🚀 go-pugleaf

In article <1371.26461650@miavx1.acs.muohio.edu> rjlewis@miavx1.acs.muohio.edu writes:
>  I understand why you hook INT 8h, but how do you call the Original Int 8h
>handler, and have it RETURN to your code?  If you call the original int 8h 
>handler, it'll end with a IRET, and won't it bounce back to the currently 
>executing program (and NOT your handler). 

   No, although you have to call the old handler in a "special" way.
An INT xx instruction does several things:
   Pushes the flags (PUSHF)
   Pushes the program counter (CS:IP)
   Fiddles with the flags a little bit (interrupt mask, etc.)
   Jumps to the handler routine

     All an IRET has to do is pop the old flags and the old CS:IP
(and maybe reset an interrupt mask, I forget).  So you can simulate
an interrupt to any address by doing

 PUSHF
 CALL FAR addr

  and the IRET will return control to right after the CALL FAR instruction,
as expected.



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