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Message-ID: <3E2753C9.4040008@kleckner.net>
Date: Thu, 16 Jan 2003 16:52:25 -0800
From: Jim Kleckner <jek-cygwin AT kleckner DOT net>
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To: cygwin AT cygwin DOT com
Subject: Re: RESOLVED: Using gcc to build a DLL discovered and linked at runtime
References: <3E25A7EE DOT 7050109 AT kleckner DOT net>
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After carefully inspecting the symbols from
generated dlls and dlls provided by TradeStation,
I found that symbols occurred with and without the
@decorations.  e.g. PPI AT 4 and PPI.

Adding -Wl,--add-stdcall-alias to the gcc line,
all worked fine.

Could this generally be a requirement for dlls
that are opened at runtime in a fashion similar to
dlopen?  If so, then some FAQ annotation would be
in order here:
  http://www.cygwin.com/cygwin-ug-net/dll.html

Jim


Jim Kleckner wrote:

>  I'm using a program called TradeStation that allows
> specifying a path name to a DLL, specifying the
> signature of a function to call, and then
> loading/calling that function.  The documentation is
> very sparse for how to do this and probably built in
> some way that depends in an obscure way on having a
> Microsoft compiler such as VisualC++ or VisualBasic to
> work properly.  I am trying to use GCC under cygwin to
> create a DLL that will dynamically open and running
> into roadblocks.
>
> A simple test file test.cpp:
>  #include "windef.h"
>  extern int __stdcall PPI(int);
>
>  __declspec(dllexport) int __stdcall PPI(int notused)
>  {
>      return 1;
>  }
>
> commands used:
>  gcc -shared -mno-cygwin -Wl,--export-dynamic 
> -Wl,--export-all-symbols  -c vmi.cpp
>  dlltool -e exports.o vmi.o -l vmi.lib
>  gcc -shared -mno-cygwin -Wl,--export-dynamic 
> -Wl,--export-all-symbols  -shared exports.o vmi.o -o vmi.dll
>
> The program just says "can't load user function".
>
> I have tried various combinations of commands but am
> wondering if there is something I'm missing.  I'm
> hoping to avoid getting out the ancient copy of VC5
> from my shelf...
>
> I will append cyg
>
> Thanks - Jim
>
>
> Resources for future travelers down this path:
>
> I have looked at a variety of sources describing
> using cygwin/gcc tools to build DLLs.
>
> The manual is here:
>  http://www.cygwin.com/cygwin-ug-net/dll.html
>
> This message contains a bug report with a complex
> example that is interesting to examine:
>  http://www.cygwin.com/ml/cygwin/2000-05/msg00663.html
>
> This one describes a "ld/dlltool/ld/dlltool/ld trick":
>  http://www.cygwin.com/ml/cygwin/2002-08/msg01002.html
> It suggests that what I am trying to do should be
> possible by just using the -shared flag.
>
> Christopher Faylor indicates that the cygwin dll
> cannot be linked at runtime because it is broken:
>  http://www.cygwin.com/ml/cygwin/2002-08/msg01042.html
>
> The dllhelpers stuff is also useful:
>  http://www.neuro.gatech.edu/users/cwilson/cygutils/dll-stuff/index.html
>
>
> [snip]


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