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<title>MIPS Object - Using as</title>
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<!--
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This file documents the GNU Assembler "as".
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Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002,
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2006, 2007 Free Software Foundation, Inc.
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<div class="node">
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<p>
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<a name="MIPS-Object"></a>Next: <a rel="next" accesskey="n" href="MIPS-Stabs.html#MIPS-Stabs">MIPS Stabs</a>,
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Previous: <a rel="previous" accesskey="p" href="MIPS-Opts.html#MIPS-Opts">MIPS Opts</a>,
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Up: <a rel="up" accesskey="u" href="MIPS_002dDependent.html#MIPS_002dDependent">MIPS-Dependent</a>
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<h4 class="subsection">9.22.2 MIPS ECOFF object code</h4>
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<p><a name="index-ECOFF-sections-1208"></a><a name="index-MIPS-ECOFF-sections-1209"></a>Assembling for a <span class="sc">mips</span> <span class="sc">ecoff</span> target supports some additional sections
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besides the usual <code>.text</code>, <code>.data</code> and <code>.bss</code>. The
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additional sections are <code>.rdata</code>, used for read-only data,
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<code>.sdata</code>, used for small data, and <code>.sbss</code>, used for small
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common objects.
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<p><a name="index-small-objects_002c-MIPS-ECOFF-1210"></a><a name="index-_0040code_007bgp_007d-register_002c-MIPS-1211"></a>When assembling for <span class="sc">ecoff</span>, the assembler uses the <code>$gp</code> (<code>$28</code>)
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register to form the address of a “small object”. Any object in the
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<code>.sdata</code> or <code>.sbss</code> sections is considered “small” in this sense.
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For external objects, or for objects in the <code>.bss</code> section, you can use
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the <code>gcc</code> <span class="samp">-G</span> option to control the size of objects addressed via
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<code>$gp</code>; the default value is 8, meaning that a reference to any object
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eight bytes or smaller uses <code>$gp</code>. Passing <span class="samp">-G 0</span> to
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<code>as</code> prevents it from using the <code>$gp</code> register on the basis
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of object size (but the assembler uses <code>$gp</code> for objects in <code>.sdata</code>
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or <code>sbss</code> in any case). The size of an object in the <code>.bss</code> section
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is set by the <code>.comm</code> or <code>.lcomm</code> directive that defines it. The
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size of an external object may be set with the <code>.extern</code> directive. For
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example, <span class="samp">.extern sym,4</span> declares that the object at <code>sym</code> is 4 bytes
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in length, whie leaving <code>sym</code> otherwise undefined.
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<p>Using small <span class="sc">ecoff</span> objects requires linker support, and assumes that the
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<code>$gp</code> register is correctly initialized (normally done automatically by
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the startup code). <span class="sc">mips</span> <span class="sc">ecoff</span> assembly code must not modify the
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<code>$gp</code> register.
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</body></html>
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