Queries Luajit bytecode mnemonic by index or name

lj-bcname.lua

#!/usr/bin/env luajit

-- Prints out LuaJIT bytecode (name, number), by number or name.
--
-- usage:   lj-bcname <bc_name|bc_number>...
--
-- example:
--
--    $ luajit-2.1 lj-bcname UCOL
--      UCOL (51)
--
--    $ luajit-2.1 lj-bcname 51 52
--      UCOL (51)
--      FNEW (52)
--
-- From:  http://www.freelists.org/post/luajit/frames-and-tail-calls,1

local function usage()
   print([[
Usage: lj-bcname <BYTECODE_NUMBER|BYTECODE_ID>...
   ]])
   os.exit(-1)
end

local bcnames = require("jit.vmdef").bcnames
local BC_LENGTH = 6 

local function trim (s)
   return (string.gsub(s, "^%s*(.-)%s*$", "%1"))
end

local function bc_arr(bcnames)
   local result = {}
   while #bcnames > 0 do
      local bc = string.sub(bcnames, 1, BC_LENGTH)
      table.insert(result, trim(bc))
      bcnames = string.sub(bcnames, BC_LENGTH + 1)
   end
   return result
end

local function bc_hash(bcnames)
   local result = {}
   for i, val in ipairs(bc_arr(bcnames)) do
      result[val] = i 
   end
   return result
end

local function print_bc(bc, index)
   print(("%s (%d)"):format(bc, index))
end

if #arg == 0 then
   usage()
end

for _, val in ipairs(arg) do
   if tonumber(val) then
      local bytecodes_by_number = bc_arr(bcnames)
      local index = tonumber(val)
      index = index + 1
      local bc = bytecodes_by_number[index]
      if bc then print_bc(bc, index - 1) end
   elseif tostring(val) then
      local bytecodes_by_name = bc_hash(bcnames)
      local bcname = val
      local index = bytecodes_by_name[bcname]
      if index then print_bc(bcname, index - 1) end
   else
      usage()
   end
end