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<a name="Traceframe-Info-Format"></a>
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<a name="Traceframe-Info-Format-1"></a>
<h3 class="section">E.18 Traceframe Info Format</h3>
<a name="index-traceframe-info-format"></a>

<p>To be able to know which objects in the inferior can be examined when
inspecting a tracepoint hit, <small>GDB</small> needs to obtain the list of
memory ranges, registers and trace state variables that have been
collected in a traceframe.
</p>
<p>This list is obtained using the &lsquo;<samp>qXfer:traceframe-info:read</samp>&rsquo;
(see <a href="General-Query-Packets.html#qXfer-traceframe-info-read">qXfer traceframe info read</a>) packet and is an XML document.
</p>
<p><small>GDB</small> must be linked with the Expat library to support XML
traceframe info discovery.  See <a href="Requirements.html#Expat">Expat</a>.
</p>
<p>The top-level structure of the document is shown below:
</p>
<div class="smallexample">
<pre class="smallexample">&lt;?xml version=&quot;1.0&quot;?&gt;
&lt;!DOCTYPE traceframe-info
          PUBLIC &quot;+//IDN gnu.org//DTD GDB Memory Map V1.0//EN&quot;
                 &quot;http://sourceware.org/gdb/gdb-traceframe-info.dtd&quot;&gt;
&lt;traceframe-info&gt;
   block...
&lt;/traceframe-info&gt;
</pre></div>

<p>Each traceframe block can be either:
</p>
<ul>
<li> A region of collected memory starting at <var>addr</var> and extending for
<var>length</var> bytes from there:

<div class="smallexample">
<pre class="smallexample">&lt;memory start=&quot;<var>addr</var>&quot; length=&quot;<var>length</var>&quot;/&gt;
</pre></div>

</li><li> A block indicating trace state variable numbered <var>number</var> has been
collected:

<div class="smallexample">
<pre class="smallexample">&lt;tvar id=&quot;<var>number</var>&quot;/&gt;
</pre></div>

</li></ul>

<p>The formal DTD for the traceframe info format is given below:
</p>
<div class="smallexample">
<pre class="smallexample">&lt;!ELEMENT traceframe-info  (memory | tvar)* &gt;
&lt;!ATTLIST traceframe-info  version CDATA   #FIXED  &quot;1.0&quot;&gt;

&lt;!ELEMENT memory        EMPTY&gt;
&lt;!ATTLIST memory        start   CDATA   #REQUIRED
                        length  CDATA   #REQUIRED&gt;
&lt;!ELEMENT tvar&gt;
&lt;!ATTLIST tvar          id      CDATA   #REQUIRED&gt;
</pre></div>


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