RE: .def files for stdcall functions (was: linking problems with the minimalist version)

[Colin Peters <colin at bird dot fu dot is dot saga-u dot ac dot jp>]

Lachlan Roche[SMTP:lr-gnu@www.wwi.com.au] wrote:
>I have been trying to use opengl with the minimalist version of gcc-win32.
>
>I am using SGI GL for windows, and Mark Kilgard's glut32.dll
>
>I created my link liraries link:
>impdef opengl.dll > opengl.def
>dlltool --dllname opengl.dll --def opengl.def --output-lib libopengl.a -v
>
>There were no func@NN type symbols in the .def files
>
>when linking a trivial test program, I get many errors of the form:
>gltest.o(.text+0x24):gltest.c: undefined reference to `glBegin@4'
>
>Every function I use from libglut.a libglu.a or libopengl.a gives the same
>link error.
>
>What am I doing wrong? (Something trivial, no doubt)

The problem is not something you are doing wrong, as such, nor is it linked
to Mingw32 really. The problem is that impdef does not generate (and cannot
as far as I can figure out) .def files with that all important @NN suffix
on stdcall (or PASCAL or WINAPI) functions.

If impdef did generate the 'right' function names (e.g. "glBegin@4") then
you could generate your import library using the -k option to dlltool and
everything would work.

Unfortunately there is no way, that I can see, to automatically determine
this information (what number goes after the @) from the contents of a
DLL. You must parse the header file! (Please correct me if I'm wrong...
I'd love to be wrong about this.)

(NOTE for those unfamiliar with the way GNU-Win32 does stdcall functions,
it puts an @ followed by the number of bytes taken up on the stack by the
arguments onto the end of the function name. This has nothing to do with
the syntax used in .def files to define ordinals.)

In short, there is no easy way around this problem except to add all those
@NNs by hand after looking at the header file. Argh! You could, of course,
also write a program which attempted to call all the OpenGL functions, and
then copy the numbers off the "undefined reference" linker errors.

My beef with all this is: why does GCC do it this way at all? What purpose
does the @NN serve? After all, GCC knows how to generate the correct
function call given a prototype, it *generates* the @NN, so it doesn't
need it to know what to do. I don't think any other compilers add on @NN
to the names of WINAPI functions like this. Why doesn't GCC just use the
plain function name and call it with PASCAL calling convention? Someone
please enlighten me.

Sorry about the rant...

Colin.

-- Colin Peters - Saga Univ. Dept. of Information Science
-- colin@bird.fu.is.saga-u.ac.jp - finger for PGP public key
-- http://www.fu.is.saga-u.ac.jp/~colin/index.html
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