-]diagnostics-print-source-range-info</b>:
Print machine parsable information about source ranges.</dt>
<dd>This option, which defaults to off, controls whether or not Clang prints
information about source ranges in a machine parsable format after the
file/line/column number information. The information is a simple sequence of
brace enclosed ranges, where each range lists the start and end line/column
locations. For example, in this output:</p>
<pre>
exprs.c:47:15:{47:8-47:14}{47:17-47:24}: error: invalid operands to binary expression ('int *' and '_Complex float')
P = (P-42) + Gamma*4;
~~~~~~ ^ ~~~~~~~
</pre>
<p>The {}'s are generated by -fdiagnostics-print-source-range-info.</p>
</dd>
</dl>
<!-- ===================================================== -->
<h4 id="cl_diag_warning_groups">Individual Warning Groups</h4>
<!-- ===================================================== -->
<p>TODO: Generate this from tblgen. Define one anchor per warning group.</p>
<dl>
<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
<dt id="opt_Wextra-tokens"><b>-Wextra-tokens</b>: Warn about excess tokens at
the end of a preprocessor directive.</dt>
<dd>This option, which defaults to on, enables warnings about extra tokens at
the end of preprocessor directives. For example:</p>
<pre>
test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
#endif bad
^
</pre>
<p>These extra tokens are not strictly conforming, and are usually best handled
by commenting them out.</p>
<p>This option is also enabled by <a href="">-Wfoo</a>, <a href="">-Wbar</a>,
and <a href="">-Wbaz</a>.</p>
</dd>
</dl>
<!-- ======================================================================= -->
<h2 id="general_features">Language and Target-Independent Features</h2>
<!-- ======================================================================= -->
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h3 id="diagnostics">Controlling Errors and Warnings</h3>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<p>Clang provides a number of ways to control which code constructs cause it to
emit errors and warning messages, and how they are displayed to the console.</p>
<h4>Controlling How Clang Displays Diagnostics</h4>
<p>When Clang emits a diagnostic, it includes rich information in the output,
and gives you fine-grain control over which information is printed. Clang has
the ability to print this information, and these are the options that control
it:</p>
<p>
<ol>
<li>A file/line/column indicator that shows exactly where the diagnostic occurs
in your code [<a href="#opt_fshow-column">-fshow-column</a>, <a
href="#opt_fshow-source-location">-fshow-source-location</a>].</li>
<li>A categorization of the diagnostic as a note, warning, error, or fatal
error.</li>
<li>A text string that describes what the problem is.</li>
<li>An option that indicates how to control the diagnostic (for diagnostics that
support it) [<a
href="#opt_fdiagnostics-show-option">-fdiagnostics-show-option</a>].</li>
<li>The line of source code that the issue occurs on, along with a caret and
ranges that indicate the important locations [<a
href="opt_fcaret-diagnostics">-fcaret-diagnostics</a>].</li>
<li>"FixIt" information, which is a concise explanation of how to fix the
problem (when Clang is certain it knows) [<a
href="opt_fdiagnostics-fixit-info">-fdiagnostics-fixit-info</a>].</li>
<li>A machine-parsable representation of the ranges involved (off by
default) [<a
href="opt_fdiagnostics-print-source-range-info">-fdiagnostics-print-source-range-info</a>].</li>
</ol></p>
<p>For more information please see <a href="#cl_diag_formatting">Formatting of
Diagnostics</a>.</p>
<h4>Controlling Which Diagnostics Clang Generates</h4>
<p>mappings: ignore, note, warning, error, fatal</p>
<p>
The two major classes are control from the command line and control via pragmas
in your code.</p>
<p>-W flags, -pedantic, etc</p>
<p>pragma GCC diagnostic</p>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<h3 id="precompiledheaders">Precompiled Headers</h3>
<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
<p><a href="http://en.wikipedia.org/wiki/Precompiled_header">Precompiled
headers</a> are a general approach employed by many compilers to reduce
compilation time. The underlying motivation of the approach is that it is
common for the same (and often large) header files to be included by
multiple source files. Consequently, compile times can often be greatly improved
by caching some of the (redundant) work done by a compiler to process headers.
Precompiled header files, which represent one of many ways to implement
this optimization, are literally files that represent an on-disk cache that
contains the vital information necessary to reduce some of the work
needed to process a corresponding header file. While details of precompiled
headers vary between compilers, precompiled headers have been shown to be a
highly effective at speeding up program compilation on systems with very large
system headers (e.g., Mac OS/X).</p>
<p>Clang supports an implementation of precompiled headers known as
<em>pre-tokenized headers</em> (PTH). Clang's pre-tokenized headers support most
of same interfaces as GCC's pre-compiled headers (as well as others) but are
completely different in their implementation. If you are interested in how
PTH is implemented, please see the <a href="PTHInternals.html">PTH Internals
document</a>.</p>
<h4>Generating a PTH File</h4>
<p>To generate a PTH file using Clang, one invokes Clang with
the <b><tt>-x <i><language></i>-header</tt></b> option. This mirrors the
interface in GCC for generating PCH files:</p>
<pre>
$ gcc -x c-header test.h -o test.h.gch
$ clang -x c-header test.h -o test.h.pth
</pre>
<h4>Using a PTH File</h4>
<p>A PTH file can then be used as a prefix header when a
<b><tt>-include</tt></b> option is passed to <tt>clang</tt>:</p>
<pre>
$ clang -include test.h test.c -o test
</pre>
<p>The <tt>clang</tt> driver will first check if a PTH file for <tt>test.h</tt>
is available; if so, the contents of <tt>test.h</tt> (and the files it includes)
will be processed from the PTH file. Otherwise, Clang falls back to
directly processing the content of <tt>test.h</tt>. This mirrors the behavior of
GCC.</p>
<p><b>NOTE:</b> Clang does <em>not</em> automatically use PTH files
for headers that are directly included within a source file. For example:</p>
<pre>
$ clang -x c-header test.h -o test.h.pth
$ cat test.c
#include "test.h"
$ clang test.c -o test
</pre>
<p>In this example, <tt>clang</tt> will not automatically use the PTH file for
<tt>test.h</tt> since <tt>test.h</tt> was included directly in the source file
and not specified on the command line using <tt>-include</tt>.</p>
<!-- ======================================================================= -->
<h2 id="c">C Language Features</h2>
<!-- ======================================================================= -->
<p>The support for standard C in clang is feature-complete except for the C99
floating-point pragmas.</p>
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<h3 id="c_ext">Extensions supported by clang</h3>
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<p>See <a href="LanguageExtensions.html">clang language extensions</a>.</p>
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<h3 id="c_modes">Differences between various standard modes</h3>
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<p>clang supports the -std option, which changes what language mode clang uses.
The supported modes for C are c89, gnu89, c94, c99, gnu99 and various aliases
for those modes. If no -std option is specified, clang defaults to gnu99 mode.
</p>
<p>Differences between all c* and gnu* modes:</p>
<ul>
<li>c* modes define "__STRICT_ANSI__".</li>
<li>Target-specific defines not prefixed by underscores, like "linux", are
defined in gnu* modes.</li>
<li>Trigraphs default to being off in gnu* modes; they can be enabled by the
-trigraphs option.</li>
<li>The parser recognizes "asm" and "typeof" as keywords in gnu* modes; the
variants "__asm__" and "__typeof__" are recognized in all modes.</li>
<li>The Apple "blocks" extension is recognized by default in gnu* modes
on some platforms; it can be enabled in any mode with the "-fblocks"
option.</li>
<li>Some warnings are different.</li>
</ul>
<p>Differences between *89 and *99 modes:</p>
<ul>
<li>The *99 modes default to implementing "inline" as specified in C99, while
the *89 modes implement the GNU version. This can be overridden for individual
functions with the __gnu_inline__ attribute.</li>
<li>Digraphs are not recognized in c89 mode.</li>
<li>The scope of names defined inside a "for", "if", "switch", "while", or "do"
statement is different. (example: "if ((struct x {int x;}*)0) {}".)</li>
<li>__STDC_VERSION__ is not defined in *89 modes.</li>
<li>"inline" is not recognized as a keyword in c89 mode.</li>
<li>"restrict" is not recognized as a keyword in *89 modes.</li>
<li>Commas are allowed in integer constant expressions in *99 modes.</li>
<li>Arrays which are not lvalues are not implicitly promoted to pointers in
*89 modes.</li>
<li>Some warnings are different.</li>
</ul>
<p>c94 mode is identical to c89 mode except that digraphs are enabled in
c94 mode (FIXME: And __STDC_VERSION__ should be defined!).</p>
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<h3 id="c_unimpl_gcc">GCC extensions not implemented yet</h3>
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<p>clang tries to be compatible with gcc as much as possible, but some gcc
extensions are not implemented yet:</p>
<ul>
<li>clang does not support __label__
(<a href="http://llvm.org/bugs/show_bug.cgi?id=3429">bug 3429</a>). This is
a relatively small feature, so it is likely to be implemented relatively
soon.</li>
<li>clang does not support attributes on function pointers
(<a href="http://llvm.org/bugs/show_bug.cgi?id=2461">bug 2461</a>). This is
a relatively important feature, so it is likely to be implemented relatively
soon.</li>
<li>clang does not support #pragma weak
(<a href="http://llvm.org/bugs/show_bug.cgi?id=3679">bug 3679</a>). Due to
the uses described in the bug, this is likely to be implemented at some
point, at least partially.</li>
<li>clang does not support #pragma align
(<a href="http://llvm.org/bugs/show_bug.cgi?id=3811">bug 3811</a>). This is a
relatively small feature, so it is likely to be implemented relatively
soon.</li>
<li>clang does not support code generation for local variables pinned to
registers (<a href="http://llvm.org/bugs/show_bug.cgi?id=3933">bug 3933</a>).
This is a relatively small feature, so it is likely to be implemented
relatively soon.</li>
<li>clang does not support decimal floating point types (_Decimal32 and
friends) or fixed-point types (_Fract and friends); nobody has expressed
interest in these features yet, so it's hard to say when they will be
implemented.</li>
<li>clang does not support nested functions; this is a complex feature which
is infrequently used, so it is unlikely to be implemented anytime soon.</li>
<li>clang does not support __builtin_apply and friends; this extension requires
complex code generator support that does not currently exist in LLVM, and there
is very little demand, so it is unlikely to be implemented anytime soon.</li>
<li>clang does not support global register variables, this is unlikely
to be implemented soon.</li>
<li>clang does not support static initialization of flexible array
members. This appears to be a rarely used extension, but could be
implemented pending user demand.</li>
</ul>
<p>This is not a complete list; if you find an unsupported extension
missing from this list, please send an e-mail to cfe-dev. This list
currently excludes C++; see <a href="#cxx">C++ Language Features</a>.
Also, this list does not include bugs in mostly-implemented features; please
see 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">
bug tracker</a> for known existing bugs (FIXME: Is there a section for
bug-reporting guidelines somewhere?).</p>
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<h3 id="c_unsupp_gcc">Intentionally unsupported GCC extensions</h3>
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<p>clang does not support the gcc extension that allows variable-length arrays
in structures. This is for a few of reasons: one, it is tricky
to implement, two, the extension is completely undocumented, and three, the
extension appears to be very rarely used.</p>
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<h3 id="c_ms">Microsoft extensions</h3>
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<p>clang has some experimental support for extensions from
Microsoft Visual C++; to enable it, use the -fms-extensions command-line
option. Eventually, this will be the default for Windows targets.
These extensions are not anywhere near complete, so please do not
file bugs; patches are welcome, though.</p>
<li>clang does not support the Microsoft extension where anonymous
record members can be declared using user defined typedefs.</li>
<li>clang supports the Microsoft "#pragma pack" feature for
controlling record layout. GCC also contains support for this feature,
however where MSVC and GCC are incompatible clang follows the MSVC
definition.</li>
<!-- ======================================================================= -->
<h2 id="objc">Objective-C Language Features</h2>
<!-- ======================================================================= -->
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<h3 id="objc_incompatibilities">Intentional Incompatibilities with GCC</h3>
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<p>No cast of super, no lvalue casts.</p>
<!-- ======================================================================= -->
<h2 id="cxx">C++ Language Features</h2>
<!-- ======================================================================= -->
<p>At this point, Clang C++ is not generally useful. However, Clang C++ support
is under active development and is progressing rapidly. Please see the <a
href="http://clang.llvm.org/cxx_status.html">C++ Status</a> page for details or
ask on the mailing list about how you can help.</p>
<p>Note that the clang driver will refuse to even try to use clang to compile
C++ code unless you pass the <tt>-ccc-clang-cxx</tt> option to the driver. If
you really want to play with Clang's C++ support, please pass that flag. </p>
<!-- ======================================================================= -->
<h2 id="objcxx">Objective C++ Language Features</h2>
<!-- ======================================================================= -->
<p>At this point, Clang C++ support is not generally useful (and therefore,
neither is Objective-C++). Please see the <a href="#cxx">C++ section</a> for
more information.</p>
<!-- ======================================================================= -->
<h2 id="target_features">Target-Specific Features and Limitations</h2>
<!-- ======================================================================= -->
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<h3 id="target_arch">CPU Architectures Features and Limitations</h3>
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<!-- ======================== -->
<h4 id="target_arch_x86">X86</h4>
<!-- ======================== -->
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<h3 id="target_os">Operating System Features and Limitations</h3>
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<!-- ======================================= -->
<h4 id="target_os_darwin">Darwin (Mac OS/X)</h4>
<!-- ======================================= -->
<p>No __thread support, 64-bit ObjC support requires SL tools.</p>
</div>
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