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<a name="Host-Configuration"></a>
<h2 class="chapter">19 Host Configuration</h2>
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<p>Most details about the machine and system on which the compiler is
actually running are detected by the <code>configure</code> script.  Some
things are impossible for <code>configure</code> to detect; these are
described in two ways, either by macros defined in a file named
<samp>xm-<var>machine</var>.h</samp> or by hook functions in the file specified
by the <var>out_host_hook_obj</var> variable in <samp>config.gcc</samp>.  (The
intention is that very few hosts will need a header file but nearly
every fully supported host will need to override some hooks.)
</p>
<p>If you need to define only a few macros, and they have simple
definitions, consider using the <code>xm_defines</code> variable in your
<samp>config.gcc</samp> entry instead of creating a host configuration
header.  See <a href="System-Config.html#System-Config">System Config</a>.
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<tr><td align="left" valign="top">&bull; <a href="Host-Common.html#Host-Common" accesskey="1">Host Common</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Things every host probably needs implemented.
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<tr><td align="left" valign="top">&bull; <a href="Filesystem.html#Filesystem" accesskey="2">Filesystem</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Your host cannot have the letter &lsquo;a&rsquo; in filenames?
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<tr><td align="left" valign="top">&bull; <a href="Host-Misc.html#Host-Misc" accesskey="3">Host Misc</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Rare configuration options for hosts.
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