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<h2 class="chapter">18 Host Configuration</h2>
<p><a name="index-host-configuration-5021"></a>
Most details about the machine and system on which the compiler is
actually running are detected by the <samp><span class="command">configure</span></samp> script. Some
things are impossible for <samp><span class="command">configure</span></samp> to detect; these are
described in two ways, either by macros defined in a file named
<samp><span class="file">xm-</span><var>machine</var><span class="file">.h</span></samp> or by hook functions in the file specified
by the <var>out_host_hook_obj</var> variable in <samp><span class="file">config.gcc</span></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>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><span class="file">config.gcc</span></samp> entry instead of creating a host configuration
header. See <a href="System-Config.html#System-Config">System Config</a>.
<ul class="menu">
<li><a accesskey="1" href="Host-Common.html#Host-Common">Host Common</a>: Things every host probably needs implemented.
<li><a accesskey="2" href="Filesystem.html#Filesystem">Filesystem</a>: Your host can't have the letter `a' in filenames?
<li><a accesskey="3" href="Host-Misc.html#Host-Misc">Host Misc</a>: Rare configuration options for hosts.
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