gdb-debug-log is a variable defined in `gdb-ui.el'.
Its value is shown below.

Documentation:
List of commands sent to and replies received from GDB.
Most recent commands are listed first.  This list stores only the last
`gdb-debug-log-max' values.  This variable is used to debug GDB-UI.

Value: 
((recv . "
\npre-prompt
\n(gdb) 
\nprompt
\n")
 (recv . "No breakpoints or watchpoints.
\n")
 (recv . "
\npost-prompt
\n")
 (send-item "server info breakpoints\n" gdb-info-breakpoints-handler)
 (recv . "
\npre-prompt
\n(gdb) 
\nprompt
\n")
 (recv . "&\"\\n\\032\\032error-begin\\n\"
\n~\"\\n\\032\\032error\\n\"
\n^error,msg=\"No registers.\"
\n(gdb) 
\n")
 (recv . "
\npost-prompt
\n")
 (send-item "server interpreter mi -stack-info-frame\n" gdb-frame-handler-1)
 (recv . "
\npre-prompt
\n(gdb) 
\nprompt
\n")
 (recv . "b add_one
\nb add_profil
\n")
 (recv . "b add_fdes
\n")
 (recv . "
\npost-prompt
\n")
 (send-item .
	    #("complete b add_\n" 9 15
	      (fontified t))))