Size optimizations for Lua 5.3 VM on ARM Cortex M4

Hi,

I am trying to get a minimal Lua VM to run on Cortex M4. I do not need the parser, only byte code execution.

I have done all the changes in https://www.lua.org/notes/ltn002.html

Also I removed all libraries except base:

** these libs are loaded by lua.c and are readily available to any Lua

** program

static const luaL_Reg loadedlibs[] = {

{"_G", luaopen_base},

// {LUA_LOADLIBNAME, luaopen_package},

// {LUA_COLIBNAME, luaopen_coroutine},

// {LUA_TABLIBNAME, luaopen_table},

// {LUA_IOLIBNAME, luaopen_io},

// {LUA_OSLIBNAME, luaopen_os},

// {LUA_STRLIBNAME, luaopen_string},

// {LUA_MATHLIBNAME, luaopen_math},

// {LUA_UTF8LIBNAME, luaopen_utf8},

// {LUA_DBLIBNAME, luaopen_debug},

#if defined(LUA_COMPAT_BITLIB)

{LUA_BITLIBNAME, luaopen_bit32},

#endif

{NULL, NULL}

};

This reduced the size to 63k for the Lua executable with maximum release optimization for x86 msvc 2015 and on cortex m4 its about 59k

I generally need only table indexing and function calls, so I compiled one of the common scripts which I intend to run on the cortex m4, and saw that it does not use most opcodes(I used chunkspy to decompile and see the opcodes).

I may need Lua's other language features later, so I decided to try optimizing its VM first.

So now I am removing some of the opcodes, which maybe a bit risky(I am commenting out the relevant vmcase in lvm.c).

What are my other options to reduce the size? I would like to bring down the Lua executable's size to about 10k like eLua!

I am not directly using eLua as it seems to have a number of other things apart from Lua which may not be easy to remove(haven't checked in detail though)

I am also trying out Lua 4.0 to see if I can get a smaller size

Thanks for your help.

Abhijit