nimlisp.nim

import posix, system, os, memfiles

var program: array[0..4, uint8] = [
  # mov eax, 42 (0x2a)
  0xb8.uint8, 0x2a.uint8, 0x00.uint8, 0x00.uint8,
  # ret
  0xc3.uint8
]

const kProgramSize: int = program.sizeof

type JitFunction = proc (): cint {. cdecl .}

when isMainModule:
  var nilMemfile: MemFile
  nilMemfile.handle = -1

  var memory: pointer = mapMem(m=nilMemfile,
                               mode=fmReadWrite,
                               mappedSize=kProgramSize,
                               mapFlags=MAP_ANONYMOUS or MAP_PRIVATE)

  moveMem(memory, program[0].addr, kProgramSize)

  assert memory.mprotect(kProgramSize, PROT_EXEC) == 0, "mprotect failed"

  var function: JitFunction = (cast[ptr JitFunction](memory.addr))[]

  discard function()