Here's the script for producing a trace of the
instructions executed. It's invoked (from the 
gdb prompt) as:
    count <begin> <end>, where <begin> and <end> are described below,
and it's supposed to print out the disassembled code
(with a bunch of cruft) to standard output.

The only catch in this thing is that I haven't figured
out how to give the script an <end> line number (see below).
Also, I haven't figured out how to get the -output
flag to work (which makes the output got to a file
rather than to the gdb session).

#arg0 of count is the line number of the
#   beginning of the region being measured
#arg1 is the address of the instruction
#   right after the region being measured; as
#   of now, obtained by 
#	info line <line-num> 
#   where <line-num> is just after the region 
#   measured 

define count
disable
break predi.c:$arg0  <---I've hardwired "predi.c"; should probably
			  be a parameter: it's the file where line
			  $arg0 lives
cont
while ($pc != $arg1)
	disass $pc ($pc+4) 
	si
end
enable
end