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<h3 class="section">E.18 Traceframe Info Format</h3>

<p><a name="index-traceframe-info-format-3635"></a>
To be able to know which objects in the inferior can be examined when
inspecting a tracepoint hit, <span class="sc">gdb</span> needs to obtain the list of
memory ranges, registers and trace state variables that have been
collected in a traceframe.

   <p>This list is obtained using the &lsquo;<samp><span class="samp">qXfer:traceframe-info:read</span></samp>&rsquo;
(see <a href="qXfer-traceframe-info-read.html#qXfer-traceframe-info-read">qXfer traceframe info read</a>) packet and is an XML document.

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

   <p>The top-level structure of the document is shown below:

<pre class="smallexample">     &lt;?xml version="1.0"?&gt;
     &lt;!DOCTYPE traceframe-info
               PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN"
                      "http://sourceware.org/gdb/gdb-traceframe-info.dtd"&gt;
     &lt;traceframe-info&gt;
        block...
     &lt;/traceframe-info&gt;
</pre>
   <p>Each traceframe block can be either:

     <ul>
<li>A region of collected memory starting at <var>addr</var> and extending for
<var>length</var> bytes from there:

     <pre class="smallexample">          &lt;memory start="<var>addr</var>" length="<var>length</var>"/&gt;
</pre>
     <li>A block indicating trace state variable numbered <var>number</var> has been
collected:

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

   <p>The formal DTD for the traceframe info format is given below:

<pre class="smallexample">     &lt;!ELEMENT traceframe-info  (memory | tvar)* &gt;
     &lt;!ATTLIST traceframe-info  version CDATA   #FIXED  "1.0"&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>
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