🚀 go-pugleaf

In comp.unix.programmer mgogala@yahoo.com wrote:
> In article <36B5EA0E.2361@imag.fr>,
>   Yves Dufournaud <Yves.Dufournaud@imag.fr> wrote:
>> Hi,
>>
>> I'am trying basic things using dlopen with g++-2.7.2.3 on sunos 5.5 :
>>
>> I'am loading a file dynamic.o using dlopen
>> this file is c++ with global object inside.
>>
>> I've compiled it using
>> g++ -shared dynamic.cc -export-dynamic
>>
>> but when I load it with a dlopen and using RTLD_NOW
>> constructor of global object are not called.
>>
>> I don't understand why (my version of g++ generate elf) ?
>>
>> please help,
>>
>> thanks,
>>
>> Yves.
>>
>> --
>> Yves Dufournaud Email Yves.Dufournaud at imag.fr equipe MOVI laboratoire
>> GRAVIR
>> --
>>
> Constructors for global objects are called from global initialization routine
> typically caled crtbegin.o, which is linked into the ELF file when it
> contains function "main". If you use dlsym and dlopen, to invoke the
> routine, your program will not call constructors for the global objects in
> that shared object. The only way to initialize global objects specified in
> the shared library is to invoke some kind of explicit creation routine and
> initialize them manually. That means to include routine named "InitMyGlobals"
> in the shared library and then use dlopen to open it and then dlsym to get
> the symbol you are looking for.
> Mladen Gogala

Yep.. That's the problem.  You can make the function mentioned (BTW, you'll
have to extern "C" so dlsym will find it due to C++ name mangling).

There is another option.  I understand in ELF, you have the .init and .fini
sections which are called automagically on loading or dlopen().  I've played
with the on Linux and I understand it's an ELF-thing.  :)

It has been a while but I believe this translates into:

extern "C" {
void init(void);
void fini(void);
}

// Create a tradition-like global initializer.

MyClass &obj;

void init(void)
{
    MyClass *o = new MyClass();

    ASSERT( o != NULL );
    obj = &o;
}

void fini(void)
{
    MyClass *o = &obj;

    delete o;
}

	Hope this helps,
		Dan
-- 
 Dan Miner    dminer@nyx.net |                                        | Doing
         Programmer/         |                                        | Linux
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