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### E.20 Branch Trace Format

In order to display the branch trace of an inferior thread, GDB needs to obtain the list of branches. This list is represented as list of sequential code blocks that are connected via branches. The code in each block has been executed sequentially.

This list is obtained using the ‘`qXfer:btrace:read`’ (see qXfer btrace 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 btrace
              PUBLIC "+//IDN gnu.org//DTD GDB Branch Trace V1.0//EN"
                     "http://sourceware.org/gdb/gdb-btrace.dtd">
    <btrace>
       block...
    </btrace>

- A block of sequentially executed instructions starting at begin and ending at end:

      <block begin="begin" end="end"/>

The formal DTD for the branch trace format is given below:

    <!ELEMENT btrace  (block* | pt) >
    <!ATTLIST btrace  version CDATA   #FIXED "1.0">

    <!ELEMENT block        EMPTY>
    <!ATTLIST block        begin  CDATA   #REQUIRED
                           end    CDATA   #REQUIRED>

    <!ELEMENT pt (pt-config?, raw?)>

    <!ELEMENT pt-config (cpu?)>

    <!ELEMENT cpu EMPTY>
    <!ATTLIST cpu vendor   CDATA #REQUIRED
                  family   CDATA #REQUIRED
                  model    CDATA #REQUIRED
                  stepping CDATA #REQUIRED>

    <!ELEMENT raw (#PCDATA)>