Re: win32 programmer, linux newb needs help: lua/luasql

[Tomas <tomas@...>]

	Hi Thomas

> > > Ok, so I then pull the latest luasql source, and examining the make it
> > > appears to want compat-5.1.  So I pull that also, and after messing with
> > > the config directories a bit, get it to compile.  I also run 'make
> > > install' after editing the config thusly (attempting to use lua 5.1):
	Today I've just upgraded some drivers with Lua 5.0 and 5.1
compatibility (but only Postgres was tested).

> > compat is needed to use lua50 with the behavior of lua51. compat is not
> > to be used with lua51.
>
> If I edit the luasql Makefile to remove the compat-5.1 object file from OBJS, 
> and rebuild,
> I get the following runtime error when executing the test.lua under lua 
> 5.1.1:
	Did you removed the `#include "compat-5.1.h"' from *.c ?

> lua: error loading module 'luasql.mysql' from file 
> '/usr/local/lib/lua/5.1/luasql/mysql.so':
>        /usr/local/lib/lua/5.1/luasql/mysql.so: undefined symbol: luaL_module
> stack traceback:
>        [C]: ?
>        [C]: in function 'require'
>        test.lua:599: in main chunk
>        [C]: ?
	I think luaL_module only exists in compat-5.1.c...

> I'm guessing that the undefined symbol is defined in the 5.1 version of 
> liblua, and it is not in 5.0 (but is provided via the compat-5.1 library).
	I think you're mixing Lua 5.0 with Lua 5.1 binaries, which
might not work...

> When I run lua as above, I am running the 5.1.1 version I built - and it was 
> statically linked to liblua.a.  I don't really understand how mysql.so is 
> meant to dynmically link to whatever library contains luaL_module - how is 
> that library specified?  The makefile only gives a LIB_OPTION of "-shared". 
> It doesn't specify liblua.so, for example, anywhere.
	It doesn't specify liblua.so because the symbol could be exported
by other file, as lhf pointed out (the executable, for instance).

> A further source of confusion to my win32 trained brain: why is the undefined 
> symbol not caught at compile time?
	If this is an external symbol which could not be found at runtime,
how could the compile caught an error?

> Is there no equivalent of "import 
> libraries" that one can link against to ensure symbols we're expecting to 
> find in a shared library are in fact available?  (and that tell us which 
> shared libraries to load on execution)
	I think the dynamic libraries model is rather different?

> Finally, what tool can I use to look at which shared libraries a program has 
> opened (and where they were loaded from?)
	You could check for dynamic libraries statically linked to
an executable or to a library with `ldd <complete-path-to-my-file>[.so]'.
But this could not solve the problem (LuaSQL drivers usually are statically
linked to the database client library but not to Lua).

	For now, I recommend one of two choices:

- use Lua 5.0 with Compat-5.1 R5: this is the safety choice :-)
- use Lua 5.1 (without Compat!) with the CVS HEAD: this was not tested!

	Hope this long letter will help you
		Tomas