<html lang="en"> <head> <title>Word - Using as</title> <meta http-equiv="Content-Type" content="text/html"> <meta name="description" content="Using as"> <meta name="generator" content="makeinfo 4.13"> <link title="Top" rel="start" href="index.html#Top"> <link rel="up" href="Pseudo-Ops.html#Pseudo-Ops" title="Pseudo Ops"> <link rel="prev" href="Weakref.html#Weakref" title="Weakref"> <link rel="next" href="Zero.html#Zero" title="Zero"> <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> <!-- This file documents the GNU Assembler "as". Copyright (C) 1991-2015 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License''. --> <meta http-equiv="Content-Style-Type" content="text/css"> <style type="text/css"><!-- pre.display { font-family:inherit } pre.format { font-family:inherit } pre.smalldisplay { font-family:inherit; font-size:smaller } pre.smallformat { font-family:inherit; font-size:smaller } pre.smallexample { font-size:smaller } pre.smalllisp { font-size:smaller } span.sc { font-variant:small-caps } span.roman { font-family:serif; font-weight:normal; } span.sansserif { font-family:sans-serif; font-weight:normal; } --></style> </head> <body> <div class="node"> <a name="Word"></a> <p> Next: <a rel="next" accesskey="n" href="Zero.html#Zero">Zero</a>, Previous: <a rel="previous" accesskey="p" href="Weakref.html#Weakref">Weakref</a>, Up: <a rel="up" accesskey="u" href="Pseudo-Ops.html#Pseudo-Ops">Pseudo Ops</a> <hr> </div> <h3 class="section">7.103 <code>.word </code><var>expressions</var></h3> <p><a name="index-g_t_0040code_007bword_007d-directive-513"></a>This directive expects zero or more <var>expressions</var>, of any section, separated by commas. <p>The size of the number emitted, and its byte order, depend on what target computer the assembly is for. <!-- on amd29k, i960, sparc the "special treatment to support compilers" doesn't --> <!-- happen-32-bit addressability, period; no long/short jumps. --> <p><a name="index-difference-tables-altered-514"></a><a name="index-altered-difference-tables-515"></a><blockquote> <em>Warning: Special Treatment to support Compilers</em> </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>In order to assemble compiler output into something that works, <samp><span class="command">as</span></samp> occasionally does strange things to ‘<samp><span class="samp">.word</span></samp>’ directives. Directives of the form ‘<samp><span class="samp">.word sym1-sym2</span></samp>’ are often emitted by compilers as part of jump tables. Therefore, when <samp><span class="command">as</span></samp> assembles a directive of the form ‘<samp><span class="samp">.word sym1-sym2</span></samp>’, and the difference between <code>sym1</code> and <code>sym2</code> does not fit in 16 bits, <samp><span class="command">as</span></samp> creates a <dfn>secondary jump table</dfn>, 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><span class="samp">.word</span></samp>’ contains <code>sym1</code> minus the address of the long-jump to <code>sym2</code>. <p>If there were several occurrences of ‘<samp><span class="samp">.word sym1-sym2</span></samp>’ before the secondary jump table, all of them are adjusted. If there was a ‘<samp><span class="samp">.word sym3-sym4</span></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. <!-- end DIFF-TBL-KLUGE --> </body></html>