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From: Venkat Iyer <venkat AT comit DOT com>
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Message-ID: <14819.48654.198000.271875@gargle.gargle.HOWL>
Date: Tue, 10 Oct 2000 18:10:38 -0700 (Pacific Daylight Time)
To: cygwin AT sourceware DOT cygnus DOT com
Subject: Exporting symbols from an executable


Greetings,

I've read everything I could (including libtool, dlltool, gcc, ld
documentation, cygwin archives, and google and alltheweb searches),
and still haven't managed to make this work.

I want to export symbols from an executable, so that they can be used
to resolve symbols at run time from dlopen'ed libraries.

a.c : defines main and f1()
b.c : defines f2() which uses f1().

I want to end up with a.exe and b.dll.  So that when a.c dlopens b.dll,
f1 is resolved.

Here's all the stuff I tried.  I have tried RTLD_GLOBAL, RTLD_LAZY
and RTLD_NOw options.

1. Generate a library (liba.a) so that b.dll can be built using
   dlltool with the exe name as the dll name.

2. Link b.c with -shared liba.a so that it resolves completely.  b.c
   does have a valid entry point.

3. Link a.c with -Wl,--export-dynamic so that all functions are
   exported.

4. Run a.c, but dlopen() always fails.
   
I am using plain vanilla latest net install of cygwin.  The only
change being the incorrect _cygwin_dll_entry prototype fix in
cygwin_dll.h

If f2 (in b.c below) is defined so: int f2(){return 1;}, then the
dlopen succeeds, so my build process seems to be mostly OK.  Any help
would be much appreciated.

The commands I use are:

bash$ dlltool --dllname a.exe --input-def a.def --output-lib liba.a
bash$ gcc -Wl,--export-dynamic a.c -o a
bash$ gcc --shared b.c -o b.dll liba.a
bash$ ./a
Failed
Function not implemented

The files are :

---a.c----
#include <errno.h>
#include <dlfcn.h>

int f1(void)
{
    return 1;
}

main()
{
    void *p = dlopen(".\\b.dll", RTLD_NOW);
    if (p == 0)
    {
	printf("Failed\n");
	printf("%s\n", strerror(errno));
    }
    else 
    {
	printf("Succeeded\n");
    }
}
----b.c----
#include <cygwin/cygwin_dll.h>

extern int f1(void);

int f2 (void)
{
    return f1();
}

DECLARE_CYGWIN_DLL(DllMain);

----a.def----
EXPORTS
   f1
----------------

-- 
Regards
_______________________________________________________________________
Venkat Iyer       venkat AT comit DOT com          Phone: 1-408-988-2988 x 136 
Comit Systems, Inc.   The Contract Engineering Company    www.comit.com


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