| <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="Deprecated.html#Deprecated" title="Deprecated"> |
| <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> |
| <!-- |
| This file documents the GNU Assembler "as". |
| |
| Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, |
| 2000, 2001, 2002, 2006, 2007, 2008, 2009, 2010 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> |
| <link rel="stylesheet" type="text/css" href="../cs.css"> |
| </head> |
| <body> |
| <div class="node"> |
| <a name="Word"></a> |
| <p> |
| Next: <a rel="next" accesskey="n" href="Deprecated.html#Deprecated">Deprecated</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">7.121 <code>.word </code><var>expressions</var></h3> |
| |
| <p><a name="index-g_t_0040code_007bword_007d-directive-500"></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-501"></a><a name="index-altered-difference-tables-502"></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> |
| |
