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| <h4 class="subsection">6.54.7 Symbol-Renaming Pragmas</h4> |
| |
| <p>For compatibility with the Solaris and Tru64 UNIX system headers, GCC |
| supports two <code>#pragma</code> directives which change the name used in |
| assembly for a given declaration. <code>#pragma extern_prefix</code> is only |
| available on platforms whose system headers need it. To get this effect |
| on all platforms supported by GCC, use the asm labels extension (see <a href="Asm-Labels.html#Asm-Labels">Asm Labels</a>). |
| |
| <dl> |
| <dt><code>redefine_extname </code><var>oldname</var> <var>newname</var><dd><a name="index-pragma_002c-redefine_005fextname-3137"></a> |
| This pragma gives the C function <var>oldname</var> the assembly symbol |
| <var>newname</var>. The preprocessor macro <code>__PRAGMA_REDEFINE_EXTNAME</code> |
| will be defined if this pragma is available (currently on all platforms). |
| |
| <br><dt><code>extern_prefix </code><var>string</var><dd><a name="index-pragma_002c-extern_005fprefix-3138"></a> |
| This pragma causes all subsequent external function and variable |
| declarations to have <var>string</var> prepended to their assembly symbols. |
| This effect may be terminated with another <code>extern_prefix</code> pragma |
| whose argument is an empty string. The preprocessor macro |
| <code>__PRAGMA_EXTERN_PREFIX</code> will be defined if this pragma is |
| available (currently only on Tru64 UNIX). |
| </dl> |
| |
| <p>These pragmas and the asm labels extension interact in a complicated |
| manner. Here are some corner cases you may want to be aware of. |
| |
| <ol type=1 start=1> |
| <li>Both pragmas silently apply only to declarations with external |
| linkage. Asm labels do not have this restriction. |
| |
| <li>In C++, both pragmas silently apply only to declarations with |
| “C” linkage. Again, asm labels do not have this restriction. |
| |
| <li>If any of the three ways of changing the assembly name of a |
| declaration is applied to a declaration whose assembly name has |
| already been determined (either by a previous use of one of these |
| features, or because the compiler needed the assembly name in order to |
| generate code), and the new name is different, a warning issues and |
| the name does not change. |
| |
| <li>The <var>oldname</var> used by <code>#pragma redefine_extname</code> is |
| always the C-language name. |
| |
| <li>If <code>#pragma extern_prefix</code> is in effect, and a declaration |
| occurs with an asm label attached, the prefix is silently ignored for |
| that declaration. |
| |
| <li>If <code>#pragma extern_prefix</code> and <code>#pragma redefine_extname</code> |
| apply to the same declaration, whichever triggered first wins, and a |
| warning issues if they contradict each other. (We would like to have |
| <code>#pragma redefine_extname</code> always win, for consistency with asm |
| labels, but if <code>#pragma extern_prefix</code> triggers first we have no |
| way of knowing that that happened.) |
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