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<h4 class="subsection">9.24.2 MIPS ECOFF object code</h4>

<p><a name="index-ECOFF-sections-1266"></a><a name="index-MIPS-ECOFF-sections-1267"></a>Assembling for a <span class="sc">mips</span> <span class="sc">ecoff</span> target supports some additional sections
besides the usual <code>.text</code>, <code>.data</code> and <code>.bss</code>.  The
additional sections are <code>.rdata</code>, used for read-only data,
<code>.sdata</code>, used for small data, and <code>.sbss</code>, used for small
common objects.

   <p><a name="index-small-objects_002c-MIPS-ECOFF-1268"></a><a name="index-g_t_0040code_007bgp_007d-register_002c-MIPS-1269"></a>When assembling for <span class="sc">ecoff</span>, the assembler uses the <code>$gp</code> (<code>$28</code>)
register to form the address of a &ldquo;small object&rdquo;.  Any object in the
<code>.sdata</code> or <code>.sbss</code> sections is considered &ldquo;small&rdquo; in this sense. 
For external objects, or for objects in the <code>.bss</code> section, you can use
the <code>gcc</code> &lsquo;<samp><span class="samp">-G</span></samp>&rsquo; option to control the size of objects addressed via
<code>$gp</code>; the default value is 8, meaning that a reference to any object
eight bytes or smaller uses <code>$gp</code>.  Passing &lsquo;<samp><span class="samp">-G 0</span></samp>&rsquo; to
<code>as</code> prevents it from using the <code>$gp</code> register on the basis
of object size (but the assembler uses <code>$gp</code> for objects in <code>.sdata</code>
or <code>sbss</code> in any case).  The size of an object in the <code>.bss</code> section
is set by the <code>.comm</code> or <code>.lcomm</code> directive that defines it.  The
size of an external object may be set with the <code>.extern</code> directive.  For
example, &lsquo;<samp><span class="samp">.extern sym,4</span></samp>&rsquo; declares that the object at <code>sym</code> is 4 bytes
in length, whie leaving <code>sym</code> otherwise undefined.

   <p>Using small <span class="sc">ecoff</span> objects requires linker support, and assumes that the
<code>$gp</code> register is correctly initialized (normally done automatically by
the startup code).  <span class="sc">mips</span> <span class="sc">ecoff</span> assembly code must not modify the
<code>$gp</code> register.

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