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 <a name="Target-Descriptions-1"></a>
 <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.
 </td></tr>
 <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.
 </td></tr>
 <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.
 </td></tr>
 <tr><td align="left" valign="top">&bull; <a href="Standard-Target-Features.html#Standard-Target-Features" accesskey="4">Standard Target Features</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Features <small>GDB</small> knows about.
 </td></tr>
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	Next: <a href="Operating-System-Information.html#Operating-System-Information" accesskey="n" rel="next">Operating System Information</a>, Previous: <a href="Agent-Expressions.html#Agent-Expressions" accesskey="p" rel="prev">Agent Expressions</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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	<hr>
	<a name="Target-Descriptions-1"></a>
	<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 — ARM, PowerPC, or <acronym>MIPS</acronym>, for example —
	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 — 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">• <a href="Retrieving-Descriptions.html#Retrieving-Descriptions" accesskey="1">Retrieving Descriptions</a>:</td><td>  </td><td align="left" valign="top">How descriptions are fetched from a target.
	</td></tr>
	<tr><td align="left" valign="top">• <a href="Target-Description-Format.html#Target-Description-Format" accesskey="2">Target Description Format</a>:</td><td>  </td><td align="left" valign="top">The contents of a target description.
	</td></tr>
	<tr><td align="left" valign="top">• <a href="Predefined-Target-Types.html#Predefined-Target-Types" accesskey="3">Predefined Target Types</a>:</td><td>  </td><td align="left" valign="top">Standard types available for target
	descriptions.
	</td></tr>
	<tr><td align="left" valign="top">• <a href="Standard-Target-Features.html#Standard-Target-Features" accesskey="4">Standard Target Features</a>:</td><td>  </td><td align="left" valign="top">Features <small>GDB</small> knows about.
	</td></tr>
	</table>

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