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Message-Id: <200002151634.KAA03715@hp2.xraylith.wisc.edu>
To: Oliver Nittka <nittka@esem.com>
cc: cygwin@sourceware.cygnus.com
Subject: Re: __stdcall in 3rd-party dll 
In-reply-to: Your message of "15 Feb 2000 10:17:53 +0100."
             <uya8m3jum.fsf@esem.com> 
Date: Tue, 15 Feb 2000 10:33:37 -0600
From: Mumit Khan <khan@NanoTech.Wisc.EDU>

Oliver Nittka <nittka@esem.com> writes:
> 
> hi everyone !
> 
> after some diggin' in the mailing-list archives and on dejanews, i've
> got some insight in the following situation, but still don't know how
> to resolve it, perhaps somebody can give me a hit over the head with
> the appropriate literature ;-)
> 
> i've got me a DLL (gpib-32.dll from national instruments), where i
> want to link against some functions (ibdev, ibwrt, ibrd: perhaps
> somebody's got that dll and wants to look for him/herself)

If I understand correctly, you have a foreign DLL that you want to link
to, and the functions in this foreign DLL are stdcall (which makes sense
since that allows LoadLibrary/GetProcessAddress to work), and you want
to create an import library to link against.

> according to the headerfile, those functions are __stdcall, but they
> are exported from the dll undecorated (without @nn).
> 
> - if i delete __stdcall from the header, my program crashes as soon as
>   it calls ibdev (stack corruption i suppose)

Wrong approach.

> 
> - if i leave the .h-file as is, i get unresolved symbols ibdev@24,
>   ibwrt@16 etc.
    ^^^^^^^^ (See later on this particular one).

Correct.

> 
> - if i create myself an import-library, using a decorated .def-file,
>   it still crashes (does it link to the correct functions, anyway ?)
>   using an undecorated import-lib still gives me unresolved symbols.

You can create an import library that will do the following:
  - create a lib with decorated names, and
  - use the undecorated exports from the DLL.

That's the kind the w32api package deals with, and here's how:

Given the following prototypes
  extern int __stdcall ibdev  (int, int, int, int, int, int);
  extern int __stdcall ibwrt  (int, void *, long);
  extern int __stdcall ibrd   (int, void *, long);

Create a .def file that looks like the following:
  
  LIBRARY "gpib-32.dll"
  EXPORTS
  ibdev@24
  ibwrt@12
  ibrd@12

and so on, and create the implib in the usual way:
  
  $ dlltool -k --output-lib libgpib-32.a gpib-32.def

Now you should be able to link against this import library in the usual
way.

I don't understand why you see ibwrt@16, it should be ibwrt@12 given the
prototype, since there're 12 bytes in the parameter list, not 16 (long
and int are both 4 bytes on ix86 running 32 bit OS).

Regards,
Mumit


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