undefined symbol: 'luaT_typenames_' when attempting to run a lua script that requires a Pallene module.

[srijan-paul]

I am trying to compile a simple C command line application that uses the Lua interpreter bundled with Pallene to run some Lua scripts.

Currently, the C script invokes the Lua interpreter on a file called app.lua, using luaL_dofile.
This works just fine with both the lua/src/lua executable and the executable built from my C source. However, when the app.lua requires a Pallene module, I get the following error:

error loading module 'pmath' from file './pmath.so':
	./pmath.so: undefined symbol: luaT_typenames_.

To reproduce the problem on a simpler scale, I used the following directory structure (everything inside Pallene's root):

└── pallene
    ├── app.lua
    ├── pmath.so
    ├── pmath.pln
    ├── main.c
    ├── game
    ├── < pallene source >

Contents of main.c:

#include "lua.h"
#include "lprefix.h"
#include "pallene_core.h"
#include "lauxlib.h"
#include "lualib.h"
#include <stdio.h>
#include <stdlib.h>

#define ASSERT(cond) \
		if (!(cond)) { \
			fprintf(stderr, "[%s %d]: assertion failed.\n", __func__, __LINE__);\
			exit(1); \
		} \

#define ERROR(...) (fprintf(stderr, __VA_ARGS__), exit(1))

int main() {
	lua_State* L = luaL_newstate();
	ASSERT(L != NULL);
	luaL_openlibs(L);
	
		
	int r = luaL_dofile(L, "./app.lua");
	if (r != LUA_OK) {
		char const* err_msg = lua_tostring(L, -1);
		fprintf(stderr, "lua interpreter exited with exitcode %d.\n", r);
		ERROR("LUA error: %s.\n", err_msg);
	}

	lua_close(L);
	return 0;
}

contents of app.lua:

local _ = require "pmath"
print "success"

contents of pmath.pln (irrevelant afaik):

export function add(a: integer, b: integer): integer
    return a + b
end

The above is compiled and run with:

gcc -I ./runtime -I ./lua/src -std=c99 -O2 -ldl -Wall -Wextra -lm -fPIC -o app main.c ./runtime/pallenelib.a ./lua/src/liblua.a

The compilation is successful, but then launching ./app throws the following runtime error when dynamically loading pmath.so:

LUA error: error loading module 'pmath' from file './pmath.so':
	./pmath.so: undefined symbol: luaT_typenames_.

However running the same with lua/src/lua executes the script successfully.

Looking into lua/src/Makefile, the LUA_T target that builds the lua executable doesn't seem to have any different dependencies save lua.o.

Here is what I tried:
I tried running nm on all .o files and executables and piping the result into grep:

nm  *.o | grep "luaT_typenames"
nm  -D *.o | grep "luaT_typenames"

This is unable to find any object files that globally export the luaT_typenames_. (marked as T).

luaT_typenames is defined in the ltm.h header file, but I cannot seem to be able to get my executable to 'see' that definition.

Next, I tried running ldd on .src/lua/lua and ./app.

The only .so that is included in the lua binary but is missing from mine is libncurses, which doesn't export the luaT_typenames.

Any help appreciated ^^

[hugomg]

Hmm... an interesting problem.

I tried running nm on all .o files and executables and piping the result into grep:

What happens if you run nm on the liblua.a and on the resulting app executable?

[hugomg]

Looks like you were doing the right thing when you ran nm -D. Apparently there's a distinction between "dynamic symbols" and "normal symbols". Only the symbols that appear in the nm -D list are visible to dynamically-linked libraries.

https://stackoverflow.com/questions/15345543/when-to-use-dynamic-option-in-nm

If we run nm -D lua/src/lua, the luaT_typenames_ is there but if we run nm -D app it's not. Perhaps it the culprit could be our compilation flags or something like that?

[hugomg]

Aha! I think I figured out what it is. On Linux we need to use the -E or --export-dynamic linker flag.
https://stackoverflow.com/questions/26294841/having-object-file-symbols-become-dynamic-symbols-in-executable

In the Lua makefile, it uses this flag when linking the lua executable.

linux-noreadline:
	$(MAKE) $(ALL) SYSCFLAGS="-DLUA_USE_LINUX" SYSLIBS="-Wl,-E -ldl"

linux-readline:
	$(MAKE) $(ALL) SYSCFLAGS="-DLUA_USE_LINUX -DLUA_USE_READLINE" SYSLIBS="-Wl,-E -ldl -lreadline"

[srijan-paul]

That's great!
I've been trying a couple of things but this doesn't seem to be working for me still.

I'm compiling like so:

gcc -Wall -std=c99 -I ./runtime -I ./lua/src -c  main.c

and linking:

gcc -o app -I ./runtime -I ./lua/src -export-dynamic -lm -ldl main.o  ./lua/src/liblua.a ./runtime/pallenelib.a

However it still croaks the very same error for me.
I also tried the -rdynamic gcc flag that passes -E to the linker, but in vain.

I tried linking with ld using similar options:

ld -o app -I ./runtime -I ./lua/src -E main.o -lm -ldl ./lua/src/liblua.a ./runtime/pallenelib.a

However this time I had the following errors:

ld: ./lua/src/liblua.a(lauxlib.o): undefined reference to symbol 'getc@@GLIBC_2.2.5'
ld: /usr/lib/libc.so.6: error adding symbols: DSO missing from command line

I'm not sure whats causing this. Could it be because of incompatible versions of libc?
getc does not require any explicit library args afaik, so it could be the version in the identifier 2.2.5?

[hugomg]

These compilation lines worked for me:

gcc -I ./runtime -I ./lua/src -std=c99 -O2 -Wall -Wextra -fPIC -c -o main.o main.c
gcc -ldl -lm -Wl,-E -o app main.o ./runtime/pallenelib.a ./lua/src/liblua.a

The -Wl,-E part passes the -E flag to the linker.

I'm not sure whats causing this. Could it be because of incompatible versions of libc?

Dunno. I'm using Fedora 33, if that helps.

[srijan-paul]

Awesome, that worked!
Thank you very much ^^