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<title>Debugging with GDB: Target Descriptions</title>
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<a name="Target-Descriptions"></a>
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<p>
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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="previous">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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<a name="Target-Descriptions-1"></a>
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<h2 class="appendix">Appendix G Target Descriptions</h2>
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<a name="index-target-descriptions"></a>
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<p>One of the challenges of using <small>GDB</small> to debug embedded systems
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is that there are so many minor variants of each processor
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architecture in use. It is common practice for vendors to start with
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a standard processor core — ARM, PowerPC, or <acronym>MIPS</acronym>, for example —
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and then make changes to adapt it to a particular market niche. Some
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architectures have hundreds of variants, available from dozens of
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vendors. This leads to a number of problems:
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</p>
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<ul>
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<li> With so many different customized processors, it is difficult for
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the <small>GDB</small> maintainers to keep up with the changes.
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</li><li> Since individual variants may have short lifetimes or limited
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audiences, it may not be worthwhile to carry information about every
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variant in the <small>GDB</small> source tree.
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</li><li> When <small>GDB</small> does support the architecture of the embedded system
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at hand, the task of finding the correct architecture name to give the
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<code>set architecture</code> command can be error-prone.
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</li></ul>
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<p>To address these problems, the <small>GDB</small> remote protocol allows a
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target system to not only identify itself to <small>GDB</small>, but to
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actually describe its own features. This lets <small>GDB</small> support
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processor variants it has never seen before — to the extent that the
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descriptions are accurate, and that <small>GDB</small> understands them.
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</p>
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<p><small>GDB</small> must be linked with the Expat library to support XML
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target descriptions. See <a href="Requirements.html#Expat">Expat</a>.
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</p>
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<table class="menu" border="0" cellspacing="0">
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<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.
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</td></tr>
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<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.
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</td></tr>
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<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
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descriptions.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Enum-Target-Types.html#Enum-Target-Types" accesskey="4">Enum Target Types</a>:</td><td> </td><td align="left" valign="top">How to define enum target types.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Standard-Target-Features.html#Standard-Target-Features" accesskey="5">Standard Target Features</a>:</td><td> </td><td align="left" valign="top">Features <small>GDB</small> knows about.
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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="previous">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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