[NTG-context] Re: Building luametatex with Lua symbols exposed

["Michal Vlasák" <lahcim8@gmail.com>]

On Wed Aug 30, 2023 at 6:23 PM CEST, Jairo A. del Rio wrote:
> Hi, beloved list. Since sources are in the distribution, I've tried
> compiling luametatex by setting LMT_STRIP in CMakeLists.txt to 0, yet the
> resulting binary still warns about undefined symbols, such as lua_gettop,
> when an external library is loaded in Lua. Any ideas on how to solve it?

Hi Jairo,

you need to expose _dynamic_ symbols in your luametatex binary. If you
are using Linux, just adding the following to the CMake invocation line
should work:

    -DCMAKE_EXECUTABLE_ENABLE_EXPORTS=1

For example, I compiled with:

    cmake -S . -B build -DCMAKE_BUILD_TYPE=Release -DCMAKE_EXECUTABLE_ENABLE_EXPORTS=1
    cmake --build build -j10

You can check the difference in dynamic symobls with:

    readelf --dyn-syms build/luametatex


Note, that while this approach doesn't require any modification to
luametatex's source files, it does export _all_ symbols, which makes
binaries bigger, and symbol resolution slower. It also exports also
symbols that are not intended to be used by external modules, like
"tex_get_x_token".

Back when luametatex source code wasn't available, I created a demo
which showed how to build a "luametatex like application" (i.e.
executable with Lua statically linked in), with exported dynamic
symbols, working with CMake on both Unix and Windows. It might interest
you:

    https://github.com/vlasakm/lua-demo

To support Windows in the case of luametatex, "#define LUA_BUILD_AS_DLL"
would need to be added when compiling Lua.

The problem with any module is, that you want to compile against exactly
the same Lua headers as the ones in luametatex, and with similar flags.
That is why the demo hosts everything in one CMake setup, but since
Lua's API hopefully doesn't change in the 5.4 series, you are probably
fine even with separate compilation.

IIRC stripping (LMT_STRIP) applies only to static symbols ("symbols")
and not the dynamic ones ("dynamic symbols"), and thus should be
irrelevant.

It seems that people had similar issues before:

   https://www.mail-archive.com/ntg-context@ntg.nl/msg97764.html
   https://www.mail-archive.com/ntg-context@ntg.nl/msg98184.html

I think it would be nice to support this "by default", but in that case,
the binary size would have to be addressed, and only the "supported"
public API of luametatex actually exposed. Support of this could also be
behind a compile time switch, but I am not sure how useful would that
be.

Michal
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