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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 |
| ‘<samp><span class="samp">etext</span></samp>’. However, ANSI C requires that the user be able to use |
| ‘<samp><span class="samp">etext</span></samp>’ as a function name without encountering an error. The |
| <code>PROVIDE</code> keyword may be used to define a symbol, such as |
| ‘<samp><span class="samp">etext</span></samp>’, 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 ‘<samp><span class="samp">etext</span></samp>’: |
| <pre class="smallexample"> SECTIONS |
| { |
| .text : |
| { |
| *(.text) |
| _etext = .; |
| PROVIDE(etext = .); |
| } |
| } |
| </pre> |
| <p>In this example, if the program defines ‘<samp><span class="samp">_etext</span></samp>’ (with a leading |
| underscore), the linker will give a multiple definition error. If, on |
| the other hand, the program defines ‘<samp><span class="samp">etext</span></samp>’ (with no leading |
| underscore), the linker will silently use the definition in the program. |
| If the program references ‘<samp><span class="samp">etext</span></samp>’ 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 |
| ‘<samp><span class="samp">__CTOR_LIST__</span></samp>’ as these are often defined as common symbols. |
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