Re: shared library, symbols names and Linux distributions

[Coda Highland <chighland@...>]

On Mon, Jul 7, 2014 at 11:13 AM, Daurnimator <quae@daurnimator.com> wrote:
> On 7 July 2014 13:57, Enrico Tassi <gares@fettunta.org> wrote:
>>
>> Shared objects are names liblua5.1.so.0.0.0 and liblua5.2.so.0.0.0, but
>> this is not enough.  You can have a library libfoo.so that is developed
>> by John and that links the former, and another library, libbar.so,
>> developed by Jack that links the latter.  Now, if I want to use both
>> libfoo and libbar the loader has to load one fist, say foo, and in turn
>> this loads liblua5.1 with all its symbols.  When it is the turn of bar,
>> even if liblua5.2 is loaded, some symbols, say lua_pushinteger, are
>> already there and take precedence.  So you end up having bar using some
>> lua5.1 symbols expecting them to be lua5.2 symbols...
>>
>> very nasty.
>> --
>> Enrico Tassi
>>
>
> (Pardon my ignorance):
> Why is this an issue?
> Surely libfoo should be effectively calling:
>     h=dlopen("liblua5.1.so.0.0.0", RTLD_LOCAL)
>     f=dlsym(h, "lua_pushinteger")
> and then using `f`?

It's more like

if lua_pushinteger does not exist {
    open liblua5.1.so.0.0.0 with RTLD_GLOBAL
}
use lua_pushinteger

So you can see the problem.

/s/ Adam