X-Recipient:	archive-cygwin AT delorie DOT com
X-SWARE-Spam-Status:	No, hits=0.1 required=5.0 tests=BAYES_00,J_CHICKENPOX_62,RCVD_NUMERIC_HELO,SPF_HELO_PASS,SPF_PASS
X-Spam-Check-By:	sourceware.org
To:	cygwin AT cygwin DOT com
From:	Sam Steingold <sds AT gnu DOT org>
Subject:	creating dynamic libraries
Date:	Fri, 25 Sep 2009 17:09:43 -0400
Lines:	48
Message-ID:	<4ABD3197.1090509@gnu.org>
Mime-Version:	1.0
User-Agent:	Thunderbird 2.0.0.22 (X11/20090625)
X-IsSubscribed:	yes
Mailing-List:	contact cygwin-help AT cygwin DOT com; run by ezmlm
List-Id:	<cygwin.cygwin.com>
List-Subscribe:	<mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive:	<http://sourceware.org/ml/cygwin/>
List-Post:	<mailto:cygwin AT cygwin DOT com>
List-Help:	<mailto:cygwin-help AT cygwin DOT com>, <http://sourceware.org/ml/#faqs>
Sender:	cygwin-owner AT cygwin DOT com
Mail-Followup-To:	cygwin AT cygwin DOT com
Delivered-To:	mailing list cygwin AT cygwin DOT com

Hi,
How do I create a dynamic library which uses data in the executable which uses it?

specifically, I have this main program:

=================== main.c
#include <stdio.h>
extern int shared_func (void);
int my_int_var = 42;
int my_int_addr = &my_int_var;

int main (void) {
   printf("[%d]\n",shared_func());
   return 0;
}
=================== main.c

and this shared library:

=================== shared.c
extern int my_int_var;
int shared_func (void) { return my_int_var; }
=================== shared.c

this is what I get on linux:

$ gcc -fPIC -shared -o shared.so shared.c
$ gcc -o main main.c shared.so
$ LD_LIBRARY_PATH=. ./main
[42]

however when I try the same trick on cygwin, I get this:

$ gcc -shared -o shared.dll shared.c
/.../6/cc1e5Kdk.o:shared.c:(.text+0x4): undefined reference to `_my_int_var'

so, what do I do?

I suppose I could extract my_int_var into a separate shared library, declare it 
there as __declspec(dllexport), then use it as __declspec(dllimport) in shared.c.
alas, this means that my_int_addr fails with
"error: initializer element is not constant".

so, is there a way to create a dll which would use data in the executable it 
will be linked against?

thanks.
Sam.


--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple

- Raw text -