Re: Bundling Lua code in your (ELF) executable.

[Tony Finch <dot@...>]

On Mon, 3 Mar 2008, David Jones wrote:
>
> There are plenty of ways of doing this (for example translate the .lua files
> into .c files that have the contents in a C string), I think mostly the reason
> why I chose this way is that I happened to be reading about the Mach-O loader
> whilst I was needing this feature.
>
> Because I use the Mach-O loader interface this technique only works on OS X;
> though the general principles will be similar on other operating systems, most
> of the work is in the platform-specific details.  Since the work was
> non-trivial I thought I'd jot down a few notes in case anyone else wanted to
> do something similar

Interesting. The easy linking is really nice.

On an ELF system with gcc and GNU binutils, you can turn a (source or
compiled) lua script into a linkable object as follows. The key magic is
the -b option which specifies the input file format, in this case, any old
binary data.

	ld -b binary -r -o MYSCRIPT.o MYSCRIPT.lua

When you link your program you must specify -export-dynamic so that the
binary file's symbols are available to dynamic objects, including the
run-time linker.

	gcc -export-dynamic -o MYPROG MYPROG.c MYSCRIPT.o

Then MYPROG can find the location of MYSCRIPT in memory using dlsym().

	void *start = dlsym(NULL, "_binary_MYSCRIPT_lua_start");
	void *end = dlsym(NULL, "_binary_MYSCRIPT_lua_end");
	luaL_loadbuffer(L, start, end-start, "MYSCRIPT");

You can also turn MYSCRIPT into a shared object using:

	ld -shared -o MYSCRIPT.so MYSCRIPT.o

Then MYPROG can use dlopen() and pass the resulting handle into the
dlsym() calls in the loadbuffer() code, or you can use the LD_PRELOAD
environment variable to link MYPROG and MYSCRIPT together at run-time.

Tony.
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