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<h4 class="subsection">3.5.3 PROVIDE</h4>

<p><a name="index-PROVIDE-448"></a>In some cases, it is desirable for a linker script to define a symbol
only if it is referenced and is not defined by any object included in
the link.  For example, traditional linkers defined the symbol
&lsquo;<samp><span class="samp">etext</span></samp>&rsquo;.  However, ANSI C requires that the user be able to use
&lsquo;<samp><span class="samp">etext</span></samp>&rsquo; as a function name without encountering an error.  The
<code>PROVIDE</code> keyword may be used to define a symbol, such as
&lsquo;<samp><span class="samp">etext</span></samp>&rsquo;, only if it is referenced but not defined.  The syntax is
<code>PROVIDE(</code><var>symbol</var><code> = </code><var>expression</var><code>)</code>.

   <p>Here is an example of using <code>PROVIDE</code> to define &lsquo;<samp><span class="samp">etext</span></samp>&rsquo;:
<pre class="smallexample">     SECTIONS
     {
       .text :
         {
           *(.text)
           _etext = .;
           PROVIDE(etext = .);
         }
     }
</pre>
   <p>In this example, if the program defines &lsquo;<samp><span class="samp">_etext</span></samp>&rsquo; (with a leading
underscore), the linker will give a multiple definition error.  If, on
the other hand, the program defines &lsquo;<samp><span class="samp">etext</span></samp>&rsquo; (with no leading
underscore), the linker will silently use the definition in the program. 
If the program references &lsquo;<samp><span class="samp">etext</span></samp>&rsquo; but does not define it, the
linker will use the definition in the linker script.

   <p>Note - the <code>PROVIDE</code> directive considers a common symbol to be
defined, even though such a symbol could be combined with the symbol
that the <code>PROVIDE</code> would create.  This is particularly important
when considering constructor and destructor list symbols such as
&lsquo;<samp><span class="samp">__CTOR_LIST__</span></samp>&rsquo; as these are often defined as common symbols.

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