ElfEXEC

-- .ELF file runner (v-1.-1.-1)
-- (c) ProgramCrafter

local function ByteStream()
  local t = {}
  local cidx = 0

  local bitstream = {
    extend = function(len, value)
      for i = 1, len do
        t[cidx + i] = value or 0
      end
      cidx = cidx + len
    end,
    put = function(...)
      for i = 1, table.pack(...).n do
        t[cidx + 1] = select(i, ...) or 0
        cidx = cidx + 1
      end
    end,
    puts = function(s)
      for i = 1, #s do
        t[cidx + i] = s:byte(i)
      end
      cidx = cidx + #s
    end,
    read = function(len)
      cidx = cidx + len
      return table.unpack(t, cidx - len + 1, cidx)
    end,
    seek = function(new_idx)
      if not new_idx then return cidx end
      cidx = new_idx
    end,
    len = function()
      return #t
    end,
    __raw = t
  }

  return bitstream
end

local function is_like(t1, t2)
  if #t1 ~= #t2 then return false end
  for i = 1, #t1 do
    if t1[i] ~= t2[i] and t2[i] then return false end
  end
  return true
end
local function assert_like(msg, t, pattern)
  local a = is_like(t, pattern) and '\27[32mOK:  ' or '\27[33mFAIL: '
  print(a .. msg .. '\27[37m')
  if a:find('FAIL') then
    print('Found', table.unpack(t))
    print('Needs', table.unpack(pattern))
    error('Assertion failure')
  end
end
local function lton(t)
  local n = 0
  for i = #t, 1, -1 do
    n = n * 256 + t[i]
  end
  return n
end

local F = false

local elf_code = '\x7F\x45\x4C\x46\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x10\x02\x00\x03\x00\x01\x00\x00\x00\x80\x80\x04\x08\x34\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x34\x00\x20\x00\x02\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x80\x00\x00\x00\x80\x80\x04\x08\x00\x00\x00\x00\x24\x00\x00\x00\x24\x00\x00\x00\x05\x00\x00\x00\x00\x10\x00\x00\x01\x00\x00\x00\xA4\x00\x00\x00\xA4\x80\x04\x08\x00\x00\x00\x00\x20\x00\x00\x00\x20\x00\x00\x00\x07\x00\x00\x00\x00\x10\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xBB\x01\x00\x00\x00\xB8\x04\x00\x00\x00\xB9\xA4\x80\x04\x08\xBA\x0D\x00\x00\x00\xCD\x80\xB8\x01\x00\x00\x00\xBB\x5D\x00\x00\x00\xCD\x80\x00\x00\x48\x65\x6C\x6C\x6F\x20\x57\x6F\x72\x6C\x64\x21\x0A'
local elf_stream = ByteStream()
elf_stream.puts(elf_code)
elf_stream.seek(0)

assert_like('E_IDENT',   {elf_stream.read(16)}, {0x7F,0x45,0x4C,0x46, 1,1,1, F,F,F,F,F,F,F,F, 16})
assert_like('E_TYPE',    {elf_stream.read(2)},  {0x02,0x00})
assert_like('E_MACHINE', {elf_stream.read(2)},  {0x03,0x00})
assert_like('E_VERSION', {elf_stream.read(4)},  {0x01,0x00,0x00,0x00})
local e_entry = lton {elf_stream.read(4)}
local e_phoff = lton {elf_stream.read(4)}
local e_shoff = lton {elf_stream.read(4)}
local e_flags = lton {elf_stream.read(4)}
assert_like('E_EHSIZE',   {elf_stream.read(2)},  {0x34,0x00})
assert_like('E_PHENTSIZE',{elf_stream.read(2)},  {0x20,0x00})
local e_phnum = lton {elf_stream.read(2)}
assert_like('E_SH...',    {elf_stream.read(6)},  {0,0,0,0,0,0})

local appmem = ByteStream()

local segments = {}
elf_stream.seek(e_phoff)
for i = 1, e_phnum do
  print('---- Segment #' .. tostring(i) .. ' ----')
  assert_like('P_TYPE', {elf_stream.read(4)}, {1,0,0,0})
  local p_offset = lton {elf_stream.read(4)}
  local p_vaddr  = lton {elf_stream.read(4)}
  assert_like('P_PADDR',{elf_stream.read(4)}, {0,0,0,0})
  local p_filesz = lton {elf_stream.read(4)}
  local p_memsz  = lton {elf_stream.read(4)}
  local p_flags  = lton {elf_stream.read(4)}
  assert_like('P_ALIGN',{elf_stream.read(4)}, {0,0x10,0,0})

  segments[i] = {r_offset = p_offset, w_offset = p_vaddr, r_len = p_filesz, w_len = p_memsz}
end

for i = 1, e_phnum do
  local cs = segments[i]
  elf_stream.seek(cs.r_offset)
  appmem.seek(cs.w_offset)
  appmem.put(elf_stream.read(cs.r_len))
  appmem.extend(cs.w_len - cs.r_len)

  print('---- Segment #' .. tostring(i) .. ' loaded into VM ----')
end

local bit32 = require 'bit32'
local band, bor, bxor, brs = bit32.band, bit32.bor, bit32.bxor, bit32.rshift

appmem.seek(e_entry)
local registers = {EAX = 0, EBX = 0, ECX = 0, EDX = 0}
local ridxs = {[0] = 'EAX', [3] = 'EBX', [1] = 'ECX', [2] = 'EDX'}
while true do
  local command = appmem.read(1)
  print('Command:', command)
  local opcode = band(command, 248)
  if opcode == 0xB8 then
    local target = ridxs[band(command, 7)]
    local value = lton {appmem.read(4)}
    print('Opcode: MOV ' .. tostring(value) .. ' ' .. target)
    registers[target] = value
  elseif command == 0xCD then
    local itype = appmem.read(1)
    if itype == 0x80 then
      print('Requested system call', registers.EAX)
      if registers.EAX == 1 then
        print('\27[32mExit code: ' .. tostring(registers.EBX) .. '\27[37m')
        return
      elseif registers.EAX == 4 then
        local cp = appmem.seek()
        appmem.seek(registers.ECX)
        local data = {appmem.read(registers.EDX)}
        print('Memory data:', table.unpack(data))
        print('\27[33m' .. string.char(table.unpack(data)) .. '\27[37m')
        appmem.seek(cp)
      end
    else
      print('Requested interrupt', registers.EAX)
    end
  else
    error('Unknown opcode')
  end

  os.sleep(0)
end