FreeBSD shellcode

  Hi. I developed some simple shellcode and sent it to my FreeBSD box along
with a custom format string to exploit Qpop 2.53. When the shellcode didn't
work and GDB reported 'illegal instruction', I compared and contrasted. To
my suprise, Qpop or FreeBSD had taken the bytes 0x80, 0x88, and 0x89 from my
shellcode. Does anyone have any idea why this occurred? I assume a range of
values is being exclused. 0x79 was fine.

-- 
  Joshua Davis
  Information Security Program Operations
  Transient Infrastructure Security Solutions