Abusing LuaJIT as a REPL for assembly language

asmrepl.lua

-- warning: this is hacky. run at your own risk.
--
-- before you run this, put sum_list.asm in a dynamic library.
--
-- on OSX that means
-- $ nasm -f macho64 sum_list.asm
-- $ libtool -dynamic sum_list.o -o libsum_list.dylib
--
-- on Linux it means
-- $ nasm -f elf64 sum_list.asm
-- $ export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:.
-- $ ld -shared sum_list.o -o libsum_list.so
--
-- when you run it use -i, like so:
-- $ luajit -i asmrepl.lua
-- this dumps you into LuaJIT's REPL after evaluating the file is done

ffi = require("ffi")
ffi.cdef[[
struct number_list {
  uint64_t number;
  struct number_list *next;
};
uint64_t sum_list(struct number_list*);
]]
asm = ffi.load("sum_list")

function sum_list(list)
  print(tonumber(asm.sum_list(list)))
end

dont_gc = {}  -- such hacky. many bad idea.
function from (min,max)
  function range (min,max,cdr)
    if max<min then return cdr end
    dont_gc[max] = ffi.new("struct number_list",{max, cdr})
    return range (min,max-1,dont_gc[max])
  end
  return range(min,max,nil)
end

sum_list.asm

bits 64
; macros for readability
%define list rdi             ; by calling convention, argument shows up here
%define accum rax            ; accumulator (literally!)
%define sublist rdx

global _sum_list   ; OSX likes pre-underscores
_sum_list:
global sum_list    ; Linux doesn't
sum_list:
  mov accum, 0               ; these are the let-bindings!
  mov sublist, list
.sum_sublist:
  cmp sublist, 0             ; is it NULL?
  jnz .else                  ; if not, goto else
  ret; accum                (because return value is rax by calling convention)
.else:
  add accum, [sublist]       ; accum+=sublist->number;
  mov sublist, [sublist+8]   ; sublist=sublist->next;
  jmp .sum_sublist