Re: Lua on SunPlus digital photo frames

[Rena <hyperhacker@...>]

On Mon, Jan 13, 2020 at 10:02 AM William Ahern
<william@25thandclement.com> wrote:
>
> On Sat, Jan 11, 2020 at 05:54:25PM -0500, Sean Conner wrote:
> > It was thus said that the Great Rena once stated:
> > >
> > > I also didn't find the bytes 19 93 0D 0A 1A 0A which are present in
> > > every compiled Lua bytecode file. (I checked raw flash and
> > > uncompressed firmware.) So it really does seem like there's no more
> > > trace of Lua itself left in here...
> >
> >   Dosn't mean it's not there.  At work, I embed Lua in one of our programs
> > and all the Lua scripts are compressed [1]---I have a custom loader that will do
> > the decompression upon loading.  I go over the technique here:
> >
> >       http://boston.conman.org/2013/03/22.1
> >       http://boston.conman.org/2013/03/23.1
> >
> >   -spc
> >
> > [1]   They are also embedded into the executable.
>
> I've done the same thing and, like you, transformed and compressed each Lua
> file individually with a simple Makefile rule. However, especially with
> precompiled bytecode chunks (which are larger than their text source), this
> turned out to create larger executables if there are too many short Lua
> source files (e.g. wrappers) and not enough long source files. In my case,
> which I suspect isn't uncommon, if would be better to compress all the
> source files together. But it makes the code more complex. I independently
> wrote code very similar to yours, which I doubt is a coincidence as that's
> the most obvious, elegant, and, in particular, transparent way to do it.
>
> For now I just disable bytecode precompiling, and compression partly offsets
> the cost of all the additional luaopen_ functions. I don't have enough long
> Lua source files for compression to pay real dividends.
>
> I guess it also matters that I *embed* an inflate implementation to avoid an
> external dependency.
>
>   https://github.com/madler/zlib/blob/master/contrib/puff/puff.c
>
> It's small, but again I don't have any big Lua source files to offset the
> cost.
>

Well, I started reverse engineering the actual code, and found that
indeed the "lua" command does absolutely nothing. Oh well. Maybe I'll
find another SunPlus device that actually has it.

-- 
Sent from my Game Boy.