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<head>
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<title>Link Options (Using the GNU Compiler Collection (GCC))</title>
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Invoking-GCC.html#Invoking-GCC" rel="up" title="Invoking GCC">
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<link href="Directory-Options.html#Directory-Options" rel="next" title="Directory Options">
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<link href="Assembler-Options.html#Assembler-Options" rel="prev" title="Assembler Options">
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</head>
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<body lang="en">
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<a name="Link-Options"></a>
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<div class="header">
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<p>
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Next: <a href="Directory-Options.html#Directory-Options" accesskey="n" rel="next">Directory Options</a>, Previous: <a href="Assembler-Options.html#Assembler-Options" accesskey="p" rel="prev">Assembler Options</a>, Up: <a href="Invoking-GCC.html#Invoking-GCC" accesskey="u" rel="up">Invoking GCC</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Options-for-Linking"></a>
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<h3 class="section">3.14 Options for Linking</h3>
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<a name="index-link-options"></a>
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<a name="index-options_002c-linking"></a>
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<p>These options come into play when the compiler links object files into
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an executable output file. They are meaningless if the compiler is
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not doing a link step.
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</p>
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<dl compact="compact">
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<dd><a name="index-file-names"></a>
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</dd>
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<dt><code><var>object-file-name</var></code></dt>
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<dd><p>A file name that does not end in a special recognized suffix is
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considered to name an object file or library. (Object files are
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distinguished from libraries by the linker according to the file
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contents.) If linking is done, these object files are used as input
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to the linker.
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</p>
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</dd>
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<dt><code>-c</code></dt>
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<dt><code>-S</code></dt>
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<dt><code>-E</code></dt>
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<dd><a name="index-c-1"></a>
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<a name="index-S-1"></a>
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<a name="index-E-1"></a>
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<p>If any of these options is used, then the linker is not run, and
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object file names should not be used as arguments. See <a href="Overall-Options.html#Overall-Options">Overall Options</a>.
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</p>
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</dd>
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<dt><code>-fuse-ld=bfd</code></dt>
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<dd><a name="index-fuse_002dld_003dbfd"></a>
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<p>Use the <code>bfd</code> linker instead of the default linker.
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</p>
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</dd>
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<dt><code>-fuse-ld=gold</code></dt>
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<dd><a name="index-fuse_002dld_003dgold"></a>
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<p>Use the <code>gold</code> linker instead of the default linker.
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</p>
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<a name="index-Libraries"></a>
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</dd>
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<dt><code>-l<var>library</var></code></dt>
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<dt><code>-l <var>library</var></code></dt>
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<dd><a name="index-l"></a>
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<p>Search the library named <var>library</var> when linking. (The second
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alternative with the library as a separate argument is only for
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POSIX compliance and is not recommended.)
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</p>
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<p>It makes a difference where in the command you write this option; the
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linker searches and processes libraries and object files in the order they
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are specified. Thus, ‘<samp>foo.o -lz bar.o</samp>’ searches library ‘<samp>z</samp>’
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after file <samp>foo.o</samp> but before <samp>bar.o</samp>. If <samp>bar.o</samp> refers
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to functions in ‘<samp>z</samp>’, those functions may not be loaded.
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</p>
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<p>The linker searches a standard list of directories for the library,
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which is actually a file named <samp>lib<var>library</var>.a</samp>. The linker
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then uses this file as if it had been specified precisely by name.
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</p>
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<p>The directories searched include several standard system directories
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plus any that you specify with <samp>-L</samp>.
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</p>
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<p>Normally the files found this way are library files—archive files
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whose members are object files. The linker handles an archive file by
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scanning through it for members which define symbols that have so far
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been referenced but not defined. But if the file that is found is an
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ordinary object file, it is linked in the usual fashion. The only
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difference between using an <samp>-l</samp> option and specifying a file name
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is that <samp>-l</samp> surrounds <var>library</var> with ‘<samp>lib</samp>’ and ‘<samp>.a</samp>’
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and searches several directories.
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</p>
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</dd>
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<dt><code>-lobjc</code></dt>
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<dd><a name="index-lobjc"></a>
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<p>You need this special case of the <samp>-l</samp> option in order to
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link an Objective-C or Objective-C++ program.
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</p>
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</dd>
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<dt><code>-nostartfiles</code></dt>
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<dd><a name="index-nostartfiles"></a>
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<p>Do not use the standard system startup files when linking.
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The standard system libraries are used normally, unless <samp>-nostdlib</samp>
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or <samp>-nodefaultlibs</samp> is used.
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</p>
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</dd>
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<dt><code>-nodefaultlibs</code></dt>
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<dd><a name="index-nodefaultlibs"></a>
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<p>Do not use the standard system libraries when linking.
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Only the libraries you specify are passed to the linker, and options
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specifying linkage of the system libraries, such as <samp>-static-libgcc</samp>
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or <samp>-shared-libgcc</samp>, are ignored.
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The standard startup files are used normally, unless <samp>-nostartfiles</samp>
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is used.
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</p>
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<p>The compiler may generate calls to <code>memcmp</code>,
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<code>memset</code>, <code>memcpy</code> and <code>memmove</code>.
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These entries are usually resolved by entries in
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libc. These entry points should be supplied through some other
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mechanism when this option is specified.
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</p>
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</dd>
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<dt><code>-nostdlib</code></dt>
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<dd><a name="index-nostdlib"></a>
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<p>Do not use the standard system startup files or libraries when linking.
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No startup files and only the libraries you specify are passed to
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the linker, and options specifying linkage of the system libraries, such as
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<samp>-static-libgcc</samp> or <samp>-shared-libgcc</samp>, are ignored.
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</p>
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<p>The compiler may generate calls to <code>memcmp</code>, <code>memset</code>,
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<code>memcpy</code> and <code>memmove</code>.
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These entries are usually resolved by entries in
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libc. These entry points should be supplied through some other
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mechanism when this option is specified.
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</p>
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<a name="index-_002dlgcc_002c-use-with-_002dnostdlib"></a>
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<a name="index-_002dnostdlib-and-unresolved-references"></a>
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<a name="index-unresolved-references-and-_002dnostdlib"></a>
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<a name="index-_002dlgcc_002c-use-with-_002dnodefaultlibs"></a>
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<a name="index-_002dnodefaultlibs-and-unresolved-references"></a>
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<a name="index-unresolved-references-and-_002dnodefaultlibs"></a>
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<p>One of the standard libraries bypassed by <samp>-nostdlib</samp> and
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<samp>-nodefaultlibs</samp> is <samp>libgcc.a</samp>, a library of internal subroutines
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which GCC uses to overcome shortcomings of particular machines, or special
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needs for some languages.
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(See <a href="http://gcc.gnu.org/onlinedocs/gccint/Interface.html#Interface">Interfacing to GCC Output</a> in <cite>GNU Compiler
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Collection (GCC) Internals</cite>,
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for more discussion of <samp>libgcc.a</samp>.)
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In most cases, you need <samp>libgcc.a</samp> even when you want to avoid
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other standard libraries. In other words, when you specify <samp>-nostdlib</samp>
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or <samp>-nodefaultlibs</samp> you should usually specify <samp>-lgcc</samp> as well.
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This ensures that you have no unresolved references to internal GCC
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library subroutines.
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(An example of such an internal subroutine is <code>__main</code>, used to ensure C++
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constructors are called; see <a href="http://gcc.gnu.org/onlinedocs/gccint/Collect2.html#Collect2"><code>collect2</code></a> in <cite>GNU Compiler Collection (GCC) Internals</cite>.)
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</p>
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</dd>
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<dt><code>-pie</code></dt>
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<dd><a name="index-pie"></a>
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<p>Produce a dynamically linked position independent executable on targets
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that support it. For predictable results, you must also specify the same
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set of options used for compilation (<samp>-fpie</samp>, <samp>-fPIE</samp>,
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or model suboptions) when you specify this linker option.
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</p>
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</dd>
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<dt><code>-no-pie</code></dt>
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<dd><a name="index-no_002dpie"></a>
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<p>Don’t produce a dynamically linked position independent executable.
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</p>
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</dd>
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<dt><code>-static-pie</code></dt>
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<dd><a name="index-static_002dpie"></a>
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<p>Produce a static position independent executable on targets that support
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it. A static position independent executable is similar to a static
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executable, but can be loaded at any address without a dynamic linker.
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For predictable results, you must also specify the same set of options
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used for compilation (<samp>-fpie</samp>, <samp>-fPIE</samp>, or model
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suboptions) when you specify this linker option.
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</p>
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</dd>
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<dt><code>-pthread</code></dt>
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<dd><a name="index-pthread-1"></a>
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<p>Link with the POSIX threads library. This option is supported on
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GNU/Linux targets, most other Unix derivatives, and also on
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x86 Cygwin and MinGW targets. On some targets this option also sets
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flags for the preprocessor, so it should be used consistently for both
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compilation and linking.
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</p>
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</dd>
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<dt><code>-rdynamic</code></dt>
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<dd><a name="index-rdynamic"></a>
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<p>Pass the flag <samp>-export-dynamic</samp> to the ELF linker, on targets
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that support it. This instructs the linker to add all symbols, not
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only used ones, to the dynamic symbol table. This option is needed
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for some uses of <code>dlopen</code> or to allow obtaining backtraces
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from within a program.
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</p>
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</dd>
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<dt><code>-s</code></dt>
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<dd><a name="index-s"></a>
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<p>Remove all symbol table and relocation information from the executable.
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</p>
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</dd>
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<dt><code>-static</code></dt>
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<dd><a name="index-static"></a>
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<p>On systems that support dynamic linking, this overrides <samp>-pie</samp>
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and prevents linking with the shared libraries. On other systems, this
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option has no effect.
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</p>
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</dd>
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<dt><code>-shared</code></dt>
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<dd><a name="index-shared"></a>
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<p>Produce a shared object which can then be linked with other objects to
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form an executable. Not all systems support this option. For predictable
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results, you must also specify the same set of options used for compilation
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(<samp>-fpic</samp>, <samp>-fPIC</samp>, or model suboptions) when
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you specify this linker option.<a name="DOCF1" href="#FOOT1"><sup>1</sup></a>
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</p>
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</dd>
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<dt><code>-shared-libgcc</code></dt>
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<dt><code>-static-libgcc</code></dt>
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<dd><a name="index-shared_002dlibgcc"></a>
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<a name="index-static_002dlibgcc"></a>
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<p>On systems that provide <samp>libgcc</samp> as a shared library, these options
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force the use of either the shared or static version, respectively.
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If no shared version of <samp>libgcc</samp> was built when the compiler was
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configured, these options have no effect.
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</p>
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<p>There are several situations in which an application should use the
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shared <samp>libgcc</samp> instead of the static version. The most common
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of these is when the application wishes to throw and catch exceptions
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across different shared libraries. In that case, each of the libraries
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as well as the application itself should use the shared <samp>libgcc</samp>.
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</p>
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<p>Therefore, the G++ driver automatically adds <samp>-shared-libgcc</samp>
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whenever you build a shared library or a main executable, because C++
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programs typically use exceptions, so this is the right thing to do.
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</p>
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<p>If, instead, you use the GCC driver to create shared libraries, you may
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find that they are not always linked with the shared <samp>libgcc</samp>.
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If GCC finds, at its configuration time, that you have a non-GNU linker
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or a GNU linker that does not support option <samp>--eh-frame-hdr</samp>,
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it links the shared version of <samp>libgcc</samp> into shared libraries
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by default. Otherwise, it takes advantage of the linker and optimizes
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away the linking with the shared version of <samp>libgcc</samp>, linking with
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the static version of libgcc by default. This allows exceptions to
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propagate through such shared libraries, without incurring relocation
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costs at library load time.
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</p>
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<p>However, if a library or main executable is supposed to throw or catch
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exceptions, you must link it using the G++ driver, or using the option
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<samp>-shared-libgcc</samp>, such that it is linked with the shared
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<samp>libgcc</samp>.
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</p>
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</dd>
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<dt><code>-static-libasan</code></dt>
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<dd><a name="index-static_002dlibasan"></a>
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<p>When the <samp>-fsanitize=address</samp> option is used to link a program,
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the GCC driver automatically links against <samp>libasan</samp>. If
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<samp>libasan</samp> is available as a shared library, and the <samp>-static</samp>
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option is not used, then this links against the shared version of
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<samp>libasan</samp>. The <samp>-static-libasan</samp> option directs the GCC
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driver to link <samp>libasan</samp> statically, without necessarily linking
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other libraries statically.
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|
</p>
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|
</dd>
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<dt><code>-static-libtsan</code></dt>
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<dd><a name="index-static_002dlibtsan"></a>
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<p>When the <samp>-fsanitize=thread</samp> option is used to link a program,
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the GCC driver automatically links against <samp>libtsan</samp>. If
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<samp>libtsan</samp> is available as a shared library, and the <samp>-static</samp>
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|
option is not used, then this links against the shared version of
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<samp>libtsan</samp>. The <samp>-static-libtsan</samp> option directs the GCC
|
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driver to link <samp>libtsan</samp> statically, without necessarily linking
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other libraries statically.
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</p>
|
|
</dd>
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<dt><code>-static-liblsan</code></dt>
|
|
<dd><a name="index-static_002dliblsan"></a>
|
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<p>When the <samp>-fsanitize=leak</samp> option is used to link a program,
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the GCC driver automatically links against <samp>liblsan</samp>. If
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<samp>liblsan</samp> is available as a shared library, and the <samp>-static</samp>
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|
option is not used, then this links against the shared version of
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<samp>liblsan</samp>. The <samp>-static-liblsan</samp> option directs the GCC
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|
driver to link <samp>liblsan</samp> statically, without necessarily linking
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other libraries statically.
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|
</p>
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|
</dd>
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<dt><code>-static-libubsan</code></dt>
|
|
<dd><a name="index-static_002dlibubsan"></a>
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|
<p>When the <samp>-fsanitize=undefined</samp> option is used to link a program,
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|
the GCC driver automatically links against <samp>libubsan</samp>. If
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<samp>libubsan</samp> is available as a shared library, and the <samp>-static</samp>
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|
option is not used, then this links against the shared version of
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|
<samp>libubsan</samp>. The <samp>-static-libubsan</samp> option directs the GCC
|
|
driver to link <samp>libubsan</samp> statically, without necessarily linking
|
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other libraries statically.
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|
</p>
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</dd>
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<dt><code>-static-libmpx</code></dt>
|
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<dd><a name="index-static_002dlibmpx"></a>
|
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<p>When the <samp>-fcheck-pointer bounds</samp> and <samp>-mmpx</samp> options are
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used to link a program, the GCC driver automatically links against
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<samp>libmpx</samp>. If <samp>libmpx</samp> is available as a shared library,
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and the <samp>-static</samp> option is not used, then this links against
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the shared version of <samp>libmpx</samp>. The <samp>-static-libmpx</samp>
|
|
option directs the GCC driver to link <samp>libmpx</samp> statically,
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without necessarily linking other libraries statically.
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</p>
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</dd>
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<dt><code>-static-libmpxwrappers</code></dt>
|
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<dd><a name="index-static_002dlibmpxwrappers"></a>
|
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<p>When the <samp>-fcheck-pointer bounds</samp> and <samp>-mmpx</samp> options are used
|
|
to link a program without also using <samp>-fno-chkp-use-wrappers</samp>, the
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GCC driver automatically links against <samp>libmpxwrappers</samp>. If
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<samp>libmpxwrappers</samp> is available as a shared library, and the
|
|
<samp>-static</samp> option is not used, then this links against the shared
|
|
version of <samp>libmpxwrappers</samp>. The <samp>-static-libmpxwrappers</samp>
|
|
option directs the GCC driver to link <samp>libmpxwrappers</samp> statically,
|
|
without necessarily linking other libraries statically.
|
|
</p>
|
|
</dd>
|
|
<dt><code>-static-libstdc++</code></dt>
|
|
<dd><a name="index-static_002dlibstdc_002b_002b"></a>
|
|
<p>When the <code>g++</code> program is used to link a C++ program, it
|
|
normally automatically links against <samp>libstdc++</samp>. If
|
|
<samp>libstdc++</samp> is available as a shared library, and the
|
|
<samp>-static</samp> option is not used, then this links against the
|
|
shared version of <samp>libstdc++</samp>. That is normally fine. However, it
|
|
is sometimes useful to freeze the version of <samp>libstdc++</samp> used by
|
|
the program without going all the way to a fully static link. The
|
|
<samp>-static-libstdc++</samp> option directs the <code>g++</code> driver to
|
|
link <samp>libstdc++</samp> statically, without necessarily linking other
|
|
libraries statically.
|
|
</p>
|
|
</dd>
|
|
<dt><code>-symbolic</code></dt>
|
|
<dd><a name="index-symbolic"></a>
|
|
<p>Bind references to global symbols when building a shared object. Warn
|
|
about any unresolved references (unless overridden by the link editor
|
|
option <samp>-Xlinker -z -Xlinker defs</samp>). Only a few systems support
|
|
this option.
|
|
</p>
|
|
</dd>
|
|
<dt><code>-T <var>script</var></code></dt>
|
|
<dd><a name="index-T"></a>
|
|
<a name="index-linker-script"></a>
|
|
<p>Use <var>script</var> as the linker script. This option is supported by most
|
|
systems using the GNU linker. On some targets, such as bare-board
|
|
targets without an operating system, the <samp>-T</samp> option may be required
|
|
when linking to avoid references to undefined symbols.
|
|
</p>
|
|
</dd>
|
|
<dt><code>-Xlinker <var>option</var></code></dt>
|
|
<dd><a name="index-Xlinker"></a>
|
|
<p>Pass <var>option</var> as an option to the linker. You can use this to
|
|
supply system-specific linker options that GCC does not recognize.
|
|
</p>
|
|
<p>If you want to pass an option that takes a separate argument, you must use
|
|
<samp>-Xlinker</samp> twice, once for the option and once for the argument.
|
|
For example, to pass <samp>-assert definitions</samp>, you must write
|
|
<samp>-Xlinker -assert -Xlinker definitions</samp>. It does not work to write
|
|
<samp>-Xlinker "-assert definitions"</samp>, because this passes the entire
|
|
string as a single argument, which is not what the linker expects.
|
|
</p>
|
|
<p>When using the GNU linker, it is usually more convenient to pass
|
|
arguments to linker options using the <samp><var>option</var>=<var>value</var></samp>
|
|
syntax than as separate arguments. For example, you can specify
|
|
<samp>-Xlinker -Map=output.map</samp> rather than
|
|
<samp>-Xlinker -Map -Xlinker output.map</samp>. Other linkers may not support
|
|
this syntax for command-line options.
|
|
</p>
|
|
</dd>
|
|
<dt><code>-Wl,<var>option</var></code></dt>
|
|
<dd><a name="index-Wl"></a>
|
|
<p>Pass <var>option</var> as an option to the linker. If <var>option</var> contains
|
|
commas, it is split into multiple options at the commas. You can use this
|
|
syntax to pass an argument to the option.
|
|
For example, <samp>-Wl,-Map,output.map</samp> passes <samp>-Map output.map</samp> to the
|
|
linker. When using the GNU linker, you can also get the same effect with
|
|
<samp>-Wl,-Map=output.map</samp>.
|
|
</p>
|
|
</dd>
|
|
<dt><code>-u <var>symbol</var></code></dt>
|
|
<dd><a name="index-u"></a>
|
|
<p>Pretend the symbol <var>symbol</var> is undefined, to force linking of
|
|
library modules to define it. You can use <samp>-u</samp> multiple times with
|
|
different symbols to force loading of additional library modules.
|
|
</p>
|
|
</dd>
|
|
<dt><code>-z <var>keyword</var></code></dt>
|
|
<dd><a name="index-z"></a>
|
|
<p><samp>-z</samp> is passed directly on to the linker along with the keyword
|
|
<var>keyword</var>. See the section in the documentation of your linker for
|
|
permitted values and their meanings.
|
|
</p></dd>
|
|
</dl>
|
|
|
|
<div class="footnote">
|
|
<hr>
|
|
<h4 class="footnotes-heading">Footnotes</h4>
|
|
|
|
<h3><a name="FOOT1" href="#DOCF1">(1)</a></h3>
|
|
<p>On some systems, ‘<samp>gcc -shared</samp>’
|
|
needs to build supplementary stub code for constructors to work. On
|
|
multi-libbed systems, ‘<samp>gcc -shared</samp>’ must select the correct support
|
|
libraries to link against. Failing to supply the correct flags may lead
|
|
to subtle defects. Supplying them in cases where they are not necessary
|
|
is innocuous.</p>
|
|
</div>
|
|
<hr>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Directory-Options.html#Directory-Options" accesskey="n" rel="next">Directory Options</a>, Previous: <a href="Assembler-Options.html#Assembler-Options" accesskey="p" rel="prev">Assembler Options</a>, Up: <a href="Invoking-GCC.html#Invoking-GCC" accesskey="u" rel="up">Invoking GCC</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
|
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</div>
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