Here it is (warning: Perl): http://pastebin.com/MFmDzY0g

It calls "objdump -d" on the binary, which is binutil's disassembler.

objdump prints each instruction out in the following format:

     5dc:       67 80 7d 00 00          cmpb   $0x0,0x0(%ebp)

The first part is the instruction offset; the second is the bytes that comprise the instruction; the third part is the instruction in AT&T assembly syntax.

The script uses regexs to cut off the front and back, then counts the number of bytes (in hex format) in the second part.

Then it calculates the average for all instructions.