### E.18 Traceframe Info Format

To be able to know which objects in the inferior can be examined when inspecting a tracepoint hit, GDB needs to obtain the list of memory ranges, registers and trace state variables that have been collected in a traceframe.

This list is obtained using the ‘`qXfer:traceframe-info:read`’ (see qXfer traceframe info read) packet and is an XML document.

GDB must be linked with the Expat library to support XML traceframe info discovery. See Expat.

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

    <?xml version="1.0"?>
    <!DOCTYPE traceframe-info
              PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN"
                     "http://sourceware.org/gdb/gdb-traceframe-info.dtd">
    <traceframe-info>
       block...
    </traceframe-info>

Each traceframe block can be either:

- A region of collected memory starting at addr and extending for length bytes from there:

      <memory start="addr" length="length"/>

- A block indicating trace state variable numbered number has been collected:

      <tvar id="number"/>

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

    <!ELEMENT traceframe-info  (memory | tvar)* >
    <!ATTLIST traceframe-info  version CDATA   #FIXED  "1.0">

    <!ELEMENT memory        EMPTY>
    <!ATTLIST memory        start   CDATA   #REQUIRED
                            length  CDATA   #REQUIRED>
    <!ELEMENT tvar>
    <!ATTLIST tvar          id      CDATA   #REQUIRED>