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>
<block begin="begin" end="end"/>
The formal DTD for the branch trace format is given below:
<!ELEMENT btrace (block)* > <!ATTLIST btrace version CDATA #FIXED "1.0"> <!ELEMENT block EMPTY> <!ATTLIST block begin CDATA #REQUIRED end CDATA #REQUIRED>