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<h2 class="appendix">Appendix G Target Descriptions</h2>
<a name="index-target-descriptions"></a>

<p>One of the challenges of using <small>GDB</small> to debug embedded systems
is that there are so many minor variants of each processor
architecture in use.  It is common practice for vendors to start with
a standard processor core &mdash; ARM, PowerPC, or <acronym>MIPS</acronym>, for example &mdash;
and then make changes to adapt it to a particular market niche.  Some
architectures have hundreds of variants, available from dozens of
vendors.  This leads to a number of problems:
</p>
<ul>
<li> With so many different customized processors, it is difficult for
the <small>GDB</small> maintainers to keep up with the changes.
</li><li> Since individual variants may have short lifetimes or limited
audiences, it may not be worthwhile to carry information about every
variant in the <small>GDB</small> source tree.
</li><li> When <small>GDB</small> does support the architecture of the embedded system
at hand, the task of finding the correct architecture name to give the
<code>set architecture</code> command can be error-prone.
</li></ul>

<p>To address these problems, the <small>GDB</small> remote protocol allows a
target system to not only identify itself to <small>GDB</small>, but to
actually describe its own features.  This lets <small>GDB</small> support
processor variants it has never seen before &mdash; to the extent that the
descriptions are accurate, and that <small>GDB</small> understands them.
</p>
<p><small>GDB</small> must be linked with the Expat library to support XML
target descriptions.  See <a href="Requirements.html#Expat">Expat</a>.
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top">&bull; <a href="Retrieving-Descriptions.html#Retrieving-Descriptions" accesskey="1">Retrieving Descriptions</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">How descriptions are fetched from a target.
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<tr><td align="left" valign="top">&bull; <a href="Target-Description-Format.html#Target-Description-Format" accesskey="2">Target Description Format</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">The contents of a target description.
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<tr><td align="left" valign="top">&bull; <a href="Predefined-Target-Types.html#Predefined-Target-Types" accesskey="3">Predefined Target Types</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Standard types available for target
                                    descriptions.
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<tr><td align="left" valign="top">&bull; <a href="Enum-Target-Types.html#Enum-Target-Types" accesskey="4">Enum Target Types</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">How to define enum target types.
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<tr><td align="left" valign="top">&bull; <a href="Standard-Target-Features.html#Standard-Target-Features" accesskey="5">Standard Target Features</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Features <small>GDB</small> knows about.
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