Re: Help with GNAT, WinNT, StdCall, dll, exported names

[Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov>]

"Peter Hend�n" <phenden@tdab.com> writes:

> I'm using gnat 3.13p, trying to build a dll that exports functions
> that are to be called by a windows service. The problem is
> that the functions are declared in the .h file as
> 
> BOOL WINAPI Foobar(LPFUNNY_STRUCT fum);
> 
> Now I have defined an Ada function for this, and
> it works fine when I export it as
> pragma Export(C, Foobar, "Foobar");.
> 
> Of course this will be called exactly once, because
> it is the wrong calling convention, and after its return
> the stack is fubar.
> 
> When I try to declare it StdCall instead of C, I am
> not able to link it. Whatever I put in the .DEF file
> it comes out wrong. I get from the last gnatlink step
> in gnatdll:
> 
> mydll.exp(.edata+0x34):fake: undefined reference to `Foobar'
> 
> I have tried everything in the gnat user's guide, searched
> this groups archive and generally banged my head against
> the wall in appropriate - and perhaps not so appropriate -
> ways. Please help!

You don't mention what C compiler you are using. I have found that
different C compilers (and different Ada compilers) have different
naming conventions, usually having to do with prepending and
underscore. Here's my matrix:

compiler    calling     function    link    DLL
            convention  name        name    name

Borland C++ Cdecl       foo         _foo    _foo
            stdcall     foo         foo     foo

Borland C   Cdecl       foo         _foo    _foo
            stdcall     foo         foo     foo

GNAT Ada    C           foo         _foo    foo
            (stdcall not supported in DLLs)

Gnu C       C           foo         _foo    foo

ObjectAda
Ada         DLL_Cdecl   foo         _foo    foo
            DLL_Stdcall foo         _foo    foo


I also have this note:

Since GNAT Ada does not support the stdcall convention for DLLs, we
use the Cdecl convention everywhere. 

That was true for 3.12, apparently it's not true anymore.

Hope this helps!

-- 
-- Stephe