[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Shared library on MinGW

From: John Pye
Subject: Re: Shared library on MinGW
Date: Wed, 15 Mar 2006 00:51:33 +1100
User-agent: Mozilla Thunderbird 1.0.7-1.1.fc4 (X11/20050929)

Hi again,

Ralf Wildenhues wrote:

* John Pye wrote on Tue, Mar 14, 2006 at 02:18:04PM CET:
Ralf Wildenhues wrote:
* John Pye wrote on Tue, Mar 14, 2006 at 06:26:31AM CET:

I just saw this thread and I have been experiencing similar problems.
Well, if you have the same problem, then using `-no-undefined' should
fix it for you.  ;-)

No, according the the posting: '-no-undefined' means that "OUTPUT-FILE does not depend on any other libraries."

Well, read the whole thread, and you'll know what I meant. :)
OK, I take your point. So what would my libtool command look like? Something like the following?

libtool --mode=link shared gcc -o myplugin.dll myplugin.o _ascend.dll

How are the links from myplugin.dll to _ascend.dll resolved at runtime? How is this different from the DLL having unresolved symbols?

My problem is the opposite: I know for sure that it *does* depend on other libraries.

On other libraries that you did not specify on the link line.  Right?
That's right. In my makefile I've just been using something like

libtool --mode=link $(CC) -module shared -o myplugin.dll myplugin.o -lm

Full details:

The external plugin DLLs contain unresolved symbols that are present in
_ascend.dll and are supposed to be resolved at load-time. The symbols
are involving in 'registering' the plugin back with the main
application, and providing error reporting capabilities.

Under Linux this all works fine. Under Windows, I can't make libtool
compile my library with these unresolved symbols.
Right.  Just won't work that way on Windows, though.  You could factor
out all common code into a common library, for example.  Or factor the
common code into a plugin.  Or provide pointers for the callbacks.

I need you to clarify that last bit. Are you saying that I can't compile a DLL with unresolved symbols that get resolved at LoadLibrary-time? That is certainly what appears to be said on the edll page.

This is my understanding.  You can specify dependent DLLs.  But the need
to do this will prevent you from creating circles in the dependency chain.
I sort of have circles and sort of don't. My _ascend.dll has symbols that are required by myplugin.dll. And my _ascend.dll will be dlopening myplugin.dll. But that's a runtime thing only: _ascend.dll doesn't need to know anything about myplugin.dll at build-time.

Am I understanding you correctly? It seems like I *don't* have a circle here...?

But it was my understanding from the libtool manual that this could be accomodated by suitable settings with libtool. For example, section 9.1 makes no mention of *not being able to do anything in particular in Windows. (In fact there are only a handful of mentions of 'windows', 'win32' and 'cygwin' in the whole manual...). Ok, so maybe I was dreaming. But maybe we could have some explanation of these issues in the manual?

Yes, that would be good.  In fact, I think there is so little mention of
this because, back in the old times this issue was present on more
systems, so it was more known to people, and so did not deserve so much
mention.  This is speculation on my part, though.
Yes, it would be really great if an experienced MinGW or Cygwin developer could add their platform-specific notes to that document. Ditto Linux, etc etc. So we know what's possible across the range of platforms.

I haven't tried the ideas listed on yet,
by the way.  If they work, libltdl may benefit from integrating some
of them (optionally).  If anybody has experience with them, I'd be
glad to learn about it.

It definitely sounds interesting. Otherwise I will have to go with some kind of technique that passes some function pointers from my _ascend.dll to my plugin DLL when it is being loaded. Which isn't so hard I guess.

Yes, for example.
The guy is saying there that it's pretty natural to use function pointers for small jobs. I'm just not sure if my scenario is exactly the type of problem he's talking about, or not.


reply via email to

[Prev in Thread] Current Thread [Next in Thread]