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<h2 class="appendix">Appendix G Target Descriptions</h2>

<p><a name="index-target-descriptions-3638"></a>
One of the challenges of using <span class="sc">gdb</span> 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:

     <ul>
<li>With so many different customized processors, it is difficult for
the <span class="sc">gdb</span> maintainers to keep up with the changes. 
<li>Since individual variants may have short lifetimes or limited
audiences, it may not be worthwhile to carry information about every
variant in the <span class="sc">gdb</span> source tree. 
<li>When <span class="sc">gdb</span> does support the architecture of the embedded system
at hand, the task of finding the correct architecture name to give the
<samp><span class="command">set architecture</span></samp> command can be error-prone. 
</ul>

   <p>To address these problems, the <span class="sc">gdb</span> remote protocol allows a
target system to not only identify itself to <span class="sc">gdb</span>, but to
actually describe its own features.  This lets <span class="sc">gdb</span> support
processor variants it has never seen before &mdash; to the extent that the
descriptions are accurate, and that <span class="sc">gdb</span> understands them.

   <p><span class="sc">gdb</span> must be linked with the Expat library to support XML
target descriptions.  See <a href="Expat.html#Expat">Expat</a>.

<ul class="menu">
<li><a accesskey="1" href="Retrieving-Descriptions.html#Retrieving-Descriptions">Retrieving Descriptions</a>:          How descriptions are fetched from a target. 
<li><a accesskey="2" href="Target-Description-Format.html#Target-Description-Format">Target Description Format</a>:        The contents of a target description. 
<li><a accesskey="3" href="Predefined-Target-Types.html#Predefined-Target-Types">Predefined Target Types</a>:          Standard types available for target
                                    descriptions. 
<li><a accesskey="4" href="Enum-Target-Types.html#Enum-Target-Types">Enum Target Types</a>:                How to define enum target types. 
<li><a accesskey="5" href="Standard-Target-Features.html#Standard-Target-Features">Standard Target Features</a>:         Features <span class="sc">gdb</span> knows about. 
</ul>

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