Poke opcodes into memory

Question

Hi I am trying to understand whether it is possible to take instruction opcodes and 'poke' them into memory or smehow convert them to a binary program. I have found an abandoned lisp project here: http://common-lisp.net/viewvc/cl-x86-asm/cl-x86-asm/ which takes x86 asm instructions and converts them into opcodes (please see example below). The project does not go further to actually complete the creation of the binary executable. Hence I would need to do that 'manually' Any ideas can help me. Thanks.

 ;; assemble some code in it
(cl-x86-asm::assemble-forms 
  '((.Entry :PUSH :EAX)
    (:SUB :EAX #XFFFEA)
    (:MOV :EAX :EBX)
    (:POP :EAX)
    (:PUSH :EAX)
    (.Exit :RET))

Processing...

;; print the assembled segment
(cl-x86-asm::print-segment)

* Segment type DATA-SEGMENT
Segment size 0000000C bytes
50 81 05 00 0F FF EA 89
03 58 50 C3

Answer 1

Clozure Common Lisp for example has this built-in. This is usually called LAP , Lisp Assembly Program .

See defx86lapfunction .

Example:

(defx86lapfunction fast-mod ((number arg_y) (divisor arg_z))
  (xorq (% imm1) (% imm1))
  (mov (% number) (% imm0))
  (div (% divisor))
  (mov (% imm1) (% arg_z))
  (single-value-return))

SBCL can do some similar with VOP (Virtual Operations).

http://g000001.cddddr.org/2011-12-08

Answer 2

I learned that it can be done using CFFI/FFI for example the very simple asm code:

(:movl 12 :eax)
(:ret)

This will be converted to the following sequence of octets: #(184 12 0 0 0 195) which in hex it is: #(B8 C 0 0 0 C3). The next step is to send it to a location in memory as such:

(defparameter pointer (cffi:foreign-alloc :unsigned-char :initial-contents #(184 12 0 0 0 195)))
;; and then execute it as such to return the integer 12:
(cffi:foreign-funcall-pointer pointer () :int)
=> result: 12

Thanks to the experts in #lisp (freenode irc channel) for helping out with this solution.