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| Next: <a href="Deprecated.html#Deprecated" accesskey="n" rel="next">Deprecated</a>, Previous: <a href="Weakref.html#Weakref" accesskey="p" rel="prev">Weakref</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p> |
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| <a name="g_t_002eword-expressions"></a> |
| <h3 class="section">7.124 <code>.word <var>expressions</var></code></h3> |
| |
| <a name="index-word-directive"></a> |
| <p>This directive expects zero or more <var>expressions</var>, of any section, |
| separated by commas. |
| </p> |
| <p>The size of the number emitted, and its byte order, |
| depend on what target computer the assembly is for. |
| </p> |
| <a name="index-difference-tables-altered"></a> |
| <a name="index-altered-difference-tables"></a> |
| <blockquote> |
| <p><em>Warning: Special Treatment to support Compilers</em> |
| </p></blockquote> |
| |
| <p>Machines with a 32-bit address space, but that do less than 32-bit |
| addressing, require the following special treatment. If the machine of |
| interest to you does 32-bit addressing (or doesn’t require it; |
| see <a href="Machine-Dependencies.html#Machine-Dependencies">Machine Dependencies</a>), you can ignore this issue. |
| </p> |
| <p>In order to assemble compiler output into something that works, |
| <code>as</code> occasionally does strange things to ‘<samp>.word</samp>’ directives. |
| Directives of the form ‘<samp>.word sym1-sym2</samp>’ are often emitted by |
| compilers as part of jump tables. Therefore, when <code>as</code> assembles a |
| directive of the form ‘<samp>.word sym1-sym2</samp>’, and the difference between |
| <code>sym1</code> and <code>sym2</code> does not fit in 16 bits, <code>as</code> |
| creates a <em>secondary jump table</em>, immediately before the next label. |
| This secondary jump table is preceded by a short-jump to the |
| first byte after the secondary table. This short-jump prevents the flow |
| of control from accidentally falling into the new table. Inside the |
| table is a long-jump to <code>sym2</code>. The original ‘<samp>.word</samp>’ |
| contains <code>sym1</code> minus the address of the long-jump to |
| <code>sym2</code>. |
| </p> |
| <p>If there were several occurrences of ‘<samp>.word sym1-sym2</samp>’ before the |
| secondary jump table, all of them are adjusted. If there was a |
| ‘<samp>.word sym3-sym4</samp>’, that also did not fit in sixteen bits, a |
| long-jump to <code>sym4</code> is included in the secondary jump table, |
| and the <code>.word</code> directives are adjusted to contain <code>sym3</code> |
| minus the address of the long-jump to <code>sym4</code>; and so on, for as many |
| entries in the original jump table as necessary. |
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